JPH0843797A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To form a color display stable in use over a long period of time by impressing voltage signals to form a display state on the selected pixels of a liquid crystal panel having chiral smectic liquid crystals and applying AC voltages on the non-selected pixels. CONSTITUTION:This liquid crystal panel has matrix electrodes which constitute pixels in the intersected parts of scanning electrodes 34a and signal electrodes 34b, colored films, dielectric films and the chiral smectic liquid crystals 35 which have dielectric anisotropy of a negative value. The liquid crystal panel has driving means for impressing the scanning signals on the scanning electrodes 34a and information signals on the signal electrodes 34b and impressing the voltage signals to form the display state on the pixels selected in such a manner and applying the AC voltages on the non-selected pixels. A protective layer 32 prevents direct contact of color filter layers with the ferroelectric chiral smectic liquid crystals (FLC) 35 and is provided with both of an insulating characteristic and orientation controllability. The color filter layers formed by coloring mordant materials, such as polyvinyl alcohol and cellulose resin, with dyes are usable as the color filter layers 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color display, and more particularly to a liquid crystal device using a chiral smectic liquid crystal suitable for a color television.

[0002]

2. Description of the Related Art In a conventional liquid crystal television panel using an active matrix driving system, thin film transistors (TFTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFTs to establish a conduction state between a source and a drain. At this time, a video image signal is applied from a source and stored in a capacitor, a liquid crystal (for example, a twisted nematic-TN liquid crystal) is driven according to the stored image signal, and a color filter layer provided for each pixel is A color display was performed by optically switching.

However, in an active matrix drive type television panel using such a TN liquid crystal, since the TFT used has a complicated structure, the number of structural steps is large and the high manufacturing cost is a bottleneck. In addition,
There is a problem that it is difficult to form a thin film semiconductor (for example, polysilicon or amorphous silicon) forming a TFT over a large area.

On the other hand, a passive matrix drive type display panel using TN liquid crystal is known as one which can be manufactured at a low manufacturing cost. In this display panel, one screen (1) is displayed as the scanning line (N) increases. The time (duty ratio) during which an effective electric field is applied to one selected point during scanning of (frame) is reduced by a ratio of 1 / N, which causes crosstalk and does not result in a high-contrast image. In addition to such drawbacks, it is difficult to control the gradation of each pixel by voltage modulation when the duty ratio is low, and therefore it is not suitable for a display panel with a high-density wiring number, particularly a liquid crystal television panel.

As a solution to such a fundamental problem of the conventional TN liquid crystal, a ferroelectric liquid crystal device having bistability has been proposed in US Pat. No. 4,367,924 of Clark and Lagerwol et al. There is.

[0006]

However, when the above-mentioned ferroelectric liquid crystal element is applied to a color display, especially a color television, there are the following problems.

That is, the most convenient method as a color display method using a liquid crystal element is a method of optically switching by driving a liquid crystal for each color unit of a color stripe filter or a color mosaic filter. A method is suitable in which color pixel units in which intersections are made to correspond to each color unit are switched by line-sequential driving.

However, in the liquid crystal element applied to the above-described method, the color filter layer is arranged on one side of the cross electrode for each color pixel unit, and if such a liquid crystal element is used for a long period of time, it is normal. It turned out that there is a problem that color display is not performed.

FIG. 1A shows a driving waveform applied to a pixel of a ferroelectric chiral smectic liquid crystal (hereinafter referred to as FLC), and FIG. 1B shows a voltage waveform applied to the liquid crystal itself in real time. There is. That is, the voltage waveform substantially applied to the FLC when the Von write pulse is applied to the FLC from between the above-mentioned cross electrodes is shown in FIG.
As shown in (b), Vo when the pulse is applied has a time constant π = RC.
ΔV at the ratio of (R; FLC resistance, C; FLC capacity)
A voltage drop occurs by o, and this voltage drop ΔVo becomes larger as the resistance R of the FLC becomes smaller, and −ΔVo having the opposite polarity is applied to the FLC at the time of pulse switching (at the falling edge of the pulse). This | -ΔVo | is the inversion threshold voltage | -Vth
If it is larger than |, for example, black writing, which is the opposite of white writing, is performed. This is because the electric field (Δ-Vo) in the opposite direction is generated by the discharge from the capacitance of the dielectric layer such as the orientation control film connected in series to the FLC at the falling edge of the pulse.

By the way, in the above-mentioned liquid crystal element for color display, the color filter is arranged in the cell, and therefore the dye in the color filter layer is eluted in the FLC in the cell, and such a liquid crystal element is used for a long period of time. Then,
There is a problem that the resistance R of the FLC in the cell decreases with time, and eventually the value of the reverse electric field −ΔVo exceeds the reversal threshold voltage and the desired optical switching drive does not operate.

When the row-sequential writing method is applied to the FLC element, for example, a first phase based on the first alignment state of the FLC at a phase t ₁ which is the first phase for all or predetermined pixels on the row. Applying a pulse that forms one display state,
There is a method of applying a pulse that inverts the first display state to the second display state based on the second alignment state of the FLC for the pixel selected at the phase t ₂ which is the phase.

In this system, the phase t ₂ is as shown in FIG.
As shown in, the pulse having the opposite polarity to the pulse applied at the phase t ₁ is applied to the pixel holding the first display state at the threshold voltage or less.

As described above, in the case of the row sequential writing method, it is necessary to maintain the display state written at the phase t ₁ without being inverted at the phase t ₂ . Therefore, it is supposed that a voltage exceeding the reversal threshold voltage should not be applied at the phase t ₂ , but it has become clear from the study by the inventors of the present invention that from the phase t ₁ to the phase t ₂ . FL when switching the pulse polarity
In C, as shown in FIG. 2B, − (aVo + ΔVo):
[A is a <| Vth | / | Von |; Vth is the threshold voltage of FLC]:
When this − (aVo + ΔVo) is larger than the reversal threshold voltage, the pixel which should hold the first display state is inverted to the second display state at the phase t ₂ , and the desired display is formed. There was a problem that could not be done.

[0014]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a liquid crystal device using a chiral smectic liquid crystal which enables a stable color display for a long period of time, especially a color television display. .

That is, according to the present invention, a matrix electrode which constitutes a pixel at an intersection of a scanning electrode and a signal electrode, a coloring film,
A liquid crystal panel having a dielectric film and a chiral smectic liquid crystal having a negative dielectric anisotropy, and a scanning signal is applied to the scanning electrodes, an information signal is applied to the signal electrodes, and thereby a display state is displayed on a selected pixel. The liquid crystal device is characterized by having a driving means for applying a voltage signal for forming a pixel and applying an AC voltage to the unselected pixels.

[0016]

FIG. 3 is a sectional view of a liquid crystal element of the present invention. 31 is a color filter layer, 31 respectively
(B), 31 (G) and 31 (R) are a blue color filter layer, a green color filter layer and a red color filter layer which form one color pixel unit. 32
Is a protective layer that prevents direct contact between the color filter layer 31 and the FLC 35, and can have both insulating properties and orientation controllability. Reference numerals 33a and 33b are substrates such as glass plates and plastic films, and 34a and 34b are striped transparent electrodes forming matrix electrodes, which are formed of a film such as ITO (Indium-Tein-Oxide).
35 is an FLC and 36 is an alignment control film, which can be omitted. 37a and 37b are crossed Nicols polarizers,
A sealing member 38 seals the gap between the substrates 33a and 33b and can also function as a spacer.

The color filter layer 31 may be formed by coloring a mordant such as polyvinyl alcohol or cellulose resin with a dye. As the dye used at this time, a cyanine dye, a merocyanine dye, an azurenium dye, a nantraquinone dye, a naphthoquinone dye, a phenol dye, a disazo dye, a trisazo dye, a tetrazo dye, or the like can be used.

Further, the color filter layer 3 used in the present invention
1 may be formed by coating various organic pigments by a vapor deposition method. As the organic pigment used at this time, a copper phthalocyan pigment, a lead phthalocyanine pigment, a perylene pigment, an indigo pigment, a thioindigo pigment, a disazo pigment, a trisazo pigment, a tetrazo pigment, or the like can be used.

In another preferred embodiment of the present invention, colored polyimide, colored polyamide, colored polyamide-imide, colored ester imide or colored polyester can be used as the color filter layer 31. In particular, polyamide (6-nylon, 66-nylon or copolymerized nylon) and polyester are soluble in various organic solvents, so that various organic pigments can be mixed therein. Further, as a method for coloring a polyimide, a polyamideimide or a polyesterimide, a dispersant (hydroxyl group, carboxyl group, in a polyamic acid solution which is a precursor thereof,
A method of dispersing an organic pigment together with an azo dye having a sulfonic acid group, a carbonamide group, a sulfonamide group, or the like as a substituent, a phthalocyanine dye, a triphenylmethane dye, or the like can be used. These colored films have very good adhesion to the protective layer 32, and good results can be obtained.

The protective layer 32 used in the present invention is not particularly limited, but silicon nitride, silicon nitride containing hydrogen, silicon carbide, silicon nitride containing hydrogen, silicon oxide, boron nitride. Substances, boron nitride containing hydrogen, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, inorganic insulating substances such as magnesium fluoride SiO and SiO ₂ , or polyvinyl alcohol, polyimide, polyamide imide, polyester imide , Polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, cellulose resin, melamine resin, urea resin, acrylic resin, photoresist resin, and other organic insulating materials are used as the insulating film. Done . Film thickness of these insulating films 500
0 Å or less, preferably 100 Å to 5000 Å, especially 50
0Å to 3000Å are suitable.

When the capacity formed by the protective layer 32 is set to 5.5 × 10 ³ PF / cm ² or more, the reversal development described above can be prevented more effectively. Its preferable capacity is 5.5 × 10 ^3.
In the range of PF / cm ^{2 to} 3.0 × 10 ⁵ PF / cm ² , 9.0 × 10 ³ PF / c for maintaining particularly sufficient insulation.
m ^{2 to} 5.5 × 10 ⁴ PF / cm ² is suitable. Furthermore, by subjecting the surface of the protective layer 32 to a uniaxial orientation treatment such as a rubbing treatment, an orientation control effect on the FLC 35 can be imparted.

The protective layer 32 and the dye or pigment in the color filter layer 31 used in the present invention are preferably selected from those which are not compatible with each other. The term "compatibility" as used herein refers to the property that the protective layer and the dye or pigment are dissolved by the same organic solvent. Regarding the solubility at this time, when the protective layer and the dye or pigment are dissolved in a ratio of 1 g or more with respect to 100 g of the organic solvent,
When the color filter layer 31 and the protective layer 32 are provided on the FLC element, the dye or pigment in the color filter layer 31 penetrates into the protective layer 32 during the long-term use of the FLC element, so that the FLC This lowers the resistance, which causes the above-mentioned malfunction.

As described above, the protective layer 32 used in the present invention is
By selecting from those which are not compatible with the dye or pigment in the color filter layer 31, FL
The operational stability of the C element in the long term can be further improved, and the protective layer 32 can be a laminated body composed of a plurality of layers.

Also, as shown in the figure, the color filter layer 31
A transparent electrode 34b is provided on top of the protective layer 3
In addition to the case where 2 is provided, the protective layer 32 used in the present invention is
It is also possible to provide directly on the color filter layer 31 and provide the transparent electrode 34b on it. At this time, it is preferable to provide an alignment control film (not shown) separately from the transparent electrode 34b. This orientation control film is the protective layer 32 described above.
It can be obtained by forming a film with the same material as above and then performing a uniaxial orientation treatment such as a rubbing treatment.

FIG. 4 is a schematic drawing of an example of an FLC cell. 11a 'and 11b' are In ₂ O ₃ and SnO.
It is a substrate (glass plate) coated with a transparent electrode such as ₂ or ITO ((indium-thein-oxide), etc., and SmC ^* phase liquid crystal oriented so that the liquid crystal molecular layer 12 is perpendicular to the glass surface is enclosed between them. The line 13 indicated by a thick line represents a liquid crystal molecule, and this liquid crystal molecule 13 is
Dipole moment (P⊥) 1 in the direction orthogonal to the molecule
Four. When a voltage above a certain threshold is applied between the electrodes on the substrates 11a and 11b, the helical structure of the liquid crystal molecules 13 is unraveled, and all the dipole moments (P⊥) 14 are oriented in the electric field direction. Can be changed. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if polarizers arranged in a crossed Nicols position above and below the glass surface are placed. It is easily understood that the liquid crystal optical modulation element has optical characteristics that change depending on the polarity of voltage application. Further, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μm), the helical structure of the liquid crystal molecules is unwound and becomes a non-helical structure even when no electric field is applied as shown in FIG. Pa or Pb
Takes either an upward (24a) or downward (24b) state. When electric fields Ea or Eb having different polarities equal to or more than a certain threshold value are applied to such a cell, as shown in FIG.
The dipole moment electric field Ea or Eb is turned upward 24a or downward 24b in accordance with the electric field vector,
Accordingly, the liquid crystal molecules are oriented in either the first stable state 23a or the second stable state 23b.

There are two advantages of using such FLC as an optical modulator. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. The second point will be described with reference to FIG. 5, for example. When the electric field Ea is applied, the liquid crystal molecules are in the first stable state 2
Although it is oriented in 3a, this state is stable even when the electric field is cut off. When a reverse electric field Eb is applied, the liquid crystal molecules are oriented in the second stable state 23b and change their orientation, but they remain in this state even when the electric field is cut off.
Further, unless the applied electric field Ea exceeds a certain threshold value, the respective alignment states are also maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, and generally 0.5 μ to 20 μ, particularly 1 μ to 5 μ is suitable. Liquid crystal having a matrix electrode structure using this type of FLC
An electro-optical device has been proposed in U.S. Pat. No. 4,367,924, for example by Clark and Lagabal.

The FLC 35 used in the present invention is most preferably a chiral smectic liquid crystal, of which the chiral smectic C phase (SmC ^* ), H phase (SmH ^* ), I phase (SmI ^* ), J phase (SmJ ^* ), K. Phase (SmK ^* ), G
Phase (SmG ^* ) and F phase (SmF ^* ) liquid crystals are suitable.

The FLG compounds may be used alone or in combination of two or more, and may be mixed with other non-dielectric liquid crystals such as nematic liquid crystals, cholesteric liquid crystals (chiral nematic liquid crystals) and smectic liquid crystals. The FLC 35 described above may have the above-described helical structure shown in FIG. 4 or may have a non-helical structure shown in FIG. In particular, in the case of having the helical structure shown in FIG. 4, one having a negative dielectric anisotropy is used as the FLC (for example, "CS-10 manufactured by Chisso Corporation").
11 (trade name): “ZLI3234 (trade name)” manufactured by Merck Ltd. It is preferable to apply a driving method for imparting bistability with a non-helical structure by applying an AC bias between both electrodes. At this time, it is also possible to apply the above-mentioned driving method of applying an AC bias to the liquid crystal element which forms the non-helical structure by making the cell thickness of the liquid crystal layer sufficiently small.

The present invention will be described below with reference to examples.

Reference Example 1 Striped I having a pitch of 100 μm and a width of 62.5 μm
A square glass substrate provided with a TO film as an electrode was prepared, the side on which the ITO film serving as the electrode was provided was set downward, and a copper phthalocyanine pigment (blue) was vacuum-deposited by a vacuum vapor deposition device. Next, this vapor-deposited layer of copper phthalocyanine pigment was patterned using a predetermined photolithography process. Then, a 5 wt% N-methylpyrrolidone solution of a polyamic acid (a dehydrated condensate of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether), which is a precursor of a polyimide resin, has a film thickness of 800Å when cured by heating. The spinner was applied so that The surface of the polyimide film after heat curing was rubbed with a rubbing treatment parallel to the stripe electrode direction. The electrode plate thus created is referred to as an A electrode plate.

On the other hand, except for the formation of the copper phthalocyanine color filter layer used when the above-mentioned A electrode plate was prepared,
A B electrode plate was prepared by exactly the same method. However, the rubbing treatment was performed in the direction perpendicular to the stripe electrodes.

Next, after a thermosetting epoxy adhesive is applied to the peripheral portion of the A electrode plate by a screen printing method except for the injection port, the striped pattern electrodes of the A electrode plate and the B electrode plate are orthogonal to each other. As described above, the distance between the two electrode plates was maintained at 2 μm with a polyimide spacer.

The following liquid crystal composition A (showing SmC ^* at 20 ° C. to 78 ° C.), which is in an isotropic phase, was injected from the injection port into the cell thus prepared, and the injection port was sealed. When this cell was cooled by gradual cooling and maintained at a temperature of 40 ° C., a pair of polarizers were provided in a crossed Nicol state, and when observed under a microscope, a non-helical structure with no alignment defect was taken and It was found that SmC ^* was formed.

[0034]

[Outside 1]

(Comparative Example) A comparative liquid crystal cell was prepared in the same manner except that a monolayer silane coupling agent layer was used in place of the polyimide protective layer used in the liquid crystal cell prepared in the above example. However, the monodomain SmC ^* was formed as in the above-mentioned example.

The above-mentioned two kinds of liquid crystal cells were left at a temperature of 80 ° C. and a relative humidity of 60% for 96 hours, and then the resistance of each liquid crystal was measured. The results are shown below (Table 1).

[0037]

[Table 1]

The resistance (Ω · cm) is measured by applying a rectangular pulse by the two-frequency method using the circuit shown in FIG. 6 and obtaining R _LC (Ω · cm) from the following equation. You can At this time, f ₁ = 32 Hz, f ₂ = 64
Hz and V = 10 volts.

[0039]

[Outside 2]

V: Measurement voltage F: Rectangular wave frequency I _C : Capacitance component current value I _R : R component current value C _LC : Liquid crystal capacitance R _LC : Liquid crystal resistance (Ω) C _LC : R _LC S / Dd: thickness of liquid crystal (cell gap) S: electrode area f

[0041]

[Outside 3]

Next, after a crossed Nicol polarizer was placed in each liquid crystal display cell after being left for 96 hours, a signal of 20 V was applied between the electrodes to drive the liquid crystal display cell. While display quality with the same good contrast was obtained, in the comparative example, the display state at the initial stage was reversed and displayed.

Reference Examples 2 and 3 In the same manner as in Reference Example 1, except that lead phthalocyanine (Reference Example 2) and perylene red (Reference Example 3) were used instead of the copper phthalocyanine used in Reference Example 1. When a liquid crystal cell was prepared and a durability test was conducted, the same results as in Reference Example 1 were obtained.

Reference Example 4 A liquid crystal was prepared in the same manner as in Reference Example 1, except that the following colored polyimide film was used as a color filter layer instead of the color filter layer formed of the copper phthalocyanine vapor deposition layer used in Reference Example 1. When a cell was prepared, the same result as in Reference Example 1 was obtained.

Preparation procedure of colored polyimide In a four-necked flask equipped with a stirrer, a reflux condenser and a thermometer, 10 parts of copper phthalocyanine was completely dissolved in 100 parts of chlorosulfonic acid, and then 21 parts of thionyl chloride was added thereto, and gradually added. The temperature was raised and maintained at 112 to 113 ° C. for 4 hours. After cooling, add ice and filter. It was washed with ice water. This paste was placed in a four-wheel flask equipped with a reflux condenser, and 100 parts of water and N-diethylaminoethylamine 21 were added.
And the mixture was stirred at room temperature for 12 hours and then heated at 60 ° C. for 1 hour. After completion of the reaction, the product was filtered, washed with water and dried to obtain a blue powder of a copper phthalocyanine derivative. Elemental analysis of this blue powder revealed that

[0046]

[Outside 4] Was found to be about 3 copper phthalocyanines introduced.

Then, a mixture of 0.1 part of the above-mentioned copper phthalocyanine derivative and 16.5 parts of α-type copper phthalocyanine was added to 100 parts of Semicofine SP-510, a precursor of polyimide, manufactured by Toray Industries, Inc. and N, It was dispersed in a solution consisting of 200 parts of N-diethylethylformamide, and was sufficiently stirred and dispersed.

This dispersion was applied by a Svinner coater so that the film thickness after heat curing would be 500 Å to prepare a colored polyimide film.

Reference Example 5 A negative resist resin (“ODUR” manufactured by Tokyo Ohka Kogyo Co., Ltd.) was further applied between the color filter layer and the polyimide layer of the (A) electrode plate and the (B) electrode plate used in Reference Example 1. An FLC element was prepared in the same manner as in Reference Example 1 except that the protective layer 2 was used, and a durability test was conducted. The results are shown in Table 2.

[0050]

[Table 2]

[0051]

EFFECTS OF THE INVENTION A stable color display can be formed by using a liquid crystal element for a color display, particularly a color television display, for a long period of time.
In particular, even when the color filter layer is applied to the dot matrix type liquid crystal element using the conventional twisted nematic (TN) and the protective layer is omitted as described above, the resistance is decreased in the TN liquid crystal layer, but the writing pulse is generated. At the fall of, there is no display state different from the written information,
Therefore, in the conventional TN mode, it is not necessary to consider the decrease in resistance. On the other hand, in the FLC, the reverse electric field generated by the discharge of the dielectric layer at the fall of the write pulse causes writing with information different from the written information, which causes a big problem in the color display using the FLC. However, the present invention can effectively solve the above-mentioned problems.

[Brief description of drawings]

FIG. 1 shows a voltage waveform during writing.

FIG. 2 shows a voltage waveform during writing in another example.

FIG. 3 is a cross-sectional view of a liquid crystal element used in the present invention.

FIG. 4 is a perspective view of a chiral smectic liquid crystal element used in the present invention.

FIG. 5 is a perspective view of another chiral smectic liquid crystal element used in the present invention.

FIG. 6 is a resistance measuring circuit used in the present invention.

Claims (3)

[Claims] 1. A liquid crystal panel having a matrix electrode which constitutes a pixel at the intersection of a scanning electrode and a signal electrode, a colored film, a dielectric film and a chiral smectic liquid crystal having a negative dielectric anisotropy, and a scanning electrode. A liquid crystal having driving means for applying a scanning signal to the pixel electrode, applying an information signal to the signal electrode, applying a voltage signal for forming a display state to a pixel selected thereby, and applying an AC voltage to a pixel not selected. apparatus. 2. The liquid crystal device according to claim 1, wherein the colored film is a film containing an organic dye or an organic pigment. 3. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal has a volume resistance value of 2.5 × 10 ¹⁰ Ω · cm or more.