JPH0431372B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a chiral smect liquid crystal device,
More specifically, the present invention relates to a drive circuit for a smectic liquid crystal panel.

(Prior Art) In recent years, liquid crystal devices using chiral smectate C phase have attracted attention as display devices with high-speed response and memory retention, and optical shutters for cameras and printers.

As a ferroelectric liquid crystal compound having this chiral smectate C phase, for example, 2-methybutyl P-[(P-n-decyloxybenzylidene)amino] is widely known, and its liquid crystal molecules are
As shown in the figure, the layer L ₁ with a constant azimuth angle ψ,
A twisted spiral structure is adopted and arranged for each of L ₂ , L ₃ , and L ₄ .

By the way, a liquid crystal cell is constructed by injecting this liquid crystal compound having a chiral smect C phase between two substrates B and B with a gap (for example, about 1 μm) smaller than the helical period (usually several μm). Then (Fig. 9A), the liquid crystal molecules lose their helical structure, and the molecular axes become parallel to the substrates B and B, with domains tilted at an angle θ clockwise from the normal direction of the layers and domains tilted counterclockwise. It has a mixture of domains tilted by θ, that is, −θ (see figure 2), and has an electric dipole in a direction perpendicular to the molecular axis.

Therefore, if one domain has an electric dipole pointing upward with respect to substrates B, B, the other domain will have an electric dipole pointing downward, thus applying an electric field between substrates B, B. Then, all the liquid crystal molecules are aligned in positions tilted either +θ or -θ from the normal direction of the layer, and when an electric field in the opposite direction is applied, the liquid crystal molecules are also reversed and tilted -θ or +θ. Arrange them all at the same position.

When polarizing plates are placed on both sides of this cell and an electric field is applied, a bright state and a dark state are generated due to the movement of liquid crystal molecules, allowing the cell to function as a display panel or light shutter (FIG. 10). The liquid crystal panel constructed in this manner has an extremely fast response speed of microseconds and an excellent property of retaining the displayed pattern even after the electric field is removed.

In particular, this memory retention property is a very useful characteristic in terms of saving drive power, but on the other hand, when changing display contents, writing in the dark state and writing in the bright state are performed in separate frame scans. Therefore, there is a problem in that it takes time to change the display pattern.

(Objective) In view of the above-mentioned problems, it is an object of the present invention to provide a novel smectic liquid crystal device having a high scanning speed and capable of writing in a bright state and a dark state in one frame scan.

(Summary of the Invention) That is, the present invention is characterized in that the gap between a pair of substrates subjected to alignment treatment is set to be equal to or less than the helical pitch of a ferroelectric chiral smectic liquid crystal compound, and one of the substrates constituting a smectic liquid crystal panel is , selectively applying an alternating signal having a time width between the first inversion time and the second inversion time of the liquid crystal compound, and an alternating signal having a time width larger than the longer inversion time. At the point.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of a smectic liquid crystal device used in the present invention, and reference numeral 1 in the figure indicates one substrate constituting a liquid crystal display panel;
Segment electrodes 1a, 1 made of transparent conductive material
A, 1a, . It is constructed by forming a horizontal alignment film layer 1c (FIG. 2A).
2 is the other substrate constituting the liquid crystal display panel;
A polyimide thin film is provided on the surface of the electrically insulating transparent plate 2b on which the common electrodes 2a, 2a, 2a... are formed perpendicularly to the segment electrodes 1a, 1a, 1a..., and the surface of this thin film is oriented in one direction. It is constructed by forming a uniaxially oriented film layer 2c which is oriented in only one direction by performing a rubbing process (FIG. 2B). These two substrates 1 and 2 are arranged in parallel with the randomly horizontally oriented thin film 1c and the uniaxially oriented film layer 2c facing each other with a gap smaller than the helical pitch of the liquid crystal compound. niS-4-
0(2-methyl)butylresolcylidene-4-
Alkyl n-thictylaniline and P-n-octylphenyl-P'-6-methyloctyloxybenzoate A display panel 6 is constructed by filling a ferroelectric chiral smect liquid crystal compound 3 made by mixing equal proportions of ferroelectric liquid crystal compounds 3 and sealing the periphery of the substrate with a sealant to form a cell structure. In addition, the symbols 4 and 5 in the figure are
Each shows a polarizing plate placed on the surface of the substrate.

When voltage is applied to the electrodes of the liquid crystal panel configured in this way and the domain reversal speed is investigated, as shown in Figure 3, when the same level of voltage is applied, the speed at which the domain changes from a bright state to a dark state is τ ₁ and the speed at which the dark state changes to the bright state τ ₂ are different, and a response time difference Δτ occurs between the two.

In the present invention, writing in a bright state and writing in a dark state are executed simultaneously by actively utilizing this time difference Δτ when switching display states.

Next, details of the drive circuit according to the present invention will be explained based on an embodiment.

FIG. 4 shows an embodiment of the present invention, in which reference numeral 7 is a common electrode drive circuit connected to the common electrodes 2a, 2a, 2a, . . . of the above-mentioned smectic liquid crystal panel 6; A segment electrode drive circuit connected to the segment electrodes 1a, 1a, 1a, . The voltage is configured to be applied to the pixel.

That is _, when selecting _a pixel, _a voltage |V ₁ A dark state write signal consisting of _a positive direction pulse P ₁ (FIG. 5a) with a duration T ₁ at a voltage |V ₁ |, and a maintenance alternating at a voltage |V ₁ /N| The first mode signal (FIG. 2) consists of a signal with a time width T ₂ equal to or longer than the time required to change from a dark state to a bright state τ 2 at the same level _of voltage |V ₁ |
With the negative direction pulse P ₃ (Figure C), the voltage |V ₁ |
A bright state write signal consisting of a pulse _P4 in the positive direction with a time width _T2 , and a second mode signal consisting of a sustain signal 2, a voltage that does not cause inversion in liquid crystal molecules when not selected |V ₁ /
It is configured to selectively output a third mode signal E consisting of an alternating signal having a time width of N|.

Next, the operation of the device thus constructed will be explained.

When no electric field is applied to the electrodes 1a and 2a, the liquid crystal molecules are enclosed in a narrow gap smaller than the helical pitch, and one end of the liquid crystal molecule is captured by the random horizontal alignment film layer 1c, but not aligned in the plane direction. Under a free state, the other end of the liquid crystal molecule is biased in one direction by the uniaxial alignment film layer 2c. As a result, all the liquid crystal molecules filled in the substrates 1 and 2 are aligned in one direction, and the entire panel surface is maintained at a uniform optical density without any pattern appearing, creating a uniform background. form.

In this state, when the first mode signal is applied, the liquid crystal molecules of the selected pixel are exposed to an electric field with a duration T ₁ that is longer than the inversion time τ ₁ and shorter than the inversion time τ ₂ at the voltage −V ₁ of the pulse P ₁ , it is fully inverted to a dark state. When pulse P ₂ is applied after this inversion, the liquid crystal molecules of the selected pixel will be inverted to the bright state because the time width T ₁ of this pulse P ₂ is shorter than the time τ ₂ for switching from the dark state to the bright state. is not possible, and the dark state, that is, pulse P ₁
The write state is maintained by A sustain signal applied after this write signal dynamically holds the liquid crystal molecules of the selected pixel in a dark state position.

When the second mode signal is applied, the liquid crystal molecules of the selected pixel will have an inversion time τ ₁ at the voltage −V of the pulse P ₃
Because it is acted upon by an electric field of longer duration T ₂ ,
Once, it changes to a dark state. However, since the pulse P ₄ that is subsequently applied has a time width T ₂ longer than the inversion time τ ₂ from the dark state to the bright state at this voltage V ₁ , the liquid crystal molecules are not affected by the pulse P ₃ . The written dark state is reversed and a bright state is written. A sustain signal applied after this write signal maintains the liquid crystal molecules of the selected pixel in a bright state.

As a result, writing in the dark state and writing in the bright state can be executed at extremely high speeds of several hundreds of microseconds. Needless to say, in the above process, the liquid crystal molecules are alternately subjected to voltages having the same voltage level and duration, so that no residual charge is generated in the pixels.

Hereinafter, in this way, either the first mode signal or the second mode signal is selected in accordance with the state to be written, and the dark state and bright state can be written by scanning one frame.

In this embodiment, after the pattern is displayed, an alternating voltage having a peak value of 1/N of the driving voltage is applied to maintain the displayed content.
Since the liquid crystal molecules are captured by one new alignment axis of the random horizontal alignment film layer 1c, the orientation of the liquid crystal molecules is maintained even if the application of the alternating voltage is removed, and the display content can be stored.

Further, in this embodiment, the first mode signal is used for writing in the dark state, and the second mode signal is used for writing in the bright state, but these may be changed as appropriate depending on the operating characteristics of the target liquid crystal panel. Needless to say.

FIG. 6 shows a second embodiment of the present invention, in which gradation display is performed using the change in pixel density with respect to the electric field application time shown in FIG. 7, and when selecting a pixel, the peak When the voltage is |V ₁ |, the time required for the tip side to change from the bright state to the dark state from V ₁ /2 τ ₁
and the time required to change from the dark state to the bright state τ ₂
The negative direction pulse P ₅ modulated by the time width Tx between (A in the same figure), the peak voltage |V ₁ | is 1/2
a dark state write signal consisting of a positive direction pulse P ₆ modulated by a time width Tx on the more advanced side;
The fourth mode signal B consists of a maintenance signal alternating with a voltage of |V ₁ /N|. The time required for the tip side to change from a dark state to a bright state from |V ₁ /2| when the peak voltage is |V ₁ | A negative-going pulse P ₇ modulated by a time width Ty larger than τ ₂ and a peak voltage of |V ₁ |,
Positive direction pulse P ₈ modulated by time width Ty
Bright state write signal and voltage |V ₁ /N
The fifth mode signal D consisting of a maintenance signal alternating with | is applied, and the third mode signal E described above is applied when not selected.

According to this embodiment, when the fourth mode signal is applied, the liquid crystal molecules in the selected pixel change to the dark state side with a concentration proportional to the voltage _-V1 and the time width Tx of this pulse _P5 (Fig. 7). ). When a pulse P ₆ is applied in such a state, the time width Ty of the peak voltage V ₁ is shorter than the reversal time τ ₂ to switch from the dark state to the bright state, so the liquid crystal molecules will be at the position of the dark state. The concentration state written by pulse _P5 is maintained. A sustain signal applied after this write signal causes the liquid crystal molecules to dynamically maintain the display density around the selected position.

When the fifth mode signal is applied, the liquid crystal molecules will move because the time width Ty of the pulse P ₇ is longer than the inversion time τ ₂ .
Once, it changes to a dark state. However, since the pulse _P8 that is subsequently applied has a time width Ty sufficient to move the liquid crystal molecules from the dark state to the bright state side, the liquid crystal molecules do not absorb the dark written by the pulse _P7 . It is moved from the state to the light state side, and the time width is
The brightness will be written in proportion to Ty. As a result, a pattern having gradation characteristics can be written in one step at a very high speed of several hundreds of microseconds.

Note that in this embodiment, gradation is given to the dark state and bright state, but the same effect can be achieved even if gradation is given only to one of them, for example, when writing in the dark state. That is clear.

In addition to the above-mentioned smectic liquid crystal with ferromagnetic properties, there are also A chiral smectate liquid crystal compound such as a pyrimidine liquid crystal compound represented by 2-methylbutyl P-[(P-n-decyloxybenzylidene)amino] can be used.

In the above embodiment, a uniaxially oriented film layer and a random horizontally oriented film layer are formed using polyimide on the surface of the substrate, but materials for forming the uniaxially oriented film include polyvinyl alcohol, polyvinyl alcohol, polyimide, etc. Organic films such as fluororesin and silane
In addition to polyimide, organic films such as epoxy, polyvinyl alcohol, fluororesin, polyurethane, silane, phenol, and urea, and SiO ₂ are used to form the random horizontal alignment film on the other substrate. It was confirmed that inorganic films made by vapor-depositing materials such as ₂ and MgF ₂ can be used.

(Effects) As described above, according to the present invention, an alternating signal having a time width between the first inversion time and the second inversion time of the liquid crystal compound, and Since the write signal is an alternating signal with a time width larger than the longer reversal time, it is possible to write the bright state and the dark state within one frame scanning period while taking advantage of memory retention and background uniformity. As a result, chiral smect liquid crystal devices such as display devices and optical shutters with high scanning speeds can be realized.

[Brief explanation of drawings]

FIG. 1 is a perspective sectional view of a device showing one embodiment of a liquid crystal panel used in the present invention, and FIG.
FIG. 3 is an explanatory diagram showing the rubbing direction of the substrate in the same device as above, FIG. 3 is an explanatory diagram showing the applied voltage and response speed in the same device, and FIG. 5A to 5E are waveform diagrams showing the operation of the same device, FIGS. 6A to 6E are waveform diagrams showing other embodiments of the present invention, and FIG. 7 is a graph showing the electric field application time and pixel density. Figure 8 is a schematic diagram showing the molecular arrangement of chiral smectic liquid crystal, and Figure 9 A and B show the arrangement of molecules when the cell gap is made smaller than the helical pitch of the liquid crystal molecules. The schematic diagram shown in FIG. 10 is an explanatory diagram showing the relationship between domains of a smectic liquid crystal and polarized light. 1... Substrate, 1a... Electrically insulating transparent plate, 1c
...Random horizontal alignment film layer, 2...Substrate, 2a...
...Electrically insulating transparent plate, 2c... Uniaxial alignment film layer, 3
...Chiral smectic liquid crystal compound.

Claims (1)

[Scope of Claims] 1. One substrate whose surface has been subjected to uniaxial alignment treatment on which electrodes are formed, the other substrate whose surface has been subjected to random horizontal alignment treatment on which electrodes have been formed, and both of the above substrates. They are arranged parallel to each other with their orientation surfaces facing each other, and in the space formed between the substrates, a layer made of a ferroelectric chiral smect liquid crystal compound is sealed with a layer thickness equal to or less than the helical pitch of the liquid crystal compound. a liquid crystal layer; a pixel with the liquid crystal layer interposed at the intersection of the electrodes of both substrates; a polarizing plate disposed to sandwich both substrates; A signal generating means for applying a voltage to the pixel; In the liquid crystal display device, the second inversion time for changing from the second state to the first state when a pulsed voltage having the other polarity is applied is longer than the inversion time of the signal generating means. at least a pair of pulsed voltages of one polarity and the other polarity, each having a time width between the first reversal time and the second reversal time, the pulsed voltage of one polarity; a first alternating voltage in which pulsed voltages of the other polarity are arranged after the first alternating voltage of the one polarity, each having a time width larger than either the first inversion time or the second inversion time. and a second alternating voltage including at least one pair of pulsed voltages of the other polarity, wherein the pulsed voltage of the one polarity is followed by the pulsed voltage of the other polarity. A liquid crystal display device characterized by outputting to a layer.