JPH0310215A - Driving method for liquid crystal display element - Google Patents

Abstract

PURPOSE:To make a liquid crystal display which has no irregularity in display light and shade and an excellent contrast ratio by using bipolar high-frequency AC pulse trains whose mean voltage level is zero, and bringing the selection and nonselection of display picture elements under time-division control and driving a liquid crystal element. CONSTITUTION:A driving waveform which contains no DC component and whose mean voltage level is zero is used and a bipolar high-frequency pulse train P1 which allows a liquid crystal material in a dimming layer to be in a saturated response state and bipolar high-frequency pulse trains P2 - P4 which make the liquid crystal material in the dimming layer below a threshold value are applied properly to respective electrodes of the liquid crystal display element on a time-division basis to perform the selection/nonselection control, thereby displaying characters and a graphic form. Namely, the element is driven at a high frequency with the bipolar pulses and then electrostatic charging which causes an offset voltage is precluded to eliminate the irregularity in display light and shade. Consequently, the display of high quality can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention is capable of electrically controlling scattering and transmission of light, has a light control layer between two substrates having electrodes, and has a light control layer between two substrates having electrodes. A driving method for a liquid crystal display element in which the layer is composed of a liquid crystal material and a transparent fixing substance, and liquid crystal droplets are dispersed in a polymer, or in which a three-dimensional network of polymers is formed in the liquid crystal phase. This relates to a driving method.

"Conventional Technology Currently, the mainstream of liquid crystal display elements is the TN type (twisted non-machining type).The TN type was first put into practical use as a numeric display element, and the element was driven using a static drive method.After that, Due to the problem of the number of circuits required to increase the information display capacity, time-division driving has become the mainstream driving method for liquid crystal display elements.In particular, for dot matrix type liquid crystal display elements, the number of driving circuits is too large, making it impractical. Therefore, many time-division driving methods have been proposed from the viewpoints of reducing the number of drive circuits and improving the contrast ratio during time-division driving.Generally, time-division driving methods include the 1/2 bias method, There are operating methods called the 1/3 bias method and the optimal bias method.

Furthermore, for AC driving, for example, there is a method of inverting the polarity every scanning period.

However, unlike the dynamic scattering type (DS), a time-division driving method for a liquid crystal display element that can control scattering or transmission of light using an electric field effect has not yet been put to practical use.

``Problem to be Solved by the Invention'' In the conventional time-division driving method of a TN type liquid crystal display element, different drive waveforms are applied to each of the display pixels and non-display pixels, which are numerous on the display screen, depending on the characters or graphics. Display unevenness is prevented by equalizing the effective values of the voltages applied to each pixel on the display surface. on the other hand,
A liquid crystal display element in which liquid crystal droplets are dispersed in a polymer, or
The polymer is formed into a three-dimensional network in the liquid crystal phase, and in the presence of an electric field, the liquid crystal molecules align in the direction of the electric field.
When the refractive index n0 of the liquid crystal and the refractive index np of the polymer are close to each other, light is transmitted, and when the electric field is removed, the liquid crystal molecules return to random alignment and scatter the light.
When driving a type liquid crystal display element using a time-division driving method, even though the effective value of the voltage is the same, unevenness in display density may occur in each display pixel and non-display pixel.
Problems such as poor contrast ratio occur.

The present invention provides a high-quality display by suppressing unevenness in display shading caused by differences in displayed figures and characters.

"Means for Solving the Problems" The driving method of the present invention uses a driving waveform that does not include a DC component and has an average voltage of zero, and the driving waveform brings the liquid crystal material in the light control layer into a saturated response state. A bipolar high-frequency pulse train that brings the liquid crystal material in the light control layer to a state below the threshold value, and these pulse trains are applied to each electrode of the display element in a time-sharing manner as appropriate. This is a driving method that controls selection and non-selection to display characters and figures.

A liquid crystal display element in which a liquid crystal layer is dispersed in a polymer, and
The conventional TN liquid crystal display element is a liquid crystal display element in which polymers are formed in a three-dimensional network in the liquid crystal layer and the liquid crystal phase forms a continuous phase.
When a liquid crystal display element is driven using a time-division driving method, unevenness in display density occurs in a large number of display pixels and non-display pixels on a display surface, and the contrast ratio deteriorates. This is because charges are charged between the two electrodes due to the drive waveform, and the charges are not discharged quickly, causing an offset voltage in the liquid crystal display element. Even when the external electric field is removed and the orientation of the liquid crystal molecules in the light control layer returns to a random state and scatters light, an internal electric field remains inside the element and connects the electrical neutral point inside the element and the ground of the drive device. Operating conditions for time-division driving as seen from the device side (when not selected, a potential difference below the dimming +A II threshold is applied to non-display pixels; when selected, the dimming The conditions under which a potential difference greater than the threshold value can be applied to display pixels to bring them into a saturated response state are deviated, and a potential difference that exceeds the threshold value is applied to non-display pixels even when they are not selected. In some cases, a potential difference required for a saturated response state is not applied to display pixels, causing uneven display shading and a decrease in contrast ratio.

When attempting to drive a conventional TN-type liquid crystal display element using the time-division driving method, a DC bias voltage is applied to the element together with the time-division drive waveform in order to reduce the influence of the generated offset voltage. It is necessary to satisfy the operating conditions for time-division driving. In addition, the offset voltage required for each individually manufactured element differs slightly, so it is troublesome to adjust the DC bias voltage to the required DC bias voltage for each element.
This DC bias voltage causes deterioration of the liquid crystal, and is insufficient as a method for driving a liquid crystal display element, which is the object of the present invention. Therefore, in order to prevent uneven display shading and to operate the device stably over a long period of time by time-division driving, it is necessary to find a method that does not charge the inside of the display device, that is, to reduce the average voltage level applied to the liquid crystal display device. What is necessary is to use a method of driving the element so that it can be made zero.

By driving with bipolar pulses and high frequency, it is possible to prevent charging of charges that cause offset voltage and eliminate unevenness in display density. The frequency of the bipolar pulse is an integral multiple of twice or more of the frequency corresponding to the selected time for displaying the pixel, and the upper limit is the dielectric relaxation frequency of the liquid crystal material used in the element, or the dielectric anisotropy of the liquid crystal material is positive. The upper limit of the frequency range showing .

A bipolar high-frequency pulse train is caused by a potential difference that occurs at the intersection between the electrodes on two substrates. It is sufficient to apply independent waveforms.

The waveform applied to the electrodes is changed according to the desired display, and the combination of independent waveforms applied to one electrode and the other electrode is changed and applied to each electrode to select pixels so as to generate the desired bipolar high-frequency pulse train. , controls non-selection and displays characters and figures. The selected pixel becomes a display pixel by aligning the liquid crystal molecules in the light control layer in the direction of the electric field due to the generation of a potential difference of the bipolar high-frequency pulse train that brings the liquid crystal material in the light control layer into a saturated response state.

It is preferable that the peak value of the bipolar high-frequency pulse train of the display pixel exceeds the saturation voltage. In the case of non-selection, a potential difference of a bipolar high-frequency pulse train is generated in the non-display pixel portion to bring the liquid crystal material in the light control layer into a state below the threshold value. Even when this waveform is applied, the liquid crystal molecules in the light control layer are in a random direction regardless of the direction of the electric field. It is preferable that the peak value in the case of non-selection is equal to or lower than the threshold voltage of the light control layer.

Examples of the electrodes of the liquid crystal display element include a combination of a scanning electrode row and a signal electrode row, a combination of a segment electrode group and a common electrode, and the like.

As described above, the driving method of the present invention uses a driving waveform in which the average voltage level 0 is zero, thereby suppressing the charging of electric charge that causes a shift in the operating point of time-division driving, and preventing uneven display shading and contrast. It is possible to improve the ratio.

The driving waveform is a bipolar high-frequency pulse train that brings the liquid crystal material in the light control layer into a saturated response state, and a bipolar high-frequency pulse train that brings the liquid crystal material in the light control layer into a state below a threshold value. This is a driving method in which characters and figures are displayed by appropriately applying voltage to display elements in a time-division manner to control selection and non-selection. This is an excellent method for time-division driving of a liquid crystal display element whose light control layer is made of a liquid crystal material and a transparent solid substance.

"Example" Example 1 Liquid crystal composition (A) Composition 1 Transition temperature 68.5°c (N-1) <-2
5°c (C-N) Refractive index n. -1,787 no =1.533 Δn=0.254 Threshold voltage (vth) 1. ], 5V
Viscosity at 20°C 59c, p.

Dielectric constant anisotropy Δε-26.9 Liquid crystal composition (A) as liquid crystal material
■r□5, birefringence: 0.254, ordinary refractive index n. :1
．． 533, dielectric anisotropy Δε: 26.9) 80% by weight,
0.4% of 2-hydroxy 2-methyl-1-phenyl-propan-1-one as a polymerization initiator and 19.6% by weight of caprolactone-modified 2-hydroxypavirate neopentyl glycol cyacrylate as a polymerizable compound were mixed. .

The nematic phase isotropic liquid phase transition temperature of this solution was examined using a differential calorimeter and was found to be 32°C. Therefore,
The sample was heated to 40°C, which is 8°C higher than this transition temperature, to provide the ultraviolet curing temperature. Average particle size 10μm as a spacer
Add a small amount of glass fiber fine powder to 20cm x 2
The ITO glass was inserted between two 0 cm ITO glass plates, the entire ITO glass was heated to 40°C, and the entire surface of the ITO glass plate was uniformly irradiated with ultraviolet rays with an intensity of 40 mW/c [to produce a liquid crystal display element. did. The energy given was 400
Corresponds to mJ/CTM. The electrode spacing of a liquid crystal display element is 1
It is 1 μm. The liquid crystal display element becomes IT when irradiated with ultraviolet rays.
The entire surface of the glass plate became cloudy and opaque.

When this liquid crystal display element was investigated, the threshold voltage V t
h-7,8' V r'ms, saturation voltage V's-t
-17.8V, ... Transmittance when no voltage is applied, 6%
, the maximum transmittance was 85%.

When the cross section of the light control layer formed between two glass substrates was observed with a scanning electron microscope, a three-dimensional network of uniform nets with a size of 1 to 1.3 μm was observed.

FIG. 1 shows a schematic diagram of an example of the configuration of a liquid crystal element and a drive circuit in an embodiment of the present invention. FIG. 2 shows an example of a specific drive waveform in the drive method of the present invention. In FIGS. 1 and 2, the scanning signal S is sequentially supplied from the scanning signal circuit 1 to the scanning electrode sections X1 to X8, and when the supply of the scanning signal S to X8 is finished, the scanning signal is sequentially supplied from Xl again. be done. The selection signal circuit 2 supplies a selection signal RC or a non-selection signal C to a desired electrode of the signal electrode portions Y1 to Y5 in accordance with a desired display.

When the selection signal RC and the scanning signal S are supplied at each intersection of the orthogonal scanning electrode section and the signal electrode section, the phase of the selection signal RC is inverted to the phase of the scanning signal, so ±3H (H is an arbitrary potential A high-frequency AC pulse train P1 with a potential difference of
is expressed, causing the liquid crystal molecules in the light control layer to enter a saturated response state, allowing light to pass through and become display pixels. Non-selection signal C and scanning signal S
When 3 4 is supplied, the phase of the non-selection signal C and the phase of the scanning signal S are in phase, so a high-frequency AC pulse train P with a potential difference of ±H is generated.
2 is generated, causing the liquid crystal molecules in the light control layer to be in a state below the threshold value, causing light scattering, resulting in a non-display pixel. During non-scanning, a high-frequency pulse train P3. When P4 occurs, the liquid crystal molecules in the light control layer become lower than the threshold value, and the pixel becomes a non-display pixel.

In the previously prepared liquid crystal display element, the above drive waveform was applied to the 7-trix electrodes shown in FIG. 1, and the drive was time-divisionally driven at 1/8 duty.

When the value of H shown in Fig. 2 was set to 8 volts and time-division driving was performed, the transmittance of each pixel when selected was 82%, and when not selected, the transmittance was 7%, and unevenness in display density did not occur. There wasn't.

On the other hand, when the above liquid crystal element was driven with a 1/3 bias method and 1/8 duty, which is the driving method for a general TN type liquid crystal display element, the transmittance when selected varied between 65% and 76%, and when not selected. The transmittance also varied between 7% and 16%, resulting in uneven display shading. Further, when the potential difference between the electrodes after applying each drive waveform of 5 was measured, it was 27 mV with the drive waveform of the present invention. - The driving waveform of a TN type liquid crystal display element used in a boat showed 1.7 .

As described above, the driving method described above produces a bipolar pulse train P1 that brings the liquid crystal molecules in the light control layer into a saturated response state, and a bipolar pulse train P2 that brings the liquid crystal molecules in the light control layer into a state below a threshold value.
P3. By appropriately generating P4 at each intersection of orthogonal electrodes, desired characters and figures could be displayed using the dots 1 to 1. The contrast ratio between different pixel displays was constant regardless of the display content, and a display without shading could be obtained.

H is 3H, when the liquid crystal molecules in the light control layer are in a saturated response state,
It is preferable to adjust so that the liquid crystal molecules in the light control layer are in a state below a threshold value.

Although the frequency of each pulse train was set to 1 ktlz, it is not limited to this frequency.

Embodiment 2 FIG. 3 shows an example of a specific drive waveform in an embodiment of the present invention. In FIGS. 1 and 3, during scanning, the scanning signal S is sequentially supplied from the scanning signal circuit 1 to the scanning electrode groups XI to X8, and when the supply of the scanning signal S to X8 is completed, the scanning signal S is sequentially supplied from the scanning signal circuit 1 to the scanning electrode groups XI to X8. A scanning signal is provided. During non-scanning, a non-scanning signal NS is supplied, and the non-scanning signal is inverted in phase to the scanning signal S. The selection signal circuit 2 selects signal electrode groups Y1~ according to the desired display.
A selection signal RC is supplied to a desired electrode of Y5. At each intersection of the orthogonal scanning electrode group and signal electrode group, when the selection signal RC and the scanning signal S are supplied, the phase of the scanning signal S is inverted to the phase of the selection signal RC, so ±3H (H is an arbitrary value) A high-frequency alternating current pulse train P1 with a potential difference (indicating the potential) is developed to bring the liquid crystal molecules in the light control layer into a saturated response state, allowing light to pass through and form display pixels. When the non-scanning signal NS and the selection signal RC are supplied, the phase of the non-scanning signal NS and the selection signal R
Since the phases of C are in the same phase, a high frequency AC pulse train P3 with a potential difference of ±H is generated, causing the liquid crystal molecules in the light control layer to be in a state below the threshold value, causing light scattering and becoming a non-display pixel.

When not selected, a high-frequency pulse train P2 to P4 with a potential difference between 1 and 2 that coincides with the scanning signal S or non-scanning signal NS is generated, and the liquid crystal molecules in the light control layer are brought into a state below the threshold value, thereby becoming a non-display pixel.

The specific driving waveform described above was actually applied to the matrix electrode type liquid crystal display element shown in FIG. 1, and time division driving was performed at 1/8 duty. The frequency of each pulse train is 1k
I went with llz. A pyridine-based liquid crystal composition (T
N+= 68.3°C1 threshold VTR= 1.15
V, , , birefringence -0,254, dielectric anisotropy -2
6, 3) and a liquid crystal display element in which a diacrylic ultraviolet curable resin was used as the transparent solid material and a three-dimensional network was formed in the liquid crystal phase as the light control layer. The threshold value of this device is 7.6 V, ffi, and the saturation voltage is 17.8 V, ms. When the value of H shown in Figure 3 was set to 8 volts and time-division driving was performed, the transmittance of each pixel when selected was 82%, and when not selected, the transmittance was 7%.
No unevenness of shading occurred in the display. The contrast ratio between different pixel displays was constant regardless of the display content, and a display without shading could be obtained.

7 8 "Effects of the Invention" According to the present invention, there is provided a liquid crystal display element in which liquid crystal droplets are dispersed in a polymer, or in which a polymer is formed in a three-dimensional network in a liquid crystal phase so that the liquid crystal phase forms a continuous phase. This technology uses a bipolar high-frequency alternating current pulse train with an average voltage level of zero to control the selection and non-selection of display pixels in a time-division manner to drive the liquid crystal display elements, allowing for time-division driving with high display quality. It has been realized. By applying a bipolar high-frequency AC pulse train to the element, deterioration of the liquid crystal is prevented, and the contrast ratio between different pixels can be kept constant regardless of the displayed content, resulting in a liquid crystal display with a good contrast ratio without uneven display shading. It provides: Conventionally, it has been thought that the above-mentioned type of liquid crystal display element cannot be driven in a time-division manner, but if the threshold of the element is steep, the driving method of the present invention can eliminate the inconvenience caused by off-sensing voltage generation in the liquid crystal element. It can be resolved,
If driven, time-division driving becomes possible, and its effects are enormous, such as the ability to significantly reduce the number of drive circuits for liquid crystal display elements with a large information display capacity.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a liquid crystal display element, and FIGS. 2 and 3 are explanatory diagrams showing examples of driving waveforms for making the present invention concrete. X1 to x8...Scanning electrode group, Y1 to Y5...Signal electrode group, S...Scanning signal group, NS...Non-scanning signal, RC
...Selection signal, C...Non-selection signal, P1 to P4...
・Pulse train.

Claims (5)

[Claims] 1. A light control layer is provided between two substrates having electrodes, the light control layer is made of a liquid crystal material and a transparent solid material, scanning electrode arrays are arranged on one substrate, and the scanning electrodes are arranged on the other substrate. A method for driving a liquid crystal display element, in which signal electrode rows are arranged to intersect with the scanning electrode groups, and these electrode rows are arranged in a matrix, and transmission and scattering of light can be electrically controlled. sequentially supplies scanning signals, supplies a signal according to a desired display to the signal electrode group, and brings the liquid crystal material in the light control layer into a saturated response state by a potential difference between the desired signal and the scanning signal. a pulse train, and a bipolar pulse train that brings the liquid crystal material in the light control layer into a state below a threshold value of the liquid crystal material due to a potential difference between the desired signal and the scanning signal or when the scanning signal is not supplied. A method for driving a liquid crystal display element, characterized in that the voltage is applied in parts to make the average voltage level of a driving waveform applied to the light control layer zero. 2. A light control layer is provided between two substrates having electrodes, the light control layer is made of a liquid crystal material and a transparent solid material, the liquid crystal material forms a continuous phase, and the transparent solid material is a liquid crystal material. A scanning electrode array is arranged on one substrate, a signal electrode array is arranged across the scanning electrode array on the other substrate, and these electrode arrays are arranged in a matrix. 2. The driving method according to claim 1, further comprising driving a liquid crystal display element arranged. 3. A bipolar pulse train that brings the liquid crystal material in the light control layer into a saturated response state due to a potential difference between the desired signal and the scanning signal, and a potential difference between the desired signal and the scanning signal or when the scanning signal is not supplied. drive a liquid crystal display element using a liquid crystal material exhibiting positive dielectric anisotropy in a frequency range with a bipolar pulse train that brings the liquid crystal material in the light control layer into a state below a threshold value. A method for driving a liquid crystal display element according to claim 1 or 2. 4. A light control layer is provided between two substrates having electrodes, the light control layer is made of a liquid crystal material and a transparent solid substance, and a segment electrode group is arranged on one substrate and divided into the other substrate. A method for driving a liquid crystal display element in which transmission and scattering of light can be electrically controlled in a liquid crystal display element having a structure in which a common electrode is arranged, wherein scanning signals are sequentially supplied to the divided common electrode group. a bipolar pulse train for supplying a signal according to a desired display to the segment electrode group and bringing the liquid crystal material in the light control layer into a saturated response state by a potential difference between the desired signal and the scanning signal; time-divisionally applying a bipolar pulse train that brings the liquid crystal material in the light control layer into a state below a threshold value of the liquid crystal material due to the potential difference between the signal and the scanning signal or when the scanning signal is not supplied. ,
A method for driving a liquid crystal display element, characterized by reducing the average voltage level of a driving waveform applied to a light control layer to zero. 5. A light control layer is provided between two substrates having electrodes, the light control layer is made of a liquid crystal material and a transparent solid material, the liquid crystal material forms a continuous phase, and the transparent solid material is a liquid crystal material. The liquid crystal material forms a continuous phase, the transparent solid material is dispersed in the liquid crystal material in a three-dimensional network, and one substrate has a group of segment electrodes. 5. The driving method according to claim 4, further comprising driving a liquid crystal display element having a structure in which a common electrode is arranged and divided on the other substrate.