JP2007304461A - Reflective liquid crystal display element and driving method thereof - Google Patents

Abstract

The present invention relates to a reflective liquid crystal display element capable of obtaining a display with a low focal conic reflectivity and a high contrast ratio, and capable of obtaining a uniform display within a display surface in a relatively short rewriting time, and its An object is to provide a driving method.
A reflective liquid crystal display device according to the present invention includes a first transparent electrode substrate, a second transparent electrode substrate, and a cholesteric liquid crystal material. Further, the reflection type liquid crystal display device according to the present invention includes a planar means 12 for bringing the cholesteric liquid crystal material into a planar state at once, a focal conic means 13 for bringing the cholesteric liquid crystal material into a focal conic state, and image writing. And writing means 14 for performing. The focal conic means 13 is characterized in that the second bipolar pulse is applied to the cholesteric liquid crystal material a plurality of times mutually with no voltage application period.
[Selection] Figure 5

Description

  The present invention relates to a reflective liquid crystal display element and a driving method thereof, and more particularly to a reflective liquid crystal display element using a cholesteric liquid crystal material and a driving method thereof.

  A cholesteric liquid crystal display element has a structure in which a cholesteric liquid crystal material is sandwiched between two glass substrates on which transparent electrodes are formed. The cholesteric liquid crystal display element displays a desired image by switching the alignment state of the cholesteric liquid crystal material between a planar state and a focal conic state (transiently homeotropic state) by applying a pulse voltage between the transparent electrodes. ing.

  When a sufficiently high voltage is applied to the cholesteric liquid crystal display element for a sufficiently long period, the liquid crystal molecules are in a homeotropic state during the application period. Thereafter, when the voltage application is stopped, the liquid crystal molecules are twisted while returning to the initial orientation (parallel to the substrate surface), and are in a planar state. In this planar state, when the helical pitch of the liquid crystal molecules is P and the average refractive index is n, light having a wavelength λ = nP can be selectively reflected. Therefore, the cholesteric liquid crystal display element uses the planar state as the bright state.

  Next, when a pulse having a voltage lower than that of the pulse for bringing the liquid crystal molecules into a homeotropic state and having a narrow pulse width is applied to the cholesteric liquid crystal display element, the liquid crystal molecules are brought into a focal conic state. In the focal conic state, the liquid crystal molecules have minute domains with different alignment states, and thus become slightly turbid but basically become transparent. Therefore, the cholesteric liquid crystal display element has a light absorption layer on the back surface to absorb external light and uses the focal conic state as black display.

  Thus, the cholesteric liquid crystal display element can be used as a reflective display element by switching the cholesteric liquid crystal material between a planar state and a focal conic state.

  Further, the planar state and the focal conic state of the cholesteric liquid crystal material can maintain the alignment state even when no voltage is applied. Therefore, in the cholesteric liquid crystal display element, it is sufficient to apply a voltage only at the time of switching the alignment state, and a display element with low power consumption can be obtained. For this reason, the cholesteric liquid crystal display element cannot use a driving method such as a TN mode liquid crystal that cannot maintain the alignment state in a normal voltage non-application state. Therefore, a unique driving method that requires a reset process must be applied to the cholesteric liquid crystal display element, as with other display elements having memory characteristics.

  The driving method of the cholesteric liquid crystal display element is roughly classified into two types: planar reset driving and focal conic reset driving. The difference between the two types of driving methods is that the state is set to the reset state because the image is written after the former image is erased once reset to the memory state of the planar state or the focal conic state. Hereinafter, the two driving methods will be described in detail.

  Normally, a liquid crystal display element that displays an image by such a driving method has pixels in a matrix configuration. Such a liquid crystal display element sequentially writes a desired image for each line after resetting all the pixels.

  In the case of the planar reset driving, all the pixels are first set to the planar state, and then necessary pixels are sequentially set to the focal conic state to display an image. On the other hand, in the focal conic reset driving, all pixels are first brought into a focal conic state, and then necessary pixels are sequentially brought into a planar state to display an image.

  In actual planar reset driving, first, a sufficiently large pulse is applied to bring the liquid crystal molecules into a homeotropic state in which the liquid crystal molecules are aligned in the electric field direction, and then the voltage application is suddenly stopped to change the liquid crystal molecules to the planar state. When the liquid crystal molecules are in a planar state, light of a specific wavelength can be reflected. This change to the planar state can be achieved with relative ease and good reproducibility. Thereafter, the liquid crystal display element changes to a focal conic state for each line, and performs black writing to display an image. However, the change from the planar state to the focal conic state can reduce the black reflectance by repeatedly writing, but if the writing for each line is repeated, the rewriting time of the image becomes longer, and the actual liquid crystal display It is not suitable as a driving method of the element.

  On the other hand, in the actual focal conic reset drive, first, the focal conic state is set. Therefore, as disclosed in Patent Document 1, a pulse equal to or higher than the threshold voltage in the homeotropic state is applied to collect the previous image in advance. To all the pixels in the planar state. Thereafter, by applying a pulse having a threshold voltage in the focal conic state, all the pixels are collectively brought into the focal conic state. Further, a voltage larger than the threshold voltage in the focal conic state and equal to or lower than the threshold voltage in the homeotropic state is written for each line, and an image is displayed by setting necessary pixels in the planar state.

  When comparing the focal conic reset driving and the planar reset driving, the focal conic reset driving is slightly inferior in reflectivity in the bright state, but the display quality is excellent from the viewpoint of contrast ratio and rewriting time. However, in the focal conic state, the orientation state is unstable, or the in-plane variation occurs in the size of a minute domain, so that the reflectivity at the time of black display varies, and therefore it is not possible to obtain a good display quality. was there.

JP 11-326871 A

  When a reflective liquid crystal display element using a cholesteric liquid crystal material is used to display an image by focal conic reset driving, it is possible to reduce the white turbidity and reflectivity by optimizing the size of the micro domain in the focal conic state. And a good display with a high contrast ratio can be obtained.

  However, the focal conic state obtained by applying a normal bipolar pulse does not have a sufficiently low reflectivity. Moreover, since the application conditions vary slightly, the reflectance of the obtained focal conic state varies, and it is difficult to obtain a favorable focal conic state with low reflectance.

  In addition, if the number of application times (repetition times) of the bipolar pulse is greatly increased, variations in application conditions and the like can be reduced, and a uniform focal conic state can be obtained. However, simply increasing the number of applied bipolar pulses does not reduce the reflectivity in the focal conic state sufficiently. On the contrary, the rewrite time increases as the number of applied pulses increases, resulting in good display. It can no longer be obtained.

  Furthermore, as described above, in the focal conic reset driving, in general, the reflectance in the focal conic state can be made lower than in the planar reset driving. However, when the focal conic reset driving shown in Patent Document 1 is used, the difference from the planar reset driving is not so large, and a display with a sufficiently high contrast ratio cannot be obtained.

  Therefore, the present invention provides a reflective liquid crystal display element capable of obtaining a display with a low focal conic reflectivity and a high contrast ratio, and capable of obtaining a uniform display within a display surface in a relatively short rewriting time, and driving thereof. It aims to provide a method.

  The solution according to the present invention includes a first transparent electrode substrate on which a plurality of scanning electrodes are formed, a second transparent electrode substrate on which a plurality of signal electrodes are formed, the first transparent electrode substrate, and the second transparent electrode. A reflective liquid crystal display device comprising a cholesteric liquid crystal material sandwiched between substrates, and applying a first bipolar pulse for bringing the cholesteric liquid crystal material into a homeotropic state for a predetermined period of time, so that the scanning electrode and the signal electrode Between the scan electrode and the signal electrode by applying a planar means for bringing all the cholesteric liquid crystal materials between them into a planar state and a second bipolar pulse having an applied voltage lower than that of the first bipolar pulse. A focal conic means for bringing all the cholesteric liquid crystal materials in between into a focal conic state, and a predetermined gap between the scanning electrode and the signal electrode. Writing means for applying a predetermined pulse to the cholesteric liquid crystal material to write an image, and the focal conic means applies the second bipolar pulse to the cholesteric liquid crystal material a plurality of times in a voltage non-application period. It is characterized by applying.

  In the reflective liquid crystal display element and the driving method thereof according to the present invention, the focal conic means applies the second bipolar pulse to the cholesteric liquid crystal material a plurality of times in mutual with no voltage application period. Can be controlled with high reproducibility, and a display with a low focal conic reflectivity and a high contrast ratio can be obtained, and a uniform display within the display surface can be obtained in a relatively short rewrite time. There is.

  A cholesteric liquid crystal display element is formed by forming a plurality of line-shaped transparent electrode patterns (scanning electrodes and signal electrodes) having an electrode width of 5 mm and an electrode interval of 1 mm on two transparent electrode substrates, and the transparent electrode pattern on each transparent electrode substrate is A liquid crystal panel arranged to be orthogonal is provided. On each transparent electrode substrate surface, an alignment film made of polyimide for aligning liquid crystal molecules parallel to the substrate surface is formed with a film thickness of 1000 angstroms. In addition, the cholesteric liquid crystal display element does not perform the rubbing process that is performed by a normal liquid crystal display element.

  Next, the cholesteric liquid crystal display element has a helical pitch of 0.35 μm, an average refractive index of 1.50 (ne = 1.58, no = 1) on a liquid crystal panel in which two transparent electrode substrates are bonded with a panel gap of 10 μm. .46) cholesteric liquid crystal material is injected. Thereafter, the liquid crystal panel is heated until the liquid crystal material is in an isotropic state, and then gradually cooled to room temperature. Thereby, the cholesteric liquid crystal display element can sandwich the cholesteric liquid crystal material in a predetermined alignment state between the scanning electrode and the signal electrode.

  The most basic driving waveform of the above-described cholesteric liquid crystal display element is shown in FIG. In addition, the alignment states of the cholesteric liquid crystal material corresponding to the first state 1, the second state 2, and the third state 3 shown in FIG. 1 are schematically shown in FIGS. In FIG. 1, when a sufficiently high voltage is applied for a sufficiently long period, the liquid crystal molecules are in a homeotropic state as shown in FIG. After that, in FIG. 1, when the voltage application is stopped, the liquid crystal molecules are twisted while returning to the initial alignment (parallel to the substrate surface), and the liquid crystal molecules are in a planar state as shown in FIG. Next, in FIG. 1, when a pulse having a voltage lower than that of a pulse that brings liquid crystal molecules into a homeotropic state and having a narrow pulse width is applied to the cholesteric liquid crystal material, the liquid crystal molecules become focal conic as shown in FIG. It becomes a state.

  The above-described cholesteric liquid crystal display element reflects green light when in a planar state. Further, in the above-described cholesteric liquid crystal display element, a black paint is applied to the back surface (reverse viewer side) of the liquid crystal panel so that black display is obtained when the focal conic state is achieved. That is, the above-described cholesteric liquid crystal display element is a reflective liquid crystal display element.

  When the above-described liquid crystal panel is used alone, green is reflected in the planar state and black is displayed in the focal conic state, so that green and black can be displayed. In addition, by adjusting the cholesteric pitch of the liquid crystal material to be injected, a similar liquid crystal panel that produces a red reflective display in the planar state and a similar liquid crystal panel that produces a blue reflective display in the planar state are separately prepared. If a cholesteric liquid crystal display element is formed by laminating liquid crystal panels, black and white or color reflection display is possible.

  The present invention relates to a cholesteric liquid crystal display element to which a driving method capable of displaying a high contrast ratio is applied, regardless of whether or not a liquid crystal panel is laminated. Therefore, in the embodiment described below, a cholesteric liquid crystal display element having only a single liquid crystal panel that performs green and black display described above will be described.

  In each of the following embodiments, a method for driving a cholesteric liquid crystal display element capable of obtaining a display with an excellent contrast ratio will be described. Before that, common portions in the driving methods of the embodiments will be described using the driving waveforms shown in FIG.

  In the drive waveform shown in FIG. 3, first, the first bipolar pulse 4 is applied to erase the previous screen at once. The first bipolar pulse 4 has a voltage equal to or higher than a threshold value that can bring the liquid crystal molecules into a homeotropic state. Specifically, in the case of the cholesteric liquid crystal display element described above, a voltage of 40 V or more and a pulse width of 50 ms or more are sufficient. However, the first bipolar pulse 4 is applied only once at the time of rewriting, and even if the pulse width is increased, the effect on the rewriting time is negligible, so that the previous screen can be completely erased. The pulse width is 100 ms with a margin. This condition of the first bipolar pulse 4 is commonly applied also in the following embodiments.

  After the application of the first bipolar pulse 4, when the voltage application is stopped, the liquid crystal molecules change to the planar state. Thereafter, the second bipolar pulse group 5 is applied to bring all the pixels into a focal conic state collectively. In addition, before applying the second bipolar pulse group 5, the no-voltage application state 6 is necessary. This voltage non-application state 6 is a period for the liquid crystal molecules to sufficiently and reliably change from the homeotropic state to the planar state, and the relationship between the period of the voltage non-application state 6 shown in FIG. 4 and the reflectance. It is sufficient to provide a period of 10 ms or longer. However, this period is also required only once at the time of rewriting, and the effect on the rewriting time is negligible, so a margin is taken to be 100 ms. Also in the following embodiments, the condition of the voltage non-application state 6 is commonly applied.

  As shown in FIG. 3, the second bipolar pulse group 5 has a second bipolar pulse set 52 in which a plurality of second bipolar pulses 51 having a lower applied voltage and a smaller pulse width than the first bipolar pulse 4 are collected, And a voltage non-application period 53.

  FIG. 5 is a block diagram of a reflective liquid crystal display element (cholesteric liquid crystal display element) according to the present invention that performs the above-described focal conic reset driving. In FIG. 5, the reflective liquid crystal display element includes a drive unit 10 and a liquid crystal panel 11. Further, the drive unit 10 includes a planar unit 12, a focal conic unit 13, and a writing unit 14 as shown in FIG.

  The planar means 12 corresponds to the period during which the first bipolar pulse 4 shown in FIG. 3 is applied. Further, the planar means 12 applies a first bipolar pulse 4 for bringing the cholesteric liquid crystal material of the liquid crystal panel 11 into a homeotropic state for a predetermined period, and collects all the cholesteric liquid crystal material between the scanning electrode and the signal electrode. To the planar state.

  The focal conic means 13 corresponds to a period in which the second bipolar pulse group 5 shown in FIG. 3 is applied. Further, the focal conic means 13 applies the second bipolar pulse group 5 including the second bipolar pulse 51 whose applied voltage is lower than that of the first bipolar pulse 4, and all the cholesteric liquid crystal material between the scanning electrode and the signal electrode. To the focal conic state.

  The writing unit 14 writes an image by applying a predetermined pulse to the cholesteric liquid crystal material between the predetermined scanning electrode and the signal electrode. Specifically, a bipolar pulse having an applied voltage higher than that of the second bipolar pulse 51 and lower than that of the first bipolar pulse 4 is applied to a cholesteric liquid crystal material between a predetermined scanning electrode and a signal electrode. The bipolar pulse applied by the writing means is not shown because it is a general driving method.

  The following embodiments are applied to the reflective liquid crystal display device having the above-described configuration and the driving method thereof.

(Embodiment 1)
Using the cholesteric liquid crystal display element described above, the batch reset condition to the planar state and the period from the reset to the planar state to the batch reset to the focal conic state (period in which no voltage is applied 6) satisfy the above conditions. Using. Specifically, the applied voltage of the first bipolar pulse 4 shown in FIG. 3 was set to 40 V, the pulse width was set to 100 ms, and the period of the voltage non-application state 6 was set to 100 ms.

  Thereafter, in the present embodiment, the second bipolar pulse group 5 shown in FIG. 6 is applied to bring the liquid crystal molecules into a focal conic state. Specifically, the voltage of the basic second bipolar pulse 51 is 30 V, the pulse width is 10 ms, and this second bipolar pulse 51 is repeated three times to form a second bipolar pulse set 52. Three sets of the second bipolar pulse sets 52 are applied while being sandwiched by a non-voltage application period 53 of 100 ms. That is, in the present embodiment, the second bipolar pulse set 52 is applied to the cholesteric liquid crystal material three times with the non-voltage application period 53 of 100 ms.

  By applying the second bipolar pulse set 52 as described above, the liquid crystal molecules of all the pixels are collectively in a focal conic state, and the cholesteric liquid crystal display element is formed by a light absorption layer provided on the back surface of the liquid crystal panel. Black display. By using the driving condition according to the present embodiment, a black display with low reflectance can be obtained in the focal conic state. It is also possible to control a fine domain in the focal conic state with good reproducibility.

  The present embodiment relates to a cholesteric liquid crystal display element to which a driving method capable of obtaining a reflective display with a high contrast ratio is applied. Therefore, originally, writing is performed for each line after the focal conic reset driving, and a desired image is written by forming a bright state portion by bringing necessary pixels into a planar state. However, changing the focal conic state to the planar state can be stably transferred by applying a general bipolar pulse. Further, since the gist of the present invention is to obtain a reflective display with a high contrast ratio, a detailed description of writing for each line is omitted.

  Since the essential part of the present embodiment is the reduction in the reflectance of black display when the focal conic state is set, the comparison with the other driving methods compares the reflectance when the focal conic state is set. Therefore, the purpose can be sufficiently achieved, and the comparison can be easily and clearly performed.

  In the present embodiment, the reflectance in the focal conic state can be reduced to about 1.6% by using the focal conic reset driving shown in FIG. 6, and a very good black display can be obtained. . Further, if the reflectance after writing in the planar state is about 30%, the contrast ratio is about 19.

  Here, for comparison with the focal conic reset driving according to the present embodiment, driving in which the voltage non-application period 53 is zero will be described below. Even when the voltage non-application period 53 is zero, the first bipolar pulse 4 having a voltage of 40 V and a pulse width of 100 ms is applied as the all-pixel batch reset condition to the planar state shown in FIG. The period is set to 100 ms.

  Further, in the all-pixel batch reset condition to the focal conic state shown in FIG. 3, the second bipolar pulse 51 having a voltage of 30 V and a pulse width of 10 ms is repeated three times to form one set, and the voltage between adjacent second bipolar pulse sets 52 is set. Three sets are applied without providing the non-application period 53. The reflectivity in the focal conic state (black display) when the voltage non-application period 53 is zero is about 3.2%. When the reflectivity after writing in the planar state is about 30%, the contrast ratio is about 9%. Therefore, it is not possible to obtain a display with high contrast.

(Embodiment 2)
The cholesteric liquid crystal display element according to the present embodiment uses the same cholesteric liquid crystal display element as that of the first embodiment, and also performs the all-pixel batch reset condition to the planar state shown in FIG. The same conditions as in Form 1 were used. Specifically, the first bipolar pulse 4 has a voltage of 40 V and a pulse width of 100 ms, and the period of the no-voltage application state 6 is 100 ms.

  Further, the cholesteric liquid crystal display element according to the present embodiment applies the second bipolar pulse group 5 shown in FIG. 6 to be in the focal conic state. Specifically, in the present embodiment, the basic second bipolar pulse 51 has a voltage of 30 V and a pulse width of 10 ms, and the second bipolar pulse 51 is repeated three times to form a second bipolar pulse set 52. In the present embodiment, three sets are applied to the second bipolar pulse set 52 with a voltage non-application period 53 of 0 ms to 2000 ms.

  That is, in the present embodiment, unlike the first embodiment, the reflectance in the focal conic state (black display) when the voltage non-application period 53 is changed from 0 ms to 2000 ms is obtained. FIG. 7 shows the dependence between the reflectance in the focal conic state and the voltage non-application time as the result.

  In the result shown in FIG. 7, when the voltage non-application time 53 is 0 ms, that is, when the second bipolar pulse 51 is applied nine times without interval, the reflectivity in the focal conic state is 4%, and after writing in the planar state The Coton Trust ratio expected to be about 30% is about 7.5. However, if the voltage non-application time 53 is 1 ms to 500 ms, the reflectivity in the focal conic state is about 2.5% or less, and it is expected that a contrast ratio of 10 or more can be obtained. In the case of the voltage non-application time 53 exceeding 500 ms, the reflectivity in the focal conic state exceeds 3% and does not become a favorable focal conic state, and a high contrast ratio cannot be expected.

  As described above, in the cholesteric liquid crystal display element according to the present embodiment, the voltage non-application time 53 of 1 ms to 500 ms is provided between the second bipolar pulse sets 52 for changing to the focal conic state, thereby forming the focal point. There is an effect that a display having a low conic reflectance and a high contrast ratio can be obtained.

(Embodiment 3)
The cholesteric liquid crystal display element according to the present embodiment also uses the same cholesteric liquid crystal display element as in the first embodiment, and also performs the all-pixel batch reset condition to the planar state shown in FIG. The same conditions as in Form 1 were used. Specifically, the first bipolar pulse 4 has a voltage of 40 V and a pulse width of 100 ms, and the period of the no-voltage application state 6 is 100 ms.

  Further, the cholesteric liquid crystal display element according to the present embodiment applies the second bipolar pulse group 5 shown in FIG. 6 to be in the focal conic state. Specifically, in the present embodiment, the basic second bipolar pulse 51 is set at a voltage of 30 V and a pulse width of 1 ms to 100 ms, and this second bipolar pulse 51 is repeated three times to form a set of second bipolar pulse sets 52. Yes. Further, in the present embodiment, three sets of second bipolar pulse sets 52 are applied with a voltage non-application period 53 of 100 ms.

  That is, in the present embodiment, unlike the first embodiment, the reflectance in the focal conic state (black display) when the pulse width of the second bipolar pulse 51 is changed from 1 ms to 100 ms is obtained. FIG. 8 shows the dependence of the reflectance in the focal conic state and the pulse width of the second bipolar pulse 51 as the result.

  In the result shown in FIG. 8, when the range of the pulse width of the second bipolar pulse 51 is in the range of 1 ms to 50 ms, the reflectivity in the focal conic state is 2.5% or less, and the reflectivity after writing in the planar state The cotton trust ratio expected to be approximately 30% is 10 or more. When the pulse width of the second bipolar pulse 51 exceeds 50 ms, it is considered that the transition to the planar state starts partially, and the reflectivity in the focal conic state rapidly increases, thereby obtaining a high contrast display. I can't.

  As described above, in the cholesteric liquid crystal display device according to the present embodiment, the reflectance of the focal conic state is low and the contrast is reduced by setting the pulse width of the second bipolar pulse 51 for changing to the focal conic state to 1 ms to 50 ms. There is an effect that a display with a high ratio can be obtained.

(Embodiment 4)
The cholesteric liquid crystal display element according to the present embodiment also uses the same cholesteric liquid crystal display element as in the first embodiment, and also performs the all-pixel batch reset condition to the planar state shown in FIG. The same conditions as in Form 1 were used. Specifically, the first bipolar pulse 4 has a voltage of 40 V and a pulse width of 100 ms, and the period of the no-voltage application state 6 is 100 ms.

  Further, the cholesteric liquid crystal display element according to the present embodiment applies the second bipolar pulse group 5 shown in FIG. 6 to be in the focal conic state. Specifically, in the present embodiment, the basic second bipolar pulse 51 is set to a voltage of 30 V and a pulse width of 10 ms, and this second bipolar pulse 51 is repeated 1 to 20 times to form a set of second bipolar pulse sets 52. It is said. Further, in the present embodiment, three sets of second bipolar pulse sets 52 are applied with a voltage non-application period 53 of 100 ms.

  That is, in the present embodiment, unlike the first embodiment, the focal conic state (when the number of repetitions of the second bipolar pulse 51 constituting the second bipolar pulse set 52 is changed from 1 to 20 times ( (Black display) reflectance. FIG. 9 shows the dependence between the reflectance in the focal conic state and the number of repetitions of the second bipolar pulse 51 as the result.

  In the result shown in FIG. 9, when the number of repetitions of the second bipolar pulse 51 constituting the pair of second bipolar pulse sets 52 is in the range of 2 to 10 times, the reflectivity in the focal conic state is about 2% or less. Thus, the cotton trust ratio expected to be about 30% after writing in the planar state is 10 or more.

  Note that if the number of repetitions of the second bipolar pulse 51 constituting the pair of second bipolar pulse sets 52 is one, the integration effect is insufficient and the reflectivity in the focal conic state cannot be reduced. Conversely, if the number of repetitions of the second bipolar pulse 51 constituting the pair of second bipolar pulse sets 52 exceeds 10, the conversion time to the focal conic state becomes longer and the reflectivity becomes higher and higher. Contrast display cannot be obtained.

  As described above, in the cholesteric liquid crystal display element according to the present embodiment, the number of repetitions of the second bipolar pulse 51 constituting the pair of second bipolar pulse groups 52 for changing to the focal conic state is 2 to 10. By setting the number of times, a display with a low reflectance in the focal conic state and a high contrast ratio can be obtained, and the conversion time to the focal conic state can be shortened.

(Embodiment 5)
The cholesteric liquid crystal display element according to the present embodiment also uses the same cholesteric liquid crystal display element as in the first embodiment, and also performs the all-pixel batch reset condition to the planar state shown in FIG. The same conditions as in Form 1 were used. Specifically, the first bipolar pulse 4 has a voltage of 40 V and a pulse width of 100 ms, and the period of the no-voltage application state 6 is 100 ms.

  Further, the cholesteric liquid crystal display element according to the present embodiment applies the second bipolar pulse group 5 shown in FIG. 6 to be in the focal conic state. Specifically, in the present embodiment, the basic second bipolar pulse 51 has a voltage of 30 V and a pulse width of 10 ms, and the second bipolar pulse 51 is repeated three times to form a second bipolar pulse set 52. Further, in the present embodiment, 1 to 20 sets of second bipolar pulse sets 52 are applied with a voltage non-application period 53 of 100 ms.

  That is, in the present embodiment, unlike the first embodiment, the reflectance in the focal conic state (black display) when the number of second bipolar pulse groups 52 is changed from 1 to 20 is obtained. FIG. 10 shows the dependency between the reflectance in the focal conic state and the number of second bipolar pulse sets 52 as the result.

  In the result shown in FIG. 10, when the second bipolar pulse set 52 is in the range of 2 to 10 sets, the reflectance in the focal conic state is about 2% or less, and the reflectance after writing in the planar state is about 30. The cotton trust ratio expected to be% is 10 or more.

  Note that when the second bipolar pulse set 52 is one set, the integration effect is insufficient, and the reflectivity in the focal conic state cannot be reduced. On the other hand, when the number of the second bipolar pulse sets 52 exceeds 10, the conversion time to the focal conic state becomes longer, and the reflectivity becomes higher, so that a high contrast display cannot be obtained.

  As described above, in the cholesteric liquid crystal display element according to the present embodiment, the reflectance of the focal conic state is obtained by setting the number of second bipolar pulse sets 52 for changing to the focal conic state to 2 to 10 sets. Display with a low contrast ratio and a high contrast ratio can be obtained, and the conversion time to the focal conic state can be shortened.

It is a figure which shows the drive waveform of the focal conic reset drive of the reflection type liquid crystal display element used as the premise of this invention. It is a figure for demonstrating the orientation state of the liquid crystal molecule of the reflection type liquid crystal display element used as the premise of this invention. It is a figure which shows the drive waveform of the reflection type liquid crystal display element which concerns on this invention. It is a graph which shows the relationship between the reflectance of a focal conic state, and the period of a voltage non-application state of the reflective liquid crystal display element which concerns on this invention. 1 is a block diagram of a reflective liquid crystal display element according to Embodiment 1 of the present invention. It is a figure which shows the drive waveform of the reflection type liquid crystal display element which concerns on Embodiment 1 of this invention. It is a graph which shows the relationship between the reflectance of the focal conic state of the reflective liquid crystal display element which concerns on Embodiment 2 of this invention, and a voltage non-application time. It is a graph which shows the relationship between the reflectance of the focal conic state of the reflective liquid crystal display element which concerns on Embodiment 3 of this invention, and the pulse width of a 2nd bipolar pulse. It is a graph which shows the relationship between the reflectance of the focal conic state of the reflective liquid crystal display element which concerns on Embodiment 4 of this invention, and the repetition frequency of the 2nd bipolar pulse which comprises one set of 2 bipolar pulses. It is a graph which shows the relationship between the reflectance of the focal conic state of the reflective liquid crystal display element which concerns on Embodiment 5 of this invention, and the number of sets of the 2nd bipolar pulse set.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st state, 2nd state, 3rd state, 4th 1 bipolar pulse group, 5 2nd bipolar pulse group, 6 voltage non-application state, 10 drive part, 11 liquid crystal panel, 12 planar means, 13 focal conic means , 14 Writing means, 51 Second bipolar pulse, 52 Second bipolar pulse set, 53 No voltage application period.

Claims (6)

A first transparent electrode substrate on which a plurality of scanning electrodes are formed;
A second transparent electrode substrate on which a plurality of signal electrodes are formed;
A reflective liquid crystal display device comprising a cholesteric liquid crystal material sandwiched between the first transparent electrode substrate and the second transparent electrode substrate,
Planar means for applying a first bipolar pulse for bringing the cholesteric liquid crystal material into a homeotropic state for a predetermined period of time so that all the cholesteric liquid crystal materials between the scan electrode and the signal electrode are in a planar state at once; ,
Applying a second bipolar pulse having a lower applied voltage than the first bipolar pulse to collectively bring all the cholesteric liquid crystal materials between the scanning electrode and the signal electrode into a focal conic state;
Writing means for writing an image by applying a predetermined pulse to the cholesteric liquid crystal material between the predetermined scanning electrode and the signal electrode;
The reflection type liquid crystal display element, wherein the focal conic means applies the second bipolar pulse to the cholesteric liquid crystal material a plurality of times mutually with no voltage application period. The reflective liquid crystal display element according to claim 1,
The reflection type liquid crystal display element, wherein the focal conic means applies a plurality of continuous second bipolar pulses as a set to the cholesteric liquid crystal material. The reflective liquid crystal display element according to claim 2,
The focal conic means is characterized in that the pulse width of the second bipolar pulse is 1 ms to 50 ms, and the voltage non-application period provided between the second bipolar pulse groups is 10 ms to 500 ms. element. The reflective liquid crystal display element according to claim 2 or 3,
A reflection type liquid crystal display element, wherein a set of the second bipolar pulse is repeated two to ten times. The reflective liquid crystal display element according to any one of claims 2 to 4,
A reflective liquid crystal display element, wherein the number of sets of the second bipolar pulses applied to the cholesteric liquid crystal material is 2 to 10 sets. A first transparent electrode substrate on which a plurality of scanning electrodes are formed, a second transparent electrode substrate on which a plurality of signal electrodes are formed, and a cholesteric liquid crystal sandwiched between the first transparent electrode substrate and the second transparent electrode substrate A reflective liquid crystal display element driving method comprising a material,
Applying a first bipolar pulse for bringing the cholesteric liquid crystal material into a homeotropic state for a predetermined period, and a planar period for bringing all the cholesteric liquid crystal materials between the scan electrode and the signal electrode into a planar state at once. ,
After the planar period, a second bipolar pulse having an applied voltage lower than that of the first bipolar pulse is applied to collectively bring all the cholesteric liquid crystal materials between the scan electrode and the signal electrode into a focal conic state. The focal conic period,
A writing period in which a predetermined pulse is applied to the cholesteric liquid crystal material between the predetermined scanning electrode and the signal electrode after the focal conic period to write an image;
In the focal conic period, the second bipolar pulse is applied to the cholesteric liquid crystal material a plurality of times mutually with no voltage application period.

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