JP2002139720A - Driving device for liquid crystal display device having memory property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain good contrast even if temperature is varied and to prevent unevenness of display in a liquid crystal display device. SOLUTION: The number of voltage pulses for transiting focal-conically is stored previously in accordance with temperature. Liquid crystal is transited focal-conically by selecting the number of pulses in accordance with surrounding temperature of a liquid crystal display device and applying voltage by the number of selected pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for driving a static liquid crystal display device using a memory type liquid crystal element.

[0002]

2. Description of the Related Art A liquid crystal display (liquid crystal display device) using a liquid crystal element is used as a portable information display device because of its light weight and thinness and low power consumption. As a liquid crystal element used for a liquid crystal display, a TN element and an STN element are widely used.

[0003] Since the liquid crystal element is used not as a light emitting element but as an optical shutter, external light is required. Therefore, for example, a transmission type STN liquid crystal display (hereinafter, referred to as a transmission type liquid crystal display) provided with a backlight (including a sidelight) as a light source is used. However, a transmissive liquid crystal display provided with a backlight has a large display power and is disadvantageous for use as a portable information display device.

For this purpose, a reflective STN liquid crystal display (hereinafter, a reflective liquid crystal display) is often used as a portable information display device. A reflective liquid crystal display can be put to practical use without using a backlight.

However, even in a reflection type liquid crystal display, at least one polarizing plate is required, so that the reflectance to external light is limited, and a display quality of sufficient brightness cannot be obtained. is there.

Accordingly, attention has been paid to a liquid crystal display that does not deteriorate display quality without using a polarizing plate for limiting the brightness of the liquid crystal display. As such a liquid crystal display, a liquid crystal display using a memory type chiral nematic liquid crystal has been proposed (George H. Heilmeier,
Joel E. Goldmacher et al. Appl. Phys. Lett., 13 (1968), 1
32).

[0007] Chiral nematic liquid crystals are produced by mixing nematic liquid crystals and optically active substances. A chiral nematic liquid crystal is sandwiched between a pair of parallel substrates, and the central axis of the torsion of the torsion structure (the helical axis) in which the director of the liquid crystal rotates at regular intervals becomes a direction perpendicular to the substrate on average. When arranged in such a manner, circularly polarized light corresponding to the direction of the twist is reflected. The center wavelength of the reflected light is the distance on the helical axis (referred to as helical pitch) during one rotation of the director of the liquid crystal parallel to the substrate surface due to the twist, and the two-dimensional parallel to the substrate surface of the nematic liquid crystal. It is the product of the average refractive index at the surface.

[0008] The phenomenon in which a chiral nematic liquid crystal reflects circularly polarized light having a specific wavelength based on the helical pitch and the refractive index of the liquid crystal is called selective reflection. And
A liquid crystal array showing this selective reflection is called a planar array.

The chiral nematic liquid crystal is a liquid crystal arrangement different from the above arrangement, in which the helical axes of a plurality of liquid crystal domains are arranged in a random direction or a non-perpendicular direction to the substrate (referred to as focal conic). Can also be taken. Focal conic shows a weak scattering state and does not reflect light of a specific wavelength unlike selective reflection.

[0010] These two states (planar and focal conic) are stable even when no electric field is applied, and the selective reflection of the planar is bright because no polarizing plate is used. A liquid crystal optical element using a chiral nematic liquid crystal and utilizing its selective reflection can function as a memory type by maintaining its liquid crystal orientation even when no electric field is applied, so that a liquid crystal optical element with low power consumption can be obtained. it can.

Japanese Patent Publication No. 53-42264 discloses a method in which a selective reflection wavelength is set outside the visible range and a pulse-like voltage is applied to a chiral nematic liquid crystal element having a positive dielectric anisotropy, which becomes transparent in the visible range with a planar. It is exemplified that the planar is changed to focal conic and the focal conic is changed to planar depending on the magnitude of the voltage amplitude. The change from focal conic to planar occurs through liquid crystal alignment (called homeotropic) in which the liquid crystal molecules are almost parallel to the direction of application of the electric field, and therefore the highest voltage is required.

In a chiral nematic liquid crystal, the effective value of a series of applied voltage waveforms does not directly determine the state after voltage erasure, but the display after voltage erasure is based on the application time and amplitude value of the immediately applied voltage pulse. Depends on. Therefore, the chiral nematic liquid crystal display has been
Unlike a liquid crystal display using an N element, it is not necessary to constantly apply a voltage to maintain the display.

As described above, there are planar and focal conic as an example of the alignment state of the chiral nematic liquid crystal. As shown in FIG. 5 (a), in the planar, many domains (indicated by a drum shape) are generated by a large number of rod-like molecules, and the helical axis direction is slightly different for each domain, and the average helical axis direction is It is oriented substantially perpendicular to the substrate surface. At this time, it is known that a specific wavelength of the incident external light is reflected. This wavelength is called a selective reflection wavelength. This reflection results in a particular color.

In the focal conic shown in FIG. 5B, the helical axis direction of each domain is randomly distributed, and a scattering phenomenon occurs. At this time, the color of the absorption layer can be displayed by providing the absorption layer on the substrate on the side opposite to the side where external light is incident.

The specific relationship between the applied voltage and the optical characteristics will be described. In order to check the applied voltage and the optical characteristics after voltage erasure, apply a voltage pulse to the chiral nematic liquid crystal element including the chiral nematic liquid crystal with positive dielectric anisotropy exhibiting selective reflection and confirm the display state. repeat. Hereinafter, a chiral nematic liquid crystal having a positive dielectric anisotropy is used as a chiral nematic liquid crystal unless otherwise specified.

When the voltage amplitude is increased while the voltage pulse application time is fixed so that the state of the liquid crystal element before application of the voltage pulse is always in a state of selective reflection, the voltage is maintained as long as the voltage amplitude is small. After blocking, the initial planar does not change and the reflectivity does not change. When the voltage amplitude is further increased, after the voltage is cut off, the liquid crystal element in the selective reflection state is in a fine scattering state, and the color of the absorption layer is displayed by the absorption layer (black display when the absorption layer is black). The orientation state at this time is focal conic. When the voltage is further increased, a planer that exhibits selective reflection for reflecting light of a specific wavelength of incident external light similar to the initial state is obtained as a state after the voltage is cut off.

Similarly, a voltage pulse is applied to a focal conic chiral nematic liquid crystal element exhibiting a fine scattering state (black display when a black absorbing layer is provided on the back surface) to display the liquid crystal element. Repeat to check the status. If the state of the liquid crystal element before voltage pulse application is always set to the initial focal conic and the voltage pulse application time is fixed and the voltage amplitude is increased, after the voltage is cut off, the initial The focal conic does not change and the reflectance hardly changes. When the voltage amplitude is further increased,
A weak selective reflection state in which fine scattering and selective reflection are mixed is obtained. When the voltage is further increased, the state after the voltage cutoff becomes a planar exhibiting selective reflection.

That is, when a voltage having a predetermined amplitude or more is applied to the planar chiral nematic liquid crystal exhibiting selective reflection and the voltage is cut off, the planar changes to focal conic, and a voltage having a larger amplitude is applied to the focal conic chiral nematic liquid crystal. Is applied, the state after the voltage cutoff becomes planar. When a high voltage is applied to become a planar state, the initial state of both the planar state and the focal conic state passes through homeotropic, in which the major axis direction of the liquid crystal molecules is aligned with the voltage application direction when a voltage is applied. After the voltage application is completed, the arrangement changes from homeotropic to planar.

[0019]

SUMMARY OF THE INVENTION In a static liquid crystal display device using a chiral nematic liquid crystal element,
The display is switched by applying a voltage for transition to planar or a voltage for transition to focal conic to each segment. FIG. 6 is an explanatory diagram showing an example of a change in a voltage waveform and an optical state when switching between planar and focal conic at each display switching timing in one segment. In the following description, the case where the selective reflection is exhibited by the planar is referred to as ON display, and the case where the color of the absorption layer is presented by the focal conic is referred to as OFF display. Turn on the ON display,
The off display is turned off.

The solid line shown as the optical state in FIG. 6 shows the transition of the optical state in a normal use environment. On the other hand, the broken line shows the transition of the optical state at the time of low temperature.

First, the transition of the optical state in a normal use environment will be described. In FIG. 6, V1 is a voltage for making a transition to planar, and V2 is a voltage for making a transition to focal conic. When making a transition to focal conic, the transition to focal conic can be hastened by alternately repeating the application of the voltage and the stop of the voltage application. FIG. 6 shows a case where the application of the voltage V2 and the stop of the voltage application are repeated, and the voltage V2 is applied in a continuous pulse shape.

When transitioning to planar, a voltage V1 is applied. The optical state during this time is homeotropic.
After applying the voltage, the optical state transitions to planar. If the applied voltage is low and the liquid crystal does not become homeotropic, then no transition to planar occurs. In homeotropic, the selective reflection is not visually recognized, and the selective reflection is visually recognized at the subsequent time T1. Therefore, the selective reflection is not visually recognized in the entire time T from the display switching timing to the next switching timing.

At the time of display switching, when making a transition to focal conic, the voltage V2 is applied in the form of a continuous pulse. During this time, the optical state changes to focal conic. The observer visually recognizes the color of the absorbing layer from when V2 is applied to when V1 is next applied (T2). However, when the application of the continuous pulse voltage is stopped, the state transition also stops.

The optical state is not constant at T1 and T2. However, the display in each period is T1, T2
It is perceived by the observer as a constant indication of the average optical state in each case.

When the temperature decreases, the liquid crystal does not become homeotropic. As a result, the state does not shift to the planar state, and the contrast is deteriorated. In addition, the transition from planar to focal conic is delayed, and the transition ends at F ′ shown in FIG. 6, so that the average optical state at time T2 approaches the planar. For this reason, at low temperatures, the contrast between the ON display and the OFF display deteriorates. Even in the case where the transition to the focal conic is not completely made, if the state is close to the focal conic, good contrast can be obtained. However, if the transition stops before the transition to focal conic has progressed enough,
The contrast will be low.

A part where the previous display is the ON display (planar) and then the OFF display (focal conic) is written, and a part where the previous display is the OFF display and the OFF display is written a plurality of times in succession. In some cases, a display difference was caused due to a difference in brightness.

In particular, a chiral nematic liquid crystal display element used outdoors is used in an environment where the temperature changes drastically, so that the contrast tends to deteriorate. For example, an instrument or the like installed outdoors may not show a good display at low temperatures.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving device for a liquid crystal display device which can maintain a good contrast even if the temperature changes and can prevent display unevenness.

[0029]

According to the present invention, there is provided a driving apparatus for a liquid crystal display device having a memory function, wherein a pulse voltage applying means for applying a pulse voltage to the liquid crystal when the state of the liquid crystal is changed from planar to focal conic. Temperature information detecting means for detecting a physical quantity corresponding to the temperature around the liquid crystal display device; and the number of pulses applied to the liquid crystal by the pulse voltage applying means is set according to the physical quantity detected by the temperature information detecting means. Pulse number setting means.

The pulse number setting means has, for example, storage means for preliminarily storing the relationship between the physical quantity corresponding to the temperature and the pulse number, and stores the pulse number corresponding to the physical quantity detected by the temperature information detecting means from the storage means. This is the configuration to be selected.

Further, according to the present invention, there is provided a driving device for a liquid crystal display device having a memory function, wherein voltage applying means for applying a predetermined voltage to the liquid crystal when the state of the liquid crystal is changed from focal conic to planar, and the liquid crystal display device. Temperature information detecting means for detecting a physical quantity corresponding to a temperature around the
Voltage level setting means for setting a level of a voltage applied to the liquid crystal by the voltage applying means in accordance with the physical quantity detected by the temperature information detecting means.

The voltage level setting means has, for example, storage means for preliminarily storing the relationship between the physical quantity corresponding to the temperature and the voltage level, and stores the voltage level corresponding to the physical quantity detected by the temperature information detecting means from the storage means. This is the configuration to be selected.

The temperature information detecting means is, for example, a resistor provided near the liquid crystal display device, the resistance of which varies with temperature, and a potential detecting means for detecting the potential of a predetermined portion which fluctuates with a change in the resistance of the resistor. This is a configuration including

[0034]

Embodiments of the present invention will be described below with reference to the drawings. A liquid crystal optical element is manufactured by sandwiching a liquid crystal composition between a pair of substrates with electrodes. An organic thin film such as polyimide or an inorganic thin film such as silica may or may not be formed on the electrode, but a polyimide formed on the electrode which is generally used for a TN liquid crystal optical element or an STN liquid crystal optical element. When the organic thin film is rubbed in one direction with a cloth or the like (referred to as rubbing), the focal conic stability of the chiral nematic liquid crystal may be lost depending on the type of the alignment film. Therefore, in order to obtain a low-power-consumption liquid crystal optical element utilizing memory properties, rubbing is not usually performed when an organic thin film used in a TN liquid crystal optical element or an STN liquid crystal optical element is provided on an electrode. Or
Alternatively, it is preferable that the electrode be in direct contact with the composition.

The distance between the electrodes can be held by a spacer or the like, and the interval is preferably 2 to 15 μm, more preferably 3 to 15 μm.
6 μm is preferred. If the distance between the electrodes is too small, the contrast decreases, and if it is too large, the driving voltage increases. FIG.
FIG. 1 shows a schematic sectional view of one example of the liquid crystal optical element of the present invention.

FIG. 1 shows glass substrates 1A and 1B, electrodes 2
A, 2B, polymer thin films 3A, 3B, a liquid crystal composition 4, and a liquid crystal optical element 10 provided with a light absorber 5 are shown.
The liquid crystal optical element 10 is an element that exhibits a selective reflection state and a fine scattering state when no voltage is applied.

The substrate supporting the electrodes may be a glass substrate or a resin substrate, or a combination of a glass substrate and a resin substrate. When used as a reflective display element, a light absorber may be provided on the inner surface or outer surface of one of the substrates, or a substrate having a light absorbing function may be used.

A small amount of spacers are scattered in the electrode surface, each side of the opposing substrate is sealed with a sealing material such as epoxy resin except for the injection hole, and the cell is filled with a liquid crystal composition by vacuum injection. The optical element 10 can be obtained.

FIG. 2 is a block diagram showing an embodiment of the driving device according to the present invention. In the driving device shown in FIG. 2, the chiral nematic liquid crystal display panel 25 includes the liquid crystal optical element 10 as each segment. The drive voltage generation circuit 26 sets the potential of the common electrode of the liquid crystal optical element 10 to a predetermined level.

The thermistor 20 has one end 20 a grounded near the chiral nematic liquid crystal display panel 25 and the other end 20 b connected to a power supply 22 via a resistor 21. The thermistor 20 decreases the resistance value when the environmental temperature increases, and increases the resistance value when the temperature decreases. Therefore, the potential of the other end 20b of the thermistor 20 changes depending on the environmental temperature.

The voltage comparison circuit 23 operates at a temperature not lower than X ° C. and lower than Y ° C.
The potential range that the other end 20b of the thermistor 20 can take is stored in advance in accordance with each temperature region such as Y ° C. or more and less than Z ° C. Hereinafter, the range of the potential corresponding to the temperature region is referred to as a potential region. The potential region is obtained using the temperature-resistance characteristic of the thermistor 20. The voltage comparison circuit 23 measures the potential of the other end 20b of the thermistor 20 every predetermined time. Then, the potential is compared with each potential region to determine which potential region the potential belongs to. The voltage comparison circuit 23
Is connected to the MPU 24 by the same number of signal lines as the potential region (that is, the same number as the temperature region), and sends a signal to the MPU 24 via a signal line corresponding to the potential region to which the measured potential belongs.

When switching between ON display and OFF display of one segment, the MPU 24 instructs the drive voltage generation circuit 26 to rewrite the display of the segment.
Further, the MPU 24 displays an OFF display (focal conic) corresponding to a plurality of signal lines connecting the voltage comparison circuit 23.
In this case, the number of pulses of the applied voltage is stored in advance. When switching to the OFF display, the MPU 24 also instructs the drive voltage generation circuit 26 on the number of pulses corresponding to the signal line receiving the signal from the voltage comparison circuit 23.

Since the environment temperature area, the potential area stored by the voltage comparison circuit 23, and the signal line correspond to each other, M
The PU 24 stores the number of pulses according to the environmental temperature.
The MPU 24 stores a larger value of the pulse number for a lower temperature region.

The drive voltage generation circuit 26 causes the segment drive circuit 27 to change the potential of the segment electrode of the liquid crystal optical element 10 in accordance with an instruction from the MPU 24. Also,
When changing from the ON display to the OFF display, the MPU2
The number of pulses specified from 4 is also transmitted to the segment drive circuit 27.

When changing to the off display, the segment drive circuit 27 sets the potential of the segment electrode so that the potential difference between the segment electrode and the common electrode becomes the voltage at the time of the off display (the voltage at the time of switching to the focal conic). Set. At this time, the segment drive circuit 27 does not keep the voltage constant, but repeats the application of the voltage and the stop of the application of the voltage, and generates the number of voltage pulses specified by the MPU 24.

When changing from the off display to the on display,
The segment drive circuit 27 sets the potential of the segment electrode so that the potential difference between the segment electrode and the common electrode becomes the voltage at the time of ON display (the voltage at the time of switching to the planar).

In this embodiment, the pulse voltage applying means for applying a pulse-like voltage to the liquid crystal is an MPU 2
4. Drive voltage generation circuit 26 and segment drive circuit 2
7 is realized. Temperature information detecting means for detecting a physical quantity corresponding to the temperature includes a thermistor 20, a resistor 21, and a power supply 22.
And a voltage comparison circuit 23. The pulse number setting means for setting the number of pulses applied to the liquid crystal is realized by the voltage comparison circuit 23 and the MPU 24.

In the driving device according to the present invention, the MPU 2
A description will be given of a change in the state of the liquid crystal optical element 10 when the switching of the ON display and the OFF display is repeated for one segment. FIG. 3 is an explanatory diagram illustrating a change in the state of the liquid crystal optical element 10. The solid line shown as the optical state in FIG. 3 shows the transition of the optical state in a normal use environment. On the other hand, the broken line shows the transition of the optical state at the time of low temperature.

The voltage at which the liquid crystal can be made homeotropic (the voltage required to make the liquid crystal transition to a planar state) is V
a. The voltage required to make a transition to focal conic is defined as Vb. The number of pulses of the voltage Vb generated in a normal use environment of the liquid crystal display device is m pulses. The number of pulses of the voltage Vb at the time of low temperature is n pulses. The number of these pulses in each temperature environment
This is the number of pulses that can make a transition to a state close to focal conic to the extent that good contrast is obtained.

If the liquid crystal display device is used in a normal use environment, the potential at the other end 20b of the thermistor 20 indicates the potential at that temperature. The voltage comparison circuit 23 measures this potential at predetermined time intervals. Then, by comparing the potential with a previously stored potential area, it is determined to which potential area the measured potential belongs. Then, a signal is sent to the MPU 24 via a signal line corresponding to the potential region. MPU2
4 selects the number of pulses corresponding to the signal line to which the signal has been sent from the number of pulses stored in advance. Here, it is assumed that m is selected as the number of pulses.

When the MPU 24 instructs the drive voltage generation circuit 26 to switch from OFF display to ON display, the drive voltage generation circuit 26 causes the segment drive circuit 27 to set the voltage Va. The segment drive circuit 27 sets the voltage Va for the segment in accordance with an instruction from the drive voltage generation circuit 26. During the application of the voltage Va, the liquid crystal optical element 10 becomes homeotropic. Also, during this time, the observer does not recognize the segment as the ON display. After the application of Va is completed, the liquid crystal optical element 10 transitions to planar.

Subsequently, at the display switching timing, M
When the PU 24 instructs the drive voltage generation circuit 26 to switch from on display to off display, the drive voltage generation circuit 26 causes the segment drive circuit 27 to set the voltage Vb. In addition, the drive voltage generation circuit 26 receives an instruction from the MPU 24 to
The number of generated pulses of the voltage Vb is also instructed to the segment drive circuit 27. The segment drive circuit 27 repeatedly sets the voltage Vb for the segment m times according to an instruction from the drive voltage generation circuit 26. During this time, the liquid crystal transitions to focal conic and maintains that state. As a result of the MPU 24 setting the number of pulses as m, the liquid crystal transits to a focal conic state or a state sufficiently close to the focal conic, and a good contrast is obtained.

When the temperature decreases, the other end 20b of the thermistor 20 indicates the potential at that temperature. The voltage comparison circuit 23 measures this potential and determines which potential region it belongs to. Then, a signal is sent to the MPU 24 via a signal line corresponding to the potential region. The MPU 24 selects the number of pulses corresponding to the signal line to which the signal has been sent. here,
It is assumed that n is selected as the number of pulses. The pulse number n at a low temperature is larger than the pulse number m in a normal use environment.

The operation of each unit when the MPU 24 instructs switching from the off display to the on display is the same as that in a normal use environment. Therefore, the segment Va is applied with the voltage Va.

When MPU 24 instructs switching from off display to on display, segment drive circuit 27 applies voltage Vb to the segment. However, the application of the voltage of Vb is repeated n times. At low temperatures, the transition to focal conic is delayed, as indicated by the broken line in FIG. At this time,
If Vb is applied only m times as in a normal use environment, the transition does not transition to a state close enough to focal conic, and the transition stops in the state of F 'shown in FIG. As a result, the average optical state at the time T2 approaches the planar state, and the contrast deteriorates. However, at low temperatures, the MPU 24 selects n as the number of pulses, and increases the number of times Vb is applied. For this reason,
Even if the ambient temperature changes, the liquid crystal transitions to focal conic or a state sufficiently close to focal conic, and good contrast is obtained. Further, there is no difference in brightness (display unevenness) between the portion where the on display is changed to the off display and the portion where the off display is written several times in succession.

Next, another embodiment of the present invention will be described. The configuration of the driving device according to this embodiment is the same as the configuration shown in FIG. The operations of the thermistor 20 and the voltage comparison circuit 23 are the same as those in the above-described embodiment.

The MPU 24 instructs the drive voltage generation circuit 26 to rewrite the display of the segment when switching the display of the segment. Further, the MPU 24 includes a voltage comparison circuit 23
Are stored in advance in correspondence with a plurality of signal lines connecting the terminals to turn on (planar). When switching to the ON display, the MPU 24 also instructs the drive voltage generation circuit 26 about the ON display voltage corresponding to the signal line that has received the signal from the voltage comparison circuit 23.

Since the environment temperature area, the potential area stored by the voltage comparison circuit 23, and the signal line correspond to each other, M
The PU 24 stores a voltage at the time of ON display according to the environmental temperature. The MPU 24 stores a larger voltage for a lower temperature region.

The drive voltage generation circuit 26 causes the segment drive circuit 27 to change the potential of the segment electrode of the liquid crystal optical element 10 in accordance with an instruction from the MPU 24. Also,
When changing from the OFF display to the ON display, the MPU2
4 is also transmitted to the segment drive circuit 27.

When the display is changed to ON, the segment drive circuit 27 sets the potential of the segment electrode so that the potential difference between the segment electrode and the common electrode becomes the voltage specified by the MPU 24.

When changing from the ON display to the OFF display,
The segment drive circuit 27 sets the potential of the segment electrode so that the potential difference between the segment electrode and the common electrode becomes the voltage at the time of OFF display (the voltage at the time of switching to focal conic). At this time, the segment driving circuit 27
The voltage application and the stop of the voltage application are repeated to generate a continuous voltage pulse. This number of pulses is M
The number of pulses indicated by the PU 24 may be a fixed value. Hereinafter, the number of pulses will be described as a fixed value m regardless of the temperature.

In this embodiment, the voltage application means for applying a predetermined level of voltage to the liquid crystal is realized by the MPU 24, the drive voltage generation circuit 26 and the segment drive circuit 27. Temperature information detecting means for detecting a physical quantity corresponding to the temperature is realized by a thermistor 20, a resistor 21, a power supply 22, and a voltage comparison circuit 23. The voltage level setting means for setting the voltage level includes the voltage comparison circuit 23 and the MP
This is realized by U24.

A description will be given of a change in the state of the liquid crystal optical element 10 when the MPU 24 repeatedly switches between ON display and OFF display for one segment in this driving device. FIG. 4 is an explanatory diagram illustrating a change in the state of the liquid crystal optical element 10. The solid line shown as the optical state in FIG. 4 shows the transition of the optical state in a normal use environment. On the other hand, the broken line shows the transition of the optical state at the time of low temperature.

In a normal use environment of the liquid crystal display device, a voltage required for transition from focal conic to planar is Vc, and a voltage necessary for transition to planar at low temperature is Vd. These voltages are voltages that can make the liquid crystal homeotropic in each temperature environment. The voltage required to make a transition to focal conic is defined as Vb. The number of pulses of the voltage Vb is m pulses.

When the liquid crystal display device is used in a normal use environment, the potential at the other end 20b of the thermistor 20 indicates the potential at that temperature. The voltage comparison circuit 23 measures this potential at predetermined time intervals, and determines which potential region the potential region belongs to. Then, through a signal line corresponding to the potential region, M
Send a signal to PU24. The MPU 24 selects a voltage corresponding to the signal line to which the signal has been sent from the voltages stored in advance. Here, it is assumed that Vc is selected as the voltage.

When the MPU 24 instructs the drive voltage generation circuit 26 to switch from OFF display to ON display, the drive voltage generation circuit 26 causes the segment drive circuit 27 to set the voltage Vc. The segment drive circuit 27 sets the voltage Vc for the segment according to the instruction of the drive voltage generation circuit 26. During the application of the voltage Vc, the liquid crystal optical element 10 becomes homeotropic. Also, during this time, the observer does not recognize the segment as the ON display. After the application of Vc is completed, the liquid crystal optical element 10 transitions to planar.

Subsequently, at the display switching timing, M
When the PU 24 instructs the drive voltage generation circuit 26 to switch from on display to off display, the drive voltage generation circuit 26 causes the segment drive circuit 27 to set the voltage Vb. The drive voltage generation circuit 26 also instructs the segment drive circuit 27 on the number m of generated pulses of the voltage Vb. The segment drive circuit 27 receives an instruction from the drive voltage generation circuit 26,
The voltage Vb is repeatedly set for the segment m times. During this time, the liquid crystal transitions to focal conic and maintains that state.

When the temperature decreases, the other end 20b of the thermistor 20 indicates the potential at that temperature. The voltage comparison circuit 23 measures this potential and determines which potential region it belongs to. Then, a signal is sent to the MPU 24 via a signal line corresponding to the potential region. The MPU 24 selects a voltage corresponding to the signal line to which the signal has been sent. Here, it is assumed that Vd is selected as the voltage. Voltage Vd at low temperature
Is higher than the voltage Vc in a normal use environment.

The operation of each unit when the MPU 24 instructs the switching from the off display to the on display is as follows.
Except for this point, it is the same as in a normal use environment. If the liquid crystal does not become homeotropic at low temperatures, the liquid crystal will not transition to the planar state. But MP
Since U24 stores the voltage corresponding to the temperature region and selects the voltage according to the temperature, the state transits to the planar even at a low temperature as shown in FIG.

The operation of each unit when the MPU 24 instructs switching from the ON display to the OFF display is the same as the operation in a normal use environment. Therefore, the voltage Vb is applied to the segment as a pulse that is repeated m times.

FIG. 3 shows a case where the MPU 24 stores the number of pulses corresponding to the temperature and selects the number of pulses at the time of OFF display. In this case, even at low temperatures, the liquid crystal transitions to a state close to focal conic, so that good contrast can be obtained. On the other hand, FIG. 4 shows a case where the MPU 24 stores a voltage corresponding to the temperature and selects the voltage at the time of the ON display. In this case, even when the temperature becomes low, the image transitions to the planar state, so that good contrast can be obtained. When the MPU 24 stores the number of pulses at the time of OFF display and the voltage at the time of ON display according to the temperature, and selects the number of pulses and the voltage according to the temperature, the difference between the optical state at the time of ON display and the optical state at the time of OFF display is obtained. Is further expanded, so that a better contrast can be obtained.

Hereinafter, specific embodiments will be described. A liquid crystal panel was manufactured as follows. That is, a polyimide thin film is formed by spinner coating on the surface of a glass substrate having a transparent electrode, which is in contact with the liquid crystal layer, and then a resin spacer having a diameter of 4 μm is scattered on the upper and lower substrate surfaces. A glass substrate was placed on the four sides excluding the injection hole with a width of about 0.4 mm through an epoxy resin printed at 0.4 mm.
mm epoxy resin was superposed (referred to as empty cells). The transparent electrode arranged on one glass substrate is a common electrode over the entire surface, and the transparent electrode arranged on the other glass substrate is an electrode corresponding to a pattern to be displayed.

Tc = 87 ° C., Δn = 0.231, Δε
= 16.5, viscosity η = 32 mPa · s, specific resistance 2 × 10
^In 84.7 parts of ¹¹ Ω · cm nematic liquid crystal,
5.1 parts of a chiral agent shown in Chemical formula 2, 5.1 parts of a chiral agent shown in Chemical formula 2, and 5.1 parts of a chiral agent shown in Chemical formula 3 are dissolved and mixed, and a chiral nematic liquid crystal having a helical pitch of about 0.34 μm ( Liquid crystal A).

[0074]

Embedded image

[0075]

Embedded image

[0076]

Embedded image

The liquid crystal A was injected into the previously prepared empty cell by a vacuum injection method, and the injection hole was sealed with an ultraviolet-curing sealing material to manufacture a liquid crystal panel.

When display is performed using this liquid crystal, the voltage at the time of off display (at the time of switching to focal conic) is set to 20.
V, the voltage application time for one pulse was 5 ms. The number of pulses is set to 2, corresponding to the respective temperature regions to which the temperatures of 20 ° C, 0 ° C, -10 ° C, and -20 ° C belong.
3, 5, and 20, and the number of pulses corresponding to each temperature was set. As described above, by setting the number of pulses according to the temperature, deterioration of the contrast can be prevented.

Also, at the time of ON display (when switching to the planar)
Was set to 10 ms. And 25 ° C, 0
The voltages were stored as 37 V, 41 V, and 50 V corresponding to the respective temperature regions to which the respective temperatures of ° C. and −10 ° C. belong, and the voltages corresponding to the respective temperatures were set. in this way,
By setting the voltage according to the temperature, it was possible to prevent the deterioration of the contrast.

[0080]

According to the present invention, a pulse voltage applying means for applying a pulse voltage to the liquid crystal when the state of the liquid crystal changes from planar to focal conic, and a physical quantity corresponding to the temperature around the liquid crystal display device Temperature information detection means for detecting the temperature information, and a pulse number setting means for setting the number of pulses applied to the liquid crystal by the pulse voltage application means according to the physical quantity detected by the temperature information detection means, Even if the temperature decreases, the state can be sufficiently shifted to a state close to focal conic, and deterioration of contrast and display unevenness can be prevented. Further, according to the present invention, a voltage applying means for applying a predetermined level of voltage to the liquid crystal when the state of the liquid crystal is changed from focal conic to planar, and a temperature for detecting a physical quantity corresponding to a temperature around the liquid crystal display device. Since the temperature detecting device is configured to include information detecting means and voltage level setting means for setting the level of the voltage applied to the liquid crystal by the voltage applying means in accordance with the physical quantity detected by the temperature information detecting means, the temperature decreases. However, it is possible to make a transition to planar and maintain the contrast.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a liquid crystal panel using a chiral nematic liquid crystal.

FIG. 2 is a block diagram illustrating an embodiment of a driving device.

FIG. 3 is an explanatory diagram showing an example of a change in the state of a liquid crystal optical element.

FIG. 4 is an explanatory diagram showing an example of a change in the state of a liquid crystal optical element.

FIG. 5 is an explanatory diagram illustrating an example of an alignment state of a chiral nematic liquid crystal.

FIG. 6 is an explanatory diagram showing a change in a state of a liquid crystal optical element in a conventional driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid crystal optical element 20 Thermistor 21 Resistance 22 Power supply 23 Voltage comparison circuit 24 MPU 25 Chiral nematic liquid crystal display panel 26 Drive voltage generation circuit 27 Segment drive circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G09G 3/20 642 G09G 3/36 3/36 G02F 1/137 505 (72) Inventor Makoto Nagai Yokohama, Kanagawa 1150 Hazawa-cho, Kanagawa-ku, Asahi Glass Co., Ltd.F-term (reference) BF38 EC13 FA19 FA22 FA54 5C080 AA10 BB05 CC01 DD30 EE28 FF07 JJ02 JJ04 JJ06 KK07

Claims (5)

[Claims] 1. A liquid crystal driving a liquid crystal display device that performs display in which one of the two stable states is turned on and the other is turned off using a liquid crystal exhibiting two stable states, a planar state and a focal conic state. A driving device for the display device, wherein a pulse voltage applying means for applying a pulsed voltage to the liquid crystal when the state of the liquid crystal changes from planar to focal conic, and detecting a physical quantity corresponding to a temperature around the liquid crystal display device Temperature information detecting means, and a pulse number setting means for setting the number of pulses to be applied to the liquid crystal by the pulse voltage applying means according to the physical quantity detected by the temperature information detecting means. For driving a liquid crystal display device having the same. 2. The method according to claim 1, wherein the pulse number setting unit includes a storage unit that stores a relationship between the physical quantity corresponding to the temperature and the pulse number in advance, and stores the pulse number corresponding to the physical quantity detected by the temperature information detecting unit from the storage unit. The driving device for a liquid crystal display device having a memory function according to claim 1, which is selected. 3. A liquid crystal driving a liquid crystal display device that performs display in which one of the two stable states is turned on and the other is turned off using a liquid crystal exhibiting two stable states of planar and focal conic. A driving device for the display device, a voltage application unit for applying a predetermined level of voltage to the liquid crystal when the state of the liquid crystal changes from focal conic to planar, and a temperature for detecting a physical quantity corresponding to a temperature around the liquid crystal display device. An information detecting means; and a voltage level setting means for setting a level of a voltage applied to the liquid crystal by the voltage applying means in accordance with the physical quantity detected by the temperature information detecting means. Drive device for liquid crystal display device. 4. The voltage level setting means has a storage means in which a relationship between a physical quantity corresponding to a temperature and a voltage level is stored in advance, and a voltage level corresponding to the physical quantity detected by the temperature information detecting means is stored in the storage means. 4. A driving device for a liquid crystal display device having a memory function according to claim 3, which is selected. 5. A temperature information detecting means, which is provided near the liquid crystal display device and has a resistance which varies with temperature, and a potential detecting means which detects a potential at a predetermined portion which fluctuates with a change in resistance of the resistor. 5. The driving device for a liquid crystal display device having a memory function according to claim 1, comprising: