JP5691799B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device.

  The liquid crystal display device includes a liquid crystal display panel in which a transparent electrode is formed on two transparent substrates, the transparent electrodes are arranged to face each other, and a liquid crystal material is filled between the substrates. By applying a voltage to the transparent electrode by the drive circuit, a voltage is applied to the liquid crystal material between the transparent electrodes to change the alignment state of the liquid crystal and display. A signal corresponding to the display image is supplied from the control circuit to the drive circuit, and the drive circuit applies a voltage to each electrode according to the supplied signal. In general, in order to prevent polarization of the liquid crystal material, the drive circuit generally applies a positive or negative voltage, that is, an AC voltage between the transparent electrodes.

  The liquid crystal material needs to change its alignment state according to the applied voltage, and has a viscosity range in which an image can be displayed. The viscosity of the liquid crystal material varies depending on the temperature. When the temperature is high, the viscosity decreases, and when the temperature is low, the viscosity increases. In other words, the usable temperature range of the liquid crystal display device is regulated by the viscosity of the liquid crystal material.

  A liquid crystal display device used for moving image display is designed to be in a usable temperature range in a normal use environment such as indoors, and the usable temperature range is rarely a problem. . In addition, when a liquid crystal display device for moving image display used outdoors is used in a low temperature environment, a sheet heater which is a sheet-like resistor is provided on the back surface of the liquid crystal display device and the sheet heater is energized. Then, the liquid crystal display panel is heated by generating heat.

  On the other hand, electronic paper is considered as a display device with low power consumption. Electronic paper can hold images without a power source, so it has low power consumption and is a reflective display device. Therefore, when used outdoors, it can display brighter images than conventional light-emitting displays. It has the characteristics.

  Various materials have been proposed as materials for electronic paper. Among them, cholesteric liquid crystal materials are used for reflective display panels, and can realize bright color display by being laminated. The cholesteric liquid crystal material is also a liquid crystal material, and the viscosity changes depending on the temperature. When the temperature becomes low, the viscosity increases and the display luminance decreases. Control of the driving method such as increasing the driving voltage so as to reduce this change has been proposed. However, when the temperature is further lowered, the liquid crystal itself becomes inoperable and cannot be driven. Electronic paper containing a cholesteric liquid crystal material is assumed to be used outdoors, and it is desired that display is possible regardless of the environmental temperature.

  These measures can be taken by placing a heater on the back as described above, but in addition to increasing the cost of adding members, it takes time to transfer heat from the back to the liquid crystal layer, so the heat generation state is always maintained. There is a problem that it is necessary to reduce power consumption.

  In addition, in an element using a liquid crystal material, it has been studied to use a transparent electrode as a heating element. The material forming the transparent electrode is a conductor, and in terms of the function of the element, it is desirable that the same voltage be applied to the entire surface of the transparent electrode by applying a voltage to one end of the transparent electrode. One end is connected to the output of the drive circuit. However, since the material forming the transparent electrode has a larger resistance than metal or the like, a certain amount of resistance exists between both ends of the transparent electrode, so that a current flows through the transparent electrode by applying a voltage to both ends. Fever. The element is heated using this heat generation. However, in order to perform such heating, it is necessary to apply a voltage across the transparent electrode. A separate drive circuit for applying a voltage to the other end of the transparent electrode is necessary, and the configuration is complicated, resulting in an increase in cost.

JP 2010-20028 A

  According to the embodiment, a liquid crystal display device that operates even at a low temperature can be realized with a simple configuration.

  According to the first aspect of the present invention, a liquid crystal display panel having two substrates each having a transparent electrode formed on an opposing surface and filled with a liquid crystal material between the substrates, and applying a voltage to the transparent electrode The driving circuit that applies a voltage to the liquid crystal material between the transparent electrodes, the control circuit that controls the driving circuit according to the display image, and the temperature sensor that detects the temperature of the liquid crystal display panel, the control circuit, When the temperature detected by the temperature sensor is equal to or lower than the predetermined temperature, the heating circuit is controlled to apply an AC signal between the opposing transparent electrodes, and the temperature detected by the temperature sensor becomes equal to or higher than the predetermined temperature. There is provided a liquid crystal display device that performs a display writing process for controlling a driving circuit in accordance with a display image to bring a liquid crystal material into a state in accordance with the display image.

  According to the embodiment, a liquid crystal display device that can operate even at a low temperature is realized simply by changing the control.

FIG. 1 is a diagram illustrating a schematic configuration of a liquid crystal display device using a cholesteric liquid crystal according to an embodiment. FIG. 2 is a diagram illustrating a cross-sectional structure of a display panel used in the embodiment. 3A and 3B are diagrams for explaining the heat treatment in the first embodiment. FIG. 3A is a voltage application path from the scan electrode drive circuit and the data electrode drive circuit to the scan electrode and the data electrode, and FIG. It is a top view which shows voltage application of (C), (C) is sectional drawing which shows the voltage application between electrodes. FIG. 4 is a diagram illustrating a switching signal, a voltage applied to the scan electrode, a voltage applied to the data electrode, a voltage applied to the liquid crystal layer, and a current flowing through the electrode in the first embodiment. FIG. 5 is a diagram showing the temperature rise when a rectangular AC voltage is applied for 30 seconds between all scan electrodes and data electrodes on the panel. FIG. 6 is a flowchart showing the operation of the liquid crystal display device of the first embodiment. FIG. 7 is a diagram illustrating a switching signal, a voltage applied to the scan electrode, a voltage applied to the data electrode, and a voltage applied to the liquid crystal layer in the second embodiment. FIG. 8 is a flowchart showing the operation of the liquid crystal display device of the second embodiment. FIG. 9 shows a voltage application path from the power source to the scan electrode and the data electrode through the scan electrode drive circuit and the data electrode drive circuit in the heat treatment of the third embodiment. FIG. 10 is a diagram illustrating a switching signal, a voltage applied to the scan electrode, a voltage applied to the data electrode, and a voltage applied to the liquid crystal layer in the third embodiment. FIG. 11 is a flowchart showing the operation of the liquid crystal display device of the third embodiment. FIG. 12 is a diagram illustrating a state change of the cholesteric liquid crystal. FIG. 13 is a flowchart showing the operation of the liquid crystal display device of the fourth embodiment.

  FIG. 1 is a diagram illustrating a schematic configuration of a liquid crystal display device using a cholesteric liquid crystal according to an embodiment. The liquid crystal display device according to the embodiment includes a display panel 10 using a cholesteric liquid crystal material, a scanning (common) electrode driving circuit 41, a data (segment) electrode driving circuit 42, a control circuit 61, a power supply 62, and a display panel. 10 and a temperature sensor 63 provided in contact with 10.

  FIG. 2 is a diagram showing a cross-sectional structure of the display panel 10 used in the embodiment.

  First, a schematic configuration of a display panel 10 using a cholesteric liquid crystal material and a display device using the same will be described with reference to FIGS.

  The display panel 10 has a configuration in which three display panels using cholesteric liquid crystal are stacked, the light absorption layer 15 is provided on the back surface side, and the surface-side functional layer 50 is adhered to the observation surface side with the transparent adhesive layer 18. The surface side functional layer 50 functions as an AG (Anti Glare) layer, an AR (anti-reflection) layer, and a protective film.

  The three laminated panels have the same configuration, and are different in that the reflection dominant wavelengths are 480 nm (blue), 550 nm (green), and 650 nm (red), respectively. Three panels are laminated | stacked in order of a blue panel, a green panel, and a red panel in order from the observation side.

  FIG. 1 shows a case where the display panel 10 is viewed from a direction perpendicular to the substrate. As described above, since the three panels have the same configuration except for the reflection wavelength, in FIG. 1, each part of the panel is shown in common by reference numerals without B, G, R, and common. These elements will be described without adding B, G, and R.

  The display panel 10 includes an upper substrate 11 on which a plurality of parallel scanning (common) electrodes 13 are formed and a lower substrate 12 on which a plurality of parallel data (segment) electrodes 14 are formed so that the electrodes face each other. The liquid crystal is filled between the substrates.

  The plurality of scanning electrodes 13 and the plurality of data electrodes 14 are transparent electrodes and are arranged so as to be orthogonal when viewed from a direction perpendicular to the substrate, and a region where the scanning electrodes 13 and the data electrodes 14 intersect is a pixel region. Become. Accordingly, the plurality of pixel electrodes are arranged in a matrix. A sealing material 16 is provided between the upper substrate 11 and the lower substrate 12 so as to surround the pixel region, and an internal space surrounded by the sealing material 16 is filled with a cholesteric liquid crystal material to form a liquid crystal layer 17. Reference numeral 20 is an injection port for filling the internal space surrounded by the sealing material 16 with the cholesteric liquid crystal material, and is sealed after the injection of the cholesteric liquid crystal material.

  In order to keep the thickness (cell gap) of the liquid crystal layer 17 uniform, spherical spacers made of resin or inorganic oxide are dispersed over the entire display surface. However, when grid-like columnar spacers are provided. There is also. The cell gap d of the liquid crystal layer 17 is preferably in the range of 2 μm ≦ d ≦ 8 μm. If the cell gap d is smaller than this range, the reflectivity of the liquid crystal layer 17 in the planar state is lowered, and if it is larger than this range, it is necessary to increase the driving voltage.

  The scanning (common) electrode drive circuit 41 is mounted with a general-purpose STN driver IC having a TCP (tape carrier package) structure, for example, and drives the plurality of scanning electrodes 13. The output terminal of the scan electrode drive circuit 41 is connected to the plurality of scan electrodes 13 by wiring 43 formed in the flexible circuit. The data (segment) electrode drive circuit 42 is mounted with a general-purpose STN driver IC having a TCP structure and drives the plurality of data electrodes 14. The output terminal of the data electrode driving circuit 42 is connected to the plurality of data electrodes 14 by wiring 44 formed in the flexible circuit. The scan electrode drive circuit 41 and the data electrode drive circuit 42 are controlled by the control circuit 61, and a power supply voltage applied to the electrodes is supplied from the power supply 62. Although it is possible to provide three scan electrode drive circuits 41 according to the three panels, one scan electrode drive circuit 41 is provided and the scan electrodes 13 of the three panels are driven in common. Is also possible.

  The temperature sensor 63 is realized by a thermistor or the like, and may be a passive type or an active type. The temperature sensor 63 is provided in contact with the upper substrate 11 of the display panel 10, but is preferably in the vicinity of the liquid crystal layer 17.

  A modification in which the data electrode 14 is formed on the upper substrate 11 and the scanning electrode 13 is formed on the lower substrate 12 is also possible.

  The liquid crystal material is a cholesteric liquid crystal obtained by adding 10 to 40% by weight of a chiral material to a nematic liquid crystal mixture. The addition ratio of the chiral material 0 is a value when the total amount of the nematic liquid crystal component and the chiral material is 100% by weight. The color of the reflected light and other various characteristics are determined by the mixing ratio of the nematic liquid crystal component and the chiral material.

  As the nematic liquid crystal component, known components can be used, but in order to relatively reduce the driving voltage of the liquid crystal layer 22, it is desirable that the dielectric anisotropy Δε is 20 ≦ Δε ≦ 50. The refractive index anisotropy Δn of the cholesteric liquid crystal is preferably 0.18 ≦ Δn ≦ 0.24. When the refractive index anisotropy Δn is smaller than this range, the reflectivity of the liquid crystal layer 17 in the planar state becomes low. On the other hand, if the refractive index anisotropy Δn is larger than this range, the scattering reflection of the liquid crystal layer 17 in the focal conic state increases, and the viscosity also increases, so the response speed decreases.

  The upper substrate 11 and the lower substrate 12 are formed of a transparent base material. Examples of such a substrate include glass or a resin base material. For example, glass substrates such as quartz glass, soda glass, borosilicate glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polysulfone (PSF), ZEONOR, ZEONEX And cyclone resins represented by product brands such as Arton (manufactured by JSR).

  The scan electrode 13 and the data electrode 14 can be formed of a known material, for example, indium tin oxide (ITO) is typical, but other indium zinc oxide (IZO), tin oxide, and the like. An oxide-based transparent conductive film such as an electrode, an electrode in which a metal such as silver in the form of an elongated fiber is arranged in a network structure, or a metal electrode such as aluminum or silicon can be used.

  In the case of a display panel using cholesteric liquid crystal as a reflective layer, an insulating film and an alignment film for controlling the alignment of liquid crystal molecules (both not shown) are coated on the transparent electrode as a functional film. Preferably it is. The insulating film has a function of preventing a short circuit between the opposing electrodes and improving the reliability of the display panel as a gas barrier layer. For the alignment film, organic films such as polyimide resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, and inorganic materials such as silicon oxide and aluminum oxide can be used.

  In the display panel 10 according to the embodiment, the liquid crystal layer 17 applies a voltage between the scanning electrode 13 and the data electrode 14 so as to reflect, for each pixel, a planar state that reflects incident light or a focal conic state that transmits incident light. The brightness can be set freely.

  Therefore, as shown in FIG. 2, the blue panel has an upper substrate 11B on which a plurality of parallel scanning electrodes 13B are formed and a lower substrate 12B on which a plurality of parallel data electrodes 14B are formed facing each other. The liquid crystal layer 17B is formed by filling the liquid crystal therebetween. A sealing material 16B is provided between the upper substrate 11B and the lower substrate 12B so as to surround the pixel region, and an internal space surrounded by the sealing material 16B is filled with a cholesteric liquid crystal material to form a blue liquid crystal layer 17B. The

  Similarly, in the green panel, an upper substrate 11G on which a plurality of parallel scanning electrodes 13G are formed and a lower substrate 12G on which a plurality of parallel data electrodes 14G are formed face each other, and a liquid crystal is filled between the substrates. The liquid crystal layer 17G is formed. A sealing material 16G is provided between the upper substrate 11G and the lower substrate 12G so as to surround the pixel region, and an internal space surrounded by the sealing material 16G is filled with a cholesteric liquid crystal material to form a green liquid crystal layer 17G. The

  Further, the red panel has an upper substrate 11R on which a plurality of parallel scanning electrodes 13R are formed and a lower substrate 12R on which a plurality of parallel data electrodes 14R are formed facing each other, and a liquid crystal is filled between the substrates. The liquid crystal layer 17R is formed. A sealing material 16R is provided between the upper substrate 11R and the lower substrate 12R so as to surround the pixel region, and an internal space surrounded by the sealing material 16R is filled with a cholesteric liquid crystal material to form a red liquid crystal layer 17R. The

  The blue panel, the green panel, and the red panel exhibit a reflection spectrum of blue, green, and red, respectively, when in a reflective state, and the respective reflection dominant wavelengths are 480 nm (blue), 550 nm (green), and 650 nm (red). It is.

  The first blue panel and the second green panel are bonded by a blue cut filter 21 having an adhesive function. The green panel of the second layer and the red panel of the third layer are bonded by a green cut cut filter 22 having an adhesive function.

  The schematic configuration of the display panel and the display device using the cholesteric liquid crystal has been described above, but the configuration and operation of such a display panel and the display device are widely known except for the temperature sensor. Description is omitted.

  In the liquid crystal display device of the embodiment, when the display screen is rewritten, the control circuit 61 receives image data supplied from the outside, and generates a control signal generated in accordance with the image data, the scan electrode driving circuit 41, the data electrode driving This is supplied to the circuit 42 and the power source 62 to perform display writing processing. The display writing process can be realized by a conventionally known method. The liquid crystal display device of the embodiment detects the temperature of the display panel 10 by the temperature sensor 63 before performing the display writing process, and performs the display writing process as before if the detected temperature is higher than a predetermined value. If the detected temperature is lower than a predetermined value, heat treatment is performed. The liquid crystal display device according to the embodiment performs the display writing process after the temperature of the display panel 10 becomes higher than a predetermined value by the heating process.

  FIG. 3 is a diagram for explaining the heat treatment in the first embodiment. FIG. 3A shows the voltage application path from the scan electrode drive circuit 41 and the data electrode drive circuit 42 to the scan electrode 13 and the data electrode 14. ) Is a top view showing voltage application between electrodes, and (C) is a cross-sectional view showing voltage application between electrodes.

  Each pixel has a configuration in which a liquid crystal material is filled between the scan electrode 13 and the data electrode 14, functions as a capacitor, and is known to be energized when an AC signal is applied between the capacitor substrates. Yes. In the embodiment, an alternating current is applied to the scanning electrode 13 and the data electrode 14 by applying an alternating current voltage to the scanning electrode 13 and the data electrode 14 and applying the alternating current.

  As shown in FIG. 3A, the scan electrode drive circuit 41 includes a shift register 45 that sequentially shifts an on / off signal that instructs on / off, and 10 V that is supplied according to the output of the shift register 45. And a row of drivers 46 that select any one of −10V and apply it to each scanning electrode 13. Similarly, the data electrode driving circuit 42 includes a shift register 47 and a column of drivers 48. In general, the scan electrode drive circuit 41 and the data electrode drive circuit 42 are realized by general-purpose ICs.

  As shown in FIG. 3A, a switching signal is input to the shift register 45 as an on / off signal, and an inverted signal of the switching signal is input to the shift register 47 as an on / off signal. The shift registers 45 and 47 output the register values while all the registers of the shift register 45 are set to the switching signal and all the registers of the shift register 47 are set to the inverted signal of the switching signal. In response to this, the driver 46 and the driver 48 select and output 10 V and −10 V, respectively. As a result, a voltage of 20 V is applied to the liquid crystal layer of each pixel. If the polarity of the switching signal is switched and the same operation as described above is performed while the driver 46 and the driver 48 maintain the output, the values of the registers of the shift registers 45 and 47 are all reversed. When the register values of the shift registers 45 and 47 are output, the driver 46 and the driver 48 become −10 V and 10 V, respectively, and output voltages that are inverted from the previous time. Thereby, a voltage of −20 V is applied to the liquid crystal layer of each pixel. By repeating the above operation, voltages of 20 V and −20 V are alternately applied to the liquid crystal layer of each pixel.

  As shown in FIGS. 3B and 3C, the scan electrode drive circuit 41 and the data electrode drive circuit 42 are composed of the scan electrode 13, the data electrode 14, and the liquid crystal layer 17 filled therebetween. This corresponds to applying an AC signal to the capacitor.

  4A to 4E show a switching signal, a voltage applied to the scanning electrode 13, a voltage applied to the data electrode 14, a voltage applied to the liquid crystal layer 17, and a current flowing through the electrode.

  As shown in FIG. 4A, the switching signal is a digital signal and changes between 1 and 0. As shown in FIGS. 4B to 4D, the voltage applied to the scan electrode 13, the voltage applied to the data electrode 14, and the voltage applied to the liquid crystal layer 17 change in a rectangular wave shape. As shown in FIG. 4E, the current flowing through the electrode changes at the changing edge of the voltage applied to the liquid crystal layer 17, and then gradually changes to the zero level.

  As described above, since the transparent electrode has a certain resistance, it generates heat when a current as shown in FIG. 4E flows, thereby causing the temperature of the liquid crystal layer 17 and further the temperatures of the substrates 11 and 12 and the like. Rises.

  FIG. 5 shows the temperature rise when a rectangular AC voltage is applied for 30 seconds between all scan electrodes and data electrodes in an actual panel. The applied voltage is changed to 5 V, 10 V, 15 V, and 20 V (± 10 V), and X indicates switching at 1 kHz, and Y indicates switching at 10 kHz. It can be seen that changing the voltage and frequency changes the amount of temperature rise. When it is desired to raise the temperature suddenly, a desired temperature change can be realized by applying a rectangular AC voltage of 20 V at a high frequency of about 10 kHz.

  In the first embodiment, a conventional liquid crystal display device using a cholesteric liquid crystal can be realized by changing only the sequence without changing the hardware, just by providing the temperature sensor 63. There is no cost increase due to the addition of members.

  FIG. 6 is a flowchart showing the operation of the liquid crystal display device of the first embodiment.

  In step S10, the control circuit 61 receives an image signal to be rewritten from the outside.

  In step S <b> 11, the control circuit 61 reads the temperature T of the panel 10 detected by the temperature sensor 63.

  In step S12, the control circuit 61 determines whether the detected temperature T is higher than the threshold temperature T0. If it is higher, the process proceeds to step S14, and if lower, the process proceeds to step S13.

  In step S13, the heating process described in FIG. 3 is performed for a predetermined time, and the process returns to step S11. Due to the heat treatment, the temperature T of the panel 10 rises.

  Hereinafter, when the detected temperature T is lower than the threshold temperature T0, steps S11 to S13 are repeated, and when the temperature T becomes higher than the threshold temperature T0, the process proceeds to step S14.

  In step S14, display writing processing for writing an image to be displayed is performed in the same manner as before.

  A liquid crystal display device using a cholesteric liquid crystal maintains a display even when a voltage is not applied to the scan electrode 13 and the data electrode 14 from the scan electrode drive circuit 41 and the data electrode drive circuit 42 once an image to be displayed is written. Is possible. Therefore, after step S14, it is desirable that the liquid crystal display device shifts to the sleep mode and stops power supply to the scan electrode drive circuit 41 and the data electrode drive circuit 42 to reduce power consumption.

  In the above heat treatment, heat is generated by the transparent electrodes (scanning electrode 13 and data electrode 14) that are in direct contact with the liquid crystal layer 17, so that the temperature of the liquid crystal layer 17 can be increased efficiently. Thereby, the power consumption for the temperature rise of the liquid crystal layer 17 can be reduced.

  On the other hand, depending on the arrangement position of the temperature sensor 63, a time delay occurs between the temperature rise of the liquid crystal layer 17 and the change of the temperature T detected by the temperature sensor 63. Therefore, there arises a problem that the temperature of the liquid crystal layer 17 rises more than necessary. When the temperature of the liquid crystal layer 17 rises more than necessary, there are problems that the liquid crystal material is deteriorated and that power consumption is increased. In the second and third embodiments described below, this problem is solved by controlling the panel temperature to be substantially constant.

  The liquid crystal display device of the second embodiment has the same hardware configuration as that of the liquid crystal display device of the first embodiment, and the frequency of the AC signal applied during the heating process is stepwise according to the detected temperature T of the panel 10. It is different to change. As shown in FIG. 5, when the frequency is between 1 kHz and 10 kHz, the higher the frequency of the AC signal, the greater the amount of heat generation, and the higher the temperature rise rate of the liquid crystal layer.

  7A to 7D show the switching signal, the voltage applied to the scanning electrode 13, the voltage applied to the data electrode 14, and the voltage applied to the liquid crystal layer 17. FIG.

  As shown in FIGS. 7A to 7D, in the first period, a rectangular wave signal having a high frequency is applied to the liquid crystal layer, and then a rectangular wave signal having a low frequency is applied to the liquid crystal layer.

  FIG. 8 is a flowchart showing the operation of the liquid crystal display device of the second embodiment.

  In step S20, the control circuit 61 receives an image signal to be rewritten from the outside.

  In step S <b> 21, the control circuit 61 reads the temperature T of the panel 10 detected by the temperature sensor 63.

  In step S22, the control circuit 61 determines whether the detected temperature T is higher than the first threshold temperature T10. If it is higher, the process proceeds to step S24, and if lower, the process proceeds to step S23.

  In step S23, heat treatment is performed for a predetermined time at a high frequency f = f10, and the process returns to step S21. Due to the heat treatment, the temperature T of the panel 10 rises at a high speed.

  Hereinafter, when the detected temperature T is lower than the first threshold temperature T10, steps S21 to S23 are repeated, and when the temperature T becomes higher than the first threshold temperature T10, the process proceeds to step S24.

  In step S24, the control circuit 61 determines whether the detected temperature T is higher than the second threshold temperature T11 (T10 <T11). If it is higher, the process proceeds to step S26, and if lower, the process proceeds to step S25.

  In step S25, heat treatment is performed for a predetermined time at a relatively high frequency f = f11 (f11 <f10), and the process returns to step S21. By the heat treatment, the temperature T of the panel 10 rises at a relatively high speed.

  Hereinafter, when the detected temperature T is higher than the first threshold temperature T10 but lower than the second threshold temperature T11, steps S21, S22, S24 and S25 are repeated, and the temperature T is higher than the second threshold temperature T11. Then, the process proceeds to step S26.

  In step S26, the control circuit 61 determines whether the detected temperature T is higher than the third threshold temperature T12 (T11 <T12). If it is higher, the process proceeds to step S28, and if lower, the process proceeds to step S27.

  In step S27, heat treatment is performed for a predetermined time at a low frequency f = f12 (f12 <f11), and the process returns to step S21. Due to the heat treatment, the temperature T of the panel 10 rises at a low speed.

  Hereinafter, when the detected temperature T is higher than the second threshold temperature T11 but lower than the third threshold temperature T12, steps S21, S22, S24, S26 and S27 are repeated, and the temperature T is changed to the third threshold temperature T12. If higher, the process proceeds to step S28.

  In step S28, display writing processing for writing an image to be displayed is performed as before.

  The liquid crystal display device of the third embodiment to be described next has substantially the same hardware configuration as the liquid crystal display device of the first embodiment, and an AC signal applied during the heat treatment according to the detected temperature T of the panel 10. It is different that the voltage of is gradually changed. In order to change the voltage of the AC signal stepwise, the power supply 62 changes the voltage supplied to the scan electrode drive circuit 41 and the data electrode drive circuit 42 during the heating process based on the voltage control signal from the control circuit 61. For example, 10V and -10V supplied in the first and second embodiments are set as maximum voltages, and are changed stepwise such as 9V and -9V, 8V and -8V, and so on. The higher the AC signal voltage, the greater the amount of heat generated, and the higher the temperature rise rate of the liquid crystal layer.

  FIG. 9 is a diagram illustrating a voltage application path from the power supply 62 to the scan electrode 13 and the data electrode 14 through the scan electrode drive circuit 41 and the data electrode drive circuit 42 in the heat treatment in the third embodiment.

  The power source 62 includes output circuits 65 and 66 that output two types of voltages supplied to the scan electrode drive circuit 41 during heat treatment, and output circuits 67 and 68 that output two types of voltages supplied to the data electrode drive circuit 42. Have. The output circuits 65 and 67 output the high potential side voltage, and the output circuits 66 and 68 output the low potential side voltage, respectively. Each of the output circuits 65 to 68 can change the output voltage based on the voltage control signal from the control circuit 61. This can be realized, for example, by preparing a plurality of sub power supplies for supplying different voltages and selecting one of the power supplies based on the voltage control signal by the switches forming the output circuits 65 to 68. Further, the output circuits 65 to 68 may be constituted by a plurality of step-down circuits having different step-down amounts, and any one of the step-down circuits may be operated based on the voltage control signal.

  10A to 10D show the switching signal, the voltage applied to the scanning electrode 13, the voltage applied to the data electrode 14, and the voltage applied to the liquid crystal layer 17. FIG.

  As shown in FIGS. 10A to 10D, in the first period, a rectangular wave signal having a high voltage is applied to the liquid crystal layer, and then the voltage applied to the liquid crystal layer is decreased stepwise. In FIG. 10, the voltage is shown to change every cycle of the rectangular wave signal for the convenience of illustration, but it is actually desirable that the voltage change every plural cycles.

  FIG. 11 is a flowchart showing the operation of the liquid crystal display device of the third embodiment.

  In step S30, the control circuit 61 receives an image signal to be rewritten from the outside.

  In step S <b> 31, the control circuit 61 reads the temperature T of the panel 10 detected by the temperature sensor 63.

  In step S32, the control circuit 61 determines whether the detected temperature T is higher than the first threshold temperature T10. If it is higher, the process proceeds to step S34, and if lower, the process proceeds to step S33.

  In step S33, heat treatment is performed for a predetermined time at a high voltage V = V10, and the process returns to step S31. Due to the heat treatment, the temperature T of the panel 10 rises at a high speed.

  Hereinafter, when the detected temperature T is lower than the first threshold temperature T10, Steps S31 to S33 are repeated, and when the temperature T becomes higher than the first threshold temperature T10, the process proceeds to Step S34.

  In step S34, the control circuit 61 determines whether the detected temperature T is higher than the second threshold temperature T11 (T10 <T11). If it is higher, the process proceeds to step S36, and if lower, the process proceeds to step S35.

  In step S35, heat treatment is performed for a predetermined time at a relatively high voltage V = V11 (V11 <V10), and the process returns to step S31. By the heat treatment, the temperature T of the panel 10 rises at a relatively high speed.

  Hereinafter, when the detected temperature T is higher than the first threshold temperature T10 but lower than the second threshold temperature T11, steps S31, S32, S34 and S35 are repeated, and the temperature T is higher than the second threshold temperature T11. Then, the process proceeds to step S36.

  In step S36, the control circuit 61 determines whether the detected temperature T is higher than the third threshold temperature T12 (T11 <T12). If it is higher, the process proceeds to step S38, and if lower, the process proceeds to step S37.

  In step S37, heat treatment is performed for a predetermined time at a low voltage V = V12 (V12 <V11), and the process returns to step S31. Due to the heat treatment, the temperature T of the panel 10 rises at a low speed.

  Hereinafter, when the detected temperature T is higher than the second threshold temperature T11 but lower than the third threshold temperature T12, Steps S31, S32, S34, S36 and S37 are repeated, and the temperature T becomes the third threshold temperature T12. If higher, the process proceeds to step S38.

  In step S38, display writing processing for writing an image to be displayed is performed as before.

  As shown in FIG. 2, in the reflective color liquid crystal display device using cholesteric liquid crystal, three panels are laminated. In the heat treatment described in the first to third embodiments, when the initial temperature is lower than the threshold temperature, the heat treatment is performed on all three panels until the display image writing process is started. It is desirable for shortening.

  The cholesteric liquid crystal has a feature that the display can be maintained without applying a voltage to the scanning electrode 13 and the data electrode 14 after the display image writing process is completed. For this reason, it is desirable to stop the power supply to the scan electrode driving circuit 41 and the data electrode driving circuit 42 from the viewpoint of power saving after the display writing process is completed.

  However, when the heat treatment is performed, it is clear that the ambient environmental temperature is lower than the threshold temperature at which the display writing process is started. Therefore, when the power supply to the scan electrode drive circuit 41 and the data electrode drive circuit 42 is stopped after the heating process and the display writing process are finished, the temperature of the display panel is lowered to be lower than the threshold temperature. When the display image is rewritten again in this state, the start of the display writing process is delayed until the heating process is completed.

  The liquid crystal display device according to the fourth embodiment to be described next is a device suitable for rewriting a display image in a relatively short cycle, and after the heating process and the display writing process are finished, the temperature of the display panel is changed. Heat treatment for maintaining the temperature is performed.

  In a display device using cholesteric liquid crystal, display is performed by setting the cholesteric liquid crystal for each pixel in a planar state that reflects incident light, a focal conic state that transmits incident light, a planar state, and a focal conic state. In order to change the state of the cholesteric liquid crystal, a voltage is applied.

  FIG. 12 is a diagram illustrating a state change of the cholesteric liquid crystal. FIG. 12 shows the state change when the voltage is changed in the case where the voltage is applied for a predetermined time, and the vertical axis is the reflectance of the liquid crystal layer. In FIG. 12, P shows the change when the initial state is the planar state, and F shows the change when the initial state is the focal conic state. The planar state has a high reflectance, and the focal conic state has the reflectance. Is small.

  When the initial state is the planar state, the planar state is maintained at a voltage lower than the voltage V0, the reflectivity decreases as the voltage becomes higher than V0, and when the voltage increases, the reflectivity is minimized, that is, the focal conic state is reached. Become. This state is maintained up to V1, and the reflectance gradually increases above V1, and the reflectance is highest, ie, the planar state above V2. On the other hand, when the initial state is the focal conic state, the minimum reflectance is maintained if the voltage is up to V1, the reflectance gradually increases above V1, and the reflectance is highest above V2, that is, the planar state. become. The state between the highest and the lowest reflectance is a state in which liquid crystal molecules in the planar state and the focal conic state are mixed.

  Therefore, in the state where the display writing process is completed, there are a planar state, a focal conic state, and a state in which they are mixed. As apparent from FIG. 12, the state does not change even when a voltage of V0 or lower is applied, regardless of the state. V0 is referred to as a visual threshold voltage.

  Therefore, in the liquid crystal display device of the fourth embodiment, after the heating process and the display writing process are completed, the heating process for maintaining the temperature of the display panel is performed at a voltage equal to or lower than the visual threshold voltage V0. Thereby, the heat treatment can be performed without changing the displayed image. In the heat treatment at a voltage of V0 or less, the heat generation amount is small, but the panel temperature is already equal to or higher than the threshold temperature by the heat treatment before the display writing process, and it is only necessary to maintain this state. Does not cause any problems.

  It should be noted that when the heat treatment at a voltage of V0 or less is insufficient, it is desirable to take measures such as increasing the sheet resistance of the transparent electrode. However, when the sheet resistance of the transparent electrode is increased, the applied voltage varies depending on the pixel position. Therefore, it is desirable to determine the sheet resistance of the transparent electrode in consideration of trade-off with the applied voltage.

  FIG. 13 is a flowchart showing the operation of the liquid crystal display device of the fourth embodiment.

  In step S40, the control circuit 61 receives an image signal to be rewritten from the outside.

  In step S <b> 41, the control circuit 61 reads the temperature T of the panel 10 detected by the temperature sensor 63.

  In step S42, the control circuit 61 determines whether the detected temperature T is higher than the threshold temperature T0. If it is higher, the process proceeds to step S44, and if lower, the process proceeds to step S43.

  In step S43, heat treatment is performed for a predetermined time, and the process returns to step S41. Due to the heat treatment, the temperature T of the panel 10 rises.

  Hereinafter, when the detected temperature T is lower than the threshold temperature T0, steps S41 to S43 are repeated, and when the temperature T becomes higher than the threshold temperature T0, the process proceeds to step S44.

  In step S44, display writing processing for writing an image to be displayed is performed.

  In step S <b> 45, the control circuit 61 reads the temperature T of the panel 10 detected by the temperature sensor 63.

  In step S46, the control circuit 61 determines whether the detected temperature T is higher than the threshold temperature T0. If it is higher, the process returns to step S45, and if it is lower, the process proceeds to step S47.

  In step S47, heat treatment is performed for a predetermined time at voltage V0, and the process returns to step S45. Due to the heat treatment, the temperature T of the panel 10 slightly increases.

  Thereafter, by repeating steps S45 to S47, the temperature can be maintained at the threshold temperature T0 without changing the image.

  The liquid crystal display device of the fourth embodiment has a laminated structure as shown in FIG. If the calorific value obtained by the heat treatment at the voltage V0 is sufficient, for example, the heat treatment at the voltage V0 is performed only on the top of the laminated structure, that is, the panel on the observation surface side (blue panel in FIG. 2). It may be.

  In addition, if the heat treatment is performed on all three panels in the heat treatment of the first to third embodiments and the first half of the heat treatment of the fourth embodiment, the time until the display writing process is started can be shortened. Further, if there is no restriction on the time until the display writing process is started, it is possible to perform the heat treatment with one or two of the three panels. In the case of one sheet, for example, the second sheet You may make it heat-process only with a panel (FIG. 2 green panel).

  As described above, according to the embodiment, it is possible to realize a liquid crystal display device that can be used even in cold outdoors without increasing the number of members and increasing the cost.

  Although the liquid crystal display device using cholesteric liquid crystal has been described as an example in the embodiment, the configuration of the embodiment is effective for any liquid crystal display device using liquid crystal.

  Although the embodiment has been described above, all examples and conditions described herein are described for the purpose of helping understanding of the concept of the invention applied to the invention and the technology. It is not intended to limit the scope of the invention, and the construction of such examples in the specification does not indicate the advantages and disadvantages of the invention. Although embodiments of the invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made without departing from the spirit and scope of the invention.

Hereinafter, the following additional notes will be disclosed with respect to the embodiment.
(Appendix 1)
A liquid crystal display panel having two substrates with transparent electrodes formed on opposite surfaces, and a liquid crystal material filled between the substrates;
A drive circuit for applying a voltage to the liquid crystal material between the transparent electrodes by applying a voltage to the transparent electrodes;
A control circuit for controlling the drive circuit according to a display image;
A temperature sensor for detecting the temperature of the liquid crystal display panel,
When the temperature detected by the temperature sensor is equal to or lower than a predetermined temperature, the control circuit performs a heating process of controlling the drive circuit to apply an AC signal between the transparent electrodes facing each other, and the temperature sensor detects A liquid crystal display device comprising: a display writing process for controlling the drive circuit in accordance with a display image to bring the liquid crystal material into a state in accordance with the display image after the temperature reaches a predetermined temperature or higher.
(Appendix 2)
The liquid crystal display device according to appendix 1, wherein the control circuit controls the drive circuit so as to change a frequency of the AC signal according to a temperature during the heat treatment.
(Appendix 3)
The liquid crystal display device according to appendix 1, wherein the control circuit controls the drive circuit so as to change a voltage of the AC signal according to temperature during the heat treatment.
(Appendix 4)
The liquid crystal material is a cholesteric liquid crystal material,
The liquid crystal display panel is a reflective liquid crystal display panel,
The liquid crystal display device according to any one of appendices 1 to 3, further comprising a light absorption layer provided on a back surface of the reflective liquid crystal display panel.
(Appendix 5)
Item 5. The liquid crystal display device according to appendix 4, wherein the liquid crystal display device includes a plurality of the stacked reflection type liquid crystal display panels and performs color display.
(Appendix 6)
6. The liquid crystal display device according to appendix 5, wherein an alternating current signal is applied between the transparent electrodes of all the plurality of reflective liquid crystal display panels during the heat treatment.
(Appendix 7)
The control circuit performs the heating process, performs the display writing process after the temperature detected by the temperature sensor is equal to or higher than a predetermined temperature, and then applies the state between the transparent electrodes to the state of the cholesteric liquid crystal material. 7. The liquid crystal display device according to any one of appendices 4 to 6, wherein an AC signal having a voltage that does not change is applied to maintain a temperature detected by the temperature sensor at a predetermined temperature or higher.

DESCRIPTION OF SYMBOLS 11 Upper substrate 12 Lower substrate 13 Scan electrode 14 Data electrode 15 Light absorption layer 16 Sealing material 17 Liquid crystal layer 30 Columnar spacer (spacer member)
41 Scan electrode drive circuit 42 Data electrode drive circuit 61 Control circuit 62 Power supply 63 Temperature sensor

Claims (5)

A liquid crystal display panel having two substrates with transparent electrodes formed on opposite surfaces, and a liquid crystal material filled between the substrates;
A drive circuit for applying a voltage to the liquid crystal material between the transparent electrodes by applying a voltage to the transparent electrodes;
A control circuit for controlling the drive circuit according to a display image;
A temperature sensor for detecting the temperature of the liquid crystal display panel,
When the temperature detected by the temperature sensor is equal to or lower than a predetermined temperature, the control circuit performs a heating process of controlling the drive circuit to apply an AC signal between the transparent electrodes facing each other, and the temperature sensor detects A liquid crystal display device comprising: a display writing process for controlling the drive circuit in accordance with a display image to bring the liquid crystal material into a state in accordance with the display image after the temperature reaches a predetermined temperature or higher.   The liquid crystal display device according to claim 1, wherein the control circuit controls the drive circuit so that the frequency of the AC signal is changed according to temperature during the heat treatment.   The liquid crystal display device according to claim 1, wherein the control circuit controls the drive circuit so that the voltage of the AC signal is changed according to temperature during the heat treatment. The liquid crystal material is a cholesteric liquid crystal material,
The liquid crystal display panel is a reflective liquid crystal display panel,
The liquid crystal display device according to claim 1, further comprising a light absorption layer provided on a back surface of the reflective liquid crystal display panel.   The liquid crystal display device according to claim 4, comprising a plurality of the stacked reflective liquid crystal display panels and performing color display.

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