JP2019015929A - Liquid crystal display device - Google Patents

Abstract

To provide a liquid crystal display device capable of more easily expressing a half tone.SOLUTION: A liquid crystal display device includes: a light source; a pair of polarizing plates separated from and opposed to each other on an optical axis of the light source; first and second liquid crystal cells disposed between the pair of polarizing plates; and a power supply connected to each of the first and second liquid crystal cells and capable of varying an effective voltage to be applied; where characteristics of the above pair of polarizing plates and the first and second liquid crystal cells are set to give a normally black state when no voltage is applied. Each of the first and second liquid crystal cells has a display pattern overlapping each other in a plan view. The power supply drives the first and second liquid crystal cells with effective voltages different from each other to display the above display pattern.SELECTED DRAWING: Figure 2-1

Description

  The present invention relates to a liquid crystal display device including a plurality of liquid crystal cells.

  Liquid crystal display devices using a plurality of stacked liquid crystal cells have been developed (for example, Patent Documents 1 to 4). By using such a liquid crystal display device, for example, various different display patterns can be displayed in a desired display area.

JP 2001-066666 A JP 2003-043449 A JP 2003-195344 A JP 2008-158174 A

  A main object of the present invention is to provide a liquid crystal display device that can more easily perform multi-gradation display of a predetermined display pattern.

  According to a main aspect of the present invention, a light source, a pair of polarizing plates disposed opposite to each other on the optical axis of the light source, and a first and a second disposed between the pair of polarizing plates. A liquid crystal cell; and a power source connected to each of the first and second liquid crystal cells and capable of changing an effective voltage to be applied, the pair of polarizing plates, and the first and second liquid crystals The cell characteristics are set so as to be in a normally black state when no voltage is applied, and each of the first and second liquid crystal cells has a display pattern overlapping each other in plan view, and the power source Provides a liquid crystal display device that displays the display pattern by driving the first and second liquid crystal cells with different effective voltages.

  By stacking the liquid crystal cells so that the segment patterns of a plurality of liquid crystal cells overlap in a plan view and setting the retardation of each liquid crystal cell to be relatively small, multi-tone display of the display pattern can be made easier. Become.

FIG. 1A is a cross-sectional view showing a liquid crystal display device according to a reference example, and FIG. 1B is a graph showing the dependence of light transmittance on the applied voltage of the liquid crystal display device. and, 2A is a cross-sectional view illustrating a basic configuration of a liquid crystal display device according to an embodiment, FIG. 2B is a plan view illustrating a display pattern of the liquid crystal display device, and FIG. 2C is a sample in which simulation is performed. FIG. 2D is a cross-sectional view showing a part of a modification of the liquid crystal display device according to the embodiment.

  FIG. 1A is a cross-sectional view showing a liquid crystal display device according to a reference example. For convenience, the relative sizes and positional relationships of the components are different from the actual ones.

  The liquid crystal display device 110 according to the reference example includes the first liquid crystal cell 10, a pair of polarizing plates 31 and 32, a light source 40, and a power supply 50. On the optical axis of the light source 40, a pair of polarizing plates 31 and 32 facing each other with a space therebetween are arranged. The first liquid crystal cell 10 is disposed between the pair of polarizing plates 31 and 32.

  The first liquid crystal cell 10 is a VA type (vertical alignment type) liquid crystal cell having a so-called segment type electrode structure. The first liquid crystal cell 10 mainly includes a lower substrate 11 and an upper substrate 12 that are disposed to face each other, and a liquid crystal layer 17 that is sandwiched between the lower substrate 11 and the upper substrate 12.

  The lower substrate 11 and the upper substrate 12 are transparent substrates such as a glass substrate and a plastic substrate. Specifically, it is a 0.7 mm thick soda lime glass substrate. The gap between the lower substrate 11 and the upper substrate 12 is held by a lot-like or spherical spacer contained in a frame-shaped sealing material (not shown) and spherical spacers that are uniformly distributed in the substrate surface. A gap d1 (also referred to as a cell thickness) between the lower substrate 11 and the upper substrate 12 is, for example, 2 μm to 6 μm.

  A common electrode 13 is provided on one surface side of the lower substrate 11 (the surface facing the upper substrate 12). A segment electrode (display electrode) 14 having a planar shape such as a desired character or figure is provided on one surface side of the upper substrate 12 (the surface facing the lower substrate 11). These electrodes 13 and 14 are formed by appropriately patterning a transparent conductive film such as indium tin oxide (ITO).

  The lower alignment film 15 is provided on one surface side of the lower substrate 11 so as to cover the lower electrode 13. Similarly, the upper alignment film 16 is provided on one surface side of the upper substrate 12 so as to cover the upper electrode 14. As these alignment films 15 and 16, vertical alignment films that restrict the alignment state of the liquid crystal layer 17 to vertical alignment (substrate normal line direction) are used. Each alignment film is subjected to a uniaxial alignment process such as a rubbing process so as to be antiparallel to each other.

  The liquid crystal layer 17 is provided between the lower substrate 11 and the upper substrate 12 so as to be surrounded by a frame-shaped sealing material (not shown). A liquid crystal member constituting the liquid crystal layer 17 is filled in a space defined by the lower substrate 11, the upper substrate 12, and the frame-shaped sealing material. For the liquid crystal member constituting the liquid crystal layer 17, for example, a negative liquid crystal material having a birefringence Δn of about 0.15 is used.

  When no voltage is applied, the alignment direction of the liquid crystal molecules constituting the liquid crystal layer 17 is substantially perpendicular to the substrate surfaces of the lower substrate 11 and the upper substrate 12. The pretilt angle of the liquid crystal molecules is about 89.5 °. When a voltage is applied between the upper and lower electrodes, the alignment direction of the liquid crystal molecules changes so as to be horizontal with respect to the substrate surfaces of the lower substrate 11 and the upper substrate 12.

  The characteristics of the pair of polarizing plates 31 and 32 and the first liquid crystal cell 10 are set so as to be in a normally black state when no voltage is applied. The pair of polarizing plates 31 and 32 are arranged so that their absorption axes are orthogonal to each other (crossed Nicols arrangement). Further, these absorption axes are arranged so as to be inclined by 45 ° with respect to the liquid crystal molecule alignment direction of the liquid crystal cell 10.

  The first liquid crystal cell 10 is multiplex driven (1/64 Duty, 1/9 Bias) by the power supply 50 at a frame frequency of 150 Hz, for example. The power supply 50 can vary the drive voltage (amplitude), for example, up to 24V.

  FIG. 1B is a graph showing changes in light transmittance with respect to drive voltage when the liquid crystal cell thickness of the liquid crystal display device according to the reference example is 2 μm, 3 μm, 4 μm, and 6 μm. The horizontal axis indicates the voltage (amplitude) value (V) for driving the liquid crystal cell, and the vertical axis indicates the intensity of light incident on the liquid crystal display device (a pair of polarizing plates and the liquid crystal cell) and the emitted light (transmitted light). ) Intensity, that is, the transmittance (%) of the liquid crystal display device.

  According to this graph, it can be seen that as the cell thickness d1 of the liquid crystal cell increases (the retardation Δn × d1 increases), the change in the light transmittance with respect to the drive voltage (the steepness of the electro-optical characteristics) also increases. When the cell thickness is thick (large retardation), high light transmittance can be achieved with a low driving voltage, while medium light transmittance is achieved by applying a medium voltage, that is, in a halftone state, When the number of gradations is increased, the drive voltage step size is reduced, and it is difficult to accurately express those gradations. On the contrary, if the cell thickness is thin (the retardation is small), even if the number of halftone gradations is large, gradation expression is easy, but high light transmittance cannot be realized unless a high voltage is applied.

  The inventors have studied a liquid crystal display device that can more easily realize halftone multi-gradation.

  FIG. 2A is a cross-sectional view illustrating a basic structure of a liquid crystal display device according to an embodiment. For convenience, the relative sizes and positional relationships of the components are different from the actual ones.

  The liquid crystal display device 100 according to the embodiment is different from the liquid crystal display device 110 according to the reference example (see FIG. 1A) between the first liquid crystal cell 10 and the polarizing plate 32 on the front side. A liquid crystal cell) 20 is inserted. Specifically, from the light source 40 side, one polarizing plate (back side polarizing plate) 31, the first liquid crystal cell (back side liquid crystal cell) 10, the second liquid crystal cell (front side liquid crystal cell) 20, and the other polarized light. Plates (front side polarizing plates) 32 are arranged in order.

  The second liquid crystal cell 20 is sandwiched between the lower substrate 21 (including the electrode 23 and the alignment film 25) and the upper substrate 22 (including the electrode 24 and the alignment film 26), and the upper substrate 21 and the lower substrate 22 that are disposed to face each other. A liquid crystal layer 27. Each component 21 to 27 has the same structure and configuration as each component 11 to 17 of the first liquid crystal cell 10. Similar to the first liquid crystal cell 10, the second liquid crystal cell 20 is a VA liquid crystal cell having a segmented electrode structure.

  The lower substrate 21 and the upper substrate 22 are transparent substrates such as a glass substrate and a plastic substrate. Specifically, it is a 0.7 mm thick soda lime glass substrate. A gap d2 between the lower substrate 21 and the upper substrate 22 is, for example, 2 μm to 6 μm.

  A common electrode 23 is provided on one side of the lower substrate 21 (on the side facing the upper substrate 22). A segment electrode (display electrode) 24 having a planar shape (see FIG. 2B) such as a desired character or figure is provided on one surface side of the upper substrate 22 (the surface facing the lower substrate 21).

  The lower alignment film 25 is provided on one surface side of the lower substrate 21 so as to cover the lower electrode 23. Similarly, the upper alignment film 26 is provided on one surface side of the upper substrate 22 so as to cover the upper electrode 24. As these alignment films 25 and 26, vertical alignment films that restrict the alignment state of the liquid crystal layer 27 to the vertical alignment (substrate normal direction) are used. Each alignment film is subjected to a uniaxial alignment process such as a rubbing process so as to be antiparallel to each other.

  The liquid crystal layer 27 is provided between the lower substrate 21 and the upper substrate 22. As the liquid crystal material, for example, a negative liquid crystal material having a birefringence Δn of about 0.15 is used.

  When no voltage is applied, the alignment direction of the liquid crystal molecules constituting the liquid crystal layer 27 is substantially perpendicular to the substrate surfaces of the lower substrate 21 and the upper substrate 22. The pretilt angle of the liquid crystal molecules is about 89.5 °. When a voltage is applied, the alignment direction of the liquid crystal molecules is substantially horizontal with respect to the substrate surfaces of the lower substrate 21 and the upper substrate 22.

  The characteristics of the polarizing plates 31 and 32 and the first and second liquid crystal cells 10 and 20 are set so as to be in a normally black state when no voltage is applied. The pair of polarizing plates 31 and 32 are arranged in a crossed Nicols manner so that their absorption axes are inclined by 45 ° with respect to the liquid crystal molecule alignment direction of the liquid crystal cells 10 and 20. The first and second liquid crystal cells 10 and 20 are arranged such that the liquid crystal molecule alignment directions are in the same direction.

  As the light source 40, for example, a fluorescent lamp or an LED light can be used. Alternatively, an edge light type backlight unit using a light guide plate may be used.

  Each of the first and second liquid crystal cells 10 and 20 is multiplex driven (1/64 Duty, 1/9 Bias) by a power source 50, for example, at a frame frequency of 150 Hz. The power supply 50 can vary the drive voltage (amplitude), for example, up to 24V.

  FIG. 2B is a plan view of the liquid crystal display device 100 as viewed from the front polarizing plate 32 side. When the first liquid crystal cell 10 is driven (voltage application state), characters and figures corresponding to the shape of the segment electrode (display electrode) 14, for example, a circular segment pattern (display pattern) S1 is displayed. Similarly, when the second liquid crystal cell 20 is driven (voltage application state), characters and figures corresponding to the shape of the segment electrode (display electrode) 24, for example, a circular segment pattern (display pattern) S2 is displayed.

  The segment patterns S1 and S2 are arranged so as to overlap in plan view, and are provided in the same position with the same shape. The first and second liquid crystal cells 10 and 20 may have display patterns that do not overlap each other in addition to the segment patterns S1 and S2. The segment patterns S1 and S2 displayed by each of the first and second liquid crystal cells are collectively referred to as a display pattern S.

  Three samples in which the cell thicknesses d1 and d2 of the first and second liquid crystal cells 10 and 20 are changed are prepared. In all three samples, the total retardation of the first and second liquid crystal cells 10 and 20 is set to about 900 nm.

  FIG. 2C is a table summarizing the parameters of the three samples. In the first sample (Sample 1), the cell thickness d1 of the first liquid crystal cell is set to 4 μm (retardation is 600 nm), and the cell thickness d2 of the second liquid crystal cell is set to 2 μm (retardation is 300 nm). In the second sample (Sample 2), the cell thicknesses d1 and d2 are both set to 3 μm (retardation is 450 nm). In the third sample (Sample 3), the cell thickness d1 is set to 6 μ (retardation is 900 nm), and the cell thickness d2 is set to 0 μm. That is, the third sample is a liquid crystal display device including only the first liquid crystal cell, and corresponds to the liquid crystal display device according to the reference example (see FIG. 1A).

  Assume that the display pattern S (see FIG. 2B) is expressed with four gradations (2-bit gradation) for these three samples. Each sample is set to have a light intensity of 24% of the light intensity of the light source (light transmittance is 24%) at the maximum luminance (3/3 gradation). In the 2/3 gradation and 1/3 gradation, the light intensity is set to 16% and 8% of the light intensity of the light source (light transmittance is 16% and 8%), respectively. In any sample, when expressing 0/3 gradation (light transmittance is almost 0%, that is, black display or dark display), a voltage of 15.0 V or less is applied to each liquid crystal cell. Or no voltage applied.

  In the first sample, when the display pattern S is expressed by 3/3 gradation, the first liquid crystal cell is driven with a voltage of about 18.5 V to 19.0 V, and the second liquid crystal cell is about 20.0 V. Drive with a voltage of. In the case of expressing 2/3 gradation, the first liquid crystal cell is driven with a voltage of about 18.5 V to 19.0 V, and the second liquid crystal cell is driven with a voltage of about 15.0 V or less (no voltage applied). As well). When expressing 1/3 gradation, the first liquid crystal cell is driven with a voltage of about 15.0 V or less (no voltage may be applied), and the second liquid crystal cell is driven with a voltage of about 20.0 V. .

  In the second sample, when the display pattern S is expressed by 3/3 gradation, one liquid crystal cell is driven with a voltage of about 20.0 V, and the other liquid crystal cell is driven with a voltage of about 18.0 V. In the case of expressing 2/3 gradation, both liquid crystal cells are driven with a voltage of about 18.0V. When expressing 1/3 gradation, one liquid crystal cell is driven at a voltage of about 18.0 V, and the other liquid crystal cell is driven at a voltage of about 15.0 V or less (no voltage may be applied).

  In the third sample, when the display pattern S is expressed by 3/3 gradation, the first liquid crystal cell is driven with a voltage of about 18.5V. In the case of expressing 2/3 gradation, the first liquid crystal cell is driven with a voltage of about 17.5V. When expressing 1/3 gradation, the first liquid crystal cell is driven with a voltage of about 16.5V.

  In the third sample using a single liquid crystal cell, the driving voltage of the liquid crystal cell is changed by about 1 V in order to change the gradation by one step. On the other hand, in the first and second samples using a plurality of liquid crystal cells, the driving voltage of one of the liquid crystal cells is changed by 2 V or more in order to change the gradation by one step.

  Compared with a liquid crystal display device using a single liquid crystal cell, a liquid crystal display device using a plurality of liquid crystal cells has a wider voltage range to be controlled for adjustment of one gradation, so that gradation adjustment is easier. Become. Such ease of gradation control in a liquid crystal display device using a plurality of liquid crystal cells will appear more prominently when a finer gradation of 2 bits or more is expressed.

  FIG. 2D is a cross-sectional view illustrating a modification 101 of the liquid crystal display device according to the embodiment. The first and second liquid crystal cells 10 and 20 may be provided separately as shown in FIG. 2A, or may be provided integrally as shown in FIG. 2D.

  The modification 101 includes a third liquid crystal cell 33 disposed between the pair of polarizing plates 31 and 32. The third liquid crystal cell 33 includes the first liquid crystal cell 10 including the substrates 11 and 12, the electrodes 13 and 14, the alignment films 15 and 16, and the liquid crystal layer 17, the substrates 12 and 21, the electrodes 23 and 24, and the alignment film 25. , 26 and the second liquid crystal cell 20 including the liquid crystal layer 27 can be regarded as an integrated configuration.

  Specifically, the substrates 11 and 21 provided with the common electrodes 13 and 23 on one side are arranged to face each other with a space therebetween, and the segment electrodes 14 are provided on both sides between the substrates 11 and 21. , 24 is inserted. The liquid crystal layer 17 is disposed between the substrates 11 and 12, and the liquid crystal layer 27 is disposed between the substrates 12 and 21.

  As mentioned above, although this invention was demonstrated based on the Example and its modification, this invention is not limited to these. For example, the first and second liquid crystal cells may be liquid crystal cells of any characteristics / drive system as long as a normally black state can be realized when no voltage is applied. One of the first and second liquid crystal cells may be a VA driving type liquid crystal cell, and the other may be a so-called IPS (in-plane switching) driving type liquid crystal cell. In this case, the IPS liquid crystal cell is arranged so that the liquid crystal molecule orientation direction when no voltage is applied is parallel or orthogonal to the absorption axis of the polarizing plate.

  In the embodiment, when the liquid crystal cell is multiplex-driven, the drive voltage (the amplitude of the applied voltage) is changed. The typical voltage value may be changed. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

DESCRIPTION OF SYMBOLS 10 ... 1st liquid crystal cell, 11, 12 ... Substrate, 13, 14 ... Electrode (segment type), 15, 16 ... Alignment film, 17 ... Liquid crystal layer, 20 ... 2nd liquid crystal cell, 21, 22 ... Substrate, DESCRIPTION OF SYMBOLS 23, 24 ... Electrode (segment type), 25, 26 ... Alignment film, 27 ... Liquid crystal layer, 31, 32 ... Polarizing plate, 40 ... Light source, 50 ... Power supply, 101, 102 ... Liquid crystal display device by an Example, 110 ... A liquid crystal display device according to a reference example.

Claims (5)

A light source;
A pair of polarizing plates disposed opposite each other on the optical axis of the light source;
First and second liquid crystal cells disposed between the pair of polarizing plates;
A power supply connected to each of the first and second liquid crystal cells and capable of changing an applied effective voltage;
With
The characteristics of the pair of polarizing plates and the first and second liquid crystal cells are set to be in a normally black state when no voltage is applied,
Each of the first and second liquid crystal cells has a display pattern that overlaps each other in plan view,
The power source is a liquid crystal display device that displays the display pattern by driving the first and second liquid crystal cells with different effective voltages.   2. The liquid crystal display device according to claim 1, wherein one of the first and second liquid crystal cells is a vertical alignment type liquid crystal cell and the other is an in-plane switching type liquid crystal cell.   2. The liquid crystal display device according to claim 1, wherein both of the first and second liquid crystal cells are vertical alignment type liquid crystal cells.   The liquid crystal display device according to claim 3, wherein the first and second liquid crystal cells have different retardations. The first and second liquid crystal cells are integrally formed,
A first substrate having an electrode formed on one side;
A second substrate disposed opposite to the first substrate and having an electrode formed on one side;
A third substrate disposed between the first and second substrates and having electrodes formed on both sides;
A first liquid crystal layer sandwiched between the first and third substrates;
A second liquid crystal layer sandwiched between the second and third substrates;
The liquid crystal display device according to claim 1, comprising:

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