JP2005265930A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device whose characteristic of an angle of view is variable. <P>SOLUTION: The liquid crystal display device which has a liquid crystal panel for driving, a liquid crystal panel for compensation which is stacked on the opposite side of the liquid crystal panel for driving from an observer side, and polarizing plate each arranged on the observer side of the liquid crystal panel for driving and the opposite side of the liquid crystal panel for compensation from the observer side, the liquid crystal panel for driving having a transparent or translucent type pixel structure and can display an image, is so constituted that the liquid crystal panel for compensation has transparent electrodes facing each other across a liquid crystal layer to apply a voltage independently of the liquid crystal panel for driving. The electrodes of the liquid crystal panel for compensation are properly divided to selectively display the characteristics of the angle of view corresponding to use environment and contents to be displayed at respective parts on the display surface of the same liquid crystal display device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device capable of adjusting viewing angle characteristics.

  It has been known that the display quality of the previous liquid crystal display device changes depending on the viewing angle (viewing angle). In other words, even when the liquid crystal display device shows very good display characteristics when viewed from the front, when viewed from the top and bottom or the left and right directions, the whole is observed as blackish (blackout), and conversely the front is whitish. Deterioration in display quality was observed, such as what was observed (whiteout), the display was reversed black and white, and was observed as a negative display (gradation inversion), and the color changed when observed from the front.

  In order to solve the display quality deterioration due to the viewing angle, a liquid crystal display element that performs phase compensation using a retardation film or a second liquid crystal panel has been proposed. The deterioration of the display quality due to the viewing angle is caused by the fact that the birefringence of the liquid crystal layer changes when observed from an oblique direction as compared to when viewed from the front. By compensating by the first liquid crystal panel and reducing the birefringence change, the display quality change due to the viewing angle is prevented.

  As such a liquid crystal display device, an example using a TN mode liquid crystal panel and a discotic liquid crystal film, an example using an STN liquid crystal panel and a compensation liquid crystal panel are known.

  For example, Patent Document 1 discloses a liquid crystal display element that improves viewing angle characteristics. FIG. 3 is a cross-sectional view showing a configuration example of a conventional liquid crystal display element that improves viewing angle characteristics. The driving liquid crystal panel 1 is arranged on the observer side (upper side in the figure), and the compensating liquid crystal panel 7 is laminated on the driving liquid crystal panel 1 on the opposite side (lower side in the figure) of the driving liquid crystal panel 1. . One polarizing plate 3 and 4 is disposed on the viewer side and the counter-viewer side of these liquid crystal panels, respectively. A driving circuit 5 for applying a driving voltage is connected to the driving liquid crystal panel 1 via an electrode (not shown), but the compensation liquid crystal panel 7 has no electrode and no voltage applying circuit and has a certain characteristic. . It consists of an optically anisotropic layer whose molecular long axis is arranged almost parallel to the main surface, and the angle between the molecular long axis and the main surface changes continuously in the thickness direction of the optically anisotropic layer. It is characterized by that. Therefore, when the angle of viewing the refractive index ellipsoid is increased, the refractive index body in the two-dimensional plane of the visual axis becomes larger in the length direction of the major axis, whereas the refractive index in the minor axis direction is larger. The resultant refractive index body in the two-dimensional plane becomes a circle. Therefore, the refractive index ellipsoid can be optically compensated, and the viewing angle characteristics are improved.

  By providing a film or liquid crystal panel that compensates for the birefringence change due to these viewing angles, the viewing angle characteristics of the liquid crystal display device are greatly improved, and it is good even when observed from a direction of a large angle with respect to the normal line of the screen. Display quality can be obtained.

Japanese Patent No. 3222909

  However, in recent years, with the development of mobile devices equipped with a liquid crystal display device such as a mobile phone, a PDA, and a notebook PC, there are increasing opportunities to observe the liquid crystal display device in an environment where there are many outsiders in the vicinity. In such an environment, contrary to the conventional case, it is necessary to lower the display quality from the surroundings and prevent the outsiders from looking into the surroundings. A situation that needs to occur. For example, there is a need for a liquid crystal display device that has a wide viewing angle characteristic in use environments such as offices, and can narrow the viewing angle characteristic when preventing outsiders when there are outsiders in the mobile application. It has been. SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device having a variable viewing angle characteristic.

  A driving liquid crystal panel disposed on the observer side, a compensation liquid crystal panel stacked on the anti-observer side of the driving liquid crystal panel, an anti-side of the observer side of the driving liquid crystal panel and the compensation liquid crystal panel In the liquid crystal display device in which one polarizing plate is disposed on each side of the observer, the driving liquid crystal panel has a pixel structure, and an image can be displayed, the compensation liquid crystal panel sandwiches a liquid crystal layer. The liquid crystal display device is configured so as to include transparent electrodes facing each other and to be able to apply a voltage independently of the driving liquid crystal panel.

  In the same liquid crystal display device, wide viewing angle and narrow viewing angle characteristics can be obtained, and a liquid crystal display device having viewing angle characteristics corresponding to the use environment can be obtained.

  In addition, by appropriately dividing the electrodes of the compensation liquid crystal panel, wide viewing angles and narrow viewing angles can be displayed in each part of the display surface of the same liquid crystal display device, and the usage environment and display A liquid crystal display device capable of selectively displaying viewing angle characteristics according to the contents can be obtained.

  The present invention provides a liquid crystal display device that displays by changing the birefringence or optical rotation of the driving panel, and the display quality such as blackening, whitening, and gradation inversion when viewed from an oblique direction is reduced. The compensation panel having birefringence or optical rotation improves the deterioration of viewing angle characteristics by compensating the optical contribution when observed from an oblique direction, and compensation is performed in the same liquid crystal display device. The present invention provides a liquid crystal display device in which viewing angle characteristics are made variable by applying a voltage to a panel and changing the degree of compensation of optical contribution in an oblique direction.

  FIG. 1 is a sectional view showing an embodiment of the present invention. The driving liquid crystal panel 1 is disposed on the observer side (upper side in the figure), and the compensating liquid crystal panel 2 is laminated on the driving liquid crystal panel 1 on the opposite side (lower side in the figure) of the driving liquid crystal panel 1. . One polarizing plate 3 and 4 is disposed on the viewer side and the counter-viewer side of these liquid crystal panels, respectively. A driving circuit 5 for applying a driving voltage is connected to the driving liquid crystal panel 1 via an electrode (not shown), and a viewing angle is changed to the compensation liquid crystal panel 2 via a transparent electrode (not shown). A compensation voltage application circuit 6 for applying a voltage for the purpose is connected.

  The liquid crystal alignment in the driving panel used in the present invention can change the polarization state and optical rotation direction of incident light such as vertical alignment, parallel alignment (uniaxial alignment), antiparallel alignment, twist alignment, and hybrid alignment. In addition, all liquid crystal display modes that can change the degree of change in the polarization state and optical rotation direction of incident light by applying a voltage to the panel can be used.

  In particular, in the case of hybrid alignment, since there is no threshold characteristic, the liquid crystal alignment changes gradually with voltage application, birefringence adjustment is easy, and viewing angle control can be performed accurately. It is. Further, in the case of the twisted orientation, display can be performed by changing the optical rotation, so that a display with a high contrast ratio can be obtained and display quality can be improved. Furthermore, in the case of parallel orientation (uniaxial orientation) and vertical orientation, it is easy to analyze the orientation state, and it is possible to easily optimize the optical characteristics design and the applied voltage of the compensation panel and the driving panel. Angle control can be easily performed.

  As the liquid crystal material in the driving panel used in the present invention, any liquid crystal material can be used as long as it has birefringence and the alignment direction can be changed by an electric field.

  As the liquid crystal material in the compensation panel used in the present invention, any liquid crystal material can be used as long as it has birefringence and the alignment direction can be changed by an electric field. The liquid crystal alignment in the compensation panel used in the present invention can change the polarization state and optical rotation direction of incident light such as vertical alignment, parallel alignment (uniaxial alignment), anti-parallel alignment, twist alignment, and hybrid alignment. In addition, all liquid crystal display modes that can change the degree of change in the polarization state and optical rotation direction of incident light by applying a voltage to the panel can be used.

  In particular, when the compensation liquid crystal panel is in a hybrid orientation, it does not have a threshold characteristic in its voltage dependence. Angle control can be performed with high accuracy. Furthermore, the hybrid alignment is particularly suitable in that it compensates for the influence of liquid crystal molecules that do not respond to voltage application existing in the vicinity of the transparent electrode interface of the driving panel and can easily widen the viewing angle.

  In addition, when an orientation whose optical characteristics gradually change in the thickness direction in the panel, such as twisted orientation and hybrid orientation, is used for the compensation panel, it can accurately compensate for changes in the optical properties due to the viewing angle of the driving panel. The display quality can be improved. Furthermore, in the case of parallel orientation (uniaxial orientation) and vertical orientation, it is easy to analyze the orientation state, and it is possible to easily optimize the optical characteristics design and the applied voltage of the compensation panel and the driving panel. Angle control can be easily performed.

  The birefringence value of the compensation panel is not particularly limited, but is preferably 50 to 500 nm, and more preferably 100 to 300 nm, from the viewpoints of display quality and coloring. The compensation panel compensates for the birefringence remaining in the driving panel to which a voltage is applied. On the other hand, the birefringence of the driving panel is changed from 0 to 500 nm by voltage application. Therefore, it is appropriate that the birefringence value of the compensation panel is 50 to 500 nm in the middle. Therefore, when using a liquid crystal having a positive dielectric anisotropy that reduces the birefringence value of the compensation panel by applying a voltage, it is appropriate that the birefringence value be 500 nm when no voltage is applied. It is. On the other hand, when a liquid crystal having negative dielectric anisotropy that increases the birefringence value of the compensation panel by applying a voltage is used, the birefringence value may be 50 nm or more when no voltage is applied. Is appropriate.

  As in the present application, when the birefringence value of the compensation panel changes due to voltage application, and when the birefringence value of the compensation panel increases with voltage application, the birefringence value when no voltage is applied is If it is configured to reduce the birefringence value of the compensation panel when a voltage is applied, the birefringence value when no voltage is applied needs to be 500 nm or less. .

Example 1
Details of this embodiment will be described below.

  A pixel structure capable of displaying an image was formed on a pair of transparent electrode substrates. An alignment film made of polyimide having a function of aligning liquid crystal molecules substantially parallel to the substrate surface was applied to each substrate, dried, baked, and then rubbed.

  The two transparent electrode substrates are bonded so that the panel gap is 4.5 μm and the liquid crystal alignment is parallel alignment (uniaxial alignment), the refractive index anisotropy (Δn) is +0.07, and the dielectric anisotropy ( A liquid crystal material having Δ∈) of +8 was injected to obtain a driving liquid crystal panel 1.

  Next, a pair of transparent substrates having transparent electrodes that are not divided into pixel structures is used, and one substrate surface is made of polyimide having a function of aligning liquid crystal molecules substantially parallel to the substrate surface by the same method as described above. A film was prepared, and an alignment film having a function of aligning liquid crystal molecules substantially perpendicular to the substrate surface was formed on the other substrate surface. The two transparent electrode substrates were bonded to each other so as to have a panel gap of 3 μm, and the same liquid crystal material as described above was injected to obtain a compensation liquid crystal panel 2. This compensation liquid crystal panel had a birefringence value of approximately 120 nm when no voltage was applied.

  Electrodes for driving by applying a voltage were attached to the two sets of liquid crystal panels, and the liquid crystal panels were laminated so as to be a driving liquid crystal panel on the observer side and a compensation panel on the counter-observer side.

  Further, a circularly polarizing plate made of a polarizing plate, a 1 / 2λ film and a 1 / 4λ film is attached to the viewer side of the laminated liquid crystal panel, and a voltage is applied to the 1 / 2λ film and the polarizing plate on the counter-observer side. Attached so as to have a circularly polarizing plate function together with the compensation panel when not applied.

  Table 1 shows the configuration of each liquid crystal panel and polarizing plate. In addition, Table 2 shows the viewing angle control characteristics (with a contrast ratio of 5 or more) obtained by applying a voltage to the compensation panel.

  Table 2 shows combinations of applied voltages for displaying black gradation. This shows that when the applied voltage of the compensation panel is changed in order to change the viewing angle range, the applied voltage of the driving panel is also changed in order to display a black gradation.

  In the liquid crystal display device obtained in this example, the viewing angle characteristics in the upward direction hardly change when a voltage is applied to the compensation panel, but the downward direction changes in the range of 30 to 60 ° and the horizontal direction in the range of 35 to 80 °. I understand that Therefore, the liquid crystal display device of the present embodiment can control from a wide viewing angle characteristic to a narrow viewing angle characteristic that prevents peeping from surrounding people.

  FIG. 2 shows that the voltage dependency of the transmittance of the driving panel changes depending on the applied voltage of the compensating panel. In FIG. 2, when the relative transmittance is near 0, the gray level is black, and near 1 is the white gray level. When the applied voltage (that is, the viewing angle range) of the compensation panel is changed, the applied voltage of the driving panel that displays the same gradation changes. Therefore, by changing the gradation display voltage setting of the driving panel according to the applied voltage of the compensation panel, the same gradation can be obtained even in different viewing angle displays.

Example 2
In the liquid crystal display device created in Example 1, the electrode structure of the compensation panel is changed. In Example 1, the compensation panel was not formed by dividing the electrode, but a solid electrode was used. In the present embodiment, the electrode surface of the compensation panel is divided into three in each of vertical and horizontal directions, and is divided into a total of nine individual voltage-applicable regions in the surface, so that a voltage can be applied independently to each region. A liquid crystal display device was prepared in the same manner as in Example 1 except for other processes and panel structures.

  The prototype liquid crystal display device can individually control the viewing angle characteristics shown in the first embodiment in nine areas on the display surface, and can have a wide viewing angle area and a peep from the periphery within the same display surface. Narrow viewing angle characteristics that prevent viewing were obtained.

Example 3
In the liquid crystal display device created in Example 1, the pixel structure of the driving panel is changed. In Example 1, a transmissive display panel was used as the drive panel. In this embodiment, a transflective panel is used as the driving panel. The pixel of the driving panel was divided into a transmissive region and a reflective region, and a step structure of 2.2 μm was created for each, and unevenness for scattering reflection having a height of 0.6 μm and a diameter of 10 μm was formed in the reflective portion. That is, the panel gap of the transmissive part is 4.5 μm, and the reflective part is 2.3 μm. All other panel structures were the same as in Example 1.

  The prototyped liquid crystal display device can control the viewing angle in the transmissive display as in the first embodiment. In addition, in the reflective display, a display with a contrast ratio of 10 or more could be obtained.

Example 4
Among the liquid crystal display devices prepared in the examples, the configuration of the compensation panel is changed and a liquid crystal material having negative dielectric anisotropy (Δε) is used. In the production of the compensation panel, the same alignment film as in Example 1 was used, the panel gap was overlapped so as to be 1.5 μm, and a liquid crystal material (Δn = + 0.07, Δε = −5) was injected. The compensation panel has a birefringence value of about 70 nm when no voltage is applied, and the birefringence value can be changed to about 110 nm by applying a voltage.

  When the liquid crystal display device was prepared in the same manner as in Example 1 except for the compensation panel, the viewing angle was narrow when no voltage was applied to the compensation panel, and peeping was prevented. A liquid crystal display device having a wide viewing angle by applying voltage could be obtained.

It is sectional drawing which shows the structure of the liquid crystal display device of this invention. It is a figure which shows that the voltage dependence of the transmittance | permeability of a drive panel changes with the applied voltages of a compensation panel. It is sectional drawing which shows the structure of the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drive liquid crystal panel 2 Compensation liquid crystal panel 3 Observer side polarizing plate 4 Anti-observer side polarizing plate 5 Drive circuit 6 Compensation voltage application circuit

Claims (9)

A driving liquid crystal panel disposed on the observer side, a compensation liquid crystal panel stacked on the anti-observer side of the driving liquid crystal panel, an anti-side of the observer side of the driving liquid crystal panel and the compensation liquid crystal panel In the liquid crystal display device in which one polarizing plate is disposed on each viewer side, the driving liquid crystal panel has a pixel structure and can display an image.
The compensation liquid crystal panel includes a transparent electrode facing the liquid crystal layer, and a voltage can be applied independently of the driving liquid crystal panel. The liquid crystal display device according to claim 1, wherein the opposing transparent electrodes of the compensation liquid crystal panel are divided into a plurality of regions within the screen. The liquid crystal display device according to claim 1, wherein the driving liquid crystal panel is a transmissive type. The liquid crystal display device according to claim 1, wherein the driving liquid crystal panel is a transflective type. 5. The liquid crystal display device according to claim 1, wherein a voltage applied to the driving liquid crystal panel can be changed according to a voltage applied to the compensation liquid crystal panel. 6. The liquid crystal display device according to claim 5, wherein the change in the voltage applied to the driving liquid crystal panel in accordance with the voltage applied to the compensation liquid crystal panel is a change in gradation display voltage setting. The liquid crystal display device according to claim 1, wherein the driving liquid crystal panel has a parallel alignment, and the compensation liquid crystal panel has a hybrid alignment. 8. The liquid crystal display according to claim 1, wherein the compensation liquid crystal panel has a positive dielectric anisotropy and has a birefringence value of 500 nm or less when no voltage is applied. apparatus. 8. The liquid crystal display according to claim 1, wherein the compensation liquid crystal panel has a negative dielectric anisotropy and has a birefringence value of 50 nm or more when no voltage is applied. apparatus.

Images