JP2003280005A - Ocb type liquid crystal display device and method for driving the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the effect for reducing display unevenness caused in the vicinity of a sealing resin is insufficient in a polar pulse applying method in the initial stage for driving an OCB type liquid crystal display device using a conventional two solvent type sealing resin. <P>SOLUTION: Display unevenness due to the reduction of specific resistance in the OCB type liquid crystal display device using a liquid crystal having high dielectric anisotropy is reduced by selecting a one solvent type sealing resin and applying pulse voltage in both polar directions in the initial stage for driving the display device to reduce electric field drift of an ionized component of an impurity in the sealing resin. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OCB type liquid crystal display device using a high dielectric constant anisotropic liquid crystal and a driving method thereof, and more particularly to a sealing resin for adhering a liquid crystal substrate and a driving method.

[0002]

2. Description of the Related Art At present, liquid crystal display devices are widely used for displaying screens of personal computers, car navigation systems, monitors and TVs. As the alignment mode of liquid crystal used for these liquid crystal displays, TN type alignment mode and STN type alignment mode using nematic liquid crystal are often used, but they have drawbacks such as slow response and narrow viewing angle.

On the other hand, in recent years, a liquid crystal display device of an IPS (horizontal plane drive) display mode driven by a lateral electric field has been put into practical use as a display mode having an excellent viewing angle, but it has a problem in response speed and aperture ratio.

Further, although there are display modes such as a ferroelectric liquid crystal having a fast response speed and a wide viewing angle, there are problems in shock resistance and temperature characteristics.

Therefore, recently, an optical compensation (OCB) type liquid crystal display mode has been attracting attention as a display mode having excellent high-speed response and a wide viewing angle for video equipment, and is being actively developed.

In the OCB type liquid crystal display mode, as shown in FIG. 4A, liquid crystal molecules (liquid crystal layer) 11 are formed on the inner surfaces of a pair of upper and lower substrates 31 and 32 facing each other for the liquid crystal display panel 100.
Liquid crystal layer 11 of splay alignment obtained by aligning 1 in a parallel direction
4 and voltage is applied between the upper and lower substrates 31 and 32 so that the liquid crystal molecules 111 of the liquid crystal layer are moved from the splay alignment as shown in FIG.
As shown in (b), a state in which the orientation is changed to a bend orientation or a bend orientation including a twist orientation, and further, FIG.
As shown in (3), it has a bend orientation state. 4A shows a state where the transmittance (luminance) is high (commonly referred to as white display) when the applied voltage is approximately 0 V and FIG. 4B shows when a low voltage is applied. c) is a state where the transmittance (luminance) is low when a high voltage is applied (commonly known as black display),
Video display is performed by the white display, the black display and the black and white intermediate display.

FIG. 5 shows a retardation plate 39 and a polarizing plate 3 for optically compensating the liquid crystal layer 111 for lower voltage driving and widening the viewing angle.
8 is a schematic sectional view of the liquid crystal display panel 100 in which a backlight 110 for providing display brightness is arranged. In FIG. 5, a plurality of switching TFT elements (the driving of the TFT elements will be described later with reference to FIG. 7) are arranged in a matrix on one of the upper and lower substrates 31, 32 (for example, the lower substrate 32). (A video screen commonly referred to as XGA has a length of 768 × width of 1024 × 3). The transmittance of the backlight 110 is controlled by the operation of the liquid crystal display panel 100.

FIG. 6 shows the voltage dependence of the transmittance of the liquid crystal display panel 100. 4, 5 and 6, the transmittance of the liquid crystal display panel 100 when the voltage of FIG. 6 is approximately 0 V corresponds to FIGS. 4A and 5A, and the voltage is approximately Vw. Fig. 4 shows the transmittance of the liquid crystal display panel when
(B) and FIG. 5 (b) respectively, and FIG. 4 shows the transmittance when the voltage value is in the vicinity of Vb sufficiently exceeding Vw.
5C corresponds to FIG. 5C.

This OCB type liquid crystal mode is a liquid crystal display device characterized in that it has a high display speed and a wide viewing angle in terms of display performance, and is currently being put into practical use for video equipment such as a liquid crystal TV.

The OCB type liquid crystal display is a mode in which an image is displayed by an applied voltage corresponding to a white display, a black display and a black and white intermediate state, but the white display (low voltage application) of FIG. 4B is used.
When the period of the state is long in time, the bend state reversely transitions to the spray state of FIG. Since it takes about 1 second to re-transfer from the splay alignment state to the bend alignment state, it is not suitable for displaying moving images such as video equipment. Therefore, it is peculiar to OCB type liquid crystal display that prevents reverse transition. The driving method was adopted.

On the other hand, FIG. 4 (b) to FIG. 4 (c), FIG.
Since it shifts from (c) to FIG. 4 (b) in a few milliseconds, it is suitable for a moving image such as a video device that requires high-speed response. Therefore, conventionally, white display (Vw value) in FIG.
In the following states, a high pulse voltage for a certain period (duty) is applied during one frame of the screen, and the high voltage pulse shown in FIGS.
It was intended to prevent reverse transfer to (a).

FIG. 7 (15 in FIG. 7 shows an enlarged portion of the switching TFT element) is a block diagram for driving the OCB type liquid crystal display device. In FIG. 7, the video signal 10 supplied from the power source is supplied to the source electrode 16 of each switching TFT element 15 of each pixel 341 from the source driver through the source line 20, and the gate electrode 18 of the switching TFT element 15 of each pixel 341 is supplied. A scanning signal (gate voltage) of the synchronization signal 11 is supplied from the power source to the gate driver via the gate line 19 from the gate driver. Gate electrode 1
The video signal 10 is input to the source electrode 16 in accordance with the timing of the ON state of the liquid crystal layer 1 and the pixel electrode 34 connected to the drain electrode 17 of the switching TFT element 15 and the liquid crystal layer 1.
A voltage is supplied to the counter electrode 33 on the other upper substrate 31 via 11 to perform liquid crystal display. Reference numeral 110 denotes a backlight, which controls the transmittance (transmitted light) of the backlight by the operation of the liquid crystal display panel 100.

[0013]

[Problems to be Solved by the Invention] However, OCB
Dielectric anisotropy Δε of liquid crystal used in the liquid crystal display mode is 1
A material having a value of 0 or more is suitable, but a material having a large dielectric anisotropy Δε of the liquid crystal has a strong polarity, so that it is easy to take in impurity ions contained in the sealing resin, and the liquid crystal has a high specific resistance. Lower.

Regarding the prior art relating to the specific resistance (reciprocal of conductivity) of the sealing resin for liquid crystal display element, Japanese Patent Laid-Open No. 2001-2
No. 20498, Japanese Patent Application Laid-Open No. 2001-220499, etc., these prior examples are such that a cured product of a sealing resin (seal adhesive) is immersed in hot water to obtain a specific resistance (conductivity) of the extracted water. ) Is measured, and its specific resistance (conductivity) is 10 ⁴ Ωcm (conductivity: 10 ⁻⁴ S
/ Cm or less) or more.

[0015]

In order to solve the above problems, the present invention measures the specific resistance of a mixture of a sealing resin and a liquid crystal.

FIG. 1A shows an xy plan view corresponding to the liquid crystal display panel 100 in the liquid crystal display device.
(B) is an enlarged view of a yz cross section of the seal resin around the liquid crystal panel taken along the line AB in the plan view. Sealing resin (commonly known as 2
Liquid seal resin) made by World Rock N
o. 780B-BS (seal resin B) and X manufactured by Mitsui Toatsu
The interaction between two kinds of seal resins N-21-S (seal resin A) and a liquid crystal material having a dielectric anisotropy Δε of 10 or more was measured.

The above-mentioned interaction is judged by the measured resistivity value.
Decided The measurement sample is a liquid crystal material and the above two types of uncured
Each of the two types of
Compare the specific resistance of the mixture with the specific resistance of the liquid crystal material alone.
It was The measurement result shows that the sealing resin B is 6 × 10.¹¹Ωcm, sea
3 x 10 for resin A^TenΩcm, 1 × 10 for liquid crystal material
¹³It was Ωcm. From the above measurement results, the conventional seal tree
Impurity components contained in the oil A and the sealing resin B are
It was found that the resistance was reduced by about 1 to 2 digits.

When a voltage is applied between both electrodes of the liquid crystal display panel 100 using the conventional seal resin, the voltage effectively applied to the pixel 341 near the seal resin in FIG. 1 is the pixel 341 at the center of the liquid crystal panel. Lower than.

As a result, it has been found that the voltage value practically applied to the pixel 341 of the liquid crystal display panel varies depending on the position of the pixel 341, and this difference causes display unevenness.

As described above, the present invention pays attention to the fact that the display unevenness and the decrease in the specific resistance of the liquid crystal are closely related, and the cause thereof is that the decrease in the specific resistance occurs due to the interaction with the sealing resin. It was found, and from that knowledge, a sealing resin that does not reduce the specific resistance of the liquid crystal was used, and a liquid crystal material having a large dielectric anisotropy was used.

In order to solve the problem of display unevenness occurring in the vicinity of the seal resin, as a first invention, a one-liquid solvent type seal resin 370 is added to KAYATORON manufactured by Nippon Kayaku.
The periphery of both substrates is adhered using a sealing agent resin of ML-3900.

As a second invention, the specific resistance of the mixture of the one-liquid solvent-type sealing resin and the liquid crystal is measured, and the specific resistance is 1/10 or less as compared with the specific resistance of the liquid crystal alone. . The specific resistance is measured by adding a mixture of seal resin and liquid crystal or a single liquid crystal to a standard volume of 1 cm ³ having electrodes on the side to prepare a measurement sample, and then applying a voltage to measure the current in the standard volume. I asked.

As a third invention, originally, the OCB type liquid crystal display mode is a mode showing an electro-optical response of several milliseconds.
In order to effectively utilize this characteristic, a liquid crystal material having a large dielectric anisotropy Δε is suitable, but the larger the dielectric anisotropy Δε, the easier it is to take in impurity ions. So, first,
Based on the second invention, it is possible to use a liquid crystal having a dielectric anisotropy Δε of 8 or more and 15 or less, which is suitable for the OCB type mode.

According to a fourth aspect of the invention, the liquid crystal layer is sprayed during the initial movement of the liquid crystal display device in which the non-display state is changed to the display state between the pixel electrode and the counter electrode using the one-liquid solvent type sealing resin. It is an invention of a driving method for applying both a transition voltage pulse for causing a transition from an orientation to a bend orientation and a voltage pulse of an opposite polarity. According to the present invention, during the initial drive period of the liquid crystal display device, only the transition voltage pulse in one direction as shown in FIG. 8 is applied in the conventional driving method, but the polarity of the pulse voltage in the initial drive period is one direction. Therefore, it is conceivable that the ionized components of the impurities progress from the surface of the sealing resin to the inside by electric field drift during the initial motion period. Therefore, a driving method for preventing the progress due to the electric field drift was invented.

As described above, the present invention provides an OCB type liquid crystal display device having a uniform display screen by reducing the occurrence of display unevenness due to the problematic impurity ions.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) An outline of a manufacturing process of the liquid crystal display panel 100 shown in FIG. 5 will be described. Counter electrode 33,
Alignment films 35 and 36 made of polyimide for aligning the liquid crystal molecules 111 are formed on the pixel electrode 34 by a method such as transfer printing. By rubbing the surfaces of the alignment films 35 and 36 with a cloth made of rayon, a process of aligning the liquid crystal molecules 111 in a predetermined direction is performed. Next, the upper substrate 3
1. After bonding the lower substrate 32 and adhering the peripheral portion with a sealing resin, liquid crystal is injected and sealed.

A voltage pulse for transition is applied to the pixel electrode 34 and the counter electrode 33 in the manufactured OCB type liquid crystal display panel 100 by the driving device as shown in FIG.
Is transferred from the splay orientation to the bend orientation. The switching TFT element 15 is ON / OFF controlled by a drive voltage input from the source line 20 and the gate line 19.
Then, by controlling the voltage value applied between the pixel electrode 34 connected to the switching TFT element 15 and the counter electrode 33, the orientation of the liquid crystal layer 111 is changed and each pixel 3 is changed.
The transmittance (luminance) of 41 is controlled to display an image.

At this time, the liquid crystal display panel 10 shown in FIG.
The one-solvent solvent type (KAYATOR manufactured by Nippon Kayaku) is used as the sealing resin 370 for bonding the periphery of the upper and lower substrates 31 and 32 of 0.
When the sealing resin C of ONML-3900) was used, display unevenness did not occur around the sealing resin 370. For comparison, when two kinds of two-liquid mixed type seal resin A and seal resin B were used, display unevenness occurred. That is, it was found that the one-liquid solvent type is less susceptible to the influence of the impurity component than the conventional two-liquid mixed type including the main agent and the curing agent.

As a result of performing the same measurement as described above in "Problems to be solved by the invention" for the sealing resin C, the specific resistance of the mixture of the sealing resin C and the liquid crystal is 5 × 10 ¹² Ωcm.
Met. The values of the specific resistance of the mixture of the three kinds of seal resin and liquid crystal are, in descending order, seal resin C (1 liquid)> seal resin B (2 liquid)> seal resin A (2 liquid).

(Second Embodiment) FIG. 2 shows a voltage waveform for applying a bidirectional polarity pulse between the pixel electrode 34 and the counter electrode 33 during the initial operation period of the OCB type liquid crystal display device. By applying the polarity pulse in both directions, it was possible to prevent the impurity ions in the seal resin from drifting in the liquid crystal due to the electric field, and to prevent the subsequent diffusion.

(Embodiment 3) FIG. 3 is a diagram showing the relationship between the dielectric anisotropy of liquid crystal and the occurrence of display unevenness when the seal resin C is used. From the figure, when the seal resin C is used, for the liquid crystal material having a dielectric anisotropy Δε of 15 or less,
The display unevenness did not occur at all. When the seal resin B and the seal resin A are used for comparison, display unevenness gradually occurs when each dielectric constant anisotropy Δε is 8 or more and 7 or more, and each dielectric anisotropy Δε is further increased. When the value was 10 or more and 8 or more, the display unevenness was unpleasant. That is, it is shown that the seal resin C is effective against other two-liquid mixed type seal resins when the dielectric constant anisotropy Δε of the liquid crystal is 8 or more.

Based on the operations described in the first to third embodiments, a liquid crystal having a dielectric anisotropy Δε of 8 or more and 15 or less, which is suitable for the OCB type liquid crystal display device, is used, and As a result of long-time drive display under the test conditions (temperature: 80 ° C., humidity: 90%), it was possible to prevent the problem of display unevenness.

[0034]

As described in detail above, by adopting the one-liquid solvent type sealing resin and the driving method according to the present invention,
It has become possible to reduce the occurrence of display unevenness due to impurity component ions that have been conventionally generated around the sealing resin.
Furthermore, it has become possible to reduce display unevenness even for liquid crystals having a dielectric anisotropy Δε of 8 or more and 15 or less. Therefore, the present invention is highly expected to be used as a video display for TVs in the future.
The industrial advantage is extremely great in manufacturing a CB type liquid crystal display device.

[Brief description of drawings]

FIG. 1A is a plan view of an OCB type liquid crystal display device of the present invention. (B) An enlarged sectional view taken along the line AB of (a) above.

FIG. 2 is a drive voltage waveform diagram of the present invention.

FIG. 3 is a diagram showing a relationship between dielectric anisotropy of a liquid crystal material of an OCB type liquid crystal display device and display unevenness around a seal.

FIG. 4 is a sectional view schematically showing the alignment of OCB type liquid crystal.

FIG. 5 is a sectional view schematically showing an OCB type liquid crystal display panel.

FIG. 6 is a diagram showing the relationship between the transmittance and the voltage of an OCB type liquid crystal display device.

FIG. 7 is a block diagram showing a driving method of an OCB type liquid crystal display device.

FIG. 8 is a conventional drive voltage waveform diagram.

[Explanation of symbols]

10 video signals 11 Sync signal 15 Switching TFT element 16 Source electrode 17 Drain electrode 18 Gate electrode 19 gate lines 20 source line 31 upper substrate 32 Lower substrate 33 Counter electrode 34 pixel electrodes 35,36 Alignment film 38 Polarizer 39 Phase plate 100 LCD display panel 110 backlight 111 Liquid crystal molecules (liquid crystal layer) 341 pixels 370 seal resin 380 Sealant

Continued front page    (72) Inventor Kazuhiro Nishiyama             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 2H088 EA03 FA04 GA02 HA08 HA16                       HA18 JA04 KA26 KA30 MA04                 2H089 MA04 NA37 PA16 QA16 RA04                       SA16 SA17 TA04 TA09 TA14                       TA15                 2H093 NA16 NC34 ND05 NE06 NE10                       NF04 NH04                 5C006 AA01 AA16 AC11 AC26 AF44                       AF73 BA15 BB16 BC11 BF27                       FA14 FA22 FA34 FA54 FA55                 5C080 AA10 BB05 DD05 DD08 DD18                       EE19 EE29 FF11 GG08 JJ02                       JJ03 JJ04 JJ05 JJ06 KK02                       KK04 KK43

Claims (4)

[Claims] 1. A liquid crystal injection device is provided around a periphery of both of the substrates by holding one substrate having switching TFT elements and pixel electrodes arranged in a matrix and the other substrate having a counter electrode at a constant gap. A liquid crystal display device in which liquid crystal is injected from the liquid crystal injection port and sealed by sealing the liquid crystal injection port by excluding the inlet, and the sealing resin is a one-liquid solvent type liquid crystal. Display device. 2. The OCB type liquid crystal display device according to claim 1, wherein a seal resin having a specific resistance of a mixture of a one-liquid solvent-type seal resin and a liquid crystal is 5 × 10 ¹² Ωcm or more is used. 3. The OCB type liquid crystal display device according to claim 1, wherein the liquid crystal has a dielectric anisotropy Δε of 8 or more and 15 or less. 4. A transfer voltage pulse for transferring the liquid crystal from the splay alignment to the bend alignment is applied between the pixel electrode and the counter electrode during the initial period for displaying the liquid crystal display device, and then the liquid crystal display device of the opposite polarity is applied. The OCB according to any one of claims 1 to 3, wherein a voltage pulse is applied.
Method of driving type liquid crystal display device.