JP4847652B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and in particular, has a liquid crystal display panel in which liquid crystal molecules having a predetermined twist angle are sealed between two transparent substrates parallel to each other, and is suitable for multiplexing driving. The present invention relates to a liquid crystal display device.
[0002]
[Prior art]
Conventionally, TN (twisted nematic) type devices have been widely used in in-vehicle liquid crystal display devices that place importance on reliability.
[0003]
FIG. 6 shows such a conventionally used TN type liquid crystal display device 1, which includes a liquid crystal display panel 2 having a main function for liquid crystal display. It is arranged.
[0004]
The liquid crystal display panel 2 has two transparent substrates 3 and 4 made of glass plates and the like that are parallel to each other. The transparent substrates 3 and 4 are bonded to each other by a frame-shaped sealing material 6.
[0005]
A liquid crystal layer 7 made of liquid crystal molecules having a predetermined twist angle is formed in a space surrounded by the transparent substrates 3 and 4 and the sealing material 6.
[0006]
A pair of transparent conductive films 8 and 9 made of ITO (indium tin oxide) or the like are formed on the inner surfaces of the transparent substrates 3 and 4 facing each other. A liquid crystal driving voltage is applied to the liquid crystal layer 7.
[0007]
A pair of alignment films 10 and 11 that are rubbed in a predetermined direction are formed inside the transparent conductive films 8 and 9, and the pair of alignment films 10 and 11 allows liquid crystal molecules to be formed. The twist angle is regulated.
[0008]
A pair of polarizing plates 13 and 14 are disposed outside the liquid crystal display panel 2, and the polarizing direction of the transmitted light is controlled by the polarizing plates 13 and 14.
[0009]
In recent years, in such a liquid crystal display device 1, in order to diversify and complicate the display, a multiplexing drive that can simplify the circuit unit and the connection by connecting many segment electrodes in common is employed. .
[0010]
In the liquid crystal display device 1 using such multiplexing drive, the duty ratio increases and the voltage margin tends to decrease as the amount of display information increases. For this reason, there is a disadvantage that a saturation voltage sufficient to prevent the occurrence of so-called crosstalk cannot be applied.
[0011]
In order to eliminate such drawbacks, it is effective to make the threshold characteristic (rising characteristic) of the liquid crystal steep, and in recent years, the twist angle of liquid crystal molecules has been increased to 180 ° or more, Proposals have been made such that the pretilt angle, which is the angle between the liquid crystal molecules and the surfaces of the transparent substrates 3 and 4 of the liquid crystal display panel 2, is about 1 °.
[0012]
[Problems to be solved by the invention]
By the way, in the TN type liquid crystal display device 1 described above, it is general to drive with a 1/4 duty or a 1/8 duty having a higher duty ratio.
[0013]
Here, when driving with high duty, that is, when driving with 1/8 duty, for example, when driving with 1/4 duty, the viewing angle from the viewing angle side to the counter viewing angle side is larger. It becomes narrower. In particular, when the 1/4 duty and 1/8 duty liquid crystal display devices are used side by side, the narrowness of the viewing angle characteristic of 1/8 duty is promoted.
[0014]
In order to solve such a problem, for example, it is conceivable to increase the twist angle of the liquid crystal molecules. However, if the twist angle is simply increased, a reverse twist domain (hereinafter abbreviated as “domain”) is considered. ) Will occur.
[0015]
The present invention has been made in view of such a problem, and can suppress the occurrence of a domain and correct the adverse effects such as narrowing of the viewing angle characteristic caused by high duty driving, and performs driving with high duty. Even in such a case, an object is to provide a liquid crystal display device capable of performing liquid crystal display of the same quality as in the case of driving with a low duty.
[0016]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the liquid crystal display device according to claim 1 of the present invention is characterized in that the twist angle of the liquid crystal molecules is 115 ° to 125 °, and the angle formed between the liquid crystal molecules and the surface of the transparent substrate. A certain pretilt angle is 0.5 ° to 1.5 °, and a ratio d / p between the thickness d of the liquid crystal layer and the pitch p of spontaneous twist of liquid crystal molecules is 0.12 to 0.24. In addition, the product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer is set to 0.45 μm to 0.65 μm.
[0017]
By adopting such a configuration, the twist angle of the liquid crystal molecules can be set to an effective value for improving the rising characteristics while suppressing the decrease in contrast, and the value of d / p is The domain margin can be improved, and the value can be set in a range suitable for suppressing the occurrence of domains due to the large twist angle of the liquid crystal.
[0018]
The liquid crystal display device according to claim 2 is characterized in that, in claim 1, the polarizing plate is disposed so that an absorption axis thereof is deviated from 15 ° to 20 ° with respect to a major axis of liquid crystal molecules initially aligned. In the point.
[0019]
And by employ | adopting such a structure, the light leakage at the time of lighting can be prevented and a contrast can be maintained appropriately.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a liquid crystal display device according to the present invention will be described with reference to FIGS.
[0021]
Note that portions having the same or similar basic configuration as those in the related art will be described using the same reference numerals.
[0022]
The liquid crystal display device 16 in this embodiment has the liquid crystal display panel 2 between the two polarizing plates 13 and 14 as in the prior art. This liquid crystal display panel 2 has almost the same basic structure as the conventional one.
[0023]
However, in the present embodiment, the pair of alignment films 10 and 11 of the liquid crystal display panel 2 have a twist angle of 115 ° to 125 ° of the liquid crystal molecules enclosed between the alignment films 10 and 11. Has been rubbed.
[0024]
That is, as shown in FIG. 1, when the liquid crystal molecules closest to the pair of alignment films 10 and 11 facing each other are D ₁ and D ₂ , respectively, the distance between the longitudinal direction of D _{1 and} the longitudinal direction of D ₂ Is formed with an angle θ corresponding to the twist angle (115 ° to 125 °).
[0025]
In general, when the twist angle of the liquid crystal is too small, the rise characteristic of the liquid crystal is deteriorated. On the other hand, when the twist angle is too large, the background blackening degree of the display segment becomes thin and the contrast is lowered. Therefore, in the present embodiment, the twist angle of the liquid crystal molecules can be set to a value in a range suitable for improving the rising characteristics while suppressing the decrease in contrast.
[0026]
In the present embodiment, the pretilt angle of the liquid crystal is set to 0.5 ° to 1.5 °. For this reason, it is possible to reduce crosstalk and improve the appearance of the liquid crystal from an oblique direction.
[0027]
Furthermore, in this embodiment, the ratio d / p between the thickness d of the liquid crystal layer 7 and the pitch p of the spontaneous twist of the liquid crystal is 0.12 to 0.24. Therefore, since the domain margin can be improved while increasing the twist angle, it is possible to effectively prevent the occurrence of domains due to the large twist angle.
[0028]
Furthermore, in the present embodiment, the retardation Δ of the liquid crystal layer 7, that is, the product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer 7 is 0.45 μm to 0.65 μm. For this reason, the rising characteristics of the liquid crystal can be improved and the viewing angle can be widened.
[0029]
Further, the polarizing plates 13 and 14 in the present embodiment are arranged so that the absorption axis thereof is deviated by 15 ° to 20 ° with respect to the major axis of the liquid crystal molecules initially aligned.
[0030]
That is, as shown in FIG. 1, the absorption axes of the pair of polarizing plates 13 and 14 are P ₁ and P ₂ , respectively, and the liquid crystal molecules closest to the polarizing plates 13 and 14 are D ₁ and D ₂ described above. In this case, P ₁ and the longitudinal direction of D ₁ are shifted by an angle φ ₁ corresponding to 15 ° to 20 ° in the clockwise and counterclockwise directions in FIG. Similarly, the longitudinal directions of P ₂ and D ₂ are also shifted by an angle φ ₂ corresponding to 15 ° to 20 ° in the clockwise and counterclockwise directions in FIG.
[0031]
Therefore, light leakage at the time of lighting can be prevented and the contrast can be further improved.
[0032]
Next, the operation of the liquid crystal display device 16 (hereinafter referred to as “this example”) in the present embodiment is compared with the conventional liquid crystal display device 1 (hereinafter referred to as “this comparative example”), with specific numerical values. Will be described.
[0033]
【Example】
In this example, LQ-5900 manufactured by Hitachi Chemical Co., Ltd. was used as the alignment films 10 and 11, and the alignment films 10 and 11 were subjected to a predetermined rubbing process so that the twist angle of the liquid crystal molecules was 120 °. . As the liquid crystal, nematic liquid crystal having a refractive index anisotropy Δn of 0.106 and positive dielectric anisotropy was used, and the thickness d of the liquid crystal layer 7 was 5.7 μm and Δnd was 0.60 μm. Further, the pitch p of the liquid crystal was 40 μm and the pretilt angle was 1 °.
[0034]
In addition, Polaratechno polarizing plate SHC-125U was disposed outside the transparent substrates 3 and 4 so that the absorption axis was shifted by 20 ° with respect to the long axis of the liquid crystal molecules.
[0035]
The liquid crystal display panel 2 in the present embodiment is a positive type liquid crystal display panel.
[0036]
The liquid crystal display device 16 formed in this way was turned on by multiplex driving with 1/8 duty and 1/4 bias.
[0037]
The results are shown in FIG. 2 and FIG.
[0038]
FIG. 2 shows a characteristic curve of a bias voltage (horizontal axis) applied to the liquid crystal layer 7 through the transparent conductive films 8 and 9 and luminance (vertical axis) with respect to the bias voltage. In addition, the luminance in FIG. 2 means the luminance evaluated at a viewing angle position with an inclination of about 10 ° with respect to a perpendicular drawn on the liquid crystal screen.
[0039]
In FIG. 2, the curve indicated by a solid line indicates a characteristic curve when the display is turned on, and the curve indicated by a broken line indicates a characteristic curve when the display is turned off. . Further, in FIG. 2, at the position of the bias voltage where the alternate long and short dash line is drawn, the difference in luminance between on and off becomes the maximum, and the contrast takes the maximum value at this position. In general, when the liquid crystal display device 16 is driven, a bias voltage is applied aiming at a bias voltage (hereinafter referred to as an optimum voltage) that maximizes the contrast.
[0040]
Here, the degree of crosstalk depends on the difference in brightness at the optimum voltage, and the larger the difference, the smaller the crosstalk.
[0041]
FIG. 3 shows the luminance ratio (%) between the luminance of the background where liquid crystal display is not performed, such as a non-display region, and the luminance of the display region at the time of OFF in relation to the viewing angle.
[0042]
In FIG. 3, a line indicating a numerical value 100 (%) means that the luminance ratio between the background and the display area at the off time is 1: 1, and no crosstalk occurs. It also means that the crosstalk increases as the luminance ratio decreases.
[0043]
As shown in FIG. 2, when the liquid crystal display device 16 in this embodiment is used, the ON curve shows the minimum luminance value and the OFF curve shows the maximum luminance value at the optimum voltage position. It can be seen that the difference between them takes the maximum value.
[0044]
As shown in FIG. 3, when the liquid crystal display device 16 in this embodiment is used, if the viewing angle is tilted obliquely with respect to the perpendicular drawn from the front side of the page to the point P in FIG. Within the range of about 45 ° from the perpendicular, the above-described change in the luminance ratio falls within the range from 100 (%) to 80 (%).
[0045]
Therefore, as shown in FIGS. 2 and 3, when the liquid crystal display device 16 according to the present embodiment is used, it can be seen that crosstalk can be reduced to a practical level and the viewing angle characteristics can be improved.
[0046]
More specifically, even when performing multiplex driving with 1/8 duty as described above, a liquid crystal display with the same quality as when driving with 1/4 duty can be realized.
[0047]
[Comparative example]
On the other hand, in this comparative example, LQ-5900 manufactured by Hitachi Chemical Co., Ltd. is used as the alignment films 10 and 11, and the alignment films 10 and 11 are subjected to a predetermined rubbing process so that the twist angle of the liquid crystal molecules becomes 100 °. gave. Further, nematic liquid crystal having a refractive index anisotropy Δn of 0.094 and a positive dielectric anisotropy was used as the liquid crystal, and the thickness d of the liquid crystal layer 7 was 6.0 μm and Δnd was 0.56. Further, the pitch p of the liquid crystal was 79 μm and the pretilt angle was 1 °.
[0048]
In addition, Polaratechno polarizing plate SHC-125U was disposed outside the transparent substrates 3 and 4 so that the absorption axis was shifted by 10 ° with respect to the long axis of the liquid crystal molecules.
[0049]
The liquid crystal display panel 2 in this comparative example is also a positive type liquid crystal display panel 2 as in the above-described embodiment.
[0050]
The liquid crystal display device 1 in this comparative example thus formed was turned on by multiplex driving with 1/8 duty and 1/4 bias.
[0051]
The results are shown in FIG. 4 and FIG.
[0052]
FIG. 4 is a characteristic curve showing the relationship between the bias voltage applied to the liquid crystal and the luminance with respect to the bias voltage, as in FIG. In addition, FIG. 5 shows the luminance ratio (%) between the background and the display area at the time of off in relation to the viewing angle, as in FIG. 3 described above.
[0053]
As shown in FIG. 4, when the liquid crystal display device 1 in this comparative example is used, the off curve shows a value smaller than the maximum luminance at the position of the optimum voltage, and the luminance of the on and off luminances. The difference is smaller than in the case of FIG.
[0054]
Further, as shown in FIG. 5, when the liquid crystal display device 1 in this comparative example is used, the luminance ratio changes significantly from 100 (%) to 30 (%) in the same viewing angle range as in FIG. Show.
[0055]
Therefore, as shown in FIGS. 4 and 5, it can be seen that the conventional liquid crystal display device 1 cannot prevent crosstalk and cannot obtain good viewing angle characteristics.
[0056]
As described above, according to the present embodiment, the twist angle of the liquid crystal molecules can be set to a value suitable for improving the rising characteristics to such an extent that the contrast does not decrease, and d / p Can be set to a value in a range suitable for improving the domain margin, so that the viewing angle characteristics can be improved even when driving with high duty, and the occurrence of domains can be suppressed. Become.
[0057]
In addition, this invention is not limited to embodiment mentioned above, A various change is possible as needed.
[0058]
【The invention's effect】
As described above, according to the liquid crystal display device of the first aspect of the present invention, it is possible to improve viewing angle characteristics while appropriately preventing the occurrence of domains, and to realize a high-quality liquid crystal display. .
[0059]
According to the liquid crystal display device according to the second aspect, in addition to the effect of the liquid crystal display device according to the first aspect, it is possible to appropriately maintain the contrast and perform higher-quality liquid crystal display.
[Brief description of the drawings]
FIG. 1 is a plan view showing a twist angle of a liquid crystal molecule and an angle relationship between the liquid crystal molecule and an absorption axis of a polarizing plate in an embodiment of a liquid crystal display device according to the invention. FIG. 2 is a liquid crystal display according to the invention. FIG. 3 is a graph showing characteristics of liquid crystal driving voltage and luminance in the embodiment of the device. FIG. 3 is a graph showing the relationship between the luminance ratio between the background and the display area when the liquid crystal display device is turned off, and the viewing angle. FIG. 4 is a diagram showing characteristics of liquid crystal driving voltage and luminance in a conventional liquid crystal display device. FIG. 5 is a view showing a luminance ratio between a background and a display area in an off state in a conventional liquid crystal display device. FIG. 6 is a cross-sectional view showing a configuration of a liquid crystal display device used conventionally [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,16 Liquid crystal display device 2 Liquid crystal display panel 3, 4 Transparent substrate 7 Liquid crystal layer 13, 14 Polarizing plate

Claims (2)

A liquid crystal display panel in which a liquid crystal layer composed of liquid crystal molecules having a predetermined twist angle is formed between two transparent substrates parallel to each other, and a polarizing plate having a predetermined absorption axis is provided outside the liquid crystal display panel. In the provided liquid crystal display device,
The twist angle of the liquid crystal molecules is 115 ° to 125 °, the pretilt angle that is an angle between the liquid crystal molecules and the surface of the transparent substrate is 0.5 ° to 1.5 °, and the thickness of the liquid crystal layer is The ratio d / p between the thickness d and the spontaneous twist pitch p of the liquid crystal molecules is 0.12 to 0.24, and the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer are A liquid crystal display device having a product Δnd of 0.45 μm to 0.65 μm. 2. The liquid crystal display device according to claim 1, wherein the polarizing plate is disposed so that an absorption axis thereof is deviated by 15 ° to 20 ° with respect to a major axis of the liquid crystal molecules initially aligned.

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