JP2579636Y2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention provides a liquid crystal display element for driving a low voltage using a TN (Swissed Nematic) liquid crystal. ° ~ 130
°, the gap length is as small as 5 to 8 μm, the value of the retardation Δn × d (μm) of the liquid crystal layer is 1.0 to 1.5 (μm), and the value of the dielectric anisotropy Δε is 15 or more. The polarizing plate has an included angle of 70 ° to 110 °.

[Industrial applications]

The present invention relates to a liquid crystal display element for displaying various information incorporated in an electronic device such as a clock or a television, for example.
In particular, the present invention relates to a low-voltage driving liquid crystal display device using a TN liquid crystal.

[Conventional technology]

As a conventional liquid crystal display device, generally, a liquid crystal is sealed between a pair of transparent substrates disposed to face each other with a sealing member interposed therebetween.
There is known a structure in which transparent electrodes are provided on the inner surfaces of the respective transparent substrates in directions intersecting each other. When the TN liquid crystal is used as the liquid crystal, the twist angle θ of the liquid crystal molecules between the transparent substrates is set to about 90 °, and the gap length d between the transparent substrates corresponding to the thickness of the liquid crystal is 9 to 9.
It is set to 10 μm.

[Problems to be solved by the invention]

In order to enable low-voltage driving in a liquid crystal display device using a TN liquid crystal, a liquid crystal having a large dielectric anisotropy Δε is generally used. However, in the above-mentioned conventional liquid crystal display element, even if a liquid crystal having the largest Δε (= 25) is used, the threshold voltage V _th for obtaining a transmittance of 50% by static driving is only at least about 1.15 V. can not be realized, thus operating voltage V _op is the lower limit is 3V 1 / 3bias 1 / 8duty, further low-voltage driving is difficult.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a liquid crystal display device capable of driving at a lower voltage.

[Means for solving the problem]

According to the present invention, at least a liquid crystal display element having a structure in which a TN liquid crystal is sealed between a pair of transparent substrates opposed to each other and a polarizing plate is arranged outside the pair of transparent substrates, has a transmittance of 50%. At least the following conditions (i) to (iv) are satisfied so that the threshold voltage to be obtained is smaller than 1 / 15V.

i) The twist angle θ of the liquid crystal molecules between the pair of transparent substrates is greater than 90 ° and 130 ° or less.

ii) The gap length d of the liquid crystal layer between the pair of transparent substrates is 5
μm or more and 8 μm or less, and the value of retardation Δn × d (μm) in the liquid crystal layer between the pair of transparent substrates is 1.0
Iii) The dielectric anisotropy Δε of the liquid crystal is 15 or more, and iv) The included angle φ of the polarizing plate is 70 ° or more and 110 ° or less.

[Action]

In the present invention, the twist angle θ of the liquid crystal is set to 90 ° <θ ≦ 130.
By making it larger than the conventional TN liquid crystal display element within the range of °, the change in the alignment state of the liquid crystal molecules when an electric field is applied becomes large, so that the threshold voltage _Vth decreases. Further, the gap d is set in the range of 5 μm ≦ d ≦ 8 μm, and
By making the size smaller than that of the TN liquid crystal display element and setting the value of Δε to 15 or more, the electric field strength becomes stronger and the interaction between the electric field and the liquid crystal molecules becomes stronger, so that further lower voltage driving becomes possible. . Further, the value of Δn × d is set to 1.0 ≦ Δn
× d ≦ 1.5, and the included angle of the pair of polarizing plates is 70 ° ≦ φ ≦ 1
By setting the angle to 10 °, coloring due to optical rotation dispersion is prevented.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a plan view showing an arrangement relationship between upper and lower polarizing plates in the embodiment.

As shown in FIG. 1, a pair of transparent substrates 1 and 2 made of glass or the like are opposed to each other at a predetermined interval with a sealing member 3 interposed therebetween. The TN liquid crystal 4 is sealed in the enclosed space surrounded by.

The inner surface of one of the transparent substrates 1 is provided in one direction (first direction).
In the figure, a plurality of transparent electrodes 5 made of an ITO film or the like extending in a direction perpendicular to the paper surface) are arranged at regular intervals. The entire surface of the transparent electrode 5 is covered with an alignment film 6, and the alignment film 6 is in direct contact with the liquid crystal 4. Also,
On the inner surface of the other transparent electrode 2, a plurality of transparent electrodes 7 made of an ITO film or the like extending in a direction perpendicular to the transparent electrode 5 are arranged at regular intervals. The entire surface of the transparent electrode 7 is covered with an alignment film 8, and the alignment film 8 is in direct contact with the liquid crystal 4. Also, on the outer surfaces of the transparent electrodes 1 and 2,
Polarizing plates 9 and 10 are provided, respectively.

Further, in the above configuration, the twist angle θ of the liquid crystal 4, the gap length d corresponding to the layer thickness of the liquid crystal 4, the product of the refractive index anisotropy Δn of the liquid crystal 4 and the gap length d, and the retardation Δn
× d, the dielectric anisotropy Δε of the liquid crystal 4 is 5 μm ≦
d ≦ 8 μm, 1.0 ≦ Δn × d ≦ 1.5, Δε ≧ 15, and the twist angle θ of the liquid crystal and the included angle φ between the upper and lower polarizers 9 and 10 are shown in FIG. like
90 ° <θ ≦ 130 ° and 70 ° ≦ φ ≦ 110 °.

Table 1 shows specific examples of the liquid crystal display device according to the present invention having various twist angles θ together with the electro-optical characteristics.
Shown in In this example, the dielectric anisotropy Δε = 25
And a liquid crystal having a refractive index anisotropy Δn = 0.150 was used.

As is clear from Table 1, the twist angle θ is changed from 90 ° to 140 °.
°, the threshold voltage V _th becomes θ = 9
At 0 °, the highest value was 1.15V, and when θ> 90 °, a lower value was obtained. In particular, twist angle θ = 110 °
At this time, the threshold voltage V _{th was} 1.09 °, and the lowest threshold voltage was obtained. Therefore, the conventional twist angle θ (θ ≒ 90 °)
By setting the angle to be larger than 90 ° <θ ≦ 130 °, the threshold voltage V _th can be made lower than the conventional one (V _th ≒ 1.15V), and it is particularly desirable that the twist angle θ is 110 °.

In Table 1, V (20%) / V (80%) indicates the ratio of the voltage required to make the light transmittance 20% or 80%. The smaller this value is, the more the on / off reaction is. It indicates that it is steep.

Table 2 shows the change of the threshold voltage _Vth for different gap lengths d. The condition in this case is that the twist angle θ is
This is the same as in Table 1 except that it was 110 °.

As is apparent from Table 2, the gap length d was set to 8 μm to 7 μm.
μm and 6μm, the threshold voltage
V _th also gradually decreases. Therefore, the threshold voltage _Vth can be further reduced by setting the gap length d to a range of 5 μm ≦ d ≦ 8 μm smaller than the conventional case (d = 9 to 10 μm).

According to Table 2, the gap length d is 6 μm, which is the shortest.
In this case, the threshold voltage V _th becomes the lowest, but on the other hand, the retardation Δn × d also becomes as small as 0.9. Becomes Therefore, the value of the retardation Δn × d (μm) is desirably 1.0 μm or more, and if Δn × d is increased to a level exceeding 1.5 (μm), the viewing angle becomes narrow and the screen becomes difficult to see. , The value of retardation Δn × d is 1.5 μm
It is desirable that: That is, the retardation Δ
By setting the value of n × d in the range of 1.0 ≦ Δn × d ≦ 1.5 (μm), the above-described coloring problem can be solved while the threshold voltage _Vth is kept low.

Further, by setting the dielectric anisotropy Δ 液晶 of the liquid crystal to a large range of Δε ≧ 15, it becomes possible to apply a large electric field to the liquid crystal layer with a small voltage, thereby further lowering the threshold voltage V _th. It becomes possible.

In addition, as shown in Table 1 above, as the twist angle θ is set to be large, the included angle (angle formed by the transmission axis) φ between the upper and lower polarizers is set to 90 °, 100 °, or its periphery. This is desirable in terms of display quality. Therefore, by setting the included angle φ of the polarizing plate in the range of 70 ° ≦ φ ≦ 110 °, the threshold voltage _Vth can be reduced while maintaining high display quality.

As described above, according to the present embodiment, in particular, the twist angle θ is set to be larger than the conventional angle (θ ≒ 90 °) in the range of 90 ° <θ ≦ 130 °, and the gap length d is set to the conventional value (d = 9 to 10 μm). ) Is set in the range of 5 μm ≦ d ≦ 8 μm and a liquid crystal having a large dielectric anisotropy Δε (Δε ≧ 15) is used, so that the threshold voltage V _th is reduced from the conventional value (V _th ≒ 1.15 V). And further lower voltage driving can be realized. Further, by setting the retardation in the range of 1.0 ≦ Δn × d ≦ 1.5 and the included angle φ of the polarization axis of the polarizing plate in the range of 70 ° ≦ φ ≦ 110 °, the problem of coloring by elliptically polarized light is solved. As a result, it is possible to further reduce the voltage while maintaining the display quality at a high level. For example, when the twist angle θ is 110 ° and the gap length d is
Is 7 μm, the retardation Δn × d is 1.05, the dielectric anisotropy Δε is 25, and the included angle φ of the polarizing plate is 100 °.
The threshold voltage V _th can be reduced from conventional 1.15V to 1.03V, thus the operating voltage V _op conventional 3V 1 / 3bias 1 / 8d
Even if the uty was lowered to 2.85V 1 / 4bias 1 / 9duty, sufficient contrast could be obtained.

The type of the liquid crystal display device to which the present invention can be applied is as follows.
It is not limited to the one shown in FIG. 1, and at least has a structure in which a TN liquid crystal is sealed between a pair of transparent substrates opposed to each other, and a polarizing plate is arranged outside the transparent substrate. The present invention can be applied to various types of liquid crystal display devices. Needless to say, the present invention can be applied to a color liquid crystal display device having a built-in color filter.

[Effect of the invention]

According to the present invention, the threshold voltage _Vth can be reduced by setting the twist angle θ, the gap length d, and the like in predetermined ranges different from those in the related art, and the voltage can be further reduced as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a plan view showing an arrangement relationship between upper and lower polarizing plates in the embodiment. 1, 2, transparent substrate 3, sealing member 4, liquid crystal,
5, 7 ... transparent electrode, 6, 8 ... alignment film, 9, 10 ... polarizing plate, θ ... twist angle, d ... gap length, Δnxd
…… Retardation, Δε …… Dielectric anisotropy, φ ...

Claims (1)

(57) [Scope of request for utility model registration] 1. A twisted nematic liquid crystal is encapsulated in at least a pair of transparent substrates arranged to face each other,
In a liquid crystal display device having a structure in which a polarizing plate is arranged outside each of the pair of transparent substrates, a liquid crystal between the pair of transparent substrates is arranged such that a threshold voltage Vth for obtaining a transmittance of 50% is smaller than 1.15 V. Twist angle θ of molecule
Is greater than 90 ° and 130 ° or less, and the gap length d of the liquid crystal layer between the pair of transparent substrates is 5 μm.
Not less than 8 μm, the value of retardation Δn × d (μm) in the liquid crystal layer between the pair of transparent substrates is not less than 1.0 and not more than 1.5 (μm), and the value of dielectric anisotropy Δε of the liquid crystal is not less than 15 A liquid crystal display device, wherein the included angle φ of the polarizing plate is 70 ° or more and 110 ° or less.