JPH01246522A - Electrooptic element - Google Patents

Abstract

PURPOSE:To enhance display contrast by making the retardation DELTAnN.dN of an optical isomer smaller than the retardation of a liquid crystal element. CONSTITUTION:The retardation DELTAnN.dN defined by the product of the double refractive index DELTAnN and layer thickness dN of the optical isomer is smaller than the retardation DELTAnS.dS of the liquid crystal element. The removal of the light from between picture elements arises and the display contrast is not obtainable if the difference DELTAnS.dS-DELTAnN.dN of the retardations of the optical isomer is larger than 0.03mum. In addition, the visual angle characteristic is extremely narrowed and, therefore, the difference of the retardations is preferably <=0.03mum. The removal in the non-voltage impressed state increases gradually and, therefore, the difference of the retardations is preferably >=0mum. The liquid crystal display element having the high contrast is thereby inexpensively obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electro-optical element.

[Conventional technology]

Traditional neutralized dry nematic mode (
The NTN mode (hereinafter referred to as NTN mode) eliminates the discoloration of the external appearance of the device, which is characteristic of the conventional supertwist nematic mode. By having one layer of optically anisotropic material, it is possible to display white on a black background or black on a white background. The NTN mode is superior to the conventional twisted nematic mode in that the electro-optic characteristic has a steep threshold, so it is possible to increase the display capacity by time-division driving.

A cross-sectional view of a conventional electro-optical element using the NTN mode and a relationship diagram of each axis are shown in FIG. 5 and FIG. 2, respectively. In FIG. 5, 1 is an upper polarizing plate, 2 is a liquid crystal cell for displaying (hereinafter referred to as a display cell), 3 is an optically anisotropic body, and 4 is a lower polarizing plate. Although a liquid crystal cell (hereinafter referred to as a compensation cell) was used as the optically anisotropic material in Example 3, it is also possible to use a polymer film or the like. The same liquid crystal 5S-4008 (manufactured by Chisso Corporation - wavelength 590 nm) is used for the display cell and the compensation cell.
By using Δn=0.15) for the light of , the twist angle of the liquid crystal of the compensation cell 2
2 was adjusted to the right 210 degrees. Angle 19 and angle 23 in FIG. 2 were both 45 degrees, and angle 21 was 009 degrees.

The liquid crystal layer thickness d was set to 6.0 μm, and the retardation Δn·d was set to 0.90 μm in both the display cell and the compensation cell.

FIG. 6 shows the results of measuring the electro-optic characteristics of a conventional electro-optical element using the NTN mode under the above conditions. However, the transmittance is as follows:
The amount of light transmitted through one polarizing plate was set as 100%.

[Problem to be solved by the invention]

However, with the electro-optical element using the NTN mode described above, when time-division driving is performed with 200 divisions and the transmittance when on is 50%, a display load ratio of 1:14 can be obtained, but this is also not suitable for TV image display. It is insufficient. TV
In order to display the image clearly enough, at least 1:30
A display of trust is required.

Furthermore, electro-optical elements using conventional NTN mode are
Because it is necessary to accurately match the display cell and compensation cell thickness g7Δnod, there are strict requirements for cell thickness.
This was a manufacturing problem.

The present invention is intended to solve these problems, and its purpose is to provide a high-contrast liquid crystal display element at low cost.

(Means for solving , Kl!) The electro-optical element of the present invention includes a liquid crystal element formed by holding twisted oriented nematic liquid crystal between two opposing electrode substrates, and at least one layer of optical anisotropy. In a liquid crystal display element comprising a body and a pair of polarizing plates disposed on both sides sandwiching them, the birefringence ΔnN and layer thickness d of the optically anisotropic body are
The liquid crystal display device is characterized in that a retardation value /ΔnN·dN defined as the product of N is smaller than the liquid crystal element retardage value 1Δns”dS.

Note that the difference in retardation between the liquid crystal cell and the optically anisotropic body with respect to light with a wavelength of 590 nm Δns"dS-
When ΔnN, IId, is larger than 0.03 μm,
The difference in retardation is preferably 0.03 μm or less because light leakage occurs between pixels, making it impossible to obtain display contrast and making the viewing angle characteristics very narrow.

Further, when the difference between Δng·dS−Δnv·dN becomes smaller than 0 μm, the gap becomes gradually thicker when no voltage is applied, so it is desirable that the difference in retardation is 0 μm or more.

EXAMPLES The present invention will be described in detail below with reference to Examples.

[Example 1] FIGS. 1 and 2 are a cross-sectional view of an electro-optical element according to Example 1 of the present invention and a relationship diagram of each axis, respectively. composition,
The axial relationship is the same as that of the conventional electro-optical element using the NTN mode described above, and the only difference is the tardage tangent Δn@d of the liquid crystal layer.

Since the same liquid crystal 5S-4008 was used for the display cell and the compensation cell with a chiral dopant added, the values of their birefringence Δns+ΔnN were almost the same, and the wavelength was 590n.
It is approximately 0.15 for light of m.

In this example, the thickness of the liquid crystal layer of the display cell is set to 6.0 μm as in the conventional technology described above, and the retardation Δns @
It was set to dS = 0.900 μm.

On the other hand, the liquid crystal layer thickness of the compensation cell is made as thin as 5.9 μm, and the retardation ΔnN adN=Q.

It was set to 885 μm. Difference in retardation between the two Δn5
"dS-80N @dN is 0.015 μm.

FIG. 3 shows the results of measuring the electro-optic characteristics of the electro-optic element in Example 1 of the present invention. Comparing this voltage transmittance curve with the voltage transmittance curve of the conventional technology shown in Figure 6, it is found that although the conventional technology has less light leakage when no voltage is applied, it is close to the threshold voltage for actual driving. In this case, the present invention has less light leakage and superior steepness. Therefore, the number of divisions is 20, assuming that the transmittance when on is 50%.
The display contrast when performing time division driving at 0 is also 1:
30, which is an improvement compared to the conventional ratio of 1:14.

[Example 2] The structure, liquid crystal, and axis relationship of the electro-optical element in Example 2 of the present invention are the same as those of the electro-optical element in Example 1 described above.

In this example, the thickness of the liquid crystal layer of the display cell was set to 6.0 am, as in the conventional technology, and Δns+a65 =0.90 μm. On the other hand, the liquid crystal layer thickness of the compensation cell is made even thinner to 5.8 μm, and the retardation ΔnN 'dw = 0
．． It was set at 870. Difference between both Noritarpsion Δns*
dS-ΔnN IIdN is 0.030 μm.

FIG. 4 shows the results of measuring the electro-optic characteristics of the electro-optic element in Example 2 of the present invention. Although the leakage light in the state where no voltage is applied is larger than that in Example 1, it is sufficiently dark near the threshold voltage and has good steepness. The display contrast when time-division driving was performed with 200 divisions at an on-time transmittance of 50% was 1:47, which is further improved than in Example 1.

〔Effect of the invention〕

As described above, the present invention improves display contrast by making the retardation 802·d9 of an optically anisotropic body smaller than the retardation 3 of the liquid crystal element in a liquid crystal display element using the NTN mode. It has the effect of increasing the

Furthermore, in the present invention, it is no longer necessary to match the retardations of the display cell and the compensation cell as in the prior art, so that the manufacturing difficulty of accurately controlling the cell thickness can be largely eliminated.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electro-optical element in an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between each axis of the electro-optical element in the embodiment of the present invention and in the prior art. FIG. 3 is a diagram showing the electro-optic characteristics of the electro-optic element in Example 1 of the present invention. FIG. 4 is a diagram showing the electro-optical characteristics of the electro-optical element in Example 2 of the present invention. FIG. 5 is a sectional view of an electro-optical element in the prior art. FIG. 6 is a diagram showing electro-optical characteristics of an electro-optical element in the prior art. 1... Upper polarizing plate 2... Liquid crystal cell for display (display cell) 3... Liquid crystal cell as an optically anisotropic body (compensation cell) 4... Lower polarizing plate 5... Display Upper substrate 6 of the cell...Transparent electrode 7...Alignment layer 8...Liquid crystal 9 of the display cell...Lower substrate 10 of the display cell...Upper substrate 11 of the compensation cell... Liquid crystal 12...lower substrate 13 of compensation cell...polarization axis (absorption axis) of upper polarizing plate 1 14...
--Rubbing direction 15 of the upper substrate 5 of the display cell --Rubbing direction 16 of the lower substrate 9 of the display cell --Rubbing direction 17 of the upper substrate 10 of the compensation cell --Rubbing direction 17 of the upper substrate 10 of the compensation cell Rubbing direction 18...Direction 19 of the polarization axis (absorption axis) of the lower polarizing plate 4...Angle of 20° between the rubbing direction 14 of the upper substrate of the display cell and the direction 13 of the polarization axis of the upper polarizing plate. ...Twist angle 21 of the liquid crystal 8 of the display cell...
Angle 22 between the rubbing direction 15 of the lower substrate of the display cell and the rubbing direction 16 of the upper substrate of the compensation cell...Twist angle 23 of the liquid crystal 11 of the compensation cell...
Angle 7ij1 between the rubbing direction 17 of the lower substrate of the compensation cell and the direction 18 of the polarization axis of the lower polarizing plate
5 tsubo force g voltage (V)

Claims (4)

[Claims] (1) A liquid crystal element formed by sandwiching twisted oriented nematic liquid crystal between two opposing electrode substrates, at least one layer of optically anisotropic material, and a pair of polarizing plates disposed on both sides with them in between. In the liquid crystal display element, a retardation Δn_N・d_N defined as the product of the birefringence Δn_N of the optically anisotropic body and the layer thickness d_N is smaller than the retardation Δn_S, d_S of the liquid crystal element. Electro-optical element. (2) Difference in retardation Δn_S・d_ between the liquid crystal element and the optically anisotropic body for light with a wavelength of 590 nm
The electro-optical element according to claim 1, wherein S-Δn_N·d_N is in a range of 0 μm or more and 0.03 μm or less. (3) The electro-optical element according to claim 1, wherein the optically anisotropic body is a twisted oriented nematic liquid crystal sandwiched between two opposing substrates. (4) The twist angle 22 of the liquid crystal of the optically anisotropic body has the same absolute value and the opposite direction as the twist angle 20 of the liquid crystal of the liquid crystal element, and Rubbing direction 16 and rubbing direction 1 of lower substrate 9 of liquid crystal element
4. The electro-optical element according to claim 3, wherein the angle 21 with respect to the second electrode 5 is about 90 degrees.