JPH01216318A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To execute a display having a high contrast, a wide visual angle, and also a more achromatic color by setting a retardation and a twist angle to a specific range. CONSTITUTION:A retardation is set to a range of >=1.4 and <=2.2. In this regard, the retardation is a value which has multiplied a refractive index anisotropy DELTAn at a room temperature of a liquid crystal and the maximum distance (cell gap) (d) between transparent electrode substrates, and when this retardation becomes under 1.4, the contrast and the visual angle dependency are not improved enough, and coloring of the display is not improved enough either. On the other hand, when the retardation exceeds 2.2, even if the liquid crystal of DELTAn=0.22 whose refractive index anisotropy is the largest among the liquid crystals which have been put to practical use is used, it is necessary to set the cell gap (d) to >=10mum, and such inconveniences as a temperature dependency of the liquid crystal element and a threshold voltage become high and the responsiveness is deteriorated are generated. Therefore, a twist angle of the liquid crystal can be set within a range of 60-150 deg. or so. In such a way, a high contrast is obtained, the visual angle dependency is improved, and an achromatic color is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a liquid crystal element in which fine irregularities are formed on the inner surface of at least one transparent electrode substrate.

``Prior art'' TN liquid crystal devices that are widely used today have problems such as coloring in the display and narrow viewing angle, so a large number of fine irregularities are formed on the inner surface of at least one of the transparent electrode substrates. Attempts have been made to address these problems by (applying matte finishing).

FIG. 1 shows a liquid crystal cell portion of an example of a liquid crystal element that has been subjected to matte processing, and reference numeral 1.1 in the figure indicates a transparent electrode substrate. Transparent electrode substrate! is a transparent electrode on the glass plate la! b and orientation @l c are formed, and fine irregularities 2 are formed on the inner surface of one transparent electrode substrate l. A liquid crystal 3 is housed between these transparent electrode substrates 1.1 so that the long axes of the molecules are continuously twisted.

By the way, the retardation (Δn−d; Δ
(n represents the refractive index anisotropy of the liquid crystal at room temperature, and d represents the cell gap) has conventionally been determined using the same procedure as for a normal TN liquid crystal element using a smooth substrate. That is, the formula of G ooch -T arry (formula (1) below)
The amount of transmitted light T when no voltage is applied is determined to be the minimum, and the retardation is less than 164, especially from 1.0 to
It was set within the range of 1.4.

T: amount of transmitted light u when no electric field is applied; 2d・Δn/λ (λ: previous wavelength) "Problem to be solved by the invention" This liquid crystal element has low contrast and improved viewing angle dependence. There was also some dissatisfaction with not being able to sufficiently achieve achromatic coloring.

"Means for Solving the Problems" In the liquid crystal element of the present invention, retardacylon is 1.4 or more,
The above problem was solved by setting the range to 2.2 or less.

Here, the retardation is a value obtained by multiplying the refractive index anisotropy of the liquid crystal at room temperature by the maximum distance (cell gap) d between the transparent FFI electrode substrates.

When the retardation is less than 1.4, the contrast,
Viewing angle dependence cannot be sufficiently improved, and display coloration cannot be sufficiently improved. When the retardation ratio exceeds 2.2, Δn= has the largest refractive index anisotropy among liquid crystals in practical use.
Even if a cell gap of 0.22 is used, the cell gap d is 10 μm.
This results in disadvantages such as increased temperature dependence and threshold voltage of the liquid crystal element, and decreased responsiveness.

In the liquid crystal element of the present invention, the twist angle of the liquid crystal is not limited to 90 degrees, but can be appropriately set in the range of about 60 to 150 degrees.

Further, in the liquid crystal element of the present invention, fine irregularities may be formed not only on one side of the transparent electrode substrate but also on both inner surfaces. The unevenness on the inner surface of the transparent electrode substrate can be formed by matting the inner surface of the glass plate, but it can also be formed by means such as forming unevenness on the alignment film portion.

Furthermore, the fine irregularities formed on the transparent electrode substrate are formed as appropriate depending on the use and specifications of the liquid crystal element, but usually the average height difference between the concave and convex parts is 1 to 5 μI, and the difference between adjacent convex parts is They are formed so that the average distance is 200 μm or less.

"Effect J" The present inventors set the retardation of a matte-finished liquid crystal element larger than that of a liquid crystal element made of a smooth substrate, thereby improving contrast and viewing angle dependence and further making the color achromatic. The reason why this is possible is considered as follows.

In a liquid crystal device in which unevenness is formed on the inner surface of a transparent electrode substrate, the cell gap d changes, so the d/p value (p
By increasing the value of the retardation (Δn-d), that is, by increasing the value of the retardation (Δn-d), the pitch of the twist of the liquid crystal) becomes partially different.

This effect can be alleviated by increasing the optical rotation of the liquid crystal molecules or by increasing the cell gap.

"Example" (Example) A liquid crystal element of the present invention was created and its contrast, black and white display quality, and viewing angle were examined.The structure of the created liquid crystal element was similar to that of the liquid crystal element shown in FIG. Since they are similar, the following description will be made with reference to FIG.

First, a method for manufacturing this liquid crystal element will be explained.

A glass plate for a substrate (a commercially available TN substrate) was prepared, and one inner surface of the glass plate was subjected to matte processing. Next, transparent electrodes 1b, 1b (made of indium tin oxide) were formed on these glass plates 1a, 1a, and then polyimide resin (5R-4110, manufactured by Osan Kagaku Co., Ltd.) was printed. Heat treated at 300°C for 30 minutes to form alignment films 1c, lc
was formed. Next, the twist angle of the liquid crystal molecules is left-handed 90
Each of the alignment films 1c and lc was subjected to rubbing treatment in the direction shown in FIG. After scattering silica-based spherical spacers 5 on one of the two transparent electrode substrates 1.1 formed in this way and printing bone cement that will become the seal 6 in a predetermined pattern, the two substrates are 1. ! were pasted together to create a liquid crystal cell with a maximum cell gap (d) of 10 μm. In addition, one transparent electrode substrate! The unevenness formed on the inner surface of the substrate had an average height difference of 5 μm, and an average distance between adjacent convex portions of 100 μm.

Next, a liquid crystal composition was injected into this liquid crystal cell, and an epoxy adhesive (manufactured by Cemedine, Cemedine Sono 1 Super 30) was applied.
) was sealed. The liquid crystal composition has a refractive index anisotropy of Δn=
Chiral agent (cholesteryl nonanoate) was added to 0.215mm liquid crystal AP-9512XX (manufactured by Chisso Corporation).
．． The one containing 2% was used. The retardation of this liquid crystal cell is Δnd=2.15.

Next, a polarizing plate was attached to the liquid crystal cell into which the liquid crystal composition was injected so that the polarization axes were parallel to each other, thereby completing a liquid crystal element.

For comparison, the refractive index anisotropy is Δn=0.128
LCD AP-9171-3XX (4'/manufactured by Co., Ltd.)
Using A, a liquid crystal element was created with the only difference being that the retardation was Δn-d=1.28.

These liquid crystal elements were tested for the following items.

■ Contrast The ratio of the brightness L1 measured from the normal direction when a voltage of 8V is applied to the brightness L1 when no voltage is applied is calculated as the contrast C (
=Ll/Ll).

As a result, C=21.0 in the comparative example, whereas C=35.4 in Example 1, confirming that the liquid crystal element of the present invention has a high contrast.

(2) Hue when no voltage is applied The color of the liquid crystal element was measured at the same position for a total of 360 degrees, in 10 steps of 36 degrees while maintaining a viewing angle of 20 degrees from the normal. The results are shown in Figure 3.

From the results shown in FIG. 3, it was confirmed that the hue of the liquid crystal element of Example 1 in the bright state is close to the light source and its change is small, and that according to the present invention, the display of the liquid crystal element can be made more achromatic.

■ When we measured the angle at which viewing angle contrast could be kept at C≧5, the liquid crystal element of the comparative example had an angle of 20 degrees, but in the example! In the case of the liquid crystal element shown in FIG.

(Examples 2 to 4) Liquid crystal elements were created that differed from Example 1 only in that the cell gap d1 and the refractive index anisotropy Δn were changed, and their contrasts and viewing angles were examined as examples! I investigated the same.

The cell gap, refractive index anisotropy, and test results are summarized in Table 1.

The same effects as in Example 1 were obtained with the liquid crystal elements of these Examples.

(Examples 5 to 7) As shown in FIGS. 4 and 5, a liquid crystal element was prepared that differed from Example 1 only in that the rubbing directions of the upper and lower substrates 1.1 were 150 degrees, 120 degrees, and 60 degrees. When it was prepared and subjected to the same test as in Example 1, the same effects as in Example 1 were obtained.

"Effects of the Invention" As explained above, the liquid crystal element of the present invention has excellent retardation! , 4 to 2°2, and the twist angle is set in the range of 60 to 150 degrees, so it is possible to achieve high contrast, wide viewing angle, and more achromatic display.

[Brief explanation of the drawing]

No.! The figure is a cross-sectional view showing the structure of a liquid crystal element, and FIG. 2 is a plan view showing the direction of the rubbing process performed in Example I.
Figure 3 is an X-Y chromaticity diagram of the hue in the bright state of the liquid crystal elements of Example 1 and Comparative Example investigated in the implementation f1JJ, Figures 4 and 5.
Each figure is a plan view showing the rubbing direction of the liquid crystal element of Example 5.6. 1...Transparent electrode substrate, 2...Minute unevenness.

Claims (1)

[Claims] A liquid crystal in which a liquid crystal is housed between two transparent electrode substrates such that the long axis of the molecules is continuously twisted, and a large number of fine irregularities are formed on the inner surface of at least one of the transparent electrode substrates. In the element, retardation (Δn・
d) is set in the range of 1.4 or more and 2.2 or less, and the twist angle is set in the range of 60 degrees or more and 150 degrees or less.