JPH0756177A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent light drop-out by spacers. CONSTITUTION:This liquid crystal display element 1 is constituted by disposing glass substrates 2, 3 formed with transparent electrodes on their inside surfaces to face each other and sticking these substrates to each other by dispersing fine spacers 4 between them, then sealing a liquid crystal 5 between the substrates. More particularly the refractive indices of the liquid crystals 5 an the spacers 4 are nearly equally selected. The refractive index (n) of the spacers is preferably selected to a refractive index nD of the liquid crystal to ordinary light in the case of the element of a TN type normally white mode, to a refractive index ne to extraordinary light in the case of the element of a TN type normally black mode and to the value between n0 and ne (most preferably the mean value thereof) in the case of the element of an STN type normally black mode, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to selection of refractive indexes of liquid crystal and spacers in a liquid crystal display device.

[0002]

2. Description of the Related Art In a liquid crystal display device 1, as shown in FIG. 1, glass substrates 2 and 3 having transparent electrodes formed on their inner surfaces are opposed to each other, and minute spacers 4 are dispersed between them and bonded together. The liquid crystal 5 is enclosed between the substrates. by the way,
The response speed, contrast, visual characteristics, etc. of the liquid crystal display element 1 change depending on the thickness of the liquid crystal layer 5. Therefore, it is generally necessary to strictly set the thickness of the liquid crystal layer 5 in accordance with the optical characteristics of the liquid crystal material. Further, if the liquid crystal layer 5 has unevenness in thickness, unevenness in display occurs, and the visibility is significantly reduced.
Therefore, in the liquid crystal display element 1, the size of the spacer 4 is appropriately selected and the thickness of the liquid crystal layer 5 is set to a desired value. Reference numerals 6 and 7 denote polarizing plates attached to the outer surfaces of the glass substrates 2 and 3.

[0003]

In the conventional liquid crystal display element, in the case of black display, since light passes through the spacer, there is a problem that the spacer looks like a white spot and deteriorates the display quality. To solve this problem, However, measures such as using black spacers have been taken. However, even if a black spacer is used, it is not a perfect countermeasure against light loss, and there is a problem that light loss occurs in the spacer and the contrast and display quality are degraded. An object of the present invention is to prevent light loss due to spacers.

[0004]

[Means for Solving the Problems]

(1) According to the invention of claim 1, two glass substrates having transparent electrodes formed on the inner surfaces thereof are opposed to each other, and fine spacers are dispersed between them to bond them together, and then a liquid crystal is interposed between the substrates. In the liquid crystal display element formed by encapsulation, the refractive indexes of the liquid crystal and the spacer are selected to be substantially equal.

(2) According to the invention of claim 2, in the liquid crystal display element according to item (1), the refractive index of the spacer is set to the ordinary light of the liquid crystal.
This is the case when the refractive index is approximately equal to t _o for t). (3) The invention of claim 3 is the liquid crystal display element according to claim 1, wherein the refractive index of the spacer is substantially equal to the refractive index n _e of the liquid crystal with respect to extraordinary light. is there.

(4) According to the invention of claim 4, in the liquid crystal display element according to item (1), the spacer has a refractive index n _o for the ordinary light and a refractive index n for the extraordinary light of the liquid crystal. _This is the case when the value is an intermediate value with _e .

[0007]

[Embodiment] As a result of studying the cause of occurrence of light missing in the spacer even if the black spacer is used, it is found that there is a considerable difference between the refractive index of the liquid crystal and the refractive index of the spacer. It was That is, since the refractive indexes of the two are different, the light incident on the liquid crystal layer is scattered around the spacer, and the scattered light is incident on the glass substrate. This is similar to the appearance of light scattering when crystals (powder) with different refractive indices are placed inside the liquid. If the refractive index of the liquid crystal matches that of the liquid, light will not scatter on the crystal surface. Therefore, in the present invention, the refractive indexes of the liquid crystal and the spacer are selected to be substantially equal (claim 1).

The closer the refractive index values of the liquid crystal and the spacer are to each other, the less light scattering should be. Therefore, it is necessary to consider the value of the refractive index of the liquid crystal in more detail. In the first place, liquid crystals have birefringence, that is, the refractive index is different between the long axis direction of liquid crystal molecules and the direction perpendicular thereto. Light that oscillates in a direction perpendicular to the long axis (optical axis) of liquid crystal molecules is called ordinary light,
Displaying the refractive index for ordinary light by n _o. Also, the light oscillating in the long axis direction of the liquid crystal molecule is extraordinary light (extrao).
It is called “rdinary light”, and the refractive index for extraordinary light is represented by n _e . The birefringence (refractive index anisotropy) Δn of the liquid crystal is defined by Δn = n _e −n _o (1). Nematic liquid crystals and smectic liquid crystals have Δn> 0, which is said to be optically positive, and cholesteric liquid crystals have Δn <0, which is optically negative. In a nematic liquid crystal or a smectic liquid crystal system, for example, n
_e ≒ _{1.5~1.72; Δn} of ≒ 0.05~0.2 things are well known.

(A) TN (Twisted Nemat)
ic) type liquid crystal, N / W (normally white) mode (white display when no voltage is applied to the liquid crystal)
Consider a case where a voltage is applied to the display element to display black (FIG. 2). In FIG. 2, the polarization directions of the polarizing plates 6 and 7 are indicated by. In black display, the alignment direction of the liquid crystal 5 is substantially perpendicular to the glass substrates 2 and 3. Polarization direction of light L incident on the liquid crystal layer 5 (same as the polarization direction of the polarizing plate 7)
Does not change while the light L travels along the major axis direction of the liquid crystal molecules 5a and is always in a direction perpendicular to the major axis, so the light L acts on the liquid crystal 5 as normal light, and the refractive index of the liquid crystal becomes n _o. Therefore, the match of the refractive index n of the spacer to the refractive index n _o of the liquid crystal is most ideal in preventing scattering of light at the spacers (claim 2).

For example, liquid crystal ZLI32 manufactured by Merck & Co., Inc.
In the case of 77, since n _e = 1.68 and n _o = 1.52, Sekisui Micropearl (n = 1.57) is preferably used for the spacer. (B) Consider a case where a TN type liquid crystal is used and a display element of an N / B (normally black) mode (black display is performed without applying a voltage to the liquid crystal) is displaying black (FIG. 3).

In black display, the alignment direction of the liquid crystal 5 is the substrates 2, 3
In contrast, it is twisted and oriented on a horizontal plane. In the liquid crystal layer 5, the polarization direction of the light L, ′, substantially coincides with the alignment direction (long axis direction) of the liquid crystal molecules. Therefore, the light L acts as extraordinary light on the liquid crystal 5, and the refractive index of the liquid crystal for this light L is n.
It becomes _e . Therefore, when the refractive index n of the spacer is coincident with the n _e, optimal consists in preventing the scattering of light by the spacer (claim 3).

In the case of Merck liquid crystal ZLI1646, n
_e = 1.56, since it is n _o = 1.48, preferably used Sekisui Ltd. Micropearl (n = 1.57) as a spacer. (C) STN (Super-Twisted Nema)
Consider a case in which the N / B mode display element displays black using a tic) type liquid crystal (FIG. 4). Inside the liquid crystal layer 5, the light L becomes elliptically polarized light, and the polarization state does not follow the alignment direction of the liquid crystal. In this case, some scattering occurs even if the refractive index of the spacer is matched with the refractive index n _e or n _o of the liquid crystal. In order to reduce the scattering, it is sufficient not to make a large difference in the refractive index between the liquid crystal and the spacer. Therefore, the refractive index n of the spacer is set between the refractive indices n _e and n _o of the liquid crystal (more preferably n _e). (Near the mean value of n _o ) is reasonable (Claim 4).

In the case of the liquid crystal ZLI1237 manufactured by Merck, n
_e = 1.632, n _o = 1.492, and (n _e + n
_{Since o} ) /2=1.562, it is preferable to use Sekisui Micropearl (n = 1.57) as the spacer. Refractive index n _o or n of the liquid crystal refractive index n of more spacers
_{Although e} or the case of setting it between them has been described, since the birefringence Δn = n _e −n _o of the liquid crystal is a relatively small value,
Also the refractive index n of the spacer simply set in the vicinity of n _e ~n _o, it can be expected a significant effect in preventing the scattering caused by the difference in refractive index of the liquid crystal and the spacer. Therefore, the present invention is not limited to the above three cases.

The present invention can be applied to all liquid crystal display elements using spacers including active matrix type.

[0015]

As described above, according to the present invention,
Since the refractive index of the spacer is set to be approximately equal to the refractive index of the liquid crystal, the scattering of light generated around the spacer is reduced, and the light loss in the spacer is reduced, which reduces the display quality due to light loss and reduces the contrast. It can prevent the deterioration.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of a liquid crystal display device according to an embodiment of the present invention and a conventional example.

FIG. 2 is a view showing an embodiment of the invention of claim 2, A is a sectional view and B is a plan view.

3A and 3B are views showing an embodiment of the invention of claim 3, wherein A is a sectional view and B is a plan view.

FIG. 4 is a view showing an embodiment of the invention of claim 4, A is a sectional view and B is a plan view.

Claims (4)

[Claims] 1. A liquid crystal display in which two glass substrates having transparent electrodes formed on their inner surfaces are opposed to each other, fine spacers are dispersed between them, and the substrates are bonded together, and then liquid crystal is sealed between the substrates. In the device, the liquid crystal display device is characterized in that the liquid crystal and the spacer have substantially the same refractive index. 2. The liquid crystal display device according to claim 1,
The refractive index of the spacer is such that the ordinary light (ordi) of the liquid crystal is
and wherein the substantially equal to the refractive index n _o for nary light). 3. The liquid crystal display element according to claim 1,
The refractive index of the spacer is determined by the extraordinary light (extr) of the liquid crystal.
refractive index n _e for aordinal light)
It is characterized by being almost equal to. 4. The liquid crystal display element according to claim 1,
The spacer has a refractive index that is an intermediate value between the refractive index n _{o of the} liquid crystal for ordinary light and the refractive index n _{e of} extraordinary light.