JPH0369917A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To form a uniform inter-substrate spacing and to obtain high display performance by forming spacers of a mixture composed of spacers whose surfaces have perpendicular orientability, and spacers whose surfaces have horizontal orientability. CONSTITUTION:Two kinds of the spacers 10b, in which the orientation of the liquid crystal molecules exhibits the perpendicular orientability and 10a in which the orientation thereof exhibits the horizontal orientability are mixed and used as the spacers 10. The spacers 10a which exhibit the horizontal orientation in the surface at the time of lighting, therefore, suppress the generation of a region where the orientation of a reverse tilt is defective. The spacers which can be the nuclei for the orientation defect at this time are the spacers 10b which exhibit the perpendicular orientability. On the other hand, the spacers 10b which exhibit the perpendicular orientability on the surface conversely suppresses the generation of the region where the orientation of the reverse tilt is defective at the tie of non-lighting. The spacers which can be the nuclei for the orientation defect at this time are the spacers 10a which exhibit the horizontal orientability. Thus, the generation of the orientation defect is suppressed both at the time of the lighting and the non-lighting without degrading the uniformity of the spacing between the substrates of the liquid crystal cell.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having an improved spacer.

(Prior Art) In recent years, liquid crystal display devices have been used not only for devices with small display sections such as watches and calculators, but also as display devices for devices with large display sections such as word processors, personal computers, and televisions. has been done.

In general, a liquid crystal display device consists of two electrode substrates each having an alignment layer formed thereon, which are stacked together with a spacer interposed therebetween to regulate the distance between the substrates.
The periphery is sealed to form a liquid crystal cell, and the liquid crystal material is sandwiched between the electrode substrates. In this case, in a large-sized liquid crystal display device, it is important to obtain uniform and stable alignment of the liquid crystal over the entire display surface.

However, in such large-sized liquid crystal display devices, it is difficult to obtain uniform and stable alignment of the liquid crystal over the entire display surface. Particularly in large liquid crystal display devices, spacer particles are densely distributed in the display area in order to achieve uniform substrate spacing over the entire large display area.
The alignment of liquid crystal molecules on the spacer surface may be disturbed, resulting in a significant deterioration of display quality.

That is, in a so-called super twist (ST) type liquid crystal display device in which liquid crystal molecules are twisted at an angle of 180° or more between a pair of electrode substrates, after liquid crystal is injected into a liquid crystal cell, the twist angle is changed in addition to the normal orientation. Alternatively, an alignment state with different twist directions (hereinafter referred to as a twist-reverse alignment defect region) may appear.

In order to eliminate this region of poor alignment, the liquid crystal display device is usually heated until the liquid crystal becomes equal to six phases, and then cooled down.

However, even with this method, the defective twist-reverse alignment region may not disappear. The boundary between the two orientation states, the normal orientation region and the defective orientation region, becomes a defect line called a disclination line.

This disclination line moves as the twist-reverse misalignment area decreases.

The spacer inhibits the movement of this disclination and, in turn, prevents the region with poor twist-reverse orientation from disappearing. As a result, regions with poor orientation remain, which significantly impairs display quality. In addition, if the lighting display is continued, a state in which the tilt direction of the liquid crystal molecules differs from the spacer in the lighting pixel (hereinafter referred to as a reverse tilt alignment defect region) occurs.
This also significantly degrades display quality.

Such problems are noticeable in ST type liquid crystal display devices, but they also occur in twisted nematic (TN) type crystal display devices with a 90' twist.

The above-mentioned problem can be alleviated by reducing the number of spacers to be distributed, since spacers often serve as cores in regions with poor orientation. However, in this case, a problem arises in that it is no longer possible to maintain uniform electrode-substrate spacing over a large area.

(Problem to be solved by the invention) In a liquid crystal display device in which a spacer is arranged between electrode substrates,
The occurrence of regions with poor twist reverse alignment and poor reverse tilt alignment was unavoidable, leading to deterioration in display quality.

This invention solves the above problem, and has a special purpose.

- To provide a liquid crystal display device that exhibits uniform and stable alignment both when lit and when not lit, and has high display performance without reducing the number of substrates, that is, while realizing uniform substrate spacing. .

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a liquid crystal display device in which a liquid crystal material and a spacer are sandwiched between two opposing electrode substrates, wherein the spacer has a vertically aligned surface. This is a liquid crystal display device characterized in that it is made of a mixture of a spacer having a horizontal alignment property and a spacer whose surface has a horizontal alignment property.

(Function) There are two possible alignments of liquid crystal molecules on the spacer surface: vertical alignment and horizontal alignment with respect to the spacer surface. In the present invention, a mixture of two types of spacers is used: one in which the liquid crystal molecules on the surface are vertically aligned and one in which the liquid crystal molecules are horizontally aligned.

Here, the liquid crystal alignment on the spacer surface means the alignment state when a liquid crystal cell is constructed using a substrate made of the same material as the spacer material, unless the spacer surface is subjected to a separate surface treatment, and With respect to the spacer, it means an alignment state in which a liquid crystal cell is constructed using a substrate made of the same material as the spacer material and subjected to the same surface treatment as that applied to the surface of the spacer.

First, a spacer exhibiting vertical alignment and a spacer exhibiting horizontal alignment are individually arranged to have a horizontal or near-horizontal inclined alignment and a positive dielectric anisotropy with respect to the substrate surface of an ST type liquid crystal display device or a TN type liquid crystal display device. When applied to a liquid crystal display device using a tropic liquid crystal material, Figures 2 and 3 show
This will be explained with reference to the figures. In each figure, the upper figure shows a cross-sectional view, and the lower figure shows a view from above.

In the case of a spacer that exhibits vertical alignment As shown in Figure 2, during lighting (see Figure a), as the liquid crystal molecules 25 on the surface of the spacer 20 move away from the spacer 20, the orientation direction of the liquid crystal molecules 25 changes approximately 90 degrees. Because an unstable alignment state of changing appears on almost the entire surface of the spacer, reverse tilt alignment failure is likely to occur.In addition, when the light is not lit (see the same figure), such an unstable state of alignment appears on the spacer surface. Since it appears only in a part of the substrate 20 and hardly disturbs the orientation regulated by the orientation layer on the surface of the substrate 21, a twist-reverse orientation defect is unlikely to occur.

■In the case of a spacer that exhibits horizontal alignment As shown in Figure 3, liquid crystal molecules 2 on the surface of the spacer 22
The orientation direction of No. 5 is not uniquely determined and becomes random. Therefore, the alignment tends to be disturbed near the spacer 22, but when the light is turned on (see a in the same figure), the force that tries to disturb it in a specific direction does not move, so a stable reverse tilt is difficult to occur. However, when the light is not lit (see the figure), the spacer 22
As the liquid crystal molecules 25 on the surface move away from the spacer 22, there is a portion where the alignment direction of the liquid crystal molecules changes by approximately 90', and this tends to cause twist-reverse alignment failure.

As described above, the use of a spacer exhibiting vertical alignment on the surface is effective against twist-reverse alignment defects during non-lighting, but is not very effective against reverse-tilt alignment defects that occur during lighting.

On the contrary, when using a spacer that exhibits horizontal orientation on the surface, it is effective against reverse tilt alignment defects that occur when the light is on, but it is not effective against twist reverse alignment defects that occur when the light is off. has no effect.

Therefore, if a vertically oriented spacer or a horizontally oriented spacer is used alone, a problem will remain either during lighting or non-lighting.

Next, the present invention will be described in which both a spacer whose surface has a vertical orientation and a spacer whose surface has a horizontal orientation are used at a mixing ratio of 1:1, for example. As described above, spacers that exhibit horizontal alignment on their surfaces during lighting have the effect of suppressing the occurrence of reverse tilt alignment failure regions, and this accounts for half of the total number of spacers. At this time, the remaining half of the number of spacers that can become the nucleus of poor orientation are spacers that exhibit vertical orientation on the surface. On the other hand, when the light is not lit, spacers that exhibit vertical alignment on the surface have the effect of suppressing the occurrence of twist-reverse alignment defects, and in this case, the number of spacers that can become the core of alignment defects is reduced by the spacers that exhibit horizontal alignment on the surface. Yes, it is still half of all spacers.

Therefore, according to the present invention, it is possible to reduce the number of spacers that can become the core of alignment defects both when lit and when not lit, without reducing the total number of spacers, that is, without deteriorating the uniformity of the substrate spacing of the liquid crystal cell. Therefore, the occurrence of alignment defects can be suppressed both during lighting and non-lighting.

In an actual liquid crystal display device, depending on the cell configuration conditions such as the twist angle of the liquid crystal, the electrode substrate spacing, the alignment film, and the liquid crystal material, the reverse tilt alignment defective area when turned on and the twist reverse alignment defective area when not lit are determined. Since the ease of occurrence may not be the same, it will be more effective if the mixing ratio of two types of spacers, one with horizontal orientation and the other with vertical orientation, is adjusted depending on each case. .

Further, the present invention is particularly effective when applied to an ST type liquid crystal display device in which precision in substrate spacing is required and spacers are densely distributed.

By the way, in order to reduce the alignment failure caused by the spacer, surface treatment of the spacer is proposed in Japanese Patent Application Laid-Open No. 57-613.
It is stated in the No. This uses a liquid crystal with negative dielectric anisotropy, the substrate surface is vertically aligned, and the birefringence electric field control (E
In the CB) type liquid crystal display device, the spacer is surface-treated to reduce the surface energy, and the liquid crystal molecules are vertically aligned on the spacer surface, thereby preventing spot-like alignment defects that occur around the spacer at the voltage application section. It is. In this technology, liquid crystal molecules are aligned horizontally with respect to the substrate surface at the voltage application section. This is to prevent alignment defects around the spacers when the substrate surface is horizontally aligned and the liquid crystal molecules are twisted when no voltage is applied. This is essentially different from what prevents twist reverse alignment defects or reverse tilt alignment defects that occur in the invention.

(Embodiment) FIG. 1 shows a sectional view of a liquid crystal display device according to an embodiment of the present invention.

In the first and second electrode substrates 1 and 2, band-shaped transparent electrodes 5 and 6 are formed on the surface of a glass substrate 3.4, respectively, and an alignment film 7.8 that has been subjected to a rubbing treatment is further provided.

The electrode substrates 1 and 2 are arranged so that the transparent electrodes 5 and 6 face each other at right angles, and the twist angle of the liquid crystal material 9 to be sealed is 240°, with a spacer 10 (described later) interposed between the substrates. The periphery is sealed with a sealant 11 to form a dot matrix type liquid crystal cell 12. A liquid crystal material 9 is sealed in the liquid crystal cell 12. In addition,
Reference numbers 13 and 14 in the figure indicate a polarizing plate, 15 indicates a backlight, and 16 indicates a drive circuit.

The electrode substrates 1 and 2 are spaced apart from each other by a spacer 10 of 5 to 7 microns. Moreover, as the spacer 10,
A mixture of spacer 1Qa showing horizontal orientation on the surface and spacer 10b showing vertical orientation on the surface was mixed with 70 to 80
It was scattered at a density of 2 pieces per area.

Liquid crystal display devices having such a configuration were fabricated using various spacer materials and different mixing ratios, and were evaluated as follows.

First, the liquid crystal display device was heated until the liquid crystal material 9 had six equal phases, then left to cool, and when the temperature returned to room temperature, the presence or absence of a defective twist-reverse alignment region was observed. Next, time-division driving was performed at a duty ratio of 1/200 and a bias ratio of 1/15, and the occurrence of reverse tilt orientation defective regions at that time was observed, and the contrast ratio was measured.

- As an example, the spacer 10a showing horizontal orientation is a silica ball spacer whose surface has been treated with Shiran (KBM603: manufactured by Shin-Etsu Silicone Co., Ltd.), and the spacer 10b showing vertical orientation on the surface is a silica ball spacer. A spacer 10 whose surface was treated with a chromium complex (FC-805: manufactured by Sumitomo 3M Co., Ltd.) was used,
The results are shown in the table when the respective mixing ratios were changed.

In this case, when using a mixture of spacer 1Qa showing horizontal orientation on the surface and spacer 10b showing vertical orientation at a ratio of 50% each, twist-reverse and reverse tilt defects occur both when lit and when not lit. The highest contrast ratio was obtained.

(See margin below) *1: Reverse tilt alignment defective area during lighting Area ratio of defective area to normal area in liquid crystal cell (%) *2
: Area ratio (%) of the defective area to the normal area in the liquid crystal cell when the device is not lit. Vertical alignment> and penzoanamine spheres treated with silane (horizontal alignment), ■Penzoanamine spheres treated with chromium complex (vertical alignment),
The same results as above were obtained when penzoanamine spheres were treated with silica (horizontal orientation), silica spheres were treated with chromium complex (vertical orientation), and penzoanamine spheres without surface treatment (horizontal orientation) were used. was gotten.

In addition, in the above embodiment, spacers whose surfaces were treated with silica spheres and penzoanamine were used, but of course they may be made of organic synthetic resins such as epoxy resins, surface-treated organic synthetic resins, metals, or other inorganic materials. . Further, the scattering density of the spacers is not limited to the above embodiment, but the present invention can be applied to other scattering densities as well.

[Effects of the Invention] According to the present invention, it is possible to achieve uniform substrate spacing without reducing the number of spacers, and to suppress the occurrence of twist reverse alignment defective regions and reverse tilt alignment defective regions. Accordingly, a liquid crystal display device having good alignment and high display quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the liquid crystal display device of the present invention, FIG. 2 is a diagram showing the arrangement of liquid crystal molecules around a spacer showing vertical alignment, and FIG. 3 is a diagram showing the arrangement of liquid crystal molecules around a spacer showing horizontal alignment. It is a diagram.

Claims (1)

[Claims] In a liquid crystal display device in which a liquid crystal material and a spacer are sandwiched between two opposing electrode substrates, the spacer is made of a mixture of a spacer whose surface has vertical alignment and a spacer whose surface has horizontal alignment. A liquid crystal display device characterized by: