JPH0220829A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To cancel a change in the state of light, to eliminate coloring at the time of slanting view, and to make a display with good view angle characteristics by canceling the effect of the polarizing operation of liquid crystal by a compensating layer when a voltage is applied to the liquid crystal. CONSTITUTION:The compensating layer 42 has refractive index anisotropy and the axial direction of the anisotropy is 90 deg. to the direction in a plane of liquid crystal molecules of the liquid crystal 40, which is sandwiched between a couple of polarizing plates 41a and 41b. The compensating layer 42 polarizes the state of light passed through the liquid crystal 40 by 90 deg. to cancel the effect of the polarizing operation of the liquid crystal 40 when a voltage is applied to the liquid crystal 40. The product DELTAn.d of the anisotropy DELTAn of the liquid crystal 40 and cell thickness (d) of the layer 42 varies by variation in the DELTAn.d of the liquid crystal 40 which is viewed slantingly. Consequently, no coloring occurs even when viewed slantingly and a display is made with good view angle characteristics.

Description

[Detailed Description of the Invention] (Summary) This invention relates to a liquid crystal display device having a configuration in which a vertically aligned liquid crystal cell is sandwiched between a pair of polarizing plates when no voltage is applied, which does not appear colored even when viewed from an angle and has good viewing angle characteristics. For the purpose of display, a compensatory layer having refractive index anisotropy and the axis direction of the anisotropy making 90 degrees with the plane direction of the liquid crystal molecules of the liquid crystal,
Superimposed on the LCD, the supplementary f! It has a structure in which an i-layer and a liquid crystal are stacked and sandwiched between a pair of polarizing plates.

[Industrial application field]

The present invention has a configuration in which a vertically aligned liquid crystal cell is sandwiched between a pair of polarizing plates when no voltage is applied (DAP (Def
rmation of A Igned Phas
es ) type) liquid crystal display device.

In recent years, simple matrix monochrome display liquid crystal panels have been actively developed, and in particular there is a demand for a liquid crystal display device capable of displaying a large capacity and high quality.

(Prior art) Figure 4 shows a diagram explaining the operation of a conventional device.
> is when no voltage is applied, and (B) in the same figure is when voltage is applied. In the same figure (A), the light 1 is transmitted through the polarizing plate 2 (the polarization direction a is 45° with respect to the direction on the plane of the liquid crystal molecules of the liquid crystal section 4).
(with an angle of .degree.), becomes linearly polarized light 3, and reaches the liquid crystal section 4. In the liquid crystal section 4, a liquid crystal 6 is provided between glass substrates 5+ and 52 on which transparent electrodes (not shown) are formed, respectively, and the liquid crystal 6 is in its initial state! 21 (when no voltage is applied from the transparent electrode), the liquid crystal molecules are vertically aligned (strictly speaking, ゛ is tilted at a slight angle, for example, to the right), and when a voltage is applied, which will be described later, the liquid crystal molecules fall, which is the so-called negative alignment. It has dielectric constant anisotropy. Linearly polarized light 3 entering liquid crystal section 4
The light passes through as it is (linearly polarized light 7) without being affected by the anisotropy of the refractive index of the liquid crystal 6, and is then blocked by the polarizing plate 8, resulting in a black display.

On the other hand, in Fig. F1 (B), the liquid crystal molecules of the liquid crystal 6 in the liquid crystal section 4 are tilted to the right by applying a voltage from the transparent electrode, and as a result, the linearly polarized light 3 is caused by the anisotropy of the refractive index of the liquid crystal 6. In other words, the polarization state is changed by the product Δn-d of the anisotropy of the refractive index and the cell thickness d, resulting in linearly polarized light 3 and linearly polarized light 9 having a linear polarization direction. The linearly polarized light 9 passes through the crossed Nicol polarizing plate 8 as it is with respect to the polarizing plate 2, resulting in a white display.

In this way, by applying a voltage to the vertically aligned liquid crystal 6 and tilting the liquid crystal molecules, light switching is performed and a black and white display is performed. This is called the DAP method.

(Problems to be Solved by the Invention) In the conventional device described above, there is no particular problem as long as the panel is viewed from the front, but when viewed from an angle, the liquid crystal
This is the same as increasing the cell thickness d of the liquid crystal 6.
The initial value of Δn-d, which is set in advance, changes. For this reason, the force that changes the polarization state of the linearly polarized light 3 acts more strongly than in the initial state, and as a result, there is a problem in that the display quality is degraded, especially when displaying white, and the display appears colored.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device that can display images with good viewing angle characteristics without being colored even when viewed from an angle.

[Means to solve the problem]

FIG. 1 shows a diagram of the principle of the present invention. In the figure, 40 is a liquid crystal having negative dielectric constant anisotropy, and 41a and 41b are a pair of polarizing plates. Reference numeral 42 denotes a compensation layer which has anisotropy in refractive index, the axial direction of the anisotropy making an angle of 90° with the plane direction of the liquid crystal molecules of the liquid crystal 40, and is superimposed on the liquid crystal 40. The pair of polarizing plates 41a is formed by overlapping the compensation layer 42 and the liquid crystal 40.

41b.

(Function) In the present invention, the compensation layer 42 has the function of polarizing the state of light passing through the liquid crystal 40 by 90°.
It acts to cancel the polarization effect of the liquid crystal 40 when a voltage is applied to the liquid crystal 40. Therefore, when viewed from an angle, the Δn-d of the liquid crystal 40 changes as much as the Δn-d of the liquid crystal 40 changes,
These compensate for changes in light conditions.

〔Example〕

FIG. 2 shows a configuration diagram of an embodiment of the present invention. In the same figure, 2
0 is a liquid crystal display panel, which is composed of a glass substrate 21, matrix-like transparent electrodes 22a and 22b, an alignment agent 23, a liquid crystal 24, a glass substrate 25, and a sealing material 26. LCD 2
4 is a nematic liquid crystal whose anisotropy Δε of dielectric constant ε is negative (liquid crystal molecules are vertically aligned when no voltage is applied, and fall when a voltage is applied), and the cell thickness is, for example, 5 μι. The product of the refractive index anisotropy Δn and the cell thickness d of the liquid crystal 24 is approximately 0.25 μl.
is set to . The alignment agent 23 is a mixture of a vertically aligned chromium complex and a horizontally aligned polyimide resin, and by rubbing, the liquid crystal 24 is aligned and tilted slightly to the right, and the direction of the liquid crystal molecules of the liquid crystal 24 on the plane is adjusted. is 45° with respect to the polarization direction of the polarizing plate 27.

The polarizing plates 27 and 28 are, for example, Nicol parallel to the polarizing plate 27, and the polarization direction is at an angle of 45° with respect to the direction C on the plane of the liquid crystal molecules of the liquid crystal 24.

29 is a compensation layer, for example, a stretched film made of transparent polymer, etc., and the product of the refractive index anisotropy Δn and the film thickness d is the liquid crystal 2.
The direction of the axis ne of the refractive index anisotropy Δn is at an angle of 90° with respect to the plane direction of the liquid crystal molecules of the liquid crystal 24.

FIG. 3 shows a diagram explaining the operation of the device of the present invention.
A) is when no voltage is applied, and (B) is when no voltage is applied.

In the same figure (A), light 1 passes through a polarizing plate 27 (the polarization direction a has an angle of 45° with respect to the direction on the plane of the liquid crystal molecules of the liquid crystal 24) and becomes linearly polarized light 30,
The liquid crystal 24 is reached.

LCD 24 is in its initial state! g (voltage) applied at 1°), the liquid crystal molecules are vertically aligned (strictly speaking, tilted at a slight angle, for example, to the right), and the liquid crystal molecules fall when a voltage is applied, which will be described later, resulting in so-called negative dielectric gravity. It has the following. The linearly polarized light 30 that has entered the liquid crystal 24 remains as it is without being affected by the anisotropy of the refractive index of the liquid crystal 24 (the linearly polarized light 31
) and then enters the compensation layer 29. Linear polarized light 31
When passing through the compensation layer 29, the polarization direction is changed by 90° due to the effect of refractive index anisotropy (because the axis ne of the refractive index anisotropy of the compensation layer 29 is at an angle of 45° with the linearly polarized light 31). ), the light is emitted as linearly polarized light 32.

Then, the linearly polarized light 32 is blocked by the polarizing plate 28, resulting in a black display.

On the other hand, in the same figure (B), when the liquid crystal 24 is applied with a voltage, the liquid crystal molecules tilt to the right, and as a result, the linearly polarized light 30 is affected by the anisotropy of the refractive index of the liquid crystal 24, that is, it is refracted. The product of the rate anisotropy Δn and the cell thickness d Δn−d(
= approximately 0.25 μr*) t, - Therefore, the polarization state is changed and becomes linearly polarized light 33 having a polarization direction perpendicular to linearly polarized light 30. In this case, Δn-d of the liquid crystal 24 is 0.
In the range of 23 μm to 0.27 μm, linearly polarized light 33 is perpendicular to linearly polarized light 30. The linearly polarized light 33 is connected to the compensation layer 29 (Δn-d is 0.23 μm to 0.27 μm
+1 range), the polarization direction changes to 90° due to the effect of refractive index anisotropy at the same time as when no voltage is applied.
' is changed to linearly polarized light 34 (same as linearly polarized light 30), and passes through the polarizing plate 28 as it is, resulting in a white display.

Let us now consider the compensation effect of the compensation layer 29 when voltage is applied. Product Δ of refractive index anisotropy Δn and thickness d
The anisotropic directions of the liquid crystal 24 and the compensation wa 29 with the same n−d are shifted by 90 degrees, and in such a configuration, the compensation tri
The layer 29 counteracts the polarizing effect of the liquid crystal 24 so that the linearly polarized light 34 is identical to the linearly polarized light 31. Therefore,
Compensate f by the amount that △n-d of the liquid crystal 24 changes when viewed from an angle.
The Δn-d of the aff129 also changes, which cancels out changes in the state of light and prevents color from appearing when viewed from an angle. In this case, the angle of about 30 degrees (conventionally about 1
It can be seen without coloring even when viewed from an angle of 5 degrees, and the viewing angle characteristics are better than before.

〔Effect of the invention〕

As explained above, according to the present invention, the compensation layer works to cancel the polarizing effect of the liquid crystal, especially when a voltage is applied to the liquid crystal, thereby canceling out changes in the state of light and When viewed from above, no color appears and the display has good viewing angle characteristics.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a diagram explaining the operation of the device of the present invention, and Fig. 4 is a diagram explaining the operation of the conventional device. It is. In the figure, 20 is a liquid crystal panel, 24.40 is a liquid crystal, 27.28.41a and 41b are polarizing plates, 29.42 is a compensation layer, and 30.31.32.33 is linearly polarized light.

Claims (3)

[Claims] (1) In a liquid crystal display device having a configuration in which a liquid crystal (40) having negative dielectric constant anisotropy is sandwiched between a pair of polarizing plates (41a) (41b), having an anisotropy of refractive index, the anisotropy If the axis direction of the polarity is the above liquid crystal (
A compensation layer (42) forming an angle of 90 degrees with the plane direction of the liquid crystal molecules of 40) is stacked on the liquid crystal (40), and the stack of the compensation layer (42) and the liquid crystal (40) is stacked as the pair. A liquid crystal display device characterized in that it is sandwiched between polarizing plates (41a) and (41b). (2) In the liquid crystal (40), when no voltage is applied, the liquid crystal molecules are aligned and tilted in one direction and are oriented substantially vertically, and the polarization direction of the polarizing plates (41a) and (41b) is the same as that of the liquid crystal (40).
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device forms an angle of 45° with respect to the plane direction of the liquid crystal molecules of 0). (3) The liquid crystal display device according to claim 1, wherein the compensation layer (42) is a stretched polymer film.