JPH04214535A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal device having an excellent contrast and visual angle characteristic. CONSTITUTION:This device is constituted by laminating two sheets of TN type liquid crystal panels which are reverse in twist directions between a pair of polarizing plates 7 and 8 and using the incident side of light as the driving panel 9 and the exit side of light as the compensation panel 10 so that the major axis directions of the nearest molecules 9O, 10i of the liquid crystal molecules between two sheets of these liquid crystal panels 9 and 10 intersect orthogonally with each other. A drichromatic dye of p type is added to the liquid crystal of the driving panel 9 and a dichromatic dye of an n type is added to the liquid crystal of the compensation panel 10.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] In recent years, display devices using liquid crystals have become
It has come to be used in display devices including office automation equipment. The present invention relates to improving contrast and viewing angle characteristics in a liquid crystal display device.

0002

[Prior Art] The TN method has been widely used in conventional liquid crystal display devices, but this method utilizes the fact that liquid crystal is twisted and oriented, and when a voltage is applied, the twist is untwisted and the liquid crystal molecules rise. It is being displayed.

FIG. 8 is a diagram showing the effect of the angle between liquid crystal molecules and incident light. As shown in (a), when the incident light 2 is parallel to the long axis of the liquid crystal molecule 1, the optical effect of the liquid crystal is minimal, and as shown in (c), the incident light 2 is parallel to the long axis of the liquid crystal molecule 1. When the light 2 is perpendicular, the optical effect of the liquid crystal is maximized. As shown in (b), when the incident light 2 is oblique to the long axis of the liquid crystal molecule 1, the optical effect of the liquid crystal is
The state is intermediate between (a) and (b) above.

FIG. 9 is a diagram showing the operation of a TN-type liquid crystal panel. (a) shows the state where the applied voltage is 0, (b) shows the state where the applied voltage is medium, and (c) shows the state where the applied voltage is high. be. This liquid crystal display panel has a liquid crystal sealed between two glass substrates 3 and 4, and a light source is provided on the back.When the transmitted light is maximum, it is in a bright state, and when the transmitted light is minimum, it is in a dark state. This causes the display to take place. Now, as shown in (a), when the applied voltage is 0, when the liquid crystal display panel is viewed from the front, the liquid crystal molecules 1 are at right angles to the incident light 2, so the optical effect of the liquid crystal is maximized. . On the other hand, when viewed from an angle, 5
, 6, since the incident light is oblique to the liquid crystal molecules 1, the optical effect of the liquid crystal becomes medium.

As shown in (b), when the applied voltage is medium, most of the liquid crystal molecules 1 are oblique to the glass substrates 3 and 4, so when viewed from the front, the optical properties of the liquid crystal relative to the incident light 2 are The effect is medium. However, when viewed from an angle at position A,
Since the incident light 5 is parallel to the liquid crystal molecules 1, the optical effect of the liquid crystal is minimized.Conversely, when viewed obliquely at position B, the incident light 6 is perpendicular to the liquid crystal molecules 1, so the optical effect of the liquid crystal is minimized. is maximum. Therefore, depending on the viewing position, it may be in a bright state, a dark state, or an intermediate state.

As shown in (c), when the applied voltage is large, the liquid crystal molecules 1 are perpendicular to the glass substrates 3 and 4, and when viewed from the front, the liquid crystal molecules 1 and the incident light 2 are parallel to each other. Therefore, the optical effect of the liquid crystal is minimized. However, when viewed obliquely, the incident lights 5 and 6 are oblique to the liquid crystal molecules 1, so the optical effect of the liquid crystal becomes medium.

When voltages are applied in the order of (a), (b), and (c), when looking at the panel from the front, the optical effects are large, medium, and
The order is small, and the display is light, gray, and black.
When viewed from diagonal position B, the display becomes medium, large, and medium, and when viewed from diagonal position A on the opposite side, the optical effects are medium, small, and medium, that is, the display becomes gray and black. , the display becomes gray and the order of light and darkness is reversed, making the display appear to be inverted.

[0008]

[Problem to be solved by the invention] In this way, the conventional T.
In N-type liquid crystal display devices, the display state changes depending on the viewing angle, and the viewing angle characteristics are poor, making it difficult to view. Moreover, the contrast was also insufficient.

A technical object of the present invention is to address such problems and to realize a liquid crystal display device with excellent contrast and viewing angle characteristics.

0010

[Means to solve the problem]

(1) Two TN type liquid crystal panels with opposite twist directions are stacked between a pair of polarizing plates 7 and 8, with the light incident side serving as the driving panel 9 and the light exiting side serving as the compensation panel 10. . Furthermore, the structure is such that the major axes of the nearest molecules 9o and 10i of the liquid crystal molecules between the two liquid crystal panels 9 and 10 are perpendicular to each other. A p-type dichroic dye is added to the liquid crystal of the drive panel 9, and an n-type dichroic dye is added to the liquid crystal of the compensation panel 10.

(2) The pair of polarizing plates 7 and 8 have orthogonal polarization directions. Furthermore, the alignment direction of the liquid crystal molecules 9i close to the input polarizing plate 7 of the drive panel 9 is parallel to the transmission axis 7a of the input polarizing plate 7, and the alignment direction of the liquid crystal molecules 10o close to the output polarizing plate 8 of the compensation panel 10 and the transmission axis 8 of the output polarizing plate 8
a are parallel to each other.

(3) Unlike the liquid crystal display device described in (1) above, a dichroic dye is not added to the liquid crystal of the drive panel 9, but a p-type dichroic dye is added to the liquid crystal of the compensation panel 10. The configuration is as follows.

(4) In the configuration of (3) above, a pair of polarizing plates 7 and 8
have orthogonal polarization directions. Then, the alignment direction of the liquid crystal molecules 9i close to the incident polarizing plate 7 of the driving panel 9 and the transmission axis 7a of the incident polarizing plate 7 are perpendicular to each other, and the compensation panel 10
The alignment direction of the liquid crystal molecules 10o adjacent to the output polarizing plate 8 and the transmission axis 8a of the output polarizing plate 8 are configured to be perpendicular to each other.

[0014]

According to claims 1 and 2, a p-type dichroic dye is added to the driving panel 9 and an n-type dichroic dye is added to the compensation panel 10. 4 is a configuration in which no dichroic dye is added to the drive panel 9, but a p-type dichroic dye is added to the compensation panel 10.

In the structures of claims 1 and 2, the dichroic dye added to the drive panel 9 acts to absorb light when the voltage is OFF, but does not absorb light when the voltage is ON.

Originally, when the voltage is OFF, even if there is no dye, the pair of polarizing plates 7 and 8 are in a crossed nicol state, resulting in a dark state, but if the two liquid crystal panels 9 and 10 are filled with dichroic dye, By adding it to a structure that absorbs transmitted light, the contrast of the liquid crystal panel is further improved.

[0017] Moreover, when this liquid crystal panel is viewed from an angle, the dichroic pigment absorbs the light that would otherwise pass through even in the dark, so even when viewed from an angle, the contrast decreases. The viewing angle range expands.

In the configurations of claims 3 and 4, the dichroic dye similarly acts to improve the contrast and widen the viewing angle range, but the dichroic dye acts to improve the contrast and widen the viewing angle range.
Since it is added only to claims 1 and 2, the effect is
It's not as big as the composition. However, if a dichroic dye is added to the liquid crystal of the drive panel 9, the impurity ions may reduce the voltage retention of the liquid crystal cell, and n-type dichroic dyes are not so common. Considering this, this second method is also quite effective.

[0019]

EXAMPLE Next, how the liquid crystal display device according to the present invention is actually implemented will be explained by way of example. Figure 2, Figure 3
FIG. 4 is an exploded perspective view showing an example of a liquid crystal display device in which dichroic dye is added to both the drive panel and the compensation panel.
FIG. 2 is a perspective view illustrating the effects of n-type and p-type dichroic dyes.

Reference numeral 7 denotes a polarizing plate on the incident side, and 8 denotes a polarizing plate on the output side, which are arranged in a crossed nicol configuration so that their polarization directions are orthogonal to each other. Between this pair of polarizing plates 7 and 8, two TN type liquid crystal panels 9 with opposite twist directions,
10 are stacked, the input polarizing plate 7 side is a driving panel 9 connected to a power supply, and the output polarizing plate 8 side is a compensation panel 10.

The two liquid crystal panels 9 and 10 are configured such that the long axes of the nearest molecules 9o and 10i of the liquid crystal molecules are perpendicular to each other. Furthermore, the alignment direction of the liquid crystal molecules 9i close to the input polarizing plate 7 of the drive panel 9 is parallel to the transmission axis 7a of the input polarizing plate 7, and the alignment direction of the liquid crystal molecules 10o close to the output polarizing plate 8 of the compensation panel 10 and the transmission axis 8a of the output polarizing plate 8 are configured to be parallel to each other. This can be achieved by changing the composition of the liquid crystal and the alignment film.

A p-type dichroic dye 11 is added to the liquid crystal of the drive panel 9, and an n-type dichroic dye 11 is added to the liquid crystal of the compensation panel 10.
A type of dichroic dye 12 is added.

As shown in FIG. 4, the n-type and p-type dichroic dyes have completely opposite effects. Figure 4 (a) (b)
is a diagram showing the action of an n-type dichroic dye, where the polarization plane L of the incident light and the long axis 12 of the n-type dichroic dye molecule are shown in (a).
When the directions (dye transmission axes) are perpendicular, the n-type dichroic dye 12 absorbs the incident light and no transmitted light is generated. On the other hand, as shown in (b), the polarization plane L of the incident light
is parallel to the long axis 12 direction of the n-type dichroic dye molecule, the n-type dichroic dye 12 does not absorb the incident light and the light is transmitted.

On the other hand, in the case of p-type dichroic dye, (c)
If the polarization plane L of the incident light is perpendicular to the long axis 11 of the p-type dichroic dye molecule, the p-type dichroic dye 11 does not absorb the incident light and the light is transmitted. do. In contrast,
As shown in (d), when the polarization plane L of the incident light is parallel to the long axis 11 direction of the p-type dichroic dye molecule, the p-type dichroic dye 11 absorbs the incident light, No transmitted light is generated.

When such a dichroic dye is added to a liquid crystal, the molecules 11 and 12 of the dichroic dye are aligned in the direction of the liquid crystal molecules. That is, in the drive panel 9, the liquid crystal molecules are twisted to the left (rotated to the left as they advance), so the molecules 11 of the p-type dichroic dye are also oriented to the left, and the incident light is also twisted to the left as shown by 13. Proceed while rotating to the left. In the compensation panel 10, the liquid crystal molecules are twisted to the right (rotated to the right as they advance), so the n-type dichroic dye molecules 12 are also oriented to the right, and the incident light is also twisted to the right as shown by 14. Proceed while rotating.

Now, when light is irradiated onto the back surface of the liquid crystal display device with no voltage applied to the drive panel 9 as shown in FIG. 2, only light having the same polarization direction as the transmission axis 7a of the polarizing plate 7 on the incident side is produced. passes through the polarizing plate 7, and as shown at 13, rotates counterclockwise due to the liquid crystal molecules of the drive panel 9,
The light is emitted from the drive panel 9 after being rotated by exactly 90 degrees. At this time, as shown in Fig. 4(d), the incident light L and p
Since the molecules 11 of this type of dichroic dye are parallel, light is absorbed. However, not all of the light is reliably absorbed, and the remaining transmitted light is almost certainly absorbed by the next compensation panel 10. In other words, since the structure is such that the long axes of the liquid crystal molecules 9o and 10i closest to each other between the two liquid crystal panels 9 and 10 are perpendicular to each other, the polarization plane L of the light emitted from the drive panel 9 is compensated. It is perpendicular to the nearest liquid crystal molecule 10i of the panel 10. Therefore, in the compensation panel 10, the incident light L travels in a state perpendicular to the n-type dichroic dye molecules 12, as shown in FIG. 4(a).
As explained above, the incident light is absorbed and no transmitted light is emitted.

In this way, when no voltage is applied, the incident light is absorbed by the dichroic dye in both the drive panel 9 and the compensation panel 10. Since the polarizing plates 7 and 8 are crossed nicols, when no voltage is applied, the state is dark even when no dichroic dye is added, but by adding dichroic dye to the two liquid crystal panels, Transmitted light can be blocked reliably, further improving contrast.

Furthermore, even when the liquid crystal panel is viewed from an angle, the transmitted light is absorbed and blocked by the dichroic dye, so that even when viewed from an angle, the contrast does not decrease and the viewing angle range is expanded.

Next, as shown in FIG. 3, when a voltage is applied to the drive panel 9, the liquid crystal molecules 9v in the drive panel 9
are aligned in a direction perpendicular to the liquid crystal panel, and as a result, the p-type dichroic dye 11 is also aligned in a direction perpendicular to the liquid crystal panel. Therefore, the light L transmitted through the incident side polarizing plate 7 is perpendicular to the n-type dichroic dye molecules 11, as shown in FIG. 4(c).
As explained above, it is not absorbed by dichroic dyes and is transmitted through them. Moreover, since it does not rotate during transmission, it becomes parallel to the liquid crystal molecules 10i on the driving panel 9 side in the compensation panel 10, and n
It advances parallel to the dichroic dye molecules 12 of the type and while rotating clockwise. During this period, the incident light L and the n-type dichroic dye molecules 12 are parallel to each other and can be transmitted, as explained in FIG. 4(b). In this way, in the voltage application state, the drive panel 9
Incident light can pass through both the compensating panel 10 and the compensating panel 10 enters a bright state.

By the way, when a dichroic dye or the like is added to the liquid crystal in the drive panel 9, the resistance value decreases and it becomes difficult to maintain the voltage application state. Also, known dichroic dyes include ad-based and anthraquinone-based dyes, and naphthoquinone-based perylene quinophthalone-based dyes. Distinguishing between n-type and p-type is done by processing these materials, but it is difficult to process them into n-type, and high-quality n-type dichroic dyes are difficult to obtain.

5 and 6 show a structure in which only a p-type dichroic dye is used and there is no need to add a dichroic dye to the drive panel 9. This configuration differs from the configurations in FIGS. 2 and 3 in that no dichroic dye is added to the drive panel 9, and that a p-type dichroic dye is added to the liquid crystal of the compensation panel 10. , the alignment direction of liquid crystal molecules 9i close to the input polarizing plate 7 of the drive panel 9 and the transmission axis 7a of the input polarizing plate 7 are orthogonal, and the alignment direction of the liquid crystal molecules 10o close to the output polarizing plate 8 of the compensation panel 10 and the transmission axis 8a of the output polarizing plate 8 are configured to be orthogonal to each other.

Now, as shown in FIG. 5, when no voltage is applied to the drive panel 9, the light L transmitted through the polarizing plate 7 on the incident side rotates counterclockwise while being perpendicular to the liquid crystal molecules of the drive panel 9. Since the incident light L travels and enters the compensation panel 10 in a state rotated by 90 degrees, the incident light L travels in the compensation panel 10 while rotating clockwise in a state parallel to the molecules 11 of the p-type dichroic dye. When the incident light L is parallel to the molecules of the p-type dichroic dye, it is absorbed by the p-type dichroic dye and cannot be transmitted, as shown in FIG. 4(d).

In this way, a structure capable of absorbing transmitted light can be realized without adding a dichroic dye to the drive panel 9 and without using an n-type dichroic dye.

When voltage is applied to the drive panel 9,
As shown in FIG. 6, since the liquid crystal molecules 9v in the drive panel 9 are aligned perpendicularly to the liquid crystal panel, the incident light L does not rotate.
It continues as it is and crosses perpendicularly to the p-type dichroic dye molecules 11 in the compensation panel 10. As a result, in the compensation panel 10, the incident light L is transmitted to the molecules 11 of the p-type dichroic dye.
Because it rotates clockwise and advances at right angles to the
) The incident light is transmitted, resulting in a bright state.

FIG. 7 shows the driving panel 9 and the compensation panel 10.
This is a diagram illustrating a cross-sectional structure of a glass substrate 17 having a transparent electrode 15 formed on its inner surface (the transparent electrode 15 can be omitted in the compensation panel 10) and an alignment film 16 formed thereon;
Similarly, a transparent electrode 18 is formed on the inner surface, and a glass substrate 20 on which an alignment film 19 is formed is placed opposite to the glass substrate 20, and the periphery is sealed with a sealing material 21. A liquid crystal 22 is sealed between both glass substrates 17 and 20. Two sets of such liquid crystal panels are prepared, and in the case of the configurations shown in FIGS. 2 and 3, a p-type dichroic dye is added to the liquid crystal of the drive panel 9, and an n-type dichroic dye is added to the liquid crystal of the compensation panel Add dichroic dye. At this time, approximately 2 wt% of black dichroic dye was added to each liquid crystal panel, and a twist angle of 90° was adopted for the liquid crystal. Compared to the conventional TN liquid crystal panel, the contrast increased from about 100 to 150. , viewing angle characteristics are ±30 for both top, bottom, left, and right when the contrast is 10 or more.
It was possible to spread out approximately 10 degrees from 10 degrees, and achieve an angle of 40 degrees or more. Note that good effects were also observed when the twist angle was in the range of about 45° to 180°.

[0036]

As described above, according to the present invention, a p-type dichroic dye is added to the drive panel 9, an n-type dichroic dye is added to the compensation panel 10, and both liquid crystal panels By having a structure in which these two layers are stacked, the absorption characteristics of transmitted light are excellent, and the contrast is significantly improved. Moreover, even when viewing the liquid crystal panel from an angle, the contrast does not deteriorate and the viewing angle range is expanded.

As described in claims 3 and 4, by adding a p-type dichroic dye to the compensation panel 10 without adding a dichroic dye to the drive panel 9, the voltage maintenance of the liquid crystal cell is achieved. A liquid crystal display device with excellent contrast and viewing angle characteristics can be realized without deteriorating properties and without using an n-type dichroic dye that is difficult to manufacture.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view illustrating the basic principle of a liquid crystal display device according to the present invention.

FIG. 2 is an exploded perspective view of an embodiment in which a dichroic dye is added to both a drive panel and a compensation panel in a state where no voltage is applied.

FIG. 3 is an exploded perspective view of a voltage application state in an example in which dichroic dyes are added to both the drive panel and the compensation panel.

FIG. 4 is a perspective view illustrating the effects of n-type and p-type dichroic dyes.

FIG. 5 is an exploded perspective view of an embodiment in which only a p-type dichroic dye is used and no dichroic dye is required to be added to the drive panel in a state where no voltage is applied.

FIG. 6 is an exploded perspective view of a voltage application state in an example in which only a p-type dichroic dye is used and there is no need to add a dichroic dye to the drive panel.

FIG. 7 is a cross-sectional view illustrating the cross-sectional structures of a drive panel and a compensation panel.

FIG. 8 is a diagram showing the effect of the angle between liquid crystal molecules and incident light.

FIG. 9 is a diagram showing the function of a conventional TN type liquid crystal panel.
(a) shows a state in which the applied voltage is 0, (b) shows a state in which the applied voltage is medium, and (c) shows a state in which the applied voltage is high.

[Explanation of symbols]

1 Liquid crystal molecules 2 Incident light 3, 4 Glass substrates 5, 6 Obliquely incident light L Incident/transmitted light (polarization plane) 7 Incident (side) polarizing plate 7a Transmission axis of input polarizing plate 8 Output (side) polarizing plate 8a Transmission axis 9 of output polarizing plate Drive panel 9i Liquid crystal molecules 9 on the input polarizing plate side of the drive panel
o Liquid crystal molecules 10 on the compensation panel side of the drive panel
Compensation panel 10i Liquid crystal molecules 1 on the driving panel side in the compensation panel
0o Liquid crystal molecules 11 on the output polarizing plate side of the compensation panel
P-type dichroic dye (molecules) 12 N-type dichroic dye (molecules) 13 Progress state of transmitted light in the drive panel 14
Progress of transmitted light in compensation panel

Claims (4)

[Claims] Claim 1: Two TN-type liquid crystal panels with opposite twist directions are stacked between a pair of polarizing plates (7) and (8), and the light incident side is used as a drive panel (9) to emit light. The side is the compensation panel (10), and the two liquid crystal panels (
9) The nearest neighbor molecule of liquid crystal molecules between (10) (9o) (1
A p-type dichroic dye is added to the liquid crystal of the drive panel (9), and an n-type dichroic dye is added to the liquid crystal of the compensation panel (10). A liquid crystal display device characterized in that it is made by adding. 2. The polarization directions of the pair of polarizing plates (7) and (8) are orthogonal to each other, and the orientation direction of the liquid crystal molecules (9i) close to the incident polarizing plate (7) of the drive panel (9). and the transmission axis (7a) of the incident polarizing plate (7) are parallel,
and the alignment direction of the liquid crystal molecules (10o) close to the output polarizing plate (8) of the compensation panel (10) and the output polarizing plate (8).
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is configured such that the transmission axis (8a) of the liquid crystal display device is parallel to the transmission axis (8a) of the liquid crystal display device. 3. Two TN type liquid crystal panels with opposite twist directions are stacked between a pair of polarizing plates (7) and (8), and the light incident side is used as a driving panel (9), and the light is emitted. The side is the compensation panel (10), and the two liquid crystal panels (
9) The nearest neighbor molecule of liquid crystal molecules between (10) (9o) (1
0i) so that their long axes are perpendicular to each other, no dichroic dye is added to the liquid crystal of the drive panel (9), and a p-type dichroic dye is added to the liquid crystal of the compensation panel (10). A liquid crystal display device characterized by: 4. The polarization directions of the pair of polarizing plates (7) and (8) are orthogonal to each other, and the alignment direction of the liquid crystal molecules (9i) close to the incident polarizing plate (7) of the drive panel (9). and the transmission axis (7a) of the incident polarizing plate (7) are orthogonal to each other,
and the alignment direction of the liquid crystal molecules (10o) close to the output polarizing plate (8) of the compensation panel (10) and the output polarizing plate (8).
4. The liquid crystal display device according to claim 3, wherein the transmission axis (8a) of the liquid crystal display device is configured to be perpendicular to the transmission axis (8a).