JPH06301006A - Color liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [Purpose] Coloring the transmitted light without using a color filter to increase the light transmittance and sufficiently increase the brightness of the display. [Structure] STN type liquid crystal cell 30 and this liquid crystal cell 30
A pair of polarizing plates 41, 42 arranged in between and a phase plate 40 arranged between the liquid crystal cell 30 and one polarizing plate 41, and the pair of polarizing plates 41, 42.
The transmission axis of was shifted obliquely by a predetermined angle with respect to the optical axis of the phase plate 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device.

[0002]

2. Description of the Related Art As a liquid crystal display device, there is a color liquid crystal display device which can obtain a colored display. FIG. 3 is a cross-sectional view of a conventional color liquid crystal display device. This liquid crystal display device includes a liquid crystal cell 10 having a color filter and a liquid crystal cell 1.
It is composed of a pair of polarizing plates 21 and 22 which are arranged with 0 interposed therebetween.

The liquid crystal cell 10 has transparent electrodes 13 and 14
And a pair of upper and lower transparent substrates 11 and 12 on which the alignment films 15 and 16 are formed are bonded to each other via a frame-shaped sealing material 18, and are surrounded by the sealing material 18 between the two substrates 11 and 12. A liquid crystal 19 is sealed in a closed region. One substrate of the liquid crystal cell 10, for example, the lower substrate 12 in the figure,
A color filter 17 for coloring the transmitted light is provided.

The color filter 17 is provided on the substrate 12
The transparent electrode 14 on the substrate 12 side is formed on a protective film (not shown) that covers the color filter 17. Further, as the liquid crystal cell 10,
Generally, the molecules 19a of the liquid crystal 19 are twist-aligned between the substrates 11 and 12 at a twist angle of about 90 °.
N (Twisted Nematic) type is used.

The pair of polarizing plates 21 and 22 are arranged such that their transmission axes are substantially parallel to each other, and the transmission axes of these polarizing plates 21 and 22 are liquid crystal on one substrate side of the liquid crystal cell 10. It is almost parallel to the molecular orientation direction.

There are two types of liquid crystal display devices, a transmissive type and a reflective type in which a reflecting plate is arranged on the back surface.
A color liquid crystal display device equipped with a color filter is generally
It is of a transmissive type as shown in FIG.

In the color liquid crystal display device, a light source (not shown) is arranged on the back surface side thereof, and both substrates 1 of the liquid crystal cell 10 are arranged.
The display is driven by applying a voltage between the electrodes 13 and 14 of Nos. 1 and 12, and the light from the light source is linearly polarized by the polarizing plate 22 on the incident side (the lower side in FIG. 3) to the liquid crystal cell 10. Incident.

The linearly polarized light that has entered the liquid crystal cell 10 passes through the color filter 17 and the liquid crystal layer, and the liquid crystal cell 1
0 is emitted, but in that case, light having a wavelength other than the wavelength band corresponding to the color of the color filter 17 is absorbed by the color filter 17, so that the light emitted from the liquid crystal cell 10 is colored in the color of the color filter 17. Become light.

When no voltage is applied between the electrodes 13 and 14 of the liquid crystal cell 10, that is, when the liquid crystal molecules 19a are twist-aligned, the light passing through the liquid crystal cell 10 is polarized by the liquid crystal 19. Since the linearly polarized light in the direction substantially orthogonal to the linearly polarized light that has entered the liquid crystal cell 10 when it has finished passing through the liquid crystal layer, the linearly polarized light that has exited the liquid crystal cell 10 at this time is the exit side (upper side in FIG. 3). Polarizing plate 2
1 is absorbed, and the display is in a dark (black) state.

On the other hand, when a voltage is applied between the electrodes 13 and 14 of the liquid crystal cell 10, the liquid crystal molecules 19a rise and orient substantially vertically to the surfaces of the substrates 11 and 12, and the polarization effect of the liquid crystal 19 is almost eliminated. The linearly polarized light that has entered the cell 10 exits the liquid crystal cell 10 as it is. And
At this time, the linearly polarized light emitted from the liquid crystal cell 10 is transmitted through the emission side polarizing plate 21, and the display becomes a bright display of the color colored by the color filter 17.

[0011]

However, since the above-mentioned conventional color liquid crystal display device colors the transmitted light by using the color filter 17, it has a problem that the light transmittance is low and therefore the display is dark. There is.

This is due to the absorption of light by the color filter 17. Since the color filter 17 also absorbs light in the wavelength band corresponding to the color with a considerably high absorption rate, coloring through the color filter 17 is performed. The light becomes light in which the amount of light is significantly reduced compared to the light in the wavelength band before entering the color filter 17, and the display becomes dark.

Although the color liquid crystal display device shown in FIG. 3 is of a transmissive type, if a reflection plate is arranged on the back surface of this color liquid crystal display device to form a reflection type device, light is incident from the front side of the device. Since the light reflected by the reflecting plate on the back surface and emitted to the front surface side passes through the color filter 17 twice and the light amount is doubly reduced, the display is considerably darkened and becomes almost unusable as a display device.

It is an object of the present invention to provide a color liquid crystal display device capable of coloring transmitted light without using a color filter to increase the light transmittance and sufficiently increase the display brightness. It is a thing.

[0015]

In the color liquid crystal display device of the present invention, liquid crystal is enclosed between a pair of transparent substrates having transparent electrodes, and the molecules thereof are twist-aligned between the substrates at a twist angle of 180 to 270 °. And a pair of polarizing plates arranged with the liquid crystal cell sandwiched therebetween, and a phase plate arranged between the liquid crystal cell and one of the polarizing plates, and the pair of polarizing plates. The transmission axis of is shifted by a predetermined angle with respect to the optical axis of the phase plate.

[0016]

In this color liquid crystal display device, the transmitted light is colored by the polarization action of the phase plate, and the polarization action of the phase plate and the liquid crystal cell in which the liquid crystal molecules are twist-aligned at a twist angle of 180 to 270 °. The polarized light is used to color the transmitted light into another color, and the linearly polarized light that enters the phase plate through one polarizing plate becomes elliptically polarized light due to the polarization effect of the phase plate in the process of passing through this phase plate. Therefore, of this elliptically polarized light, only the wavelength light of the polarization component that passes through the other polarizing plate passes through this polarizing plate and becomes colored light.

In the liquid crystal display device, the light incident through one of the polarizing plates passes through the phase plate and the liquid crystal cell, so that no voltage is applied between the electrodes of the liquid crystal cell, that is, the liquid crystal. When the molecules of the liquid crystal of the cell are twisted, the transmitted light is also polarized by the liquid crystal cell, and the light transmitted through the other polarizing plate is a light of a different color from the colored light by the polarization of the phase plate. become.

When a voltage is applied between the electrodes of the liquid crystal cell, the polarization effect of the liquid crystal cell changes in response to the change of the alignment state of the liquid crystal molecules, so that the polarization effects of both the phase plate and the liquid crystal cell are changed. When the color of the colored light due to changes due to the liquid crystal molecules rises almost perpendicularly to the substrate surface, the polarization effect due to the liquid crystal cell is almost eliminated, and the light transmitted through the other polarizing plate is It becomes colored light only by the polarization effect.

Therefore, according to the color liquid crystal display device of the present invention, the transmitted light can be colored without using a color filter as in the conventional liquid crystal display device, and therefore, the amount of the colored light is incident on the display device. The amount of light in the wavelength band that becomes the colored light out of the
By increasing the light transmittance, the brightness of the display can be sufficiently increased.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a color liquid crystal display device. This color liquid crystal display device includes a liquid crystal cell 30.
A pair of polarizing plates 41, 42 are arranged so as to be sandwiched, and a phase plate 40 is arranged between the liquid crystal cell 30 and one polarizing plate (the upper polarizing plate in this embodiment) 41. There is. The liquid crystal display device of this embodiment is of a reflective type, and a reflection plate 43 is arranged on the back surface (lower surface of the lower polarizing plate 42) thereof.

The liquid crystal cell 30 is of STN (Super Twisted Nematic) type. That is, in this liquid crystal cell 30, a pair of upper and lower transparent substrates 31 and 32, on which transparent electrodes 33 and 34 are formed and alignment films 35 and 36 are formed on the transparent electrodes 33 and 34, are joined together through a frame-shaped sealing material 37. A liquid crystal 38 is sealed in a region surrounded by the sealing material 37 between the substrates 31 and 32.
8a is 180 to 270 between both substrates 31 and 32.
Twisted at a twist angle of °.

The phase plate 40 has its optical axis (fast axis or slow axis) inclined at a predetermined angle with respect to the liquid crystal molecule alignment direction on the phase plate adjacent substrate (upper substrate) 31 side of the liquid crystal cell 30. The pair of polarizing plates 41 and 42 are arranged such that their transmission axes are slanted by a predetermined angle with respect to the optical axis of the phase plate 40.

FIG. 2 shows the alignment direction of liquid crystal molecules of the liquid crystal cell 30 and the optical axis of the phase plate 40 in the liquid crystal display device.
FIG. 4 is a plan view showing transmission axes of a pair of polarizing plates 41 and 42, in which 31a indicates a liquid crystal molecule alignment direction on the upper substrate 31 side of the liquid crystal cell 30, and 32a indicates a liquid crystal molecule alignment direction on the lower substrate 32 side. ing.

As shown in FIG. 2, liquid crystal molecule alignment directions 31a and 32a on both substrates 31 and 32 of the liquid crystal cell 30 are arranged.
Are in the directions inclined by a predetermined angle θ in opposite directions with respect to the reference line (horizontal line in the figure) O, and the molecules 38a of the liquid crystal 38 are
Has a twist orientation from the lower substrate 32 side toward the upper substrate 31 side, as shown by the arrow T in the drawing.

In this embodiment, as the liquid crystal cell 30, the liquid crystal molecule alignment directions 31a, 3 on both substrates 31, 32 side are arranged.
The angle θ between 2a and the reference line O is 30 °, and the liquid crystal molecules 38a are twist-aligned at a twist angle of 240 °. Further, in FIG. 2, 40a is the optical axis of the phase plate 40, and here the slow phase is used. The axis is shown. 41a is a transmission axis of the upper polarizing plate 41, and 42a is a transmission axis of the lower polarizing plate 22.

In this embodiment, the phase plate 40 is used.
With respect to the reference line O by a predetermined tilt angle ψ
Therefore, the phase plate 40
The slow axis 40a of the liquid crystal cell 30 and the liquid crystal molecule orientation direction 31a of the liquid crystal cell 30 on the phase plate adjacent substrate 31 side are deviated by ψ−θ °.

Further, in this embodiment, both polarizing plates 41 and 4 are
The two transmission axes 41a and 42a are made substantially parallel to each other, and the transmission axes 41a and 42a of the polarizing plates 41 and 42 are
Are shifted obliquely by 45 ° with respect to the slow axis 40a of the phase plate 40.

In the above color liquid crystal display device, the transmitted light is colored by the polarization effect of the phase plate 40, and the polarization effect of the phase plate 40 and the liquid crystal molecules 38a are twist-aligned at a twist angle of 240 °. Liquid crystal cell 30
The polarized light causes the transmitted light to be colored in another color.

First, the coloring of the transmitted light due to the polarization effect of the phase plate 40 will be described. External light (natural light or light from an illumination light source) is linearly polarized by the upper polarizing plate 41, and this upper polarizing plate is used. The slow axis 40a is deviated from the transmission axis 41a of the beam 41 by approximately 45 ° and enters the phase plate 40. In the process of passing through the phase plate 40, the phase plate 40 is polarized by the retardation Re according to the value of Re. It becomes elliptically polarized light.

When the elliptically polarized light emitted from the phase plate 40 is directly transmitted through the liquid crystal cell 30 and is incident on the lower polarization plate 42, only the wavelength light of the polarization component which is transmitted through the lower polarization plate 42 among the elliptically polarized light is transmitted. Since the light passes through the lower polarizing plate 42, the light (linearly polarized light) that has passed through the lower polarizing plate 42 becomes colored light.

Next, the coloring of the transmitted light due to the polarization effect of the liquid crystal cell 30 will be described. In this liquid crystal display device, the light incident through the upper polarizing plate 41 passes through the phase plate 40 and liquid crystal molecules. Since it passes through the liquid crystal cell 30 which is twist-aligned at a twist angle of 240 °, no voltage is applied between the electrodes 33 and 34 of the substrates 31 and 32 of the liquid crystal cell 30, that is, the liquid crystal molecules 38a are twist-aligned. In the state in which the transmitted light is transmitted, the transmitted light is subjected to the polarization effect according to the retardation value of the liquid crystal cell 30.

That is, the slow axis 40a of the phase plate 40
Since the liquid crystal molecule alignment direction 31a on the phase plate adjacent substrate (upper substrate) 31 side of the liquid crystal cell 30 is obliquely deviated by a predetermined angle (φ−θ °), the phase plate 40 passes through the phase plate 40. The light that has become elliptically polarized light by the polarization action of is further changed in polarization state while passing through the liquid crystal layer of the liquid crystal cell 30.

Therefore, when no voltage is applied to the liquid crystal cell 30, the light transmitted through the lower polarizing plate 42 becomes colored light of a different color from the colored light due to the polarization effect of the phase plate 40. The color of the colored light at this time is determined by the retardation Re of the phase plate 40 and the retardation of the liquid crystal cell 30.

The retardation Re of the phase plate 40 is
Is Δn · d of the phase plate 40 (refractive index anisotropy Δn of the phase plate
And the plate thickness d), the retardation of the liquid crystal cell 30 is Δn · d of the liquid crystal cell 30 (the product of the refractive index anisotropy Δn of the liquid crystal 38 and the liquid crystal layer thickness d) and the liquid crystal molecule 30a.
It depends on the twist angle of.

The electrodes 33 and 34 of the liquid crystal cell 30 are also provided.
When a voltage is applied between the liquid crystal molecules 38a, the liquid crystal molecules 38a rise from the twist alignment state to the rising alignment as the applied voltage rises, and the polarization in the liquid crystal cell 30 corresponds to the change in the alignment state of the liquid crystal molecules 38a. Since the action changes, the color of the colored light due to the polarization action of both the phase plate 40 and the liquid crystal cell 30 changes.

Further, the liquid crystal molecules 38a are attached to the substrates 31, 32.
When the liquid crystal cell 30 rises almost vertically to the surface, the polarization effect of the liquid crystal cell 30 is almost eliminated, and the lower polarizing plate 4
The light that has passed through 2 becomes colored light due to only the polarization effect of the phase plate 40 described above.

That is, the retardation of the liquid crystal cell 30 is determined by the Δn · d of the liquid crystal cell 30 and the twist angle of the liquid crystal molecules 30a as described above, but the birefringence phase difference Δn of the liquid crystal 38 is determined by applying a voltage. The liquid crystal molecules 3a become smaller as the molecules 38a are vertically aligned,
When 8a rises vertically, it becomes "0" and Δn
Since d = 0 and the twist angle of the liquid crystal molecule 30a finally becomes 0 ° (vertical state), the retardation of the liquid crystal cell 30 finally becomes "0".

When a voltage for vertically aligning the liquid crystal molecules 38a is applied to the liquid crystal cell 30, the retardation of the liquid crystal cell 30 becomes "0" and the polarization effect by the liquid crystal cell 30 disappears, so that the phase plate 40 is used. The elliptically polarized light that has exited is transmitted through the liquid crystal cell 30 as it is, and the lower polarization plate 42
The light that is incident on the lower polarizing plate 42 and is transmitted to the phase plate 4
It becomes colored light only by the polarization action of 0.

Further, the light passing through the lower polarizing plate 42 is reflected by the reflecting plate 43 and is emitted to the upper surface side of the display device in a route opposite to the above-mentioned optical route, so that the display by the color of the emitted light is performed. can get.

Therefore, according to the color liquid crystal display device described above, the transmitted light can be colored without using a color filter as in the conventional color liquid crystal display device, and thus the amount of the colored light is incident on the display device. Since it is almost the same as the amount of light in the wavelength band that becomes pre-colored light,
By increasing the light transmittance, the brightness of the display can be sufficiently increased.

That is, in the conventional color liquid crystal display device, the amount of colored light passing through the color filter is considerably reduced as compared with the amount of light in the wavelength band which becomes colored light in the light incident on the display device. In the color liquid crystal display device,
Such a decrease in light amount hardly occurs. For this reason,
Even if the color liquid crystal display device of the above embodiment is a reflection type, the display brightness is sufficient.

Further, in the conventional color liquid crystal display device, the display color is determined by the color of the color filter, but in the color liquid crystal display device of the above embodiment, the phase plate 40 is used.
Light due to the polarization effect of the phase plate 40 and the liquid crystal cell 30.
And colored light due to both polarization effects are obtained, and the colors of the colored light due to both polarization effects are obtained.
Since it changes according to the applied voltage to 0, the display color can be arbitrarily changed.

The following [Table 1] to [Table 4] show display examples of the color liquid crystal display device. The numerical values shown in each table are all approximate values, and the applied voltage values are effective values. The display color is a color when the display of the liquid crystal display device is viewed from the vertical direction.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

As shown in [Table 1] to [Table 4], the color liquid crystal display device can display at least three or more colors by controlling the voltage applied to the liquid crystal cell 30. Yes, in particular, in the example of [Table 4], it is possible to perform colored display of four colors.

In the above embodiment, the liquid crystal display element 30 is used.
As the liquid crystal molecule 38a, a liquid crystal molecule having a twisted orientation at a twist angle of 240 ° was used.
The liquid crystal molecule twist angle may be arbitrarily selected in the range of 180 to 270 °.

Further, in the above embodiment, the polarizing plates 41 and 42 are
The transmission axes 41a and 42a of the
It is shifted by about 45 ° with respect to the polarizing plates 41, 42.
The transmission axes 41a and 42a may be displaced with respect to the fast axis of the phase plate 40, and in that case, the same effect as that of the above embodiment can be obtained.

Further, in the above embodiment, the polarizing plates 41, 4
Although the two transmission axes 41a and 42a are substantially parallel to each other,
The transmission axes 41a and 42a of the polarizing plates 41 and 42 may be substantially orthogonal to each other.

In the above embodiment, the phase plate 40 is arranged between the liquid crystal cell 30 and the upper polarizing plate 41, but the phase plate 40 is arranged between the liquid crystal cell 30 and the lower polarizing plate 42. Good. Further, the number of phase plates is not limited to one, and a plurality of phase plates may be used. In that case, a display color corresponding to the total retardation of the plurality of phase plates can be obtained. When using a plurality of phase plates, these phase plates may be distributed and arranged above and below the liquid crystal cell 30. The present invention can be applied not only to the reflective type but also to a transmissive type liquid crystal display device.

[0053]

The color liquid crystal display device of the present invention is a liquid crystal cell in which liquid crystal is enclosed between a pair of transparent substrates having transparent electrodes and the molecules of the liquid crystal molecules are twist-aligned between the substrates at a twist angle of 180 to 270 °. And a pair of polarizing plates arranged across the liquid crystal cell, and a phase plate arranged between the liquid crystal cell and one polarizing plate, and the transmission axes of the pair of polarizing plates are Since the phase plate is shifted obliquely at a predetermined angle with respect to the optical axis, the transmitted light is colored without using a color filter to increase the light transmittance and display brightness. Can be high enough.

[Brief description of drawings]

FIG. 1 is a sectional view of a color liquid crystal display device showing an embodiment of the present invention.

FIG. 2 is a plan view showing an alignment direction of liquid crystal molecules of a liquid crystal cell, a slow axis of a phase plate, and a transmission axis of a pair of polarizing plates according to an embodiment of the present invention.

FIG. 3 is a sectional view of a conventional color liquid crystal display device.

[Explanation of symbols]

 30 ... Liquid crystal cell 31, 32 ... Transparent substrate 31a, 32a ... Liquid crystal molecule alignment direction 33, 34 ... Transparent electrode 35, 36 ... Alignment film 38 ... Liquid crystal 38a ... Liquid crystal molecule 40 ... Phase plate 40a ... Slow axis 41, 42 ... Polarizing plates 41a, 42a ... Transmission axis 43 ... Reflector

Claims (1)

[Claims] 1. A liquid crystal is sealed between a pair of transparent substrates on which transparent electrodes are formed, and molecules of the liquid crystal are enclosed between the substrates in a range of 180 to 270.
A liquid crystal cell twist-aligned at a twist angle of °, a pair of polarizing plates arranged across the liquid crystal cell, and a phase plate arranged between the liquid crystal cell and one polarizing plate, A color liquid crystal display device, wherein the transmission axes of the pair of polarizing plates are slanted at a predetermined angle with respect to the optical axis of the phase plate.