JPH06308481A - Color liquid crystal display device - Google Patents

Abstract

PURPOSE:To make the brightness of display very high by coloring transmitted light without using a color filter and making the light transmissivity high. CONSTITUTION:The device is provided with a liquid crystal cell 30 obtained by sealing liquid crystal 38 between a pair of transparent substrates 31 and 32 on which transferent electrodes 33 and 34 are formed, and making a molecule 38a twisted and oriented; a polarizing plate 40; and a reflector 41. The polarizing plate 40 is arranged on the surface side of the liquid crystal cell 30, the reflector 41 is arranged on the back surface side of the liquid crystal cell 30, and also the transmission axis of the polarizing plate 40 is obliquely deviated at a specified angle with respect to the liquid crystal molecule oriented direction on the side of the substrate 31 adjacent to the polarizing plate on the liquid crystal cell 30.

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. 4 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 the electrodes 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. 4) and is incident on 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. , The linearly polarized light in a 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. 4). 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. 4 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]

A color liquid crystal display device of the present invention comprises a liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates having transparent electrodes and the molecules of which are twist-aligned between the substrates. Polarizing plate and a reflecting plate, the polarizing plate is arranged on the front surface side of the liquid crystal cell, the reflecting plate is arranged on the rear surface side of the liquid crystal cell, and the transmission axis of the polarizing plate is the liquid crystal cell. Of the polarizing plate adjacent to the polarizing plate, the liquid crystal molecules are obliquely displaced by a predetermined angle with respect to the alignment direction. In the present invention, it is desirable that the deviation angle between the transmission axis of the polarizing plate and the liquid crystal molecule alignment direction on the polarizing plate adjacent substrate side of the liquid crystal cell is 45 ± 5 °.

[0016]

This color liquid crystal display device is of a reflection type in which light incident from the front surface side is reflected by the reflection plate on the rear surface side and displayed. The incident light from the front surface side is reflected by the polarizing plate and the liquid crystal cell. The light passes through the liquid crystal cell and the polarizing plate and is emitted again.

In this color liquid crystal display device, since the transmission axis of the polarizing plate and the liquid crystal molecule alignment direction on the side of the liquid crystal cell adjacent to the polarizing plate are obliquely displaced by a predetermined angle, the liquid crystal molecules of the liquid crystal cell are twisted. In the state of
The linearly polarized light that has entered the liquid crystal cell through the polarizing plate becomes elliptically polarized light due to the polarization action of this liquid crystal cell in the process of passing through the liquid crystal cell, and its polarization state is reflected in the process of passing through the liquid crystal cell again after being reflected by the reflector. The light that has been further changed and has been subjected to the polarization effect twice by the liquid crystal cell is incident on the polarizing plate.

Further, when a voltage is applied between the electrodes of the liquid crystal cell, the polarization effect of the liquid crystal cell changes due to the change of the alignment state of the liquid crystal molecules. When light with a polarization state different from that in the non-applied state enters the polarizing plate, and when the liquid crystal molecules rise almost vertically, the polarization effect of the liquid crystal cell is almost eliminated, and the linearly polarized light entering through the polarizing plate is The liquid crystal cell passes through the liquid crystal cell twice in the polarization state and enters the polarizing plate.

If the light incident on the polarizing plate is the same linearly polarized light as at the time of incidence, all wavelength light is transmitted through the polarizing plate, and at this time, the emitted light becomes uncolored light and is incident on the polarizing plate. When the light to be emitted is non-linearly polarized light, only the light having the wavelength of the polarization component that passes through the polarizing plate passes through the polarizing plate, and the emitted light becomes colored light.

Therefore, according to the color liquid crystal display device of the present invention, it is possible to color transmitted light without using a color filter as in the conventional liquid crystal display device, and therefore the amount of 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.

[0021]

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 one liquid crystal cell 30 in which liquid crystal molecules are twisted and one polarizing plate 40.
And one reflecting plate 41, and the polarizing plate 4
0 is arranged on the front surface side of the liquid crystal cell 30, and
Is arranged on the back surface side of the liquid crystal cell 30. In this example, a TN type liquid crystal cell 30 is used.

The TN type liquid crystal cell 30 has a transparent electrode 3
3, 34, and a pair of upper and lower transparent substrates 31, 32 on which horizontal alignment films 35, 36 are formed.
7 and the liquid crystal 38 is sealed in a region surrounded by the sealing material 37 between the substrates 31 and 32.
The horizontal alignment films 35 and 36 on the substrates 31 and 32 are aligned in a direction substantially orthogonal to each other, and the molecules 38a of the liquid crystal 38 are twist-aligned between the substrates 31 and 32 at a twist angle of about 90 °. ing.

The polarizing plate 40 is adhered to the outer surface of a front surface side substrate (hereinafter referred to as an upper substrate) 31 of the liquid crystal cell 30, and the reflection plate 41 is a rear surface side substrate (hereinafter referred to as a lower substrate) 32 of the liquid crystal cell 30. The polarizing plate 40 is arranged so that its transmission axis is slanted at a predetermined angle with respect to the liquid crystal molecule alignment direction on the polarizing plate adjacent substrate (upper substrate) 31 side of the liquid crystal cell 30. .

FIG. 2 is a plan view showing the alignment direction of the liquid crystal molecules of the liquid crystal cell 30 and the transmission axis of the polarizing plate 40.
Reference symbol a is a liquid crystal molecule alignment direction on the upper substrate 31 side of the liquid crystal cell 30, and reference symbol 32a is a liquid crystal molecule alignment direction on the lower substrate 32 side of the liquid crystal cell 30.

As shown in FIG. 2, the liquid crystal molecule alignment directions 31a and 32a on both substrates 31 and 32 side of the liquid crystal cell 30.
Are deviated from each other by approximately 90 °, and the molecules 38a of the liquid crystal 38 are
As shown by an arrow T in the figure, the twist direction is twisted counterclockwise in the figure from the lower substrate 32 side to the upper substrate 31 side at a twist angle of approximately 90 °.

Further, in FIG. 2, reference numeral 40a denotes a polarizing plate 40.
In this embodiment, the deviation angle ψ between the transmission axis 40a of the polarizing plate 40 and the liquid crystal molecule alignment direction 31a on the polarizing plate adjacent substrate 31 side of the liquid crystal cell 30 is 45 °.

This color liquid crystal display device is of a reflection type in which light incident from the front surface side (natural light or light from an illumination light source) is reflected by the reflection plate 41 on the rear surface side and displayed. Incident light is generated by the polarizing plate 40 and the liquid crystal cell 30.
The liquid crystal cell 30 is again reflected by the reflection plate 41 and passes through the liquid crystal cell 30.
And goes out through the polarizing plate 41. In addition, this color liquid crystal display device includes electrodes 3 of both substrates 31 and 32 of the liquid crystal cell 30.
A display is driven by applying a voltage between 3 and 34.

In this color liquid crystal display device, the transmission axis 40a of the polarizing plate 40 and the liquid crystal molecule alignment direction 30a of the liquid crystal cell 30 on the polarizing plate adjacent substrate 31a side are obliquely displaced by a predetermined angle. When the molecules 38a of the liquid crystal 38 are twist-aligned, the polarizing plate 40
The linearly polarized light that has entered the liquid crystal cell 30 through the liquid crystal cell 30 becomes elliptically polarized light due to the polarization effect of the liquid crystal cell 30 in the process of passing through the liquid crystal cell 30, and is reflected by the reflection plate 41 and again in the process of passing through the liquid crystal cell 30. The polarization state changes further,
Light that has been polarized by the liquid crystal cell 30 twice enters the polarizing plate 40.

Further, when a voltage is applied between the electrodes 33 and 34 of the liquid crystal cell 30, the alignment state of the liquid crystal molecules 38a changes from the twist alignment state to rise alignment with respect to the surfaces of the substrates 31 and 32, and accordingly. Since the polarization effect of the liquid crystal molecules 38a changes, the light that has been subjected to the polarization effect twice by the liquid crystal cell 30 enters the polarizing plate 40 as light having a polarization state different from the state in which no voltage is applied.

Further, when the liquid crystal molecules 38a rise almost vertically, the polarization effect of the liquid crystal cell 30 is almost eliminated, and the linearly polarized light incident through the polarizing plate 40 passes through the liquid crystal cell 30 twice in the polarization state. It enters the polarizing plate 40.

That is, the polarization action of the liquid crystal cell 30 in which the liquid crystal molecules 38a are twisted is determined by the product Δn · d of the refractive index anisotropy Δn of the liquid crystal 38 and the liquid crystal layer thickness d, and the liquid crystal molecules 38.
Although it depends on the twist angle of a, the refractive index anisotropy Δn of the liquid crystal 38 is apparently the liquid crystal molecule 3 when the voltage is applied.
8a becomes smaller as the liquid crystal molecules 38a are vertically aligned and becomes "0" when the liquid crystal molecules 38a are vertically aligned, so that the value of Δn · d of the liquid crystal cell 30 finally becomes "0". The polarization effect of the liquid crystal cell 30 disappears.

If the light incident on the polarizing plate 40 is the same linearly polarized light as at the time of incidence, all wavelength light is transmitted through the polarizing plate 40, and at this time, the outgoing light becomes uncolored light, and When the light incident on 40 is non-linearly polarized light,
Of the light, only the wavelength light of the polarization component that passes through the polarizing plate 40 passes through this polarizing plate 40, and the emitted light becomes colored light.

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. Therefore, 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,
The color liquid crystal display device of the above embodiment is of a reflection type, but its display brightness is sufficient. The brightness of the display in the color liquid crystal display device will be described. The intensity I of light emitted from the display device is expressed by the following equation (1).

[0035]

[Equation 1]

The value of the light intensity I obtained by the equation (1) is
In white display, that is, the liquid crystal molecules 38 of the liquid crystal cell 30.
When a is vertically orientated and the emitted light becomes uncolored light, it is 1/2 of the intensity of all wavelength light (visible light) incident on the display device, and this light intensity I is in the visible light band. Since it is uniform in all wavelengths of light, the brightness of white display of a normal TN type liquid crystal display device (transmission type device in which a pair of polarizing plates are arranged with a TN type liquid crystal cell sandwiched therebetween) without a color filter is A bright display is also obtained.

That is, the intensity I'of the emitted light in the above-mentioned normal TN type liquid crystal display device is expressed by the following equation (2),
The light intensity I'in white display is I = 1/2 for light of a certain wavelength, but I <1/2 for light of other wavelengths.
Becomes

[0038]

[Equation 2]

On the other hand, the light intensity I in white display of the color liquid crystal display device is I = 1/2 for all wavelength light as described above, and therefore the brightness of white display is , Which is brighter than the brightness of white display of a normal TN type liquid crystal display device.

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 liquid crystal cell 3 is used.
By controlling the applied voltage to 0, the liquid crystal cell 3
The colored light obtained by the polarization action of 0 can be changed.

FIG. 3 is a CIE chromaticity diagram of the above-mentioned color liquid crystal display device, and here shows the chromaticity when the value of Δn · d of the liquid crystal cell 30 is Δn · d = 900 nm.
As shown in this chromaticity diagram, the display color of the color liquid crystal display device is in the state of no voltage, that is, the state in which the liquid crystal molecules 38a are twist-aligned as the voltage applied to the liquid crystal cell 30 is increased. Changes from the initial display color in Fig. 3 to the final display color "white" in the maximum voltage state, that is, in the state where the liquid crystal molecules 38a are vertically oriented and aligned. The display color has high purity.

The value of Δn · d of the liquid crystal cell 30 is Δn.
D = 900 nm, the liquid crystal molecule twist angle is 90 °, and the shift angle ψ between the transmission axis 40a of the polarizing plate 40 and the liquid crystal molecule alignment direction 30a on the polarizing plate adjacent substrate 41a side of the liquid crystal cell 30.
Is 45 °, when the liquid crystal molecules 38a are twist-aligned, the liquid crystal cell 30 is provided on the back side (reflector plate 41).
The light that becomes elliptically polarized light in the process of passing toward the side) is close to the linearly polarized light when it enters through the polarizing plate 40 in the process of passing toward the surface side (polarizing plate 40 side) of the liquid crystal cell 30. It becomes linearly polarized light.

Therefore, in this color liquid crystal display device, the initial display color is "almost white" in the state where the liquid crystal molecules 38a are homogeneously aligned and the voltage is zero, and the display color corresponding to the higher voltage is displayed. Change is almost white (initial display color) →
Green → blue → yellow → white (final display color).

Therefore, the color liquid crystal display device is
By controlling the voltage applied to the liquid crystal cell 30, the display color can be arbitrarily changed to each of the above colors. Further, the color liquid crystal display device includes one liquid crystal cell 30 in which liquid crystal molecules are twist-aligned, and one polarizing plate 40,
Since it is composed of only three elements, one reflecting plate 41, the structure is simple and can be obtained at low cost.

In the above embodiment, the shift angle ψ between the transmission axis 40a of the polarizing plate 40 and the liquid crystal molecule alignment direction 31a of the liquid crystal cell 30 on the side of the polarizing plate adjacent substrate 31 is 45 °. Is not limited to 45 ° and can be arbitrarily selected. However, in order to sufficiently obtain the coloring effect of the liquid crystal cell 30, it is desirable that the shift angle ψ be 45 ± 5 °.

In the above embodiment, the liquid crystal cell 30 is of the TN type in which the twist angle of the liquid crystal molecules is approximately 90 °, but this liquid crystal cell has 180 to 80 liquid crystal molecules.
An STN (Super Twisted Nematic) type in which twist orientation is performed at a twist angle of 27 ° may be used.

[0047]

The color liquid crystal display device of the present invention includes a liquid crystal cell in which liquid crystal is enclosed between a pair of transparent substrates having transparent electrodes and the molecules of which are twist-aligned, a polarizing plate, and a reflector. The polarizing plate is disposed on the front surface side of the liquid crystal cell, the reflector is disposed on the back surface side of the liquid crystal cell, and the transmission axis of the polarizing plate is a liquid crystal on the polarizing plate adjacent substrate side of the liquid crystal cell. Since the light is shifted obliquely by a predetermined angle with respect to the molecular orientation direction, the transmitted light can be colored to increase the light transmittance without using a color filter, and the display brightness can be sufficiently increased.

[Brief description of drawings]

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

FIG. 2 is a plan view showing a liquid crystal molecule alignment direction of a liquid crystal cell and a transmission axis of a polarizing plate according to an embodiment of the present invention.

FIG. 3 is a CIE chromaticity diagram of a color liquid crystal display device according to an embodiment of the present invention.

FIG. 4 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 ... Polarizing plate 40a ... Transmission axis 41 ... Reflector plate

Claims (2)

[Claims] 1. A liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates having transparent electrodes and the molecules of which are twist-aligned between the substrates, a polarizing plate, and a reflection plate. A plate is arranged on the front surface side of the liquid crystal cell, the reflection plate is arranged on the back surface side of the liquid crystal cell, and the transmission axis of the polarizing plate is with respect to the liquid crystal molecule alignment direction on the polarizing plate adjacent substrate side of the liquid crystal cell. A color liquid crystal display device characterized by being slanted by a predetermined angle. 2. The deviation angle between the transmission axis of the polarizing plate and the alignment direction of liquid crystal molecules on the side of the liquid crystal cell adjacent to the polarizing plate is 45 ± 5 °.
The color liquid crystal display device according to claim 1, wherein