JP3289386B2 - Color liquid crystal display - Google Patents

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.

[0002]

2. Description of the Related Art As a liquid crystal display device, there is a color liquid crystal display device capable of obtaining a colored display. FIG. 3 is a cross-sectional view of a conventional color liquid crystal display device. The liquid crystal display device includes a liquid crystal cell 10 having a color filter and a liquid crystal cell 1 having a color filter.
It comprises a pair of polarizing plates 21 and 22 sandwiched between 0.

The liquid crystal cell 10 has transparent electrodes 13 and 14.
And a pair of upper and lower transparent substrates 11 and 12 having alignment films 15 and 16 formed thereon are joined 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 the region indicated by the arrow. One substrate of the liquid crystal cell 10, for example, the lower substrate 12 in the figure,
A color filter 17 for coloring 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) covering the color filter 17. Further, as the liquid crystal cell 10,
In general, T is obtained by twisting molecules 19a of the liquid crystal 19 between the substrates 11 and 12 at a twist angle of about 90 °.
An N (twisted nematic) type is used.

The transmission axes of the pair of polarizing plates 21 and 22 are substantially parallel to each other, and the transmission axes of the polarizing plates 21 and 22 are aligned with the liquid crystal on one substrate side of the liquid crystal cell 10. It is in a direction substantially parallel to the molecular orientation direction.

There are two types of liquid crystal display devices: a transmission type and a reflection type in which a reflection plate is disposed on the back surface.
In general, a color liquid crystal display device having a color filter is
It is of a transmission type as shown in FIG.

In the above-mentioned color liquid crystal display device, a light source (not shown) is arranged on the back side, 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, 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) and is applied to the liquid crystal cell 10. Incident.

Then, the linearly polarized light incident on the liquid crystal cell 10 passes through the color filter 17 and the liquid crystal layer, and
0 is emitted. In this case, since 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, the light emitted from the liquid crystal cell 10 is colored in the color of the color filter 17. It becomes 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 twisted, light passing through the liquid crystal cell 10 is polarized by the liquid crystal 19. When the light passes through the liquid crystal layer, it becomes linearly polarized light in a direction substantially orthogonal to the linearly polarized light that has entered the liquid crystal cell 10. In this case, the linearly polarized light that has exited the liquid crystal cell 10 is on the emission side (upper side in FIG. 3). Polarizer 2
1 and the display becomes dark (black).

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 align almost perpendicular 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 incident on 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 passes through the emission-side polarizing plate 21, and the display becomes a bright display colored by the color filter 17.

[0011]

However, since the above-mentioned conventional color liquid crystal display uses the color filter 17 to color transmitted light, it has a problem that light transmittance is low and display is dark. I have.

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

Although the color liquid crystal display device shown in FIG. 3 is of a transmission type, if a reflection plate is arranged on the back surface of the 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 backside reflection plate and emitted to the front side passes through the color filter 17 twice and reduces the amount of light, the display becomes considerably dark, making it almost unusable as a display device.

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

[0015]

In the color liquid crystal display device of the present invention, a liquid crystal is sealed between a pair of transparent substrates on which transparent electrodes are formed, and molecules of the liquid crystal are twist-aligned between the two substrates at a twist angle of 180 to 270 °. a liquid crystal cell is, a pair of polarizing plates disposed across the liquid crystal cell, the liquid crystal cell
Between the liquid crystal cell and one of the polarizers.
Phase with retardation greater than retardation
A pair of polarizing plates, and the pair of polarizing plates emit the polarizing plates.
Elliptically polarized light by the phase plate and the liquid crystal cell.
And the polarization action of the liquid crystal cell in the elliptically polarized light.
In order to transmit colored light in the corresponding wavelength band, the pair
At a predetermined angle with respect to the slow axis of the phase plate.
It is characterized by being arranged obliquely shifted .

[0016]

In the 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 twisted at a twist angle of 180 to 270 °. The polarized light causes the transmitted light to be colored in another color, and the linearly polarized light that has entered the phase plate through one of the polarizers becomes elliptically polarized light by the polarization effect of the phase plate in the process of passing through the phase plate. Therefore, of the elliptically polarized light, only the light having the wavelength of the polarized light component transmitted through the other polarizing plate is transmitted through the polarizing plate and becomes colored light.

In the above-mentioned liquid crystal display device, since the light incident through one of the polarizing plates passes through the phase plate and the liquid crystal cell, no voltage is applied between the electrodes of the liquid crystal cell. When the liquid crystal molecules of the cell are in a twisted orientation, the transmitted light is also subjected to a polarization action by the liquid crystal cell, and the light transmitted through the other polarizer is a different color light from the colored light due to the polarization action of the phase plate. become.

When a voltage is applied between the electrodes of the liquid crystal cell, the polarization action in the liquid crystal cell changes in response to the change in the alignment state of the liquid crystal molecules. When the color of the colored light is changed, and the liquid crystal molecules rise almost perpendicularly to the substrate surface, the polarization action by the liquid crystal cell is almost eliminated, and the light transmitted through the other polarizing plate is reflected by the above-described phase plate. It becomes colored light only by the polarization action.

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. Since it is almost the same as the amount of light in the wavelength band that becomes the colored light of the light to be emitted,
By increasing the light transmittance, the brightness of the display can be sufficiently increased.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a color liquid crystal display device. This color liquid crystal display device has a liquid crystal cell 30.
A pair of polarizers 41 and 42 are disposed with the phase plate 40 therebetween, and a phase plate 40 is disposed between the liquid crystal cell 30 and one of the polarizers (the upper polarizer in this embodiment) 41. I have. The liquid crystal display device of this embodiment is of a reflection type, and a reflection plate 43 is disposed on the back surface (the lower surface of the lower polarizing plate 42).

The liquid crystal cell 30 is of the STN (super twisted nematic) type. That is, in the liquid crystal cell 30, a pair of upper and lower transparent substrates 31, 32, on which transparent electrodes 33, 34 are formed and alignment films 35, 36 are formed, are joined via 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 between 180 and 270 between the two substrates 31 and 32.
It is twist-oriented at a twist angle of °.

The phase plate 40 has its optic 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 with their transmission axes shifted at a predetermined angle to the optical axis of the phase plate 40.

FIG. 2 shows the orientation of liquid crystal molecules of the liquid crystal cell 30 in the liquid crystal display device, the optical axis of the phase plate 40,
It is a top view which shows the transmission axis of a pair of polarizing plates 41 and 42. In the figure, 31a shows the liquid crystal molecule orientation direction of the upper substrate 31 side of the liquid crystal cell 30, and 32a shows the liquid crystal molecule orientation direction of the lower substrate 32 side. ing.

As shown in FIG. 2, the liquid crystal molecule alignment directions 31a, 32a on both substrates 31, 32 of the liquid crystal cell 30 are shown.
Are inclined in a direction opposite to each other by a predetermined angle θ with respect to a reference line (horizontal line in the figure).
Are twist-oriented from the lower substrate 32 side toward the upper substrate 31 side, as indicated by the arrow T in the drawing.

In this embodiment, as the liquid crystal cell 30, the liquid crystal molecule orientation directions 31a, 3a on both substrates 31, 32 are used.
The angle θ between 2a and the reference line O was 30 °, respectively, and the liquid crystal molecules 38a were twisted at a twist angle of 240 °. In FIG. 2, reference numeral 40a denotes an optical axis of the phase plate 40, 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
At a predetermined inclination angle with respect to the reference line O.
And obliquely intersect with each other.
Is shifted by ψ-θ ° from the liquid crystal molecule alignment direction 31 a of the liquid crystal cell 30 on the side of the phase plate adjacent substrate 31.

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

In the color liquid crystal display device described above, the transmission light is colored by the polarization action of the phase plate 40, and the STN type in which the polarization action of the phase plate 40 and the liquid crystal molecules 38a are twisted at a twist angle of 240 °. Liquid crystal cell 30
The transmitted light is colored in another color by the polarization action of the light.

First, the coloring of the transmitted light by the polarization action 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 The light is incident on the phase plate 40 in which the slow axis 40a is shifted from the transmission axis 41a of the phase plate 41 by approximately 45 °, and undergoes a polarization action according to the value of the retardation Re of the phase plate 40 in the process of passing through the phase plate 40. It becomes elliptically polarized light.

Then, when the elliptically polarized light emitted from the phase plate 40 passes through the liquid crystal cell 30 as it is and enters the lower polarizing plate 42, only the wavelength light of the polarization component transmitted through the lower polarizing plate 42 out of the elliptically polarized light. Since the light passes through the lower polarizing plate 42, light (linearly polarized light) passing through the lower polarizing plate 42 becomes colored light.

Next, the coloring of transmitted light by the polarization action of the liquid crystal cell 30 will be described. In this liquid crystal display device, light incident through the upper polarizing plate 41 causes the phase plate 40 and liquid crystal molecules to pass through. A state in which no voltage is applied between the electrodes 33 and 34 of the substrates 31 and 32 of the liquid crystal cell 30 because the liquid crystal molecules 38a are twisted in alignment with the liquid crystal cell 30 that has been twisted at a twist angle of 240 °. In this state, the transmitted light is subjected to a polarization action according to the value of the retardation of the liquid crystal cell 30.

That is, the slow axis 40a of the phase plate 40
And the liquid crystal molecule orientation direction 31 a of the liquid crystal cell 30 on the side of the phase plate adjacent substrate (upper substrate) 31 is obliquely shifted by a predetermined angle (ψ−θ °). The light that has become elliptically polarized due to the polarization action can further change the 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 having a different color from the colored light due to the polarization action 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 Δn · d of the phase plate 40 (refractive index anisotropy Δn of the phase plate).
And the thickness d of the liquid crystal cell 30, and the retardation of the liquid crystal cell 30 is Δn · d (the product of the refractive index anisotropy Δn of the liquid crystal 38 and the thickness d of the liquid crystal layer) of the liquid crystal cell 30 and the liquid crystal molecules 30 a.
And the twist angle.

The electrodes 33 and 34 of the liquid crystal cell 30 are used.
When a voltage is applied between the liquid crystal molecules 38a, the liquid crystal molecules 38a rise and align from the twist alignment state as the applied voltage increases, 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 formed on the substrates 31, 32.
When the liquid crystal cell 30 rises almost perpendicularly to the surface, the polarizing action by the liquid crystal cell 30 is almost eliminated, and the lower polarizing plate 4
The light transmitted through 2 becomes colored light only due to the polarization action 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. The liquid crystal molecules 3a become smaller as the molecules 38a are aligned in the rising direction.
8a is “0” when the liquid crystal molecules are vertically oriented and Δn
D = 0, and the twist angle of the liquid crystal molecules 30a finally becomes 0 ° (vertical state), so that the retardation of the liquid crystal cell 30 finally becomes “0”.

When a voltage is applied to the liquid crystal cell 30 so that the liquid crystal molecules 38a vertically rise and align, the retardation of the liquid crystal cell 30 becomes "0" and the polarization effect of the liquid crystal cell 30 is eliminated. Is transmitted through the liquid crystal cell 30 as it is and the lower polarizing plate 42
Is incident on the phase plate 4 and transmitted through the lower polarizing plate 42.
It becomes colored light only by the polarization action of 0.

The light passing through the lower polarizing plate 42 is reflected by the reflection plate 43 and exits to the upper surface of the display device through a path opposite to the above-mentioned optical path. can get.

Therefore, according to the above-described color liquid crystal display device, the transmitted light can be colored without using a color filter as in the conventional color liquid crystal display device, and therefore, the amount of the colored light is incident on the display device. Because it is almost the same as the amount of light in the wavelength band that becomes the pre-colored light of the 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 light amount of the colored light passing through the color filter is considerably reduced as compared with the light amount in the wavelength band which becomes the colored light of the light incident on the display device. In a color liquid crystal display,
Such a decrease in the amount of light hardly occurs. For this reason,
Even if the color liquid crystal display device of the above embodiment is of a reflective type, the display brightness is sufficient.

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
The colored light due to the polarization action of the phase plate 40 and the liquid crystal cell 30
And the colored light due to both polarization actions is obtained, and the color of the colored light due to both polarization actions is
Since it changes according to the applied voltage to 0, the display color can be arbitrarily changed.

The following Tables 1 to 4 show display examples of the above-mentioned color liquid crystal display device. The numerical values shown in each table are 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 Tables 1 to 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. In particular, in the example of [Table 4], four-color display can be performed.

In the above embodiment, the liquid crystal display element 30
The liquid crystal molecules 38a are twisted at a twist angle of 240 ° as a liquid crystal display element 30.
May be arbitrarily selected in the range of 180 to 270 °.

In the above embodiment, the polarizing plates 41 and 42 are used.
The transmission axes 41a and 42a of the phase plate 40
Of the polarizing plates 41 and 42,
May be shifted with respect to the fast axis of the phase plate 40, in which case the same effect as in 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 disposed between the liquid crystal cell 30 and the upper polarizing plate 41. However, the phase plate 40 is disposed between the liquid crystal cell 30 and the lower polarizing plate 42. Is also good. The number of phase plates is not limited to one, and a plurality of phase plates may be used. In this case, a display color corresponding to the total retardation of the plurality of phase plates can be obtained. When a plurality of phase plates are used, these phase plates may be distributed above and below the liquid crystal cell 30. The present invention is not limited to the reflection type, but can be applied to a transmission type liquid crystal display device.

[0053]

The color liquid crystal display device according to the present invention comprises a liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates on which transparent electrodes are formed and molecules of which are twist-aligned between the two substrates at a twist angle of 180 to 270 °. And a pair of polarizing plates sandwiching the liquid crystal cell, and the liquid crystal cell and one polarized light.
And a retardation of the liquid crystal cell.
And a phase plate having a larger retardation,
The pair of polarizing plates are arranged such that the linearly polarized light emitted from the polarizing plate is
The phase plate and the liquid crystal cell are used to make elliptically polarized light.
Wavelength band of circularly polarized light according to the polarization action of the liquid crystal cell
In order to transmit the colored light, the transmission of the pair of polarizing plates
Shift the axis at a predetermined angle to the slow axis of the phase plate
Since they are arranged , the transmitted light can be colored without using a color filter to increase the light transmittance, and the display brightness can be sufficiently increased.

[Brief description of the drawings]

FIG. 1 is a cross-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, a slow axis of a phase plate, and a transmission axis of a pair of polarizing plates according to one embodiment of the present invention.

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

[Explanation of symbols]

 Reference Signs List 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: reflection plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 500 G02F 1/1335 G02F 1/13363

Claims (1)

(57) [Claims] A liquid crystal is sealed between a pair of transparent substrates on which a transparent electrode is formed, and molecules of the liquid crystal are interposed between the two substrates.
Liquid crystal cell twist-aligned at a twist angle of °, a pair of polarizing plates sandwiched between the liquid crystal cells, and a liquid crystal cell disposed between the liquid crystal cell and one of the polarizing plates.
Greater than the retardation of the crystal cell
And a pair of polarizing plates , wherein the pair of polarizing plates converts linearly polarized light emitted from the polarizing plate.
The phase plate and the liquid crystal cell are used to make elliptically polarized light.
Wavelength band of elliptically polarized light according to the polarization action of the liquid crystal cell
In order to transmit the colored light in the region, the transmission of the pair of polarizing plates is performed.
Shift the excess axis at a predetermined angle to the slow axis of the phase plate.
A color liquid crystal display device characterized by being arranged in a position .