JP4318794B2 - Transmission type liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmissive liquid crystal display device using a non-absorbing color filter.
[0002]
[Prior art]
For example, as disclosed in JP-A-10-282324, a liquid crystal display color filter using a cholesteric liquid crystal or a chiral nematic liquid crystal has been proposed.
[0003]
This color filter has superior performance in luminance and color purity compared to conventional color filters using pigments and dyes. In particular, there is an advantage that the wavelength of the selectively reflected light changes depending on the temperature, and furthermore, the use of an ultraviolet curable cholesteric liquid crystal capable of maintaining the liquid crystal state by irradiation with ultraviolet rays can be easily manufactured as compared with the conventional case.
[0004]
The cholesteric liquid crystal and chiral nematic liquid crystal as described above have a characteristic that the director spirally changes in space in addition to the long-range alignment order of the liquid crystal molecular axes. That is, in the plane parallel to the liquid crystal molecular axis, the liquid crystal has the same alignment order as the nematic phase, but when moving to the adjacent plane, this local alignment direction is slightly rotated, and this is successively continuous. And has a spiral structure.
[0005]
On the other hand, natural light can be divided into right-handed circularly polarized light and left-handed circularly polarized light. In cholesteric liquid crystal or chiral nematic liquid crystal, both right-handed circularly polarized light and left-handed circularly polarized light are parallel to the spiral axis of the liquid crystal. Is incident on the liquid crystal, it reflects only the circularly polarized light component having the same rotational direction as the twist direction of the liquid crystal, and transmits the other circularly polarized light component.
[0006]
At this time, since the phase of the reflected light does not change with respect to the incident light, the polarization direction before and after the incident of the reflected light is unchanged, and the wavelength of the reflected light is equal to the twist pitch of the cholesteric liquid crystal or chiral nematic liquid crystal. It changes with it. This pitch varies depending on the addition amount of a chiral agent that generates a twisting force in the liquid crystal and an appropriate external field (for example, temperature, electric field, magnetic field, etc.).
[0007]
This pitch can be adjusted by adding a chiral agent having a different turning ability or a chiral agent having an opposite volume. For example, if a left-handed chiral agent is added to a right-handed spirally structured liquid crystal, the reflection wavelength will be different even if the liquid crystal is cured at the same temperature.
[0008]
Therefore, by controlling the above parameters in the visible range, it is possible to form a color filter in which the reflected light is red, green, and blue, and by overlapping two such color filters, A color filter in which the transmitted light is red, green, and blue can be formed.
[0009]
Here, in the case of using a color filter made of cholesteric liquid crystal or chiral nematic liquid crystal as described above, for example, as disclosed in JP-A-9-318807, a cholesteric liquid crystal for a color filter is provided between two glass substrates. Is disposed on the light incident side of the liquid crystal cell.
[0010]
This is because, in the case of a liquid crystal cell currently used mainly in a transmissive liquid crystal display device, for example, a TN cell, the polarization plane of incident linearly polarized light is rotated by 90 ° at the maximum by ON / OFF of a voltage applied to the liquid crystal, Or, since this is an optical rotation mode driving method that passes through without rotation, when a color filter made of cholesteric liquid crystal or chiral nematic liquid crystal is used, circularly polarized light that has passed through the color filter is transmitted by a quarter wavelength plate. This is because the light is incident on the liquid crystal cell after being converted into linearly polarized light.
[0011]
[Problems to be solved by the invention]
In the transmissive liquid crystal display device as described above, it is indispensable to dispose a color filter in the liquid crystal cell in order to perform color display without parallax. Therefore, a quarter wavelength plate is also provided in the liquid crystal cell. There was no freedom of design.
[0012]
In addition, a normal quarter-wave plate is thick and difficult to arrange in a liquid crystal cell, has low heat resistance, and is colored when an alignment film is fired on the inner surface of a glass substrate. There was a problem.
[0013]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a liquid crystal display device in which a quarter-wave plate can be disposed outside the liquid crystal cell.
[0014]
[Means for Solving the Problems]
The present invention comprises a light source and one of a cholesteric liquid crystal layer or a chiral nematic liquid crystal layer as in claim 1, and each pixel has red, green, and blue regions, and each region is incident from the light source. and of the light was directed to a light of a respective wavelength regions, the right-hand circularly polarized light or transmitted through only one of the left-hand circularly polarized light, reflecting the other light and right-handed circularly polarized light or left-handed circular polarization of the other wavelength region And a liquid crystal layer disposed on the light exit surface side of the color filter, and an electrode for applying an electric field to the liquid crystal layer, and the operation mode of the liquid crystal layer depends on whether the applied voltage is on or off. The above object is achieved by a transmissive liquid crystal display device comprising a liquid crystal cell having a phase shift amount of 0 or π.
[0015]
Further, in the transmissive liquid crystal display device, the ¼ wavelength which is disposed on the light exit surface side of the liquid crystal cell and converts the incident circularly polarized light into linearly polarized light by shifting the phase of the light by ¼ wavelength. A linear polarizing plate that is disposed on the light exit surface side of the quarter wavelength plate and transmits only one of two types of linearly polarized light whose polarization planes emitted from the quarter wavelength plate are orthogonal to each other; May be provided.
[0016]
In the present invention, the operation mode of the liquid crystal layer in the liquid crystal cell is a birefringence mode in which the amount of phase shift of transmitted light is π or 0 by ON / OFF of the applied voltage, and circularly polarized light transmitted through the color filter is left as it is. Since it can be modulated, a quarter wave plate can be placed outside the liquid crystal cell.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0018]
As shown in FIG. 1, a transmissive liquid crystal display device 10 according to an example of an embodiment of the present invention includes a light source 12 that emits non-polarized light and a right-handed circle out of the light incident from the light source 12. A circularly polarized light separating film 14 that transmits one of the polarized light or the left-handed circularly polarized light component and reflects the other, and a color that is disposed on the light exit surface side of the circularly polarized light separating film 14 and is sandwiched between the pair of glass substrates 16A and 16B A filter 18 and a liquid crystal cell 20; a quarter-wave plate 22 disposed on the light-emitting surface side of the liquid-crystal cell 20; and a linearly polarizing plate 24 disposed on the light-emitting surface side of the quarter-wave plate 22 It is prepared for.
[0019]
In FIG. 1, symbols R and L indicate right-handed circularly polarized light and left-handed circularly polarized light, respectively. In addition, “← →” and “•” (see FIG. 2) indicate electric field vibration vectors of linearly polarized light, respectively, “← →” is an in-plane direction, and “•” is a direction perpendicular to the plane.
[0020]
The light source 12 is a transparent thin film-like white surface light source made of electroluminescence or the like on a thin film sandwiched between transparent resin sheets having transparent electrodes. A reflective layer 12A made of a thin film is disposed.
[0021]
This reflective layer 12A reflects, for example, the R circularly polarized light component emitted from the light source 12 and reflected by the circularly polarized light separating film 14, toward the circularly polarized light separating film 14 again. At this time, the phase of the polarized light component is inverted, Alternatively, the light utilization rate is improved as an L circularly polarized light component that can be transmitted through the circularly polarized light separating film 14 in a non-polarized state.
[0022]
In addition, this invention is not limited to this, You may use the backlight used for a normal liquid crystal display.
[0023]
The circularly polarized light separating film 14 is composed of, for example, a cholesteric liquid crystal film. In the example of this embodiment, the circularly polarized light L is transmitted and the circularly polarized light R is reflected. Instead of the polarization separation film 14, a combination of a selectively reflective linear polarization separation film and a quarter wave plate may be used.
[0024]
The color filter 18 is composed of, for example, a cholesteric film or a chiral nematic film as disclosed in JP-A-9-318807.
[0025]
FIG. 1 shows four pixels in the liquid crystal cell 20 and respective parts corresponding thereto. Further, as shown in the figure, the color filter 18 has red, green, and blue regions per pixel, and each region is light in the respective wavelength region, and only the left-handed circularly polarized light L is obtained. It transmits light and reflects light in other wavelength regions and right-handed circularly polarized light R.
[0026]
The liquid crystal cell 20 is a birefringence control (ECB) type, and controls the birefringence of the liquid crystal layer in the liquid crystal cell 20 by applying an electric field. The liquid crystal cell 20 is a VAN method, a PAN method, a HAN method, or the like. The phase shift amount of the transmitted light is set to 0 or π by turning on and off the applied voltage.
[0027]
Therefore, when the applied voltage is ON, the incident left-handed circularly polarized light L has a phase shift amount of 0, and thus is transmitted as it is. As shown in FIG. It is converted into circularly polarized light R and emitted.
[0028]
The circularly polarized light separating film 14 is formed by laminating three or more films having birefringence, and further laminating a quarter wavelength layer, and the film having birefringence as described above is In addition to the cholesteric liquid crystal film, a substance exhibiting in-plane birefringence such as a polycarbonate resin, a polyester resin, or a polyvinyl alcohol resin can be obtained by a method such as stretching.
[0029]
The quarter-wave plate 22 is a phase plate made of a polymer material such as polyimide, and has a function of converting incident circularly polarized light into linearly polarized light or vice versa. Accordingly, the quarter wavelength plate 22 converts the left-handed circularly polarized light L and the right-handed circularly polarized light R emitted from the liquid crystal cell 20 into two types of linearly polarized light whose polarization planes are orthogonal to each other.
[0030]
The linearly polarizing plate 24 is arranged so that the polarization direction of the transmitted light coincides with the direction of the electric field vibration vector of the linearly polarized light “← →” converted from the left-handed circularly polarized light L.
[0031]
In the transmissive liquid crystal display device 10, the non-polarized light emitted from the light source 12 is transmitted only by the left-handed circularly polarized light L in the circularly polarized light separating film 14, enters the color filter 18, and is right-handed circularly polarized light. R is reflected and returned to the direction of the light source 12.
[0032]
This reflected light is reflected by the reflective layer 12A and is converted to left-handed circularly polarized light L by shifting the phase by 180 °, or becomes non-polarized light and half of the left-handed circularly polarized light L is converted into the circularly polarized light separating film 14. And enters the color filter 18.
[0033]
In the color filter 18, in the R, G, and B regions of each pixel, only light in the corresponding wavelength region is transmitted, and light in other wavelength regions is reflected. The reflected light reaches the reflective layer 12A through the circularly polarized light separating film 14, and is reflected again in the direction of the color filter 18.
[0034]
In the liquid crystal cell 20, when the applied voltage is ON, the incident left-handed circularly polarized light L is transmitted as it is and is incident on the quarter-wave plate 22, where the phase of the light is shifted by a quarter wavelength. ← → ”is converted into linearly polarized light and emitted from the linearly polarizing plate 24 as display light. At this time, as shown in FIG. 3, the transmitted light intensity and the display light intensity of the liquid crystal cell 20 increase with the applied voltage.
[0035]
On the other hand, as shown in FIG. 2, when the applied voltage of the liquid crystal cell 20 is OFF, the phase of the transmitted light is shifted by π, so that the incident left-handed circularly polarized light L is changed to right-handed circularly polarized light R. The quarter wavelength plate 22 is converted to “·” linearly polarized light, but this cannot be transmitted through the linearly polarizing plate 24, so that dark display is obtained.
[0036]
In this transmissive liquid crystal display device 10, the liquid crystal cell 20 can modulate the incident circularly polarized light as it is by ON / OFF of the applied voltage, and therefore, the quarter wavelength plate 22 is provided in the glass substrates 16 A and 16 B. There is no need.
[0037]
Therefore, a quarter-wave plate having a large thickness can be used, and since the quarter-wave plate is outside the liquid crystal cell, it is not colored when the alignment film is formed. .
[0038]
Further, by rotating the polarization direction of the linear polarizing plate 24 by 90 °, bright display is performed when the applied voltage of the liquid crystal cell 20 is OFF as shown in FIG. 4, and dark display is performed when the applied voltage of the liquid crystal cell 20 is ON. It can also be a normally white mode display.
[0039]
In the transmissive liquid crystal display device 10 according to the example of the above embodiment, the quarter wavelength plate 22 is provided between the liquid crystal cell 20 and the linear polarizing plate 24. However, the quarter wavelength plate 22A is provided. It can also be provided adjacent to the light exit surface side of the color filter 18.
[0040]
In this case, since the liquid crystal cell 26 provided adjacent to the quarter wavelength plate 22A modulates linearly polarized light, it becomes a driving method in an optical rotation mode.
[0041]
【The invention's effect】
Since the present invention is configured as described above, it is not always necessary to provide a quarter-wave plate in the liquid crystal cell, and it has an excellent effect that the degree of freedom in design increases. In addition, by providing a quarter-wave plate outside the liquid crystal cell, it is possible to prevent coloring during firing of the alignment film of the cell.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an enlarged main part of a transmissive liquid crystal display device according to a first example of an embodiment of the present invention. FIG. 2 shows a dark display state of the transmissive liquid crystal display device. FIG. 3 is a schematic cross-sectional view similar to FIG. 1. FIG. 3 is a diagram showing a change in relative transmittance according to an applied voltage in a liquid crystal cell in the transmissive liquid crystal display device. Diagram showing change in relative transmittance due to applied voltage in the liquid crystal cell when rotated
DESCRIPTION OF SYMBOLS 10 ... Transmission type liquid crystal display device 12 ... Light source 12A ... Reflective layer 14 ... Circularly polarized light separation film 16A, 16B ... Glass substrate 18 ... Color filter 20, 26 ... Liquid crystal cell 22, 22A ... 1/4 wavelength plate 24 ... Linear polarizing plate

Claims (2)

It consists of a light source and one of a cholesteric liquid crystal layer or a chiral nematic liquid crystal layer, and each pixel has red, green, and blue regions, and each region has light in the respective wavelength region of light incident from the light source. a is a color filter transmits one of right-hand circularly polarized light or left-handed circular polarization only reflects light and right-handed circularly other polarized light or left-handed circular polarization of the other wavelength region, the light exit surface of the color filter A liquid crystal layer arranged on the side and an electrode for applying an electric field to the liquid crystal layer, and the operation mode of the liquid crystal layer is such that the phase shift amount of transmitted light becomes 0 or π depending on ON / OFF of the applied voltage. A transmissive liquid crystal display device. The quarter-wave plate according to claim 1, which is disposed on the light-emitting surface side of the liquid crystal cell and converts the incident circularly polarized light into linearly-polarized light by shifting the phase of the light by a quarter wavelength, A linearly polarizing plate that is disposed on the light exit surface side of the / 4 wavelength plate and transmits only one of the two types of linearly polarized light whose polarization planes are orthogonal to each other, which is emitted from the ¼ wavelength plate. A transmissive liquid crystal display device.

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