JP4494552B2 - 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, and more particularly to a transmissive liquid crystal display device using a selective transmission / reflection color filter.
[0002]
[Prior art]
The transmissive color liquid crystal display device performs color display by irradiating backlight light from behind the liquid crystal cell and emitting light transmitted through the liquid crystal cell or light before transmission through the color filter from the surface of the liquid crystal panel. I am doing so.
[0003]
As such a liquid crystal display device, there is one in which a cholesteric film in which cholesteric liquid crystal is dispersed as a color filter is disposed on the light incident side of a liquid crystal cell as disclosed in, for example, Japanese Patent Laid-Open No. 9-318807.
[0004]
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.
[0005]
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.
[0006]
On the other hand, natural light can be divided into right-handed circularly polarized light and left-handed circularly polarized light, and the cholesteric liquid crystal or chiral nematic liquid crystal has the above-mentioned right-handed and left-handed light components incident in parallel to the spiral axis of the liquid crystal. , Only the circularly polarized light component having the same rotational direction as the twist direction of the liquid crystal is reflected and the other circularly polarized light component is transmitted.
[0007]
At this time, since the phase of the reflected light does not change with respect to the incident light, the polarization direction is unchanged before and after the incident of the reflected light, and the wavelength of the reflected light depends on the twist pitch of the cholesteric liquid crystal or chiral nematic liquid crystal. Change. 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.).
[0008]
Therefore, by controlling the above parameters in the visible range, red, green and blue transmitted light can be formed, and light other than the transmitted light is reflected to the light source side and reused. Thus, the luminance can be set higher than that of the conventional color filter.
[0009]
[Problems to be solved by the invention]
However, when the color filter composed of the cholesteric liquid crystal or the chiral nematic liquid crystal as described above is used for a liquid crystal display, the backlight light from the back surface can be turned on / off with good contrast. For light, since the color filter reflects light having a wavelength other than that transmitted (complementary color light), the reflected light of complementary color is emitted as display light on the display surface.
[0010]
In this case, there is no problem when the usage environment of the liquid crystal display is dark, but in a bright environment, there is a problem that the color display on the display surface is disturbed by the color of the reflected light, resulting in a decrease in contrast.
[0011]
The present invention has been made in view of the above-mentioned conventional problems, and is a color filter for a transmissive liquid crystal display device capable of obtaining accurate color display and high contrast on the display surface even in a bright place with a lot of external light. An object of the present invention is to provide a transmissive liquid crystal display device including the above.
[0014]
[Means for Solving the Problems]
This invention, as claimed in claim 1, a backlight device for emitting backlight from the light exit surface, and a color filter that is disposed on the light exit surface side of the backlight device, the light exit side of the color filter are arranged, the oN / OFF of the applied voltage, the liquid crystal cell position loved shift amount of transparently light is to be a 0 or [pi, between the light exit surface side or the color filter and the liquid crystal cell of the liquid crystal cell A quarter wavelength plate that is arranged to shift the phase of transmitted light by a quarter wavelength, and a position on the light exit surface side of the liquid crystal cell and the light exit surface side of the quarter wavelength plate, A linearly polarizing plate that transmits linearly polarized light emitted from the one when the voltage is ON and blocks linearly polarized light when no voltage is applied, and the transmitted light intensity and display light intensity of the liquid crystal cell are Increase with applied voltage , The color filter, the light-transmissive substrate, at least red, green, arranged and patterned so as to correspond to each color of blue, among the corresponding color wavelength light, one of the right-hand circularly polarized light or left-handed circularly polarized light A selectively transmitting / reflecting liquid crystal layer composed of one of cholesteric liquid crystal or chiral nematic liquid crystal that transmits only the circularly polarized light and reflects the other circularly polarized light and non-corresponding wavelength light, and is formed on the light incident side of the selectively transmitting / reflecting liquid crystal layer. The above object is achieved by a transmissive liquid crystal display device comprising a colored layer of the same color as the transmitted light.
[0015]
In the present invention, a color filter for a transmissive liquid crystal display device includes a selectively transmissive reflective liquid crystal layer made of one of cholesteric liquid crystal or chiral nematic liquid crystal, and transmitted light formed on the external light incident side of the selective transmissive reflective liquid crystal layer. Because it is composed of colored layers of the same color, even when used in a bright environment with a lot of external light, the incident external light is absorbed by the colored layer before reaching the selectively transmissive reflective liquid crystal layer, and the color filter Therefore, the backlight layer that has passed through is hardly absorbed by the colored layer, and therefore, adverse effects due to reflection of external light can be reduced without reducing the light use efficiency.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0017]
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 backlight device 12 that emits backlight light including wavelength light of red, green, and blue colors, And a selective transmission / reflection type color filter 14 that is patterned for each pixel, transmits only the corresponding wavelength light of red, green, and blue and reflects others, and further, the light exit surface of the backlight device 12 The circularly polarized light separating film 16, the color filter 14, the liquid crystal cell 20, the quarter wavelength plate 22, and the linearly polarizing plate 24 are stacked in this order.
[0018]
The color filter 14 and the liquid crystal cell 20 are disposed so as to be sandwiched between a pair of glass substrates 18A and 18B.
[0019]
The backlight device 12 is composed of, for example, a thin-film electroluminescence cell sandwiched between transparent resin sheets having transparent electrodes, and on the back side (lower side in FIG. 1), a reflection made of, for example, a metal thin film. Layer 12A is disposed.
[0020]
The reflection layer 12A is emitted from the electroluminescence cell, reflected by the circularly polarized light separating film 16 (described later), for example, reflects the right-handed circularly polarized light component again toward the circularly polarized light separating film 16, and at this time, the phase of the polarized light component Is used as a left-handed circularly polarized light component that can be transmitted through the circularly polarized light separating film 16 in whole or in part.
[0021]
Here, 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. 3) indicate electric field vibration vectors of linearly polarized light, respectively, “← →” is an in-plane direction, and “•” is a direction perpendicular to the plane.
[0022]
In the example of this embodiment, the circularly polarized light separating film 16 transmits the left-handed circularly polarized light L and reflects the right-handed circularly polarized light R. The film having birefringence is laminated in three or more layers. In addition, a quarter wavelength layer is laminated thereon. A film having birefringence as described above can be obtained by a method such as stretching a substance exhibiting in-plane birefringence such as a polycarbonate resin, a polyester resin, or a polyvinyl alcohol resin.
[0023]
Further, as the circularly polarized light separating film, a cholesteric liquid crystal is used, and the cholesteric liquid crystal has a spectrum, whereby the right-handed circularly polarized light R can be reflected in all visible light regions.
[0024]
As shown in FIG. 2 in an enlarged manner, the color filter 14 includes a selective transmission / reflection liquid crystal layer 14A and a colored layer 14B formed on the light exit surface side. Reference numeral 14C in FIG. 2 indicates a black matrix.
[0025]
The selective transmission / reflection liquid crystal layer 14A is composed of a cholesteric liquid crystal layer or a chiral nematic liquid crystal layer laminated on the glass substrate 18A. Of the backlight light which is non-polarized light, the left-handed light transmitted through the circularly polarized light separating film 16 is used. (Or right-handed) Reflects light of wavelengths other than red, green, and blue corresponding to circularly polarized light.
[0026]
Similar to the selective transmission / reflection liquid crystal layer 14A, the colored layer 14B is patterned for each pixel, and a pigment or dye having the same color as the light transmitted through the corresponding selective transmission / reflection liquid crystal layer 14A is photocurable. It is formed dispersed in a transparent resin.
[0027]
The selective transmission / reflection layer 14A of the color filter 14 may be made of a cholesteric film or a chiral nematic film as disclosed in, for example, Japanese Patent Application Laid-Open No. 9-318807.
[0028]
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 14 has R, G, and B 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 left-handed circularly polarized light L in other wavelength regions.
[0029]
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.
[0030]
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.
[0031]
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-wave plate 22 converts the left-handed circularly polarized light L and the right-handed circularly polarized light R incident from the liquid crystal cell 20 into two types of linearly polarized light whose polarization planes are orthogonal to each other.
[0032]
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.
[0033]
In the transmissive liquid crystal display device 10, the non-polarized light emitted from the backlight device 12 passes only the left-handed circularly polarized light L through the circularly polarized light separating film 16 and enters the color filter 14.
[0034]
In the color filter 14, in the R, G, and B regions of each pixel of the selective transmission / reflection liquid crystal layer 14A, only light in the corresponding wavelength region is transmitted, and light in other wavelength regions is reflected.
[0035]
The colored layer 14B is patterned into R, G, and B similarly to the selective transmission / reflection liquid crystal layer 14A and is colored in the same color as the selective transmission / reflection liquid crystal layer 14A. The light of each color is transmitted without being absorbed and enters the liquid crystal cell 20.
[0036]
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 enters the quarter-wave plate 22, where the phase of the light is shifted by a quarter wavelength. The light is converted into linearly polarized light “← →” and emitted from the linearly polarizing plate 24 as display light. At this time, the transmitted light intensity and the display light intensity of the liquid crystal cell 20 increase with the applied voltage.
[0037]
On the other hand, as shown in FIG. 3, when the voltage applied to 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, and 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.
[0038]
When the use environment of the transmissive liquid crystal display device 10 is bright and there is a lot of external light, external light enters through the linearly polarizing plate 24, the quarter-wave plate 22 and the liquid crystal cell 20 and reaches the color filter 14. .
[0039]
In the color filter 14, there is a colored layer 14B on the outside light incident side, and the colored layer 14B has the same color as the color of light transmitted through the selective transmission / reflection liquid crystal layer 14A. Only light is transmitted and others are absorbed.
[0040]
The light transmitted through the colored layer 14B is also transmitted through the selective transmission / reflection liquid crystal layer 14A of the same color.
[0041]
Therefore, external light does not generate complementary reflected light in the selective transmission / reflection liquid crystal layer 14A, and a display with higher contrast can be obtained even in a bright place.
[0042]
The colored layer 14B is formed by dispersing and coloring a pigment in a light transmissive resin, but the present invention is not limited to this, and the light transmitted through the selectively transmissive reflective liquid crystal layer 14A What is necessary is just to be colored in the same color.
[0043]
The quarter wavelength plate 22 is disposed between the liquid crystal cell 20 and the linear polarizing plate 24, but it may be disposed between the color filter 14 and the liquid crystal cell 20. In this case, the liquid crystal cell 20 is of a type that controls the direction of the polarization plane of linearly polarized light.
[0044]
【Example】
Examples of the color filter will be described in detail.
[0045]
First, in order to create a cholesteric liquid crystal layer as a selective transmission / reflection liquid crystal layer, a black pigment-dispersed photocurable resin is applied to a thickness of 1.5 μm on an alkali-free glass, and a black matrix is formed using a photomask. Exposed.
[0046]
Thereafter, a black matrix pattern is formed by performing alkali development, and then a photocurable cholesteric liquid crystal is applied to the thickness of 5 μm thereon, and the temperature is adjusted so that the central wavelength of the cholesteric liquid crystal is 450 nm. Then, one pixel pattern portion of the three pixel patterns of RGB (red, green, blue) was exposed with a photomask.
[0047]
Thereafter, the temperature was changed so that the reflection center wavelength by the cholesteric liquid crystal layer was adjusted to 550 nm, and the remaining portion was exposed entirely.
[0048]
Further, a photo-curing resin was applied thereon with a thickness of 5 μm, and mask exposure was performed in the same manner, so that a portion having a reflection center wavelength of 450 nm and a portion having a reflection center wavelength of 650 nm were adjusted.
[0049]
At this time, by forming the reflection center wavelength different from that of the previously formed cholesteric liquid crystal layer, a certain pixel reflects RG light and transmits only B light, and a certain pixel reflects RB light and reflects G. In some pixels, it is possible to reflect only GB light and transmit only R light in a certain pixel, thereby forming a selective transmission / reflection liquid crystal layer patterned in three colors of RGB.
[0050]
Next, a red pigment-dispersed photocurable resin (manufactured by Fuji Film Ohlin) is applied to the formed selective transmission / reflection liquid crystal layer to a thickness of 1 μm, and the selective transmission / reflection liquid crystal layer is coated using a photomask. A red filter was formed only on the red transmitting part.
[0051]
In the same procedure, each color of green and blue was repeated to finally form a colored layer that was patterned to form a color filter as shown in FIG.
[0052]
Next, a liquid crystal cell group was formed using the color filter. As a spacer, SP-203 (3 μm) manufactured by Sekisui Fine Chemical was dispersed, and liquid crystal ZLI-4792 manufactured by Merck was injected into the cell. As a result, a liquid crystal cell was formed in which birefringence occurred due to the retardation and thickness of the liquid crystal, and the phase changed by π depending on whether or not a voltage was applied.
[0053]
Further, a commercially available quarter wavelength plate was attached on the liquid crystal cell, and a linear polarizing plate was attached at an angle of 45 ° with respect to the fast axis.
[0054]
When the liquid crystal cell including the color filter completed as described above was placed on the backlight device on which the circularly polarized light separating film was placed, the light passed through the linearly polarizing plate in the state where no voltage was applied to the liquid crystal cell. In the state where voltage was applied to the liquid crystal cell, the colored light was seen to be transmitted through the applied pixel portion, and it could be used as a liquid crystal display panel.
[0055]
On the other hand, when the usage environment is brightened and external light is made incident from the front surface, almost no reflection of the complementary color light is observed in the selective transmission / reflection liquid crystal layer (cholesteric liquid crystal layer). The contrast of the liquid crystal display was improved about three times as compared with the case of the color filter having only the cholesteric liquid crystal layer without using.
[0056]
【The invention's effect】
Since the present invention is configured as described above, there is almost no complementary color reflected light of external light incident on the liquid crystal display device, which can greatly improve the contrast of the image on the display surface. Has an effect.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a transmissive liquid crystal display device according to an example of an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a color filter in the transmissive liquid crystal display device. Schematic sectional view showing the dark state of a transmissive liquid crystal display device.
DESCRIPTION OF SYMBOLS 10 ... Transmission-type liquid crystal display device 12 ... Backlight apparatus 14 ... Color filter 14A ... Selective transmission reflection liquid crystal layer 14B ... Colored layer 16 ... Circularly polarized light separation film 20 ... Liquid crystal cell 22 ... 1/4 wavelength plate 24 ... Linear polarizing plate

Claims (1)

A backlight device for emitting backlight from the light exit surface, and a color filter that is disposed on the light exit surface side of the backlight device is disposed on the light exit side of the color filter, the ON / OFF of the applied voltage, Toru a liquid crystal cell position loved shift amount of the over light is to be a 0 or [pi, this is arranged on one of between the light exit surface side or the color filter and the liquid crystal cell of the liquid crystal cell, a phase of the transmitted light 1 ¼ wavelength plate that shifts by ¼ wavelength, and linearly polarized light that is arranged at a position on the light exit surface side of the liquid crystal cell and on the light exit surface side of the quarter wavelength plate and that emits light from the one when the voltage is ON. A linearly polarizing plate that transmits and blocks linearly polarized light when no voltage is applied. The transmitted light intensity and display light intensity of the liquid crystal cell increase with an applied voltage, and the color The filter is light transmissive On the conductive substrate, is patterned and arranged corresponding to each color of at least red, green, and blue, and transmits only one circularly polarized light of right-handed circularly polarized light or left-handed circularly polarized light among the corresponding wavelength light, A selective transmission / reflection liquid crystal layer composed of one of cholesteric liquid crystal or chiral nematic liquid crystal that reflects the other circularly polarized light and non-corresponding wavelength light, and the same color as the transmitted light formed on the external light incident side of the selective transmission / reflection liquid crystal layer A transmissive liquid crystal display device.

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