JP2004287324A - Semitransmissive liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve deterioration of a liquid crystal generated by UV, reduction of luminosity and the differences of transmittance and a NTSC ratio generated by the difference between optical paths in a transmission mode and a reflection mode, in a liquid crystal display using a fluorescent body which emits light by UV irradiation. <P>SOLUTION: The liquid crystal display device is constituted by disposing a color filter patterned in a wavelength band region corresponding to at least two colors between first and second substrates and a semitransmissive reflection film and the fluorescent body at the lower part of the color filter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device having excellent brightness and color reproducibility during reflection and transmission.
[0002]
[Prior art]
2. Description of the Related Art A conventional liquid crystal display device uses radiant energy of both ultraviolet light and visible light by using a phosphor that emits light when irradiated with UV (hereinafter referred to as ultraviolet light) (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-T-2001-512248 (pages 12 to 13, FIGS. 3, 4, and 6)
[0004]
[Problems to be solved by the invention]
However, the technique described in Patent Document 1 alone has the following disadvantages when used as a liquid crystal device. Substrates, transparent electrodes, polarizing plates, liquid crystals, and the like, which are components of a display device through which ultraviolet light and visible light are incident and transmitted, are required to have transparency and light resistance to ultraviolet light. However, ITO, which is generally used as a transparent electrode, is transparent to visible light, but has a large absorption in the ultraviolet region, making it impossible to efficiently transmit ultraviolet light to the phosphor. Similarly, in a configuration in which the transparent electrode is located in front of the phosphor, the ultraviolet rays cannot be efficiently transmitted to the phosphor. Therefore, the fluorescent light emission by the ultraviolet ray cannot be sufficiently used, and the brightness in the case of observation by reflection has little improvement effect as compared with the case where only the visible light is used. In addition, when a generally used liquid crystal is irradiated with ultraviolet rays for a long time, a part of the liquid crystal molecules is decomposed, and this decomposition product causes problems such as image sticking. Therefore, at present, the polarizing plate has a function of absorbing ultraviolet rays to protect the liquid crystal from ultraviolet rays. However, Patent Document 1 does not describe a solution to such a problem. Further, Patent Document 1 discloses a transmission-type configuration and a reflection-type configuration, but does not provide a configuration for simultaneously realizing display functions during transmission and reflection.
[0005]
Further, when a color display is performed using an additive color mixture using R (red), G (green), and B (blue) color filters in a configuration that simultaneously realizes the display function at the time of transmission and at the time of reflection, They will also be used during transmission. In the case of observation by reflection, the external light takes an optical path that passes through the color filter twice as compared with the case of observation by transmission. For this reason, the color development of the color filter has a large difference between transmission and reflection. There is no description in the prior art regarding this difference as a problem, and there is no description of a solution. According to the CIE1931 XYZ color system recommended by the International Commission on Illumination regarding the difference between the saturation and lightness of the color filter, the saturation is represented by R (red) G (green) at the chromaticity coordinates xy in the XYZ color system. ) The chromaticity coordinates of each of R (red), G (green), and B (blue) in the NTSC1953 system defined by the National Television System Committee are calculated on the area of a triangle obtained by connecting the chromaticity coordinates of B (blue). Expressed by the ratio of the area of the triangle obtained by connecting. Generally used as NTSC ratio. Brightness is represented by a Y value. In the case of a color filter, a white Y value obtained by summing R (red), G (green), and B (blue) Y values is used as the transmittance. The transmittance at the time of reflection indicates the transmittance of a double pass when D65 is used as a light source.
[0006]
FIG. 4 is a graph showing the relationship between the transmittance and the NTSC ratio of a dark color transmission color filter used in a transmission type liquid crystal display and a light color reflection color filter used in a reflection type liquid crystal display. Here, the color material of the color filter is controlled to adjust the transmittance and the NTSC ratio. As shown by the diamonds in the figure, when observing the reflection display with the transmission color filter, the transmission color filter is used in the double pass of going and returning, so that the transmittance decreases and the NTSC ratio increases. On the contrary, as shown by the circles in the figure, when observing the transmissive display with the reflective color filter, the reflective color filter is used in a single pass, so that the transmittance increases and the NTSC ratio decreases. As shown in FIG. 4, even if the color material of the color filter is controlled, it is impossible to adjust the difference between the transmittance and the NTSC ratio due to the optical path difference between the transmission and the reflection.
[0007]
An object of the present invention has a function of displaying light by reflecting light incident from the outside of the liquid crystal display element and transmitting light incident from the side opposite to the external light in the configuration disclosed in Patent Document 1. A structure is realized, and further, deterioration of liquid crystal and a decrease in brightness due to ultraviolet rays at the time of reflection are improved. Another object of the present invention is to improve the difference between the transmittance and the NTSC ratio due to the optical path difference between the transmission and reflection of the color filter at the time of additive color mixture using a color filter.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a liquid crystal display device according to the present invention includes a color filter patterned into a wavelength band of two or more colors between a first substrate and a second substrate; A transflective display device comprising: a phosphor that emits light upon irradiation with ultraviolet light, wherein the transflective film and the phosphor are provided below the color filter, and the visible light that has entered from the first substrate side is translucent. The display was reflected by the reflective film, and the wavelength of light emitted by the phosphor by absorbing ultraviolet light incident from the second substrate side was in the transmission wavelength band of the patterned color filter, and the phosphor emitted light. The display is made to transmit light. With such a configuration, it is possible to realize a function of reflecting and displaying light that has entered from the outside, and transmitting and displaying light that has entered from the side opposite to the outside light. In addition, only visible light is used during reflection, and ultraviolet light is converted into visible light with a phosphor during transmission, so that the transparent electrodes and liquid crystal have a structure that does not transmit ultraviolet light, thereby improving the deterioration of liquid crystal and the absorption of ultraviolet light. ing.
[0009]
Further, a backlight that emits ultraviolet light was disposed on the back side of the second substrate. This backlight irradiates the phosphor with ultraviolet rays from the side of the second substrate, reflects the ultraviolet rays that have not been absorbed by the phosphor and is reflected by the reflective layer, and irradiates the phosphors again. It can irradiate the body and improve the brightness during transmission.
[0010]
Further, the semi-transmissive reflective film is formed of a reflective film having a light-transmitting region, and a phosphor is disposed in the light-transmitting region. Further, the light transmission region is constituted by a hole or a slit provided in the reflection film, and a phosphor is provided in the hole or the slit. The semi-transmissive reflection film having such a configuration is a metal reflection film made of aluminum or the like which does not transmit ultraviolet light, converts ultraviolet light into visible light through a hole or a slit as a light transmission area and uses the light as transmitted light, and the ultraviolet light enters the liquid crystal. The structure is not used to prevent the deterioration of the liquid crystal. At the time of reflection, visible light is reflected by a reflection area other than the hole or the slit for display.
[0011]
Further, the semi-transmissive reflection film is constituted by a selective reflection film made of a dielectric multilayer film or a selective reflection film using cholesteric selective reflection, and is configured to transmit ultraviolet rays and reflect visible light. Even in such a configuration, ultraviolet light is converted into visible light and used as transmitted light, and the structure is such that ultraviolet light does not enter the liquid crystal, thereby preventing deterioration of the liquid crystal. In reflection, visible light can be reflected and displayed.
[0012]
Further, the color filter is composed of three pixel patterns of R (red), G (green), and B (blue), and the phosphors are three colors of R, G, and B so as to correspond to each pixel pattern of the color filter. And the saturation of the color filter is set to 21 or less for the D65 light source.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The liquid crystal display device according to the present invention includes a color filter patterned into two or more wavelength bands, a semi-transmissive reflective film, and a fluorescent light emitted by ultraviolet irradiation between the first substrate and the second substrate. And a transflective film and a phosphor were arranged below the color filter. Furthermore, by making the wavelength of the light emitted by the phosphor be in the transmission wavelength band of the patterned color filter, visible light incident from the first substrate side is reflected by the semi-transmissive reflective film for display. At the same time, display is performed by absorbing ultraviolet light incident from the second substrate side and transmitting light emitted by the phosphor. That is, in the liquid crystal display device having such a configuration, the transflective film and the phosphor are arranged below the color filter, and at the time of reflection, external light is irradiated from the first substrate side, and only visible light is used. The display is performed by reflecting the light on the transflective film. At the time of transmission, ultraviolet light is irradiated from the second substrate side, and the ultraviolet light transmitted through the semi-transmissive reflection film is converted into visible light by a phosphor to realize a transmissive display using only visible light. The liquid crystal displays by modulating the polarization state of visible light using only visible light. In order to select only visible light from outside light, an upper polarizing plate or an ultraviolet absorbing filter that absorbs ultraviolet light may be disposed on the first substrate side. With this configuration, the liquid crystal can be protected from ultraviolet rays.
[0014]
Further, by arranging a backlight for irradiating ultraviolet rays on the back side of the second substrate, a liquid crystal display device that can be used in a reflective mode in bright outdoors and turned on in a dark place to display in a transmissive mode is realized. are doing. The brightness at the time of reflection can be adjusted by changing the ratio of transmission and reflection of the transflective film. Further, the brightness at the time of transmission can be adjusted by controlling the ultraviolet intensity of the backlight.
[0015]
Further, in performing a color display using additive color mixture by three pixel patterns of R (red), G (green) and B (blue), the present liquid crystal display device has the following improvements. First, the phosphor is also patterned so as to emit fluorescent light in three colors of R, G, and B corresponding to the respective pixel patterns of the three colors of the color filter, and is provided between the first substrate and the second substrate. . According to this configuration, the distance between the pixel of the color filter and the phosphor can be set to be sufficiently short compared to the pixel size, so that when transmitted, light emitted in a specific color pattern of the phosphor is the same color of the color filter. It is possible to efficiently enter the pattern and to enter the pattern of other colors in a small amount. Taking R (red) as an example, the light emitted by the red phosphor efficiently enters only the pixels of the R (red) color filter, and the adjacent pixels of G (green) and B (blue) Light is incident on. Other colors (green, blue) work similarly. Therefore, it is possible to display a dark color without using a dark color filter at the time of transmission. Therefore, the color depth of the color filter can be determined by considering only the brightness at the time of reflection. If the saturation of the color filter is set to 21% or less of the NTSC ratio in reflection with respect to the D65 light source, the reflection can be made bright and the color at the time of transmission can be maintained at a dark level.
[0016]
As a result, the NTSC ratio of the color filter during transmission is improved. Therefore, even when a light color reflection color filter having an NTSC ratio of 21 or less for a D65 light source is used as a reflection color filter, the NTSC ratio at the time of transmission can be made higher than the NTSC ratio at the time of reflection. However, when the NTSC ratio of the color filter is increased to 21 or more, the transmittance at the time of reflection deteriorates, and the display at the time of reflection becomes dark. In order to secure the brightness at the time of reflection, it is desirable to set the NTSC ratio of the color filter to 21 or less.
[0017]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a main configuration of the liquid crystal display device of the present embodiment. As shown, a liquid crystal is sandwiched between the first substrate 5 and the second substrate 13. A transparent substrate made of glass, plastic, or the like is used as an upper substrate 2, and a color filter 3 is provided on the back surface thereof. In the color filter 3, red R3, green G3, and blue B3 are patterned by a coloring material layer of a dye or a pigment. Each patterned colored layer constitutes a pixel. Further, an upper transparent electrode 4 is provided on the color filter. Similar to a general liquid crystal display device, a film forming process for an alignment film or an insulating film (not shown) and an alignment process such as rubbing may be performed.
[0018]
On the other hand, a transparent substrate such as glass or plastic is also used for the lower substrate 12, and a thin plate is used to reduce absorption of ultraviolet rays. The transflective film 11 is formed on the surface of the lower substrate 12. As the transflective film 11, a metal film such as aluminum or silver can be used. The transflective film 11 has a hole as a transmissive area facing the pixel of the color filter 3 on the first substrate 5. This transmission region can be formed by patterning. A phosphor 10 is provided in the transmission region, a top surface thereof is covered with a transparent resin layer 9 made of an acrylic resin, an epoxy resin or the like, a lower transparent electrode 8 is further provided thereon, and an inner polarizing plate 7 is provided thereon. Have been. The second substrate 13 is configured as described above.
[0019]
Phosphor 10 is coated with a rare-earth three-wavelength phosphor of the same color so as to face red R3, green G3 and blue B3 of the color filter. Here, an inorganic rare-earth three-wavelength phosphor is used, but a transparent organic phosphor having better coatability may be used. The color filter 3 and the phosphor 10 may be determined in accordance with the number of colors for color display, and may be one color in the case of a mono color.
[0020]
When an element such as a thin film transistor or a thin film diode is provided on the lower substrate 12 side, a phosphor 10 is formed in an opening of the element by photolithography, and a transparent resin layer 9 and a lower transparent electrode 8 are further formed thereon. To form In this case, when the phosphor made of glass in which semiconductor nanoparticles are dispersed is made into fine particles and diluted with a solvent, the coating properties are further improved, and the patterning accuracy and productivity can be improved.
[0021]
The inner polarizer 7 is a molecularly crystallized thin-film polarizer and also has a function of an alignment film for liquid crystal. Therefore, a TN type liquid crystal is used, and a normal alignment film is used on the upper transparent electrode 4. When the inner polarizing plate 7 is not used, a guest-host type liquid crystal in which a dichroic dye is mixed in the liquid crystal may be used. Further, instead of the TN type, STN type liquid crystal may be used.
[0022]
The first substrate 5 and the second substrate 13 are adhered to each other with a certain gap maintained by a sealing material mixed with a spacer, and a liquid crystal 6 is sealed in the gap between these substrates to form a liquid crystal display element. are doing. The upper polarizing plate 1 is adhered to the front side of the first substrate 5, and its polarization axis is set according to the rubbing direction of the alignment film formed on the adhered substrate. A phase difference plate may be laminated.
[0023]
In such a configuration, when external light 14 (that is, sunlight or light for indoor lighting) enters from the first substrate side, the incident light is reflected by the semi-transmissive reflective film 11 of the liquid crystal display element, and again. The light is transmitted through the liquid crystal display element in the reverse direction, whereby a reflective display can be performed. On the other hand, the ultraviolet light 15 emitted from the second substrate side is converted into visible light by the phosphor 10, whereby a transmissive display can be performed.
[0024]
FIG. 2 schematically shows a configuration in which the color filter 3 is arranged on the second substrate 13 side in the configuration of FIG. Such a configuration can further reduce the distance between the color filter 3 and the phosphor 10 as compared with the configuration of FIG. 1, and can increase the color of transmission.
[0025]
FIG. 3 schematically shows still another configuration. As shown in the figure, an ultraviolet absorbing filter 16 is adhered to the front side of the first substrate 5, and the upper polarizing plate 1 shown in FIG. 1 is formed on the rear surface of the upper transparent electrode 4 as the inner polarizing plate 7. . The transflective film 11 is composed of a dielectric multilayer film in which a high-refractive-index layer and a low-refractive-index layer are stacked, and transmits ultraviolet light and reflects visible light. The refractive index of the high refractive index layer may have a range of 2.0 to 2.5, for example _{TiO 2,} ZrO 2, may be configured SnO ₂ and the like. The refractive index of the low refractive index layer to which may in the range of 1.3 to 1.6, for example _{SiO 2,} AlF 3, may be configured CaF ₂ and the like. The composite phosphor 17 is obtained by laminating the phosphor 10 and the color filter 3 shown in FIG. As the fluorescent material, a color filter in which a pigment is dispersed is laminated on a fluorescent material in which fine particles of a fluorescent material made of glass in which semiconductor nanoparticles are dispersed are dispersed. The advantage of such a configuration is that the transflective film 11 is not divided into a transmissive region and a reflective region as compared with the configuration of FIG. And transmission luminance can be improved.
[0026]
Next, FIG. 6 schematically shows a configuration using a backlight for the liquid crystal display device having the configuration shown in FIG. Here, the backlight 21 uses an ultraviolet light source as the light source 18. An ultraviolet light emitting LED or a black light can be used as the ultraviolet light source. The light guide plate 19 is made of a resin that absorbs only a small amount of ultraviolet light, and the reflection layer 20 is disposed on the back surface. The backlight 21 irradiates ultraviolet rays 22 absorbed by the phosphor from the side of the second substrate 13 and irradiates ultraviolet rays 23 not absorbed by the phosphor. The ultraviolet rays 23 not absorbed by the phosphor become the ultraviolet rays 24 reflected by the semi-transmissive reflection film, and become the ultraviolet rays 25 reflected again by the reflection layer to irradiate the phosphor again. Therefore, the phosphor can be irradiated with the ultraviolet rays without waste, and the luminance at the time of transmission can be improved.
[0027]
Next, the mechanism for improving the difference between the transmittance and the NTSC ratio due to the optical path difference between the transmission and reflection of the color filter at the time of additive color mixture using the color filter will be described in detail. In the present invention, a color filter having a light color can be used as a color filter for transmission for reflection, and it is possible to make the color at the time of transmission dark, although the reflection can be made bright. In order to solve the conventional problem that the NTSC ratio is reduced when the reflection color filter is used during transmission, the present invention uses an ultraviolet light source as the light source 18 of the backlight 21 and uses the red and green reflection color filters 3. , A pattern of phosphors 10 of three colors of red, green, and blue corresponding to the pixel patterns of three colors of blue is formed below the color filter 3. The RGB pattern of the phosphor 10 is aligned with the RGB of the color filter 3. Accordingly, ultraviolet light is emitted through the light guide plate 19 to emit fluorescent light in the patterns R (red), G (green), and B (blue) of the phosphor 10, and light that emits fluorescence in the specific color pattern of the phosphor is the same color of the color filter. The light is efficiently incident on the pattern, and is less incident on the patterns of other colors. Taking a red phosphor as an example, the red phosphor that has received ultraviolet light emits red fluorescence and efficiently enters the R of the color filter 3 and enters a small amount of G and B. Similarly, G (green) and B (blue) also efficiently enter the same color filter. In such a configuration, the distance between the phosphor 10 and the color filter 3 can be made within 20 μm, so that the fluorescent light emitted from the phosphor enters the color filters of almost the same color. Therefore, even when a light color filter is used, the NTSC ratio of the color filter at the time of transmission is dominated by the color of the fluorescent light source.
[0028]
In this embodiment, a 0.8 μm-thick color filter shown in the table of FIG. 5 is used as a reflection type color filter. The spectrum is shown by R, G, and B in FIG. The spectrum of the fluorescent light source emitted by the phosphor is also shown as the R light source, the G light source, and the B light source in FIG. The effect of improving the NTSC ratio and transmittance at the time of reflection and transmission is also shown in the table of FIG. In the drawing, the condition that the RGB color mixture is described in the method item is a case where the three color RGB phosphors corresponding to each of the three RGB color pixel patterns of the color filter are not patterned and mixed color white light is emitted. In this case, the NTSC ratio at the time of transmission is small and the color is light. The condition that there is no RGB phosphor color filter in the method item is a case where there is no color filter but phosphors of three colors of R (red), G (green) and B (blue) are patterned. In this case, the NTSC ratio increases and the color of the transmission becomes darker. However, the reflection is displayed in black and white because there is no color filter. Therefore, no numerical value is described in the table. The condition described as “RGB phosphor color filter” in the method item is the highest NTSC ratio at the time of transmission, and the transmittance is also large. Color can be displayed even during reflection and brightness can be increased. Therefore, even if a reflection color filter having a light color is used, the NTSC ratio at the time of transmission can be increased and a dark display can be achieved, and the brightness at the time of reflection can be maintained.
[0029]
【The invention's effect】
As described above, according to the liquid crystal display device of the present invention, as compared with the configuration of the related art, while reflecting and displaying light incident from the outside, light incident from the opposite side of the external light is transmitted. Display function can be realized. In addition, only visible light is used during reflection, and ultraviolet light is converted into visible light with a phosphor during transmission, so that the transparent electrodes and liquid crystal have a structure that does not transmit ultraviolet light, thereby improving the deterioration of liquid crystal and the absorption of ultraviolet light. ing.
[0030]
Further, even if a dark color filter is not used, the color depth of the color filter can be determined only by considering the brightness at the time of reflection. That is, if the saturation of the color filter is set to 21% or less of the NTSC ratio in reflection with respect to the D65 light source, it is possible to realize a liquid crystal display device in which reflection is bright and color at the time of transmission is maintained at a dark level. As a result, it is possible to increase the commercial value in the field of electronic devices such as personal computers, cameras, mobile phones, watches, etc., in which liquid crystal display devices are frequently used in the consumer goods market.
[Brief description of the drawings]
FIG. 1 is an example of a schematic diagram showing a configuration of a liquid crystal display device of the present invention.
FIG. 2 is another example of a schematic view showing the configuration of the liquid crystal display device of the present invention.
FIG. 3 is another example of a schematic view showing the configuration of the liquid crystal display device of the present invention.
FIG. 4 is a graph showing the relationship between the transmittance of a color filter and the NTSC ratio in a conventional technique.
FIG. 5 is a diagram showing the effect of improving the NTSC ratio and the transmittance of the color filter according to the liquid crystal display device of the present invention.
FIG. 6 is a schematic diagram showing a configuration using a backlight in the liquid crystal display device of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 upper polarizing plate 2 upper substrate 3 color filter 4 upper transparent electrode 5 first substrate 6 liquid crystal 7 inner polarizing plate 8 lower transparent electrode 9 transparent resin layer 10 phosphor 11 transflective film 12 lower substrate 13 second substrate 14 Outside light 15 UV

Claims (7)

A transflective type including, between the first substrate and the second substrate, a color filter patterned in a wavelength band of two or more colors, a transflective film, and a phosphor that emits light when irradiated with ultraviolet light. A display device,
The transflective film and the phosphor are provided below a color filter,
Visible light incident from the first substrate side is reflected by the transflective film for display,
The wavelength of light emitted by the phosphor by absorbing ultraviolet light incident from the second substrate side is in the transmission wavelength band of the patterned color filter, and the light emitted by the phosphor is transmitted to display. A transflective liquid crystal display device. The transflective liquid crystal display device according to claim 1, wherein a backlight that emits ultraviolet light is provided on a back side of the second substrate. The transflective liquid crystal display device according to claim 1, wherein the transflective film is a reflective film having a light transmissive area, and the phosphor is disposed in the light transmissive area. 4. The transflective liquid crystal display device according to claim 3, wherein the light transmission region is configured by a hole or a slit provided in the reflection film, and the phosphor is provided in the hole or the slit. 5. 3. The transflective liquid crystal display device according to claim 1, wherein the transflective film is formed of a selective reflection film, and transmits ultraviolet light and reflects visible light. The color filter is composed of three pixel patterns of R (red), G (green), and B (blue), and the fluorescent material also has R (red) so as to correspond to each pixel pattern of the color filter. , G (green), and B (blue) are patterned with phosphors that emit fluorescence in three colors, and the color filter has a saturation of 21 or less with respect to a D65 light source. 6. The liquid crystal display device according to claim 5. The liquid crystal display according to claim 6, wherein the phosphor is formed by patterning a phosphor made of glass in which semiconductor nanoparticles are dispersed into three colors of R (red), G (green), and B (blue). apparatus.

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