JP2991714B2 - Color display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color display device having high brightness, high contrast, and excellent viewing angle characteristics.

Conventional technology Currently, word processors, personal computers, televisions, CAD / CAM
Most of the display devices used for CRT (cathode ray tube) are CRT (cathode ray tube), from monochrome devices that can display A4 full pages to devices that can display high-quality full colors. Various items ranging from ″ to 40 ″ are used for office or entertainment purposes. However, the CRT has disadvantages such as a large volume, which is difficult to reduce in thickness, and a high voltage is required. Therefore, a flat-plate large-capacity, low-cost full-color display device is strongly demanded.

2. Description of the Related Art Conventionally, as a flat panel type color display device, a plasma display, a flat CRT, a fluorescent display tube and the like are under development, and a liquid crystal pocket television is already commercialized. The former three have problems that the luminous efficiency is low at present, the panel structure is complicated and expensive, and it is difficult to increase the size. On the other hand, liquid crystal full-color display devices are being actively developed for full-color enlargement due to the ease of enlargement and the like. For example, The Institute of Television Engineers of Japan, 8th volume, No. 4, pages 1-6, Showa
It is listed in 59. To achieve full-color display with liquid crystal, liquid crystal is usually simply a panchromatic light valve (hereinafter
A color image is displayed on a two-dimensional surface by additive color mixture by providing red, green, and blue color filters on the electrode in a strip or dot shape.

Fig. 2 shows a twisted nematic type (hereinafter abbreviated as TN).
The configuration and operation of a conventional full-color panel using a liquid crystal display mode will be described. The TN type full-color matrix panel includes a pair of glass substrates 2 and 8, each having a transparent row electrode 3 and a transparent column electrode 7 made of indium oxide or the like.
A nematic liquid crystal 4 having a positive dielectric anisotropy (Δε) is sandwiched therebetween, and a pair of polarizing plates 1 and 9 are provided outside glass substrates 2 and 8.

Red (R), green (G),
A blue (B) color filter layer 5 is regularly provided on each column electrode (or row electrode). Although the panel is illustrated in a simplified manner, usually, an alignment treatment layer for defining the alignment of liquid crystal molecules is provided on the color filter layer side surface and the row electrode side surface, and the liquid crystal molecules are provided on each substrate. On the surface, it is arranged in a specific direction almost parallel to the substrate, and the arrangement direction of the molecules is one substrate and the other substrate,
The orientation is almost 90 ° different, and the molecular arrangement direction is gradually twisted from one substrate to the other, and after all, it is pre-orientated on the surface of both substrates so that almost 90 ° twist occurs between both substrates Processing has been done. A liquid crystal color panel is usually used in a transmission type in order to obtain a bright display. That is, the white back light source 10 is provided on the back of the panel. When a linear light source, such as a fluorescent lamp, is used as the light source 10, a light diffusing plate (not shown) is connected to the light source 10 and a liquid crystal in order to obtain uniform brightness without unevenness on the two-dimensional display surface. It is provided between the panels. If the light source 10 is a planar light source such as electroluminescence, a light diffusing plate is unnecessary. The above is an example of a conventional full-color liquid crystal panel. The biggest disadvantages of the conventional technology are: (1) Conventional TN type full-color display panel or FLC
In the type color panel, the luminous flux utilization rate from the light source 10 is low. That is, when a color display is intended, the light source 10
The light spectrum must contain red, blue, and green light components. Since light from a normal light source is natural light, when passing through the polarizing plate 1, about 50% of the luminous flux is absorbed by the polarizing plate and lost. Whether the display medium is a liquid crystal or an electro-optic crystal plate, in a display system using a polarizing plate, a monochrome panel or a color panel,
This 50% light loss is inevitable. A further disadvantage of the color panel as compared with the monochrome panel arises from the insertion of the color filter layer 5. That is, the polarizers 1 and 9 shown in FIG. 2 are assumed to be neutral polarizers, and the white luminous flux from the rear light source 10 is
The light becomes white linearly polarized light. Whether the white linearly polarized light enters the liquid crystal layer 4 through the color filter layer or exits the liquid crystal layer 4 and enters the filter layer 5 as shown in the figure, light of a specific wavelength is absorbed by each color filter layer.

In other words, the green and blue components are absorbed when passing through the red filter layer, the red and green components are absorbed when passing through the blue filter layer, and the red and blue components are absorbed when passing through the green filter layer. The energy of the original white light will be reduced to about one third. If the light passing through the liquid crystal layer 4 and the color filter layer is linearly polarized light and its polarization axis coincides with the polarization axis of the polarizing plate 9, light passing through the polarizing plate 9 basically has a light loss. There is no. As described above, even if the polarizers 1, 9 and the color filter 5 are ideal, the light energy passing through the color panel is almost 50%.
× 33% = 16.5%. The liquid crystal panel itself is usually characterized by low voltage and low current and low power, but when it comes to a liquid crystal color panel, as described above,
Since a back light source is required and only a part of the luminous flux of the back light source can be used, the fact is that the low power characteristic of the liquid crystal is greatly impaired.

Problems to be Solved by the Invention The problems to be solved by the present invention are (1) voltage drop and deterioration of threshold characteristics due to a color filter in a conventional color panel, and (2) problems due to a color filter in a conventional color panel. It is a decrease in brightness.

Means for Solving the Problems In order to solve the above problems, the color display device of the present invention has a structure in which a pair of transparent substrates each having a transparent electrode are opposed to each other on an electrode surface side. A liquid crystal element that can change the property is sandwiched, and a phosphor layer that emits light of a different color is separately applied between the transparent electrode on the back side of the pair of transparent substrates and the transparent electrode. A light source that excites and emits light from the phosphor layer is provided at the back, and includes means for applying a voltage to each of the transparent electrodes.

Function The present invention has an LV effect that modulates optical scattering by applying a voltage to TN liquid crystal, STN liquid crystal (super twist liquid crystal), ECB liquid crystal (electrically controlled birefringent mode), ferroelectric liquid crystal (FLC), etc. Alternatively, a GH (guest-host) type liquid crystal mode in which a dichroic dye is added to the liquid crystal, or an electro-optical modulation in which the optical transmittance can be modulated by a voltage of a dispersion system in which acicular fine particles are dispersed in a highly insulating organic solvent. The device is a light valve (LV), and the color light obtained by causing the excitation light source to emit a phosphor layer painted in a pattern that emits light of different colors is modulated by an electro-optic modulator. That is, since the energy of the excitation light can be used to emit 100% color light by separately applying phosphor layers different in emission color without basically using a color filter as in the prior art, each color is bright and has high contrast. An excellent image can be displayed.

Embodiment Hereinafter, an embodiment of the color display device of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the color display panel of the present invention basically comprises a phosphor excitation light source 13, a phosphor layer 11 for emitting colored light,
The electro-optic modulator 14 includes a polarizing plate 9 if necessary.
As the phosphor excitation light source 13, a light source that emits substantially single wavelength light of blue to ultraviolet is used. The R, G, and B phosphor layers 11 each emit light of R, G, and B by excitation light from the light source 13, respectively. In the figure, it is provided in a stripe shape, but may be of course provided in a mosaic shape. The phosphor layer 11 is separately coated on the substrate 8 transparent to the excitation light by a method such as printing. The case where the electro-optic modulator 14 is a ferroelectric GH type liquid crystal cell (hereinafter abbreviated as GH-FLC) will be described more specifically. The GH-FLC is particularly suitable as the electro-optic modulator 14 of the present invention because it can realize a large-capacity display with a simple matrix configuration and has both high-speed response and high contrast. That is, a dichroic color is formed between the electrode surfaces 7 and 3 of a pair of glass or plastic substrates 2 and 8 provided with a transparent conductive film (hereinafter abbreviated as ITO) such as indium oxide, tin oxide, and a metal thin film. A chiral smectic C liquid crystal 4 in which a dye is dissolved is subjected to an initial alignment treatment substantially parallel to the substrate to form a so-called Book-shelf configuration. The illustration of an alignment film for aligning the liquid crystal molecules in a specific direction and, if necessary, so as to have an appropriate tilt angle with respect to the electrode surface is omitted. The molecular orientation treatment is performed by obliquely depositing SiO or the like between the electrodes. In the XY matrix panel for displaying characters, images, etc., the pair of ITOs are patterned into strips as shown in the figure, and the strips ITO are arranged so as to be orthogonal to each other. The intersection of the two electrodes forms one pixel 15.

In the GH-FLC mode, in order to obtain a high contrast, the polarizing axis of the polarizing plate is arranged and used so as to match the molecular axis of the liquid crystal in which the molecular alignment is achieved by applying a positive or negative voltage between the electrodes. Is done. A phosphor layer formed by printing or the like usually has severe irregularities, is not suitable for uniformly aligning liquid crystal molecules, and is liable to cause deterioration of contrast characteristics, display unevenness, and the like. In such a case, it is desirable to further form a surface smoothing layer 16 on the phosphor layer 11 by printing, spin coating, roll coating, or the like. The ITO transparent electrode is formed on this smoothing layer and processed into a narrow band by photoetching.

As the phosphor used in the present invention, those widely used for so-called photoluminescence such as a fluorescent lamp can be used. That is, Eu3 + activated phosphor is typical for red emission, Y2O3: Eu3 + Y (P, V) 04: Eu3 + (Y, Gd) BO3: Eu3 + Y2O2S: Eu3 + Others 3.5MgO.0.5MgF2.GeO2: Mn For green light emission, a Tb3 + activated phosphor is typical. LaPO4: Ce3 +, Tb3 + Eu2 + -activated phosphor is typical for blue light emission, BaMg2Al16027: Eu2 + (Sr, Ca) 5 (PO4) 3Cl: Eu2 + Sr2P207: Eu2 + Ca5 (PO4) 3 (F, Cl): Sb3 + (Ba, Ca, Mg) 5 (PO4) 3Cl: Eu2 + Sr5 (PO4) 3Cl: Eu2 + Other MgWO4, CaWO4, Sr2P207: SnCa5 (PO4) 3 (F, Cl): Sb3 + Y2O2S: Tm3 +

On the other hand, the light source used in the present invention must have a radiation spectrum suitable for exciting and emitting the phosphor. It is also desirable that the conversion efficiency from electric energy to radiant energy be as high as possible. As an example, a fluorescent lamp using ultraviolet light emitted by arc discharge in mercury vapor is suitable. In a fluorescent lamp, a small amount of mercury and a few Torr of an odd gas such as argon are sealed in a glass tube, and a fluorescent substance is applied to the inner wall of the tube. A pair of electrodes is sealed at both ends of the tube. The surface of the electrode is coated with an electron-emitting substance. In a low-pressure mercury discharge lamp, about 60% of the electric energy input to the lamp is converted into ultraviolet energy mainly having a wavelength of 254 nm. It is not impossible to directly use 254 nm if glass or plastic that transmits this wavelength is used for the transparent substrate 8, but if the mercury vapor pressure is increased, longer wavelength components such as 313 nm and 365 nm increase, and the range of choice of the transparent substrate is limited. spread. Alternatively, a fluorescent lamp provided with a phosphor on the inner wall of the lamp tube for converting ultraviolet light having a wavelength of 254 nm generated by discharge into light having a longer wavelength up to about 450 nm may be used. 450 nm is usually required as a blue light component for full color display. If the excitation light has a wavelength near 450 nm, the blue (B) phosphor layer is not necessarily provided. If the emission spectrum of the phosphor is not sufficiently appropriate, it is easy to optimize the color light spectrum by forming a color filter layer on the phosphor layer, on the smooth layer, or on any electrode surface. is there. In this case, the color energy is not generated by the R, G, B filters from the white light as in the conventional case, but is merely generated by the phosphor layer and the spectrum of the subsequent light is simply modulated. Absent.

Effect of the Invention In the conventional color liquid crystal panel, TN mode or FLC
The basic combination was a mode liquid crystal light valve, stripe or mosaic R, G, B color filters, and a white back light source. In this case, the energy of the white back light source is reduced to 1/3 or less by the R, G, and B color filter layers.

The first feature of the present invention is the brightness of the display. That is, instead of using the conventional color filter,
Since the R, G, and B phosphor layers having different emission spectra are used, most of the light energy of the light source can be used for the excitation energy of the R, G, and B phosphors. Therefore, if the material selection of the light source and the substrate is optimized and the absorption loss until reaching the phosphor is reduced as much as possible, a display panel having three times higher efficiency than the conventional one can be obtained in principle.

A second feature of the present invention resides in that the phosphor layer is smoothed as necessary and an electrode layer is provided thereon. In this way, the voltage applied between the electrodes is effectively applied to the liquid crystal layer, while the orientation of the liquid crystal is made uniform, the driving voltage is reduced, the threshold characteristics are improved, and the contrast, brightness, color purity, etc. are achieved. This greatly contributes to the improvement of display quality.

[Brief description of the drawings]

FIG. 1 is a perspective view of a color display device of the present invention, and FIG. 2 is a perspective view of a conventional full-color liquid crystal panel. 2 ... Transparent substrate, 3 ... Transparent row electrode, 4 ... Electro-optical modulation element layer, 7 ... Transparent column electrode, 8 ... Transparent substrate, 9 ...
Polarizing plate, 11 phosphor layer, 13 phosphor excitation light source, 14
... Electro-optical modulator, 15 pixels, 16 phosphor smoothing layer.

Continuing on the front page (72) Inventor Hiroyuki Onishi 1006 Oji Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. References JP-A-57-205778 (JP, A) JP-A-61-138233 (JP, A) JP-A-60-61725 (JP, A)

Claims (11)

(57) [Claims] An electrode surface of a pair of transparent substrates each having a transparent electrode is opposed to each other, and a liquid crystal element whose light transmittance can be changed by a voltage is sandwiched between these electrodes. A phosphor layer that emits light of a different color is separately applied between the rear transparent substrate and the transparent electrode, and a light source that excites and emits the phosphor layer is provided behind the rear transparent substrate, A color display device comprising: means for applying a voltage to each of the transparent electrodes. 2. The color display device according to claim 1, wherein the light source utilizes gas discharge of low-pressure mercury vapor. 3. The light source according to claim 1, wherein the light source emits light having a wavelength shorter than at least 450 nm.
The color display device according to the item. 4. A color display device according to claim 1, wherein said phosphor layers are respectively colored so as to emit red, green and blue light. 5. A color display according to claim 1, wherein the liquid crystal device is a device comprising a nematic liquid crystal, a chiral nematic liquid crystal, a smectic A liquid crystal, a chiral smectic C liquid crystal or a chiral smectic I liquid crystal. apparatus. , 6. The color display device according to claim 5, wherein a dichroic dye is added to the liquid crystal element. 7. The color display device according to claim 5, wherein a polarizing plate is provided on a substrate side of the color display device for observing a display. 8. The color display device according to claim 1, wherein the liquid crystal element is a liquid dispersion system in which needle-like or plate-like fine particles are dispersed in a high-resistance liquid. 9. The color display device according to claim 1, wherein the substrate provided with the phosphor layer is transparent to excitation light applied to the phosphor layer. 10. The phosphor layer on the transparent substrate further includes a surface smoothing layer, and the transparent electrode is provided on the surface smoothing layer. The color display device according to (1). 11. The color display device according to claim 1, wherein a color filter layer for color adjustment is provided on one of inner surfaces of the transparent substrate.