JPH0467296B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to thin flat plates such as rear light sources of transmissive liquid crystal display devices, pixels for large screen display panels, reading light sources for information equipment, and light sources for general lighting. The present invention relates to a flat light source used in a field in which it is required.

[Conventional technology]

For example, a liquid crystal display device utilizes the function of a liquid crystal as a light switch, which undergoes a phase transition under the action of an electric field and thermal energy and exhibits polarizing properties.Currently, light is received from the liquid crystal display surface and reflected back to form a display pattern. Two methods have been put into practical use: a reflective type that allows recognition, and a transmissive type that allows light to enter and pass through from behind the liquid crystal to recognize the displayed pattern.

However, although the liquid crystal operates as a light switch, it does not emit light by itself, so a light source is essential in order to realize a bright display pattern. In particular, the transmissive type is used as an OA terminal, and a transmissive color liquid crystal display device as shown in FIG. 2 is currently being proposed.

In FIG. 2, reference numeral 1 denotes a liquid crystal display section, which includes a first liquid crystal-filled vacuum container 2, a first transparent electrode 3 formed on the inner surface of the first liquid-crystal-filled vacuum container 2, and a first transparent electrode 3 formed on the inner surface of the first liquid crystal-filled vacuum container 2. The first electrode provided to cover the electrode 3
a liquid crystal alignment film 4, and a second liquid crystal-filled vacuum container 5 disposed opposite to the first liquid-crystal-filled vacuum container 2.
and a plurality of second transparent electrodes 6a, 6 formed in a matrix on the inner surface of the second liquid crystal-filled vacuum container 5.
b, 6c, ... and second transparent electrodes 6a, 6b, 6
Colored layers 7a, 7 formed on the upper surfaces of c, . . . , respectively
b, 7c, ... and second transparent electrodes 6a, 6b, 6
a second liquid crystal alignment film 8 provided so as to cover the colored layers 7a, 7b, 7c, a liquid crystal 9 sealed between the first and second liquid crystal sealed vacuum containers 2 and 5, It is composed of a first polarizing plate 10 disposed on the outer surface side of the first liquid crystal-filled vacuum container 2 and a second polarizing plate 11 disposed on the outer surface side of the second liquid crystal-filled vacuum container 5. . Reference numeral 12 denotes a straight tube fluorescent lamp which serves as a rear light source and is disposed behind the liquid crystal display section 1, that is, on the side of the second polarizing plate 11. A plurality of straight fluorescent lamps 12 are arranged in parallel according to the display area of the liquid crystal display section 1. There is. A light diffusing plate 13 is disposed between the fluorescent lamps 12 and the liquid crystal display section 1 and makes the luminous flux from the plurality of fluorescent lamps 12 uniform.

In the transmissive color liquid crystal display device having the above configuration, the fluorescent lamp 12 is turned on, and an electric potential is generated between the first transparent electrode 3 and the second transparent electrode 6a, 6b, 6c, . . . according to a desired display pattern. give. Here, for example, if no potential is generated between the first transparent electrode 3 and the second transparent electrode 6a, but a potential is generated between the first transparent electrode 3 and the second transparent electrode 6b, Liquid crystal molecules 9 between transparent electrodes 3 and 6a
The liquid crystal molecules 9b between the transparent electrodes 3 and 6b have a molecular crystal structure that allows light to pass through. As a result, no light is emitted from the portion facing the second transparent electrode 6a, and light corresponding to the color of the colored layer 7b is emitted from the portion facing the second transparent electrode 6b. A desired display pattern can be obtained.

However, in the above device, since a plurality of fluorescent lamps 12 are arranged according to the display area, uneven brightness tends to occur on the light diffusion plate 13. As a method to prevent this brightness unevenness, the light diffusing plate 1 of the fluorescent lamp 12
3 or increase the number of fluorescent lamps 12 to increase the arrangement density. However, in the former method, the device itself becomes large and the thickness in the thickness direction becomes large.
One of the advantages of using the liquid crystal display section 1 as the device is lost. In addition, in the latter method, the fluorescent lamp 1
2, the power consumption increases as a light source consisting of the liquid crystal display section 1, which not only makes it impossible to take advantage of low power consumption, which is one of the advantages of using the liquid crystal display section 1, but also reduces the efficiency of the fluorescent lamp 12 due to the temperature rise of the light source section. This caused problems such as deterioration of the periphery of the liquid crystal display section 1 and the light diffusing plate 13. Further, it was necessary to prepare button light lamps 12 according to the size of the display section.

In addition, although the conventional example above uses a normal fluorescent lamp as the light source, in order to maintain the lifespan of a television, a glow discharge fluorescent lamp using a cold cathode is used as the light source behind the transmissive liquid crystal display device. It has also been proposed to use it as a power source. However, in fluorescent lamps that use glow discharge, as the distance between the electrodes increases to accommodate the enlargement of the display surface, the starting voltage increases, making it difficult to start, and the discharge restriking voltage also increases. The noise also increases and causes noise in the liquid crystal drive circuit, causing malfunction of the display device, making it unsuitable for large transmissive liquid crystal display devices such as office automation display terminals.

Therefore, it has been desired to develop a light source that has a thin, uniform brightness surface and discharges at a low starting voltage as a rear light source for a liquid crystal display device. Therefore, a surface discharge type rear light source as shown in FIGS. 3 and 4 can be considered. In the figure, 14 is a discharge vessel made of flat glass with mercury 17 and rare gas sealed inside, and a first vessel 15 and a second vessel sealed with flanges to each other. 16, and each container 15, 16 has a pair of opposing inner planes 15a, 16a. 18 _11-18
No is a plurality of electrodes provided in a matrix of m rows and n columns on one inner plane 16a of the discharge vessel 14,
Each electrode 18 ₁₁ to 18 _no has a protective layer 19 ₁₁ to 19 _n, respectively.
covered by _o . Reference numeral 20 denotes a phosphor coated on the inner surface of the discharge vessel 14 except for the electrodes 18 ₁₁ to 18 _no . The protective layer 19 ₁₁ to 19 _no is the electrode 18 ₁₁ to
18 _No. 1 dielectric with excellent secondary electron emission characteristics.

In the flat light source having the above configuration, each electrode 18
Apply voltage to ₁₁ to 18 _no to discharge, and phosphor 2
Light emission occurs by exciting 0, and a thin flat light source with a uniform brightness surface can be obtained with a low starting voltage.

[Problem that the invention seeks to solve]

However, in the flat light source described above, electric field concentration tends to occur at the boundary around the electrode during discharge,
The electrode protective layer and insulating layer become spattered, making it impossible to stably emit secondary electrons, making the discharge unstable, and eventually causing the lamp to stop lighting up, resulting in a short lifespan.Furthermore, ultraviolet rays are only used on the light-emitting surface. Therefore, there was a problem in that it was not possible to fully satisfy the demand for a high-brightness light source and the more advanced demand for uniformity of brightness.

In order to solve the above-mentioned problems, the present invention aims to provide a long-life thin surface discharge planar light source that has a structure that can increase the brightness of the light emitting surface and improve the uniformity of the brightness at the same time. shall be.

[Means for solving problems]

This invention provides a plurality of electrodes in a matrix on one inner surface of a flat discharge vessel, a dielectric layer on the top surface of the electrodes, a protective layer on the top surface of the dielectric layer, and the dimensions of the protective layer. An insulating sheet having through holes 10% or more smaller than that of the protective layer is provided on the top surface of the protective layer, and the surface of the insulating sheet excluding the through holes is coated with phosphor to a thickness of 20 μm or more,
Furthermore, this upper layer is coated with a dielectric film having a thickness of 1 mm or less, and the other inner surface is coated with a phosphor.

[Effect]

The insulating sheet prevents electric field concentration that tends to occur at the boundary around the electrode, and prevents spatter on the electrode protective layer and insulating layer.The phosphor coated on this insulating sheet also helps to diffuse light. The effect improves the uniformity of the brightness of the light emitting surface that radiates from the other plane to the outside, and the increase in the area of the phosphor increases the amount of visible light conversion of ultraviolet rays, improving the brightness of the light emitting surface. This isolates the phosphor on the surface of the insulator sheet from direct ion bombardment caused by discharge, thereby preventing deterioration.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 21 is a flat discharge vessel;
A side wall 25 that is open on both sides, and a flat plate 22 made of glass that emits light and closes the other open side.
and a flat plate 23 made of glass or ceramics that closes one opening of the side wall 25. 18 ₁₁ ~ 18 _no is on the flat plate 23, m
A plurality of electrodes arranged in a matrix of rows and n columns, the distance between each electrode is in the range of 20 to 100 mm, in this example 50 mm, and a thick film of aluminum or other conductive metal with a thickness of 2 to 10 μm is used. It is formed by vapor deposition or thick film printing, etc., and a discharge is generated between two electrodes by time-division driving. 30 is this electrode 18
₁₁ - ₁₈ It is a dielectric film made of a high voltage material that uniformly accumulates surface charge and speeds up the response characteristics of discharge application pulses.
Ta ₂ O ₅ , SiO ₂ or Si ₃ N ₄ . 19 is made of an inorganic oxide such as MgO, CeO ₂ , CaO or (Sr, Ca)O on this dielectric film 30 and has a thickness of 10
~800 nm protective layer 28 is closely adhered on this protective layer 19, corresponds to the electrodes 18 ₁₁ to 18 _no , and is an insulator having a thickness of 1 mm or less and having through holes 29 of 10% or less of this protective layer 19. The sheet protects the border around the electrode from direct ion bombardment. Further, on the upper surface of this insulating sheet 28, a phosphor layer 31 is provided, excluding the through holes, with a phosphor layer 31 coated with phosphor having a thickness of 20 μm or more using a thick film printing method or the like. 32 is provided on the upper layer of this phosphor 31 layer.
It is a dielectric material with a thickness of 1 mm or less that transmits ultraviolet rays of 60 nm to 360 nm, and is made of, for example, MgF ₂ , SiO ₂ , or SiO ₂ sheets. 20 is a phosphor coated on the inner surface of the flat plate 22 and excited by ultraviolet rays.

The side wall 25 and the flat plates 22, 23 are sealed together with a glass frit, and the difference in coefficient of thermal expansion of the glass frit from the coefficient of thermal expansion of the side wall 25 and the flat plates 22, 23 is 20% or less. .
Similarly, the insulating sheet 28 is one having a thermal expansion coefficient of 20% or less with respect to the side wall 25 and the flat plates 22 and 23.

Reference numeral 27 denotes an exhaust pipe for evacuating the inside of the flat discharge vessel 21 and sealing mercury or rare gas inside.

The phosphor 20 has colored layers 7a, 7b, and 7b shown in FIG. 2 in order to efficiently realize color display.
It is an ultraviolet-excited three-wavelength range emitting phosphor based on the three primary colors of light that matches the spectral transmittance of 7c...
1st range of 445nm or more and 475nm or less, 525nm or more
Second range below 555nm and above 595nm 625nm
It is mainly emitted in the third range below, and has a spectral distribution in which the sum of the radiant energy in these three ranges is 45% or more of the radiant energy in the range of 380 nm or more and 780 nm or less, for example, 30 wt. % _Y2O2 : Eu3 ⁺ phosphor 49% by _{weight LaPO4} :
Ce ³⁺ , Tb ³⁺ phosphor 21% by weight (Sr, Ba) ₉
(PO ₄ ) ₆ SrCl ₂ : Comprised of Eu ²⁺ phosphor.
The coating thickness is 100 μm or less, for example, 60 μm.

Furthermore, the flat discharge vessel 21 contains mercury in an amount that can maintain a saturated vapor pressure of 5 mg or more.
A rare gas mixture in the range of 10 Torr, or a mixture of 1 to several 100 Torr without mercury, for example, 50 Torr of helium and xenon as main components, is sealed, in this example 10 mg of mercury and 20 Torr.
It is filled with a rare gas mixture whose main components are argon and neon.

In the flat light source configured as above,
Each of the electrodes ₁₈₁₁ to _18no is connected to a drive circuit (not shown) so that time-division driving is performed between the two electrodes, and two adjacent electrodes are sequentially selected to perform time-division discharge between these two electrodes. will be held. Then, these two selected electrodes move sequentially and discharge,
When a discharge occurs between the final electrodes, the process returns to the first electrode, and the process is repeated. By the way, if the discharge current between these two electrodes exceeds 100 mA, the electrodes 18 ₁₁ ~ 1
8. As the deterioration of _{the no} . In addition, the scanning period of discharge (for example, starting from the discharge of electrodes 18 ₁₁ to 18 ₁₂ and starting from electrode 1
The discharge of 8 _no-1 and 18 _no is one scan. )teeth,
If it is less than 30Hz, you will feel the flickering of the light, which can cause eye fatigue when used for long periods of time, such as on OA display terminals, so 30Hz or more is required.

The ultraviolet rays generated by the time-division discharge between the two electrodes arranged in the matrix form
0 is excited, and the outside of the upper flat plate 22 of the discharge vessel 21 is irradiated with light having uniform brightness. Furthermore, the phosphor layer 31 provided on the upper surface of the insulating sheet 28 converts the ultraviolet rays generated within the discharge vessel into visible light, and scatters and reflects the visible light generated within the vessel to the opposing light emitting surface. To simultaneously achieve uniform brightness and high brightness on a light emitting surface. Moreover, since this phosphor is covered with a dielectric layer that transmits ultraviolet rays, it is not directly exposed to the discharge space, and the phosphor layer is prevented from sputtering due to direct ion bombardment caused by the discharge. ,
Moreover, this dielectric material can also reduce the discharge starting voltage. In addition, the insulating sheet 28 prevents electric field concentration that tends to occur at the boundary around the electrode, eliminates spatter on the electrode protective layer and insulating layer, stabilizes discharge, and extends life.

〔Effect of the invention〕

As described above, in the present invention, one inner surface of a flat discharge vessel having a pair of opposing inner surfaces is coated with a protective layer, and the protective layer is coated on a plurality of electrodes arranged in a matrix. An insulator sheet with through holes of 10% or less of the layer at positions corresponding to each electrode is provided in close contact with the above protective layer, a phosphor layer is provided on the top surface of this insulator sheet, and a phosphor layer is provided on the top surface of this insulator sheet. Since a dielectric layer is provided on the top surface and a phosphor is coated on the other inner surface of the flat discharge vessel, the insulating sheet prevents the electrode protective layer and the insulating layer from sputtering due to the generation of a concentrated electric field at the boundary around the electrode. In addition, the phosphor layer converts the ultraviolet rays generated in the discharge vessel into visible light, and scatters and reflects this visible light to the opposing light emitting surface, resulting in uniform brightness on the light emitting surface. It is possible to further increase the brightness and brightness. In addition, this phosphor is covered with a dielectric layer that transmits ultraviolet rays, and the discharge space is not exposed, which prevents deterioration of the phosphor from direct ion bombardment caused by discharge. It is possible to realize a long-life flat light source that also has the effect of lowering the discharge starting voltage and can stably maintain brightness uniformity and high brightness over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view and a longitudinal sectional view with the middle part omitted, showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing a transmissive color liquid crystal display device, and FIG. 3 is a longitudinal sectional view of a conventional flat light source. The longitudinal sectional view and FIG. 4 are partial plan views of the electrode portion. Symbols 18 ₁₁ to 18 _no in the figure: Electrode, 19: Protective layer, 20: Phosphor, 21: Flat discharge vessel, 22, 23: Flat plate, 25: Side wall, 27:
... Exhaust pipe, 28 ... Insulator sheet, 29 ... Through hole, 30 ... Dielectric layer, 31 ... Phosphor layer, 32 ... Dielectric layer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A flat discharge vessel having a pair of opposing inner planes and in which a rare gas or a rare gas and mercury is sealed, and a matrix-shaped discharge vessel provided on one inner plane of the discharge vessel. a dielectric layer provided on the top surface of each of the electrodes, a protective layer covering the portions of the top surface of the dielectric layer that are necessary for discharge, and a , and has a through hole with a size of 10% or less of this protective layer, and an insulating sheet closely attached to the top surface of the protective layer, and a part other than the through hole on the top surface of this insulating sheet.
It is characterized by comprising a phosphor coated with a thickness of 20 μm or more, a dielectric coated on the upper surface of the phosphor with a thickness of 1 mm or less, and a phosphor coated on the other inner surface. A flat light source. 2. The insulating sheet according to claim 1, wherein the insulating sheet has a thickness of 1 mm or less and is made of glass or ceramic material whose thermal expansion coefficient difference with the discharge vessel does not exceed 20%. Flat light source. 3. The electrode according to claim 1 or 2, characterized in that the distance between each electrode is in the range of 20 to 100 mm, and the electrode is made of a conductor that can allow a discharge current of 1 to 100 mA. Flat light source.