JP2001290146A - Field sequential liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a field sequential liquid crystal display device using an organic EL element whose service life is enhanced as a back light. SOLUTION: The field sequential liquid crystal display device is characterized in that the organic EL element 1 is used for back light and a light diffusion member 2 formed by incorporating particles 21 for light diffusion into a liquid cooling medium 22 is provided between the organic EL element 1 and a liquid crystal panel 3. The light diffusion member 2 has a function to form a surface emitting light by scattering stripe-shaped light emission of the organic EL element 1 and a function to remove the heat generated by driving the organic EL element 1 through a transparent substrate 11. Water and the like can be used as the cooling medium and metal particles, glass beads, resin particles, resin particles coated with metal, pigment, emulsion particles and the like can be used as the particles for light diffusion. The light diffusion member 2 is preferably provided so as to be able to circulate through an outer and inner sides of a volume chamber K.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field sequential liquid crystal display, and more particularly, to a field sequential liquid crystal display using an organic electroluminescence (EL) element as a backlight.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 9-188875 describes that an organic EL element is used for a backlight of a liquid crystal panel. Further, Japanese Patent Application Laid-Open No. 9-325317 discloses a color liquid crystal display device using an organic EL element as a backlight. The display device disclosed in this publication is a field-sequential type liquid crystal display device (hereinafter, also referred to as an “FS liquid crystal display device”). A liquid crystal panel that changes each time to display an image, a backlight that is arranged on the back of the liquid crystal panel so as to be capable of sequentially switching and irradiating three primary colors of light, A control circuit for sequentially changing the illumination light of the backlight among the three colors.

The above-mentioned backlight is a surface light source capable of freely switching each of the three primary colors, and for example, comprises an organic EL element in which three types of organic EL films capable of emitting the three primary colors are arranged in a stripe pattern or the like. The organic EL element is configured to emit surface light in red, green, and blue for each field or frame in the screen display period by the control circuit. In addition, a diffusion plate made of resin or the like in which metal powder is dispersed may be provided between the organic EL element and the liquid crystal panel in order to make the stripe-shaped light emission of each color into surface light emission.

In the backlight of the FS liquid crystal display device, the frequency for determining one screen display period is, for example, 60 Hz (about 1 Hz).
6.7 msec), the three primary colors are displayed during this screen display period, and the display time per color is 6 ms.
ec or less. In the conventional FS liquid crystal display device, a period (writing period) W of scanning the liquid crystal panel and writing a signal for liquid crystal alignment (writing period) in the display time is 1 msec, and a period until the response of the liquid crystal to the written signal ends ( The response time (M) is set to 4 msec, and the period (lighting period) L for turning on the backlight is set to about 1 msec.

[0005]

However, when an organic EL element is used as a backlight under the above-described driving conditions, the element is repeatedly driven at a high speed and with a high luminance, so that the element generates a large amount of heat. As a result, the life of the organic EL element is significantly shortened. Even if the organic EL element is to be cooled by removing the generated heat, a liquid crystal panel or the like is arranged on the transparent substrate side of the organic EL element, and the organic EL film and the electrodes are generally laminated on the transparent substrate. Therefore, the cooling efficiency of the element from the back side of the organic EL element was low, and it was difficult to cool the organic EL element from the outside of the FS liquid crystal display device.

An object of the present invention is to provide an FS which uses an organic EL element for a backlight and has an improved lifespan.
It is to provide a liquid crystal display device.

[0007]

The FS liquid crystal display device according to the first invention uses an organic EL element as a backlight, and includes light diffusing particles in a liquid cooling medium between the organic EL element and the liquid crystal panel. It is characterized in that an included light diffusion member is provided. As the light diffusion particles, at least one selected from metal particles, glass beads, resin particles, metal-coated resin particles, and pigments can be used as in the second invention. Further, as in the third invention, emulsion particles may be used. It is preferable that the light diffusing member is provided so as to be able to circulate as in the fourth invention.

Hereinafter, the present invention will be described in detail. The “organic EL element” used for the backlight in the FS liquid crystal display device of the present invention usually includes a transparent substrate and an organic EL laminated film formed by laminating an anode, an organic EL film, and a cathode on the transparent substrate. Prepare.

As the transparent substrate, a transparent substrate made of a material having such a degree that the visibility of characters, figures and the like by light emission of the organic EL laminated film is not impaired can be used.
It is preferable that the organic EL element has both the strength enough to maintain the shape as the surface layer of the organic EL element and the hardness such that the surface is not easily damaged. As such a substrate, a substrate made of polyethylene terephthalate, polyether sulfone, polycarbonate, or the like can be used in addition to glass. The transparent substrate may be colorless and transparent, or may be colored and transparent with an appropriate color tone.

In the organic EL laminated film, the organic EL film disposed between both electrodes has at least a light emitting layer, and may have a hole transport layer and / or an electron transport layer in addition to the light emitting layer. And may further have a hole injection layer and / or an electron injection layer. Various known materials can be used for the materials constituting the anode, the cathode, and the organic EL film. A method for forming each of these layers may be appropriately selected from methods such as a vacuum evaporation method, a spin coating method, a casting method, a sputtering method, and an LB method.

As the "liquid crystal panel", a conventionally known one may be used. For example, an active matrix type using a TFT, a simple matrix type, and a passive driving structure can be used. The liquid crystal is OCB (optica
A liquid crystal in an (ly compensated bend cell) mode is preferable, but the present invention is not limited thereto.

Between the transparent substrate of the organic EL element and the back of the liquid crystal panel, there is provided a "light diffusing member" in which a liquid cooling medium contains light diffusing particles. As the “cooling medium” used in the light diffusing member, a liquid that is liquid at normal temperature and normal pressure and has light transmittance is used, and a colorless and transparent liquid is preferable. For example, one or more selected from water, alcohol, low molecular weight polyethylene glycol and the like can be used, and water is most preferably used.

The material of the "light diffusing particles" is not particularly limited as long as it is stable to the cooling medium. For example, metals such as Cr and Al; talc, silica, alumina,
Metal compounds such as titanium oxide, zinc oxide, lead carbonate, lead hydroxide, barium carbonate, barium sulfate, calcium carbonate, aluminum hydroxide, and kaolin; various glasses; various synthetic or natural resins; and composite materials thereof. be able to. The light diffusion particles may be made of a liquid. In order to prevent sedimentation of the particles and the like, particles for light diffusion made of a material having a specific gravity similar to that of the cooling medium are preferable. For example, when water is used as the cooling medium, the specific gravity is 0.9 to 4 (more preferably). Is 0.9 to 1.1)
It is preferable to use light diffusion particles made of the following materials.

The average particle diameter of the light diffusion particles is 10 nm.
The range is preferably from 100 to 100 μm. When the average particle diameter is too small, light from the organic EL element cannot be sufficiently diffused. On the other hand, if the average particle size is too large, the dispersion stability decreases, and a large amount of light diffusion particles are required to obtain the desired diffusion performance, which is not preferable.

Examples of the light-diffusing particles preferably used in the present invention include metal particles, glass beads, resin particles, metal-coated resin particles and pigments (any of organic pigments and inorganic pigments, such as TiO _{2 and} other white pigments). Pigments are more preferable), and emulsion particles (which may be any of water-in-oil or oil-in-water liquid particles, resin emulsion particles, etc.). Of these, only one kind may be used, or two or more kinds may be used in combination. Further, particles and the like which have been used by being added to a resin in a conventional diffusion plate can also be used as the light diffusion particles of the present invention. The content ratio of the light diffusing particles is preferably 40 to 80% by volume, and more preferably 50 to 60% by volume, based on the entire light diffusing member. If the content is too small, sufficient light diffusion performance cannot be obtained, and if it is too large, light loss due to the light diffusion member becomes excessive and the brightness of the backlight becomes insufficient.

The light diffusing member of the present invention may contain a surfactant for the purpose of improving the dispersion stability of the light diffusing particles. In particular, when the light diffusion particles are composed of a liquid, a surfactant is usually used to disperse the liquid in a cooling medium to form emulsion particles and the like. Surfactants include anionic,
Either cationic or nonionic surfactants may be used, but nonionic surfactants such as polyoxyethylene nonylphenyl ether are preferably used.

As a method of disposing a light diffusing member between the organic EL element and the liquid crystal panel, a volume chamber is defined by a transparent material such as glass or film so as to be in contact with the light emitting side surface of the transparent substrate of the organic EL element. Then, a method of enclosing the light diffusing member in the volume chamber can be cited. This light diffusing member is preferably provided so as to be able to circulate inside and outside the volume chamber, thereby improving the cooling performance.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically by way of examples. (1) Configuration of FS liquid crystal display device As shown in FIG. 1, an organic EL element (backlight) 1
A FS liquid crystal display device having a screen size of 4 inches (aspect ratio 3: 4) including the light diffusion member 2 and the liquid crystal panel 3 was manufactured.

First, the structure of the organic EL device 1 will be described. As shown in FIG. 1, on a transparent substrate 11 made of soda-lime glass, an anode made of ITO, an organic EL film,
And an organic EL laminated film 12 formed by sequentially laminating a cathode made of aluminum and an aluminum alloy (both not shown). This organic EL film is a stripe pattern (width: 0.55 mm, pitch: 0.73 m) of three types of organic EL films capable of emitting three primary colors of red, green, and blue, respectively.
m). Reference symbols R, G, and B in FIG. 1 schematically indicate portions of the organic EL laminated film 12 that emit red, green, and blue light when driven, respectively. A sealing member 13 formed by pressing a stainless steel plate having a thickness of 0.4 mm into a dish shape is joined to the back surface of the transparent substrate 11 (the surface on the side where the organic EL laminated film 12 is formed). Thereby, the organic EL laminated film 12 is hermetically sealed.

The light diffusing member 2 is obtained by dispersing resin beads (light diffusing particles) 21 having an average particle diameter of 10 μm in water (cooling medium) 22. The content ratio of the resin beads 21 to the light diffusing member 2 is as follows. 50% by volume. The resin beads 21 used were “Micropearl” manufactured by Sekisui Fine Chemical Co., Ltd. This light diffusion member 2
It is housed in a 1 mm-thick volume chamber K defined by a glass plate 41 and a spacer member 42 made of stainless steel. The spacer member 42 is joined to the glass substrate 41 and the transparent substrate 11 by an adhesive (not shown). As shown in FIG. 2, both left and right ends of the spacer member 42 project from the organic EL element 1 to form a hollow cooling pipe 42.
1 and the space inside the cooling pipe 421 is a volume chamber K
Communicates with the top and bottom of the

The liquid crystal panel 3 is a monochrome active matrix type, and displays an image by changing the transmittance of primary color light incident from the back for each pixel in accordance with an image signal. One of the two transparent substrates is formed with a number of scanning lines corresponding to the number of vertical pixels, and the other transparent substrate is formed with a number of signal lines corresponding to the number of horizontal pixels (both are shown). Zu). The organic EL element 1 and the liquid crystal panel 3 have a control circuit (not shown) that scans the liquid crystal panel 3 during a screen display period of one field or one frame and sequentially changes the illumination light of the organic EL element 1 between three colors. Is connected.

(2) Function of Light Diffusion Member This FS liquid crystal display device has a writing period W = 1 m, for example.
sec, the response time of the liquid crystal M = 4 msec, and the organic EL
The element is driven under the condition of a lighting period L = 1 msec. The operation of the light diffusing member at this time will be described with reference to FIGS. The arrow H in FIGS. 1 and 2 indicates the moving direction of the light diffusing member 3.

The stripe-shaped irradiation light from the organic EL element 1 is incident on the light diffusing member 2, where it is diffused by the resin beads 21 to emit surface light, and is incident on the rear surface of the liquid crystal panel 3 to display an image. Further, the heat generated by the organic EL element 1 is transmitted to the light diffusing member 2 through the transparent substrate 11, and the light diffusing member 2 which has been heated and has a reduced specific gravity rises in the volume chamber K. As shown in FIG. 2, after the light diffusion member 2 reaches the upper end of the volume chamber K, the supply of heat from the organic EL element 1 is interrupted after flowing into the cooling pipe 421, so that the cooling pipe is naturally cooled. 421 flows down and returns from the lower end of the volume chamber K. By circulating the light diffusion member 2 in this manner, the organic EL element 1 can be efficiently cooled.

As shown in FIG. 3, the life of the organic EL element used as a backlight in the FS liquid crystal display device of the present invention largely depends on the temperature. FIG.
In the graph, the horizontal axis represents the environmental temperature during use of the organic EL element, and the vertical axis represents the luminance half-life as an index of the element life. As can be seen from FIG. 3, when the ambient temperature is lowered by 20 ° C., the luminance half time is extended about twice. Therefore, by using a light diffusing member having a function of cooling the organic EL element as in the FS liquid crystal display device of the above embodiment, the life of the organic EL element as a backlight can be greatly improved. Further, since the light diffusion member also has a function as a conventional diffusion plate, even if the stripe shape of the organic EL film is enlarged as compared with the case where this light diffusion member is not used, uniform surface light is incident on the liquid crystal panel. Can be done. This simplifies the configuration of the organic EL element, which is advantageous in manufacturing, and reduces energy loss.

Although the light diffusing member is circulated by convection in the above embodiment, the light diffusing member may be forcibly circulated using a pump or the like. In this case, the driving of the pump or the like may be continuous or intermittent. In the above embodiment, the light diffusing member is naturally cooled. However, the light diffusing member drawn from the volume chamber K can be cooled by a heat exchanger or the like. Further, in the above embodiment, the spacer member constituting the cooling pipe was used, and the light diffusing member was extracted from the cooling pipe and cooled. However, as shown in FIG. Spacer member 4 having ears 422
2, the heat of the light diffusing member may be released from the ears 422.

[0026]

According to the FS liquid crystal display of the present invention, a light diffusing member having a cooling function is disposed on the surface of an organic EL element used for a backlight.
The heat generated from the L element is removed through the transparent substrate to remove the organic E.
The L element can be cooled. Since the light diffusing member has a cooling function in addition to the function as the conventional diffusing plate, the FS liquid crystal display device according to the present invention can be more easily compared with a case where a cooling member is provided separately from the diffusing plate. Can be reduced in thickness.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an FS liquid crystal display device of an embodiment.

FIG. 2 is a view in the direction of arrow II in FIG. 1;

FIG. 3 is a characteristic diagram showing a relationship between a use temperature and a life of an organic EL element.

FIG. 4 is a front view showing an FS liquid crystal display device of another embodiment.

[Explanation of symbols]

1; organic EL element (backlight), 11; transparent substrate,
12; organic EL laminated film, 2; light diffusion member, 21; resin beads (light diffusion particles), 22; water (cooling medium), 3: liquid crystal panel, 41; glass plate, 42; spacer member, 42
1; cooling pipe.

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Claims (4)

[Claims] 1. A field-sequential liquid crystal display device using an organic EL element for a backlight, wherein light diffusion particles are contained in a liquid cooling medium between the organic EL element and a liquid crystal panel. A field sequential liquid crystal display device provided with a member. 2. The field sequential liquid crystal display device according to claim 1, wherein the light diffusion particles are at least one selected from metal particles, glass beads, resin particles, metal-coated resin particles, and pigments. 3. The field sequential liquid crystal display device according to claim 1, wherein said light diffusion particles are emulsion particles. 4. The field sequential liquid crystal display device according to claim 1, wherein said light diffusing member is provided so as to be able to circulate.