JP2006330450A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device of which total manufacturing cost is reduced by eliminating an expensive optical film such as prism sheet and using a relatively low-cost optical film. <P>SOLUTION: In the liquid crystal display device in which the optical film is disposed between a surface light emission optical source 12 and a liquid crystal panel 14, only a plurality of diffusion films 16, preferably only two sheets of diffusion films are disposed as the optical film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device in which an optical film is disposed between a surface emitting light source and a liquid crystal panel. More specifically, the present invention relates to a liquid crystal display device in which the entire manufacturing cost is reduced by devising the optical film.

  A liquid crystal display device generally includes a light source and a liquid crystal display unit (hereinafter referred to as “liquid crystal panel”). As the light source, a surface emitting light source is generally used. A surface-emitting light source is often a unit composed of a linear light source, a reflecting plate, and a diffusing plate. However, in a field that requires strong brightness, such as a liquid crystal display device for a television, a linear light source is placed directly under the liquid crystal panel. A plurality of direct type surface emitting light sources are used. In addition, a plate having a three-dimensional shape having convex protrusions between adjacent linear light sources may be employed instead of a flat plate as the reflecting plate. Further, when the required brightness cannot be obtained even with the direct type surface emitting light source as described above, a film or sheet having various optical characteristics (hereinafter referred to as “optical film”) is used as the surface emitting light source and the liquid crystal panel. It is often placed between and used. These optical films greatly improve the front luminance of the liquid crystal display device.

  Among the optical films described above, there is a light diffusion film (hereinafter referred to as “diffusion film”) as a relatively inexpensive one. This diffusion film is obtained by bonding a large number of transparent spherical resins to the film surface, and is generally available (for example, trade name “Opulse” manufactured by Eiwa Co., Ltd.). The diffusion film not only eliminates the unevenness of light emission of the surface light source, but also uniforms the light emission, and the light incident from the back surface of the spherical resin adhesive surface is condensed to some extent by the lens action of the spherical resin, thereby increasing the front luminance. There is work to improve.

  Further, as an optical film different from the above-described diffusion film, there is a prism sheet that has a high light collecting effect by chevron processing on the film surface, and using this prism sheet as an optical film of a liquid crystal display device, for example, It is described in Patent Documents 1 and 2. That is, Patent Document 1 describes that front luminance is improved by using a light diffusing sheet in which a light diffusing member and a prism sheet are overlapped. Patent Document 2 describes that the front luminance is improved by using a planar light emitting device in which a prism sheet is arranged. The prism sheet is expensive because it has a dramatic effect of improving the front brightness, but is an almost indispensable member for liquid crystal display devices that require strong brightness. The prism sheet is generally available (for example, a brightness enhancement film manufactured by Sumitomo 3M).

JP-A-9-127314 JP 2004-71576 A

  In recent years, there has been a strong demand for cost reduction of liquid crystal display devices. For this reason, in parallel with the technical innovation of the liquid crystal display device itself, the omission of members that have been used so far has been considered.

  However, since the techniques described in Patent Documents 1 and 2 both use an expensive prism sheet as an optical film, it is difficult to reduce the cost of the liquid crystal display device.

  The present invention has been made in view of the above-described circumstances, and omits an expensive optical film such as a prism sheet, and uses a relatively inexpensive optical film, thereby reducing the overall manufacturing cost. An object is to provide an apparatus.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when a prism sheet is used in an application that requires strong brightness, a relatively inexpensive diffusion is used instead of the prism sheet. It has been found that by using a plurality of films, the same front luminance improvement effect as that obtained when an expensive prism sheet is used can be obtained. In other words, it has been found that this can be omitted in applications where a conventional prism sheet is indispensable.

  The present invention has been made on the basis of the above-described knowledge, and in a liquid crystal display device in which an optical film is disposed between a surface emitting light source and a liquid crystal panel, the optical film is composed of only a plurality of diffusion films. A liquid crystal display device is provided.

  In this case, it is more preferable that the optical film is composed of only two diffusion films from the viewpoint of cost reduction of the liquid crystal display device.

  According to the present invention, it is possible to reduce the manufacturing cost of the liquid crystal display device by using a plurality of relatively inexpensive diffusion films instead of the expensive prism sheet. That is, in the present invention, by using a plurality of diffusion films instead of one prism sheet, the reason is not clear, but a superior front luminance improvement effect is obtained compared with the case of using one prism sheet. It is what

  In a prism sheet aiming at high functionality with a single film, it is considered that the production cost for the light condensing effect is not commensurate with the demand for advanced manufacturing technology. On the other hand, the diffusion film has a higher light collecting effect than the production cost. Therefore, in the present invention, the cost of the liquid crystal display device can be reduced by using a plurality of diffusion films.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples. FIG. 1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention. In the liquid crystal display device 10 of this example, two diffusion films 16 and 16 are disposed as optical films between the surface emitting light source 12 and the liquid crystal panel 14. As the liquid crystal panel 14, for example, a known one having a liquid crystal element, a color filter, a polarizing plate, and the like can be used. The surface emitting light source 12 is a direct type surface emitting light source in which a plurality of linear light sources 22 are arranged in parallel between the reflecting plate 18 and the diffusing plate 20. The reflector 18 has a three-dimensional shape having a mountain-shaped convex portion 24 between adjacent linear light sources 22. In addition, as the linear light source 22, a straight tube fluorescent lamp etc. can be used, for example.

  The diffusion film 16 described above is not particularly limited, but a film that is transparent as a whole and does not absorb a specific color is preferable. As such a diffusion film, for example, a film containing resins such as polymethacrylate, polyacrylonitrile, polyester, epoxy resin, polyethylene, polypropylene, and inorganic fillers such as silica can be suitably used.

  The structure of the diffusing film is various, but any film having light diffusibility may be used. For example, a resin-made spherical particle having a particle diameter of 1 to 20 μm is uniformly applied with a paint containing a binder on at least one surface of a plastic film, and then dried and used preferably. In addition, the said particle | grain does not need to be a perfect sphere if it meets the objective of improving light diffusibility, and an elliptical sphere or a star shape may be sufficient.

  In the present invention, the diffusion film has a crystallization nucleating agent, a crystallization accelerator, an aerated nucleating agent, an antioxidant, an antistatic agent, an anti-ultraviolet agent, a light stabilizer, as long as the properties are not affected. Various additives such as a fluorescent brightening agent, a compatibilizing agent, a lubricant, a reinforcing agent, a flame retardant, a crosslinking agent, a crosslinking aid, a plasticizer, a thickener, and a thickener may be blended. Moreover, the resin containing the said additive may be laminated | stacked on a diffusion film, and the coating material containing the said additive may be coated.

  Further, the material for forming the reflection plate 18 of the surface-emitting light source 12 is not particularly limited, but a foamed sheet having a diffuse reflectance of 95% or more, preferably 97% or more is suitable and particularly preferable. Is a thermoplastic resin film or sheet having fine bubbles or pores having an average bubble diameter of not less than the wavelength of light and not more than 50 μm, preferably not more than 20 μm, more preferably not more than 10 μm. Examples of the material of the thermoplastic resin film or sheet include, for example, general-purpose resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polychlorinated biphenyl, polyethylene terephthalate, and polyvinyl alcohol, polycarbonate, polybutylene terephthalate, polyethylene naphthalate, and polyamide. , Polyacetal, polyphenylene ether, ultrahigh molecular weight polyethylene, polysulfone, polyethersulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, polyetheretherketone, polyimide, polytetrafluoroethylene, liquid crystal polymer, fluororesin, etc. Examples include engineering plastics, copolymers or mixtures thereof. Among these, polyester, polyphenylene sulfide, polypropylene, and cyclopolyolefin are preferable because of their good heat resistance and impact resistance. In addition, antioxidants, ultraviolet inhibitors, lubricants, pigments, reinforcing agents, and the like can be appropriately added to the thermoplastic resin. Moreover, you may form by apply | coating the coating layer containing these additives.

  More specifically, as an example of the foamed sheet, a polyester-based sheet in which an extruded sheet of thermoplastic polyester is impregnated with carbon dioxide gas under high pressure and then heated and foamed has an internal cell diameter of 50 μm or less. A foam sheet (for example, MCPET (registered trademark) manufactured by Furukawa Electric Co., Ltd.) can be used.

  Another preferred example of the material for forming the reflector is a film or sheet of a thermoplastic resin containing a filler, in which a large number of voids are formed with the filler as a nucleus. In this case, in the film or sheet, the thermoplastic resin film or sheet containing the filler is formed by forming an unstretched film or sheet containing the filler and stretching the unstretched film or sheet. A porous stretched film or sheet in which a large number of voids are formed as nuclei is preferable.

  Moreover, as the diffusion plate 20 of the surface-emitting light source 12, an acrylic resin plate (for example, Acrylite L (registered trademark) manufactured by Mitsubishi Rayon Co., Ltd.) or the like can be used.

  Hereinafter, the present invention will be described by way of examples. The front luminance of the liquid crystal display device was measured as follows.

(Measurement of front brightness)
An experimental surface light source having the same configuration as that of a surface light source used in a liquid crystal display device for a liquid crystal television requiring strong brightness was produced, and the surface light source was allowed to stand for 1 hour or more to stabilize the output. In Examples and Comparative Examples, an optical film (diffusion film, prism sheet) was fixed to the light emitting surface of the surface emitting light source. Thereafter, at a position 0.35 m away from the light-emitting surface, the luminance at a total of 16 points is measured with a luminance meter (trade name BM-9 manufactured by Topcon Corporation) at a central portion of the surface-emitting light source and above and below each at 0.5 cm intervals. ), And the average of these values was defined as the front luminance value. As the diffusion film and the prism sheet, the same materials as those used for the liquid crystal television were used.

Example 1
The luminance was measured by stacking two diffusion films on the light emitting surface of the surface emitting light source. As a result, the front luminance was 221.0 cd / m ² .

(Comparative Example 1)
The luminance was measured without overlaying the optical film on the light emitting surface of the surface emitting light source. As a result, the front luminance was 166.4 cd / m ² .

(Comparative Example 2)
One sheet of diffusion film was placed on the light emitting surface of the surface emitting light source, and the luminance was measured. As a result, the front luminance was 205.8 cd / m ² .

(Comparative Example 3)
Luminance was measured with one prism sheet superimposed on the light emitting surface of the surface light source. As a result, the front luminance was 215.7 cd / m ² .

  The results are shown in Table 1. In addition, the estimated costs in each case are expressed by ○ and × in the order of low, and the overall evaluation based on the balance between the luminance and the cost is expressed by ○ and × in the desirable order together with Table 1.

  From the results shown in Table 1, when two diffusion films are used instead of one prism sheet, a superior front luminance improvement effect is obtained compared with the case where one prism sheet is used. According to this, it can be seen that the manufacturing cost of the liquid crystal display device can be reduced while maintaining the excellent front luminance of the liquid crystal display device.

  On the other hand, when a diffusion film was not used without using a prism sheet (Comparative Example 1), it was a matter of course that the front luminance was insufficient, but one diffusion film was used. Even in the case (Comparative Example 2), the front luminance is not sufficient.

1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Surface emitting light source 14 Liquid crystal panel 16 Diffusing film 18 Reflecting plate 20 Diffusing plate 22 Linear light source 24 Convex part

Claims (4)

  A liquid crystal display device in which an optical film is disposed between a surface-emitting light source and a liquid crystal panel, wherein the optical film comprises only a plurality of diffusion films.   The liquid crystal display device according to claim 1, wherein the optical film includes only two diffusion films.   3. The liquid crystal display device according to claim 1, wherein the surface-emitting light source is a direct-type surface-emitting light source in which a plurality of linear light sources are disposed between a reflection plate and a diffusion plate.   The liquid crystal display device according to claim 3, wherein the reflecting plate has a three-dimensional shape having a convex portion between adjacent linear light sources.

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