JP2007213972A - Lighting system and display device provided with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device greatly improving display definition by preventing unevenness in luminance with a simple method. <P>SOLUTION: The liquid crystal display device includes a light absorbing layer in an area without any light guide plate prism and eliminates reflected light which can cause the unevenness in the luminance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light guide, an illumination device, and a liquid crystal display device.

  Liquid crystal display devices used in mobile phones, portable small TVs, portable game machines, PDAs, small notebook personal computers, etc. have good lighting characteristics and low heat generation and noise instead of cold cathode tubes. An illumination device using an LED element as a light source has been frequently used.

  In general, a transmissive color liquid crystal display device uses an illumination device using a white point light source as a backlight, and has a light guide plate and a light source disposed on its side end surface as a basic configuration. The illuminated light is reflected by a prism shape formed on the surface opposite to the light exit surface of the light guide plate and emitted from the light exit surface, thereby illuminating an object to be illuminated such as a liquid crystal panel.

FIG. 4 shows a cross section of a conventional liquid crystal display device. An illumination device 21 is provided behind the liquid crystal display element 6. The illumination device 21 includes a point light source 1, a light guide plate 2 formed of a transparent resin such as acrylic resin, a diffusion sheet 4 for uniformly diffusing light, and condensing scattered light in the x and y directions, respectively. The first prism sheet 5a and the second prism sheet 5b are provided (see, for example, Non-Patent Document 1). The light guide plate 2 is formed with a prism 3a for emitting incident light to the upper surface so that the vicinity of the point light source is sparse and becomes denser as it is separated so that the light is emitted uniformly. Here, the prism 3a has a concave shape. FIG. 5 shows a configuration of a liquid crystal display device including light guide plates having different prism shapes. Here, the prism 3b has a convex shape. In any configuration, the incident light 7a incident on the light guide plate 2 from the point light source 1 is reflected by the prism and emitted to the liquid crystal display element 6 side. Then, after being uniformed by the diffusion sheet 4, the light is condensed in the normal direction by the first prism sheet 5a and the second prism sheet 5b.
Hiroshi Okada, “Development Trend of Prism Sheet for LCD Backlight” Monthly Display, April 2004, p.14-21

  In a liquid crystal display device for a portable device such as a cellular phone, a point light source is often installed in the vicinity of an effective display area due to a demand for compactness. FIG. 6 schematically shows a state in which such a liquid crystal display device is seen from the opposite side of the point light source. As shown in the figure, when the liquid crystal display device is viewed from the opposite side of the point light source, only the light ray 7b close to the point light source is observed among the light rays 7b and 7c reflected by the region without the prism of the light guide plate. Therefore, a luminance unevenness phenomenon occurs in which only the vicinity of the point light source appears bright. FIG. 7 schematically shows such luminance unevenness.

  Accordingly, an object of the present invention is to prevent luminance unevenness when a display device is perspectively viewed even when a point light source is installed in the vicinity of a display area.

  Therefore, in the liquid crystal display device of the present invention, a light absorption layer is provided in an area of the light guide plate where there is no prism, and reflected light that causes uneven brightness is removed.

  In the liquid crystal display device of the present invention, reflected light in an area where there is no prism can be removed by the light absorption layer, so that uneven brightness when viewed from the perspective can be prevented regardless of the position of the point light source.

  The illumination device of the present invention includes a point light source and a light guide plate that guides light from the incident point light source to the irradiation surface, and prisms are formed at predetermined intervals on a surface opposite to the irradiation surface of the light guide plate. A light absorbing layer is provided in an area where the prism is not formed.

  Further, a minute uneven surface is formed in an area where no prism is formed, and a light absorption layer is provided on the uneven surface. The shape of the prism formed here was a convex shape or a concave shape.

  In addition, the display device of the present invention includes a non-self-luminous display element, a point light source, and a light guide plate that guides light emitted from the point light source to the display element, and on the surface of the light guide plate opposite to the display element. Prisms with a predetermined interval are formed, and a light absorption layer is provided in an area without the prisms.

  Further, when a liquid crystal display element is used as the display element, a diffusion sheet for uniformly diffusing light between the liquid crystal display element and the light guide plate, and for condensing scattered light in the x direction and the y direction, respectively. A prism sheet may be provided.

  Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described in detail with reference to FIGS.

  The configuration of the liquid crystal display device of this example is schematically shown in FIG. As shown in the drawing, a light guide plate 2 for illuminating the liquid crystal display element is provided behind the liquid crystal display element 6, and a point light source 1 such as an LED is disposed as a point light source on the side surface of the light guide plate. In addition, between the liquid crystal display element 6 and the light guide plate 2, the diffuser sheet 4 is refracted as light diffusing means for improving the brightness and uniformity of the entire lighting device, and light spread in the horizontal and vertical directions with respect to the light source is refracted. Prism sheets 5 a and 5 b are provided between the liquid crystal display element 6 and the diffusion sheet 4 as refracting means for condensing light in the front direction. On the lower surface of the light guide plate 2, prisms for emitting light incident from the point light source 1 to the display element side are formed sparsely in the vicinity of the LED light source 1 and densely as the distance from the point light source 1 increases, and the emitted light is uniform. Designed to be A light absorbing layer 8 is provided in a region where there is no prism.

  Incident light 7a from the point light source 1 is reflected by the prism and emitted to the display element side. On the other hand, the incident light 7b, which has been a cause of luminance unevenness when viewed from the conventional perspective, is absorbed by the light absorption layer 8 and is not emitted to the outside. Accordingly, even when the display device is viewed obliquely, no large luminance unevenness is observed, and the display quality is greatly improved as compared with the case where there is no light absorption layer.

  The light absorbing layer 8 may be coated with a black pigment such as carbon black, or a resin in which a plurality of pigments or dyes are mixed, or may be formed by vacuum deposition of a material having low reflectance such as chromium oxide. Further, the same effect can be obtained even if the reflectance is lowered by forming films having different refractive indexes in multiple layers.

  FIG. 2 shows a second embodiment to which the present invention is applied, in which the prism of the light guide plate 2 is formed in a convex shape. The light absorption layer 8 was provided in a region without a prism, and the same effect as in Example 1 was obtained.

  FIG. 3 shows a third embodiment to which the present invention is applied, in which a region without a prism of the light guide plate 2 is made into a satin finish with minute irregularities and a light absorption layer 8 is provided thereon. In Example 1, it was difficult to reduce the light reflection at the boundary between the light guide plate and the light absorption layer, and some luminance unevenness remained, but the light reflection was reduced by making the light guide plate a satin finish. As a result, the absorption efficiency of the light absorption layer is increased, and further luminance unevenness can be achieved.

  As described above, the present invention eliminates uneven luminance when a display device is obliquely provided only by providing a light absorption layer, and provides a compact and excellent illumination device, and thus a liquid crystal display device. Can do.

  The present invention is not only effective as a display device for a small portable information device that is essential to be compact, but also has a merit in terms of space saving even in a desktop type device, and a wide range of applications can be considered.

It is sectional drawing which shows the liquid crystal display device of this invention typically. It is sectional drawing which shows typically the other Example of the liquid crystal display device of this invention. It is sectional drawing which shows typically the other Example of the liquid crystal display device of this invention. It is sectional drawing which shows the conventional liquid crystal display device typically. It is sectional drawing which shows the conventional liquid crystal display device typically. It is sectional drawing explaining the case where the conventional liquid crystal display device is perspective. It is a schematic diagram which shows the brightness nonuniformity which generate | occur | produces when the conventional liquid crystal display device is perspective.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Point light source 2 Light guide plate 3a, 3b Prism 4 Diffusion sheet 5a, 5b Prism sheet 6 Liquid crystal display element 7a, 7b, 7c Light beam 8 Light absorption layer

Claims (5)

A lighting device comprising a point light source and a light guide plate for guiding light from the incident point light source to an irradiation surface,
An illumination device, wherein a prism is formed at a predetermined interval on a surface opposite to the irradiation surface of the light guide plate, and a light absorption layer is provided in an area where the prism is not formed.   The illumination device according to claim 1, wherein a minute uneven surface is formed in an area where the prism is not formed, and the light absorption layer is provided on the uneven surface.   The lighting device according to claim 1, wherein the prism has a convex shape or a concave shape.   A display device comprising: the illumination device having the configuration according to claim 1; and a non-self-luminous display element that is illuminated with light from an irradiation surface of the illumination device. A display device comprising a non-self-luminous display element, a point light source, and a light guide plate that guides emitted light from the point light source to the display element,
A display device, wherein a surface of the light guide plate opposite to a display element has prisms with a predetermined interval, and a light absorption layer is provided in an area without the prisms.