JP2008277078A - Backlight unit, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit reduced in in-plane luminance difference, and a display device improved in visibility. <P>SOLUTION: Serrate projecting parts 8b are formed on the side surface 8a of a light guide plate 8, and the projecting part 8b is composed of a first surface 801 and a second surface 802. The first surface 801 is permeable by light from an LED 11, and the second surface 802 is semi-permeable to the light having passed through the first surface 801. The light emitted from an emission surface 11b passes through the first surface 801 and travels to the second surface 802. In a semi-permeable film 13, light having intensity equivalent to its reflectivity is emitted toward the light guide plate 8 as reflected light. Light having intensity equivalent to the permeability of the projecting part 8b passes through the semi-permeable film 13, and is emitted toward the adjacent projecting part 8b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a backlight unit and a display device.

  In recent years, a liquid crystal display device has a relatively simple structure, can be easily reduced in thickness and weight by selecting constituent members, and can be driven at a low voltage. It is actively used for TVs, video cameras, and vehicle instrument panels.

  For example, in a transmissive liquid crystal display device, a very thin liquid crystal layer of about several μm oriented in a predetermined direction, a pair of transparent thin substrates that sandwich the liquid crystal layer, and a polarizer and A pair of polarizing plates constituting the analyzer. Wiring patterned in a predetermined shape is formed on the substrate surface on the side where the liquid crystal layer is provided. When a voltage is applied to the liquid crystal layer through this wiring, the alignment of the liquid crystal changes, and the amount or wavelength of light transmitted through the liquid crystal layer changes. In the liquid crystal display device, desired display is performed using this.

  In such a liquid crystal display device, generally, a backlight unit is provided on the back side of the liquid crystal layer, that is, on the non-viewer side. There are a sidelight type and a direct type in the backlight unit, but the sidelight type is often adopted because it is advantageous in terms of thinning and heat countermeasures (for example, see Patent Document 1).

  The sidelight-type backlight unit includes a light guide plate and a light source disposed on the side of the light guide plate. Here, a chip-type LED (Light Emitting Diode) is used as the light source. The light emitted from the LED enters the inside from the side surface of the light guide plate. And it injects into a liquid-crystal layer through the diffuser plate provided in the viewer side of the light-guide plate. On the other hand, a reflection plate is provided on the non-viewer side of the light guide plate, and light emitted from the light guide plate to the non-viewer side is reflected by the reflection plate and enters the liquid crystal layer in the same manner as described above.

Japanese Patent Laid-Open No. 2004-177876

  FIG. 3 is a partial plan view of a conventional backlight unit. As shown in this figure, a plurality of LEDs 102 are arranged along the side surface 101 a of the light guide plate 101. The LED 102 emits light by electric power supplied from a circuit board (not shown) provided in the backlight unit through an electrode terminal (not shown).

  In FIG. 3, the light emitted from the LED 102 enters the inside from the side surface 101 a of the light guide plate 101 as indicated by an arrow. Then, after multiple reflection inside the light guide plate 101, the light enters the liquid crystal layer (not shown). However, since there is no light source in the region 103 located between the adjacent LEDs 102, it is difficult for light from the LEDs 102 to enter the side surface 101 a of the light guide plate 101 facing the region 103. Further, it is not easily affected by multiple reflections inside the light guide plate 101. For this reason, the luminance of the shaded portion 104 in the figure is lower than the other portions, and is visually recognized as a clear dark portion on the liquid crystal display device.

  The above problem can be improved by increasing the number of LEDs 102 and reducing the area of the region 103 (shortening the distance between the LEDs). However, LEDs are expensive, and increasing the number thereof is not preferable because it causes a large price increase.

  The present invention has been made in view of these points. That is, an object of the present invention is to provide a backlight unit that reduces a luminance difference in a plane.

  Another object of the present invention is to provide a display device with improved visibility by using the above backlight unit.

  Other objects and advantages of the present invention will become apparent from the following description.

A first aspect of the present invention is a backlight unit that introduces light from a light source into the inside through a side surface of a light guide plate and emits light from one main surface of the light guide plate.
There is only one light source,
The side surface is provided with a saw-tooth-shaped convex portion composed of a first surface and a second surface,
The light source is disposed at an end portion on the side surface side where the convex portion is provided, and the first surface on the light source side is transmissive to light from the light source,
The second surface is semi-transmissive to the light transmitted through the first surface;
An angle θ formed by the imaginary line on the side surface and the second surface is 40 degrees ≦ θ ≦ 50 degrees.

  In this invention, it is preferable that the reflectance in the said 2nd surface of the light of the said light source which injects from the said 1st surface side is 60%-80%.

  In the present invention, the second surface may be coated with a silver film or an aluminum film.

A second aspect of the present invention includes a display panel,
A display unit having a backlight unit disposed on a back surface of the display panel and connected to the display panel,
The backlight unit is a backlight unit according to the first aspect of the present invention.

  According to the first aspect of the present invention, there is only one light source, and the side surface of the light guide plate is provided with a sawtooth-shaped convex portion including a first surface and a second surface, The second surface is transmissive to the light from the light source, and the second surface is semi-transmissive to the light transmitted through the first surface, and is formed by the imaginary line on the side surface and the second surface. Since the angle θ is 40 degrees ≦ θ ≦ 50 degrees, it is possible to suppress the occurrence of a low luminance portion in the region inside the light guide plate.

  According to the second aspect of the present invention, a display device with improved visibility is obtained.

  FIG. 1 is a schematic cross-sectional view of the liquid crystal display device according to the present embodiment.

  As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal display panel 2 and a backlight unit 3 disposed on the back surface of the liquid crystal display panel 2 and connected to the liquid crystal display panel 2. Here, the backlight unit 3 is a sidelight type backlight unit.

  The liquid crystal display panel 2 includes a pair of transparent substrates 4 and 5 that sandwich a liquid crystal layer (not shown). Further, these substrates are sandwiched between a pair of polarizing plates 6 and 7. And the backlight unit 3 is provided in the position which opposes the polarizing plate 7 by the side of a counter-viewer.

  The backlight unit 3 includes a light guide plate 8, a diffusion plate 9 provided on the viewer side of the light guide plate 8, a reflection plate 10 provided on the non-viewer side of the light guide plate 8, and the side of the light guide plate 8. The LED 11 is provided in a frame case 12 and a frame case 12 for housing them. Here, the LED 11 is a light source in the backlight unit 3 and emits light by electric power supplied from a circuit board (not shown) provided in the backlight unit 3 through an electrode terminal (not shown).

  In the present embodiment, the backlight unit is not provided with a plurality of LEDs, but only one high-brightness LED is provided.

  FIG. 2 is a partial plan view of the backlight unit in the present embodiment. In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same parts.

  As shown in FIG. 2, the LED 11 is disposed at the end portion on the side surface 8 a side of the light guide plate 8, and the light leaking from the LED 11 to the side surface 8 a side of the light guide plate 8 is the side surface 8 a. Then, the light enters the light guide plate 8. In this invention, the light radiate | emitted along the virtual line 14 of the side surface 8 from the output surface 11b of LED11 is utilized actively. For this reason, the present embodiment is characterized in that the side surface 8a of the light guide plate 8 is provided with a sawtooth-shaped convex portion 8b.

  The convex portion 8 b is configured by a first surface 801 and a second surface 802. The first surface 801 is light transmissive, and the second surface 802 is semi-transmissive. More specifically, the first surface 801 is transmissive to the light from the LED 11, and the second surface 802 is semi-transmissive to the light transmitted through the first surface 801. The first surface 801 can be formed of the same transmissive material as the side surface 8 a of the light guide plate 8. On the other hand, the second surface 802 can be formed by coating the same transmissive material as the side surface 8a of the light guide plate 8 with a semi-transmissive material.

  Examples of the semi-permeable material include metal films such as a silver film and an aluminum film. When the intensity of the reflected light with respect to the intensity of the incident light is taken as the reflectance and the intensity of the transmitted light from the convex part with respect to the intensity of the incident light on the convex part is taken as the transmittance, these values in the metal film are within the light guide plate. The value is such that light is introduced as uniformly as possible. Specifically, the reflectance is 60% to 80%, the transmittance is preferably 20% to 40%, the reflectance is about 65%, and the transmittance is about 35%. preferable.

  As an example, the light guide plate 8 having a sawtooth-shaped convex portion 8b on the side surface 8a is formed using an acrylic resin. Next, the semipermeable membrane 13 is provided on the second surface 802 of the convex portion 8b. For example, the semipermeable membrane 13 can be formed by attaching a silver tape to the second surface 802. Alternatively, a semi-transmissive film 13 may be formed by forming a silver film on the second surface 802 using a vacuum deposition method, a plating method, or the like.

  The light emitted from the emission surface 11 b facing the first surface 801 by the LED 11 passes through the first surface 801 and travels toward the second surface 802. In the semi-transmissive film 13, light having an intensity corresponding to the reflectance is emitted as reflected light into the light guide plate 8. On the other hand, light having an intensity corresponding to the transmittance of the convex portion 8b passes through the semi-transmissive film 13 and is emitted to the adjacent convex portion 8b side.

The inclination angle θ of the second surface 802, that is, the angle θ formed between the imaginary line 14 on the side surface 8 a of the light guide plate 8 and the second surface 802 is the light reflected from the second surface 802 inside the light guide plate 8. The angle at which the light can enter. In particular,
It is preferable that the relationship of 40 degrees ≦ θ ≦ 50 degrees is established.

  Thus, in this embodiment, one high-brightness LED 11 is provided, and the light emitted from the LED 11 is dispersed so that the light uniformly enters the light guide plate 8. According to this structure, it can suppress that a part with a low brightness | luminance arises in the area | region inside the light-guide plate corresponding between LED. That is, a backlight unit with reduced in-plane luminance difference can be obtained. By using this backlight unit, a display device with improved visibility can be provided.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

It is typical sectional drawing of the liquid crystal display device in this Embodiment. It is a fragmentary top view of the backlight unit in this Embodiment. It is a partial top view of the conventional backlight unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal display panel 3 Backlight unit 4, 5 Substrate 6, 7 Polarizing plate 8 Light guide plate 9 Diffusing plate 10 Reflecting plate 11 LED
12 Frame case 13 Semi-permeable membrane 801 1st surface 802 2nd surface 8a Side surface 8b Convex part 11b Output surface

Claims (4)

In the backlight unit that introduces light from the light source into the inside through the side surface of the light guide plate and emits light from one main surface of the light guide plate,
There is only one light source,
The side surface is provided with a saw-tooth-shaped convex portion composed of a first surface and a second surface,
The light source is disposed at an end portion on the side surface side where the convex portion is provided, and the first surface on the light source side is transmissive to light from the light source,
The second surface is semi-transmissive to the light transmitted through the first surface;
An angle θ formed by the imaginary line on the side surface and the second surface satisfies 40 ° ≦ θ ≦ 50 °. 2. The backlight unit according to claim 1, wherein a reflectance of the light of the light source incident from the first surface side on the second surface is 60% to 80%. The backlight unit according to claim 1, wherein the second surface is covered with a silver film or an aluminum film. A display panel;
A display unit having a backlight unit disposed on a back surface of the display panel and connected to the display panel,
The display device according to claim 1, wherein the backlight unit is the backlight unit according to claim 1.