JP3377478B2 - Reflection sheet and backlight unit using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflecting sheet for reducing the emission of light rays to the back side of a backlight unit, and a backlight unit using this reflecting sheet.

[0002]

2. Description of the Related Art As a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side to emit light is popular, and a backlight unit is provided on the lower surface side of the liquid crystal layer. The backlight unit 20 generally includes a rod-shaped lamp 21 as a light source and the lamp 2 as shown in FIG.
1. A rectangular plate-shaped light guide plate 23 arranged so that its end portion follows 1
And a plurality of optical sheets 22 laminated on the front surface side of the light guide plate 23, and a reflection sheet 26 laminated on the back surface side of the light guide plate 23. The optical sheets 22 have specific optical properties such as refraction and diffusion, and specifically, the light diffusion sheet 24 and the light diffusion sheet 24 disposed on the front surface side of the light guide plate 23. The prism sheet 25 and the like arranged on the front side correspond to this.

The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 23 from the lamp 21 is reflected by reflection dots or reflection sheets (not shown) on the back surface of the light guide plate 23 and each side surface. The light is emitted from the surface of the light guide plate 23. The light beam emitted from the light guide plate 23 enters the light diffusion sheet 24, is diffused, and is emitted from the surface of the light diffusion sheet 24. After that, the light rays emitted from the light diffusion sheet 24 are incident on the prism sheet 25, and emitted by the prism portion 25a formed on the surface of the prism sheet 25 as a light ray having a distribution having a peak in the substantially normal direction. Thus, the light beam emitted from the lamp 21 is
The light is diffused by the light diffusing sheet 24 and is refracted by the prism sheet 25 so as to show a peak in the substantially normal direction, and further illuminates the entire surface of the liquid crystal layer (not shown) above. It should be noted that no matter how the reflection performance of the light guide plate 23 is improved, a certain amount of light rays will be emitted to the back surface side as well, so that on the back surface side of the light guide plate 23, the emission of light rays to the back surface side is reduced. , A reflection sheet 2 for improving the brightness of a liquid crystal display device
6 are provided.

As the reflection sheet 26, conventionally, a sheet made of a synthetic resin in which a white pigment such as titanium oxide is dispersed in order to satisfy the high reflection property and the concealing property, and a void for scattering light ( Air bubbles) and those with a matt surface.

[0005]

In the above-mentioned conventional reflection sheet 26, since the concealing property is not so high, the reflectance is different in the part supporting the backlight unit 20, such as the frame, and the liquid crystal display device has a brightness. There may be unevenness.

In order to prevent such an inconvenience, it is necessary to perform printing for reducing the reflectance on the portion of the frame or the like that causes the uneven brightness, or printing for improving the concealing property on the back surface of the reflection sheet 26. However, the manufacturing process is complicated by the amount of printing.

The present invention has been made in view of these inconveniences, and aims to reduce a loss of a light beam emitted from a lamp and improve brightness by using a reflection sheet which can improve reflection efficiency and concealment property. The purpose of the present invention is to provide a backlight unit that can be used.

[0008]

The invention made to solve the above-mentioned problems is to provide a lamp and a lamp along the lamp.
Light guide that is installed and guides the light emitted from the lamp to the front side
Plate and the front side of this light guide plate,
Diffuses the emitted rays evenly and refracts them toward the normal direction.
In the backlight unit with the optical sheet
It is placed on the back side of the light guide plate to prevent light rays from escaping to the back side.
A reflective sheet that reduces the inclination of a specific direction
The surface has a surface, and the inclined surface has a plurality of stripes.
And is inclined in the width direction.
Has an inclination angle of 5 ° or more and 20 ° or less, and the inclined surface is flat.
Smooth, the inclined surface is made of synthetic resin,
It is a reflective sheet characterized by the above.

In the backlight unit, the peak direction of light rays emitted from the back surface of the light guide plate is inclined at a predetermined angle with respect to the normal direction (downward), and this direction is constant by the light guide plate. Therefore, (a) a linear lamp, (b) a light guide plate which is arranged along the lamp and guides a light beam emitted from the lamp to the front surface side, and (c) which is arranged on the front surface side of the light guide plate. A liquid crystal display device including an optical sheet that uniformly diffuses a light beam emitted from the light guide plate and refracts the light beam toward the normal direction side, and (d) a reflection sheet disposed on the back surface side of the light guide plate. In the backlight unit of, by arranging the reflection sheet so that the intersection angle between the peak direction of the light beam emitted from the back surface of the light guide plate and the inclined surface is minimized, the inclined surface of the reflection sheet has a shallow angle of light rays. Tends to be incident and reflected by the inclined surface. In this way, since the reflective sheet exhibits high reflection efficiency, it is possible to reduce the loss of light rays emitted from the back surface side and improve the brightness.

[0010] The inclined surface, a plurality of stripe-shape, so as to incline in the width direction. Here, the “width direction” means a direction orthogonal to the longitudinal direction of the stripe-shaped (that is, elongated strip-shaped) inclined surface. By doing so, the height of the unevenness formed on the surface of the reflection sheet due to the inclined surface is reduced, and an increase in the thickness of the reflection sheet due to the provision of the inclined surface can be reduced. . Further, it is possible to reduce the occurrence of uneven brightness due to the inclined surface. Further, with this structure, unevenness is formed on the surface of the reflection sheet, and sticking with the laminated light guide plate is prevented.

The inclination angle of the inclined surface is preferably smaller than the angle formed by the peak direction of the incident light ray with respect to the sheet surface. Here, the "sheet surface" means the reference surface of the sheet, and when flat, it coincides with the upper surface or the lower surface. As described above, the reflection sheet is arranged so that the angle formed by the inclined surface with respect to the peak direction of the incident light ray is reduced, but the peak of the incident light ray with the inclination angle of the inclined surface as the reference of the sheet surface. If the angle is smaller than the angle formed by the directions, the number of light rays incident on the inclined surface increases, and as a result, the amount of light reflected to the surface side can be increased.

[0012] inclination angle of the inclined surface, and 20 ° or less 5 ° or more. This is because if the inclination angle of the inclined surface is smaller than the above range, the above-described effect of promoting the reflection efficiency is not so great, and conversely, if the inclination angle exceeds the above range, the thickness of the reflection sheet increases, and the liquid crystal display This is because it goes against the demand for thinner devices.

As a method of promoting the reflection efficiency on the inclined surface, it is possible to make the inclined surface smooth or to form it from a synthetic resin having a large refractive index.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a schematic perspective view showing a reflection sheet according to an embodiment of the present invention, and FIG. 2 is a schematic side view illustrating a reflection function of the reflection sheet shown in FIG.
[Fig. 4] is a graph showing light emission characteristics on the back surface side of a general light guide plate (luminance distribution on the back surface side of the light guide plate).

The reflection sheet 1 is a synthetic resin sheet disposed on the back surface side of the light guide plate of the backlight unit, and (a) reduces the light rays emitted from the light guide plate to the back surface side of the liquid crystal display. The purpose is to improve the brightness of the device, and (b) hide the device and the like existing on the back surface side of the backlight unit.

The synthetic resin that can be used for the reflection sheet 1 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. Can be mentioned.

On the surface of the reflection sheet 1, slender strip-shaped inclined surfaces 2 are formed in stripes (a large number of adjacent inclined surfaces are parallel to each other).
Is formed in. All of these inclined surfaces 2 are inclined at a predetermined angle in a certain direction, and a more elongated strip-shaped vertical surface 3 is provided between the adjacent inclined surfaces 2. for that reason,
The reflection sheet 1 has a substantially saw-toothed sectional shape.

The function of the reflection sheet 1 will be described. As shown in FIG. 2, a certain amount of light rays are emitted from the back surface of the light guide plate 5 in the backlight unit 4,
The peak direction of the light beam is not vertically downward, but is inclined at a predetermined angle to the side opposite to the side where the lamp 6 is arranged. Figure 3
Shows the light emission characteristic on the back side of a general light guide plate, which has a peak in the direction of 70 ° from the vertical lower side. Therefore, in the backlight unit 4 for the liquid crystal display device, the inclined surface 2 is arranged on the back surface side of the light guide plate 5 so as to be parallel to the lamp 6 and face the opposite side of the lamp 6, and thus the back surface of the light guide plate 5 is formed. The crossing angle between the peak direction of the light ray emitted from the and the inclined surface 2 is minimized, and the light ray enters the inclined surface 2 of the reflection sheet 1 at a shallow angle. Therefore, the effect of upwardly reflecting the light rays leaking downward from the back surface of the light guide plate 5 is strengthened, and the loss of light rays emitted from the back surface side can be reduced.

The inclination angle θ of the inclined surface 2 of the reflection sheet 1
Is preferably smaller than the angle formed by the peak direction of the incident light ray with respect to the sheet surface X. If this inclination angle θ is made larger than the angle of the incident light with respect to the sheet surface X in the peak direction,
The amount of light rays incident on the vertical surface 3 increases, and the above-described reflecting function of the inclined surface 2 is not exerted.

Further, specifically, the inclination angle θ of the inclined surface 2 is preferably 5 ° or more and 20 ° or less. If the inclination angle θ is less than 5 °, the above-described reflection function of the inclined surface 2 is not effectively exhibited, and conversely, if the inclination angle θ exceeds 20 °, the area of the vertical surface 3 becomes large. The amount of light rays incident on the inclined surface 2 is reduced, the reflection function of the inclined surface 2 is reduced, and the thickness of the reflection sheet 1 is increased, which violates the demand for thinning the backlight unit 4. .

In order to enhance the reflection function of the inclined surface 2, for example, the inclined surface 2 may be made smooth, and the reflection sheet 1 may be made of synthetic resin having a large refractive index.

The width of the inclined portion 2 is 5 μm or more and 1000
μm or less is preferable. This is because if the width of the inclined portion 2 is smaller than the above range, it becomes difficult to manufacture it precisely, and if it exceeds the above range, the transmitted light rays may have stripe-shaped uneven brightness. is there.

As a method of forming the reflection sheet 1 having the above-described structure, (a) a synthetic resin is laminated on a sheet mold having an inverted surface shape of the reflection sheet 1 and the sheet mold is peeled off. A method of forming the inclined surface 2 on the surface,
(B) An injection molding method of injecting a molten resin into a mold having an inverted shape of the surface of the reflection sheet 1, (c) reheating the sheeted resin, and between the mold and the metal plate similar to the above. Method of transferring the shape by pressing with a sandwich, (d) Reflective sheet 1
An extruded sheet molding method in which a molten sheet-shaped resin is passed through a nip between a roll having an inverted surface on the peripheral surface and another roll, and the above-mentioned shape is transferred, (e) a UV curable resin is applied to a base film Then, the shape is transferred to an uncured UV curable resin by pressing it onto a roll having an inverted shape similar to the above, and then the UV curable resin is cured by applying ultraviolet rays, (f) EB instead of the UV curable resin There is a method of using a cured resin.

The reflection sheet of the present invention is not limited to the above embodiment, and for example, the sheet-shaped portion and the triangular prism-shaped portion having the inclined surface 2 may be formed of different synthetic resins. is there. Further, in order to improve the reflection function, it is possible to include fine bubbles inside the reflection sheet 1. Further, the vertical surface 3 provided between the pair of adjacent inclined surfaces 2 may not be perpendicular to the bottom surface.

[0025]

As described above, according to the reflection sheet of the present invention, the reflection efficiency and the hiding property can be improved. Therefore, according to the backlight unit using this reflection sheet, the loss of the light emitted from the lamp can be reduced, and the brightness can be improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a reflection sheet according to an embodiment of the present invention.

FIG. 2 is a schematic side view illustrating a reflection function of the reflection sheet of FIG.

FIG. 3 is a graph showing a light output characteristic on the back surface side of a general light guide plate.

FIG. 4 is a schematic perspective view showing a general backlight unit.

[Explanation of symbols]

1 Reflective sheet 2 slope 3 vertical plane 4 backlight unit 5 Light guide plate 6 lamps

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Claims (2)

(57) [Claims] 1. A lamp and an arrangement along the lamp
Light guide plate that guides the light emitted from the lamp to the front side
And is arranged on the front side of this light guide plate and emits from the light guide plate
Light that uniformly diffuses the reflected light and refracts it toward the normal direction
In a backlight unit having a learning sheet,
It is placed on the back side of the light guide plate to reduce the emission of light rays to the back side.
It is a reflective sheet that decreases, It has an inclined surface inclined in a specific direction on the surface, A plurality of the inclined surfaces are formed in a stripe shape and are arranged in the width direction.
That is inclined, The inclination angle of the inclined surface is 5 ° or more and 20 ° or less, The inclined surface is smooth, The inclined surface is made of synthetic resin, A reflective sheet characterized in that 2. A linear lamp, a light guide plate arranged along the lamp to guide a light beam emitted from the lamp to a front surface side, and a light guide plate arranged on the front surface side of the light guide plate, An optical sheet that uniformly diffuses the emitted light and refracts it toward the normal direction side, and an optical sheet that is arranged on the back surface side of the light guide plate so that the angle of intersection between the peak direction of the light emitted from the back surface of the light guide plate and the inclined surface is minimized. A backlight unit for a liquid crystal display device, which is provided with the reflection sheet according to claim 1 .