JP2001166115A - Reflection sheet and backlight unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection sheet which can improve the reflection efficiency and hiding property, and to provide a back light unit which can decrease the loss in the rays emitted from a lamp and which can improve the luminance by that reflection sheet. SOLUTION: The reflection sheet 1 is disposed on the back face of a back light unit and decreases dissipation of rays to the back face side. The sheet 1 has inclined faces 2 inclined in a specified direction on its surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface to emit light has become widespread, and a backlight unit is provided on a lower surface side of the liquid crystal layer. As shown in FIG. 4, the backlight unit 20 generally includes a rod-shaped lamp 21 as a light source and a lamp 2.
1 is a light guide plate 23 in the form of a rectangular plate arranged so that the end thereof is along
And a plurality of optical sheets 22 stacked on the front surface side of the light guide plate 23 and a reflection sheet 26 stacked on the back surface side of the light guide plate 23. The optical sheets 22 have specific optical properties such as refraction and diffusion, respectively. Specifically, the light diffusion sheet 24 and the light diffusion sheet 24 disposed on the surface side of the light guide plate 23 are provided. The prism sheet 25 disposed on the front side corresponds to the above.

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 a reflection dot or a reflection sheet (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. Light 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. Thereafter, the light beam emitted from the light diffusion sheet 24 enters the prism sheet 25, and is emitted by the prism portion 25a formed on the surface of the prism sheet 25 as a light beam having a distribution which shows a peak in a substantially normal direction. Thus, the light beam emitted from the lamp 21 is
The light is diffused by the light diffusion sheet 24, is refracted by the prism sheet 25 so as to show a peak in a substantially normal direction, and further illuminates the entire liquid crystal layer (not shown) above. Note that no matter how the reflection performance of the light guide plate 23 is improved, a certain amount of light is emitted to the back surface side. Reflection sheet 2 for improving the brightness of a liquid crystal display device
6 are provided.

Conventionally, as the reflection sheet 26, a sheet made of a synthetic resin in which a white pigment such as titanium oxide is dispersed in order to satisfy high reflectivity, concealing property, etc., and a void ( (Bubbles) are dispersed, and the surface is formed in a mat shape.

[0005]

In the above-mentioned conventional reflection sheet 26, since the concealing property is not so high, the reflectivity differs in a portion such as a frame supporting the backlight unit 20, and the brightness of the liquid crystal display device is increased. Unevenness may occur.

In order to prevent such inconvenience, it is necessary to perform printing for reducing the reflectance on the above-mentioned frame or the like which causes the uneven brightness, or to perform printing for improving the concealment property on the back surface of the reflection sheet 26. Therefore, the manufacturing process is complicated by the printing.

The present invention has been made in view of these disadvantages, and aims to reduce the loss of light rays emitted from a lamp and improve the brightness by using such a reflective sheet that can improve the reflection efficiency and the concealment property. It is an object of the present invention to provide a backlight unit that can be used.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The invention is directed to a reflection sheet provided on a back side of a backlight unit for reducing radiation of a light beam to the back side, and in a specific direction. It is a reflection sheet characterized in that it has an inclined surface that is inclined at an angle.

In the backlight unit, the peak direction of light 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. Accordingly, (a) a linear lamp, (b) a light guide plate disposed along the lamp and guiding light emitted from the lamp to the front side, and (c) a light guide plate disposed on the front side of the light guide plate. A liquid crystal display device comprising: an optical sheet for uniformly diffusing a light beam emitted from the light guide plate and refracting the light beam toward the normal direction; and (d) a reflection sheet disposed on the back surface side of the light guide plate. In the backlight unit, by arranging the reflecting 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 light beam is formed at a shallow angle to the inclined surface of the reflecting sheet. Is incident, and the tendency to be reflected on the inclined surface is increased. As described above, since the reflection sheet has high reflection efficiency, light loss radiated from the back surface side can be reduced, and luminance can be improved.

It is preferable that a plurality of the inclined surfaces are formed in a stripe shape and inclined 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 for the inclined surface is reduced, and an increase in the thickness of the reflective sheet due to the provision of the inclined surface can be reduced. . Further, it is possible to reduce the occurrence of luminance unevenness due to the inclined surface. Furthermore, with this configuration,
Irregularities are formed on the surface of the reflection sheet, and sticking with the light guide plate to be laminated is prevented.

It is preferable that the inclination angle of the inclined surface is smaller than the angle formed by the peak direction of the incident light with respect to the sheet surface. Here, the “sheet surface” means a reference surface of the sheet, and when flat, coincides with the upper surface or the lower surface. As described above, the reflection sheet is provided so as to reduce the angle formed by the inclined surface with respect to the peak direction of the incident light. When 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 on the surface side can be increased.

The angle of inclination of the inclined surface is preferably 5 ° or more and 20 ° or less. This is because if the inclination angle of the inclined surface is smaller than the above range, the effect of promoting the reflection efficiency is not so large, and if the inclination angle exceeds the above range, the thickness of the reflection sheet is increased, and the liquid crystal display This is because it is against the demand for a thin device.

Further, as a method of promoting the reflection efficiency on the inclined surface, there are a method of smoothing the inclined surface and a method of forming the inclined surface from a synthetic resin having a large refractive index.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIG. 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 of FIG.
Is a graph showing light emission characteristics (luminance distribution on the back side of the light guide plate) on the back side of a general light guide plate.

The reflection sheet 1 is a sheet made of a synthetic resin disposed on the back side of the light guide plate of the backlight unit, and (a) reduces the light radiated from the light guide plate to the back side and performs liquid crystal display. It is intended to improve the luminance of the device, and (b) to conceal a device or the like present on the back 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. No.

On the surface of the reflection sheet 1, a slender strip-shaped inclined surface 2 is formed in a stripe shape (a large number of strips are adjacent and parallel to each other).
Is formed. All of these inclined surfaces 2 are inclined at a predetermined angle in a certain direction, and a narrower strip-shaped vertical surface 3 is interposed between adjacent inclined surfaces 2. for that reason,
The reflection sheet 1 has a substantially saw blade-shaped cross section.

The function of the reflection sheet 1 will be described. As shown in FIG. 2, a certain amount of light is 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 vertical downward but is inclined at a predetermined angle to the side opposite to the side where the lamp 6 is provided. FIG.
Fig. 7 shows light emission characteristics on the back side of a general light guide plate, which has a peak in a direction of 70 ° from below vertically. Therefore, in the backlight unit 4 for a 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 to the lamp 6, so that the back surface of the light guide plate 5 is provided. The intersection angle between the peak direction of the light beam emitted from the light source and the inclined surface 2 is minimized, and the light beam enters the inclined surface 2 of the reflection sheet 1 at a small angle. Therefore, the effect of reflecting light rays leaking downward from the rear surface of the light guide plate 5 upward is increased, and the loss of light rays radiated from the rear 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 with respect to the sheet surface X. When this inclination angle θ is larger than the angle of the peak direction of the incident light with respect to the sheet surface X,
The amount of light rays incident on the vertical surface 3 increases, and the reflection function by the inclined surface 2 as described above is not exhibited.

The angle of inclination θ of the inclined surface 2 is preferably in the range of 5 ° to 20 °. When the inclination angle θ is smaller than 5 °, the reflection function by the above-described inclined surface 2 is not effectively exerted. Conversely, when the inclination angle θ exceeds 20 °, the area of the vertical surface 3 increases. The amount of light 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 is contrary to the demand for a thin backlight unit 4. .

In order to enhance the reflection function of the inclined surface 2, for example, the inclined surface 2 may be smoothed, and the reflection sheet 1 may be formed of a 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 preferred. This is because if the width of the inclined portion 2 is smaller than the above range, it is difficult to manufacture accurately, and conversely, if the width exceeds the above range, striped luminance unevenness may occur in transmitted light. is there.

The method of forming the reflection sheet 1 having the above-described structure is as follows. (A) A synthetic resin is laminated on a sheet mold having a shape obtained by inverting the 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 in which a molten resin is injected into a mold having an inverted shape of the surface of the reflection sheet 1, and (c) a sheet-like resin is reheated to form a gap between the same mold and a metal plate as described above. A method of transferring the shape by pressing between, (d) reflection sheet 1
An extruded sheet molding method in which a molten sheet-like resin is passed through the nip between a roll having an inverted surface shape on the peripheral surface and another roll, and the above shape is transferred. (E) UV curable resin is applied to the base film Then, the shape is transferred to an uncured UV-curable resin by pressing it onto a roll having the same inverted shape as described above, and then the UV-curable resin is cured by applying ultraviolet rays. (F) EB instead of UV-curable resin There is a method using a cured resin.

The reflection sheet of the present invention is not limited to the above embodiment. For example, the sheet-like portion and the triangular prism-like portion having the inclined surface 2 can be formed of different synthetic resins. is there. Further, in order to improve the reflection function, it is also 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 concealing property can be improved. Therefore, according to the backlight unit using the reflection sheet, loss of light emitted from the lamp can be reduced, and luminance can be improved.

[Brief description of the 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 light emission characteristics on the back side of a general light guide plate.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflection sheet 2 Inclined surface 3 Vertical surface 4 Backlight unit 5 Light guide plate 6 Lamp

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H038 AA55 BA06 BA45 2H042 DD02 DE04 2H091 FA14Z FA41Z FB02 FB04 FC17 FC19 FC23 FD06 LA03 LA18

Claims (7)

[Claims] 1. A reflection sheet disposed on the back side of a backlight unit to reduce the diffusion of light rays to the back side, the reflection sheet having an inclined surface inclined in a specific direction on the surface. . 2. The reflection sheet according to claim 1, wherein the plurality of inclined surfaces are formed in a stripe shape and are inclined in a width direction. 3. The reflection sheet according to claim 1, wherein an inclination angle of the inclined surface is smaller than an angle of the peak direction of the incident light with respect to the sheet surface. 4. The reflection sheet according to claim 1, wherein the inclination angle of the inclined surface is not less than 5 ° and not more than 20 °. 5. The reflection sheet according to claim 1, wherein the inclined surface is smooth. 6. The reflection sheet according to claim 1, wherein the reflection sheet is formed of a synthetic resin having a large refractive index. 7. A linear lamp, a light guide plate disposed along the lamp and guiding light emitted from the lamp to a front surface side, a light guide plate disposed on the front surface side of the light guide plate, and An optical sheet for uniformly diffusing the emitted light rays and refracting the light rays toward the normal direction; and disposing the optical sheet on the rear face side of the light guide plate such that the intersection angle between the peak direction of the light rays emitted from the back face of the light guide plate and the inclined surface is minimized. A backlight unit for a liquid crystal display device, comprising: the reflection sheet according to any one of claims 1 to 6.