JP3188430B2 - Lens 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 lens sheet used for a backlight unit of a liquid crystal display and a backlight unit using the same.

[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 the lower surface side of the liquid crystal layer. As shown in FIG. 5A, the backlight unit 20 generally includes a linear lamp 21 as a light source, and a substantially rectangular plate-shaped light guide arranged such that an end of the lamp 21 extends along the lamp 21. A light plate 22, a light diffusion sheet 23 disposed on the upper surface side of the light guide plate 22, and a lens sheet (also referred to as “prism sheet”) 24 disposed on the upper surface side of the light diffusion sheet 23 are provided. . In FIG. 5A, one lens sheet 24 is provided.
Although only two lenses are described, two lens sheets 24 may be provided. Further, a light control sheet may be provided above the lens sheet 24 in some cases.

The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 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 22 and each side surface of the light guide plate 22. Reflected by
The light is emitted from the surface of the light guide plate 22. This light beam enters the light diffusion sheet 23, is diffused by the light diffusion sheet 23, and is emitted from the surface of the light diffusion sheet 23. Thereafter, the light beam emitted from the light diffusion sheet 23 enters the lens sheet 24, is emitted from the surface of the lens sheet 24, and illuminates the entire liquid crystal layer (not shown) further above.

[0004] The brightness distribution of the light emitted from the surface of the light guide plate 22 differs depending on the type of the light guide plate 22, and exhibits a strong peak in a specific direction, for example, obliquely upward. In accordance with the light output characteristics of the light guide plate 21, the peak direction of the light beam emitted from the light guide plate 21 is the normal direction (the direction perpendicular to each sheet such as a lens sheet and a light diffusion sheet arranged in parallel). The same applies to the following).
And the refractive power of the lens sheet 24 is set.

[0005]

In the above-mentioned conventional lens sheet 24, as shown in FIG. 5 (b), the sectional shape of the lens portion 25 is triangular, and the lens portion 25 contributing to refraction has a triangular shape. Since the side surface 26 is a plane inclined at a predetermined angle, the light beam in the specific direction A can be refracted in the normal direction, but the light beams in directions B and C slightly different from the specific direction A are larger than the normal direction. It is shifted and emitted. In other words, if the specific direction A that can be refracted in the normal direction is set as the peak direction of the passing light beam, only the light beam in the peak direction can be directed in the normal direction. The light rays will be directed in a direction that is significantly deviated from the normal direction.

According to the lens sheet 24, of the pair of side surfaces 26 and 27 constituting the lens portion 25, only the side surface 26 that is nearly perpendicular to the peak direction of the passing light beam contributes to refraction of the light beam. The side surface 27 that is nearly parallel to the peak direction of the passing light beam hardly contributes to the refraction of the light beam,
Rather, it may work against refraction in the normal direction.

The present invention has been made in view of these inconveniences. A lens capable of refracting all light rays in a direction within a predetermined angle range near the normal direction and not contributing to refraction of the light rays in the normal direction. It is an object of the present invention to provide a lens sheet capable of reducing refraction in a direction other than a normal direction due to a side surface of a part.

[0008]

The invention made to solve the above-mentioned problem is a lens sheet laminated on a light diffusion sheet and refracting a peak direction of an emitted light beam in a normal direction, wherein the lens sheet has a light exit surface side. A plurality of ridged lens portions are arranged in parallel, the cross-sectional shape of one side surface of the lens portion is convexly curved, and the other side surface is flat.
According to this means, since the cross-sectional shape of the one side surface of the lens portion is convexly curved, the inclination angle of the one side surface is larger at a lower position, smaller at a higher position, and has a smaller height. Changes gradually. On the other hand, it is considered that the amount of passing light passes through a lower position on one side surface as the inclination angle in that direction is smaller, and the amount of light passing through a higher position on one side surface is larger as the inclination angle is larger. Therefore,
By bending the one side so that the direction of the ray passing through each height position on one side can be refracted in the normal direction,
Light in many directions can be directed in a substantially normal direction.

It is preferable that the one side surface has the same sectional shape as a part of the sectional shape of the imaging lens. According to this means, many light rays in a direction within the predetermined angle range can be refracted in a substantially normal direction.

It is preferable that the inclination angle of the other side surface opposite to the one side surface is larger than the inclination angle of the passing light beam in the peak direction. According to this means, by arranging the lens sheet such that the other side surface and the peak direction of the passing light beam become substantially parallel, almost no light beam passes through the other side surface. Therefore, it is possible to prevent the passing light beam from being refracted in directions other than the normal direction by the other side surface.
The “tilt angle” described in this specification is an angle based on the sheet surface of the lens sheet.

When the above-described lens sheet is used for a backlight unit, the amount of light emitted in the normal direction can be increased by the lens sheet as described above.
The brightness of the liquid crystal display device can be improved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIG. 1 is a perspective view showing a lens sheet according to an embodiment of the present invention, FIG. 2 is a partial sectional view of the lens sheet of FIG. 1, and FIG. 3 illustrates a backlight unit equipped with the lens sheet of FIG. FIG. 4 is a schematic perspective view, and FIG. 4 is a partial cross-sectional view showing a lens sheet according to a different form from the lens sheet of FIG.

The lens sheet 1 shown in FIG.
It comprises a plurality of lens parts 3 formed in parallel and adjacent to the surface of the sheet part 2. The lens portion 3 has a side surface 5 on one side and a side surface 4 on the other side, and is a ridge having a substantially triangular cross section. The other side 4 is the seat 2
And a plane perpendicular to it.

On the other hand, the side surface 5 on one side of the lens portion 3 is a curved surface having a cylindrical peripheral surface. The cross-sectional shape of the one side surface 5 is the same as a part of the cross-sectional shape of the imaging lens. Such an imaging lens may be a spherical lens or an aspherical lens. However, when a part of the cross-sectional shape of the aspherical lens is used, the side surface 5 does not become a complete cylindrical peripheral curved surface.

According to the lens sheet 1 having the above-described shape, since the side surface 5 of the lens portion 3 through which the light beam passes is curved in the shape of an imaging lens, the light beam A in a predetermined direction can be refracted in the normal direction. And light ray C having a smaller inclination angle than light ray A
Also, the light ray B having a large inclination angle can be refracted in the normal direction. That is, many light rays in a direction within the predetermined angle range can be directed in a substantially normal direction. In addition, since the other side surface 4 does not allow light rays to pass therethrough, the side surface 4 does not cause refraction in directions other than the normal direction, and allows all light rays to pass through the side surface 5 that can be refracted in the normal direction. Can be.

The lens sheet 1 is transparent, preferably colorless and transparent because it is necessary to transmit light rays. The material is not particularly limited. For example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, Polycarbonate, polystyrene,
Synthetic resins such as polyolefin, cellulose acetate, and weather-resistant vinyl chloride are exemplified.

Although the size of the lens sheet 1 is not particularly limited, the thickness of the sheet portion 2 is not less than 50 μm and not more than 500 μm.
m or less is preferable. This is because if the thickness of the sheet portion 2 is less than the above range, the strength as a lens sheet cannot be secured, and if the thickness of the sheet portion 2 exceeds the above range, the brightness of the liquid crystal display device decreases. This is because the thickness of the backlight unit is increased, which is against the demand for thinning the liquid crystal display device. The size of the lens unit 3 is, for example, 30 μm or more and 200 μm or less at the bottom and 10 μm or more and 200 μm or less in height.

As a method for forming the lens sheet 1 described above, a synthetic resin is laminated on a sheet mold having a shape in which the lens unit 3 is inverted, and the sheet mold is peeled off to form the lens unit 3 on the surface of the sheet unit 2. , An injection molding method in which a molten resin is injected into a mold having an inverted shape of the lens portion 3, and a resin formed into a sheet, which is reheated and sandwiched between the same mold and a metal plate as described above. A method of transferring the shape by pressing with a press, a method of extruding a sheet-like resin in a molten state through a nip between a roll having an inverted shape of the lens part 3 on the peripheral surface and another roll, and transferring the shape, A method in which a UV curable resin is applied to a base film, pressed onto a roll having the same inverted shape as above, and the shape is transferred to an uncured UV curable resin. Hardening How to use the EB curing resin in place of fat, there is a method of coating such that the central axis of the spindle shape of the paint mixing a light diffusing agent are aligned.

As shown in FIG. 3, the backlight unit 10 in which the lens sheet 1 of FIG. 1 is incorporated has a lamp 11 as a light source, and is disposed beside the lamp 11 and emitted from the lamp 11. The light guide plate 12 guides light rays toward the front side, a light diffusion sheet 13 stacked on the front side of the light guide plate 12, and the lens sheet 1 stacked on the front side of the light diffusion sheet 13. The lens sheet 1 in the backlight unit 10 is disposed so that the side surface 5 of the lens unit 3 and the peak direction of the light beam intersect.

The trajectory of light rays in the backlight unit 10 will be described. First, a light beam is emitted from the lamp 11 and is guided into the light guide plate 12. Next, the light rays in the light guide plate 12 are reflected by reflection dots, reflection sheets (not shown) or side surfaces on the back side of the light guide plate 12, and the light diffusion sheet 1 on the upper side.
3 is emitted. The light beam emitted upward is diffused while passing through the light diffusion sheet 13 and is emitted to the lens sheet 1.
The light rays incident on the lens sheet 1 in this manner are
Due to the light emission characteristics of the light diffusion sheet 2 and the light diffusion sheet 13, the light diffusion sheet 13 is inclined in a specific direction. The lens sheet 1 refracts light rays inclined in a specific direction by the lens portion 3 in the normal direction.
The light is emitted upward. At this time, according to the lens sheet 1, since many rays in the direction within the predetermined angle range can be directed in the substantially normal direction as described above,
Even if the direction of the light beam incident on the lens sheet 1 is shifted, the light beam can be directed in the normal direction, and many directional components other than the peak direction of the light beam can be directed in the substantially normal direction.
Therefore, in the backlight unit 10, most of the light beam diffused by the light diffusion sheet 13 by the lens sheet 1 is directed in the normal direction and is emitted to a further upper deflection film (not shown) or the like. The brightness of the screen of the device can be improved.

The lens sheet 15 shown in FIG.
The surface has a protruding lens portion 17, and one side surface 19 of the lens portion 17 has the same curved surface as a part of the cross-sectional shape of the imaging lens, and further has the other side surface 18 of the lens portion 17.
Is the same as the above-mentioned lens sheet 1 in that
However, the side surface 18 of the lens sheet 15 is the sheet portion 1
6 in that it is not perpendicular but inclined at a predetermined angle. The inclination angle of the side surface 18 is set to be larger than the peak direction of the passing light beam. The lens sheet 15 also
Similarly to the lens sheet 1 described above, the side surface 19 can direct many light beams in a direction within a predetermined angle range in a substantially normal direction, and can reduce light beams passing through the side surface 18. The material and manufacturing method of the lens sheet 15 are the same as those of the lens sheet 1.

[0022]

[0023]

As described above, according to the lens sheet of the present invention, the following effects can be exhibited. That is, (1) many light beams whose peak directions are within a predetermined angle range can be emitted substantially in the normal direction. Therefore, the tolerance for the light output characteristics of the light guide plate and the light diffusion sheet can be improved.

(2) In the luminance distribution of the passing light beam, not only the peak direction component but also other components can be refracted in a substantially normal direction. Therefore, the amount of light output in the normal direction can be dramatically increased as compared with the conventional lens sheet.

(3) By reducing the passage of light rays on the side surface of the lens portion that does not contribute to refraction in the normal direction, the adverse effect of refraction in a direction other than the normal direction by the side surface can be reduced. As described above, the side surfaces capable of refracting light beams in various directions in the normal direction can be effectively utilized. From this viewpoint as well, the amount of light emitted in the normal direction by the lens sheet can be increased.

[Brief description of the drawings]

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

FIG. 2 is a partial sectional view showing the lens sheet of FIG.

FIG. 3 is a schematic perspective view illustrating a backlight unit equipped with the lens sheet of FIG. 1;

FIG. 4 is a partial cross-sectional view showing a lens sheet according to a form different from the lens sheet of FIG.

5A is a schematic perspective view illustrating a general backlight unit, and FIG. 5B is a schematic cross-sectional view of a lens unit illustrating a direction of a light beam passing through a general lens sheet. It is.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lens sheet 2 sheet portion 3 lens portion 4 other side surface 5 one side surface 10 backlight unit 11 lamp 12 light guide plate 13 light diffusion sheet 15 lens sheet 16 sheet portion 17 lens portion 18 other side surface 19 one side side

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 5/02 G02B 3/06 G02B 3/08 G02F 1/1335-1/13363

Claims (4)

(57) [Claims] 1. A lens sheet for <br/> have a lens portion of the projection into multiple parallel light exit surface side, cross-sectional shape of one side of the side surface of the lens portion is convexly curved, the other side A lens sheet having a flat side surface . 2. The lens sheet according to claim 1, wherein a cross-sectional shape of the one side surface is the same as a part of a cross-sectional shape of the imaging lens. 3. The lens sheet according to claim 1, wherein an inclination angle of the other side surface opposite to the one side surface is larger than an inclination angle of a peak direction of a passing light beam. 4. A backlight unit comprising the lens sheet according to claim 1.