JP4837814B2 - Light diffusion sheet and backlight unit using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light diffusion sheet incorporated in a backlight unit of a liquid crystal display device and a backlight unit using the same.
[0002]
[Prior art]
In the liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface is widely used, and a backlight unit is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 4, the backlight unit 20 generally includes a rod-shaped lamp 21 serving as a light source, a rectangular plate-shaped light guide plate 22 arranged so that an end thereof is along the lamp 21, and a light guide plate. The light diffusion sheet 23 disposed on the front surface side of the light diffusion sheet 23 and the prism sheet 24 disposed on the front surface side of the light diffusion sheet 23 are provided.
[0003]
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 reflective dot or a reflection sheet (not shown) on the back surface of the light guide plate 22 and each side surface. Emitted from the surface. The light beam emitted from the light guide plate 22 enters the light diffusion sheet 23, is diffused, and is emitted from the surface of the light diffusion sheet 23. Thereafter, the light beam emitted from the light diffusion sheet 23 is incident on the prism sheet 24 and is emitted as a light beam having a distribution having a peak in a substantially upward direction by the prism portion 24 a formed on the surface of the prism sheet 24. In this way, the light emitted from the lamp 21 is diffused by the light diffusion sheet 23 and refracted by the prism sheet 24 so as to have a peak in a substantially directly upward direction. Illuminate.
[0004]
In consideration of the light condensing characteristics of the prism sheet 24, a backlight unit in which a prism sheet is further disposed on the surface side of the prism sheet 24, and a light diffusion sheet is disposed on the surface side of the prism sheet 24. Backlight units are also popular today.
[0005]
As the light diffusion sheet 23 of the backlight unit 20 having the above-described structure, as shown in FIG. 5B, a transparent base layer 25 and a light diffusion layer 26 laminated on the surface of the base layer 25. The one provided with is generally used. The light diffusing layer 26 includes a plurality of hemispherical lens portions 27 as shown in FIGS. 5A and 5B, or a synthetic resin in a binder made of a synthetic resin (not shown). In addition, a structure in which spherical beads made of glass or the like are dispersed is used.
[0006]
[Problems to be solved by the invention]
The conventional light diffusion sheet such as the light diffusion sheet 23 has the following disadvantages. That is,
(1) Since the lens portion 27 and the beads that contribute to light diffusion are spherical in principle, a gap 28 is formed no matter how densely arranged, and an area of the light diffusion layer 26 that does not contribute to diffusion is generated. Therefore, there is a predetermined limit to improving the diffusion efficiency.
[0007]
(2) Since the light diffusing ability is extremely different between the lens portion 27 and the gap 28 as described above, uneven brightness tends to occur.
[0008]
(3) Since the lens part 27 and the beads exhibiting the light diffusing ability are spherical in principle, it is difficult to adjust the viewing angle.
[0009]
The present invention has been made in view of these disadvantages, and provides a light diffusion sheet that has high diffusion efficiency, can suppress the occurrence of uneven brightness, and can adjust the viewing angle, and a backlight unit using the same. It is the purpose.
[0010]
The invention made to solve the above problems comprises a base material layer and a light diffusion layer laminated on the surface of the base material layer, and the light diffusion layer has a hexagonal bottom surface and is curved in a convex shape. In addition, the polygonal lens portion having a convex curved surface that exhibits light diffusion ability is densely arranged on the surface of the base material layer without a gap, and the maximum width of the bottom surface of the polygonal lens portion is 1 μm or more and 10 μm or less. It is a sheet. According to the light diffusion sheet, since the polygon lens portions are densely arranged, there is no gap and the entire sheet surface is covered with the polygon lens portion. Therefore, the light diffusion sheet has no portion that does not contribute to light diffusion. In other words, the area contributing to diffusion is maximized, so that the diffusion efficiency can be dramatically improved. Further, since there is no smooth surface that does not contribute to diffusion, there is no extreme difference in diffusivity, and as a result, there is little luminance unevenness. Furthermore, when the curvature of the polygonal lens portion is reduced, the stress applied to the upper surface of the polygonal lens portion is dispersed. In addition, the viewing angle can be adjusted by changing the curvature of the polygon lens portion.
[0011]
The bottom surface of the polygonal lens part is hexagonal. Since the hexagon is a polygon with the maximum number of angles that can be densely arranged without a gap, the diffusivity close to that of a spherical lens can be exhibited when compared with a single lens.
[0013]
Furthermore, the bottom surface of the polygonal lens portion is preferably a regular hexagon . By using a regular hexagonal polygon lens portion in this way, the diffusing power can be made uniform and the occurrence of uneven brightness can be further prevented.
[0014]
The maximum width of the bottom surface of the polygonal lens part are 1μm or 10μm or less. In this way, by setting the maximum width of the bottom surface of the polygon lens portion within the above range, both the formability of the polygon lens portion and the light diffusibility can be satisfied.
[0015]
It is preferable to apply a synthetic resin having a different refractive index on the upper surface side of the polygon lens portion to form the upper surface smoothly. According to this means, the concave and convex portions of the polygonal lens portion are covered with synthetic resin, and the upper surface of the light diffusion sheet is smoothed. Therefore, when assembling or transporting the backlight unit, it is overlapped with other sheets. Even if it uses, the damage formed when the unevenness | corrugation of a polygonal lens part contact | abuts can be prevented, Therefore The fall of the optical performance by a damage can be prevented.
[0016]
The refractive index difference between the polygonal lens portion and the synthetic resin coated on the upper surface thereof is preferably 0.01 or more and 0.5 or less. According to this means, a sufficient diffusing ability as a light diffusion sheet can be exhibited, and a decrease in light transmittance due to reflection at the interface between the polygon lens portion and the upper surface side synthetic resin can be reduced.
[0017]
In the light diffusion sheet, an anti-sticking layer in which beads are dispersed in a binder can be laminated. In this way, by sticking the anti-sticking layer to the light diffusion sheet, sticking with a light guide plate, a prism sheet or the like disposed on the front surface side or the back surface side can be prevented.
[0018]
Therefore, a back for a liquid crystal display device comprising a lamp, a light guide plate arranged on the side of the lamp and guiding light emitted from the lamp to the front side, and a light diffusion sheet arranged on the surface side of the light guide plate When the light diffusing sheet of the present invention is used in the light unit, the light diffusing sheet has high diffusibility as described above, so that unevenness in luminance can be prevented.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. 1A and 1B are a schematic plan view and a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention.
[0020]
The light diffusing sheet 1 in FIG. 1 includes a base material layer 2 and a light diffusing layer 3 laminated on the surface side of the base material layer 2.
[0021]
Since the base material layer 2 is required to transmit light, it is made of a synthetic resin that is transparent, particularly colorless and transparent. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . Although the thickness of the base material layer 2 is not specifically limited, For example, they are 10 micrometers or more and 500 micrometers or less, Preferably they are 75 micrometers or more and 250 micrometers or less. When the thickness of the base material layer 2 is less than the above range, inconveniences such as curling easily occur when the light diffusion layer 3 is formed, and handling becomes difficult. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the luminance of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which is contrary to the demand for thinning of the liquid crystal display device. It will also be a thing.
[0022]
The light diffusion layer 3 has a large number of polygonal lens portions 4 protruding closely without gaps. The polygonal lens portion 4 has a regular hexagonal bottom surface, is curved in a convex shape, and has a convex curved surface that exhibits light diffusing ability. By using the regular hexagonal polygon lens portion 4 in this way, it can be densely arranged without a gap, and the uniformity of diffusibility and diffusivity can be improved.
[0023]
The synthetic resin used for the polygonal lens portion 4 is not particularly limited as in the case of the base material layer 2. For example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistance And vinyl chloride.
[0024]
The maximum width of the bottom surface of the polygonal lens portion 4 is preferably 1 μm or more and 100 μm or less, and particularly preferably 1 μm or more and 10 μm or less. This is because if the maximum width of the bottom surface of the polygon lens portion 4 is smaller than the above range, the formation of the polygon lens portion 4 becomes difficult. Conversely, if the maximum width exceeds the above range, the light as a light diffusion sheet This is because diffusibility cannot be obtained.
[0025]
As a method for forming the light diffusion sheet 1 having the above structure, there are a method of forming the light diffusion layer 3 separately after the base material layer 2 is formed, and a method of integrally forming the base material layer 2 and the light diffusion layer 3. Yes, specifically
(A) A method in which a synthetic resin is laminated on a sheet mold having a shape obtained by inverting the surface shape of the light diffusing layer 3, and the polygon lens portion 4 is formed on the surface by peeling the sheet mold;
(B) an injection molding method in which a molten resin is injected into a mold having an inverted shape of the surface of the light diffusion layer 3;
(C) A method of transferring the shape by re-heating the sheeted resin and pressing between the same mold and metal plate as described above,
(D) An extruded sheet molding method in which a molten sheet-shaped resin is passed through a nip between a roll having a reverse shape of the surface of the light diffusion layer 3 on the peripheral surface and another roll, and the above shape is transferred.
(E) A UV curable resin is applied to the base film and pressed onto a roll having the same reverse shape as described above to transfer the shape to an uncured UV curable resin, and then UV is applied to cure the UV curable resin. Method,
(F) There is a method of using an EB curable resin instead of a UV curable resin.
[0026]
Therefore, a rod-shaped lamp 21 as a light source as shown in FIG. 4, a rectangular plate-shaped light guide plate 22 arranged so that the end thereof is along the lamp 21, and light disposed on the surface side of the light guide plate 22. In the backlight unit 20 including the diffusion sheet 23 and the prism sheet 24 disposed on the surface side of the light diffusion sheet 23, if the light diffusion sheet 1 is used as the light diffusion sheet 23, the diffusion of the light diffusion sheet 1 is performed. Therefore, it is possible to prevent the occurrence of luminance unevenness.
[0027]
The light diffusing sheet 5 in FIG. 2 is formed by laminating a base material layer 2 and a light diffusing layer 3 including a polygonal lens portion 4 in the same manner as the light diffusing sheet 1, and in addition, sticking on the back side of the base material layer 2. The prevention layer 6 is laminated.
[0028]
The anti-sticking layer 6 is composed of a binder 7 and beads 8 dispersed in the binder 7 and prevents sticking with a prism sheet or the like disposed on the surface side by the beads 8 protruding from the binder 7. is there.
[0029]
Examples of the polymer used for the binder 7 include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, and epoxy resin. In addition to the above-described polymer, the binder 7 may contain, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like. Since the binder 7 needs to transmit light, it is transparent, and colorless and transparent is particularly preferable.
[0030]
The beads 8 are substantially spherical, and examples of the material thereof include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide. The beads 8 are preferably transparent in order to increase the amount of light transmitted through the light diffusion sheet 5, and are particularly preferably colorless and transparent.
[0031]
The average particle diameter of the beads 8 is preferably 1 μm or more and 30 μm or less, and particularly preferably 1 μm or more and 15 μm or less from the viewpoint of preventing sticking. The amount of the bead 8 is relatively small, the beads 8 are separated from each other and dispersed in the binder 7, and most of the beads 8 have their upper ends protruding from the binder 7. The thickness of the anti-sticking layer 4 (the thickness of the binder 7 excluding the beads 8) is not particularly limited, but is, for example, about 1 μm or more and 10 μm or less.
[0032]
The light diffusing sheet 10 in FIG. 3 is the same as the light diffusing sheet 1 in FIG. 1 in that the light diffusing sheet 10 includes a base material layer 2 and a light diffusing layer 3. In the light diffusion sheet 10, the synthetic resin 11 is applied on the upper surface side of the light diffusion layer 3, and the upper surface is formed smoothly. By smoothing the upper surface in this way, even when used repeatedly, other sheets are not damaged and optical performance can be prevented from being deteriorated.
[0033]
The refractive index difference between the polygonal lens portion 4 of the light diffusion layer 3 and the synthetic resin 11 coated on the upper surface side is preferably 0.01 or more and 0.5 or less. This is because if the difference in refractive index is smaller than the above range, the diffusing ability of the polygonal lens portion 4 becomes small, and the optical performance as a light diffusion sheet cannot be exhibited. This is because light rays transmitted through the interface between the resin 4 and the synthetic resin 11 are reflected, resulting in a decrease in light transmittance.
[0034]
The light diffusing sheet of the present invention is not limited to the above embodiment. For example, the bottom surface of the polygonal lens portion 4 is not limited to a regular hexagon, and may be a simple hexagon as long as it can be closely arranged without a gap. , It may be square.
[0035]
【The invention's effect】
As described above, according to the light diffusion sheet of the present invention, the light diffusibility is enhanced. Therefore, according to the backlight unit using this light diffusion sheet, it is possible to prevent the occurrence of luminance unevenness. Further, according to the light diffusion sheet, the viewing angle can be adjusted by changing the convex curvature of the polygonal lens portion.
[Brief description of the drawings]
FIG. 1A is a schematic plan view showing a light diffusion sheet according to an embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of the light diffusion sheet of FIG.
FIG. 2 is a schematic cross-sectional view showing a light diffusion sheet according to a different form from the light diffusion sheet of FIG.
3 is a schematic cross-sectional view showing a light diffusing sheet according to a different form from the light diffusing sheet of FIGS. 1 and 2. FIG.
FIG. 4 is a schematic perspective view showing a general backlight unit.
5A is a schematic plan view showing a general light diffusion sheet, and FIG. 5B is a schematic cross-sectional view of the light diffusion sheet of FIG. 5A.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light diffusion sheet 2 Base material layer 3 Light diffusion layer 4 Polygon lens part 5 Light diffusion sheet 6 Sticking prevention layer 7 Binder 8 Bead 10 Light diffusion sheet 11 Synthetic resin 20 Backlight unit 21 Lamp 22 Light guide plate 23 Light diffusion sheet 24 Prism Sheet 25 Base material layer 26 Light diffusion layer 27 Lens portion 28 Gap

Claims (6)

A base material layer;
A light diffusion layer laminated on the surface of the base material layer;
With
This light diffusing layer has a hexagonal bottom surface, curved in a convex shape, and a polygonal lens portion having a convex curved surface that exhibits light diffusing ability is densely disposed on the surface of the base material layer without gaps,
The light diffusion sheet, wherein the maximum width of the bottom surface of the polygon lens portion is 1 μm or more and 10 μm or less.   The light diffusion sheet according to claim 1, wherein the bottom surface of the polygonal lens portion is a regular hexagon.   The light diffusion sheet according to claim 1 or 2, wherein a synthetic resin having a different refractive index is coated on the upper surface side of the polygon lens portion, and the upper surface is formed smoothly.   The light diffusion sheet according to claim 3, wherein a difference in refractive index between the polygonal lens portion and the synthetic resin applied on the upper surface side is 0.01 or more and 0.5 or less.   The light diffusion sheet according to any one of claims 1 to 4, wherein an anti-sticking layer in which beads are dispersed in a binder is laminated.   The lamp, a light guide plate that is arranged on the side of the lamp and guides light emitted from the lamp to the front side, and is disposed on the surface side of the light guide plate. A backlight unit for a liquid crystal display device comprising a light diffusion sheet.

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