JP4488597B2 - 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 used for a backlight unit incorporated in a liquid crystal display device and a backlight unit using the light diffusion sheet.
[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. 3A, the backlight unit 20 is generally composed of a rod-shaped lamp 21 as a light source, and a rectangular plate-shaped light guide plate 22 disposed so that an end thereof is along the lamp 21. The light diffusion sheet 23 disposed on the surface side of the light guide plate 22 and the prism sheet 24 disposed on the 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. 3B, a transparent base layer 25 and a light diffusion layer 26 laminated on the surface of the base layer 25. And a sticking prevention layer 27 laminated on the back surface of the base material layer 25 is generally used, and the light diffusion layer 26 is made of synthetic resin, glass or the like in a binder 27 made of synthetic resin. The structure in which the beads 28 are dispersed and the anti-sticking layer 29 has a structure in which the beads 31 are dispersed in the same binder 30 is generally used.
[0006]
[Problems to be solved by the invention]
By the way, since the above-mentioned light diffusion sheet 23 is required to have optical performance, an acrylic resin or a styrene resin having a high light diffusibility is generally used for the polymer constituting the binders 27 and 30, and the beads 28. , 31 are generally acrylic beads.
[0007]
Since the binder 30 of the anti-sticking layer 29 using such an acrylic resin or styrene resin is not so hard, a plurality of the light diffusing sheets 23 are stacked in the case of manufacturing, transportation, storage, etc. When the light unit 20 is assembled on the prism sheet 24 having irregularities, the back surface of the light diffusion sheet 23 is scratched by the beads 28 protruding from the surface of the light diffusion sheet 23 or the prism portion 24a of the prism sheet 24. It was difficult to handle.
[0008]
In addition, since the acrylic beads used for the beads 28 protruding from the front and back surfaces of the light diffusion sheet 23 are relatively hard, the prism sheet 24 disposed on the front and back surfaces of the light diffusion sheet 23 in the backlight unit 20 is used. There is a risk of scratching the back surface and the surface of the light guide plate 22.
[0009]
The present invention has been made in view of these inconveniences, and a light diffusion sheet that does not damage each other even when stacked and can increase the light output rate to the surface side, and brightness using the same. The purpose of this is to provide a backlight unit with improved brightness.
[0010]
[Means for Solving the Problems]
The invention made to solve the above problems is a light diffusing sheet comprising a light diffusing layer in which beads are dispersed in a binder and a base material layer, and a silicone resin is used as a main polymer constituting the binder. In this case, elastic silicone beads are used as the beads.
[0011]
According to the light diffusion sheet, the following effects can be achieved. That is,
(1) Since a relatively hard silicone resin is used as the main polymer of the binder, scratch resistance is obtained, and as described above, the light diffusion sheets or the optical sheets such as the light diffusion sheet and the prism sheet. Even if they are used repeatedly, scratches on the surface can be reduced. In order to effectively exhibit such action, the binder preferably has a pencil hardness of 2H or more.
[0012]
(2) Since the elastic silicone beads that are relatively soft and highly slidable are used for the beads dispersed in the light diffusion layer, when the other optical sheet is used on the light diffusion sheet, the light Damage to other optical sheets due to beads protruding on the surface of the diffusion sheet is reduced. In order to exert such action, the rubber hardness of the elastic silicone beads is preferably 20 or more and 60 or less.
[0013]
(3) The light diffusing sheet uses a relatively hard silicone resin as the binder of the light diffusing layer, and uses a relatively soft elastic silicone bead for the dispersed beads. It is possible to reduce the destruction of the light diffusion layer even when subjected to bending or external impact.
[0014]
(4) Since the binder and beads constituting the light diffusing layer both use a silicone resin, a) the beads are highly dispersible in the binder, enabling uniform dispersion. The adhesive strength of the light diffusion layer is large, and the rigidity of the light diffusion layer can be increased.
[0015]
(5) Since the refractive index of the elastic silicone beads used as beads is smaller than that of other resin beads, the tendency to collect light transmitted through the elastic silicone beads is increased while maintaining a predetermined diffusivity. . This is considered to be caused by an increase in the focal length due to the refraction of light rays emitted from the beads into the air (refractive index = 1). Therefore, according to the light diffusion sheet, light scattering in a direction other than the surface side that does not contribute to luminance due to diffusion by beads can be reduced, and loss of light can be reduced. In order to effectively perform such a light collecting function, the refractive index of the beads is preferably 1.45 or less.
[0016]
In the light diffusion sheet, fluorine-crosslinked acrylic beads may be further used as the beads. According to this means, the diffusibility can be enhanced by the acrylic beads while exhibiting the above-described action. Therefore, the diffusibility of the light diffusion sheet can be controlled by adjusting the blending ratio of the fluorine-crosslinked acrylic beads. In addition, since the said fluorine bridge | crosslinking acrylic bead also has a comparatively small refractive index, even if there are many fluorine bridge | crosslinking acrylic beads with respect to an elastic silicone bead, the above-mentioned condensing function is not reduced.
[0017]
Another invention made to solve the above problems is a light diffusing sheet comprising a light diffusing layer, a base material layer, and an anti-sticking layer in which beads are dispersed in a binder in this order, and the binder Silicone resin is used as the main polymer constituting the resin, and elastic silicone beads are used as the beads.
[0018]
According to the light diffusion sheet, since a relatively hard silicone resin is used for the binder constituting the anti-sticking layer, the scratch resistance on the back surface is improved, and the light diffusion sheets are in contact with each other as described above. Alternatively, even if the light diffusion sheet and the prism sheet are used in an overlapping manner, damage to the back surface can be reduced. In addition, since the elastic silicone beads that are relatively soft and highly slippery are used for the beads dispersed in the anti-sticking layer, other optical sheets are scratched by the beads protruding on the back surface of the light diffusion sheet. Is reduced.
[0019]
Therefore, for a liquid crystal display device comprising a lamp, a light guide plate that guides light rays emitted from the lamp to the surface side, and a light diffusion sheet that is disposed on the surface side of the light guide plate and guides light rays substantially uniformly in the surface direction In the backlight unit, when the light diffusion sheet is used, handling at the time of assembly or the like is facilitated, and the luminance can be improved by the light collecting function.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention.
[0021]
1 includes a base material layer 2, a light diffusion layer 3 laminated on the surface side of the base material layer 2, and an anti-sticking layer 4 laminated on the back surface side of the base material layer 2. It is configured.
[0022]
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 curl are likely to occur when the resin composition for forming the light diffusion layer 3 is applied, 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.
[0023]
The light diffusion layer 3 is composed of a binder 5 and beads 6 dispersed in the binder 5. Due to refraction and reflection at the interface between the binder 5 and the beads 6, the light beam that passes through the light diffusion layer 3 from the back surface side to the front surface side can be uniformly diffused. Further, by providing beads 6 whose upper ends protrude from the binder 5 or those embedded in the binder 5, the light beam can be diffused better. The thickness of the light diffusion layer 3 (meaning the thickness of the binder 5 portion excluding the beads 6) is not particularly limited, but is, for example, about 1 μm or more and 30 μm or less.
[0024]
Silicone resin is used as the main polymer constituting the binder 5. In addition to the above-mentioned polymer, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like may be blended in the binder 5. Since the binder 5 needs to transmit light, it is transparent, and colorless and transparent is particularly preferable.
[0025]
The beads 6 have a substantially spherical shape, and elastic silicone beads are mainly used, and fluorine-crosslinked acrylic beads are blended according to diffusibility. The beads 6 are preferably transparent in order to increase the amount of light transmitted through the light diffusing sheet 1, and particularly preferably colorless and transparent.
[0026]
The particle size of the beads 6 is preferably 0.1 μm or more and 100 μm or less, and particularly preferably 1 μm or more and 50 μm or less. This is because if the particle size of the beads 6 is less than the above range, the light diffusion effect is insufficient, and conversely, if the particle size exceeds the above range, the resin composition for forming the light diffusion layer 3 is applied. This is because the work becomes difficult.
[0027]
The amount of beads 6 in the light diffusion layer 3 is preferably 0.1 part or more and 500 parts or less, particularly preferably 5 parts or more and 300 parts or less, with respect to 100 parts of the polymer content in the binder 5. If the blending amount is less than the above range, the above-mentioned total light transmittance improving effect becomes insufficient. On the other hand, even if the blending amount exceeds the above range, the total light transmittance is decreased. Because to do.
[0028]
The anti-sticking layer 4 is composed of a binder 7 and beads 8 dispersed in the binder 7 and prevents sticking with a light guide plate or the like disposed on the back side by the beads 8 protruding from the binder 7. is there. The binder 7 and the beads 8 in the anti-sticking layer 4 are the same as those in the light diffusion layer 3.
[0029]
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.
[0030]
As a method for producing the light diffusing sheet 1 having the above-described structure, a resin composition for a light diffusing layer in which beads 6 are mixed almost uniformly with a silicone varnish constituting a binder 5 is applied to the surface of the base material layer 2 and heated. The step of forming the light diffusing layer 3 by curing the silicone varnish by applying a resin composition for the anti-sticking layer in which the beads 8 are mixed almost uniformly with the silicone varnish constituting the binder 7 and heated. And the step of forming the anti-sticking layer 4 by curing.
[0031]
Since the binders 5 and 7 made of silicone resin are relatively hard as described above, scratch resistance is improved and handling is facilitated. Moreover, since the said light diffusion sheet 1 does not get much damage | wound, the fall of the brightness | luminance by a damage | wound can be prevented. In consideration of effectively exhibiting such scratch resistance, the pencil hardness of the binders 5 and 7 is preferably 2H or more. Here, “pencil hardness” is based on the pencil scratch value described in 8.4 of the test method defined in JIS-K-5400.
[0032]
In addition, elastic silicone beads are used as the diffusing agent, and the beads 6 and 8 protruding from the front and back surfaces of the light diffusing sheet 1 are relatively soft. However, the damage to other optical sheets is reduced. From this point of view, the handleability is promoted and the occurrence of uneven brightness due to scratches can be reduced. In consideration of effectively exhibiting the scratch resistance, the rubber hardness of the beads 6 and 8 (elastic silicone beads) is preferably 20 or more and 60 or less. Here, the “rubber hardness” means a value obtained from a physical test method for vulcanized rubber specified in JIS-K-6301 using an A-type hardness tester.
[0033]
Further, since the light diffusion layer 3 of the light diffusion sheet 1 is made of the same type of silicone resin, the binders 5 and 7 and the beads 6 and 8 are evenly molded. , Durability is increased.
[0034]
Next, the diffusion function of the light diffusion sheet 1 will be described. First, FIG. 2A shows a light transmission simulation result in the case of acrylic beads 9 (refractive index: about 1.5) that are generally used as a diffusing agent for a light diffusing sheet. As shown in FIG. 2A, the light beam emitted from the bead 9 having a refractive index of about 1.5 is focused in the vicinity of the bead 9 and emitted at a relatively wide angle. On the other hand, the elastic silicone beads and the fluorine-crosslinked acrylic beads used for the beads 6 of the light diffusion sheet 1 have a relatively low refractive index, specifically 1.4 or less, and therefore, as shown in FIG. In addition, the light beam emitted from the bead 6 is focused at a position relatively away from the bead 6, and the light emission angle is relatively small. Therefore, according to the light diffusing sheet 1, the light diffusing sheet 1 has a function of reducing light emitted in a direction not contributing to luminance and condensing on the surface side while maintaining diffusivity to some extent. The luminance of the backlight unit using 1 can be improved.
[0035]
In addition, the light-diffusion sheet of this invention is not limited to the said embodiment, For example, a general acrylic bead may be mixed as the bead 6, and the above-mentioned effect can be exhibited to some extent. Further, the means of the present invention using a silicone-based resin as a binder and an elastic silicone bead as a bead can be applied to either the light diffusion layer 3 or the anti-sticking layer 4 to prevent the above-described scratch resistance and scratch prevention. And high strength can be exhibited.
[0036]
【The invention's effect】
As described above, according to the light diffusion sheet of the present invention, even when they are stacked, they are not damaged each other and the light output rate to the surface side can be increased. Therefore, according to the backlight unit using the light diffusion sheet, the luminance can be improved without increasing the energy consumption.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention.
2A is a light transmission simulation diagram when general acrylic beads (refractive index: about 1.5) are used, and FIG. 2B is an elastic silicone bead (refractive index) of the light diffusion sheet of FIG. : About 1.4) is a light transmission simulation diagram.
FIG. 3A is a schematic perspective view illustrating a general backlight unit, and FIG. 3B is a schematic cross-sectional view illustrating a general bead coating type light diffusion sheet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light diffusing sheet 2 Base material layer 3 Light diffusing layer 4 Anti-sticking layer 5 Binder 6 Beads 7 Binder 8 Beads

Claims (7)

A light diffusing sheet comprising a light diffusing layer in which beads are dispersed in a binder and a base material layer,
Silicone resin is used as the main polymer constituting the binder,
The binder has a pencil hardness of 2H or more,
Light diffusion sheet, wherein the slip-resistant rubber hardness of 20 or more 60 or less is higher elastic silicone beads are used as the beads.   The light diffusion sheet according to claim 1, wherein fluorine-crosslinked acrylic beads are further used as the beads. A light diffusion sheet comprising a light diffusion layer, a base material layer, and an anti-sticking layer in which beads are dispersed in a binder, in this order,
Silicone resin is used as the main polymer constituting the binder,
The light diffusing sheet according to claim 1, wherein an elastic silicone bead is used as the bead.   The light diffusion sheet according to claim 3, wherein the binder has a pencil hardness of 2H or more.   The light diffusion sheet according to claim 3 or 4, wherein the rubber hardness of the elastic silicone beads is 20 or more and 60 or less.   The light diffusion sheet according to any one of claims 1 to 5, wherein the refractive index of the beads is 1.45 or less.   The lamp, a light guide plate for guiding light emitted from the lamp to the surface side, and a light guide plate disposed on the surface side of the light guide plate to guide the light beam substantially uniformly in the surface direction. A backlight unit for a liquid crystal display device comprising the light diffusion sheet described above.

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