JP3374112B2 - Optical 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 an optical sheet suitable for a light diffusing sheet, a prism sheet or the like incorporated in a backlight unit of a liquid crystal display device and a backlight unit using the same.

[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. As shown in FIG. 8A, such a backlight unit 50 generally has a rod-shaped lamp 51 as a light source and a rectangular plate-shaped light guide plate 52 arranged so that an end portion is along the lamp 51. And a plurality of optical sheets 53 laminated on the front surface side of the light guide plate 52. This optical sheet 5
3 respectively have specific optical properties such as refraction and diffusion. Specifically, the light diffusion sheet 54 disposed on the front surface side of the light guide plate 52 and the front surface side of the light diffusion sheet 54 are disposed. The provided prism sheet 55 or the like is applicable.

Explaining the function of the backlight unit 50, first, the light rays incident on the light guide plate 52 from the lamp 51 are reflected by the reflection dots or reflection sheets (not shown) on the back surface of the light guide plate 52 and each side surface. The light is emitted from the surface of the light guide plate 52. The light beam emitted from the light guide plate 52 enters the light diffusion sheet 54, is diffused, and is emitted from the surface of the light diffusion sheet 54. After that, the light rays emitted from the light diffusion sheet 54 are incident on the prism sheet 55, and emitted by the prism portion 55 a formed on the surface of the prism sheet 55 as light rays having a distribution showing a peak in a substantially right above direction. Thus, the light beam emitted from the lamp 51 is
The light is diffused by the light diffusing sheet 54, and is refracted by the prism sheet 55 so as to show a peak in a substantially upward direction, and further illuminates the entire liquid crystal layer (not shown) above.

Although not shown, there is also a backlight unit in which a light diffusing sheet or a prism sheet is further arranged on the surface side of the prism sheet 55 in consideration of the light condensing characteristic of the prism sheet 55.

As the light diffusing sheet 54 of the backlight unit 50 having the above-mentioned structure, the one in which a base material layer 56 and a light diffusing layer 57 as shown in FIG. 8B are laminated is generally used. The light diffusing layer 57 has a structure in which beads 59 made of synthetic resin, glass or the like are dispersed in a binder 58 made of synthetic resin. As shown in FIG. 9, the light diffusing sheet 54 having such a structure mainly focuses the passing light rays on the vicinity of the beads 59 by refracting at the outer surface of the beads 59, and as a result, diffuses the light rays at a predetermined distance.

[0006]

In the above conventional light diffusing sheet 54, since substantially spherical beads 59 are used,
The light rays passing therethrough are diffused in a wide range (see FIG. 9), and are also diffused in directions not required by the backlight unit 50. As a result, in the conventional backlight unit 50, the amount of emitted light is inevitably reduced by the amount that the light diffusion sheet 54 diffuses the light rays in an unnecessary direction.

As the conventional light diffusing sheet, in addition to the light diffusing sheet 54 in which the light diffusing layer 57 in which the beads 59 are dispersed is laminated on the surface, fine unevenness is formed on the surface by embossing or the like. There is also a light diffusion sheet,
Each type of light diffusing sheet mainly has a function of diffusing transmitted light rays, and additionally has a function of changing the peak direction of outgoing light rays to the upper side by the light diffusing function. Therefore, in the conventional light diffusion sheet, in order to increase the angle changing function of directing the transmitted light rays in the normal direction, it is necessary to necessarily increase the light diffusion function, and if the light diffusion function is increased too much, On the contrary, the amount of light emitted in the required normal direction may decrease, and the brightness of the liquid crystal display device using the backlight unit 50 may decrease.

Further, since the prism sheet 55 has a function of changing the angle of rays passing through the prism portion 55a on the surface to the normal direction as described above, the inclination angle of the prism portion 55a is changed to change the refraction direction. It is not easy because it involves a design change of the mold etc.

The present invention has been made in view of these inconveniences, and makes it possible to control the light emission characteristics by an easy method.
An object of the present invention is to provide an optical sheet that can increase the amount of light emitted in the normal direction and a backlight unit that can improve the brightness using the optical sheet.

[0010]

SUMMARY OF THE INVENTION The invention made to solve the above problems is an optical sheet having specific optical properties, wherein an optical sheet having beads dispersed in a binder is used.
It is equipped with a functional layer, and in the binder of the optical functional layer
Refractive index control filler is dispersed, the refractive index control filler
With an optical sheet having a particle size of 1 nm or more and 400 nm or less
is there. Here, the “refractive index control filler” refers to inorganic fine particles such as a metal oxide that is filled in a material and controls the refractive index of the material.

According to the optical sheet, since the refractive index control filler is dispersed inside the sheet, the refractive index of the optical sheet can be controlled by the characteristics of the dispersed refractive index control filler and the dispersion density thereof. Therefore, the refraction direction of the light ray incident on the optical sheet can be controlled, and as a result, the transmitted light ray can be refracted and emitted in an arbitrary direction. That is, the angle changing function of the optical sheet can be easily adjusted. Further, depending on the portion in which the refractive index control filler is dispersed, it is possible to impart optical characteristics for diffusing or condensing light rays, and it is possible to arbitrarily control the optical characteristics by controlling the refractive index. Well
Also, a refractive index control filler is added to the binder of the optical functional layer.
By dispersing, the refractive index of the binder can be controlled arbitrarily.
You can Therefore, the refraction of the base layer and binder
The rate difference can be controlled more easily and arbitrarily.
As a result, it controls the refraction direction of the rays that pass through those interfaces.
be able to. Therefore, from this means as well,
It is possible to easily adjust the changing angle direction. Also, buy
Refractive index difference between the beads and the beads and the refraction between the beads and the outside world
The rate difference can be controlled arbitrarily. Therefore, Vine
Refraction at the interface between the bead and the beads and emission from the beads to the outside
You can control the refraction when doing so that the beads
The focal length of the light beam emitted from
It Therefore, in this way,
By controlling the optical characteristics of the optical sheet
It is possible to arbitrarily control from diffusion to light collection. Refractive index
The particle size of the control filler was 1 nm or more and 400 nm or less
The particle size of the refractive index control filler is smaller than the above range.
It becomes difficult to mix it into the base made of
However, it is difficult to manufacture ultrafine particles with a particle size smaller than the above range.
It is because there is, on the contrary, the particle size of the refractive index control filler
When the value exceeds the above range, the wavelength is larger than the wavelength of visible light and it is transparent.
Because it becomes impossible to maintain sex
It

When the optical sheet has a transparent base material layer, it is preferable to disperse the refractive index control filler in the base material layer. According to this means, it is possible to control the refractive index of the base material layer as described above, and as a result, it is possible to control the difference in refractive index between both sides of the base material layer surface. Therefore, it is possible to control the refraction directions of light rays entering and exiting the base material layer, and it is possible to easily adjust the angle changing function of the optical sheet by utilizing the action.

[0013]

[0014]

As described above, the control of the optical characteristics, which is the object of the present invention, is performed by controlling the difference in refractive index between the base layer and the binder, the difference in refractive index between the binder and beads, and the difference in refractive index between the beads and the external space. Since the above is controlled, a high refractive index control filler having a high refractive index or a low refractive index control filler having a low refractive index can be used as the refractive index control filler.

As such a high-refractive-index controlling filler, it is preferable to use one or more selected from the group consisting of titanium oxide, zinc sulfide and cerium oxide. These substances have a relatively high refractive index, and have a large effect of increasing the refractive index. It should be noted that increasing the refractive index of each element made of synthetic resin or the like with such a high refractive index control filler is easier than decreasing the refractive index with a low refractive index control filler described later, and has a large refractive index control effect.

As the low refractive index control filler, it is preferable to use one kind or two or more kinds selected from the group consisting of calcium fluoride, magnesium fluoride and silicon oxide. These materials have a relatively low refractive index,
The effect of lowering the refractive index is relatively large.

[0018]

The density of the refractive index control filler may be graded so that the refractive index continuously changes in the vicinity of the interface between the respective constituents in which the refractive index control filler is dispersed. By doing this, reflection at the interface of each component can be reduced,
The light transmittance can be improved.

The optical sheet of the present invention is provided with a sticking prevention layer having resin beads dispersed in a binder on the back surface of the base material layer, and the refractive index control filler can be dispersed in the binder and / or the beads. By thus providing the sticking prevention layer on the back surface of the base material layer, sticking can be prevented even when the optical sheet is overlaid on another sheet. In addition, by controlling the refractive index of the binder of the sticking prevention layer, it is possible to arbitrarily control the gonio property.

Therefore, the lamp, the light guide plate which is arranged on the side of the lamp and guides the light beam emitted from the lamp to the front side, and the optical sheet which is arranged on the surface side of the light guide plate and uniformly guides the light beam in the front side direction. In a backlight unit for a liquid crystal display device including the optical sheet, when the optical sheet of the present invention is used as the optical sheet, the optical sheet according to the optical characteristics of the light diffusion sheet or the prism sheet that constitutes the backlight unit. It is possible to control the intensity of the optical characteristics, that is, the goniomorphic characteristics, the diffusion characteristics, and the light condensing characteristics, and thereby to improve the light output amount in the normal direction. Therefore, the brightness of the liquid crystal display device using the backlight unit can be improved.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention, and FIG. 2 shows a light transmission simulation result when a high refractive index filler is used as the refractive index control filler of the optical sheet of FIG. FIG. 3 is an explanatory view showing a light transmission simulation result when a low refractive index filler is used as the refractive index control filler of the optical sheet of FIG. 1, and FIGS. 4 to 8 are respectively the optical sheet of FIG. FIG. 3 is a schematic cross-sectional view showing an optical sheet according to a different form.

The optical sheet 1 shown in FIG. 1 comprises a base layer 2 and an optical functional layer 3 laminated on the front side of the base layer 2. Since the base material layer 2 needs to transmit light rays, the base material layer 2 is formed of a transparent, particularly colorless and transparent synthetic resin. 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. . The thickness of the base material layer 2 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 75 μm.
It is set to 250 μm or less. When the thickness of the base material layer 2 is less than the above range, curling may be likely to occur when the resin composition forming the optical functional layer 3 is applied. On the contrary, when the thickness of the base material layer 2 exceeds the above range,
The brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which violates the demand for a thinner liquid crystal display device.

The optical functional layer 3 is composed of a binder 4 and beads 5 dispersed in the binder 4. Examples of the polymer used for the binder 4 include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamide imide, and epoxy resin. In addition to the above polymers, the binder 4 may be blended with, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, or the like. The binder 4 is transparent because it needs to transmit light rays, and is preferably colorless and transparent.

Examples of the material of the beads 5 include acrylic resin, polyurethane, polyvinyl chloride, polystyrene,
Examples thereof include polyacrylonitrile and polyamide. The beads 5 are preferably transparent in order to increase the amount of light rays transmitted through the light diffusion sheet 1, and particularly preferably colorless and transparent.

The particle size of the beads 5 is 0.1 μm or more and 100.
μm or less is preferable, and 1 μm or more and 50 μm or less is particularly preferable. This is because when the particle diameter of the beads 5 is less than the above range, the light diffusion effect becomes insufficient, and conversely, when the particle diameter exceeds the above range, the resin composition for forming the optical functional layer 3 is formed. This is because coating becomes difficult. The particle size of the beads 5 is 100 beads 5 arbitrarily extracted.
Of the particle is measured with a microscope to measure the diameter of the particle, and the average is calculated. When the beads 5 are not spherical, the size of the beads 5 in any one direction and the size of the beads 5 in the direction orthogonal thereto are averaged.

The compounding amount of the beads 5 of the optical functional layer 3 is 0.1 with respect to 100 parts by weight of the polymer content in the binder 4.
The amount is preferably not less than 500 parts by weight and more preferably not less than 10 parts and not more than 300 parts by weight. This is because when the amount is less than the above range, the light diffusion effect becomes insufficient, and conversely, when the amount exceeds the above range, the resin composition for forming the optical functional layer 3 is formed. This is because coating becomes difficult.

The refractive index control filler 6 is dispersed in the binder 4, which is a characteristic of the optical sheet 1. As described above, the refractive index control filler 6 is for controlling the refractive index of the mixed / dispersed material, and is an inorganic fine particle such as a metal oxide. Therefore,
The refractive index control filler 6 is roughly classified into a high refractive index filler that improves the refractive index and a low refractive index filler that lowers the refractive index.

The high refractive index filler is inorganic fine particles having a high refractive index, and specifically, aluminum oxide (alumina), tantalum oxide, titanium oxide (rutile, anatase), zinc sulfide, zirconium oxide, cerium oxide,
Examples thereof include tin oxide and indium oxide. Among them, titanium oxide, zinc sulfide and cerium oxide are preferable because of their high refractive index, and one or more selected from these groups may be used.

The low refractive index filler is inorganic fine particles having a low refractive index, and specific examples thereof include calcium fluoride, magnesium fluoride, lanthanum fluoride, silicon oxide and the like, among which the low refractive index is low. Therefore, calcium fluoride, magnesium fluoride and silicon oxide are preferable, and one or more selected from these groups may be used.

The particle size of the refractive index control filler 6 is preferably 1 nm or more and 400 nm or less, and particularly preferably 5 nm or more and 80 nm or less. This is because if the particle size of the refractive index control filler 6 is smaller than the above range, it becomes difficult to mix it in the binder 4, and it is difficult to produce ultrafine particles of such a size. This is because if the particle diameter of the rate control filler 6 exceeds the above range, the rate control filler 6 is larger than the wavelength of visible light and the transparency cannot be maintained.

The shape of the refractive index control filler 6 is not particularly limited, and examples thereof include spherical shape, cubic shape, needle shape, rod shape, spindle shape, plate shape, scale shape, and fiber shape. Among them, the scale-like shape and the plate-like shape are preferable for improving heat resistance and thermal dimensional stability.

The blending amount of the refractive index control filler 6 is 100.
0.01 part by weight or more to 10 parts by weight of binder 4
The amount is preferably 0 parts by weight or less, particularly preferably 10 parts by weight or more and 100 parts by weight or less. This is because if the blending amount of the refractive index control filler 6 is less than the above range, the control of the refractive index cannot be sufficiently achieved, and conversely, if the blending amount exceeds the above range, the binder 4 is added to the binder 4. Is difficult to disperse, and the mechanical properties of the optical sheet 1 are adversely affected.

Next, the effect of using a high refractive index filler as the refractive index control filler 6 will be described. In this case, the refractive index of the binder 4 becomes higher than the refractive index of the base material layer 2 and the beads 5, and the transmitted light is refracted toward the normal direction side at the interface between the base material layer 2 and the binder 4 (FIG. 1). (Indicated by an arrow inside). That is, the optical sheet 1 in this case has a function of changing the angle due to the difference in refractive index. Further, since the refractive index of the binder 4 is larger than the refractive index of the beads 5, it acts so as to separate the focal position of the light beam that has passed through the beads 5 from the beads 5, in other words, to further focus the light. Now, the refractive index of the beads 5 is 1.49, and the binder 4
FIG. 2 shows the result of the light transmission simulation when the refractive index of is 0.8. Comparing this FIG. 2 with the simulation result in the case where the binder and the bead shown in FIG. 9 have the same refractive index, it can be seen that in the case of FIG.

On the other hand, the effect of using a low refractive index filler as the refractive index control filler 6 will be described. In this case, the refractive index of the binder 4 becomes lower than the refractive index of the base material layer 2 or the beads 5, and an action opposite to the above case occurs. That is, the angle changing characteristic due to the interface between the base material layer 2 and the binder 4 is reduced, and the diffusion characteristic appears depending on the magnitude of the refractive index of the binder 4 and the beads 5. In this case, FIG. 3 shows the result of light transmission simulation in which the refractive index of the beads 5 is 1.49 and the refractive index of the binder 4 is 1.3.
Comparing the case of FIG. 3 with the case of FIG. 9 above, it can be seen that the diffusion characteristic is enhanced in this case.

The optical sheet 11 of FIG. 4 is composed of a base material layer 2 and an optical functional layer 3. In this optical functional layer 3, beads 5 are dispersed in a binder 4 and a refractive index control filler 6 is contained. It is similar to the optical sheet 1 of FIG. 1 in that it is dispersed. In the optical sheet 11, the refractive index control filler 6 is dispersed in the beads 5, and the refractive index of the beads 5 can be controlled. Therefore, according to the optical sheet 11, by controlling the magnitude of the refractive index between the beads 5 and the binder 4 and the difference between them, the optical characteristics from light collection to diffusion can be arbitrarily adjusted.

The optical sheet 21 of FIG. 5 is composed of a base material layer 2 and an optical functional layer 3. In this optical functional layer 3, beads 5 are dispersed in a binder 4 and a refractive index control filler 6 is contained. It is similar to the optical sheet 1 of FIG. 1 and the optical sheet 11 of FIG. 2 in that they are dispersed. The optical sheet 21
, The refractive index control filler 6a is dispersed in the binder 4, and the refractive index control filler 6b is dispersed in the beads 5.
Therefore, the optical sheet 21 can control both the refractive index of the binder 4 and the refractive index of the beads 5.
Therefore, between the base material layer 2 and the binder 4, the binder 4
It becomes easy to control the magnitude of the refractive index and the difference between the beads 5 and the beads 5 and between the beads 5 and the outside world, and the controllable width is expanded. As a result, according to the optical sheet 21, it is possible to easily and arbitrarily control the optical characteristics such as the angle changing characteristics, the light collecting characteristics, and the diffusion characteristics.

The optical sheet 31 of FIG. 6 comprises only the base material layer 2 having the irregularities 7 formed on the surface thereof, and the refractive index control filler 6 is dispersed therein. Therefore, the optical sheet 31 can control the refractive index of the base material layer 2 arbitrarily, and can control the refraction direction of the light ray in the bottom face of the base material layer 2 arbitrarily. That is, the optical sheet 31 has a gonio characteristic,
The angle changing direction can be controlled arbitrarily.

The optical sheet 41 of FIG. 7 comprises a base material layer 2 and an optical functional layer 3, and further comprises a sticking prevention layer 8 in which beads 10 are dispersed in a binder 9 on the back surface of the base material layer 2. The refractive index control filler 6 is dispersed in this binder 9. Therefore, the optical sheet 41 can arbitrarily control the refractive index of the binder 9 of the sticking prevention layer 8, and as a result, the transmitted light rays at the lower surface of the binder 9 and the interface between the binder 9 and the base material layer 2 can be controlled. The refraction direction can be controlled. Therefore, the optical sheet 41 can arbitrarily control its gonio characteristic.

The optical sheet of the present invention is not limited to the above embodiment, and the refractive index control filler can be dispersed in each component in any combination. Further, it is preferable that the dispersion density of the refractive index control filler is inclined near the interface and the refractive index is continuously changed near the interface of each constituent element. By doing so, it is possible to reduce reflection at the interface of each constituent element and improve the transmittance of light rays.

[0041]

As described above, according to the optical sheet of the present invention, it is possible to arbitrarily control the optical characteristics such as the angle changing characteristic, the light condensing characteristic, the diffusion characteristic and the like. Can be used to increase the amount of light emitted in the normal direction. Therefore, the backlight unit using the optical sheet can improve the brightness without increasing the power consumption. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a result of light transmission simulation when beads have a refractive index of 1.49 and a binder has a refractive index of 1.8 in the optical sheet of FIG.

FIG. 3 is an explanatory diagram showing a result of light transmission simulation when beads have a refractive index of 1.49 and a binder has a refractive index of 1.3 in the optical sheet of FIG.

FIG. 4 is a schematic cross-sectional view showing an optical sheet of a form different from that of the optical sheet of FIG.

5 is a schematic cross-sectional view showing an optical sheet having a different form from the optical sheets of FIGS. 1 and 4. FIG.

6 is a schematic cross-sectional view showing an optical sheet of a different form from the optical sheets of FIGS. 1, 4 and 5. FIG.

FIG. 7 is a schematic cross-sectional view showing an optical sheet of a different form from the optical sheets of FIGS. 1, 4, 5, and 6.

FIG. 8A is a schematic perspective view showing a general backlight unit, and FIG. 8B is a schematic sectional view showing a general light diffusion sheet.

FIG. 9 is an explanatory diagram showing a light transmission simulation result in the case where the beads have a refractive index of 1.49 and the binder has a refractive index of 1.49 in the light diffusion sheet of FIG. 8B.

[Explanation of symbols]

1 Optical sheet 2 Base material layer 3 Optical functional layer 4 binders 5 beads 6 Refractive index control filler 6a Refractive index control filler 6b Refractive index control filler 7 unevenness 8 Anti-sticking layer 9 binders 10 beads 11 Optical sheet 21 Optical sheet 31 Optical sheet 41 Optical sheet

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-127315 (JP, A) JP-A-11-287902 (JP, A) JP-A-11-160505 (JP, A) JP-A-10- 265580 (JP, A) JP 11-194204 (JP, A) JP 7-218705 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (9)

(57) [Claims] 1. An optical sheet having specific optical properties, comprising an optical functional layer in which beads are dispersed in a binder.
And a refractive index control filler in the binder of the optical functional layer.
Are dispersed, and the particle diameter of the refractive index control filler is 1 nm or more and 400 nm or more.
The following is an optical sheet. 2. The optical sheet according to claim 1, further comprising a transparent base material layer, wherein the refractive index control filler is dispersed in the base material layer. 3. The claim 1, wherein said refractive index control filler as a high refractive index control filler is used
Is the optical sheet described in 2 . 4. The method of claim lower refractive index as the refractive index control filler low refractive index control filler is used 1 also
Is the optical sheet described in 2 . As claimed in claim 5 wherein said high refractive index control filler, titanium oxide, claims are used one or more of those are selected from the group consisting of zinc sulfide and cerium oxide
The optical sheet according to item 3 . As claimed in claim 6, wherein said low refractive index control filler, optical of claim 4 calcium fluoride, one selected from the group consisting of magnesium fluoride and silicon oxide or two or more of those it is used Sheet. 7. A claim tilting the density of the refractive index control filler to the refractive index in the vicinity of the interface of each component which the refractive index control filler dispersed is continuously changed 1
To the optical sheet according to claim 6 . 8. comprises a sticking preventive layer resin beads are dispersed in a binder on the back side the base material layer, claim 1, the refractive index control filler dispersed in a binder and / or in the beads of the sticking prevention layer Claim
7. The optical sheet according to any one of 7 . 9. A lamp, a light guide plate for guiding the light emitted from the lamp on the front side is disposed on the side of the lamp, according to claim uniformly directing light rays are disposed on the surface side of the light guide plate on the front side direction A backlight unit for a liquid crystal display device, comprising the optical sheet according to claim 1 .