JP2002328208A - Light-diffusing sheet and back light unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-diffusing sheet which hardly distorts even by the heat generated by a lamp and to provide a back light unit by using the sheet. SOLUTION: The light-diffusing sheet 1 consists of a base sheet 3 and a light-diffusing layer 5 formed on the surface of the base sheet 3. The light- diffusing layer 5 is composed of resin beads 9, a polyhedral minute inorganic filler 11 and an additive (not shown in the figure) dispersed in a binder 7. As for the polyhedral minute inorganic filler 11, ZnO, CdS, CdSe and CdTh having a tetrahedral form or WO3 , SnO2 , In2 O3 and In2 S3 having a hexahedral form or WO3 having octahedral form or Si3 N4 having an aggregated cubic form can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion sheet used for a backlight unit incorporated in a liquid crystal display and a backlight unit using the light diffusion sheet.

[0002]

2. Description of the Related Art Conventionally, as a backlight unit incorporated in a liquid crystal display device, a lamp as a light source, a light guide plate disposed beside the lamp to guide light emitted from the lamp to the front side, and A light guide plate provided with a light diffusion sheet laminated on the front side of the light guide plate (the screen side of the liquid crystal display device) is used.

[0003] As the light diffusion sheet, for example, a resin composition in which resin beads are dispersed on the surface of a base sheet made of a synthetic resin such as polyethylene terephthalate is applied.
One in which a light diffusion layer is formed has been proposed (for example, see Japanese Utility Model Laid-Open No. 5-73602). In this light diffusion sheet, the light transmitted through the light diffusion layer is uniformly diffused by the resin beads, and the brightness of the screen of the liquid crystal display device is increased.

Further, in order to suppress partial adhesion (sticking) between the back surface of the light diffusion sheet and the surface of the light guide plate and to prevent luminance unevenness on the screen, a resin composition in which resin beads are dispersed is formed by coating. There is also proposed a light diffusion sheet having the anti-sticking layer provided on the back surface of the base sheet (for example, see Japanese Utility Model Laid-Open No. 7-8803).

[0005]

However, these light diffusion sheets have a drawback that they are easily deformed by heat because the base sheet is made of synthetic resin. On the other hand, the lamp, which is a light source, generates heat simultaneously with light emission. Generally, a portion of the light diffusion sheet near the lamp is exposed to a temperature of about 80 ° C. to 90 ° C. Therefore, the light diffusion sheet may be partially deformed due to thermal deformation. When the flexure occurs, there is a problem that luminance unevenness of the screen occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of this problem, and has as its object to provide a light diffusion sheet which is unlikely to be bent even by the heat generated by a lamp, and a backlight unit using the same. .

[0007]

The light diffusion sheet according to the first invention is a light diffusion sheet comprising a transparent base sheet and a light diffusion layer provided on the front side of the base sheet,
The light diffusion layer is configured by dispersing beads and a fine inorganic filler having a polyhedral shape in a binder.

[0008] In the light diffusion sheet according to the present invention,
Since the inorganic filler having a polyhedral shape is contained in the binder of the light diffusion layer, the apparent crystallinity and glass transition temperature of the light diffusion sheet can be increased, and the heat resistance can be increased. Therefore, it becomes possible to suppress the bending of the light diffusion sheet.

Further, in the case of the fine inorganic filler having a polyhedral shape, even if the amount added to the binder is small,
Deflection of the light diffusion sheet can be sufficiently sufficiently suppressed. Thus, in the light diffusion sheet to which the addition amount of the fine inorganic filler is small, it is possible to easily perform the coating operation of the resin composition forming the light diffusion layer when the sheet is manufactured.

[0010] A light diffusion sheet according to a second invention comprises a transparent base sheet, a light diffusion layer provided on the front side of the base sheet, and an anti-sticking layer provided on the back side of the base sheet. The sticking prevention layer is formed by dispersing beads and a fine inorganic filler having a polyhedral shape in a binder.

[0011] In the light diffusion sheet according to the present invention,
Since the fine inorganic filler having a polyhedral shape is contained in the binder of the anti-sticking layer, the apparent crystallinity and glass transition temperature of the light diffusion sheet can be increased, and the heat resistance can be increased. Therefore, it becomes possible to suppress the bending of the light diffusion sheet.

Further, in the case of the fine inorganic filler having a polyhedral shape, even if the amount added to the binder is small,
Deflection of the light diffusion sheet can be sufficiently sufficiently suppressed. Thus, in the light diffusion sheet to which the addition amount of the fine inorganic filler is small, it is possible to easily apply the resin composition forming the anti-sticking layer at the time of manufacturing the sheet.

In the first and second inventions, the fine inorganic filler having a polyhedral shape may be a fine inorganic material having a tetrahedral shape. The fine inorganic substance having a tetrahedral shape may be zinc oxide, and the fine inorganic substance having a tetrahedral shape may be a cadmium compound. In this case, the cadmium compound may be cadmium sulfide, cadmium selenide or cadmium telluride.

In the first and second inventions, the fine inorganic filler having a polyhedral shape may be a fine inorganic material having a hexahedral shape. The small inorganic substance having a hexahedral shape may be tungsten oxide, and the small inorganic substance having a hexahedral shape may be tin oxide. Further, the fine inorganic substance having a hexahedral shape may be an indium compound. In this case, the indium compound may be indium oxide or indium sulfide.

In the first and second aspects of the present invention, the fine inorganic filler having a polyhedral shape may be a fine inorganic material having an octahedral shape. The minute inorganic substance having an octahedral shape may be tungsten oxide.

Further, in the first and second inventions,
The fine inorganic filler having a polyhedral shape may be a fine inorganic material having an aggregated cubic shape. The fine inorganic substance having the aggregated cubic shape may be silicon nitride.

In the first and second inventions, the average particle diameter of the beads is 0.1 μm or more and 50 μm or less, and the average particle diameter of the polyhedral fine inorganic filler is 5 nm or more and 1 μm or less. Preferably less than the meter. By setting the size of the beads and the fine inorganic filler having a polyhedral shape in the above range, it becomes possible to suppress the deflection of the light diffusion sheet while maintaining good light diffusing properties or good sticking prevention performance. .

In the first and second inventions, the blending amount of the fine inorganic filler having a polyhedral shape is 0.1 to 200 parts by weight based on 100 parts by weight of the polymer in the binder. Is preferred. By setting the blending amount of the fine inorganic filler having a polyhedral shape in the above range, it is possible to achieve both the heat resistance of the light diffusion sheet and the easiness of the sheet manufacturing operation.

According to a third aspect of the present invention, there is provided a backlight unit for a liquid crystal display device, comprising: a light source; a light guide plate disposed on a side of the light source for guiding light emitted from the light source in a front side direction; and a light guide plate disposed on a front side of the light guide plate. And the light diffusion sheet according to the first or second invention.

In the backlight unit for a liquid crystal display device according to the present invention, a light diffusion sheet capable of suppressing the above-described bending due to heat is used.
It is possible to suppress luminance unevenness of the liquid crystal display device.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing a light diffusion sheet 1 according to one embodiment of the present invention. The light diffusion sheet 1 shown in FIG. 1 includes a base sheet 3 and a light diffusion layer 5 provided on one surface side of the base sheet 3. In the light diffusion sheet 1, the side where the light diffusion layer 5 is provided is the front side (that is, the screen side of the liquid crystal display device), and the other surface side of the base sheet 3 where the light diffusion layer 5 is not provided is the back side. It is.

The base sheet 3 is made of, for example, a synthetic resin such as polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. The base sheet 3 is transparent because it is necessary to transmit light, and is preferably colorless and transparent.

The thickness of the base sheet 3 is not particularly limited, but is, for example, not less than 38 micrometers and not more than 250 micrometers. If the thickness of the base sheet 3 is less than the above range, curling may be likely to occur when the resin composition forming the light diffusion layer 5 is applied.
Conversely, if the thickness of the base sheet 3 exceeds the above range, the brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit 13 described later in FIG. This is contrary to the demand for thinner.

The light diffusion layer 5 is composed of a binder 7, resin beads 9 dispersed in the binder 7 and a fine inorganic filler having a polyhedral shape (hereinafter referred to as a polyhedral fine inorganic filler) 11. I have. Although not shown in FIG. 1, the light diffusion layer 5 contains an additive dispersed in the binder 7. Thickness of light diffusion layer 5 (thickness of binder 7 excluding resin beads 9; FIG. 1)
At T ₁ . ) Is not particularly limited,
For example, it is about 1 micrometer or more and about 30 micrometers or less.

By dispersing the polyhedral-shaped fine inorganic filler 11 in the light diffusion layer 5 as described above, the apparent crystallinity and glass transition temperature of the light diffusion sheet 1 can be increased. Thereby, the light diffusion sheet 1
Of the light diffusion sheet 1 can be suppressed.

Further, by dispersing the resin beads 9 in the light diffusion layer 5 as described above, it is possible to uniformly diffuse the light transmitted through the light diffusion layer 5 from the back side to the front side. In this case, a part of the resin beads 9 has an upper end protruding from the binder 7. By providing the resin beads 9 embedded in the binder 7 and the projecting resin beads 9 in this manner, the light beam can be more diffused.

The dispersion of the polyhedral micro-inorganic filler 11 as described above makes it possible to increase the apparent crystallinity and glass transition temperature of the light diffusion sheet 1 because the polyhedral micro-fine particles This is because the inorganic filler 11 behaves in the same manner as the crystalline portion of the crystalline polymer and hinders the thermal movement of the molecular side chains of the polymer used for the binder 7.

Here, from the viewpoint of suppressing the deflection of the light diffusion sheet, a fine inorganic compound having no polyhedral shape, for example, colloidal silica, smectite, colloidal calcium carbonate, mica, or the like is used as a fine inorganic filler in a binder. It is believed that they can be dispersed. Even with these fine inorganic fillers that do not have a polyhedral shape, they exhibit the same behavior as the crystalline part of the crystalline polymer, hinder the thermal movement of the molecular side chains of the polymer used for the binder, and appear as a light diffusion sheet. It is believed that the above crystallinity and glass transition temperature can be improved. For this reason, it is considered that the heat resistance of the light diffusion sheet can be increased and the bending of the light diffusion sheet can be reduced even by the fine inorganic filler having no polyhedral shape.

However, in order to sufficiently suppress the deflection of the light diffusion sheet by using a fine inorganic filler having no polyhedral shape such as colloidal silica, it is necessary to add a large amount of the fine inorganic filler to the binder. it is conceivable that. For example, using colloidal silica as a fine inorganic filler to sufficiently suppress the deflection of the light diffusion sheet,
It is considered necessary to add 10 to 500 parts by weight of colloidal silica to 100 parts by weight of the polymer in the binder. When such a large amount of the fine inorganic filler is added, it may be difficult to apply the resin composition for forming the light diffusion layer.

On the other hand, when the polyhedral-shaped fine inorganic filler 11 is used as in the present invention, compared with the case where the fine inorganic filler having no polyhedral shape is used, the molecular weight of the polymer used for the binder 7 is increased. It is possible to further improve the effect of hindering the thermal motion of the side chain, and it is possible to further increase the apparent crystallinity and the glass transition temperature of the light diffusion sheet 1. Therefore, by using the polyhedral-shaped fine inorganic filler 11, it is possible to realize a sufficient deflection suppressing effect of the light diffusion sheet 1 with a smaller amount of addition than when using the fine inorganic filler having no polyhedral shape. Becomes For example, by adding 0.1 to 200 parts by weight, preferably 5 to 150 parts by weight of the polyhedral-shaped fine inorganic filler 11 to 100 parts by weight of the polymer in the binder 7, the light diffusing sheet 1 Can be sufficiently suppressed.

As described above, in the light diffusion sheet 1 provided with the light diffusion layer 5 in which the polyhedral fine inorganic filler 11 is dispersed in the binder 7, the addition amount of the polyhedral fine inorganic filler 11 is small. Even so, it becomes possible to sufficiently prevent deflection due to heat. In such a light diffusion sheet 1, since the addition amount of the polyhedral-shaped fine inorganic filler 11 in the light diffusion layer 5 is small, it is possible to easily apply the resin composition forming the light diffusion layer 5. Become.

The reason why the effect of preventing the thermal motion of the molecular side chain of the polymer used for the binder 7 when the polyhedral-shaped fine inorganic filler 11 is used is further improved is as follows when the outermost diameter is the same. The surface area of the fine inorganic filler is larger in the case of the fine inorganic filler having a polyhedral shape than the fine inorganic filler having no polyhedral shape, so it is estimated that the number of contacts with the molecular side chains of the polymer increases. .

The polymer used for the binder 7 includes, for example, acrylic resin, polyurethane, polyester, fluorine resin, silicon resin, polyamideimide, epoxy resin and the like. The polymer used for the binder 7 may be a thermosetting type, an ultraviolet setting type, or a two-component setting type.

The resin beads 9 have a substantially spherical shape, and examples of the material include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and the like. The resin beads 9 are preferably transparent in order to increase the amount of light passing through the light diffusion sheet 1, and are particularly preferably colorless and transparent.

The average particle diameter of the resin beads 9 is preferably 1 micrometer or more and 50 micrometers or less,
The thickness is particularly preferably from 2 micrometers to 20 micrometers. If the average particle diameter is less than the above range, the light diffusion effect may be insufficient. Conversely, if the average particle diameter exceeds the above range, it may be difficult to apply the resin composition forming the light diffusion layer 5.
The average particle diameter of the resin beads 9 was 100 arbitrarily extracted.
It is derived by measuring the particle diameter by enlarging the individual resin beads 9 with a microscope, and simply averaging them.

Although the spherical resin beads 9 are used in this case, the shape of the resin beads 9 is not limited to a spherical shape. When the shape of the resin bead 9 is not spherical, the value obtained by averaging the size of the resin bead 9 in an arbitrary direction and the size of the resin bead 9 in a direction orthogonal thereto is defined as the particle diameter of the resin bead 9. .

In this embodiment, the resin beads 9
However, instead of the resin beads 9, those which can exhibit a light diffusion function, for example, glass beads or the like may be used.

The compounding amount of the resin beads 9 in the light diffusion layer 5 is preferably 0.1 to 500 parts by weight, more preferably 10 to 300 parts by weight, based on 100 parts by weight of the polymer in the binder 7. Particularly preferred. If the amount is less than the above range, the light diffusion effect may be insufficient. Conversely, if the amount exceeds the above range, it may be difficult to apply the resin composition for forming the light diffusion layer 5.

Examples of the polyhedral-shaped fine inorganic filler 11 include:
For example, a fine inorganic material having a tetrahedral shape, a fine inorganic material having a hexahedral shape, a fine inorganic material having an octahedral shape, and a fine inorganic material having an aggregated cubic shape can be used.

As the fine inorganic substance having a tetrahedral shape,
For example, ZnO, and CdS, CdSe and CdT
A cadmium compound such as e can be used. Also,
Examples of the fine inorganic substance having a hexahedral shape include W
O ₃ , SnO ₂ , and indium compounds such as In ₂ O ₃ and In ₂ S ₃ can be used. WO ₃ can be used, for example, as the octahedral minute inorganic substance. Incidentally, WO _3, usually the particles have a hexahedral shape, particle by generating condition is octahedral. Further, as the fine inorganic substance having the aggregated cubic shape, for example, Si ₃ N ₄ can be used.

In the case where inorganic fine particles such as ZnO, CdS, CdSe, and CdTe are used as the polyhedral fine inorganic filler 11 in the form of tetrahedral (totala pot) crystal particles, inorganic fine particles having other shapes are used. Since the entanglement between the inorganic filler and the molecular side chains of the polymer in the coating layer is better than when using as an inorganic filler, the apparent crystallinity and the glass transition temperature can be increased, and the resin Increases rigidity. For this reason, it is possible to realize a particularly favorable bending prevention effect of the light diffusion sheet 1. Therefore, as the polyhedral-shaped fine inorganic filler 11, it is particularly preferable to use inorganic fine particles such as ZnO, CdS, CdSe, and CdTe having a tetrahedral crystal particle shape (tetrapot shape).

The polyhedral-shaped fine inorganic filler 11 has a very small particle diameter on the order of nanometers. For this reason,
In the light diffusion layer 5 in which the polyhedral-shaped fine inorganic filler 11 is dispersed in the binder 7, there is no possibility that the light transmission is inhibited by the polyhedral-shaped fine inorganic filler 11. Therefore, good optical performance is maintained in the light diffusion sheet 1.

In order to prevent the loss of the light beam passing through the light diffusion sheet 1, it is preferable to reduce the average particle diameter of the polyhedral-shaped fine inorganic filler 11. Specifically, the average particle diameter is preferably less than 1 micrometer, and particularly preferably 400 nanometers or less, which is equal to or less than the visible wavelength of light. Further, the average particle diameter is preferably 100 nanometers or less, because it is possible to prevent the light diffusion sheet 1 from becoming pale and turbid under the influence of the short wavelength. Considering the occurrence of agglomeration, it is particularly preferable that the average particle diameter is 50 nm or less. Polyhedral-shaped fine inorganic filler 11
The lower limit of the average particle diameter is not particularly limited since the smaller the average particle diameter is, the average particle diameter of the generally obtained polyhedral-shaped fine inorganic filler 11 is 1 nanometer or more.

The average particle diameter of the polyhedral-shaped fine inorganic filler 11 is obtained by magnifying a 100 polyhedral-shaped fine inorganic filler 11 arbitrarily extracted with a microscope, measuring the particle diameter, and simply averaging the particles. Is derived by In this case, the value obtained by averaging the dimension of the polyhedral-shaped fine inorganic filler 11 in one arbitrary direction and the dimension in the direction orthogonal thereto is the value of the polyhedral-shaped fine inorganic filler 11.
Particle diameter.

For example, ZnO, CdS, CdSe, or CdTe having a tetrahedral shape and a particle diameter of 0.1 to 50 nanometers may be used as the polyhedral fine inorganic filler 11. For example, a typical average particle diameter of ZnO (BE
T method) is 31 nanometers.

Further, as a polyhedral fine inorganic filler 11 may be used _{WO 3, SnO 2, In 2} O 3, In 2 S 3 particles diameter 0.1 to 50 nanometers with a hexahedral shape. Further, as the polyhedral inorganic filler 11, WO having a particle diameter of 0.1 to 50 nanometers having an octahedral shape is used.
₃ or a polyhedral inorganic filler 11
As an example, Si ₃ N ₄ having a particle diameter of 0.1 to 50 nanometers having an aggregated cubic shape may be used.

The blending amount of the polyhedral-shaped fine inorganic filler 11 in the light diffusion layer 5 depends on the amount of polymer 10 in the binder 7.
0.1 parts by weight or more and 200 parts by weight or less, preferably 5 parts by weight or more and 150 parts by weight or less with respect to 0 parts by weight. If the amount is less than the above range, thermal deformation of the light diffusion sheet 1 may not be sufficiently prevented. Conversely, if the amount exceeds the above range, it may be difficult to apply the resin composition forming the light diffusion layer 5.

An additive (not shown) dispersed in the binder 7 in the light diffusion layer 5 is added to impart heat resistance, antistatic property and durability to the light diffusion sheet 1. Specific examples include an antistatic agent, inorganic fine particles other than the above-mentioned polyhedral metal oxide, and the like, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like. In the present embodiment, the additive is dispersed in the binder 7, but an embodiment in which the additive is not blended is also possible.

In the light diffusion sheet 1, the back surface of the base sheet 3 is smooth, but the back surface may be subjected to, for example, embossing to improve the light diffusion performance and the sticking prevention performance.

Further, in order to improve the slipperiness of the surface of the light diffusion layer 5 and prevent the surface from being damaged, a silicon-based or fluorine-based additive, a polymer wax, or the like may be added to the binder 7. . Further, in order to apply a hard coat to the surface of the light diffusion layer 5, an acrylic paint modified with silicon may be applied to the surface of the light diffusion layer 5.

FIG. 2 is a schematic diagram for explaining the structure of the backlight unit 13 incorporating the light diffusion sheet 1 shown in FIG. This backlight unit 13
Is a lamp 15 as a light source, and this lamp 15
And a light guide plate 17 for guiding light emitted from the lamp 15 to the front side and a light diffusion sheet 1 stacked on the front side of the light guide plate 17. In FIG. 2, the light guide plate 17 and the light diffusion sheet 1 are shown separated for convenience of description, but the front side surface of the light guide plate 17 and the back side surface of the light diffusion sheet 1 are actually in contact.

In this backlight unit 13,
The light beam 19 is first emitted from the lamp 15 and guided into the light guide plate 17. Next, the light beam 19 is reflected by a reflection dot or a reflection sheet (not shown) on the back side of the light guide plate 17 and guided to the light diffusion sheet 1 above. And ray 1
Numerals 9 are uniformly diffused when passing through the light diffusion sheet 1, and are further sent to an upper deflection film (not shown).

In this backlight unit 13,
The lamp 15 generates heat simultaneously with light emission. Therefore, the temperature around the lamp 15 is, for example, about 80 ° C. to 90 ° C.
Therefore, the vicinity of the lamp 15 of the light diffusion sheet 1 (that is, the vicinity of the left end in FIG. 2) is exposed to a high temperature. However, since the light diffusing sheet 1 contains the light diffusing layer 5 and the polyhedral minute inorganic filler 11, it is unlikely to be bent by heat. Therefore, it is possible to suppress luminance unevenness on the screen of the liquid crystal display device.

FIG. 3 is a schematic sectional view showing a light diffusion sheet 21 according to another embodiment of the present invention. The light diffusion sheet 21 includes the base sheet 3, the light diffusion layer 5 provided on the front side of the base sheet 3, and the anti-sticking layer 23 provided on the back surface of the base sheet 3. . The configurations of the base sheet 3 and the light diffusion layer 5 are the same as those of the embodiment shown in FIG.

The anti-sticking layer 23 comprises a binder 25, resin beads 27 dispersed in the binder 25, and a polyhedral fine inorganic filler 29. The materials of the binder 25, the resin beads 27, and the polyhedral shaped inorganic filler 29 are the same as those used for the light diffusion layer 5. Although not shown in FIG. 3, the anti-sticking layer 23 contains an additive dispersed in the binder 25. This additive is the same as that used in the light diffusion layer 5.

The thickness of the anti-sticking layer 23 (the thickness of the binder 25 excluding the resin beads 27; represented by T ₂ in FIG. 3) is not particularly limited, but is, for example, about 1 μm or more and 10 μm or less. It has been.

By dispersing the polyhedral fine inorganic filler 29 in the anti-sticking layer 23 as described above, the apparent crystallinity and glass transition temperature of the light diffusion sheet 21 can be increased. Thereby, the heat resistance of the light diffusion sheet 21 can be enhanced, and the bending of the light diffusion sheet 21 can be suppressed.

In this case, similarly to the case of the polyhedral fine inorganic filler 11 of the light diffusion sheet 1 in FIG. 1, the polyhedral fine inorganic filler 29 has a polyhedral shape.
The effect of hindering the thermal movement of the molecular side chains of the polymer used for the binder 25 can be further improved, and the apparent crystallinity and glass transition temperature of the light diffusion sheet 21 can be further increased. . Therefore, in the polyhedral-shaped fine inorganic filler 29, it is possible to realize a sufficient effect of suppressing the deflection of the light diffusion sheet 21 with a small amount of addition. In such a light diffusion sheet 21 to which the addition amount of the polyhedral-shaped fine inorganic filler 29 is small, it is possible to easily apply the resin composition for forming the anti-sticking layer 23.

Since the compounding amount of the resin beads 27 is relatively small, the resin beads 27 are dispersed in the binder 25 apart from each other. Most of the resin beads 27 have lower ends protruding from the binder 25. When the light diffusion sheet 21 is stacked on the light guide plate 17 (see FIG. 2), the lower end of the protruding resin beads 27 comes into contact with the surface of the light guide plate 17. Therefore, the entire back surface of the light diffusion sheet 21 does not contact the light guide plate 17. Thereby, sticking between the light diffusion sheet 21 and the light guide plate 17 is prevented, and luminance unevenness on the screen of the liquid crystal display device can be suppressed.

In this light diffusion sheet 21, the polyhedral fine inorganic fillers 11 and 29 are dispersed in both the light diffusion layer 5 and the anti-sticking layer 23. However, only the light diffusion layer 5 has the polyhedral fine inorganic filler. The agent 11 may be dispersed, or the polyhedral fine inorganic filler 29 may be dispersed only in the sticking prevention layer 23. The light diffusion layer 5 is not formed by dispersing the resin beads 9 but is formed by, for example, embossing or the like.
The polyhedral-shaped fine inorganic filler 29 may be dispersed only in 3. Of course, the light diffusion layer 5 and the anti-sticking layer 2
It is preferable to disperse the polyhedral-shaped fine inorganic fillers 11 and 29 in both of them, since the deflection of the light diffusion sheet 21 can be suppressed more reliably.

[0062]

As described above, according to the present invention,
It is possible to obtain a light diffusion sheet that is unlikely to be bent even by the heat generated by the lamp, and a backlight unit using the same.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a light diffusion sheet according to one embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a configuration of a backlight unit in which the light diffusion sheet shown in FIG. 1 is incorporated.

FIG. 3 is a schematic cross-sectional view showing a light diffusion sheet according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1,21 Light diffusion sheet 3 Base sheet 5 Light diffusion layer 7,25 Binder 9,27 Resin beads 11,29 Fine inorganic filler having polyhedral shape 13 Backlight unit 15 Lamp 17 Light guide plate 19 Light beam 23 Sticking prevention layer

Claims (18)

[Claims] 1. A light diffusion sheet comprising: a transparent base sheet; and a light diffusion layer provided on a front side of the base sheet, wherein the light diffusion layer has beads and a polyhedral shape in a binder. A light diffusing sheet characterized by being dispersed with a fine inorganic filler. 2. A light diffusion sheet comprising: a transparent base sheet; a light diffusion layer provided on a front side of the base sheet; and a sticking prevention layer provided on a back side of the base sheet. The light diffusion sheet, wherein the anti-sticking layer is formed by dispersing beads and a fine inorganic filler having a polyhedral shape in a binder. 3. The light diffusing sheet according to claim 1, wherein the polyhedral fine inorganic filler is a fine inorganic material having a tetrahedral shape. 4. The fine inorganic substance having a tetrahedral shape,
The light diffusion sheet according to claim 3, wherein the light diffusion sheet is zinc oxide. 5. The fine inorganic substance having a tetrahedral shape,
The light diffusion sheet according to claim 3, wherein the light diffusion sheet is a cadmium compound. 6. The light diffusion sheet according to claim 5, wherein the cadmium compound is cadmium sulfide, cadmium selenide, or cadmium telluride. 7. The light diffusion sheet according to claim 1, wherein the polyhedral minute inorganic filler is a hexahedral minute inorganic substance. 8. The fine inorganic substance having a hexahedral shape,
The light diffusion sheet according to claim 7, wherein the light diffusion sheet is tungsten oxide. 9. The fine inorganic substance having a hexahedral shape,
The light diffusion sheet according to claim 7, wherein the light diffusion sheet is tin oxide. 10. The fine inorganic substance having a hexahedral shape,
The light diffusion sheet according to claim 7, wherein the light diffusion sheet is an indium compound. 11. The light diffusion sheet according to claim 10, wherein said indium compound is indium oxide or indium sulfide. 12. The light diffusing sheet according to claim 1, wherein the inorganic filler having a polyhedral shape is a fine inorganic material having an octahedral shape. 13. The fine inorganic substance having an octahedral shape,
The light diffusion sheet according to claim 12, wherein the light diffusion sheet is tungsten oxide. 14. The light diffusing sheet according to claim 1, wherein the fine inorganic filler having a polyhedral shape is a fine inorganic material having a coherent cubic shape. 15. The light diffusion sheet according to claim 14, wherein the fine inorganic substance having the aggregated cubic shape is silicon nitride. 16. An average particle diameter of the beads is 0.1 μm or more and 50 μm or less, and an average particle diameter of the fine inorganic filler having a polyhedral shape is 5 nm or more and less than 1 μm. The light diffusion sheet according to any one of claims 1 to 15, wherein: 17. The amount of the fine inorganic filler having a polyhedral shape is 0.1 to 200 parts by weight based on 100 parts by weight of the polymer in the binder. 17. The light diffusion sheet according to any one of 1 to 16. 18. A light source, a light guide plate disposed on a side of the light source for guiding light emitted from the light source in a front direction, and disposed on a front side of the light guide plate. A backlight unit for a liquid crystal display device, comprising: a light diffusion sheet.