JP3430098B2 - Light diffusion sheet and backlight unit using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing sheet used in a backlight unit incorporated in a liquid crystal display device and a backlight unit using this light diffusing 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 which is arranged on the side of the lamp and guides the light emitted from the lamp in the surface direction, and A light diffusing sheet laminated on the surface side of the light guide plate (screen side of the liquid crystal display device) is used.

As the light diffusion sheet, a resin composition in which beads such as acrylic beads and glass beads are dispersed is applied to the surface of a base material sheet made of a synthetic resin such as polyethylene terephthalate to obtain a resin composition. It has been proposed that a light diffusion layer in which beads are dispersed in a binder is formed on the surface of a base material sheet (for example, in Japanese Utility Model Publication No.
73602, etc.). In this light diffusion sheet, the light rays that pass through the light diffusion layer are uniformly diffused by the beads, and the brightness of the screen of the liquid crystal display device is increased.

Further, in order to prevent partial adhesion (sticking) between the back surface of the light diffusion sheet and the surface of the light guide plate to prevent uneven brightness of the screen, a resin composition in which beads such as acrylic beads and glass beads are dispersed. A light diffusion sheet having a sticking prevention layer formed by coating on the back surface of a base material sheet has also been proposed (for example, Japanese Utility Model Publication No. 7-8803).
No.

[0005]

The above conventional light diffusing sheet is generally wound or stacked and provided for storage and transportation. However, acrylic beads, glass beads, etc. used for diffusing light are used. Because the beads are relatively hard, the overlapping light diffusion sheets rub against each other due to vibration during transportation,
They hurt each other. If a backlight unit is constructed using such a light diffusing sheet, the liquid crystal display device will have uneven brightness.

Therefore, it is considered that a hard coat material is used for the resin composition for coating the upper surface or the lower surface of the light diffusing sheet, and the hardness of the binder made of the resin composition is increased to reduce scratches. Conversely, the higher the hardness of the binder, the more brittle it becomes.

The present invention has been made in view of these inconveniences, and an object thereof is to provide a light diffusion sheet that does not damage each other even when they are stacked, and a backlight unit using the same.

[0008]

The invention made to solve the above-mentioned problems is to provide a light diffusion layer in which beads are dispersed in a binder, a transparent substrate layer, and an anti-sticking layer in which beads are dispersed in a binder. And a glass transition temperature of −60 ° C. or higher as a material for the light diffusion layer and the sticking prevention layer.
A soft elastomer material having a temperature of 5 ° C. or less is used ,
As a material, the thickness is 50 micrometers or more and 250
It is characterized in that a synthetic resin below a chromometer is used.

According to this means, since the soft elastomer material having a low glass transition temperature is used as the material of the light diffusing layer, even if the light diffusing sheets are rubbed with each other by rolling or stacking as described above. , Can prevent from damaging each other.

[0010]

In the case of the light diffusion sheet having the sticking prevention layer on the back surface, the beads used for the sticking prevention layer may damage each other, but according to this means, the sticking prevention layer is soft and has a low glass transition temperature. Since the elastomer material is used, it is possible to prevent the sticking prevention layer from damaging each other.

[0012]

According to this means, since the soft elastomer material is used for both the light diffusion layer on the front surface side and the sticking prevention layer on the back surface side of the light diffusion sheet, the light diffusion layer and the sticking prevention are prevented from being damaged by the beads. Layers can be achieved together.

The soft elastomer material may be used in the beads of the light diffusion layer and / or the sticking prevention layer. Since the light diffusion sheet has a problem of preventing scratches due to beads at the time of stacking as described above, by forming the beads that cause scratches from a soft material, the scratches can be directly and effectively prevented. Can be prevented.

The soft elastomer material may be used as a binder for the light diffusion layer and / or the sticking prevention layer. By using a soft material for the binder in this way, cushioning properties are imparted to the support of the beads, and scratches due to the beads during stacking can be reduced.

Polyurethane is preferable as the soft elastomer material. Polyurethane has high elasticity and has a great effect of preventing scratches. Polyurethane has high solvent resistance (particularly alcohol resistance) and high heat resistance, and is suitable for a light diffusion sheet.

Therefore, a liquid crystal display provided with a lamp, a light guide plate which is arranged on the side of the lamp and guides a light beam emitted from the lamp to the surface direction, and a light diffusion sheet which is arranged on the surface side of the light guide plate. In the backlight unit for the device, when the light diffusing sheet of the above-mentioned means is used, it is possible to suppress the uneven brightness of the liquid crystal display device.

The "glass transition temperature" described in the present specification refers to an inspection scanning calorimetric analysis (D
The value measured by SC) is adopted.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a partial cross-sectional view showing a light diffusing sheet according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view illustrating a configuration of a backlight unit using the light diffusing sheet of FIG. 1, and FIG. FIG. 3 is a partial cross-sectional view showing a light diffusing sheet according to a different form from the light diffusing sheet of FIG. 1.

The light diffusion sheet 1 shown in FIG.
And a light diffusion layer 3 laminated on the surface of the base sheet 2. The base sheet 2 is made of synthetic resin such as polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. The base sheet 2 is transparent because it needs to transmit light rays, and colorless and transparent is particularly preferable. Further, the thickness of the base material sheet 2 is not particularly limited, but for example, 50 micrometers or more and 25
It is less than 0 micrometer. This is because when the thickness of the base material sheet 2 is less than the above range, curling may easily occur when the resin composition forming the light diffusion layer 3 is applied, and conversely, the base material. This is because if the thickness of the sheet 2 exceeds the above range, the brightness of the liquid crystal display device decreases, and the thickness of the backlight unit 6 increases, which violates the demand for thinning of the liquid crystal display device.

The light diffusion layer 3 comprises a binder 4 and beads 5 dispersed in the binder 4.
By the beads 5 thus dispersed in the light diffusion layer 3,
Light rays that pass through the light diffusion layer 3 from the back side to the front side can be uniformly diffused. Thickness of light diffusion layer 3 (beads 5
The thickness of the binder 4 portion excluding) is not particularly limited, but is, for example, about 10 micrometers or more and 30 micrometers or less.

The material of the beads 5 is a soft material having a low glass transition temperature, specifically, a glass transition temperature of -10.
A soft elastomer material having a temperature of 0 ° C. or higher and 30 ° C. or lower, preferably −60 ° C. or higher and 25 ° C. or lower is used. Examples of materials that can be used for the beads 5 include polyurethane, silicone rubber, polystyrene, and thermoplastic polyester. Among them, polyurethane is preferable from the viewpoint of solvent resistance and heat resistance. The beads 5 are transparent because they need to transmit light rays, and colorless and transparent are particularly preferable.

Similarly, a binder 4 having a low glass transition temperature and being soft is used. Specifically, the glass transition temperature is −100 ° C. or higher and 30 ° C. or lower, preferably −60 ° C. or higher 2
A soft elastomer material having a temperature of 5 ° C. or lower is used. Examples of the polymer usable for the binder 4 include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, 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, an antistatic agent, or the like. The binder 4 is transparent because it needs to transmit light rays, and is preferably colorless and transparent.

The beads 5 are substantially spherical and are preferably transparent in order to increase the amount of light rays that pass through the light diffusing sheet 1, and more preferably colorless and transparent. This bead 5
The average particle diameter of is preferably 1 micrometer or more and 50 micrometer or less, and 2 micrometer or more 2
Particularly preferred is 0 micrometer or less. If the average particle diameter is less than the above range, the light diffusion effect may be insufficient. On the other hand, when the average particle diameter exceeds the above range, it may be difficult to apply the resin composition forming the light diffusion layer 3. The average particle diameter of the beads 5 is derived by enlarging 100 arbitrarily extracted particles with a microscope, measuring the particle diameters, and simply averaging them. Further, when the beads 5 are not spherical, the average value of the dimension based on an arbitrary one direction and the dimension based on the direction orthogonal to the arbitrary direction is used.

As described above, since the beads 5 and the binder 4 constituting the light diffusing layer 3 are soft, the light diffusing sheets 1 do not damage each other even if they are stacked.

The compounding amount of the beads 5 in the light diffusion layer 3 is
The polymer content in the binder 4 is 0.
The amount is preferably 1 part by weight or more and 500 parts by weight or less, particularly preferably 0.5 parts by weight or more and 300 parts by weight or less. If the blending amount of the beads 5 is less than the above range, the light diffusion effect may be insufficient. On the contrary, if the blending amount exceeds the above range, it may be difficult to apply the resin composition for forming the light diffusion layer 5.

In this light diffusion sheet 1, the back surface of the base material sheet 2 is a smooth surface, but the back surface may be subjected to, for example, embossing to improve the light diffusion performance and the sticking prevention performance.

The backlight unit 6 in which the light diffusion sheet 1 of FIG. 1 is incorporated is, as shown in FIG. 2, a lamp 7 serving as a light source and a lamp 7 arranged laterally of the lamp 7 to emit light. Light guide plate 8 that guides the reflected light in the front side direction
And the light diffusion sheet 1 laminated on the front side of the light guide plate 8. Although the light guide plate 8 and the light diffusion sheet 1 are shown separated from each other in FIG. 2 for convenience of description, the front side surface of the light guide plate 8 and the back side surface of the light diffusion sheet 1 are actually in contact with each other.

The trajectory of the light beam 9 in the backlight unit 6 will be described. First, the light beam 9 is emitted from the lamp 7 and guided into the light guide plate 8. Next, the light beam 9 in the light guide plate 8 is reflected by the reflection dots or the reflection sheet (not shown) on the back side of the light guide plate 8 and is emitted to the upper light diffusion sheet 1. The light rays 9 emitted upward are uniformly diffused when passing through the light diffusion sheet 1, and are further sent to a deflection film (not shown) or the like above.

In the backlight unit 6, if the light diffusing sheet 1 is scratched, the light rays 9 do not diffuse uniformly,
The light is polarized in one direction, and uneven brightness occurs on the screen of the liquid crystal display device. Therefore, by using the light diffusing sheet 1 that is not easily scratched, the uneven brightness of the screen of the liquid crystal display device can be suppressed.

The light diffusion sheet 10 of FIG. 3 has a base sheet 2 and a light diffusion layer 3 provided on the front side of the base sheet 2 as in the case of the light diffusion sheet 1 of FIG. Sheet 2
The sticking prevention layer 11 is provided on the back surface of the above. Also in the light diffusion sheet 10, the base sheet 2 and the light diffusion layer 3 are the same as those of the embodiment shown in FIG.

The sticking prevention layer 11 is composed of a binder 12 and small-diameter beads 13 dispersed in the binder 12. The materials of the binder 12 and the beads 13 are the same as those used in the light diffusion layer 3. As described above, since the sticking prevention layer 11 on the back surface side of the light diffusion sheet 10 is also made of the soft elastomer material, it is possible to further prevent the scratches generated when the layers are stacked. The beads 13 are also substantially spherical and are preferably transparent in order to increase the amount of light rays passing through the light diffusion sheet 10, and particularly preferably colorless and transparent. The average particle diameter of the beads 5 is preferably 1 micrometer or more and 15 micrometers or less from the viewpoint of preventing sticking as described above.
A micrometer or more and 5 micrometers or less are particularly preferable. Thickness of the sticking prevention layer 11 (beads 13
The thickness of the portion of the binder 12 except the above is not particularly limited, but is, for example, about 1 micrometer or more and 10 micrometers or less.

The beads 13 are mixed in a relatively small amount, and the beads 13 are separated from each other and dispersed in the binder 12,
The lower end of most of the beads 13 is projected from the binder 12. When this light diffusing sheet 10 is laminated on the light guide plate 8 similarly to the light diffusing sheet 1 of the backlight unit 6 in FIG. The entire back surface does not come into contact with the light guide plate 8. As a result, sticking between the light diffusion sheet 10 and the light guide plate 8 is prevented, and uneven brightness on the screen of the liquid crystal display device is suppressed.

The light-diffusing sheet of the present invention is not limited to the above embodiment, and for example, one of the beads or the binder in the light-diffusing layer or the sticking prevention layer may be formed of a soft elastomer material so as to be overlapped with the beads. The effect of preventing scratches at the time of alignment can be achieved.

[0035]

As described above, according to the light diffusing sheet of the present invention, it is possible to prevent the overlapping light diffusing sheets from being damaged by each other even when they are stacked or wound up during storage or transportation. Therefore, the performance and economy of the backlight unit using such a light diffusion sheet can be improved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention.

2 is a schematic cross-sectional view illustrating the configuration of a backlight unit using the light diffusion sheet of FIG.

FIG. 3 is a partial cross-sectional view showing a light diffusion sheet according to a different form from the light diffusion sheet of FIG.

[Explanation of symbols]

1 Light diffusion sheet 2 Base sheet 3 Light diffusion layer 4 binders 5 beads 6 backlight unit 7 lamps 8 Light guide plate 9 rays 10 Light diffusion sheet 11 Anti-sticking layer 12 binders 13 beads

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-178911 (JP, A) JP-A-10-158492 (JP, A) JP-A-10-319243 (JP, A) JP-A-7- 218705 (JP, A) JP-A-6-59105 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (5)

(57) [Claims] 1. A light diffusion sheet comprising a light diffusion layer in which beads are dispersed in a binder, a transparent substrate layer, and a sticking prevention layer in which beads are dispersed in a binder, in this order. A soft elastomer material having a glass transition temperature of −60 ° C. or higher and 25 ° C. or lower is used as the material of the layer and the sticking prevention layer, and the thickness thereof is used as the material of the base material layer.
50 micrometers or more and 250 micrometers or less
A light diffusing sheet, characterized in that the above synthetic resin is used. 2. The light diffusion sheet according to claim 1, wherein the soft elastomer material is used in a binder of the light diffusion layer and the sticking prevention layer. 3. The light diffusing sheet according to claim 1, wherein the soft elastomer material is used in beads of the light diffusing layer and the sticking prevention layer. 4. The light diffusion sheet according to claim 1, wherein the soft elastomer material is polyurethane. 5. A lamp, a light guide plate arranged laterally of the lamp for guiding a light beam emitted from the lamp in a surface direction, and a light guide plate arranged on the surface side of the light guide plate. A backlight unit for a liquid crystal display device, comprising: