JP2002258018A - Light diffusion sheet and backlight unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion sheet being in no danger of secondary contamination due to bleeding of additives and having uniform sliding property on the surface and a backlight unit using the same. SOLUTION: The light diffusion sheet is provided with a transparent substrate layer 3 and a light diffusion layer 5 comprising beads 9 dispersed in a binder 7 and is characterized by using an acrylic resin having at least a part of its side chains substituted by a fluorine compound as the binder 7 of the light diffusion layer 5.

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 incorporated in a backlight unit of a liquid crystal display 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 has become widespread, and a backlight unit is provided on the lower surface side of the liquid crystal layer. Generally, as shown in FIG. 3A, the backlight unit 50 includes a rod-shaped lamp 51 as a light source and a rectangular plate-shaped light guide plate 52 arranged such that an end thereof is along the lamp 51. And a plurality of optical sheets 53 stacked on the front surface side of the light guide plate 52. This optical sheet 5
Reference numerals 3 denote specific optical properties such as refraction and diffusion, and more specifically, a light diffusion sheet 54 disposed on the surface side of the light guide plate 52 and a light diffusion sheet 54 disposed on the surface side of the light diffusion sheet 54. The prism sheet 55 to be provided corresponds to this.

The function of the backlight unit 50 will be described. First, a light beam incident on the light guide plate 52 from the lamp 51 is reflected by a reflection dot or a reflection sheet (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. Light 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. Thereafter, the light beam emitted from the light diffusion sheet 54 enters the prism sheet 55 and is emitted by the prism portion 55a formed on the surface of the prism sheet 55 as a light beam having a distribution having a peak substantially right above. Thus, the light beam emitted from the lamp 51 is
The light is diffused by the light diffusion sheet 54, is refracted by the prism sheet 55 so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above.

[0004] Although not shown, there is also a backlight unit in which a light diffusion sheet or a prism sheet is further disposed on the surface side of the prism sheet 55 in consideration of the light-collecting characteristics of the prism sheet 55 described above.

[0005] As the light diffusion sheet 54 of the backlight unit 50 having the above-described structure, a structure in which a base layer 56 and a light diffusion layer 57 as shown in FIG. The light diffusion layer 57 has a structure in which beads 59 made of a synthetic resin, glass, or the like are dispersed in a binder 58 made of a synthetic resin.

The light diffusion layer 5 in the light diffusion sheet 54
As a polymer constituting the binder 58 of No. 7, a thermosetting or two-component curing type acrylic resin, urethane resin, polyester resin, or the like is used, and the slipperiness of the surface of the light diffusion layer 57 is improved. Silicon-based or fluorine-based additives, polymer wax, or the like may be added to the binder 58 for the purpose of preventing damage.

[0007]

In the modification of the surface of the binder 58 with the additive as described above, it is difficult to uniformly disperse the additive in the polymer constituting the binder 58. Unevenness occurs, and as a result, it is difficult to uniformly impart the slipperiness to the surface of the light diffusion layer 57, and there is a possibility that unevenness in brightness due to uneven dispersion of the additive may occur.

Further, the additive may bleed out on the surface of the light diffusion sheet 54 due to environmental changes such as temperature and changes over time, and the additive bleed out to the surface may cause secondary contamination.

The present invention has been made in view of these disadvantages, and there is no fear of secondary contamination due to bleed-out of an additive, and a light diffusion sheet having a uniform sliding property on a surface and a backlight using the same. The purpose is to provide units.

[0010]

Means for Solving the Problems The invention made to solve the above problems is a light diffusion sheet comprising a transparent base material layer and a light diffusion layer in which beads are dispersed in a binder. An acrylic resin in which at least a part of a side chain is substituted with a fluorine compound is used as a binder of the light diffusion layer.

According to the light diffusion sheet, the following effects can be obtained. That is, (1) Since the acrylic resin in which the side chain is substituted with a fluorine compound is used as the material of the binder, the slip property of the light diffusion layer surface can be improved by the fluorine compound substituted with the side chain, As a result, the light diffusion sheet can have improved scratch resistance. Therefore, handling of the light diffusing sheet becomes easy at the time of assembling, storing, and transporting the backlight unit.

(2) Unlike the conventional addition type, the fluorine compound contributing to the slipping property is chemically bonded to the acrylic resin of the matrix, so that the additive does not bleed out and the addition overflowed to the surface. There is no risk of secondary contamination by the agent.

(3) According to the light diffusion sheet, since the fluorine compound contributing to the slip property is substituted on the side chain of the acrylic resin constituting the binder, uniform mixing of the fluorine compound in the binder can be achieved. This makes it possible to impart uniform slipperiness, and does not cause uneven brightness due to uneven dispersion of additives.

(4) In the above-mentioned conventional addition type, the resin composition for forming the light diffusion layer by coating (comprising a binder polymer and beads before curing) reduces the surface tension by the addition of the additive. , Resulting in low viscosity. On the other hand, in the binder of the light diffusion layer of the light diffusion sheet, inorganic particles such as metal oxides are sometimes dispersed and blended in order to enhance heat resistance, antistatic property, etc. Since it is difficult to uniformly disperse inorganic fine particles having a relatively large specific gravity in the composition, it is difficult to uniformly impart heat resistance, antistatic properties, and the like by mixing the inorganic fine particles. On the other hand, according to the light diffusion sheet, since the fluorine compound contributing to the slip property is substituted on the side chain of the acrylic resin as the binder, it is possible to minimize the decrease in the surface tension of the resin composition, As a result, uniform dispersion of the inorganic fine particles in the binder of the light diffusion layer is facilitated,
The disadvantages of the above-mentioned addition types can be reduced.

(5) Since the fluorine compound is not physically separated and dispersed in the acrylic resin of the binder of the light diffusion sheet but is substituted on the side chain of the acrylic resin of the binder, the light diffusion The stability of the resin composition for forming the layer is high, and the workability in the coating step and the like is improved.

(6) By substituting the side chain of the acrylic resin with a fluorine compound, the refractive index of the binder can be made smaller than that of a normal acrylic resin. Therefore, the difference in the refractive index between the binder and the beads to be dispersed can be increased, and the diffusivity can be increased.

Also, in a light diffusion sheet provided with a transparent base material layer, a light diffusion layer, and a sticking prevention layer in which beads are dispersed in a binder, at least one of side chains is added to the binder of the sticking prevention layer. It is preferable to use an acrylic resin whose part is substituted with a fluorine compound. According to such a light diffusion sheet, the above-mentioned effect can be exhibited also in the anti-sticking layer.

The above fluorine compounds include fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, fluorohexyl, fluoroheptyl, fluorooctyl, fluorononyl, fluorodecyl, fluoroundecyl, fluorododecyl, fluoroisopropyl, fluoroisobutyl , Fluoroisopentyl, and fluoroneopentyl may be used. When such a fluorine compound is used, the hydrophobicity of the side chain of the acrylic resin is improved, the hydrophobic group is transferred to the coating film surface as a functional segment, and the slipperiness of the light diffusion layer surface can be improved. Is particularly preferred.

The substitution amount of the fluorine compound is as follows.
It is preferably from 0 × 10 ⁻⁸ mol / g to 1.0 mol / g. By setting the substitution amount of the fluorine compound to the above range,
The slipperiness sufficient to prevent the light diffusing sheet from being damaged and the high diffusivity due to a decrease in the refractive index can be exhibited.

Therefore, (a) a lamp, (b) a substantially rectangular plate-like light guide plate for guiding light rays emitted from the lamp to the surface side, and (c) light diffusion disposed on the surface side of the light guide plate In a backlight unit for a liquid crystal display device equipped with a sheet, when the light diffusion sheet of the present invention is used as the light diffusion sheet, the slipperiness is high, and the workability during assembly is improved. In addition, since the bleed out of the surfactant does not occur as in the conventional light diffusion sheet, it is possible to prevent the light diffusion sheet from being sticky or whitening, and as a result, it is possible to prevent luminance unevenness and a decrease in luminance of the liquid crystal display device. Can be prevented.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIG. 1 is a schematic sectional view showing a light diffusion sheet according to one embodiment of the present invention, and FIG.
FIG. 4 is a schematic cross-sectional view showing a light diffusion sheet according to a mode different from the light diffusion sheet of FIG.

The light diffusing sheet 1 shown in FIG. 1 comprises a base layer 3 and a light diffusing layer 5 provided on the surface of the base layer 3.

The base layer 3 is made of, for example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin,
It is formed from a synthetic resin such as polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. The base material layer 3 is transparent because it needs to transmit light, and is preferably colorless and transparent. The thickness of the base material layer 3 is not particularly limited.
It is not less than 2 μm and not more than 250 μm. When the thickness of the base material layer 3 is less than the above range, curling may be easily caused when the resin composition for forming the light diffusion layer 5 is applied. Conversely, if the thickness of the base layer 3 exceeds the above range, the brightness of the liquid crystal display device may decrease,
Further, the thickness of the backlight unit is increased, which is against the demand for thinning the liquid crystal display device.

The light diffusion layer 5 comprises a binder 7, resin beads 9 dispersed in the binder 7, and an additive 11. By dispersing the resin beads 9 in the light diffusion layer 5, it is possible to uniformly diffuse the light that passes through the light diffusion layer 5 from the back side to the front side. Part of the resin beads 9 has an upper end projecting 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 thickness of the light diffusing layer 5 (thickness of the binder 7 portion excluding the resin beads 9. Represented by T ₁ in FIG. 1.) Is particularly but not limited to, for example, there is a degree more than 30μm or less 1 [mu] m.

The polymer used for the binder 7 includes:
An acrylic resin in which at least a part of a side chain is substituted with a fluorine compound is used. In this way, the fluorine compound substituted on the side chain of the acrylic resin improves the slipperiness of the surface of the light diffusion sheet 1. Even when the light diffusion sheet 1 is overlapped with a prism sheet or the like, the surface of the light diffusion sheet 1 is prevented from being damaged.
In addition, since the fluorine compound for exhibiting such a scratch-preventing effect is substituted on the side chain of the acrylic resin of the matrix and chemically bonded, the additive for preventing scratches such as the conventional addition type is used. No bleed-out and no risk of secondary contamination.

As the fluorine compound, fluoromethyl, fluoroethyl, fluoropropyl,
1 or selected from the group consisting of fluorobutyl, fluoropentyl, fluorohexyl, fluoroheptyl, fluorooctyl, fluorononyl, fluorodecyl, fluoroundecyl, fluorododecyl, fluoroisopropyl, fluoroisobutyl, fluoroisopentyl, fluoroneopentyl Two or more kinds are used, and among them, fluorooctyl is particularly preferred. According to such fluorooctyl, the effect of improving hydrophobicity is remarkably high, and the effect of improving the slip property of the surface of the coating film (light diffusion layer 5) due to the orientation characteristics of the functional segments can be remarkably increased.

The lower limit of the substitution amount of the fluorine compound is preferably 1.0 × 10 ⁻⁸ mol / g.
0 × 10 ⁻⁵ mol / g is particularly preferred. This is because the slipperiness of the surface of the coating film (light diffusion layer 5) is exhibited when the replacement amount is equal to or more than the former, and the slipperiness developed when the replacement amount is equal to or more than the latter is sufficient. Further, the upper limit of the substitution amount of the fluorine compound is preferably 1.0 mol / g, and 1.0 × 10
^-2 mol / g is particularly preferred. This is because if the substitution amount is exceeded, the physical properties of the binder 7, especially water repellency, oil repellency,
This is because the slipperiness and weather resistance are improved, but conversely, the coatability and adhesion to the base material layer are reduced. further,
In order to lower the refractive index of the binder 7 and improve the diffusivity of the light diffusion sheet 1, the substitution amount of the fluorine compound may be set to 1.0 × 10 ⁻⁸ mol / g or more and 1.0 mol / g or less.

Additive 11 adds heat resistance to light diffusion sheet 1,
Antistatic properties, which are added to impart durability and the like, and specific examples include antistatic agents, inorganic fine particles such as metal oxides, plasticizers, stabilizers, deterioration inhibitors, dispersants, and the like. Can be In the case of the light-diffusing sheet 1, the side chain of the acrylic resin is replaced with a fluorine compound instead of dispersing an additive such as wax for the purpose of preventing damage as described above. As described above, it is easy to uniformly disperse the additive 11 in the binder 7 without reducing the viscosity of the resin composition constituting the binder 7.

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 size of the resin beads 9 is 1 μm to 5 μm.
0 μm or less is preferable, and 2 μm or more and 20 μm or less is particularly preferable. If the average particle size is less than the above range, the light diffusion effect may be insufficient. Conversely, if the average particle size exceeds the above range, it may be difficult to apply the resin composition forming the light diffusion layer 5.

The mixing amount of the resin beads 9 in the light diffusion layer 5 is 50 to 100 parts of the polymer in the binder 7.
0 parts or less are preferable, and 10 parts or more and 300 parts or less are especially preferable. 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.

In the light diffusion sheet 1, the back surface of the base material layer 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.

The light diffusion sheet 21 shown in FIG. 2 includes a base layer 3, a light diffusion layer 5 and a base layer 3 provided on the front side of the base layer 3.
Is formed from the anti-sticking layer 23 provided on the back surface. The configurations of the base layer 3 and the light diffusion layer 5 are the same as those of the embodiment shown in FIG.

The anti-sticking layer 23 includes a binder 25 and resin beads 27 dispersed in the binder 25.
And an additive 29. This binder 2
5. The materials of the resin beads and the additive 29 are the same as those used for the light diffusion layer 5. By using an acrylic resin in which at least a part of the side chain is substituted with a fluorine compound for the binder 25 of the sticking prevention layer 23, the effect of preventing scratches on the back side of the light diffusion sheet 21 without bleeding out can be obtained. Can be expressed. The thickness of the anti-sticking layer 23 (the resin beads 27)
The thickness of the binder 25 excluding the thickness. In FIG. 2, T ₂
It is represented by ) Is not particularly limited, for example, 1 μm
It is about 10 μm or less.

Since the 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 laminated on the light guide plate (see FIG. 3), the lower ends of the protruding resin beads 27 come into contact with the surface of the light guide plate. Therefore, the entire back surface of the light diffusion sheet 21 does not contact the light guide plate. Thereby, the light diffusion sheet 21
And the light guide plate are prevented from sticking, and uneven brightness on the screen of the liquid crystal display device is suppressed.

In the light diffusion sheet 21, both the binders 7 and 2 of the light diffusion layer 5 and the sticking prevention layer 23 are used.
Although a fluorine compound substituted acrylic resin is used for 5, a fluorine compound substituted acrylic resin covering only the binder 7 of the light diffusion layer 5 may be used, or only the binder 25 of the sticking prevention layer 23 may be substituted for the fluorine compound. An acrylic resin may be used. Further, instead of dispersing the resin beads 9, the light diffusion layer 5 may be formed by, for example, embossing or the like, and a fluorine compound-substituted acrylic resin may be used only for the binder 25 of the sticking prevention layer 23. Of course, it is preferable to use a fluorine compound-substituted acrylic resin for both the binders 7 and 25 of the light diffusion layer 5 and the anti-sticking layer 23 because the effect of preventing the light diffusion sheet 21 from being damaged is increased.

The light diffusion sheet of the present invention is not limited to the above embodiment.
Alternatively, glass beads capable of exhibiting a light diffusion function, for example, glass beads may be used. Further, the binders 7 and 25 of the light diffusion layer 5 and the anti-sticking layer 23 correspond to the additive 1
Those not blending 1 are also possible. Further, instead of the resin beads 9, one that can exhibit a light diffusion function, for example, glass beads may be used.

[0038]

As described above, according to the light diffusion sheet of the present invention, (a) the surface can exhibit uniform slipperiness,
(B) no unevenness in brightness due to uneven dispersion as in the addition type (b), which has a uniform and high anti-scratch effect;
(C) there is no risk of secondary contamination due to bleed-out of additives and the like; (d) there is no decrease in viscosity, uniform dispersion of the additives is facilitated; and (e) resin for forming the light diffusion layer. Effects such as a high stability of the composition, a reduction in the refractive index of the binder (f) and an increase in the diffusivity can be achieved.

[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 sectional view showing a light diffusion sheet according to a mode different from the light diffusion sheet of FIG.

3A is a schematic perspective view showing a general backlight unit, and FIG. 3B is a schematic cross-sectional view showing a conventional general light diffusion sheet.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light diffusion sheet 3 base material layer 5 light diffusion layer 7 binder 9 resin beads 11 additive 21 light diffusion sheet 23 anti-sticking layer 25 binder 27 resin beads 29 additive

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13357 C08L 101: 00 // C08L 101: 00 F21Y 103: 00 F21Y 103: 00 G02B 1/10 Z F term (reference) 2H042 BA02 BA04 BA12 BA20 2H091 FA23X FA23Z FA32X FA32Z FA41Z FB02 FB12 LA01 LA18 2K009 BB13 BB24 BB28 CC09 CC24 CC26 DD02 EE03 4F006 AA02 AA12 AA15 AA17 AA24 AB09

Claims (5)

[The claims] 1. A light diffusion sheet comprising a transparent base material layer and a light diffusion layer in which beads are dispersed in a binder, wherein at least a part of the side chain is a fluorine compound in the binder of the light diffusion layer. A light diffusion sheet characterized by using an acrylic resin substituted with: 2. A light diffusion sheet comprising a transparent base material layer, a light diffusion layer, and a sticking prevention layer in which beads are dispersed in a binder, wherein the binder of the sticking prevention layer has at least a side chain. A light diffusion sheet characterized by using an acrylic resin partially substituted with a fluorine compound. 3. The above-mentioned fluorine compound includes fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, fluorohexyl, fluoroheptyl, fluorooctyl, fluorononyl, fluorodecyl, fluoroundecyl, fluorododecyl, fluoroisopropyl, The light diffusion sheet according to claim 1 or 2, wherein one or more kinds selected from the group consisting of fluoroisobutyl, fluoroisopentyl, and fluoroneopentyl are used. 4. The amount of substitution of the fluorine compound is 1.0 ×
The light diffusion sheet according to claim 1, wherein the light diffusion sheet has a content of 10 ⁻⁸ mol / g or more and 1.0 mol / g or less. 5. A lamp, a substantially rectangular plate-shaped light guide plate for guiding light emitted from the lamp to the front surface side, and a light guide plate disposed on the front surface side of the light guide plate.
A backlight unit for a liquid crystal display device, comprising the light diffusion sheet according to any one of the above.