JP4897992B2 - Light diffusion sheet and backlight unit using the same - Google Patents

Description

【００４４】
上記表１に示すように、実施例１〜４の光拡散シートに傷付き防止効果があることが確認され、実施例２〜４の光拡散シートの傷付き防止効果が大きくなっている。一方、比較例の光拡散シートには傷付き防止効果は確認されなかった。
【００４５】
【発明の効果】
以上説明したように、本発明の光拡散シートによれば、製造、運搬、保存等の際に複数枚を重ねた場合でも、裏面の傷付きが防止でき、取扱いが容易である。また、本発明の光拡散シートを用いたバックライトユニットは、傷付き防止性が高いため、組付けが容易である。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係る光拡散シートを示す模式的断面図である。
【図２】（ａ）及び（ｂ）は共に図１の光拡散シートの傷付き防止機構を示す説明図である。
【図３】本発明の第２実施形態に係る光拡散シートを示す模式的断面図である。
【図４】本発明の第３実施形態に係る光拡散シートを示す模式的断面図である。
【図５】（ａ）は一般的なバックライトユニットを示す模式的斜視図で、（ｂ）及び（ｃ）は（ａ）のバックライトユニットとその構成を異にする一般的なバックライトユニットを示す模式的断面図である。
【図６】一般的な光拡散シートを示す模式的断面図である。
【符号の説明】
１ 光拡散シート
２ 基材層
３ａ 光拡散層
３ｂ 光拡散層
３ｃ 光拡散層
４ スティッキング防止層
５ バインダー
６ ワックス
６ａ ワックス
６ｂ ワックス
７ ビーズ
８ バインダー
９ ワックス
１１ 光拡散シート
２１ 光拡散シート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light diffusion sheet incorporated in a backlight unit of a liquid crystal display device and a backlight unit using the same.
[0002]
[Prior art]
In the liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface is widely used, and a backlight unit is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 5A, the backlight unit 50 is generally composed of a rod-shaped lamp 51 as a light source, and a rectangular plate-shaped light guide plate 52 disposed so that the end of the lamp 51 is along the end. The light diffusion sheet 53 disposed on the surface side of the light guide plate 52 and the prism sheet 54 disposed on the surface side of the light diffusion sheet 53 are provided.
[0003]
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. Emitted from the surface. The light beam emitted from the light guide plate 52 enters the light diffusion sheet 53, is diffused, and is emitted from the surface of the light diffusion sheet 53. Thereafter, the light beam emitted from the light diffusion sheet 53 is incident on the prism sheet 54 and is emitted as a light beam having a distribution having a peak in a substantially upward direction by the prism portion 54 a formed on the surface of the prism sheet 54. In this way, the light beam emitted from the lamp 51 is diffused by the light diffusion sheet 53 and refracted by the prism sheet 54 so as to show a peak in a substantially directly upward direction. Illuminate.
[0004]
In consideration of the light condensing characteristics of the prism sheet 54 described above, there is also a backlight unit 70 in which the prism sheet 54 is further disposed on the surface side of the prism sheet 54 (see FIG. 5C). A backlight unit 80 in which a light diffusing sheet 53 is further disposed on the surface side is in widespread use today (see FIGS. 5B and 5C).
[0005]
As the light diffusion sheet 53 of the backlight unit 50 having the above-described structure, a laminate of a base material layer 55 and a light diffusion layer 56 as shown in FIG. 6 is generally used, and sticking is performed on the back surface. Some layers have a prevention layer 59 laminated thereon. This light diffusion layer 56 has a structure in which beads 58 made of synthetic resin, glass, etc. are dispersed in a binder 57 made of synthetic resin, and the sticking prevention layer 59 also has a structure in which beads 61 are dispersed in the same binder 60. have.
[0006]
[Problems to be solved by the invention]
In many cases, a plurality of optical sheets such as the above-described light diffusion sheet 53 are stacked in a process such as manufacture, storage, and conveyance. On the other hand, in the conventional general light diffusion sheet 53, since the beads 58 and 61 protrude on the front and back surfaces (see FIG. 6), when a plurality of sheets are stacked as described above, The contact surfaces are rubbed together, and the protruding beads 58 and 61 may damage the contact surfaces, that is, the front and back surfaces of the light diffusion sheet 53.
[0007]
In particular, in the light diffusion sheet 53 arranged on the surface side of the prism sheet 54 as shown in FIGS. 5B and 5C, the scratches are easily seen, and the inconvenience on the backlight unit is great. .
[0008]
The present invention has been made in view of these disadvantages, and even when used repeatedly during storage, transport, assembly of a backlight unit, etc., a light diffusion sheet that can prevent the occurrence of damage to the front and back surfaces of each other And a backlight unit using the same.
[0009]
[Means for Solving the Problems]
An invention made to solve the above problems is a light diffusing sheet comprising a light diffusing layer and a base material layer, wherein the light diffusing layer is obtained by dispersing wax in a binder. It is. Here, “wax” means an organic substance having a low viscosity alkyl group that is solid or semi-solid at room temperature and dissolves at a specific temperature, and is classified into a natural wax, a synthetic wax, and a compounded wax.
[0010]
According to the light diffusing sheet, the light transmitted through the interface between the binder in the light diffusing layer and the dispersed wax is refracted in various directions, so beads are used as in the conventional light diffusing sheet. Even without it, it can exhibit diffusibility. Thus, since it is not necessary to use a bead in order to obtain a diffusivity, even if it uses it repeatedly, the damage prevention property which can prevent the generation | occurrence | production of the mutual surface and back surface can be exhibited. Further, according to the light diffusion sheet, the wax particles dispersed in the binder are melted by pressure and frictional heat acting on the surface of the light diffusion sheet, and exist in a state like a lubricating oil on the surface of the light diffusion sheet. Since the wax particles grow in various directions according to the force acting on the surface and crystallize in that state, slip properties, blocking resistance, and abrasion resistance are imparted, and the above-mentioned scratch resistance is promoted. Can do.
[0011]
Beads may be further dispersed in the binder of the light diffusion layer. By dispersing the beads in this manner, the same light diffusibility as that of a conventional bead coating type light diffusion sheet can be obtained. In addition, according to this means, irregularities due to beads are formed on the surface in the same manner as in the conventional light diffusion sheet of bead coating type. However, the occurrence of damage can be reduced.
[0012]
Another invention made to solve the above problems is a light diffusion sheet comprising a light diffusion layer, a base material layer, and an anti-sticking layer in this order, wherein the anti-sticking layer has a wax dispersed in the binder. It is characterized by being. According to such means, the above-described scratch resistance can be imparted to the anti-sticking layer on the back surface of the light diffusion sheet by the wax dispersed in the binder of the anti-sticking layer.
[0013]
It is preferable to further disperse beads in the binder of the anti-sticking layer. According to this means, the anti-sticking property can be promoted by the dispersed beads while having the anti-damage property by the wax as described above.
[0014]
The wax dispersed in the light diffusion layer or anti-sticking layer may be projected from the outer surface of the binder. When the wax particles are protruded from the outer surface of the binder in this manner, the wax particles are present on the surface of the light diffusing sheet in the state of lubricating oil by the pressure and frictional heat as described above, or the force that the wax particles act on the surface. Accordingly, it is promoted to extend in various directions, and the scratch resistance of the light diffusion sheet can be further improved.
[0015]
The average particle size of the wax is preferably 1 μm or more and 25 μm or less. This is because if the average particle size of the wax is smaller than the above range, dispersion in the binder becomes difficult. Conversely, if the average particle size exceeds the above range, the light transmittance decreases, and the strength of the light diffusion layer decreases. This is because inconveniences such as these may occur.
[0016]
The blending amount of the wax with respect to the binder is preferably 0.5% by mass or more and 5% by mass or less. This is because if the blending amount of the wax is smaller than the above range, the above-described scratch resistance cannot be sufficiently exhibited, and conversely if it exceeds the above range, the light transmittance may be lowered. Because there is.
[0017]
As the wax, one or more selected from the group consisting of polyethylene wax, polypropylene wax and polytetrafluoroethylene wax may be used. Since these waxes have a melting point of 100 ° C. to 400 ° C., they do not melt when used as a light diffusing sheet in a backlight unit, are stacked, and are melted and deformed and scratched only when some external force acts on the surface. Preventive properties can be exhibited.
[0018]
Accordingly, in a backlight unit for a liquid crystal display device including a lamp, a light guide plate that guides light emitted from the lamp to the front surface side, and a light diffusion sheet disposed on the front surface side of the light guide plate, such light diffusion is performed. When the above-described light diffusion sheet of the present invention is used as the sheet, it is possible to prevent the light diffusion sheet from being scratched on the front surface and the back surface, and the handling during production, transportation, storage and the like becomes easy.
[0019]
In particular, a lamp, a light guide plate that guides light emitted from the lamp to the surface side, a light diffusion sheet disposed on the surface side of the light guide plate, a prism sheet disposed on the surface side of the light diffusion sheet, In a backlight unit for a liquid crystal display device provided with a light diffusing sheet disposed on the surface side of the prism sheet, the above-described light diffusing sheet of the present invention is used as a light diffusing sheet on the surface side where scratches are easily visible. It is very effective.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to the first embodiment of the present invention, FIGS. 2A and 2B are explanatory views showing a scratch preventing mechanism of the light diffusion sheet of FIG. FIG. 4 is a schematic cross-sectional view showing a light diffusion sheet according to a second embodiment of the present invention, and FIG. 4 is a schematic cross-sectional view showing a light diffusion sheet according to the third embodiment of the present invention.
[0021]
The light diffusing sheet in FIG. 1 includes a base material layer 2 and a light diffusing layer 3 a laminated on the front side of the base material layer 2. Since the base material layer 2 is required to transmit light, it is made of a synthetic resin that is transparent, particularly colorless and transparent. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . Although the thickness of the base material layer 2 is not specifically limited, For example, they are 10 micrometers or more and 500 micrometers or less, Preferably they are 75 micrometers or more and 250 micrometers or less. When the thickness of the base material layer 2 is less than the above range, curling may easily occur when the resin composition forming the light diffusion layer 3a is applied. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the luminance of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which is contrary to the demand for thinning of the liquid crystal display device. It will also be a thing.
[0022]
The light diffusion layer 3 a is composed of a binder 5 and a wax 6 dispersed in the binder 5. In this way, the refraction and reflection at the interface of the wax 6 dispersed in the binder 5 can uniformly diffuse the light beam transmitted through the light diffusion layer 3a from the back side to the front side. Moreover, the wax 6 can diffuse light rays better by providing a wax whose upper end protrudes from the binder 5 or is embedded in the binder 5. The thickness of the light diffusion layer 3a (meaning the thickness of the binder 5 portion excluding the wax 6) is not particularly limited, but is, for example, about 1 μm to 30 μm.
[0023]
Moreover, since the wax 6 is an organic substance having a low viscosity alkyl group that is solid or semi-solid at normal temperature and dissolves at a specific temperature as described above, the light diffusion sheet 1 is given scratch resistance. Can do. As a mechanism for preventing damage by the wax 6, as shown in FIG. 2 (a), the wax 6a is melted by the pressure and frictional heat acting on the surface of the light diffusing sheet 1, and becomes a liquid and becomes a light diffusing sheet. This is considered to be due to the presence of lubricating oil on one surface. The liquefied wax 6a is crystallized on the surface of the light diffusion sheet 1 to protect the surface. On the other hand, in the case of the wax 6b having a high melting point, as shown in FIG. 2B, the portion of the wax 6b that protrudes from the surface of the light diffusion sheet extends in the direction of the external force that acts on the surface of the light diffusion sheet and crystallizes. It is believed that there is. Therefore, in order to effectively exhibit the scratch preventing mechanism, the wax 6 may be projected from the outer surface of the binder.
[0024]
The wax 6 is not particularly limited, and natural wax, synthetic wax and compounded wax can be used. These natural waxes include plant systems such as wood wax, animal systems such as beeswax, mineral systems such as montan wax, and petroleum systems such as paraffin wax. Synthetic waxes include synthetic hydrocarbons such as polyethylene waxes, modified waxes such as paraffin wax derivatives, hydrogenated waxes such as hardened castor oil, and fatty acid amides such as stearamide.
[0025]
In particular, polyethylene wax, polypropylene wax, and polytetrafluoroethylene wax are preferable as the wax 6 of the present invention, and one or more selected from these groups may be used as the wax 6. Such polyethylene wax is made of polyethylene having a low molecular weight (molecular weight: 1000 to 10000) and has a relatively high melting point of 100 ° C. to 130 ° C., and therefore can provide excellent scratch resistance. In addition, since polypropylene wax has a higher melting point and is harder than polyethylene wax, it can provide better scratch resistance. Since polytetrafluoroethylene wax has a very high melting point of about 370 ° C., the scratch resistance can be remarkably improved. Note that it is effective to use polyethylene wax or the like that exhibits the scratch prevention mechanism shown in FIG. 2 (a) and polytetrafluoroethylene wax or the like that exhibits the scratch prevention mechanism shown in FIG. 2 (b).
[0026]
The blending amount of the wax 6 in the binder 5 is preferably 0.1% by mass or more and 10% by mass or less, and particularly preferably 0.5% by mass or more and 5% by mass or less. This is because when the blending amount of the wax 6 is smaller than the above range, the above-described scratch resistance cannot be sufficiently exhibited. Conversely, when the blending amount of the wax 6 exceeds the above range, This is because the transmittance may decrease.
[0027]
The wax 6 has an average particle size of 100 nm to 50 μm, and particularly preferably 1 μm to 25 μm. This is because if the average particle size of the wax 6 is smaller than the above range, dispersion in the binder 5 becomes difficult. Conversely, if the average particle size exceeds the above range, the light transmittance is reduced. This is because there is a possibility that inconveniences such as lowering may occur.
[0028]
Examples of the polymer used for the binder 5 include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, and epoxy resin. In addition to the above-mentioned polymer, the binder 5 may contain, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like. Since the binder 5 needs to transmit light, it is transparent, and colorless and transparent is particularly preferable.
[0029]
The light diffusing sheet 11 shown in FIG. 3 includes a base material layer 2 and a light diffusing layer 3b laminated on the surface. The light diffusing layer 3b includes a binder 5 and wax 6 and beads dispersed in the binder 5. 7. The light diffusing sheet 11 can exhibit the same light diffusibility as a conventional bead coating type light diffusing sheet by the beads 7 dispersed in the binder 5. The base material layer 2, the binder 5, and the wax 6 in the light diffusion sheet 11 are the same as those in the light diffusion sheet 1 in FIG.
[0030]
The beads 7 are substantially spherical, and examples of the material thereof include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide. The beads 7 are preferably transparent in order to increase the amount of light transmitted through the light diffusing sheet 11, and particularly preferably colorless and transparent.
[0031]
The particle diameter (average particle diameter) of the beads 7 is preferably 0.1 μm or more and 100 μm or less, and particularly preferably 1 μm or more and 50 μm or less. If the particle size of the beads 7 is less than the above range, the light diffusing effect is insufficient. Conversely, if the particle size exceeds the above range, the resin composition for forming the light diffusing layer 3b is applied. This is because the work becomes difficult.
[0032]
The blending amount of the beads 7 in the light diffusion layer 3b is preferably 0.1 part or more and 500 parts or less, particularly preferably 10 parts or more and 300 parts or less with respect to 100 parts of the polymer content in the binder 5. This is because if the blending amount is less than the above range, the light diffusion effect becomes insufficient. Conversely, if the blending amount exceeds the above range, the application of the resin composition for forming the light diffusion layer 3b. This is because the work becomes difficult. Here, the numerical value indicated by “part” means a ratio based on mass.
[0033]
4 includes a base material layer 2, a light diffusion layer 3c laminated on the front side of the base material layer 2, and an anti-sticking layer 4 laminated on the back surface of the base material layer 2. The light diffusion sheet 21 shown in FIG. Yes. The light diffusion layer 3 c of the light diffusion sheet 21 is the same as a conventional bead coating type light diffusion sheet and has a structure in which beads 7 are dispersed in a binder 5. The binder 5 of the base material layer 2 and the light diffusion layer 3c in the light diffusion sheet 21 is the same as that of the light diffusion sheet 1 of FIG. 1, and the beads 7 of the light diffusion layer 3c are the light diffusion sheet 11 of FIG. It is the same.
[0034]
The anti-sticking layer 4 is composed of a binder 8 and a wax 9 dispersed in the binder 8. (a) The wax 9 prevents sticking with the light guide plate 52 (see FIG. 5A) and scratches. Effects such as promoting adhesion prevention, (b) promoting light diffusibility by refraction and reflection at the interface of the wax 9, and the like can be achieved. The binder 8 and the wax 9 in the anti-sticking layer 4 are the same as the binder 5 and the wax 6 of the light diffusion layer 3a in the light diffusion sheet 1.
[0035]
The light diffusing sheet of the present invention is not limited to the above embodiment. For example, a light diffusing sheet provided with a sticking prevention layer in which wax and beads are dispersed in a binder is also possible. The anti-sticking property can be promoted. In addition, a light diffusion sheet in which wax is dispersed in both the light diffusion layer and the anti-sticking layer is also possible. According to such a light diffusion sheet, the scratch resistance can be further improved.
[0036]
【Example】
EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, of course, this invention should not be interpreted limitedly based on description of this Example.
[0037]
[Example 1]
A coating liquid for a light diffusion layer is produced by adding 20% by mass of acrylic beads and 1% by mass of polyethylene wax to an acrylic binder, and this coating liquid is used as a base material layer made of polyethylene terephthalate. The light diffusion sheet of Example 1 was obtained by coating at a basis weight of 10 g / m ² .
[0038]
[Example 2]
A light diffusion sheet of Example 2 was obtained in the same manner as in Example 1 except that 2% by mass of polyethylene wax was added.
[0039]
[Example 3]
A light diffusion sheet of Example 3 was obtained in the same manner as in Example 1 except that 3% by mass of polyethylene wax was added.
[0040]
[Example 4]
A light diffusion sheet of Example 4 was obtained in the same manner as in Example 1 except that 5% by mass of polyethylene wax was added.
[0041]
[Comparative example]
A comparative light diffusing sheet was obtained in the same manner as in Example 1 except that no polyethylene wax was added.
[0042]
[Evaluation of characteristics]
Using the light diffusing sheets of Examples 1 to 4 and the comparative example, the friction fastness test of JIS-L-0823 was performed to determine the scratch resistance. The results are shown in Table 1 below.
[0043]
[Table 1]

[0044]
As shown in Table 1 above, it was confirmed that the light diffusion sheets of Examples 1 to 4 had an effect of preventing scratches, and the effect of preventing damage of the light diffusion sheets of Examples 2 to 4 was increased. On the other hand, the damage preventing effect was not confirmed in the light diffusion sheet of the comparative example.
[0045]
【Effect of the invention】
As described above, according to the light diffusion sheet of the present invention, even when a plurality of sheets are stacked during manufacture, transportation, storage, etc., scratches on the back surface can be prevented and handling is easy. Moreover, since the backlight unit using the light diffusion sheet of the present invention has high scratch resistance, it is easy to assemble.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a light diffusion sheet according to a first embodiment of the present invention.
FIGS. 2A and 2B are explanatory views showing a scratch preventing mechanism for the light diffusion sheet of FIG.
FIG. 3 is a schematic cross-sectional view showing a light diffusion sheet according to a second embodiment of the present invention.
FIG. 4 is a schematic cross-sectional view showing a light diffusion sheet according to a third embodiment of the present invention.
5A is a schematic perspective view showing a general backlight unit, and FIG. 5B and FIG. 5C are general backlight units having a configuration different from that of the backlight unit of FIG. It is a typical sectional view showing.
FIG. 6 is a schematic cross-sectional view showing a general light diffusion sheet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light diffusion sheet 2 Base material layer 3a Light diffusion layer 3b Light diffusion layer 3c Light diffusion layer 4 Sticking prevention layer 5 Binder 6 Wax 6a Wax 6b Wax 7 Bead 8 Binder 9 Wax 11 Light diffusion sheet 21 Light diffusion sheet

Claims (7)

A light diffusion sheet comprising a light diffusion layer and a base material layer,
The light diffusion layer is a dispersion of wax particles and beads in a binder ,
As the wax particles, polytetrafluoroethylene wax particles are used, or polytetrafluoroethylene wax particles and polyethylene wax particles are used in combination . A light diffusion sheet comprising a light diffusion layer, a base material layer, and an anti-sticking layer in this order,
The anti-sticking layer is a dispersion of wax particles and beads in a binder ,
As the wax particles, polytetrafluoroethylene wax particles are used, or polytetrafluoroethylene wax particles and polyethylene wax particles are used in combination . The light diffusion sheet according to claim 1, wherein the wax particles protrude from an outer surface of the binder. The light diffusion sheet according to any one of claims 1 to 3, wherein an average particle diameter of the wax particles is 1 µm or more and 25 µm or less. The light-diffusion sheet of any one of Claims 1 thru | or 4 whose compounding quantity of the wax particle to the said binder is 0.5 mass% or more and 5 mass% or less. Lamp and a liquid crystal display which includes a light guide plate for guiding the light emitted from the lamp to the surface side, and a light diffusing sheet according to any one of claims 1 to 5 is arranged on the surface side of the light guide plate Backlight unit for equipment. A lamp, a light guide plate for guiding light emitted from the lamp to the surface side, a light diffusion sheet disposed on the surface side of the light guide plate, a prism sheet disposed on the surface side of the light diffusion sheet, and the prism The backlight unit for liquid crystal display devices provided with the light-diffusion sheet of any one of Claims 1 thru | or 5 arrange | positioned at the surface side of a sheet | seat.

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