JP2003100127A - Reflecting sheet and back light unit using the sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflecting sheet capable of preventing secular deterioration such as yellowing and a back light unit capable of increasing a brightness by using the reflecting sheet and capable of preventing the secular deterioration of quality. SOLUTION: This reflecting sheet for back light unit capable of reducing the diffusion of light beam comprises a white synthetic resin base material sheet layer 2 and an ultraviolet absorbing layer 3 stacked on the front surface of the base material sheet layer 2. The ultraviolet absorbing layer 3 comprises a base material polymer 4 containing ultraviolet absorbing agent or a base material polymer 4 having ultraviolet absorbing groups connected to molecular chains. The ultraviolet absorbing layer 3 may be formed of a base material polymer 4 containing ultraviolet stabilizing agent or a base material polymer 4 having ultraviolet stabilizing groups in the molecular chains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection sheet for a backlight unit that reduces light emission, and a backlight unit using this reflection sheet.

[0002]

2. Description of the Related Art As a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side to emit light is widely used, and an edge light type or a direct type backlight unit is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 5, the edge light type backlight unit 40 generally includes a rod-shaped lamp 41 as a light source, and a rectangular plate-shaped light guide plate arranged so that an end portion is along the lamp 41. 43 and a plurality of optical sheets 4 laminated on the front surface side of the light guide plate 43.
2 and a reflection sheet 46 laminated on the back side of the light guide plate 43.
Equipped with. This optical sheet 42,
It has specific optical properties such as refraction and diffusion,
Specifically, the light diffusion sheet 44 arranged on the front surface side of the light guide plate 43, the prism sheet 45 arranged on the front surface side of the light diffusion sheet 44, and the like are applicable.

The function of the backlight unit 40 will be described. First, a light beam incident on the light guide plate 43 from the lamp 41 is reflected by reflection dots (not shown) and each side surface on the back surface of the light guide plate 43, and the light guide plate 43 is reflected. 43 is emitted from the surface. The light beam emitted from the light guide plate 43 is a light diffusion sheet 44.
Is incident on, diffused and emitted from the surface of the light diffusion sheet 44. Thereafter, the light beam emitted from the light diffusion sheet 44 enters the prism sheet 45, and the prism sheet 45
By the prism portion 45a formed on the surface of, the light is emitted as a light beam having a distribution showing a peak in the substantially normal direction. Thus, the light beam emitted from the lamp 41 is diffused by the light diffusing sheet 44 and refracted by the prism sheet 45 so as to show a peak in the substantially normal direction. It is to illuminate.

On the other hand, the light emitted from the back surface of the light guide plate 43 is reflected to the front surface side to the extent that the liquid crystal screen does not flicker to improve the brightness (reflectivity), and it is arranged on the back surface side of the backlight unit 40. A reflective sheet 46 is provided on the back surface side of the light guide plate 43 for the purpose of preventing the device, the frame, and the like from being visually recognized (concealment).

As the reflection sheet 46, conventionally,
(A) A synthetic resin sheet in which a white pigment such as titanium oxide is dispersed, (b) A synthetic resin sheet in which voids (air bubbles) for scattering light are dispersed,
(C) A sheet having a matte surface is used.

[0006]

When the backlight unit 40 using the conventional reflection sheet 46 is used,
Yellowing or the like of the reflective sheet 46 occurs over time, which causes deterioration in quality such as a backlit screen having a yellowish tint and reduced brightness.

The present invention has been made in view of these inconveniences, and a reflection sheet which does not deteriorate with time such as yellowing, and the use of such a reflection sheet improves brightness and temporally deteriorates quality. It is an object of the present invention to provide a backlight unit capable of preventing the above.

[0008]

As a result of intensive studies to solve the above problems, the present inventor has found that the above-mentioned deterioration of the reflecting sheet with time, such as yellowing, is included in the light rays emitted from the lamp. We found that a small amount of ultraviolet rays was the main factor.

As a result, the invention made to solve the above-mentioned problems is a reflection sheet for a backlight unit, which is provided with a base material sheet layer made of white synthetic resin and which reduces the emission of light rays. It is characterized in that an ultraviolet absorbing layer is provided on the surface side of the sheet layer.

According to the reflecting sheet, the ultraviolet absorbing layer laminated on the front surface side of the base sheet layer absorbs a small amount of ultraviolet rays emitted from the lamp and can prevent deterioration with time such as yellowing. it can.

The ultraviolet absorbing layer preferably has a base polymer and an ultraviolet absorber contained in the base polymer. According to this means, the ultraviolet absorbing function can be effectively exhibited by the ultraviolet absorbent contained in the ultraviolet absorbing layer. Further, since the ultraviolet absorbent is contained in the base polymer and protected, it is possible to prevent the ultraviolet absorbent from being lost during storage and transportation of the reflective sheet, assembling work of the backlight unit, or use.

The content of the ultraviolet absorber with respect to the base polymer is preferably 0.1% by mass or more and 10% by mass or less. By blending the ultraviolet absorber to the base polymer that constitutes the ultraviolet absorbing layer to this extent, the yellowing preventing effect of the reflection sheet can be effectively exhibited.

The above-mentioned ultraviolet absorber is one or more selected from the group consisting of salicylic acid-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers and cyanoacrylate-based ultraviolet absorbers. Should be used. These ultraviolet absorbers have a high ultraviolet absorbing function, good compatibility with polymers, and good thermal stability, and therefore are suitable for preventing photodegradation of the reflective sheet, particularly yellowing.

Further, the ultraviolet absorbing layer preferably has a base polymer having an ultraviolet absorbing group bonded to a molecular chain. According to this means, ultraviolet rays are absorbed by the ultraviolet ray absorbing groups bonded to the molecular chains of the base polymer forming the ultraviolet ray absorbing layer, and it is possible to prevent deterioration with time such as yellowing. Further, since a substance having an ultraviolet absorbing function is incorporated as a functional group into the molecular chain of the base polymer, the durability of the ultraviolet absorbing function is significantly improved.

Further, the ultraviolet absorbing layer may contain an ultraviolet stabilizer or a base polymer having an ultraviolet stabilizing group bonded to its molecular chain. According to this means, radicals generated by ultraviolet rays, active oxygen, etc. are inactivated (decomposed, trapped, etc.) by the ultraviolet stabilizer or the ultraviolet stabilizing group contained in the ultraviolet absorbing layer, and deterioration of the ultraviolet absorbing layer and thus the reflection sheet is prevented. It can be reduced.

As the above-mentioned UV stabilizer or UV-stabilizing group, a hindered amine-based UV stabilizer or a hindered amine-based UV-stabilizing group is preferable. This hindered amine-based UV stabilizer or absorbing group has a high UV-stabilizing function and high durability, so that the durability and weather resistance of the reflective sheet can be significantly improved.

Further, in the reflecting sheet, beads made of a soft elastomer material may be dispersed and contained in the ultraviolet absorbing layer. According to this means, it is possible to form a soft convex portion by beads on the surface of the reflection sheet. Therefore, in the backlight unit, the reflection sheet comes into contact with the back surface of the light guide plate arranged on the front surface side in a scattered manner by the soft convex portions of the beads, and as a result, the back surface of the light guide plate is damaged. Can be prevented.
Further, the light diffusing property can be imparted by the beads dispersedly contained in the ultraviolet absorbing layer, and the light diffusing property of the ultraviolet absorbing layer can promote the reflectivity and hiding property of the reflecting sheet.

The beads are preferably soft urethane beads having a relatively low glass transition temperature and excellent solvent resistance and heat resistance.

On the other hand, in the reflecting sheet, it is preferable that air bubbles are further dispersed and contained in the ultraviolet absorbing layer. According to this means, a fine soft convex portion is formed on the surface by the bubbles dispersed in the ultraviolet absorbing layer, and the scratch resistance to the back surface of the light guide plate is exhibited similarly to the beads contained in dispersion, and, The reflectivity and the hiding property can be promoted.

Further, the reflection sheet may further include a high concealment layer laminated on the back side of the base sheet layer, and the high concealment layer may be formed by applying a coating material containing a white pigment. According to this means, the high concealing layer laminated on the back surface side of the base material sheet layer can remarkably improve the reflectivity and concealing property of the reflective sheet.

Therefore, (a) a linear lamp, (b) a light guide plate which is arranged along the lamp and guides the light beam emitted from the lamp to the front side, and (c) the front side of the light guide plate. And an optical sheet that diffuses the light emitted from the light guide plate substantially uniformly and refracts the light toward the normal direction side,
(D) In the backlight unit for a liquid crystal display device equipped with the reflection sheet of the present invention arranged on the back surface side of the light guide plate, the reflection sheet has a function of preventing yellowing over time as described above. As a result, it is possible to prevent the backlight screen from becoming yellowish over time and to reduce the brightness, and it is possible to improve the quality. Also,
Due to the prevention of scratches on the back surface of the light guide plate caused by the reflection sheet, it is possible to prevent a decrease in brightness and uneven brightness due to scratches on the back surface of the light guide plate, and to improve workability such as assembly. You can

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a reflection sheet according to an embodiment of the present invention, and FIGS. 2 to 4 are schematic cross-sectional views showing a reflection sheet having a different form from the reflection sheet of FIG.

The reflection sheet 1 of FIG. 1 has a base sheet layer 2
And an ultraviolet absorbing layer 3 laminated on the surface of the base sheet layer 2.

The base sheet layer 2 is made of white synthetic resin. This white synthetic resin is a synthetic resin containing a white pigment and fine bubbles dispersed therein as described above. The synthetic resin that can be used for the base sheet 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. To be Among them, polyethylene terephthalate, which has excellent heat resistance, is preferable.

The thickness of the base sheet layer 2 is not particularly limited, but is, for example, 50 μm or more and 250 μm or less. When the thickness of the base sheet layer 2 is less than the above range, curling may easily occur when the resin composition forming the ultraviolet absorbing layer 3 is applied. On the contrary, when the thickness of the base material sheet layer 2 exceeds the above range, the brightness of the liquid crystal display device may be lowered, and the thickness of the backlight unit becomes large to meet the demand for thinning of the liquid crystal display device. It will also be contrary.

The white pigment contained is the same as in the conventional reflection sheet, and specifically, titanium oxide (titanium white), zinc oxide (zinc white), lead carbonate (lead white), barium sulfate, carbonic acid. Calcium (chalk) or the like can be used. Of these, titanium oxide is preferable because it has a large effect of improving the hiding property. Also, the bubbles contained in the dispersion are similar to those of the conventional reflection sheet.

The ultraviolet absorbing layer 3 is composed of a base polymer 4 and an ultraviolet absorber contained in the base polymer 4. The thickness of the ultraviolet absorbing layer 3 is not particularly limited, but is, for example, about 3 μm or more and 30 μm or less.

The material used for the base polymer 4 is not particularly limited, and for example, acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamide imide, epoxy resin and the like can be used. . In addition, in the base polymer 4,
In addition to the above polymers, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, an antistatic agent, etc. may be blended. The base polymer 4 is generally transparent, but in order to impart reflectivity and concealability to the base sheet layer 2,
White pigments and bubbles may be dispersed.

The ultraviolet absorber contained in the ultraviolet absorbing layer 3 is not particularly limited as long as it is a compound that absorbs ultraviolet rays and can be efficiently converted into heat energy and is stable to light. Known ones can be used. Among them, a salicylic acid-based UV absorber, a benzophenone-based UV absorber, a benzotriazole-based UV absorber that has a high UV-absorbing function, has good compatibility with the base polymer 4, and is stably present in the base polymer 4. And cyanoacrylate-based UV absorbers are preferred, and one or more selected from these groups may be used.

In the ultraviolet absorbing layer 3, the lower limit of the content of the above ultraviolet absorbent with respect to the base polymer 4 is 0.
1% by mass, particularly 1% by mass, more preferably 3% by mass,
The upper limit of the content of the ultraviolet absorber is 10% by mass,
It is particularly preferably 8% by mass, more preferably 5% by mass. This is because if the blending amount of the ultraviolet absorber with respect to the base polymer 4 constituting the ultraviolet absorbing layer is smaller than the above lower limit, the effect of preventing the yellowing and the like of the reflection sheet 1 cannot be effectively exhibited. On the contrary, when the compounding amount of the ultraviolet absorber exceeds the above upper limit, the base polymer 4 is adversely affected and the strength and durability of the ultraviolet absorbing layer 3 are deteriorated.

As a method of manufacturing the reflection sheet 1,
(A) a step of adjusting the resin composition for the ultraviolet absorbing layer 3 by mixing the base polymer 4 with an ultraviolet absorbent, and laminating this resin composition on the surface of the base sheet layer 2 by a method such as coating. And a manufacturing process including a step of forming the ultraviolet absorbing layer 3,
(B) A step of laminating the resin composition constituting the base polymer 4 on the surface of the base sheet layer 2 by a method such as coating, and impregnating the laminated layer formed in this step with an ultraviolet absorber. A manufacturing method including a step of forming the ultraviolet absorbing layer 3 is possible.

According to the reflective sheet 1, the base sheet layer 2 made of white synthetic resin has the same reflectivity and concealing property as the conventional reflective sheet, and is laminated on the front surface side of the base sheet layer 2. The ultraviolet absorbing layer 3 which absorbs ultraviolet rays emitted from the lamp can prevent temporal deterioration such as yellowing. That is, by using the same base material sheet layer 2 as that of the conventional reflecting sheet and laminating the ultraviolet absorbing layer 3 on the surface thereof, it is possible to easily and reliably prevent the yellowing of the reflecting sheet 1 over time. it can.

The ultraviolet absorbing layer 3 can also be formed from a base polymer having an ultraviolet absorbing group in the molecular chain (for example, "Udable UV" series manufactured by Nippon Shokubai Co., Ltd.). As described above, by using the base polymer having an ultraviolet absorbing group in the molecular chain for the ultraviolet absorbing layer 3, it is possible to prevent deterioration of the ultraviolet absorbing function due to bleed-out of the ultraviolet absorbent. Further, by further containing an ultraviolet absorber in the base polymer having the ultraviolet absorbing group bonded thereto, the ultraviolet absorbing function of the ultraviolet absorbing layer 3 can be further improved.

The reflective sheet 11 shown in FIG. 2 has a base sheet layer 2 and an ultraviolet absorbing layer 12 laminated on the surface of the base sheet layer 2, as in the reflective sheet 1 shown in FIG. . The base sheet layer 2 is the same as the reflection sheet 1 shown in FIG.

The ultraviolet absorbing layer 12 is formed of the base polymer 4 and the ultraviolet absorber contained in the base polymer 4, like the ultraviolet absorbing layer 3 of the reflection sheet 1. The base polymer 4, the ultraviolet absorber, and the compounding amount thereof are the same as those of the reflection sheet 1. The ultraviolet absorbing layer 12 further contains beads 13 made of a soft elastomer material dispersed in the base polymer 4. The upper end of the bead 13 is projected from the outer surface of the base polymer 4, and the like, so that the surface of the reflective sheet 1 has a soft convex portion 14 that is smoothly curved. Therefore, in the backlight unit, the reflection sheet 1 comes into contact with the light guide plate disposed on the front surface side of the reflection sheet 11 at the scattered convex portions 14 in a scattered manner, so that the back surface of the light guide plate is damaged. The sticking is reduced.

Surface roughness (Ra) of this ultraviolet absorbing layer 12
The lower limit of is preferably 5 μm, particularly 7 μm, and more preferably 9 μm. On the other hand, the upper limit of the surface roughness (Ra) is preferably 20 μm, particularly 17 μm, and more preferably 14 μm. This is because if the surface roughness (Ra) of the ultraviolet absorbing layer 12 is smaller than the above lower limit, it becomes difficult to effectively achieve the above-described scratch prevention due to the scattered point contact with the back surface of the light guide plate. On the contrary, if the surface roughness (Ra) exceeds the upper limit, the rough convex portion 14 may adversely damage the back surface of the light guide plate. The above-mentioned "surface roughness (Ra)" has a cutoff value of 8 mm and an evaluation length of 40 mm.
Is the value of.

The beads 13 are made of a soft elastomer material having a low glass transition temperature. Due to the beads 13 made of the soft elastomer material, the hardness of the convex portion 14 formed on the surface of the ultraviolet absorbing layer 12 becomes relatively small, and the scratch resistance of the back surface of the light guide plate is effectively exhibited.

The specific lower limit of the glass transition temperature of this soft elastomer material is -100 ° C, especially -80 ° C.
Further, −60 ° C. is preferable, and the upper limit thereof is 30 ° C.
Particularly, 25 ° C., and further 20 ° C. are preferable. This is because when the glass transition temperature of the soft elastomer material constituting the beads 13 exceeds the upper limit, the hardness of the convex portion 14 on the surface of the reflection sheet 11 becomes large, and the scratch resistance to the back surface of the light guide plate is effectively prevented. When the glass transition temperature of the soft elastomer material is lower than the lower limit, the convex portion 14 on the surface of the reflection sheet 11 is crushed, and the surface of the ultraviolet absorbing layer 12 becomes a light guide plate. This is because it comes into contact with the back surface and it becomes impossible to effectively exhibit the above-mentioned scratch resistance.

Specific examples of the soft elastomer material that can be used for the beads 13 include polyurethane, silicone rubber, polystyrene and thermoplastic polyester. Among them, soft urethane beads are preferable from the viewpoint of solvent resistance and heat resistance.

The lower limit of the average particle size of the beads 13 is
3 μm, particularly 5 μm, more preferably 7 μm, and the upper limit thereof is 40 μm, particularly 30 μm, and further preferably 20 μm. This is because if the average particle diameter of the beads 13 is less than the above lower limit, it becomes difficult to project the beads 13 from the base polymer 4 to form the convex portion 14, and the surface roughness of the ultraviolet absorbing layer 12 becomes small. This is because the surface roughness (Ra) cannot be within the above range, and conversely, when the average particle diameter of the beads 13 exceeds the above upper limit, the surface roughness (Ra) of the ultraviolet absorbing layer 12 exceeds the above range and scratches occur. The anti-sticking property is reduced, and the ultraviolet absorbing layer 12 is formed by coating the resin composition.
Is difficult to form.

The lower limit of the compounding amount of the beads 13 with respect to 100 parts of the polymer content of the base polymer 4 is preferably 0.1 part, particularly 5 parts, and more preferably 10 parts. On the other hand, the upper limit of the blending amount of the beads 13 is 500 parts, particularly 300 parts,
Further, 100 parts is preferable. Here, the numerical value shown by "part" means the ratio based on mass. This is beads 13
This is because the surface roughness (Ra) of the ultraviolet absorbing layer 12 cannot be within the above range when the compounding amount is less than the above lower limit, and conversely, when the above upper limit is exceeded, the coating of the resin composition is performed. This is because it becomes difficult to form the ultraviolet absorbing layer 12 due to the above conditions.

The beads 13 are preferably transparent, especially colorless and transparent. By using the transparent beads 13 as described above, it is possible to impart light diffusing property to the ultraviolet absorbing layer 12, and as a result, the light rays emitted to the surface side due to reflection on the base material sheet layer 2 or the like are diffused and concealed. It can promote sex.

As a method of manufacturing the reflection sheet 11,
Basically, a step of preparing a resin composition for the ultraviolet absorbing layer 12 by mixing the base polymer 4 with an ultraviolet absorber and beads 13 and applying the resin composition to a base sheet layer by a method such as coating. 2 is laminated on the surface and the ultraviolet absorbing layer 12 is formed.

According to the reflection sheet 11, like the reflection sheet 1, the white synthetic resin base material sheet layer 2 has the same reflectivity and concealing property as the conventional reflection sheet.
Ultraviolet absorbing layer 12 laminated on the front surface side of the base sheet layer 2
The ultraviolet light emitted from the lamp can be absorbed by this to prevent temporal deterioration such as yellowing. Further, according to the reflection sheet 11, the soft convex portion 14 on the surface of the ultraviolet absorbing layer 12 can prevent the back surface of the light guide plate disposed on the front surface from being damaged. Furthermore, since the unevenness is formed on the surface of the reflective sheet 11 by the beads 13 of the ultraviolet absorbing layer 12, the reflectivity to the surface side, and thus the concealing property can be enhanced.

The reflection sheet 21 of FIG. 3 is provided with a base sheet layer 2 and an ultraviolet absorbing layer 22 laminated on the surface of the base sheet layer 2 as in the reflection sheet 1 of FIG. . The base sheet layer 2 is the same as the reflection sheet 1.

The ultraviolet absorbing layer 22 is formed of the base polymer 4 and the ultraviolet absorbent contained in the base polymer 4, like the ultraviolet absorbing layer 3 of the reflection sheet 1.
In addition, bubbles 23 are dispersedly contained in the base polymer 4. Due to the dispersion of the bubbles 23, a large number of convex portions 24 are formed substantially uniformly on the surface. In this way, the convex portion 24 on the surface of the reflection sheet 21 is elastic and soft and has a smooth curve because the bubbles 23 are present therein.
Therefore, in the backlight unit, the reflection sheet 21 comes into contact with the light guide plate disposed on the front surface side of the reflection sheet 21 at the soft convex portions 24 in a scattered manner, and the back surface of the light guide plate is not scratched. Will be reduced. The surface roughness (Ra) of the ultraviolet absorbing layer 22 is the same as that of the reflection sheet 11 shown in FIG.
Is the same as.

The bubbles 23 are minute portions containing some gas existing in the base polymer 4, and the shape thereof is not particularly limited, and examples thereof include spherical shape, granular shape, polyhedral shape, spinach sugar shape, random shape, spindle shape and the like. Various shapes are possible.
However, as the shape of the bubbles 23, spherical closed cells are preferable in terms of the ease of forming the soft convex portion 24 and the promotion of the concealing property due to the high light diffusivity. Further, the bubbles 23 are present inside the base polymer 4 in principle, but the base polymer 4
There may be open air bubbles that are open on the surface of, and the open air bubbles promote the formation of the convex portions 24 and the light diffusivity.

The gas contained in the bubbles 23 is determined by the method of forming the bubbles 23 and is not particularly limited.
For example, when a foaming agent is used as described below, air, nitrogen gas, carbon dioxide, ammonia gas, etc. are filled depending on the type of the foaming agent.

The lower limit of the average diameter of the bubbles 23 is 0.5 μ.
m, particularly 1 μm, more preferably 5 μm, and the upper limit of the average diameter is 50 μm, especially 40 μm, and further 30 μm.
m is preferred. This is because if the average diameter of the bubbles 23 is smaller than the above lower limit, it becomes difficult to form the convex portions 24, and the surface roughness (Ra) of the ultraviolet absorbing layer 22 cannot be within the above range. On the contrary, when the average diameter exceeds the above upper limit, the strength of the ultraviolet absorbing layer 22 decreases.

The lower limit of the volume ratio of the bubbles 23 to the base polymer 4 is preferably 1 vol%, particularly 10 vol%, more preferably 20 vol%, and the upper limit of the volume ratio is 8.
0 vol%, particularly 70 vol% and more preferably 60 vol% are preferred. This is because if the volume ratio of the bubbles 23 is smaller than the lower limit, it becomes difficult to set the surface roughness (Ra) of the ultraviolet absorbing layer 22 by the convex portions 24 in the preferable range.
This is also because the effect of promoting the concealing property due to the light diffusing property is reduced, and conversely, when the volume ratio of the bubbles 23 exceeds the above upper limit, the strength and durability of the ultraviolet absorbing layer 22 decrease. .

As a method of manufacturing the reflection sheet 21,
Basically, a resin composition for the ultraviolet absorbing layer 22 is obtained by adding and kneading a foaming agent and an ultraviolet absorbent into a resin composition (mainly a thermosetting resin is a main polymer) constituting the base polymer 4. And a step of coating the surface of the base sheet layer 2 with the resin composition, and the base polymer 4 is thermally cured by heating and the foaming agent is foamed to absorb the ultraviolet rays in which the bubbles 23 are dispersed. Laminating the layer 22.

According to the reflection sheet 21, similar to the reflection sheet 1, the base sheet layer 2 made of white synthetic resin has the same reflectivity and concealing property as the conventional reflection sheet.
Ultraviolet absorbing layer 22 laminated on the front surface side of the base sheet layer 2
The ultraviolet light emitted from the lamp can be absorbed by this to prevent temporal deterioration such as yellowing. Further, like the reflection sheet 11, the reflection sheet 21 can prevent the soft convex portion 14 on the surface of the ultraviolet absorbing layer 22 from scratching the back surface of the light guide plate disposed on the front surface side. Further, the reflection sheet 21 is provided with the ultraviolet absorbing layer 22.
Since the unevenness is formed on the surface by the bubbles 23, it is possible to enhance the reflectivity to the surface side, and thus the hiding property.

The reflection sheet 31 shown in FIG. 4 is the base sheet layer 2
And the ultraviolet absorbing layer 12 laminated on the surface of the base sheet layer 2, the reflection sheet 11 of FIG.
Since it is similar to the above, the same reference numerals are given and the description thereof is omitted.
Further, the reflection sheet 21 includes a high concealment layer 32 laminated on the back surface of the base material sheet layer 2.

The high concealing layer 32 has a concealing property and a reflecting property, and is specifically formed by coating the back surface of the base sheet layer 2 with a coating material 34 containing a white pigment 33. The paint 34 used for the high concealing layer 32 is not particularly limited, and a general paint is used. The white pigment 33 is not particularly limited, and the same white pigment as the white pigment contained in the base sheet layer 2 is used.

The lower limit of the blending amount of the white pigment 33 with respect to the solid content of the paint 34 is preferably 70% by mass, and particularly preferably 80% by mass. On the other hand, the upper limit of the blending amount is preferably 95% by mass, and particularly preferably 90% by mass. This is because when the blending amount of the white pigment 33 is smaller than the lower limit, the effect of improving the reflectance and the hiding property by the high concealing layer 32 becomes small, and conversely, when the blending amount of the white pigment 33 exceeds the upper limit, This is because it becomes difficult to apply the paint 34.

The lower limit of the coating amount (converted to solid content) of the paint 34 and
Then, 1g / m^Two, Especially 5g / m ^Two, 10 g /
m^TwoIs preferred. On the other hand, on the above coating amount (solid content conversion)
The limit is 50 g / m^Two, Especially 45 g / m^Two,further
40 g / m^TwoIs preferred. This is because the coating amount of the paint 34 is
When it is less than the lower limit, the reflectivity of the high concealing layer 32 is high.
Also, the effect of improving the hiding property becomes small, and conversely,
When the coating amount exceeds the above upper limit, the thickness of the high concealing layer 32 increases.
However, it does not meet the demand for thinner backlight units.
And the reduction of the strength of the high concealing layer 32.
It is.

Particle diameter of white pigment 33 (average particle diameter)
Is preferably 100 nm or more and 30 μm or less, and 200 n
Particularly preferred is m or more and 20 μm or less. This is because if the particle size of the white pigment 33 is smaller than the above range, it becomes difficult to effectively exhibit the above-mentioned concealing property. This is because it becomes difficult to disperse the particles uniformly, and the back surface of the reflection sheet 31 becomes rough.

As a method of manufacturing the reflection sheet 31,
Basically, a step of adjusting the resin composition for the ultraviolet absorbing layer 12 by mixing the base polymer 4 with the ultraviolet absorber and the beads 13, and laminating the resin composition on the surface of the base sheet layer 2. By doing so, a step of forming the ultraviolet absorbing layer 12, a step of blending the white pigment 33 into the paint 34, and a step of applying the paint 34 to the back surface of the base sheet layer 2 to stack the high concealment layer 32. Consists of.

According to the reflecting sheet 31, like the reflecting sheet 1, the white synthetic resin base sheet layer 2 has the same reflectivity and concealing property as the conventional reflecting sheet,
Ultraviolet absorbing layer 12 laminated on the front surface side of the base sheet layer 2
As a result, deterioration over time such as yellowing can be prevented. Further, like the reflection sheet 11, the beads 13 of the ultraviolet absorption layer 12 can prevent the back surface of the light guide plate disposed on the front surface from being damaged, and the ultraviolet absorption layer 12 can be prevented.
Due to the unevenness of the surface and the light diffusivity of the beads 13, it is possible to enhance the reflectivity and concealment to the surface side. According to the reflective sheet 31, the high concealing layer 32 on the back surface of the base sheet layer 2 can further significantly improve the reflectivity and the concealability.

Therefore, in the edge light type backlight unit 40 as shown in FIG. 5, the reflection sheet 46 is used.
When the above reflection sheets 1, 11, 21, and 31 are used as the above, since the reflection sheet 1 and the like have the effect of preventing deterioration such as yellowing as described above, the backlight screen becomes yellowish and the brightness decreases. Can be prevented. In particular, when the reflection sheets 11, 21 and 31 having the soft convex portions 14 and 24 on the surface are used, the reflection sheet 11 and the like exhibit the above-mentioned scratch prevention property, and therefore the light guide plate 43.
It is possible to prevent the occurrence of uneven brightness due to scratches on the back surface of the backlight unit 40, and facilitate the work of assembling the backlight unit 40. Further, by using the reflection sheet 31 provided with the high concealment layer 32 on the back surface side, the high concealment property and the reflectivity of the high concealment layer 32 can reduce the loss of light rays radiated from the back surface side and improve the brightness. Further, it is possible to prevent the frame or the like arranged on the back surface side from being visually recognized from the screen, and it is possible to promote the occurrence of uneven brightness.

The reflection sheet of the present invention is not limited to the above embodiment, and for example, the resin forming the base sheet layer 2 does not include the ultraviolet absorbing layers 3, 12, 22 containing the ultraviolet absorber. It is also possible to contain an ultraviolet absorber therein, and similarly, it is possible to exert the effect of preventing deterioration such as yellowing.

The ultraviolet absorbing layer can also be formed from the base polymer 4 containing an ultraviolet stabilizer or the base polymer 4 having an ultraviolet stabilizing group bonded to its molecular chain. This ultraviolet stabilizer or ultraviolet stabilizing group inactivates radicals generated by ultraviolet rays, active oxygen, etc., and can improve the ultraviolet stability, weather resistance, etc. of the ultraviolet absorbing layer and thus the reflecting sheet. As the ultraviolet stabilizer or the ultraviolet stable group, a hindered amine ultraviolet stabilizer or a hindered amine ultraviolet stable group having high stability against ultraviolet rays is preferably used. Incidentally, the ultraviolet absorbing layer may have both the ultraviolet stabilizer or the ultraviolet stabilizing group and the ultraviolet absorbing agent or the ultraviolet stabilizing group, and by the combination thereof, deterioration prevention by ultraviolet rays and weather resistance are markedly improved. .

[0063]

As described above, according to the reflection sheet of the present invention, the effect of preventing deterioration such as yellowing can be achieved. Further, according to the backlight unit using the reflection sheet of the present invention, it is possible to prevent the backlight screen from becoming yellowish and the brightness from decreasing over time.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view showing a reflection sheet having a form different from that of the reflection sheet shown in FIG.

FIG. 3 is a schematic cross-sectional view showing a reflection sheet having a different form from the reflection sheets of FIGS. 1 and 2.

FIG. 4 is a schematic cross-sectional view showing a reflection sheet of a different form from the reflection sheets of FIGS. 1, 2 and 3.

FIG. 5 is a schematic perspective view showing a general edge light type backlight unit.

[Explanation of symbols]

1 ... Reflective sheet 2 ... Base sheet layer 3 ... UV absorbing layer 4 ... Base polymer 11 ... Reflective sheet 12 ... UV absorbing layer 13 ... Beads 14 ... Convex portion 21 ... Reflective sheet 22 ... UV absorbing layer 23 ... bubbles 24 ... Convex portion 31 ... Reflective sheet 32 ... High concealing layer 33: White pigment 34 ... Paint

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 9/00 324 G09F 9/00 324 336 336C 336J 9/35 9/35 // F21Y 103: 00 F21Y 103 : 00 F term (reference) 2H042 BA02 BA03 BA12 BA13 BA14 BA20 2H091 FA01Z FA14Z FA21Z FA23Z FA32Z FA41Z FB02 LA17 LA18 5C094 AA10 BA43 ED13 5G435 AA03 BB12 BB15 EE23 EE27 FF02 FF06 FF08 FF12

Claims (12)

[Claims] 1. A substrate sheet layer made of white synthetic resin,
A reflective sheet for a backlight unit for reducing the emission of light rays, characterized in that an ultraviolet absorbing layer is provided on the front surface side of the base sheet layer. 2. The reflection sheet according to claim 1, wherein the ultraviolet absorbing layer has a base polymer and an ultraviolet absorber contained in the base polymer. 3. The reflection sheet according to claim 2, wherein the content of the ultraviolet absorber with respect to the base polymer is 0.1% by mass or more and 10% by mass or less. 4. The one or more selected from the group consisting of salicylic acid type ultraviolet absorbers, benzophenone type ultraviolet absorbers, benzotriazole type ultraviolet absorbers and cyanoacrylate type ultraviolet absorbers as the ultraviolet absorbers. The reflective sheet according to claim 2 or 3, wherein a reflective sheet is used. 5. The reflection sheet according to claim 1, wherein the ultraviolet absorbing layer has a base polymer having an ultraviolet absorbing group bonded to a molecular chain. 6. The reflection sheet according to claim 1, wherein the ultraviolet absorbing layer has an ultraviolet stabilizer or a base polymer having an ultraviolet stabilizing group bonded to a molecular chain. 7. The reflection sheet according to claim 6, wherein a hindered amine UV stabilizer or a hindered amine UV stabilizer is used as the UV stabilizer or UV stabilizer. 8. The reflection sheet according to claim 1, wherein beads made of a soft elastomer material are dispersedly contained in the ultraviolet absorbing layer. 9. The reflection sheet according to claim 8, wherein the beads are soft urethane beads. 10. The reflection sheet according to claim 1, wherein air bubbles are dispersed and contained in the ultraviolet absorbing layer. 11. The high concealing layer further laminated on the back surface side of the base sheet layer, wherein the high concealing layer is formed by applying a coating material containing a white pigment. The reflection sheet according to any one of claims 1 to 10. 12. A linear lamp, a light guide plate which is arranged along the lamp and guides a light beam emitted from the lamp to a front surface side, and a light guide plate which is arranged on the front surface side of the light guide plate and is arranged from the light guide plate. An optical sheet for diffusing an emitted light beam substantially uniformly and refracting it toward a normal direction side, and the reflection sheet according to any one of claims 1 to 11 arranged on the back surface side of the light guide plate. Backlight unit for the liquid crystal display device to be equipped.