KR20040014770A - Reflection sheet and backlight unit using the same - Google Patents

Abstract

PURPOSE: A reflecting sheet is provided to have high reflectivity and a high concealing property, and to be applied to a backlight unit, so that the backlight unit can improve brightness by reducing light loss. CONSTITUTION: A material sheet layer(2) is made of a white synthetic resin. The white synthetic resin contains white pigments or minute bubbles. The material sheet layer(2) has a thickness of more than 50 micrometers and less than 250 micrometers. A high concealing layer(3) is formed by applying a paint(5) which contains white pigments(4) on an inner side of the material sheet layer(2). Luminosity of the high concealing layer(3) is more than 95.

Description

Reflective sheet and backlight unit using the same {REFLECTION SHEET AND BACKLIGHT UNIT USING THE SAME}

The present invention relates to a reflective sheet for a backlight unit which reduces light emission and a backlight unit using the reflective sheet.

Background Art [0002] A liquid crystal display device has a back light system that emits light by illuminating the liquid crystal layer from the back side, and a backlight unit such as an edge light type or a direct type is provided on the bottom surface of the liquid crystal layer. Such an edge light type backlight unit 20 generally includes a rod-shaped lamp 21 as a light source and a rectangular plate-shaped light guide plate disposed so as to follow an end portion of the lamp 21 as a light source. 23, a plurality of optical sheets 22 laminated on the front side of the light guide plate 23, and a reflective sheet 26 laminated on the back side of the light guide plate 23 are provided. Each of the optical sheets 22 has specific optical properties such as refraction and diffusion, and specifically, the light diffusion sheet 24 and the light diffusion sheet 24 arranged on the surface side of the light guide plate 23. The prism sheet 25 etc. which are arrange | positioned at the surface side of () are corresponded.

Referring to the function of the backlight unit 20, first, light rays incident on the light guide plate 23 from the lamp 21 are reflected from the reflection dots (not shown) and the respective side surfaces of the light guide plate 23, and the light guide plate ( 23) Emitted from the surface. Light rays emitted from the light guide plate 23 enter the light diffusion sheet 24, are diffused, and are emitted from the surface of the light diffusion sheet 24. Thereafter, the light rays emitted from the light diffusion sheet 24 are incident on the prism sheet 25, and the prism portions 25a formed on the surface of the prism sheet 25 exhibit peaks in a substantially normal direction. It is emitted as a light beam. In this way, the light rays emitted from the lamp 21 are diffused by the light diffusion sheet 24 and refracted by the prism sheet 25 to show a peak in a substantially normal direction. To illuminate the entire floor.

On the other hand, to improve the brightness by reflecting light rays emitted from the back surface of the light guide plate 23 to the surface side so that the liquid crystal screen does not flash (reflective), an apparatus and a frame arranged on the back side of the backlight unit 20, the frame Reflecting sheet 26 is arranged on the back side of the light guide plate 23 for the purpose of preventing the naked eye from being visually confirmed (hidden). As the reflective sheet 26, conventionally, (a) a white pigment such as titanium oxide is dispersed in a sheet made of a synthetic resin, or (b) a void (bubble) for scattering light is dispersed in a sheet made of a synthetic resin. and (c) sheet surfaces formed into mats are used.

Since the concealability is not so high in the conventional reflective sheet 26, there is a fear that the reflectance is increased in the portion of the frame or the like that supports the backlight unit 20, resulting in luminance stain.

In order to prevent such a problem, it is necessary to perform a printing for reducing the reflectance on a portion of the frame or the like which is the cause of the luminance stain or printing for improving the concealment on the back surface of the reflective sheet 26. Only printing makes the manufacturing process complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and includes a reflective sheet having high reflectivity and concealability, and a backlight unit capable of improving luminance and preventing luminance spots by reducing loss of light by using such a reflective sheet. It is for the purpose of providing.

BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing which shows the reflecting sheet which concerns on one Embodiment of this invention.

FIG. 2 is a schematic cross-sectional view showing a reflective sheet different from the reflective sheet of FIG. 1.

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

An invention made to solve the above problems is a reflection sheet for a backlight unit which reduces light emission, and includes a base sheet layer made of a white synthetic resin and a high concealment layer laminated on the back side of the base sheet layer. The brightness of the high concealed layer (L ^* ) is characterized in that more than 95. Here, "white synthetic resin" means a synthetic resin that has a white color due to the mixing of white pigment, dispersion of microbubbles or the like. In addition, "brightness L ^* " is a numerical value prescribed | regulated by JIS-Z8729.

According to the reflective sheet, the base sheet layer made of a white synthetic resin can achieve the same reflectivity and concealability as the conventional reflective sheet, and has a high brightness (L ^* ) of 95 or more laminated on the back side of the base sheet layer. The concealment layer can significantly improve the reflectivity and the concealment.

The high concealment layer of the reflection sheet may be formed by coating a coating material containing a white pigment. In this way, by coating the paint containing the white pigment, a high concealment layer of lightness (L ^* ) of 95 or more filled with a high density of the white pigment is laminated on the back side of the base sheet layer, and the reflective and Effective concealment can be achieved.

As a compounding quantity of the white pigment with respect to solid content of the said coating material, 70 mass% or more and 95 mass% or less are preferable. By making the compounding quantity of a white pigment into the said range, the brightness (L ^* ) of a high concealment layer can be raised to 95 or more, and the improvement of the said reflectivity and concealment can be promoted.

As coating amount of the said coating material, 1 g / m <2> or more and 50 g / m <2> or less are preferable in conversion of solid content. By making the coating amount of the said coating material into the said range, the brightness (L ^* ) of a high concealment layer can be raised to 95 or more, and the said reflectivity and concealability can be improved effectively.

As said white pigment, titanium oxide is preferable. Titanium oxide has the most excellent effect of improving concealment, and also has a high effect of improving durability, weather resistance and the like, so that the life of the reflective sheet can be extended.

In the reflection sheet, a light diffusion layer may be laminated on the surface side of the base sheet layer. According to this means, the light rays reflected by the reflecting sheet are diffused by the light diffusing action of the light diffusing layer laminated on the surface side of the base sheet layer, and the concealment can be further improved.

As this light-diffusion layer, it is suitable to have a binder and the light-diffusion agent disperse | distributed in this binder. According to this means, since high light diffusing property is achieved by the light diffusing agent dispersed in the binder, the effect of increasing the reflectivity and hiding property is great.

Moreover, as a light-diffusion layer, what has a base polymer and the bubble disperse | distributed in this base polymer is also suitable. According to this means, since high light diffusivity is achieved by reflection and refraction at the interface of bubbles dispersed in the base polymer, the reflectivity and concealment can be improved.

Soft urethane beads can be used as the light diffusing agent. According to this means, since the flexible urethane beads which are arranged on the surface of the reflecting sheet and protrude from the back surface of the light guide plate come into contact with the back surface of the light guide plate, damage to the back surface of the light guide plate, in particular, the irregularities and the like formed on the back surface can be reduced.

Therefore, (a) a linear lamp, (b) a light guide plate arranged so as to follow the lamp, and a light guide plate for guiding light rays generated from the lamp to the surface side, and (c) arranged on the surface side of the light guide plate, A backlight unit for a liquid crystal display device comprising an optical sheet which diffuses light beams emitted by the light beams substantially uniformly and refracts toward the normal direction, and (d) the reflective sheet of the present invention arranged on the rear surface side of the light guide plate. Since the reflective sheet achieves high reflectivity and concealability, the light loss emitted from the back surface side can be reduced, and the luminance can be improved. In addition, generation of luminance spots can be prevented even without printing on a frame or the like as in the conventional backlight unit.

[Description of Preferred Embodiment]

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail, referring an appropriate drawing.

The reflective sheet 1 of FIG. 1 includes a base sheet layer 2 and a high concealment layer 3 laminated on the back surface of the base sheet layer 2.

The base sheet layer 2 is formed of a white synthetic resin. As described above, the white synthetic resin is a synthetic resin containing dispersion of white pigment and microbubbles. The synthetic resin usable 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, weather resistant vinyl chloride, and the like. have. Especially, the polyethylene terephthalate excellent in heat resistance is preferable. In addition, as a white pigment to contain, it is the same as that of the conventional reflecting sheet, and the white pigment used for the high concealment layer 3 mentioned later is used specifically. In addition, the bubbles contained in the dispersion are the same as in the conventional reflective sheet.

Although the thickness of this base material sheet layer 2 is not specifically limited, For example, they are 50 micrometers or more and 250 micrometers or less. If the thickness of the base material sheet layer 2 is less than the said range, curling may become easy to produce when the resin composition which forms the high-closing layer 3 is coated. On the contrary, when the thickness of the base sheet layer 2 exceeds the above range, the thickness of the backlight unit becomes large, which is counter to the demand for thinning of the liquid crystal display device.

The high concealment layer 3 is not particularly limited as long as the above concealability can be achieved. Specifically, the high concealment layer 3 is coated with a coating 5 containing a white pigment 4 on the back surface of the base sheet layer 2. Is formed. In addition, as a coating material used for this high concealment layer 3, it does not specifically limit but a general thing is used.

It said cover layer (3) Lightness (L ^*) (lightness (L ^*) on the back surface of the other words, the art reflective sheet (1)) of is to be at least 95, 97 or more is particularly preferable. By making the brightness L ^* of the high concealment layer 3 into the said range, the said reflectivity and concealability become high, without causing the fall of the quality of a backlight unit (flashing etc.).

The white pigment 4 is not particularly limited, and examples thereof include titanium oxide (titanium bag), zinc oxide (zinc), lead carbonate (light white), barium sulfate, calcium carbonate (chalk) and the like. . Especially, titanium oxide with a large concealment improvement effect is preferable.

As a minimum of the compounding quantity of the white pigment 4 with respect to solid content of the said coating material 5, 70 mass% is preferable and 80 mass% is especially preferable. On the other hand, as an upper limit of the said compounding quantity, 95 mass% is preferable and 90 mass% or less is especially preferable. When the compounding quantity of the white pigment 4 is smaller than the said lower limit, the improvement effect of the said reflectivity and concealability by the high concealment layer 3 becomes small, On the contrary, when the compounding quantity of the white pigment 4 exceeds the said upper limit, This is because coating of the coating material 5 becomes difficult.

As a minimum of coating amount (solid content conversion) of the coating material 5, 1 g / m <2>, especially 5 g / m <2>, and 10 g / m <2> are preferable. On the other hand, as an upper limit of the said coating amount (solid content conversion), 50 g / m <2>, especially 45 g / m <2>, 40g / m <2> is preferable. When the coating amount of the coating material 5 is smaller than the said lower limit, the improvement effect of the said reflective and concealability by the high concealment layer 3 becomes small, On the contrary, when the coating amount of the coating material 5 exceeds the said upper limit, This is because the thickness of the concealment layer 3 increases, which is contrary to the request for thinning of the backlight unit, and also causes a decrease in the strength of the high concealment layer 3.

As for the particle size (average particle diameter) of the white pigment 4, 100 nm or more and 30 micrometers or less are preferable, and 200 nm or more and 20 micrometers or less are especially preferable. This means that if the particle size of the white pigment 4 is smaller than the above range, it is difficult to achieve the concealability effectively. On the contrary, if the particle size of the white pigment 4 exceeds the above range, it is uniformly dispersed in the paint 5. This is because it becomes difficult and the back surface of the reflective sheet 1 becomes rough.

As a manufacturing method of the said reflection sheet 1, the process of adjusting the coating material 5 by mix | blending a white pigment 4 basically, and coating this coating material 5 on the back surface of the base material sheet layer 2 The process takes place.

According to the reflecting sheet 1, the base sheet layer 2 made of white synthetic resin can achieve the same reflectivity and concealability as the conventional reflecting sheet, and the high concealment layer on the back surface of the base sheet layer 2 By (3), the reflectivity and concealment can be significantly improved. In addition, since the reflective sheet 1 includes the high concealment layer 3 on the back surface side of the base sheet layer 2, the light rays reflected from the high concealment layer 3 to the surface side contain a white pigment or the like. Since the base sheet layer 2 is transmitted, the light of the liquid crystal screen due to dispersion and shielding of the reflected light by the base sheet layer 2 is enhanced, and the concealability is improved.

The reflective sheet 11 of FIG. 2 is provided with the base sheet layer 2 and the high concealment layer 3 laminated | stacked on the back surface of this base sheet layer 2 similarly to the said reflective sheet 1 of FIG. Doing. About this base material sheet layer 2 and the high shielding layer 3, the same code | symbol is attached | subjected and description is abbreviate | omitted. The reflective sheet 11 is further provided with a light diffusing layer 12 laminated on the surface of the base sheet layer 2.

The light diffusing layer 12 is not particularly limited as long as it achieves light diffusing property. Specifically, as shown in FIG. 2, the binder 13 and the light diffusing agent 14 dispersed in the binder 13 are shown. It is suitable to have. Thus, since the light diffusing agent 14 dispersed in the binder 13 achieves high light diffusing property, the light rays emitted to the surface side (for example, the light rays reflected on the surface side in the high concealment layer 3). This spreads, and as a result, concealability can be further improved. Moreover, since unevenness | corrugation is formed in the surface of the light-diffusion layer 12 by the light-diffusion agent 14, reflectivity improves and concealability also becomes high due to this reflectivity improvement.

Examples of the polymer used for the binder 13 include acrylic resins, polyurethanes, polyesters, fluororesins, silicone resins, polyamideimide, epoxy resins, and the like. In the binder 13, a plasticizer, a stabilizer, a deterioration agent, a dispersing agent, an antistatic agent, etc. may be mix | blended besides said polymer. Although this binder 13 is generally transparent, you may disperse | distribute a white pigment and a bubble so that reflective and concealability may be provided similarly to the base material layer 2.

The light diffusing agent 14 is a particle having a property of diffusing light rays, and classified into inorganic fillers and organic fillers. As the inorganic filler, specifically, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used. As a specific material of the organic filler, acryl, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and the like can be used.

The shape of the light diffusing agent 14 is not particularly limited, and examples thereof include spherical shape, cube shape, needle shape, rod shape, fusiform shape, plate shape, flaky shape, fibrous shape, and the like. In consideration of this, spherical beads are preferable.

As a minimum of the particle diameter (average particle diameter) of the light-diffusion agent 14, 0.1 micrometer is preferable and 1 micrometer is especially preferable. On the other hand, as an upper limit of the particle diameter of the light-diffusion agent 14, 100 micrometers is preferable and 50 micrometers is especially preferable. This means that if the particle diameter of the light diffusing agent 14 is less than the lower limit, promotion of concealability due to the light diffusing effect will be insufficient. On the contrary, if the particle size of the light diffusing agent 14 is exceeded, the light diffusing layer 12 may be formed by coating of a resin composition or the like. This is because formation becomes difficult.

As the light diffusing agent 14, when the glass transition temperature is low and soft, specifically, a soft elastomer material having a glass transition temperature of -100 ° C or more and 30 ° C or less, preferably -60 ° C or more and 25 ° C or less is used. good. Thus, when a soft elastomer material is used for the light diffusing agent 14 which protrudes on the surface of the said reflection sheet 11, the damage to the light guide plate arrange | positioned at the surface side of the said reflection sheet 11 can be reduced. As such a soft elastomer material, polyurethane, silicone rubber, polystyrene, thermoplastic polyester, etc. are mentioned, for example, Polyurethane is preferable especially from solvent resistance, heat resistance, etc. Therefore, soft urethane beads are most preferable in terms of the hardness and the shape.

As a minimum of the compounding quantity of the light-diffusion agent 14 with respect to 100 parts of polymer components of the binder 13, 0.1 part is preferable, 5 parts are especially preferable, and 10 parts are more preferable. On the other hand, as an upper limit of the compounding quantity of the said light diffusing agent 14, 300 parts are preferable, 200 parts are especially preferable, and 100 parts are more preferable. Here, the numerical value represented by "part" means the ratio based on mass. When the compounding quantity of the light diffusing agent 14 is less than the said lower limit, promotion of the concealability by a light-diffusion effect will become inadequate, On the contrary, when exceeding the said upper limit, the light-diffusion layer 12 of coating of a resin composition etc. will be carried out. Formation becomes difficult.

As a manufacturing method of the said reflection sheet 11, basically, the process of adjusting the coating material 5 by mix | blending the white pigment 4, and coating this coating material 5 on the back surface of the base material sheet layer 2 A process and a process of coating and drying the thing which mixed the light-diffusion agent 14 in the binder 13 on the surface of this base material sheet layer 2 are carried out.

According to the reflective sheet 11, similarly to the reflective sheet 1, the base sheet layer 2 made of white synthetic resin achieves the same reflectivity and concealment as the conventional reflective sheet, and the base sheet layer 2 By the high concealment layer 3 on the back side, the reflectivity and concealment can be significantly improved. In addition, since the reflective sheet 11 includes the light diffusion layer 12 on the surface side of the substrate sheet layer 2, the reflective sheet 11 diffuses the light emitted to the surface side by reflection of the high concealment layer 3, and conceals it. It can promote sex. Moreover, since the unevenness | corrugation is formed in the surface by the light-diffusion layer 12 containing the light-diffusion agent 14, the said reflective sheet 11 can improve the reflectivity to the surface side, and also the concealment property also in this point. .

Therefore, in the edge light type backlight unit 20 as shown in FIG. 3, when the reflective sheet 1 of FIG. 1 or the reflective sheet 11 of FIG. 2 is used as the reflective sheet 26, the reflection is performed. Since the sheets 1 and 11 have high reflectivity, the light loss emitted from the back surface side can be reduced, and the brightness can be improved. In addition, since the reflective sheets 1 and 11 have high concealability, it is possible to prevent the frames and the like arranged on the rear surface side from being confirmed from the screen and to prevent the occurrence of luminance smears.

In addition, the reflecting sheet of this invention is not limited to the said embodiment, For example, it is also possible to make a light-diffusion layer into the structure which a bubble is disperse | distributed in a base polymer. It is possible to achieve high light diffusivity by reflection and refraction at the interface of bubbles, and the reflectivity and concealability can be improved. In addition, since the light diffusion layer is softened by dispersion of bubbles, damage to the light guide plate on the surface side is reduced.

As a manufacturing method of the light-diffusion layer which the said bubble disperses, it does not specifically limit but a well-known manufacturing method can be employ | adopted. After coating on the surface of a sheet layer, there exists a method of making it thermoset and foaming a foaming agent. Moreover, from the viewpoint of achieving effective light diffusivity, the average diameter of the bubbles is preferably 0.5 µm or more and 100 µm or less, and the volume ratio of the bubbles to the base polymer is preferably 1 vol% or more and 80 vol% or less.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is described based on an Example, this invention is not interpreted limitedly based on description of this Example.

EXAMPLE

As a base material sheet layer, 85 mass% of titanium oxide was mixed with a polyurethane resin composition using the sheet made from white PET (polyethylene terephthalate) ("LUIRA-E60L" by Toray Corporation), and it was used for a high concealment layer. A paint was prepared, and the paint was coated on the back surface of the base sheet layer at a coating amount of 40 g / m 2 (solid content) to laminate a high concealment layer, and the brightness (L ^* ) of the back surface (high concealment layer) was 97.7. The reflective sheet of Example was obtained.

Comparative Example 1

A commercially available reflective sheet obtained by laminating a concealment layer on the back surface of the base sheet layer was obtained, and was used as the reflective sheet of Comparative Example 1. The brightness L ^* of the back surface (hidden layer) of this reflective sheet was 93.5.

Comparative Example 2

The reflective sheet of Comparative Example 2 consisting of only the substrate sheet layer was obtained.

[Evaluation of Characteristics]

The brightness (L ^* ) of the concealment layer of the reflection sheet of the said Example and the comparative example 1 is 10 of the numerical value measured using the brand name "Multi-Light Spectrophotometer (MSC-IS-2DH)" of Suga Test Co., Ltd. Point average. Using the reflecting sheet of the above-mentioned example and the reflecting sheets of Comparative Examples 1 and 2, the reflectance of each reflecting sheet and the edge light type backlight unit as shown in FIG. 3 were loaded and the front luminance was measured. This reflectance is shown in Table 1 below, and the front luminance is shown in Table 2 below.

As shown in Table 1 and Table 2, the reflective sheet of the Example showed a high reflectance and front luminance compared to the reflective sheet of Comparative Example 2 which is generally used in the past. Moreover, the reflectance of the reflecting sheet of the Example improved by about 1% compared with the reflecting sheet of the comparative example 1 which is commercially available. In addition, compared to the backlight unit loaded with the reflective sheet of Comparative Example 1, the average luminance of the backlight unit loaded with the reflective sheet of Example was improved by about 3%.

The reflective sheet of the present invention has high reflectivity and concealability, and the backlight unit including the reflective sheet can improve luminance and prevent luminance unevenness by reducing loss of light.

Claims (10)

As a reflection sheet for a backlight unit which reduces light emission, A base sheet layer made of white synthetic resin and a high concealment layer laminated on the back side of the base sheet layer, Reflective sheet, characterized in that the brightness (L ^* ) of the high concealment layer is 95 or more. The reflection sheet according to claim 1, wherein the high concealment layer is formed by coating a coating material containing a white pigment. The reflection sheet according to claim 2, wherein a compounding amount of the white pigment to the solid content of the paint is 70% by mass or more and 95% by mass or less. The reflection sheet according to claim 2, wherein the coating amount of the coating material is 1 g / m 2 or more and 50 g / m 2 or less in terms of solid content. The reflective sheet according to claim 2, wherein the white pigment is titanium oxide. The reflective sheet according to claim 1, wherein a light diffusion layer is laminated on the surface side of the base sheet layer. The reflective sheet according to claim 6, wherein the light diffusing layer has a binder and a light diffusing agent dispersed in the binder. 8. The reflective sheet according to claim 7, wherein soft urethane beads are used as the light diffusing agent. The reflection sheet according to claim 6, wherein the light diffusion layer has a base polymer and bubbles dispersed in the base polymer. With lamps on board, A light guide plate arranged to follow this lamp, for guiding light rays generated from the lamp toward the surface; An optical sheet which is arranged on the surface side of the light guide plate and diffuses light rays emitted from the light guide plate substantially uniformly and refracts toward the normal direction; A backlight unit for a liquid crystal display device comprising a reflective sheet arranged on the rear surface side of the light guide plate, The reflective sheet includes a base sheet layer made of white synthetic resin and a high hiding layer laminated on the back side of the base sheet layer, The brightness unit (L ^* ) of this high concealment layer is 95 or more, The backlight unit for liquid crystal display devices characterized by the above-mentioned.