JP2008512719A - Reflective sheet and backlight unit using the same - Google Patents

Abstract

In the reflection sheet for the backlight unit, the soft coating layer is formed of elastomeric acrylic beads or elastomeric nylon beads as a soft coating layer formed on at least one of the base material sheet layer and the surface of the base material sheet layer. And a reflective sheet comprising a soft coating layer containing at least one soft elastomeric bead selected from the group consisting of microcapsule resin beads whose core portion is filled with air or an organic substance, and a liquid crystal employing the same Provided is a backlight unit for a display device. The reflective sheet further includes a metal reflective layer. The reflective sheet having the soft coating layer is excellent in friction resistance and impact resistance. Further, the reflection sheet comprising the soft coating layer and the metal reflection layer is excellent not only in friction resistance and impact resistance but also in specular reflectance and luminance increase rate. Therefore, the reflection sheet can be usefully applied to a light guide plate of a backlight unit having a low surface hardness or requiring a surface protection due to a surface prism pattern.
[Selection] Figure 2

Description

  The present invention relates to a reflective sheet capable of protecting a light guide plate and a backlight unit employing the same.

  A back light unit for illuminating the liquid crystal layer to emit light is provided on the back surface of the liquid crystal layer of the liquid crystal display device. In such a backlight unit, as shown in FIG. 1, the edge light type backlight unit 100 is a rod-shaped cold cathode fluorescent lamp (CCFL) disposed along the side surface of a rectangular light guide plate 104 as a light source. ) 101, a plurality of optical sheets 106 laminated on the front surface side of the light guide plate 104, and a reflective sheet 102 laminated on the back surface side of the light guide plate 104. Each layer of the optical sheet 106 has photochemical properties such as refraction and diffusion. Specifically, the light diffusion sheet 108 is disposed on the surface side of the light guide plate 104, and on the surface side of the light diffusion sheet 108. The prism sheet 110 etc. to be arranged are included.

  The function of the backlight unit 100 is as follows. First, the light beam that has entered the light guide plate 104 from the fluorescent lamp 101 is reflected from a reflection point (not shown) on the back surface of the light guide plate 104 and each side surface, and is emitted from the entire surface of the light guide plate 104. That is, the light guide plate 104 acts like a surface light source. Light rays emitted from the light guide plate 104 are incident on the light diffusion sheet 108 and diffused, and are emitted from the surface of the light diffusion sheet 108. The light beam emitted from the light diffusion sheet 108 is incident on the prism sheet 110 and is emitted as a light beam having a distribution representing a peak in the direction of the normal line through the prism portion 110-1 formed on the surface of the prism sheet 110. Accordingly, the light emitted from the fluorescent lamp 101 is diffused by the light diffusion sheet 108 while being refracted by the prism sheet 110, and illuminates the front surface of the liquid crystal layer (not shown) thereon.

  As described above, the reflection sheet 102 is disposed on the back surface of the light guide plate 104. Conventionally, the reflective sheet 102 is usually composed of a white opaque polyester film or a laminated film, and a large amount of organic or inorganic filler is used for the purpose of increasing the reflectance on the surface or both sides of the white opaque polyester film. What formed the hard coating layer to contain was mainly used. Such a reflection sheet 102 efficiently reflects light rays directed to the base structure on the surface of the light guide panel, and covers the light diffusion sheet. This increases the brightness of the LCD and prevents the backlight unit 100 from being seen in the base structure from the front of the LCD.

  Therefore, the surface of the reflection sheet 102 must be uniform with respect to the entire surface of the light guide plate 104 so that the light rays are uniformly reflected in all directions.

  On the other hand, in the case of an acrylic resin light guide plate that is normally used as the light guide plate 104, since the surface hardness is relatively high, contact friction that occurs when the light guide plate 104 and the reflective sheet are contacted during backlight assembly, The surface was rarely damaged by external impact. Further, since the surface of most conventional light guide plates is smooth and the surface of the printed layer below the light guide plate is also smooth, the surface characteristics of the reflective sheet have not been a problem.

  However, recently, in order to further increase the brightness of the LCD, a light guide plate having a prism pattern on the top or bottom of the light guide plate has been developed and gradually used. The light guide plate of the prism pattern is a light guide plate in which a three-dimensional prism pattern is formed on the surface of the light guide plate by injection molding or laser processing, and since the upper end of the prism pattern is sharp, a conventional hard surface reflecting sheet or hard bead is used. When a reflective sheet having a protruding coating surface is used, there is a problem in that the prism pattern is destroyed due to friction or external impact, thereby causing a decrease in luminance due to poor appearance or optical loss.

  Recently, polyolefin-based light guide plates are easily used for injection molding and have a low specific gravity. However, since the surface hardness of the polyolefin-based light guide plate is low, it has the same problems as when the prism pattern light guide plate is used. An acrylic light guide plate for use in a plastic LCD backlight unit disclosed in Korean Patent Publication No. 2004-0039222 is manufactured through mixing or chemical reaction of plastic rubber or metal having a high level of flexibility. . However, since the surface hardness of the light guide plate is also low in the case of the acrylic light guide plate, the same problem occurs when the light guide plate having the prism pattern described above is used.

  In order to solve such problems, Korean Patent Publication No. 2003-0025192 discloses a reflection sheet having a damage prevention layer containing polyurethane beads or silicon rubber beads on a base sheet. However, since polyurethane beads are substantially inflexible, damage to the light guide plate cannot be prevented. Although silicon rubber beads are flexible, there is a problem in that non-reacted monomers and oligomers flow out from the surface of the silicon beads, resulting in uneven brightness.

  Accordingly, a first object of the present invention is to provide a reflective sheet that can simultaneously prevent optical deterioration such as luminance unevenness and sufficiently protect the surface of the light guide plate.

  A second object of the present invention is to provide a backlight unit for a liquid crystal display device that employs the reflection sheet and can improve luminance and make luminance uniform.

  In order to achieve the first object, the present invention includes a base sheet layer and a soft coating layer formed on at least one of the base sheet layer, and the soft coating layer includes an elastomeric acrylic layer. A reflective sheet for a backlight unit, comprising at least one soft elastomeric bead selected from the group consisting of a bead, an elastomeric nylon bead, and a microcapsule resin bead whose core is filled with air or an organic substance provide.

  The reflective sheet according to the present invention further includes laminating a metal reflective layer and a transparent resin layer in this order between the base sheet layer and the soft coating layer.

In order to achieve the second object, the present invention provides:
A light source that emits rays,
A light guide plate that conducts the light beam and includes a side surface serving as an incident surface of the light beam, a lower surface, and an upper surface serving as a light exit surface;
An optical sheet that is disposed on the upper surface of the light guide plate, uniformly diffuses the light emitted from the light guide plate, and refracts the diffused light in the vertical direction to the upper surface of the optical sheet, and the light guide plate A reflective sheet that is disposed on the lower surface of the light source and reflects light rays from the light source to the light guide plate,
The reflective sheet is
A base sheet layer, and a soft coating layer formed on at least one of the base sheet layers, wherein the soft coating layer includes elastomeric acrylic beads, elastomeric nylon beads, and a core portion that is air or organic. There is provided a backlight unit for a liquid crystal display device including a soft coating layer containing at least one soft elastomeric bead selected from the group consisting of microcapsule resin beads filled with a substance.

  In addition, the present invention provides a liquid crystal display device comprising the reflective sheet according to the present invention.

  The reflective sheet according to the present invention includes soft elastomer-based beads having a specially selected elasticity, and includes a soft coating layer having excellent impact resistance and friction resistance. It is possible to sufficiently protect the surface of the light guide plate without causing any deterioration. In addition, the reflection sheet of the present invention may further include a metal reflection layer, and the reflection sheet according to such an embodiment has further excellent luminance characteristics.

  The reflection sheet according to the present invention has a soft coating layer and exhibits excellent friction resistance and impact resistance, and when it further includes a metal reflection layer, not only friction resistance and impact resistance but also specular reflection. Also excellent in rate and brightness. Therefore, the reflective sheet of the present invention can be usefully applied to a light guide plate of a backlight unit having a low surface hardness or requiring surface protection due to a surface prism pattern. Specifically, when the reflection sheet of the present invention is employed in the backlight unit, it is possible to effectively prevent the light guide plate from being damaged, and to prevent a decrease in luminance and luminance unevenness due to the damage to the light guide plate. In addition, the luminance of the backlight unit can be improved.

  The reflector sheet according to the present invention will be described in more detail with reference to the accompanying drawings and preferred embodiments.

  FIG. 2 is a schematic cross-sectional view showing a reflection sheet 10 for a backlight unit according to an embodiment of the present invention. As shown in FIG. 2, the reflective sheet 10 is formed on the base sheet layer 2 made of white opaque resin, and the base sheet layer 2, and the elastomeric acrylic beads, the elastomeric nylon beads, and the core portion are formed. It includes a soft coating layer 4 containing soft elastomeric beads 6 having at least one rubber elasticity selected from the group consisting of microcapsule resin beads filled with air or an organic substance.

  When the reflective sheet 10 according to this embodiment is applied to a backlight unit, the light guide plate is in contact only with the surface of the soft coating layer 4 formed by the soft elastomeric beads 6. As a result, the surface damage of the light guide plate is significantly reduced. Further, it is possible to minimize frictional damage caused by winding or stacking the reflective sheet 10 during storage or transportation.

  The base sheet layer 2 made of white opaque resin imparts basic reflectivity and concealment to the reflective sheet 10. The “white opaque resin” of the base material sheet layer 2 means a resin which takes on a white color by mixing white pigments and dispersing fine bubbles. Examples of resins that can be used for the base sheet layer 2 include polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polyethylene naphthalate (PNT), acrylic resin, polycarbonate resin, polystyrene, polyolefin, cellulose acetate, and poly A polyester resin containing vinyl chloride can be mentioned, but is not limited thereto. Among these, PET having excellent heat resistance is preferable.

  The thickness of the base sheet layer 2 is preferably in the range of 100 to 300 μm, but is not particularly limited. When the thickness of the substrate sheet layer 2 is less than 100 μm, there is a concern that the luminance of the backlight unit and the luminance of the liquid crystal display device using the backlight unit are lowered due to the weak reflectivity of the substrate sheet 2. On the other hand, if it exceeds 300 μm, curling may occur during the assembly process or storage. In addition, the thickness of the backlight unit increases, making it difficult to manufacture a thin liquid crystal display device.

  Examples of white pigments include, but are not limited to, titanium oxide, silicon oxide, zinc oxide, lead carbonate, barium sulfate, calcium carbonate and aluminum oxide. Among these, titanium oxide having high concealability is preferable.

  The average particle size of the white pigment is preferably 0.1 to 50 μm, and more preferably 0.1 to 5 μm. When the average particle size of the white pigment is less than 0.1 μm, the reflective and concealing properties of the reflective sheet 10 are insufficient. On the other hand, when the average particle size of the white pigment exceeds 50 μm, the reflective properties of the reflective sheet 10 and There is concern that concealment will be uneven.

  In addition, the air bubbles that can be dispersed in the base sheet layer 2 can be appropriately adjusted in content, average particle size, and the like so as to have reflectivity and concealment of the reflection sheet 10 as in the case of the conventional reflection sheet. .

  The soft coating layer 4 contains a binder 8 and soft elastomeric beads 6. The soft elastomeric beads 6 are dispersed in the binder 8. Since the reflective sheet 10 includes the soft elastomeric beads 6, a plurality of protrusions are formed. Therefore, when the reflective sheet 10 is disposed on the back surface of the light guide plate, only the plurality of protrusions are in contact with the back surface of the light guide plate, and therefore the entire surface of the reflective sheet 10 does not contact the light guide plate. Thereby, the adhesion between the reflection sheet 10 and the light guide plate and the luminance unevenness of the liquid crystal display device screen are prevented. The thickness of the soft coating layer 4 (thickness of the binder 8 excluding the soft elastomeric beads 6) is not particularly limited, but is, for example, 1 to 50 μm, preferably 1 to 20 μm.

  As the soft elastomeric beads 6, at least one kind of soft elastomeric beads selected from the group consisting of elastomeric acrylic beads, elastomeric nylon beads, and microcapsule resin beads with a core portion filled with air or an organic substance is used. The Since the surface hardness of the protruding portion of the soft coating layer 4 is reduced by the soft elastomeric beads 6, the surface of the light guide plate is prevented from being damaged. In particular, the soft elastomeric beads 6 used in the present invention have an elastic recovery rate of 30 to 90%, preferably an elastic recovery of 50 to 70% through adjustment of the degree of crosslinking, adjustment of crystallinity and / or molecular weight. It has been adjusted to have a rate. When the elastic recovery rate of the soft elastomeric beads 6 is less than 30%, the surface of the protruding portion of the soft coating layer 4 becomes hard, so that the rubber elastic function cannot be substantially exhibited. As a result, the surface of the light guide plate There is concern that will be damaged. On the other hand, if it exceeds 90%, it becomes difficult to produce fine soft elastomeric beads.

  The elastomeric acrylic beads are homopolymers of alkyl acrylates and / or alkyl methacrylates and (meth) acrylonitrile, (meth) acrylamide, methyl (meth) acrylate, and / or N-methylol (meth) acrylamide, or It means a soft elastomeric bead made of a copolymer and having rubber elasticity. The physical properties of the homopolymer or copolymer resin are greatly affected by the type of the side chain alkyl group. In general, homopolymers or copolymers of alkyl acrylate monomers have a low glass transition temperature and impart elasticity and softness. Alkyl methacrylate homopolymers or copolymers have a high glass transition temperature. , Exhibiting hard properties (ie, weak elasticity and softness). Therefore, it is preferable to use a homopolymer or copolymer of an alkyl acrylate monomer having an excellent elastic recovery rate as the elastomeric acrylic beads in the present invention. As the alkyl group, a C1-C10 alkyl group, preferably a C1-C6 alkyl group, more preferably a C1-C4 alkyl group is used.

  The elastomeric nylon rubber beads mean soft elastomeric beads made of nylon resin such as nylon 6, nylon 66, nylon 7, nylon 46, nylon 11 or nylon 12. Since the softness and elastic recovery rate of nylon rubber beads are mainly influenced by the crystallinity, the above-mentioned elastic recovery rate can be obtained by appropriately adjusting the crystallinity. In general, nylon 11 and nylon 12 have a higher elastic recovery rate than nylon 6 and nylon 66.

  The microcapsule beads in which the core portion is filled with air or an organic material are not particularly limited as long as they have the elastic recovery rate described above. As a specific example, a core portion of a bead made of a homopolymer or a copolymer obtained from an alkyl acrylate monomer, an alkyl methacrylate monomer, and / or a (meth) acrylonitrile monomer is made of air or an organic substance. Mention may be made of filled elastomeric hollow beads. The organic material may be liquid or solid. In particular, the organic material having a lower hardness than the hollow beads of the outer layer is preferable because of its high elastic recovery rate. Examples of the organic substance include alkyl acrylate esters, alkyl methacrylate esters, low-boiling hydrocarbons, and polymers thereof. The alkyl group is a C1 to C10 alkyl group, preferably a C1 to C6 alkyl group, and more preferably a C1 to C4 alkyl group. The low boiling point hydrocarbons include C3 to C15 hydrocarbons, but are preferably butane, pentane, hexane, heptane, octane, nonane, decane, and the like.

  The shape of the soft elastomeric bead 6 used in the present invention is not particularly limited as long as a relatively smooth protrusion is formed on the surface of the soft coating layer 4 and damage to the light guide plate can be prevented. For example, a spherical shape, a spheroid shape, a spindle shape, a fiber shape, and the like can be mentioned. Among them, a spherical shape having excellent damage prevention properties is particularly preferable. As the soft elastomeric beads 6, those having a monodispersed or polydispersed particle size distribution can be used, and the average particle size is preferably 1 to 100 μm, more preferably 3 to 20 μm. When the average particle size is 1 μm, the particle size is very small, so even if it has rubber elasticity, the soft elastomeric beads 6 are completely covered in the soft coating layer 4 and do not function properly, exceeding 100 μm Then, the coating work is difficult, and the adhesive strength of the binder resin is weak, so that there may be a problem that the soft elastomeric beads 6 are detached.

  The content of the soft elastomeric beads 6 is preferably in the range of 0.1 to 50% by mass, more preferably 0.5 to 30% by mass, based on the total mass of the soft coating layer 4, and 1 to 5% by mass. More preferably. When the content of the soft elastomeric beads 6 is less than 0.1% by mass, the amount of beads distributed per unit area decreases, and a sufficient effect cannot be obtained. On the other hand, if the amount exceeds 50% by mass, the content of the binder 8 relative to the soft elastomeric beads 6 is insufficient, causing problems that the soft elastomeric beads 6 are detached or the adhesion to the base sheet layer 2 is insufficient. Can do.

  The binder 8 is formed by coating an appropriate resin composition, covers the soft elastomeric beads 6 on the entire surface of the base sheet layer 2 and fixes them. The binder 8 is at least one of an inorganic filler, a curing agent, a plasticizer, a dispersant, a leveling agent, an antistatic agent, an ultraviolet absorber, an antioxidant, a viscosity modifier, a lubricant, and a light stabilizer. Can further be included.

  The pencil hardness of the binder 8 is 4B to 2H, preferably 2B to H, and more preferably HB. When the soft elastomeric beads 6 are coated with the binder 8 having the pencil hardness described above, the binder 8 absorbs the external pressure acting on the surface of the reflective sheet 10, and the light guide plate disposed on the surface of the reflective sheet 10 in the backlight unit. Damage can be reduced.

  Non-limiting examples of resins used to form the binder 8 include acrylic resins, polyester resins, polyether polyol resins, polyester polyol resins, polyurethane resins, silicone resins, fluorine resins, polyamideimide resins, and epoxy resins. And ultraviolet curable resins, and these resins may be used alone or in combination of two or more. Further, the resin used for the binder 8 is preferably transparent so as not to affect the reflectivity and concealment by the base sheet layer 2, and is particularly preferably colorless and transparent.

  The number average molecular weight of the resin used for forming such a binder 8 is preferably 1,000 to 500,000, more preferably 5,000 to 100, from the viewpoint of processability and physical properties. 1,000.

  Examples of acrylic resins used to form the binder 8 include single weights of alkyl acrylate monomers or alkyl methacrylate monomers such as polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate and polyethyl methacrylate. Mention may be made of coalescence or copolymer resins with acrylonitrile, acrylamide and / or N-methylolacrylamide monomers.

  When a polyol resin is used as the resin for forming the binder 8, a polyisocyanate compound can be contained as a curing agent in the resin composition, and this cured product becomes a polyurethane resin. Use of this polyisocyanate compound increases the effective speed of the resin composition. Therefore, even if a cationic antistatic agent that increases the dispersion stability of the inorganic filler is contained in the resin composition, the cationic charging The decrease in the curing reaction rate due to the inhibitor can be sufficiently supplemented.

  The polyisocyanate compound is preferably a toluene diisocyanate derivative, a xylene diisocyanate derivative or an aliphatic diisocyanate derivative, and particularly preferably a single xylene diisocyanate derivative or a mixture of the xylene diisocyanate derivative and an aliphatic diisocyanate derivative. The xylene diisocyanate derivative is an aromatic diisocyanate derivative in which the reaction rate of the resin composition is high and yellowing and deterioration due to heat or ultraviolet rays are relatively small. Accordingly, it is possible to reduce a decrease in the transmittance of the reflective sheet 10 over time. On the other hand, aliphatic diisocyanate derivatives are less effective in improving the reaction rate than aromatic diisocyanate derivatives, but yellowing and deterioration due to heat and / or ultraviolet rays are extremely small. A balance of speed improvements and reductions such as yellowing and degradation can be achieved.

  The aliphatic diisocyanate derivative is preferably an isophorone diisocyanate derivative or a hexamethylene diisocyanate derivative. Such isophorone diisocyanate derivatives and hexamethylene diisocyanate derivatives have a relatively large improvement in the curing reaction rate, and can promote productivity and heat resistance.

  The compounding amount of the polyisocyanate compound is 2 to 20% by mass, preferably 5 to 15% by mass, based on the mass of the resin in the resin composition for forming the binder. Thus, the improvement of the cure reaction rate of a resin composition can be effectively achieved by making the compounding quantity of a polyisocyanate compound into the said range.

  As described above, the resin composition for forming the binder 8 can further include an inorganic filler. By dispersing the inorganic filler in the binder 8, the heat resistance of the soft coating layer 4 and ultimately the reflection sheet 10 can be increased. As a result, in the backlight unit, deformation of the reflection sheet 10 due to exposure to heat from the light source or moisture in the air can be significantly suppressed.

  The inorganic filler is particularly preferably an inorganic oxide, but is not limited thereto. The inorganic oxide is defined by various oxygen-containing metal compounds in which a metal element is mainly bonded to oxygen atoms to form a three-dimensional network. Moreover, as a metal element which comprises an inorganic oxide, the element selected from periodic table II-VI is preferable, and the element selected from periodic table III-V is still more preferable. Among these, an element selected from Si, Al, Ti and Zr is particularly preferable, and colloidal silica is most preferable as the inorganic filler. The shape of the inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, but is not particularly limited.

  The average particle size of the inorganic filler is preferably 0.1 to 10 μm, and more preferably 0.1 to 5 μm. When the average particle size of the inorganic filler is less than 0.1 μm, the surface energy of the inorganic filler is increased, so that aggregation or the like is likely to occur. On the other hand, when the average particle size exceeds 10 μm, the soft coating layer 4 becomes cloudy. However, there is a concern that the reflective and concealing properties of the reflective sheet 10 are affected.

  The mixing amount of the inorganic filler is preferably 1 to 500% by weight, more preferably 1 to 200% by weight, and most preferably 1 to 50% by weight based on the weight of the resin in the resin composition for forming the binder 8. It is. When the mixing amount of the inorganic filler is less than 1% by mass, there is a concern that the heat resistance of the reflection sheet 10 cannot be sufficiently obtained. Conversely, when the mixing amount exceeds 500% by mass, it is difficult to mix the resin composition. Further, there is a concern that the damage prevention property of the soft coating layer 4 is lowered. On the other hand, as the inorganic filler, one having an organic polymer fixed on the surface or containing an organic polymer in fine particles can be used.

  The resin composition for forming the binder 8 can contain an antistatic agent. Non-limiting specific examples of this antistatic agent include anionic antistatic agents such as alkyl sulfate compounds and organophosphate compounds, and cationic charging such as quaternary ammonium salts, imidazoline compounds and betaine derivatives. Nonionic antistatic agents such as inhibitors, polyethylene glycols, polyoxyethylene sorbitan monostearic acid esters and ethanolamides, and polymeric antistatic agents such as polyacrylic acid. Among these, cationic antistatic agents that have a relatively large antistatic effect and do not inhibit the stability of the dispersed state of the inorganic filler particles are preferable. Of the cationic antistatic agents, quaternary ammonia salt compounds and betaine derivatives that can further promote the antistatic property to the hydrophobic binder 8 are particularly preferable.

  The mixing amount of the antistatic agent is 0.1 to 10% by mass, preferably 0.5 to 5% by mass based on the mass of the resin in the resin composition for forming the binder 8. When the amount of the antistatic agent used is less than 0.1% by mass, there is a concern that the antistatic effect cannot be sufficiently exhibited. On the contrary, when the amount of the antistatic agent used exceeds 10% by mass, the soft coating is applied. There is concern that the strength of layer 4 will be reduced.

  Next, a method for manufacturing the reflection sheet 10 according to this embodiment will be described. First, the resin constituting the binder 8 and the soft elastomeric beads 6 are added to the solvent and mixed well so that the elastomeric beads 6 are dispersed in particle size. If necessary, any additive described above can be further added to the resin composition for forming the soft coating layer 4. Then, the resin composition is coated on the surface of the white opaque base sheet 2 using one of known coating methods, dried, and then formed into a soft coating layer 4, thereby realizing the present embodiment. Thus, the reflection sheet 10 can be obtained.

  FIG. 3 is a schematic cross-sectional view showing a reflective sheet 20 according to another embodiment of the present invention. As shown in FIG. 3, the reflection sheet 20 includes a concealing coating layer 12 laminated on the back surface of the base sheet layer 2 in addition to the component layers constituting the reflection sheet 10 according to the embodiment shown in FIG. 2. Furthermore, it has. In the reflection sheet 20 according to another embodiment illustrated in FIG. 3, the base sheet layer 2 and the soft coating layer 4 are the same as those in FIG.

  The concealment coating layer 12 laminated on the back surface of the base sheet layer 2 contains a white pigment and plays a role of further improving the concealability and reflectivity of the reflection sheet 20. The average particle diameter of the white pigment is preferably in the range of 0.1 to 50 μm, and the content of the white pigment is preferably in the range of 10 to 90% by mass based on the total mass of the masking coating layer 12. When the content of the white pigment is less than 10% by mass, the effect of improving the reflectivity and the hiding property is insufficient. On the contrary, when the content of the white pigment exceeds 90% by mass, the resin composition for forming the hiding coating layer 12 is used. Coating and formation become difficult.

  Next, a method for manufacturing the reflection sheet 20 according to this embodiment shown in FIG. 3 will be described.

  First, the manufacturing method of the reflective sheet 10 according to this embodiment will be described. First, the resin constituting the binder 8 and the soft elastomeric beads 6 are added to the solvent and mixed well so that the elastomeric beads 6 are dispersed in particle size. If necessary, any additive described above can be further added to the resin composition for forming the soft coating layer 4. Then, the resin composition is coated on the surface of the white opaque base sheet 2 using one of known coating methods, dried, and then the soft coating layer 4 is formed. Then, the resin composition for forming the concealing coating layer 12 is coated on the opposite surface of the base sheet 2, coated on the soft coating layer 4 using one of the known coating methods, dried, and then concealed. By forming the layer 12, the reflection sheet 20 according to this embodiment shown in FIG. 3 is obtained. On the other hand, in the manufacture of the reflection sheet 20 according to this embodiment shown in FIG. 3, the masking coating layer 12 may be formed before the soft coating layer 4.

  The amount of resin, white pigment and other additives used in the resin composition for forming the cover coating layer 12 is not particularly limited. The white pigment may be the same as the white pigment contained in the base sheet layer 2.

1 to 50 g / m ² coating amount of hiding coating layer 12 resin composition for forming a dry basis, preferably 5~45g / m ^2, more preferably a 10 to 40 g / m ^2. When the coating amount of the resin composition is less than 1 g / m ² , the effect of improving the reflectivity and concealment is small, and conversely, when the coating amount of the paint exceeds 50 g / m ² , the thickness of the concealing coating layer 22 increases. As a result, the thickness of the backlight unit can be reduced and the strength of the masking coating layer 12 can be reduced.

  Like the reflective sheet 10 according to the present embodiment illustrated in FIG. 2, the reflective sheet 20 according to another embodiment illustrated in FIG. 3 exhibits reflectivity and concealment by the base sheet layer 2, and is a soft coating layer. 4 can prevent light guide plate damage and adhesion more efficiently. Moreover, reflectivity and concealment can be further improved by the concealment coating layer 12 laminated on the back surface of the base sheet layer 2.

  FIG. 4 is a schematic sectional view showing a reflective sheet 30 according to another embodiment of the present invention. Referring to FIG. 4, the reflective sheet 30 includes a metal layer in order between the base sheet layer 2 and the soft coating layer 4 in addition to the component layers constituting the reflective sheet 10 according to an embodiment of the present invention illustrated in FIG. 2. A reflective layer 14 and a transparent resin layer 16 are further provided. In the reflective sheet 30 of this embodiment shown in FIG. 4, the base sheet layer 2 and the soft coating layer 4 are the same as those shown in FIG. To do. In the reflective sheet 30 according to an embodiment of the present invention, the reflection of light is achieved by the metal reflective layer 14, and the base sheet layer 2 is not always formed by an opaque sheet material, but may be formed by a transparent sheet. it can.

  Since the metal reflection layer 14 has a high light beam reflectivity, the reflection sheet 30 provided with the metal reflection layer 14 is further improved in reflectivity as compared with the sheet not including the metal reflection layer 14. Therefore, when the reflection sheet 30 according to the present embodiment is used for the backlight unit, the luminance of the light emitted from the light guide plate is further improved. The metal reflectivity 14 is formed of a metal having a property of reflecting light. Examples include, but are not limited to copper, silver, aluminum, tin, gold, brass, bronze, and stainless steel. Among them, silver (Ag) that does not absorb light and has a high specular reflectance is preferable. The metal reflection layer 14 is formed by a generally known metal layer forming method such as vacuum vapor deposition or sputtering.

  The thickness of the metal reflective layer 14 is not limited to this, but is 50 to 2000 mm, preferably 100 to 1500 mm, and more preferably 500 to 1000 mm. When the thickness of the metal reflective layer 14 is less than 50 mm, not only the effect of improving the reflectance is insufficient, but also a space is generated so that it is difficult to form a thin film. If the thickness is greater than 2000 mm, the manufacturing cost increases due to the slowness of vacuum deposition or sputtering, and no further increase in reflectance can be expected.

  The transparent resin layer 16 is not particularly limited as long as it can be formed of a transparent film such as polyester, polycarbonate, and polyolefin. Although the thickness of the transparent resin layer 16 is not specifically limited, 0.1-100 micrometers is preferable. When the thickness of the transparent resin layer 16 is less than 0.1 μm, there is a problem that the protective function of the metal reflective layer 14 is insufficient. When the thickness exceeds 100 μm, the specular reflectance of the metal reflective layer 14 is reduced. Problems arise.

  In general, an antioxidant layer (not shown) for protecting the metal reflective layer 14 is formed between the base sheet 2 and the metal reflective layer 14. The anti-oxidation layer protects the metal reflection layer 14 from oxidation, moisture in the atmosphere, and contamination due to contact with impurities, and inorganic substances such as Si and Ti, or their oxides, or anti-oxidants, UV absorbers, etc. It is formed from an organic polymer resin containing the additive.

  Next, a method for manufacturing the reflection sheet 30 according to this embodiment shown in FIG. 4 will be described.

First, a composite film having the metal reflective layer 14 laminated on the surface of the transparent resin layer 16 is formed. For this purpose, a metal vapor can be obtained by using a normal vacuum deposition method or a laminating method and applying high energy generated by the formation of high energy radiation and / or heat to the metal in a high vacuum chamber of about 10 ⁻⁵ torr or less. Evaporate. This metal vapor is laminated on the surface of the transparent resin layer 16 made of polyester, polycarbonate, polyolefin or the like, and then forms a composite film having the metal reflective layer 14 laminated on the surface of the transparent resin layer 16. . If necessary, an antioxidant layer for protecting the metal reflective layer 14 can be formed by vapor deposition of an inorganic substance or coating an organic polymer resin on the metal reflective layer 14. The composite film is laminated so that the metal reflection layer 14 is adjacent to the base sheet layer 2 on the surface of the opaque or transparent base sheet layer 2. At this time, it is preferable to use an appropriate adhesive in order to increase the adhesive force between the metal reflective layer 14 of the composite film and the base sheet layer 2. The adhesive is preferably resistant to yellowing caused by light and heat. For example, an acrylic adhesive, an acrylic-modified urethane adhesive, or the like can be used. Finally, by forming the soft coating layer 4 by the method described above, the reflective sheet 30 can be manufactured according to the embodiment shown in FIG.

  FIG. 5 is a schematic cross-sectional view showing a reflective sheet 40 according to another embodiment of the present invention. As shown in FIG. 5, the reflective sheet 40 further includes a masking coating layer 12 laminated on the back surface of the base sheet layer 2 in addition to the component layers constituting the reflective sheet 30 shown in FIG. 4. ing. In the reflective sheet 40 according to another embodiment of the present invention shown in FIG. 5, the base sheet layer 2 and the soft coating layer 4 are the same as those in FIG. Is omitted. In the reflection sheet 40 according to an embodiment of the present invention, the light reflectivity is achieved by the metal reflection layer 14, and the base sheet layer 2 is not always formed by an opaque sheet material, but is formed by a transparent sheet. You can also.

  In the reflection sheet 40 according to the present embodiment, after obtaining the reflection sheet 30 illustrated in FIG. 4 according to the method for manufacturing the reflection sheet 30, the masking coating layer 12 is formed on the back surface of the base sheet layer 2 according to the method described above. Can be manufactured. In this case, it is a matter of course that the masking coating layer 12 can be formed before the soft coating layer 4.

  The above-described reflective sheets 10 and 20 according to the present invention exhibit reflectivity and concealment by the base sheet layer 2 and use a specially selected soft elastomeric bead having rubber elasticity to provide impact resistance and friction resistance. By providing the soft coating layer 4 that is excellent, it is possible to efficiently prevent damage to the light guide plate due to scratches or adhesion. The reflection sheets 30 and 40 further including the metal reflection layer 14 are further improved in reflectivity compared to the reflection sheets 10 and 20 not including the metal reflection layer 14. In addition, the reflection sheets 20 and 40 that further include the masking coating layer 12 on the back surface of the base sheet layer 2 have further improved reflectivity and masking properties than the reflection sheets 10 and 30 that do not include the masking coating layer 12.

  Accordingly, in the backlight unit, when the reflection sheets 10, 20, 30 and 40 according to the present invention are arranged on the back surface of the light guide plate (104 in FIG. 1), damage to the light guide plate can be prevented as described above. Occurrence of brightness unevenness of the LCD panel due to damage to the back surface of the light guide plate can be prevented, and the assembly operation of the backlight unit is facilitated. In particular, when the reflection sheet 30 or 40 further including the metal reflection layer 14 having a high reflectance is used, the luminance of the backlight unit can be further improved. Further, when the reflection sheet 20 or 40 having the masking coating layer 12 on the back surface of the base material sheet 2 is used, a structure such as a frame arranged on the back surface of the masking coating layer 12 appears on the screen. Therefore, it is possible to prevent the occurrence of luminance unevenness.

  Hereinafter, the reflective sheet according to the present invention will be described in more detail by way of examples. However, this is for illustrative purposes, and the scope of the present invention is not limited by these examples.

  Each physical property test described in Table 1 was carried out by the following method.

-Elastic recovery rate of soft elastomeric beads-
Using a compression tester (Shimadzu Corporation, PCT-200), the compression load is 1 gf / mm ² , compression displacement limit: particle diameter × 10%, and temperature: 20 ± 1 ° C. The elastic recovery rate of the elastomeric beads was measured.

After applying a load to the bead until the bead volume was compressed to 10%, the load was removed, and the diameter of the bead before and after the load was measured according to the following formula to determine the elastic recovery rate.
Elastic recovery rate (%) = [(bead diameter after loading) / (bead diameter before loading)] × 100

-Friction resistance-
Each reflective sheet sample manufactured in Examples and Comparative Examples was cut into A4 paper size, and then the friction resistance of the soft coating film of each reflective sheet was measured as follows. That is, after a reflective sheet sample is laminated on the light guide plate so that the soft coating film of the reflective sheet sample is brought into contact with the polyolefin-based light guide plate, it is 20 gf / cm ² using a self-made friction resistance measuring device. The reflective sheet sample was pulled up at a linear velocity of 3 m / min under the above load, and the degree of scratches generated on the prism pattern surface of the light guide plate was confirmed with the naked eye and evaluated as follows.
○: When no scratch was found on the surface of the prism pattern on the light guide plate ×: When no scratch was found on the surface of the prism pattern on the light guide plate

-Impact resistance-
As in the case of the friction resistance test, the reflective sheet is laminated on the prism pattern light guide plate so that the soft coating layer of the reflective sheet is in contact with the triangular prism pattern surface of the prism pattern light guide plate, and then the diameter produced by itself. Using a push tester equipped with a 2 mm circular lip, hitting the upper surface of the reflective sheet 10,000 times under a load of 10 gf / cm ² , the degree of white spots generated on the light guide plate Was confirmed with an optical microscope. The white spots are generated when the pattern is collapsed, and the impact resistance was evaluated as follows.
○: When a white spot was not found when observed with an optical microscope at 100 magnifications ×: When a white spot was found when observed with an optical microscope at 100 magnifications

-Adhesive strength of polyester film-
The surface of the soft coating layer of the reflective sheet sample was cross-hatched with a razor to form 100 square cells having a size of 0.2 cm in width and 0.2 cm in length. A polyester adhesive tape (Nitto Denko, NO31B-35) was used to adhere to the surface of the soft coating film on which the square cells were formed, and then the adhesive tape was quickly peeled off by hand. The adhesive force at this time was evaluated as follows.
○: When none of the square cells are detached ×: When even one of the square cells is detached

-Reflectance (550nm)-
The specular reflectance of the standard white sheet contrast sheet sample was measured at a wavelength of 550 nm using a reflectance measurement spectrophotometer (HunterLab, ColorQuest XE).

-Opacity-
As the opacity index of the reflecting sheet sample, the opacity of the reflecting sheet sample was measured in transmission mode using an optical density measuring device (Macbeth, TR1224).

-Brightness change rate-
After a reflective sheet, a light guide plate, one light diffusion sheet, and two prism sheets are laminated in this order on a 14-inch LCD backlight, the reflective sheet of the backlight unit is applied to each of the reflective sheet samples produced in the examples and comparative examples. The brightness at the center of the backlight was measured with a luminance meter (Topcon, BM7). The luminance change rate of each backlight unit is that the luminance measured with a white opaque polyester film (Toray, E60L) as the reflecting surface is “1”, and the luminance change rate is 1.05, the luminance increases by 5%. To express.

Example 1
100 parts by mass of an alkyl acrylate ester resin (Aekyung Chemical Co., Ltd, Acrydic AA-960-50), 100 parts by mass of a mixed solvent of toluene and methyl ethyl ketone (50:50), an average particle size of about 8 μm, 2 parts by mass of elastomeric acrylic beads (cross-linked polymethyl acrylate agent, Sekisui Chemical, ACX-806) with an elastic recovery of about 64%, 20 parts of isocyanate curing agent (Aekyung Chemical Co., Ltd, DN-980S) And 0.3 parts by weight of an ultraviolet absorber (Irganox 1010) were uniformly mixed, and then stirred to produce a composition for forming a soft coating layer.

  This resin composition was coated on a white opaque PET base sheet (Toray, E60L) having a thickness of about 188 μm using a table coater and then dried to provide a soft coating layer having a dry thickness of about 8 μm. A reflective sheet was obtained, which was cut to A4 paper size and used as a sample.

-Example 2-
Instead of the elastomeric acrylic beads, 2 parts by mass of elastomeric nylon beads (Ganz Chemical Co., Ltd, GPA-700) made of nylon 12 having an average particle size of about 7 μm and an elastic recovery of about 66% are used. A4 sheet size reflective sheet sample provided with a soft coating layer having a dry thickness of about 7 μm was obtained in the same manner as in Example 1 except that it was used.

Example 3
Instead of the acrylic rubber beads, hollow soft microcapsule resin beads having an average particle diameter of about 5 μm and an elastic recovery of about 59% (cross-linked polymethyl acrylate 96% by mass and silicon dioxide 4% by mass, Matsumoto Yuji Co ., Ltd, S100) A4 sheet size reflective sheet sample provided with a soft coating layer having a dry thickness of about 6 μm was obtained in the same manner as in Example 1 except that 2 parts by mass were used.

Example 4
100 parts by mass of acrylic resin (Aekyung Chemical Co., Ltd, Acrydic AA-960-50) as binder resin, 100 parts by mass of a mixed solvent of toluene and methyl ethyl ketone (50:50), and an average particle diameter of about 0.4 μm 30 parts by mass of titanium particles, 10 parts by mass of silica particles having an average particle diameter of about 2 μm, and 20 parts by mass of an isocyanate curing agent (DN-980S) were mixed uniformly, and then stirred to produce a composition for forming a concealing coating. . The resin composition is coated on the back surface of a white opaque PET base sheet (Toray, E60L) having a thickness of about 188 μm using a table coater and then dried to obtain a concealing coating layer having a dry thickness of about 25 μm. It is done.

  Next, a soft coating layer having a dry thickness of about 8 μm was formed on the PET base sheet on the opposite side of the masking coating layer by the method described in Example 1. The resulting product was cut to A4 paper size to obtain a reflective sheet sample.

-Example 5
A composite film (Kyoto) in which a silver (Ag) reflective layer having a thickness of about 35 mm and a transparent polyethylene terephthalate (PET) film having a thickness of about 25 μm are laminated on a white opaque PET substrate sheet (Toray, E60L) having a thickness of 188 μm Nakai Corporation, Kirara Flex # 25) was laminated so that the silver (Ag) reflective layer was in contact with the PET substrate sheet. At this time, an acrylic resin adhesive (Aekyung Chemical Co., Ltd, AUP310) was coated on the PET base sheet before lamination.

  Next, 100 parts by mass of an alkyl acrylate resin (Acrydic AA-960-50), 100 parts by mass of a mixed solvent of toluene and methyl ethyl ketone (50:50), an average particle diameter of about 8 μm, and an elastic recovery rate 2 parts by mass of elastomeric acrylic beads of about 64%, 20 parts by mass of polyisocyanate curing agent (DN-980S), and 0.3 part by mass of ultraviolet absorber (Irganox 1010) are mixed uniformly, and then mixed with softness. A composition for forming a coating layer was produced. When this resin composition is coated on the transparent PET film using a table coater and then dried, a reflective sheet having a soft coating layer having a dry thickness of about 8 μm is obtained. The sample was cut.

-Example 6
Except that 2 parts by mass of elastomeric nylon 12 beads (Ganz Chemical Co., Ltd, GPA-700) having an average particle diameter of about 7 μm and an elastic recovery rate of about 66% were used instead of the elastomeric acrylic beads. In the same manner as in Example 5, a reflective sheet sample of A4 paper size provided with a soft coating layer having a dry thickness of about 7 μm was obtained.

-Example 7-
Instead of the elastomeric acrylic beads, the hollow soft microcapsule resin beads having an average particle diameter of about 5 μm and an elastic recovery of about 59% (96% by mass of crosslinked polymethyl acrylate and 4% by mass of silicon dioxide, Matsumoto A reflective sheet sample of A4 paper size provided with a soft coating layer having a dry thickness of about 6 μm was obtained in the same manner as in Example 5 except that 2 parts by mass of Yuji Co., Ltd., S100) was used.

-Comparative Example 1-
The white opaque PET substrate sheet (Toray, E60L) of Example 1 that was not subjected to the coating treatment was used as a reflective sheet, and the friction resistance, impact resistance, and the like were evaluated.

-Comparative Example 2-
Same as Example 1 except that 2 parts by mass of hard acrylic beads (Sekisui Chemical, MS10X-8D) having an average particle size of about 8 μm and an elastic recovery rate of about 9% were used instead of the elastomeric acrylic beads. In this manner, a reflective sheet sample of A4 paper size having a soft coating layer having a dry thickness of about 8 μm was obtained.

-Comparative Example 3-
A4 paper size equipped with a soft coating layer having a dry thickness of about 8 μm in the same manner as in Example 1 except that the amount of the elastomeric acrylic beads (ACX-806) was changed to 0.05 parts by mass. A reflective sheet sample was obtained.

-Comparative Example 4-
A4 paper size reflective sheet provided with a soft coating layer having a dry thickness of about 8 μm in the same manner as in Example 1 except that the amount of the elastomeric acrylic beads (ACX-806) was changed to 55 parts by mass. A sample was obtained.

-Comparative Example 5-
A4 sheet size reflective sheet sample was obtained in the same manner as in Example 5 except that the soft coating layer was not used.

  That is, a composite film in which a silver (Ag) reflective layer having a thickness of about 35 mm and a transparent polyethylene terephthalate (PET) film having a thickness of about 25 μm are laminated on a white opaque PET base sheet (Toray, E60L) having a thickness of 188 μm. (Kyoto Nakai Corporation, Kirara Flex # 25) was laminated so that the silver (Ag) reflective layer was in contact with the PET substrate sheet. At this time, an acrylic resin adhesive (Aekyung Chemical Co., Ltd, AUP310) was coated on the PET base sheet before lamination. The sample thus obtained was cut into A4 paper size to prepare a sample.

  Table 1 shows the results of measuring the physical properties of the respective reflective sheet samples produced in Examples 1 to 7 and Comparative Examples 1 to 5.

  Referring to Table 1, the reflective sheet samples of Examples 1 to 7 according to the present invention have superior friction resistance and impact resistance compared to the reflective sheets of Comparative Examples 1 to 3 and 5 that did not have a soft coating layer. It can be seen that In the case of the reflective sheet samples of Examples 5 to 7 provided with a silver reflective layer, it can be seen that they are excellent not only in friction resistance and impact resistance but also in specular reflectance and luminance increase rate. In the case of the reflective sheet sample of Example 4 provided with the hiding layer, it can be seen that the opacity is excellent and the hiding property is greatly improved.

  In the case of the reflective sheet samples of Comparative Examples 1 and 2 that do not have all of the soft coating layer and the silver reflective layer, it can be seen that the friction resistance, impact resistance, specular reflectance and luminance increase rate are all very low. In the case of the reflective sheet sample of Comparative Example 3, although the soft coating layer was provided, the amount of the soft elastomeric beads used was very small, so the effect of improving the friction resistance and impact resistance was insufficient. . In the case of the reflective sheet sample of Comparative Example 4 having a large amount of soft elastomeric beads, the friction resistance and impact resistance are excellent, but the coating layer is not formed so much and the adhesion to polyester is weak. In the case of the reflective sheet sample of Comparative Example 5 in which a silver reflective layer was formed without a soft coating layer, the specular reflectance and the luminance increase rate were excellent, but the friction resistance and impact resistance were weak. .

  As described above, the reflective sheet according to the present invention includes a soft coating layer and exhibits excellent friction resistance and impact resistance. It can also be seen that when the reflective sheet further comprises a metal reflective layer, not only the friction resistance and impact resistance but also the specular reflectance and the luminance increase rate are excellent. Therefore, the reflective sheet of the present invention can be usefully applied to a light guide plate of a backlight unit having a low surface hardness or requiring surface protection due to a surface prism pattern. Specifically, when the reflection sheet of the present invention is employed in the backlight unit, it is possible to effectively prevent the light guide plate from being damaged, and it is possible to prevent a decrease in luminance and uneven luminance due to damage to the light guide plate. In addition, the luminance of the backlight unit can be improved.

FIG. 1 is a schematic perspective view showing a conventional edge light type backlight unit. FIG. 2 is a schematic cross-sectional view showing a reflective sheet according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a reflective sheet according to another embodiment of the present invention. FIG. 4 is a schematic cross-sectional view illustrating a reflective sheet according to another embodiment of the present invention. FIG. 5 is a schematic sectional view showing a reflective sheet according to another embodiment of the present invention.

Claims (21)

In the reflective sheet for the backlight unit,
As a soft coating layer formed on at least one surface of the base sheet layer and the base sheet layer surface, the soft coating layer is made of elastomeric acrylic beads, elastomeric nylon beads, and the core part is air or an organic substance. A reflective sheet comprising a soft coating layer containing at least one soft elastomeric bead selected from the group consisting of microcapsule resin beads filled with.   The reflective sheet according to claim 1, further comprising a metal reflective layer and a transparent resin layer in order between the base sheet layer and the soft coating layer.   A concealing coating layer formed on the surface of the base sheet opposite to the soft coating layer, selected from the group consisting of titanium oxide, silicon oxide, zinc oxide, lead carbonate, barium sulfate, calcium carbonate and aluminum oxide The reflective sheet according to claim 1, further comprising a masking coating layer containing at least one white pigment.   The reflective sheet according to claim 1, wherein an average particle diameter of the soft elastomeric beads is in a range of 1 to 100 μm.   The reflective sheet according to claim 1, wherein a content of the soft beads is in a range of 0.1 to 50% by mass based on a total mass of the soft coating layer.   The reflective sheet according to claim 1, wherein the elastic recovery rate of the soft elastomeric beads in the soft coating layer is 30 to 90%.   The reflective sheet according to claim 2, wherein the metal reflective layer is a silver reflective layer.   The reflective sheet according to claim 2, wherein the transparent resin layer is a transparent polyester layer.   The average particle size of the white pigment is in the range of 0.1 to 50 μm, and the content of the white pigment is in the range of 10 to 90% by mass based on the total mass of the masking coating layer. Item 4. The reflection sheet according to Item 3.   The reflective sheet according to claim 1, wherein the base sheet layer is a white opaque resin sheet. In backlight units for liquid crystal display devices,
A light source that emits light,
A light guide plate that conducts the light beam and includes a side surface serving as an incident surface of the light beam, a lower surface, and an upper surface serving as a light exit surface;
An optical sheet that is disposed on the upper surface of the light guide plate, uniformly diffuses the light emitted from the light guide plate, and refracts the diffused light in the vertical direction to the upper surface of the optical sheet, and the light guide plate A reflective sheet that is disposed on the lower surface of the light source and reflects light rays from the light source to the light guide plate,
The reflective sheet is
A base sheet layer, and a soft coating layer formed on at least one of the base sheet layers, wherein the soft coating layer includes elastomeric acrylic beads, elastomeric nylon beads, and a core portion that is air or organic. A backlight unit for a liquid crystal display device comprising a soft coating layer containing at least one soft elastomeric bead selected from the group consisting of microcapsule resin beads filled with a substance.   The backlight unit according to claim 11, further comprising a metal reflection layer and a transparent resin layer in order between the base sheet layer and the soft coating layer.   A concealing coating layer formed on the surface of the base sheet opposite to the soft coating layer, selected from the group consisting of titanium oxide, silicon oxide, zinc oxide, lead carbonate, barium sulfate, calcium carbonate and aluminum oxide The backlight unit according to claim 11, further comprising an opaque coating layer containing at least one white pigment.   The backlight unit according to claim 11, wherein the soft elastomeric beads have an average particle size in the range of 1 to 100 μm.   The backlight unit according to claim 11, wherein the content of the soft beads is in the range of 0.1 to 50 mass% based on the total mass of the soft coating layer.   The backlight unit according to claim 11, wherein the elastic recovery rate of the soft elastomeric beads of the soft coating layer is 30 to 90%.   The backlight unit according to claim 12, wherein the metal reflective layer is a silver reflective layer.   The backlight unit according to claim 12, wherein the transparent resin layer is a transparent polyester layer.   The average particle size of the white pigment is in the range of 0.1 to 50 μm, and the content of the white pigment is in the range of 10 to 90% by mass based on the total mass of the masking coating layer. Item 14. The backlight unit according to Item 13.   The backlight unit according to claim 11, wherein the base sheet layer is a white opaque resin sheet.   A liquid crystal display device comprising the reflective sheet according to any one of claims 1 to 10.

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