OPTICAL PANELS, BACKLIGHTS, LIQUID CRYSTAL DISPLAYS, AND COMMUNICATION MACHINES

Abstract

Optical plate 5 consists of a substrate layer 11 and a coating layer 12 arranged on the first surface of substrate layer 11. In the case where coating layer 12 contains an antistatic agent, when optical plate 5 is placed in an environment of 65°C and 95% RH for 48 hours, the percentage of the contaminated area on the surface of coating layer 12 is less than 20%. In the case where the first intermediate layer 21 containing an antistatic agent is arranged between substrate layer 11 and coating layer 12, the antistatic agent content in coating layer 12 is lower than the antistatic agent content in the first intermediate layer 21.

Description

Optical sheet, backlight unit, liquid crystal display device and information device

[0001] The present disclosure relates to an optical sheet, a backlight unit, a liquid crystal display device, and an information device.

[0002] In recent years, liquid crystal display devices (hereinafter also referred to as LCDs (liquid crystal displays)) have been widely used as display devices for various information devices such as smartphones and tablet terminals. The main types of backlight units (hereinafter also referred to as BLUs) for LCDs are direct-type, in which a light source is placed on the back of the liquid crystal panel, and edge-light, in which a light source is placed near the side of the liquid crystal panel.

[0003] A conventional edge-lit BLU 101 (see Patent Document 1) shown in FIG. 13 includes a light source 102, a rectangular light guide plate 103 arranged with its edge aligned with the light source 102, multiple optical sheets 104 arranged on the front side of the light guide plate 103, and a reflective sheet 105 arranged on the rear side of the light guide plate 103. The multiple optical sheets 104 include a lower light diffusion sheet 106, a prism sheet 107, and an upper light diffusion sheet 108. The lower light diffusion sheet 106 is overlaid on the front side of the light guide plate 103 and primarily functions as a light diffusion sheet. The prism sheet 107 is overlaid on the front side of the lower light diffusion sheet 106, and the upper light diffusion sheet 108, which has a refracting function in the normal direction, is overlaid on the front side of the prism sheet 107 and slightly diffuses light to suppress brightness unevenness caused by the shape of the prism portion of the prism sheet 107, etc.

[0004] A light diffusion sheet generally includes a substrate layer and a coating layer laminated on the surface side of the substrate layer and having a resin matrix and resin beads. An antistatic agent is added to the coating layer of the light diffusion sheet to prevent dust from adhering to the coating layer during the assembly process.

[0005] Japanese Patent Application Laid-Open No. 2005-77448

[0006] The antistatic performance of the light diffusion sheet is manifested by the bleed-out of the antistatic agent over time. Therefore, depending on the type and amount of the antistatic agent, foreign matter such as lumps or crystals derived from the antistatic agent may be generated, causing contamination of the sheet surface.

[0007] An object of the present disclosure is to provide an optical sheet that can suppress surface contamination caused by an antistatic agent.

[0008] To achieve the above-mentioned object, the present inventors conducted extensive research and found that by selecting the type of antistatic agent, adjusting the amount of antistatic agent added, selecting the resin material for the coating layer, and controlling crosslinking, the area ratio of contaminated areas on the surface of the coating layer can be reduced to less than 20% even when the optical sheet is placed in an environment of 65°C and 95% RH for 48 hours. The present inventors also found that by providing an intermediate layer containing an antistatic agent between the coating layer and the substrate layer and configuring the coating layer to have a lower antistatic agent content than the intermediate layer, it is possible to impart antistatic properties to the optical sheet while suppressing staining of the sheet surface caused by the antistatic agent. Note that configuring the coating layer to have a lower antistatic agent content than the intermediate layer also includes a configuration in which the coating layer is substantially free of antistatic agent.

[0009] The optical sheet according to the present disclosure has been made based on the above findings. Specifically, a first optical sheet according to the present disclosure is an optical sheet comprising a substrate layer and a coating layer provided on a first surface of the substrate layer, the coating layer containing an antistatic agent, and when the optical sheet is placed in an environment of 65°C and 95% RH for 48 hours, the area ratio of contaminated regions on the surface of the coating layer is less than 20%. Also, a second optical sheet according to the present disclosure is an optical sheet comprising a substrate layer and a coating layer provided on a first surface of the substrate layer, the first intermediate layer containing an antistatic agent is provided between the substrate layer and the coating layer, and the content of the antistatic agent in the coating layer is lower than the content of the antistatic agent in the first intermediate layer.

[0010] The first optical sheet according to the present disclosure has a simple configuration and can suppress staining of the sheet surface caused by an antistatic agent. In the first optical sheet according to the present disclosure, if the antistatic agent is an ionic liquid or a reactive emulsifier, the amount of foreign matter such as lumps or crystals caused by the antistatic agent can be reduced. In the first optical sheet according to the present disclosure, an intermediate layer substantially free of an antistatic agent may be provided between the substrate layer and the coating layer.

[0011] The second optical sheet according to the present disclosure can suppress staining of the sheet surface caused by antistatic agents without limiting the options for the type of antistatic agent that can be used. In the second optical sheet according to the present disclosure, the coating layer may be substantially free of antistatic agents. The first intermediate layer may be an adhesive layer that bonds the substrate layer and the coating layer. In this case, a second intermediate layer containing an antistatic agent may be provided between the first intermediate layer and the coating layer. Alternatively, in the second optical sheet according to the present disclosure, an adhesive layer that is substantially free of antistatic agents may be provided between the substrate layer and the first intermediate layer. In the second optical sheet according to the present disclosure, sufficient antistatic performance is achieved when the half-life of the electrostatic potential according to JIS L 1094 Method A is 30 seconds or less. In the second optical sheet according to the present disclosure, when the optical sheet is placed in an environment of 65°C and 95% RH for 48 hours, if the decrease in contact angle on the surface of the coating layer is 10 degrees or less, the deposition of foreign matter such as lumps or crystals derived from the antistatic agent on the surface of the coating layer can be suppressed. The second optical sheet according to the present disclosure may further include an anti-sticking layer provided on the second surface of the substrate layer, the anti-sticking layer being substantially free of an antistatic agent, and a second intermediate layer containing an antistatic agent being provided between the substrate layer and the anti-sticking layer. Alternatively, the second optical sheet according to the present disclosure may further include an anti-sticking layer provided on the second surface of the substrate layer, the anti-sticking layer containing an antistatic agent, and a second intermediate layer containing an antistatic agent being provided between the substrate layer and the anti-sticking layer, the content of the antistatic agent in the anti-sticking layer being lower than the content of the antistatic agent in the second intermediate layer. When the second optical sheet according to the present disclosure is placed in an environment of 65° C. and 95% RH for 48 hours, the area ratio of contaminated regions on the surface of the coating layer may be less than 20%.

[0012] A backlight unit according to the present disclosure includes a light source and the first or second optical sheet according to the present disclosure. The backlight unit according to the present disclosure includes the first or second optical sheet according to the present disclosure, which can prevent contamination of the optical sheet surface caused by the antistatic agent, thereby preventing a decrease in brightness. In the backlight unit according to the present disclosure, the first or second optical sheet according to the present disclosure may be, for example, a light diffusion sheet.

[0013] A liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure and a liquid crystal display panel. The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure, and thus can suppress a decrease in brightness on the display screen.

[0014] The information device according to the present disclosure includes the liquid crystal display device according to the present disclosure. The information device according to the present disclosure includes the liquid crystal display device according to the present disclosure, and therefore, it is possible to suppress a decrease in brightness on the display screen.

[0015] According to the present disclosure, an optical sheet can be provided that can suppress surface contamination caused by an antistatic agent.

[0016] 1 is a schematic cross-sectional view showing a backlight unit according to an embodiment; FIG. 2 is a schematic cross-sectional view showing a light diffusion sheet according to an embodiment; FIG. 3 is a schematic cross-sectional view showing a liquid crystal display device according to an embodiment; FIG. 4 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 1; FIG. 5 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 2; FIG. 6 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 3; FIG. 7 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 4; FIG. 8 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 5; FIG. 9 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 6; FIG. 10 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 7; FIG. 11 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 8; FIG. 12 is a schematic cross-sectional view showing a light diffusion sheet according to Modification 9; FIG. 13 is a schematic perspective view showing a conventional edge-lit backlight unit.

[0017] (Embodiments) Hereinafter, optical sheets, backlight units, liquid crystal display devices, and information devices according to embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments, and can be modified as desired within the scope of the technical concept of the present disclosure. In addition, in this disclosure, the "front side" refers to the viewer side of the liquid crystal display device, and the "rear side" refers to the opposite side.

[0018] <Backlight Unit> FIG. 1 is a schematic cross-sectional view showing a backlight unit according to this embodiment, and FIG. 2 is a schematic cross-sectional view showing an upper light diffusion sheet according to this embodiment.

[0019] The backlight unit shown in Figure 1 is an edge-lit type backlight unit, and includes a light guide sheet 1 that guides light rays incident from an end face to the front face side, a light source 2 that irradiates light rays toward the end face of the light guide sheet 1, a lower light diffusion sheet 3 that is superimposed on the front face side of the light guide sheet 1, a prism sheet 4 that is arranged on the front face side of the lower light diffusion sheet 3, an upper light diffusion sheet 5 that is superimposed on the front face side of the prism sheet 4, and a reflective sheet 6 that is arranged on the back face side of the light guide sheet 1.

[0020] The lower light diffusion sheet 3 diffuses light rays incident from the back side while concentrating them in the normal direction (i.e., concentrating and diffusing light). The prism sheet 4 refracts light rays incident from the back side toward the normal direction. The upper light diffusion sheet 5 slightly diffuses light rays incident from the back side to suppress brightness unevenness caused by the shape of the prism parts of the prism sheet 4, etc. The reflective sheet 6 reflects light rays emitted from the back side of the light guide sheet 1 toward the front side, allowing them to enter the light guide sheet 1 again.

[0021] <Upward Light Diffusion Sheet> As shown in Figures 1 and 2, the upward light diffusion sheet 5 is disposed on the surface side of the prism sheet 4, and in this embodiment, it is particularly superimposed directly on the surface of the prism sheet 4 (without any other sheet interposed therebetween). The upward light diffusion sheet 5 includes a base layer 11 and a coating layer 12 laminated on the surface side of the base layer 11. The coating layer 12 is a light diffusion layer. The upward light diffusion sheet 5 is configured as a two-layer structure of the base layer 11 and the coating layer 12.

[0022] The base layer 11 is formed mainly from a transparent (e.g., colorless and transparent) synthetic resin, since it is necessary for the base layer 11 to transmit light. The main component of the base layer 11 is not particularly limited, and examples of the main component of the base layer 11 include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. The term "main component" refers to the component with the highest content, e.g., a component with a content of 50% by mass or more.

[0023] The lower limit of the average thickness of the substrate layer 11 is preferably about 10 μm, more preferably about 35 μm, and even more preferably about 50 μm. On the other hand, the upper limit of the average thickness of the substrate layer 11 is preferably about 500 μm, more preferably about 250 μm, and even more preferably about 188 μm. If the average thickness of the substrate layer 11 is less than the lower limit, curling may occur when the coating layer 12 is formed by coating. Conversely, if the average thickness of the substrate layer 11 exceeds the upper limit, the brightness of the liquid crystal display device may decrease and the demand for a thinner liquid crystal display device may not be met. Note that the "average thickness" refers to the average value of thicknesses at any 10 points.

[0024] The coating layer 12 constitutes the outermost surface of the upper light diffusion sheet 5. The coating layer 12 has a resin matrix 13 and resin beads 14 dispersed in the resin matrix 13. The coating layer 12 contains the resin beads 14 dispersed at a substantially uniform density. The resin beads 14 are surrounded by the resin matrix 13. By dispersing the resin beads 14 in the resin matrix 13, minute irregularities are formed on the surface of the coating layer 12, and these irregularities allow the coating layer 12 to diffuse light to the outside. The resin beads 14 may be inorganic particles. Examples of inorganic particles that can be used include inorganic beads such as silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, and mixtures thereof.

[0025] The lower limit of the average thickness of the coating layer 12 is, for example, about 1 μm, and more preferably about 2 μm. On the other hand, the upper limit of the average thickness of the coating layer 12 is, for example, about 20 μm, and more preferably about 15 μm. If the average thickness of the coating layer 12 is less than the lower limit, the resin beads 14 cannot be reliably fixed by the resin matrix 13, and the resin beads 14 may fall off from the coating layer 12. Conversely, if the average thickness of the coating layer 12 exceeds the upper limit, it becomes difficult to form minute, high-density irregularities on the surface of the coating layer 12, and as a result, it may be difficult to sufficiently suppress glare caused by interference with the cell arrangement of the liquid crystal panel disposed on the surface side of the upper light diffusion sheet 5.

[0026] The resin matrix 13 must be light-transmitting, and is therefore primarily composed of a transparent (particularly colorless and transparent) synthetic resin. Examples of suitable synthetic resins include thermosetting resins and active energy ray-curable resins. Examples of suitable thermosetting resins include epoxy resins, silicone resins, phenolic resins, urea resins, unsaturated polyester resins, melamine resins, alkyd resins, polyimide resins, acrylic resins, amide-functional copolymers, and urethane resins. Examples of suitable active energy ray-curable resins include ultraviolet-curable resins that crosslink and cure upon irradiation with ultraviolet light, and electron-beam-curable resins that crosslink and cure upon irradiation with electron beams. These resins may be appropriately selected from polymerizable monomers and polymerizable oligomers. To improve adhesion to the substrate layer 11 and prevent the resin beads 14 from falling off the coating layer 12, examples of suitable active energy ray-curable resins include acrylic, urethane, or acrylic urethane-based ultraviolet-curable resins.

[0027] In this embodiment, an antistatic agent is added to the resin matrix 13. That is, the coating layer 12 contains an antistatic agent. The type of antistatic agent is not particularly limited as long as it does not contain PFAS (an organic fluorine compound). For example, various antistatic agents, such as electron-conductive, ion-conductive, and conjugated electron-conductive, may be used. Examples of electron-conductive antistatic agents include metals and metal oxides such as indium tin oxide (ITO), aluminum-doped zinc oxide (ZZAO), and antimony tin oxide. Examples of ion-conductive antistatic agents include nonionic types (glycerin fatty acid esters, polyoxyethylene alkyl ether salts, polyoxyethylene alkylamines, alkyldiethanolamides, etc.), anionic types (alkyl sulfonates, alkylbenzene sulfonates, alkyl phosphates, etc.), cationic types (tetraalkylammonium salts, trialkylbenzylammonium salts, etc.), and amphoteric types (alkylpentaine, alkylimidazolium pentaine, etc.). Examples of conjugated electron type antistatic agents include polythiophene, polyacetylene, polypyrrole, and polyaniline.

[0028] In this embodiment, depending on the type of antistatic agent selected, the amount of the antistatic agent added, the material of the resin matrix 13, and crosslinking control can be adjusted to suppress the area ratio of contaminated areas on the surface of the coating layer 12 to less than 20% even when the upper light diffusion sheet 5 is placed in an environment of 65°C and 95% RH for 48 hours. To achieve this, a polymeric ion-conductive antistatic agent may be used. Examples of polymeric ion-conductive antistatic agents include polyether types (polyethylene oxide, polyetheramideimide, etc.), quaternary ammonium salt types (methacrylimide copolymer, maleimide copolymer, etc.), sulfonic acid types (polystyrene sulfonate, etc.), betaine types (carbobetaine graft copolymer, etc.), and electrolytic polymer copper conjugates.

[0029] Alternatively, when an ionic liquid such as the AS series manufactured by ADEKA Corporation or the Elexcel (registered trademark) IL or AS series manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., or a reactive emulsifier such as the ADEKA REASOAP SR, SE, ER or NE series manufactured by ADEKA Corporation is used as the antistatic agent, the amount of foreign matter such as lumps or crystals generated due to the antistatic agent can be particularly reduced.

[0030] The resin matrix 13 may contain additives other than the antistatic agent. Examples of additives that can be used include silicone-based additives and fluorine-based additives. The content of the additives in the resin matrix 13, calculated as solid content, relative to 100 parts by mass of the synthetic resin component may be, for example, 0.05 parts by mass or more and 5 parts by mass or less.

[0031] The resin beads 14 are resin particles that have the property of transmitting and diffusing light. The resin beads 14 are formed primarily from a transparent, particularly colorless and transparent, synthetic resin. Examples of the primary component of the resin beads 14 include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, and polyacrylonitrile. The shape of the resin beads 14 is not particularly limited and may be, for example, spherical, cubic, needle-like, rod-like, spindle-like, plate-like, scale-like, or fibrous. However, spherical shapes are particularly preferred because of their excellent light diffusion properties.

[0032] The particle size of the resin beads 14 is preferably equal to or greater than the wavelength of the light emitted by the light source 2 (hereinafter also referred to as the light source wavelength) and is as small as possible, and the upper limit of the average particle size of the resin beads 14 may be, for example, about 2 μm, more preferably about 1 μm. If the average particle size of the resin beads 14 is less than the light source wavelength, the unevenness on the surface of the coating layer 12 will be too small, resulting in insufficient light diffusion and the risk of not being able to sufficiently suppress the occurrence of brightness unevenness due to the shape of the prism portions of the prism sheet 4. Conversely, if the average particle size of the resin beads 14 exceeds the upper limit, numerous relatively large unevenness will be formed on the surface of the coating layer 12, which may not be able to sufficiently suppress the occurrence of glare due to interference with the cell arrangement of the liquid crystal panel.

[0033] The lower limit of the refractive index of the resin beads 14 is preferably 1.46, and more preferably 1.48, for example. On the other hand, the upper limit of the refractive index of the resin beads 14 is preferably 1.60, and more preferably 1.59, for example. By setting the refractive index of the resin beads 14 within the above range, the difference in refractive index from the resin matrix 13 can be adjusted appropriately (for example, to 0.05 or less), which makes it easier to suppress brightness unevenness caused by the shape of the protruding prism portions of the prism sheet 4. Note that the "refractive index" refers to the refractive index for light with a wavelength of 589.3 nm (the D line of sodium).

[0034] The lower limit of the arithmetic mean roughness Ra of the surface of the coating layer 12 (i.e., the surface of the upper light diffusion sheet 5) may be, for example, about 0.1 μm, more preferably about 0.2 μm. On the other hand, the upper limit of the arithmetic mean roughness Ra of the surface of the coating layer 12 may be, for example, about 1.5 μm, more preferably about 1.0 μm. If the arithmetic mean roughness Ra of the surface of the coating layer 12 is less than the lower limit, the surface irregularities of the coating layer 12 may be too small, resulting in insufficient light diffusion and insufficient suppression of brightness variations due to the shape of the protruding prisms of the prism sheet 4. Conversely, if the arithmetic mean roughness Ra of the surface of the coating layer 12 exceeds the upper limit, numerous relatively large irregularities may be formed on the surface of the coating layer 12, resulting in insufficient suppression of glare due to interference with the cell arrangement of the liquid crystal panel. The "arithmetic mean roughness Ra" refers to a value measured in accordance with JIS B0601-1994.

[0035] The lower limit of the content of the resin matrix 13 in the coating layer 12 may be, for example, about 10% by mass, more preferably about 20% by mass. On the other hand, the upper limit of the content of the resin matrix 13 in the coating layer 12 may be, for example, about 80% by mass, more preferably about 75% by mass. If the content of the resin matrix 13 is less than the lower limit, the light diffusibility of the coating layer 12 may be too high, resulting in an insufficient brightness of the liquid crystal display device. Conversely, if the content of the resin matrix 13 exceeds the upper limit, the number of resin beads 14 in the coating layer 12 may be insufficient, making it difficult to form minute, high-density irregularities on the surface of the coating layer 12. This may result in insufficient suppression of glare due to interference with the cell arrangement of the liquid crystal panel disposed on the surface side of the upper light diffusion sheet 5.

[0036] The lower limit of the content of resin beads 14 in the coating layer 12 may be, for example, about 20% by mass, more preferably about 25% by mass. On the other hand, the upper limit of the content of resin beads 14 in the coating layer 12 may be, for example, about 90% by mass, more preferably about 80% by mass. If the content of resin beads 14 in the coating layer 12 is less than the lower limit, it may be difficult to form minute, high-density irregularities on the surface of the coating layer 12, which may result in insufficient suppression of glare due to interference with the cell arrangement of the liquid crystal panel disposed on the surface side of the upper light diffusion sheet 5. Conversely, if the content of resin beads 14 in the coating layer 12 exceeds the upper limit, the light diffusivity of the coating layer 12 may be too high, resulting in insufficient brightness of the liquid crystal display device.

[0037] The lower limit of the haze value of the upper light diffusion sheet 5 may be, for example, about 10%, more preferably about 30%, and even more preferably about 40%. On the other hand, the upper limit of the haze value of the upper light diffusion sheet 5 may be about 90%, more preferably about 70%. If the haze value of the upper light diffusion sheet 5 is less than the lower limit, brightness unevenness caused by the shape of the protruding prism portion of the prism sheet 4 may not be sufficiently suppressed. Conversely, if the haze value of the upper light diffusion sheet 5 exceeds the upper limit, the brightness of the liquid crystal display device may be insufficient. Note that "haze value" refers to a value measured in accordance with JIS K 7136:2000.

[0038] <Method for manufacturing upper light diffusion sheet> The method for manufacturing the upper light diffusion sheet 5 is not particularly limited, but may include, for example, a step of forming a sheet body that constitutes the base layer 11 (hereinafter referred to as the base layer formation step) and a step of laminating a coating layer 12 on one side of this sheet body (hereinafter referred to as the light diffusion layer lamination step).

[0039] The base layer forming step is not particularly limited, but for example, a method can be used in which a molten thermoplastic resin is extruded through a T-die and then the extruded product is stretched in the layer longitudinal direction and layer width direction to form a sheet. Well-known extrusion molding methods using a T-die include, for example, the polishing roll method and the chill roll method. Furthermore, a method for stretching the sheet can include, for example, a tubular film biaxial stretching method and a flat film biaxial stretching method.

[0040] The light diffusion layer lamination process may include, for example, a process of preparing a coating liquid containing a resin matrix 13 and resin beads 14 (hereinafter referred to as a preparation process), a process of applying the coating liquid prepared in the preparation process to one side of a sheet body (hereinafter referred to as a coating process), and a process of drying and curing the coating liquid applied in the coating process (hereinafter referred to as a curing process). In the preparation process, a coating liquid containing an active energy ray-curable resin as the main component of the resin matrix 13 and also containing the resin beads 14 may be prepared. In the method for producing an upper light diffusion sheet, if an active energy ray-curable resin is used as the main component of the resin matrix 13, after the coating liquid is applied in the application process, the active energy ray-curable resin can be easily cured relatively quickly by irradiating it with ultraviolet light, for example, in the curing process. Furthermore, in the preparation process of the manufacturing method for the upper light diffusion sheet, a coating liquid containing a large amount of resin beads 14 with a small particle size and a small amount of resin beads with a large particle size is prepared, whereby the small particle size resin beads can suppress the occurrence of glare caused by interference with the cell arrangement of the liquid crystal panel, while the large particle size resin beads can prevent sticking with the liquid crystal panel.

[0041] The manufacturing method of the upper light diffusion sheet 5 may further include a surface treatment step, prior to the light diffusion layer lamination step, in which corona discharge treatment, ozone treatment, low-temperature plasma treatment, glow discharge treatment, oxidation treatment, primer coating treatment, undercoat treatment, anchor coating treatment, etc. is performed on the surface of the sheet body on which the light diffusion layer is to be laminated.

[0042] <Prism Sheet> Because the prism sheet 4 needs to transmit light rays, it is formed primarily from a transparent (e.g., colorless and transparent) synthetic resin. The prism sheet 4 has a base layer 15 and a protrusion row consisting of a plurality of protruding prism portions 16 laminated on the surface of the base layer 15. The protruding prism portions 16 are laminated in a striped pattern on the surface of the base layer 15. The protruding prism portions 16 are triangular prisms whose back surfaces are in contact with the surface of the base layer 15.

[0043] The lower limit of the thickness of the prism sheet 4 (the height from the rear surface of the base layer 15 to the apex of the protruding prism portion 16) may be, for example, about 50 μm, more preferably about 100 μm. Meanwhile, the upper limit of the thickness of the prism sheet 4 may be, for example, about 200 μm, more preferably about 180 μm. The lower limit of the pitch p (see FIG. 2 ) of the protruding prism portions 16 in the prism sheet 4 may be, for example, about 20 μm, more preferably about 30 μm. Meanwhile, the upper limit of the pitch p of the protruding prism portions 16 in the prism sheet 4 may be, for example, about 100 μm, more preferably about 60 μm. The apex angle of the protruding prism portions 16 may be, for example, 85° or more and 95° or less. The lower limit of the refractive index of the protruding prism portions 16 may be, for example, 1.5, more preferably 1.55. Meanwhile, the upper limit of the refractive index of the protruding prism portions 16 may be, for example, 1.7.

[0044] The backlight unit of this embodiment shown in FIG. 1 is not limited to having only one prism sheet 4, and may further include another prism sheet superimposed on the prism sheet 4. In this case, it is preferable that the ridge lines of the multiple protruding prism portions 16 of the prism sheet 4 and the ridge lines of the multiple protruding prism portions of the other prism sheet are perpendicular to each other. In this way, light rays incident from the lower light diffusion sheet 3 can be refracted toward the normal direction by one prism sheet, and light rays emitted from the prism sheet can be refracted by the other prism sheet so as to travel approximately perpendicular to the rear surface of the upper light diffusion sheet 5. The material, thickness, pitch of the protruding prism portions, apex angle of the protruding prism portions, and refractive index of the protruding prism portions of the other prism sheet may be the same as those of the prism sheet 4.

[0045] <Under-use light diffusion sheet> The under-use light diffusion sheet 3 has a base layer 17, a coating layer 18 disposed on the front side of the base layer 17, and an anti-sticking layer 19 disposed on the back side of the base layer 17. The coating layer 18 is a light diffusion layer and constitutes the outermost surface of the under-use light diffusion sheet 3. The base layer 17 of the under-use light diffusion sheet 3 may have a configuration similar to that of the base layer 11 of the above-mentioned upper-use light diffusion sheet 5. The coating layer 18 of the under-use light diffusion sheet 3 has a light diffusing agent and a binder therefor. The coating layer 18 of the under-use light diffusion sheet 3 may contain an antistatic agent similar to that of the coating layer 12 of the above-mentioned upper-use light diffusion sheet 5.

[0046] The light diffusing agent used in the coating layer 18 is a particle having the property of diffusing light rays, and is roughly classified into inorganic fillers and organic fillers. Examples of inorganic fillers that can be used include silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, and mixtures thereof. Examples of organic fillers that can be used include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, and polyacrylonitrile. The shape of the light diffusing agent is not particularly limited and may be, for example, spherical, cubic, needle-like, rod-like, spindle-like, plate-like, scale-like, fibrous, or the like, although spherical shapes are preferred due to their excellent light diffusing properties.

[0047] The lower limit of the average particle diameter of the light diffusing agent used in the coating layer 18 may be, for example, about 1 μm, more preferably about 2 μm. On the other hand, the upper limit of the average particle diameter of the light diffusing agent may be, for example, about 50 μm, more preferably about 20 μm, and even more preferably about 15 μm. If the average particle diameter of the light diffusing agent is less than the lower limit, the unevenness of the surface of the coating layer 18 may be small, and the light diffusing properties required for the lower light diffusing sheet 3 may not be achieved. Conversely, if the average particle diameter of the light diffusing agent exceeds the upper limit, the thickness of the lower light diffusing sheet 3 may increase, and uniform diffusion may become difficult.

[0048] The lower limit of the binder content in the coating layer 18 may be, for example, about 15% by mass, more preferably about 30% by mass. On the other hand, the upper limit of the binder content in the coating layer 18 may be, for example, about 48% by mass, more preferably about 45% by mass. If the binder content is less than the lower limit, the light diffusing agent may not be reliably fixed by the binder. Conversely, if the binder content exceeds the upper limit, the light diffusing properties may be insufficient.

[0049] The lower limit of the content of the light diffusing agent in the coating layer 18 may be, for example, about 52% by mass, more preferably about 55% by mass. On the other hand, the upper limit of the content of the light diffusing agent in the coating layer 18 may be, for example, about 85% by mass, more preferably about 70% by mass. If the content of the light diffusing agent is less than the lower limit, the light diffusing properties may be insufficient. Conversely, if the content of the light diffusing agent exceeds the upper limit, the light diffusing agent may not be securely fixed by the binder.

[0050] The lower limit of the arithmetic mean roughness Ra of the surface of the coating layer 18 may be, for example, about 0.1 μm, more preferably about 0.2 μm. On the other hand, the upper limit of the arithmetic mean roughness Ra of the surface of the coating layer 18 may be, for example, about 5 μm, more preferably about 3 μm, and even more preferably about 2 μm. If the arithmetic mean roughness Ra of the surface of the coating layer 18 is less than the lower limit, the light diffusibility may be insufficient. Conversely, if the arithmetic mean roughness Ra of the surface of the coating layer 18 exceeds the upper limit, the light transmittance may decrease, resulting in insufficient brightness of the liquid crystal display device.

[0051] The anti-sticking layer 19 is formed by dispersing resin beads in a resin matrix. These resin beads are arranged in a scattered manner on the back surface side of the base layer 17. Due to the scattered arrangement of the resin beads, the anti-sticking layer 19 has a plurality of convex portions formed by the resin beads and flat portions where no resin beads are present. The anti-sticking layer 19 comes into scattered contact with the light guide sheet 1 arranged on the back surface side at the plurality of convex portions, but does not come into contact over the entire back surface, thereby preventing sticking and suppressing brightness unevenness in the liquid crystal display device.

[0052] The lower limit of the haze value of the lower-use light diffusion sheet 3 may be, for example, about 80%, more preferably about 85%, and even more preferably about 90%. If the haze value of the lower-use light diffusion sheet 3 is less than the lower limit, the light diffusion properties may be insufficient. The upper limit of the haze value of the lower-use light diffusion sheet 3 may be, for example, about 95%.

[0053] <Light Guide Sheet> The light guide sheet 1 is a sheet-like optical component that propagates light emitted from the light source 2 inside and then emits it from its surface. The light guide sheet 1 may be formed with a generally wedge-shaped cross section or a generally flat plate-like shape. The light guide sheet 1 must be translucent and is therefore formed primarily from a transparent (e.g., colorless and transparent) resin. The primary component of the light guide sheet 1 is not particularly limited, but may be a synthetic resin such as polycarbonate, which has excellent transparency and strength, or acrylic resin, which has excellent transparency and scratch resistance. Polycarbonate has excellent transparency and a high refractive index. Therefore, when the light guide sheet 1 is primarily composed of polycarbonate, total reflection is more likely to occur at the interface with the air layer (the layer formed in the gap between the light guide sheet 1 and the lower light diffusion sheet 3, and the layer formed in the gap between the light guide sheet 1 and the reflective sheet 6), thereby enabling efficient propagation of light. Furthermore, since polycarbonate has heat resistance, it is less likely to deteriorate due to heat generated by the light source 2 .

[0054] <Light Source> The light source 2 is arranged so that its irradiation surface faces (or abuts) the end face of the light guide sheet 1. Various light sources, for example, light-emitting diodes (LEDs), can be used as the light source 2. Specifically, a plurality of LEDs arranged along the end face of the light guide sheet 1 can be used as the light source 2.

[0055] <Reflective sheet> As the reflective sheet 6, for example, a white sheet in which a filler is dispersed in a base resin such as polyester, or a mirror sheet in which the specular reflectivity is enhanced by vapor-depositing a metal such as aluminum or silver onto the surface of a film made of polyester or the like can be used.

[0056] <Liquid Crystal Display Device> FIG. 3 is a schematic cross-sectional view showing a liquid crystal display device according to this embodiment.

[0057] The liquid crystal display device shown in Fig. 3 has a configuration in which a liquid crystal panel 31 is disposed on the front surface side (the front surface side of the upper light diffusion sheet 5) of the backlight unit shown in Fig. 1. That is, the liquid crystal display device shown in Fig. 3 includes a light guide sheet 1 that guides light rays incident from an end face to the front surface side, a light source 2 that irradiates light rays toward the end face of the light guide sheet 1, a lower light diffusion sheet 3 superimposed on the front surface side of the light guide sheet 1, a prism sheet 4 disposed on the front surface side of the lower light diffusion sheet 3, an upper light diffusion sheet 5 superimposed on the front surface side of the prism sheet 4, a reflective sheet 6 disposed on the back surface side of the light guide sheet 1, and the liquid crystal panel 31 superimposed on the front surface side of the upper light diffusion sheet 5.

[0058] The liquid crystal panel 31 is disposed directly (without any other sheets interposed therebetween) on the surface of the upper light diffusion sheet 5. The liquid crystal panel 31 has a front-side polarizing plate 32 and a back-side polarizing plate 33 disposed substantially parallel to each other with a predetermined gap therebetween, and a liquid crystal cell 34 disposed therebetween. The front-side polarizing plate 32 and the back-side polarizing plate 33 each include a polarizer such as an iodine-based polarizer, a dye-based polarizer, or a polyene-based polarizer, and a pair of transparent protective films disposed on both sides of the polarizer. The transmission axis directions of the front-side polarizing plate 32 and the back-side polarizing plate 33 are orthogonal to each other.

[0059] The liquid crystal cell 34 has a function of controlling the amount of light transmitted therethrough, and various known liquid crystal cells can be used. The liquid crystal cell 34 is generally a laminated structure including a substrate, a color filter, a counter electrode, a liquid crystal layer, a pixel electrode, a substrate, etc. A transparent conductive film such as ITO is used for the pixel electrode. The display mode of the liquid crystal cell 34 may be, for example, twisted nematic (TN), virtual alignment (VA), in-place switching (IPS), ferroelectric liquid crystal (FLC), anti-ferroelectric liquid crystal (AFLC), optically compensatory bend (OCB), super twisted nematic (STN), hybrid aligned nematic (HAN), etc. The pixel pitch of the liquid crystal panel 31 (pixel pitch of the liquid crystal cell) may be, for example, about 25 μm or less.

[0060] <Modification 1 of Top Light Diffusion Sheet> The top light diffusion sheet 5 of this modification differs from the top light diffusion sheet 5 of the embodiment shown in FIG. 2 in that the coating layer 12 does not substantially contain an antistatic agent, and an adhesive layer 21 containing an antistatic agent is provided between the substrate layer 11 and the coating layer 12, as shown in FIG. 4 . That is, the top light diffusion sheet 5 of this modification is configured as a three-layer structure of the substrate layer 11, the adhesive layer 21, and the coating layer 12. The adhesive layer 21 is a first intermediate layer. The adhesive layer 21 may contain the same antistatic agent as the coating layer 12 of the embodiment. The adhesive layer 21 may be a primer layer or an easy-adhesive layer that bonds the substrate layer 11 and the coating layer 12, to which an antistatic agent has been added.

[0061] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 does not substantially contain an antistatic agent, and an adhesive layer containing an antistatic agent may be provided between the base layer 17 and the coating layer 18, as in this modified example.

[0062] <Modification 2 of Top Light Diffusion Sheet> The top light diffusion sheet 5 of this modification differs from the top light diffusion sheet 5 of Modification 1 shown in Fig. 4 in that, instead of the adhesive layer 21 containing an antistatic agent, it has an adhesive layer 22 that is substantially free of an antistatic agent and a thin layer 23 that contains an antistatic agent, as shown in Fig. 5 . That is, the top light diffusion sheet 5 of this modification is configured as a four-layer structure including a substrate layer 11, an adhesive layer 22, a thin layer 23, and a coating layer 12. The thin layer 23 is a first intermediate layer. The thin layer 23 may contain an antistatic agent similar to that of the coating layer 12 of the above embodiment. The thin layer 23 may be made of the same resin as that of the coating layer 12 of the above embodiment, to which an antistatic agent has been added.

[0063] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 does not substantially contain an antistatic agent, and an adhesive layer that does not substantially contain an antistatic agent and a thin layer that contains an antistatic agent may be provided between the base layer 17 and the coating layer 18, as in this modified example.

[0064] <Modification 3 of Top-Application Light Diffusion Sheet> The top-application light diffusion sheet 5 of this modification differs from the top-application light diffusion sheet 5 of Modification 1 shown in Fig. 4 in that, as shown in Fig. 6, a thin layer 23 similar to that of Modification 2 is provided between the adhesive layer 21 similar to that of Modification 1 and the coating layer 12. That is, the top-application light diffusion sheet 5 of this modification is configured as a four-layer structure of the base layer 11, adhesive layer 21, thin layer 23, and coating layer 12. The adhesive layer 21 is a first intermediate layer, and the thin layer 23 is a second intermediate layer.

[0065] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 does not substantially contain an antistatic agent, and an adhesive layer and a thin layer each containing an antistatic agent may be provided between the base layer 17 and the coating layer 18, as in this modified example.

[0066] <Modification 4 of Top Light Diffusion Sheet> The top light diffusion sheet 25 of this modification differs from the top light diffusion sheet 5 of the embodiment shown in Fig. 2 in that, as shown in Fig. 7, an anti-sticking layer 26 is provided on the back surface side of the base layer 11. The top light diffusion sheet 25 of this modification shown in Fig. 7 can be applied to the backlight unit shown in Fig. 1 in place of the top light diffusion sheet 5 of the embodiment. That is, the top light diffusion sheet 25 of this modification also slightly diffuses light rays incident from the back surface side to suppress brightness unevenness caused by the shape of the protruding prism portions 16 of the prism sheet 4, and suppresses glare caused by interference with the cell arrangement of a liquid crystal panel (not shown) disposed on the front surface side of the top light diffusion sheet 25.

[0067] The upper light diffusion sheet 25 of this modified example includes a base material layer 11, a coating layer 12 laminated on the front side of the base material layer 11, and an anti-sticking layer 26 laminated on the back side of the base material layer 11. The upper light diffusion sheet 25 is configured as a three-layer structure of the base material layer 11, the coating layer 12, and the anti-sticking layer 26. The base material layer 11 and the coating layer 12 of the upper light diffusion sheet 25 may have the same configuration as the base material layer 11 and the coating layer 12 of the upper light diffusion sheet 5 of the above embodiment.

[0068] The anti-sticking layer 26 forms the back surface of the upper light diffusion sheet 25. Because the anti-sticking layer 26 must transmit light, it is formed primarily from a transparent (e.g., colorless and transparent) synthetic resin. The anti-sticking layer 26 is formed as a film with a flat back surface and a substantially uniform thickness. The anti-sticking layer 26 is configured to partially abut against the apexes of the protruding prism portions 16 of the prism sheet 4 disposed on the back surface of the upper light diffusion sheet 25, thereby preventing sticking with the prism sheet 4. Examples of the main component of the anti-sticking layer 26 that can be used include polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, methyl (meth)acrylate-styrene copolymer, polyolefin, cycloolefin polymer, cycloolefin copolymer, cellulose acetate, weather-resistant vinyl chloride, and active energy ray-curable resin. In particular, when an acrylic resin is used as the main component of the sticking prevention layer 26, the strength of the back surface of the upper light diffusion sheet 25 is increased, and it becomes easier to prevent the back surface from being scratched.

[0069] The lower limit of the average thickness of the anti-sticking layer 26 may be, for example, about 1 μm, more preferably about 2 μm. On the other hand, the upper limit of the average thickness of the anti-sticking layer 26 may be, for example, about 10 μm, more preferably about 8 μm. If the average thickness of the anti-sticking layer 26 is less than the lower limit, scratches on the back surface of the upper light diffusion sheet 25 may not be reliably prevented. Conversely, if the average thickness of the anti-sticking layer 26 exceeds the upper limit, the brightness of the liquid crystal display device may decrease.

[0070] The upper limit of the arithmetic mean roughness Ra of the back surface of the anti-sticking layer 26 may be, for example, about 0.04 μm, more preferably about 0.035 μm, and even more preferably about 0.03 μm. If the arithmetic mean roughness Ra of the back surface of the anti-sticking layer 26 exceeds the upper limit, there is a risk that the protruding prism portions 16 of the prism sheet 4 may be scratched due to contact with the anti-sticking layer 26. The lower limit of the arithmetic mean roughness Ra of the back surface of the anti-sticking layer 26 is not particularly limited, and may be, for example, 0.01 μm.

[0071] The manufacturing method of the upper light diffusion sheet 25 may include, for example, a step of forming a sheet body that constitutes the base layer 11 (hereinafter referred to as a base layer forming step), a step of laminating a coating layer 12 on one side of the sheet body (hereinafter referred to as a light diffusion layer laminating step), and a step of laminating an anti-sticking layer 26 on the other side of the sheet body that constitutes the base layer 11 (hereinafter referred to as an anti-sticking layer laminating step).As the anti-sticking layer laminating step, for example, a method of forming the anti-sticking layer 26 simultaneously with the sheet body that constitutes the base layer 11 by co-extrusion, a method of laminating the anti-sticking layer 26 by coating the other side of the sheet body, or the like can be used.

[0072] As described above, the base layer forming step in the manufacturing method of the upper light diffusion sheet 25 may be performed simultaneously with the anti-sticking layer laminating step by co-extrusion, or may be performed separately from the anti-sticking layer laminating step. When the base layer forming step and the anti-sticking layer forming step are performed separately, the base layer forming step can be performed in the same manner as the base layer forming step of the upper light diffusion sheet 5 of the above embodiment. Furthermore, the light diffusion layer laminating step in the manufacturing method of the upper light diffusion sheet 25 can also be performed in the same manner as the light diffusion layer laminating step of the upper light diffusion sheet 5 of the above embodiment.

[0073] In the upper light diffusion sheet 25 of this modified example, an anti-sticking layer 26 is laminated on the back side of the base material layer 11, so that uneven brightness caused by the shape of the protruding prism portion 16 of the prism sheet 4 can be suppressed, while improving the sticking prevention with the prism sheet 4 and the scratch prevention of the back side of the upper light diffusion sheet 25.

[0074] In the upper light diffusion sheet 25 of this modified example, the anti-sticking layer 26 may contain the same antistatic agent as in the coating layer 12 of the above embodiment.

[0075] In the lower light diffusion sheet 3 (see FIG. 1) of the embodiment, the anti-sticking layer 19 may contain an antistatic agent, as in this modification.

[0076] <Modification 5 of Top Light Diffusion Sheet> The top light diffusion sheet 5 of this modification differs from the top light diffusion sheet 5 of Modification 1 shown in FIG. 4 in that, as shown in FIG. 8 , an anti-sticking layer 26 similar to that of Modification 4 is provided on the back side of the substrate layer 11. However, in this modification, the anti-sticking layer 26 does not substantially contain an antistatic agent. Furthermore, in this modification, an adhesive layer 27 containing an antistatic agent is provided between the substrate layer 11 and the anti-sticking layer 26. That is, the top light diffusion sheet 5 of this modification has a five-layer structure including the anti-sticking layer 26, the adhesive layer 27, the substrate layer 11, the adhesive layer 21, and the coating layer 12. The adhesive layer 27 is a second intermediate layer. The adhesive layer 27 may contain an antistatic agent similar to that of the coating layer 12 of the above embodiment. The adhesive layer 27 may be a primer layer or an easy-adhesive layer that bonds the substrate layer 11 and the anti-sticking layer 26, to which an antistatic agent has been added.

[0077] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 and the anti-sticking layer 19 do not substantially contain an antistatic agent, and adhesive layers containing an antistatic agent may be provided between the base layer 17 and the coating layer 18, and between the base layer 17 and the anti-sticking layer 19, as in this modified example.

[0078] <Modification 6 of Top-Application Light Diffusion Sheet> The top-application light diffusion sheet 5 of this modification differs from the top-application light diffusion sheet 5 of the embodiment shown in Fig. 2 in that, as shown in Fig. 9, an adhesive layer 22 that does not substantially contain an antistatic agent is provided between the base material layer 11 and the coating layer 12. That is, the top-application light diffusion sheet 5 of this modification is configured as a three-layer structure of the base material layer 11, the adhesive layer 22, and the coating layer 12. The adhesive layer 22 is an intermediate layer.

[0079] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 contains an antistatic agent, and an adhesive layer that does not substantially contain an antistatic agent may be provided between the base layer 17 and the coating layer 18, as in this modified example.

[0080] <Modification 7 of Upper Light Diffusion Sheet> The upper light diffusion sheet 5 of this modification differs from the upper light diffusion sheet 5 of the embodiment shown in FIG. 2 in that, as shown in FIG. 10 , an adhesive layer 51 containing an antistatic agent is provided between the substrate layer 11 and the coating layer 12, and the content of the antistatic agent in the coating layer 12 is lower than the content of the antistatic agent in the adhesive layer 51. That is, the upper light diffusion sheet 5 of this modification is configured as a three-layer structure of the substrate layer 11, the adhesive layer 51, and the coating layer 12. The adhesive layer 51 is a first intermediate layer. The adhesive layer 51 may contain the same antistatic agent as the coating layer 12 of the embodiment. The adhesive layer 51 may be a primer layer or an easy-adhesive layer that bonds the substrate layer 11 and the coating layer 12, to which an antistatic agent has been added.

[0081] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 contains an antistatic agent, and an adhesive layer containing an antistatic agent is provided between the base layer 17 and the coating layer 18, as in this modified example, and the content of the antistatic agent in the coating layer 18 may be lower than the content of the antistatic agent in the adhesive layer.

[0082] <Modification 8 of Top Light Diffuser Sheet> The top light diffuser sheet 5 of this modification differs from the top light diffuser sheet 5 of Modification 7 shown in FIG. 10 in that, as shown in FIG. 11 , an anti-sticking layer 26 similar to that of Modification 4 is provided on the back side of the substrate layer 11. However, in this modification, the anti-sticking layer 26 does not substantially contain an antistatic agent. Furthermore, in this modification, an adhesive layer 52 containing an antistatic agent is provided between the substrate layer 11 and the anti-sticking layer 26. That is, the top light diffuser sheet 5 of this modification has a five-layer structure including the anti-sticking layer 26, the adhesive layer 52, the substrate layer 11, the adhesive layer 51, and the coating layer 12. The adhesive layer 52 is a second intermediate layer. The adhesive layer 52 may contain an antistatic agent similar to that of the coating layer 12 of the above embodiment. The adhesive layer 52 may be a primer layer or an easy-adhesive layer that bonds the substrate layer 11 and the anti-sticking layer 26, to which an antistatic agent has been added.

[0083] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 contains an antistatic agent, and the anti-sticking layer 19 does not substantially contain an antistatic agent, and adhesive layers containing an antistatic agent may be provided between the base layer 17 and the coating layer 18, and between the base layer 17 and the anti-sticking layer 19, as in this modified example.

[0084] <Ninth Modification of Top Light Diffusion Sheet> The top light diffusion sheet 5 of this modification differs from the top light diffusion sheet 5 of the eighth modification shown in Fig. 11 in that, as shown in Fig. 12 , an anti-sticking layer 28 containing an anti-static agent is provided instead of the anti-sticking layer 26 which contains substantially no anti-static agent, and the content of the anti-static agent in the anti-sticking layer 28 is lower than the content of the anti-static agent in the adhesive layer 52. In other words, the top light diffusion sheet 5 of this modification is configured as a five-layer structure including the anti-sticking layer 28, the adhesive layer 52, the base layer 11, the adhesive layer 51, and the coating layer 12.

[0085] In the lower light diffusion sheet 3 of the above embodiment (see Figure 1), the coating layer 18 and the anti-sticking layer 19 contain an antistatic agent, and adhesive layers containing an antistatic agent may be provided between the base layer 17 and the coating layer 18, and between the base layer 17 and the anti-sticking layer 19, as in this modified example.

[0086] <Features of the Embodiments and Modifications> The optical sheets (hereinafter referred to as "first optical sheets") of the above-described embodiment and modification 4 and modification 6, namely, the upper light diffusion sheets 5 and 25 and the lower light diffusion sheet 3, comprise base layers 11 and 17 and coating layers 12 and 18 formed on the surfaces of the base layers 11 and 17. The coating layers 12 and 18 contain an antistatic agent. When the optical sheets are placed in an environment of 65°C and 95% RH for 48 hours, the area ratio of contaminated areas on the surfaces of the coating layers 12 and 18 is less than 20%. The first optical sheets can suppress contamination of the sheet surface caused by the antistatic agent with a simple configuration. In the first optical sheets, if the antistatic agent is an ionic liquid or a reactive emulsifier, the amount of foreign matter, such as lumps and crystals, resulting from the antistatic agent can be reduced. In the first optical sheets, an intermediate layer (e.g., adhesive layer 22) substantially free of antistatic agents may be provided between the base layers 11 and 17 and the coating layers 12 and 18.

[0087] The upper light diffusion sheet 5 and the lower light diffusion sheet 3, which are the optical sheets of the first to third, fifth, and seventh variations (hereinafter referred to as "second optical sheets"), comprise substrate layers 11 and 17 and coating layers 12 and 18 formed on the substrate layers 11 and 17. A first intermediate layer containing an antistatic agent is provided between the substrate layers 11 and 17 and the coating layers 12 and 18, and the antistatic agent content in the coating layers 12 and 18 is lower than that in the first intermediate layer. The second optical sheet can suppress staining of the sheet surface caused by the antistatic agent without limiting the options for the type of antistatic agent that can be used. In the second optical sheet, the coating layers 12 and 18 may be substantially free of an antistatic agent. The first intermediate layer may be an adhesive layer 21 that bonds the substrate layers 11 and 17 to the coating layers 12 and 18. In this case, a second intermediate layer (thin layer) 23 containing an antistatic agent may be provided between the first intermediate layer and the coating layer 12, 18. Alternatively, in the second optical sheet, an adhesive layer 22 containing substantially no antistatic agent may be provided between the substrate layer 11, 17 and the first intermediate layer. In the second optical sheet, sufficient antistatic performance can be obtained when the half-life of the electrostatic potential measured by Method A of JIS L 1094 is 30 seconds or less. When the second optical sheet is placed in an environment of 65°C and 95% RH for 48 hours, the decrease in contact angle on the surface of the coating layer 12, 18 is 10 degrees or less, which can prevent the deposition of foreign matter such as lumps or crystals derived from the antistatic agent on the surface of the coating layer 12, 18. The second optical sheet further comprises anti-sticking layers 26, 19 provided on the back surfaces of the substrate layers 11, 17, and the anti-sticking layers 26, 19 are substantially free of an antistatic agent, and a second intermediate layer (e.g., adhesive layer 27) containing an antistatic agent may be provided between the substrate layers 11, 17 and the anti-sticking layers 26, 19.Alternatively, the second optical sheet may further include anti-sticking layers 28, 19 provided on the back surfaces of the base layers 11, 17, the anti-sticking layers 28, 19 containing an antistatic agent, and a second intermediate layer (e.g., adhesive layer 52) containing the antistatic agent may be provided between the base layers 11, 17 and the anti-sticking layers 28, 19, the content of the antistatic agent in the anti-sticking layers 28, 19 being lower than the content of the antistatic agent in the second intermediate layer. Note that when the second optical sheet is placed in an environment of 65°C and 95% RH for 48 hours, the area ratio of contaminated areas on the surfaces of the coating layers 12, 18 may be less than 20%.

[0088] The backlight unit of the above embodiment (including the modified example) includes the light source 2 and the first or second optical sheet, which can suppress contamination of the optical sheet surface caused by the antistatic agent, thereby suppressing a decrease in brightness. A liquid crystal display device including this backlight unit and a liquid crystal display panel can suppress a decrease in brightness on the display screen. Similarly, an information device including this liquid crystal display device can suppress a decrease in brightness on the display screen.

[0089] EXAMPLES The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0090] Example 1 An optical sheet (underside light diffusion sheet) of Example 1 was manufactured as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 38 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the primer layer. The antistatic agent used was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13) Ether sulfate (Na). Next, an acrylic resin was wet-coated onto the surface of the base layer with the primer layer to form an 8 μm thick coating layer. A blend of acrylic beads and styrene beads with particle sizes of 1 to 15 μm was added to the coating layer, and no antistatic agent was added. Next, a urethane acrylate resin was transferred onto the back surface of the base layer to form an 8 μm thick anti-sticking layer. No resin beads (light diffusing agent) were added to the anti-sticking layer.

[0091] Example 2 An optical sheet (underside light diffusion sheet) of Example 2 was manufactured as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 38 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the primer layer. The antistatic agent used was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 ) Ether sulfate (Na). Next, an acrylic styrene resin was wet coated onto the surface of the base layer with the primer layer to form a 10 μm thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, but no antistatic agent was added. Next, a urethane acrylate resin was transferred onto the back surface of the base layer to form an 8 μm thick anti-sticking layer. No resin beads (light diffusing agent) were added to the anti-sticking layer.

[0092] Example 3 An optical sheet (underside light diffusion sheet) of Example 3 was manufactured as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 38 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the primer layer. The antistatic agent used was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13) Ether sulfate (Na). Next, an acrylic styrene resin was wet-coated on the surface of the base layer with the primer layer to form a 10 μm thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, but no antistatic agent was added. Next, a urethane acrylate resin was wet-coated on the back surface of the base layer to form a 5 μm thick anti-sticking layer. Urethane beads with a particle size of 1 to 25 μm were added to the anti-sticking layer, but no antistatic agent was added.

[0093] Example 4 An optical sheet (upper light diffusion sheet) of Example 4 was manufactured as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 75 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the primer layer. The antistatic agent used was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 ) Ether sulfate (Na). Next, a urethane acrylate resin was wet-coated onto the surface of the base layer with the primer layer to form a 5 μm thick coating layer. Acrylic beads with a particle size of 1 to 15 μm were added to the coating layer, but no antistatic agent was added. Next, a urethane acrylate resin was wet-coated onto the back surface of the base layer to form an 8 μm thick anti-sticking layer. No resin beads (light diffusing agent) were added to the anti-sticking layer.

[0094] Reference Example The manufacturing method of the optical sheet (underside light diffusion sheet) of the Reference Example differs from that of Example 1 in that no antistatic agent was added to the primer layer. That is, the optical sheet of the Reference Example does not contain an antistatic agent.

[0095] Comparative Example 1 The manufacturing method of the optical sheet (underside light diffusion sheet) of Comparative Example 1 differs from Example 1 in that no antistatic agent was added to the primer layer, but a low molecular weight surfactant acting as an antistatic agent was added to the coating layer. Sanol (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation was used as the antistatic agent. The amount of antistatic agent added was 1.5 parts by mass per 100 parts by mass of the constituent resin of the coating layer.

[0096] Comparative Example 2 The manufacturing method of the optical sheet (underside light diffusion sheet) of Comparative Example 2 differs from Example 2 in that no antistatic agent was added to the primer layer, but a low molecular weight surfactant acting as an antistatic agent was added to the coating layer. Sanol (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation was used as the antistatic agent. The amount of antistatic agent added was 1.2 parts by mass per 100 parts by mass of the constituent resin of the coating layer.

[0097] Example 5 The manufacturing method of the optical sheet (underside light diffusion sheet) of Example 5 differs from that of Example 1 in that an antistatic agent was not added to the primer layer, but was added to the coating layer. As in Example 1, the antistatic agent was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 The amount of the antistatic agent added was 1.5 parts by mass per 100 parts by mass of the resin constituting the coating layer.

[0098] Example 6 The manufacturing method of the optical sheet (underside light diffusion sheet) of Example 6 differs from that of Example 1 in that an antistatic agent was not added to the primer layer, but was added to the coating layer. As in Example 1, the antistatic agent was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 The amount of the antistatic agent added was 3 parts by mass per 100 parts by mass of the resin constituting the coating layer.

[0099] Example 7 The manufacturing method of the optical sheet (underside light diffusion sheet) of Example 7 differs from that of Example 1 in that an antistatic agent was not added to the primer layer, but was added to the coating layer. As in Example 1, the antistatic agent was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 The amount of the antistatic agent added was 5 parts by mass per 100 parts by mass of the resin constituting the coating layer.

[0100] <Evaluation of Examples> For the optical sheets of Examples 1 to 4, Reference Example 1, and Comparative Examples 1 and 2, the electrical resistivity and surface roughness Ra of the sheet surface were measured, a charging voltage test was performed, an ash (ash adhesion) test was performed, the contact angle of the sheet surface was measured, and the occurrence of stains on the sheet surface was observed. The results shown in Table 1 are average values ​​for five samples.

[0101]

[0102] The specific details of each measurement and test are as follows. Electrical resistivity was measured in accordance with JIS K 6911 using a Hioki E.E. Corporation flat sample electrode SME-8310. A voltage of 500 V was applied to a 10 cm square area of ​​the measurement sample for 25 seconds, and the resistance value was measured to calculate the electrical resistivity. Surface roughness Ra was measured in accordance with JIS B0601-1994 using a Mitutoyo Corporation surface roughness measuring instrument Surftest SJ-210, with the measurement probe in contact with the surface of the measurement sample for a length of 40 mm. The electrostatic charge test was conducted in accordance with JIS L 1094, Method B (frictional electrostatic charge measurement method) and JIS L 1094, Method A (half-life measurement method) using a frictional electrostatic charge tester RST-300A manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd. (1) The maximum electrostatic charge value was measured when the drum to which the test sample was attached was rubbed with a friction cloth conforming to JIS L 0803 #3 for 60 seconds while rotating (400 rpm), (2) the electrostatic charge value was measured 60 seconds after the friction was stopped, and (3) the number of seconds required for the electrostatic charge value to decrease by half from the maximum electrostatic charge value was measured. In the ash test, the test sample was placed on a cloth conforming to JIS L 0803 #3 and rubbed for 5 seconds about 10 times. Then, in a constant temperature and humidity chamber at 23°C and 50% RH, Dabaco ash prepared in advance was brought close to the friction surface of the test sample to a distance of 1 cm, and it was examined whether the ash adhered to the test sample. For the contact angle measurement, an automatic contact angle meter DMo-601 manufactured by Kyowa Interface Science Co., Ltd. was used to measure the angle of the water droplet (contact angle) 1 second after dropping a 1 μg water droplet on the sheet surface for each measurement sample before the environmental test (untreated), after the environmental test at "65°C, 95% RH, 48 hours", and after the environmental test at "85°C, 85% RH, 48 hours". For the observation of the occurrence of stains on the sheet surface, three optical sheets of the measurement sample were stacked, and the environmental test at "65°C, 95% RH, 48 hours" was carried out. Then, a 1.5 mm diameter drop was measured at the center of the middle sheet of the three stacked sheets. 2 The area was observed under a microscope at a magnification of 2000 times, and a case where the ratio of the area free of attached matter (contaminants) was 80% or more of the total observed area was marked as ◯, and a case where it was less than 80% was marked as ×. Note that by observing the middle sheet of the three stacked sheets, foreign matter not derived from the antistatic agent, which was generated by direct exposure to the environment, was prevented from being observed.

[0103] As shown in Table 1, in Examples 1 to 4, in which no antistatic agent was added to the coating layer, the electrical resistivity of the sheet surface was higher than in Comparative Examples 1 and 2, in which an antistatic agent was added to the coating layer. However, the half-life of the electrostatic charge was 30 seconds or less, and there was almost no ash adhesion in the ash test, indicating no problems with antistatic performance. Meanwhile, in Examples 1 to 4, staining of the sheet surface caused by the antistatic agent was sufficiently suppressed, whereas in Comparative Examples 1 and 2, staining of the sheet surface caused by the antistatic agent was not sufficiently suppressed. Furthermore, in the results of the contact angle test, the change (decrease) in the contact angle before and after the environmental test was suppressed to 10 degrees or less in Examples 1 to 4, whereas the change (decrease) in the contact angle before and after the environmental test exceeded 20 degrees in Comparative Examples 1 and 2.

[0104] Furthermore, in Examples 5 to 7, in which an antistatic agent was added to the coating layer, antistatic performance was obtained at the same level as in Comparative Examples 1 and 2, and further, when the occurrence of staining on the sheet surface was observed as described above, staining on the sheet surface caused by the antistatic agent was sufficiently suppressed, as in Examples 1 to 4. That is, when the optical sheets of Examples 5 to 7 were placed in an environment of 65°C and 95% RH for 48 hours, the area ratio of the contaminated region on the surface of the coating layer was less than 20%.

[0105] Additional Examples The present disclosure will be explained in further detail below with reference to Examples 8 to 12.

[0106] Example 8 An optical sheet (underside light diffusion sheet) of Example 8 was manufactured as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was formed on the surface of a substrate layer with an average thickness of 38 μm, primarily composed of polyethylene terephthalate. A surfactant-type antistatic agent was then added to the primer layer. The antistatic agent used was Sannoru (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 1.2 parts by mass per 100 parts by mass of the resin constituting the primer layer. Next, an acrylic styrene-based resin was wet-coated onto the primer layer formed on the surface of the substrate layer to form a 10 μm-thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, and a polymeric ion-conducting antistatic agent was also added. The antistatic agent used was Sannoru (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 The amount of the antistatic agent added was 0.5 parts by mass relative to 100 parts by mass of the resin constituting the coating layer.

[0107] Example 9 An optical sheet (underside light diffusion sheet) of Example 9 was produced as follows. First, a primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 38 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the primer layer. The antistatic agent used was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13) ether sulfate (Na). The amount of antistatic agent added was 1.5 parts by mass per 100 parts by mass of the constituent resin of the primer layer. Next, an acrylic styrene resin was wet-coated onto the primer layer formed on the surface of the substrate layer to form a 10 μm-thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, along with a surfactant-type antistatic agent. The antistatic agent used was Sannoru (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 0.5 parts by mass per 100 parts by mass of the constituent resin of the coating layer.

[0108] Example 10 The optical sheet (underside light diffusion sheet) of Example 10 was manufactured as follows. First, a first primer layer composed of an acrylic resin and a thermoset acrylate resin was formed on the surface of a substrate layer with an average thickness of 50 μm, primarily composed of polyethylene terephthalate. A surfactant-type antistatic agent was then added to the first primer layer. The antistatic agent used was Sannoru® EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 1.2 parts by mass per 100 parts by mass of the resin constituting the first primer layer. Next, an acrylic-styrene resin was wet-coated onto the first primer layer formed on the surface of the substrate layer to form a 10 μm-thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, but no antistatic agent was added.

[0109] A second primer layer composed of an acrylic resin and an acrylate resin thermoset was applied to the back surface of the substrate layer, and a surfactant-type antistatic agent was added to the second primer layer. The antistatic agent used was Sannoru® EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 1.2 parts by mass per 100 parts by mass of the resin constituting the second primer layer. Next, a urethane acrylate resin was transferred onto the second primer layer applied to the back surface of the substrate layer to form an 8 μm-thick anti-sticking layer. Resin beads (light diffusing agent) and anti-static agent were not added to the anti-sticking layer.

[0110] Example 11 An optical sheet (underside light diffusion sheet) of Example 11 was produced as follows. First, a first primer layer composed of an acrylic resin and a thermoset acrylate resin was provided on the surface of a substrate layer having an average thickness of 50 μm and mainly composed of polyethylene terephthalate, and a polymeric ion-conducting antistatic agent was added to the first primer layer. The antistatic agent used was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 ) ether sulfate (Na). The amount of antistatic agent added was 1.5 parts by mass per 100 parts by mass of the constituent resin of the first primer layer. Next, an acrylic styrene resin was wet-coated onto the first primer layer formed on the surface of the substrate layer to form a 10 μm-thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, along with a surfactant-type antistatic agent. The antistatic agent used was Sannoru (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 0.5 parts by mass per 100 parts by mass of the constituent resin of the coating layer.

[0111] A second primer layer made of a thermosetting acrylic resin and an acrylate resin was provided on the back surface of the substrate layer, and a polymeric ion-conducting antistatic agent was added to the second primer layer. The antistatic agent was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 ) Ether sulfate (Na). The amount of antistatic agent added was 1.5 parts by mass per 100 parts by mass of the constituent resin of the second primer layer. Next, a urethane acrylate resin was transferred onto the second primer layer provided on the back surface of the base layer to form an 8 μm thick anti-sticking layer. No resin beads (light diffusing agent) or anti-static agent were added to the anti-sticking layer.

[0112] Example 12 The optical sheet (underside light diffusion sheet) of Example 12 was manufactured as follows. First, a first primer layer composed of an acrylic resin and a thermoset acrylate resin was formed on the surface of a substrate layer with an average thickness of 50 μm, primarily composed of polyethylene terephthalate. A surfactant-type antistatic agent was then added to the first primer layer. The antistatic agent used was Sannoru® EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation. The amount of antistatic agent added was 1.2 parts by mass per 100 parts by mass of the resin constituting the first primer layer. Next, an acrylic-styrene resin was wet-coated onto the first primer layer formed on the surface of the substrate layer to form a 10 μm-thick coating layer. Acrylic beads with a particle size of 1 to 25 μm were added to the coating layer, along with a surfactant-type antistatic agent. Sannoru® EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation was used as the antistatic agent. The amount of the antistatic agent added was 0.5 parts by mass relative to 100 parts by mass of the resin constituting the coating layer.

[0113] A second primer layer made of a thermosetting acrylic resin and an acrylate resin was provided on the back surface of the substrate layer, and a polymeric ion-conducting antistatic agent was added to the second primer layer. The antistatic agent was Sannol (registered trademark) TD-3130 (polyoxyethylene alkyl (C 13 ) ether sulfate (Na). The amount of antistatic agent added was 1.5 parts by mass per 100 parts by mass of the constituent resin of the second primer layer. Next, a urethane acrylate resin was transferred onto the second primer layer provided on the back surface of the base layer to form an 8 μm thick anti-sticking layer. A surfactant-type anti-static agent was added to the anti-sticking layer. Sanol (registered trademark) EH-1145M (alkyl (C8) sulfate ester MEA salt) manufactured by Lion Corporation was used as the anti-static agent. The amount of anti-static agent added was 0.5 parts by mass per 100 parts by mass of the constituent resin of the anti-sticking layer. Note that resin beads (light diffusing agent) were not added to the anti-sticking layer.

[0114] <Evaluation of Additional Examples> For the optical sheets of Examples 8 to 12, the electrical resistivity of the front and back surfaces of the sheets was measured, a charging voltage test was performed, an ash (ash adhesion) test was performed, and the occurrence of stains on the sheet surface was observed, in the same manner as in Examples 1 to 4. The results shown in Table 2 are average values ​​for five samples.

[0115]

[0116] As shown in Table 2, in Examples 8 to 12, the electrical resistivity of the sheet surface was lower than that of Examples 1 to 4, and the electrical resistivity of the sheet back surface was even lower than that of the sheet surface. Furthermore, in Examples 8 to 12, the half-life of the electrostatic voltage was 10 seconds or less, and there was almost no ash adhesion in the ash test, indicating no problems with antistatic performance. Furthermore, in Examples 8 to 12, staining of the sheet surface caused by the antistatic agent was sufficiently suppressed.

[0117] <Layer Charging Evaluation> During the manufacturing process of optical sheets, optical sheets cut to a size that can be incorporated into a backlight unit are sometimes transported in a stacked state. If the stacked optical sheets become charged with electricity, it becomes difficult to stack the optical sheets with their edges aligned. Therefore, the inventors of the present application performed the layer charging evaluation described below on the optical sheets of Examples 1 to 12, Reference Example 1, and Comparative Examples 1 and 2.

[0118] First, three A4-sized optical sheets to be evaluated, a B4-sized flannel cloth attached to a flat plate to prevent wrinkles, and an air-blowing static eliminator were prepared. Next, one A4-sized optical sheet was placed on the flannel cloth attached to the plate, and a 500g weight was placed on the optical sheet. The flannel cloth and the optical sheet were then rubbed parallel to each other in a circle with a radius of approximately 100mm 10 times. After rubbing the three optical sheets in this manner, the air-blowing static eliminator was activated. The edge of the topmost optical sheet was grasped at a position approximately 500mm from the front of the static eliminator and lifted vertically to a height of 500mm for approximately 5 seconds. If the other optical sheets that were not gripped fell away from the topmost optical sheet simultaneously (i.e., the optical sheets were not in close contact with each other), the test was evaluated as "good" (best). Furthermore, when the top optical sheet is lifted, two or more optical sheets including that optical sheet are lifted in close contact, but the optical sheets that are not being held fall apart within 10 seconds (when the air blown by the static eliminator releases the close contact of the optical sheets), it was judged as △ (good). Furthermore, when the top optical sheet is lifted, two or more optical sheets including that optical sheet are lifted in close contact, and the close contact of the two or more optical sheets is maintained even after 10 seconds, it was judged as × (unacceptable).

[0119] As a result of the above-described laminated charge evaluation, Examples 1 to 4 were rated △, the Reference Example was rated ×, and Comparative Examples 1 and 2 and Examples 5 to 12 were rated ○.

[0120] (Other Embodiments) Although embodiments of the present disclosure (including modifications and examples; the same applies hereinafter) have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. In other words, the description of the above-described embodiments is essentially merely exemplary and is not intended to limit the present disclosure, its applications, or its uses.

[0121] The optical sheet of the above embodiment may have a two-layer structure of a substrate layer and a coating layer, or a three-layer structure of a substrate layer, a coating layer, and an anti-sticking layer. Also, another layer such as an intermediate layer may be provided between the substrate layer and the coating layer or between the substrate layer and the anti-sticking layer.

[0122] In the optical sheet of the above embodiment, an antistatic agent is added to the coating layer or to the intermediate layer between the substrate layer and the coating layer, but an antistatic agent may also be added to the substrate layer, or an antistatic agent-containing layer may be provided between two substrate layers.

[0123] The backlight unit according to the present disclosure can be embodied in various modified and improved forms in addition to the above-described embodiment. For example, the backlight unit may include optical sheets other than the upper light diffusion sheet, prism sheet, and lower light diffusion sheet on the front side of the light guide sheet. Furthermore, the backlight unit is not limited to an edge-lit backlight unit, but may also be, for example, a direct-type backlight unit in which a diffuser plate and a light source are disposed on the rear side of the lower light diffusion sheet. Furthermore, the specific configurations of the prism sheet, light diffusion sheet, light guide sheet, light source, and reflective sheet in the backlight unit are not particularly limited, and various configurations can be employed. For example, the light diffusion sheet is not limited to a bead-coated light diffusion sheet, but may also be a light diffusion sheet shaped like a pyramid sheet. Optical sheets with these various configurations may contain an antistatic agent, as with the optical sheets of the above-described embodiment.

[0124] The backlight unit according to the present disclosure can be used in a wide range of applications, such as relatively large display devices such as personal computers and LCD televisions, mobile phone terminals such as smartphones, and portable information terminals such as tablet terminals.

[0125] In the above embodiment, in the light diffusion sheet including the base layer and the coating layer formed on the base layer, the unevenness is formed on the surface of the light diffusion sheet by dispersing resin beads in the resin matrix of the coating layer that becomes the light diffusion layer. However, instead of this, for example, the unevenness may be formed on the surface of the light diffusion sheet by using a mold to which the unevenness formed by dispersing resin beads in the resin matrix is ​​transferred, or by using a laser printer device that memorizes the unevenness.

[0126] REFERENCE SIGNS LIST 1 Light guide sheet 2 Light source 3 Lower light diffusion sheet 4 Prism sheet 5 Upper light diffusion sheet 6 Reflective sheet 11 Base material layer 12 Coating layer 13 Resin matrix 14 Resin beads 15 Base material layer 16 Protruding prism portion 17 Base material layer 18 Coating layer 19 Anti-sticking layer 21 Adhesive layer 22 Adhesive layer 23 Thin layer 25 Upper light diffusion sheet 26 Anti-sticking layer 27 Adhesive layer 28 Anti-sticking layer 31 Liquid crystal panel 32 Front polarizing plate 33 Rear polarizing plate 34 Liquid crystal cell 51 Adhesive layer 52 Adhesive layer

Claims

1. An optical sheet comprising a base layer and a coating layer provided on a first surface of the base layer, wherein the coating layer contains an antistatic agent, and when the optical sheet is placed in an environment of 65°C and 95% RH for 48 hours, the area ratio of contaminated areas on the surface of the coating layer is less than 20%.

2. The optical sheet according to claim 1, wherein an intermediate layer substantially not containing an antistatic agent is provided between the substrate layer and the coating layer.

3. An optical sheet comprising a base layer and a coating layer provided on a first surface of the base layer, wherein a first intermediate layer containing an antistatic agent is provided between the base layer and the coating layer, and the content of the antistatic agent in the coating layer is lower than the content of the antistatic agent in the first intermediate layer.

4. The optical sheet according to claim 3, wherein the coating layer is substantially free of an antistatic agent.

5. The optical sheet according to claim 3, wherein the first intermediate layer is an adhesive layer that bonds the base layer and the coating layer.

6. The optical sheet according to claim 5, wherein a second intermediate layer containing an antistatic agent is provided between the first intermediate layer and the coating layer.

7. The optical sheet according to claim 3, wherein an adhesive layer substantially not containing an antistatic agent is provided between the base layer and the first intermediate layer.

8. The optical sheet according to claim 3, wherein the half-life of the electrostatic voltage according to JIS L 1094 Method A is 30 seconds or less.

9. The optical sheet according to claim 3, wherein when the optical sheet is placed in an environment of 65° C. and 95% RH for 48 hours, the contact angle on the surface of the coating layer is reduced by 10 degrees or less.

10. The optical sheet according to claim 3, further comprising an anti-sticking layer provided on a second surface of the base layer, the anti-sticking layer being substantially free of an antistatic agent, and a second intermediate layer containing an antistatic agent being provided between the base layer and the anti-sticking layer.

11. An optical sheet as described in claim 3, further comprising an anti-sticking layer provided on a second surface of the base layer, the anti-sticking layer containing an antistatic agent, a second intermediate layer containing an antistatic agent being provided between the base layer and the anti-sticking layer, and the content of the antistatic agent in the anti-sticking layer being lower than the content of the antistatic agent in the second intermediate layer.

12. The optical sheet according to claim 3, wherein when the optical sheet is placed in an environment of 65° C. and 95% RH for 48 hours, the area ratio of contaminated regions on the surface of the coating layer is less than 20%.

13. A backlight unit comprising a light source and the optical sheet according to any one of claims 1 to 12.

14. A liquid crystal display device comprising the backlight unit according to claim 13 and a liquid crystal display panel.

15. An information device comprising the liquid crystal display device according to claim 14.

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