TW201727324A - Upper light diffusing sheet and backlight unit - Google Patents

Abstract

An object of the present invention is to provide a light diffusion sheet for an upper surface, which can suppress unevenness in brightness caused by a shape of a stripe prism portion protruding from a prism sheet disposed on a back surface side, and can suppress a pixel pitch from a liquid crystal panel. The occurrence of flicker caused by interference. The upper light-scattering sheet is disposed on the surface side of the prism sheet of the backlight unit of the liquid crystal display device, and includes a base material layer and a light diffusion layer laminated on the surface side of the base material layer, the light diffusion layer having a resin matrix and dispersed in the resin matrix In the resin beads, the volume-based particle size distribution of the resin beads has a mode diameter of 2.5 μm or more and 5.5 μm or less, a density per unit area of 9000 particles/mm 2 or more and 24,000 particles/mm 2 or less, and an average thickness of the light diffusion layer of 2 μm or more. 9 μm or less. Preferably, the coefficient of variation of the particle diameter of the volume-based particle size distribution of the resin beads is 42% or less.

Description

Upper light diffusing sheet and backlight unit

The present invention relates to an upper light diffusing sheet and a backlight unit.

The liquid crystal display device is widely used as a flat panel display by utilizing the characteristics of being thin, lightweight, and low in power consumption, and its use is expanding in portable information terminals such as mobile phones such as televisions, personal computers, and smart phones, and tablet terminals.

In such a liquid crystal display device, a backlight system that illuminates a liquid crystal panel from the back side is widely used, and a backlight unit such as a side light type or a direct type is mounted. As shown in FIG. 5, the edge-lit backlight unit 101 included in such a liquid crystal display device includes a light source 102, a square plate-shaped light guide plate 103, and an end portion disposed along the light source 102. The sheet 104 is superposed on the surface side of the light guide plate 103, and the reflection sheet 105 is disposed on the back side of the light guide plate 103. The light guide plate 103 is usually made of synthetic resin, and is made of polycarbonate, acrylic resin or the like as a main component. As the light source 102, an LED (Light Emitting Diode), a cold cathode tube, or the like is used, and from the viewpoints of miniaturization and energy saving, LEDs are currently widely used. Further, as the optical sheet 104, (1) a lower light diffusing sheet 106 mainly having a light diffusing function is superposed on the surface side of the light guiding plate 103, and (2) is superposed on the surface side of the lower light diffusing sheet 106 to have light. The prism sheet 107 having a refractive function toward the normal direction side; (3) superimposed on the surface side of the prism sheet 107, and suppressing uneven brightness due to the shape of the prism portion of the prism sheet 107 by slightly diffusing the light. The light-diffusing sheet 108 (refer to Japanese Laid-Open Patent Publication No. 2005-77448). In addition, the above-mentioned light diffusing sheet usually includes a base material layer and a light diffusion layer, and the light diffusion layer is laminated on the surface side of the base material layer, and has a resin base and resin beads.

Prior art literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-77448

However, it has been found that such a conventional light-diffusing sheet is produced on the surface side of the light-diffusing sheet which is disposed on the liquid crystal display device in which the pixel pitch of the liquid crystal panel is minimized. The flicker caused by the interference of the pixel spacing of the liquid crystal panel (also known as "shining", "not smooth", "slightly rough", "moire fringe", "interference of light", "uneven", "bright spots" "). Further, as a result of intensive studies, the present inventors have found that by reducing the particle diameter of the resin beads of the light diffusion layer of the upper light diffusion sheet, the unevenness of the surface of the light diffusion layer can be made fine, and the flicker can be reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an upper light diffusing sheet and a backlight unit, which can suppress uneven brightness caused by the shape of a prism portion of a prism sheet disposed on the back side. And it is possible to suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel.

An upper light diffusing sheet of the present invention for solving the above problems is disposed on a surface side of a prism sheet of a backlight unit of a liquid crystal display device, and the upper light diffusing sheet is provided with a substrate layer and laminated on the base a light diffusion layer on the surface side of the material layer, the light diffusion layer having a resin matrix and resin beads dispersed in the resin matrix, wherein a volume-based particle size distribution of the resin beads has a mode diameter of 2.5 μm or more and 5.5 μm or less The density per unit area is 9000/mm ² or more and 24,000 pieces/mm ² or less, and the average thickness of the light diffusion layer is 2 μm or more and 9 μm or less.

Since the light diffusion layer of the upper light diffusion sheet has a resin base and a resin bead, irregularities due to the resin beads are formed on the surface of the light diffusion layer. Therefore, the above-described light-diffusing sheet can diffuse light incident from the back side by the unevenness, and can suppress unevenness in brightness caused by the shape of the strip-shaped prism portion protruding from the prism sheet. Further, since the mode diameter of the volume-based particle size distribution of the resin beads of the upper light-scattering sheet, the density per unit area, and the average thickness of the light-diffusing layer are set within the range, it is possible to randomly and finely and randomly Since the unevenness is formed, it is possible to suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel.

Preferably, the coefficient of variation of the particle diameter as the volume-based particle size distribution of the resin beads is 42% or less. By setting the coefficient of variation of the particle diameter of the volume-based particle size distribution of the resin beads to be equal to or less than the upper limit, it is easy to form minute and high-density irregularities on the surface of the light-diffusing layer, and it is possible to more reliably suppress the liquid crystal panel. The occurrence of flicker caused by interference of pixel spacing.

It is preferable that the particle size width as the volume-based particle size distribution of the resin beads is 13 μm or more and 20 μm or less. By setting the particle size width of the volume-based particle size distribution of the resin beads within the above range, it is easy to form minute and high-density irregularities on the surface of the light-diffusing layer, and it is possible to more reliably suppress the pixel pitch from the liquid crystal panel. The occurrence of flicker caused by interference.

Preferably, the average particle diameter D50 of the volume-based particle size distribution of the resin beads is 5.7 μm or less. By setting the average particle diameter D50 of the volume-based particle size distribution of the resin beads to be equal to or less than the upper limit, it is possible to suppress flicker caused by interference with the pixel pitch of the liquid crystal panel by using a large number of resin beads having a small particle diameter, and It is possible to prevent adhesion to a liquid crystal panel or the like by using a small number of resin beads having a relatively large particle diameter.

It is preferable that the center line average roughness Ra of the surface of the light diffusion layer is 0.3 μm or more and 1 μm or less. By setting the center line average roughness Ra of the surface of the light diffusion layer within the above range, it is possible to more reliably suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel.

Preferably, the ten-point average roughness Rz of the surface of the light-diffusing layer is 1.5 μm or more and 4.5 μm or less, and the average length RSm of the roughness curve element is 30 μm or more and 100 μm or less. By setting the ten point average roughness Rz of the surface of the light diffusion layer and the average length RSm of the roughness curve elements within the range, it is possible to more reliably suppress flicker caused by interference with the pixel pitch of the liquid crystal panel. happened.

Preferably, the resin beads of the light diffusion layer are substantially separated from the surface of the substrate layer. Thus, by substantially separating the resin beads of the light diffusion layer from the surface of the substrate layer, the mode diameter of the volume-based particle size distribution of the resin beads, the density per unit area, and the average thickness of the light diffusion layer are set in the In the case of the above-described range, it is easy to form minute and high-density irregularities on the surface of the light-diffusing layer, and it is possible to more reliably suppress the occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel.

Further, a backlight unit of the present invention for solving the above problem includes: a light guide sheet that guides light incident from an end surface toward a surface side; a light source that illuminates light toward an end surface of the light guide sheet; a sheet overlapping the surface side of the light guide sheet; a prism sheet disposed on a surface side of the lower light diffusion sheet; and an upper light diffusion sheet superposed on a surface side of the prism sheet, wherein As described above, the light diffusing sheet is used, and the above-mentioned upper light diffusing sheet is used.

Since the upper light diffusing sheet of the present invention is superposed on the surface side of the prism sheet of the backlight unit, the light emitted from the prism sheet is diffused by the unevenness of the surface of the light diffusing layer formed on the upper light diffusing sheet. It is possible to suppress unevenness in brightness caused by the shape of the prism portion of the prism sheet or the like. Further, since the mode diameter of the volume-based particle size distribution of the resin beads of the upper light-scattering sheet of the backlight unit, the density per unit area, and the average thickness of the light-diffusing layer are respectively within the range, it is possible to be small and The unevenness is randomly formed at a high density, and occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel can be suppressed.

Preferably, the ratio of the average particle diameter D50 of the resin beads to the average pitch of the ridgelines of the prism sheet is 0.06 or more and 0.25 or less. By setting the ratio of the average particle diameter D50 of the resin beads to the average pitch of the ridge lines of the prism sheet within the above range, the light emitted from the prism sheet can be appropriately diffused by the upper light diffusion sheet. It is possible to more reliably suppress unevenness in brightness caused by the shape of the prism portion of the prism sheet or the like.

Further, in the present invention, the "surface side" means the side of the person who views the liquid crystal display device, and the "back side" means the side opposite to the "surface side". The "mode diameter of the volume reference particle size distribution" refers to the mode diameter calculated from the cumulative distribution measured by the laser diffraction method. The "density per unit area of the resin beads" means any one obtained by irradiating a laser beam from the surface side of the light diffusion layer and scanning the surface shape from the convex portion to the concave portion of the fine unevenness formed on the surface of the light diffusion layer. The density (unit/mm ² ) per unit area of the resin beads measured by the laser image of 10 parts was averaged. The "average thickness of the light diffusion layer" means the average interface of the surface of the light diffusion layer and the average thickness of the average interface of the back surface of the light diffusion layer. The "average particle diameter of the volume-based particle size distribution" means the average particle diameter calculated from the cumulative distribution measured by the laser diffraction method. "Center line average roughness Ra" and "average length RSm of roughness curve elements" refer to values of JIS-B0601:2001, cut-off length (λc) of 2.5 mm, and evaluation length of 12.5 mm. The "ten-point average roughness Rz" means a value of 22.5 mm in accordance with JIS-B0601:1994, a cut-off length (λc) of 2.5 mm, and an evaluation length of 12.5 mm. "The resin beads are substantially separated from the surface of the substrate layer" means that 50% or more of the resin beads are separated from the surface of the substrate layer, and preferably 60% or more of the resin beads are separated from the surface of the substrate layer, and more preferably 70% or more. The resin beads are separated from the surface of the substrate layer.

As described above, the upper light diffusing sheet and the backlight unit of the present invention can suppress unevenness in brightness caused by the shape of the prism portion of the prism sheet, and can suppress occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel. .

The above description of the disclosure and the following description of the embodiments of the present invention are intended to illustrate and explain the spirit and principles of the invention, and to provide further explanation of the scope of the invention.

The detailed features and advantages of the present invention are set forth in the Detailed Description of the Detailed Description of the <RTIgt; </ RTI> <RTIgt; </ RTI> </ RTI> </ RTI> <RTIgt; The objects and advantages associated with the present invention can be readily understood by those skilled in the art. The following examples are intended to describe the present invention in further detail, but are not intended to limit the scope of the invention.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings as appropriate.

[Backlight unit]

The backlight unit of the liquid crystal display device of FIG. 1 includes a prism sheet 4 and an upper light diffusion sheet 5 disposed on the surface side of the prism sheet 4. The backlight unit is an edge-lit backlight unit, and includes a light guide sheet 1 that guides light incident from the end surface toward the surface side; the light source 2 illuminates light toward the end surface of the light guide sheet 1; and the lower light diffusion sheet 3 overlaps On the surface side of the light guiding sheet 1, the prism sheet 4 is disposed on the surface side of the lower light diffusing sheet 3, and the upper light diffusing sheet 5 is superposed on the surface side of the prism sheet 4. Further, the backlight unit further includes a reflection sheet 6 disposed on the back side of the light guide sheet 1. The light diffusing sheet 3 is used to condense the light incident from the back side while diffusing toward the normal side (concentrating and diffusing). The prism sheet 4 refracts light incident from the back side toward the normal direction side. The upper light-diffusing sheet 5 suppresses the unevenness of the brightness caused by the shape of the prism portion of the prism sheet 4 or the like by diffusing the light incident from the back side to some extent, and suppresses the surface of the light-diffusing sheet 5 disposed on the upper surface. The flicker caused by the interference of the pixel pitch of the liquid crystal panel (not shown) on the side. The reflection sheet 6 reflects the light emitted from the back side of the light guide sheet 1 toward the front side, and returns to the light guide sheet 1 again.

<Upper light diffusing sheet>

The upper light-diffusing sheet 5 is disposed on the surface side of the prism sheet 4 of the backlight unit of the liquid crystal display device, and in the present embodiment, it is particularly directly (not by other sheets or the like) superposed on the surface of the prism sheet 4. The upper light diffusion sheet 5 includes a base material layer 11 and a light diffusion layer 12 laminated on the surface side of the base material layer 11 . The upper light diffusion sheet 5 is configured as a base layer 11 and a two-layer structure of the light diffusion layer 12 directly laminated on the surface of the base material layer 11.

(base material layer)

Since the base material layer 11 needs to transmit light, a transparent, particularly colorless, transparent synthetic resin is used as a main component. The main component of the base material layer 11 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, and polyolefin. , cellulose acetate, weather resistant vinyl chloride, etc. Among them, polyethylene terephthalate having good transparency and high strength is preferable, and polyethylene terephthalate having improved bending properties is particularly preferable. Further, the "main component" means a component having the highest content, and is, for example, a component having a content of 50% by mass or more.

The lower limit of the average thickness of the base material layer 11 is preferably 10 μm, more preferably 35 μm, still more preferably 50 μm. On the other hand, the upper limit of the average thickness of the base material layer 11 is preferably 500 μm, more preferably 250 μm, still more preferably 188 μm. If the average thickness of the base material layer 11 is less than the lower limit, there is a problem that curling occurs when the light diffusion layer 12 is formed by coating. On the other hand, if the average thickness of the base material layer 11 exceeds the upper limit, there is a problem that the brightness of the liquid crystal display device is lowered, and there is a problem that the thinning requirements of the liquid crystal display device are not satisfied. In addition, "average thickness" means the average value of the thickness of arbitrary 10 points.

(light diffusion layer)

The light diffusion layer 12 constitutes the outermost surface of the upper light diffusion sheet 5. The light diffusion layer 12 has a resin base 13 and resin beads 14 dispersed in the resin base 13. The light diffusion layer 12 is dispersed with the resin beads 14 at substantially equal density. The resin beads 14 are surrounded by the resin base 13 . The light diffusion layer 12 diffuses light to the outside through minute irregularities formed on the surface.

The lower limit of the average thickness of the light diffusion layer 12 is 2 μm, and more preferably 3 μm. On the other hand, the upper limit of the average thickness of the light diffusion layer 12 is 9 μm, more preferably 7 μm, still more preferably 5 μm. If the average thickness of the light-diffusing layer 12 is less than the lower limit, there is a problem that the resin beads 14 cannot be properly fixed by the resin substrate 13, and the resin beads 14 are detached from the light-diffusing layer 12. On the other hand, if the average thickness of the light-diffusing layer 12 exceeds the upper limit, there is a problem in that it is difficult to form minute and high-density irregularities on the surface of the light-diffusing layer 12, and as a result, it is not sufficiently suppressed and disposed on the surface. The occurrence of flicker caused by the interference of the pixel pitch of the liquid crystal panel on the surface side of the light diffusion sheet 5 occurs.

Since the resin base 13 needs to transmit light, a transparent, particularly colorless, transparent synthetic resin is formed as a main component. Examples of the synthetic resin include a thermosetting resin and an actinic radiation curable resin. In addition, as the synthetic resin, a photochemical irradiation-curable resin which is easy to hold the resin beads 14 in a state where the resin beads 14 are separated from the surface of the base material layer 11 to be described later is preferable.

Examples of the thermosetting resin include an epoxy resin, an anthracene resin, a phenol resin, a urea resin, an unsaturated polyester resin, a melamine resin, an alkyd resin, a polyimide resin, an acrylic resin, and an amino functional copolymer. , polyurethane resin, etc.

The ultraviolet ray-curable resin which is crosslinked and cured by irradiation with ultraviolet rays, and an electron ray-curable resin which is crosslinked and cured by irradiation with an electron beam, etc., can be used as the actinic radiation-curable resin. The body and the polymerizable oligomer are appropriately selected and used. In addition, as the actinic radiation-curable resin, it is preferable to improve the adhesion to the base material layer 11 and to prevent the resin beads 14 from being detached from the light-diffusing layer 12, and to cure the acrylic, urethane or acrylic urethane ultraviolet curing. Type resin.

As the polymerizable monomer, a (meth) acrylate monomer having a radical polymerizable unsaturated group in a molecule is preferably used, and among them, a polyfunctional (meth) acrylate is preferable. The polyfunctional (meth) acrylate is not particularly limited as long as it is a (meth) acrylate having two or more ethylenically unsaturated bonds in the molecule. Specific examples thereof include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, and 1,6-hexanediol. (Meth) acrylate, neopentyl glycol di(meth) acrylate, polyethylene glycol di(meth) acrylate, hydroxypivalic acid neopentyl glycol di(meth) acrylate, dicyclopentane Di-(meth) acrylate, caprolactone modified dicyclopentenyl di(meth) acrylate, ethylene oxide modified di(meth) acrylate, allylated cyclohexyl bis ( Methyl) acrylate, isocyanurate di(meth) acrylate, trimethylolpropane tri(meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate Dipentaerythritol tri(meth)acrylate, propionic acid modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide modified trimethylolpropane tri(meth)acrylic acid Ester, tris(propylene oxyethyl) isocyanurate, propionic acid modified dipentaerythritol penta (methyl) Acrylate, dipentaerythritol hexa (meth) acrylate, ethylene oxide modified dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate. One type of the above-mentioned polyfunctional (meth) acrylate may be used alone, or two or more kinds of the above-mentioned polyfunctional (meth) acrylate may be used in combination. Among them, preferred is dipentaerythritol tri(meth)acrylate.

Further, in addition to the polyfunctional (meth) acrylate, a monofunctional (meth) acrylate may be contained for the purpose of lowering the viscosity and the like. Examples of the monofunctional (meth) acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. Amyl methacrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, (meth) acrylate Octaalkyl ester, isobornyl (meth)acrylate, and the like. One type of the above-mentioned monofunctional (meth) acrylate may be used alone, or two or more kinds of the above-mentioned monofunctional (meth) acrylate may be used in combination.

Examples of the polymerizable oligomer include an oligomer having a radical polymerizable unsaturated group in the molecule, and examples thereof include an epoxy (meth)acrylate oligomer and a polyurethane (methyl). An acrylate type oligomer, a polyester (meth) acrylate type oligomer, a polyether (meth) acrylate type oligomer, etc.

For example, by esterifying (meth)acrylic acid with an epoxy ring of a lower molecular weight bisphenol type epoxy resin or a novolac type epoxy resin, the epoxy (meth)acrylate type can be obtained. Polymer. Further, a carboxyl-modified epoxy (meth) acrylate oligomer obtained by partially modifying the epoxy (meth) acrylate-based oligomer with a dicarboxylic acid anhydride can also be used. For example, the urethane (meth) acrylate system can be obtained by esterifying a urethane oligomer obtained by reacting a polyether polyol or a polyester polyol with a polyisocyanate with (meth)acrylic acid. Oligomer. For example, a hydroxyl group of a polyester oligomer having a hydroxyl group at both terminals obtained by condensation of a polyvalent carboxylic acid and a polyhydric alcohol can be esterified with (meth)acrylic acid, thereby obtaining the polyester (methyl group). ) an acrylate-based oligomer. Further, the hydroxyl group at the terminal of the oligomer obtained by adding an alkylene oxide to the polyvalent carboxylic acid may be esterified with (meth)acrylic acid, thereby obtaining the polyester (methyl). Acrylate oligomer. The hydroxyl group of the polyether polyol can be esterified with (meth)acrylic acid, whereby the polyether (meth)acrylate-based oligomer can be obtained.

Further, as the actinic radiation curable resin, an ultraviolet curable epoxy resin is also suitably used. The ultraviolet curable epoxy resin may, for example, be a cured product such as a bisphenol A epoxy resin or a glycidyl ether epoxy resin. When the main component of the resin base 13 is an ultraviolet curable epoxy resin, the upper light diffusing sheet 5 can suppress volume shrinkage during curing, and it is easy to form a desired uneven shape on the surface side of the base material layer 11. In addition, by making the main component of the resin base 13 an ultraviolet curable epoxy resin, the upper light diffusing sheet 5 improves the flexibility of the resin base 13, and it is possible to improve the prevention of the light diffusing sheet 5 disposed on the upper surface. Damage to the surface of the liquid crystal panel or the like. Further, when an ultraviolet curable epoxy resin is used as the actinic radiation curable resin, it is preferred that the (meth) acrylate monomer or (meth) acrylate oligomer is not contained. Other polymerizable monomers and polymerizable oligomers. Thereby, the flexibility of the resin base 13 can be further improved, and the damage prevention performance can be further improved.

When the ultraviolet curable resin is used as the actinic radiation-curable resin, it is preferable to add 0.1 part by mass or more and 5 parts by mass or less of the photopolymerization initiator to 100 parts by mass of the resin. The initiator for photopolymerization is not particularly limited, and examples of the polymerizable monomer having a radical polymerizable unsaturated group in the molecule and the polymerizable oligomer include benzophenone, benzoin, and tetra. Methyl ketone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-diethoxy Acetophenone, benzoin dimethyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1- Ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylacetone-1, 1-[4-(2-hydroxyethyl) Oxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, bis(cyclopentadienyl)-bis[2,6-difluoro-3-(pyrrole-1- Phenyl]titanium, 2-benzyl-2-dimethylamino-1-(4-morpholinylphenyl)-butanone-1, 2,4,6-trimethylbenzhydrylbiphenyl Phosphine oxide and the like. In addition, examples of the polymerizable oligomer having a cationically polymerizable functional group in the molecule include an aromatic onium salt, an aromatic diazonium salt, an aromatic iodonium salt, a metallocene compound, and a benzoin sulfonate. Further, each of the monomers of the above compounds may be used, or a plurality of the compounds described above may be used in combination.

Further, in addition to the synthetic resin, the resin matrix 13 may further contain an additive. Examples of the additive include a lanthanoid additive, a fluorine-based additive, and an antistatic agent. In addition, the content of the additive in the resin base 13 with respect 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.

The resin beads 14 are resin particles having a property of transmitting light through diffusion. The resin beads 14 have a transparent, particularly colorless, transparent synthetic resin as a main component. The main component of the resin beads 14 may, for example, be an acrylic resin, an acrylonitrile resin, a polyurethane, a polyvinyl chloride, a polystyrene, a polyamide or a polyacrylonitrile. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is particularly preferred.

The shape of the resin beads 14 is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scaly shape, and a fibrous shape. Among them, a spherical shape having good light diffusibility is preferable. .

The resin beads 14 of the light diffusion layer 12 may abut against the surface of the base material layer 11, but are preferably substantially separated from the surface of the base material layer 11. For the upper light-diffusing sheet 5, for example, a photo-irradiation-curable resin can be used as a main component of the resin substrate 13, and a coating of the resin beads 14 dispersed in the actinic radiation-curable resin can be applied to the surface of the base layer 11. In the liquid, the actinic radiation-curable resin is cured in a state where the resin beads 14 and the surface of the base material layer 11 are separated, whereby the resin beads 14 are fixed in a state of being separated from the surface of the base material layer 11. By substantially separating the resin beads 14 from the surface of the base material layer 11, the upper light diffusion sheet 5 easily forms minute and high-density irregularities on the surface of the light diffusion layer 12, and can more reliably suppress the liquid crystal panel. The occurrence of flicker caused by interference of pixel spacing. Further, the "separation of the resin beads from the surface of the base material layer" also includes the concept of a resin bead which does not directly abut against the surface of the base material layer, and the resin beads which are not directly in contact with the surface of the base material layer are and The resin beads that abut the surface of the layer abut on the other resin beads. Further, for example, it is possible to confirm whether or not the resin beads are separated from the surface of the base material layer by observing the cross section in the thickness direction of the upper light diffusion sheet with a laser microscope.

The lower limit of the mode diameter of the volume-based particle size distribution of the resin beads 14 is 2.5 μm, preferably 4.5 μm, more preferably 4.7 μm, still more preferably 4.9 μm. On the other hand, the upper limit of the mode diameter of the resin beads 14 is 5.5 μm, preferably 5.4 μm, and more preferably 5.3 μm. If the mode diameter of the resin beads 14 is smaller than the lower limit, there is a problem that the unevenness of the surface of the light diffusion layer 12 becomes too small, the light diffusibility is insufficient, and the shape of the prism portion of the prism sheet 4 cannot be sufficiently suppressed. The unevenness of brightness caused by the like and the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel. On the other hand, if the mode diameter of the resin beads 14 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light diffusion layer 12, and the pixel pitch from the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by the interference.

The lower limit of the density per unit area of the resin beads 14 is 9000 pieces/mm ² , more preferably 11500 pieces/mm ² , and still more preferably 14,000 pieces/mm ² . On the other hand, the upper limit of the density per unit area of the resin beads 14 is 24,000 pieces/mm ² , more preferably 21,000 pieces/mm ² , and still more preferably 20,000 pieces/mm ² . If the density per unit area of the resin bead 14 is less than the lower limit, there is a problem that brightness unevenness caused by the shape or the like of the protruding strip-shaped prism portion of the prism sheet 4 cannot be sufficiently suppressed, and the surface of the light diffusion layer 12 exists. The increase in density of the concavities and convexities is insufficient, and the problem of occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel cannot be sufficiently suppressed. On the other hand, if the density per unit area of the resin beads 14 exceeds the upper limit, there is a problem that light incident from the back side is excessively diffused, and the brightness of the liquid crystal display device is lowered.

The upper limit of the coefficient of variation of the particle diameter as the volume-based particle size distribution of the resin beads 14 is preferably 42%, more preferably 41%, still more preferably 40%, and particularly preferably 39%. If the coefficient of variation exceeds the upper limit, there is a problem in that relatively large irregularities are excessively formed on the surface of the light diffusion layer 12, and occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel cannot be sufficiently suppressed. . On the other hand, as the lower limit of the coefficient of variation, it is preferably 30%, and more preferably 35%. If the coefficient of variation is less than the lower limit, there is a problem that the unevenness of the surface of the light diffusion layer 12 is excessively uniform, and the light cannot be appropriately diffused.

The lower limit of the particle size width as the volume-based particle size distribution of the resin beads 14 is preferably 13 μm, more preferably 14 μm, still more preferably 15 μm. On the other hand, the upper limit of the particle size width of the resin beads 14 is preferably 20 μm, more preferably 19 μm, still more preferably 18 μm. If the particle size width of the resin beads 14 is less than the lower limit, there is a problem in that the unevenness of the surface of the light diffusion layer 12 is excessively uniform, and light is not properly diffused. On the other hand, if the particle size width of the resin beads 14 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light diffusion layer 12, and the pixel pitch from the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by interference. Further, the "particle size width of the volume-based particle size distribution of the resin beads" can be obtained by subtracting the minimum diameter from the maximum diameter of the particle diameter of the volume-based particle size distribution of the resin beads.

The upper limit of the average particle diameter D50 as the volume-based particle size distribution of the resin beads 14 is preferably 5.7 μm, more preferably 5.5 μm, still more preferably 5 μm. On the other hand, the lower limit of the average particle diameter D50 as the volume-based particle size distribution of the resin beads 14 is preferably 4 μm, more preferably 4.3 μm, still more preferably 4.5 μm. If the average particle diameter D50 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light diffusion layer 12, and flicker caused by interference with the pixel pitch of the liquid crystal panel cannot be sufficiently suppressed. happened. On the other hand, when the average particle diameter D50 is less than the lower limit, there is a problem that the unevenness on the surface of the light diffusion layer 12 is too small, the light diffusibility is insufficient, and the shape of the prism portion of the prism sheet 4 cannot be sufficiently suppressed. The brightness is uneven.

The upper limit of the particle diameter D70 as the volume-based particle size distribution of the resin beads 14 is preferably 6.4 μm, more preferably 6.2 μm, still more preferably 5.9 μm. On the other hand, the lower limit of the particle diameter D70 which is the volume-based particle size distribution of the resin beads 14 is preferably 5.1 μm, more preferably 5.3 μm, still more preferably 5.4 μm. If the particle diameter D70 of the volume-based particle size distribution of the resin bead 14 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light-diffusing layer 12, and the pixel with the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by the interference of the spacing. On the other hand, if the particle diameter D70 of the volume-based particle size distribution of the resin bead 14 is smaller than the lower limit, there is a problem that the unevenness of the surface of the light-diffusing layer 12 becomes too small, the light diffusibility is insufficient, and the prism sheet 4 cannot be sufficiently suppressed. Unevenness of brightness caused by the shape of the prism portion or the like.

The lower limit of the refractive index of the resin beads 14 is preferably 1.46, and more preferably 1.48. 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. When the refractive index of the resin bead 14 is within the above range, the refractive index difference with the resin base 13 can be appropriately adjusted, whereby the shape of the strip prism portion 16 protruding from the prism sheet 4 to be described later can be easily suppressed. The resulting brightness is uneven. In addition, "refractive index" means the refractive index of the light of the wavelength of 589.3 nm (the D line of sodium).

The lower limit of the center line average roughness Ra of the surface of the light diffusion layer 12 is preferably 0.3 μm, more preferably 0.4 μm, still more preferably 0.5 μm. On the other hand, the upper limit of the center line average roughness Ra of the surface of the light diffusion layer 12 is preferably 1 μm, more preferably 0.9 μm, still more preferably 0.8 μm. If the center line average roughness Ra of the surface of the light diffusion layer 12 is smaller than the lower limit, there is a problem that the unevenness of the surface of the light diffusion layer 12 becomes too small, the light diffusibility is insufficient, and the protrusion by the prism sheet 4 cannot be sufficiently suppressed. Unevenness of brightness caused by the shape of the strip prism portion or the like. On the other hand, if the center line average roughness Ra of the surface of the light diffusion layer 12 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light diffusion layer 12, and the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by the interference of the pixel spacing.

The lower limit of the ten point average roughness Rz of the surface of the light diffusion layer 12 is preferably 1.5 μm, more preferably 2 μm, still more preferably 2.5 μm. On the other hand, the upper limit of the ten point average roughness Rz as the surface of the light diffusion layer 12 is preferably 4.5 μm, more preferably 4 μm, still more preferably 3.6 μm. If the ten-point average roughness Rz of the surface of the light-diffusing layer 12 is smaller than the lower limit, there is a problem that the unevenness of the surface of the light-diffusing layer 12 becomes too small, the light diffusibility is insufficient, and the protrusion by the prism sheet 4 cannot be sufficiently suppressed. Unevenness of brightness caused by the shape of the strip prism portion or the like. On the other hand, if the ten-point average roughness Rz of the surface of the light-diffusing layer 12 exceeds the upper limit, there is a problem that a relatively large unevenness is excessively formed on the surface of the light-diffusing layer 12, and the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by interference of pixel spacing.

The lower limit of the root mean square roughness Rq of the surface of the light diffusion layer 12 is preferably 0.55 μm, more preferably 0.65 μm, still more preferably 0.7 μm. On the other hand, the upper limit of the root mean square roughness Rq of the surface of the light diffusion layer 12 is preferably 0.9 μm, more preferably 0.85 μm, still more preferably 0.8 μm. When the root mean square roughness Rq of the surface of the light diffusion layer 12 is less than the lower limit, there is a problem that the unevenness of the surface of the light diffusion layer 12 becomes too small, the light diffusibility is insufficient, and the protrusion by the prism sheet 4 cannot be sufficiently suppressed. Unevenness of brightness caused by the shape of the strip prism portion or the like. On the other hand, if the root mean square roughness Rq of the surface of the light diffusion layer 12 exceeds the upper limit, there is a problem that a relatively large unevenness is formed excessively on the surface of the light diffusion layer 12, and the liquid crystal panel cannot be sufficiently suppressed. The occurrence of flicker caused by the interference of the pixel spacing. In addition, the "root mean square roughness Rq" means a value of an evaluation length of 12.5 mm in accordance with JIS-B0601:2001, a cutoff length (λc) of 2.5 mm, and an evaluation length of 12.5 mm.

The lower limit of the average length RSm of the roughness curve element of the surface of the light diffusion layer 12 is preferably 30 μm, more preferably 40 μm, still more preferably 50 μm. On the other hand, the upper limit of the average length RSm of the roughness curve element of the surface of the light diffusion layer 12 is preferably 100 μm, more preferably 80 μm, still more preferably 60 μm. If the average length RSm of the roughness curve elements of the surface of the light diffusion layer 12 is smaller than the lower limit, there is a problem that the unevenness of the surface of the light diffusion layer 12 is too small, the light diffusibility is insufficient, and the prism sheet 4 cannot be sufficiently suppressed. The unevenness of brightness caused by the shape of the protruding strip prism portion or the like. On the other hand, if the average length RSm of the roughness curve elements on the surface of the light diffusion layer 12 exceeds the upper limit, there is a problem in that it is difficult to form minute and high-density irregularities on the surface of the light diffusion layer 12, and it is not possible to sufficiently suppress the The occurrence of flicker caused by the interference of the pixel pitch of the liquid crystal panel occurs.

The lower limit of the amount of lamination (in terms of solid content) of the light-diffusing layer 12 is preferably 2 g/m ² , more preferably 2.2 g/m ² , still more preferably 2.4 g/m ² . On the other hand, the upper limit of the amount of lamination of the light diffusion layer 12 is preferably 3 g/m ² , more preferably 2.8 g/m ² , still more preferably 2.6 g/m ² . When the lamination amount of the light diffusion layer 12 is less than the lower limit, there is a problem that the resin beads 14 cannot be reliably fixed by the resin substrate 13, and the resin beads 14 are detached from the light diffusion layer 12. On the other hand, if the amount of lamination of the light-diffusing layer 12 exceeds the upper limit, there is a problem in that it is difficult to form minute and high-density irregularities on the surface of the light-diffusing layer 12, and as a result, it is not sufficiently suppressed and disposed on the surface. The occurrence of flicker due to interference of the pixel pitch of the liquid crystal panel on the surface side of the light diffusion sheet 5 occurs.

The lower limit of the content ratio of the resin base 13 as the light diffusion layer 12 is preferably 50% by mass, more preferably 52% by mass. On the other hand, the upper limit of the content ratio of the resin base 13 as the light diffusion layer 12 is preferably 69% by mass, more preferably 67% by mass. When the content ratio of the resin base 13 is less than the lower limit, the light diffusibility of the light diffusion layer 12 may become too high, and the brightness of the liquid crystal display device may not become sufficiently high. On the other hand, when the content ratio of the resin base 13 exceeds the upper limit, there is a problem in that the number of the resin beads 14 in the light diffusion layer 12 is insufficient, and it is difficult to form minute and high-density irregularities on the surface of the light diffusion layer 12. The occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel disposed on the surface side of the upper light diffusion sheet 5 cannot be sufficiently suppressed.

The lower limit of the content ratio of the resin beads 14 as the light diffusion layer 12 is preferably 31% by mass, more preferably 33% by mass. On the other hand, the upper limit of the content ratio of the resin beads 14 as the light diffusion layer 12 is preferably 50% by mass, more preferably 48% by mass. When the content ratio of the resin beads 14 of the light-diffusing layer 12 is less than the lower limit, there is a problem in that it is difficult to form minute and high-density irregularities on the surface of the light-diffusing layer 12, and it is not possible to sufficiently suppress the arrangement and the above-mentioned arrangement. The occurrence of flicker due to interference of the pixel pitch of the liquid crystal panel on the surface side of the light diffusion sheet 5 occurs. On the other hand, if the content ratio of the resin beads 14 of the light-diffusing layer 12 exceeds the upper limit, there is a problem that the light diffusibility of the light-diffusing layer 12 becomes too high, and the brightness of the liquid crystal display device cannot be sufficiently high.

As the resin beads 14, it is preferred to use a first bead and a second bead having an average particle diameter smaller than the first bead. The unevenness of the light diffusion layer 12 is formed by using the resin beads 14 in which the second beads having an average particle diameter smaller than that of the first resin beads are mixed in addition to the first beads, whereby the light diffusion sheet 5 can be used for the above. The light diffusion layer 12 forms a large number of minute irregularities. Therefore, by mixing the first beads and the second beads as the resin beads 14, the upper light diffusion sheet 5 easily suppresses interference with the pixel pitch of the liquid crystal panel caused by minute irregularities caused by the second resin beads. The occurrence of flicker occurs.

In the case where the resin beads 14 include the first beads and the second beads, the average particle diameter D50 of the second beads may be, for example, 1.9 μm or more and 2.5 μm or less. Further, the average particle diameter D50 of the first beads may be, for example, 5 μm or more and 6.5 μm or less. By setting the average particle diameter D50 of the first bead and the second bead to be within the above range, the upper light-diffusing sheet 5 can suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel, and can It is easy to prevent adhesion to the liquid crystal panel.

In the case where the resin beads 14 contain the first beads and the second beads, the lower limit of the ratio (mass ratio) of the content of the second beads to the content of the first beads is preferably 0.4, more preferably 0.45. On the other hand, the upper limit of the ratio of the content of the second beads to the content of the first beads is preferably 0.6, more preferably 0.55. If the ratio of the content is less than the lower limit, there is a problem that it is difficult to suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel. On the other hand, if the ratio of the content exceeds the upper limit, there is a problem that the unevenness of the surface of the light-diffusing layer 12 becomes excessively uniform, and the light cannot be appropriately diffused.

The lower limit of the haze value of the above-mentioned light diffusing sheet 5 is preferably 50%, and more preferably 52%. On the other hand, the upper limit of the haze value of the above-mentioned light diffusing sheet 5 is preferably 70%, and more preferably 68%. If the haze value of the upper light-diffusing sheet 5 is smaller than the lower limit, there is a problem in that unevenness in brightness due to the shape of the protruding strip-shaped prism portion of the prism sheet 4, and the like are not sufficiently suppressed. The occurrence of flicker caused by the interference of the pixel pitch of the liquid crystal panel occurs. On the other hand, if the haze value of the upper light-scattering sheet 5 exceeds the upper limit, there is a problem that the brightness of the liquid crystal display device becomes insufficient. In addition, "haze value" means a value measured in accordance with JIS-K7361:2000.

As shown in FIG. 2, in the backlight unit, adjacent protruding strip prism portions in a cross section perpendicular to a ridge line of the protruding strip prism portion 16 of the prism sheet 4 to be described later are preferable. A plurality of resin beads 14 are disposed in a region between the apexes of 16 (a region between the straight lines passing through the apexes of the protruding strip-shaped prism portions 16 and perpendicular to the back surface of the prism sheet 4). Further, the lower limit of the ratio of the average particle diameter D50 of the resin beads 14 to the average pitch p of the ridge lines of the prism sheet 4 is preferably 0.06, and more preferably 0.08. On the other hand, the upper limit of the ratio of the average particle diameter D50 of the resin beads 14 to the average pitch p of the ridge lines of the prism sheet 4 is preferably 0.25, and more preferably 0.23. If the ratio of the average particle diameter D50 of the resin beads 14 to the average pitch p of the ridge lines of the prism sheet 4 is smaller than the lower limit, the shape of the strip-shaped prism portion 16 protruding from the prism sheet 4 cannot be sufficiently suppressed. The problem of uneven brightness. On the other hand, if the ratio of the average particle diameter D50 of the resin beads 14 to the average pitch p of the ridge lines of the prism sheet 4 exceeds the upper limit, there is a problem that it is difficult to form a minute and high density on the surface of the light diffusion layer 12. The unevenness does not sufficiently suppress the occurrence of flicker caused by interference with the pixel pitch of the liquid crystal panel disposed on the surface side of the upper light diffusion sheet 5.

<Prism sheet>

Since the prism sheet 4 needs to transmit light, a transparent, particularly colorless, transparent synthetic resin is formed as a main component. The prism sheet 4 has a base material layer 15 and a projection row composed of a plurality of protruding strip prism portions 16 laminated on the surface of the base material layer 15. The protruding strip prism portions 16 are laminated on the surface of the base material layer 15 in a stripe shape. The protruding strip prism portion 16 is a triangular prism-shaped body whose back surface is in contact with the surface of the base material layer 15.

The lower limit of the thickness of the prism sheet 4 (the height from the back surface of the base material layer 15 to the apex of the protruding strip prism portion 16) is preferably 50 μm, and more preferably 100 μm. On the other hand, the upper limit of the thickness of the prism sheet 4 is preferably 200 μm, and more preferably 180 μm. Further, the lower limit of the pitch p (refer to FIG. 2) of the protruding strip prism portion 16 of the prism sheet 4 is preferably 20 μm, and more preferably 30 μm. On the other hand, the upper limit of the pitch p of the protruding strip prism portion 16 as the prism sheet 4 is preferably 100 μm, and more preferably 60 μm. Further, as the vertex angle of the protruding strip prism portion 16, it is preferably 85 or more and 95 or less. Further, as the lower limit of the refractive index of the protruding strip prism portion 16, it is preferably 1.5, and more preferably 1.55. On the other hand, the upper limit of the refractive index of the protruding strip prism portion 16 is preferably 1.7.

In addition, the backlight unit is not limited to having only one prism sheet 4, and may have other prism sheets superposed on the prism sheet 4. Further, in this case, it is preferable that the ridge line of the plurality of protruding strip-shaped prism portions 16 of the prism sheet 4 is perpendicular to the ridge line of the plurality of protruding strip-shaped prism portions of the other prism sheets. By arranging the ridge line of the protruding strip prism portion 16 of the prism sheet 4 perpendicularly to the ridge line of the protruding strip prism portion of the other prism sheet, the prism sheet can be incident from the lower light diffusion sheet 3 by the one prism sheet. The light is refracted toward the normal side, and the light emitted from one of the prism sheets is caused to travel substantially perpendicularly to the back surface of the upper light diffusing sheet 5 by the other prism sheet. Further, the material for forming the other prism sheet, the thickness, the pitch of the protruding strip-shaped prism portions, the apex angle of the protruding strip-shaped prism portion, and the refractive index of the protruding strip-shaped prism portion may be the same as those of the prism sheet 4.

<Light Guide>

The light guide sheet 1 is a sheet-shaped optical member that internally propagates light emitted from the light source 2 and is emitted from the surface. The light guiding sheet 1 may be formed in a substantially wedge shape in cross section, or may be formed in a substantially flat shape. Since the light guide sheet 1 needs to have translucency, a transparent, particularly colorless, transparent resin is formed as a main component. The main component of the light guiding sheet 1 is not particularly limited, and examples thereof include polycarbonates having good transparency and strength, and synthetic resins such as acrylic resins which are excellent in transparency and scratch resistance. Among them, as the main component of the light guiding sheet 1, polycarbonate is preferable. Since the polycarbonate has a good transparency and a high refractive index, it is formed on the air layer (the layer formed in the gap with the lower light diffusion sheet 3 disposed on the surface side of the light guide sheet 1 and on the light guide sheet). The interface of the layer of the gap of the reflection sheet 6 on the back side of 1 is likely to be totally reflected, and light can be efficiently transmitted. Further, since polycarbonate has heat resistance, deterioration or the like due to heat generation of the light source 2 is less likely to occur.

<light source>

The irradiation surface of the light source 2 is disposed to face (or abut against) the end surface of the light guiding sheet 1. As the light source 2, various light sources can be used, and for example, a light emitting diode (LED) can be used. Specifically, as the light source 2, a light source in which a plurality of light emitting diodes are arranged along the end surface of the light guiding sheet 1 can be used.

<Bottom light diffuser>

The lower light diffusion sheet 3 has a base material layer 17 , a light diffusion layer 18 disposed on the surface side of the base material layer 17 , and an adhesion prevention layer 19 disposed on the back surface side of the base material layer 17 . The base material layer 17 of the lower light diffusion sheet 3 may have the same configuration as the base material layer 11 of the above-described upper light diffusion sheet 5. The light diffusion layer 18 of the lower light diffusion sheet 3 has a light diffusion material and a binder.

The light diffusing material is a particle having a property of diffusing light, and is roughly classified into an inorganic filler and an organic filler. Examples of the inorganic filler include cerium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, cerium sulfide, magnesium citrate or a mixture thereof. Specific examples of the organic filler include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamine, polyacrylonitrile, and the like. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is particularly preferred.

The shape of the light-diffusing material is not particularly limited, and may be, for example, a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, a fiber shape, or the like. Among them, a ball having good light diffusibility is preferable. Shaped beads.

The lower limit of the average particle diameter of the light-diffusing material is preferably 8 μm, and more preferably 10 μm. On the other hand, the upper limit of the average particle diameter of the light-diffusing material is preferably 50 μm, more preferably 20 μm, still more preferably 15 μm. When the average particle diameter of the light-diffusing material is less than the lower limit, there is a problem in that the unevenness of the surface of the light-diffusing layer 18 is small, and the light diffusibility which is necessary for the lower light-diffusing sheet 3 is not satisfied. On the other hand, if the average particle diameter of the light-diffusing material exceeds the upper limit, there is a problem that the thickness of the lower light-diffusing sheet 3 is increased and it is difficult to uniformly diffuse.

The lower limit of the content ratio of the binder as the light diffusion layer 18 is preferably 15% by mass, more preferably 30% by mass. On the other hand, the upper limit of the content ratio of the binder as the light diffusion layer 18 is preferably 48% by mass, more preferably 45% by mass. If the content of the binder is less than the lower limit, there is a problem that the light-diffusing material cannot be reliably fixed by the binder. On the other hand, if the content rate of the binder exceeds the upper limit, there is a problem that light diffusibility becomes insufficient.

The lower limit of the content ratio of the light diffusing material as the light diffusion layer 18 is preferably 52% by mass, more preferably 55% by mass. On the other hand, the upper limit of the content ratio of the light-diffusing material as the light-diffusing layer 18 is preferably 85% by mass, more preferably 70% by mass. If the content ratio of the light diffusing material of the light diffusion layer 18 is less than the lower limit, there is a problem that the light diffusibility becomes insufficient. On the other hand, if the content ratio of the light diffusing material of the light diffusion layer 18 exceeds the upper limit, there is a problem that the light diffusing material cannot be reliably fixed by the binder.

The lower limit of the center line average roughness Ra of the surface of the light diffusion layer 18 is preferably 1.1 μm, more preferably 1.3 μm, still more preferably 1.4 μm. On the other hand, the upper limit of the center line average roughness Ra of the surface of the light diffusion layer 18 is preferably 5 μm, more preferably 3 μm, still more preferably 2 μm. If the center line average roughness Ra of the surface of the light diffusion layer 18 is smaller than the lower limit, there is a problem that the light diffusibility is insufficient. On the other hand, when the center line average roughness Ra of the surface of the light diffusion layer 18 exceeds the upper limit, there is a problem that the light transmittance is lowered and the brightness of the liquid crystal display device is insufficient.

The lower limit of the ten point average roughness Rz of the surface of the light diffusion layer 18 is preferably 5 μm, more preferably 6 μm, still more preferably 7 μm. On the other hand, the upper limit of the ten point average roughness Rz as the surface of the light diffusion layer 18 is preferably 20 μm, more preferably 15 μm, still more preferably 10 μm. If the ten point average roughness Rz of the surface of the light diffusion layer 18 is smaller than the lower limit, there is a problem that the light diffusibility is insufficient. On the other hand, if the ten-point average roughness Rz of the surface of the light-diffusing layer 18 exceeds the upper limit, there is a problem that the light transmittance is lowered and the luminance of the liquid crystal display device is insufficient.

The lower limit of the root mean square roughness Rq of the surface of the light diffusion layer 18 is preferably 1.2 μm, more preferably 1.5 μm, still more preferably 1.7 μm. On the other hand, the upper limit of the root mean square roughness Rq of the surface of the light diffusion layer 18 is preferably 2.5 μm, more preferably 2.2 μm, still more preferably 2 μm. If the root mean square roughness Rq of the surface of the light diffusion layer 18 is smaller than the lower limit, there is a problem that the light diffusibility becomes insufficient. On the other hand, when the root mean square roughness Rq of the surface of the light diffusion layer 18 exceeds the upper limit, there is a problem that the light transmittance is lowered and the luminance of the liquid crystal display device is insufficient.

The adhesion preventing layer 19 is formed by dispersing resin beads in a resin matrix. The resin beads are disposed on the back side of the base material layer 17 in a scattered manner. By arranging the resin beads in a scatter manner, the adhesion preventing layer 19 has a plurality of convex portions formed by the resin beads and a flat portion in which the resin beads are not present. The adhesion preventing layer 19 is abutted against the light guiding sheet 1 disposed on the back side by the plurality of convex portions, and is prevented from adhering by not contacting the entire surface of the back surface, thereby suppressing the liquid crystal display device. Uneven brightness.

The lower limit of the haze value of the lower light-diffusing sheet 3 is preferably 80%, more preferably 85%, still more preferably 90%. If the haze value of the lower light-diffusing sheet 3 is smaller than the lower limit, there is a problem that the light diffusibility is insufficient. Further, the upper limit of the haze value of the lower light diffusion sheet 3 may be, for example, 95%.

<reflection sheet>

Examples of the reflection sheet 6 include a white sheet obtained by dispersing a filler in a base resin such as polyester, and a mirror surface obtained by depositing a metal such as aluminum or silver on the surface of a film formed of polyester or the like. A mirror sheet or the like having improved reflectivity.

<advantage>

Since the light diffusion layer 12 of the upper light diffusion sheet 5 has the resin base 13 and the resin beads 14, irregularities due to the resin beads 14 are formed on the surface of the light diffusion layer 12. Therefore, the above-described light-diffusing sheet 5 diffuses light incident from the back side by the unevenness, and it is possible to suppress unevenness in brightness caused by the shape or the like of the strip-shaped prism portion 16 that protrudes from the prism sheet 4. Further, since the mode diameter of the volume-based particle size distribution of the resin beads 14 and the density per unit area and the average thickness of the light diffusion layer 12 are respectively within the ranges, the upper light-diffusing sheet 5 can be minute and high in density. The unevenness is formed randomly, so that occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel can be suppressed.

Since the upper light diffusion sheet 5 is superposed on the surface side of the prism sheet 4, the light emitted from the prism sheet 4 is diffused by the unevenness of the surface of the light diffusion layer 12 formed by the upper light diffusion sheet 5, The backlight unit can suppress luminance unevenness caused by the shape or the like of the protruding strip prism portion 16 of the prism sheet 4. Further, since the mode diameter of the volume-based particle size distribution of the resin beads 14 of the upper light-scattering sheet 5, the density per unit area, and the average thickness of the light-diffusing layer are respectively within the ranges, the backlight unit can be minute Further, the unevenness is randomly formed at a high density, and occurrence of flicker due to interference with the pixel pitch of the liquid crystal panel can be suppressed.

<Manufacturing method of upper light diffusing sheet>

The method for producing the upper light-diffusing sheet 5 includes a flow of forming a sheet constituting the base material layer 11 (a base material layer forming flow); and a flow of laminating the light diffusion layer 12 on one surface side of the sheet body. (Light diffusion layer lamination flow).

(Substrate layer formation process)

The formation process of the base material layer is not particularly limited, and for example, extrusion molding of a molten thermoplastic resin from a T die may be mentioned, and then the extrusion molded body may be formed to extend in the layer longitudinal direction and the layer width direction. The method of the slice. As a well-known extrusion molding method using a T-die, a polishing roll method, a cooling roll method, etc. are mentioned, for example. Further, examples of the method of stretching the sheet include a tubular film biaxial stretching method and a flat film biaxial stretching method.

(Light diffusion layer lamination process)

The light diffusion layer lamination process includes a flow of preparing a coating liquid containing the resin base 13 and the resin beads 14 (preparation flow); and a flow of applying the coating liquid prepared by the preparation process to one side of the sheet body (Coating process); and a process of drying and solidifying the coating liquid applied by the coating process (curing flow). Preferably, in the preparation flow, a coating liquid containing the actinic radiation curable resin as the main component of the resin matrix 13 and including the first beads and the second beads mixed as the resin beads 14 is prepared. In the method for producing the upper light-diffusing sheet, the actinic radiation-curable resin is used as a main component of the resin base 13, and after the coating liquid is applied in the coating flow, for example, ultraviolet rays are irradiated in the curing process. The actinic radiation curable resin can be easily cured faster. Therefore, by curing the actinic radiation curable resin in a state where the resin beads 14 are separated from one surface of the sheet, it is easy to fix the resin beads 14 in a state where they are separated from one side of the sheet. Further, in the method for producing the upper light-diffusing sheet, by preparing a coating liquid in which the first beads and the second beads are mixed as the resin beads 14 in the preparation flow, the light diffusion layer 12 can be made to contain a large amount of particle diameters. The smaller resin beads can suppress the occurrence of flicker caused by the interference of the pixel pitch with the liquid crystal panel by the resin beads having a small particle diameter, and can easily prevent the liquid crystal panel from being passed through the resin beads having a large particle diameter. Sticking.

Further, the method for producing the upper light diffusion sheet may further include performing a corona discharge treatment, an ozone treatment, and a low temperature on a surface on which the light diffusion layer of the sheet is laminated before the light diffusion layer lamination step. Surface treatment processes such as plasma treatment, glow discharge treatment, oxidation treatment, undercoat treatment, undercoat treatment, and adhesion coating treatment.

[Upper light diffuser]

Instead of the upper light diffusing sheet 5 of Fig. 1, the upper light diffusing sheet 25 of Fig. 3 can be used for the backlight unit of Fig. 1. The upper light-diffusing sheet 25 suppresses unevenness in brightness caused by the shape of the protruding strip-shaped prism portion of the prism sheet, and the like, and suppresses the unevenness of light emitted from the light-distributing sheet 25 disposed on the upper surface. The occurrence of flicker due to the interference of the pixel pitch of the liquid crystal panel (not shown) on the front side. The upper light diffusion sheet 25 includes a base material layer 11 , a light diffusion layer 12 laminated on the surface side of the base material layer 11 , and an adhesion prevention layer 26 laminated on the back surface side of the base material layer 11 . The upper light diffusion sheet 25 is configured as a base layer 11 , a light diffusion layer 12 directly laminated on the surface of the base material layer 11 , and a three-layer structure in which the adhesion prevention layer 26 is directly laminated on the back surface of the base material layer 11 . The base material layer 11 and the light diffusion layer 12 of the upper light diffusion sheet 25 are the same as those of the upper light diffusion sheet 5 of Fig. 1, and therefore the same reference numerals are attached thereto, and the description thereof is omitted.

(adhesion prevention layer)

The adhesion preventing layer 26 constitutes the rearmost surface of the upper light diffusion sheet 25. Since the adhesion preventing layer 26 needs to transmit light, a transparent, particularly colorless, transparent synthetic resin is formed as a main component. The adhesion preventing layer 26 is formed into a film shape having a flat back surface and a substantially uniform thickness. The adhesion preventing layer 26 is partially in contact with the top of the protruding prism portion of the prism sheet disposed on the back surface side of the upper light diffusion sheet 25, whereby adhesion to the prism sheet can be prevented. Examples of the main component of the adhesion preventing layer 26 include polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, and methyl (meth)acrylate. a styrene copolymer, a polyolefin, a cycloolefin polymer, a cyclic olefin copolymer, cellulose acetate, weather resistant vinyl chloride, a photochemical irradiation curable resin, and the like. Among them, an acrylic resin which can increase the strength of the back surface of the upper light-diffusing sheet 25 and can easily prevent damage of the back surface is preferable.

The lower limit of the average thickness of the adhesion preventing layer 26 is preferably 1 μm, and more preferably 2 μm. On the other hand, the upper limit of the average thickness of the adhesion preventing layer 26 is preferably 10 μm, and more preferably 8 μm. If the average thickness of the adhesion preventing layer 26 is less than the lower limit, there is a problem that the back surface of the upper light diffusion sheet 25 cannot be reliably prevented from being injured. On the other hand, if the average thickness of the adhesion preventing layer 26 exceeds the upper limit, there is a problem that the brightness of the liquid crystal display device is lowered.

The upper limit of the center line average roughness Ra of the back surface of the adhesion preventing layer 26 is preferably 0.04 μm, more preferably 0.035 μm, still more preferably 0.03 μm. When the center line average roughness Ra of the back surface of the adhesion preventing layer 26 exceeds the upper limit, there is a problem that the strip-shaped prism portion protruding in the prism sheet is damaged by the contact with the adhesion preventing layer 26. In addition, the lower limit of the center line average roughness Ra of the back surface of the adhesion preventing layer 26 is not particularly limited, and may be, for example, 0.01 μm.

<Manufacturing method of upper light diffusing sheet>

The method for producing the upper light-diffusing sheet 25 includes a flow of forming a sheet body constituting the base material layer 11 (a base material layer forming flow), and a flow of laminating the light diffusion layer 12 on one surface side of the sheet body ( The light diffusion layer lamination process) and the flow of the adhesion prevention layer 26 on the other surface side of the sheet body constituting the base material layer 11 (adhesion prevention layer lamination flow).

(Adhesion prevention layer lamination process)

As the stacking process of the adhesion preventing layer, for example, a method of forming the adhesion preventing layer 26 simultaneously with the sheet constituting the base material layer 11 by a co-extrusion method, and a method of performing the adhesion preventing layer 26 on the other surface side of the sheet body may be mentioned. A method of laminating the adhesion preventing layer 26 is applied.

Further, the base material layer forming flow in the method for producing the upper light diffusion sheet 25 may be performed simultaneously with the adhesion preventing layer lamination flow by a co-extrusion method as described above, or may be separately performed separately. Adhesion prevention layer lamination process. In the case where the base material layer forming flow is performed separately from the adhesion preventing layer forming flow, the base material layer forming flow can be performed by the same method as the base material layer forming flow of the upper light diffusing sheet 5 of Fig. 1 . In addition, the light diffusion layer lamination flow in the method of manufacturing the upper light diffusion sheet 25 may be performed in the same manner as the light diffusion layer lamination flow of the upper light diffusion sheet 5 of FIG.

<advantage>

Since the adhesion preventing layer 26 is laminated on the back surface side of the base material layer 11, the upper light diffusing sheet 25 can suppress unevenness in brightness caused by the shape of the stripe prism portion protruding from the prism sheet, and can be suppressed by In addition to the occurrence of flicker due to the interference of the pixel pitch of the liquid crystal panel, it is possible to improve the adhesion preventing property against adhesion to the prism sheet and the performance of preventing the back surface of the upper light diffusing sheet 25 from being injured.

[Liquid Crystal Display Module]

The liquid crystal display module of FIG. 4 includes a light guide sheet 1 that guides light incident from the end surface toward the surface side, a light source 2 that illuminates light toward the end surface of the light guide sheet 1, and a lower light diffusion sheet 3 that overlaps the light guide sheet. a surface side of 1; a prism sheet 4 disposed on the surface side of the lower light diffusion sheet 3; an upper light diffusion sheet 5 superposed on the surface side of the prism sheet 4; and a reflection sheet 6 disposed on the back side of the light guide sheet 1; The liquid crystal panel 31 is superposed on the surface side of the upper light diffusion sheet 5. In other words, the liquid crystal display module has a configuration in which the liquid crystal panel 31 is disposed on the surface side of the upper light diffusing sheet 5 of the backlight unit of FIG.

<LCD panel>

The liquid crystal panel 31 is disposed directly on the surface of the upper light diffusion sheet 5 (without passing through other sheets or the like). The liquid crystal panel 31 includes surface-side polarizing plates 32 and back-side polarizing plates 33 which are disposed substantially in parallel and spaced apart by a predetermined interval, and liquid crystal molecules 34 disposed therebetween. The front-side polarizing plate 32 and the back-side polarizing plate 33 are composed of, for example, a polarizing plate such as an iodine-based polarizing plate, a dye-based polarizing plate, and a polyene-based polarizing plate, and a pair of transparent protective films disposed on both sides thereof. The surface-side polarizing plate 32 and the back-side polarizing plate 33 are perpendicular to the transmission axis direction.

The liquid crystal molecules 34 have a function of controlling the amount of light transmitted, and various known structures are employed. The liquid crystal molecules 34 are generally a laminated structure composed of a substrate, a color filter, a counter electrode, a liquid crystal layer, a pixel electrode, a substrate, and the like. The pixel electrode is a transparent conductive film such as ITO. As the display mode of the liquid crystal molecules, for example, TN (Twisted Nematic), VA (Virtical Alignment), IPS (In-Place Switching), FLC ( Ferroelectric Liquid Crystal, AFLC (Anti-ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN (Supper Twisted Nematic), HAN (Hybrid Aligned Nematic) and the like. The pixel pitch (the pixel pitch of the liquid crystal molecules) of the liquid crystal panel 31 can be set to, for example, 25 μm or less.

<advantage>

Since the liquid crystal display module includes the above-described light diffusing sheet 5, it is possible to suppress unevenness in brightness caused by the shape or the like of the stripe prism portion 16 of the prism sheet 4. Further, since the liquid crystal display module has the upper light diffusion sheet 5 disposed on the back side of the liquid crystal panel 31, it is possible to suppress irregularities and liquid crystals on the surface of the light diffusion layer 12 formed on the upper light diffusion sheet 5. The occurrence of flicker caused by the interference of the pixel pitch of the panel 31 occurs.

[Other embodiments]

Further, in addition to the above-described methods, the upper light diffusing sheet and the backlight unit of the present invention may be implemented in various modifications and improvements. For example, the backlight unit may include the optical sheet other than the upper light diffusion sheet, the prism sheet, and the lower light diffusion sheet on the surface side of the light guide sheet. Further, the backlight unit need not necessarily be an edge type backlight unit, and may be, for example, a direct type backlight unit in which a diffusion plate and a light source are disposed on the back side of the lower light diffusion sheet.

The specific structure of the prism sheet, the light diffusion sheet, the light guide sheet, the light source, and the reflection sheet of the backlight unit is not particularly limited, and members of various structures may be employed.

The upper light diffusion sheet is preferably a two-layer structure of a base material layer and a light diffusion layer; or a three-layer structure of a base material layer, a light diffusion layer, and an adhesion prevention layer, but between the base material layer and the light diffusion layer Alternatively, other layers may be provided between the substrate layer and the adhesion preventing layer.

The backlight unit can be used for a relatively large display device such as a personal computer and a liquid crystal television, and a portable information terminal such as a mobile phone terminal such as a smart phone or a tablet terminal.

[Examples]

Hereinafter, the present invention will be described in further detail by way of examples, but the invention is not limited to these examples.

[Example 1]

The surface of the base material layer having an average thickness of 75 μm containing polyethylene terephthalate as a main component is laminated on a light diffusion layer in which a resin bead is dispersed in a resin matrix containing a UV curable resin as a main component. The upper light diffusion sheet of Example 1 was produced. As the resin beads, a resin bead obtained by mixing a first bead having a large average particle diameter and a second bead having an average particle diameter smaller than the first bead at a ratio of 2:1 (mass ratio) was used. Further, the amount of the light diffusion layer laminated was 2.5 g/m ² , the content of the resin matrix of the light diffusion layer was 66.61% by mass, and the average thickness of the light diffusion layer was 3.5 μm. 6 is a partially enlarged cross-sectional photograph of the upper light diffusing sheet of Example 1.

[Embodiment 2]

The above-mentioned light diffusing sheet of Example 2 was produced in the same manner as in Example 1 except that the content of the resin matrix of the light-diffusing layer was 52.57% by mass. The light diffusion layer had an average thickness of 3.7 μm.

[Example 3]

On the surface of the base material layer which is the same as the base material layer of the first embodiment, a light diffusion layer in which an acrylic resin bead having an average particle diameter of 3 μm is dispersed in a resin matrix containing a UV curable resin as a main component is laminated. The upper light diffusing sheet of Example 3 was used. The lamination amount of the light diffusion layer was 3 g/m ² , the content of the resin matrix of the light diffusion layer was 68.00% by mass, and the average thickness of the light diffusion layer was 3.2 μm.

[Comparative Example 1]

On the surface of the base material layer which is the same as the base material layer of the first embodiment, a light diffusion layer in which an acrylic resin bead having an average particle diameter of 8 μm is dispersed in a resin matrix containing a UV curable resin as a main component is laminated. The upper light diffusing sheet of Comparative Example 1. The lamination amount of the light diffusion layer was 4 g/m ² , the content of the resin matrix of the light diffusion layer was 71.40% by mass, and the average thickness of the light diffusion layer was 4.5 μm.

[Comparative Example 2]

On the surface of the base material layer which is the same as the base material layer of the first embodiment, a light diffusion layer in which an acrylic resin bead having an average particle diameter of 7 μm is dispersed in a resin matrix containing a UV curable resin as a main component is laminated. The upper light diffusing sheet of Comparative Example 2 was used. The lamination amount of the light diffusion layer was 4.1 g/m ² , the content of the resin matrix of the light diffusion layer was 69.90% by mass, and the average thickness of the light diffusion layer was 4.5 μm.

<mode diameter>

The mode diameter of the volume-based particle size distribution of the resin beads in the light-diffusing layer was measured using a "Laser Scattering Particle Size Distribution Analyzer LA-950" manufactured by Horiba, Ltd. The measurement results are shown in Table 1.

<density of resin beads>

The laser beam "VK-X100 series" manufactured by KEYENCE Co., Ltd. was used to measure the laser beam from the surface side of the light-diffusing layer and the minute unevenness formed on the surface of the light-diffusing layer from the convex portion to the concave portion. A laser image of any 10 parts obtained by scanning the surface shape. The density per unit area (number/mm ² ) of the resin beads in each portion was measured, and the density per unit area of the resin beads of the light diffusion layer was determined by averaging the values. The measurement results are shown in Table 1.

<variation coefficient>

The volume distribution of the resin beads was measured from the analytical scattered light of the resin beads using a "Laser Scattering Particle Size Distribution Analyzer LA-950" manufactured by Horiba, Ltd., and the arithmetic standard deviation was divided by the average. The value, thereby measuring the coefficient of variation of the volume-based particle size distribution of the resin beads. The measurement results are shown in Table 1.

<granularity width>

The particle size width of the volume-based particle size distribution of the resin beads of the light-diffusing layer was measured using a "Laser Scattering Particle Size Distribution Analyzer LA-950" manufactured by Horiba, Ltd. The measurement results are shown in Table 1.

<particle size>

The average particle size distribution of the resin beads of the light diffusion layer accumulated from the small diameter was measured using a "Laser Scattering Particle Size Distribution Analyzer LA-950" manufactured by Horiba, Ltd. Diameter D50 and particle size D70. The measurement results are shown in Table 1.

<Center line average roughness Ra, average length of roughness curve elements RSm>

The center line average roughness Ra of the surface of the light diffusion layer and the average length RSm of the roughness curve elements were measured in accordance with JIS-B0601:2001, cutoff length (λc) 2.5 mm, and evaluation length 12.5 mm. The measurement results are shown in Table 1.

<10 point average roughness Rz>

The ten-point average roughness Rz of the surface of the light diffusion layer was measured in accordance with JIS-B0601:1994, cut-off length (λc) of 2.5 mm, and evaluation length of 12.5 mm. The measurement results are shown in Table 1.

<Haze value>

The haze value of the upper light-diffusing sheet was measured in accordance with JIS-K7361:2000 using "HZ-2" manufactured by Suga Test Instruments Co., Ltd. The measurement results are shown in Table 1.

Table 1

<The presence or absence of flickering>

The upper light-diffusing sheet of the first to third embodiments and the comparative examples 1 and 2 was placed between the prism sheet of the edge-light type backlight unit of the liquid crystal display device and the liquid crystal panel, and the presence or absence of flicker was visually confirmed, according to the following criteria. An assessment was made. The evaluation results are shown in Table 2.

A does not see flicker at all.

B You can see the flicker when you stare at it, and you cannot confirm the flicker by normal eyesight.

C The flicker is seen by normal visual inspection.

<The presence or absence of brightness unevenness based on prism shape>

The upper light diffusing sheets of Examples 1 to 3 and Comparative Examples 1 and 2 were assembled between the prism sheet of the edge-light type backlight unit of the liquid crystal display device and the liquid crystal panel, and the brightness unevenness based on the prism shape was visually confirmed. Whether or not it was evaluated according to the following criteria. The evaluation results are shown in Table 2.

A The brightness unevenness based on the prism shape is not seen at all.

B See uneven brightness based on prism shape.

<Injury of the upper light diffusing sheet>

The upper light diffusing sheets of Examples 1 to 3 and Comparative Examples 1 and 2 were punched into a rectangular shape of 22.10 cm × 12.45 cm, and 500 samples were produced. The presence or absence of damage of 0.15 mm or more was confirmed for the sample, and it was evaluated based on the following criteria. The evaluation results are shown in Table 2.

A The proportion of samples having a damage of 0.15 mm or more is less than 2%.

B The ratio of the sample having the damage of 0.15 mm or more is 2% or more and 7% or less.

The proportion of samples having a damage of 0.15 mm or more exceeds 11%.

Table 2

[evaluation result]

As shown in Table 2, the upper light diffusing sheets of Examples 1 to 3 can be obtained by setting the mode diameter of the volume-based particle size distribution of the resin beads, the density per unit area, and the average thickness of the light-diffusing layer to the above values. At the same time, flicker caused by interference with the pixel pitch of the liquid crystal panel and brightness unevenness based on the prism shape are suppressed. Further, it has been found that the upper light diffusing sheet of the second embodiment has finer and higher density unevenness than the light diffusing layer of the upper light diffusing sheet of the first embodiment, and it is possible to more reliably suppress the occurrence of flicker. Further, it has been found that the upper light-diffusing sheet of the third embodiment is capable of reliably suppressing the occurrence of flicker, and the surface of the light-diffusing layer is reduced in size, so that the surface is easily damaged and the usability is lowered. On the other hand, it was found that the unevenness of the surface of the light diffusion layer of the upper light diffusion sheet of Comparative Examples 1 and 2 was rough, and the occurrence of flicker could not be suppressed.

[Industrial Applicability]

As described above, the upper light-diffusing sheet and the backlight unit of the present invention can suppress unevenness in brightness caused by the shape of the protruding strip-shaped prism portion of the prism sheet, and can suppress interference caused by the pixel pitch of the liquid crystal panel. The occurrence of flicker is suitable for use in various liquid crystal display devices.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

1‧‧‧Light guide
2‧‧‧Light source
3‧‧‧Use light diffuser
4‧‧ ‧ prism sheet
5‧‧‧Use light diffuser
6‧‧‧reflector
11‧‧‧Substrate layer
12‧‧‧Light diffusion layer
13‧‧‧Resin matrix
14‧‧‧Resin beads
15‧‧‧Substrate layer
16‧‧‧Outstanding strip prism
17‧‧‧Substrate layer
18‧‧‧Light diffusion layer
19‧‧‧Adhesion prevention layer
25‧‧‧Use light diffuser
26‧‧‧Adhesion prevention layer
31‧‧‧LCD panel
32‧‧‧Surface side polarizer
33‧‧‧Back side polarizer
34‧‧‧liquid crystal molecules
101‧‧‧Side-lit backlight unit
102‧‧‧Light source
103‧‧‧Light guide plate
104‧‧‧ optical film
105‧‧‧reflector
106‧‧‧Use light diffuser
107‧‧ ‧ prism sheet
108‧‧‧Use light diffuser

1 is a schematic cross-sectional view showing a backlight unit according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing an arrangement state of a light diffusing sheet and a prism sheet for use in the backlight unit of Fig. 1; 3 is a schematic cross-sectional view showing an upper light diffusion sheet of an embodiment different from the upper light diffusion sheet of the backlight unit of FIG. 1. 4 is a schematic cross-sectional view showing a liquid crystal display module according to an embodiment of the present invention. Fig. 5 is a perspective view showing a conventional edge-lit backlight unit. Fig. 6 is a partially enlarged cross-sectional view showing the upper light diffusing sheet of the first embodiment.

1‧‧‧Light guide

2‧‧‧Light source

3‧‧‧Use light diffuser

4‧‧ ‧ prism sheet

5‧‧‧Use light diffuser

6‧‧‧reflector

11‧‧‧Substrate layer

12‧‧‧Light diffusion layer

13‧‧‧Resin matrix

14‧‧‧Resin beads

15‧‧‧Substrate layer

16‧‧‧Outstanding strip prism

17‧‧‧Substrate layer

18‧‧‧Light diffusion layer

19‧‧‧Adhesion prevention layer

Claims (9)

An upper light diffusion sheet disposed on a surface side of a prism sheet of a backlight unit of a liquid crystal display device, wherein the upper light diffusion sheet is characterized in that the upper light diffusion sheet has a substrate layer and a laminate a light diffusion layer on a surface side of the substrate layer, the light diffusion layer having a resin matrix and a plurality of resin beads dispersed in the resin matrix, the volume diameter of the volume-based particle size distribution of the resin beads being 2.5 μm or more and 5.5 μm or less, the density per unit area is 9000/mm ² or more and 24,000 pieces/mm ² or less, and the average thickness of the light diffusion layer is 2 μm or more and 9 μm or less. The upper light-diffusing sheet according to claim 1, wherein a coefficient of variation of the particle diameter of the volume-based particle size distribution of the resin beads is 42% or less. The above-mentioned light-diffusing sheet according to claim 1, wherein the particle-based width distribution of the volume-based particle size distribution of the resin beads is 13 μm or more and 20 μm or less. The upper light-diffusing sheet according to claim 1, wherein the average particle diameter D50 of the volume-based particle size distribution of the resin beads is 5.7 μm or less. The upper light diffusion sheet according to claim 1, wherein the surface of the light diffusion layer has a center line average roughness Ra of 0.3 μm or more and 1 μm or less. The upper light diffusing sheet according to claim 1, wherein the surface of the light diffusing layer has a ten point average roughness Rz of 1.5 μm or more and 4.5 μm or less, and an average length RSm of the roughness curve element of 30 μm or more and 100 μm or less. The upper light diffusion sheet according to claim 1, wherein the resin beads of the light diffusion layer are substantially separated from a surface of the base material layer. A backlight unit of a liquid crystal display device, comprising: a light guide sheet, guiding a light incident from an end surface toward a surface side; a light source illuminating the light toward the end surface of the light guide sheet; And superimposed on the surface side of the light guide sheet; a prism sheet disposed on a surface side of the lower light diffusion sheet; and an upper light diffusion sheet superposed on a surface side of the prism sheet, the liquid crystal display The backlight unit of the device is characterized in that the upper light diffusion sheet described in claim 1 is used as the upper light diffusion sheet. The backlight unit of the liquid crystal display device according to claim 8, wherein a ratio of an average particle diameter D50 of the resin beads to an average pitch of ridge lines of the prism sheet is 0.06 or more and 0.25 or less.