JP2013080017A - Prism sheet and backlight unit using the same - Google Patents

Abstract

The present invention provides a prism sheet that can prevent glare of the screen and occurrence of an interference pattern, and that can promote improvement in front luminance and thinning, and a backlight unit for a liquid crystal display device using the prism sheet.
A prism sheet 1 includes a transparent base layer 2, a bead coating layer 3 in which beads 7 are dispersed in a binder 6 laminated on a surface side of the base layer, and the bead coating layer. And a plurality of protruding prism portions 5 arranged in a stripe shape on the surface side. A sheet-like portion 4 is disposed between the bead coating layer and the protruding prism portion, and the sheet-like portion and the protruding prism portion are integrally formed.
[Selection] Figure 1

Description

  The present invention relates to a prism sheet suitable for a backlight unit of a liquid crystal display device and a backlight unit for a liquid crystal display device using the prism sheet.

  In the liquid crystal display device, a backlight method in which a liquid crystal layer is illuminated from the back surface is widely used, and a backlight unit such as an edge light type or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 2, the edge light type backlight unit 50 basically includes a linear lamp 51 as a light source, and a rectangular plate-shaped light guide plate disposed so that the end of the lamp 51 is along the end. 52, a light diffusion sheet 53 disposed on the surface side of the light guide plate 52, and a prism sheet 54 disposed on the surface side of the light diffusion sheet 53.

  The function of the backlight unit 50 will be described. First, a light beam incident on the light guide plate 52 from the lamp 51 is reflected by a reflective dot or a reflection sheet (not shown) on the back surface of the light guide plate 52, and is reflected from the surface of the light guide plate 52. Emitted. Light rays emitted from the light guide plate 52 enter the light diffusion sheet 53, are diffused by the light diffusion sheet 53, and are emitted from the surface of the light diffusion sheet 53. Thereafter, the light beam emitted from the light diffusion sheet 53 enters the prism sheet 54 and is emitted as a light beam having a distribution that has a peak in a substantially normal direction by the protruding prism portion 54a formed on the surface of the prism sheet 54.

  Thus, the light beam emitted from the lamp 51 is diffused by the light diffusion sheet 53, refracted by the prism sheet 54 so as to show a peak in a substantially normal direction, and further a liquid crystal layer (not shown) on the surface side. The entire surface is illuminated.

  This prism sheet can increase the proportion of light emitted to the front side (direction perpendicular to the plane direction of the prism sheet) by surface design based on geometric optics, but due to the regularly arranged prism portions 54a. Interference patterns tend to appear, and glare may occur.

  For this reason, it has been proposed to prevent the occurrence of glare by arranging an upper diffusion sheet on the surface side of the prism sheet (see JP 2002-256053 A).

  However, when the upper diffusion sheet is provided on the surface side of the prism sheet as described in the above publication, not only the front luminance enhanced by the prism sheet is lowered, but also the number of optical sheets is increased and the back surface for the liquid crystal display device is increased. Contrary to the demand for thinner light units.

Japanese Patent Application Laid-Open No. 2002-256053

  The present invention has been made in view of such inconveniences, and can prevent screen glare and occurrence of interference patterns without providing an upper diffusion sheet between the prism sheet and the liquid crystal layer. It is an object of the present invention to provide a prism sheet capable of promoting the improvement and thinning of the display and a backlight unit for a liquid crystal display device using the prism sheet.

The invention made to solve the above problems is
A transparent substrate layer;
Laminated on the surface side of the base material layer, and a bead coating layer in which beads are dispersed in a binder;
It is a prism sheet provided with the some protrusion prism part arrange | positioned in stripe form on the surface side of this bead coating layer.

  Since the prism sheet has a bead coating layer between the base material layer and the ridge prism portion, the light incident on the bead coating layer is internally diffused by the beads, and this diffused light is diffused into the ridge prism. Can be incident on the part. Therefore, the prism sheet can alleviate the light condensing characteristics of the prism sheet, and can prevent screen glare and occurrence of interference patterns.

  In the prism sheet, a sheet-like portion is disposed between the bead coating layer and the protruding prism portion, and the sheet-like portion and the protruding prism portion are integrally formed. Good. By arranging the sheet-like part between the bead coating layer and the ridge prism, the beads appeared on the surface side of the bead coating layer, and an uneven shape was present on the surface of the bead coating layer. Even so, it is possible to reliably form the protruding prism portion having an accurate shape. That is, in the prism sheet, it is also possible to directly form the protruding prism portion on the surface of the coating layer, in this case, depending on the uneven shape of the surface of the bead coating layer, There is a possibility that the shape near the valleys between the projecting prism parts may not be formed accurately, and in relation to this, the presence of the uneven shape on the surface of the bead coating layer by arranging the sheet-like part as described above. Therefore, it is possible to reliably form the protruding prism portion having an accurate shape.

  The average thickness of the bead coating layer is preferably 1 μm or more and 10 μm or less. As a result, the light incident on the bead coating layer can be diffused accurately and reliably, and the demand for thinning the liquid crystal display device can be met.

As the lamination of the bead coating layer is preferably 2 g / ^{m 2} or more 10 g / ^{m 2} or less. As a result, the light incident on the bead coating layer can be diffused accurately and reliably, and the demand for thinning the liquid crystal display device can be met.
Furthermore, the average particle diameter of the beads 7 is preferably 1 μm or more and 10 μm or less. Thereby, the effects such as light diffusion are sufficient, and the bead coating layer can be easily formed.

  The variation coefficient of the particle size of the beads is preferably 30% or less. Thereby, since the particle diameter of the beads contained in this bead coating layer is made uniform, the light incident on the bead coating layer can be uniformly diffused internally.

  The refractive index of the binder is preferably larger than the refractive index of the beads. As a result, a binder having a high refractive index can be used. For this reason, the light emitted from the base material layer toward the bead coating layer is hardly totally reflected at the binder interface, and the light can be effectively used.

  The difference between the refractive index of the binder and the refractive index of the beads is preferably 0.01 or more and 0.60 or less. If the difference in refractive index between the binder and the beads is smaller than the lower limit, internal diffusion in the bead coating layer may be insufficient. If the upper limit is exceeded, total reflection increases at the bead interface. This is because the haze value becomes too high and the front luminance may be deteriorated.

  Therefore, in the backlight unit for a liquid crystal display device that disperses the light emitted from the lamp and guides it to the surface side, when the prism sheet is provided, it is possible to prevent glare of the screen and generation of an interference pattern, and to improve the front luminance and reduce the thickness. Can be promoted.

  Here, the “surface side” means the viewing side of the display when the liquid crystal display module is incorporated into the liquid crystal display module. The “back side” means the side opposite to the “front side”. The “particle diameter variation coefficient” was calculated by the following equation (1).

  Coefficient of variation (%) = standard deviation of particle diameter of beads / average particle diameter of beads (1)

  As described above, the prism sheet of the present invention can reduce the light condensing characteristics of the prism sheet, can prevent the occurrence of screen glare and interference patterns, and can improve the front luminance. Thinning of a backlight unit for a liquid crystal display device by reducing the number of sheets is promoted.

It is typical sectional drawing which shows the prism sheet which concerns on one Embodiment of this invention. It is typical sectional drawing of the backlight unit for liquid crystal display devices using the conventional prism sheet.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. 1 includes a transparent base material layer 2, a bead coating layer 3 in which beads 7 are dispersed in a binder 6, a sheet-like portion 4 laminated on the surface of the bead coating layer 3, A plurality of protruding prism portions 5 are provided in this order from the back side to the front side.

  Since the base material layer 2 needs to transmit light, it is made of a synthetic resin that is transparent, particularly colorless and transparent. The synthetic resin used for the base material layer 2 is not particularly limited. For example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistant vinyl chloride, active energy ray curing. Mold resin and the like.

  The average thickness of the base material layer 2 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 35 μm or more and 250 μm or less, and particularly preferably 50 μm or more and 188 μm or less. When the thickness of the base material layer 2 is less than the above range, curling tends to occur when exposed to heat in the backlight unit, which may make handling difficult. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the brightness of the liquid crystal display device may be lowered, and the thickness of the backlight unit may be increased to violate the demand for thinning the liquid crystal display device. is there.

  The bead coating layer 3 is laminated on the surface of the base material layer 2. The bead coating layer 3 includes a plurality of beads 7 that are spaced apart from each other and a binder 6 that fixes the beads 7 to the base material layer 2.

  The beads 7 are arranged and fixed at substantially equal density on the surface side of the base material layer 2 by the binder 6. Due to the difference in refractive index between the beads 7 and the binder 6, the bead coating layer 3 diffuses incident light rays internally.

  The material of the beads 7 is roughly classified into inorganic fillers and organic fillers. Specifically, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used as the inorganic filler. Specific examples of the organic filler include acrylic resin, silicone resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, and the like. Among these, acrylic resins and silicone resins that have high transparency and do not inhibit light transmission are particularly preferable.

  The lower limit of the average particle diameter of the beads 7 is preferably 1 μm, particularly 1.5 μm, more preferably 2 μm, and the upper limit of the average particle diameter is preferably 10 μm, particularly 7 μm, more particularly 4 μm. If the average particle diameter of the beads 7 is less than the above range, the effects such as light diffusion may be insufficient. On the contrary, if the average particle diameter of the beads 7 exceeds the above range, it may be difficult to apply the bead coating layer forming material. The average particle diameter of the beads 7 is derived by enlarging 100 arbitrarily extracted beads 7 with a microscope, measuring the diameter of the particles, and simply averaging them. If the bead 7 is not spherical, the bead 7 dimension in any one direction and the bead 7 dimension in a direction orthogonal thereto are averaged.

  As the beads 7, a monodisperse bead group having a narrow particle size distribution width can be suitably used. Specifically, the coefficient of variation of the particle diameter of the beads 7 is preferably 30% or less, particularly preferably 20% or less, and particularly preferably 10% or less. Thereby, since the particle diameter of the beads contained in this bead coating layer is made uniform, the light incident on the bead coating layer can be uniformly diffused internally.

The average thickness of the bead coating layer 3 is preferably larger than the average particle diameter of the beads 7. Thereby, the bead 7 does not protrude too much from the surface of the bead coating layer 3, and the surface roughness of the bead coating layer 3 can be within a certain range.
The lower limit of the average thickness of the bead coating layer 3 is preferably 1 μm, particularly 3 μm, and more particularly 5 μm. On the other hand, the upper limit of the average thickness of the bead coating layer 3 is preferably 10 μm, particularly 8 μm, and more particularly 6 μm. If the average thickness of the bead coating layer 3 is smaller than the above range, the beads 7 may not be fixed. On the contrary, if the average thickness of the bead coating layer 3 exceeds the above range, the prism sheet 1 may be required to be thinned.

  Moreover, as a minimum of the compounding quantity of the bead 7 (the compounding quantity of solid content conversion with respect to 100 parts of base polymer in the polymer composition which is a binder forming material), 1 part is preferable, and 1.5 parts is particularly preferable. 2 parts is even more particularly preferred. On the other hand, the upper limit of the amount of the beads 7 is preferably 5 parts, particularly preferably 3 parts, and even more preferably 2.5 parts. If the blending amount of the beads 7 is less than the above range, light diffusion by the beads 7 may be insufficient. On the other hand, if the blending amount of the beads 7 exceeds the above range, the internal diffusion due to the beads 7 becomes too large, and the front luminance may be lowered.

The lower limit of the amount of the bead coating layer 3 is preferably ² g / m ^{2 and} particularly preferably 4 g / m ² . In contrast, the upper limit of the lamination of the bead coating layer 3 is preferably 10 g / ^{m 2,} particularly preferably 8 g / ^{m 2.} If the amount of the bead coating layer 3 is smaller than the above range, the beads 7 may not be fixed. On the other hand, if the amount of the bead coating layer 3 exceeds the above range, the prism sheet 1 may be required to be thin.

  The arithmetic average roughness (Ra) of the surface of the bead coating layer 3 is preferably 0.3 μm or less, particularly preferably 0.2 μm or less, and particularly preferably 0.1 μm or less. When the arithmetic average roughness exceeds the upper limit, diffusion on the surface (interface) of the bead coating layer 3 becomes too large, and the front luminance may be lowered. The arithmetic average roughness (Ra) of the surface of the bead coating layer 3 is preferably 0.01 μm or more, particularly preferably 0.03 μm or more, and particularly preferably 0.05 μm.

  The 10-point average roughness (Rz) of the surface of the bead coating layer 3 is preferably 1.4 μm or less, particularly preferably 1 μm or less, and particularly preferably 0.8 μm or less. If this ten-point average roughness (Rz) is larger than the above upper limit, the uneven shape becomes too rough, and there is a possibility that diffusion at the interface of the bead coating layer 3 becomes large. The 10-point average roughness (Rz) on the surface of the bead coating layer 3 is preferably 0.2 μm or more, particularly preferably 0.3 μm or more, and particularly preferably 0.4 μm or more.

  Further, the refractive index of the beads 7 is preferably smaller than the refractive index of the binder 6. As a result, a binder 6 having a high refractive index can be used. For this reason, the light emitted from the base material layer 2 toward the bead coating layer 3 is hardly totally reflected at the interface of the binder 6, and the light can be effectively used. Figured.

  Furthermore, the difference between the refractive index of the binder 6 and the refractive index of the beads 7 is preferably from 0.01 to 0.60, particularly preferably from 0.02 to 0.1. If the difference in refractive index between the binder 6 and the beads 7 is smaller than the above range, the internal diffusion may not be sufficiently exhibited. On the other hand, if the difference in refractive index exceeds the above range, reflection at the interface of the beads 7 increases, and the haze value becomes too high, and the front luminance may be inferior. Specifically, it is possible to use, for example, silicon beads having a refractive index of 1.45 to 1.5 as the beads 7 and a binder made of an acrylic resin having a refractive index of 1.5 to 1.53 as the binder 6. It is.

  The binder 6 is formed by curing a polymer composition containing a base polymer. Thus, the bead 7 is being fixed to the surface side of the base material layer 2 because the polymer composition hardens | cures and the binder 6 is formed.

  As the base polymer, an acrylic resin is preferably used, but the base polymer is not particularly limited. For example, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, epoxy resin, ultraviolet ray It is also possible to use a curable resin or the like. The base polymer is preferably a polyol that has high processability and can easily form the bead coating layer 3 by means such as coating. Moreover, since the base polymer used for the binder 6 needs to transmit light, it is transparent, and colorless and transparent is preferable. In addition, the said polymer may use 2 or more types together.

  Examples of the polyol include (a) a polyester polyol obtained under conditions of excess hydroxyl group and (b) a monomer component containing a hydroxyl group-containing unsaturated monomer, and a (meth) acryl unit. Etc. are preferred. The binder 6 having such a polyester polyol or acrylic polyol as a base polymer has high weather resistance and can suppress yellowing of the bead coating layer 3. In addition, you may use together this polyester polyol and acrylic polyol.

  In addition to the base polymer, the polymer composition for forming the binder 6 is, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an antistatic agent, an ultraviolet absorber, and an antioxidant. , Viscosity modifiers, lubricants, light stabilizers and the like may be appropriately blended. Among these, it is preferable to mix | blend a ultraviolet absorber, Thereby, the function which cuts the ultraviolet-ray of a transmitted ray can be provided to a binder. By providing such an ultraviolet ray cutting function, the prism sheet 1 can cut a small amount of ultraviolet rays emitted from the lamp of the backlight unit, and can prevent the liquid crystal layer from being destroyed by the ultraviolet rays.

  The ultraviolet absorber is not particularly limited as long as it is a compound that absorbs ultraviolet rays and can be efficiently converted into thermal energy, and is stable to light, and a known one can be used. . Among them, salicylic acid-based UV absorbers, benzophenone-based UV absorbers, benzotriazole-based UV absorbers, and cyanoacrylates that have a high UV-absorbing function, have good compatibility with the above-mentioned base polymer, and exist stably in the base polymer. System ultraviolet absorbers are preferable, and one or more selected from these groups may be used. Further, as the ultraviolet absorber, a polymer having an ultraviolet absorbing group in a molecular chain (for example, “Udable UV” series of Nippon Shokubai Co., Ltd.) is also preferably used. By using a polymer having an ultraviolet absorbing group in such a molecular chain, the compatibility with the base polymer is high, and deterioration of the ultraviolet absorbing function due to bleeding out of the ultraviolet absorbent or the like can be prevented. A polymer having an ultraviolet absorbing group in the molecular chain can be used as the base polymer of the binder 6. Moreover, it is also possible to use the polymer to which the ultraviolet absorbing group is bonded as the base polymer of the binder 6 and further to contain an ultraviolet absorber in the base polymer, thereby further improving the ultraviolet absorbing function.

  As a minimum of content with respect to the base polymer of the said ultraviolet absorber, 0.1 mass% is preferable, 1 mass% is especially preferable, and 3 mass% is further especially preferable. On the other hand, the upper limit of the content of the ultraviolet absorber is preferably 10% by mass, particularly preferably 8% by mass, and even more preferably 5% by mass. If the content of the ultraviolet absorber is smaller than the above range, the ultraviolet absorbing function may not be sufficiently achieved. On the contrary, when the content of the ultraviolet absorber is larger than the above range, the base polymer is adversely affected, and the strength and durability of the binder 6 may be lowered.

  An ultraviolet stabilizer (including a base polymer in which an ultraviolet stabilizing group is bonded to a molecular chain) may be used instead of or together with the ultraviolet absorber. By this ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen and the like are inactivated, and ultraviolet stability, weather resistance and the like can be improved. As this ultraviolet stabilizer, a hindered amine ultraviolet stabilizer having high stability against ultraviolet rays is preferably used. In addition, the deterioration prevention and weather resistance with respect to an ultraviolet-ray are improved significantly by using together an ultraviolet absorber and a ultraviolet-ray stabilizer.

  Next, a method for forming the bead coating layer 3 will be described. The method for forming the bead coating layer 3 includes: (a) a step of producing a polymer composition for a bead coating layer by mixing beads 7 with the polymer composition constituting the binder 6; and (b) this bead. A step of forming the bead coating layer 3 by laminating the polymer composition for the coating layer on the surface of the transparent base material layer 2 and curing it.

  The means for laminating the polymer composition for bead coating layer is not particularly limited, and various known methods are employed. Specific examples of the laminating means include a gravure coating method, a roll coating method, a bar coating method, a blade coating method, and a spray coating method.

  The plurality of protruding prism portions 5 are arranged in a stripe shape on the surface side of the bead coating layer 3, and the sheet-like portion 4 is interposed between the bead coating layer 3 and the protruding prism portion 5. It is arranged. Here, the sheet-like portion 4 and the ridge prism portion 5 are integrally formed from the same material. Even if the beads 7 are exposed on the surface side of the bead coating layer 3 and the surface of the bead coating layer 3 has an uneven shape, the sheet-like portion 4 allows the protruding prism portion 5 having an accurate shape to be formed. It can be reliably formed. In other words, when the protruding prism portion is directly formed on the surface of the bead coating layer, the shape near the valley between the protruding prism portions may not be accurately formed due to the uneven shape of the surface of the bead coating layer. On the other hand, by arranging the sheet-like portion 4 as described above, the protruding prism portion 5 having an accurate shape can be reliably formed regardless of the presence of the irregular shape on the surface of the bead coating layer 3. Can do. In addition, the said sheet-like part 4 is laminated | stacked on the bead coating layer 3 surface so that a back surface may be in close contact with the said bead coating layer 3 surface.

  Although the average thickness of this sheet-like part 4 is not specifically limited, It is good in it being 2 micrometers or more and 5 micrometers or less. By setting the average thickness of the sheet-like portion 4 in the above range, the protruding prism portion 5 having an accurate shape can be reliably formed, and the prism sheet 1 can be prevented from becoming too thick. .

The protruding prism portion 5 has a triangular prism shape whose one side surface (bottom surface) is in contact with the surface of the sheet-like portion 4. The cross-sectional shape of the ridge prism portion 5 is generally a right isosceles triangle having an apex angle α of 90 ° and a base angle β of 45 °.
The lower limit of the width (W) of the bottom surface of the ridge prism portion 5 is preferably 10 μm, and particularly preferably 30 μm. On the other hand, the upper limit of the width (W) is preferably 1000 μm, and particularly preferably 400 μm. This is because if the width (W) of the bottom surface of the ridge prism portion 5 exceeds the above upper limit, glare, luminance unevenness, and the like may occur.

  The sheet-like portion 4 and the protruding prism portion 5 are made of a synthetic resin that is transparent and particularly colorless and transparent because it is necessary to transmit light. The refractive index of the sheet-like part 4 and the protruding prism part 5 is preferably 1.3 or more and 1.8 or less, particularly preferably 1.45 or more and 1.6 or less, and particularly preferably 1.5 or more and 1.53 or less. preferable. Further, the difference between the refractive index of the sheet-like portion 4 (and the protruding prism portion 5) and the refractive index of the binder 6 is preferably 0.1 or less, and particularly preferably 0.01 or less.

  Moreover, as a synthetic resin which forms the sheet-like part 4 and the protrusion prism part 5, active energy ray hardening resin is employ | adopted suitably. As this active energy ray curable resin, those cured with active energy rays such as ultraviolet rays and electron beams can be employed. For example, polyesters, epoxy resins, polyester (meth) acrylates, epoxy (meth) acrylates, urethanes. Examples include (meth) acrylate resins such as (meth) acrylate. Of these, (meth) acrylate resins are preferred from the viewpoint of their optical properties and the like. The active energy ray-curable composition used for such a cured resin is, for example, described as polyvalent acrylate and / or polyvalent methacrylate (hereinafter referred to as polyvalent (meth) acrylate) in terms of handleability and curability. ), Monoacrylate and / or monomethacrylate (hereinafter referred to as mono (meth) acrylate), and those having a photopolymerization initiator by active energy rays as a main component. Typical polyvalent (meth) acrylates include, for example, polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane poly (meth) acrylate, and the like. Two or more of these may be used in combination. Examples of mono (meth) acrylates include mono (meth) acrylates of monoalcohols and mono (meth) acrylates of polyols.

The manufacturing method of the prism sheet 1 is not particularly limited as long as the above structure can be formed, but generally a transparent base material layer 2 is formed, and a bead coating layer 3 is formed on the surface side thereof. Then, the protrusion prism portion 5 and the sheet-like portion 4 are manufactured by a method of integrally forming. Specifically, the method of forming the ridge prism portion 5 is as follows. (A) Synthetic resin is applied to a sheet mold having a reverse shape of the surface shape of the prism sheet 1 (surface shape formed by a plurality of ridge prism portions 5). A method of forming the protruding prism portion 5 and the like by laminating and peeling the sheet mold,
(B) an injection molding method in which a molten resin is injected into a mold having a reverse shape of the surface shape of the prism sheet 1;
(C) A method of transferring the shape by re-heating the sheeted resin and pressing between the same mold and metal plate as described above,
(D) an extrusion sheet molding method in which a molten resin is passed through a nip between a roll mold having a reverse shape of the surface shape of the prism sheet 1 on the peripheral surface and another roll, and the shape is transferred;
(E) An ultraviolet curable resin is applied to the bead coating layer 3, and the shape is transferred to an uncured ultraviolet curable resin by pressing against the sheet mold, mold or roll mold having the same inverted shape as above, A method of curing an ultraviolet curable resin by applying ultraviolet rays,
(F) An uncured ultraviolet curable resin is filled and applied to a mold or roll mold having the same inverted shape as described above, pressed and leveled by the bead coating layer 3, and irradiated with ultraviolet rays to form an ultraviolet curable resin. A curing method,
(G) There is a method of using an electron beam curable resin instead of an ultraviolet curable resin.

  The prism sheet 1 is used in a backlight unit of a known liquid crystal display device. Specifically, the prism sheet 1 is disposed between the light guide plate and the liquid crystal layer. More specifically, the prism sheet 1 is disposed on the surface side of the light diffusion sheet 53 as illustrated in FIG. 2, and is disposed between the light diffusion sheet 53 and the liquid crystal layer.

  Since the prism sheet 1 includes the bead coating layer 3 between the base material layer 2 and the surface-side protruding prism portion 5, the light incident on the bead coating layer 3 is internally diffused by the beads 7. Then, this diffused light can be incident on the protruding prism portion 5. Therefore, the prism sheet 1 can alleviate the light condensing characteristics of the prism sheet, and can prevent the occurrence of screen glare and interference patterns without providing a conventional upper diffusion sheet.

  In addition, since the prism sheet 1 contains the ultraviolet absorber in the binder 6, the prism sheet 1 cuts a small amount of ultraviolet rays emitted from the lamp of the backlight unit and destroys the liquid crystal layer by the ultraviolet rays. Can be prevented.

  Furthermore, in the above-described embodiment, the description has been given of the case where the bead coating layer is formed on the surface of the base material layer. However, another layer is interposed on the surface of the base material layer, and the bead coating is performed on the surface of this other layer. The layer formed can be appropriately changed in design, and is within the range intended by the present invention as long as the bead coating layer is laminated on the surface side of the base material layer.

  Moreover, in the said embodiment, although what provided the sheet-like part between the bead coating layer and the protrusion prism part was demonstrated, in this invention, a sheet-like part is not an essential structural requirement. Further, even when the sheet-like portion is provided, the sheet-like portion is not limited to the one in which the sheet-like portion is laminated on the surface of the bead coating layer as in the above embodiment, and the sheet-like portion is provided on the surface side of the bead coating layer. As long as it is laminated, another layer may be interposed between the bead coating layer and the sheet-like portion.

  As described above, the prism sheet of the present invention and the backlight unit using the prism sheet can prevent screen glare and interference patterns. As a result, it is possible to promote improvement in front luminance and reduction in thickness of the backlight unit by reducing the number of optical sheets.

DESCRIPTION OF SYMBOLS 1 Prism sheet 2 Base material layer 3 Bead coating layer 4 Sheet-like part 5 Projection prism part 6 Binder 7 Bead 50 Backlight unit 51 Lamp 52 Light guide plate 53 Light diffusion sheet 54 Prism sheet 54a Projection prism part

Claims (9)

A transparent substrate layer;
Laminated on the surface side of the base material layer, and a bead coating layer in which beads are dispersed in a binder;
A prism sheet comprising a plurality of protruding prism portions arranged in a stripe pattern on the surface side of the bead coating layer.   The prism sheet according to claim 1, wherein a sheet-like portion is disposed between the bead coating layer and the protruding prism portion, and the sheet-like portion and the protruding prism portion are integrally formed.   The prism sheet according to claim 1 or 2, wherein an average thickness of the bead coating layer is 1 µm or more and 10 µm or less. 4. The prism sheet according to claim 1, wherein the amount of the bead coating layer is 2 g / m ² or more and 10 g / m ² or less.   The prism sheet according to any one of claims 1 to 4, wherein an average particle diameter of the beads is 1 µm or more and 10 µm or less.   The prism sheet according to any one of claims 1 to 5, wherein a variation coefficient of the particle diameter of the beads is 30% or less.   The prism sheet according to any one of claims 1 to 6, wherein a refractive index of the binder is larger than a refractive index of the beads.   The prism sheet according to any one of claims 1 to 7, wherein a difference between a refractive index of the binder and a refractive index of the beads is 0.01 or more and 0.60 or less. In the backlight unit for a liquid crystal display device that guides the light emitted from the lamp to the surface side by dispersing,
A backlight unit for a liquid crystal display device, comprising the prism sheet according to claim 1.

Images