TW201741747A - Optical sheet for liquid crystal display device, backlight unit for liquid crystal display device and production method of optical sheet for liquid crystal display device - Google Patents

Abstract

An optical sheet for a liquid crystal display device includes a plurality of protruding portions provided scatteredly on a back face, in which the protruding portions each have a flattened semi-spherical shape or a flattened conical shape with a rounded apex. The protruding portions may each have a half spheroidal shape. An occupancy area ratio of the plurality of protruding portions may be no less than 2% and no greater than 80%. An average diameter of the protruding portions may be no less than 5 [mu]m and no greater than 60 [mu]m, and an average height of the protruding portions may be no less than 0.5 [mu]m. A diffraction grating shape with multiple rows that are oriented in a single direction on the back face in a region where the plurality of protruding portions are absent.

Description

Optical sheet for liquid crystal display device, backlight unit for liquid crystal display device, and method for producing optical sheet for liquid crystal display device

The present invention relates to an optical sheet for a liquid crystal display device, a backlight unit for a liquid crystal display device, and a method for producing an optical sheet for a liquid crystal display device.

As a transmissive liquid crystal display device, a backlight system that irradiates a liquid crystal layer from the back surface is widely used, and a backlight unit such as an edge light type (side light type) or a direct type is provided on the back side of the liquid crystal layer. As shown in FIG. 19, the sidelight type backlight unit 101 generally includes a light source 102, a square plate-shaped light guide sheet 103 disposed along the end portion of the light source 102, and a light-emitting sheet 103 disposed on the front surface side of the light guide sheet 103. A plurality of optical sheets 104. The optical sheet 104 has an optical function such as diffusion and refraction of transmitted light. For example, the light diffusion sheet 105 disposed on the surface side of the light guide sheet 103 and having a light diffusion function is disposed on the surface side of the light diffusion sheet 105 and has The prism sheet 106 having a refractive function toward the normal direction side.

When the function of the backlight unit 101 is described, first, the light incident from the light source 102 to the light guide sheet 103 is reflected by the reflection point or the reflection sheet (not shown) and the side surfaces of the back surface of the light guide sheet 103, and It is emitted from the surface of the light guiding sheet 103. Light emitted from the surface of the light guiding sheet 103 is incident on the light diffusion sheet 105 and is diffused to be emitted from the surface. The light emitted from the surface of the light-diffusing sheet 105 is incident on the prism sheet 106, and is refracted toward the normal direction side by the plurality of ridge prism portions formed on the surface, and is emitted to the liquid crystal (not shown) on the surface side. The entire surface of the layer is illuminated. In addition, as the optical sheet 104, the optical sheet 104 is disposed on the surface side of the prism sheet 106, and the light is slightly diffused to suppress the shape of the plurality of ridge prism portions of the prism sheet 106. The upper light-diffusing sheet having uneven brightness, the microlens sheet having a refractive function toward the normal direction side, and a wide-angle light diffusing function.

The optical sheet 104 has an optical function such as diffusion and refraction of transmitted light as described above, and is used for the purpose of uniformizing the luminance of the backlight unit and increasing the luminance in the front direction. In the optical sheet 104, as shown in FIG. 20, the optical material sheet 104 has a base material layer 111 (optical layer) mainly composed of a synthetic resin, and is laminated on the surface side of the base material layer 111. The light diffusion layer 112 and an anti-adhesion layer 113 laminated on the back side of the base material layer 111. The anti-adhesion layer 113 prevents the occurrence of moire fringes due to adhesion (adhesion) between the back surface of the light diffusion sheet 105 and the surface of the light guide sheet 103. The anti-adhesion layer 113 generally has a spherical bead 114 and a binder 115 that covers the bead 114, and is prevented from adhering by a convex portion that protrudes toward the back side by the bead 114 (refer to Japanese Laid-Open Patent Publication No. 2010-26231).

However, since the conventional anti-adhesion layer having the beads 114 and the binder 115 as described above forms a convex portion by the protrusion of the beads 114, the convex portion is likely to have a shape similar to the shape of the beads 114. Therefore, the average diameter and the average height of the convex portion are likely to be the same, and the R of the tip end portion (lower end portion) of the convex portion is likely to be small. Therefore, according to the conventional anti-adhesion layer 113 described above, there is a risk of damage to the surface of the light guiding sheet 103 that is in contact with the convex portion. Further, if damage occurs on the surface of the light guiding sheet 103 as described above, there is a risk that unevenness in brightness occurs due to the incident light.

Prior art literature:

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-26231.

The present invention has been made in view of such circumstances, and an object of the invention is to provide an optical sheet for a liquid crystal display device and a method for producing an optical sheet for a liquid crystal display device which can prevent adhesion of other optical members disposed on the back side while preventing adhesion. Further, another object of the present invention is to provide a backlight unit for a liquid crystal display device which can prevent adhesion and can prevent damage of an optical member.

An optical sheet for a liquid crystal display device according to the present invention, which is provided with a plurality of convex portions on a back surface of the optical sheet, and the convex portion is a flat hemisphere. The body or the front end is rounded into a flat cone.

In the optical sheet for a liquid crystal display device, a plurality of convex portions are provided in a scattered manner on the back surface, and the optical sheet for a liquid crystal display device and other optical members disposed on the back side of the optical sheet for the liquid crystal display device are used for the plurality of convex portions. Partially partial. Therefore, the optical sheet for a liquid crystal display device can prevent adhesion to other optical members disposed on the back side. Further, in the optical sheet for a liquid crystal display device, the curved surface of the front end portion (lower end portion) of the plurality of convex portions is compared by a flattened cone having a flattened hemisphere or a tip end portion being rounded. It is gentle, whereby damage to the surface of other optical members disposed on the back side can be prevented.

The convex portion is preferably a semi-divided ellipsoid. By making the convex portion a semi-divided ellipsoid, it is possible to more reliably prevent damage to the surface of another optical member disposed on the back side of the optical sheet for a liquid crystal display device.

The ratio of the area occupied by the plurality of convex portions is preferably 2% or more and 80% or less. By setting the area ratio of the plurality of convex portions to the above-described range, adhesion to other optical members disposed on the back side can be sufficiently prevented, and damage to the surface of the other optical members can be more reliably prevented.

The average diameter of the convex portion is preferably 5 μm or more and 60 μm or less, and is preferably 0.5 μm or more as an average height. When the average diameter and the average height of the convex portion are within the above range, adhesion to other optical members disposed on the back side of the optical sheet for a liquid crystal display device can be more reliably prevented.

A region in which the plurality of convex portions are not present in the back surface is preferably provided with a plurality of grating shapes oriented in one direction. In this manner, by providing a plurality of stripe shapes oriented in one direction in a region where the plurality of convex portions are not present on the back surface, light can be diffused in the width direction of the grating shape, and the viewing angle in the width direction can be sufficiently ensured. .

The above-mentioned grating shape is suitable for exhibiting a scratch or hairline shape in one direction. As described above, by making the grating shape appear in a rubbing or hairline shape in one direction, light can be easily and reliably diffused in the width direction of the grating shape.

It is also preferable to have a grating shape continuous with the grating shape on the back side of the plurality of convex portions. By also having a grating shape continuous to the grating shape on the back side of the plurality of convex portions, light can be more uniformly diffused in the width direction of the grating shape, and the width of the grating shape can be more accurately ensured. Direction of view.

A backlight unit for a liquid crystal display device according to the present invention, which is provided with a light guide sheet that guides light incident from an end surface toward a surface side, and is disposed along the end surface of the light guide sheet. One or a plurality of LED light sources and one or a plurality of optical sheets superposed on the surface side of the light guiding sheet, and at least one of the one optical sheet or the plurality of optical sheets is used.

Since the backlight unit for a liquid crystal display device includes the optical sheet, adhesion of the optical sheet and other optical members disposed on the back side of the optical sheet can be prevented as described above, and damage to the surface of the other optical member can be prevented.

Further, a method for producing an optical sheet for a liquid crystal display device according to the present invention, which is a method for producing an optical sheet for a liquid crystal display device having a plurality of convex portions on a back surface The convex portion is a flat hemisphere or a flat cone whose front end portion is rounded, and the manufacturing method includes a roll having a reverse shape having a back surface shape in which the plurality of convex portions are scattered in a surface. a step of transporting a strip-shaped resin film onto the surface of the roll, a step of supplying an ultraviolet curable resin composition between the resin film and the roll, and a step of irradiating the ultraviolet curable resin composition with ultraviolet rays.

In the method for producing an optical sheet for a liquid crystal display device, it is possible to use a roll having a reversed shape in which a flattened hemispherical shape or a flattened tapered shape of a tip end portion is rounded, and the resin is used. One side of the film is formed into a plurality of flat hemispherical shapes or flattened pyramid-shaped convex portions whose front end portions are rounded. Therefore, in the method for producing an optical sheet for a liquid crystal display device, it is possible to manufacture an optical article capable of preventing adhesion by using a plurality of convex portions in contact with other optical member portions, thereby preventing adhesion of other optical members that are in contact with the plurality of convex portions. sheet.

In the present invention, the "surface side" means the viewer side of the liquid crystal display device, and the "back side" means the opposite side. The term "hemisphere" means a three-dimensional shape in which a spherical shape is cut in one plane and includes a "spherical defect", specifically a circular or elliptical bottom surface and a spherical shape continuous from the periphery of the bottom surface. . The "cone" is a concept that includes a cone and a pyramid. The "flat semi-divided ellipsoid" refers to a shape in which a virtual spheroid that rotates an ellipse around a minor axis is split in half by a vertical plane perpendicular to the minor axis including a long axis. The "occupation area ratio of the plurality of convex portions" means the ratio of the occupied area of the plurality of convex portions to the planar area of the surface on which the plurality of convex portions are formed. The "diameter" of each convex portion means the diameter of the base, and the "average diameter of the convex portion" means a value obtained by arbitrarily extracting ten convex portions and averaging the intermediate values of the maximum diameter and the minimum diameter of the base of each convex portion. The "height" of each convex portion means the length from the base of each convex portion to the protruding end, and "the average height of the convex portion" means that 10 convex portions are arbitrarily extracted and the length from the base to the protruding end of each convex portion is averaged. Value. The "raster shape" is not limited to a grating shape in which optical characteristics are closely adjusted, but a shape in which the incident light is diffracted in a broad sense. "Scratch or hairline in one direction" means a shape formed by orienting a plurality of elongated lesions into one direction.

Invention effect:

As described above, the optical sheet for a liquid crystal display device of the present invention can prevent adhesion and can reliably prevent damage of other optical members disposed on the back side. The backlight unit for a liquid crystal display device of the present invention can prevent adhesion and can reliably prevent damage of the optical member. Further, in the method for producing an optical sheet for a liquid crystal display device of the present invention, it is possible to manufacture an optical sheet capable of preventing adhesion and reliably preventing damage of other optical members disposed on the back side.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment

"Backlight unit"

The backlight unit for a liquid crystal display device of FIG. 1 (hereinafter also simply referred to as "backlight unit") 1 is a side light type backlight unit, and is a backlight unit for a liquid crystal display device using a plurality of LED light sources. The backlight unit 1 includes a light guiding film 2 that guides light incident from the end surface toward the light guide sheet on the front surface side, a plurality of LED light sources 3 that are disposed along the end surface of the light guiding film 2, and a light guide film 2 that is superposed on the light guiding film 2 A plurality of optical sheets for liquid crystal display devices on the surface side (hereinafter also simply referred to as "optical sheets"). The backlight unit 1 has a light diffusion sheet 5 that is directly superimposed on the surface of the light guiding film 2 (without spacing of other sheets or the like), and a prism sheet 6 that is directly superposed on the surface of the light diffusion sheet 5 (without spacing other sheets or the like) as a plurality of Optical sheet. Further, the backlight unit 1 further includes a reflection sheet 7 disposed on the back side of the light guiding film 2. The light-diffusing sheet 5 diffuses light incident from the back side and collects light (concentrated light diffusion) toward the normal direction side. The prism sheet 6 refracts light incident from the back side toward the normal direction side. The reflection sheet 7 reflects the light emitted from the back surface of the light guiding film 2 and re-enters the light guiding film 2 again. Incidentally, in FIG. 1, the reflection sheet 7, the light guide film 2, the light diffusion sheet 5, and the prism sheet 6 are separately separated, but actually the surface of the reflection sheet 7 and the back surface of the light guide film 2 and the light guide film 2 are separated. The surface and the back surface of the light diffusion sheet 5, the surface of the light diffusion sheet 5, and the back surface of the prism sheet 6 are in contact with each other.

<Light diffusion sheet>

As shown in FIG. 2, the light diffusion sheet 5 is provided with a base material layer 11, a light diffusion layer 12 laminated on the surface side of the base material layer 11, and a back layer 13 laminated on the back side of the base material layer 11. Further, the light diffusion sheet 5 has a plurality of convex portions 13a as anti-adhesion portions on the back surface (back surface of the back layer 13) in a scattered manner. The plurality of convex portions 13a are integrally formed with the back layer 13 (that is, a plurality of convex portions 13a and back layers 13 are integrally formed). The light diffusion sheet 5 is formed in a square shape in plan view. The light diffusion sheet 5 is composed of the base material layer 11, the light diffusion layer 12, the back layer 13, and the plurality of convex portions 13a (that is, the light diffusion sheet 5 does not have the base material layer 11, the light diffusion layer 12, the back layer 13, and the like. Other layers than the convex portion 13a).

(base material layer)

The base material layer 11 needs to transmit light, and thus is formed to be transparent. The base material layer 11 is mainly composed of a synthetic resin. The main component of the base material layer 11 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, acrylic-urethane resin, polycarbonate, and polyphenylene. Ethylene, polyolefin, cellulose acetate, weather resistant vinyl chloride, etc. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending properties is particularly preferable. In addition, the "main component" means the component which has the most content, and is a component of 50 mass % or more, for example.

The lower limit of the average thickness of the base material layer 11 is preferably 10 μm, more preferably 23 μm, still more preferably 38 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 above lower limit, there is a risk of occurrence of curling in the case where the light diffusion layer 12 is formed by coating. Further, if the average thickness of the base material layer 11 is less than the above lower limit, there is a risk that bending tends to occur. On the contrary, if the average thickness of the base material layer 11 exceeds the above upper limit, there is a risk that the brightness of the backlight unit 1 is lowered, and there is a risk that the thinning of the backlight unit 1 is not required. 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 light diffusion sheet 5. The light diffusion layer 12 has a plurality of beads 14 and a binder 15 therefor. The beads 14 are surrounded by a binder 15. The light diffusion layer 12 is dispersed and contains a plurality of beads 14 so that light transmitted from the back side to the surface side is substantially uniformly diffused. Further, in the light-diffusing layer 12, fine irregularities are formed substantially uniformly on the surface of the plurality of beads 14, and the concave portions and the convex portions of the fine uneven portions are formed in a lens shape. The light-diffusing layer 12 exhibits an excellent light-diffusing function by the lens action of the fine unevenness, and has a refractive function of refracting the transmitted light toward the normal direction side by the light-diffusing function and causing the transmitted light to be macroscopically concentrated toward the normal direction. The concentrating function of light.

The beads 14 are resin particles having a property of diffusing light. The main component of the 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 preferable, and polymethyl methacrylate (PMMA) is particularly preferable.

The shape of the bead 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 fiber shape. Among them, a spherical shape excellent in light diffusibility is preferable.

The lower limit of the average particle diameter of the beads 14 is preferably 1 μm, more preferably 2 μm, still more preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the beads 14 is preferably 15 μm, more preferably 10 μm, still more preferably 8 μm. When the average particle diameter of the bead 14 is less than the above lower limit, the unevenness on the surface of the light diffusion layer 12 is small, and there is a risk that the light diffusibility required as the light diffusion sheet 5 cannot be satisfied. On the other hand, if the average particle diameter of the beads 14 exceeds the above upper limit, there is a risk that the thickness of the light diffusion sheet 5 increases and it is difficult to uniformly diffuse. Incidentally, the "average particle diameter of the beads" means the average particle diameter of the plurality of beads calculated from the volume-based particle size distribution measured by the laser diffraction method.

The lower limit of the amount of the beads 14 to be added (the amount of the polymer component as the material for forming the binder 15 to the amount of the polymer component in terms of the amount of the polymer component) is preferably 10 parts by mass, more preferably 20 parts by mass, more preferably 50 parts by mass. On the other hand, the upper limit of the amount of the beads 14 to be added is preferably 500 parts by mass, more preferably 300 parts by mass, and still more preferably 200 parts by mass. If the blending amount of the beads 14 is less than the above lower limit, there is a risk that the light diffusibility is insufficient. On the contrary, if the blending amount of the beads 14 exceeds the above upper limit, there is a risk that the beads 14 are not accurately fixed by the binder 15.

The binder 15 is formed by curing (crosslinking, etc.) a polymer composition containing a polymer of a base material. The fixing beads 14 are disposed at substantially equal density over the entire surface of the base material layer 11 by the bonding agent 15. In addition, the polymer composition for forming the binder 15 may be suitably blended with, for example, a micro inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an antistatic agent, and an ultraviolet absorber. , antioxidants, viscosity modifiers, lubricants, light stabilizers, etc.

(back layer)

The back layer 13 needs to transmit light, and thus is formed to be transparent. The back layer 13 is formed mainly of a synthetic resin. The main component of the back layer 13 is not particularly limited, and examples thereof include a thermosetting resin and an active energy ray-curable resin.

Examples of the thermosetting resin include an epoxy resin, an anthrone resin, a phenol resin, a urea resin, an unsaturated polyester resin, a melamine resin, an alkyd resin, an acrylic resin, a guanamine functional copolymer, a polyurethane resin, and the like. .

Examples of the active energy ray-curable resin include an ultraviolet curable resin which is crosslinked and cured by irradiation with ultraviolet rays, and an electron beam curable resin which is crosslinked and cured by irradiation with an electron beam. It can be suitably selected and used from a polymerizable monomer and a polymeric oligomer. In particular, the active energy ray-curable resin is preferably an acrylic, urethane or urethane urethane-based ultraviolet curable resin.

The plurality of convex portions 13a are integrally formed with the back layer 13 using the same main component as the back layer 13 (that is, a plurality of convex portions 13a and back layers 13 are integrally formed).

Each of the convex portions 13a is a flat hemisphere or a flat cone whose front end portion is rounded, and in particular, in the present embodiment, is a flat half-segment rotation as shown in Figs. 3(a) and 3(b). Ellipsoid. By making each convex portion 13a a flat semi-divided spheroid, it is possible to more reliably prevent damage of the surface of another optical member disposed on the back side. The plurality of convex portions 13a are randomly (not regular) protruded from the back surface of the back layer 13. In the light-diffusing sheet 5, by providing a plurality of convex portions 13a in a random manner, it is possible to prevent the occurrence of moire fringes based on the plurality of convex portions 13a. Incidentally, the "semi-segmented ellipsoidal shape" is not limited to a semi-divided ellipsoidal shape in a strict sense, and includes a shape in which the base is a perfect circle and the outer surface is formed into a dome shape by a curved surface.

The lower limit of the average radius of curvature of the front end portion of the convex portion 13a is preferably 20 μm, and more preferably 50 μm. On the other hand, the upper limit of the average radius of curvature of the tip end portion of the convex portion 13a is preferably 200 μm, and more preferably 100 μm. When the average radius of curvature is less than the lower limit, there is a risk that damage occurs on the surface of the light guiding film 2 disposed on the back side of the light diffusing sheet 5. On the other hand, when the average radius of curvature exceeds the above upper limit, the contact area between the convex portion 13a and the surface of the light guiding film 2 becomes large, and there is a risk that unevenness in brightness occurs due to light incident on the abutting portion. Incidentally, the "average curvature radius of the tip end portion of the convex portion" means an average value of the curvature radius of the back surface average interface and the farthest portion of the back layer of the arbitrarily extracted ten convex portions.

The lower limit of the average diameter D1 of the convex portion 13a is preferably 5 μm, more preferably 7 μm, still more preferably 10 μm. On the other hand, the upper limit of the average diameter D1 of the convex portion 13a is preferably 60 μm, more preferably 50 μm, still more preferably 40 μm, and particularly preferably 20 μm. When the average diameter D1 of the convex portion 13a is less than the lower limit, the radius of curvature of the distal end portion of the convex portion 13a is too small to sufficiently ensure the height H of the convex portion 13a, and the light guiding film disposed on the back side of the light diffusion sheet 5 is provided. The surface of 2 is at risk of injury. On the other hand, when the average diameter D1 of the convex portion 13a exceeds the above upper limit, the height of the convex portion 13a is excessively large in order to keep the radius of curvature of the distal end portion of the convex portion 13a in a preferable range, and there is a risk of violating the requirement for thinning of the backlight unit. .

The lower limit of the average height H of the convex portion 13a is preferably 0.5 μm, more preferably 0.8 μm, still more preferably 1.0 μm. On the other hand, the upper limit of the average height H of the convex portion 13a is preferably 6 μm, more preferably 5 μm, still more preferably 4 μm. When the average height H of the convex portion 13a is less than the lower limit, the light diffusion sheet 5 and the light guiding film 2 are likely to be in contact with each other except for the convex portion 13a, and light is generated due to light incident on the abutting portion. The risk of unevenness. On the other hand, when the average height H of the convex portion 13a exceeds the above upper limit, there is a risk of violating the requirement for the thinning of the backlight unit, and there is a risk of damaging the surface of the other optical member (light guiding film 2) disposed on the back side.

It is preferable that the heights H are uniform between the plurality of convex portions 13a. The upper limit of the coefficient of variation of the height H of the plurality of convex portions 13a is preferably 0.2, more preferably 0.1, still more preferably 0.05. When the coefficient of variation of the height H of the plurality of convex portions 13a exceeds the above upper limit, the height H of the plurality of convex portions 13a becomes uneven, and the convex portion 13a having a large load deflection is present, and the surface of the light guiding film 2 is formed thereon. The risk of injury. On the other hand, the lower limit of the coefficient of variation of the height H of the plurality of convex portions 13a is not particularly limited, and may be, for example, zero. Incidentally, the "variation coefficient" of the heights of the plurality of convex portions refers to a value obtained by dividing the standard deviation of the heights of the 20 convex portions that are arbitrarily extracted by the average height.

The lower limit of the ratio (H/D1) of the average height H of the plurality of convex portions 13a to the average diameter D1 is preferably 0.02, more preferably 0.05, still more preferably 0.10. On the other hand, the upper limit of the above ratio (H/D1) is preferably 0.2, more preferably 0.15, still more preferably 0.12. When the ratio (H/D1) is less than the lower limit, the contact area between the plurality of convex portions 13a and the surface of the light guiding film 2 is increased, and there is a risk that unevenness in brightness occurs due to light incident on the abutting portion. On the other hand, when the ratio (H/D1) exceeds the above upper limit, the tip end portions of the plurality of convex portions 13a become too sharp, and there is a risk that the surface of the light guiding film 2 is damaged.

The lower limit of the average pitch of the convex portions 13a is preferably 200 μm, more preferably 300 μm, still more preferably 400 μm. On the other hand, the upper limit of the average pitch of the convex portions 13a is preferably 1000 μm, more preferably 900 μm, still more preferably 800 μm. When the average pitch of the convex portions 13a is less than the above lower limit, the number of the convex portions 13a is too large, and there is a risk that the surface of the light guiding film 2 is damaged. In addition, when the average pitch of the convex portions 13a is less than the lower limit, the number of the convex portions 13a is too large, and when a grating shape is formed on the surface on which the convex portions 13a are formed as in the embodiment to be described later, there is a risk of lowering the grating performance. . On the other hand, if the average pitch of the convex portions 13a exceeds the above upper limit, there is a risk that the number of the convex portions 13a is insufficient and the adhesion cannot be sufficiently prevented. Incidentally, the "average pitch" of the convex portions means an average value of the pitches of the extracted convex portions and the other convex portions adjacent to the convex portions.

The lower limit of the occupied area ratio of the plurality of convex portions 13a is preferably 2%, more preferably 3%, still more preferably 4%. On the other hand, the upper limit of the area ratio of the plurality of convex portions 13a is preferably 80%, more preferably 70%, still more preferably 60%, and particularly preferably 40%. When the ratio of the area occupied by the plurality of convex portions 13a is less than the above lower limit, there is a risk that the adhesion cannot be sufficiently prevented. On the other hand, if the area ratio of the plurality of convex portions 13a exceeds the above upper limit, there is a risk that the surface of the light guiding film 2 is damaged.

The lower limit of the ratio of the average diameter D1 of the convex portion 13a to the average particle diameter of the beads 14 is preferably 3, more preferably 4, still more preferably 5. On the other hand, the upper limit of the above ratio is preferably 9, more preferably 8, and still more preferably 7. When the ratio is less than the lower limit, the amount of light incident on the convex portion 13a is insufficient, and it is difficult to sufficiently introduce light by the convex portion 13a, and the amount of light that is specularly reflected by the back surface of the back layer 13 of the light diffusion sheet 5 is changed. Big risk. On the other hand, when the above ratio exceeds the above upper limit, there is a risk that the curved shape of the convex portion 13a is too gentle and it is difficult to introduce light by the convex portion 13a.

The plurality of convex portions 13a are formed mainly of a synthetic resin. In addition, the plurality of convex portions 13 do not include beads inside. In the light-diffusing sheet 5, since the plurality of convex portions 13a do not contain beads, it is possible to prevent the surface of the light-guiding film 2 disposed on the back surface side of the light-diffusing sheet 5 from being damaged by the falling of the beads.

<Prism sheet>

As shown in FIG. 4, the prism sheet 6 is provided with a base material layer 16, a prism array 17 laminated on the surface side of the base material layer 16, and a back layer 18 laminated on the back side of the base material layer 16. The prism array 17 is configured by arranging a plurality of ridge prism portions 17a in parallel. Further, the prism sheet 6 is provided with a plurality of convex portions 18a as anti-adhesion portions on the back surface of the back layer 18. The prism sheet 6 is composed of a base material layer 16, a prism array 17, a back layer 18, and a plurality of convex portions 18a (that is, the prism sheet 6 does not have the base material layer 16, the prism array 17, the back layer 18, and the plurality of convex portions 18a. Other layers than others). The prism sheet 6 is formed in a square shape in plan view.

The base material layer 16 and the prism array 17 need to transmit light, and thus are formed to be transparent. The base material layer 16 and the prism array 17 are composed of a synthetic resin as a main component. The main component of the base material layer 16 and the prism array 17 is the same as the main component of the base material layer 11 of the light diffusion sheet 5. In addition, as the main component of the base material layer 16 and the prism array 17, a thermosetting resin, an active energy ray-curable resin, or the like similar to the plurality of convex portions 13a of the light diffusion sheet 5 may be used. The direction of the prism array 17 (the ridge line direction of the plurality of ridge prism portions 17a) is perpendicular to the light emission direction of the light source 3 in the present embodiment.

The lower limit of the height from the back surface of the base material layer 16 of the prism sheet 6 to the apex of the ridge prism portion 17a is preferably 50 μm, more preferably 100 μm. On the other hand, the upper limit of the above height is preferably 200 μm, and more preferably 180 μm. The lower limit of the average pitch of the plurality of ridge prism portions 17a of the prism sheet 6 is preferably 10 μm, more preferably 20 μm. On the other hand, the upper limit of the average pitch of the plurality of ridge prism portions 17a is preferably 100 μm, more preferably 60 μm. The apex angle of the ridge prism portion 17a is preferably 85° or more and 95° or less. Further, the base angle of the ridge prism portion 17a is preferably 42° or more and 48° or less. The lower limit of the refractive index of the prism sheet 6 is preferably 1.5, and more preferably 1.55. On the other hand, the upper limit of the refractive index of the prism sheet 6 is preferably 1.7. Incidentally, the "average pitch of the ridge prism portions" means the average pitch of the contiguous ten ridge prism portions that are arbitrarily extracted. In addition, the "refractive index" means a refractive index of light having a wavelength of 589.3 nm (D-ray of sodium), and is a test piece having a flat shape of 70 mm and a thickness of 2 mm and measuring at a temperature of 23 ° C. The average of 3 times. Further, the "refractive index of the prism sheet" means the refractive index of the ridge strip portion.

The backing layer 18 needs to transmit light and is thus formed to be transparent. The back layer 18 is formed mainly of a synthetic resin. The main component of the back layer 18 can be the same as the main component of the back layer 13 of the above-described light diffusion sheet 5.

The plurality of convex portions 18a are integrally formed with the back layer 18 using the same main component as the back layer 18 (that is, a plurality of convex portions 18a and back layers 18 are integrally formed).

The plurality of convex portions 18a constitute the rearmost surface of the prism sheet 6. Each of the convex portions 18a is a flat hemisphere or a flat cone whose front end portion is rounded, and is particularly a flat semi-divided ellipsoid in the present embodiment. The plurality of convex portions 18a are randomly (not regular) protruded from the back surface of the back layer 18. The specific shape of the plurality of convex portions 18a is the same as that of the plurality of convex portions 13a of the light diffusion sheet 5.

The lower limit of the ratio of the average diameter of the convex portions 18a to the average pitch of the ridge prism portions 17a is preferably 0.1, more preferably 0.3, still more preferably 0.5. On the other hand, the upper limit of the above ratio is preferably 6.0, more preferably 3.0, still more preferably 1.0. When the ratio is less than the lower limit, the amount of light incident on the convex portion 18a is insufficient, and it is difficult to sufficiently introduce light by the convex portion 18a, and the amount of light that is specularly reflected by the back surface of the back layer 18 of the prism sheet 6 is increased. risks of. On the other hand, when the above ratio exceeds the above upper limit, there is a risk that the curved shape of the convex portion 18a is too gentle and it is difficult to introduce light by the convex portion 18a.

<light guide film>

The light guiding film 2 emits light that is incident from the end surface substantially uniformly from the surface. The light guiding film 2 is formed in a substantially square shape in plan view, and is formed into a plate shape (non-wedge shape) having a substantially uniform thickness. The light guiding film 2 has a plurality of concave portions 9 recessed toward the surface side on the back surface. Further, the light guiding film 2 has an anti-adhesion portion on the back surface. Specifically, the light guiding film 2 has a plurality of raised portions 8 that are present around the plurality of concave portions 9 and protrude toward the back side as the above-described anti-adhesion portion. The raised portion 8 is provided adjacent to the concave portion 9, and the inner side surface of the raised portion 8 is continuous with the surface on which the concave portion 9 is formed.

The lower limit of the average thickness of the light guiding film 2 is preferably 100 μm, more preferably 150 μm, still more preferably 200 μm. On the other hand, the upper limit of the average thickness of the light guiding film 2 is preferably 600 μm, more preferably 580 μm, still more preferably 550 μm. When the average thickness of the light guiding film 2 is less than the above lower limit, there is a risk that the strength of the light guiding film 2 is insufficient, and there is a risk that light emitted from the light source 3 cannot be sufficiently incident on the light guiding film 2 . On the contrary, if the average thickness of the light guiding film 2 exceeds the above upper limit, there is a risk that the thinning of the backlight unit 1 is not required.

The plurality of concave portions 9 function as a light scattering portion that scatters incident light toward the surface side. Each of the recesses 9 is formed in a substantially circular shape in plan view. Further, each of the concave portions 9 is formed to gradually reduce the diameter toward the surface side. The shape of the concave portion 9 is not particularly limited, and may be a hemispherical shape, a semi-elliptical shape, a conical shape, a conical ladder shape or the like. Among them, the shape of the concave portion 9 is preferably a hemispherical shape or a semi-elliptical shape. By making the concave portion 9 hemispherical or semi-elliptical, the formability of the concave portion 9 can be improved, and the light incident on the concave portion 9 can be suitably scattered.

The raised portion 8 is continuously formed from a surface of the back surface of the light guiding film 2 that is perpendicular to the thickness direction of the light guiding film 2. Specifically, the ridge portion 8 is continuously formed from the flat surface of the back surface of the light guiding film 2 . The raised portion 8 is formed in a substantially annular shape in a plan view so as to surround the concave portion 9. The light guiding film 2 is formed in a substantially annular shape in a plan view so as to surround the concave portion 9 with the raised portion 8, so that the concave portion 9 and the near side of the concave portion 9 and the reflection disposed on the back side of the light guiding film 2 can be easily and reliably prevented. Sheet 7 is tight.

The light guiding film 2 has flexibility. By having flexibility, the light guiding film 2 can suppress damage of the reflection sheet 7 disposed on the back side. The light guiding film 2 needs to transmit light, and thus is formed to be transparent. The light guiding film 2 is composed of a synthetic resin as a main component.

Examples of the main component of the light guiding film 2 include polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, and methyl (meth)acrylate-benzene. Ethylene copolymer, polyolefin, cycloolefin polymer, cyclic olefin copolymer, cellulose acetate, weather resistant vinyl chloride, active energy ray-curable resin, and the like. Among them, as the main component of the light guiding film 2, polycarbonate or acrylic resin is preferable. Since the polycarbonate is excellent in transparency and has a high refractive index, the light guide film 2 contains polycarbonate as a main component, so that total reflection easily occurs on the upper and lower surfaces of the light guiding film 2, and light can be efficiently transmitted. Further, since polycarbonate has heat resistance, deterioration or the like due to heat generation of the light source 3 is less likely to occur. Further, since polycarbonate has a smaller water absorption property than an acrylic resin or the like, the dimensional stability is high. Therefore, the light guiding film 2 can suppress deterioration over the years by including polycarbonate as a main component. On the other hand, since the acrylic resin has high transparency, the loss of light of the light guiding film 2 can be reduced.

<LED light source>

The plurality of LEDs 3 are arranged along one end surface of the light guiding film 2. The plurality of LED light sources 3 are disposed such that each light emitting surface faces and faces (or abuts) one end surface of the light guiding film 2.

<reflection sheet>

The reflection sheet 7 is disposed on the back side of the light guide film 2 so as to be in contact with the plurality of raised portions 8 formed on the back surface of the light guiding film 2 . The reflection sheet 7 reflects the light emitted from the back surface of the light guiding film 2 to the upper side. The reflective sheet 7 is a white sheet in which a filler is dispersed in a base material resin such as polyester, and a mirror sheet having a specular reflectance by vapor-depositing a metal such as aluminum or silver on the surface of a film formed of polyester. .

<advantage>

Since the optical sheets (the light-diffusing sheet 5 and the prism sheet 6) are provided with a plurality of convex portions 13a and 18a in a scattered manner on the back surface, the optical sheet and other optical members disposed on the back side of the optical sheet use the plurality of convex portions. The portions 13a and 18a are partially abutted. Therefore, the optical sheet can prevent adhesion to other optical members disposed on the back side. Further, since the convex portions 13a and 18a of the optical sheet are flat hemispheres or flat cones whose front end portions are rounded, the curved surfaces of the front end portions (lower end portions) of the plurality of convex portions 13a and 18a are compared. The gradation makes it possible to prevent damage to the surface of other optical members disposed on the back side.

Since the backlight unit 1 includes the optical sheet (the light diffusion sheet 5 and the prism sheet 6), adhesion of the optical sheet and other optical members disposed on the back side of the optical sheet can be prevented as described above, and other optical members can be prevented. Damage to the surface.

<Method of Manufacturing Optical Sheet>

Next, a method of manufacturing the optical sheet will be described. Here, a method of manufacturing the optical sheet in the above-described light diffusion sheet 5 will be described. The method for producing an optical sheet includes a resin film transport step, an ultraviolet curable resin composition supply step, and an ultraviolet irradiation step. Moreover, this optical sheet manufacturing method has the light-diffusion layer lamination process.

(manufacturing device)

The method of manufacturing the optical sheet is performed using, for example, the manufacturing apparatus 21 of Fig. 5 . The manufacturing apparatus 21 has a pair of press rolls 22, 23 arranged in parallel adjacent manner. The pair of press rolls 22 and 23 are provided with temperature control means so that the surface (circumferential surface) temperature can be controlled to an optimum temperature. As the pair of pressing rolls 22, 23, a metal elastic roll comprising a metal roll and a flexible roll whose surface is covered with an elastomer is preferably used. Further, one press roller 23 has a plurality of recesses on the surface (circumferential surface). Specifically, the one pressure roller 23 has an inverted shape in which the back surface shape of the plurality of convex portions 13a is provided in a scatter manner on the surface.

(Resin film transport process)

In the resin film transporting step, the strip-shaped resin film A is transported to the surfaces of the pair of press rolls 22 and 23. Specifically, in the resin film transport step, the resin film A forming the base material layer 11 of the light diffusion sheet 5 is transported between the pair of press rolls 22 and 23.

(Ultraviolet curable resin composition supply step)

In the ultraviolet curable resin composition supply step, an ultraviolet curable resin composition is supplied between the resin film A and one of the press rolls 23. In the ultraviolet curable resin composition supply step, the resin film A and the ultraviolet curable resin composition supplied to one surface of the resin film A are pressed by a pair of press rolls 22 and 23. In the ultraviolet curable resin composition supply step, a plurality of convex portions 13a are transferred on the outer surface (one side surface) of the ultraviolet curable resin composition laminated on one surface of the resin film A.

(UV irradiation process)

In the ultraviolet irradiation step, the ultraviolet curable resin composition in which the plurality of convex portions 13a are transferred by the ultraviolet curable resin composition supply step is irradiated with ultraviolet rays to cure the ultraviolet curable resin composition. In the ultraviolet irradiation step, a plurality of convex portions 13a are formed on one surface of the resin film A.

(Light diffusion layer lamination process)

In the light diffusion layer laminating step, after the ultraviolet irradiation step, a coating liquid containing a plurality of beads 14 and a binder composition is applied onto the other surface of the resin film A, and the applied coating liquid is dried and cured. . In the light diffusion layer lamination step, the light diffusion layer 12 is laminated on the other surface of the resin film A.

Here, the step of laminating the light diffusion layer 12 after forming the plurality of convex portions 13a has been described. The method for producing the light diffusion sheet is not limited to this step, and may be formed after laminating the light diffusion layer 12. Projections 13a.

In the case where the optical sheet is the light-diffusing sheet 5, the same resin film transport step and ultraviolet curable resin composition supply can be used. It is manufactured by a process and an ultraviolet irradiation process. Specifically, as a method of producing the prism sheet 6, (a) the active energy ray-curable resin is applied to the other surface of the resin film after the ultraviolet irradiation step, and is pressed against the prism array 17 a sheet mold, a mold or a roll mold having an inverted shape, a shape transferred onto an uncured active energy ray-curable resin, and a method of irradiating an active energy ray to cure the active energy ray-curable resin; (b) another pressure roller The circumferential surface of 23 forms an inverted shape of the prism array 17, and a resin in a molten state is introduced into the other surface of the resin film, and the above-described shape is transferred. Further, as the method of manufacturing the prism sheet, a plurality of convex portions may be formed after the prism rows 17 are formed.

<advantage>

In the method for producing the optical sheet, a roll 24 having a flat hemispherical shape or a flat pan-shaped convex portion 13a, 18a having a rounded front end portion can be used, and one surface of the resin film can be used. A plurality of convex portions 13a, 18a are formed. Therefore, in the method for producing an optical sheet for a liquid crystal display device, it is possible to prevent adhesion by a plurality of convex portions 13a and 18a from coming into contact with other optical member portions, and to prevent contact with the plurality of convex portions 13a and 18a. Optical sheets (light diffusing sheets 5 and prism sheets 6) damaged by optical members.

Second Embodiment

"Backlight unit"

The backlight unit 31 for a liquid crystal display device of FIG. 6 is a side light type backlight unit, and is a backlight unit for a liquid crystal display device using a plurality of LED light sources. The backlight unit 31 includes a light guide film 2 that guides light incident from the end surface toward the light guide sheet on the front surface side, a plurality of LED light sources 3 that are disposed along the end surface of the light guide film 2, and a light guide film 2 that is superposed on the light guide film 2 A plurality of optical sheets 32 on the surface side. The backlight unit 31 has a lenticular sheet 33 that is directly superimposed on the surface of the light guiding film 2 (without spacing of other sheets or the like), and a prism sheet 6 that directly overlaps the surface of the lenticular sheet 33 (without spacing other sheets, etc.) as a plurality of Optical sheet 32. Further, the backlight unit 31 further includes a reflection sheet 7 disposed on the back side of the light guiding film 2. In addition, in FIG. 6, the reflection sheet 7, the light guide film 2, the microlens sheet 33, and the prism sheet 6 are separately described, but actually, the surface of the reflection sheet 7, the back surface of the light-guide film 2, and the light-guide film 2 are isolate|separated. The surface and the back surface of the lenticular sheet 33, the surface of the lenticular sheet 33, and the back surface of the prism sheet 6 are in contact with each other. The light guide film 2, the LED light source 3, the prism sheet 6, and the reflection sheet 7 of the backlight unit 31 are the same as those of the backlight unit 1 of Fig. 1, and therefore the same reference numerals will be given thereto, and the description thereof will be omitted.

<Microlens sheet>

As shown in FIG. 7, the lenticular sheet 33 includes a base material layer 34, a microlens array 35 laminated on the surface side of the base material layer 34, and a back layer 36 laminated on the back side of the base material layer 34. The microlens array 35 is composed of a plurality of microlenses 35a projecting from the surface of the base material layer 34. Further, the lenticular sheet 33 has a plurality of convex portions 36a as anti-adhesion portions on the back surface of the back layer 36 in a scattered manner. The lenticular sheet 33 is composed of a base material layer 34, a microlens array 35, a back layer 36, and a plurality of convex portions 36a (that is, the lenticular sheet 33 does not have the base material layer 34, the microlens array 35, the back layer 36, and the like. Other layers than the convex portion 36a). The lenticular sheet 33 is formed in a square shape in plan view.

The base material layer 34 and the microlens array 35 need to transmit light, and thus are formed to be transparent. The base material layer 34 and the microlens array 35 are composed of a synthetic resin as a main component. The main component of the base material layer 34 and the microlens array 35 is the same as the main component of the base material layer 11 of the light diffusion sheet 5. In addition, as the main component of the base material layer 34 and the microlens array 35, a thermosetting resin, an active energy ray-curable resin, or the like similar to the back layer 13 of the light diffusion sheet 5 may be used.

The average thickness of the base material layer 34 can be, for example, the same as the average thickness of the base material layer 11 of the light diffusion sheet 5 described above. The microlens array 35 may be integrally formed with the base material layer 34 (i.e., may be integrally formed with the base material layer 34) or may be formed separately from the base material layer 34.

The microlens 35a is formed in a hemispherical shape (including a shape similar to a hemisphere). Incidentally, the microlens 35a may be formed in a convex lens shape as shown in FIG. 7, or may be formed in a concave lens shape. The plurality of microlenses 35a are densely and geometrically disposed on the surface of the base material layer 34. Specifically, the plurality of microlenses 35a are arranged on the surface of the base material layer 34 in an equilateral triangle lattice pattern. Therefore, the pitch of the plurality of microlenses 35a and the inter-lens distance S1 are all constant. The arrangement pattern can also arrange the plurality of microlenses 35a most densely. Incidentally, the arrangement pattern of the plurality of microlenses 35a is not limited to the above-described triangular lattice pattern which can be densely filled, and may be, for example, a square lattice pattern or a random pattern. According to this random pattern, generation of moire fringes is reduced when overlapping with other optical members.

The lower limit of the average diameter D2 of the microlens 35a is preferably 10 μm, more preferably 100 μm, still more preferably 200 μm. On the other hand, the upper limit of the average diameter D2 of the microlens array 35a is preferably 1000 μm, more preferably 700 μm, still more preferably 500 μm. When the average diameter D2 of the microlens 35a is less than the above lower limit, the influence of diffraction becomes large, and it is easy to cause deterioration of optical performance or color decomposition. On the other hand, if the average diameter D2 of the microlens 35a exceeds the above upper limit, there is a risk that the thickness is increased or the brightness is uneven. Incidentally, the "average diameter of the microlens" means a value obtained by averaging the average diameters of the bases of the arbitrarily extracted ten microlenses. In addition, the average diameter of each microlens means the intermediate value of the largest diameter and the minimum diameter of a base.

The lower limit of the ratio of the height of the microlens 35a to the height of the radius of curvature is preferably 0.6, and more preferably 0.75. On the other hand, as the upper limit of the above height ratio, 1 is preferable. When the height ratio is within the above range, the refractive action of the lens of the microlens 35a is effectively exhibited, and the optical function such as condensing of the lenticular sheet 33 is remarkably improved.

The upper limit of the interval ratio (S1/D2) of the average inter-lens distance S1 of the microlens 35a with respect to the average diameter D2 is preferably 0.5, and more preferably 0.2. By setting the above-described spacing ratio (S1/D2) to the above upper limit or lower, the flat portion that does not contribute to the optical function is reduced, and the optical function such as condensing of the lenticular sheet 33 is remarkably improved.

The lower limit of the filling ratio of the plurality of microlenses 35a is preferably 40%, more preferably 60%. By setting the filling ratio of the plurality of microlenses 35a to the above lower limit or more, the area occupied by the plurality of microlenses 35a is increased, and the optical function such as the condensing of the lenticular sheet 33 is remarkably improved. Incidentally, the "filling rate" of the plurality of microlenses refers to the area ratio of the microlenses per unit area in plan view.

The lower limit of the refractive index of the microlens array 35 is preferably 1.3, more preferably 1.45. On the other hand, the upper limit of the refractive index of the microlens array 35 is preferably 1.8, and more preferably 1.6. Further, as the refractive index of the microlens array 35, 1.5 is particularly preferable. When the refractive index of the microlens array 35 is within the above range, the refractive action of the lens in the microlens array 35 is effectively exhibited, and an optical function such as condensing of the lenticular sheet 33 is improved.

The backing layer 36 needs to transmit light and is thus formed to be transparent. The back layer 36 is formed mainly of a synthetic resin. The main component of the back layer 36 can be the same as the main component of the back layer 13 of the above-described light diffusion sheet 5.

The plurality of convex portions 36a are integrally formed with the back layer 36 using the same main component as the back layer 36 (that is, the plurality of convex portions 36a and the back layer 36 are integrally formed).

The plurality of convex portions 36a constitute the rearmost surface of the lenticular sheet 33. Each of the convex portions 36a is a flat hemisphere or a flat cone whose front end portion is rounded, and is particularly a flat semi-divided ellipsoid in the present embodiment. The plurality of convex portions 36a are protruded from the back surface of the back layer 36 randomly (without regularity). The specific shape of the plurality of convex portions 36a is the same as that of the plurality of convex portions 13a of the light diffusion sheet 5.

The lower limit of the ratio of the average diameter of the convex portion 36a to the average diameter D2 of the microlens 35a is preferably 0.05, more preferably 0.07, still more preferably 0.1. On the other hand, the upper limit of the above ratio is preferably 1, more preferably 0.5, still more preferably 0.3. When the ratio is less than the lower limit, the amount of light incident on the convex portion 36a is insufficient, and it is difficult to sufficiently introduce light by the convex portion 36a, and the amount of light that is specularly reflected by the back surface of the back layer 36 of the lenticular sheet 33 is changed. Big risk. On the other hand, when the above ratio exceeds the above upper limit, there is a risk that the curved shape of the convex portion 36a is too gentle and it is difficult to introduce light by the convex portion 36a.

<Method of Manufacturing Microlens Sheet>

The microlens sheet 33 can be produced by using the same resin film transporting step, ultraviolet curable resin composition supplying step, and ultraviolet irradiation step as the above-described method of manufacturing the light diffusing sheet 5. Specifically, as a method of producing the lenticular sheet 33, (a) the active energy ray-curable resin is applied to the other surface of the resin film after the ultraviolet ray irradiation step, and is pressed against the microlens. a sheet mold, a mold or a roll mold of a transfer mold of the array 35, a shape transferred onto an uncured active energy ray-curable resin, and a method of irradiating an active energy ray to cure the active energy ray-curable resin; (b) another method The circumferential surface of one pressure roller forms an inverted shape of the microlens array 35, and a resin in a molten state is introduced into the other surface of the resin film to transfer the shape. Incidentally, as the method of manufacturing the lenticular sheet, a plurality of convex portions may be formed after the microlens array 35 is formed.

<advantage>

Since the lenticular sheet 33 has a plurality of convex portions 36a in a scatter manner on the back surface, adhesion to other optical members disposed on the back side can be prevented as described above, and damage of the surface of other optical members can be prevented.

The manufacturing method of the microlens sheet can easily and reliably manufacture the microlens sheet 33 which can prevent adhesion to other optical members disposed on the back side as described above and can prevent damage of the surface of other optical members.

Third Embodiment

<Light diffusion sheet>

The light diffusion sheet 41 of Fig. 8 is used for the backlight unit 1 of Fig. 1 instead of the light diffusion sheet 5 of Fig. 2 . The light diffusion sheet 41 includes a base material layer 11 , a light diffusion layer 12 laminated on the surface side of the base material layer 11 , and a back layer 42 laminated on the back surface side of the base material layer 11 . Further, the light diffusion sheet 41 has a plurality of convex portions 13a as anti-adhesion portions on the back surface of the back layer 42 in a scatter manner. The plurality of convex portions 13a are integrally formed with the back layer 42 (that is, a plurality of convex portions 13a and back layers 42 are integrally formed). The light diffusion sheet 41 is formed in a square shape in plan view. The light diffusion sheet 41 is composed of a base material layer 11, a light diffusion layer 12, a back layer 42 and a plurality of convex portions 13a (that is, the light diffusion sheet 41 does not have a base material layer 11, a light diffusion layer 12, and a back layer 42. And other layers than the plurality of convex portions 13a). The base material layer 11, the light-diffusing layer 12, and the plurality of convex portions 13a of the light-diffusing sheet 41 are the same as those of the light-diffusing sheet 5 of FIG. 2, and therefore the same reference numerals will be given, and the description thereof will be omitted.

The back layer 42 needs to transmit light, and thus is formed to be transparent. The back layer 42 is formed mainly of a synthetic resin. The main component of the back layer 42 can be the same as the main component of the back layer 13 of the above-described light diffusion sheet 5.

The light diffusion sheet 41 has a plurality of stripe shapes 43 oriented in one direction in a region where the plurality of convex portions 13a are not present in the back surface of the back layer 42 (the back surface of the light diffusion sheet 41). The grating shape 43 has a shape in which a plurality of concave and convex strips are formed in one direction. The light-diffusing sheet 41 is provided with the grating shape 43 so that the light reaching the grating shape 43 can be diffused in the width direction of the grating shape 43 (the vertical direction of the plurality of uneven strips in the average orientation direction). The grating shape 43 preferably exhibits a scratch or hairline shape that is oriented in one direction. In the light-diffusing sheet 41, the grating shape 43 is caused to have a rubbing or hairline shape in one direction, so that light can be easily and reliably diffused in the width direction of the grating shape 43. Incidentally, the "average orientation direction of the plurality of embossed strips" means the average orientation direction of the plurality of concave portions constituting the plurality of ridges.

The grating shape 43 is formed substantially uniformly (substantially equal in density) over all the regions except the plurality of convex portions 13a on the back surface of the back layer 42. Further, as shown in FIGS. 9 and 10, a plurality of irregular strips of the grating shape 43 are formed, and the longitudinal direction thereof is along a direction parallel to one end of the back surface of the back layer 42. Specifically, the longitudinal direction of the plurality of embossed strips is along the outgoing direction of the light from the light source (that is, the plurality of embossed strips are oriented in the outgoing direction of the light from the light source). The upper limit of the inclination angle of the light ray of each of the uneven strips with respect to the emission direction is preferably ±30°, more preferably ±15°, still more preferably ±5°. Further, each of the embossed strips may be randomly oriented within the range of the above-described tilt angle (that is, the orientation directions of the embossed strips may not be completely uniform). As described above, by causing the orientation direction of each of the embossed strips to be in a random state, it is possible to suppress the occurrence of rainbow-like unevenness in the liquid crystal display device due to the plurality of embossed strips. Incidentally, the concave portions of the plurality of concave and convex strips are preferably formed independently of each other in addition to the direction in which the light is diffused, but a part of the concave portions may be intersected with each other.

The longitudinal direction of the concave portion of the plurality of concave and convex strips may be continuous over both ends of the back layer 42. For example, the average length of the concave portions of the plurality of concave and convex strips is preferably 10000 times or less, and more preferably 5,000 times or less with respect to the average width of the concave portion. . Moreover, it is preferable that the lower limit of the average length of the concave portion of the plurality of uneven strips is twice or more, and more preferably three times or more with respect to the average width of the concave portions. When the average length of the concave portions of the plurality of embossed strips exceeds the above upper limit, there is a risk that it is difficult to form a plurality of embossed strips in a random orientation direction and to form a high density in order to suppress occurrence of rainbow unevenness in the liquid crystal display device. On the other hand, when the average length of the concave portions of the plurality of embossed strips is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased with respect to the amount of light reaching the grating shape 43. Incidentally, the "average length of the concave portions of the plurality of concave and convex strips" means an average value of the lengths of the 20 concave portions that are arbitrarily extracted.

Further, the length of the concave portion of the plurality of embossed strips is preferably random. In the light-diffusing sheet 41, the length of the concave portion of the plurality of concave-convex strips is random, and it is possible to suppress the occurrence of rainbow-like unevenness in the liquid crystal display device due to the plurality of uneven strips.

The width L1 of the concave portion of the plurality of embossed strips is preferably random. Further, as shown in FIG. 9, the width L1 of the concave portion of each of the uneven strips is preferably changed randomly along the longitudinal direction of the concave portion of the uneven strip. In the light-diffusing sheet 41, the width L1 of the concave portion of the plurality of uneven strips is made random, and it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of uneven strips.

The lower limit of the average width of the concave portions of the plurality of embossed strips is preferably 10 nm, more preferably 50 nm, still more preferably 100 nm. On the other hand, the upper limit of the average width of the concave portion as the plurality of embossed strips is preferably 30 μm, more preferably 20 μm, still more preferably 10 μm. When the average width of the concave portions of the plurality of embossed strips is less than the above lower limit, there is a risk that the formability of the grating shape 43 is lowered. On the other hand, when the average width of the concave portions of the plurality of embossed strips exceeds the above upper limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently ensured. Incidentally, the width of the concave portion of each of the uneven strips is preferably randomly formed in the longitudinal direction within the above range. By randomly forming the width of the concave portion of each of the uneven strips within the above range, it is possible to prevent moire fringes caused by interference with other members (prism sheets or liquid crystal cells) having a periodic pitch, and can be prevented. Color decomposition occurs regularly to prevent rainbow inequality. In addition, the "average width of the concave portion of the plurality of concave and convex strips" means the width of the average interface of the front end of the convex portion of the plurality of concave and convex strips at any point other than the both end portions in the longitudinal direction except for the arbitrarily extracted 20 concave portions. average value.

The pitch of the plurality of embossed strips is preferably random. In the light-diffusing sheet 41, the pitch of the plurality of uneven strips is made random, and it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of uneven strips. Incidentally, the "average pitch of the plurality of embossed strips" means an average value of the pitches of the 20 embossed strips adjacent to each other on a straight line perpendicular to the average orientation direction of the plurality of embossed strips.

The lower limit of the average pitch of the plurality of embossed strips is preferably 10 nm, more preferably 50 nm, still more preferably 100 nm. On the other hand, the upper limit of the average pitch of the plurality of embossed strips is preferably 40 μm, more preferably 30 μm, still more preferably 20 μm, and particularly preferably 10 μm. When the average pitch of the plurality of embossed strips is less than the above lower limit, there is a risk that the formability of the grating shape 43 is lowered. On the other hand, if the average pitch of the plurality of embossed strips exceeds the above upper limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased.

The upper limit of the standard deviation of the pitch of the plurality of embossed strips is preferably 10 μm, more preferably 9 μm, still more preferably 7 μm. When the standard deviation of the pitch of the plurality of embossed strips exceeds the above upper limit, the pitch of the plurality of embossed strips is too uneven, and the amount of light that cannot be diffused in the width direction of the grating shape 43 is uniformly increased in the entire formed region of the plurality of embossed strips. risks of. On the other hand, the lower limit of the standard deviation of the pitch of the plurality of embossed strips can be, for example, 4 μm from the viewpoint of easily arranging the plurality of embossed strips in a random direction. Incidentally, the "standard deviation of the pitch of the plurality of embossed strips" means the standard deviation of the pitch of the 20 embossed strips arbitrarily extracted.

The lower limit of the average number of per-unit lengths of the concave portions of the plurality of concave-convex strips in the direction perpendicular to the average orientation direction of the plurality of embossed strips is preferably 10 pieces/mm, more preferably 50 pieces/mm, still more preferably 100 pieces/ Mm. On the other hand, the upper limit of the average number of the above-mentioned average is preferably 10,000 pieces/mm, more preferably 5,000 pieces/mm, still more preferably 1,000 pieces/mm. When the number of the averages is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased with respect to the amount of light reaching the grating shape 43. On the other hand, if the average number of the above-described upper limits exceeds the above upper limit, there is a risk that the formability of the grating shape 43 is lowered.

The lower limit of the average depth D3 of the concave portion of the plurality of embossed strips is preferably 10 nm, more preferably 500 nm, further preferably 1 μm, and particularly preferably 2 μm. On the other hand, the upper limit of the average depth D3 is preferably 10 μm, more preferably 5 μm, still more preferably 3 μm. When the average depth D3 is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased. On the contrary, if the average depth D3 exceeds the above upper limit, there is a risk that the strength of the back layer 42 is lowered. In addition, the "average depth of the concave portion of the plurality of embossed strips" means an average value of the depth from the average interface of the tips of the plurality of embossed strips to the bottom of the arbitrarily extracted 20 recesses.

Further, the upper limit of the standard deviation of the depth of the concave portion of the plurality of embossed strips is preferably 4 μm, more preferably 3 μm, still more preferably 2.5 μm. When the standard deviation of the depth exceeds the above upper limit, the depth of the concave portion of the plurality of embossed strips is too uneven, and there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be uniformly increased in the entire formation region of the grating shape 43. On the other hand, the lower limit of the standard deviation of the depth is not particularly limited, and may be, for example, 0.3 μm. In addition, the "standard deviation of the depth of a plurality of embossed strips" means the standard deviation of the depth of the recessed part of the 20 embossing strips arbitrarily extracted.

The lower limit of the arithmetic mean roughness (Ra) based on the direction parallel to the direction in which the plurality of embossed strips are oriented is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), preferably 0.005 μm, more preferably 0.05 μm, further preferably 0.1 μm. On the other hand, the arithmetic mean roughness (Ra) based on the direction parallel to the orientation direction of the plurality of embossed strips as the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43 The upper limit is preferably 1.5 μm, more preferably 1.2 μm, still more preferably 1 μm. When the arithmetic mean roughness (Ra) is less than the lower limit, there is a risk that the effect of suppressing occurrence of a hot spot to be described later is insufficient. On the other hand, when the arithmetic mean roughness (Ra) exceeds the above upper limit, the amount of light diffused in a direction parallel to the direction in which the plurality of embossed strips are oriented is increased with respect to the amount of light diffused in the width direction of the grating shape 43, and the amount of light that is diffused in the width direction of the grating shape 43 is large. The risk of a viewing angle in a direction perpendicular to the direction in which the light exits the light source. In addition, "arithmetic mean roughness (Ra)" means a value when the λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the arithmetic mean roughness (Ra) based on the direction perpendicular to the direction in which the plurality of embossed strips are oriented is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), preferably 0.01 μm, more preferably 0.1 μm, further preferably 0.5 μm. On the other hand, the arithmetic mean roughness (Ra) based on the direction perpendicular to the orientation direction of the plurality of embossed strips as the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43 The upper limit is preferably 5 μm, more preferably 3 μm, still more preferably 1.5 μm. When the arithmetic mean roughness (Ra) is less than the lower limit, the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased. On the contrary, if the arithmetic mean roughness (Ra) exceeds the above upper limit, there is a risk that it is difficult to control the exit angle of the light.

Further, the arithmetic mean roughness (Ra) based on the direction parallel to the direction in which the plurality of embossed strips are oriented is formed on the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) and The arithmetic mean roughness (Ra) based on the direction in which the orientation directions of the plurality of embossed strips are perpendicular is preferably included in the above range. The light diffusion sheet 41 has an arithmetic mean roughness (Ra) based on a direction parallel to the orientation direction of the plurality of embossed strips and an arithmetic mean roughness based on a direction perpendicular to the orientation direction of the plurality of embossed strips ( Ra is in the above range, so that the amount of light diffused in the width direction of the grating shape 43 is sufficiently increased, and the angle of view in the direction perpendicular to the light emission direction of the light source is easily widened.

As the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), the arithmetic mean roughness (Ra) and the ratio are based on the direction perpendicular to the direction in which the plurality of concave and convex strips are oriented. The direction in which the orientation directions of the embossed strips are parallel is the lower limit of the difference in the arithmetic mean roughness (Ra) of the reference, preferably 0.5 μm, more preferably 0.7 μm, still more preferably 1 μm. When the difference between the arithmetic mean roughness (Ra) is equal to or higher than the lower limit, the amount of light diffused in the width direction of the grating shape 43 is sufficiently increased, and the angle of view in the direction perpendicular to the light emission direction of the light source is easily widened. On the other hand, the upper limit of the difference in the arithmetic mean roughness (Ra) may be, for example, 1.9 μm.

The lower limit of the maximum height (Ry) based on the direction parallel to the direction in which the plurality of embossed strips are oriented is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), preferably 0.1 μm. More preferably, it is 1 μm, and further preferably 1.5 μm. On the other hand, as the upper limit of the maximum height (Ry) based on the direction parallel to the direction in which the plurality of embossed strips are oriented, the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) Preferably, it is 3 μm, more preferably 2.5 μm, further preferably 2 μm. When the maximum height (Ry) is less than the lower limit, there is a risk that the effect of suppressing the occurrence of hot spots is insufficient. On the other hand, when the maximum height (Ry) exceeds the upper limit, the amount of light diffused in a direction parallel to the direction in which the plurality of concave and convex strips are oriented increases with respect to the amount of light diffused in the width direction of the grating shape 43, and the light source cannot be sufficiently ensured. The risk of the angle of view of the light exiting the direction of the vertical direction. In addition, "maximum height (Ry)" means a value when the cutoff λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the maximum height (Ry) based on the direction perpendicular to the direction in which the plurality of embossed strips are oriented, which is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), is preferably 4 μm. It is more preferably 5 μm, further preferably 6 μm. On the other hand, as the upper limit of the maximum height (Ry) based on the direction perpendicular to the direction in which the plurality of embossed strips are oriented, the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) Preferably, it is 12 μm, more preferably 10 μm, further preferably 9 μm. When the maximum height (Ry) is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased. On the contrary, if the maximum height (Ry) exceeds the above upper limit, there is a risk that it is difficult to control the exit angle of the light.

As the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43, the maximum height (Ry) with respect to the direction perpendicular to the orientation direction of the plurality of concave and convex strips The direction in which the orientation direction of the strips is parallel is the lower limit of the difference in the maximum height (Ry) of the reference, preferably 4 μm, more preferably 5 μm, still more preferably 6 μm. When the difference between the maximum heights (Ry) is equal to or greater than the lower limit, the amount of light diffused in the width direction of the grating shape 43 is sufficiently increased, and the angle of view in the direction perpendicular to the light emission direction of the light source is easily widened. On the other hand, the upper limit of the difference in the maximum height (Ry) may be, for example, 11 μm.

The lower limit of the ten-point average roughness (Rz) based on the direction parallel to the direction in which the plurality of embossed strips are oriented, as the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), It is preferably 0.1 μm, more preferably 0.5 μm, still more preferably 1 μm. On the other hand, as the outer surface forming the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), the ten-point average roughness (Rz) based on the direction parallel to the orientation direction of the plurality of concave-convex stripes The upper limit of the) is preferably 2.5 μm, more preferably 2 μm, still more preferably 1.5 μm. When the ten-point average roughness (Rz) is less than the above lower limit, there is a risk that the effect of suppressing the occurrence of hot spots is insufficient. On the other hand, when the ten-point average roughness (Rz) exceeds the above-described upper limit, the amount of light diffused in a direction parallel to the direction in which the plurality of embossed strips are oriented is increased with respect to the amount of light diffused in the width direction of the grating shape 43, and it is difficult to sufficiently The risk of ensuring a viewing angle in a direction perpendicular to the direction in which the light exits the light source. In addition, the "ten-point average roughness (Rz)" is a value when the cutoff λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the ten-point average roughness (Rz) based on the direction perpendicular to the orientation direction of the plurality of embossed strips as the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), It is preferably 4 μm, more preferably 5 μm, further preferably 6 μm. On the other hand, as the outer surface forming the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), the ten-point average roughness (Rz) based on the direction perpendicular to the orientation direction of the plurality of concave-convex stripes The upper limit of the layer is preferably 10 μm, more preferably 8 μm, still more preferably 7 μm. When the ten-point average roughness (Rz) is less than the above lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased. On the contrary, if the ten-point average roughness (Rz) exceeds the above upper limit, there is a risk that it is difficult to control the exit angle of the light.

As the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), the ten-point average roughness (Rz) and the reference with respect to the direction perpendicular to the orientation direction of the plurality of concave and convex strips The direction in which the orientation directions of the plurality of embossed strips are parallel is the lower limit of the difference between the ten-point average roughness (Rz) of the reference, preferably 3 μm, more preferably 4 μm, still more preferably 4.5 μm. When the difference between the ten-point average roughness (Rz) is equal to or higher than the lower limit, the amount of light diffused in the width direction of the grating shape 43 is sufficiently increased, and the angle of view in the direction perpendicular to the light-emitting direction of the light source is easily widened. On the other hand, the upper limit of the difference of the ten-point average roughness (Rz) may be, for example, 9 μm.

The lower limit of the root mean square slope (RΔq) based on the direction parallel to the direction in which the plurality of embossed strips are oriented is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), preferably 0.05, more preferably 0.2, further preferably 0.25, particularly preferably 0.3. On the other hand, as the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43, the root mean square slope (RΔq) based on the direction parallel to the orientation direction of the plurality of concave and convex strips The upper limit is preferably 0.5, more preferably 0.45, further preferably 0.4. When the root mean square slope (RΔq) is less than the above lower limit, there is a risk that the effect of suppressing the occurrence of hot spots is insufficient. On the other hand, when the root mean square slope (RΔq) exceeds the above upper limit, the amount of light diffused in a direction parallel to the direction in which the plurality of uneven strips are oriented increases with respect to the amount of light diffused in the width direction of the grating shape 43, and it is difficult to sufficiently ensure the amount of light. The risk of a viewing angle in a direction perpendicular to the direction in which the light exits the light source. Incidentally, the "root mean square slope (RΔq)" means a value obtained in accordance with JIS-B0601:2001.

The lower limit of the root mean square slope (RΔq) based on the direction perpendicular to the direction in which the plurality of embossed strips are oriented is the outer surface of the grating shape 43 (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed), preferably 0.5, more preferably 0.7, further preferably 1. On the other hand, as the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43, the root mean square slope (RΔq) based on the direction perpendicular to the orientation direction of the plurality of concave and convex strips The upper limit is preferably 2.5, more preferably 2, further preferably 1.8. When the root mean square slope (RΔq) is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 43 cannot be sufficiently increased. On the contrary, if the root mean square slope (RΔq) exceeds the above upper limit, there is a risk that it is difficult to control the exit angle of the light.

As the outer surface (the back surface of the back layer 42 where the plurality of convex portions 13a are not formed) forming the grating shape 43, the root mean square slope (RΔq) with respect to the direction perpendicular to the orientation direction of the plurality of concave and convex strips The lower limit of the root mean square slope (RΔq) of the reference parallel direction of the embossed strips is preferably 0.5, more preferably 0.7, still more preferably 1. When the difference between the root mean square slopes (RΔq) is equal to or greater than the lower limit, the amount of light diffused in the width direction of the grating shape 43 is sufficiently increased, and the angle of view in the direction perpendicular to the light emission direction of the light source is easily widened. On the other hand, the upper limit of the difference in the root mean square slope (RΔq) may be, for example, 2.2.

<Brightness unevenness reduction function>

Next, a function of reducing the luminance unevenness of the light diffusion sheet 41 and the backlight unit including the light diffusion sheet 41 will be described with reference to FIGS. 11 and 12 . First, the amount of light emitted from the plurality of LED light sources 3 of the backlight unit 1 of FIG. 1 and incident on the light guiding film 2 will be described with reference to FIG. The light emitted from the plurality of LED light sources 3 is incident substantially perpendicularly from the end surface (incident end surface) of the light guiding film 2 facing the plurality of LED light sources 3, and propagates toward the end surface opposed to the incident end surface. At this time, the light emitted from the plurality of LED light sources 3 generates a region X in which the amount of light is extremely large, particularly in the vicinity of the light incident portion of the light guiding film 2, due to the strong directivity. On the other hand, since the plurality of LED light sources 3 are arranged at a predetermined interval, a region Y having a very small amount of light is generated between the vicinity of the light incident portion of the light guiding film 2 (between the adjacent regions X).

Next, a function of reducing the luminance unevenness of the light diffusion sheet 41 and the backlight unit including the light diffusion sheet 41 will be described with reference to FIG. The light emitted from the surface side of the light-guide film 2 from the above-described region X is often incident on the back surface of the back layer 42 of the light diffusion sheet 41 in a state in which the light is emitted along the plurality of LED light sources 3. Further, it is considered that the light incident on the back surface of the back layer 42 of the light diffusion sheet 41 is diffused in the width direction of the grating shape 43 by the grating shape 43 having the plurality of irregularities along the light emission direction of the plurality of LED light sources 3. That is, it is considered that the light incident on the grating shape 43 is diffused in the direction of the region Y in plan view as shown in FIG. Therefore, it is considered that the amount of light in the region X in the plan view and the amount of light in the region Y are made uniform, and the luminance unevenness of the backlight unit is lowered.

<Method of Manufacturing Light-Diffusing Sheet>

Next, a method of manufacturing the light diffusion sheet 41 will be described. The method for producing the light diffusion sheet 41 includes a resin film transport step, an ultraviolet curable resin composition supply step, and an ultraviolet irradiation step. Moreover, the manufacturing method of this optical sheet 41 further has the light-diffusion layer lamination process. In the light-diffusing sheet 41, a pressure roller having a reverse shape having a back surface shape of the plurality of convex portions 13a and the grating shape 43 described above is used instead of the one pressure roller 23 described above, and the light diffusion sheet described above can be used. The manufacturing method of 5 is manufactured in the same manner.

<advantage>

Since the light diffusion sheet 41 is provided with a plurality of convex portions 13a in a scattered manner on the back surface, adhesion to other optical members disposed on the back side can be prevented as described above, and damage of the surface of other optical members can be prevented. Further, the light diffusion sheet 41 has a plurality of grating shapes 43 oriented in one direction in a region where the plurality of convex portions 13a are not present in the back surface, so that light can be diffused in the width direction of the grating shape 43 and can be sufficiently Make sure that the angle of view is in the width direction.

The method for producing the light-diffusing sheet can be easily and reliably manufactured, as described above, to prevent adhesion to other optical members disposed on the back side, to prevent damage of the surface of other optical members, and to sufficiently secure the grating shape 43. The light diffusion sheet 41 of the viewing angle in the width direction.

Fourth Embodiment

<Light diffusion sheet>

The light diffusion sheet 46 of Fig. 13 is used for the backlight unit of Fig. 1 instead of the light diffusion sheets 5, 41 of Figs. 2 and 8. The light-diffusing sheet 46 is configured similarly to the light-diffusing sheet 41 of FIG. 8 except that it has a grating shape 47 continuous with the grating shape 43 on the back side of the plurality of convex portions 13a.

<Method of Manufacturing Light-Diffusing Sheet>

The method for producing the light diffusion sheet 46 includes a resin film transport step, an ultraviolet curable resin composition supply step, and an ultraviolet irradiation step. Moreover, the manufacturing method of this optical sheet 46 further has the light-diffusion layer lamination process. The light-diffusing sheet 46 has a surface having a reverse shape including a plurality of convex portions 13a, a grating shape 43 and a back surface shape of the grating shape 47 formed on the back side of the plurality of convex portions 13a in succession with the grating shape 43. In addition to the above-described one pressure roller 23, the roller can be manufactured by the same method as the above-described method of manufacturing the light diffusion sheet 5.

<advantage>

The light diffusion sheet 46 also has a grating shape 47 continuous with the grating shape 43 on the back side of the plurality of convex portions 13a, so that light can be more uniformly diffused from the width direction of the grating shapes 43, 47, and can be more accurately The viewing angle in the width direction of the grating shapes 43, 47 is ensured.

The method for producing the light-diffusing sheet can be easily and reliably manufactured as described above to prevent adhesion to other optical members disposed on the back side, to prevent damage of the surface of other members, and to more accurately ensure the shape of the grating. The light diffusing sheet 46 has a viewing angle of 43 and 47 in the width direction.

Other Implementations

In addition to the above-described embodiments, the optical sheet, the backlight unit, and the optical sheet manufacturing method of the present invention may be implemented in various modifications and improvements. For example, the optical sheet is not limited to the light diffusion sheet, the prism sheet, and the lenticular sheet having the above configuration. For example, the optical sheet may be a light-diffusing sheet in which fine irregularities are formed on the surface of the light-diffusing layer by embossing. Further, when the optical sheet is a light-diffusing sheet, it is not necessarily required to be a lower-light diffusing sheet disposed directly above the light guiding sheet, or may be disposed on the surface side of the prism sheet and suppressed by slightly diffusing light. The upper light diffusing sheet is uneven in brightness due to the shape of the prism array of the prism sheet or the like. In the case where the optical sheet is a light diffusion sheet and the optical sheet has a grating shape, the optical path that is emitted from the light source and incident on the grating shape can be made long, so that it is easy to increase the width of the light in the width direction of the grating shape. Diffusion effect. Therefore, when the optical sheet is a light diffusion sheet, it is easy to improve the brightness unevenness suppression effect of the backlight unit.

The optical sheet may have other layers than the layers described in the above embodiments. For example, the optical sheet may have another resin layer laminated between the base material layer and the optical layer (light diffusion layer, prism array, microlens array) or between the base material layer and the back layer.

In the case where the optical sheet has a grating shape, the optical sheet is also preferably disposed on the back surface of the sheet body to which the two prism sheets are bonded. The sheet to which the two prism sheets are bonded is less likely to form an air layer between the prism sheets, and thus the concealing property is low. On the other hand, in the backlight unit in which the optical sheet is disposed on the back surface of the sheet body, the optical sheet can diffuse light in the width direction of the grating shape, so that the concealing effect can be sufficiently enhanced.

The optical sheet can be formed into a grating shape at a portion other than the back surface. For example, the optical sheet may have a grating shape on the surface of the base material layer or the back surface of the optical layer (light diffusion layer, prism array, microlens array).

The grating shape described above can be arranged, for example, as shown in FIG. In FIG. 14, the grating shape 51 is formed in a certain area from one end of the back layer 52 (the edge on the side opposite to the light source 53 in plan view) to the other end side. Further, a region of the back surface of the back layer 52 where the grating shape 51 is not formed constitutes a flat surface. Incidentally, the specific configuration of the grating shape 51 is the same as that of the light diffusion sheet 41 of Fig. 8 .

The lower limit of the ratio (L3/L2) of the length L3 between the one end and the other end of the region forming the gate shape 51 to the length L2 between the one end of the back layer 52 and the other end is preferably 0.15, more preferably 0.2, further Preferably 0.25. On the other hand, the upper limit of the length ratio (L3/L2) is preferably 0.5, more preferably 0.45, still more preferably 0.4. If the length ratio (L3/L2) is less than the above lower limit, there is a risk that it is difficult to suppress the occurrence of hot spots in an all-round manner. On the other hand, when the length ratio (L3/L2) exceeds the above upper limit, there is a risk that light rays in a region other than the hot spot are easily diffused in the width direction of the grating shape 51.

Further, the grating shape described above can be arranged, for example, as shown in FIG. The grating shape 61 of Fig. 15 gradually decreases from the one end of the back surface of the back layer 62 (the edge on the side facing the light source 63 in plan view) to the other end side uneven strip. With this configuration, the optical sheet can also suppress the occurrence of hot spots. Further, since the optical sheet gradually decreases from the edge facing the light source 63 to the other end side uneven strip, the amount of light diffused in the width direction of the grating shape 61 can be reduced in addition to the hot spot.

The specific shape of the grating shape is not limited to the shape of the above-described embodiment, and may be, for example, a shape having a concave portion having a U-shaped cross section as shown in FIG. 16 and a concave portion having a triangular cross section as shown in FIG. The shape of the recessed portion having a slit shape as shown in FIG. 18 is as shown in FIG. Further, the plurality of embossed strips may be oriented in a direction perpendicular to the direction in which the light source exits.

The backlight unit preferably has a plurality of LED light sources, but may have only one LED light source. Further, the specific type of the optical sheet of the backlight unit is not particularly limited. The backlight unit preferably has a plurality of optical sheets on the surface side of the light guiding sheet, but may have only one optical sheet.

The light guide sheet is not necessarily the light guide film described above, and may be, for example, a light guide plate having a large thickness.

The backlight unit does not need to be an edge type backlight unit, and may be a direct type backlight unit.

In addition, even when the backlight unit is a side light type backlight unit, it is not necessary to be a single-sided side light type backlight unit in which an LED light source is disposed only along one end surface of the light guide sheet, and may be along the light guide sheet. The opposite pair of end faces are provided with a side light type backlight unit of the LED light source, and a full peripheral side light type backlight unit in which the LED light source is disposed along each end surface of the light guide sheet.

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

Example:

Hereinafter, the present invention will be described in further detail by way of examples, but the invention should not be construed as limited.

No.1

The light-diffusing sheet was produced using the manufacturing apparatus 21 of FIG. 5 in which a plurality of concave portions having the same shape were formed at substantially equal density on the circumferential surface of one pressure roller 23. First, a resin film mainly composed of an acrylic urethane resin and forming a base material layer of a light diffusion sheet is transported between a pair of press rolls 22 and 23. In addition, an ultraviolet curable resin composition containing an urethane urethane resin as a main component is supplied between the resin film and the one pressure roller 23, and the resin film and the ultraviolet curable resin composition are extruded by a pair of press rolls 22 and 23. Pressure. Thereby, a plurality of convex portions of a semi-divided spheroidal shape, which is an inverted shape of a plurality of concave portions, are transferred onto the outer surface of the ultraviolet curable resin composition. Further, the ultraviolet curable resin composition to which a plurality of convex portions are transferred is irradiated with ultraviolet rays to cure the ultraviolet curable resin composition. Next, a coating liquid containing a plurality of beads and a binder composition is applied to a surface of the resin film opposite to the side on which the ultraviolet curable resin composition is laminated, and the coating liquid is dried and solidified to form a coating liquid. The light diffusion layer was obtained as a light diffusion sheet of No. 1. The ratio of the average height, the average diameter, and the average height of the plurality of convex portions of No. 1 to the average diameter and the occupied area are as shown in Table 1.

"No. 2 to No. 6"

In the same manufacturing method as in No. 1, the ratio of the average height, the average diameter, the average height to the average diameter, and the occupied area of the plurality of convex portions are the same as those of No. 1 except for those shown in Table 1. Light diffusing sheets of .2 to No. 6.

"No. 7 to No. 13"

In the same manner as in No. 1, the light-diffusing sheet of No. 7 to No. 13 having the same configuration as that of No. 1 except for the area occupied by the plurality of convex portions was produced.

<adhesion>

The light-diffusing sheets of No. 1 to No. 13 are disposed between the light-guiding film and the prism sheet, and a plurality of LED light sources are disposed along one end surface of the light-guiding film to form a side-light type backlight unit. A 20 mm square glass plate was placed on the surface of the prism sheet of the backlight unit, and the surface of the glass plate was pressed at a pressure of 5 kgf. In the pressed state, light is emitted from the plurality of LED light sources to the end faces of the light guiding film, and the surface of the glass plate is released in the state in which the light is emitted. The presence or absence of a bright spot was observed from the surface side of the glass plate in the squeezed state and the state after extrusion, and it evaluated based on the following criteria. The evaluation results are shown in Table 2.

A: No bright spots were observed in any of the extruded state and the extruded state.

B: A bright spot was observed only in the region of 30% or less of the surface of the glass plate in a pressed state.

C: A bright spot was observed only in a region of more than 30% of the surface of the glass plate in a pressed state.

D: A bright spot was observed in a region of more than 30% of the surface of the glass plate in a pressed state, and a bright spot of about several seconds was also observed after the extrusion.

E: A bright spot was observed in a region of more than 30% of the surface of the glass plate in a pressed state, and the same bright spot as the pressed state was continuously observed after the pressing.

<damage>

The light diffusion sheets of No. 1 to No. 13 are disposed between the light guiding film and the prism sheet, and a plurality of LED light sources are arranged along one end surface of the light guiding film. Further, a reflection sheet and an aluminum plate are disposed in this order on the back side of the light guiding film, and a liquid crystal panel is disposed on the surface of the prism sheet. In this state, 160 g of spherical acrylic balls were dropped from a height position of 300 mm from the surface of the liquid crystal panel. Thereafter, light was emitted from the end faces of the light guiding film from the plurality of LED light sources, and the surface of the light guiding film was observed to be damaged in the state in which the light was emitted and the light was emitted, and the evaluation was performed according to the following criteria. The evaluation results are shown in Table 2.

A: No damage was observed at all in any of the state in which the light was emitted and the state after the light was emitted.

B: A slight whitening loss was observed only when the light was emitted.

C: Light white damage was observed only in the light-emitting state, but the contour of the damage appeared to be blurred.

D: A deep white damage was observed only in the light-emitting state.

E: Damage was observed in any of the state in which the light was emitted and the state after the light was emitted.

"Evaluation results"

As shown in Table 1 and Table 2, it is understood that the light diffusion sheet of No. 1 having an average height of a plurality of convex portions of 1.1 μm, an average diameter of 10.2 μm, and an average height to an average diameter of 0.11 is sufficiently prevented. The light guiding film is in close contact and no damage to the light guiding film is caused. On the other hand, as shown in No. 2 and No. 3, as the average height and the average diameter ratio of the plurality of convex portions became small, bright spots were observed by the above-described adhesion test. This bright spot is caused by the fact that the convex portion of the light diffusion sheet is broken or the like, and the adhesion region between the light diffusion sheet and the light guiding film is increased, and the light transmission is high in the adhesion region. Further, as shown in No. 4 to No. 6, it is found that the average height and the average diameter ratio of the plurality of convex portions are larger than those of No. 1, and the light guiding film is easily formed by the plurality of convex portions. Damage to the surface.

Further, as shown in Tables 1 and 2, it is understood that the plurality of convex portions have an average height of 1.1 μm, an average diameter of 10.2 μm, and a ratio of the average height to the average diameter of 0.11, and a plurality of convex portions. The light diffusion sheets of No. 1, No. 9 and No. 10 having an area ratio of 5% to 30% were sufficiently prevented from adhering to the light guiding film, and damage to the light guiding film was not caused. On the other hand, as shown in No. 7 and No. 8, it is understood that the light diffusion sheet and the light guiding film are adhered to each other as the area ratio of the plurality of convex portions is less than 2%. This is considered to be because the light diffusion sheet is likely to abut against the light guiding film at a portion other than the plurality of convex portions. Furthermore, as shown in No. 11 to No. 13, it is understood that the adhesion between the light-diffusing sheet and the light-guiding film deteriorates as the area ratio of the plurality of convex portions exceeds 50%. This is considered to be because if the ratio of the area occupied by the plurality of convex portions is too high, the optical function is likely to be lowered due to the contact portion between the plurality of convex portions and the surface of the light guiding film. Further, as shown in No. 11 to No. 13, it is understood that the damage of the light-diffusing sheet to the surface of the light-guiding film deteriorates as the area ratio of the plurality of convex portions exceeds 50%. This is considered to be because when the contact surface between the surface of the light guiding film and the plurality of convex portions is excessive, damage is likely to occur due to the contact portion between the plurality of convex portions and the surface of the light guiding film.

Industrial availability:

As described above, the optical sheet of the present invention can prevent sticking and prevent damage of other optical members disposed on the back side, and is therefore suitable for various liquid crystal display devices such as high-quality transmissive liquid crystal display devices.

1, 31‧‧‧Backlight unit for liquid crystal display device (backlight unit)
2‧‧‧Light guide film
3, 53, 63‧‧‧ Light source
32‧‧‧Optical sheets for optical display devices (optical sheets)
5, 41, 46‧ ‧ light diffuser
6‧‧ ‧ Prism board
7‧‧‧reflector
8‧‧‧ Uplift
9‧‧‧ recess
11, 16, ‧ ‧ ‧ base material layer
12‧‧‧Light diffusion layer
13a, 18a, 36a‧‧ ‧ convex
14‧‧‧ beads
15‧‧‧Adhesive
17‧‧‧ Prism column
17a‧‧‧ convex strip prism
21‧‧‧ Manufacturing equipment
22, 23‧‧‧ pressure roller
33‧‧‧Microlens
35‧‧‧Microlens array
35a‧‧‧microlens
13, 18, 36, 42, 52, 62‧‧ ‧ back layer
43, 47, 51, 61‧‧‧ raster shapes
101‧‧‧Backlight unit
102‧‧‧Light source
103‧‧‧Light guide
104‧‧‧ optical film
105‧‧‧Light diffuser
106‧‧ ‧ Prism board
111‧‧‧ base material layer
112‧‧‧Light diffusion layer
113‧‧‧Anti-adhesion layer
114‧‧‧ beads
115‧‧‧Adhesive
A‧‧‧ resin film

FIG. 1 is a schematic end view showing a backlight unit for a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a schematic partial enlarged view showing a light diffusion sheet of the backlight unit of FIG. 1. FIG. Fig. 3 is a schematic enlarged view showing a convex portion of the light diffusion sheet of Fig. 2, wherein (a) is a side view and (b) is a rear view. 4 is a schematic partial enlarged view showing a prism sheet of the backlight unit of FIG. 1. Fig. 5 is a schematic view showing a manufacturing apparatus of the light diffusion sheet of Fig. 2; FIG. 6 is a schematic end view showing a backlight unit according to an embodiment different from the backlight unit of FIG. 1. FIG. Fig. 7 is a schematic partial enlarged view showing a lenticular sheet of the backlight unit of Fig. 6. Fig. 8 is a schematic end view showing a light diffusion sheet according to an embodiment different from the light diffusion sheet of Fig. 2 . Figure 9 is a schematic rear view of the light diffusing sheet of Figure 8. Fig. 10 is a partial end elevational view, taken along line A-A of the light diffusing sheet of Fig. 8. Fig. 11 is a schematic plan view showing a hot spot of a backlight unit for a liquid crystal display device. Fig. 12 is a schematic view for explaining a function of reducing the luminance unevenness of the light diffusion sheet of Fig. 8; FIG. 13 is a schematic rear view showing a light diffusion sheet according to an embodiment different from the light diffusion sheet of FIGS. 2 and 8. Fig. 14 is a schematic rear view showing an optical sheet according to another embodiment of the present invention. Fig. 15 is a schematic rear view showing an optical sheet different from the optical sheet of Fig. 14. Fig. 16 is a schematic end view showing a grating shape according to another embodiment of the present invention. Fig. 17 is a schematic end view showing a grating shape according to a form different from the grating shape of Fig. 16; Fig. 18 is a schematic end view showing a grating shape according to a form different from the grating shape of Figs. 16 and 17; 19 is a schematic perspective view showing a conventional sidelight type backlight unit. Fig. 20 is a schematic end view showing a conventional light diffusion sheet.

1‧‧‧Backlight unit for liquid crystal display device (backlight unit)

2‧‧‧Light guide film

3‧‧‧Light source

5‧‧‧Light diffuser

6‧‧ ‧ Prism board

7‧‧‧reflector

8‧‧‧ Uplift

9‧‧‧ recess

11, 16‧‧‧ base material layer

12‧‧‧Light diffusion layer

13a, 18a‧‧‧ convex

14‧‧‧ beads

15‧‧‧Adhesive

17‧‧‧ Prism column

17a‧‧‧ convex strip prism

13, 18‧‧‧ back layer

Claims (9)

An optical sheet for a liquid crystal display device, which is an optical sheet for a liquid crystal display device having a plurality of convex portions on a back surface thereof, wherein the convex portions are flat hemispheres or front end portions Round cones in a round shape. The optical sheet for a liquid crystal display device according to claim 1, wherein the convex portions are semi-divided ellipsoids. The optical sheet for a liquid crystal display device according to claim 1, wherein an area ratio of the convex portions is 2% or more and 80% or less. The optical sheet for a liquid crystal display device according to claim 1, wherein the convex portions have an average diameter of 5 μm or more and 60 μm or less and an average height of 0.5 μm or more. The optical sheet for a liquid crystal display device according to claim 1, further comprising a plurality of stripe-shaped grating shapes oriented in one direction in a region where the plurality of convex portions are not present in the back surface. The optical sheet for a liquid crystal display device according to claim 5, wherein the grating shape exhibits a rubbing or hairline shape in one direction. The optical sheet for a liquid crystal display device according to claim 5, wherein the back surface side of the convex portions further has another grating shape continuous with the grating shape. A backlight unit for a liquid crystal display device, comprising: a light guide sheet that guides light incident from an end surface toward a surface side; a single or a plurality of LED light sources disposed along the end surface of the light guide sheet; and the light guide A single or a plurality of optical sheets on which the surface side of the sheet overlaps, wherein the single optical sheet or at least one of the optical sheets uses the optical sheet for a liquid crystal display device of claim 1. A method for producing an optical sheet for a liquid crystal display device, which is characterized in that the optical sheet for a liquid crystal display device is provided with a plurality of convex portions on a back surface, and the convex portions are flat hemispheres or The front end portion is formed into a circular flat cone, and the manufacturing method includes: using a roll having a reverse shape having a back surface shape of the convex portions in a scatter manner, and conveying a resin in a strip shape to the surface of the roller a step of a film; a step of supplying an ultraviolet curable resin composition between the resin film and the roll; and a step of irradiating the ultraviolet curable resin composition with ultraviolet rays.