JP2017207736A - 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

PROBLEM TO BE SOLVED: To provide an optical sheet capable of preventing sticking as well as preventing scratching on another optical member disposed on a back face side of the sheet.SOLUTION: An optical sheet 1 for a liquid crystal display device includes a plurality of protruding portions 13a, 18a scattered on a back face of the sheet, in which the protruding portions 13a, 18a each have a flattened semi-spherical shape or a flattened conical shape with a rounded apex. Preferably, the protruding portions 13a, 18a are half-split spheroids. An occupancy area ratio of the plurality of protruding portions 13a, 18a is preferably 2% or more and 80% or less. An average diameter of the protruding portions 13a, 18a is preferably 5 μm or more and 60 μm or less, and an average height is preferably 0.5 μm or more. A diffraction grating pattern with multiple rows oriented in one direction is preferably disposed on the back face in a region where the plurality of protruding portions 13a, 18a are absent. The diffraction grating pattern is preferably a pattern resembling scratch marks or hairlines in the one direction. The optical sheet preferably has a diffraction grating pattern also on a back face side of the plurality of protruding portions 13a, 18b, continuing to the above diffraction grating pattern.SELECTED DRAWING: Figure 1

Description

  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 illuminates a liquid crystal layer from the back is widespread, and an edge light type (side light type), a direct type, etc. are provided on the back side of the liquid crystal layer. Yes. As shown in FIG. 19, the edge light type backlight unit 101 generally includes a light source 102, a rectangular plate-shaped light guide sheet 103 that is disposed so that an end thereof is along the light source 102, and And a plurality of optical sheets 104 disposed on the surface side of the light guide sheet 103. The optical sheet 104 has optical functions such as diffusion and refraction with respect to transmitted light. For example, the optical sheet 104 is disposed on the surface side of the light guide sheet 103 and mainly has a light diffusing sheet 105 having a light diffusing function. A prism sheet 106 that is disposed on the surface side of the diffusion sheet 105 and has a refractive function toward the normal direction is used.

  The function of the backlight unit 101 will be described. First, a light beam incident on the light guide sheet 103 from the light source 102 is reflected by the reflective dots or the reflection sheet (not shown) on the back surface of the light guide sheet 103 and each side surface to guide the light. The light is emitted from the surface of the sheet 103. Light rays emitted from the surface of the light guide sheet 103 enter the light diffusion sheet 105, are diffused, and are emitted from the surface. Light rays emitted from the surface of the light diffusion sheet 105 enter the prism sheet 106, are refracted and emitted toward the normal direction side by a plurality of convex prism portions formed on the surface, and further, the surface side is illustrated. Not illuminate the entire liquid crystal layer. Although not shown, the optical sheet 104 is disposed on the surface side of the prism sheet 106 and is caused by the shape of a plurality of convex prism portions of the prism sheet 106 by slightly diffusing light rays. An upward light diffusing sheet that suppresses uneven brightness, a microlens sheet having a function of refraction toward the normal direction side, and a wide-angle light diffusing function are also used.

  As described above, the optical sheet 104 has optical functions such as diffusion and refraction with respect to transmitted light, and is used for the purpose of uniforming the luminance of the backlight unit, increasing the luminance in the front direction, and the like. Taking the light diffusion sheet 105 as an example, the optical sheet 104 is laminated on a base layer 111 (optical layer) containing synthetic resin as a main component and on the surface side of the base layer 111 as shown in FIG. And a sticking prevention layer 113 laminated on the back surface side of the base material layer 111. This anti-sticking layer 113 prevents the inconvenience that moire occurs when the back surface of the light diffusion sheet 105 is sticked (adhered) to the surface of the light guide sheet 103. This anti-sticking layer 113 generally has a spherical bead 114 and a binder 115 that covers the bead 114, and sticking is prevented by a convex portion protruding to the back surface due to the bead 114 (special feature). (See JP 2010-26231).

  However, as described above, the conventional anti-sticking layer having the beads 114 and the binder 115 is formed with protrusions due to the protrusions of the beads 114, and thus the protrusions tend to have a shape approximate to the shape of the beads 114. Therefore, the average diameter and average height of the convex portions are likely to be approximately the same, and R at the tip portion (lower end portion) of the convex portion is likely to be small. For this reason, according to the conventional anti-sticking layer 113, there is a possibility that the surface of the light guide sheet 103 in contact with the convex portion may be damaged. And when a damage | wound arises on the surface of the light guide sheet 103 in this way, there exists a possibility that a brightness nonuniformity may generate | occur | produce due to the light ray which injected into this damage | wound.

JP 2010-26231 A

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

  An optical sheet for a liquid crystal display device according to the present invention made to solve the above problems is an optical sheet for a liquid crystal display device having a plurality of convex portions on the back surface in a scattered manner, and the convex portions are flat hemispheres. It is a flat cone with a rounded body or tip.

  Since the optical sheet for a liquid crystal display device includes a plurality of protrusions on the back surface, the optical sheet for the liquid crystal display device and another optical member disposed on the back surface side of the optical sheet for the liquid crystal display device. Are partially abutted by the plurality of convex portions. Therefore, the said optical sheet for liquid crystal display devices can prevent sticking with the other optical member arrange | positioned by the back surface side. Further, in the optical sheet for a liquid crystal display device, the convex portion is a flat hemisphere or a flat cone with rounded tip portions, so that the curved surfaces of the tip portions (lower end portions) of the plurality of convex portions are formed. As a result, the surface of other optical members disposed on the back surface can be prevented from being damaged.

  The convex part may be a half spheroid. As described above, since the convex portion is a half spheroid, it is possible to more reliably prevent the surface of another optical member disposed on the back side of the optical sheet for the liquid crystal display device from being damaged. it can.

  The occupation area ratio of the plurality of convex portions is preferably 2% or more and 80% or less. In this way, when the occupation area ratio of the plurality of convex portions is within the above range, it is possible to sufficiently prevent sticking with another optical member disposed on the back surface side, and to the surface of the other optical member. Can be more reliably prevented.

  The average diameter of the convex portions is preferably 5 μm or more and 60 μm or less, and the average height is preferably 0.5 μm or more. Thus, when the average diameter and average height of the convex portions are within the above range, sticking with other optical members disposed on the back side of the optical sheet for the liquid crystal display device can be prevented more reliably. can do.

  A region of the back surface where the plurality of convex portions are not present may be provided with a multi-striped diffraction grating shape oriented in one direction. In this way, by providing a multi-row-shaped diffraction grating shape oriented in one direction in a region of the back surface where the plurality of convex portions do not exist, light can be diffused in the width direction of the diffraction grating shape. And a sufficient viewing angle in the width direction can be secured.

  The diffraction grating shape may exhibit a scratch mark or a hairline shape in one direction. Thus, when the diffraction grating shape exhibits a scratch mark or a hairline shape in one direction, light can be easily and reliably diffused in the width direction of the diffraction grating shape.

  The back surfaces of the plurality of convex portions may have a diffraction grating shape that is continuous with the diffraction grating shape. Thus, by having the diffraction grating shape continuous with the diffraction grating shape also on the back surface side of the plurality of convex portions, light can be diffused uniformly in the width direction of the diffraction grating shape. The viewing angle in the width direction can be ensured more accurately.

  A backlight unit for a liquid crystal display device according to the present invention, which has been made to solve the above problems, is disposed along a light guide sheet that guides light incident from an end face to the surface side, and the end face of the light guide sheet. A backlight unit for a liquid crystal display device comprising one or more LED light sources and one or more optical sheets superimposed on the surface side of the light guide sheet, wherein at least one of the one or more optical sheets The optical sheet is used.

  Since the backlight unit for a liquid crystal display device includes the optical sheet, it can prevent sticking of the optical sheet and other optical members disposed on the back side of the optical sheet as described above. It is possible to prevent the surface of another optical member from being damaged.

  Furthermore, the method for producing an optical sheet for a liquid crystal display device according to the present invention, which has been made to solve the above-mentioned problems, is a method for producing an optical sheet for a liquid crystal display device having a plurality of convex portions scattered on the back surface. , Using a roll having a reverse surface shape with a plurality of convex portions scattered on the surface, and sending a belt-shaped resin film to the roll surface, and an ultraviolet curable resin between the resin film and the roll A step of supplying a composition; and a step of irradiating the ultraviolet curable resin composition with ultraviolet rays, wherein the convex portion is a flat hemisphere or a flat cone having a rounded tip. To do.

  The method for producing the optical sheet for a liquid crystal display device uses a roll having a reverse shape of a plurality of convex portions formed on a surface as a flat hemispherical shape or a flat cone shape with rounded tips. On the other hand, a plurality of flat hemispherical shapes or flat cone-shaped convex portions with rounded tips can be formed on the side surface. Therefore, the manufacturing method of the optical sheet for a liquid crystal display device can prevent sticking by partially contacting the other optical member by the plurality of convex portions, and can damage the other optical member contacting the plurality of convex portions. An optical sheet capable of preventing sticking can be manufactured.

  In the present invention, “front side” means the viewer side in the liquid crystal display device, and “back side” means the opposite. The “hemisphere” is a concept including a “spherical notch” which means a solid shape obtained by cutting a sphere into one plane, and specifically, a circular or elliptical bottom surface and a spherical surface continuous from the periphery of the bottom surface. The shape which has. The “cone” is a concept including a cone and a pyramid. The “flat spheroid spheroid shape” refers to a shape obtained by halving a virtual spheroid obtained by rotating an ellipse around a minor axis by a plane perpendicular to the minor axis including the major axis. “Occupied area ratio of the plurality of convex portions” refers to a ratio of the occupied area of the plurality of convex portions to the plane area of the surface on which the plurality of convex portions are formed. The “diameter” of each convex portion means the diameter at the base, and the “average diameter of the convex portion” means that ten convex portions are arbitrarily extracted, and the maximum diameter and the minimum diameter at the base of each convex portion. The average value of the intermediate values. The “height” of each convex portion refers to the length from the base to the protruding end of each convex portion, and the “average height of the convex portion” arbitrarily extracts ten convex portions. The average value of the length from the base of the part to the protruding end. The “diffraction grating shape” is not limited to those in which optical characteristics are strictly adjusted, and refers to a shape that widely diffracts incident light. “Abrasion trace shape or hairline shape in one direction” refers to a shape in which a number of elongated scratches are formed by being oriented in one direction.

  As described above, the optical sheet for a liquid crystal display device of the present invention can prevent sticking and can surely prevent damage to other optical members disposed on the back surface side. The backlight unit for a liquid crystal display device of the present invention can prevent sticking and reliably prevent the optical member from being damaged. In addition, the method for producing an optical sheet for a liquid crystal display device according to the present invention produces an optical sheet that can prevent sticking and reliably prevent other optical members disposed on the back surface side from being damaged. Can do.

1 is a schematic end view showing a backlight unit for a liquid crystal display device according to an embodiment of the present invention. It is a typical partial enlarged view which shows the light-diffusion sheet | seat of the backlight unit of FIG. It is a typical enlarged view which shows the convex part of the light-diffusion sheet | seat of FIG. 2, Comprising: (a) is a side view, (b) is a back view. It is a typical partial enlarged view which shows the prism sheet of the backlight unit of FIG. It is a schematic diagram which shows the manufacturing apparatus of the light-diffusion sheet | seat of FIG. It is a typical end view which shows the backlight unit which concerns on embodiment different from the backlight unit of FIG. It is a typical partial enlarged view which shows the micro lens sheet | seat of the backlight unit of FIG. It is a typical end view which shows the light-diffusion sheet which concerns on embodiment different from the light-diffusion sheet | seat of FIG. It is a typical back view of the light diffusion sheet of FIG. It is an AA partial fragmentary end view of the light diffusion sheet of FIG. It is a typical top view which shows the hot spot in the backlight unit for liquid crystal display devices. It is a schematic diagram for demonstrating the brightness nonuniformity reduction function by the light-diffusion sheet | seat of FIG. It is a typical back view which shows the light-diffusion sheet which concerns on embodiment different from the light-diffusion sheet of FIG.2 and FIG.8. It is a typical back view which shows the optical sheet which concerns on other embodiment of this invention. It is a typical back view which shows the optical sheet different from the optical sheet of FIG. FIG. 6 is a schematic end view showing a diffraction grating shape according to another embodiment of the present invention. FIG. 17 is a schematic end view showing a diffraction grating shape according to a different form from the diffraction grating shape of FIG. 16. FIG. 18 is a schematic end view showing a diffraction grating shape according to a different form from the diffraction grating shape of FIGS. 16 and 17. It is a typical perspective view which shows the conventional edge light type backlight unit. It is a typical end view which shows the conventional light-diffusion sheet.

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

[First embodiment]
[Backlight unit]
A backlight unit for a liquid crystal display device (hereinafter, also simply referred to as “backlight unit”) 1 in FIG. 1 is an edge light type backlight unit, and is a backlight unit for a liquid crystal display device using a plurality of LED light sources. is there. The backlight unit 1 includes a light guide film 2 that is a light guide sheet that guides light incident from an end surface to the front surface side, a plurality of LED light sources 3 disposed along the end surface of the light guide film 2, a light A plurality of optical sheets for liquid crystal display devices (hereinafter also simply referred to as “optical sheets”) superimposed on the surface side of the guide film 2 are provided. The backlight unit 1 includes, as a plurality of optical sheets, a light diffusing sheet 5 that is directly superimposed on the surface of the light guide film 2 (without interposing other sheets), and a direct (other sheet) on the surface of the light diffusing sheet 5. And the prism sheet 6 to be stacked. The backlight unit 1 further includes a reflective sheet 7 disposed on the back side of the light guide film 2. The light diffusion sheet 5 condenses (condenses and diffuses) the light incident from the back side while diffusing the light in the normal direction. The prism sheet 6 refracts light incident from the back side toward the normal direction. The reflection sheet 7 reflects the light beam emitted from the back surface of the light guide film 2 and makes it incident on the light guide film 2 again. In FIG. 1, the reflection sheet 7, the light guide film 2, the light diffusion sheet 5, and the prism sheet 6 are illustrated separately from each other, but actually, the surface of the reflection sheet 7, the back surface of the light guide film 2, the light The front surface of the guide film 2 and the back surface of the light diffusion sheet 5, the front 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 includes a base material layer 11, a light diffusion layer 12 laminated on the front surface side of the base material layer 11, and a back layer 13 laminated on the back surface side of the base material layer 11. With. In addition, the light diffusion sheet 5 includes a plurality of convex portions 13 a that are sticking prevention portions on the back surface (the back surface of the back layer 13). The plurality of convex portions 13a are integrally formed with the back layer 13 (that is, the plurality of convex portions 13a and the back layer 13 are integrally formed). The light diffusion sheet 5 is formed in a planar view shape. The light diffusion sheet 5 includes a base material layer 11, a light diffusion layer 12, a back layer 13, and a plurality of convex portions 13a (that is, the light diffusion sheet 5 includes the base material layer 11, the light diffusion layer 12, and the back surface). No other layers other than the layer 13 and the plurality of convex portions 13a).

(Base material layer)
Since the base material layer 11 needs to transmit light, it is formed transparent. The base material layer 11 has a synthetic resin as a main component. The main component of the base material layer 11 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, acrylic urethane resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending performance is particularly preferable. The “main component” refers to a component having the highest content, for example, a component having a content of 50% by mass or more.

  As a minimum of average thickness of base material layer 11, 10 micrometers is preferred, 23 micrometers is more preferred, and 38 micrometers is still more preferred. On the other hand, as an upper limit of the average thickness of the base material layer 11, 500 micrometers is preferable, 250 micrometers is more preferable, and 188 micrometers is more preferable. If the average thickness of the base material layer 11 is less than the lower limit, curling may occur when the light diffusion layer 12 is formed by coating. Moreover, when the average thickness of the base material layer 11 is less than the said minimum, there exists a possibility that it may become easy to produce bending. On the contrary, when the average thickness of the base material layer 11 exceeds the upper limit, the luminance of the backlight unit 1 may be lowered and the backlight unit 1 may not be required to be thinned. Note that “average thickness” refers to an average value of thicknesses at 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 thereof. The beads 14 are surrounded by a binder 15. The light diffusing layer 12 contains a plurality of beads 14 so as to diffuse light transmitted from the back surface side to the front surface side substantially uniformly. Further, the light diffusion layer 12 has fine irregularities formed substantially uniformly on the surface by a plurality of beads 14, and the concave and convex portions of the fine irregularities are formed in a lens shape. The light diffusing layer 12 exhibits an excellent light diffusing function due to the lens action of such fine unevenness, and the refractive function that refracts the transmitted light to the normal direction side due to this light diffusing function and the transmitted light to the normal line. It has a light condensing function that condenses macroscopically in the direction.

  The beads 14 are resin particles having a property of diffusing light. Examples of the main component of the beads 14 include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyamide, polyacrylonitrile, and the like. Among them, an acrylic resin having high transparency is preferable, and polymethyl methacrylate (PMMA) is particularly preferable.

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

  The lower limit of the average particle diameter of the beads 14 is preferably 1 μm, more preferably 2 μm, and even 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, and even more preferably 8 μm. If the average particle diameter of the beads 14 is less than the above lower limit, the unevenness of the surface of the light diffusion layer 12 becomes small and the light diffusibility necessary for the light diffusion sheet 5 may not be satisfied. Conversely, if the average particle diameter of the beads 14 exceeds the above upper limit, the thickness of the light diffusion sheet 5 may increase, and uniform diffusion may be difficult. The “average particle diameter of beads” refers to the average particle diameter of a plurality of beads calculated from a volume-based particle size distribution measured by a laser diffraction method.

  The lower limit of the blending amount of the beads 14 (the blending amount in terms of solid content with respect to 100 parts by mass of the polymer in the polymer composition that is the forming material of the binder 15) is preferably 10 parts by mass, more preferably 20 parts by mass, 50 Part by mass is more preferable. On the other hand, the upper limit of the amount of the beads 14 is preferably 500 parts by mass, more preferably 300 parts by mass, and even more preferably 200 parts by mass. If the blending amount of the beads 14 is less than the lower limit, the light diffusibility may be insufficient. On the contrary, if the blending amount of the beads 14 exceeds the upper limit, the beads 14 may not be fixed accurately by the binder 15.

  The binder 15 is formed by curing (crosslinking or the like) a polymer composition containing a base polymer. The beads 14 are arranged and fixed on the entire surface of the base material layer 11 at a substantially equal density by the binder 15. The polymer composition for forming the binder 15 includes, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, an antistatic agent, an ultraviolet absorber, an antioxidant, and a viscosity modifier. An agent, a lubricant, a light stabilizer and the like may be appropriately blended.

(Back layer)
The back layer 13 is formed to be transparent because it needs to transmit light. The back layer 13 is formed with a synthetic resin as a main component. 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 epoxy resins, silicone resins, phenol resins, urea resins, unsaturated polyester resins, melamine resins, alkyd resins, acrylic resins, amide functional copolymers, urethane resins, and the like.

  Examples of the active energy ray curable resin include an ultraviolet curable resin that is crosslinked and cured by irradiating ultraviolet rays, and an electron beam curable resin that is crosslinked and cured by irradiating an electron beam. In addition, it can be appropriately selected from polymerizable oligomers. Especially, as said active energy ray hardening-type resin, acrylic type, urethane type, or an acrylic urethane type ultraviolet curable resin is preferable.

  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, the plurality of convex portions 13a and the back layer 13 are integrally formed).

  Each convex portion 13a is a flat hemisphere or a flat cone with a rounded tip, and in this embodiment, as shown in FIGS. 3 (a) and 3 (b), a flat half-spheroidal ellipse. Is the body. Since each convex part 13a is a flat half spheroid, it can prevent more reliably the surface of the other optical member arrange | positioned by the back surface side. The plurality of convex portions 13 a are provided on the back surface of the back layer 13 at random (without regularity). The light diffusing sheet 5 can prevent moiré from being generated based on the plurality of convex portions 13a by randomly projecting the plurality of convex portions 13a. The “half-spheroidal shape” is not limited to a strict half-spheroid shape, but includes a shape in which the base is a perfect circle and the outer surface is formed in a dome shape by a curved surface. .

  As a minimum of the average curvature radius of the tip part of convex part 13a, 20 micrometers is preferred and 50 micrometers is more preferred. On the other hand, the upper limit of the average radius of curvature of the tip of the convex portion 13a is preferably 200 μm, and more preferably 100 μm. If the average radius of curvature is less than the lower limit, the surface of the light guide film 2 disposed on the back side of the light diffusion sheet 5 may be damaged. On the contrary, if the average radius of curvature exceeds the upper limit, the contact area between the convex portion 13a and the surface of the light guide film 2 is increased, and brightness unevenness may occur due to light rays incident on the contact portion. There is. The “average radius of curvature of the tip of the convex portion” refers to the average value of the radius of curvature in the portion farthest from the back surface average interface of the back layer of the 10 convex portions that are arbitrarily extracted.

The lower limit of the average diameter _{D 1} of the convex portion 13a, 5 [mu] m are preferred, more preferably 7 [mu] m, more preferably 10 [mu] m. In contrast, the upper limit of the mean diameter _{D 1} of the protrusion 13a, 60 [mu] m is preferred, 50 [mu] m is more preferable, more preferably 40 [mu] m, 20 [mu] m is particularly preferred. If the average diameter D ₁ of the convex portion 13a is less than the above lower limit, in order to secure a sufficient height H of the convex portion 13a has a radius of curvature of the tip portion of the projection 13a is too small the light diffusing sheet 5 There is a possibility that the surface of the light guide film 2 disposed on the back side may be damaged. Conversely, the average diameter D ₁ of the convex portion 13a is more than the above upper limit, the convex portion 13a in order to keep the preferable range of the radius of curvature of the tip of the height is too large backlight unit of the projection 13a There is a risk that it may be against the request for thinning.

  As a minimum of average height H of convex part 13a, 0.5 micrometer is preferred, 0.8 micrometer is more preferred, and 1.0 micrometer is still more preferred. On the other hand, the upper limit of the average height H of the convex portions 13a is preferably 6 μm, more preferably 5 μm, and even more preferably 4 μm. If the average height H of the convex portion 13a is less than the lower limit, the light diffusion sheet 5 and the light guide film 2 are likely to come into contact with each other other than the convex portion 13a. There is a risk of uneven brightness. On the contrary, if the average height H of the convex portion 13a exceeds the above upper limit, the optical unit may be against the request for thinning of the backlight unit, and another optical member (light guide film 2) disposed on the back side. There is a risk of scratching the surface.

  It is preferable that the plurality of convex portions 13a have a uniform height H. 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, and even more preferably 0.05. When the variation coefficient 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 non-uniform, and the load is biased to the convex portions 13a having a large height. The surface of the guide film 2 may be damaged. On the other hand, the lower limit of the variation coefficient of the height H of the plurality of convex portions 13a is not particularly limited, and may be 0, for example. 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 20 convex portions arbitrarily extracted by the average height.

The lower limit of the ratio of the mean height H with respect to the average diameter _{D 1} of the plurality of projections 13a (H / _{D 1),} preferably from 0.02, more preferably 0.05, more preferably 0.10. On the other hand, the upper limit of the ratio (H / D ₁ ) is preferably 0.2, more preferably 0.15, and even more preferably 0.12. When the ratio (H / D ₁ ) is less than the lower limit, the contact area between the plurality of convex portions 13a and the surface of the light guide film 2 is increased, and luminance is caused by light rays incident on the contact portion. There may be unevenness. On the other hand, if the ratio (H / D ₁ ) exceeds the upper limit, the tips of the plurality of convex portions 13a are too sharp and the surface of the light guide film 2 may be damaged.

  As a minimum of average pitch of convex part 13a, 200 micrometers is preferred, 300 micrometers is more preferred, and 400 micrometers is still more preferred. On the other hand, the upper limit of the average pitch of the convex portions 13a is preferably 1000 μm, more preferably 900 μm, and still more preferably 800 μm. If the average pitch of the convex portions 13a is less than the above lower limit, the number of the convex portions 13a increases so that the surface of the light guide film 2 may be damaged. Further, if the average pitch of the convex portions 13a is less than the lower limit, the number of the convex portions 13a increases too much, and when the diffraction grating shape is formed on the formation surface of the convex portions 13a as in the embodiment described later, Diffraction grating performance may be reduced. Conversely, if the average pitch of the convex portions 13a exceeds the above upper limit, the number of the convex portions 13a is insufficient, and sticking may not be sufficiently prevented. The “average pitch” of the convex portions refers to an average value of pitches of the ten convex portions arbitrarily extracted, and the extracted convex portions and other convex portions closest to these convex portions.

  The lower limit of the occupied area ratio of the plurality of convex portions 13a is preferably 2%, more preferably 3%, and even more preferably 4%. On the other hand, the upper limit of the occupied area ratio of the plurality of convex portions 13a is preferably 80%, more preferably 70%, still more preferably 60%, and particularly preferably 40%. If the occupation area ratio of the plurality of convex portions 13a is less than the lower limit, sticking may not be sufficiently prevented. Conversely, if the occupation area ratio of the plurality of convex portions 13a exceeds the above upper limit, the surface of the light guide film 2 may be damaged.

The lower limit of the ratio of the mean diameter D ₁ of the protrusion 13a with respect to the average particle diameter of the beads 14, 3 are preferred, 4, and still more preferably 5. On the other hand, the upper limit of the ratio is preferably 9, more preferably 8, and even more preferably 7. If the ratio is less than the lower limit, the amount of light incident on the convex portion 13a may be insufficient, making it difficult to sufficiently capture light by the convex portion 13a, and the back surface of the back layer 13 of the light diffusing sheet 5. There is a possibility that the amount of specularly reflected light may increase. On the other hand, if the ratio exceeds the upper limit, the curved shape of the convex portion 13a becomes too smooth, and it may be difficult to take in light rays by the convex portion 13a.

  The plurality of convex portions 13a are formed with synthetic resin as a main component. Moreover, the some convex part 13 does not contain the bead inside. In the light diffusing sheet 5, since the plurality of convex portions 13 a do not contain beads, the surface of the light guide film 2 disposed on the back side of the light diffusing sheet 5 is damaged due to the dropping of the beads. Can be prevented.

<Prism sheet>
As shown in FIG. 4, the prism sheet 6 includes a base material layer 16, a prism row 17 laminated on the front surface side of the base material layer 16, and a back layer 18 laminated on the back surface side of the base material layer 16. Prepare. The prism row 17 is configured by arranging a plurality of convex prism portions 17a in parallel. Further, the prism sheet 6 includes a plurality of convex portions 18 a that are sticking preventing portions on the back surface of the back layer 18 in a scattered manner. The prism sheet 6 includes a base material layer 16, a prism row 17, a back layer 18, and a plurality of convex portions 18a (that is, the prism sheet 6 includes the base material layer 16, the prism row 17, the back layer 18, and a plurality of protrusions 18a). No other layers other than the convex portion 18a). The prism sheet 6 is formed in a planar view shape.

  The base material layer 16 and the prism row 17 are formed to be transparent because it is necessary to transmit light. The base material layer 16 and the prism row 17 are mainly composed of synthetic resin. As a main component of the base material layer 16 and the prism row 17, the same synthetic resin as the main component of the base material layer 11 of the light diffusion sheet 5 can be cited. Further, as the main component of the base material layer 16 and the prism row 17, it is also possible to use the same thermosetting resin, active energy ray curable resin, or the like as the plurality of convex portions 13a of the light diffusion sheet 5. In the present embodiment, the direction of the prism row 17 (the ridge line direction of the plurality of convex prism portions 17a) is perpendicular to the light emission direction of the light source 3.

  As a minimum of the height from the back of substrate layer 16 of prism sheet 6 to the peak of convex prism part 17a, 50 micrometers is preferred and 100 micrometers is more preferred. On the other hand, the upper limit of the height is preferably 200 μm, and more preferably 180 μm. As a minimum of the average pitch of a plurality of convex prism parts 17a in prism sheet 6, 10 micrometers is preferred and 20 micrometers is more preferred. On the other hand, the upper limit of the average pitch of the plurality of convex prism portions 17a is preferably 100 μm, and more preferably 60 μm. The apex angle of the convex prism portion 17a is preferably 85 ° or more and 95 ° or less. Moreover, as a base angle of the convex prism part 17a, 42 degrees or more and 48 degrees or less are preferable. 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. The “average pitch of the convex prism portion” refers to an average pitch of ten consecutive convex prism portions that are arbitrarily extracted. “Refractive index” refers to the refractive index of light with a wavelength of 589.3 nm (sodium D-line), measured at a temperature of 23 ° C. using a flat test piece having a side of 70 mm and a thickness of 2 mm. Means the average value of the number of tests performed three times. The “refractive index of the prism sheet” refers to the refractive index of the convex prism portion.

  Since the back layer 18 needs to transmit light, it is formed transparent. The back layer 18 is formed with a synthetic resin as a main component. The main component of the back layer 18 can be the same as the main component of the back layer 13 of the light diffusion sheet 5 described above.

  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, the plurality of convex portions 18a and the back layer 18 are integrally formed).

  The plurality of convex portions 18 a constitute the outermost back surface of the prism sheet 6. Each convex part 18a is a flat hemisphere or a flat cone with a rounded tip, and in particular in the present embodiment is a flat halved spheroid. The plurality of convex portions 18 a are provided on the back surface of the back layer 18 at random (without regularity). The specific shape of the plurality of convex portions 18 a is the same as that of the plurality of convex portions 13 a of the light diffusion sheet 5.

  As a minimum of ratio of average diameter of convex part 18a to average pitch of convex prism part 17a, 0.1 is preferred, 0.3 is more preferred, and 0.5 is still more preferred. On the other hand, the upper limit of the ratio is preferably 6.0, more preferably 3.0, and even more preferably 1.0. If the ratio is less than the lower limit, the amount of light incident on the convex portion 18a may be insufficient, making it difficult to sufficiently capture light by the convex portion 18a, and the mirror surface on the back surface of the back layer 18 of the prism sheet 6 There is a possibility that the amount of reflected light becomes large. On the other hand, if the ratio exceeds the upper limit, the curved shape of the convex portion 18a becomes too smooth, and it may be difficult to take in light rays by the convex portion 18a.

<Light guide film>
The light guide film 2 emits light incident from the end face from the surface substantially uniformly. The light guide film 2 is formed in a substantially square shape in plan view, and is formed in a plate shape (non-wedge shape) having a substantially uniform thickness. The light guide film 2 has a plurality of recesses 9 that are recessed on the front surface side on the back surface. Moreover, the light guide film 2 has a sticking prevention part on the back surface. Specifically, the light guide film 2 has a plurality of raised portions 8 that exist around the plurality of recesses 9 and protrude to the back surface side as the sticking prevention portion. The raised portion 8 is provided adjacent to the recessed portion 9, and the inner surface of the raised portion 8 is continuous with the formation surface of the recessed portion 9.

  As a minimum of average thickness of light guide film 2, 100 micrometers is preferred, 150 micrometers is more preferred, and 200 micrometers is still more preferred. On the other hand, the upper limit of the average thickness of the light guide film 2 is preferably 600 μm, more preferably 580 μm, and further preferably 550 μm. If the average thickness of the light guide film 2 is less than the above lower limit, the strength of the light guide film 2 may be insufficient, and the light emitted from the light source 3 is sufficiently incident on the light guide film 2. You may not be able to. On the other hand, if the average thickness of the light guide film 2 exceeds the above upper limit, there is a possibility that the request for thinning the backlight unit 1 may not be met.

  The plurality of concave portions 9 function as light scattering portions that scatter incident light to the surface side. Each recess 9 is formed in a substantially circular shape in plan view. Moreover, each recessed part 9 is formed so that a diameter may be gradually reduced toward the surface side. The shape of the recess 9 is not particularly limited, and may be a hemispherical shape, a semi-ellipsoidal shape, a conical shape, a truncated cone shape, or the like. Especially, as a shape of the recessed part 9, a hemispherical shape or a semi-ellipsoidal shape is preferable. When the concave portion 9 has a hemispherical shape or a semi-ellipsoidal shape, the moldability of the concave portion 9 can be improved, and light incident on the concave portion 9 can be suitably scattered.

  The raised portion 8 is formed continuously from a surface perpendicular to the thickness direction of the light guide film 2 on the back surface of the light guide film 2. Specifically, the raised portion 8 is formed continuously from the flat surface on the back surface of the light guide film 2. The raised portion 8 is formed in a substantially annular shape in plan view so as to surround the recessed portion 9. The light guide film 2 is formed in a substantially annular shape in plan view so that the raised portion 8 surrounds the concave portion 9, so that the concave portion 9 and the vicinity of the concave portion 9 are disposed on the back side of the light guide film 2. Can be easily and reliably prevented.

  The light guide film 2 has flexibility. By having flexibility, the light guide film 2 can suppress damage to the reflection sheet 7 disposed on the back surface side. The light guide film 2 is formed to be transparent because it is necessary to transmit light. The light guide film 2 is composed mainly of a synthetic resin.

  As main components of the light guide film 2, polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, methyl (meth) acrylate-styrene copolymer, polyolefin, cycloolefin polymer, cycloolefin copolymer, cellulose acetate, weather resistance And reactive vinyl chloride, active energy ray-curable resin, and the like. Especially, as a main component of the light guide film 2, a polycarbonate or an acrylic resin is preferable. Polycarbonate is excellent in transparency and has a high refractive index. Therefore, when the light guide film 2 contains polycarbonate as a main component, total reflection is likely to occur on the upper and rear surfaces of the light guide film 2, and light can be efficiently propagated. it can. In addition, since polycarbonate has heat resistance, it is difficult for the light source 3 to be deteriorated by heat generation. Furthermore, since polycarbonate has less water absorption than acrylic resin, dimensional stability is high. Therefore, the light guide film 2 can suppress deterioration over time by including polycarbonate as a main component. On the other hand, since acrylic resin has high transparency, light wear in the light guide film 2 can be reduced.

<LED light source>
The plurality of LEDs 3 are arranged along one end face of the light guide film 2. Each of the plurality of LED light sources 3 is disposed such that the light emission surface faces (or abuts) one end surface of the light guide film 2.

<Reflection sheet>
The reflection sheet 7 is disposed on the back surface side of the light guide film 2 so as to come into contact with the plurality of raised portions 8 formed on the back surface of the light guide film 2. The reflection sheet 7 reflects light emitted from the back surface of the light guide film 2 upward. As the reflective sheet 7, regular reflection is enhanced by depositing a metal such as aluminum or silver on the surface of a white sheet in which a filler is dispersed in a base resin such as polyester or a film formed from polyester. Specular sheet etc. are mentioned.

<Advantages>
Since the optical sheet (the light diffusion sheet 5 and the prism sheet 6) includes a plurality of convex portions 13a and 18a on the back surface in a scattered manner, the optical sheet and other optical elements disposed on the back surface side of the optical sheet. The member partially abuts on the plurality of convex portions 13a and 18a. Therefore, the optical sheet can prevent sticking with other optical members disposed on the back surface side. Further, in the optical sheet, since the convex portions 13a and 18a are flat hemispheres or flat cones with rounded tip portions, the curved surfaces of the tip portions (lower end portions) of the plurality of convex portions 13a and 18a. Becomes comparatively gentle, thereby preventing the surface of another optical member disposed on the back surface side from being damaged.

  Since the backlight unit 1 includes the optical sheet (the light diffusion sheet 5 and the prism sheet 6), sticking of the optical sheet and other optical members disposed on the back side of the optical sheet is performed as described above. While being able to prevent, the surface of another optical member can be prevented from being damaged.

<Optical sheet manufacturing method>
Next, a method for manufacturing the optical sheet will be described. Here, a manufacturing method when the optical sheet is the above-described light diffusion sheet 5 will be described. The manufacturing method of the said optical sheet is equipped with a resin film conveyance process, an ultraviolet curable resin composition supply process, and an ultraviolet irradiation process. Moreover, the manufacturing method of the said optical sheet is equipped with a light-diffusion layer lamination process.

(manufacturing device)
The manufacturing method of the optical sheet is performed using, for example, the manufacturing apparatus 21 in FIG. The manufacturing apparatus 21 has a pair of pressing rolls 22 and 23 that are arranged adjacent to each other in parallel. The pair of pressing rolls 22 and 23 is provided with temperature control means, and is configured to be able to control the surface (circumferential surface) temperature to an optimum temperature. As the pair of pressing rolls 22 and 23, it is preferable to use a metal elastic roll composed of a metal roll and a flexible roll whose surface is covered with an elastic body. Moreover, one press roll 23 has a some recessed part on the surface (circumferential surface). Specifically, one of the pressing rolls 23 has a reverse shape of a back surface provided with the above-described plurality of convex portions 13a on the surface.

(Resin film transport process)
In the resin film conveying step, the belt-shaped resin film A is sent to the surfaces of the pair of pressing rolls 22 and 23. Specifically, in the resin film conveying step, the resin film A forming the base material layer 11 of the light diffusion sheet 5 is sent between the pair of pressing rolls 22 and 23.

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

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

(Light diffusion layer lamination process)
In the light diffusion layer lamination step, after the ultraviolet irradiation step, a coating liquid containing a plurality of beads 14 and a binder composition is applied to the other side surface of the resin film A, and the applied coating liquid is dried and cured. . By this light diffusion layer lamination step, the light diffusion layer 12 is laminated on the other side surface of the resin film A.

  In addition, although the procedure which laminates | stacks the light-diffusion layer 12 after forming the several convex part 13a was demonstrated here, the manufacturing method of the said light-diffusion sheet is not limited to this procedure, The light-diffusion layer 12 is used. You may form the some convex part 13a after laminating | stacking.

  Further, here, the manufacturing method in the case where the optical sheet is the light diffusion sheet 5 has been described. However, even in the case where the optical sheet is the prism sheet 6, the same resin film transporting process, the ultraviolet curable resin composition as described above. It can manufacture using a supply process and an ultraviolet irradiation process. Specifically, the manufacturing method of the prism sheet 6 includes: (a) a sheet mold having an inverted shape of the prism row 17 by applying an active energy ray-curable resin to the other side surface of the resin film after the ultraviolet irradiation step. , A method of transferring the shape to an uncured active energy ray curable resin by pressing against a mold or a roll die, and curing the active energy ray curable resin by applying an active energy ray, (b) of the other pressing roll 23 Examples include a method in which a reverse shape of the prism row 17 is formed on the peripheral surface, a molten resin is passed through the other side surface of the resin film, and the shape is transferred. As a method for manufacturing the prism sheet, a plurality of convex portions may be formed after the prism row 17 is formed.

<Advantages>
The manufacturing method of the optical sheet includes a roll 24 having a flat hemispherical shape or a reverse shape of a plurality of flat cone-shaped convex portions 13a, 18a rounded at the front end portion on one surface of the resin film. A plurality of convex portions 13a and 18a can be formed. Therefore, the manufacturing method of the optical sheet for a liquid crystal display device can prevent sticking by partially contacting other optical members by the plurality of convex portions 13a and 18a, and also contacts the plurality of convex portions 13a and 18a. An optical sheet (light diffusion sheet 5 and prism sheet 6) that can prevent damage to other optical members can be manufactured.

[Second Embodiment]
[Backlight unit]
The backlight unit 31 for a liquid crystal display device in FIG. 6 is an edge 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 is a light guide sheet that guides light incident from the end surface to the front surface side, a plurality of LED light sources 3 disposed along the end surface of the light guide film 2, And a plurality of optical sheets 32 superimposed on the surface side of the guide film 2. The backlight unit 31 includes, as a plurality of optical sheets 32, a microlens sheet 33 that is directly stacked on the surface of the light guide film 2 (without interposing other sheets or the like), and directly on the surface of the microlens sheet 33 (others). And a prism sheet 6 to be stacked. The backlight unit 31 further includes a reflective sheet 7 disposed on the back side of the light guide film 2. In FIG. 6, the reflection sheet 7, the light guide film 2, the microlens sheet 33, and the prism sheet 6 are illustrated separately from each other, but actually, the surface of the reflection sheet 7, the back surface of the light guide film 2, the light The front surface of the guide film 2 and the back surface of the microlens sheet 33, the front surface of the microlens sheet 33, and the back surface of the prism sheet 6 are in contact. The light guide film 2, the LED light source 3, the prism sheet 6, and the reflection sheet 7 in the backlight unit 31 are the same as the backlight unit 1 in FIG.

<Micro lens sheet>
As shown in FIG. 7, the microlens sheet 33 includes a base layer 34, a microlens array 35 that is stacked on the front side of the base layer 34, and a back layer 36 that is stacked on the back side of the base layer 34. With. The microlens array 35 is composed of a plurality of microlenses 35 a protruding from the surface of the base material layer 34. Further, the microlens sheet 33 includes a plurality of convex portions 36 a that are sticking preventing portions on the back surface of the back layer 36 in a scattered manner. The microlens sheet 33 includes a base material layer 34, a microlens array 35, a back layer 36, and a plurality of convex portions 36a (that is, the microlens sheet 33 is composed of the base material layer 34, the microlens array 35, the back surface, and the like. No other layers other than the layer 36 and the plurality of convex portions 36a). The microlens sheet 33 is formed in a planar view shape.

  The base material layer 34 and the microlens array 35 are formed to be transparent because it is necessary to transmit light. The base material layer 34 and the microlens array 35 are composed mainly of synthetic resin. As a main component of the base material layer 34 and the microlens array 35, the same synthetic resin as the main component of the base material layer 11 of the light diffusion sheet 5 can be cited. Further, as the main component of the base material layer 34 and the microlens array 35, the same thermosetting resin, active energy ray curable resin, and the like as the back layer 13 of the light diffusion sheet 5 can be used.

  The average thickness of the base material layer 34 can be the same as, for example, 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 (that is, may be formed integrally 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 approximating a hemisphere). 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 35 a are relatively densely and geometrically disposed on the surface of the base material layer 34. Specifically, the plurality of microlenses 35 a are arranged in a regular triangular lattice pattern on the surface of the base material layer 34. Thus, all the plurality of pitch and the lens distance S ₁ of the microlens 35a is constant. With this arrangement pattern, the plurality of microlenses 35a can be arranged most densely. The arrangement pattern of the plurality of microlenses 35a is not limited to the triangular lattice pattern that can be densely packed, and for example, a square lattice pattern or a random pattern is also possible. According to this random pattern, the occurrence of moire is reduced when superimposed on other optical members.

The lower limit of the average diameter _{D 2} of the microlens 35a, 10 [mu] m is preferable, 100 [mu] m, and still more preferably 200 [mu] m. In contrast, the upper limit of the mean diameter _{D 2} of the microlens array 35a, 1000 .mu.m, more preferably 700 .mu.m, more preferably 500 [mu] m. If the average diameter D ₂ of the microlens 35a is less than the above lower limit, the influence of the diffraction is large, it tends to occur degradation and color degradation of optical performance. Conversely, when the average diameter D ₂ of the micro lenses 35a exceeds the upper limit, it may become liable to increase and brightness unevenness in thickness. The “average diameter of microlenses” refers to a value obtained by averaging the average diameters at the bases of 10 microlenses that are arbitrarily extracted. The average diameter of each microlens means an intermediate value between the maximum diameter and the minimum diameter at the base.

  The lower limit of the height ratio of the height of the microlens 35a to the radius of curvature is preferably 0.6, and more preferably 0.75. On the other hand, the upper limit of the height ratio is preferably 1. When the height ratio is within the above range, the lens-like refraction action of the microlens 35a is effectively achieved, and the optical function such as light collection of the microlens sheet 33 is remarkably improved.

The upper limit of the distance ratio (S ₁ / D ₂ ) with respect to the average diameter D ₂ of the average inter-lens distance S ₁ of the microlens 35 a is preferably 0.5, and more preferably 0.2. Thus, by setting the spacing ratio (S ₁ / D ₂ ) to be equal to or less than the upper limit, flat portions that do not contribute to the optical function are reduced, and the optical function such as light collection of the microlens sheet 33 is remarkably increased. Be improved.

  As a minimum of a filling rate of a plurality of micro lenses 35a, 40% is preferred and 60% is more preferred. Thus, by setting the filling rate of the plurality of microlenses 35a to be equal to or higher than the above lower limit, the occupied area of the plurality of microlenses 35a is increased, and the optical functions such as light collection of the microlens sheet 33 are remarkably improved. . The “filling ratio” of a plurality of microlenses refers to the area ratio of microlenses per unit area in plan view.

  The lower limit of the refractive index of the microlens array 35 is preferably 1.3, and 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. The refractive index of the microlens array 35 is particularly preferably 1.5. When the refractive index of the microlens array 35 is within the above range, the lens-like refraction action in the microlens array 35 is effectively achieved, and the optical function such as light collection of the microlens sheet 33 is enhanced.

  Since the back layer 36 needs to transmit light, it is formed transparent. The back layer 36 is formed with a synthetic resin as a main component. The main component of the back layer 36 can be the same as the main component of the back layer 13 of the light diffusion sheet 5 described above.

  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 36 a constitute the outermost surface of the microlens sheet 33. Each convex part 36a is a flat hemisphere or a flat cone with a rounded tip, and in particular in the present embodiment, is a flat halved spheroid. The plurality of convex portions 36 a are provided on the back surface of the back layer 36 at random (without regularity). The specific shape of the plurality of convex portions 36 a is the same as that of the plurality of convex portions 13 a of the light diffusion sheet 5.

The lower limit of the ratio of the average diameter of the projections 36a with respect to the average diameter _{D 2} of the microlens 35a, preferably 0.05, more preferably 0.07, still more preferably 0.1. On the other hand, the upper limit of the ratio is preferably 1, more preferably 0.5, and still more preferably 0.3. If the ratio is less than the lower limit, the amount of light incident on the convex portion 36a may be insufficient, making it difficult to sufficiently capture light by the convex portion 36a, and the back surface of the back layer 36 of the microlens sheet 33. There is a possibility that the amount of specularly reflected light may increase. On the other hand, if the ratio exceeds the upper limit, the curved shape of the convex portion 36a becomes too gentle, and it may be difficult to take in light rays by the convex portion 36a.

<Manufacturing method of microlens sheet>
The microlens sheet 33 can be manufactured using the same resin film conveyance process, ultraviolet curable resin composition supply process, and ultraviolet irradiation process as those of the light diffusion sheet 5 described above. Specifically, as a manufacturing method of the microlens sheet 33, (a) an active energy ray curable resin is applied to the other side surface of the resin film after the ultraviolet irradiation step described above, and an inversion type of the microlens array 35 is formed. A method of transferring the shape to an uncured active energy ray-curable resin by pressing against a sheet mold, mold or roll die, and applying the active energy ray to cure the active energy ray-curable resin, (b) the other pressing Examples include a method of forming the inverted shape of the microlens array 35 on the peripheral surface of the roll, and passing the molten resin through the other side surface of the resin film, and transferring the shape. In addition, as a manufacturing method of the microlens sheet, a plurality of convex portions may be formed after the microlens array 35 is formed.

<Advantages>
Since the microlens sheet 33 has a plurality of protrusions 36a on the back surface in a scattered manner, as described above, it can prevent sticking with other optical members disposed on the back surface side, It is possible to prevent the surface of another optical member from being damaged.

  The microlens sheet manufacturing method can prevent sticking with other optical members disposed on the back side as described above, and can prevent the surface of other optical members from being scratched. The microlens sheet 33 can be easily and reliably manufactured.

[Third embodiment]
<Light diffusion sheet>
8 is used in the backlight unit 1 of FIG. 1 instead of the light diffusion sheet 5 of FIG. The light diffusion sheet 41 includes a base material layer 11, a light diffusion layer 12 laminated on the front 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. In addition, the light diffusion sheet 41 includes a plurality of convex portions 13 a that are sticking prevention portions on the back surface of the back layer 42 in a scattered manner. The plurality of convex portions 13a are integrally formed with the back layer 42 (that is, the plurality of convex portions 13a and the back layer 42 are integrally formed). The light diffusion sheet 41 is formed in a planar view shape. The light diffusion sheet 41 includes 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 includes the base material layer 11 and the light diffusion layer 12). And no other layers other than the back layer 42 and the plurality of convex portions 13a). The base material layer 11, the light diffusion layer 12, and the plurality of convex portions 13a of the light diffusion sheet 41 are the same as the light diffusion sheet 5 in FIG.

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

  The light diffusing sheet 41 is a multi-striped diffraction grating shape 43 oriented in one direction in a region where the plurality of convex portions 13a do not exist in the back surface of the back layer 42 (back surface of the light diffusing sheet 41). Is provided. The diffraction grating shape 43 has a shape in which a large number of irregularities are formed along one direction. The light diffusion sheet 41 includes the diffraction grating shape 43 so that the light beam that has reached the diffraction grating shape 43 is diffused in the width direction of the diffraction grating shape 43 (perpendicular to the average orientation direction of a number of irregularities). Can do. It is preferable that the diffraction grating shape 43 exhibits a scratch mark or a hairline shape in one direction. The light diffusion sheet 41 can easily and surely diffuse light in the width direction of the diffraction grating shape 43 because the diffraction grating shape 43 exhibits a scratch mark or a hairline shape in one direction. In addition, "the average orientation direction of many uneven | corrugated strips" means the average orientation direction of several recessed part which comprises many uneven | corrugated strips.

  The diffraction grating shape 43 is formed substantially uniformly (substantially at the same density) over the entire region other than the plurality of convex portions 13 a on the back surface of the back layer 42. Moreover, as shown in FIGS. 9 and 10, the longitudinal direction of the numerous ridges forming the diffraction grating shape 43 is parallel to one end of the back surface of the back layer 42. Specifically, the longitudinal direction of the multiple concavo-convex strips is along the direction of light emission from the light source (that is, the multiple concavo-convex strips are aligned in the direction of light output from the light source). The upper limit of the inclination angle with respect to the emission direction of the light rays of each uneven strip is preferably ± 30 °, more preferably ± 15 °, and further preferably ± 5 °. Furthermore, the concavo-convex ridges may be randomly oriented within the range of the inclination angle (that is, the orientation directions of the concavo-convex ridges may not be completely coincident). In this way, by making the alignment direction of each concavo-convex line random, it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to a large number of concavo-convex lines. In addition, although it is preferable that the recessed parts of many uneven | corrugated strips are each independently formed, when controlling the spreading | diffusion direction of a light ray, one part recessed part may cross | intersect.

  The concave portions of the multiple ridges may be continuous in the longitudinal direction across both ends of the back layer 42. For example, the average length of the multiple concavo-convex recesses is 10,000 times or less with respect to the average width of the recesses. Is preferable, and 5000 times or less is more preferable. Moreover, as a minimum of the average length of the recessed part of many uneven | corrugated strips, 2 times or more are preferable with respect to the average width of a recessed part, and 3 times or more are more preferable. If the average length of the concaves and convexes of the large number of concaves and convexes exceeds the above upper limit, it may be difficult to form a large number of concaves and convexes in a random orientation direction and high density in order to suppress the occurrence of rainbow unevenness in the liquid crystal display device . On the contrary, if the average length of the concave portions of the many ridges is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 is sufficiently increased with respect to the light amount of the light beam reaching the diffraction grating shape 43. You may not be able to. In addition, "the average length of the recessed part of many uneven | corrugated strips" means the average value of the length of 20 recessed parts extracted arbitrarily.

  Moreover, it is preferable that the length of the recessed part of many uneven | corrugated strips is random. The light diffusing sheet 41 can suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the large number of concaves and convexes due to the random lengths of the concaves and convexes in the large number of concaves and convexes.

Width L ₁ of the concave portion of the large number of concave-convex is preferably random. Moreover, as shown in FIG. 9, it is preferable that the width L ₁ of the concave portion of each concavo-convex line changes randomly along the longitudinal direction of the concave portion of the concavo-convex line. The light diffusion sheet 41 by the width L ₁ of the concave portion of the large number of concave-convex is random, it is possible to suppress the rainbow unevenness is generated in the liquid crystal display device due to a number of irregularities Article.

  As a minimum of the average width of the crevice of many uneven strips, 10 nm is preferred, 50 nm is more preferred, and 100 nm is still more preferred. On the other hand, the upper limit of the average width of the concave portions of the many ridges is preferably 30 μm, more preferably 20 μm, and even more preferably 10 μm. If the average width of the concave portions of the many ridges is less than the lower limit, the moldability of the diffraction grating shape 43 may be lowered. On the contrary, if the average width of the concave portions of the many ridges exceeds the upper limit, there is a possibility that a sufficient amount of light diffused in the width direction of the diffraction grating shape 43 cannot be secured. In addition, it is preferable that the width | variety of the recessed part of each uneven | corrugated strip is formed at random along the longitudinal direction within the said range. Since the width of the concave portion of each concave and convex strip is randomly formed within the above range, moire caused by interference with other members (prism sheet or liquid crystal cell) having a periodic pitch can be prevented and color separation can be performed. Can be prevented from occurring regularly, and rainbow unevenness and the like can be prevented. The “average width of the concave portions of the many ridges” is the width at the average interface of the tips of the convex portions of the concavo-convex portions at arbitrary points excluding the both ends in the longitudinal direction of the 20 arbitrarily extracted concave portions. The average value of

  It is preferable that the pitch of a large number of uneven strips is random. The light diffusing sheet 41 can suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the large number of concavo-convex stripes due to the random pitch of the concavo-convex stripes. The “average pitch of many ridges” means the average value of the pitches of 20 ridges adjacent on a straight line perpendicular to the average orientation direction of many ridges.

  As a minimum of the average pitch of many uneven ridges, 10 nm is preferred, 50 nm is more preferred, and 100 nm is still more preferred. On the other hand, as an upper limit of the average pitch of a large number of irregularities, 40 μm is preferable, 30 μm is more preferable, 20 μm is further preferable, and 10 μm is particularly preferable. If the average pitch of a large number of irregularities is less than the lower limit, the moldability of the diffraction grating shape 43 may be reduced. On the contrary, if the average pitch of the many ridges exceeds the upper limit, the amount of light diffused in the width direction of the diffraction grating shape 43 may not be increased sufficiently.

  As an upper limit of the standard deviation of the pitch of a large number of irregularities, 10 μm is preferable, 9 μm is more preferable, and 7 μm is more preferable. If the standard deviation of the pitch of the many ridges exceeds the above upper limit, the pitch of the many ridges becomes too uneven, and the amount of light diffused in the width direction of the diffraction grating shape 43 is spread over the entire region where the many ridges are formed. There is a possibility that it cannot be increased uniformly. On the other hand, the lower limit of the standard deviation of the pitch of a large number of concave and convex lines can be set to 4 μm, for example, because a large number of concave and convex lines can be easily arranged in a relatively random direction. The “standard deviation of the pitch of a large number of uneven strips” refers to the standard deviation of the pitch of 20 irregular strips arbitrarily extracted.

  The lower limit of the average number per unit length of the concave portions of the multiple uneven strips in the direction perpendicular to the average orientation direction of the multiple uneven strips is preferably 10 / mm, more preferably 50 / mm, and 100 / mm is more preferable. On the other hand, the upper limit of the average number is preferably 10000 / mm, more preferably 5000 / mm, and still more preferably 1000 / mm. If the average existence number is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 with respect to the amount of light reaching the diffraction grating shape 43 may not be sufficiently increased. On the contrary, if the average number exceeds the upper limit, the moldability of the diffraction grating shape 43 may be lowered.

The lower limit of the average depth _{D 3} of the concave portion of the large number of concave-convex, 10 nm are preferred, 500 nm are more preferable, and more preferably 1 [mu] m, 2 [mu] m is particularly preferred. On the other hand, the upper limit of the average depth _{D 3,} 10 [mu] m is preferable, 5 [mu] m, and still more preferably 3 [mu] m. When the average depth D ₃ is less than the above lower limit, there may not be sufficiently increased the amount of light diffused in the width direction of the diffraction grating pattern 43. Conversely, the average depth D ₃ is more than the upper limit, the strength of the backing layer 42 may be reduced. The “average depth of the concave portions of the many ridges” means an average value of the depth from the average interface at the tips of the convex portions of the many ridges to the bottom of the 20 concave portions arbitrarily extracted.

  Moreover, as an upper limit of the standard deviation of the depth of the recessed part of many uneven | corrugated strips, 4 micrometers is preferable, 3 micrometers is more preferable, and 2.5 micrometers is further more preferable. When the standard deviation of the depth exceeds the above upper limit, the depths of the concave portions of the numerous ridges become too uneven, and the amount of light diffused in the width direction of the diffraction grating shape 43 is distributed to the entire formation region of the diffraction grating shape 43. There is a possibility that it cannot be increased uniformly. On the other hand, the lower limit of the standard deviation of the depth is not particularly limited, and can be set to 0.3 μm, for example. The “standard deviation of the depths of the many ridges” refers to the standard deviation of the depths of the recesses of the 20 ridges extracted arbitrarily.

  Lower limit of arithmetic average roughness (Ra) on the basis of the orientation direction and parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 0.005 μm, more preferably 0.05 μm, and even more preferably 0.1 μm. On the other hand, the arithmetic average roughness (Ra) based on the orientation direction and the parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). The upper limit is preferably 1.5 μm, more preferably 1.2 μm, and even more preferably 1 μm. If the arithmetic average roughness (Ra) is less than the lower limit, the effect of suppressing the occurrence of hot spots described later may be insufficient. On the contrary, when the arithmetic average roughness (Ra) exceeds the upper limit, the amount of light diffused in the direction parallel to the alignment direction of a number of projections and depressions with respect to the amount of light diffused in the width direction of the diffraction grating shape 43 increases. There is a risk that it may be difficult to ensure a sufficient viewing angle in the direction perpendicular to the light-emitting direction of the light source. The “arithmetic average roughness (Ra)” refers to a value having a cutoff λc of 0.8 mm and an evaluation length of 4 mm in accordance with JIS-B0601: 1994.

  Lower limit of arithmetic average roughness (Ra) on the basis of the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 0.01 μm, more preferably 0.1 μm, and even more preferably 0.5 μm. On the other hand, the arithmetic average roughness (Ra) based on the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). Is preferably 5 μm, more preferably 3 μm, and even more preferably 1.5 μm. If the arithmetic average roughness (Ra) is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 may not be sufficiently increased. Conversely, when the arithmetic average roughness (Ra) exceeds the upper limit, it may be difficult to control the light emission angle.

  Further, the arithmetic average roughness (Ra) based on the orientation direction and the parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). In addition, the arithmetic average roughness (Ra) based on the orientation direction and the vertical direction of a large number of projections and depressions is preferably included in the above range. The light diffusion sheet 41 has an arithmetic average roughness (Ra) based on the orientation direction and the parallel direction of a large number of irregularities and an arithmetic average roughness (Ra) based on the orientation direction and a direction perpendicular to the orientation directions of the numerous irregularities. Is within the above range, the amount of light diffused in the width direction of the diffraction grating shape 43 can be sufficiently increased to easily widen the viewing angle of the light source in the direction perpendicular to the light beam emission direction.

  Arithmetic mean roughness (Ra) and many on the outer surface (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) on which the diffraction grating shape 43 is formed, based on the orientation direction and the vertical direction of a number of projections and depressions The lower limit of the difference between the orientation direction of the ridges and the arithmetic average roughness (Ra) based on the parallel direction is preferably 0.5 μm, more preferably 0.7 μm, and even more preferably 1 μm. When the difference in the arithmetic average roughness (Ra) is equal to or greater than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 is sufficiently increased, and the viewing angle in the direction perpendicular to the light-emitting direction of the light source is sufficient. Easy to spread. On the other hand, the upper limit of the difference in the arithmetic average roughness (Ra) can be set to 1.9 μm, for example.

  As a lower limit of the maximum height (Ry) on the basis of the orientation direction and the parallel direction of a number of projections and depressions on the outer surface on which the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 0.1 μm, preferably 1 μm, and more preferably 1.5 μm. On the other hand, the maximum height (Ry) on the basis of the direction parallel to the orientation direction and the parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). As an upper limit, 3 micrometers is preferable, 2.5 micrometers is more preferable, and 2 micrometers is further more preferable. If the maximum height (Ry) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. On the other hand, when the maximum height (Ry) exceeds the upper limit, the amount of light diffused in the direction parallel to the alignment direction of the many irregularities with respect to the amount of light diffused in the width direction of the diffraction grating shape 43 increases. It may be difficult to ensure a sufficient viewing angle in the direction perpendicular to the direction of light emission. “Maximum height (Ry)” refers to a value with a cutoff λc of 0.8 mm and an evaluation length of 4 mm in accordance with JIS-B0601: 1994.

  As a lower limit of the maximum height (Ry) on the basis of the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 4 μm, more preferably 5 μm, and even more preferably 6 μm. On the other hand, the maximum height (Ry) on the basis of the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). As an upper limit, 12 micrometers is preferable, 10 micrometers is more preferable, and 9 micrometers is further more preferable. If the maximum height (Ry) is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 may not be increased sufficiently. Conversely, if the maximum height (Ry) exceeds the upper limit, it may be difficult to control the light emission angle.

  The maximum height (Ry) based on the orientation direction and the vertical direction of a number of projections and depressions on the outer surface on which the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) and a large number The lower limit of the difference between the alignment direction of the projections and depressions and the maximum height (Ry) based on the parallel direction is preferably 4 μm, more preferably 5 μm, and even more preferably 6 μm. When the difference in the maximum height (Ry) is equal to or greater than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 is sufficiently increased to sufficiently increase the viewing angle in the direction perpendicular to the light beam emission direction of the light source. Easy to spread. On the other hand, the upper limit of the difference in the maximum height (Ry) can be set to 11 μm, for example.

  The ten-point average roughness (Rz) of the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) with respect to the alignment direction and the parallel direction of a number of projections and depressions. As a minimum, 0.1 micrometer is preferable, 0.5 micrometer is more preferable, and 1 micrometer is further more preferable. On the other hand, the ten-point average roughness (Rz) based on the alignment direction and the parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). ) Is preferably 2.5 μm, more preferably 2 μm, and even more preferably 1.5 μm. If the ten-point average roughness (Rz) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. On the contrary, if the ten-point average roughness (Rz) exceeds the upper limit, the amount of light diffused in the direction parallel to the alignment direction of a large number of projections and depressions with respect to the amount of light diffused in the width direction of the diffraction grating shape 43 increases. There is a risk that it may be difficult to ensure a sufficient viewing angle in the direction perpendicular to the light-emitting direction of the light source. The “ten-point average roughness (Rz)” refers to a value having a cutoff λc of 0.8 mm and an evaluation length of 4 mm in accordance with JIS-B0601: 1994.

  The ten-point average roughness (Rz) of the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) on the basis of the orientation direction and the vertical direction of a number of projections and depressions As a minimum, 4 micrometers is preferred, 5 micrometers is more preferred, and 6 micrometers is still more preferred. On the other hand, a ten-point average roughness (Rz) based on the orientation direction and the vertical direction of a number of projections and depressions on the outer surface (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) on which the diffraction grating shape 43 is formed. ) Is preferably 10 μm, more preferably 8 μm, and even more preferably 7 μm. If the ten-point average roughness (Rz) is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 may not be increased sufficiently. On the other hand, if the ten-point average roughness (Rz) exceeds the upper limit, it may be difficult to control the light emission angle.

  Ten-point average roughness (Rz) based on the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) The lower limit of the difference between the alignment direction of a large number of irregularities and the ten-point average roughness (Rz) based on the parallel direction is preferably 3 μm, more preferably 4 μm, and even more preferably 4.5 μm. When the difference in the ten-point average roughness (Rz) is equal to or more than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 is sufficiently increased, and the viewing angle in the direction perpendicular to the light-emitting direction of the light source It is easy to spread enough. On the other hand, the upper limit of the difference of the ten-point average roughness (Rz) can be set to 9 μm, for example.

  Lower limit of root mean square slope (RΔq) on the basis of the orientation direction and the parallel direction of a number of projections and depressions on the outer surface on which the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 0.05, more preferably 0.2, even more preferably 0.25, and particularly preferably 0.3. On the other hand, the root mean square slope (RΔq) on the basis of the orientation direction and the parallel direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). Is preferably 0.5, more preferably 0.45, and still more preferably 0.4. If the root mean square slope (RΔq) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. On the contrary, when the root mean square slope (RΔq) exceeds the upper limit, the amount of light diffused in the direction parallel to the alignment direction of a number of projections and depressions with respect to the amount of light diffused in the width direction of the diffraction grating shape 43 increases. There is a risk that it may be difficult to ensure a sufficient viewing angle in the direction perpendicular to the light-emitting direction of the light source. “Root mean square slope (RΔq)” refers to a value according to JIS-B0601: 2001.

  Lower limit of root-mean-square slope (RΔq) with respect to the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) Is preferably 0.5, more preferably 0.7, and even more preferably 1. On the other hand, the root mean square slope (RΔq) on the basis of the orientation direction and the vertical direction of a number of projections and depressions on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed). The upper limit of is preferably 2.5, more preferably 2, and even more preferably 1.8. If the root mean square slope (RΔq) is less than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 may not be sufficiently increased. Conversely, if the root mean square slope (RΔq) exceeds the upper limit, it may be difficult to control the light emission angle.

  The root mean square slope (RΔq) and many on the outer surface where the diffraction grating shape 43 is formed (the back surface of the back layer 42 on which the plurality of convex portions 13a are not formed) with respect to the orientation direction and the vertical direction of a number of projections and depressions The lower limit of the difference between the root-mean-square slope (RΔq) based on the alignment direction of the ridges and the parallel direction is preferably 0.5, more preferably 0.7, and even more preferably 1. When the difference of the root mean square slope (RΔq) is equal to or greater than the lower limit, the amount of light diffused in the width direction of the diffraction grating shape 43 is sufficiently increased, so that the viewing angle in the direction perpendicular to the light emitting direction of the light source is sufficient. Easy to spread. On the other hand, the upper limit of the difference of the root mean square slope (RΔq) can be set to 2.2, for example.

<Brightness unevenness reduction function>
Next, with reference to FIG.11 and FIG.12, the brightness nonuniformity reduction function of the said backlight unit provided with the said light-diffusion sheet | seat 41 and the said light-diffusion sheet | seat 41 is demonstrated. First, with reference to FIG. 11, the amount of light emitted from the plurality of LED light sources 3 in the backlight unit 1 of FIG. 1 and incident on the light guide film 2 will be described. Light rays emitted from the plurality of LED light sources 3 are incident substantially perpendicularly from an end face (incident end face) of the light guide film 2 facing the plurality of LED light sources 3 and propagate toward an end face opposite to the incident end face. . At this time, since the light beams emitted from the plurality of LED light sources 3 have strong directivity, a region X having an extremely large amount of light is generated particularly in the vicinity of the light beam incident portion of the light guide film 2. On the other hand, since the plurality of LED light sources 3 are arranged at predetermined intervals, a region Y having an extremely small amount of light is provided between the light incident portions in the light guide film 2 (between adjacent regions X). Will occur.

  Subsequently, with reference to FIG. 12, the luminance unevenness reducing function of the light diffusion sheet 41 and the backlight unit including the light diffusion sheet 41 will be described. Most of the light rays emitted from the region X to the surface side of the light guide film 2 are incident on the back surface of the back layer 42 of the light diffusion sheet 41 in a state along the light emission direction of the plurality of LED light sources 3. . Then, the light beam incident on the back surface of the back layer 42 of the light diffusion sheet 41 is formed in the width direction of the diffraction grating shape 43 by the diffraction grating shape 43 having a large number of projections and depressions along the light emission direction of the plurality of LED light sources 3. It is thought that it is spread. That is, it is considered that the light beam incident on the diffraction grating shape 43 is diffused in the region Y direction in plan view as shown in FIG. Thereby, it is considered that the amount of light in the region X and the amount of light in the region Y in plan view are made uniform, and luminance unevenness in the backlight unit is reduced.

<Method for producing light diffusion sheet>
Next, a method for manufacturing the light diffusion sheet 41 will be described. The manufacturing method of the light diffusing sheet 41 includes a resin film conveying step, an ultraviolet curable resin composition supplying step, and an ultraviolet irradiation step. Further, the method for manufacturing the optical sheet 41 includes a light diffusion layer stacking step. The light diffusing sheet 41 is the above-described one except that, instead of the one pressing roll 23 described above, a pressing roll having a reverse shape of the back surface including the plurality of convex portions 13a and the diffraction grating shape 43 is used. It can be manufactured by a method similar to the method for manufacturing the light diffusion sheet 5.

<Advantages>
Since the light diffusion sheet 41 includes a plurality of convex portions 13a on the back surface in a scattered manner, as described above, it can prevent sticking with other optical members disposed on the back surface side, It is possible to prevent the surface of another optical member from being damaged. Furthermore, since the light diffusion sheet 41 includes a multi-striped diffraction grating shape 43 oriented in one direction in a region of the back surface where the plurality of convex portions 13a are not present, the light diffusion sheet 41 is provided in the width direction of the diffraction grating shape 43. Light can be diffused, and a sufficient viewing angle in the width direction can be secured.

  As described above, the manufacturing method of the light diffusion sheet can prevent sticking with other optical members disposed on the back surface side, and can prevent the surface of other optical members from being scratched. In addition, the light diffusion sheet 41 capable of sufficiently ensuring the viewing angle in the width direction of the diffraction grating shape 43 can be easily and reliably manufactured.

[Fourth embodiment]
<Light diffusion sheet>
A light diffusion sheet 46 in FIG. 13 is used in the backlight unit in FIG. 1 instead of the light diffusion sheets 5 and 41 in FIGS. The light diffusing sheet 46 is configured in the same manner as the light diffusing sheet 41 of FIG. 8 except that it also has a diffraction grating shape 47 continuous with the diffraction grating shape 43 on the back side of the plurality of convex portions 13a.

<Method for producing light diffusion sheet>
The manufacturing method of the light diffusion sheet 46 includes a resin film conveyance process, an ultraviolet curable resin composition supply process, and an ultraviolet irradiation process. The method for manufacturing the optical sheet 46 includes a light diffusion layer stacking step. The light diffusion sheet 46 is formed on the back surface side of the plurality of convex portions 13a in succession to the plurality of convex portions 13a, the diffraction grating shape 43, and the diffraction grating shape 43 instead of the one pressing roll 23 described above. It can be manufactured by the same method as the manufacturing method of the light diffusion sheet 5 described above, except that a pressure roll having a reverse shape of the back surface shape including the diffraction grating shape 47 is used.

<Advantages>
Since the light diffusion sheet 46 has a diffraction grating shape 47 that is continuous with the diffraction grating shape 43 on the back surface side of the plurality of convex portions 13a, light is diffused uniformly in the width direction of the diffraction grating shapes 43 and 47. In addition, the viewing angle in the width direction of the diffraction grating shapes 43 and 47 can be ensured more accurately.

  As described above, the manufacturing method of the light diffusion sheet can prevent sticking with other optical members disposed on the back surface side, and can prevent the surface of other optical members from being scratched. In addition, the light diffusion sheet 46 capable of ensuring the viewing angle in the width direction of the diffraction grating shapes 43 and 47 more accurately can be easily and reliably manufactured.

[Other Embodiments]
In addition, the manufacturing method of the optical sheet which concerns on this invention, a backlight unit, and an optical sheet can be implemented in the aspect which gave various change and improvement other than the said aspect. For example, the optical sheet is not limited to the light diffusion sheet, the prism sheet, and the microlens sheet having the above-described configuration. For example, the optical sheet may be a light diffusion sheet in which fine irregularities are formed on the surface of the light diffusion layer by embossing. In addition, when the optical sheet is a light diffusion sheet, it is not necessarily a lower light diffusion sheet disposed directly above the light guide sheet, but is disposed on the surface side of the prism sheet and slightly diffuses light rays. Therefore, the upper light diffusion sheet that suppresses luminance unevenness due to the shape of the prism row of the prism sheet or the like may be used. Note that when the optical sheet is an upward light diffusion sheet and the optical sheet has a diffraction grating shape, the light path from the light source to be incident on the diffraction grating shape can be made relatively long. It is easy to enhance the light diffusion effect in the width direction of the shape. Therefore, when the optical sheet is an upward light diffusing sheet, it is easy to increase the luminance unevenness suppressing effect in the backlight unit.

  The optical sheet may have other layers than the layers described in the above embodiment. For example, in the optical sheet, another resin layer may be 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. .

  When the optical sheet has a diffraction grating shape, the optical sheet is preferably disposed on the back surface of a sheet body in which two prism sheets are bonded. A sheet body in which two prism sheets are bonded together has low concealability because an air layer is hardly formed between the prism sheets. On the other hand, the backlight unit in which the optical sheet is disposed on the back surface of the sheet body can sufficiently improve the concealment effect because the optical sheet can diffuse light in the width direction of the diffraction grating shape. be able to.

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

  The diffraction grating shape may be arranged as shown in FIG. 14, for example. In FIG. 14, the diffraction grating shape 51 is formed in a certain region from one end of the back layer 52 (the edge on the side facing the light source 53 in plan view) to the other end side. Moreover, the area | region where the diffraction grating shape 51 in the back surface of the back layer 52 is not formed is comprised as a flat surface. The specific configuration of the diffraction grating shape 51 is the same as that of the light diffusion sheet 41 of FIG.

As a lower limit of the ratio (L ₃ / L ₂ ) of the length L ₃ between one end and the other end of the region where the diffraction grating shape 51 is formed with respect to the length L ₂ between one end and the other end of the back layer 52 0.15 is preferable, 0.2 is more preferable, and 0.25 is more preferable. On the other hand, the upper limit of the length ratio (L ₃ / L ₂ ) is preferably 0.5, more preferably 0.45, and even more preferably 0.4. If the length ratio (L ₃ / L ₂ ) is less than the lower limit, it may be difficult to completely suppress the occurrence of hot spots. On the other hand, if the length ratio (L ₃ / L ₂ ) exceeds the upper limit, it may be easy to diffuse light rays in a region other than the hot spot in the width direction of the diffraction grating shape 51.

  Further, the diffraction grating shape may be arranged as shown in FIG. 15, for example. In the diffraction grating shape 61 of FIG. 15, the ratio of the uneven stripes gradually decreases from 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. The optical sheet can suppress the occurrence of hot spots even with such a configuration. Further, since the optical sheet has a gradually decreasing ratio of the uneven stripes from the edge facing the light source 63 to the other end, the amount of light diffused in the width direction of the diffraction grating shape 61 except for the hot spot Can be reduced.

  The specific shape of the diffraction grating shape is not limited to the shape of the above-described embodiment. For example, a shape having a concave portion having a U-shaped cross section as shown in FIG. 16, a cross section as shown in FIG. A shape having a triangular recess or a shape having a slit-like recess as shown in FIG. Moreover, the said many uneven | corrugated strip may be orientated in the orthogonal | vertical direction with respect to the light emission direction of a light source.

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

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

  The backlight unit is not necessarily an edge light type backlight unit, and may be a direct type backlight unit.

  In addition, even if the backlight unit is an edge light type backlight unit, it is necessary to be a one-side edge light type backlight unit in which an LED light source is disposed only along one end surface of the light guide sheet. And a double-sided edge light type backlight unit in which LED light sources are arranged along a pair of opposite end faces of the light guide sheet, or an all-around edge light in which LED light sources are arranged along each end face of the light guide sheet A type backlight unit may be used.

  The backlight unit can be used for relatively large display devices such as personal computers and liquid crystal televisions, mobile phone terminals such as smartphones, and portable information terminals such as tablet terminals.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[No. 1]
A light diffusing sheet was manufactured using the manufacturing apparatus 21 of FIG. 5 in which a plurality of concave portions having the same shape were formed on the peripheral surface of one pressing roll 23 at substantially equal density. First, the resin film which has acrylic urethane resin as a main component and forms the base material layer of a light-diffusion sheet was sent between a pair of press rolls 22 and 23. Moreover, the ultraviolet curable resin composition which has an acrylic urethane resin as a main component is supplied between the said resin film and one press roll 23, and the said resin film and an ultraviolet curable resin composition are made into a pair of press rolls 22 and 23. Pressed. As a result, a plurality of halved spheroid-shaped convex portions, which are inverted shapes of the plurality of concave portions, were transferred to the outer surface of the ultraviolet curable resin composition. Furthermore, the ultraviolet curable resin composition to which the plurality of convex portions were transferred was irradiated with ultraviolet rays to cure the ultraviolet curable resin composition. Subsequently, a coating liquid containing a plurality of beads and a binder composition is applied to the 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 cured. A light diffusing layer was formed using 1 light diffusion sheet was obtained. No. Table 1 shows the average height, the average diameter, the ratio of the average height to the average diameter, and the occupied area ratio of the plurality of convex portions.

[No. 2-No. 6]
No. 1 except that the average height, the average diameter, the ratio of the average height to the average diameter, and the occupied area ratio of the plurality of convex portions are as shown in Table 1. No. 1 having the same configuration as in FIG. 2-No. 6 light diffusion sheets were produced.

[No. 7-No. 13]
No. No. 1 except that the occupation area ratio of the plurality of convex portions is as shown in Table 1 by the same production method as in Table 1. No. 1 having the same configuration as in FIG. 7-No. Thirteen light diffusion sheets were produced.

<Adhesion>
No. 1-No. 13 light diffusion sheets are disposed between the light guide film and the prism sheet, and a plurality of LED light sources are disposed along one end surface of the light guide film to form an edge light type backlight unit. did. A 20 mm square glass plate was disposed on the surface of the prism sheet of the backlight unit, and the surface of the glass plate was pressed with a pressure of 5 kgf. In this pressed state, light was emitted from the plurality of LED light sources to the end face of the light guide film, and further, the pressure on the glass plate surface was released in this light emitted state. In the pressed state and the state after pressing, the presence or absence of bright spots was observed from the surface side of the glass plate and evaluated according to the following criteria. The evaluation results are shown in Table 2.
A: A bright spot is not observed in any of the pressed state and the pressed state.
B: Bright spots are observed in a region of 30% or less of the glass plate surface only in the pressed state.
C: Bright spots are observed in a region exceeding 30% of the glass plate surface only in the pressed state.
D: A bright spot is observed in a region exceeding 30% of the surface of the glass plate in the pressed state, and a bright spot is observed for several seconds after pressing.
E: A bright spot is observed in a region exceeding 30% of the surface of the glass plate in the pressed state, and a bright spot similar to that in the pressed state is continuously observed after pressing.

<Scratch property>
No. 1-No. Thirteen light diffusion sheets were disposed between the light guide film and the prism sheet, and a plurality of LED light sources were disposed along one end surface of the light guide film. Further, a reflective sheet and an aluminum plate were disposed in this order on the back side of the light guide film, and a liquid crystal panel was disposed on the surface of the prism sheet. In this state, 160 g of a spherical acrylic ball was dropped from a height of 300 mm from the surface of the liquid crystal panel. Thereafter, light was emitted from the plurality of LED light sources to the end face of the light guide film, and the presence or absence of scratches on the surface of the light guide film was observed in the light emission state and the state after the light emission, and evaluated according to the following criteria. The evaluation results are shown in Table 2.
A: No scratch is observed at all in the light emission state and the state after the light emission.
B: Scratches are observed slightly whitish only in the light emission state.
C: Although the scratch is observed as light white only in the light emission state, the outline of the scratch appears blurred.
D: Scratches are observed as a relatively dark white only in the light emission state.
E: Scratches are observed in both the light emission state and the state after light emission.

[Evaluation results]
As shown in Table 1 and Table 2, the average height of the plurality of convex portions is 1.1 μm, the average diameter is 10.2 μm, and the ratio of the average height to the average diameter is 0.11. It can be seen that the light diffusion sheet No. 1 is sufficiently prevented from being in close contact with the light guide film and is not damaged. In contrast, no. 2 and no. As shown in FIG. As the average height and average diameter of the plurality of convex portions becomes smaller than 1, bright spots are observed by the above-described adhesion test. This bright spot is caused by an increase in the contact area between the light diffusion sheet and the light guide film due to crushing of the convex portion of the light diffusion sheet, and the transmission of light in the contact area is increased. is there. Furthermore, no. 4-No. As shown in FIG. It can be seen that the surface of the light guide film is easily damaged due to the plurality of protrusions as the average height and average diameter of the plurality of protrusions are larger than 1.

  Further, as shown in Table 1 and Table 2, the light diffusion sheet has an average height of a plurality of convex portions 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. No. in which the occupied area ratio of the plurality of convex portions is 5% to 30%. 1, no. 9 and no. It can be seen that No. 10 light diffusion sheet is sufficiently prevented from being in close contact with the light guide film and is not damaged. In contrast, no. 7 and no. As shown in FIG. 8, it can be seen that the light diffusion sheet and the light guide film are closely adhered as the occupied area ratio of the plurality of convex portions becomes lower than 2%. This is considered because the light diffusion sheet is likely to come into contact with the light guide film at portions other than the plurality of convex portions. Furthermore, no. 11-No. As shown in FIG. 13, it can be seen that the adhesion between the light diffusion sheet and the light guide film deteriorates as the occupied area ratio of the plurality of convex portions exceeds 50%. This is considered to be because if the occupation area ratio of the plurality of convex portions becomes 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 guide film. No. 11-No. As shown in FIG. 13, it can be seen that as the occupation area ratio of the plurality of convex portions exceeds 50%, the damage property of the light diffusion sheet to the light guide film surface is deteriorated. This is because if the contact portion between the surface of the light guide film and the plurality of convex portions becomes excessive, scratches are likely to occur due to the contact portion between the plurality of convex portions and the surface of the light guide film. Conceivable.

  As described above, the optical sheet of the present invention can prevent sticking and prevent damage to other optical members disposed on the back surface side, so that a high-quality transmissive liquid crystal display device, etc. Suitable for various liquid crystal display devices.

1,31 Backlight unit for liquid crystal display (backlight unit)
2 Light guide film 3, 53, 63 Light source 32 Optical sheet for liquid crystal display (optical sheet)
5, 41, 46 Light diffusing sheet 6 Prism sheet 7 Reflecting sheet 8 Raised portion 9 Recessed portion 11, 16, 34 Base material layer 12 Light diffusing layer 13a, 18a, 36a Convex portion 14 Beads 15 Binder 17 Prism array 17a Convex prism portion 21 Manufacturing apparatus 22, 23 Press roll 33 Micro lens sheet 35 Micro lens array 35a Micro lens 13, 18, 36, 42, 52, 62 Back layer 43, 47, 51, 61 Diffraction grating shape 101 Backlight unit 102 Light source 103 Optical sheet 104 Optical sheet 105 Light diffusion sheet 106 Prism sheet 111 Base material layer 112 Light diffusion layer 113 Sticking prevention layer 114 Bead 115 Binder A Resin film

Claims (9)

An optical sheet for a liquid crystal display device comprising a plurality of convex portions on the back surface in a scattered manner,
An optical sheet for a liquid crystal display device, wherein the convex portion is a flat hemisphere or a flat cone having a rounded tip.   The optical sheet for a liquid crystal display device according to claim 1, wherein the convex portion is a half spheroid.   The optical sheet for a liquid crystal display device according to claim 1 or 2, wherein an occupation area ratio of the plurality of convex portions is 2% or more and 80% or less.   4. The optical sheet for a liquid crystal display device according to claim 1, wherein the convex portion has an average diameter of 5 μm to 60 μm and an average height of 0.5 μm or more.   The optical sheet for a liquid crystal display device according to any one of claims 1 to 4, wherein a plurality of ridge-like diffraction grating shapes oriented in one direction are provided in a region of the back surface where the plurality of convex portions do not exist. .   The optical sheet for a liquid crystal display device according to claim 5, wherein the diffraction grating shape exhibits a scratch mark or a hairline shape in one direction.   The optical sheet for a liquid crystal display device according to claim 5, wherein the optical sheet for a liquid crystal display device has a diffraction grating shape that is continuous with the diffraction grating shape on the back surface side of the plurality of convex portions. A light guide sheet that guides light incident from the end face to the surface side;
One or more LED light sources disposed along the end face of the light guide sheet;
A backlight unit for a liquid crystal display device comprising one or more optical sheets superimposed on the surface side of the light guide sheet,
A backlight unit for a liquid crystal display device, wherein the optical sheet according to any one of claims 1 to 7 is used for at least one of the one or more optical sheets. A method for producing an optical sheet for a liquid crystal display device comprising a plurality of convex portions on the back surface in a scattered manner,
Using a roll having on the surface a reverse shape of the back surface comprising the plurality of convex portions in a scattered manner,
Sending the belt-shaped resin film to the roll surface;
Supplying an ultraviolet curable resin composition between the resin film and the roll;
Irradiating the ultraviolet curable resin composition with ultraviolet rays,
The method for producing an optical sheet for a liquid crystal display device, wherein the convex portion is a flat hemisphere or a flat cone having a rounded tip.

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