TWI684049B - Optical sheet for liquid crystal display device, and backlight unit for liquid crystal display device - Google Patents

Abstract

An optical sheet for a liquid crystal display device has functions of condensing rays of light with respect to a specific direction in a plane of the optical sheet, and diffusing rays of light with respect to a direction perpendicular to the specific direction. A backlight unit for a liquid crystal display device includes: a light guide film for guiding rays of light incident on an end face of the light guide film toward a front face side; at least one LED light source disposed along the end face of the light guide film; the optical sheet disposed on the front face side; and a prism sheet disposed on a front face of the optical sheet, with the specific direction being parallel to a direction of rays of light emitted by the at least one LED light source and perpendicular to a direction of prism rows of the prism sheet.

Description

Light diffusion sheet for liquid crystal display device and backlight unit for liquid crystal display device

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

As a transmissive liquid crystal display device, a backlight method in which a liquid crystal layer is irradiated from the back has been popularized, and a backlight unit of an edge light type (side light type), a directly below type, or the like is provided on the back side of the liquid crystal layer. As shown in FIG. 21, the edge-light type backlight unit 101 generally includes a plurality of LED light sources 102, a square plate-shaped light guide sheet 103 disposed on the plurality of LED light sources 102 along the end surface, and superposed on the A plurality of optical sheets 104 on the surface side of the light guide sheet 103. The optical sheet 104 has optical functions such as diffusion and refraction of transmitted light. For example, a light diffusion sheet 105 which is arranged on the surface side of the light guide sheet 103 and mainly has a light diffusion function, and which is arranged on the surface side of the light diffusion sheet 105 and which has The prism sheet 106 and the like having a refractive function toward the normal direction side (see Japanese Patent Laid-Open No. 2005-77448).

To describe the function of the backlight unit 101, first, the light incident from the plurality of LED light sources 102 to the light guide sheet 103 is reflected at the reflection point or the reflection sheet (not shown) and each side surface of the back surface of the light guide sheet 103 Reflect and exit from the surface of the light guide sheet 103. The light emitted from the surface of the light guide sheet 103 enters the light diffusion sheet 105 and is diffused, and is emitted from the surface. The light emitted from the surface of the light diffusing sheet 105 enters the prism sheet 106, is refracted toward the normal direction side by a plurality of ribs prism portions formed on the surface, and then exits the liquid crystal layer (not shown) on the surface side The entire surface is illuminated. In addition, although not shown, as the optical sheet 104, it is also used: by arranging the surface side of the prism sheet 106 and slightly diffusing the light to suppress the shape of the plurality of ridged prism portions of the prism sheet 106, etc. An upper light diffusion sheet that causes uneven brightness, a microlens sheet having a refraction function toward the normal direction side and a wide-angle light diffusion function, etc.

In this backlight unit 101, a plurality of LED light sources 102 are sequentially arranged on one end surface of the light guide sheet 103, and therefore the light emitted from the surface of the light guide sheet 103 includes a large amount of light that is inclined in the emission direction of the plurality of LED light sources 102 Directivity. In the backlight unit 101, the light having the directivity is diffused by the light diffusion sheet 105, and then the lump sheet 106 is raised toward the normal direction side, thereby increasing the brightness in the front direction.

Existing technical literature

Patent Literature

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

Problems to be solved by the invention

However, the inventors conducted studies and found that the edge light type backlight unit 101 using a plurality of LED light sources 102 as described above cannot sufficiently increase the front brightness. This reason is not necessarily clear, but the reason is considered to be that the exit direction of the outgoing light from the light diffusion sheet 105 has a deviation, and the deviation of the exit direction is not consistent with the optical characteristics of the prism sheet 106, so the prism sheet 106 is used in the normal direction The proportion of rising light is reduced.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical sheet for a liquid crystal display device and a backlight unit for a liquid crystal display device including the optical sheet, which can sufficiently increase the front brightness of the backlight unit having a thin sheet.

Means for solving the problem

The optical sheet for a liquid crystal display device of the present invention completed to solve the above-mentioned problems is characterized by being an optical sheet for a liquid crystal display device that exerts a specific optical function on transmitted light. The light collection function based on the direction and the diffusion function based on the direction perpendicular to the specific direction.

In this optical sheet for a liquid crystal display device, in a backlight unit including a prism sheet in which the direction of the prism row is arranged in a direction perpendicular to the light direction of the LED light source, if the prism sheet is on the back side of the prism sheet, By arranging the specific direction so that the direction of the mirror row is perpendicular, the front brightness of the backlight unit can be sufficiently improved. This reason is not necessarily clear, but it is considered that the reason is that the light emitted from the LED light source and incident on the optical sheet for the liquid crystal display device is condensed in the above-mentioned specific direction and diffuses in the vertical direction of the above-mentioned specific direction, thereby The light rays emitted from the optical sheet of the display device and incident on the prism sheet rise up to a desired angle at a high ratio under the action of the prism column.

The optical sheet for a liquid crystal display device may have a plurality of grating shapes oriented in the specific direction. In this way, by providing a plurality of stripe-shaped grating shapes oriented in the specific direction, light can be diffused in the width direction of the grating shape, so that the light-gathering function based on the specific direction can be easily and reliably performed And the diffusion function based on the direction perpendicular to the specific direction.

The grating shape may be scratched or hairlined in the specific direction. In this way, by making the grating shape have scratches or hairlines in the specific direction, light can be easily and reliably diffused in the width direction of the grating shape.

The optical sheet for a liquid crystal display device may be a light diffusion sheet including a base layer and a light diffusion layer laminated on one side of the base layer. In this way, by making the optical sheet for a liquid crystal display device a light diffusion sheet including a base material layer and a light diffusion layer laminated on one side of the base material layer, it is easy to improve the light-concentrating function based on the specific direction And the diffusion function based on the direction perpendicular to the specific direction.

The light diffusion layer may have beads and its binder. In this way, by providing the light diffusion layer with beads and its binder, the light condensing function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction can be more reliably improved.

The haze value of the optical sheet for a liquid crystal display device is preferably 60% or more and 95% or less. In this way, by making the haze value within the above range, it is easier to improve the light-concentrating function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction.

The backlight unit for a liquid crystal display device of the present invention completed to solve the above-mentioned problems includes a light guide film that guides light incident from the end surface to the surface side, and one or more LEDs arranged along the end surface of the light guide film A light source, the optical sheet arranged on the surface side of the light guide film, and a prism sheet arranged on the surface side of the prism sheet, the specific direction of the optical sheet being parallel to the light direction of the LED light source and parallel to the prism sheet The direction of the column is vertical.

In the backlight unit for a liquid crystal display device, since the specific direction of the optical sheet is parallel to the light direction of the LED light source and is perpendicular to the direction of the row of the row of the sheet, the light passing through the sheet is focused The vertical direction of the column of light in the column of light is diffused to the direction of the column of column, so that the front brightness can be sufficiently improved.

In addition, in this invention, the "surface side" means the viewer side of a liquid crystal display device. In addition, "back surface" refers to the surface opposite to the front surface side. The "grating shape" is not limited to the shape of the grating whose optical characteristics are strictly adjusted, but broadly refers to the shape that diffracts incident light. "Scratch-shaped or hairline-shaped in one direction" refers to a shape formed by a plurality of elongated scars oriented in one direction. The "haze value" refers to a value obtained in accordance with JIS-K-7136:2000.

Invention effect

As described above, the optical sheet for a liquid crystal display device of the present invention can sufficiently improve the front brightness of the backlight unit. In addition, the backlight unit for a liquid crystal display device of the present invention can sufficiently increase the front brightness.

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

[First Embodiment]

[Backlight unit]

The backlight unit for a liquid crystal display device of FIG. 1 (hereinafter also simply referred to as “backlight unit”) is an edge light type backlight unit, which is a backlight unit for a liquid crystal display device using a plurality of LED light sources. The backlight unit includes a light guide film 1 that guides light incident from the end surface to the surface side, a plurality of LED light sources 2 arranged along the above-mentioned end surface of the light guide film 1, and a plurality of light source films superimposed on the surface side of the light guide film 1 Optical sheet 3. As the plurality of optical sheets 3 described above, a light diffusion sheet (lower light diffusion sheet 4) of the present invention arranged on the surface side of the light guide film 1 and a first prism sheet arranged on the surface side of the lower light diffusion sheet 4 are provided 5. The second yam sheet 6 arranged on the surface side of the first yam sheet 5 and the light diffusion sheet (upper light diffusion sheet 7) arranged on the surface side of the second yam sheet 6. In addition, the backlight unit further includes a reflection sheet 8 disposed on the lower back side of the light guide film 1. The lower light diffusion sheet 4 diffuses the light incident from the back side and condenses the light toward the normal direction side (condenses and diffuses the light). The first yam sheet 5 and the second yam sheet 6 refract the light incident from the back side toward the normal direction side. Specifically, the direction of the row of rows of the first row of sheets 5 and the second row of sheets 6 (the direction of the ridgeline of the convex strip section) is orthogonal, and the first row of sheets 5 makes the light incident from the lower light diffusion sheet 4 It is refracted in the direction perpendicular to the direction of the column array and the normal direction side, and the light beam emitted from the first panel sheet 5 is refracted by the second panel sheet 6 so as to travel approximately perpendicular to the back surface of the liquid crystal display element. The upper light diffusion sheet 7 diffuses the light incident from the back side to some extent to suppress uneven brightness caused by the shape and the like of the row of the first row of sheets 5 and the second row of sheets 6. The reflection sheet 8 reflects the light emitted from the back side of the light guide film 1 toward the front side, and enters the light guide film 1 again.

<Lower light diffusion sheet>

As shown in FIG. 2, the lower light diffusion sheet 4 includes a base layer 11, a light diffusion layer 12 stacked on one side of the base layer 11, and a back layer 13 stacked on the back side of the base layer 11. The lower light diffusion sheet 4 is formed in a square shape in plan view. The lower light diffusing sheet 4 is composed of the base material layer 11, the light diffusing layer 12 and the back layer 13 (that is, the lower light diffusing sheet 4 does not have other than the base material layer 11, the light diffusing layer 12 and the back layer 13 Floor).

The specific direction in the plane of the lower light diffusion sheet 4 is parallel to the light direction (light emission direction) of the plurality of LED light sources 2. In addition, the above-mentioned specific direction of the lower light diffusion sheet 4 and the direction of the row of the first row of sheets 5 of the first row of sheets 5 directly arranged on the surface side of the lower sheet of light diffusion 4 (that is, arranged without other optical sheets) vertical. The lower light diffusion sheet 4 is an optical sheet for a liquid crystal display device having a specific optical function for transmitted light (light incident from the rear side and exiting from the front side), and has a specific direction in the plane as the optical function (The light direction of the plurality of LED light sources 2) is a light condensing function based on the reference and a diffusion function based on the direction perpendicular to the specific direction (the direction of the line of the first lug sheet 5). That is, the lower light diffusing sheet 4 has a diffusion anisotropy higher in the diffusion function in the direction perpendicular to the specific direction than in the plane.

(Substrate layer)

The base material layer 11 needs to transmit light and is therefore transparent. The base material layer 11 mainly contains synthetic resin. The main component of the base material layer 11 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, and polyolefin. Cellulose acetate, weather-resistant vinyl chloride, etc. Among them, polyethylene terephthalate having excellent transparency and high strength is preferred, and polyethylene terephthalate having improved bending performance is particularly preferred. In addition, "main component" means the component with the largest content, for example, the component whose content is 50 mass% or more.

(Light diffusion layer)

The light diffusion layer 12 is laminated on the surface side of the base material layer 11. The light diffusion layer 12 constitutes the outermost surface of the lower light diffusion sheet 4. The light diffusion layer 12 has a plurality of beads 14 and its adhesive 15. The beads 14 are surrounded by the adhesive 15. The light diffusion layer 12 contains a plurality of beads 14 dispersed, so that the light transmitted from the back side to the front side is diffused substantially uniformly. In addition, the light diffusion layer 12 is formed with fine irregularities on the surface substantially uniformly due to the plurality of beads 14, and each concave portion and convex portion of the fine irregularities are formed in a lens shape. The light diffusing layer 12 exerts an excellent light diffusing function by the lens action of the fine irregularities, and due to the light diffusing function, it has a refraction function that refracts transmitted light toward the normal direction side and condenses the transmitted light macroscopically on the normal Directional light-gathering function.

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

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 fibrous shape. Among them, a spherical shape excellent in light diffusibility is preferable.

The binder 15 is formed by curing (crosslinking, etc.) a polymer composition containing a base polymer. The beads 14 are arranged and fixed to the entire surface of the base material layer 11 with a substantially uniform density by the adhesive 15. In addition, the polymer composition used to form the binder 15 may be appropriately mixed with, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, antistatic agents, and ultraviolet absorbers , Antioxidants, viscosity modifiers, lubricants, light stabilizers, etc.

(Back layer)

The back layer 13 constitutes the rearmost surface of the lower light diffusion sheet 4. The back layer 13 needs to transmit light and is therefore transparent. 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 thermosetting resins and active energy ray curing resins.

Examples of the thermosetting resins include epoxy resins, silicone resins, phenol resins, urea resins, unsaturated polyester resins, melamine resins, alkyd resins, acrylic resins, amide functional copolymers, and polyurethane resins. .

Examples of the active energy ray-curable resin include ultraviolet-curable resins that are cross-linked and cured by irradiation with ultraviolet rays, and electron-ray-curable resins that are cross-linked and cured by irradiation with electron rays. The polymerizable monomer and polymerizable oligomer can be appropriately selected and used. Among them, the active energy ray-curable resin is preferably an acrylic, urethane, or acrylic urethane ultraviolet-curable resin.

The lower light diffusion sheet 4 has a plurality of grating shapes 16 oriented in the specific direction on the back surface of the back layer 13 (the back surface of the lower light diffusion sheet). The grating shape 16 has a shape in which a plurality of uneven stripes are formed along the above-mentioned specific direction. The lower light diffusing sheet 4 includes the grating shape 16, so that the light reaching the grating shape 16 can be diffused in the width direction of the grating shape 16 (the direction perpendicular to the average orientation direction of the plurality of uneven lines). As a result, the lower light diffusion sheet 4 exhibits the light-concentrating function based on the specific direction as described above and the diffusion function based on the direction perpendicular to the specific direction. The grating shape 16 preferably exhibits scratches or hairlines in the above-mentioned specific direction. In the lower light diffusion sheet 4, by making the grating shape 16 show scratches or hairlines in the specific direction, light can be easily and reliably diffused in the width direction of the grating shape 16. In addition, the "average orientation direction of a plurality of uneven stripes" refers to the average orientation direction of a plurality of concave portions constituting a plurality of uneven stripes.

The grating shape 16 is formed substantially uniformly (approximately equal density) over the entire area of the back surface of the back layer 13. In addition, as shown in FIGS. 3 and 4, the longitudinal direction of the plurality of concave and convex stripes forming the grating shape 16 is along the light direction of the plurality of LED light sources 2 (that is, the plurality of concave and convex stripes are oriented to the light direction of the plurality of LED light sources 2) . As the upper limit of the inclination angle of each concave-convex strip with respect to the light direction, it is preferably ±30°, more preferably ±15°, and still more preferably ±5°. Furthermore, the concave-convex strips may be randomly oriented within the above-mentioned range of inclination angles (that is, the orientation directions of the concave-convex strips may not be completely consistent). In this way, by making the orientation directions of the uneven stripes random, it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of uneven stripes. In addition, in terms of controlling the diffusion direction of the light, the concave portions of the plurality of concave and convex stripes are preferably formed independently of each other. However, a part of the concave portions may cross each other.

The longitudinal direction of the concave portions of the plurality of concave and convex stripes may be continuous at both ends of the back layer 13, for example, the average length of the concave portions of the plurality of concave and convex stripes with respect to the average width of the concave portions is preferably 10000 times or less, and more preferably 5000 times or less. In addition, as the lower limit of the average length of the concave portions of the plurality of concave and convex stripes, the average width of the concave portions is preferably 2 times or more, and more preferably 3 times or more. If the average length of the concave portions of the plurality of embossed stripes exceeds the above upper limit, there is a risk that it is difficult to form the plurality of embossed stripes in a random orientation direction with high density in order to suppress the occurrence of rainbow unevenness in the liquid crystal display device. Conversely, if the average length of the concave portions of the plurality of embossed stripes is less than the above lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 16 relative to the amount of light reaching the grating shape 16 cannot be sufficiently increased. In addition, "the average length of the concave part of a plurality of uneven|corrugated strips" means the average value of the length of 20 concave parts arbitrarily extracted.

In addition, the lengths of the concave portions of the plurality of uneven lines are preferably random. In the lower light diffusion sheet 4, by making the lengths of the concave portions of the plurality of irregularities random, it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of irregularities.

The width L ₁ of the concave portion of the plurality of uneven lines is preferably random. In addition, as shown in FIG. 3, the width L ₁ of the concave portion of each concave-convex strip is preferably randomly changed along the longitudinal direction of the concave portion of the concave-convex strip. In respect of the light diffusion sheet 4, the irregularities by a plurality of strips of width L ₁ of the concave portion is random, it can be suppressed by the plurality of concave-convex unevenness in the case of the liquid crystal display device produced rainbow.

The lower limit of the average width of the concave portions of the plurality of uneven lines is preferably 10 nm, more preferably 50 nm, and still more preferably 100 nm. On the other hand, the upper limit of the average width of the concave portions of the plurality of uneven lines is preferably 30 μm, more preferably 20 μm, and still more preferably 10 μm. If the average width of the concave portions of the plurality of concave and convex stripes is less than the above lower limit, there is a risk that the moldability of the grating shape 16 is lowered. Conversely, if the average width of the concave portions of the plurality of uneven stripes exceeds the upper limit, there is a risk that the amount of light diffused in the width direction of the grating shape 16 cannot be sufficiently secured. In addition, it is preferable that the width of the concave portion of each concave-convex strip is randomly formed along the longitudinal direction within the above range. By randomly forming the width of each concave-convex strip within the above-mentioned range, it is possible to prevent moiré caused by interference with other members having a periodic pitch (such as a sheet or a liquid crystal cell), etc. Color decomposition occurs regularly to prevent rainbow inequality. In addition, the "average width of the concave portions of the plurality of concave and convex stripes" refers to the average of the average width of the average interface of the 20 concave portions arbitrarily extracted excluding any points at both ends in the longitudinal direction at the tips of the convex portions of the multiple concave and convex stripes value.

The pitch of the plurality of concave and convex stripes is preferably random. In the lower light diffusion sheet 4, by making the pitch of the plurality of irregularities irregular, it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of irregularities. In addition, the "average pitch of a plurality of concave and convex stripes" refers to the average value of the pitches of 20 concave and convex stripes adjacent to each other on a straight line perpendicular to the average orientation direction of the multiple concave and convex stripes.

The lower limit of the average pitch of the plurality of uneven stripes is preferably 10 nm, more preferably 50 nm, and still more preferably 100 nm. On the other hand, the upper limit of the average pitch of the plurality of uneven lines is preferably 10 μm, more preferably 9 μm, and still more preferably 7 μm. If the average pitch of the plurality of concave and convex stripes is less than the above lower limit, there is a risk that the moldability of the grating shape 16 is reduced. Conversely, if the average pitch of the plurality of concave and convex stripes exceeds the upper limit, there is a risk that the amount of light diffused in the width direction of the grating shape 16 cannot be sufficiently increased.

The upper limit of the standard deviation of the pitch of the plurality of uneven lines is preferably 10 μm, more preferably 9 μm, and still more preferably 7 μm. If the standard deviation of the pitches of the plurality of embossed stripes exceeds the upper limit, the pitches of the plurality of embossed stripes are too uneven, and there is a possibility that the amount of light diffused in the width direction of the grating shape 16 cannot be uniformly increased over the entire formation area of the plurality of embossed stripes risk. On the other hand, the lower limit of the standard deviation of the pitches of the plurality of concave and convex stripes may be, for example, 4 μm from the viewpoint of arranging the plurality of concave and convex stripes in a relatively random direction. In addition, the "standard deviation of the pitch of a plurality of irregularities" means the standard deviation of the pitch of 20 irregularities extracted arbitrarily.

The lower limit of the number per unit length of the concave portions of the plurality of concave and convex stripes in the direction perpendicular to the average orientation direction of the plurality of concave and convex stripes is preferably 10 pieces/mm, more preferably 50 pieces/mm, and still more preferably 100 pieces/mm. On the other hand, the upper limit of the average number is preferably 10,000 pieces/mm, more preferably 5,000 pieces/mm, and still more preferably 1,000 pieces/mm. If the average number is less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 16 relative to the amount of light reaching the grating shape 16 cannot be sufficiently increased. Conversely, if the average number exceeds the upper limit, the moldability of the grating shape 16 may be reduced.

The lower limit of the average depth D ₁ of the concave portions of the plurality of uneven stripes is preferably 10 nm, more preferably 500 nm, still more preferably 1 μm, and particularly preferably 2 μm. On the other hand, the upper limit of the average depth D ₁ is preferably 10 μm, more preferably 5 μm, and still more preferably 3 μm. If the average depth D _{1 is} less than the lower limit, there is a risk that the amount of light diffused in the width direction of the grating shape 16 cannot be sufficiently increased. Conversely, if the average depth D ₁ exceeds the upper limit, there is a risk of lowering the strength of the back layer 13. In addition, the "average depth of the concave portions of the plurality of concave and convex stripes" refers to the average value of the depth from the average interface of the tops of the convex portions of the plurality of concave and convex stripes to the bottom of the 20 concave portions arbitrarily extracted.

In addition, the upper limit of the standard deviation of the depth of the concave portions of the plurality of uneven lines is preferably 4 μm, more preferably 3 μm, and still more preferably 2.5 μm. If the standard deviation of the depth exceeds the upper limit, the depths of the concave portions of the plurality of embossed stripes are too uneven, and there is a risk that the amount of light diffused in the width direction of the grating shape 16 cannot be uniformly increased throughout the entire formation area of the grating shape 16. On the other hand, the lower limit of the standard deviation of the depth is not particularly limited, and may be 0.3 μm, for example. In addition, "the standard deviation of the depth of a plurality of irregularities" means the standard deviation of the depth of the concave portions of 20 irregularities extracted arbitrarily.

The upper limit of the arithmetic average roughness (Ra) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes is preferably 1.5 μm, more preferably It is 1.2 μm, further preferably 1 μm. If the arithmetic average roughness (Ra) exceeds the upper limit, there is a risk that the light-concentrating function based on the specific direction will be insufficient. On the other hand, as the lower limit of the arithmetic average roughness (Ra) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes, for example, it may be 0.005μm. In addition, "arithmetic mean roughness (Ra)" means the value when the cut-off λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the arithmetic average roughness (Ra) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 0.01 μm, and more preferably It is 0.1 μm, further preferably 0.5 μm. On the other hand, the upper limit of the arithmetic average roughness (Ra) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 5 μm , More preferably 3 μm, still more preferably 1.5 μm. If the arithmetic average roughness (Ra) is less than the lower limit, there is a risk that the diffusion function based on the direction perpendicular to the specific direction is insufficient. On the contrary, if the above arithmetic average roughness (Ra) exceeds the above upper limit, there is a risk that it is difficult to control the exit angle of light.

In addition, on the outer surface (back surface of the back layer 13) where the grating shape 16 is formed, the arithmetic average roughness (Ra) based on the direction parallel to the orientation direction of the plurality of uneven stripes and the orientation with the plurality of uneven stripes The arithmetic average roughness (Ra) with the direction perpendicular to the direction as a reference is preferably included in the above range. The lower light diffusion sheet 4 is based on the arithmetic average roughness (Ra) based on the direction parallel to the orientation direction of the plurality of concave and convex stripes and the direction perpendicular to the orientation direction of the plurality of concave and convex stripes The arithmetic average roughness (Ra) is within the above range, so that it is easy to simultaneously improve the light gathering function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction.

As the arithmetic average roughness (Ra) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes and the orientation direction with the plurality of concave and convex stripes The parallel direction is the lower limit of the difference in arithmetic average roughness (Ra) based on the reference, and is preferably 0.5 μm, more preferably 0.7 μm, and still more preferably 1 μm. By making the difference in the arithmetic mean roughness (Ra) equal to or more than the lower limit, it is easy to simultaneously improve the light-concentrating function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction. On the other hand, the upper limit of the difference in the arithmetic mean roughness (Ra) may be 1.9 μm, for example.

The upper limit of the maximum height (Ry) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes is preferably 3 μm, and more preferably 2.5 μm , Further preferably 2 μm. If the maximum height (Ry) exceeds the upper limit, there is a risk that the light-concentrating function based on the specific direction is insufficient. On the other hand, the lower limit of the maximum height (Ry) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes may be, for example, 0.1 μm . The "maximum height (Ry)" refers to the value when the cut-off λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the maximum height (Ry) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 4 μm, more preferably 5 μm, It is more preferably 6 μm. On the other hand, the upper limit of the maximum height (Ry) of the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 12 μm, more preferably It is 10 μm, further preferably 9 μm. If the maximum height (Ry) is less than the lower limit, there is a risk that the diffusion function based on the direction perpendicular to the specific direction is insufficient. Conversely, if the maximum height (Ry) exceeds the upper limit, there is a risk that it is difficult to control the angle of light emission.

The maximum height (Ry) based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes as the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed and the direction parallel to the orientation direction of the plurality of concave and convex stripes The lower limit of the difference in maximum height (Ry) as a reference is preferably 4 μm, more preferably 5 μm, and still more preferably 6 μm. By making the difference in the maximum height (Ry) equal to or greater than the lower limit, it is easy to simultaneously improve the light-concentrating function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction. On the other hand, the upper limit of the difference in the maximum height (Ry) may be, for example, 11 μm.

As the upper limit of the ten-point average roughness (Rz) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concavo-convex stripes, it is preferably 2.5 μm, more It is preferably 2 μm, and more preferably 1.5 μm. If the ten-point average roughness (Rz) exceeds the upper limit, there is a risk that the light-concentrating function based on the specific direction will be insufficient. On the other hand, as the lower limit of the ten-point average roughness (Rz) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes, for example, 0.1μm. The "ten-point average roughness (Rz)" refers to the value when the cut-off λc is 0.8 mm and the evaluation length is 4 mm in accordance with JIS-B0601:1994.

The lower limit of the ten-point average roughness (Rz) of the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 4 μm, more preferably 5 μm, more preferably 6 μm. On the other hand, the upper limit of the ten-point average roughness (Rz) of the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 10 μm , More preferably 8 μm, still more preferably 7 μm. If the ten-point average roughness (Rz) is less than the lower limit, there is a risk that the diffusion function based on the direction perpendicular to the specific direction is insufficient. Conversely, if the above-mentioned ten-point average roughness (Rz) exceeds the upper limit, there is a risk that it is difficult to control the exit angle of light.

The ten-point average roughness (Rz) based on the direction perpendicular to the orientation direction of the plurality of concavo-convex stripes as the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed and the orientation direction corresponding to the plurality of concavo-convex stripes The parallel direction is the lower limit of the difference in ten-point average roughness (Rz) based on the reference, and is preferably 3 μm, more preferably 4 μm, and still more preferably 4.5 μm. By making the difference of the ten-point average roughness (Rz) above the lower limit, it is easy to simultaneously improve the light-concentrating function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction. On the other hand, the upper limit of the difference between the ten-point average roughness (Rz) may be, for example, 9 μm.

On the other hand, the upper limit of the root-mean-square slope (RΔq) of the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed based on the direction parallel to the orientation direction of the plurality of concave and convex stripes is preferably 0.5, It is more preferably 0.45, and still more preferably 0.4. If the root-mean-square slope (RΔq) exceeds the upper limit, there is a risk that the light-concentrating function based on the specific direction will be insufficient. On the other hand, the lower limit of the root mean square slope (RΔq) on the outer surface (back surface of the back layer 13) forming the grating shape 16 based on the direction parallel to the orientation direction of the plurality of concave and convex stripes may be, for example, 0.05. In addition, "root mean square slope (RΔq)" means the value obtained based on JIS-B0601:2001.

The lower limit of the root-mean-square slope (RΔq) of the outer surface (the back surface of the back layer 13) on which the grating shape 16 is formed based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes is preferably 0.5, more preferably 0.7 , Further preferably 1. On the other hand, the upper limit of the root-mean-square slope (RΔq) of the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed based on the direction perpendicular to the orientation direction of the plurality of concavo-convex stripes is preferably 2.5, It is more preferably 2, and even more preferably 1.8. If the root mean square slope (RΔq) is less than the lower limit, there is a risk that the diffusion function based on the direction perpendicular to the specific direction will be insufficient. Conversely, if the root mean square slope (RΔq) exceeds the upper limit, there is a risk that it is difficult to control the exit angle of light.

As the outer surface (back surface of the back layer 13) on which the grating shape 16 is formed, the root mean square slope (RΔq) based on the direction perpendicular to the orientation direction of the plurality of concave and convex stripes and the orientation direction parallel to the plurality of concave and convex stripes The direction of is the lower limit of the difference of the root mean square slope (RΔq) of the reference, and is preferably 0.5, more preferably 0.7, and still more preferably 1. By making the difference of the root mean square slope (RΔq) equal to or greater than the lower limit, it is easy to simultaneously improve the light-concentrating function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction. On the other hand, the upper limit of the difference in the root mean square slope (RΔq) may be 2.2, for example.

The lower limit of the haze value of the lower light diffusion sheet 4 is preferably 60%, more preferably 70%, and still more preferably 80%. On the other hand, the upper limit of the haze value of the lower light diffusion sheet 4 is preferably 95%, and more preferably 93%. The lower light diffusion sheet 4 having such a high haze value makes it easier to improve the light-concentrating function based on the specific direction in the above-mentioned plane and the diffusion function based on the direction perpendicular to the specific direction.

＜珜鏡片>

The first yam sheet 5 and the second yam sheet 6 have a base layer, and a yam row including a plurality of convex ridges stacked on the surface of the base layer. The above-mentioned base material layer and the column are required to transmit light and are therefore transparent. The above-mentioned base material layer and arrogance row are formed with a synthetic resin as a main component. The direction of the yam row of the first yam piece 5 is substantially orthogonal to the direction of the yam row of the second yam piece 6. In addition, as described above, the direction of the row of rows of the first row of sheets 5 is perpendicular to the specific direction described above. The first yam sheet 5 and the second yam sheet 6 have a preferred angle of incidence for raising light in the normal direction.

<Upper light diffusion sheet>

The upper light diffusion sheet 7 includes a base layer, a light diffusion layer laminated on the front side of the base layer and having a plurality of beads and its binder, and a protective layer laminated on the back side of the base layer. The upper light diffusion sheet 7 is composed of a base layer, a light diffusion layer directly laminated on the surface of the base layer, and a protective layer directly laminated on the back of the base layer (excluding the base layer, the light diffusion layer and the Layers other than the protective layer). The upper light diffusion sheet 7 is formed in a square shape in plan view.

The base material layer of the upper light diffusion sheet 7 may have the same structure as the base material layer 11 of the lower light diffusion sheet 4. The protective layer of the upper light diffusion sheet 7 may have the same configuration as the back layer 13 of the lower light diffusion sheet 4 except that the grating shape 16 is not provided. On the other hand, the light diffusion layer of the upper light diffusion sheet 7 does not need to have the same high light diffusibility as the light diffusion layer 12 of the lower light diffusion sheet 4, and therefore, the lower limit of the amount of the light diffusion agent blended is preferably 5 parts by mass, more preferably 10 parts by mass, and, as an upper limit, preferably 40 parts by mass, more preferably 30 parts by mass.

<Light guide film>

The light guide film 1 allows the light incident from the end surface to exit substantially uniformly from the surface. The light guide film 1 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 1 has a plurality of recesses 17 sunk on the front side on the back side. In addition, the light guide film 1 has an anti-adhesion portion on the back. Specifically, the light guide film 1 has a plurality of raised portions 18 existing around the plurality of concave portions 17 and protruding toward the back side as the above-mentioned anti-adhesion portion. The raised portion 18 is provided adjacent to the recessed portion 17, and the inner surface of the raised portion 18 is continuous with the forming surface of the recessed portion 17.

The plurality of concave portions 17 function as light scattering portions that scatter incident light toward the surface side. Each recess 17 is formed in a substantially circular shape in plan view. In addition, each concave portion 17 is formed so as to gradually decrease in diameter toward the surface side. The shape of the concave portion 17 is not particularly limited, and may be hemispherical, semiellipsoidal, conical, circular truncated, or the like. Among them, the shape of the concave portion 17 is preferably hemispherical or hemispherical. By making the concave portion 17 hemispherical or semi-ellipsoidal, the moldability of the concave portion 17 can be improved, and light incident on the concave portion 17 can be appropriately scattered.

The raised portion 18 is continuously formed from the surface of the back surface of the light guide film 1 perpendicular to the thickness direction of the light guide film 1. In detail, the raised portion 18 is continuously formed from the flat surface of the back surface of the light guide film 1. The raised portion 18 is formed in a substantially circular ring shape in a plan view so as to surround the concave portion 17. The light guide film 1 is formed in a substantially circular ring shape in a plan view so that the raised portion 18 surrounds the recessed portion 17, so that the reflection of the recessed portion 17 and the vicinity of the recessed portion 17 and the rear surface of the light guide film 1 can be easily and reliably prevented Piece 8 is tightly closed.

The light guide film 1 has flexibility. Since the light guide film 1 has flexibility, it is possible to suppress damage to the reflection sheet 8 disposed on the back side. The light guide film 1 needs to transmit light and is therefore transparent. The light guide film 1 is composed of a synthetic resin as a main component.

<LED light source>

The plurality of LED light sources 2 are arranged along the end surface of the light guide film 1. The plurality of LED light sources 2 are arranged such that the light exit surface and the end face of the light guide film 1 face (or abut).

<Reflecting sheet>

The reflection sheet 8 reflects light emitted from the back of the light guide film 1 toward the front side. Examples of the reflective sheet 8 include: a white sheet in which a filler is dispersed in a base resin such as polyester; and a mirror sheet in which the surface of a film formed of polyester is vapor-deposited with metals such as aluminum and silver to improve specular reflectivity Wait.

＜Front brightness enhancement function＞

Next, referring to FIGS. 5 and 6, the function of improving the front brightness of the lower light diffusion sheet 4 and the backlight unit will be described. First, referring to FIG. 5, the light emission characteristics of the backlight unit using the conventional lower light diffusion sheet 114 will be described. The light rays emitted from the plurality of LED light sources 2 enter the light guide film 1 from an end surface (incident end surface) opposed to the plurality of LED light sources 2 substantially perpendicularly, and propagate toward the end surface opposite to the incident end surface from the light guide film 1 Surface shot. The light emitted from the surface of the light guide film 1 has directivity including a large amount of light inclined in the light emission direction of the plurality of LED light sources 2. Then, the light emitted from the surface of the light guide film 1 enters from the back of the lower light diffusion sheet 114 and is isotropically diffused, and then exits from the surface of the lower light diffusion sheet 114. However, the light emitted from the lower light diffusion sheet 114 diffuses in a direction parallel to the light directions of the plurality of LED light sources 2 by the above-described isotropic diffusion, so that the Since the incident angle is likely to vary, it is difficult to effectively refract the first lug sheet 5 to the normal direction side. Therefore, the backlight unit using the conventional lower light diffusion sheet 114 cannot sufficiently increase the brightness in the front direction.

On the other hand, as shown in FIG. 6, in the backlight unit using the lower light diffusion sheet 4, the lower light diffusion sheet 4 has diffusion based on the direction perpendicular to the light directions of the plurality of LED light sources 2. Function and light condensing function based on the direction parallel to the light direction, it is possible to maintain the optimal angle of incidence of the light that is not incident at the optimal angle with respect to the column of the conventional backlight unit with respect to the column of the column , And make it spread in the direction of the column. Therefore, the backlight unit using the lower light diffusion sheet 4 can effectively refract the light incident on the first prism sheet 5 toward the normal direction side by the first prism sheet 5. Therefore, the backlight unit using the lower light diffusion sheet 4 can sufficiently increase the brightness in the front direction.

<Advantages>

For this optical sheet (lower light diffusion sheet 4), in the backlight unit provided with the first prism sheet 5 in which the direction of the prism row is arranged in a direction perpendicular to the light direction of the LED light source 2, if the By arranging the specific direction so that the rear side of the one sheet 5 is perpendicular to the direction of the row of rows, the front brightness of the backlight unit can be sufficiently improved.

In addition, since the optical sheet is the lower light diffusion sheet 4 provided with the base material layer 11 and the light diffusion layer 12 laminated on the surface side of the base material layer 11, it is easy to improve the light condensing function based on the specific direction and to The diffusion function based on the direction perpendicular to the specific direction. In particular, for this optical sheet, since the light diffusion layer 12 has a plurality of beads 14 and its adhesive 15, it is easy to more surely improve the light-concentrating function based on the above-mentioned specific direction and perpendicular to the specific direction Direction-based diffusion function.

With regard to the backlight unit, since the specific direction of the lower light diffusion sheet 4 is parallel to the light directions of the plurality of LED light sources 2 and perpendicular to the direction of the row of the first row of sheets 5, the light is transmitted through the lower The light diffused by the light diffusion sheet 4 is condensed in the vertical direction of the column of the first column 5 and diffused in the direction of the column of columns, thereby sufficiently improving the front brightness.

<Manufacturing method of lower light diffusion sheet>

Next, the method for manufacturing the lower light diffusion sheet 4 will be described. The manufacturing method of this downward light diffusion sheet includes a resin film conveying step, an ultraviolet curing resin composition supply step, an ultraviolet irradiation step, and a light diffusion layer laminating step.

(Manufacturing equipment)

The manufacturing method of the lower light diffusion sheet is performed using, for example, the manufacturing apparatus 21 of FIG. 7. The manufacturing apparatus 21 has a pair of pressure rollers 22 and 23 arranged adjacent to each other in parallel. The pair of pressure rollers 22 and 23 is configured to include a temperature control unit and can control the surface (peripheral surface) temperature to an optimal temperature. As the pair of pressing rollers 22 and 23, a metal elastic roller including a metal roller and a flexible roller whose surface is covered with an elastic body is preferably used. In addition, one pressing roller 23 has the reverse shape of the back surface shape of the lower light diffusion sheet 4 having the grating shape 16 described above on the surface.

(Resin film transportation process)

In the above-mentioned resin film conveying step, the belt-shaped resin film X is conveyed to the surfaces of the pair of pressure rollers 22 and 23. Specifically, in the above-mentioned resin film conveying step, the resin film X forming the base material layer 11 of the lower light diffusion sheet 4 is conveyed between the pair of press rollers 22 and 23.

(Supply process of ultraviolet curable resin composition)

In the ultraviolet curable resin composition supply step, the ultraviolet curable resin composition is supplied between the resin film X and one pressure roller 23. In the ultraviolet curable resin composition supply step, the resin film X and the ultraviolet curable resin composition supplied to one side of the resin film X are pressed by a pair of pressure rollers 22 and 23. In this ultraviolet curable resin composition supply step, the grating shape 16 is transferred on the outer surface (one lateral side) of the ultraviolet curable resin composition laminated on one lateral side of the resin film X.

(Ultraviolet irradiation process)

In the ultraviolet irradiation step, the ultraviolet curable resin composition transferred with the grating shape 16 in the ultraviolet curable resin composition supply step is irradiated with ultraviolet rays, and the ultraviolet curable resin composition is cured. In this ultraviolet irradiation step, the grating shape 16 is formed on one side of the resin film X.

The quantum dot may be formed of PbS, PbSe, CdSe, CdS, InAs, or InP, but is not limited thereto.

(Light diffusion layer lamination process)

In the light diffusion layer lamination step, after the ultraviolet irradiation step, a coating liquid including a plurality of beads 14 and a binder composition is applied to the other side surface of the resin film X, and the coating liquid after further coating is dried and Curing. In this light diffusion layer lamination step, the light diffusion layer 12 is laminated on the other side of the resin film X.

<Advantages>

The method for manufacturing the lower light diffusion sheet can easily and reliably manufacture the lower light diffusion sheet 4 that can sufficiently increase the front brightness of the backlight unit.

[Second Embodiment]

<Lower light diffusion sheet>

The lower light diffusion sheet 31 of FIG. 8 is used in the backlight unit of FIG. 1 instead of the lower light diffusion sheet 4 of FIG. 2. The lower light diffusion sheet 31 includes a base layer 11, a light diffusion layer 12 disposed on the front side of the base layer 11, and a back layer 32 laminated on the back side of the base layer 11. In addition, the lower light diffusion sheet 31 is provided with a plurality of convex portions 34 as anti-adhesion portions in a scatter shape on the back surface of the back layer 32 (the back surface of the lower light diffusion sheet 31 ). The plurality of protrusions 34 are integrally formed with the back layer 32 (that is, the plurality of protrusions 34 and the back layer 32 are integrally formed). The lower light diffusion sheet 31 is formed in a square shape in plan view. The lower light diffusion sheet 31 is composed of the base material layer 11, the light diffusion layer 12, the back layer 32, and the plurality of convex portions 34 (that is, the lower light diffusion sheet 31 does not have the base material layer 11, the light diffusion layer 12, Other layer than the back layer 32 and the plurality of convex portions 34). The base material layer 11 and the light diffusion layer 12 of the lower light diffusion sheet 31 are the same as the lower light diffusion sheet 4 of FIG. 2, so the same reference numerals are given and their description is omitted.

The specific direction in the plane of the lower light diffusion sheet 31 is parallel to the light directions of the plurality of LED light sources. In addition, the above-mentioned specific direction of the lower light diffusion sheet 31 is perpendicular to the direction of the row of the first row of sheets arranged directly on the surface side of the lower sheet of light diffusion 31 (that is, arranged without other optical sheets). . The lower light diffusion sheet 31 is an optical sheet for a liquid crystal display device that has a specific optical function for transmitted light (light incident from the rear side and exiting from the front side), and has a specific direction in the plane as the optical function The light-concentrating function based on the reference and the diffusion function based on the direction perpendicular to the specific direction.

The back layer 32 needs to transmit light and is therefore transparent. The back layer 32 is formed with a synthetic resin as a main component. The main component of the back layer 32 may be the same as the main component of the back layer 13 of the lower light diffusion sheet 4 described above.

The lower light diffusion sheet 31 has a plurality of grating shapes 33 oriented in the specific direction in a region where the plurality of convex portions 34 are not present on the back surface of the back layer 32. The grating shape 33 has a shape in which a plurality of uneven stripes are formed along the above-mentioned specific direction. The lower light diffusion sheet 31 includes the grating shape 33, and thus the light reaching the grating shape 33 can be diffused in the width direction of the grating shape 33 (the vertical direction of the average orientation direction of the plurality of uneven lines). As a result, the lower light diffusion sheet 31 exhibits the light-condensing function based on the specific direction and the diffusion function based on the direction perpendicular to the specific direction. Note that the specific shape of the grating shape 33 is the same as that of the lower light diffusion sheet 4 of FIG. 2, so its description is omitted.

As shown in FIGS. 9 and 10, each convex portion 34 has a flat half-split rotation ellipsoid shape. A plurality of protrusions 34 are randomly (not regularly) protrudingly provided on the back surface of the back layer 32. The lower light diffusion sheet 31 is provided with a plurality of convex portions 34 randomly protruding, so that it is possible to prevent the occurrence of moiré due to the plurality of convex portions 34. In addition, the "flat half-segmented spheroid shape" refers to a shape in which a virtual spheroid formed by rotating an ellipse about the short axis as a center is divided into half planes including the long axis and perpendicular to the short axis. In addition, the "half-segmented spheroid shape" is not limited to a strict half-segmented spheroid shape, and includes a base having a perfect circular shape and an outer surface formed into a dome shape by a curved surface.

The lower limit of the average radius of curvature of the tip of the convex portion 34 is preferably 5 μm, and more preferably 10 μm. On the other hand, the upper limit of the average radius of curvature of the tip of the convex portion 34 is preferably 50 μm, and more preferably 25 μm. If the average radius of curvature is less than the lower limit, there is a risk of damage to the surface of the light guide film disposed on the back side of the lower light diffusion sheet 31. Conversely, if the average radius of curvature exceeds the upper limit, the contact area between the convex portion 34 and the surface of the light guide film becomes larger, and there is a risk of uneven brightness due to light incident on the contact portion. In addition, the "average radius of curvature of the tip portion of the convex portion" refers to the average value of the radius of curvature of the portion of the ten convex portions that are arbitrarily extracted and farthest from the average interface of the back surface of the back layer.

The lower limit of the average diameter D ₂ of the convex portion 34 is preferably 25 μm, more preferably 27 μm, and still more preferably 30 μm. On the other hand, the upper limit of the average diameter D ₂ of the convex portion 34 is preferably 45 μm, more preferably 42 μm, and still more preferably 40 μm. If the average diameter D _{2 of the} convex portion 34 is less than the above lower limit, in order to sufficiently ensure the height H of the convex portion 34, the radius of curvature of the tip portion of the convex portion 34 becomes too small, and is present in the lower light diffusion sheet 31 The surface of the light guide film on the back side creates a risk of damage. Conversely, if the average diameter D _{2 of the} convex portion 34 exceeds the upper limit, the height H of the convex portion 34 becomes too large in order to maintain the radius of curvature of the tip portion of the convex portion 34 in a preferred range, and there is a violation of the backlight unit The risk of thinning requirements. In addition, the "diameter" of each convex part means the diameter of a base. In addition, the "average diameter of convex portions" refers to a value obtained by arbitrarily extracting 10 convex portions and averaging the median value of the maximum diameter and the minimum diameter on the base of each convex portion.

The lower limit of the average height H of the convex portion 34 is preferably 2 μm, and more preferably 3 μm. On the other hand, the upper limit of the average height H of the convex portion 34 is preferably 5 μm, and more preferably 4 μm. If the average height H of the convex portion 34 is less than the above lower limit, the lower light diffusing sheet 31 and the light guide film are easily contacted even in the portion other than the convex portion 34, and there is light due to the light incident on the contact portion Risk of uneven brightness. Conversely, if the average height H of the convex portion 34 exceeds the above upper limit, there is a risk of violating the requirement for thinning the backlight unit. It should be noted that the "height" of each convex portion refers to the length of each convex portion from the base to the protruding end, and the "average height of the convex portions" refers to: arbitrarily extracting 10 convex portions from the base to the protruding end. The average length value.

The plurality of convex portions 34 preferably make their heights H uniform. The upper limit of the coefficient of variation of the height H of the plurality of convex portions 34 is preferably 0.2, more preferably 0.1, and still more preferably 0.05. If the coefficient of variation of the height H of the plurality of protrusions 34 exceeds the upper limit, the height H of the plurality of protrusions 34 becomes uneven, and the load is biased toward the protrusions 34 having a large height, and thus exists on the surface of the light guide film Risk of injury. On the other hand, the lower limit of the coefficient of variation of the height H of the plurality of convex portions 34 is not particularly limited, and may be 0, for example. In addition, the "variation coefficient" of the height of a some convex part means the value which divided the standard deviation of the height of 20 convex parts arbitrarily extracted by the average height.

The lower limit of the ratio (H/D ₂ ) of the average height H of the plurality of convex portions 34 to the average diameter D ₂ is preferably 0.08, and more preferably 0.09. On the other hand, the upper limit of the above ratio (H/D ₂ ) is preferably 0.2, more preferably 0.15, and still more preferably 0.12. If the above ratio (H/D ₂ ) is less than the above lower limit, the contact area between the plurality of convex portions 34 and the surface of the light guide film becomes larger, and there is a risk of uneven brightness due to light incident on the contact portion. Conversely, if the above ratio (H/D ₂ ) exceeds the above upper limit, there is a risk that the tips of the plurality of convex portions 34 are too sharp and damage the surface of the light guide film.

The lower limit of the average pitch of the convex portions 34 is preferably 100 μm, more preferably 200 μm, and still more preferably 300 μm. On the other hand, the upper limit of the average pitch of the convex portions 34 is preferably 1.0 mm, more preferably 0.7 mm, and still more preferably 0.5 mm. If the average pitch of the convex portions 34 is less than the above lower limit, the number of convex portions 34 becomes too large, and there is a risk of damage to the surface of the light guide film. Conversely, if the average pitch of the convex portions 34 exceeds the above upper limit, the number of convex portions 34 is insufficient, and there is a risk that adhesion cannot be sufficiently prevented. In addition, the "average pitch" of a convex part means arbitrarily extracting 10 convex parts, and the average value of the pitch of each extracted convex part and the other convex parts which are most adjacent to these convex parts.

The lower limit of the occupied area ratio of the plurality of convex portions 34 is preferably 2%, more preferably 3%, and still more preferably 4%. On the other hand, the upper limit of the occupied area ratio of the plurality of convex portions 34 is preferably 10%, more preferably 8%, and still more preferably 6%. If the occupied area ratio of the plurality of convex portions 34 is less than the above lower limit, there is a risk that adhesion cannot be sufficiently prevented. Conversely, if the occupied area ratio of the plurality of convex portions 34 exceeds the upper limit, there is a risk of damage to the surface of the light guide film. In addition, the "occupation area ratio of a plurality of convex portions" refers to the ratio of the occupation area of the convex portions with respect to the planar area of the surface on which the plurality of convex portions are formed.

The lower limit of the ratio of the average diameter D ₂ of the convex portion 34 to the average particle diameter of the beads 14 is preferably 3, more preferably 4, and even more preferably 5. On the other hand, the upper limit of the above 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 34 is insufficient, and there is a risk that it is difficult to sufficiently take in light through the convex portion 34. Conversely, if the above ratio exceeds the upper limit, the curved shape of the convex portion 34 becomes too gentle, and there is a risk that it is difficult to take in light through the convex portion 34.

The plurality of convex portions 34 are formed with synthetic resin as a main component. In addition, the plurality of convex portions 34 do not contain beads inside. In the lower light diffusion sheet 31, since the plurality of convex portions 34 do not contain beads, it is possible to prevent the surface of the light guide film disposed on the back side of the lower light diffusion sheet 31 from being damaged due to the falling off of the beads Case.

<Manufacturing method of lower light diffusion sheet>

Next, the method for manufacturing the lower light diffusion sheet 31 will be described. The method for manufacturing the lower light diffusion sheet 31 includes a resin film conveying step, an ultraviolet curable resin composition supply step, an ultraviolet irradiation step, and a light diffusion layer lamination step. For the lower light diffusion sheet 31, instead of the above-mentioned one pressure roller 23, the reverse shape of the back surface shape of the lower light diffusion sheet 31 having the above-mentioned plurality of convex portions 34 and the grating shape 33 on the surface is used Other than this, the pressure roller can be manufactured by the same method as the manufacturing method of the lower light diffusion sheet 4 described above.

<Advantages>

As for the lower light diffusion sheet 31, as described above, in the backlight unit provided with the first prism sheet in which the direction of the prism row is arranged in the direction perpendicular to the light direction of the LED light source, if the By arranging the specific direction perpendicularly to the direction of the 珜鏡 row on the back side of a 珜鏡 row, the front brightness of the backlight unit can be sufficiently improved. In addition, since the lower light diffusion sheet 31 has a plurality of convex portions 34 in a scatter shape on the back surface, the lower light diffusion sheet 31 and the light guide film disposed on the back side of the lower light diffusion sheet 31 pass through the multiple The convex portions 34 partially abut. Therefore, the lower light diffusion sheet 31 can prevent adhesion to the light guide film disposed on the back side. Furthermore, in the lower light diffusion sheet 31, since the convex portion 34 is a flat half-divided rotational ellipsoid, the curved surface of the tip portion (lower end portion) of the plurality of convex portions 34 becomes relatively gentle, thereby It is possible to prevent damage to the surface of the light guide film disposed on the back side.

The method for manufacturing the lower light diffusion sheet can easily and reliably manufacture the lower light diffusion sheet 31. The lower light diffusion sheet 31 can sufficiently improve the front brightness of the backlight unit and can prevent the light guide disposed on the back side The damage of the film can prevent the adhesion to the light guide film.

[Third Embodiment]

<Lower light diffusion sheet>

The lower light diffusion sheet 36 of FIG. 11 is used in the backlight unit of FIG. 1 instead of the lower light diffusion sheets 4 and 31 of FIGS. 2 and 8. The lower light diffusion sheet 36 has the same structure as the lower light diffusion sheet 31 of FIG. 8 except that it has a grating shape 37 continuous with the grating shape 33 on the back side of the plurality of convex portions 34.

<Manufacturing method of light diffusion sheet>

Next, a method for manufacturing the lower light diffusion sheet 36 will be described. The method for manufacturing the lower light diffusion sheet 36 includes a resin film conveying step, an ultraviolet curable resin composition supply step, an ultraviolet irradiation step, and a light diffusion layer laminating step. For the lower light diffusion sheet 36, instead of the above-mentioned one pressing roller 23, a surface having the above-mentioned plurality of convex portions 34, a grating shape 33, and continuous to the grating shape 33 and formed on the plurality of convex portions is used. The back side of the grating shape 37 on the back side of the lower light diffusion sheet 36 of the reverse shape of the grating shape 37 can be manufactured by the same method as the manufacturing method of the lower light diffusion sheet 4 described above .

<Advantages>

The lower light diffusion sheet 36 also has a grating shape 37 continuous with the grating shape 33 on the back side of the plurality of convex portions 34, so that the front brightness of the backlight unit can be more accurately increased.

[Other embodiments]

It should be noted that the optical sheet and the backlight unit according to the present invention can be implemented in various modified and improved forms other than the above-mentioned forms. For example, the optical sheet is not limited to the lower light diffusion sheet having the above-mentioned configuration, and may be a microlens sheet in which a microlens array is arranged on the surface side of the base material layer.

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

The light diffusion layer does not necessarily need to be laminated on the front surface side of the base material layer, and may be laminated on the back surface side of the base material layer. In addition, the light diffusion layer does not need to have beads and its binder. For example, it may be a light diffusion layer in which an uneven shape is formed on the outer surface by embossing or the like.

In addition, the optical sheet may not include the above-mentioned back layer. As a configuration that does not include the above-mentioned back layer, for example, a configuration in which a grating shape is formed on the back surface of the base layer. In addition, as a configuration that does not include the above-mentioned back layer, a configuration in which a grating shape and a plurality of convex portions are formed on the back surface of the base material layer may also be mentioned. As a method of manufacturing such an optical sheet without a back layer, for example, a roll having a reverse shape of a grating shape on the surface, or a reverse shape of a grating shape and a plurality of convex portions, and a resin for forming a substrate layer are used An extrusion molding method in which the composition is supplied from the T-die between the press roll and other press rolls to transfer the shape.

In the case where the optical sheet has an anti-adhesion portion, the shape of the anti-adhesion portion is not limited to the shape of the above embodiment. The optical sheet may have, for example, a plurality of convex portions 44, 54, 64, and 74 as shown in FIGS. 12 to 15 as the anti-adhesion portion.

The convex portion 44 of FIG. 12 is formed in a truncated pyramid shape. Specifically, the convex portion 44 is formed in a quadrangular truncated cone shape whose base end side bottom surface area is larger than the front end side bottom surface area. The lower limit of the average height of the plurality of convex portions 44 is preferably 2 μm, and more preferably 3 μm. On the other hand, the upper limit of the average height is preferably 10 μm, and more preferably 7 μm. If the average height is less than the lower limit, there is a risk that the anti-sticking effect cannot be sufficiently obtained. Conversely, if the average height exceeds the upper limit, there is a risk that the convex portion 44 becomes unnecessarily large.

The lower limit of the ratio of the average height of the plurality of convex portions 44 to the average length of one side of the bottom surface on the base end side is preferably 0.05, and more preferably 0.1. On the other hand, the upper limit of the above ratio is preferably 1, more preferably 0.7, and still more preferably 0.5. If the above ratio is less than the above lower limit, there is a risk that the anti-sticking effect cannot be sufficiently obtained. Conversely, if the ratio exceeds the upper limit, there is a risk of damage to other members disposed on the back side.

The convex portion 54 of FIG. 13 is formed in a cylindrical shape, and in detail, is formed in a cylindrical shape. The average height of the plurality of convex portions 54 may be the same as the average height of the plurality of convex portions 44 described above. The ratio of the average height of the plurality of convex portions 54 to the average diameter may be the same as the ratio of the average height of the plurality of convex portions 44 to the average length of one side of the bottom surface on the base end side.

The convex portion 64 of FIG. 14 is formed in a truncated cone shape having a bottom surface area greater than the bottom surface area on the distal end side. The average height of the plurality of convex portions 64 may be the same as the average height of the plurality of convex portions 44 described above. In addition, the ratio of the average height of the plurality of convex portions 64 to the average diameter at the base end side may be the same as the ratio of the average height of the plurality of convex portions 44 to the average length at one side of the bottom surface on the base end side.

The convex portion 74 of FIG. 15 is formed in a trumpet shape whose diameter gradually decreases from the base end side toward the tip end side. The average height of the plurality of convex portions 74 may be the same as the average height of the plurality of convex portions 44 described above. In addition, the ratio of the average height of the plurality of convex portions 74 to the average diameter at the base end side may be the same as the ratio of the average height of the plurality of convex portions 44 to the average length at one side of the bottom surface on the base end side.

The optical sheet is also preferably arranged on the back surface of the sheet body obtained by bonding two prism sheets. It is difficult to form an air layer between the 珜鏡sheets after the two 鏜鏡sheets are bonded together, so the concealability is low. In contrast, in the backlight unit in which the optical sheet is arranged on the back surface of the sheet body, since the optical sheet can diffuse light in the width direction of the grating shape, the concealing effect can be sufficiently improved. In addition, in the case where the optical sheet is disposed on the back surface of the sheet body formed by laminating the two prism sheets, it is preferable that the direction of the prism rows of the prism sheet on the back side of the two prism sheets be the same as the above The specific directions in the plane are orthogonal.

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

The specific shape of the above-mentioned grating shape is not limited to the shape of the above-mentioned embodiment, and may be, for example, a shape having a concave portion having a U-shaped cross-section angle as shown in FIG. 16 or a concave portion having a triangular cross-section as shown in FIG. 17. The shape, the shape having a slit-like recess as shown in FIG. 18, and the like. In addition, the plurality of concave and convex stripes may be oriented in a direction perpendicular to the light exit direction of the light source.

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

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

In addition, even in the case where the backlight unit is an edge light type backlight unit, it is not necessary to be a single-sided edge light type backlight unit in which an LED light source is arranged along only one end surface of the light guide film, and may be along the light guide film. A pair of opposing end surfaces is provided with an edge light type backlight unit on both sides of the LED light source, and a full peripheral edge light type backlight unit with an LED light source is arranged along each end surface of the light guide film.

The backlight unit can be used in relatively large display devices such as personal computers, LCD TVs, mobile phone terminals such as smart phones, and portable information terminals such as tablet terminals.

Examples

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

[Example]

The resin film containing polyethylene terephthalate as the main component is transported to the surface of one roller and the other roller having a reverse shape with a grating shape on the surface, and ultraviolet rays are supplied between the one roller and the resin film Curable resin composition. The laminated body is pressed with a pair of pressure rollers in a state where the ultraviolet curable resin is laminated on the resin film, and the grating shape is transferred on the outer surface of the ultraviolet curable resin composition. Next, the ultraviolet curable resin composition to which the above-mentioned grating shape is transferred is irradiated with ultraviolet rays to cure the ultraviolet curable resin composition. Furthermore, a coating liquid containing a plurality of beads and a binder composition is applied to the surface of the resin film on the side where the ultraviolet curable resin composition is not laminated, and the applied coating liquid is dried and cured to form a light diffusion layer To obtain the light diffusion sheet of the embodiment. The average width of the concave portions of the plurality of concavo-convex stripes forming the grating shape of the light diffusion sheet is 9.3 μm, the average depth of the concave portions is 2.8 μm, the average pitch is 9.3 μm, and the standard deviation of the pitches of the multiple concavo-convex stripes is 6.54 μm. The standard deviation of the depth of each embossed strip is 1.13 μm, and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of embossed strips is 1.34 μm.

[Comparative example]

A light diffusion sheet of a comparative example was obtained in the same manner as the example except that the grating shape was not formed.

<Emitted light characteristics>

The light diffusing sheets of Examples and Comparative Examples are arranged on the surface of the light guide film of the edge light type backlight unit in which a plurality of LED lights are arranged along one end surface of the light guide film. In addition, the light-diffusion sheet of an Example is arrange|positioned so that the average orientation direction of a some uneven|corrugated strip may be parallel to the light direction of a some LED light source. In this state, the light is emitted from a plurality of LED light sources, using "EZContrast" manufactured by ELDIM, the LED light source side of the light direction of the LED light source is 90°, and the light emission direction side is -90°, and the backlight unit’s The light exit surface side was 0°, and the relationship between the exit angle and brightness of the exit light of each light diffusion sheet was measured using viewing angle characteristics in the range of 80° to -80°. The relationship between the output light angle and brightness of the light diffusion sheet of the example is shown in FIG. 19, and the relationship between the output light angle and brightness of the light diffusion sheet of the comparative example is shown in FIG. 20. In addition, the highest light-emitting angle measured from this viewing angle characteristic is shown in Table 1.

<Backlight brightness>

The light diffusion film of the example and the comparative example is placed between the light guide film of the backlight unit of the smartphone "iPhone (registered trademark) 6" made by Apple Inc. "PAR36-3A"), lights at a current of 40mA and a voltage of 18.05V. A color brightness meter "BM-7" made by Topcon was placed at a position 1 m in the vertical direction based on the light exit surface of the backlight unit, and the brightness of the central portion of the light exit surface of the backlight unit was measured at a measurement angle of 0.2° . The measurement results are shown in Table 1.

<Evaluation result>

As shown in FIG. 19, FIG. 20, and Table 1, it can be seen that the light diffusion sheet of the example has an excellent light-concentrating function toward the normal direction side compared to the light diffusion sheet of the comparative example, and can improve the brightness of the backlight unit. As shown in FIG. 19, FIG. 20, and Table 1, it can be seen that, compared with the light diffusion sheet of the comparative example, the light diffusion sheet of the embodiment has a light-gathering function based on the light directions of a plurality of LED light sources and a plurality of LEDs. The diffusion function based on the direction perpendicular to the light direction of the light source is more excellent.

Industrial availability

As described above, the optical sheet of the present invention can sufficiently improve the front brightness of the backlight unit, and therefore is suitable for various liquid crystal display devices such as high-quality transmissive liquid crystal display devices.

1‧‧‧Light-guiding film 2‧‧‧LED light source 3‧‧‧Optical sheet 4‧‧‧Lower light diffusion sheet 5‧‧‧‧1st prism sheet 6‧‧‧2nd prism sheet 7‧‧‧upper Light diffusion sheet 8‧‧‧Reflective sheet 11‧‧‧Base layer 12‧‧‧Light diffusion layer 13‧‧‧Back layer 14‧‧‧‧Bead 15‧‧‧Binder 16‧‧‧Grating shape 17‧‧ ‧Concave part 18‧‧‧Bulking part 21‧‧‧Manufacture device 22‧‧‧Press roller 23‧‧‧Press roller 31‧‧‧Lower light diffusion sheet 32‧‧‧Back layer 33‧‧‧Grating shape 34‧‧ ‧Convex part 36‧‧‧Lower light diffusion sheet 37‧‧‧Grating shape 44‧‧‧Convex part 54‧‧‧Convex part 64‧‧‧Convex part 74‧‧‧Convex part 101‧‧‧Backlight unit 102‧ ‧‧LED light source 103‧‧‧Light guide 104104‧‧‧Optical sheet 105‧‧‧Light diffusion sheet 106‧‧‧Leng film 114‧‧‧‧Lower light diffusion sheet

FIG. 1 is a schematic end view showing a backlight unit for a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a schematic enlarged end view showing the light diffusion sheet of the backlight unit of FIG. 1. FIG. 3 is a schematic back view of the light diffusion sheet of FIG. 2. FIG. 4 is an end view of the light diffusion sheet of FIG. 3 taken along line AA. FIG. 5 is a schematic diagram for explaining light emission characteristics in a conventional backlight unit. 6 is a schematic diagram for explaining light emission characteristics in the backlight unit of FIG. 1. FIG. 7 is a schematic diagram showing an apparatus for manufacturing the light diffusion sheet of FIG. 2. 8 is a schematic partial end view showing a light diffusion sheet of an embodiment different from the light diffusion sheet of FIG. 2. 9 is a schematic back view of the light diffusion sheet of FIG. 8. FIG. 10 is an end view of the BB line part of the light diffusion sheet of FIG. 9. 11 is a schematic back view showing a light diffusion sheet of an embodiment different from the light diffusion sheet of FIGS. 2 and 8. FIG. 12 is a schematic perspective view showing an example of the convex portion of the light diffusion sheet of FIGS. 8 and 11. 13 is a schematic perspective view showing a convex portion of an embodiment different from the convex portion of FIG. 12. 14 is a schematic perspective view showing a convex portion in an embodiment different from the convex portions of FIGS. 12 and 13. 15 is a schematic perspective view showing a convex portion in an embodiment different from the convex portions of FIGS. 12 to 14. FIG. 16 is a schematic end view showing a grating shape of another embodiment of the present invention. FIG. 17 is a schematic end view showing a grating shape of an embodiment different from the grating shape of FIG. 16. 18 is a schematic end view showing a grating shape in an embodiment different from the grating shapes of FIGS. 16 and 17. FIG. 19 is a graph showing the relationship between the light exit angle and the brightness of the light diffusion sheet of the embodiment. 20 is a graph showing the relationship between the light exit angle and the brightness of the light diffusion sheet of the comparative example. 21 is a schematic perspective view showing a conventional edge light type backlight unit.

1‧‧‧Light guide film

2‧‧‧LED light source

3‧‧‧Optical sheet

4‧‧‧Lower light diffusion sheet

5‧‧‧The first piece

6‧‧‧ 2nd piece

7‧‧‧Upper light diffuser

8‧‧‧Reflective film

11‧‧‧ Base layer

12‧‧‧ light diffusion layer

13‧‧‧Back

14‧‧‧ beads

15‧‧‧Binder

17‧‧‧recess

18‧‧‧Bulge

Claims (4)

A light diffusion sheet for a liquid crystal display device, characterized in that it is a light diffusion sheet for a liquid crystal display device that exhibits a specific optical function for transmitted light; as the optical function, it has a specific direction in a plane as a reference A light-concentrating function and a diffusion function based on a direction perpendicular to the specific direction; comprising a base material layer, a light diffusing layer laminated on one surface side of the base material layer, and a light-diffusing layer laminated on the base material layer A back layer on the back side of the; the light diffusion layer has a bead and an adhesive; and the light diffusion sheet is provided on the back side of one of the back layers to be oriented in the specific direction and direct light to the width direction A grating shape of diffused strips. The light diffusion sheet for a liquid crystal display device according to claim 1, wherein the grating shape presents a scratch or a hairline in the specific direction. The light diffusion sheet for a liquid crystal display device according to claim 1, wherein the haze value is 60% or more and 95% or less. A backlight unit for a liquid crystal display device, comprising: a light guide film that guides a light incident from an end surface to a surface side; one or more LED light sources arranged along the end surface of the light guide film; The light diffusion sheet of any one of claims 1 to 3 on the surface side of the light guide film; and a prism sheet arranged on the surface side of the light diffusion sheet; wherein the light The specific direction of the diffusion sheet is parallel to a light direction of the LED light source and perpendicular to the direction of a column of the column.

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