WO2017104677A1

WO2017104677A1 - Optical sheet for backlight unit and backlight unit

Info

Publication number: WO2017104677A1
Application number: PCT/JP2016/087122
Authority: WO
Inventors: 原田　賢一; 啓土波川; 忠仁福田; 有希松野
Original assignee: 恵和株式会社
Priority date: 2015-12-17
Filing date: 2016-12-13
Publication date: 2017-06-22

Abstract

The purpose of the present invention is to provide an optical sheet for a backlight unit with which the occurrence of hot spots can be suppressed. This optical sheet for a backlight unit is for a liquid crystal display device, with which light rays emitted from an LED light source are guided to the front surface side, the optical sheet being characterized by being provided with one or more resin layers and in that a plurality of fine grooves oriented in a specific direction are formed on the front surface side or reverse surface side of at least one of these resin layers. Preferably, the mean number of the plurality of fine grooves per unit length of the plurality of fine grooves in the direction perpendicular to the mean orientation direction is 10 to 10,000 grooves/mm. Preferably, the arithmetic mean roughness(Ra) of the direction perpendicular to the orientation direction of the plurality of fine grooves on the surface of the resin layer(s) on which the plurality of fine grooves are formed is 0.01 to 5 ìm. The plurality of fine grooves may c onstitute a diffraction grating.

Description

Optical sheet for backlight unit and backlight unit

The present invention relates to an optical sheet for a backlight unit and a backlight unit.

Liquid crystal display devices are widely used as flat panel displays taking advantage of thin, lightweight, low power consumption, etc., and their applications are such as TVs, personal computers, mobile phone terminals such as smartphones, and portable information terminals such as tablet terminals every year. It is expanding.

Such a liquid crystal display device is widely used as a backlight system that irradiates a liquid crystal panel from the back side, and is equipped with backlight units such as an edge light type (side light type) and a direct type. As an edge light type backlight unit 101 provided in such a liquid crystal display device, generally, as shown in FIG. 18, a light source 102 and a rectangular plate shape disposed so that an end thereof is along the light source 102. The light guide sheet 103, a plurality of optical sheets 104 disposed on the front surface side of the light guide sheet 103, and a reflection sheet 105 disposed on the back surface side of the light guide sheet 103. As the optical sheet 104, (1) a light diffusion sheet 106 that is superimposed on the surface side of the light guide sheet 103 and mainly has a light diffusion function, and (2) is superimposed on the surface side of the light diffusion sheet 106 for bottom, Prism sheet 107 having a function of refraction in the normal direction side, (3) Superimposing on the surface side of the prism sheet 107, and slightly diffusing the light rays, uneven brightness due to the shape of the prism portion of the prism sheet 107, etc. An upper light diffusion sheet 108 for suppression is used (see Japanese Patent Application Laid-Open No. 2005-77448).

JP 2005-77448 A

As the light source 102 provided in such a backlight unit 101, LEDs are widely used from the viewpoint of miniaturization and energy saving. However, a backlight unit using LEDs has a hot spot (on the display screen). In this case, a phenomenon in which bright and dark portions occur due to the local increase in luminance in the vicinity of the light source occurs, and this hot spot causes luminance unevenness of the liquid crystal display device. The cause of this is not clear, but although the conventional light diffusion sheet diffuses, it is considered that the hot spot is generated when the light beam of the highly directional LED is diffused. The occurrence of luminance unevenness due to the hot spots described above may become more conspicuous due to the thinning of the backlight unit, the use of high-brightness LEDs, the reduction in the number of LEDs, the enlargement of the liquid crystal display device, and the like.

In view of these inconveniences, the present inventors diligently studied and found that hot spots can be suppressed by disposing a predetermined plurality of fine grooves in the optical path in the backlight unit.

The present invention has been made in view of such circumstances, and an object thereof is to provide an optical sheet for a backlight unit and a backlight unit capable of suppressing hot spots.

An optical sheet for a backlight unit according to the present invention made to solve the above problems is an optical sheet for a backlight unit of a liquid crystal display device that guides a light beam emitted from an LED light source to the surface side. The resin layer is characterized in that a plurality of fine grooves oriented in a specific direction are formed on the front surface side or the back surface side of at least one of these resin layers.

The backlight unit optical sheet can suppress the occurrence of hot spots when used in a backlight unit using LEDs as a light source. Although the cause of this is not necessarily clear, since a plurality of fine grooves oriented in a specific direction are formed in the resin layer of the backlight unit optical sheet, the light beam that passes through the region defined by the plurality of fine grooves Is propagated in the width direction of a plurality of microgrooves, and it is considered that the generation of hot spots can be suppressed even for light beams of LEDs with high directivity.

The average number of the plurality of fine grooves per unit length in the direction perpendicular to the average orientation direction of the plurality of fine grooves is preferably 10 pieces / mm or more and 10,000 pieces / mm or less. As described above, when the average number of the micro-grooves per unit length in the direction perpendicular to the average orientation direction of the micro-grooves is within the above range, it passes through the region defined by the micro-grooves. The transmitted light is sufficiently propagated in the width direction of the plurality of fine grooves, and the generation of hot spots can be more reliably suppressed.

The arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves on the surface where the plurality of fine grooves of the resin layer is formed is preferably 0.01 μm or more and 5 μm or less. Thus, the occurrence of hot spots occurs when the arithmetic mean roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves on the surface of the resin layer on which the plurality of fine grooves are formed is within the above range. Can be easily and reliably suppressed.

The plurality of fine grooves may constitute a diffraction grating. As described above, when the plurality of micro grooves constitute a diffraction grating, a diffraction phenomenon occurs in which a certain path difference occurs between light beams passing through a region defined by the plurality of micro grooves, and this diffraction phenomenon causes a hot spot. It is easy to suppress generation | occurrence | production of this easily and reliably.

The optical sheet includes a base film, a light diffusion layer having a plurality of beads and a binder stacked on the base film, and a protective layer stacked on the back side of the base film. It may be a light diffusion sheet. Thus, when the optical sheet is a light diffusing sheet, it is easy to emit a light beam that is substantially uniform over the entire surface.

The plurality of fine grooves may be formed on the back side of the protective layer. Thus, when the plurality of fine grooves are formed on the back side of the protective layer, the air layer present on the back side of the protective layer when the backlight unit optical sheet is used in a backlight unit. The light beam passing through the region partitioned by the plurality of fine grooves is easily propagated sufficiently in the width direction of the plurality of fine grooves using the difference in refractive index.

The optical sheet may include a functional layer having an uneven shape on the surface. Thus, by providing a functional layer having a concavo-convex shape on the surface, it is easy to emit light that is substantially uniform over the entire surface.

It is preferable that one resin layer has a plurality of fine irregularities on the surface, and the plurality of fine grooves are formed on the surface of the resin layer having the plurality of fine irregularities. Thus, one resin layer has a plurality of fine irregularities on the surface, and the plurality of fine grooves are formed on the surface of the resin layer having the plurality of fine irregularities. Can be propagated in the width direction of the plurality of fine grooves and light can be diffused by the plurality of fine irregularities. Thereby, a moire prevention effect, a color separation prevention effect, a viewing angle expansion effect, etc. can be improved.

Further, the backlight unit of the liquid crystal display device according to the present invention, which has been made to solve the above problems, includes a light guide film or light guide plate that guides light incident from the end face side to the surface side, and the light guide film or light One or a plurality of LED light sources disposed on the end face side of the guide plate and emitting light to the end face of the light guide film or the light guide plate, and the optical sheet superimposed on the surface side of the light guide film or the light guide plate With.

Since the backlight unit of the liquid crystal display device includes the optical sheet, generation of hot spots can be suppressed as described above.

The optical sheet may be directly superimposed on the surface of the light guide film or light guide plate. As described above, the optical sheet is directly superimposed on the surface of the light guide film or the light guide plate, so that generation of hot spots can be sufficiently suppressed.

In plan view, the average orientation direction of the plurality of fine grooves of the optical sheet on the basis of the average direction of light rays from the LED light source in the light guide film or light guide plate is preferably ± 45 ° or less. Thus, when the average orientation direction of the plurality of fine grooves of the optical sheet is equal to or less than the upper limit, the occurrence of hot spots can be easily and reliably suppressed.

In the present invention, “front side” means the viewer side in the liquid crystal display device, and “back side” means the opposite. “Specific direction” means a specific direction. “Resin layer” refers to a layer mainly composed of synthetic resin. The “main component” refers to a component having the highest content, for example, a component having a content of 50% by mass or more. “Diffraction grating” refers to a structure that diffracts incident light. The “average orientation direction of a plurality of microgrooves” refers to a value obtained by arbitrarily extracting 20 microgrooves and averaging the orientation directions of straight lines passing through both ends of the extracted microgrooves in the longitudinal direction. Further, the “average number of a plurality of fine grooves” means an average value of the number of a plurality of fine grooves present at any ten locations. “Arithmetic average roughness (Ra)” refers to a value with a cutoff λc of 0.8 mm and an evaluation length of 4 mm in accordance with JIS-B0601: 1994. "The average direction of the light beam from the LED light source in the light guide film or light guide plate" means the maximum intensity of the incident direction of the light beam emitted from the LED light source in the light guide film or light guide plate when viewed from the surface side. The direction in which light is emitted.

As described above, the optical sheet for a backlight unit and the backlight unit of the present invention can suppress the occurrence of hot spots.

It is a typical end view showing a backlight unit according to an embodiment of the present invention. It is a typical partial enlarged view which shows the optical sheet, light guide film, and light source of the backlight unit of FIG. FIG. 3 is a schematic enlarged back view of the optical sheet in FIG. 2. FIG. 3 is an enlarged end view taken along line AA of the optical sheet of FIG. FIG. 2 is a schematic plan view showing hot spots in the backlight unit of FIG. 1. It is a typical top view for demonstrating the brightness nonuniformity reduction function in the backlight unit of FIG. It is a typical end view which shows the optical sheet which concerns on the form different from the optical sheet of FIG. It is a typical end view which shows the optical sheet which concerns on the form different from the optical sheet of FIG.2 and FIG.7. It is a typical end view which shows the optical sheet which concerns on the form different from the optical sheet of FIG.2, FIG7 and FIG.8. FIG. 10 is a schematic end view showing an optical sheet according to a different form from the optical sheets of FIG. 2 and FIGS. FIG. 11 is a schematic end view showing an optical sheet according to a different form from the optical sheets of FIGS. 2 and 7 to 10. FIG. 12 is a schematic end view showing an optical sheet according to a different form from the optical sheets of FIGS. 2 and 7 to 11. FIG. 13 is a schematic enlarged back view of the optical sheet of FIG. 12. FIG. 13 is a schematic enlarged back view for explaining a plurality of fine grooves of an optical sheet according to a different form from the optical sheets of FIGS. 2 and 7 to 12. FIG. 6 is a schematic end view showing a fine groove according to another embodiment of the present invention. FIG. 16 is a schematic end view showing a fine groove according to a form different from the fine groove of FIG. 15. FIG. 17 is a schematic end view showing a fine groove according to a form different from the fine groove of FIGS. 15 and 16. It is a typical perspective view which shows the conventional edge light type backlight unit. No. It is a partial expansion plane photograph of 1 base film. No. 2 is a partially enlarged plan view of a base film of No. 2; No. 3 is a partially enlarged plan view of a substrate film 3. No. 1 in Example 1. It is a side view photograph of 1 light diffusion sheet. No. in the comparative example. 5 is a side photograph of the light diffusing sheet of FIG.

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

[First embodiment]
[Backlight unit]
The backlight unit of the liquid crystal display device of FIG. 1 is an edge light type backlight unit, and is a backlight unit of a liquid crystal display device that guides light emitted from one or a plurality of LED light sources 2 to the surface side. The backlight unit includes a light guide film 1 that guides light incident from the end surface to the surface side, and a plurality of LED light sources 2 that are disposed on the end surface side of the light guide film 1 and emit light to the end surface of the light guide film 1. And a plurality of optical sheets 3 superimposed on the surface side of the ride guide film 1. As the plurality of optical sheets 3, a light diffusion sheet (lower light diffusion sheet 4) disposed on the surface side of the light guide film 1 and a first disposed on the surface side of the lower light diffusion sheet 4. A prism sheet 5, a second prism sheet 6 disposed on the surface side of the first prism sheet 5, and a light diffusion sheet (upper light diffusion sheet 7) disposed on the surface side of the second prism sheet 6. Have The backlight unit further includes a reflection sheet 8 disposed on the back side of the light guide film 1. The lower light diffusion sheet 4 condenses (condenses and diffuses) the light incident from the back surface side while diffusing the light rays. The first prism sheet 5 and the second prism sheet 6 refract light rays incident from the back side toward the normal direction side. Specifically, in the first prism sheet 5 and the second prism sheet 6, the ridge line directions of the projecting prism portions are orthogonal, and the first prism sheet 5 radiates the light incident from the lower light diffusion sheet 4. Refracted in the direction perpendicular to the direction and in the normal direction, and further refracts the light emitted from the first prism sheet 5 so that the second prism sheet 6 travels substantially perpendicular to the back surface of the liquid crystal display element. . The upper light diffusing sheet 7 diffuses light incident from the back side to some extent to suppress luminance unevenness caused by the shape of the protruding prism portions of the first prism sheet 5 and the second prism sheet 6. The reflection sheet 8 reflects the light beam emitted from the back surface side of the light guide film 1 to the front surface side and makes it incident on the light guide film 1 again.

<Light diffusion sheet for lower use>
As shown in FIG. 2, the lower light diffusion sheet 4 is directly superimposed on the surface of the light guide film 1 (without other sheets or the like). The lower light diffusion sheet 4 is laminated on the base film 11, the surface side of the base film 11, the light diffusion layer 12 having a plurality of beads 14 and its binder 15, and the back side of the base film 11. The protective layer 13 is provided. The lower light diffusion sheet 4 is composed of three layers: a base film 11, a light diffusion layer 12 that is directly laminated on the surface of the base film 11, and a protective layer 13 that is directly laminated on the back surface of the base film 11. (There are no layers other than the base film 11, the light diffusion layer 12, and the protective layer 13). The lower light diffusion sheet 4 is formed in a planar view shape. As will be described later, the lower light diffusion sheet 4 has a plurality of fine grooves 16 formed on the back surface of the protective layer 13, and is configured as an optical sheet for a backlight unit of the present invention.

(Base film)
The base film 11 is a resin layer mainly composed of a synthetic resin. Since the base film 11 is required to transmit light, the base film 11 is formed mainly of a transparent, particularly colorless and transparent synthetic resin. The main component of the base film 11 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending performance is particularly preferable.

The lower limit of the average thickness of the base film 11 is preferably 10 μm, more preferably 35 μm, and even more preferably 50 μm. On the other hand, the upper limit of the average thickness of the base film 11 is preferably 500 μm, more preferably 250 μm, and even more preferably 188 μm. If the average thickness of the base film 11 is less than the lower limit, curling may occur when the light diffusion layer 12 is formed by coating. Further, if the average thickness of the base film 11 is less than the lower limit, there is a possibility that bending is likely to occur. On the contrary, when the average thickness of the base film 11 exceeds the above upper limit, the luminance of the liquid crystal display device may be lowered and the liquid crystal display device may not be required to be thinned. Note that “average thickness” refers to an average value of thicknesses at arbitrary 10 points.

(Light diffusion layer)
The light diffusion layer 12 is a resin layer mainly composed of a synthetic resin. The light diffusion layer 12 constitutes the outermost surface of the lower light diffusion sheet 4. The light diffusion layer 12 contains a plurality of beads 14 dispersed at substantially equal density. The beads 14 are surrounded by a binder 15. The light diffusion layer 12 includes a plurality of beads 14 in a dispersed manner, thereby diffusing light transmitted from the back surface side to the front surface side substantially uniformly. Further, the light diffusion layer 12 has fine irregularities formed substantially uniformly on the surface by a plurality of beads 14, and the concave and convex portions of the fine irregularities are formed in a lens shape. The light diffusing layer 12 exhibits an excellent light diffusing function due to the lens action of such fine unevenness, and the refractive function that refracts the transmitted light to the normal direction side due to this light diffusing function and the transmitted light to the normal line. It has a light condensing function that condenses macroscopically in the direction.

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

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

The lower limit of the average particle diameter of the beads 14 is preferably 1 μm, more preferably 2 μm, and even more preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the beads 14 is preferably 50 μm, more preferably 20 μm, and even more preferably 15 μm. If the average particle diameter of the beads 14 is less than the above lower limit, the unevenness of the surface of the light diffusion layer 12 becomes small, and the light diffusibility necessary for the light diffusion sheet may not be satisfied. On the contrary, if the average particle diameter of the beads 14 exceeds the upper limit, the thickness of the lower light diffusion sheet 4 may increase, and uniform diffusion may be difficult.

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

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

(Protective layer)
The protective layer 13 is a resin layer mainly composed of synthetic resin. A plurality of fine grooves 16 are formed on the back surface of the protective layer 13. The plurality of fine grooves 16 preferably constitute a diffraction grating. The fine groove 16 is preferably formed in a hairline shape. The lower light diffusion sheet 4 has a plurality of fine grooves 16 formed on the back surface side of the protective layer 13, so that the back surface of the protective layer 13 is used when the lower light diffusion sheet 4 is used in a backlight unit. A light beam passing through a region defined by the plurality of microgrooves 16 is easily propagated sufficiently in the width direction of the plurality of microgrooves using a difference in refractive index with the air layer present on the side. Moreover, since the plurality of fine grooves 16 are formed on the back surface side of the protective layer 13 in the lower light diffusion sheet 4, the surface of the light guide film 1 and the back surface of the protective layer 13 are in partial contact. Therefore, the lower light diffusion sheet 4 can prevent sticking with the light guide film 1. Further, the lower light diffusing sheet 4 has a diffraction phenomenon in which a certain path difference is generated between light beams passing through a region defined by the plurality of fine grooves 16 by the plurality of fine grooves 16 constituting a diffraction grating. Occurring and it is easy to suppress the occurrence of hot spots easily and reliably by this diffraction phenomenon.

As shown in FIG. 3, the plurality of fine grooves 16 are formed substantially uniformly (substantially at the same density) over the entire area of the back surface of the protective layer 13. Each fine groove 16 has a substantially U-shaped cross section (that is, each fine groove 16 is not formed in a triangular cross section). Since each fine groove 16 is configured to have a substantially U-shaped cross section, the diffusion direction of light rays is appropriately adjusted, and the hot spot relaxation effect can be improved. Moreover, the mass productivity of the lower light diffusion sheet 4 can be improved because each fine groove 16 has a substantially U-shaped cross section. As shown in FIGS. 2 to 4, the plurality of fine grooves 16 have a longitudinal direction along a direction parallel to one end of the back surface of the protective layer 13. Specifically, the plurality of fine grooves 16 have a longitudinal direction along the average direction of light rays from the plurality of LED light sources 2. Further, the orientation direction of each fine groove 16 is random (that is, the orientation direction of each fine groove 16 is not completely coincident). Thus, by making the orientation direction of each microgroove 16 random, it is possible to suppress the occurrence of rainbow unevenness in the liquid crystal display device due to the plurality of microgrooves 16. The plurality of fine grooves 16 are preferably formed independently for controlling the light diffusion direction, but some of the fine grooves 16 may cross each other.

In plan view, the upper limit of the average orientation direction of the plurality of fine grooves 16 on the basis of the average direction of light rays from the LED light source 2 in the light guide film 1 is preferably ± 45 °, more preferably ± 15 °, ± 0 ° is more preferable. If the average orientation direction exceeds the upper limit, it may be difficult to propagate light rays in a direction perpendicular to the light emission direction of the plurality of LED light sources 2 and in a horizontal direction. In contrast, the backlight unit can easily and reliably suppress the occurrence of hot spots when the average orientation direction is not more than the upper limit.

As shown in FIG. 3, the plurality of fine grooves 16 are formed in an elongated and substantially linear shape in plan view. Further, the width of each fine groove 16 changes randomly along the longitudinal direction of the fine groove 16. The longitudinal lower limit of the average length L ₁ of the plurality of fine grooves 16 is preferably at least 2 times the average width L _2, 3 times or more is more preferable. On the other hand, the longitudinal direction of the average maximum length L ₁ of the plurality of fine grooves 16, but may be continuous across the two ends of the protective layer 13 without particularly limited, for example, the average width L ₂ On the other hand, it is preferably 10,000 times or less and more preferably 5000 times or less. When the longitudinal direction of the average length L ₁ of the plurality of fine grooves 16 is less than the above lower limit, there may not be sufficiently increased the amount of light propagating in the width direction of the plurality of fine grooves 16. Conversely, when the average length L ₁ longitudinal plurality of the fine groove 16 exceeds the upper limit, and a plurality of fine grooves 16 in order to suppress the occurrence of rainbow stains of the liquid crystal display device random orientation density It may be difficult to form. The “average length in the longitudinal direction of the plurality of fine grooves” refers to the average value of the lengths in the longitudinal direction at the average interface of the resin layers of the 20 fine grooves extracted arbitrarily.

The lower limit of the average width _{L 2} of the plurality of fine grooves 16, 10 nm are preferred, more preferably 50 nm, more preferably 100 nm. On the other hand, the upper limit of the average width _{L 2} of the plurality of fine grooves 16, 40 [mu] m is preferred, 30 [mu] m is more preferable, still more preferably 20 [mu] m, 10 [mu] m is particularly preferred. If the average width L ₂ of the plurality of fine grooves 16 is less than the above lower limit, there is a risk of lowering the moldability of the fine groove 16. Conversely, if the average width L ₂ of the plurality of fine grooves 16 exceeds the above upper limit, there may not be sufficiently increased the amount of light propagating in the width direction of the plurality of fine grooves 16. The width L ₂ of each of the fine grooves 16 are preferably formed at random in the longitudinal direction in the above range. Width L ₂ of each of the fine grooves 16 it is possible to prevent the moire caused by interference with other members (a prism sheet or a liquid crystal cell) or the like having a periodic pitch by being formed at random in the above range, color It is possible to prevent rainbow unevenness and the like by preventing the decomposition from occurring regularly. The “average width of the plurality of fine grooves” refers to the average value of the widths at the average interface of the resin layers at arbitrary points excluding both ends in the longitudinal direction of the 20 fine grooves arbitrarily extracted.

The lower limit of the average pitch of the plurality of fine grooves 16 is preferably 10 nm, more preferably 50 nm, and even more preferably 100 nm. On the other hand, the upper limit of the average pitch of the plurality of fine grooves 16 is preferably 40 μm, more preferably 30 μm, still more preferably 20 μm, and particularly preferably 10 μm. If the average pitch of the plurality of fine grooves 16 is less than the lower limit, the moldability of the plurality of fine grooves 16 may be reduced. Conversely, if the average pitch of the plurality of fine grooves 16 exceeds the above upper limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be increased sufficiently. The “average pitch of the plurality of fine grooves” refers to the average value of the pitches of any ten adjacent fine grooves in the direction perpendicular to the average orientation direction of the plurality of fine grooves.

The upper limit of the standard deviation of the pitch of the plurality of fine grooves 16 is preferably 10 μm, more preferably 9 μm, and even more preferably 7 μm. If the standard deviation of the pitch of the plurality of fine grooves 16 exceeds the upper limit, the pitch of the plurality of fine grooves 16 becomes non-uniform, and the amount of light propagated in the width direction of the plurality of fine grooves 16 cannot be increased uniformly. There is a fear. On the other hand, the lower limit of the standard deviation of the pitch of the plurality of fine grooves 16 can be set to 4 μm, for example, because the plurality of fine grooves 16 are easily arranged in a relatively random direction. The “standard deviation of the pitch of the plurality of fine grooves” refers to the standard deviation of the pitch of the 20 fine grooves that are arbitrarily extracted.

Also, the average width L ₂ and the average pitch of the plurality of fine grooves 16 are preferably both included in the above range. The lower light diffusion sheet 4, by the average width L ₂ and the average pitch of the plurality of fine grooves 16 are included in both the above-mentioned range, sufficient amount of light is propagated in the width direction of the plurality of fine grooves 16 It can be easily and reliably increased.

The lower limit of the average number of the micro-grooves 16 per unit length in the direction perpendicular to the average orientation direction of the micro-grooves 16 is preferably 10 / mm, more preferably 50 / mm, and 100 / mm is more preferable. On the other hand, the upper limit of the average number is preferably 10000 / mm, more preferably 5000 / mm, and still more preferably 1000 / mm. If the average existence number is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be sufficiently increased. On the other hand, if the average number exceeds the upper limit, the moldability of the plurality of fine grooves 16 may be reduced.

The lower limit of the average depth _{D 1} of the plurality of fine grooves 16, 10 nm are preferred, 500 nm are more preferable, and more preferably 1 [mu] m, 2 [mu] m is particularly preferred. In contrast, the upper limit of the average depth _{D 1} of the plurality of fine grooves 16, 30 [mu] m is preferred, 10 [mu] m is more preferable, still more preferably 5 [mu] m, 3 [mu] m is particularly preferred. If the average depth D ₁ of the plurality of fine grooves 16 is less than the above lower limit, there may not be sufficiently increased the amount of light propagating in the width direction of the plurality of fine grooves 16. Conversely, there is a possibility that the average depth D ₁ of the fine groove 16 is more than the upper limit, strength of the protective layer 13 is lowered. The “average depth of the plurality of fine grooves” refers to an average value of the depth from the average interface to the bottom of the resin layer of 20 fine grooves that are arbitrarily extracted.

Further, the upper limit of the standard deviation of the depth of the plurality of fine grooves 16 is preferably 4 μm, more preferably 3 μm, and even more preferably 2.5 μm. When the standard deviation of the depth of the plurality of fine grooves 16 exceeds the above upper limit, the depth of the plurality of fine grooves 16 becomes non-uniform, and the amount of light propagated in the width direction of the plurality of fine grooves 16 is increased uniformly. You may not be able to. On the other hand, the lower limit of the standard deviation of the depth of the plurality of fine grooves 16 is not particularly limited, and can be, for example, 0.3 μm. The “standard deviation of the depth of a plurality of fine grooves” refers to a standard deviation of the depth of 20 fine grooves that are arbitrarily extracted.

The lower limit of the arithmetic average roughness (Ra) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.005 μm. 05 μm is more preferable, and 0.1 μm is even more preferable. On the other hand, the upper limit of the arithmetic average roughness (Ra) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 1.5 μm. 1.2 μm is more preferable, and 1 μm is more preferable. If the arithmetic average roughness (Ra) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. Conversely, when the arithmetic average roughness (Ra) exceeds the upper limit, the amount of light propagated in the direction parallel to the orientation direction of the plurality of microgrooves 16 relative to the amount of light propagated in the width direction of the plurality of microgrooves 16 is large. There is a risk.

The lower limit of the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.01 μm, 1 μm is more preferable, and 0.5 μm is more preferable. On the other hand, the upper limit of the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 5 μm. More preferably, 1.7 μm is further preferable, and 1.5 μm is particularly preferable. If the arithmetic average roughness (Ra) is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be increased sufficiently. Conversely, when the arithmetic average roughness (Ra) exceeds the upper limit, it may be difficult to control the light emission angle.

In addition, the arithmetic average roughness (Ra) in the direction parallel to the orientation direction of the plurality of microgrooves 16 on the surface (back surface) where the plurality of microgrooves 16 are formed in the protective layer 13 and the direction perpendicular to the orientation direction of the plurality of microgrooves 16. The arithmetic average roughness (Ra) in the direction is preferably included in the above range. The lower light diffusing sheet 4 has the arithmetic average roughness (Ra) in the direction parallel to the orientation direction of the plurality of fine grooves 16 and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16. By being within the range, the amount of light propagating in the width direction of the plurality of fine grooves 16 can be sufficiently increased to easily and reliably suppress the occurrence of hot spots.

The arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of microgrooves 16 and the direction parallel to the orientation direction of the plurality of microgrooves 16 on the surface (back surface) of the protective layer 13 where the plurality of microgrooves 16 are formed. The lower limit of the difference from the arithmetic average roughness (Ra) is preferably 0.5 μm, more preferably 0.7 μm, and even more preferably 1 μm. When the difference in the arithmetic average roughness (Ra) is equal to or more than the lower limit, the amount of light propagated in the width direction of the plurality of microgrooves 16 is increased to easily and reliably reduce the luminance unevenness of the liquid crystal display device. . On the other hand, the upper limit of the difference in the arithmetic average roughness (Ra) can be set to 1.9 μm, for example.

The lower limit of the maximum height (Ry) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.1 μm, and more preferably 1 μm. 1.5 μm is more preferable. On the other hand, the upper limit of the maximum height (Ry) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 3 μm, and 2.5 μm. Is more preferable, and 2 μm is more preferable. If the maximum height (Ry) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. Conversely, when the maximum height (Ry) exceeds the upper limit, the amount of light propagated in the direction parallel to the orientation direction of the plurality of microgrooves 16 with respect to the amount of light propagated in the width direction of the plurality of microgrooves 16 increases. There is a fear. The “maximum height (Ry)” is a value with a cutoff λc of 0.8 mm and an evaluation length of 4 mm in accordance with JIS-B0601: 1994.

The lower limit of the maximum height (Ry) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 4 μm, more preferably 5 μm, 6 μm is more preferable. On the other hand, the upper limit of the maximum height (Ry) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 12 μm and more preferably 10 μm. Preferably, 9 μm is more preferable. If the maximum height (Ry) is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be increased sufficiently. Conversely, if the maximum height (Ry) exceeds the upper limit, it may be difficult to control the light emission angle.

The maximum height (Ry) in the direction perpendicular to the orientation direction of the plurality of microgrooves 16 and the maximum in the direction parallel to the orientation direction of the plurality of microgrooves 16 on the surface (back surface) of the protective layer 13 where the plurality of microgrooves 16 are formed. As a minimum of a difference with height (Ry), 4 micrometers is preferred, 5 micrometers is more preferred, and 6 micrometers is still more preferred. When the difference in the maximum height (Ry) is equal to or greater than the lower limit, it is easy to reliably and reliably reduce luminance unevenness of the liquid crystal display device by increasing the amount of light transmitted in the width direction of the plurality of fine grooves 16. On the other hand, the upper limit of the difference in the maximum height (Ry) can be set to 11 μm, for example.

The lower limit of the ten-point average roughness (Rz) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.1 μm. 0.5 μm is more preferable, and 1 μm is even more preferable. On the other hand, the upper limit of the ten-point average roughness (Rz) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 2.5 μm. 2 μm is more preferable, and 1.5 μm is more preferable. If the ten-point average roughness (Rz) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. Conversely, when the ten-point average roughness (Rz) exceeds the upper limit, the amount of light propagated in the direction parallel to the orientation direction of the plurality of microgrooves 16 relative to the amount of light propagated in the width direction of the plurality of microgrooves 16 is increased. May grow. The “ten-point average roughness (Rz)” is a value with a cutoff λc of 0.8 mm and an evaluation length of 4 mm according to JIS-B0601: 1994.

The lower limit of the ten-point average roughness (Rz) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 4 μm and more preferably 5 μm. Preferably, 6 μm is more preferable. On the other hand, the upper limit of the ten-point average roughness (Rz) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 10 μm, more preferably 8 μm. 7 μm is more preferable. If the ten-point average roughness (Rz) is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be increased sufficiently. On the other hand, if the ten-point average roughness (Rz) exceeds the upper limit, it may be difficult to control the light emission angle.

The ten-point average roughness (Rz) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 and the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed. The lower limit of the difference from the ten-point average roughness (Rz) is preferably 3 μm, more preferably 4 μm, and even more preferably 4.5 μm. When the difference in the ten-point average roughness (Rz) is equal to or greater than the lower limit, the amount of light propagated in the width direction of the plurality of microgrooves 16 is increased to easily and reliably reduce the luminance unevenness of the liquid crystal display device. easy. On the other hand, the upper limit of the difference of the ten-point average roughness (Rz) can be set to 9 μm, for example.

The lower limit of the root mean square slope (RΔq) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) of the protective layer 13 on which the plurality of fine grooves 16 are formed is preferably 0.05. 2 is more preferable, 0.25 is more preferable, and 0.3 is particularly preferable. On the other hand, the upper limit of the root mean square slope (RΔq) in the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.5, 0.45 is more preferable, and 0.4 is more preferable. If the root mean square slope (RΔq) is less than the lower limit, the effect of suppressing the occurrence of hot spots may be insufficient. Conversely, when the root mean square slope (RΔq) exceeds the upper limit, the amount of light propagated in a direction parallel to the orientation direction of the plurality of microgrooves 16 relative to the amount of light propagated in the width direction of the plurality of microgrooves 16 is large. There is a risk. The “root mean square slope (RΔq)” is a value according to JIS-B0601: 2001.

The lower limit of the root mean square slope (RΔq) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 0.5. 7 is more preferable, and 1 is more preferable. On the other hand, the upper limit of the root mean square slope (RΔq) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) where the plurality of fine grooves 16 of the protective layer 13 are formed is preferably 2.5, 2 is more preferable, and 1.8 is more preferable. If the root mean square slope (RΔq) is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 may not be increased sufficiently. Conversely, if the root mean square slope (RΔq) exceeds the upper limit, it may be difficult to control the light emission angle.

The root mean square slope (RΔq) in the direction perpendicular to the orientation direction of the plurality of fine grooves 16 and the direction parallel to the orientation direction of the plurality of fine grooves 16 on the surface (back surface) of the protective layer 13 on which the plurality of fine grooves 16 are formed. The lower limit of the difference from the root mean square slope (RΔq) is preferably 0.5, more preferably 0.7, and even more preferably 1. When the difference of the root mean square slope (RΔq) is not less than the above lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 16 can be increased to easily and reliably reduce luminance unevenness of the liquid crystal display device. . On the other hand, the upper limit of the difference of the root mean square slope (RΔq) can be set to 2.2, for example.

Examples of the main component of the protective layer 13 include polycarbonate, acrylic resin, urethane resin, acrylic-urethane copolymer, polyethylene terephthalate, polyethylene naphthalate, polystyrene, methyl (meth) acrylate-styrene copolymer, polyolefin, and cycloolefin. Examples thereof include polymers, cycloolefin copolymers, cellulose acetate, weather resistant vinyl chloride, and active energy ray curable resins. Especially, the acrylic resin which raises the intensity | strength of the back surface of the said light diffusion sheet 4 for the said lower, and is easy to prevent this back surface damage is preferable.

The lower limit of the average thickness of the protective layer 13 is preferably 1 μm and more preferably 5 μm. On the other hand, the upper limit of the average thickness of the protective layer 13 is preferably 50 μm and more preferably 10 μm. If the average thickness of the protective layer 13 is less than the above lower limit, there is a possibility that scratches on the back surface of the lower light diffusion sheet 4 cannot be prevented accurately. Conversely, if the average thickness of the protective layer 13 exceeds the upper limit, the luminance of the liquid crystal display device may be reduced.

The lower limit of the refractive index of the protective layer 13 is preferably 1.36, more preferably 1.4, and still more preferably 1.43. On the other hand, the upper limit of the refractive index of the protective layer 23 is preferably 1.7, more preferably 1.5, and even more preferably 1.49. When the refractive index of the protective layer 13 is within the above range, the refractive index difference between the protective layer 13 and the air layer existing on the back side of the protective layer 13 is utilized to propagate in the width direction of the plurality of fine grooves 16. Therefore, it is easy to reduce the luminance unevenness of the liquid crystal display device easily and surely.

<Prism sheet>
The 1st prism sheet 5 and the 2nd prism sheet 6 have a base material layer and the projection row | line | column which consists of a some protrusion prism part laminated | stacked on the surface of this base material layer. The base material layer and the protruding prism portion are resin layers mainly composed of a transparent, particularly colorless and transparent synthetic resin, because it is necessary to transmit light. The ridge line directions of the plurality of ridge prism portions of the first prism sheet 5 and the ridge line directions of the plurality of ridge prism portions of the second prism sheet 6 are substantially orthogonal.

The lower limit of the thickness of the first prism sheet 5 and the second prism sheet 6 (height from the back surface of the base material layer to the top of the protruding prism portion) is preferably 50 μm, and more preferably 100 μm. On the other hand, as an upper limit of the thickness of the 1st prism sheet 5 and the 2nd prism sheet 6, 200 micrometers is preferable and 180 micrometers is more preferable. Moreover, as a minimum of the pitch of the protrusion prism part in the 1st prism sheet 5 and the 2nd prism sheet 6, 30 micrometers is preferable and 40 micrometers is more preferable. On the other hand, the upper limit of the pitch of the protruding prism portions in the first prism sheet 5 and the second prism sheet 6 is preferably 100 μm, and more preferably 60 μm. Further, the apex angle of the protruding prism portion is preferably 85 ° or more and 95 ° or less. As a minimum of the refractive index of the 1st prism sheet 5 and the 2nd prism sheet 6, 1.5 is preferred and 1.55 is more preferred. On the other hand, the upper limit of the refractive index of the first prism sheet 5 and the second prism sheet 6 is preferably 1.7. The “refractive index of the prism sheet” refers to the refractive index of the protruding prism portion.

<Upper light diffusion sheet>
The upper light diffusion sheet 7 includes a base film, a light diffusion layer that is laminated on the surface side of the base film, a plurality of beads and a binder thereof, and a protective layer that is laminated on the back side of the base film. Prepare. The upper light diffusion sheet 7 is composed of three layers: a base film, a light diffusion layer directly laminated on the surface of the base film, and a protective layer directly laminated on the back surface of the base film (base film). And no other layers than the light diffusion layer and the protective layer). The upper light diffusion sheet 7 is formed in a planar view shape.

The base film, the light diffusion layer, and the protective layer of the upper light diffusion sheet 7 are all resin layers mainly composed of a synthetic resin. The base film of the upper light diffusion sheet 7 can have the same configuration as the base film 11 of the lower light diffusion sheet 4. Further, the protective layer of the upper light diffusion sheet 7 can have the same configuration as the protective layer 13 of the lower light diffusion sheet 4 except that a plurality of fine grooves are not formed. On the other hand, the light diffusing layer of the upper light diffusing sheet 7 does not require the same high light diffusibility as the light diffusing layer 12 of the lower light diffusing sheet 4, so that the lower limit of the amount of the light diffusing agent is 5 Mass parts are preferred, 10 parts by mass are more preferred, and the upper limit is preferably 40 parts by mass and more preferably 30 parts by mass.

<Light guide film>
The light guide film 1 emits light incident from the end face from the surface substantially uniformly. 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 that are recessed on the front surface side on the back surface. Moreover, the light guide film 1 has a sticking prevention part on the back surface. Specifically, the light guide film 1 has a plurality of raised portions 18 that exist around the plurality of recesses 17 and protrude to the back surface side as the sticking prevention 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 formation surface of the recessed portion 17. The light guide film 1 is a resin layer mainly composed of a synthetic resin.

The lower limit of the average thickness of the light guide film 1 is preferably 100 μm, more preferably 150 μm, and even more preferably 200 μm. On the other hand, the upper limit of the average thickness of the light guide film 1 is preferably 600 μm, more preferably 580 μm, and even more preferably 550 μm. If the average thickness of the light guide film 1 is less than the lower limit, the strength of the light guide film 1 may be insufficient, and the light from the LED light source 2 cannot be sufficiently incident on the light guide film 1. There is a fear. On the other hand, if the average thickness of the light guide film 1 exceeds the above upper limit, there is a possibility that the demand for thinning the backlight unit may not be met.

The plurality of concave portions 17 function as light scattering portions that scatter incident light to the surface side. Each recess 17 is formed in a substantially circular shape in plan view. Moreover, each recessed part 17 is formed so that a diameter may be gradually reduced toward the surface side. The shape of the recess 17 is not particularly limited, and may be a hemispherical shape, a semi-ellipsoidal shape, a conical shape, a truncated cone shape, or the like. Especially, as a shape of the recessed part 17, a hemispherical shape or a semi-ellipsoidal shape is preferable. When the concave portion 17 has a hemispherical shape or a semi-ellipsoidal shape, the moldability of the concave portion 17 can be improved, and the light incident on the concave portion 17 can be suitably scattered.

The raised portion 18 is formed continuously from a surface perpendicular to the thickness direction of the light guide film 1 on the back surface of the light guide film 1. Specifically, the raised portion 18 is formed continuously from the flat surface on the back surface of the light guide film 1. The raised portion 18 is formed in a substantially annular shape in plan view so as to surround the recessed portion 17. The light guide film 1 is formed in a substantially annular shape in plan view so that the raised portion 18 surrounds the concave portion 17, so that the concave portion 17 and the vicinity of the concave portion 17 are disposed on the back side of the light guide film 1. Can be easily and reliably prevented.

The light guide film 1 has flexibility. By having flexibility, the light guide film 1 can suppress damage to the reflective sheet 8 disposed on the back surface side. Since the light guide film 1 needs to transmit light, the light guide film 1 is configured to be transparent, particularly colorless and transparent.

The main components of the light guide film 1 are polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, methyl (meth) acrylate-styrene copolymer, polyolefin, cycloolefin polymer, cycloolefin copolymer, cellulose acetate, weather resistance And reactive vinyl chloride, active energy ray-curable resin, and the like. Especially, as a main component of the light guide film 1, a polycarbonate or an acrylic resin is preferable. Polycarbonate is excellent in transparency and has a high refractive index. Therefore, when the light guide film 1 contains polycarbonate as a main component, total reflection is likely to occur on the front and back surfaces of the light guide film 1, and light can be propagated efficiently. it can. Moreover, since polycarbonate has heat resistance, the LED light source 2 is unlikely to deteriorate due to heat generation. Furthermore, since polycarbonate has less water absorption than acrylic resin, dimensional stability is high. Therefore, the light guide film 1 can suppress aged deterioration by including polycarbonate as a main component. On the other hand, since acrylic resin has high transparency, it is possible to reduce light wear in the light guide film 1.

<LED light source>
The plurality of LED light sources 2 are disposed along the end surface of the light guide film 1. Each of the plurality of LED light sources 2 is disposed such that the light emitting surface faces (or abuts) the end surface of the light guide film 1.

<Reflection sheet>
The reflection sheet 8 has a resin layer mainly composed of synthetic resin. The reflection sheet 8 may be configured as a white resin layer in which a filler is dispersed in a base resin such as polyester, and a metal such as aluminum or silver is vapor-deposited on the surface of the resin layer formed from polyester or the like. It may be configured as a specular sheet with improved regular reflection.

<Brightness unevenness reduction function>
Next, with reference to FIG. 5 and FIG. 6, the luminance unevenness reducing function of the lower light diffusion sheet 4 and the backlight unit will be described. First, with reference to FIG. 5, the light quantity of the light emitted from the plurality of LED light sources 2 and incident on the light guide film 1 will be described. Light rays emitted from the plurality of LED light sources 2 are incident substantially perpendicularly from an end face (incident end face) facing the plurality of LED light sources 2 of the light guide film 1 and propagate toward an end face facing the incident end face. . At this time, since the light beams emitted from the plurality of LED light sources 2 have high directivity, a region X having an extremely large amount of light is generated particularly in the vicinity of the light beam incident portion of the light guide film 1. On the other hand, since the plurality of LED light sources 2 are arranged at predetermined intervals, a region Y with an extremely small amount of light is provided between the light incident portions in the light guide film 1 (between adjacent regions X). Will occur.

Subsequently, the luminance unevenness reducing function of the lower light diffusion sheet 4 and the backlight unit will be described with reference to FIG. Most of the light rays emitted from the region X to the surface side of the light guide film 1 are incident on the back surface of the protective layer 13 of the lower light diffusion sheet 4 in a state along the light emission direction of the plurality of LED light sources 2. Is done. Then, the light incident on the back surface of the protective layer 13 of the lower light diffusion sheet 4 propagates in the width direction of the plurality of microgrooves 16 by the plurality of microgrooves 16 along the light emission direction of the plurality of LED light sources 2. It is thought that it is done. That is, it is considered that the light rays incident on the plurality of fine grooves 16 are propagated in the region Y direction in plan view as shown in FIG. Thereby, it is considered that the light amount of the region X and the light amount of the region Y in a plan view are made uniform, and the luminance unevenness of the liquid crystal display device is reduced.

<Advantages>
When the backlight unit optical sheet (the lower light diffusion sheet 4) is used in a backlight unit that uses an LED as a light source, the occurrence of hot spots can be suppressed. Although the cause of this is not necessarily clear, a plurality of fine grooves 16 oriented in a specific direction are formed in the resin layer of the backlight unit optical sheet, so that it passes through a region defined by the plurality of fine grooves 16. Therefore, it is considered that the generation of hot spots can be suppressed even when the light beam of the LED having high directivity is propagated in the width direction of the plurality of fine grooves 16.

The backlight unit optical sheet (the lower light diffusion sheet 4) is laminated on the surface of the base film 11 and the base film 11, and has a plurality of beads 14 and a binder 15 for the light diffusion. Since the layer 12 and the protective layer 13 laminated on the back side of the base film 11 are provided, it is easy to emit light that is substantially uniform over the entire surface.

The backlight unit includes the optical sheet for the backlight unit (the lower light diffusion sheet 4), thereby suppressing the occurrence of hot spots as described above.

Since the optical sheet (the lower light diffusion sheet 4) is directly superimposed on the surface of the light guide film 1, the backlight unit can sufficiently suppress the occurrence of hot spots.

<Manufacturing method of light diffusion sheet for lower use>
As a manufacturing method of the said lower light diffusion sheet 4, the process (base film formation process) which forms the sheet body which comprises the base film 11, and the protective layer 13 are laminated | stacked on the one surface side of this sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 12 on the other surface side of the sheet body (light diffusion layer laminating step).

(Base film forming process)
The base film forming step is not particularly limited. For example, a molten thermoplastic resin is extruded from a T die, and then the extruded body is stretched in the layer longitudinal direction and the layer width direction to form a sheet body. The method of doing is mentioned. As a known extrusion molding method using a T-die, for example, a polishing roll method and a chill roll method can be cited. Examples of the stretching method of the extruded product include a tubular film biaxial stretching method and a flat film biaxial stretching method.

(Protective layer lamination process)
As the protective layer laminating step, for example, after applying a coating liquid containing a protective layer forming material to one surface side of the sheet body formed in the base film forming step, the inverted shape of the plurality of fine grooves 16 is formed. There is a method in which a plurality of fine grooves 16 are transferred to one surface side of a coating film obtained by applying the coating liquid using a mold on the surface. The method for applying the coating liquid is not particularly limited, and various methods such as a spin coating method, a spray method, a slide coating method, a dip method, a bar coating method, a roll coater method, a screen printing method, etc. Is mentioned. Moreover, as said metal mold | die, the thing by which the reverse shape of the some fine groove 16 was formed in the surface of a metal roll or a metal plate, for example can be used. In the protective layer lamination step, the coating film may be dried as necessary. Moreover, in the said protective layer lamination process, after transferring the some fine groove | channel 16 to the one surface side of the said coating film, a coating film should just be hardened by heating, ultraviolet irradiation, etc. In addition, the said base film formation process and a protective layer lamination process can also be performed simultaneously, for example by the coextrusion molding method. Furthermore, in the protective layer laminating step, after laminating a sheet body obtained by curing the protective layer forming material on one surface side of the base film, a plurality of fine grooves 16 are formed on one surface of the sheet body by laser, file, or the like. A plurality of fine grooves 16 may be formed in the sheet body by using a photolithography method and an etching method.

(Light diffusion layer lamination process)
Examples of the light diffusion layer laminating step include a method in which a coating liquid containing a plurality of beads 14 and a binder composition is applied to the other surface side of the sheet body, and the applied coating liquid is dried and cured. It is done.

In addition, the manufacturing method of the said light diffusion sheet for lower is the corona discharge treatment, the ozone treatment, the low temperature plasma treatment, the glow discharge on the surface of the sheet body on which the light diffusion layer is laminated before the light diffusion layer lamination step. You may further provide the surface treatment process which performs a process, an oxidation process, a primer coat process, an undercoat process, an anchor coat process, etc.

<Advantages>
The manufacturing method of the said downward light diffusion sheet can manufacture the said downward light diffusion sheet 4 which can suppress generation | occurrence | production of a hot spot as mentioned above easily and reliably.

[Second Embodiment]
<Light diffusion sheet for lower use>
The lower light diffusion sheet 24 of FIG. 7 is used in the edge light type backlight unit of FIG. 1 instead of the lower light diffusion sheet 4 of FIG. 7 is laminated on the surface side of the base film 25, the light diffusion layer 12 having a plurality of beads 14 and its binder 15, and the back surface of the base film 25. And a protective layer 26 laminated on the side. The lower light diffusion sheet 24 is composed of three layers: a base film 25, a light diffusion layer 12 directly laminated on the surface of the base film 25, and a protective layer 26 laminated directly on the back surface of the base film 25. (There are no layers other than the base film 25, the light diffusion layer 12, and the protective layer 26). The lower light diffusion sheet 24 is formed in a planar view shape. The light diffusion layer 12 is the same as the lower light diffusion sheet 4 in FIG.

(Base film)
The base film 25 is a resin layer mainly composed of a synthetic resin. Since the base film 25 needs to transmit light, it is formed of a synthetic resin that is transparent, particularly colorless and transparent, as a main component. The main component of the base film 25 is not particularly limited, and examples thereof include the same synthetic resin as the main component of the base film 11 of the lower light diffusion sheet 4 in FIG. The average thickness of the base film 25 can be the same as that of the base film 11 of the downward light diffusion sheet 4 in FIG.

The base film 25 has a plurality of fine grooves 27 formed on the back surface. The plurality of fine grooves 27 preferably constitute a diffraction grating. The plurality of fine grooves 27 are preferably formed in a hairline shape.

The plurality of fine grooves 27 are formed substantially uniformly (with substantially equal density) over the entire area of the back surface of the base film 25. Each fine groove 27 has a substantially U-shaped cross section (that is, each fine groove 27 is not formed in a triangular cross section). Moreover, the longitudinal direction of the plurality of fine grooves 27 is parallel to one end of the back surface of the base film 25. Specifically, the plurality of fine grooves 27 have a longitudinal direction along the average direction of light rays from the plurality of LED light sources. Furthermore, the orientation direction of each fine groove 27 is random. The plurality of fine grooves 27 are preferably formed independently for controlling the light diffusion direction, but some of the fine grooves 27 may cross each other. The average orientation direction, the average length in the longitudinal direction, the average width, the average pitch, the standard deviation of the pitch, the number of existing units per unit length, the average depth, and the standard deviation of the depth of the plurality of fine grooves 27 are as follows: 1 can be the same as the plurality of fine grooves 16 of the lower light diffusion sheet 4 in FIG. Also, arithmetic average roughness (Ra), maximum height (Ry), ten points in the direction parallel to the orientation direction of the plurality of fine grooves 27 on the surface (back surface) of the base film 25 where the plurality of fine grooves 27 are formed. Average roughness (Rz), root mean square slope (RΔq), arithmetic average roughness (Ra) in the alignment direction and perpendicular direction of the plurality of fine grooves 27, maximum height (Ry), ten-point average roughness (Rz) The root mean square slope (RΔq) can be the same as that of the back surface of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

The lower limit of the refractive index of the base film 25 is preferably 1.51, more preferably 1.53, and even more preferably 1.55. On the other hand, the upper limit of the refractive index of the base film 25 is preferably 1.7, more preferably 1.67, and even more preferably 1.65. The lower light diffusing sheet 24 has a refractive index of the base film 25 and a refractive index of another layer (protective layer 26) laminated on the surface (back surface) where the plurality of fine grooves 27 are formed in the base film 25. The larger the difference is, the easier it is to increase the amount of light transmitted in the width direction of the plurality of fine grooves 27. In this regard, if the refractive index of the base film 25 is less than the lower limit, the difference in refractive index between the base film 25 and the protective layer 26 is not sufficiently increased and propagates in the width direction of the plurality of fine grooves 27. There is a possibility that the amount of light cannot be increased sufficiently. Conversely, if the refractive index of the base film 25 exceeds the above upper limit, the resin that can be used for the base film 25 may be limited. The “refractive index” means a refractive index in light having a wavelength of 589.3 nm (sodium D-line), and was measured at a temperature of 23 ° C. using a flat test piece having a side of 70 mm and a thickness of 2 mm. It means the average value of the number of tests 3 times.

The lower limit of the difference between the refractive index of the base film 25 and the refractive index of the other layer (protective layer 26) laminated on the surface (back surface) of the base film 25 on which the plurality of fine grooves 27 are formed is 0. 01 is preferred, 0.05 is more preferred, and 0.07 is even more preferred. If the difference in refractive index is less than the lower limit, the amount of light propagated in the width direction of the plurality of fine grooves 27 may not be increased sufficiently. On the other hand, the upper limit of the difference in refractive index can be set to 0.15, for example.

(Protective layer)
The protective layer 26 is a resin layer mainly composed of synthetic resin. Examples of the main component of the protective layer 26 include the same synthetic resin as the main component of the protective layer 26 of the lower light diffusion sheet 4 in FIG. In addition, the average thickness of the protective layer 26 can be the same as that of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

The lower limit of the refractive index of the protective layer 26 is preferably 1.36, more preferably 1.4, and still more preferably 1.43. On the other hand, the upper limit of the refractive index of the protective layer 26 is preferably 1.51, more preferably 1.5, and even more preferably 1.49. If the refractive index of the protective layer 26 is less than the lower limit, the resin that can be used for the protective layer 26 may be limited. Conversely, if the refractive index of the protective layer 26 exceeds the above upper limit, the difference in refractive index between the base film 25 and the protective layer 26 is not sufficiently increased, and the amount of light propagated in the width direction of the plurality of fine grooves 27 is sufficient. There is a possibility that it cannot be increased.

<Manufacturing method of light diffusion sheet for lower use>
As the manufacturing method of the lower light diffusion sheet 24, a step of forming a sheet body constituting the base film 25 (base film forming step), and a protective layer 26 is laminated on one surface side of the sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 12 on the other surface side of the sheet body (light diffusion layer laminating step). In addition, the light diffusion layer lamination process in the manufacturing method of the said lower light diffusion sheet 24 is the same as the light diffusion layer lamination process of the lower light diffusion sheet 4 of FIG.

(Base film forming process)
As the base film forming step, for example, a molten thermoplastic resin is extruded from a T die, and a mold having a reverse shape of a plurality of fine grooves 27 on the surface is used. And an extrusion molding method for transferring the plurality of fine grooves 27. Moreover, in the said base film formation process, you may extend | stretch the said extrusion molding in a layer longitudinal direction and a layer width direction. As a known extrusion molding method using a T-die, for example, a polishing roll method and a chill roll method can be cited. In addition, as the mold, for example, a metal roll or a metal plate having a plurality of fine grooves 27 with an inverted shape formed on the surface thereof can be used. Furthermore, examples of the stretching method of the extruded product include a tubular film biaxial stretching method and a flat film biaxial stretching method. In the base film forming step, after forming the extruded body, a plurality of fine grooves 27 may be formed on one surface of the extruded body by laser, file, photolithography, etching, or the like. Good.

(Protective layer lamination process)
Examples of the protective layer laminating step include a coating method in which a coating liquid containing a protective layer forming material is applied to one side of the sheet formed in the base film forming step, and then dried and cured. . Examples of the method for applying the coating liquid include the same method as in the protective layer laminating step of the light diffusion sheet 4 for the lower side in FIG.

<Advantages>
The lower light diffusion sheet 24 can suppress the occurrence of hot spots. Further, the lower light diffusion sheet 34 easily emits light that is substantially uniform over the entire surface.

The manufacturing method of the lower light diffusion sheet can easily and reliably manufacture the lower light diffusion sheet 24 capable of suppressing the generation of hot spots.

[Third embodiment]
<Light diffusion sheet for lower use>
The lower light diffusion sheet 34 in FIG. 8 is used in the edge light type backlight unit of FIG. 1 instead of the lower

light diffusion sheets

4 and 24 in FIGS. 8 is laminated on the surface side of the base film 35, the light diffusion layer 36 having a plurality of beads 38 and its binder 39, and the back surface of the base film 35. And a protective layer 37 laminated on the side. The lower light diffusion sheet 34 is composed of three layers: a base film 35, a light diffusion layer 36 that is directly laminated on the surface of the base film 35, and a protective layer 37 that is directly laminated on the back surface of the base film 35. (There are no layers other than the base film 35, the light diffusion layer 36, and the protective layer 37). The lower light diffusion sheet 34 is formed in a planar view shape.

(Base film)
The base film 35 is a resin layer mainly composed of a synthetic resin. Since the base film 35 needs to transmit light, it is formed of a synthetic resin that is transparent, particularly colorless and transparent, as a main component. The main component of the base film 35 is not particularly limited, and examples thereof include the same synthetic resin as the main component of the base film 11 of the lower light diffusion sheet 4 in FIG. The average thickness of the base film 35 can be the same as that of the base film 11 of the downward light diffusion sheet 4 in FIG.

The base film 35 has a plurality of fine grooves 40 formed on the surface. The plurality of fine grooves 40 preferably constitute a diffraction grating. The specific configuration of the plurality of fine grooves 40 can be the same as that of the plurality of fine grooves 27 of the lower light diffusion sheet 24 in FIG. That is, the surface of the base film 35 of the lower light diffusion sheet 34 is formed in the same manner as the back surface of the lower light diffusion sheet 24 in FIG.

The refractive index of the base film 35 can be the same as that of the base film 25 of the lower light diffusion sheet 24 in FIG. Further, the difference between the refractive index of the base film 35 and the refractive index of the binder 39 of the light diffusion layer 36 is the same as the difference between the refractive indexes of the base film 25 and the protective layer 26 of the lower light diffusion sheet 24 in FIG. It can be.

(Light diffusion layer)
The light diffusion layer 36 is a resin layer mainly composed of synthetic resin. The light diffusion layer 36 constitutes the outermost surface of the lower light diffusion sheet 34. The light diffusion layer 36 contains a plurality of beads 38 dispersed at substantially equal density. The beads 38 are surrounded by a binder 39. The light diffusing layer 36 contains a plurality of beads 38 so as to diffuse light transmitted from the back surface side to the front surface side substantially uniformly. The light diffusion layer 36 has fine irregularities formed substantially uniformly on the surface by a plurality of beads 38, and the concave and convex portions of the fine irregularities are formed in a lens shape. The light diffusing layer 36 exhibits an excellent light diffusing function by the lens action of the fine unevenness, and the refractive function and the transmitted light are refracted in the normal direction due to the light diffusing function. It has a light condensing function that condenses macroscopically in the direction.

As the main component of the beads 38, the same beads as the beads 14 of the lower light diffusion sheet 4 in FIG. 1 can be used. Further, the shape, average particle diameter, and blending amount of the beads 38 can be the same as those of the lower light diffusion sheet 4 in FIG.

The binder 39 is formed by curing (crosslinking or the like) a polymer composition containing a base polymer. The beads 38 are arranged and fixed at substantially equal density on the entire surface of the base film 35 by the binder 39.

The lower limit of the refractive index of the binder 39 is preferably 1.36, more preferably 1.4, and still more preferably 1.43. On the other hand, the upper limit of the refractive index of the binder 39 is preferably 1.7, preferably 1.6, more preferably 1.55, and even more preferably 1.49. If the refractive index of the binder 39 is less than the lower limit, the resin that can be used for the binder 39 may be limited. Conversely, if the refractive index of the binder 39 exceeds the upper limit, the difference in refractive index between the base film 25 and the binder 39 is not sufficiently increased, and the amount of light propagated in the width direction of the plurality of fine grooves 40 is sufficiently increased. There is a risk that it cannot be done.

(Protective layer)
The protective layer 37 is a resin layer mainly composed of synthetic resin. The back surface of the protective layer 37 is formed as a flat surface. As a main component of the protective layer 37, the same synthetic resin as the main component of the protective layer 13 of the lower light diffusion sheet 4 in FIG. Further, the average thickness of the protective layer 37 may be the same as that of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

<Manufacturing method of light diffusion sheet for lower use>
As the manufacturing method of the lower light diffusion sheet 34, a step of forming a sheet body constituting the base film 35 (base film forming step), and a protective layer 37 is laminated on one surface side of the sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 36 on the other surface side of the sheet body (light diffusion layer laminating step). In the manufacturing method of the lower light diffusion sheet, a plurality of fine grooves 40 are formed on the other surface side of the extrusion-molded body in the base film forming step, and a plurality of fine grooves are formed on one surface of the extrusion-molded body. Except not forming 40, it can carry out similarly to the manufacturing method of the light diffusion sheet 24 for the bottom of FIG.

<Advantages>
The lower light diffusion sheet 34 can suppress the occurrence of hot spots. Further, the lower light diffusion sheet 34 easily emits light that is substantially uniform over the entire surface.

The manufacturing method of the lower light diffusion sheet can easily and reliably manufacture the lower light diffusion sheet 34 capable of suppressing the generation of hot spots.

[Fourth embodiment]
<Light diffusion sheet for lower use>
The lower light diffusion sheet 44 in FIG. 9 is used in the edge light type backlight unit of FIG. 1 instead of the lower

light diffusion sheets

4, 24 and 34 in FIGS. 9 is laminated on the surface side of the base film 11, the light diffusion layer 45 having a plurality of beads 46 and its binder 47, and the back surface of the base film 11. And a protective layer 37 laminated on the side. The lower light diffusion sheet 44 is composed of three layers: a base film 11, a light diffusion layer 45 that is directly laminated on the surface of the base film 11, and a protective layer 37 that is directly laminated on the back surface of the base film 11. (There are no layers other than the base film 11, the light diffusion layer 45, and the protective layer 37). The lower light diffusion sheet 44 is formed in a planar view shape. The base film 11 of the lower light diffusion sheet 44 has the same configuration as the base film 11 of the lower light diffusion sheet 4 in FIG. 8 has the same configuration as that of the protective layer 37 of the lower light diffusion sheet 34 in FIG.

(Light diffusion layer)
The light diffusion layer 45 is a resin layer mainly composed of a synthetic resin. The light diffusion layer 45 constitutes the outermost surface of the lower light diffusion sheet 44. The light diffusion layer 45 contains a plurality of beads 46 dispersed at substantially equal density. The beads 46 are surrounded by a binder 47. The light diffusion layer 45 disperses and contains a plurality of beads 46 so that light transmitted from the back surface side to the front surface side is diffused substantially uniformly. Further, the light diffusion layer 45 is formed with a plurality of beads 46 having fine irregularities substantially uniformly on the surface, and exhibits an excellent light diffusion function due to the lens action of the fine irregularities, resulting from this light diffusion function. It has a refraction function that refracts transmitted light in the normal direction and a light condensing function that condenses transmitted light macroscopically in the normal direction. Furthermore, the light diffusion layer 45 has a plurality of fine grooves 48 formed on the surface. That is, the lower light diffusion sheet 44 has a plurality of fine grooves 48 formed on a surface having a plurality of fine irregularities. The lower light diffusing sheet 44 has a plurality of fine grooves 48 formed on a surface having a plurality of fine irregularities, so that the light is propagated in the width direction of the plurality of fine grooves 48 by the plurality of fine grooves 48. Light can be diffused by a plurality of fine irregularities. Thereby, a moire prevention effect, a color separation prevention effect, a viewing angle expansion effect, etc. can be improved. The plurality of fine grooves 48 preferably constitute a diffraction grating. A specific configuration of the plurality of fine grooves 48 can be the same as that of the plurality of fine grooves 16 of the lower light diffusion sheet 4 in FIG. 1. The “fine unevenness” means that, for example, the arithmetic average roughness (Ra) is 1.0 μm or more, preferably 1.5 μm or more, and more preferably 2.0 μm or more.

The main component of the beads 46 may be the same as the main component of the beads 14 of the lower light diffusion sheet 4 in FIG. Further, the shape, average particle diameter, and blending amount of the beads 46 can be the same as those of the lower light diffusion sheet 4 in FIG. Furthermore, the binder 47 can be formed by curing (crosslinking or the like) a polymer composition containing the same base polymer as the binder 15 of the lower light diffusion sheet 1 in FIG.

<Manufacturing method of light diffusion sheet for lower use>
As a manufacturing method of the lower light diffusion sheet 44, a step of forming a sheet body constituting the base film 11 (base film forming step), and a protective layer 37 is laminated on one surface side of the sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 45 on the other surface side of the sheet body (light diffusion layer laminating step). In addition, the base film formation process in the manufacturing method of the said lower light diffusion sheet 44 is the same as the base film formation process of the lower light diffusion sheet 4 of FIG. 1, and the manufacturing method of the said lower light diffusion sheet 44 The protective layer laminating step is the same as the protective layer laminating step of the lower light diffusion sheet 24 in FIG.

(Light diffusion layer lamination process)
As the light diffusion layer laminating step, for example, after applying a coating liquid containing a plurality of beads 46 and a binder composition to the other surface side of the sheet body formed in the base film forming step, a plurality of fine grooves There is a method in which a plurality of fine grooves 48 are transferred to one surface side of a coating film obtained by applying a coating liquid using a mold having 48 inversion shapes on the surface. Further, in the light diffusion layer stacking step, a mold having a plurality of fine irregularities on the surface in addition to the inverted shape of the plurality of fine grooves 48 may be used. By using a mold having a plurality of fine irregularities on the surface in the light diffusion layer laminating step, fine irregularities are formed on the surface of the light diffusion layer 45, and excellent light diffusion is achieved by the lens action of the fine irregularities. It is possible to improve the refraction function for refracting the transmitted light beam to the normal direction side and the condensing function for macroscopically condensing the transmitted light beam in the normal direction due to this light diffusion function. Examples of the method for applying the coating liquid include the same method as in the protective layer laminating step of the light diffusion sheet 4 for the lower side in FIG. In addition, as the mold, as in the protective layer laminating step of the lower light diffusion sheet 4 in FIG. 1, for example, a metal roll or a metal plate with a plurality of fine grooves 48 formed in an inverted shape is used. Can do. In the light diffusion layer laminating step, the coating film may be dried as necessary. In the light diffusing layer laminating step, after the coating liquid applied to the other surface side of the base film is cured, a plurality of fine grooves 48 are formed on the other surface of the cured coating liquid by laser, file, or the like. May be formed.

<Advantages>
The lower light diffusion sheet 44 can suppress the generation of hot spots. Further, the lower light diffusion sheet 44 easily emits light that is substantially uniform over the entire surface. Furthermore, in the backlight unit, the diffraction effect by the diffraction grating generally appears more prominently as the distance between the LED light source and the diffraction grating increases. Therefore, when the diffraction grating is formed on the surface of the light diffusion layer 9 constituting the outermost surface of the lower light diffusion sheet 44, luminance unevenness of the liquid crystal display device can be more reliably reduced.

The manufacturing method of the lower light diffusion sheet can easily and reliably manufacture the lower light diffusion sheet 44 capable of suppressing the generation of hot spots.

[Fifth embodiment]
<Light diffusion sheet for lower use>
The lower light diffusion sheet 54 of FIG. 10 is used in the edge light type backlight unit of FIG. 1 in place of the lower

light diffusion sheets

4, 24, 34, 44 of FIG. 1 and FIGS. 10 is laminated on the surface side of the base film 35, the light diffusion layer 36 having a plurality of beads 38 and a binder 39 thereof, and the back surface of the base film 35. And a protective layer 13 laminated on the side. The lower light diffusion sheet 54 is composed of three layers: a base film 35, a light diffusion layer 36 that is directly laminated on the surface of the base film 35, and a protective layer 13 that is directly laminated on the back surface of the base film 35. (There are no layers other than the base film 35, the light diffusion layer 36, and the protective layer 13). The lower light diffusion sheet 54 is formed in a planar view shape. The base film 35 and the light diffusion layer 36 of the lower light diffusion sheet 54 have the same configuration as the base film 35 and the light diffusion layer 36 of the lower light diffusion sheet 34 of FIG. The protective layer 13 of the diffusion sheet 54 has the same configuration as the protective layer 13 of the lower light diffusion sheet 4 in FIG. That is, the lower light diffusion sheet 54 has a plurality of fine grooves formed in a plurality of resin layers, specifically, a plurality of fine grooves are formed in two layers of the base film 35 and the protective layer 13. Yes.

<Manufacturing method of light diffusion sheet for lower use>
As the manufacturing method of the lower light diffusion sheet 54, a step of forming a sheet body constituting the base film 35 (base film forming step), and the protective layer 13 is laminated on one surface side of the sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 36 on the other surface side of the sheet body (light diffusion layer laminating step). The base film formation step and the light diffusion layer lamination step in the manufacturing method of the lower light diffusion sheet 54 are performed in the same manner as the base film formation step and the light diffusion layer lamination step of the lower light diffusion sheet 34 in FIG. Can do. Moreover, the protective layer lamination process in the manufacturing method of the said lower light diffusion sheet 54 can be performed similarly to the protective layer lamination process of the lower light diffusion sheet 4 of FIG.

<Advantages>
Since the lower light diffusion sheet 54 has a plurality of fine grooves formed in the two resin layers, generation of hot spots can be more reliably suppressed. Further, the lower light diffusion sheet 54 easily emits light that is substantially uniform over the entire surface.

[Sixth embodiment]
<Light diffusion sheet for lower use>
The lower light diffusion sheet 64 of FIG. 11 is used in the edge light type backlight unit of FIG. 1 instead of the lower

light diffusion sheets

4, 24, 34, 44, and 54 of FIG. 1 and FIGS. 11 is laminated on the surface side of the base film 35, the light diffusion layer 45 having a plurality of beads 46 and its binder 47, and the back surface of the base film 35. And a protective layer 13 laminated on the side. The lower light diffusion sheet 64 is composed of three layers: a base film 35, a light diffusion layer 45 that is directly laminated on the surface of the base film 35, and a protective layer 13 that is directly laminated on the back surface of the base film 35. (There are no other layers other than the base film 35, the light diffusion layer 45, and the protective layer 13). The lower light diffusion sheet 64 is formed in a planar view shape. The base film 35 of the lower light diffusion sheet 64 has the same configuration as the base film 35 of the lower light diffusion sheet 34 in FIG. The light diffusion layer 45 of the lower light diffusion sheet 64 has the same configuration as the light diffusion layer 45 of the lower light diffusion sheet 44 of FIG. Further, the protective layer 13 of the lower light diffusion sheet 64 has the same configuration as the protective layer 13 of the lower light diffusion sheet 4 in FIG. That is, the lower light diffusion sheet 64 has a plurality of fine grooves formed in a plurality of resin layers. Specifically, a plurality of fine grooves are formed in three layers of the base film 35, the light diffusion layer 45, and the protective layer 13. Grooves are formed.

<Manufacturing method of light diffusion sheet for lower use>
As a manufacturing method of the said light diffusion sheet 64 for the said downward, the process (base film formation process) of forming the sheet body which comprises the base film 35, and the protective layer 13 are laminated | stacked on the one surface side of this sheet body. A step (protective layer laminating step) and a step of laminating the light diffusion layer 45 on the other surface side of the sheet body (light diffusion layer laminating step). The base film forming step in the manufacturing method of the lower light diffusion sheet 64 can be performed in the same manner as the base film forming step of the lower light diffusion sheet 34 in FIG. Moreover, the protective layer lamination process in the manufacturing method of the said lower light diffusion sheet 64 can be performed similarly to the protective layer lamination process of the lower light diffusion sheet 4 of FIG. Furthermore, the light diffusion layer stacking step in the method for manufacturing the lower light diffusion sheet 64 can be performed in the same manner as the light diffusion layer stacking step of the lower light diffusion sheet 44 of FIG.

<Advantages>
Since the lower light diffusion sheet 64 has a plurality of fine grooves formed in the three resin layers, generation of hot spots can be more reliably suppressed. Further, the lower light diffusion sheet 64 easily emits light that is substantially uniform over the entire surface.

[Seventh embodiment]
<Light diffusion sheet for lower use>
12 and 13 is replaced with the edge light type backlight unit of FIG. 1 instead of the lower

light diffusion sheets

4, 24, 34, 44, 54, 64 of FIGS. Used for. 12 is laminated on the surface side of the base film 11, the light diffusion layer 12 having a plurality of beads 14 and their binders 15, and the back surface of the base film 11. And a protective layer 75 laminated on the side. The lower light diffusion sheet 74 is composed of three layers: a base film 11, a light diffusion layer 12 that is directly laminated on the surface of the base film 11, and a protective layer 75 that is directly laminated on the back surface of the base film 11. (There are no layers other than the base film 11, the light diffusion layer 12, and the protective layer 75). The lower light diffusion sheet 74 is formed in a planar view shape. The base film 11 and the light diffusion layer 12 of the lower light diffusion sheet 74 are the same as the base film 11 and the light diffusion layer 12 of the lower light diffusion sheet 4 in FIG. Description is omitted.

(Protective layer)
The protective layer 75 is a resin layer mainly composed of a synthetic resin. As a main component of the protective layer 75, the same synthetic resin as the main component of the protective layer 13 of the lower light diffusion sheet 4 in FIG. The average thickness of the protective layer 75 can be the same as that of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

The protective layer 75 has a plurality of fine grooves 76 formed on the back surface. The protective layer 75 has a plurality of fine grooves 76 formed in a certain region from one end to the other end of the back surface. Specifically, the protective layer 75 has a plurality of fine grooves 76 formed in a certain region from the edge facing the plurality of LED light sources in the plan view to the other end side. Further, a region where the plurality of fine grooves 76 are not formed on the back surface of the protective layer 75 is configured as a flat surface. Each fine groove 76 has a substantially U-shaped cross section (that is, each fine groove 76 is not formed in a triangular cross section). The plurality of fine grooves 76 preferably constitute a diffraction grating.

As a lower limit of the ratio (L ₄ / L ₃ ) of the length L ₄ between one end and the other end of the region where the plurality of fine grooves 76 are formed to the length L ₃ between the one end and the other end of the back surface of the protective layer 75 Is preferably 0.15, more preferably 0.2, and even more preferably 0.25. On the other hand, the upper limit of the length ratio (L ₄ / L ₃ ) is preferably 0.5, more preferably 0.45, and still more preferably 0.4. If the length ratio (L ₄ / L ₃ ) is less than the lower limit, it may be difficult to completely suppress the occurrence of hot spots. On the other hand, when the length ratio (L ₄ / L ₃ ) exceeds the upper limit, there is a risk that light in a region other than the hot spot is likely to propagate in the width direction of the plurality of fine grooves 76.

The longitudinal direction of the plurality of fine grooves 76 is parallel to one end of the back surface of the protective layer 75. Specifically, the plurality of fine grooves 76 have a longitudinal direction along the average direction of light rays from the plurality of LED light sources. Furthermore, the orientation direction of each fine groove 76 is random. The plurality of fine grooves 76 are preferably formed independently for controlling the light diffusion direction, but some of the fine grooves 76 may cross each other. The average orientation direction, the average length in the longitudinal direction, the average width, the average pitch, the standard deviation of the pitch, the average number of units per unit length, the average depth, and the standard deviation of the depth of the plurality of fine grooves 76 Can be the same as the plurality of fine grooves 16 of the lower light diffusion sheet 4 in FIG. The arithmetic average roughness (Ra), maximum height (Ry), and ten-point average in the direction parallel to the orientation direction of the plurality of fine grooves 76 on the surface (back surface) of the protective layer 75 where the plurality of fine grooves 76 are formed. Roughness (Rz), root mean square slope (RΔq) and arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves 27, maximum height (Ry), ten-point average roughness (Rz), The root mean square slope (RΔq) can be the same as that of the back surface of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

<Manufacturing method of light diffusion sheet for lower use>
As a manufacturing method of the said lower light diffusion sheet 74, the method similar to the manufacturing method of the lower light diffusion sheet 4 of FIG. 1 is mentioned, for example.

<Advantages>
Since the plurality of fine grooves 76 are formed in a certain region from one end of the back surface of the protective layer 75 to the other end side, the lower light diffusion sheet 74 can suppress the occurrence of hot spots. Further, the lower light diffusion sheet 74 has a flat surface in the back surface of the protective layer 75 where the plurality of fine grooves 76 are not formed, and thus is propagated in the width direction of the plurality of fine grooves 76 other than the hot spot. Increase in the amount of light emitted can be suppressed. For this reason, the lower light diffusion sheet 74 easily and reliably emits light that is substantially uniform over the entire surface.

[Other Embodiments]
In addition, the optical sheet for backlight units and the backlight unit according to the present invention can be implemented in various modifications and improvements in addition to the above aspects. For example, the backlight unit may use a light guide plate instead of the light guide film described above. Further, the optical sheet for the backlight unit does not have to be a lower light diffusion sheet, and may be, for example, a light guide film, a prism sheet, an upper light diffusion sheet, or a reflection sheet shown in FIG. It may be a plate. That is, a plurality of fine grooves oriented in a specific direction may be formed on the surface side or the back side of the resin layer of the light guide film, prism sheet, upper light diffusion sheet or reflection sheet or light guide plate described above. . For example, when the optical sheet for the backlight unit is an upper light diffusion sheet and a plurality of fine grooves form a diffraction grating, the distance between the LED light source and the diffraction grating can be increased. It is easy to improve the effect. For this reason, when the backlight unit optical sheet is an upward light diffusion sheet, it is easier to reliably reduce luminance unevenness of the liquid crystal display device. In addition, when the optical sheet for the backlight unit is an upper light diffusion sheet, the structure where the plurality of fine grooves are formed and the plurality of fine grooves are the same as those of the above-described light diffusion sheet for the bottom. Can do.

The optical sheet for the backlight unit is preferably disposed on the back surface of a sheet body obtained by bonding two prism sheets. A sheet body in which two prism sheets are bonded together has low concealability because an air layer is hardly formed between the prism sheets. In contrast, the backlight unit in which the optical sheet for the backlight unit is disposed on the back surface of the sheet body can increase the amount of light that is propagated in the width direction of the plurality of fine grooves. The hiding effect can be sufficiently improved.

When the optical sheet for the backlight unit is a light diffusion sheet (lower light diffusion sheet or upper light diffusion sheet), even if a plurality of fine grooves are formed on the back surface of the light diffusion layer and / or the surface of the protective layer. In addition, a plurality of fine grooves may be formed on arbitrary front and / or back surfaces of the plurality of resin layers.

When a plurality of fine grooves are formed in a certain region of the resin layer of the backlight unit optical sheet, this region can be formed in an arbitrary resin layer. For example, when the optical sheet for the backlight unit is a light diffusion sheet, the regions where the plurality of fine grooves are formed are the front and back surfaces of the base film, the front and back surfaces of the light diffusion layer, and / or the front and back surfaces of the protective layer. Either of them may be formed. Moreover, the area | region in which this some fine groove | channel is formed may be formed in 2 layers or 3 layers among a base film, a light-diffusion layer, and a protective layer.

The plurality of fine grooves may be arranged as shown in FIG. 14, for example. The plurality of fine grooves 86 in FIG. 14 gradually decrease in the ratio of presence from the edge facing the plurality of LED light sources 82 on the front surface and / or back surface of the resin layer to the other end side. The backlight unit optical sheet can suppress the occurrence of hot spots even with this configuration. In addition, the optical sheet for the backlight unit has a plurality of fine grooves 86 that gradually decrease from the edge facing the LED light source 82 to the other end side. The amount of light propagating in the width direction 86 can be reduced. The average orientation direction, the average length in the longitudinal direction, the average width, the average pitch, the standard deviation of the pitch, the average number of existing units per unit length, the average depth, and the standard deviation of the depth of the plurality of fine grooves 86 Can be the same as the plurality of fine grooves 16 of the lower light diffusion sheet 4 in FIG. Further, the arithmetic average roughness (Ra), the maximum height (Ry), and the ten-point average roughness (Rz) in the direction parallel to the orientation direction of the plurality of fine grooves 86 on the surface of the resin layer on which the plurality of fine grooves 86 are formed. ), Root mean square slope (RΔq) and arithmetic mean roughness (Ra), maximum height (Ry), ten-point mean roughness (Rz), root mean square slope in the direction perpendicular to the orientation direction of the plurality of fine grooves 27 (RΔq) can be the same as that of the back surface of the protective layer 13 of the lower light diffusion sheet 4 in FIG.

The configuration of the light diffusing sheet is not limited to the three-layered body of the base film, the light diffusing layer, and the protective layer. For example, between the base film and the light diffusing layer, or between the base film and the protective layer. Another layer may be laminated between the layers. Further, the light diffusion sheet may have, for example, a sticking prevention layer in which a plurality of beads are dispersed in a resin matrix instead of the protective layer, and a plurality of fine grooves are formed in the sticking prevention layer. May be. Furthermore, the light diffusion layer does not necessarily have a protective layer.

The light diffusing layer of the light diffusing sheet does not need to have beads and its binder, and for example, a structure in which the surface of the resin layer is embossed can be adopted. Further, a plurality of fine grooves may be formed on the surface having fine irregularities formed by this embossing.

The backlight unit optical sheet may have a functional layer having an uneven shape on the surface. Moreover, when the optical sheet for a backlight unit has such a functional layer, the functional layer may be configured as a resin layer, and a plurality of fine grooves may be formed on the front surface or the back surface of the functional layer. A plurality of fine grooves may be formed on the front surface or the back surface of another layer laminated on the functional layer. In addition, as such uneven | corrugated shape, an emboss shape, a prism shape, a wave shape etc. are mentioned, for example.

Further, the specific shape of the plurality of fine grooves is not limited to the shape of the above-described embodiment. For example, the cross-sectional angle U-shape as shown in FIG. 15 and the cross-sectional triangle shape as shown in FIG. 17 may be formed in a slit shape as shown in FIG.

The backlight unit preferably has a plurality of LED light sources, but may have only one LED light source. Further, the specific type of the optical sheet 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 may have only one optical sheet.

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

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

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[No. 1]
A base film-forming resin mainly composed of polyethylene terephthalate is extruded from a T-die, and a mold having a reverse shape of a plurality of fine grooves on the surface is used. A substrate film having an average thickness of 75 μm was produced by transferring the grooves. Further, a light diffusion layer having a plurality of beads and a binder is laminated on the surface of the base film on which a plurality of fine grooves are formed. 1 light diffusion sheet was obtained. The difference between the refractive index of the base film of the light diffusion sheet and the refractive index of the binder was 0.09. The average width of the fine grooves of this light diffusion sheet is 9.3 μm, the average depth is 2.8 μm, the average pitch is 9.3 μm, the standard deviation of the pitch of the plurality of fine grooves is 6.54 μm, and the plurality of fine grooves The standard deviation of the depth was 1.13 μm, and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves was 1.34 μm. Note that FIG. It is a partial expansion plane photograph of 1 base film.

[No. 2]
No. A sheet body having an average thickness of 75 μm was formed using the same resin as in No. 1. Furthermore, a plurality of fine grooves were formed by laser on one surface of the sheet body to produce a base film. Further, on the surface of the base film on which a plurality of fine grooves were formed, No. A light diffusion layer having a plurality of beads and a binder similar to those of No. 1 is laminated. 2 light diffusion sheets were obtained. The average width of the fine grooves of this light diffusion sheet is 26.9 μm, the average depth is 6.44 μm, the average pitch is 26.9 μm, the standard deviation of the pitch of the plurality of fine grooves is 5.56 μm, the depth of the plurality of fine grooves The standard deviation of the thickness was 2.38 μm, and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves was 0.92 μm. Note that FIG. 2 is a partially enlarged plan view of a base film of No. 2;

[No. 3]
No. A sheet body having an average thickness of 75 μm was formed using the same resin as in No. 1. Furthermore, a plurality of fine grooves were formed with a file on one surface of the sheet body to produce a base film. Further, on the surface of the base film on which a plurality of fine grooves were formed, No. A light diffusion layer having a plurality of beads and a binder similar to those of No. 1 is laminated. 3 light diffusion sheet was obtained. The average width of the fine grooves of this light diffusion sheet is 1.0 μm, the average length is 30 mm, the average depth is 0.5 μm, the average pitch is 18.84 μm, the standard deviation of the pitch of the plurality of fine grooves is 8.29 μm, The standard deviation of the depth of the plurality of fine grooves was 0.56 μm, and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves was 0.30 μm. Note that FIG. 3 is a partially enlarged plan view of a substrate film 3.

[No. 4]
No. A sheet body having an average thickness of 75 μm was formed using the same resin as in No. 1. Further, a plurality of fine grooves were formed on one surface of the sheet body with a cutting bite to produce a base film. Further, on the surface of the base film on which a plurality of fine grooves were formed, No. A light diffusion layer having a plurality of beads and a binder similar to those of No. 1 is laminated. 4 light diffusion sheets were obtained. The average width of the fine grooves of this light diffusion sheet is 32.7 μm, the average depth is 28.1 μm, the average pitch is 31.5 μm, the standard deviation of the pitch of the plurality of fine grooves is 9.73 μm, the depth of the plurality of fine grooves The standard deviation of the thickness was 0.89 μm, and the arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of fine grooves was 4.30 μm.

[No. 5]
No. except that a plurality of fine grooves are not formed. 1 in the same manner as in No. 1. 5 light diffusion sheet was obtained.

No. 1-No. Table 1 shows the quality of the light diffusion sheet 5.

[Examples 1 to 5]
No. A liquid crystal having a plurality of LED light sources such that the average orientation direction of the plurality of fine grooves with respect to the average direction of light rays from the plurality of LED light sources in the light guide film is the angle shown in Table 2. It laminated | stacked on the surface side of the light guide film of the edge light type backlight unit of a display apparatus. Note that FIG. It is a side view photograph of 1 light diffusion sheet.

[Examples 6 to 10]
No. A liquid crystal having a plurality of LED light sources such that the average orientation direction of the plurality of fine grooves with respect to the average direction of light rays from the plurality of LED light sources in the light guide film is an angle shown in Table 2. It laminated | stacked on the surface side of the light guide film of the edge light type backlight unit of a display apparatus.

[Examples 11 to 15]
No. 3 is a liquid crystal having a plurality of LED light sources such that the average orientation direction of the plurality of fine grooves based on the average direction of light rays from the plurality of LED light sources in the light guide film is the angle shown in Table 2. It laminated | stacked on the surface side of the light guide film of the edge light type backlight unit of a display apparatus.

[Examples 16 to 20]
No. 4 is a liquid crystal having a plurality of LED light sources such that the average orientation direction of the plurality of fine grooves based on the average direction of light rays from the plurality of LED light sources in the light guide film is an angle shown in Table 2. It laminated | stacked on the surface side of the light guide film of the edge light type backlight unit of a display apparatus.

[Comparative example]
No. 5 light diffusion sheets were laminated on the surface side of the light guide film of the edge light type backlight unit of the liquid crystal display device having a plurality of LED light sources. Note that FIG. 5 is a side photograph of the light diffusing sheet of FIG.

<Half angle>
For Examples 1 to 20 and Comparative Example, the half-value angle of the front luminance of the light diffusion sheet was measured using “EzContrast” manufactured by ELDIM. The measurement results are shown in Table 2.

<Luminance unevenness>
The backlight units of Examples 1 to 20 and the comparative example were incorporated in a liquid crystal display device, and images of the liquid crystal display device were observed. The presence or absence of uneven brightness was confirmed visually and evaluated according to the following criteria.
A: No luminance unevenness is confirmed.
B: When observed, slight luminance unevenness is confirmed in the vicinity of the light source in plan view.
C: Brightness unevenness is slightly observed in the vicinity of the light source in a plan view even when no gaze is observed.
D: Brightness unevenness is confirmed without gazing.

<Evaluation results>
As shown in Table 2, Examples 1 to 20 in which the average orientation direction of the plurality of fine grooves based on the average direction of light rays from the plurality of LED light sources in the light guide film is 45 ° or less are compared with the comparative example. It has been found that the half-value angle of the luminance in the vertical direction of the light from the LED light source is increased, thereby suppressing luminance unevenness. Moreover, it turned out that the half value angle of the brightness | luminance in the perpendicular direction of the light ray from a LED light source becomes large, and a brightness nonuniformity is easy to be suppressed, so that the average orientation direction of a some fine groove becomes small. Further, Examples 1 to 5 in which a plurality of fine grooves are formed using a mold, Examples 6 to 10 in which a plurality of fine grooves are formed by a laser, and Examples 16 to 10 in which a plurality of fine grooves are formed by a cutting tool. No. 20 can form a desired fine groove as compared with Examples 11 to 15 in which a plurality of fine grooves are formed by a file, thereby increasing the half-value angle of the luminance in the vertical direction of the light from the LED light source, and uneven luminance. It turns out that it is easy to suppress. In addition, as shown in FIGS. 22 and 23, it was found that the occurrence of hot spots caused by the LED light source was suppressed according to the light diffusion sheet in Example 1 as compared with the light diffusion sheet in the comparative example.

As described above, since the optical sheet for a backlight unit and the backlight unit of the present invention can suppress hot spots, they are suitably used for various liquid crystal display devices such as a high-quality transmissive liquid crystal display device. .

DESCRIPTION OF SYMBOLS 1

Light guide film

2,82 LED light source 3

Optical sheet

4,24,34,44,54,64,74 Lower light diffusion sheet 5 First prism sheet 6 Second prism sheet 7 Upper light diffusion sheet 8

Reflective sheet

11 , 25, 35

Base film

12, 36, 45

Light diffusion layer

13, 26, 37, 75

Protective layer

14, 38, 46

Beads

15, 39, 47

Binder

16, 27, 40, 48, 76, 86 Fine groove 17 Concave portion 18 Raised portion 101 Edge light type backlight unit 102 Light source 103 Light guide sheet 104 Optical sheet 105 Reflective sheet 106 Light diffusion sheet for lower side 107 Prism sheet 108 Light diffusion sheet for upper side

Claims

An optical sheet for a backlight unit of a liquid crystal display device for guiding light emitted from an LED light source to the surface side,
Comprising one or more resin layers,
An optical sheet for a backlight unit, wherein a plurality of fine grooves oriented in a specific direction are formed on the front side or the back side of at least one of the resin layers.
2. The backlight unit optical according to claim 1, wherein an average number of the plurality of fine grooves per unit length in a direction perpendicular to an average orientation direction of the plurality of fine grooves is 10 / mm or more and 10,000 / mm or less. Sheet.
The arithmetic average roughness (Ra) in the direction perpendicular to the orientation direction of the plurality of microgrooves on the surface of the resin layer on which the microgrooves are formed is 0.01 μm or more and 5 μm or less. The optical sheet for backlight units as described.
The optical sheet for a backlight unit according to claim 1, 2 or 3, wherein the plurality of fine grooves constitute a diffraction grating.
The optical sheet is
A base film;
Laminated on the surface side of this base film, a light diffusion layer having a plurality of beads and its binder, and
An optical sheet for a backlight unit according to any one of claims 1 to 4, wherein the optical sheet is a light diffusing sheet comprising a protective layer laminated on the back side of the base film.
The optical sheet for a backlight unit according to claim 5, wherein the plurality of fine grooves are formed on the back side of the protective layer.
The optical sheet for a backlight unit according to any one of claims 1 to 4, further comprising a functional layer having a concavo-convex shape on a surface thereof.
8. The method according to claim 1, wherein one resin layer has a plurality of fine irregularities on a surface, and the plurality of fine grooves are formed on a surface of the resin layer having the plurality of fine irregularities. The optical sheet for backlight units as described.
A light guide film or a light guide plate that guides light incident from the end surface side to the surface side;
One or a plurality of LED light sources disposed on the end face side of the light guide film or light guide plate and emitting light rays to the end face of the light guide film or light guide plate;
The backlight unit of a liquid crystal display device provided with the optical sheet of any one of Claims 1-8 superimposed on the surface side of the said light guide film or light guide plate.
The backlight unit of the liquid crystal display device according to claim 9, wherein the optical sheet is directly superimposed on a surface of the light guide film or the light guide plate.
The average orientation direction of the plurality of fine grooves of the optical sheet based on the average direction of light rays from the LED light source in the light guide film or light guide plate in plan view is ± 45 ° or less. The backlight unit according to 10.