JP5182639B2 - Optical sheet, backlight unit and display device - Google Patents

Description

  The present invention relates to an illumination optical path control optical sheet having an optical shape for condensing and / or diffusing light on at least one surface of a substrate, and further using this optical sheet, a liquid crystal panel The present invention relates to a backlight unit that illuminates an image display element such as the above from the back side, and a display device including the backlight unit.

In recent years, liquid crystal display devices using TFT liquid crystal panels and STN liquid crystal panels have been commercialized mainly for color notebook PCs (personal computers) in the OA field. In such a liquid crystal display device, a so-called backlight method is generally employed in which a light source is disposed on the back side (opposite to the observer) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source. .
The backlight units employed in this type of backlight method are roughly classified into a “light guide plate light guide method” (so-called edge light method) and a “direct type”.

As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 11 is generally known.
In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and a light guide plate 79 made of a transparent base material such as PMMA (polymethyl methacrylate) or acrylic is installed on the lower surface side thereof. A diffusion film (diffusion layer) 78 is provided on the light exit surface side of the light guide plate 79. On the lower surface of the light guide plate 79, a scattering reflection pattern portion for scattering and reflecting light so as to be uniform in the direction of the liquid crystal panel 72 is provided by printing or the like, and a reflection film ( A reflective layer 77 is provided.

In addition, a light source lamp 76 is attached to a side end portion of the light guide plate 79, and a reflector 81 having a high reflectivity is provided on the back surface thereof. The scattering reflection pattern portion is a mixture of white titanium dioxide (TiO ₂ ) powder mixed with a transparent adhesive solution or the like formed in a predetermined pattern, for example, a dot pattern, and enters the light guide plate 79. The light is given directivity and led to the light exit surface side to increase the brightness.
Furthermore, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 12, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is used. ) 74 and 75 are proposed. The prism films 74 and 75 condense the light diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

  On the other hand, the direct type is used in a liquid crystal display device such as a large-sized liquid crystal TV in which it is difficult to use a light guide plate. As a direct type liquid crystal display device, a device illustrated in FIG. 13 is generally known. This device emits light emitted from a light source 51 such as a fluorescent tube arranged on the lower surface side of a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 and diffuses light diffused by a diffusion film 82 with high efficiency. Focus on the display area. A reflector 52 is disposed on the back surface of the light source 51.

By the way, in the above-mentioned backlight unit, etc., an optical (lens) in which a large number of convex lens patterns such as prisms are arranged in order to improve the luminance of the backlight unit and improve the light diffusibility and uniformity. ) Sheet is used.
Usually, an optical sheet is cut into a predetermined shape after manufacture, integrated with a display device through transportation and assembly to an assembly factory, and displayed and used after transportation to a store. In all of these processes, the surface of the optical sheet is exposed to the risk of scratching and coming into contact with other members such as the back surface of another optical sheet laminated by vibration during manufacturing, assembly, transportation, etc. It is. In particular, since the optical sheet is usually made of a synthetic resin, the shape of lens parts such as a lens pattern is often made of a material that is easily damaged, which causes the optical performance to be remarkably deteriorated due to, for example, irregular reflection of light transmitted through the scratch.

  In order to prevent this, it is effective to physically harden the surface having an optical shape or to make it slippery. However, these methods are not highly versatile because it is necessary to limit the materials or to provide a coating step. In addition, sticking a protective film to the surface of the lens sheet is a highly versatile method, but the number of steps to remove the protective film when using the optical sheet is increased, and the protective film is eventually discarded. It is difficult to say that it is an efficient way to produce waste.

As means for preventing the lens pattern of such an optical lens sheet from being scratched, for example, a lens film described in Patent Document 1 has been proposed.
For this optical sheet, a method has been proposed in which a lens pattern transferred onto a sheet base material is taken up by a take-up roller. This lens pattern has a contact prevention protrusion with a height higher than that of the many convex shapes formed on the sheet base material in order to prevent the convex tips transferred and formed on the sheet base material from contacting and deforming. A part is provided in a part, and when it winds up, the contact prevention protrusion part contacts a sheet base material, and other many convex shapes do not contact a sheet base material.
In this case, it is specified that the difference in height between the contact preventing protrusion and the convex shape having a height lower than this is 5.0 μm, at least 1.0 μm.

The optical sheet described in Patent Document 2 is configured by arranging a plurality of prism elements on one surface from which light is emitted, and the first prism element is formed higher than the second prism element. The prism element has a blunt tip shape such as a flat top, and the second prism element has a sharp tip. The height difference Δ between the first and second prism elements is set to about 2 μm to 10 μm. Since the first prism element has a blunt tip, it is assumed that it is not easily damaged even if it is rubbed during transportation, storage, use, etc., and the second prism element is easily damaged but has the maximum gain in on-axis light. .
In addition to the conventionally used prisms, lenticular lenses, microlenses, and polygonal pyramids, there are proposals for various optical shapes as shown in Patent Documents 3 and 4 for the purpose of improving the performance of optical sheets. However, new shapes are expected to increase.
JP 2008-203776 A Special table 2008-517256 JP 2008-515026 A Special table 2008-102497

However, the optical sheet described in Patent Document 1 is limited to a case where the optical sheet is wound in a roll shape, and needs to be cut into predetermined dimensions when used by being mounted on a display. When the cut optical sheets are stacked and stored or mounted on a display device such as a television set, the above-described height difference between the contact-preventing protrusions and other convex shapes, which are lens elements, is abraded. Then, the tip of another convex lens element is damaged, and if it is attached to a display, the optical characteristics may be deteriorated.
Further, in the optical sheet described in Patent Document 2, the height difference Δ between the first and second prism elements is about 2 μm to 10 μm. By rubbing the surface with an object or the like, the second lens element having a sharp tip is scratched, and there is a problem that the optical performance is deteriorated.

  In view of such circumstances, the present invention provides an optical sheet that suppresses damage to an optical member for condensing or diffusing even if it is rubbed with another member, and does not deteriorate optical performance, and the optical sheet. An object of the present invention is to provide a backlight unit and a display device using the display.

An optical sheet according to the present invention is an optical sheet having an optical shape for condensing or diffusing light on at least one surface of a substrate, and the optical shape includes the optical projection having the highest height and the optical projection. And a ratio of the total area of the optical protrusions to the area of the optical sheet in a plan view is 4% or more and 45% or less, and the base of the optical protrusions. The height from the material is set as h, and the optical element excluding the optical protrusion is set to the highest height from the base material as hi, so that the following formula (1) is satisfied .
20 μm <h-hi ≦ 100 μm (1)
The optical protrusion is a cylindrical lens, and the optical element has a lenticular lens group in which a plurality of compound prism lenses are arranged,
The composite prism lens has a shape in which a plurality of prism lenses having curved side surfaces on both sides are partially overlapped and integrated in the arrangement direction of the composite prism lens,
The width in the arrangement direction of the compound prism lenses in the single prism lens is set as a pitch P0, and the deviation in the arrangement direction of the compound prism lens from one prism lens in the compound prism lens and the other prism lens adjacent to the one prism lens is performed. When the distance that does not overlap is the shift amount △,
(1/5) P0 ≦ △ ≦ (2/3) P0 (2)
The curved side surface of the prism lens has the relationship of the above formula (2), and the lens shape thereof is defined by the following formula (3), and the tangent at the other end portion of the curved side surface extending from one end portion of the prism lens. An optical sheet, wherein an inclination angle θ with respect to the surface of the optical sheet is 25 ° or more and 50 ° or less .

In the above equation (3), A, B, and C are correction coefficients. When the pitch of the composite prism lens is normalized to 1, z is a position function in the height direction of the composite prism lens, and r is It is a position variable in the width direction of the composite prism lens.

According to the present invention, when the top portion of the optical member of the optical sheet is a corner portion, the brightness is high, but there is a characteristic that the top portion of the optical element is in contact with or scratched with other members. Such damage can be protected by an optical projection having a height higher than that of the optical element. For this reason, scratches or the like are unlikely to occur at the top of the optical element having an area of 50% or more of the optical sheet, so that it is possible to sufficiently exhibit the light condensing or diffusing characteristics of the light transmitted through the optical sheet and maintain high luminance. In addition, high brightness can be ensured even in the optically protruding portion in a region having no scratch.
In particular, when the optical element includes a top portion having a corner portion having a relatively high luminance, the optical element can be protected by an optical projection having a relatively low luminance and a height higher than that of the optical element, and a decrease in luminance due to scratches can be suppressed.
In addition, if the height difference h-hi between the optical protrusion and the optical element is within the range of the above formula (1), the optical element is reliably protected by the optical protrusion and hardly damaged, and the optical sheet is made of synthetic resin. When manufacturing, an optical sheet having good optical characteristics can be obtained without bubbles being enclosed in the deepest optical protrusion of the mold. On the other hand, if the height difference h-hi is 20 μm or less, the optical sheet is likely to be scratched due to the top of the optical element coming into contact with another optical sheet or the like due to vibration or the like, and the light condensing or diffusing characteristics are deteriorated. Also, if the height difference h-hi exceeds 100 μm, when producing an optical sheet by injection molding or the like with a synthetic resin, there is no escape space for bubbles mixed in the synthetic resin filled in the deepest optical protrusion, and the optical protrusion The optical characteristics are deteriorated by being contained in the case.

According to the optical sheet of the present invention, the composite prism lens has a shape in which a plurality of prism lenses having curved side surfaces are partially overlapped and integrated, so that the condensing effect by the curved side surfaces of the plurality of prism lenses is large and the luminance is high. Since a wide viewing angle can be obtained and side lobes can be suppressed, useless light that deviates from the visual direction can be reduced.
Moreover, according to the present invention, the curved side surface of the compound prism lens is formed by the lens shape defined by the expression (3), so that the light collecting effect can be enhanced, and the tangent at the other end of the curved side surface. Is set in the range of 25 ° to 50 °, the balance between the light condensing effect and the visual field range can be secured. In addition, an optical sheet in which the converging effect and the visual field range are balanced is obtained only in a range where the curved side surface of the curved side defined by the above formula (3) and the inclination angle θ match with each other. ) If each coefficient in the formula is out of the specified range, the light collecting effect cannot be obtained, or side lobes are likely to occur.
In the above equation (3), k is a spherical surface when k = 0, an ellipse when -1 <k <0, a paraboloid when k = -1, and a hyperboloid when k <-1.

The optical protrusion may have a roundness at the top.
If the top of the optical projection is rounded, it will be hard to be damaged, but light will diffuse and the center brightness will be relatively low.On the other hand, if the height and distribution required for the optical projection are set, the brightness will be maintained. It becomes possible to give scratch resistance.
Further, the pencil height of the material of the optical sheet may be 4H or less, and when the pencil hardness is higher than 4H, the flexibility is lowered and the handling property at the time of processing is lowered.

Moreover, the optical protrusion and the optical element have a cylindrical shape, and may be arranged in parallel to each other, or the optical protrusion and the optical element may be arranged so as to cross each other.
The optical protrusion is preferably a cylindrical lens, and the optical element is preferably a prism lens. As a result, the optical projection having a high height protects the optical element and is not easily damaged, and the optical element has higher light collection characteristics and relatively high brightness.

The display backlight unit according to the present invention includes at least a light source and the optical sheet according to any one of claims 1 to 7 on a back surface of an image display element that defines a display image. And
ADVANTAGE OF THE INVENTION According to this invention, it can suppress that an optical element of an optical sheet is damaged, and can make a brightness | luminance higher.
The light source may be a cold cathode tube, LED, EL, or semiconductor laser.

The display device according to the present invention includes an image display element including a liquid crystal display element that defines a display image in accordance with transmission / shielding in pixel units, a light source, and the backlight unit according to claim 8 or 9. It is characterized by providing.
ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the optical element of an optical sheet damages, and can display a high-intensity image.

In the optical sheet, the backlight unit and the display device according to the present invention, the difference in height between the optical projection having the highest height and the optical element having a lower height is set in a range from 20 μm to 100 μm. Since the ratio of the total area of the optical protrusions to the area of the optical sheet is 4% or more and 45% or less, it is the highest in the state where the optical sheet is stacked or stored and moved or stored, or attached to the display device. The top of the optical element having a relatively high brightness can be protected by the high optical projection to prevent scratches, and the scratch resistance can be improved, and the brightness of the entire optical sheet including the optical projection can be kept high. Thereby, the luminance of the backlight unit and the display device can be maintained high.
In addition, according to the present invention, the compound prism lens has a shape in which a plurality of prism lenses having curved side surfaces are partially overlapped and integrated, so that the condensing effect by the curved side surfaces of the plurality of prism lenses is large and wide with high brightness. A viewing angle can be obtained, and side lobes can be suppressed, so that useless light deviating from the visual direction can be reduced.
Moreover, according to the present invention, the curved side surface of the compound prism lens is formed by the lens shape defined by the expression (3), so that the light collecting effect can be enhanced, and the tangent at the other end of the curved side surface. Is set in the range of 25 ° to 50 °, the balance between the light condensing effect and the visual field range can be secured. In addition, an optical sheet in which the converging effect and the visual field range are balanced is obtained only in a range where the curved side surface of the curved side defined by the above formula (3) and the inclination angle θ match with each other. ) If the coefficients in the equation are out of the specified range, the light collecting effect cannot be obtained, or side lobes tend to occur.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 to 4 show an optical sheet and a display device according to the first embodiment of the present invention. FIG. 1 is a configuration diagram of a main part of the display device including the optical sheet according to the first embodiment. FIG. FIG. 3 is a side view of the optical sheet, and FIG. 4 is a side view showing a state in which the optical sheets are stacked.
A display device 1 shown in FIG. 1 includes a backlight unit 2 and a liquid crystal panel (liquid crystal display element) 3 as an image display element. In the backlight unit 2, for example, a plurality of light sources 4 composed of cold cathode fluorescent lamps (CCFTs) arranged at predetermined intervals, and a reflector 5 that is disposed on the back surface of the light source 4 and reflects emitted light on the back surface side. The lamp house 6 is configured as described above. Furthermore, a light diffusion plate 7 as a light diffusion layer for diffusing light entering from the light source 4 is disposed on the front side of the light source 4 in the light irradiation direction.
The light source 4 is not limited to a cold cathode tube, and an EL, LED, semiconductor laser, or the like can be employed. The liquid crystal panel 3 is configured by sandwiching a liquid crystal element 10 between polarizing plates 9 and 9.
In addition, although the display apparatus 1 by this embodiment shows a liquid crystal display device, if it is a display apparatus which displays an image with light, such as not only this but a projection screen apparatus, a plasma display apparatus, and an EL display apparatus, the display apparatus 1 of FIG. Any type.

The optical sheet 12 has the configuration shown in FIGS. 2 and 3, and a plurality of lens elements for condensing or diffusing light are arranged on one surface of a base portion 13 that is a base material. As these lens elements, a plurality of optical protrusions 14 made of a substantially semi-elliptical cylindrical lens are arranged in parallel at predetermined intervals. Between the optical protrusions 14, for example, prism lenses having a substantially triangular prism shape in cross section are arranged as optical elements 15 in a direction substantially orthogonal to the optical protrusion 14.
The optical protrusion 14 is formed with a height higher than the base 13 than the optical element 15 made up of a large number of arranged prism lenses. For example, when a plurality of optical sheets 12 are stacked and stored, transported, etc. The base 13 of the optical sheet 12 is protected from coming into contact with the top of the optical element 15 having a corner such as 90 °.

The optical element 15 is not limited to a prism lens, and a lens shape made of a cylindrical lens, a lenticular lens, a microlens, a polygonal pyramid, or a combination thereof may be adopted. The optical element 15 is not limited in the type or shape of the optical shape, but from the viewpoint of preventing the lens portion from being damaged by having higher brightness than the optical projection 14, an optical shape having a corner at the top is adopted. Is appropriate.
The optical projection 14 is not limited to a cylindrical lens shape, and a prism, a microlens, a polygonal pyramid, or a lens shape obtained by combining these can be appropriately employed. The optical protrusion 14 is not limited in the type or shape of the optical shape, but is an optical shape having a rounded top with no corners, such as a substantially semi-cylindrical shape to prevent scratching by scratching the top. It is preferable.
Since the optical protrusion 14 also has a cylindrical lens shape, it has an optical characteristic of condensing or diffusing transmitted light.

Further, the height of the optical projection 14 having the highest height is defined as h with reference to the base portion 13 of the optical sheet 12, and the height of each optical element 15 having a height lower than the optical projection 14 and a corner at the top is defined as h. As hi, h is preferably the same height among the plurality of optical protrusions 14, but the height hi of the optical element 15 can be set to any height as long as the following expression (1) is satisfied. In the optical sheet 12 shown in FIG. 2, the optical elements 15 have a plurality of different heights hi, and all the optical elements 15 satisfy the following formula (1).
20 μm <h-hi ≦ 100 μm (1)
Here, if the height difference h-hi between the optical protrusion 14 and the optical element 15 is within the range of the expression (1), the optical element 15 is reliably protected by the optical protrusion 14 and is less likely to be scratched by scratching or the like. An optical sheet 12 with good optical characteristics is manufactured without air bubbles being caught in the deepest optical projection 14 when the optical sheet 12 is made of synthetic resin by an injection molding method or the like while ensuring high brightness. it can.

  On the other hand, when the height difference h-hi is 20 μm or less, the tops of the plurality of optical elements 15 of the optical sheet 12 are stacked on top of each other due to bending or vibration of the optical sheet 12 stacked during storage or transportation. There is an inconvenience that scratches are likely to occur due to contact with the base portion 13 of another optical sheet 12, and light condensing through the scratches is scattered to deteriorate the light collecting characteristics. When the height difference h-hi exceeds 100 μm, when the optical sheet 12 is manufactured by injection molding or the like with a synthetic resin, the molten synthetic resin is melted with the optical element 15 having the lowest height hi as a reference. Since there is no escape space for bubbles mixed in the synthetic resin filled in the optical projection 14 to fill the mold, the defective product in which the optical characteristics of the optical sheet 12 deteriorate due to being enclosed in the optical projection 14 is manufactured. There is a risk of malfunction occurring.

Further, in the plan view of the optical sheet 12, the area ratio of the optical protrusions 14 to the area of the optical sheet 12 is As / S, where S is the area of the optical sheet 12 and As is the total area of the plurality of optical protrusions 14. Is 4% or more and 45% or less.
If the area ratio As / S is within the above numerical range, the optical projections 14 of the optical sheet 12 are in contact with the other members such as the base 13 of the other optical sheet 12 and the optically microscopically. When the protrusion 14 touches the other optical sheet 12, it is possible to prevent the optical element 15 which is another lens portion from coming into contact with the optical element 12 and prevent the optical element 15 from being damaged. On the other hand, if the area ratio As / S is less than 4%, the top of the optical element 15 is likely to come into contact with the base 13 of the other optical sheet 12 due to bending or vibration, and if it exceeds 45%, the optical protrusion 14 The contact area of the other optical sheet 12 with the base portion 13 is increased, and scratches are likely to increase, which greatly affects the optical characteristics to be exhibited by the optical protrusion 14.
In addition, since the optical protrusion 14 also has a function of optical characteristics for condensing or diffusing transmitted light, high brightness can be maintained by the optical protrusion 14.

  Although there is no restriction | limiting in the material used for the optical sheet 12 in this embodiment, since there is no meaning which employ | adopts the structure of this embodiment with the raw material which is hard to damage, it is appropriate to use the material whose pencil hardness is 4H or less.

As the main material of the optical sheet 12, for example, polycarbonate, acrylic-styrene copolymer, polystyrene, styrene-butadiene-acrylonitrile copolymer, or cycloolefin polymer may be used.
The optical sheet 12 preferably includes transparent particles dispersed in a main material, and the refractive index of these main materials and the refractive index of the transparent particles are different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the refractive index difference is 0.5 or less. The average particle size of the transparent particles is preferably 0.5 to 30.0 μm.

As the transparent particles, transparent particles made of an inorganic oxide or transparent particles made of a synthetic resin can be used. For example, examples of the transparent particles made of an inorganic oxide include particles made of silica, alumina or the like. Moreover, transparent particles made of synthetic resin include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof; melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP ( Examples thereof include fluorine-containing polymer particles such as tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles.
These transparent particles may be used as a mixture of two or more kinds. Alternatively, the plate-like member constituting the optical sheet 12 may have a structure having a fine cavity containing air in the main material, and the diffusion performance is improved by the difference in refractive index between the main material and air. Can be obtained.
The optical sheet 12 may have a single layer structure or a multilayer structure, and may include a transparent layer.

The optical sheet 12 can be manufactured by an extrusion method, a casting method, or an injection method. As the plate-like member for producing the optical sheet 12, one having a thickness of 12 μm or more and 1 mm or less can be used. When the thickness is less than 12 μm, there is no rigidity capable of withstanding the processing by the manufacturing method described above, and when the thickness exceeds 1 mm, there is no flexibility capable of withstanding the processing.
The optical sheet 12 may be manufactured by a UV curing method.
When prepared by the UV curing method, a UV curable resin is applied onto the base portion 13 which is a sheet-like base material, a mold having a desired shape is pressed, and then UV irradiation is performed to irradiate the base portion 13 and the optical projection. The optical sheet 12 including the portion 14 and the optical element 15 is obtained. As the sheet-like substrate, PET (polyethylene terephthalate), polycarbonate, acrylic, polypropylene films and the like well known in the art can be used.

The light diffusing plate 7 can be made of the same main material as that of the optical sheet 12 and may be configured to include the transparent particles described above. The refractive index of these main materials and the refractive index of transparent particles need to be different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the refractive index difference may be 0.5 or less.
Moreover, since it is necessary to permeate | transmit the light which injected into the light diffusing plate 7, it is desirable that the average particle diameter of a transparent particle is 0.5-30.0 micrometers. Alternatively, the light diffusing plate 7 may adopt a structure in which fine cavities containing air are contained as transparent particles in the main material, and in this case, the diffusion performance is obtained by the difference in refractive index between the main material and air. be able to.

When the optical sheet 12 according to the present embodiment is used, as shown in FIG. 4, when the manufactured optical sheet 12 is stacked and stored in a box or the like, vibration or dropping occurs when the optical sheet 12 is transported or stored. Even if there is an impact such as, the plurality of optical sheets 12 in the stacked state are in contact with the optical projections 14 of the lower optical sheet 12 with the base portions 13 of the other optical sheets 12 placed on the upper stage. . Therefore, even if the top of the optical projection 14 of the lower optical sheet 12 is rubbed by the base 13 of the upper optical sheet 12, even if the optical projection 14 is damaged, it does not contact the optical element 15 having the corner apex. It wo n’t hurt.
Therefore, when the optical sheet 12 is mounted on the display device 1 and the light from the light source 4 passes through the light diffusion plate 7 and the optical sheet 12, some of the light that passes through the scratched portion of the optical protrusion 14 is refracted. However, the light that passes through the part of the optical projection 14 that is not scratched or the light that passes through the optical element 15 that is a prism lens is condensed or diffused to cause the liquid crystal element 3 to pass through. It will be transparent.
In addition, even when something contacts or collides with the surface of the optical sheet 12 in a state where the optical sheet 12 is incorporated in the display device 1, the top of the optical element 15 is contacted with the optical projection 14 first. The possibility of contact is small and scratches are difficult to occur. Alternatively, in the display device 1, even if the liquid crystal element 3 is pressed and curved toward the optical sheet 12, the top of the optical element 15 is protected because the optical projection 14 contacts and receives the liquid crystal element 3.

Next, the operation of the display device 1 according to the first embodiment will be described.
In FIG. 1, light from the light source 4 enters the diffusion plate 7 and is emitted as diffused light. Thereafter, the light diffused from the exit surface of the light diffusion plate 7 enters the optical sheet 12. In the optical sheet 12, the light transmitted through the optical element 15 is collected, and the light transmitted through the optical protrusion 14 is partly transmitted light at the part that is damaged during transportation or the like. Is condensed and emitted along the characteristics of the cylindrical lens.
Then, the condensed light transmitted through the light sheet 12 is emitted as light La, the light La reaches the liquid crystal element 10 sandwiched between the polarizing plates 9 of the liquid crystal panel 3, and the light transmitted therethrough is diffused to the outside. The light is emitted and is visually recognized by an observer.

As described above, even if the optical sheet 12 according to the present embodiment is a relatively soft material having a pencil hardness of 4H or less, the lens member surface which is one surface thereof is higher than the optical element 15 made of a prism lens, and the difference exceeds 20 μm. Since the optical projection 14 having a thickness of 100 μm or less is provided, it is possible to prevent the optical element 15 having a high light collection / diffusion performance from being damaged due to contact of other members, etc., and the optical performance including the optical projection 14 is high. Can be secured. Therefore, it is not necessary to stick a protective film or apply a coating layer on the lens member surface of the optical sheet 12.
Further, in the backlight unit 2 and the display device 1 on which the optical sheet 12 is mounted, the optical sheet 12 can be given scratch resistance to exhibit high luminance characteristics.

Next, other embodiments and modifications of the optical sheet according to the present invention, and other display devices will be described with reference to FIGS. 5 to 10, but the same or similar parts as the optical sheet 12 and the display device 1 according to the above-described embodiments. The members are denoted by the same reference numerals and the description thereof is omitted.
5 and 6 show an optical sheet 20 according to the second embodiment of the present invention.
In this optical sheet 20, in the optical sheet 12 according to the first embodiment, a plurality of compound prism lenses 21 are arranged as optical elements 15 in a direction substantially orthogonal to the optical protrusions 14 instead of the prism lenses. The compound prism lens 21 has a substantially petal shape in cross-sectional view and is arranged in the same direction, and as shown in FIG. They are partially overlapped and shifted by a shift amount Δ in the arrangement direction to be combined or integrated. The two prism lenses 21a and 21a have the same shape that is symmetric with respect to the left and right, but are not necessarily symmetric with respect to the left and right.
The shift amount Δ is set in the range of the following expression (2) when the arrangement pitch of the prism lenses 21a is P0.
(1/5) P0 ≦ Δ ≦ (2/3) P0 (2)
Here, if the shift amount Δ is smaller than the lower limit value (1/5), the light condensing effect is small, and if it exceeds the upper limit value (2/3) P0, side lobes are likely to occur, which is not desirable.

The compound prism lens 21 has four curved side surfaces 21aa and 21ab having long and short convex curved surfaces, and the luminance distribution of light from the light source 4 transmitted through the optical sheet 20 is condensed in the front direction (axial direction). Highly effective and side lobe is unlikely to occur. In addition, since there is a degree of freedom in design with respect to the curved side surfaces 21aa and 21ab defined by the following equation (3), for example, when it is desired to concentrate strongly on the front side or to obtain a wide viewing angle, the side shape must be changed for each. It is possible to obtain desired characteristics.
Each apex R0 of the pair of prism lenses 21a and 21a of the composite prism lens 21 forms a corner.

Here, the curved side surfaces 21aa and 21ab of the compound prism lens 21 are defined as follows.
In FIG. 6, focusing on one lens curved surface with the apex R0 of one prism lens 21a forming the composite prism lens 21 as a boundary, one end of the lens overlapping the base material 13 is denoted by R1.
Then, assuming that the curved side surface 21aa starts from the lens one end R1, the inclination angle θ of the tangent L at an arbitrary point of the lens curved surface with respect to the surface of the substrate 13 is 25 ° or more between the lens one end R1 and the apex R0. A point that is 50 ° or less is defined as the other end R2 of the curved side surface 21aa. In this case, between the lens one end R1 and the other end R2, the inclination angle θ of the tangent line La with respect to the base material 13 at an arbitrary point is set to a convex curved surface having a size exceeding 50 °, and the lens one end R1. The inclination angle θ of the tangent line L gradually decreases from the second end portion R2 toward the other end portion R2, and the inclination angle θ of the tangent line La is in the range of 25 ° to 50 ° for the first time at the other end portion R2.
Here, if the inclination angle θ at the other end R2 is less than 25 °, the field of view is widened, but the light condensing effect is low. Conversely, if it exceeds 50 °, the field of view is narrow and side lobes are likely to occur.
The lens curved surface that forms a convex shape outward from the lens one end R1 to the other end R2 is defined as a curved side surface 21aa, and the same definition is applied to the other curved side surface 21ab of the prism lens 21a. . As the lens shapes of the curved side surfaces 21aa and 21ab, the general formula of the aspheric lens shape shown by the following formula (3) is applied.
However, in the composite prism lens 21, the curved side surface 21ab is defined to have a relatively short length from the trough where the curved side surfaces 21ab, 21ab intersect each other to the other end R2.

In the above equation (3), z is a function of r, which is a position variable in the width direction of the composite prism lens 21, and the value represents the height direction of the composite prism lens 21. In Equation (3), k = 0 is a spherical surface, −1 <k <0 is an ellipse, k = −1 is a paraboloid, k <−1 is a hyperboloid, 1 / R is a coefficient for r, A, B, and C are correction term coefficients.
Further, the coefficients 1 / R, A, B, and C in the above equation (3) are within a specified range (−10 <1 / R <10, −5 <A <5, −10 <B <10, −30 <C < When deviating from 30), there is a drawback that a light condensing effect cannot be obtained or a side lobe easily occurs. That is, a lens sheet that provides a balance between the light collection effect and the field-of-view range is provided only in a range in which the curved shape represented by the expression (3) matches the inclination angle θ.
The prism lenses 21a and 21a constituting the compound prism lens 21 have defined curved side surfaces 21aa and 21ab, and the shape thereof is symmetrical in the range of the curved side surface 21ab having a short length from the valley portion to the top portion R0. It is desirable. In this case, since the composite prism lens 21 is also bilaterally symmetric, the optical sheet 20 having no bias in the visual field range is formed.

Here, as a first aspect of the tip portion including the apex R0 of each prism lens 21a of the composite prism lens 21, the curved side surfaces 25aa and 21ab may extend to the apex R0. Further, the curved side surfaces 21aa and 21ab may be provided with the other end R2 at a position in the vicinity of the apex that does not reach the apex R0, and the other end R2 and the apex R0 may be connected by a straight line to form a roof-shaped tip. . Thereby, a visual field range can be narrowed and the condensing effect can be improved.
Further, the other end R2 of the curved side surfaces 21aa and 21ab is positioned in the vicinity of the apex R0 that does not reach the apex R0 of the prism lens 21a, and the other end R2 and the apex R0 are formed by a convex curved surface having a radius of curvature R. May be formed. Thereby, the visual field range is widened and the wear resistance is improved.
However, if the radius of curvature R of the convex curved surface at the tip is too large, the brightness is lowered. Therefore, the radius R is preferably R ≦ P0 / 5 when the pitch of the prism lens 21a is P0.
Also in this embodiment, the height difference h−hi between the optical protrusion 14 and the optical element 15 including the composite prism lens 21 satisfies the above expression (1), and the optical protrusion occupies the area of the optical sheet 20 in plan view. The area ratio As / S of the part 14 is 4% or more and 45% or less.

Since the display device 1 including the optical sheet 20 according to the present embodiment has the above-described configuration, light emitted from the light source 5 to the liquid crystal panel 3 side can pass through the light diffusion plate 7 and exhibit sufficient light scattering performance. The light is emitted as diffused uniform light and is incident on the incident surface of the optical sheet 20.
In the optical sheet 20, a plurality of compound prism lenses 21 and optical protrusions 14 are arranged as optical elements 15 on the exit surface side in a substantially orthogonal direction, and the curved side surfaces 21aa and 21ab of each compound prism lens 21 are (3 ) Is formed so as to be refracted and condensed by the four curved side surfaces 21aa and 21ab for each compound prism lens 21, so that the condensing effect toward the liquid crystal panel 3 is obtained. Large and can suppress the occurrence of side lobes.
Further, light passing through each tip including the apex R0 having the convex curved surface having the radius R of the compound prism lens 21 is refracted within a range in which a decrease in luminance can be suppressed, and the field of view is widened.
In addition, the optical projection 14 constituting the cylindrical lens is also condensed and emitted toward the liquid crystal panel 3.
Therefore, the light condensed by the liquid crystal panel 3 has high axial brightness, and the peak width of the curve of the brightness distribution can be appropriately widened to suppress side lobes.

  As described above, according to the optical sheet 20 according to the present embodiment, the same effects as the optical sheet 12 according to the first embodiment can be obtained, and the curved side surfaces 21aa and 21ab forming the aspherical shape of each composite prism lens 21 can be obtained. As the shape swells outward, the field of view range can be expanded and the light collection characteristics can be enhanced to exhibit high luminance and smooth luminance distribution characteristics without side lobes.

Next, an optical sheet 25 according to a third embodiment of the present invention will be described with reference to FIG.
In the optical sheet 25 shown in FIG. 7, an optical protrusion 14 made of a substantially cylindrical lens is disposed on one side of the base portion 13, for example, in the center, and a prism lens 26 having a substantially triangular prism shape is formed as an optical element 15 on both sides of the optical protrusion 14. Are arranged in parallel. The heights hi of the plurality of prism lenses 26 from the base portion 13 may be appropriately different or may be the same, but the height difference (h-hi) between the optical projection 14 and the prism lens 26 is expressed by the above equation (1). Satisfied. Similarly, the area ratio As / S between the optical sheet 25 and the total area of the optical protrusions 14 is also set in the range of 4% to 45%.

  FIG. 8 shows an optical sheet 28 according to the fourth embodiment. An optical protrusion 14 made of a substantially cylindrical lens is disposed on one side of the base 13 at the center, for example, and the second optical element 15 described above as the optical element 15 on both sides thereof. The compound prism lens 21 shown in the embodiment is arranged in parallel with the optical protrusion 14. The heights hi of the plurality of compound prism lenses 21 from the base 13 may be appropriately different or may be the same, but the height difference (h-hi) between the optical projection 14 and the compound prism lens 26 is the above formula (1). Satisfied. Similarly, the area ratio (As / S) between the optical sheet 28 and the total area of the optical protrusions 14 is set in the range of 4% to 45%.

The optical protrusion 14 provided on the base 13 of the optical sheet is preferably in the form of a cylindrical lens, but it may also be in the form of dots (mountain shapes) arranged dispersedly.
FIG. 9 shows a modification of the optical sheet according to the embodiment. In the optical sheet 30 according to this modification, the optical protrusions 14 and the optical elements 15 are formed in dots instead of columns. In addition, the optical projections 14 are disposed at the four corners of the base 13, and the optical elements 15 are arranged inside thereof. Even in this case, the height difference (h-hi) between the optical protrusion 14 and the optical element 15 satisfies the above-described expression (1). Similarly, the area ratio (As / S) between the optical sheet 30 and the total area of the optical protrusions 14 is also set in the range of 4% to 45%.
The optical protrusion 14 is formed in, for example, a mountain shape, and the optical element 15 is formed in a quadrangular pyramid shape. However, a dot shape can be adopted as appropriate. Even in this case, it is preferable that the optical element 15 is formed so that the tip has a corner portion to enhance the light collecting effect and improve the luminance. In FIG. 9, gaps remain between the optical projections 14 and the optical elements 15 on the base 13, but these gaps are made as small as possible and not provided in order to improve the light collecting property and diffusibility. More preferred.

As described above, when both the optical protrusion 14 and the optical element 15 have a cylindrical shape and / or a triangular prism shape, the optical protrusion 14 and the optical element 15 may both be arranged in parallel. Alternatively, they may be arranged in an intersecting manner, for example, by making them orthogonal. Further, the cylindrical optical projections 14 may be arranged so as to intersect each other, and in this case, the optical elements 15 may be arranged between the intersections.
In each of the above-described embodiments, the optical projection 14 for protecting the optical element 15 is formed in a cylindrical shape. However, it may be in a prism shape such as a substantially triangular column shape, and in this case, wear of a sharp top is suppressed. In order to do this, the top may be chamfered in an R shape, or may be chamfered in a flat shape.
In addition, the optical protrusion 14 that protects the optical element 15 from scratches is preferably a cylindrical lens shape rather than a dot shape as shown in the modification. One of the optical protrusion 14 and the optical element 15 may be formed in a dot shape, and the other may be formed in a cylindrical shape.
In either case, it is only necessary to satisfy the above formula (1) and the range of the area ratio As / S.
Moreover, in each optical sheet 12, 20, 25, 28, 30, the pitch between the optical protrusion 14 and the optical element 15 is not particularly limited, but if it is within the range of 10 μm to 300 μm, It is preferable because moire can be eliminated.

  Next, the display device according to the second embodiment will be described with reference to FIG. 10, but the same or similar parts, members, and the like as those of the display device 1 according to the first embodiment described above will be described using the same reference numerals. . The display device 33 shown in FIG. 10 is different from the display device 1 according to the first embodiment in that separate optical sheets 34 and 35 are arranged on the front and rear surfaces of the optical sheet 12 (or the optical sheets 20, 25, and 28) in the present embodiment. It is installed. These other optical sheets 34 and 35 are condensing or diffusing members. For example, a diffusing sheet or prism sheet well known in the art is appropriately used for the light source side.

As the other optical sheets 34 and 35, an appropriate condensing optical sheet can be adopted. For example, a substantially triangular prismatic lens or a substantially semi-elliptical cylindrical lens not provided with the optical projection 14 for protecting the optical element is arranged in the same direction. You may be comprised by the lenticular lens sheet arranged in multiple rows.
In addition, the other optical sheets 34 and 35 are arranged in directions orthogonal to each other so that the columnar lenses are orthogonal to each other across the optical sheet 12.

The display device 33 according to the second embodiment has the above-described configuration. Next, the operation of the display device 33 will be described.
In FIG. 10, the light K from the light source 4 enters the diffuser plate 7 and is emitted as diffused light. Thereafter, the light enters the optical sheet 34 from the exit surface of the diffusion plate 7, is condensed, and enters the optical sheet 12. In the optical sheet 12, the light transmitted through the optical element 15 is collected, and the light transmitted through the optical protrusion 14 is partly transmitted light at the part that is damaged during transportation or the like. Is condensed and emitted along the characteristics of the cylindrical lens.
Then, the condensed light transmitted through the light sheet 12 passes through another optical sheet 35 and is finally emitted as La from its emission surface. The light La reaches the liquid crystal element 10 sandwiched between the polarizing plates 9 of the liquid crystal panel 3, and the light transmitted therethrough is emitted as diffused light to the outside and is visually recognized by an observer. It should be noted that not only another optical sheet 34 but also another optical sheet may be appropriately disposed between the optical sheet 12 and the diffusion plate 7 or may be deleted as shown in the first embodiment.

Examples will be described below.
(Manufacturing method of optical sheet according to Comparative Examples 1 to 5 and Examples 1 to 11)
An optical sheet manufactured by arranging a plurality of columnar composite prism lenses 21 shown in the second embodiment by the mold roll A is referred to as Comparative Example 1. The optical sheet according to Comparative Example 1 and its mold roll A have a pitch P of the composite prism lens 21 of 66 μm, a shift amount Δ of the prism lens 21a of 18 μm, a pitch P0 of the prism lens 21a of 48 μm, and a height from the base (hereinafter referred to as the height). Cylindrical optical shape with a size of 27.5 μm is simply formed.
The optical sheet 28 according to the fourth embodiment manufactured by arranging the optical projections 14 made of cylindrical lenses between the compound prism lenses 21 (optical elements 15) by the mold roll B is taken as Example 1 (see FIG. 8). ). The optical sheet 28 according to the first embodiment and its mold roll B have a lens pitch of 132 μm and a height of 47... For every 19 pitches of the composite prism lens 21 (height 27.5 μm, pitch P 66 μm) of the mold roll A described above. One 6 μm semi-elliptical cylindrical lens is formed as an optical projection 14 and arranged.
Example 2 shows an optical sheet 20 according to the second embodiment, which is manufactured by disposing an optical projection 14 forming a semi-elliptical cylindrical lens perpendicular to the composite prism lens 21 (optical element 15) by the mold roll C. And The optical sheet 20 and the mold roll C according to Example 2 are semi-elliptical with a lens width of 132 μm and a height of 47.6 μm perpendicular to the composite prism lens 21 (height 27.5 μm, pitch P 66 μm) of the mold roll A. The cylindrical lenses (optical projections 14) are arranged at a pitch of 1320 μm.

These mold rolls A, B, and C were respectively arranged as first mold rolls in the vicinity of the extruder. The thermoplastic polycarbonate resin sheet is melted, molded by an extruder, and molded by the first mold roll before the thermoplastic polycarbonate resin sheet is cooled and cured to obtain an extruded sheet having a lenticular lens, respectively. It was. The thickness of each optical sheet was 320 μm.
As the thermoplastic polycarbonate, M1201Z and ML1103 from Teijin Chemicals Ltd. were appropriately blended and used to obtain an extruded sheet having diffusibility. The Hz (haze) at a thickness of 320 μm was adjusted to 15%.
All the extruded sheets were cut into a square sheet of 730 mm × 310 mm from the center to obtain three types of optical sheets. The optical sheet obtained from the mold roll A (Comparative Example 1), the optical sheet 28 obtained from the mold roll B (Example 1), and the optical sheet 20 obtained from the mold roll C (Example 2) did.

In addition, a mold roll D was prepared in which triangular prism prism lenses (optical elements 15) with an apex angle of 90 ° were arranged at a pitch of 55.0 μm and a height of 27.5 μm. For every 200 prism lenses of the mold roll D, 1, 4, 20, 32, 45, and 60 semi-elliptical cylindrical lenses (optical projections 14) having a lens pitch of 132 μm and a height of 47.6 μm are respectively spaced. The mold rolls E to J that were opened and arranged were prepared. Further, a semi-elliptical cylindrical shape having a lens pitch of 132 μm, a height of 37.6 μm, 47.6 μm, 57.6 μm, 67.6 μm, 77.6 μm, and 127.6 μm per 200 prism lenses of the mold roll D. Mold rolls K to P each having five lenses (optical protrusions 14) arranged at predetermined intervals were prepared.
Then, a UV curable resin is applied on the PET sheet, and the mold rolls D to P are pressed onto the PET sheet, and then UV (ultraviolet rays) is irradiated and cured from the PET side, thereby sequentially obtaining UV cured sheets. It was.
All UV-cured sheets were cut out from the center into 730 mm × 310 mm squares to obtain 11 types of optical sheets. About these optical sheets, the optical sheet obtained from the mold roll D is set as Comparative Example 2, the optical sheets obtained from the mold rolls E to J are set as Comparative Example 3, Examples 3 to 6, and Comparative Example 4 in this order. The optical sheets obtained from the rolls K to P were set as Comparative Example 5 and Examples 7 to 11, respectively.

(Measurement of pencil hardness of each optical sheet material)
The resin sheet which does not shape an optical shape with the material used for Comparative Example 1 and Examples 1 and 2 was extruded, and a hardness test was performed according to JIS K5600-5-4. Similarly, the resin sheet which does not shape an optical shape with the material used for Comparative Examples 2-5 and Examples 3-11 was created, and the hardness test was similarly implemented. As a result, the pencil hardness of the material used in Comparative Example 1 and Examples 1-2 was 6B, and the pencil hardness of the material used for the other optical sheets was 4H.

(Brightness measurement of each optical sheet)
Each obtained optical sheet is incorporated in the display device 1 according to the first embodiment, a white screen is displayed on the liquid crystal panel 3, and 50cm away from the screen of the liquid crystal panel 3 with respect to the screen of the liquid crystal panel 3 by Top-3 SR-3A. The center brightness was measured from the distance. The structure of the backlight unit 2 uses a Teijin Chemicals diffusion plate 65HLW as the light diffusion plate 7 in addition to the light source 4 and the reflection plate 5, and the optical sheets of Comparative Examples 1 to 5 and Examples 1 to 11 above it. Was measured. In the backlight unit 2, the luminance when only the light diffusing plate 7 is provided on the light source 4 and the reflecting plate 5 is 1, and on the basis of this, Comparative Examples 1 to 5 and Examples 1 to 5 are disposed above the light diffusing plate 7. The luminance ratio was calculated by measuring the luminance when 11 optical sheets were installed. The results are shown in Table 1 below.

  In Table 1, in both Comparative Examples 1 and 2, the height of the prism lens is 27.5 μm, and the area ratio of the optical protrusion 14 is zero. The maximum height hi of the optical element 15 in Comparative Examples 3 to 5 and Examples 1 to 11 is 27.5 μm, and the height of the optical protrusion 14 is displayed. Each area ratio in Comparative Examples 3 to 5 and Examples 1 to 11 is a ratio (As / S) of the total area As of the optical protrusion 14 to the area S of each optical sheet.

(Evaluation of damaged optical sheet)
The obtained optical sheets in Comparative Examples 1 to 5 and Examples 1 to 11 are stacked 20 (see FIG. 4), wrapped with a vinyl sheet, and the three vinyl sheets are stacked and stored in a cardboard box. And a gap between them was filled with a cushioning material made of styrene foam. The cardboard box was subjected to a vibration test to evaluate whether or not the optical protrusion 14 and the optical element 15 of each optical sheet were damaged. In the initial stage, optical sheets with no scratches were packed, unpacked after the vibration test, and the number of optical sheets with scratches was counted.
In the vibration test, the random vibration specified in Appendix A Table 1 of JIS Z 0232 was applied. The vibration was performed for 30 minutes only in the normal direction (z direction) of the surface having the lens portion of the optical sheet. The evaluation of the presence / absence of scratches can be made by incorporating the optical sheet after the vibration test into the display device 1, displaying a white screen, and in any of ± 80 ° up / down / left / right directions with respect to the normal of the optical sheet center. If it was visually recognized from the above, there was a scratch. The results are shown in Table 1. Those in which no defects were visually recognized were regarded as acceptable.

 From Table 1, it was found that the optical shape having a corner at the top is easily damaged regardless of the pencil hardness of the optical sheet material. In addition, it was found that the use of the optical sheet according to the embodiment of the present invention improves the scratching.

It is principal part sectional drawing which shows the structure of the display apparatus by 1st embodiment of this invention. It is a perspective view of the optical sheet by 1st embodiment of this invention. It is a side view of the optical sheet shown in FIG. It is a side view which shows the state which laminated | stacked the optical sheet shown in FIG. It is a perspective view of the optical sheet by 2nd embodiment. It is a figure explaining the shift amount of the prism lens in the compound prism lens of the optical sheet shown in FIG. It is a perspective view of the optical sheet by 3rd embodiment. It is a perspective view of the optical sheet by 4th embodiment. It is a perspective view which shows the modification of the optical sheet by embodiment. It is principal part sectional drawing which shows the structure of the display apparatus by 2nd embodiment of this invention. It is explanatory drawing which shows the structure of the display apparatus by the light-guide plate light guide system by a prior art. It is explanatory drawing which shows the structure of the display apparatus by the other light-guide plate light guide system by a prior art. It is explanatory drawing which shows the structure of the display apparatus by the direct type system by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 33 Display apparatus 2 Backlight unit 3 Liquid crystal panel 4 Light source 7 Light diffusing plate 10 Liquid crystal element 12, 20, 25, 28 Optical sheet 13 Base part 14 Optical protrusion 15 Optical element 21 Compound prism lens (optical element)
21a Prism lens 21aa, 21ab Curved side surface 26 Prism lens (optical element)

Claims (9)

An optical sheet having an optical shape for condensing or diffusing light on at least one surface of a substrate,
The optical shape has an optical protrusion having the highest height and a plurality of optical elements having a height lower than the optical protrusion,
The ratio of the total area of the optical protrusions to the area of the optical sheet in plan view is 4% or more and 45% or less,
The height of the optical protrusion from the base material is h, and the highest optical element from the base material among the optical elements excluding the optical protrusion is hi and the following equation (1) is satisfied :
20 μm <h-hi ≦ 100 μm (1)
The optical protrusion is a cylindrical lens, and the optical element has a lenticular lens group in which a plurality of compound prism lenses are arranged,
The composite prism lens has a shape in which a plurality of prism lenses having curved side surfaces on both sides are partially overlapped and integrated in the arrangement direction of the composite prism lens,
The width in the arrangement direction of the compound prism lenses in the single prism lens is set as a pitch P0, and the deviation in the arrangement direction of the compound prism lens from one prism lens in the compound prism lens and the other prism lens adjacent to the one prism lens is performed. When the distance that does not overlap is the shift amount △,
(1/5) P0 ≦ △ ≦ (2/3) P0 (2)
The curved side surface of the prism lens has the relationship of the above formula (2), and the lens shape thereof is defined by the following formula (3), and the tangent at the other end portion of the curved side surface extending from one end portion of the prism lens. An optical sheet, wherein an inclination angle θ with respect to the surface of the optical sheet is 25 ° or more and 50 ° or less .

In the above equation (3), A, B, and C are correction coefficients. When the pitch of the composite prism lens is normalized to 1, z is a position function in the height direction of the composite prism lens, and r is It is a position variable in the width direction of the composite prism lens. The optical sheet according to claim 1, wherein the optical protrusion has a rounded top. The optical sheet according to claim 1 or 2, wherein a pencil height of the material of the optical sheet is 4H or less. The optical sheet according to claim 1, wherein the optical protrusion and the optical element have a cylindrical shape and are arranged in parallel to each other. The optical sheet according to claim 1, wherein the optical protrusion and the optical element have a cylindrical shape and are arranged so as to intersect each other. 6. The optical sheet according to claim 1, wherein the optical protrusion is a cylindrical lens, and the optical element is a prism. A display backlight unit comprising at least a light source and the optical sheet according to any one of claims 1 to 6 on a back surface of an image display element that defines a display image. The backlight unit according to claim 7 , wherein the light source is a cold cathode tube, an LED, an EL, or a semiconductor laser. 9. A display device comprising: an image display element comprising a liquid crystal display element that defines a display image in accordance with transmission / shading in pixel units; a light source; and a backlight unit according to claim 7 or 8. .

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