JP2009116014A - Lens sheet, optical sheet for display, and backlight unit and display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin optical sheet having high strength and high display quality in which a lens sheet having a multilayer structure and a light diffusion layer are integrated together, and a backlight unit and a display device using the optical sheet. <P>SOLUTION: The lens sheet 1 includes a number of out-going side lens parts 2 aligned projectively on an emitting side, a protrusion 3 protruded to an incident side, and a translucent/semi-reflecting layer closest to a light incident surface 102. The optical sheet 25 includes the lens sheet 1 and a light diffusion layer 25 which are integrated together by one or more fixing elements 29 in a clearance between the light incident surface 102 of the lens sheet 1 and a light emitting surface 101 of the light diffusion plate 25. The backlight unit and the display device use the optical sheet 39. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention illuminates from the back side a liquid crystal panel in which a transmissive / non-transmissive lens sheet and a display optical member in pixel units or a display element in which a display pattern is defined according to a transparent state / scattering state is arranged. The present invention relates to a backlight unit and a display device.

  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 in which a light source is arranged on the back side (observer side) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source is employed.

  As a backlight unit employed in this type of backlight system, a light source lamp such as a cold cathode fluorescent lamp (CCFT) is roughly divided into a flat light guide plate made of acrylic resin having excellent light transmittance. There are a “light guide plate light guide method” for reflecting (a so-called edge light method) and a “direct type method” that does not use a light guide plate.

  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. 13 is generally known.

  This is provided with a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 at the top, and a light guide plate 79 made of a transparent base material such as a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic on the lower surface side. Is installed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate.

  Further, a scattering reflection pattern portion for efficiently scattering and reflecting the light introduced into the light guide plate 79 in the direction of the liquid crystal panel 72 is provided on the lower surface of the light guide plate 79 by printing or the like. A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion (not shown).

Further, the light guide plate 79 is provided with a light source lamp 76 at the side end, and further covers the back side of the light source lamp 76 so that the light from the light source lamp 76 can be efficiently incident on the light guide plate 79. Thus, a high-reflectance lamp reflector 81 is provided. The scattering reflection pattern portion is formed by printing, drying, and forming a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern. The light incident on the light plate 79 is imparted with directivity and guided to the light exit surface side, which is a device for increasing the brightness.

  Furthermore, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 14, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is provided. ) 74 and 75 are proposed. The prism films 74 and 75 are configured to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, in the apparatus illustrated in FIG. 13, the control of the viewing angle is left only to the diffusibility of the diffusion film 78, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.
Furthermore, in the apparatus using the prism film illustrated in FIG. 17, two prism films are required, which not only causes a large decrease in the amount of light due to the absorption of the film but also increases the cost due to the increase in the number of members. It was also.

  On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.

  As a direct liquid crystal display device, a device illustrated in FIG. 15 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and is emitted from a light source 51 made of a fluorescent tube or the like on the lower surface side thereof and diffused by an optical sheet such as a diffusion film 82. The light is condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, a reflector 52 is disposed on the back surface of the light source 51.

  However, even in the apparatus illustrated in FIG. 15, the control of the viewing angle is left only to the diffusibility of the diffusion film 82, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.

Therefore, as one solution, as shown in FIG. 17, a brightness enhancement film (Brightness Enhancement Film BEF), which is a registered trademark of US 3M, shown in FIG. A method of arranging the light diffusion film 84 is employed. Here, BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a transparent member.
This prism has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” to the viewer, or “recycle”. To do.

When using the display (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally on the normal direction side with respect to the display screen.
When the repetitive array structure of prisms is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the parallel direction of the prism groups Are stacked and used in combination so that they are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.
As a patent document disclosing that a brightness control member having a repetitive array structure of prisms represented by BEF is adopted for a display, there are many known as exemplified in Patent Documents 1 to 3. Yes.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 In the optical sheet using the BEF as a brightness control member as described above, light from the light source is finally emitted from the film at a controlled angle by refraction. Thus, it is possible to control to increase the light intensity in the visual direction of the viewer.

However, there are unexpected light rays that are unnecessarily emitted laterally without proceeding in the visual direction of the viewer. For this reason, as shown in FIG. 18, the light intensity distribution emitted from the optical sheet using BEF has the light intensity when the viewer's visual direction, that is, the angle with respect to the visual direction F is 0 ° (corresponding to the axial direction). Although most enhanced, there is a problem that a small light intensity peak occurs in the vicinity of ± 90 ° from the front, that is, light (side lobes) emitted from the lateral direction is increased.
A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° is more desirable.

  In addition, when only the on-axis luminance is excessively improved, the peak width of the luminance distribution curve is remarkably narrowed, and the viewing area is extremely limited. Therefore, in order to increase the peak width appropriately, the prism sheet and There is a problem that it is necessary to newly use a light diffusing film as a separate member, which increases the number of members.

  As described above, this optical sheet is required not only to improve the light utilization efficiency but also to have various functions such as removing unevenness of the light source and securing the viewing area of the display. It is configured by overlapping sheets. However, if the number of optical sheets is large, the work for assembling the display becomes complicated, and there is a problem that it is affected by dust between the optical sheets and hinders miniaturization and thinning.

By the way, in such a liquid crystal display device, light weight, low power consumption, high brightness, and thinning are strongly demanded as market needs, and accordingly, a backlight unit mounted on the liquid crystal display device is also provided. Light weight, low power consumption, and high brightness are required.
In particular, in a color liquid crystal display device that has recently made remarkable progress, the panel transmittance of the liquid crystal panel is remarkably lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain power consumption.

  However, as described above, it is difficult to say that the conventional apparatus sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and low power consumption. Development of a backlight unit and a display device that can realize a liquid crystal display device with electric power is awaited.

  The present invention provides an optical sheet that achieves high display quality and low price by optimizing the configuration of the lens sheet, thereby obtaining desired luminance and diffusibility with a single lens sheet, and the optical sheet. An object of the present invention is to provide a backlight unit and a display device using the above.

In order to achieve the above object, the present invention takes the following measures.
That is, the invention of claim 1 is an optical sheet for uniformizing and / or converging the light emitted from the light source, and is provided with at least one type of emission side lens portion arranged in a row so as to protrude toward the emission side, and incident It is a lens sheet provided with the protrusion part which protruded in the side.
In the invention of claim 2, Pi = Po × n (n is an integer), where Pi is the pitch of the projections on the incident side and Po is the pitch of the exit side lens parts.
The lens sheet according to claim 1, wherein the relationship is as follows.
A third aspect of the present invention is the lens sheet according to the first or second aspect, wherein the incident-side protruding portion is disposed corresponding to a valley portion of the emission-side lens portion.
According to a fourth aspect of the present invention, in the lens sheet according to any one of the first to third aspects, the lens sheet has a laminated structure of at least two layers when viewed from a direction perpendicular to the sheet surface. is there.
The invention of claim 5 is characterized in that, in the laminated structure, the thickness of the layer closest to the protruding portion is 10 to 70 μm from the valley portion of the protruding portion, and includes at least one metal-based particle. The lens sheet according to any one of claims 1 to 4.
The invention according to claim 6 is characterized in that the particle size of the metal-based particles contained in the layer closest to the protruding portion is 5 μm or less and the addition amount is 40% by weight or less. It is a lens sheet of description.
The invention according to claim 7 is characterized in that the difference between the reflectance of the peak portion of the protruding portion and the reflectance of the valley portion of the protruding portion is 50% or more. It is a sheet.
The invention according to claim 8 is the lens sheet according to any one of claims 1 to 7, characterized in that a trough and a vertex of the lens of the exit side lens portion are rounded.
The invention according to claim 9 is the lens sheet according to any one of claims 1 to 8, characterized in that a valley portion and a vertex of the incident side protruding portion are rounded.
The invention according to claim 10 is the lens sheet according to any one of claims 1 to 9, wherein an ultraviolet absorber is added to at least one layer in the lens sheet.
The invention of claim 11 is an optical sheet for display, wherein the lens sheet of claims 1 to 10 is integrated with a light diffusion plate while maintaining a gap.
A twelfth aspect of the invention is a backlight unit using the display optical sheet according to the eleventh aspect.
A thirteenth aspect of the present invention is a display device using the backlight unit according to the twelfth aspect.

  By optimizing the configuration and shape of the lens sheet of the present invention, it is possible to achieve the desired brightness, orientation range, uniformity, etc., and it is possible to reduce the thickness and cost by reducing the number of members. is there. Also, by integrating the lens sheet and the light diffusion layer, the assembly process can be simplified, and the backlight unit can achieve the desired light image effect, uniformity, etc. while being thin and maintaining sufficient strength A display device can be provided.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a side view showing an example of a backlight unit and a display device according to an embodiment of the present invention.
The backlight unit according to the embodiment of the present invention includes a plurality of cylindrical light sources 41 housed in a lamp house 43, and a liquid crystal panel in which light H from each light source 41 is sandwiched between polarizing plates 31 and 33. 35 is provided with an optical sheet 39 to be supplied to 35. In the figure, reference numeral 45 denotes a light reflecting plate disposed on the back side of the plurality of light sources 41.
The display device according to the embodiment of the present invention is a device including the light source 41, the optical sheet 39, and the liquid crystal panel 32 thereon. In this case, the display device is a liquid crystal display device. However, the display device is not limited thereto, and includes a display screen device that displays an image using light, such as a projection screen device, a plasma display, and an EL display. If so, it doesn't matter.

Light H from the light source 41 enters the light diffusion layer 25 and is diffused, and the diffused light enters the lens sheet 1 and is emitted as light K. Here, the lens sheet 1 causes the light diffused by the light diffusion layer 25 and emitted from the emission surface 101 of the light diffusion layer 25 to enter the gap 200 formed between the adjacent protrusions 2. The light is condensed by the exit side lens unit 3 and irradiated to the liquid crystal panel 32 as light K.
FIG. 2A is a cross-sectional view illustrating a configuration example of the lens sheet 1. This lens sheet 1 is provided with a plurality of emission side lenses 3 that are arranged side by side so as to protrude toward the emission side, and a protruding portion 2 that protrudes toward the incident side. Here, it arrange | positions corresponding to the position of the trough part U formed between the unit emission side lenses 3 adjacent to each other, and the position containing the perpendicular drawn from the trough part U to the lens sheet 1 in the perpendicular direction. The positions of the protruding portions 2 formed on the back surface side of the surface on which the exit side lens portion 3 of the lens sheet 1 is formed substantially coincide with each other.
In addition, the gap 200 is disposed at a position including a perpendicular line perpendicular to the lens sheet 1 from the apex of the unit emitting side lens 3.

FIG. 2B illustrates a lens sheet 1 having a two-layer structure in which a first layer and a second layer are respectively provided from the base V of the projecting portion 2 on the incident side toward the exit side lens portion 3. It is an example.
Similarly, FIG. 2C shows a total of four layers, a first layer, a second layer, a third layer, and a fourth layer, respectively, from the base V of the protrusion on the incident side toward the exit side lens unit 3. It is an example of the lens sheet 1 which shows the laminated structure which consists of. The number of lens sheets 1 stacked is not limited to this four-layer structure, and may be formed of four or more layers.
Furthermore, FIG.2 (d) is the lens sheet 1 comprised from the laminated structure in which the protrusion part 2 consists of a total of two layers, a 1st layer and a 2nd layer. Here, when the height of the protruding portion is T, the first layer occupies from the bottom V of the protruding portion to the height S.

FIG. 3 shows an example of the lens shape of the exit side lens portion 3 of the lens sheet 1.
FIG. 3A shows a case where the exit side lens unit 3 has a triangular prism shape. FIG. 3B shows a case where the exit side lens portion has a cylindrical shape. FIG. 3C and FIG. 3D are examples of lens shapes in which the exit side lens unit 3 forms the second lens array Z on the first lens array Y. FIG.
Further, the exit side lens unit 3 includes a prism lens whose lens side surface is linear or outwardly curved. That is, a pyramidal microprism, an arc-shaped cylindrical lens array, a microlens array in which hemispherical lenses are arranged, or a combination of these lenses may be used.
Moreover, in the above-mentioned exit side lens part 3, the trough part of each lens and the edge part of the top part may be rounded.

Moreover, it is desirable that the shape of the protrusion 2 on the incident surface of the lens sheet 1 is a cone and a column.
FIG. 4 shows the shape of the protruding portion protruding to the incident surface side of the lens sheet 1.
FIG. 4A shows a case where the protrusion has a rectangular parallelepiped shape. FIG. 4B shows a case where the protrusion has a trapezoidal shape. FIG. 4C shows a case where the protrusion has a triangular prism shape. In FIG. 4D, the protruding portion has a convex cylindrical shape.
The shape of the projecting portion 3 includes a lenticular shape, a trapezoidal shape, a prism shape and the like extending in one direction, a polygonal cone, a cone (or a truncated cone, a truncated cone, etc.), a polygonal column, a columnar column such as a cylinder, Alternatively, a structure such as a spherical shape (or a hemispherical shape) or an ellipsoid may be used. Further, the shape of the protruding portion 2 may be an unspecified shape as long as the height is constant.
Furthermore, when providing these lens shapes, the above-described one type of lens structure may be used as a whole or a plurality of types of lens structures may be used in combination.

The arrangement of the protrusions 2 on the incident surface side of the lens sheet 1 is desirably a periodic shape such as a stripe shape or a dotted line, and is appropriately selected according to the design of the lens pitch Po.
In particular, since a moire defect or the like is less likely to occur, the lens pitch Pi of the incident-side protrusion 2 (the distance connecting the midpoints of the bases V of the adjacent unit protrusions) is the lens pitch Po ( An integral multiple of the distance between the lens vertices of adjacent exit side lens portions), that is, Pi = Po × n (n is an integer)
It is preferable to satisfy the relationship. Further, since the protrusion 2 on the incident side may reduce the area of the incident plane and impair the optical characteristics, it is desirable that the occupied area be small. In this case, Pi> Po and Pi = Po × n (n is 2 or more) Integer)
It is better to satisfy the relationship.

FIG. 5A shows a modification of the projecting portion 2 of the present invention, in which the lens pitch of the projecting portion 2 is doubled with respect to the lens pitch Po of the exit side lens portion 3.
FIG. 5B shows the protrusion 2 in which the lens pitch is three times the lens pitch Po of the exit side lens.
Further, two or more types having different lens pitches Pi may be combined as shown in FIG. At this time, the trough portion U of the exit side lens portion 2 and the optical axis of the projecting portion 3 (perpendicular lines extending vertically from the trough portion U to the lens sheet 1 are formed on the back surface of the lens sheet 1. Matching the midpoint of the base V) is one of the effective methods for reducing moire with the horizontal or vertical cell structure of the panel when the lens sheet 1 is incorporated in a display. . In order to obtain the effect of reducing moire, the optical axis deviation is desirably within 5%, and more effective is within 3%.

  Next, as the performance required for the lens sheet 1, high brightness can be mentioned. As a method for increasing the brightness, there is a method in which a layer (reflective layer) having a function of reflecting light is provided on the protruding portion 2 protruding from the light incident surface of the lens sheet 1. By providing a reflective layer with a reflectance of 60% or more on the protrusion 2, the incident light in the vertical oblique direction (60 to 90 degrees) leading to the light loss of the exit side lens portion 3 is reduced, and the reflected light is It returns to the light source side and is reused as recursive light. The reflectance needs to be 60% or more, and preferably 70% or more. If it is lower than 60%, there is a possibility of being visually recognized as a bright part in a field of low brightness. If it is 80% or more, it is not visually recognized even in a low-luminance visual field.

As a typical method of providing a reflective layer on the protruding portion 2 of the light incident surface of the lens sheet 1, there is a method shown below.
There is a method of applying an ink obtained by dispersing and mixing high refractive index transparent particles, or a sticky / adhesive layer obtained by dispersing and mixing high refractive index transparent particles.
In addition, there is a method in which a metal particle or a high refractive index transparent particle kneaded in a binder is formed by transfer, or a white foil or a metal foil is laminated.
However, since both methods have many kinds of materials and a large number of processes, the use of these methods leads to an increase in the price of the lens sheet 1.

  Therefore, in the present invention, the lens sheet 1 is configured by a method of providing a high refractive index layer having a reflection function on the incident surface side of the lens sheet 1.

FIG. 6 shows an optical path of the lens sheet 1 having a two-layer structure in which a high refractive index layer is provided in the first layer.
In FIG. 6A, since the high refractive index layer is formed as the first layer only on the protrusion 2, the light incident on the protrusion 2 is reflected, but the light enters from the gap 200. That is, since the gap 200 is provided so as to face the apex of the emission side lens portion provided in the lens sheet 1, only the light narrowed by the corresponding gap 200 is guided to the emission side lens portion. . That is, since the gap 200 functions like a slit, only the light with a narrowed diffusion angle out of the light emitted from the light diffusion layer 25 is incident on the emission side lens unit 3. Light that is incident on the side lens portion from an oblique direction is reduced, so that it is possible to reduce light that is unnecessarily emitted in the lateral direction without proceeding in the visual direction of the viewer (the traveling direction of the light K in FIG. 1). . Further, the light that could not pass through the gap 200 is reflected by the protrusion 2 and returned to the light diffusion layer 25 side.
FIG. 6B shows a case where the first high-refractive index layer is laminated not only on the protrusion 2 but also on the incident surface of the gap 200. In this case, since the thickness of the first layer is thin on the incident surface of the air gap 200, the reflectance is low and the light transmittance is high. That is, a part of the light incident on the gap 200 is reflected by the high refractive index layer, but most of the light is incident. On the other hand, the protrusion 2 has a high reflectance because the first layer is thick. That is, most of the light incident from the protrusion 2 is reflected. Thereby, the lens sheet 1 with a high condensing function can be obtained.

FIG. 7 shows the relationship between the thickness of the first layer and the reflectance in the high refractive index layer (white layer) having a reflecting function, and the relationship between the layer concentration (ratio of metal particles mixed in the transparent resin) and the reflectance. Is shown.
In order to obtain a high reflectance, the higher the concentration and the thicker the layer, the better. However, if the thickness of the first layer is too thick, the light transmittance from the incident surface of the gap 200 of the lens sheet 1 is lowered, leading to a decrease in luminance. Therefore, it is important that the bottom V of the projecting portion 2 shows a higher reflectivity, and that the reflectivity at the entrance surface of the gap 200 is lower than that at the entrance surface of the air gap 200. The difference needs to be 50% or more, preferably 60% or more.
Furthermore, in this case, the transparent particles are desirably metal particles having a high refractive index and an average particle diameter of 5 μm or less, and preferably an average particle diameter of 1 μm or less. In addition, when the average particle size is 0.1 μm or less, it is difficult to obtain a desired reflectance.
The amount of metal particles added to the first layer is desirably 40% by weight or less, and in particular, 20% by weight or less is preferable in consideration of the transmittance of the incident surface of the gap 200. Furthermore, the thickness of the first layer is desirably 70 μm or less from the viewpoint of transmittance.

  Here, examples of the metal-based particles as the high refractive index transparent particles include titanium oxide, barium sulfate, magnesium carbonate, zinc oxide, clay, aluminum hydroxide, zinc sulfide, silica, and silicone. Examples of the metal particles or the metal foil include aluminum and silver. One kind of these high refractive index transparent particles, metal particles or metal foil may be used, or a plurality of kinds may be used in combination. In addition to metal particles, acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene-hexa) Fluorine-containing polymer particles such as a fluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer) may be mixed and used.

  Further, the second layer, the third layer, the fourth layer,... May be made of only a transparent resin without adding transparent particles. However, as described above, it is more preferable to add a small amount of a diffusing agent in order to mitigate light loss called side lobe caused by the shape of the exit side lens portion 3. The transparent particles are not limited to one type, and two or more types may be used. The second layer, the third layer, and the fourth layer may have the same layer configuration or different configurations.

  As the transparent particles to be added to the second layer, the third layer, the fourth layer,..., Transparent particles made of an inorganic oxide or transparent particles made of a 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. Further, transparent particles made of resin include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene). Fluoropolymer particles such as fluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), silicone resin particles, and the like.

  Examples of the transparent resin include polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, AS resin, PET, and polypropylene. Can be used.

And the lens sheet 1 can be manufactured by disperse | distributing transparent particles in these transparent resins, and carrying out extrusion molding.
In the extrusion method, a thermoplastic resin is heated and melted with an extruder, extruded from a T-die, and formed into a sheet. The co-extrusion method is used in the case of a laminated sheet, and a plurality of extruders are used to carry out lamination extrusion from a lamination die such as a feed block die and a manifold die to form a multilayer sheet.

The thickness of the lens sheet 1 is desirably 100 to 500 μm. The thickness of the lens sheet 1 is determined by the optical characteristics and the manufacturing process, or the required physical characteristics of the lens sheet 1.
When the thickness of the lens sheet 1 is less than 100 μm, the lens sheet 1 does not have a strain and thus has a drawback that wrinkles are generated.
On the other hand, when the thickness of the lens sheet 1 exceeds 500 μm, there is a disadvantage that the transmittance of light from the light source 41 is deteriorated. Furthermore, the thickness varies depending on the size of the backlight unit or display device used. For example, in a display device having a diagonal size of 37 inches or more, the thickness is desirably 200 μm or more and less than 400 μm.

  Next, the light diffusion layer 25 that is under the lens sheet 1 and enters the light H from the light source 41 from the incident surface 100 and diffuses to the non-incident surface 101 side will be described.

  The light scattering layer 25 includes a transparent resin and transparent particles dispersed in the transparent resin, and the refractive index of the transparent resin and the refractive index of the transparent particles are different. Here, the difference between the refractive index of the transparent resin and the refractive index of the transparent particles is preferably 0.02 or more. If the difference in refractive index is smaller than this, sufficient light diffusion performance cannot be obtained. Further, the refractive index difference may be 0.5 or less.

  Therefore, the light diffusion layer 25 needs to transmit the light incident on the light diffusion layer 25 while scattering the light. For this reason, it is desirable that the transparent particles contained in the light diffusion layer 25 have an average particle diameter of 1 to 20 μm. Preferably, it contains at least three kinds of spherical particles having an average particle diameter of 4 to 20 μm, spherical particles having an average particle diameter of 1 to 3 μm, and irregular particles having an average particle diameter of 2 to 6 μm. By adding the spherical particles, the viewing angle characteristic gradually falls toward the wide angle while maintaining the wide viewing angle from the center. By adding spherical particles, the spread of the viewing angle from the center is small but diffusive, and the center exhibits a relatively high viewing angle characteristic. In addition, by adding amorphous particles, the viewing angle characteristics are sharp and high at the center, rapidly drop, and widen at the bottom. By adding these three types in a well-balanced manner, there is an effect of condensing at the center while having diffusibility, and the brightness of the center can be obtained. Alternatively, the light diffusion layer 25 may have a structure having a fine cavity containing air in a transparent resin, and the diffusion performance may be obtained by a difference in refractive index between the transparent resin and air.

Further, by using the light diffusion layer 25 produced as described above in a laminated manner with the lens sheet 1, it is possible to optimize the optical characteristics such as the brightness and orientation characteristics of the optical sheet 39.
Further, as shown in FIG. 8A, the stacking method may be only superposition as shown in FIG. 8A. However, as shown in FIG. 8B, the light diffusion layer 25 may be bonded to the entire surface using the fixing element 29. As shown in FIG. 8 (c), the fixing elements 29 may be partially bonded together.

  Next, a case where a contact / adhesive layer is used as the fixing element 29 will be described. The position where the adhesive / adhesive layer is applied is at least partly outside the display area of the light diffusion layer 25 and the lens sheet 1 (which means an area other than that used for image display when the lens sheet 1 is incorporated in the display device). Jointly. However, in some cases, the contact / adhesive layer may be in the display area as long as the image display quality of the display (for example, the fixed element 29 is visually recognized from the display) is not affected.

As an example, the position for attaching the contact / adhesive layer is shown in FIGS. 9 (a) to 9 (d).
FIG. 9A shows a case where a contact / adhesive layer is applied to the entire periphery of the light diffusion layer 25.
FIG. 9B and FIG. 9C show a case where the adhesive / adhesive layer is applied only to a pair of opposite sides of the light diffusion layer 25.
FIG. 9C shows the case where the contact / adhesive layer is applied to the four corners of the light diffusion layer 25.
FIG. 9 (d) shows a case where the contact / adhesive layer is applied in the form of dots on the entire periphery of the light diffusion layer 25. Here, also in the case of FIG. 9 (b) and FIG. 9 (c), the contact / adhesive layer may be applied in a dot shape as necessary.

Examples of the adhesive / adhesive include acrylic, urethane, rubber, and silicone adhesives / adhesives. In either case, since it is used in a high-temperature backlight, it is desirable that the storage elastic modulus G ′ is 1.0E + 04 Pa or more at 100 ° C. If the value is lower than this, the light diffusion layer 25 and the lens sheet 1 may be displaced during use. In order to secure the gap 200 stably, transparent fine particles, for example, beads may be mixed in the contact / adhesive layer.
The adhesive may be a double-sided tape or a single layer.

  Furthermore, when a contact / adhesive is used in the display area, light absorption must be within 1%. If it exceeds 1%, the integrated light quantity emitted from the optical sheet 39 decreases, and the front luminance decreases regardless of the shape of the lens sheet 1.

Here, the fixing element 29 does not occupy the entire area between the non-incident surface 101 of the light diffusion layer 25 and the incident surface 102 of the lens sheet 1.
That is, it is possible to provide a gap 200 provided between the light diffusion layer 25 and the lens sheet 1 of FIG. 1 and transmitting the light diffused by the light diffusion layer 25 to the lens sheet 1 on the non-scattering layer side. . As a result, the light transmitted through the gap 200 can be collected and guided to the lens sheet 1. The gap 200 is made of a gas such as air or nitrogen, for example.

  Further, the height of the protruding portion 2 needs to keep the gap 200 between the lens sheet 1 and the light diffusion layer 25 at 200 nm or more in order to prevent optical adhesion due to distortion of the optical sheet 39. On the other hand, if the thickness of the gap 200 exceeds 2 mm, the visibility of the protruding portion 2 is increased, which causes unevenness.

  Therefore, when the fixing element 29 is used on the entire surface of the protruding portion 2 and the emission surface 101 of the light diffusing plate 25, the height of the protruding portion is preferably 5 to 60 μm in order to keep the gap 200. Further, when a contact / adhesive agent is used for the fixing element 29, the thickness is preferably 20 μm or less.

  The ground contact area of the emission surface 101 of the protrusion 2 is the total contact area of the protrusion 2 in contact with the non-incident surface 101 of the light diffusion layer 25 in order to prevent a decrease in adhesive strength and a decrease in front luminance. It is desirable that the area be 0.01 to 60% with respect to the area of the incident surface 101. Furthermore, it is more preferable that the installation area of the light diffusing layer 25 of the protruding portion 2 on the non-incident surface 101 is 1% or more and 20% or less in order to minimize the luminance reduction.

In addition, the size of grounding of one of the protrusions 2 (in some cases, a group of protrusions 2) to the non-incident surface 101 of the light diffusion layer 25 reduces the visibility of unevenness due to the protrusion 2 from the upper surface of the optical sheet 39. Therefore, regarding the structure such as a lenticular shape, a trapezoidal shape, and a prism shape extending in one direction, it is preferable that the line width of the grounded portion joined to the lens sheet 1 is 50 μm or less.
Further, it is preferable that the area of the ground contact portion of a structure such as a cone (or a truncated cone, a truncated cone, or the like), a polygonal column, a cylinder, or the like, a rectangular parallelepiped, a sphere (or hemisphere), or an ellipsoid is 2500 μm ² or less.
In order to further improve the visibility, the line width is more preferably 3 μm and the area is 900 μm ² or less.

  The lens sheet 1 and the optical sheet 39 formed as described above can be used not only in the case where the light source 41 is a cold cathode fluorescent lamp but also in a display device using an LED, an EL, a semiconductor laser, or the like.

  Here, when an LED is used as the light source of the display device, as shown in FIG. 12A, an array of red, green, and blue LEDs is used, and the array of red, green, and blue LEDs is guided by a light guide plate or the like. That are uniformly emitted as white light, or light from an array of red, green, and blue LEDs using a diffuser or the like as shown in FIG. It can be used also for what can be emitted. Moreover, when using white LED, it is applicable to both Fig.12 (a) and FIG.12 (b).

In addition, the backlight unit is becoming thinner and thinner, and accordingly, the distance between the light source 41 and the optical sheet 39 is shortened. However, if the optical sheet 39 of the present invention is used, a direct type or a side edge type is used. Even in the backlight unit, there is no influence of visibility such as a dark spot generated between the light source lamps, and the backlight unit can be used sufficiently.
Furthermore, the size of the optical sheet 39 is also increasing along with the increase in the size of the display device, but the optical sheet 39 of the present invention is thin and strong, and further has excellent display quality. It can be sufficiently used for such a large display device.

  FIG. 17 shows an embodiment in which the optical sheet 39 according to the present invention is used in a direct backlight unit and a display device using the backlight unit.

  FIG. 10 shows an embodiment in which the optical sheet 39 according to the present invention is used for the side edge type light guide plate 47.

  FIG. 17 shows an embodiment in which an EL light source is used as the light source of the display using the optical sheet 39 according to the present invention.

FIG. 12A shows an embodiment in which the LED light source 51 is used with the optical sheet 39 according to the present invention as a light source of a display.
FIG. 12B shows an embodiment in which the LED light source 53 is used with the optical sheet 39 according to the present invention as the light source of the display.

(Examination of diffusing agent type)
Example 1
In order to examine the type of diffusing agent used in the high refractive index layer having a reflecting function, three types of diffusing agents (alumina, titanium oxide, zinc oxide) having a particle size of about 0.3 μm were examined. The layer thicknesses are all constant 20 μm. The exit side lens portion 3 is a cylindrical lens having a lens height of 50 μm and a lens pitch of 150 μm, and the protruding portion 2 has a rectangular parallelepiped shape having a depth of 50 μm and a lens pitch of 150 μm. The thickness of the lens sheet 1 is 400 μm.
Table 1 shows the luminance of the lens sheet 1 and the evaluation results of the diffusibility. The luminance was evaluated by a relative ratio when the target luminance was set to 1, and the diffusivity was determined as ◯ when the lamp image disappeared and x when the lamp image disappeared. As a result, it was difficult to increase the brightness with only one zinc oxide, and the desired diffusibility could not be obtained. However, it was confirmed that brightness and good light diffusivity can be obtained by adjusting the concentration of titanium oxide and alumina.

(Examination of particle size of diffusing agent)
(Example 2)
In order to examine the particle size of the diffusing agent used in the high refractive index layer having a reflection function, titanium oxide having a particle size of 0.2 μm and titanium oxide having a particle size of 0.03 μm were added and examined.
The evaluation results are shown in Table 2. When one kind of titanium oxide having a particle size of 0.03 μm was added, the amount added was adjusted to obtain a desired luminance, but the high refractive index layer was yellowish and could not be used as the optical sheet 39. It was.
(Example 3)
A study was made by adding zinc oxide having a particle size of 0.3 μm and zinc oxide having a particle size of 0.03 μm, respectively. The evaluation results are shown in Table 2. When zinc oxide having a particle size of 0.03 μm was added, the desired luminance was obtained, but it was very yellowish and could not be used as an optical sheet. Moreover, good diffusibility was not obtained.
From the above, it was confirmed that in order to add 0.03 μm of titanium oxide and zinc oxide to the high refractive index layer, it was necessary to add another diffusing agent and to study with two or more diffusing agents.

(Layer thickness of high refractive index layer)
Example 4
The layer thickness of the high refractive index layer was examined. Change the titanium oxide concentration with a particle size of 0.3μm in three types (5.0%, 10.0%, 13.3%), change the thickness of the high refractive index layer to 10-30μm, and the transmittance at that time Evaluated. In this evaluation, in order to consider only the layer thickness, the exit side lens part and the protruding part are not provided. The evaluation results are shown in Table 3. In the case of this test condition, it was confirmed that the transmittance decreased as the thickness of the high refractive index layer increased at all concentrations.
From this result, it is possible to adjust the transmittance and the reflectance by changing the layer thickness. When a rectangular parallelepiped rib shape having a depth of 60 μm is provided as the protruding portion, the trough U is about the top of the lens. A difference in transmittance of 40% or more occurred.

It is explanatory drawing which shows the illustrative display apparatus which concerns on embodiment of this invention. (A) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (C) It is explanatory drawing which shows the exemplary lens sheet side view which concerns on embodiment of this invention. (D) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (A) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (C) It is explanatory drawing which shows the exemplary lens sheet side view which concerns on embodiment of this invention. (D) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (A) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (C) It is explanatory drawing which shows the exemplary lens sheet side view which concerns on embodiment of this invention. (D) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (A) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the illustrative lens sheet side view which concerns on embodiment of this invention. (C) It is explanatory drawing which shows the exemplary lens sheet side view which concerns on embodiment of this invention. (A) It is explanatory drawing which shows the assumed optical path which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the optical path assumed concerning embodiment of this invention. It is explanatory drawing which shows the relationship between the thickness and density | concentration of a high refractive index layer (white layer) of the lens sheet concerning embodiment of this invention, and a reflectance. (A) It is explanatory drawing of the side surface which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (B) It is explanatory drawing of the side which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (C) It is explanatory drawing of the side which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (A) It is explanatory drawing which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (B) It is explanatory drawing which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (C) It is explanatory drawing which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. (D) It is explanatory drawing which shows arrangement | positioning of the exemplary fixing element which concerns on embodiment of this invention. It is explanatory drawing which shows the illustrative display apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the illustrative display apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the illustrative display apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the perspective view of BEF by a prior art. It is explanatory drawing which shows the structural example of the optical sheet for liquid crystal displays by a prior art. It is explanatory drawing which shows the light intensity distribution radiate | emitted from the optical sheet using BEF.

Explanation of symbols

H, K: Light, T: Projection lens height, S: Height from the bottom, U ... Valley, V ... Bottom, Y ... First lens array, Z ... Second lens array, Po ... Projection Part pitch, Pi ... lens pitch, 1 ... lens sheet, 2 ... projection, 3 ... exit side lens part, 4 ... first layer, 5 ... second layer, 6 ... third layer, 7 ... fourth layer, 25 ... Light diffusing layer, 29 ... Fixed element, 31, 33 ... Polarizing plate, 32 ... Liquid crystal panel, 35 ... Liquid crystal layer, 39 ... Display sheet, 41 ... Light source, 43 ... Lamp house, 45 ... Light reflector, 47 ... Light guide plate, 49 ... EL light source, 51, 53 ... LED light source, 100 ... non-incident surface of light diffusing layer, 101 ... light emitting surface of light diffusing layer, 102 ... light incident surface of lens sheet, 200 ... gap

Claims (13)

  An optical sheet for uniformizing and / or converging light emitted from a light source, comprising: at least one type of emission side lens portion that is arranged in a row so as to protrude toward the emission side; and a protrusion portion that protrudes toward the incidence side. A lens sheet comprising: When the pitch of the projecting portion on the incident side is Pi and the pitch of the exit side lens portion is Po,
Pi = Po × n (n is an integer)
The lens sheet according to claim 1, wherein:   The lens sheet according to claim 1, wherein the incident-side protruding portion is disposed corresponding to a valley portion of the exit-side lens portion.   4. The lens sheet according to claim 1, wherein the lens sheet has a laminated structure of at least two layers when viewed from a direction perpendicular to the sheet surface. 5.   In the laminated structure, the thickness of the layer closest to the protruding portion is 10 to 70 µm from the valley portion of the protruding portion, and includes at least one kind of metal-based particles. Item 5. The lens sheet according to Item 4.   6. The lens sheet according to claim 1, wherein a particle size of the metal-based particles contained in a layer closest to the protruding portion is 5 μm or less and an addition amount is 40 wt% or less.   The lens sheet according to claim 1, wherein a difference between the reflectance of the peak portion of the protruding portion and the reflectance of the valley portion of the protruding portion is 50% or more.   The lens sheet according to claim 1, wherein a trough portion and a vertex of the lens of the emission side lens portion are rounded.   The lens sheet according to claim 1, wherein a valley portion and a vertex of the incident side protruding portion are rounded.   The lens sheet according to claim 1, wherein an ultraviolet absorber is added to at least one layer in the lens sheet.   11. An optical sheet for display, wherein the lens sheet according to claim 1 is integrated with a light diffusion plate while maintaining a gap.   A backlight unit using the optical sheet for display according to claim 11.     A display device using the backlight unit according to claim 12.