JP2012237978A - Optical sheet and planar light source device using the same - Google Patents

Abstract

[PROBLEMS] To reduce the cost by increasing the distance between LEDs and reducing the number of elements used, and in a backlight that is reduced in thickness by reducing the distance between a first optical sheet and a reflective film. Provided is an optical sheet that can eliminate uneven brightness.
An optical sheet of the present invention is an optical sheet having a rectangular outer shape, and a plurality of convex or concave quadrangular pyramid shapes formed on one surface, wherein the base surface of the quadrangular pyramid shape is provided. The angle between the long diagonal of the rhombus and the long side of the outer shape of the optical sheet is 10 ° or less.
[Selection] Figure 1

Description

  The present invention relates to an optical sheet and a planar light source device using the optical sheet.

  In recent years, a display device has been replaced by a liquid crystal display instead of a display using a cathode ray tube, and the screen has been increased in size. Although the light source of the backlight mainly uses a cold cathode tube, in recent years, the shift to the LED light source (Light Emitting Diode) is rapidly progressing.

  There are two types of LED light source irradiation methods: an edge light method and a direct type. The edge light method can be reduced in thickness, and the number of LEDs used is smaller than that of the direct type, so that the cost can be reduced. Therefore, the edge light method has become the mainstream in the market. On the other hand, the direct type is capable of local dimming in a small area and is easy to increase in size compared to the edge light. Therefore, the direct type is the mainstream in high performance models and large models.

  In the direct type, a light source is installed on the back side of the liquid crystal panel to irradiate light. However, if the distance between the optical sheet and the reflective film is shortened in order to reduce the thickness of the backlight, uneven brightness occurs. Therefore, increasing the thickness is one of the major drawbacks of the direct type.

  In order to enable thinning in the direct type, the direct type light source device disclosed in Patent Document 1 eliminates luminance unevenness by stacking a plurality of sheets containing light diffusion components. However, the use of a plurality of optical sheets leads to an increase in cost and further increases the optical path length that passes through the diffusing component, resulting in a new problem of lowering the front luminance. Further, the direct light source device disclosed in Patent Document 2 attempts to eliminate luminance unevenness by using an optical sheet having a bowl-shaped lens formed on the surface in an orthogonal manner. However, even with this method, the use of two bowl-shaped lens-shaped optical sheets leads to an increase in cost and a new problem that the viewing angle in the horizontal direction of the screen becomes narrow.

JP 2010-49937 A JP 2010-44941 A

  When a large amount of a diffusing agent is added to a flat plate or an optical sheet with random irregularities of about 1 μm ≦ Ra ≦ 50 μm to eliminate uneven brightness, the uneven brightness in the direct type LED backlight can be improved by adding the diffuser. The resolving power can be effectively increased. However, the optical sheet having such a surface shape cannot collect light in a specific direction, and the main effect is to broaden the light distribution uniformly. Therefore, even if a diffusing agent is added to a certain level or more, the luminance unevenness eliminating ability cannot be sufficiently improved.

  An optical sheet having a lens arranged in a straight bowl shape on the light exit surface can improve light diffusivity in the vertical direction with the linear light source by arranging the bowl lens parallel to the linear light source, and also increase the front brightness. Can be raised. For this reason, it is considered that an optical sheet configuration for a light source is optimal for thinning a cold cathode tube liquid crystal television and reducing the number of cold cathode tubes.

However, since a liquid crystal television of the type directly under the LED is a point light source, a linear saddle-shaped lens can diffuse light in a direction perpendicular to the eyelid, but hardly diffuses light in a direction parallel to the eyelid. Therefore, an optical sheet formed with an independent lens has been developed. Since such an optical sheet can diffuse light isotropically, it is possible to achieve a high degree of brightness non-uniformity compared to a bowl-shaped lens sheet.
However, the distance between the first optical sheet (hereinafter sometimes referred to as “first optical sheet”) in the direction from the reflector and the light source to the liquid crystal panel side in order to reduce the thickness. In the light source device in which the number of LED elements is reduced in order to reduce the cost, the upper part of the central part of the LED elements arranged in a grid (the part where the LED elements are not arranged) The angle of light incident on the part becomes severe. As a result, the problem that a new dark spot arises in the center part of LED (1) element arrange | positioned at a grid | lattice form has arisen.

  An object of the present invention is to provide an optical sheet capable of eliminating luminance unevenness in a direct type LED backlight having a short distance between a first optical sheet and a reflecting sheet, and a planar light source device including them. It is.

  As a result of intensive studies to solve the above problems and the problems of the prior art, the inventors formed a quadrangular pyramid on the light exit surface side of the optical sheet containing the diffusing agent, and determined the shape to a specific angle. It has been found that the above-mentioned problems can be solved by arranging them so as to intersect with each other, and the present invention has been completed.

  The optical sheet of the present invention is an optical sheet having a rectangular outer shape and a plurality of convex or concave quadrangular pyramid shapes formed on one surface, wherein the base surface of the quadrangular pyramid has a narrow angle ( [theta] 1) is a rhombus of 75 [deg.] to 88 [deg.], and the angle formed between the longer diagonal of the rhombus and the long side of the outer shape of the optical sheet is 10 [deg.] or less. It is preferable that the quadrangular pyramid shape is concave and the quadrangular pyramid shape is arranged in the direction of each side of the rhombus. In the quadrangular pyramid shape, the intersection angle (θ2) between the slope of the quadrangular pyramid and the basal plane is preferably 20 ° ≦ θ2 ≦ 70 °.

  The planar light source device of the present invention is a planar light source device having a light source including a plurality of point light sources arranged in a grid on a plate, and the optical sheet on the light output side of the light source, the optical sheet The narrow angle of the crossing angle (θ3) formed by the rhombic diagonal line on the bottom surface of the quadrangular pyramid shape formed on the surface and the arrangement direction of the point light sources is 15 ° or less. The light source has a rectangular opening on the light exit side, and the optical sheet is arranged so that the longitudinal direction thereof is in the same direction as the longitudinal direction of the opening, and is closer to the light exit surface than the optical sheet. It is preferable that at least one prism sheet is arranged such that the lens extending direction of the prism sheet is the same as the longitudinal direction of the opening.

  By using the optical sheet of the present invention, the light incident on the first optical sheet disposed immediately above the central portion of the LED light source disposed in a lattice shape is efficiently emitted to the viewer side. Further, the light emitted from the optical sheet passes through the microlens sheet and the prism sheet, and is emitted in a direction in which it can easily be raised in the front direction. Therefore, the dark spot at the center of the LED light source can be improved, and a high-quality image with little luminance unevenness can be provided.

It is a cross-sectional schematic diagram which shows the structure of a display apparatus. It is explanatory drawing which shows an example of the cross-sectional shape of the quadrangular pyramid shape shape | molded by the optical sheet of this invention. It is explanatory drawing which shows another example of the cross-sectional shape of the quadrangular pyramid shape shape | molded by the optical sheet of this invention. It is explanatory drawing which shows another example of the cross-sectional shape of the quadrangular pyramid shape shape | molded by the optical sheet of this invention. It is explanatory drawing which shows another example of the cross-sectional shape of the quadrangular pyramid shape shape | molded by the optical sheet of this invention. It is a schematic diagram of an LED direct type backlight device. It is explanatory drawing of a prism sheet. It is a top view which shows the example of arrangement | positioning of LED used for the LED direct type | mold backlight of this invention. It is a top view which shows the other example of arrangement | positioning of LED used for the LED direct type | mold backlight of this invention. It is a top view explaining the example of arrangement | positioning of LED and a 1st optical sheet. It is a top view explaining other example of arrangement of LED and the 1st optical sheet. It is a top view explaining other example of arrangement of LED and the 1st optical sheet. It is a top view explaining other example of arrangement of LED and the 1st optical sheet. It is a laser microscope observation image of the optical sheet (injection molded product) of Example 2. It is an electron microscope observation image of the optical sheet (injection molded product) of Example 2.

  The following description is made with reference to the drawings and the like, but the present invention is not limited to the embodiments of the drawings.

  In the present specification, the first optical sheet refers to an optical sheet arranged first in the direction from the light source to the liquid crystal panel, and the second and subsequent optical sheets are the second, third, and fourth, respectively. And the optical sheets in the order of arrangement (see FIG. 1). The optical sheet closest to the front panel corresponds to the fourth optical sheet 6 in FIG. As long as the purpose of installation (for example, improvement in luminance) of these optical sheets can be achieved without causing other obstruction factors (for example, significant increase in thickness, increase in cost), there is no upper limit on the number of sheets.

Hereinafter, the physical configuration such as the surface shape of the optical sheet according to the present invention will be described first, and then the chemical composition, the method of combining other sheets, and the like will be described.
<Surface shape of optical sheet>
In the optical sheet of the present invention, an independent quadrangular pyramid (hereinafter sometimes referred to as “unit lens”) group is formed on the light exit surface side. The base surface of the quadrangular pyramid shape is a rhombus.
However, if the intersection angle (narrow angle) θ1 between the two opposing bottoms of the rhombus becomes too acute, the light incident on the LED light source central part is totally reflected on the surface of the quadrangular pyramid. Since light is not emitted sufficiently, dark lines are generated. Therefore, the crossing angle (narrow angle) of the two opposing bases of the rhombus is desirably 75 ° ≦ θ1 ≦ 88 °, more desirably 78 ° ≦ θ1 ≦ 86 °, and further desirably 80 ° ≦ θ1 ≦ 85 °.

  The shape to be formed on the light exit surface of the optical sheet of the present invention may be a substantially quadrangular pyramid shape, the width of the cross section perpendicular to the arbitrary base and passing through the center is P2, and the height of the base and top of the optical element When H is H2, these distances are not particularly limited. In view of ease of molding, it is preferable that 20 μm ≦ P2 ≦ 300 μm, 10 μm ≦ H2 ≦ 200 μm. Moreover, when the crossing angle between these quadrangular pyramidal slopes and the basal plane is θ2, θ2 is preferably 20 ° to 70 °, more preferably 30 ° to 60 °, and more preferably 40 ° to 50 °. The slope portion may be a straight line, or may be a curve whose slope changes continuously, such as an ellipse or a part of a hyperbola. Also, the shape of the part from the middle part to the apex may be an acute shape (FIG. 2), but it may be rounded (FIG. 3) or flat (FIG. 4). The shape which the top part is depressed may be sufficient (FIG. 5). The quadrangular pyramid shape may be a convex shape, but may be a concave shape for ease of molding. By adopting such a shape, incident light at a deep angle incident on a position away from the light source can be raised in the front direction, so that dark lines generated between the light sources can be improved.

  In a thin direct type LED backlight, if the light incident angle at the middle part of two LEDs is deep and there are few slopes on the slope of the quadrangular pyramid, light cannot be launched effectively, and as a result, the dark part remains, resulting in brightness Cause unevenness. Therefore, when the projection line length of the slope portion is L2, it is preferable that L2 / P2 ≧ 20%, more preferably L2 / P2 ≧ 40%, and L2 / P2 ≧ 50%. Further preferred.

Regarding the arrangement of the unit lenses, they may be arranged randomly without regularity, or may be arranged with a certain regularity.
In the optical sheet of the present invention, the structure of the connecting portion between adjacent independent shapes is not particularly limited as long as it does not affect the target optical performance.

  For example, if you want to achieve only the optical performance as designed for the independent shape with the entire optical sheet, ideally, all the outer peripheral lines of the base surface of the independent shape (quadrangular pyramid shape) should match the base line That is, it is preferable to arrange the unit lenses without any gap. In particular, an aspect in which quadrangular pyramid shapes are arranged in the direction of each side of the rhombus is preferable.

However, the interval between the independent shapes in a range that does not affect the optical performance of the entire optical sheet is substantially equal to that there is no gap, and is an equivalent range of the present invention. For example, in the step of transferring the independent shape of the optical sheet of the present invention, a slight gap is given so that release after shape transfer is facilitated. With respect to the cross-sectional shape between the independent shapes given to the optical sheet of the present invention by this slight gap, any shape such as a straight line, a concave curve, or a V-shape can be used as long as the optical performance is not affected. The invention is synonymous with no gap.
Conversely, in order to assist or enhance the optical performance of the unit lens of the present invention, or to supplement other optical performance, a shape corresponding to the purpose is provided with a gap between the lowest portions of adjacent unit lenses. May be added.

  In the optical sheet of the present invention, these surface shapes are set on the light exit surface side. On the other hand, the surface shape configuration on the light incident surface side of the optical sheet of the present invention is not particularly limited and can be appropriately selected from flat surfaces, embossed surfaces, mat surfaces, surfaces having optical elements such as lenses, etc. An embossed surface and a mat surface are preferably used from the viewpoints of preventing sticking, preventing sound noise, and exhibiting a light scattering effect.

  The thickness of the optical sheet of the present invention can be appropriately adjusted and is not particularly limited, but is usually preferably 0.3 mm or more, more preferably 0.5 mm or more, preferably 10 mm or less, more preferably 5 mm or less. It is. If the thickness is 0.3 mm or more, the light diffusing action is better, and the rigidity is high and the shape stability is improved. If the thickness is 10 mm or less, the entire apparatus to which the optical sheet of the present invention is applied can be made more compact. .

The outer shape of the optical sheet of the present invention is rectangular.
The angle formed by the longer diagonal of the rhombus on the bottom surface of the substantially quadrangular pyramid shape formed on the surface (the diagonal connecting the vertices of the narrow angle) and the long side of the optical sheet outer shape is 10 ° or less. is necessary. When this angle is 10 ° or less, when the optical sheet of the present invention is used in a planar light source device having a rectangular housing, it is possible to suppress a difference in luminance uniformity due to a viewing angle. The angle is more preferably 5 ° or less, and further preferably 0 ° (the longer diagonal of the rhombus on the bottom surface of the substantially quadrangular pyramid shape formed on the surface is parallel to the long side of the optical sheet outer shape). is there.

<Configuration of optical sheet>
[Transparent thermoplastic resin]
The thermoplastic resin constituting the optical sheet of the present invention is not particularly limited as long as it is transparent and has an appropriate strength as a main component of the optical sheet. For example, polycarbonate resin; acrylic resin such as polymethyl methacrylate; styrene resin such as polystyrene, polyvinyl toluene and poly (p-methylstyrene); MS resin (copolymer of methyl methacrylate and styrene); norbornene resin Polyolefin resin; polyarylate resin; polyethersulfone resin; and mixed resins of two or more of these can be used. A polycarbonate resin, a styrene resin, or a norbornene resin is preferably used.

  The refractive index of the resin is not particularly limited, but the larger the refractive index difference from the air layer (refractive index n = 1.0), the larger the refractive angle and the better the diffusion performance, so n ≧ 1.3 is desirable. N ≧ 1.4 is more desirable, and n ≧ 1.45 is even more desirable. Of these, the polycarbonate resin is particularly preferable as a resin for an optical sheet because it is excellent in transparency, heat resistance, and processability and has a good balance. In addition, an ultraviolet absorber, a fluorescent brightening agent, a flame retardant, and the like may be included as necessary.

[Light diffusion layer]
The optical sheet of the present invention may be composed of only a transparent resin, but in order to adjust the light diffusibility, a light diffusing layer made of particles having a light diffusing ability may be provided. The light diffusing layer may be uniformly or randomly dispersed in the entire optical sheet, only the lens portion, the entire portion other than the lens portion, only the light exit surface layer, only the light entrance surface layer, or the intermediate layer.
In the light diffusion layer, light diffusing particles having a difference in refractive index of 0.01 or more from the transparent resin are dispersed in the thermoplastic resin, and the difference in refractive index is 0.01 or more. Is preferably 0.05 or more, more preferably 0.1 or more. Further, a lens-like optical element may be provided on the surface for the purpose of adjusting the diffusion direction and diffusion ratio of light diffusion and increasing the luminance uniformity in the viewing angle direction.

[Light diffusing agent]
Examples of the material for the light diffusing particles include (meth) acrylic resins, styrene resins, polyurethane resins, polyester resins, silicone resins, fluorine resins, and synthetic resins such as copolymers thereof; glass; And clay compounds such as smectite and kaolinite; inorganic oxides such as silica and alumina; and the like. Of these materials, (meth) acrylic resins, silicone resins, and silica are particularly suitable. The light diffusing agent may be a single material, a mixture of single materials, a mixed material, or a mixture of mixed materials of these exemplified materials.

  The volume average particle size of the light diffusing particles is preferably 0.1 to 50 μm, more preferably 0.3 to 10 μm, and further preferably 0.5 to 5 μm. When the particle size of the light diffusing particles is out of the above range, there is a possibility that sufficient light diffusing properties cannot be exhibited.

  The ratio between the thermoplastic resin and the light diffusing particles may be adjusted as appropriate, but the diffusivity is the difference in refractive index Δn between the base resin and the diffusing agent resin, the volume average particle diameter D50 of the diffusing agent particles (light diffusing particles). When the concentration of the light diffusing particles with respect to 100 parts by weight of the base resin is C, it is preferable that 0.01 ≦ Δn × D50 × C ≦ 0.50. Under such severe backlight conditions, effective unevenness elimination cannot be achieved unless the diffusing effect of the diffusing agent and the diffusing effect of the lens are used together. However, when Δn × D50 × C <0.01, Since the effect is too weak, it is not possible to achieve sufficient luminance unevenness elimination. On the other hand, when Δn × D50 × C> 0.50, the diffusion effect due to the diffusing agent becomes too strong, and the photorefractive effect due to the concave quadrangular pyramid shape formed on the light exit surface is weakened. It becomes difficult to start up in the direction, and a dark portion is generated between the light sources, so that it is impossible to eliminate luminance unevenness.

  When it is necessary to further enhance the anisotropic light diffusion performance as the optical performance of the optical sheet of the present invention, low crosslink density organic fine particles that can exhibit anisotropic light diffusibility at the time of molding the optical sheet can also be used. Monomers used as raw materials for the low crosslink density organic fine particles include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, n -Butyl (meth) acrylate, iso-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, hydroxyethyl (meth) acrylate, (Meth) acrylates such as hydroxypropyl (meth) acrylate; styrenes such as styrene, p-methylstyrene, vinyltoluene, pt-butylstyrene; N-phenylmaleimide, N-cyclohexylmaleimide, N-benzyl Maleimides such as reimide; (meth) acrylamide, (meth) acrylamides such as N-methylol (meth) acrylamide; acrylonitriles such as (meth) acrylonitrile; N-vinylpyrrolidone; or two of these The above can be mixed and used.

  Examples of the crosslinking agent used as a raw material for the crosslinked organic fine particles include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) ) Acrylates, polyfunctional (meth) acrylates such as bishydroxyethyl bisphenol A di (meth) acrylate; radical polymerizable crosslinking agents such as divinyloxyethoxy (meth) acrylate, diallyl phthalate, allyl (meth) acrylate, divinylbenzene; Polyfunctional epoxy compounds such as bisphenol A diglycidyl ether, diethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether; Or a polyfunctional isocyanate compound such as N-methylol melamine or N-methylol benzoguanamine; or a mixture of two or more thereof. it can.

  The crosslinked organic fine particles for exhibiting anisotropic diffusibility preferably have a crosslinking density of 0.001% or more and 0.12% or less. Such organic fine particles having a low cross-linking density are spherical or substantially spherical at the raw material stage, but are formed into an ellipsoidal shape or a rod shape at a predetermined position (layer, etc.) of the optical sheet due to heat, shearing force, etc. received during molding of the optical sheet. When this shape is changed, anisotropic diffusivity is expressed. In addition, a crosslinking density is a numerical value calculated | required by following Formula (1).

Fn (c): number of functional groups of the crosslinking agent used for production of radical polymerized crosslinked fine particles, provided that Fn (c) ≧ 2
Mw (c): Molecular weight of the crosslinking agent used for producing the radical polymer-based crosslinked fine particles W (c): Mass blending ratio (%) of the crosslinking agent used for producing the radical polymer-based crosslinked fine particles
W (m): Mass blending ratio (%) of monomer used for production of radical polymerized crosslinked fine particles
However, W (m) + W (c) = 100

[Antioxidant]
An antioxidant may be added to at least one of the organic fine particles including the low crosslink density organic fine particles of the present invention or the thermoplastic resin. The antioxidant can suppress coloring of the thermoplastic resin and organic fine particles due to oxidation and deterioration during heat molding. Therefore, the brightness of the light source device to which the optical sheet of the present invention is applied can be more reliably exhibited.

  A conventionally well-known thing can be used as antioxidant. For example, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-1-hydroxyphenyl) propionate, etc. Hindered phenolic antioxidants; tris (2,4-di-t-butylphenyl) phosphite, tris [2-[[2,4,8,10-tetra-t-butyldibenzo [d, f] [ Phosphorous antioxidants such as 1,3,2] dioxaphosphin-6-yl] oxy] ethyl] amine; thiodiethylenebis [3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate] and the like having no aromatic ring, pentaerythrityltetrakis (3-laurylthiopropionate) Sulfur-based antioxidants such as; lactone-based antioxidants such as the reaction product of 3-hydroxy-5,7-di-t-butyl-furan-2-one and o-xylene; Hydroxylamine antioxidants such as oxidation products of alkylamines; 3,4-dihydro-2,5,7,8-tetramethyl-2- (4,8,12-trimethyltridecyl) -2H-benzopyran- Vitamin E antioxidants such as 6-ol can be used.

  Although the usage-amount of antioxidant may be adjusted suitably, normally, what is necessary is just to add about 0.005 mass% or more and 0.3 mass% or less with respect to a thermoplastic resin.

<Surface light source device>
The planar light source device of the present invention has a light source including a plurality of point light sources arranged in a grid on a plate, and the optical sheet on the light output side of the light source.

  The point light source used in the planar light source device of the present invention is preferably an LED. As the LED light source, a Lambertian type in which the peak of the emission intensity is the normal direction of the LED light source installation surface or a side emission type LED in which the peak is inclined from the normal is preferably used. In the present invention, a side-emission type in which a lens or a light flux controlling member is installed on an LED chip is particularly preferably used because luminance unevenness of the surface light source device is easily reduced or eliminated.

  Among them, the light distribution pattern may be a lens having a substantially rotationally symmetric emission distribution having an emission intensity peak at a deep angle of 30 ° or more from the normal of the LED light source installation surface, or an LED provided with a light flux control member. preferable. Furthermore, using a LED with a lens or a light flux control member having a substantially rotationally symmetric emission distribution with a light distribution pattern having an emission intensity peak at a deep angle of 45 ° or more from the normal of the LED light source installation surface, Even in a planar light source device in which the LED light source arrangement interval is enlarged, or a thin planar light source device in which the interval between the reflection sheet and the optical sheet in which the LED light source is arranged is reduced, it becomes easier to eliminate and reduce luminance unevenness, More preferred.

  As the light source, for example, as shown in FIG. 1, a point light source (LED) is disposed on a bottom plate of a housing, and an opening is provided on the upper surface thereof. The bottom plate on which the point light source is disposed is not particularly limited, but a reflecting plate and a reflecting film are preferable. And the point light source is arrange | positioned on this board, ie, the same plane. In addition, arrangement | positioning in a grid | lattice form means the aspect which the point light source has arrange | positioned in each intersection part of a grating | lattice.

In the planar light source device, the optical sheet has a plane in which a quadrangular pyramid shape is formed on the light output side, a plane in which the quadrangular pyramid shape is formed, and a plane in which the point light source is disposed. Are installed in parallel.
The optical sheet of the present invention is preferably used as the first optical sheet in order to efficiently use its high optical performance adjustment capability in other optical sheets and apparatus settings. By using it as the first optical sheet, the luminance in the viewing angle direction in the intermediate region between adjacent LEDs of the light source device can be improved, and the effect of eliminating luminance unevenness can be maximized.

FIG. 6 shows a structural diagram of the LED and the first optical sheet, and FIGS. In addition, these figures are examples of LED arrangement, and this invention is not necessarily limited to these arrangements.
Here, the distance between the surface on which the LED (1) of the LED direct type backlight is disposed and the first optical sheet is H1, and the distance of the largest interval among the arrangement intervals of the LED (1) is P1. In this case, it is difficult to eliminate luminance unevenness as the value of P1 / H1 increases. The conditions up to about P1 / H1 = 2.0 are not so difficult to eliminate luminance unevenness, and even if it is not the optical sheet proposed in the present invention, it can be dealt with by sufficiently adding a diffusing agent. However, when P1 / H1 = about 2.5, it is difficult to eliminate luminance unevenness in a general optical sheet only by adding a diffusing agent.

  When θ2 of the quadrangular pyramid-shaped slope portion of the optical sheet is 30 to 60 °, the optical sheet of the present invention is disposed as the first optical sheet directly above the central portion of the LED light source disposed in a lattice shape. The ratio and the angle at which light incident on the light is emitted vary depending on the orientation direction of the unit lens. This is due to the relationship between the incident light and the angle of the surface forming the quadrangular pyramid. When the smaller angle of the crossing angles of the diagonal of the quadrangular pyramid and the array direction of the LED (1) is θ3, In the case of θ3 = 45 ° (FIG. 10), most of the incident light from the light source is reflected because the angle formed with the surface forming the quadrangular pyramid is greater than or equal to the critical angle and is reflected back to the light source side. Light is not sufficiently emitted from one optical sheet, and a dark spot remains directly above the central portion of the LED light source arranged in a lattice shape.

  When θ3 = 0 ° (FIG. 11) and the diagonal direction of the quadrangular pyramid and the arrangement direction of the LEDs (1) are parallel, the first LED arranged directly above the central portion (10) of the LED light source arranged in a lattice shape. Since the light incident on the optical sheet of the present invention which is the optical sheet (3) is smaller than the critical angle with the surface forming the quadrangular pyramid, most of the light is emitted in the direction of the observation plane, The dark spot immediately above the central portion (10) of the LED light sources arranged in a shape is improved.

  θ3 can be arranged at an arbitrary value of 0 ° ≦ θ3 ≦ 45 °. However, the closer to θ3 = 0 °, the higher the effect of eliminating the dark spot. Therefore, it is desirable that θ3 is as close as possible to θ3 = 0 °. 0 ° ≦ θ3 ≦ 15 ° is preferable, 0 ° ≦ θ3 ≦ 10 ° is more preferable, 0 ° ≦ θ3 ≦ 5 ° is further preferable, and θ3 = 0 ° is most preferable.

<Combination with the second optical sheet and other optical sheets>
In addition, when the optical sheet of the present invention is used as the first optical sheet, as the other optical sheet, a prism sheet, a diffusion sheet, a diffusion sheet with a lens, a reflective polarizing film, and the like can be used, and combinations thereof are also possible. A combination suitable for the conditions of the light source device and the like can be selected. At this time, it is preferable to use a diffusion sheet or a diffusion sheet with a lens as the optical sheet closest to the front panel. In particular, by using at least one prism sheet for the second and subsequent optical sheets, it is possible to further eliminate luminance unevenness and achieve high luminance and brightness uniformity on the light exit surface immediately before the front panel.

The effect of the present invention is further increased by disposing the prism sheet closer to the observation surface than the first optical sheet (3). Although there is no restriction on the lens extension direction of the prism sheet to be arranged, the extension direction of the lens and the longitudinal direction of the light source device are considered as a display device because the viewing angle in the horizontal direction is more important than the vertical direction. Are preferably parallel.
The lens shape of the prism sheet may have an acute angle at the top or may be rounded. Further, the tilt angle of the prism lens is not particularly limited, but is preferably 70 to 110 °, more preferably 80 to 100 °, and still more preferably 85 to 95 ° from the viewpoint of the ability to increase the front luminance and the ability to eliminate luminance unevenness. is there. In addition, as the lens shape, one type of the same shape may be used repeatedly, or a substantially similar lens group may be used repeatedly at random to eliminate moire. Further, the top of the ridge may be straight or wavy. In addition, the light incident surface may be a flat surface, may be matted using an arbitrary mold, or may have a lens shape. An appropriate amount of a diffusing agent may be added to the base material for improving diffusibility.

  When at least one prism sheet is used in the light source device, the light emitted from the first optical sheet (3) (11) is eliminated in eliminating the dark spot immediately above the central portion (10) of the LED light source arranged in a grid pattern. ) Direction becomes even more important. The y-axis direction component of the emitted light (11) with respect to the prism sheet is defined by assuming that the lens ridge extending direction of the prism sheet (see FIG. 7) is the x axis, the lens array direction is the y axis, and the direction perpendicular to the sheet surface is the z axis. When 0 is 0, most of the light is totally reflected on the light exit surface of the prism sheet regardless of the components in the x-axis direction and z-axis direction, and is reflected back to the light source side, so that almost no light is emitted to the observation surface side. .

  As the y-axis direction component of the emitted light (11) with respect to the prism sheet increases, the ratio of the emitted light from the prism sheet increases. When the y-axis direction component is sufficiently larger than the x-axis / z-axis direction component, most of the light is emitted in the observation plane direction according to Snell's law according to the ratio of the x-axis / z-axis component. Therefore, in order to increase the luminance in the observation plane direction, it is important to adjust the angle of the quadrangular pyramid surface so that the y-axis direction component of the emitted light (11) becomes large.

The bottom surface of the quadrangular pyramid shape having an arbitrary inclination angle formed on the light exit surface of the optical sheet is designed as a rhombus, and is arranged so that the longitudinal direction of the rhombus diagonal line is parallel to the x-axis direction of the prism sheet (FIG. 12). (The prism sheet is not shown in the figure)), improving the dark spot directly above the central portion (10) of the LED light sources arranged in a grid without substantially impairing the performance of eliminating the unevenness of dark lines generated between LEDs. can do. In such an arrangement, the y-axis direction component of the light emitted from the first optical sheet (3) becomes stronger, and the intensity of the light emitted from the prism sheet in the observation surface direction also becomes stronger. It can be improved.
On the other hand, the optical sheet of the present invention, which is the first optical sheet (3), is arranged so that the longitudinal direction of the rhombus diagonal and the x-axis direction of the prism sheet are parallel (FIG. 13 (the prism sheet is not shown)). Since the x-axis direction component of the light emitted from the beam becomes stronger and the total amount of light reflected by the prism sheet increases, the dark spot becomes stronger on the contrary.

  Therefore, when using another optical sheet, the light source has a rectangular opening on the light output side, and the optical sheet is arranged so that the longitudinal direction thereof is the same as the longitudinal direction of the opening. In addition, it is preferable that at least one prism sheet is disposed closer to the light exit surface than the optical sheet so that the lens extending direction of the prism sheet is the same as the longitudinal direction of the opening.

  The optical sheet of the present invention and the direct type light source device having the optical sheet can diffuse light in a desired direction, and as a result, can maintain the uniformity of the light. The power consumption and manufacturing cost can be reduced, and the liquid crystal display device can be made thinner, which is extremely useful in the industry.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

1. Optical sheet Example 1
To 100 parts by weight of a polycarbonate resin (Teijin Chemicals, L1225WX), 0.2 part by weight of a diffusing agent (SL-200, manufactured by Daiichi Woolen) was added and mixed. Using the obtained mixture as a raw material, a light-emitting surface lens-shaped optical sheet was manufactured by injection molding using a metal mold subjected to fine processing. The concave / convex shape of the metal mold was such that convex quadrangular pyramidal lenses with rhombus bottoms were arranged vertically and horizontally so that their bases were adjacent to each other. The height of each lens was 73 μm, the crossing angle (narrow angle) was 88 °, and the angle between the slope and the basal plane was 44 °, and the distance between the tops of the lenses arranged continuously was 150 μm. Twelve 10 cm square samples were prepared as the light exit surface lens shaped optical sheet. The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 0 °.

Example 2
A metal mold used for injection molding is a convex / concave shape in which the concave / convex shape is rhombus-shaped, and is arranged in a row in a vertical and horizontal direction. Each lens has a height of 73 μm, a crossing angle of 85 °, and a slope. An optical sheet (30 cm × 40 cm) was produced in the same manner as in Example 1 except that the angle between the top surface of the lens and the base surface was 44 °, and the distance between the tops of the continuously arranged lenses was 151 μm. And used for evaluation.
FIGS. 14 and 15 show photographs of the surface shape of the optical sheet observed using a laser microscope (manufactured by Keyence Corporation, VK9700) and an electron microscope (manufactured by Hitachi Kyowa Engineering Co., Ltd., S-3500).

Example 3
A metal mold used for injection molding has convex and concave shapes arranged in a series of convex and quadrangular pyramidal lenses with rhombuses on the bottom, each having a lens height of 73 μm, an intersection angle of 80 °, and a slope. An optical sheet (30 cm × 40 cm) was produced in the same manner as in Example 1 except that the angle between the top surface of the lens and the base surface was 44 °, and the distance between the tops of the lenses arranged continuously was changed to a metal mold with a distance of 153 μm. And used for evaluation.

Example 4
A metal mold used for injection molding has convex and concave shapes arranged in a vertical and horizontal fashion with convex and concave shapes having rhombus bottoms, each lens height 73 μm, crossing angle 75 °, slope An optical sheet (30 cm × 40 cm) was produced in the same manner as in Example 1 except that the angle between the top surface of the lens and the base surface was 44 °, and the distance between the tops of the continuously arranged lenses was changed to a metal mold having a length of 155 μm. And used for evaluation.

Comparative Example 1
The metal mold used for injection molding has convex and concave pyramid-shaped lenses with a concave-convex shape and a square bottom, and is arranged in a row and column. Each lens has a height of 73 μm, a crossing angle of 90 °, and a slope. A light emitting surface lens-shaped optical sheet is produced in the same manner as in Example 1 except that the angle between the top surface of the lens and the base surface is 44 °, and the distance between the tops of the continuously arranged lenses is 150 μm. did. Twelve 10 cm square samples were prepared as the light exit surface lens shaped optical sheet. The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 0 °.

Comparative Example 2
In the same manner as in Comparative Example 1, a sample of the light exit surface lens shaped optical sheet was produced.
The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 3
In the same manner as in Example 1, a sample of the light exit surface lens shaped optical sheet was produced.
The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 4
In the same manner as in Example 2, a sample of the light exit surface lens shaped optical sheet was produced.
The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 5
In the same manner as in Example 3, a sample of the light exit surface lens shaped optical sheet was produced.
The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 6
In the same manner as in Example 4, a sample of the light exit surface lens shaped optical sheet was produced.
The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 7
A metal mold used for injection molding has convex and concave pyramid-shaped lenses with a concave and convex shape and a square bottom, and is arranged in a row and column continuously. Each lens has a height of 73 μm, a crossing angle of 70 °, and a slope. A light emitting surface lens-shaped optical sheet is produced in the same manner as in Example 1 except that the angle between the base and the bottom surface is 44 °, and the distance between the tops of the continuously arranged lenses is changed to a metal mold of 159 μm. did. Twelve 10 cm square samples were prepared as the light exit surface lens shaped optical sheet. The end surface of each sample was flattened using a cutting machine, and each end surface was adhered using methylene chloride to obtain a 30 cm × 40 cm optical sheet, which was used for evaluation. The angle formed by the longer diagonal of the rhombus on the bottom surface of the concave quadrangular pyramid shape formed on the surface of the optical sheet (30 cm × 40 cm) and the long side of the optical sheet outer shape was 45 °.

Comparative Example 8
The metal mold used for injection molding has convex and concave shapes arranged in a series of convex and quadrangular pyramidal lenses with rhombus bottoms, with individual lens heights of 73 μm and crossing angles of 70 °. An optical sheet (30 cm × 40 cm) was prepared and used for evaluation in the same manner as in Example 1 except that the distance between the tops of the continuously arranged lenses was changed to a metal mold having a length of 159 μm.

  In this example and comparative example, an optical sheet was obtained by bonding a plurality of samples obtained using an injection molding machine. However, the manufacturing method is not limited to this, and an injection molding metal having a size larger than that of the surface light source device. A single optical sheet may be obtained using a mold, the shape may be shaped by a roll transfer method by extrusion molding, or the rhombus shape may be controlled to an arbitrary shape by controlling the stretching strength good.

2. Planar light source device As a light source, a white reflector is provided on the inner surface of a plastic case having an inner width of 730 mm, a depth of 456 mm, and a maximum depth of 26 mm (adjustable to an arbitrary depth, the upper surface being an opening). A direct type LED light source in which diffused LEDs with a lens having a diameter of 15 mm are arranged in a grid pattern at intervals of 50 mm on a reflector is used. On this light source, the optical sheet was disposed so that the lens processing surface was on top. On this first optical sheet, a commercially available prism sheet (manufactured by Sumitomo 3M, BEF II 90/50: apex angle 90 degrees, pitch 50 μm), microlens sheet (manufactured by Hiroshige Kogyo (Suzhou) Co., Ltd.) ML24M: one side A surface light source device was fabricated by arranging an optical sheet in which hemispherical convex lens groups are finely arranged on the surface of the first optical sheet, a microlens sheet, a prism sheet, and a microlens sheet in this order. .
In addition, it arrange | positioned so that the long side direction of an optical sheet may turn into the same direction as the long side direction of the said light source. In the optical sheets of Examples 1 to 4 and Comparative Examples 1 and 8, θ3 is 0 °, and in the optical sheets of Comparative Examples 2 to 7, θ3 is 45 °.

<Evaluation of brightness and brightness unevenness>
Luminance unevenness was observed visually and with a two-dimensional color luminance meter (manufactured by Konica Minolta Sensing, CA-2000) from a position 500 mm away from the center of the direct surface light source device in the vertical direction. The luminance unevenness is evaluated in 10 stages, and the larger the value, the smaller the luminance unevenness. The evaluation results are shown in Table 1.

  By using the form of the present invention, the surface light source device that reduces the cost by increasing the distance between the LEDs and reducing the number of elements used, and the distance between the first optical sheet and the reflective film is shortened to reduce the thickness. Therefore, the present invention is extremely useful in the industry because it is possible to effectively eliminate luminance unevenness.

1: LED
2: Light source 3: First optical sheet 4: Second optical sheet 5: Third optical sheet 6: Fourth optical sheet 7: Front panel 10: Central portion 11 of LED light sources arranged in a grid pattern: Output light P1 from the first optical sheet (3) P1: Distance between the LED elements H1: Distance between the bottom surface of the first optical sheet (3) and the LED (1) arrangement surface P2: Width of square pyramid H2: Square pyramid Height L2: Length of the projected line of the slope of the quadrangular pyramid θ1: Crossing angle (narrow angle) of two sets of opposing bases of the quadrangular pyramid
θ2: Crossing angle between the slope and base surface of the independently shaped optical element θ3: Crossing angle of diagonal line of the pyramid and LED (1) in the arrangement direction θ4: From LED (1) to the upper part of the lattice LED central part (10) Incident angle to the arranged optical sheet (3)

Claims (5)

An optical sheet having a rectangular outer shape, and a plurality of convex or concave quadrangular pyramid shapes on one surface,
The base surface of the quadrangular pyramid is a rhombus whose narrow angle (θ1) is 75 ° to 88 °,
An optical sheet, wherein an angle formed between the longer diagonal of the rhombus and the long side of the outer shape of the optical sheet is 10 ° or less.   The optical sheet according to claim 1, wherein the quadrangular pyramid shape is concave and the quadrangular pyramid shape is arranged in the direction of each side of the rhombus.   3. The optical sheet according to claim 1, wherein the quadrangular pyramid has an intersection angle (θ2) between a slope of the quadrangular pyramid and a base surface of 20 ° ≦ θ2 ≦ 70 °. A planar light source device having a light source including a plurality of point light sources arranged in a grid pattern on a plate, and the optical sheet according to any one of claims 1 to 3 on a light output side of the light source,
A planar shape characterized in that a narrow angle of a crossing angle (θ3) formed by a rhombic diagonal line of a bottom surface of a quadrangular pyramid shape formed on the surface of the optical sheet and an arrangement direction of the point light sources is 15 ° or less. Light source device. The light source has a rectangular opening on the light output side, and the optical sheet is disposed so that the longitudinal direction thereof is the same as the longitudinal direction of the opening,
The at least 1 prism sheet is arrange | positioned so that the lens extension direction of this prism sheet may become the same direction as the longitudinal direction of the said opening part in the light emission surface side rather than the said optical sheet. A planar light source device.