JP2012234047A - Optical sheet and surface light source device using the optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet that eliminates luminance unevenness in a direct-lighting type surface light source device including a plurality of LED light sources arranged therein, even when a distance between installation positions of the LED light source and the optical sheet is reduced or the interval of the LED light sources is increased, and to provide a surface light source device for a liquid crystal display device.SOLUTION: The optical sheet comprises a resin optical sheet in which a plurality of inverted quadrangular pyramids are formed in a matrix on one sheet surface in such a manner that two pairs of opposing bottom sides of the inverted quadrangular pyramid extend parallel in the respective two directions, and prisms are continuously arranged parallel to one another on the other sheet surface. The extending directions of the two pairs of bottom sides opposing to each other of the inverted quadrangular pyramids intersect each other at an angle of 60° to 89° (narrow angle). The cross-sectional shape of the prism is a joined form of a triangle and/or a part of a triangle and a part of a curved line. Each extending direction of the bottom sides of the inverted quadrangular pyramids and the extending direction of the prisms intersect at an angle of 30° to 60° (narrow angle).

Description

  The present invention relates to an optical sheet for a planar light source device used for illumination of a liquid crystal display panel or the like, and a planar light source device using the optical sheet.

  Liquid crystal display devices for displaying images are widely used for large displays such as thin televisions and thin monitors. In these liquid crystal display devices, a backlight unit is used to irradiate a liquid crystal display panel that does not have self-luminous properties. The backlight unit includes, for example, a light guide plate and an LED (light emitting diode) light source disposed on an end face of the light guide plate, guides light from the light source, and irradiates the liquid crystal display panel from the entire main surface. In addition, there is a direct type in which an LED light source is disposed directly under a liquid crystal panel without using a light guide plate, and the liquid crystal panel is irradiated from the entire main surface of the light diffusion plate or optical sheet.

  In recent years, with the increase in screen size of liquid crystal televisions, demands for weight reduction and thinning have increased, but with the edge type using a light guide plate, it is difficult to reduce the weight of the television itself due to the increase in the weight of the light guide plate itself. At the same time, it has become difficult to increase the brightness of the display screen. On the other hand, the direct type that does not use a light guide plate can be reduced in weight because there is no light guide plate, but because the directivity of the LED light source is strong, the portion directly above the LED becomes very bright, causing significant luminance unevenness, and the entire light exit surface In order to obtain irradiation light with little luminance unevenness, it is necessary to narrow the arrangement interval of the LED light sources or to sufficiently separate the distance between the light diffusion plate and the LED light source, and it is difficult to reduce the thickness and reduce the cost.

  Patent Document 1 discloses a method in which a light flux controlling member is attached on an LED element, the directivity to a portion directly above the LED is relaxed, and brightness and darkness when used as a light source of a direct type backlight is disclosed. In Patent Document 2, for the purpose of eliminating luminance unevenness in a direct-type backlight unit in which an LED light source is arranged on a matrix, the surface has a concave portion of a substantially inverted polygonal pyramid or a substantially inverted polygonal frustum shape, and has a concave shape. A light diffusing plate having a total light transmittance of 65% to 100% with the surface as the light incident surface, and a total light transmittance of 30% to 80% with the opposite surface of the surface having the concave shape as the light incident surface. It is disclosed to use. Patent Document 3 discloses a first transparent layer having a plurality of long V-shaped protrusions and a plurality of falls arranged in a matrix system for the purpose of uniforming the luminance distribution while increasing the light utilization rate from the light source. Disclosed is an optical sheet for a backlight in which a light-diffusing layer sandwiched between a second transparent layer, a first transparent layer, and a second transparent layer formed with a micro concave portion such as a square pyramid or a square frustum are disclosed. ing.

JP 2009-117207 A JP 2010-117707 A JP 2008-139878 A

  However, further reduction in the number of LED light sources for reducing the backlight cost, or further thinning of the liquid crystal television, specifically, between a plurality of LED light sources installed on a reflective sheet as shown in FIG. The ratio between the closest distance (L) and the distance (D) between the top of the LED and the surface of the optical sheet on the point light source side, not the distance to the surface on the point light source side of the reflective sheet and optical sheet However, even when L / D is 2.5 or more, the present situation is that the problem that the luminance unevenness can be solved is not satisfied.

  That is, it is possible to distribute light widely in a range other than directly above the LED by arranging the light flux control member on the LED element as a point light source of the direct type backlight, but the light diffusion plate arranged on the LED light source side If the distance between the LED light source and the LED light source is reduced or the arrangement distance of the LED light source is increased, a light / dark pattern is generated due to the shape of the light flux controlling member. It is difficult to reduce the thickness of the apparatus and the number of LED light sources.

  On the other hand, the backlight unit is arranged on the reflective sheet under the strict condition of L / D ≧ 2.5, which is required for further thinning the backlight unit or reducing the number of LEDs used by expanding the arrangement interval of the LED light sources. The surface of the LED light source having a concave portion having a substantially inverted polygonal pyramid or substantially inverted polygonal frustum-shaped concave portion and a total light transmittance of 65% to 100% with the surface having the concave shape as a light incident surface A light diffusion plate having a total light transmittance of 30% to 80% with the opposite surface as the light incident surface, and a fine particle as a light diffusion agent coated on the surface of the thermoplastic film on the diffusion plate. "Diffusion sheet", prism sheet, microlens sheet, reflective polarizing sheet, etc. that have been superposed on the light diffusion plate from the past, are simply superposed on the optical sheet so that brightness unevenness is greatly reduced or eliminated. The Rukoto, has come to limit occurs.

  Furthermore, in order to express the luminance uniformity as a planar light source without reducing the luminance of the light source as much as possible, fine concave and convex shapes such as fine falling quadrangular pyramids and prisms were formed on both the light incident surface and the light emitting surface. A light diffusing plate has been proposed, but if you simply place a falling quadrangular pyramid or prism, you can use a highly directional LED light source, make the backlight unit thinner, or increase the number of LED light sources. It is difficult to develop a planar light source with a high degree of uniformity under the strict condition of L / D ≧ 2.5, which is required in reducing the above.

  The present invention has been made in view of the above-described problems, and an object thereof is a planar light source capable of realizing further thinning or further reduction in the number of LED light sources in a direct type backlight provided with LED light sources. An object is to provide an optical sheet for a device and a planar light source device including the optical sheet.

  In order to achieve the above object, the present invention employs the following means. That is, in the first invention, a plurality of falling quadrangular pyramids are formed in a matrix shape on one sheet surface so that two opposing bottoms of the falling quadrangular pyramids extend in two directions in parallel, A resin optical sheet in which prisms are continuously formed in parallel on the other sheet surface, and the extending directions of the two opposing bottom sides of the falling quadrangular pyramid intersect at 60 ° to 89 ° (narrow angle). And the cross-sectional shape of the prism is a shape in which a triangle and / or a part of a triangle and a part of a curve are joined, and each extending direction of the base of the falling quadrangular pyramid and the extending direction of the prism are Also intersects at 30 ° to 60 ° (narrow angle).

  According to a second invention, in the optical sheet of the first invention, the diagonal line of the longer bottom surface of the falling quadrangular pyramid formed on one surface and the extending direction of the prism formed on the other surface are 0. It intersects at a angle of 15 ° (narrow angle).

  According to a third invention, in the optical sheet of the first or second invention, the base of the falling quadrangular pyramid is 10 μm to 1000 μm, and the base in the cross-sectional shape perpendicular to the extending direction of the prism is 10 μm to 1000 μm. Features.

  4th invention is an optical sheet of 1st-3rd invention, The inclination | tilt angle with respect to the optical sheet horizontal surface of the side surface of a fallen quadrangular pyramid is 30 degrees-60 degrees, and a convex part perpendicular | vertical to the extension direction of a prism The internal angle of both sides of the triangle in the cross-sectional shape, or the extended line crossing angle (inner angle) of both sides of the triangular portion in the convex cross-sectional shape in which a part of the triangle and a part of the curve are joined is 60 ° to 120 °. And

  In a fifth aspect of the optical sheet of the first to fourth aspects of the invention, the layer thickness occupies a thickness of 50% or more of the total thickness of the optical sheet including the falling quadrangular pyramids and prism portions formed on both sides. A resin composition in which a light diffusing agent is blended with a transparent resin is used.

  6th invention is related with a planar light source device, and has a reflective sheet, a plurality of LED light sources installed on a reflective sheet, and an optical sheet according to claims 1 to 5.

  By using the optical sheet of the present invention for a planar light source device using a plurality of LEDs arranged on a reflective sheet as a light source, the LED light source arrangement interval is larger than the conventional interval, or the LED light source and the optical sheet Even if the interval is reduced, the luminance unevenness can be reduced or eliminated. In addition, the planar light source device using the optical sheet of the present invention can reduce or eliminate luminance unevenness even if the LED light source arrangement interval is larger than the conventional interval or the interval between the LED light source and the optical sheet is reduced. Therefore, as a direct type planar light source device in which LED light sources are arranged, it is possible to further reduce the thickness and further reduce the number of LED light sources for cost reduction and power consumption reduction.

It is a conceptual diagram (a top view and a sectional view) showing that one surface which is an example of an optical sheet embodiment of the present invention is a falling quadrangular pyramid shaping surface, and the other surface is a prism shaping surface. . It is simplified sectional drawing which shows one example of embodiment which has arrange | positioned the optical sheet of this invention on several LED light source with a general purpose optical sheet. It is a simplified sectional view showing another example of an embodiment which arranged the optical sheet of the present invention on a plurality of LED light sources with a general-purpose optical sheet. It is a simplification of the extrusion molding method which is an example of the manufacturing method of the optical sheet of the present invention. It is a LED light source arrangement | positioning figure of the backlight used for brightness nonuniformity evaluation.

  Hereinafter, an optical sheet according to an embodiment of the present invention and a planar light source device using the optical sheet will be described in detail. As shown in FIG. 1, the optical sheet of the present invention has a plurality of falling quadrangular pyramids on one sheet surface, and two sets of opposed bases of the falling quadrangular pyramids extend in two directions in parallel, respectively. In the resin optical sheet, prisms are continuously formed in parallel on the other sheet surface, and the extending directions of the two opposing bottom sides of the falling quadrangular pyramids are 70 ° to 89 ° ( And the cross-sectional shape of the prism is a shape in which a triangle and / or a part of the triangle and a part of the curve are joined, and each extending direction of the base of the falling quadrangular pyramid and the extension of the prism The present invention is an optical sheet characterized in that the present directions intersect each other at 30 ° to 60 ° (narrow angle).

  FIG. 2 is a schematic cross-sectional view showing an example of a planar light source device using the optical sheet of the present invention. On the reflection sheet 9, a plurality of LED light sources 10 are arranged at the closest interval (L), and the optical sheet 11 of the present invention is disposed above the plurality of LED light sources 10 in a matrix shape. 1 is installed at a distance (D) of the reflection sheet surface from the light incident surface of the optical sheet 11 so that 1 faces the LED light source side. The light from the LED light source 10 is partially reflected by the optical sheet 11 of the present invention toward the light source side, and part of the light is diffused and deflected in the opposite direction to the LED light source 10 side to obtain a planar light source device. It plays an important role in reducing or eliminating luminance unevenness. In this example, the prism sheet 12 and the microlens sheet 13 are superimposed on the optical sheet of the present invention in order to improve the luminance in the front direction of the planar light source device and further improve the luminance unevenness.

  FIG. 3 is a schematic sectional view showing another example of the planar light source device using the optical sheet of the present invention. Unlike FIG. 2, the plurality of LED light sources 10 are arranged at the closest interval (L) on the reflective sheet 9, and the optical sheet 11 of the present invention is continuously formed in parallel above the prism. It is installed at a distance (D) between the reflection sheet surface and the light incident surface of the optical sheet 11 so that the surface 5 faces the LED light source 10 side. The light from the LED light source 10 is partially reflected by the optical sheet 11 of the present invention toward the light source side, and part of the light is diffused and deflected in the opposite direction to the LED light source 10 side to obtain a planar light source device. It plays an important role in reducing or eliminating luminance unevenness. In this example, the prism sheet 12 and the microlens sheet 13 are superimposed on the optical sheet of the present invention in order to improve the luminance in the front direction of the planar light source device and further improve the luminance unevenness.

  The optical sheet of the present invention is formed in a matrix so that a plurality of falling quadrangular pyramids are formed on one surface, and two sets of opposing bases of the falling quadrangular pyramids extend in two directions in parallel. It is essential that the two extending directions intersect at 60 ° to 89 ° (narrow angle). This makes it possible to expand the reflection and refraction range of the four sides of the falling quadrangular pyramid, which plays an important role as a lens, as compared with the case where the two extending directions intersect at 90 °, and the direction from the LED light source. High-efficiency light can be efficiently diffused. On the other hand, when the crossing angle in the extending direction is less than 60 °, a luminance difference in the vertical and horizontal directions of the surface light source tends to occur. Although it depends on the arrangement pattern of the LED light source arranged on the reflection sheet, from the viewpoint of adjusting the optical path of incident light and outgoing light by the four side surfaces of the falling quadrangular pyramid corresponding to the arrangement pattern of the LED light source, For brightness leveling, the angle is more preferably 70 ° to 88 ° (narrow angle), and further preferably 80 ° to 87 ° (narrow angle).

  The base of the falling quadrangular pyramid is preferably 10 μm to 1000 μm. If it is less than 10 μm, it is difficult to efficiently form a falling quadrangular pyramid shape on the sheet surface, and if it exceeds 1000 μm, it is difficult to level the luminance as a planar light source. From the viewpoint of easy formation and brightness leveling, 30 μm to 500 μm is more preferable. Further, the inclination angle of the side surface of the falling quadrangular pyramid with respect to the horizontal plane of the optical sheet is preferably 30 ° to 60 °, and if it falls outside this range, the luminance as a surface light source by adjusting the optical path of incident light and outgoing light from the four side surfaces of the falling quadrangular pyramid It becomes difficult to eliminate unevenness.

  On the other surface of the optical sheet of the present invention, a prism having a cross-sectional shape perpendicular to the horizontal plane of the optical sheet and perpendicular to the extending direction is a triangle and / or a part of the triangle and a part of the curve are joined. They are continuously formed in parallel. The base in the cross-sectional shape of the convex part perpendicular to the extending direction of the prism is 10 μm to 1000 μm, and like the falling quadrangular pyramid, it is more preferably 30 μm to 500 μm from the viewpoint of ease of formation and luminance leveling. The internal angle of both sides of the triangle, or the extended line crossing angle (inner angle) of both sides of the triangular portion in the convex cross-sectional shape in which a part of the triangle and a part of the curve are joined is 60 ° to 120 °, more preferably 75 ° to 105 °. It is. If the base and inner angle in the cross-sectional shape of the projection perpendicular to the prism extending direction are out of the above range, it becomes difficult to eliminate luminance unevenness as a surface light source by adjusting the optical path of incident light and outgoing light.

  In the optical sheet of the present invention, a falling quadrangular pyramid is formed on one surface of the matrix so that two sets of opposing bases of the bottom surface extend in two directions intersecting at 60 ° to 89 ° (narrow angle) in parallel. The other surface is perpendicular to the sheet surface and perpendicular to the extending direction, and the prism is continuous with a triangle and / or a part of the triangle and a part of the curve. However, it is essential that each extending direction of the base of the falling quadrangular pyramid and the extending direction of the prism intersect at 30 ° to 60 ° (narrow angle). . Even if this crossing angle (narrow angle) is less than 30 ° or exceeds 60 °, it is difficult to eliminate luminance unevenness in a planar light source having the severe condition that L / D ≧ 2.5. It becomes. In other words, each side of the falling quadrangular pyramid and the slope of the prism formed on the opposing surface are in a three-dimensionally twisted position, so that the effect of reflecting and diffusing light from the light source is increased, and the LED light source arrangement interval However, even if the interval is larger than the conventional interval or the interval between the LED light source and the optical sheet is reduced, the luminance unevenness as a planar light source can be reduced or eliminated. Most preferably, the longer diagonal of the bottom surfaces of the plurality of falling quadrangular pyramids formed on one surface and the extending direction of the prism formed on the other surface are 0 ° to 15 ° (narrow angle). This is the case when crossing.

  The transparent resin constituting the optical sheet of the present invention is not particularly limited as long as it is colorless and 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; poly Arylate resin; polyethersulfone resin, or a mixture of two or more of these can be used. A polycarbonate resin, a styrene resin or a norbornene resin is preferably used. Among these, polycarbonate resin is particularly preferable as a resin for an optical sheet because it is excellent in transparency, heat resistance, and workability and has a good balance.

  In order to adjust the light diffusibility of the optical sheet of the present invention, a light diffusing agent may be dispersed in the transparent resin, and in particular, the optical sheet of the present invention is used as a light diffusing plate disposed closest to the LED light source. In some cases, it is preferable to form a light diffusing layer in which a light diffusing agent is dispersed in a transparent resin in order to improve light diffusibility. As the light diffusing agent, any of organic fine particles, inorganic fine particles, and organic-inorganic hybrid fine particles can be used. For example, (meth) acrylic resin, styrene resin, amino resin, polyester resin, silicone Organic fine particles such as glass-based resins, fluorine-based resins, and copolymers thereof; inorganic fine particles such as glass, smectite, kaolinite, silica, alumina, titanium oxide, and zirconium oxide; organic-inorganic hybrid systems such as acrylic-silica Examples thereof include fine particles. Of these materials, (meth) acrylic resins, silicone resins, and silica are particularly suitable.

  The average particle size of the light diffusing agent is preferably 0.3 μm to 15 μm, and even if it is smaller or larger than this, the light diffusing effect is greatly reduced, which is not preferable, and more preferably 0.5 μm to 10 μm. The optimal amount of light diffusing agent is the light distribution characteristics and arrangement interval of the LED light source on the reflective sheet, the distance between the light incident surface of the optical sheet and the reflective sheet, and the refractive index difference between the transparent resin constituting the optical sheet and the light diffusing agent. Although it varies depending on the particle size of the light diffusing agent, it is preferably dispersed in an amount of 0.01 to 20 parts by mass with respect to 100 parts by mass of the transparent resin. If it is less than 0.01 part by mass, the light diffusion effect by the diffusing agent is weak, and if it exceeds 20 parts by mass, the luminance is greatly lowered, which is not preferable.

The light diffusing layer may extend over the entire thickness of the optical sheet, or may form a layer structure with the transparent layer. However, in order to exhibit the function as a light diffusing plate, it is preferable to form so as to occupy a thickness of 50% or more of the thickness of the optical sheet, although it depends on the type and particle diameter of the diffusing agent used.
The light diffusing layer may be installed in the middle of the thickness direction of the optical sheet, and is formed to have a layer thickness that occupies 50% or more of the thickness of the sheet from any surface of the optical sheet. May be.

  As a method for producing the optical sheet of the present invention, a resin mixture obtained by uniformly blending the above-mentioned transparent resin with a heat stabilizer or the like, or a resin mixture obtained by uniformly blending the above-described transparent resin with a light diffusing agent and further a heat stabilizer, etc. Extrusion molding and injection molding using a mold in which a reverse shape pattern of a desired inverted quadrangular pyramid pattern is engraved on a substantially entire surface and a mold in which a reverse shape pattern of a desired prism shape pattern is engraved It can be obtained by press molding or the like. Among them, the method by extrusion molding is particularly preferable from the viewpoints of easy multilayering and high production efficiency such as the formation of a light diffusion layer, a surface functional layer such as an antistatic performance and a light absorption layer having a specific wavelength, and the like. .

  The shape and size of the optical sheet of the present invention may be cut according to the shape and size of the planar light source device to be used, or may be molded using a mold according to the final size, and the thickness depends on the size and use of the surface light source device to be used. Depending on the installation position of the optical sheet, when used as a light diffusing plate, it is necessary to suppress deformation due to thermal influence from the LED light source and to play a role as a support for other optical sheets. 5 mm to 4 mm is preferable. Moreover, when using as an optical sheet piled up on a light diffusing plate, 0.2-1.5 mm is preferable from a viewpoint of thickness reduction of a planar light source device.

  The planar light source device of the present invention requires a plurality of LED light sources installed on a reflection sheet and the optical sheet of the present invention, but converts light from the LED light source into a planar shape by the optical sheet of the present invention. The diffused light can be further reflected or refracted to provide an optical sheet for increasing the luminance uniformity, or an optical sheet for condensing light in the front direction of the planar light source.

  Examples of the optical sheet for further adjusting the brightness uniformity and condensing light in the front direction of the planar light source include existing microlens sheets, prism sheets, lenticular sheets, diffusion sheets, and reflective polarizing sheets. It is done. Furthermore, a plurality of the optical sheets of the present invention can be used in an overlapping manner. In this case, it is preferable to use an optical sheet having a light diffusion layer on the LED light source side and to superimpose the optical sheet of the present invention having no light diffusion layer on the opposite side of the LED light source. By forming this optical sheet configuration, it is possible to further increase the luminance uniformity as a planar light source and the light condensing property in the front direction of the planar light source.

  In the planar light source device of the present invention, the surface on which the plurality of falling quadrangular pyramids are formed may be arranged so as to face the LED light source side, and the cross-sectional shape perpendicular to the sheet horizontal plane and perpendicular to the prism extending direction is used. The LED light source on the reflective sheet may be installed such that a surface in which prisms having a shape in which a triangle and / or a part of a triangle and a part of a curve are joined in parallel is directed to the LED light source side. The optimal orientation can be selected according to the arrangement pattern, the distance between the light incident surface of the optical sheet and the reflection sheet, and the light distribution characteristics of the LED light source.

  The LED light source used in the planar light source device of the present invention is preferably a Lambertian type whose emission intensity peak is the normal direction of the LED light source installation surface or a side emission type white LED whose direction is inclined from the normal line. However, 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 of the reduction in luminance unevenness of the planar light source device and ease of elimination.

  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.

  There is no restriction | limiting in particular as an LED light source arrangement method, The parallel arrangement | sequence of a linear arrangement | sequence set, a grid | lattice form, a zigzag arrangement, etc. are used.

  The reflection sheet used in the planar light source device of the present invention is a white sheet, and is made of a metal plate having a reflection function, a film, a metal foil, a film on which aluminum or the like is vapor-deposited, emitted light from the LED light source, LED light source The reflected light from the optical sheet installed above is returned to the light exiting direction of the optical sheet again, and also plays a role in leveling the incident angle to the optical sheet. It plays an important role.

  In a direct type planar light source device using an LED light source, the level at which luminance unevenness can be substantially eliminated is closest to a plurality of LED light sources installed on a reflection sheet as shown in FIGS. When expressed by L / D which is the ratio of the distance L between the light reflecting surface of the reflecting sheet and the distance D between the light receiving surface from the LED light source of the optical sheet closest to the LED light source side of the optical sheet configuration, the present invention By using this optical sheet configuration, it was possible to realize a planar light source device with L / D ≧ 2.5, which was difficult with the conventional optical sheet configuration.

  Next, the planar light source device according to the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

<Example 1>
100 parts by weight of polycarbonate (“Iupilon (registered trademark) E-2000”: manufactured by Mitsubishi Engineering Plastics), 0.15 weight of silicone fine particles (“Tospearl (registered trademark) 120”: manufactured by Momentive Performance) as a light diffusing agent Part, 0.1 parts by weight of a phosphorus-based antioxidant (“Irgaphos (registered trademark) 168”: manufactured by BASF) as a heat stabilizer is blended, and the following three rolls and a set of winding rolls are provided. The optical sheet (1) of the present invention was produced by setting the peripheral speed ratio of the third roll and the winding roll to 100/105 using an extrusion molding machine (FIG. 4).
First roll: mirror roll,
Second roll: Prism-shaped shaping roll having a V-shaped groove continuous substantially parallel to the roll rotation direction,
Third roll: An inverted quadrangular pyramid shaped forming roll in which a quadrangular pyramid is formed on the entire surface so that the extending direction of two pairs of opposite sides on the bottom side intersects the rotation direction of the roll at ± 44 °.
In the obtained optical sheet (1), two sets of opposite crossing angles (narrow angles) of the bottom surface are 86 ° on one surface, and a falling quadrangular pyramid having a rhombus bottom surface with a side of 150 μm is in a matrix form. An optical element having a thickness of 1.5 mm, in which a prism having an isosceles triangular cross-sectional shape with a height of 25 μm, a pitch of 50 μm, and an apex angle of 90 ° is formed in parallel on the other surface It was a sheet. The extending direction of the prism and the major axis direction of the rhombus forming the bottom surface of the falling quadrangular pyramid were substantially parallel (crossing angle (narrow angle) 0 to 15 °).

<Example 2>
Example 100 parts by weight of polycarbonate (“Iupilon E-2000”: manufactured by Mitsubishi Engineering Plastics) and 0.1 part by weight of a phosphorus-based antioxidant (“Irgaphos 168”: manufactured by BASF) as a heat stabilizer An optical sheet (2) was obtained by setting the peripheral speed ratio of the third roll and the winding roll to 100/104 using the same roll configuration and extruder as in No. 1.
The obtained optical sheet (2) has a four-sided roll having a rhombus bottom surface having a crossing angle (narrow angle) in the extending direction of two sets of opposing bases of 84 ° on one surface and a side of 150 μm. A pyramid is formed in a matrix shape, and a prism having an isosceles triangular cross-section with a height of 25 μm, a pitch of 49 μm, and an apex angle of 89 ° is formed in parallel on the other surface. The optical sheet was 8 mm. The extending direction of the prism and the major axis direction of the rhombus forming the bottom surface of the falling quadrangular pyramid were substantially parallel (crossing angle (narrow angle) 0 to 15 °).

<Example 3>
100 parts by weight of polycarbonate (“Iupilon E-2000”: manufactured by Mitsubishi Engineering Plastics), 0.15 parts by weight of silicone fine particles (“Tospearl 120”: manufactured by Momentive Performance) as a light diffusing agent, and phosphorus as a thermal stabilizer A heat stabilizer is added to 100 parts by mass of a resin composition (A) containing 0.1 part by mass of an antioxidant (“Irgaphos 168”: manufactured by BASF) and polycarbonate (“Iupilon E2000FN”: manufactured by Mitsubishi Engineering Plastics). As a resin composition (B) containing 0.1 part by mass of a phosphorus-based antioxidant (“Irgafos 168” manufactured by BASF), the layer thickness of the resin composition (A) / the layer of the resin composition (B) The same roll as in Example 1 so that the thickness ratio is 90/10 and the light diffusion layer is formed from the prism shaping surface. With Chengdu extruder, the peripheral speed ratio of the third roll and the winding roll was set at 100/106, to obtain an optical sheet (3) by coextrusion.
The obtained optical sheet (3) has a falling quadrangular pyramid which is a rhombus whose crossing angle (narrow angle) in the extending direction of two sets of opposing bases is 85 ° on one side and whose side is 150 μm. It is shaped like a matrix, and on the other side, prisms having an isosceles triangle cross section with a height of 25 μm, a pitch of 50 μm, and an apex angle of 90 ° are shaped in parallel. The diffusion layer was an optical sheet having a thickness of 1.5 mm with 1.35 mm. The extending direction of the prism and the major axis direction of the rhombus forming the bottom surface of the falling quadrangular pyramid were substantially parallel (crossing angle (narrow angle) 0 to 15 °).

<Comparative Example 1>
100 parts by mass of polycarbonate ("Iupilon H-3000": manufactured by Mitsubishi Engineering Plastics), 0.15 parts by weight of silicone fine particles ("Tospearl 120": manufactured by Momentive Performance) as a light diffusing agent, and phosphorus as a thermal stabilizer Antioxidant ("Irgafos 168": manufactured by BASF) 0.1 parts by mass is blended, and the falling quadrangular pyramid mold and the prism-molding mold are connected to the extending directions of the two sets of the falling quadrangular pyramids. The prisms were installed so that the extending directions of the prisms intersected at a narrow angle of 45 °, and an optical sheet (4) was obtained by injection molding.
The obtained optical sheet (4) is a falling quadrangular pyramid having a square bottom surface with a crossing angle (narrow angle) in the extending direction of two sets of opposed bases of 90 ° on one surface and a side of 150 μm. Is an optical sheet in which prisms having an isosceles triangular cross-section with a height of 25 μm, a pitch of 50 μm, and an apex angle of 90 ° are molded in parallel on the other surface. . The extending direction of the prism and the extending direction of the two bases of the falling quadrangular pyramid were both optical sheets that intersected at 45 ° (narrow angle).

<Comparative example 2>
100 parts by mass of polycarbonate ("Iupilon H-3000": manufactured by Mitsubishi Engineering Plastics), 0.15 parts by weight of silicone fine particles ("Tospearl 120": manufactured by Momentive Performance) as a light diffusing agent, and phosphorus as a thermal stabilizer Antioxidant ("Irgafos 168": manufactured by BASF) 0.1 parts by mass is blended, and the falling quadrangular pyramid mold and the prism-molding mold are connected to the extending directions of the two sets of the falling quadrangular pyramids. The prisms were installed in parallel directions, and an optical sheet (5) was obtained by injection molding.
The obtained optical sheet (5) has a falling quadrangular pyramid having a square bottom surface with a crossing angle (narrow angle) in the extending direction of two sets of opposite bases of 90 ° on one surface and a side of 150 μm. Is an optical sheet in which prisms having an isosceles triangular cross section with a height of 25 μm, a pitch of 50 μm, and an apex angle of 90 ° are molded in parallel on the other surface. In addition, the extending direction of the prism and the extending direction of the two bases of the falling quadrangular pyramids were optical sheets that intersected at 0 ° and 90 ° (narrow angle).

<Examples 4 to 9 and Comparative Examples 3 to 6>
As shown in FIG. 5, nine white LEDs with a lens having an emission intensity peak at 70 ° from the normal of the installation surface are arranged in a grid pattern at intervals of 70 mm on a white reflective sheet of 210 mm × 210 mm, The light diffusing plate was installed so that the distance between the reflecting sheet and the light incident surface of the light diffusing plate was 18.5 mm, and each optical sheet was superimposed on the light emitting surface of the light diffusing plate as shown in Table 1. .

  Regarding the brightness unevenness, the light and darkness generated on the light exit surface of the uppermost optical sheet in each sheet configuration was visually evaluated, and these results are shown in Table 1.

  In addition, BEFIII manufactured by Sumitomo 3M was used for the prism sheet, DBEF manufactured by Sumitomo 3M was used for the reflective polarizing film, and PTD838 manufactured by Shinfa Intertech was used for the microlens sheet.

<Evaluation of uneven brightness>
Luminance unevenness evaluation was determined by visual observation from the normal direction of the optical sheet placed on the LED and ± 45 ° direction with respect to the normal direction, and was divided into the following five stages: 1: Bright and dark with clear boundary lines The pattern can be confirmed.
2: A clear boundary between light and dark areas is not recognized, but a light and dark pattern is clearly recognized.
3: A light and dark pattern is recognized although it is thin.
4: The light / dark pattern is almost eliminated, but the overall brightness uniformity level is not reached.
5: The presence of a bright / dark region could not be confirmed, and a uniform luminance level was obtained as a whole.

  The optical sheet and the planar light source device of the present invention are suitable for reducing the thickness and cost of an LED light source direct type liquid crystal display device.

1: Falling quadrangular pyramid shaping surface 2: Falling quadrangular pyramid ridge 3: Falling quadrangular pyramid ridge 4: Falling quadrangular pyramid valley bottom 5: Prism shaping surface 6: Prism ridge 7: Prism ridge 8: Prism valley bottom 9: Reflective sheet
10: LED light source 11: optical sheet of the present invention
12: Prism sheet
13: Microlens sheet 14: Extruder 15: First roll 16: Second roll 17: Third roll 18: Winding roll
D: Distance from the reflecting sheet surface to the light incident surface of the optical sheet closest to the LED light source side L: Shortest distance between LED arrangement intervals

Claims (6)

A plurality of falling quadrangular pyramids on one sheet surface are formed in a matrix so that two opposing bases of the falling quadrangular pyramids extend in two directions in parallel,
A resin optical sheet in which prisms are continuously formed in parallel on the other sheet surface,
The extending directions of the two opposing bases of the falling quadrangular pyramid intersect at 60 ° to 89 ° (narrow angle), and the cross-sectional shape of the prism is a triangle and / or a part of a triangle and a part of a curve. The optical sheet is characterized in that each extending direction of the base of the falling quadrangular pyramid and the extending direction of the prism intersect each other at 30 ° to 60 ° (narrow angle). .   2. The optical sheet according to claim 1, wherein the diagonal line of the bottom surface of the falling quadrangular pyramid intersects the extending direction of the prism at 0 ° to 15 ° (narrow angle). The base of the falling quadrangular pyramid is 10 μm to 1000 μm, and
3. The optical sheet according to claim 1, wherein a base in a cross-sectional shape perpendicular to the extending direction of the prism is 10 μm to 1000 μm. The inclination angle of the side surface of the falling quadrangular pyramid with respect to the horizontal plane of the optical sheet is 30 ° to 60 °, and
The internal angle of both sides of the triangle in the convex cross-sectional shape perpendicular to the extending direction of the prism, or the extended line crossing angle (internal angle) of both sides of the triangular portion in the convex cross-sectional shape in which a part of the triangle and a part of the curve are joined The optical sheet according to any one of claims 1 to 3, wherein is 60 ° to 120 °.   A resin composition in which a light diffusing agent is blended with a transparent resin is used for the layer thickness that occupies a thickness of 50% or more of the entire thickness of the optical sheet including the falling quadrangular pyramids and prism portions formed on both sides. The optical sheet according to any one of claims 1 to 4.   A planar light source device comprising: a reflective sheet; a plurality of LED (light emitting diode) light sources disposed on the reflective sheet; and the optical sheet according to claim 1.