JP2013225058A - Optical plate and direct point light source backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical plate which allows for realizing superior brightness uniformity, or specifically eliminating the darkness right above LED light sources, and reducing thickness and the number of point light sources of direct point light source backlight devices which use point light sources having high light emission intensity in the wide-angle region, and to provide a direct point light source backlight device equipped with the same.SOLUTION: An optical plate has a periodic structure on one surface (surface A) and satisfies a conditional expressions (1) and (2) expressed as: 54%≤Tt_A≤-Tt_B+124%...(1), 48%≤Tt_B≤54%...(2), where Tt_A represents total light transmittance of the optical plate, measured with a JIS K7105 compliant method, when light enters from the surface (surface A) having the periodic structure, and Tt_B represents total light transmittance of the optical plate, measured with a JIS K7105 compliant method, when light enters from a surface (surface B) opposite the surface having the periodic structure.

Description

  The present invention relates to an optical plate particularly suitable for combination with a backlight having a point light source disposed thereon, and a direct type point light source backlight device including the same.

Generally, there are two types of backlights for liquid crystal displays, called edge light type backlights and direct type backlights, but for large display devices, it is a direct type that can realize high luminance at low cost. Many backlights are used.
Conventionally, a direct type backlight is generally designed based on a linear light source such as a cold cathode tube, and a method of emitting light by using a diffusion plate or an optical film has been used.
However, in recent years, from the viewpoints of environmental problems, light source life, power saving, and image quality improvement, the use of backlights as LED light sources has become common instead of cold cathode tubes.
However, since the cold cathode tube is a linear light source, the LED is a point light source, so there is a problem that luminance unevenness becomes large, and a technology for converting a point light source into a surface light source is required for diffusion plates and optical films. It has been.
Furthermore, liquid crystal displays are strongly demanded to be thin and low in cost, and as backlights, technologies for reducing light sources, reducing optical films, and diffusing light at a short distance from the light source to the diffusion plate are required. ing.

  As a technique for converting an LED point light source into a surface light source, a technique has been proposed in which a substantially convex triangular pyramid shape having a correlation between a specific slope angle and a refractive index is formed on the light exit surface side of a light diffusion plate (for example, , See Patent Document 1.)

International Publication No. 2011/030594 Pamphlet

  In the recent backlight market, from the viewpoint of cost reduction by reducing the number of LEDs, the LED point light source has a lens cap with a lens cap, etc., and the light with a strong directivity directly above the LED is widened to the wide angle side. Even if the backlight unit is thin, it is possible to make it a surface light source with excellent luminance uniformity for LEDs that have a significant shift and have a strong light output intensity on the wide-angle side, such as LEDs with lens caps. There is a need for optical plates.

  However, in Patent Document 1, when the thickness of the backlight is reduced in a direct type point light source backlight using a point light source having a strong light output intensity on the wide angle side, uneven brightness (particularly darkness directly above the LED light source) is noticeable. There was a problem.

  Accordingly, an object of the present invention is to realize a reduction in thickness and luminance uniformity in a direct type point light source backlight device using a point light source having a strong light output intensity on the wide angle side.

As a result of intensive research and experiments, the inventors of the present application have found that an optical plate having a periodic structure on one surface (A surface) transmits all light through the optical plate when light enters from the surface having the periodic structure (A surface). The above-mentioned problem can be solved by satisfying a specific relationship between the light transmittance and the total light transmittance of the optical plate when entering from the surface opposite to the surface having the periodic structure (surface B). The headline and the present invention were completed.
That is, the present invention is as follows.

An optical plate having a periodic structure on one side (A surface), which satisfies the following formulas (1) and (2).
54% ≦ Tt_A ≦ −Tt_B + 124% (1)
48% ≦ Tt_B ≦ 54% (2)
In the formula, Tt_A is measured by a method according to JIS K7105, the total light transmittance of the optical plate when entering from the surface having the periodic structure (A surface), and Tt_B is a method according to JIS K7105. It is the total light transmittance of the optical plate when light is incident from the surface (B surface) opposite to the surface having the periodic structure.

  According to the present invention, in a direct type point light source backlight device using a point light source having a strong light output intensity on the wide angle side, it is possible to reduce the thickness of the device and achieve luminance uniformity.

Perspective view of an example of a convex triangular pyramid shape formed on the surface of an optical plate Perspective view of an example of a convex triangular pyramid shape with a curved vertex on the surface of the optical plate Perspective view of an example of a convex triangular frustum shape formed on the surface of an optical plate Front view of a convex triangular pyramid shaped on the surface of the optical plate and its cross-sectional view 5A is a top view of a convex portion for explaining the definition of g, and FIG. 5B is a partial sectional view of the convex portion for explaining the definition of g. The figure which shows the internal angle figure of the bottom triangle of the convex triangular pyramid shape shaped on the optical board surface Layer structure of optical plate (same layer, continuous layer, separate layer) The total light transmittance Tt_A of the optical plate when entering from the surface having the periodic structure defined in claim 1 of the present invention and the total light transmission of the optical plate when entering from the surface opposite to the surface having the periodic structure. Correlation diagram of rate Tt_B The figure which shows the correlation with Tt_A, Tt_B, a refractive index difference, and a diffusing agent density | concentration. Vertical sectional view of an example of the point light source backlight device of the present embodiment Light emission distribution diagram of an example of an LED light source having a light emission peak on the wide angle side Diagram showing half-value angle The figure (plan view) which shows an example of LED arrangement (grid arrangement) of a backlight The figure (plan view) which shows an example of LED arrangement (staggered arrangement) of a backlight Front view on the light exit surface side of an example of the optical plate of the present embodiment (convex triangular pyramid shape) Perspective view of an example of a convex triangular pyramid shape having a curved vertex and ridgeline formed on the surface of the optical plate

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail.
In addition, this invention is not limited to the following description, It can implement by changing variously within the range of the summary.

The optical plate of the present embodiment is an optical plate having a periodic structure on one surface (A surface), and satisfies the following formulas (1) and (2).
54% ≦ Tt_A ≦ −Tt_B + 124% (1)
48% ≦ Tt_B ≦ 54% (2)

  Tt_A is the total light transmittance of the optical plate when entering from the surface (A surface) having a periodic structure, measured by a method according to JIS K7105. Tt_B is the total light transmittance of the optical plate when light is incident from the surface (B surface) opposite to the surface having the periodic structure, which is also measured by a method in accordance with JIS K7105. Note that light incident from a surface having a periodic structure (A surface) is not easily affected by the periodic structure of the A surface, so Tt_A is a numerical value mainly reflecting the material of the optical plate. On the other hand, the light incident from the surface opposite to the surface having the periodic structure (B surface) is influenced by the surface structure of the A surface at the time of light emission, so Tt_B mainly reflects the surface structure of the A surface. It becomes a numerical value.

  In addition, although there is no designation | designated in particular about a periodic structure, it is preferable from a viewpoint of the cancellation | release of the darkness right above a LED light source, and the reduction | decrease in the thickness of a backlight apparatus that it is a convex substantially triangular pyramid shape whose bottom is a triangle.

In the convex triangular pyramid shape of the optical plate of this embodiment, the lower limit value of the angle (tilt angle) formed by the side surface in contact with the triangular bottom surface is preferably 47 ° or more, more preferably 49 ° or more, and 55 When the angle is 5 ° or more, the point light source backlight using the optical plate significantly improves the perspective luminance uniformity in addition to the luminance, color unevenness characteristics, and front luminance uniformity.
The upper limit is preferably 65 ° or less, and more preferably 64 ° or less.

  The inclination angle can be determined by observing the cross-sectional shape of the optical plate surface using a laser microscope or SEM (electron microscope).

The substantially triangular pyramid shape which is the shape of the convex portion of the optical plate of the present embodiment refers to a solid whose bottom surface is a triangle and whose top is a triangle whose point or area is smaller than the bottom, as shown in FIG. Including so-called triangular frustum.
The side surface of the convex portion of the optical plate may be a flat surface or a curved surface. When the top is a point, the apex may be pointed as shown in FIG. 1 or curved as shown in FIG. .
Further, the ridgeline of the triangular pyramid may be pointed or curved.
Furthermore, in the substantially triangular pyramid shape which is the shape of the convex portion of the optical plate of the present embodiment, the straight line (center axis) connecting the apex (or the center of the top triangle) and the center of the bottom triangle is perpendicular to the plane. It is preferable that it is not a slanting triangular pyramid.

In the optical plate of the present embodiment, the inclination angle is an angle formed by the side surface and the bottom surface of the convex portion as described above.
Even when a part of the side surface of the convex portion includes a curved surface, when the side surface of the convex portion includes a flat surface, an angle formed by the flat surface and the bottom surface is an inclination angle. When a plurality of planes are included on the side surface of the convex portion, the angle formed by the plane having the largest area and the bottom surface is the inclination angle.
When the side surfaces of the convex portions are all curved surfaces, the inclination angle is the largest angle among the angles formed by the tangential plane of the side surfaces and the bottom surface.
Further, when the substantially triangular pyramid shape is an oblique triangular pyramid, the inclination angle is the largest angle among the angles formed by the three side surfaces and the bottom surface of the convex portion.

  It is preferable that the optical plate of this embodiment is formed by periodically forming convex portions of the same shape having a substantially triangular pyramid shape on the surface thereof.

Further, from the viewpoint of color unevenness characteristics, luminance, and luminance uniformity, it is preferable that the shape and arrangement of the convex portions of the optical plate of the present embodiment satisfy the following formula (4).
0 ≦ g / (b + c + d) ≦ 0.30 (4)

B, c, and d in the formula (4) are triangular cut surface portions that appear when the convex portion is cut along a plane that passes through the following three points: H point, I point, and J point,
b shows the length of the line segment which projected on the horizontal plane the linear range B of the angle which the side surface which touches the bottom face of a triangular pyramid convex part makes.
c shows the length of the line segment which projected the part C which exists in the top side from the linear range B on the horizontal surface.
d shows the length of the line segment which projected the part D which exists in the skirt part side from the linear range B on the horizontal surface.
Point H: convex vertex (if the convex top is a plane, the center of gravity of the triangular top plane)
Point I: A point projected vertically from the H point onto the bottom triangle.
Point J: Intersection when a perpendicular line is drawn from point I to the side that is closest to point I among the sides that make up the bottom triangle.
In addition, in FIG. 4, although the straight line segment is illustrated as the part B, the part B may be a curve within an angle range that satisfies the inclination angle.

In the above formula (4), g will be described. An explanatory diagram of g is shown in FIG.
A straight line having an angle formed by the side surface and the bottom surface of the triangular cut surface that appears when the convex portion is cut along a plane passing through the following three points H ′, I ′, and J ′. The length of the line segment which projected the top side rather than the part on the horizontal surface is shown.
H ′ point: the midpoint of the line segment connecting the H point and the vertex of the triangle on the bottom surface.
I ′ point: A point projected onto the bottom triangle perpendicularly from the H ′ point.
Point J ′: Intersection when a perpendicular line is drawn from the point I ′ to the side that is closest to the point I ′ among the sides constituting the triangle on the bottom surface.

  From the viewpoint of further luminance enhancement and luminance uniformity, it is more preferable that 0.01 ≦ g / (b + c + d) ≦ 0.20, and further 0.01 ≦ g / (b + c + d) ≦ 0.10. preferable.

Furthermore, from the viewpoint of color unevenness characteristics, luminance, and luminance uniformity, it is preferable that the shape and arrangement of the convex portions of the optical plate of the present embodiment satisfy the following formulas (5) and (6).
0 ≦ c / (b + c + d) ≦ 0.20 (5)
0 ≦ d / (b + c + d) ≦ 0.40 (6)
From the viewpoint of further luminance enhancement and luminance uniformity, it is more preferable that 0.01 ≦ c / (b + c + d) ≦ 0.13, and further 0.01 ≦ c / (b + c + d) ≦ 0.06. preferable.

  Note that b, c, d, and g described above can be obtained by observing the cross-sectional shape of the optical plate surface using a laser microscope or SEM (electron microscope).

Further, in the triangular pyramid shape of the convex portion of the optical plate, the above b, c, d is the sum b + c + d, and the lower limit is preferably 5 μm or more from the viewpoint of luminance uniformity, moire and manufacturing, and is 10 μm or more. More preferably, it is more preferably 15 μm or more.
The upper limit value is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 120 μm or less.
Further, the height of the triangular pyramid shape of the convex portion of the optical plate (the distance from the bottom surface to the uppermost portion) is preferably 10 μm or more, and preferably 400 μm or less.

  When used in combination with the optical plate and the light source of the present embodiment, the luminance, color, and color are obtained by arranging a substantially triangular pyramidal convex portion on the light exit surface (A surface) side of the two surfaces of the optical plate. The backlight device is particularly excellent in unevenness characteristics and luminance uniformity (front and oblique view).

  Hereinafter, in the present specification, when used in combination with a light source, the surface closer to the light source (that is, the side facing the light source) is the light incident surface (B surface), and the surface farther from the light source. (An opposite side of the light source) is defined as a light exit surface (A surface).

A plurality of convex portions having a substantially triangular pyramid shape are provided on the surface of the optical plate.
The shape of the plurality of convex portions may be the same or different.
Moreover, there is no limitation also about the aspect of arrangement | positioning of a some convex part.
For example, it is preferable from the viewpoint of luminance uniformity and productivity that a plurality of convex portions are arranged adjacent to each other so that opposite sides of adjacent convex portion bottom face triangles are parallel to each other.
Moreover, there is no limitation also in the triangular shape of the bottom face of a convex part.
For example, as shown in FIG. 6, if the interior angles of the triangles on the bottom surface of the convex portion are α, β, and γ, respectively, | α−β |, | β−γ |, | γ−α | From the viewpoint of luminance uniformity, the angle is preferably 10 ° or less, more preferably 10 ° or less, and further preferably 5 ° or less.
Particularly preferable shapes of the triangles on the bottom surface of the convex portion are an isosceles triangle and an equilateral triangle.
Furthermore, the substantially triangular pyramid-shaped convex portion provided on the surface of the optical plate is preferably formed in a region of 70 area% or more of the horizontal plane of the optical plate from the viewpoint of luminance uniformity, and is formed in 80 area% or more. More preferably, it is formed to 90% by area or more, and more preferably 95% by area or more.

The optical plate of the present embodiment preferably includes at least (a) a lens layer and (b) a diffusion layer from the viewpoints of luminance and luminance uniformity of front and perspective.
(A) A lens layer is a layer in which a convex triangular pyramid shape is formed.
(B) A diffusion layer is a layer that diffuses light containing a transparent resin and a diffusing agent.
Both the (a) layer and the (b) layer may be formed from a single layer, or each may be formed from a plurality of layers.
As shown in FIG. 7, the (a) layer and the (b) layer may be the same layer, a continuous layer, or a separate layer.
The same layer means a layer structure in which a substantially triangular pyramid is formed on the surface of (b) the diffusion layer, that is, (a) layer is incorporated in (b) layer.
The continuous layer refers to a layer structure in which (a) the lens layer and (b) the diffusion layer are in close contact and integrated.
The separate layer refers to a configuration in which (a) a lens layer and (b) a diffusion layer exist as separate sheets, and two sheets are physically overlapped.
About a separate layer, you may arrange | position with the combination of (a) layer, (b) layer, or (b) layer, (a) layer from the side close | similar to a light source, and also (a) layer and (b) Another sheet may be placed between the layers.

Although there is no particular limitation on the material constituting the convex portion ((a) lens layer in the case of the configuration shown in FIG. 7) of the optical plate of the present embodiment, the luminance, color unevenness characteristics, front luminance uniformity, and From the viewpoint of uniformity of perspective luminance, a resin having high light transmittance is preferably used.
For example, polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and copolymers thereof; polyolefin resins such as polypropylene, polymethylpentene, and alicyclic polyolefins; polystyrene, styrene Styrene resins such as acrylonitrile copolymer, styrene-methacrylic acid copolymer, methyl methacrylate-styrene copolymer, alphamethylstyrene copolymer; acrylic resins such as polymethyl methacrylate and polyethyl acrylate; methacrylate ester resin And polycarbonate resin.

Although there are no particular limitations on the material constituting the convex portion ((a) lens layer in the case of the configuration shown in FIG. 7) of the optical plate of this embodiment, the luminance, color unevenness characteristics, front luminance uniformity, and perspective are not limited. From the viewpoint of luminance uniformity, the refractive index is preferably 1.43 or more, more preferably 1.49 or more, further preferably 1.53 or more, and particularly preferably 1.55 or more.
The upper limit of the refractive index is not particularly limited, but the refractive index is preferably 1.71 or less, more preferably 1.65 or less from the viewpoint of luminance, color unevenness characteristics, front luminance uniformity, and perspective luminance uniformity. preferable.

The refractive index can be obtained by cutting and separating the part forming the convex part, then producing a film with a smooth surface by hot pressing or the like, and using an Abbe refractometer in accordance with JIS K7142. When the convex portion cannot be smoothed, the cut portion can be crushed after the convex portion is cut, and the Becke method can be used.
In addition, the refractive index of the material forming the convex portion of the optical plate is determined by the transparent material (for example, transparent resin) of the material forming the sample, and even if a light diffusing agent is added, it is refracted by it. The rate itself does not change.
Therefore, in the case where it is difficult to measure the refractive index by the above method because the convex portion contains a light diffusing agent or the like and has diffusibility, the transparent material among the materials forming the convex portion (for example, Only the transparent resin raw material) can be formed into a film, and the refractive index of the film can be similarly determined by using an Abbe refractometer.

When the optical plate of the present embodiment has the configuration of FIG. 7, (b) the material constituting the diffusion layer is not particularly limited, and examples thereof include a resin composition containing a (transparent) resin and a diffusing agent. .
The material constituting the (b) diffusion layer of the optical plate is preferably a resin composition in which a light diffusing agent component having a refractive index different from the refractive index of the resin is dispersed in an optimal amount with an optimal particle size in a transparent resin. .
Specific examples of the resin include polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and copolymers thereof; polyolefin resins such as polypropylene, polymethylpentene, and alicyclic polyolefin Styrene resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-methacrylic acid copolymer, methyl methacrylate-styrene copolymer, alpha methyl styrene copolymer; acrylic resins such as polymethyl methacrylate and polyethyl acrylate Methacrylic acid ester resin, polycarbonate resin and the like.

Examples of the light diffusing agent include diamond, zirconium oxide, titanium oxide, zinc sulfide, white lead, zinc white (zinc oxide), aluminum oxide (alumina), acrylic resin crosslinked fine particles, styrene resin crosslinked fine particles, and silicone. -Based resin cross-linked fine particles, MS (methyl methacrylate / styrene copolymer) -based cross-linked fine particles, fluororesin fine particles, glass fine particles, silica fine particles, calcium carbonate, barium sulfate, and the like. However, the higher the difference in refractive index between the main component of the optical plate and the diffusing agent, the better from the standpoint of eliminating darkness directly above the LED and luminance uniformity.
Examples of the material having a high refractive index difference include diamond, zirconium oxide, titanium oxide, zinc sulfide, lead white, zinc white (zinc oxide), etc. Among them, the use of titanium oxide is particularly dark just above the LED. From the viewpoints of elimination of brightness, brightness uniformity, ease of production, and chemical stability.

The average particle diameter of the diffusing agent is preferably 5.5 μm or less from the viewpoints of elimination of darkness immediately above the LED, luminance uniformity, ease of production, and beautiful appearance of the optical plate, and is preferably 1.9 μm or less. More preferred. The average particle size can be determined by a particle size distribution meter.
The lower limit of the average particle diameter of the diffusing agent is not particularly specified, but is preferably 0.12 μm or more from the viewpoint of luminance uniformity. The average particle size can be determined by a particle size distribution meter.
The shape of the diffusing agent is not particularly specified, and examples thereof include a spherical shape, an elliptical shape, an indefinite shape, a needle shape, a plate shape, a hollow shape, a column shape, and a cone shape.

Further, (b) the refractive index difference between the resin constituting the diffusion layer and the light diffusing agent and the concentration of the light diffusing agent have the following ranges from the viewpoint of luminance uniformity, darkness directly above the LED, and easy manufacturing. It is preferable to satisfy.
When the refractive index difference is large such as 0.75 or more, it is preferably 0.010 mass% or more and 0.055 mass% or less, more preferably 0.010 mass% or more and 0.047 mass%. It is preferable that it is below mass%.
The upper limit of the refractive index difference is not particularly limited, but is preferably 1.25 or less.
When the refractive index difference is small such that the refractive index difference is 0.13 or less, it is preferably 1.55 mass% or more and 2.40 mass% or less.
The lower limit of the refractive index difference is not particularly limited, but is preferably 0.01 or more.
The refractive index can be measured by using an Abbe refractometer according to JIS K7142.

The total light transmittance Tt_A and Tt_B of the optical plate having a periodic structure on one side of this embodiment can eliminate the darkness just above the LED by satisfying the following expressions (1) and (2). A correlation diagram of Tt_A and Tt_B is shown in FIG.
54% ≦ Tt_A ≦ −Tt_B + 124% (1)
48% ≦ Tt_B ≦ 54% (2)
More preferably, the expression (2) and the following expression (3) are satisfied from the viewpoint of color unevenness and luminance uniformity.
60% ≦ Tt_A ≦ −7Tt_B / 3 + 188% (3)
In addition, Tt_A and Tt_B in the formula can be measured by conforming to JIS K7105, respectively. Tt_A is the total light transmittance of the optical plate obtained when the light enters from the surface having the periodic structure (A surface), and Tt_B is incident from the surface opposite to the surface having the periodic structure (B surface). It is the total light transmittance of the optical plate obtained at the time.

  Further, Tt_A and Tt_B are adjusted by changing the refractive index difference between the base resin constituting the optical plate and the light diffusing agent contained in the optical plate, and changing the diffusing agent concentration, as shown below. It is possible to control to satisfy the expressions (1), (2), and (3). FIG. 9 shows the refractive index difference between the base resin constituting the optical plate and the light diffusing agent contained in the optical plate, and the correlation between the diffusing agent concentration and Tt_A and Tt_B.

As a method for lowering Tt_A, for example, increasing the concentration of the diffusing agent, increasing the refractive index difference between the base resin of the optical plate and the diffusing agent, increasing the thickness of the optical plate, and the back surface of the optical plate (B Surface) shape is roughened, and the height of the convex triangular pyramid forming the convex triangular pyramid shape which is the optical plate surface periodic structure is increased. On the other hand, as a method of increasing Tt_A, the opposite may be performed, and as another method, the optical plate surface periodic structure other than the convex triangular pyramid shape, for example, a convex or concave quadrangular pyramid is used. And so on.
As a method for reducing Tt_B, the concentration of the diffusing agent is decreased, the difference in refractive index between the base resin and the diffusing agent of the optical plate is decreased, the thickness of the optical plate is decreased, and the back surface (B surface) of the optical plate. Examples thereof include smoothing the shape, and increasing the height of the convex triangular pyramid that forms the convex triangular pyramid shape that is a periodic structure of the optical plate. On the other hand, as a method of increasing Tt_B, the opposite may be performed, and as another method, the optical plate surface periodic structure other than the convex triangular pyramid shape, for example, a convex or concave quadrangular pyramid is used. And so on.

The optical plate of the present embodiment is preferably 0.5 to 3.0 mm, more preferably 0.7 to 2.5 mm from the viewpoint of rigidity and optical characteristics (luminance, luminance uniformity) More preferably, it is 0.7-2.0 mm.
In the case where the optical plate of the present embodiment has the configuration shown in FIG. 7, when the (a) layer and the (b) layer of the optical plate are separate layers, the (a) layer and the (b) layer are provided. The total thickness when superposed is the thickness of the optical plate.

The optical plate of this embodiment can have a laminated structure in which, in addition to the (a) layer and the (b) layer, another layer is laminated as necessary.
The layer structure can be appropriately selected according to the use and purpose.
As an example of the layer structure, if the layer made of other resin composition or compound other than the lens layer (a) layer and the diffusion layer (b) layer is an X layer, a Y layer, and a Z layer, for example, an X layer / ( a) (b) Two-layer configuration of the same layer, X layer / (a) layer / (b) layer, (a) layer / (b) layer / X layer, (a) layer / X layer / (b) 3 layers, X layer / (a) layer / (b) layer / X layer, X layer / (a) layer / (b) layer / Y layer, X layer / (a) layer / Y layer / ( b) 4 layer constitution of layer, X layer / Y layer / (a) / (b) / Y layer, X layer / (a) layer / Y layer / (b) layer / X layer, X layer / ( Examples thereof include a five-layer configuration of a) layer / Y layer / (b) layer / Z layer.
A plurality of layers composed of the same resin composition can be continuously stacked.
Further, although five or more layers may be laminated, it is preferable that the optical plate is composed of five or less layers in view of ease of manufacture.

Various additives may be blended in the optical plate of the present embodiment.
Examples of such additives include organic and inorganic dyes and pigments, matting agents, heat stabilizers, flame retardants, antistatic agents, antifoaming agents, color stabilizers, antioxidants, ultraviolet absorbers, crystals Examples include nucleating agents, brighteners, impurity scavengers, thickeners, surface conditioners and the like.

The optical plate of the present embodiment is a surface opposite to the surface on which the substantially triangular pyramid-shaped convex portions are formed, that is, from the viewpoint of luminance uniformity and rubbing with the indicator pin mounted on the backlight, that is, In a preferred embodiment when used in combination with a light source, it is preferable to provide a concavo-convex shape on the surface that becomes the light incident surface (B surface).
Specifically, the average inclination angle U of the B surface is preferably 1 degree or more and 30 degrees or less from the viewpoint of luminance and luminance uniformity, more preferably 3 degrees or more and 25 degrees or less, and more preferably 5 degrees or more. More preferably, it is 20 degrees or less.
When the average inclination angle U of the B surface is less than 1 degree, for example, if the inclination angle of the convex portion on the light exit surface (A surface) side is 55 degrees, the optical plate exhibits retroreflective properties and emitted light from the point light source. The light may return to the point light source and the brightness of the backlight may decrease. On the other hand, when the average inclination angle exceeds 30 degrees, the luminance uniformity tends to deteriorate.
The average inclination angle U is obtained by observing a cross section of the optical plate with a laser microscope, and continuously obtaining an average inclination angle of 1 μm width (inclination angle with respect to the horizontal plane of the optical plate) with a width of 1000 μm in the longitudinal direction and the short direction of the optical plate, It can be obtained by calculating an average value in the longitudinal direction and an average value in the lateral direction, and further calculating the average.
In the case where the optical plate of this embodiment has the configuration shown in FIG. 7 and the (a) layer and (b) layer are separate layers, both the (a) layer and the (b) layer are incident. It is preferable that the average inclination angle on the surface side be in the range.

The optical plate of the present embodiment can be manufactured by forming the convex portions of the material constituting each layer of the optical plate by a known method using a molding method.
For example, a melt molding method in which a resin composition containing a highly light-transmitting resin is extruded from a die in a molten state and molded using a roll processed into a desired shape; a state in which the resin composition is dissolved in a solvent Solution casting method that uses a roll that is extruded from a die and processed into a desired shape; extrusion lamination method or solid film in which a molten resin is laminated on a solid film obtained by surface shaping by the solution casting method Dry lamination method of laminating layers; Method of hot press molding using a press die processed into a desired shape from a plate extruded from a die in a molten state; and injection using a die processed into a desired shape Examples of the method include molding.
Among these, the melt molding method is the most preferable molding method from the viewpoints of productivity and environmental suitability.

As shown in FIG. 10, the backlight device of this embodiment has a configuration in which a point light source base on which a plurality of point light sources (LEDs) are arranged, a reflection sheet, and an optical plate of this embodiment are arranged in this order.
In the direct type point light source backlight device of the present embodiment, the optical plate is disposed above the point light source, and on the surface (A surface) side opposite to the surface facing the point light source, The convex part of the substantially triangular pyramid shape in which the bottom face mentioned above is a triangle is formed.

In the direct type point light source backlight device of the present embodiment, it is preferable to use a white resin sheet having a diffuse reflectance of 90% or more as the reflective sheet shown in FIG. preferable.
The diffuse reflectance is measured every 10 nm when light having a wavelength of 450 nm to 700 nm is incident on the sheet at an incident angle of 0 degree using a spectrophotometer such as a spectrophotometer UV-2200 manufactured by Shimadzu Corporation. And it can obtain | require by calculating an average reflectance.

In the direct type point light source backlight device of the present embodiment, at least one of the point light sources is a point light source having a light peak angle of ± 26 ° or more and ± 85 ° or less from the viewpoint of luminance and luminance uniformity. preferable. Furthermore, when the light peak angle is ± 45 ° or more and ± 80 ° or less, particularly excellent luminance and luminance uniformity can be achieved.
As the point light source, for example, an LED light source with a lens cap mounted on the SharpLC46L5 whose outgoing distribution is shown in FIG.

In the point light source of the present embodiment, the relative light intensity at 0 ° with respect to the luminance of the light peak angle is preferably 5% or more and 50% or less from the viewpoint of luminance uniformity, and further, the relative light intensity at 0 ° is It is preferably 15% or more and 50% or less.
The light peak angle can be measured with a spectral radiance meter CS-2000 manufactured by Konica Minolta. As a method, the aperture angle is 1 degree, an ND filter (1/10) is added to the camera, the distance between the CS-2000 and the LED is 1000 mm, and the angle of the CS-2000 is in increments of 0 degree to 90 degrees. The light peak distribution can be obtained by measuring the light emission distribution and reading the angle at which the luminance is maximum.
FIG. 12 is a diagram for explaining the light emission angle (hereinafter, half-value angle) at a position where the light emission relative intensity with respect to the luminance of the light peak angle is 50%.
From the viewpoint of luminance uniformity, the half-value angle is preferably ± 5 ° or more and ± 50 ° or less, and more preferably ± 10 ° or more and ± 50 ° or less.

  Conditions other than the light emission distribution are not particularly limited. For example, a type that excites a yellow phosphor by a blue LED, a one-chip type pseudo white LED that excites a green or red phosphor by a blue LED; red / green / Multi-chip type that produces white light by combining blue LEDs, one-chip type pseudo white LED that combines near-ultraviolet LED and red / green / blue phosphor, and combination of red / green / blue laser It is done.

There is no particular limitation on the arrangement method of the plurality of point light sources of the direct type point light source backlight of this embodiment, but more excellent luminance uniformity by arranging the distances between the point light sources as uniformly as possible. Demonstrate sex.
Specifically, an arrangement method (FIG. 13) in which point light sources are arranged in a square lattice or a rectangular lattice at equal intervals in the vertical direction and the horizontal direction in the direct type point light source backlight unit, An arrangement method (FIG. 14) in which the screens are arranged in a staggered pattern (or a triangular lattice pattern) at equal intervals in the vertical and horizontal directions of the screen can be preferably employed.
Here, the lattice refers to the arrangement of vertices constituting a square and a rectangle, and the staggered pattern refers to the arrangement of vertices that constitute a rhombus quadrilateral.

  In the direct type point light source backlight device of the present embodiment, as shown in FIG. 10, the spatial distance H between the uppermost part of the point light source and the optical plate is from the viewpoint of eliminating darkness directly above the LEDs and uniformity of luminance. It is preferable that it is 3 mm or more and 25 mm or less, and a more preferable spatial distance is 5 mm or more and 20 mm or less. Here, the spatial distance H between the top of the point light source and the optical plate is a measurement of the spatial distance (unit: mm) from all the top of the point light source mounted on the backlight to the B surface of the optical plate. It is an average value.

The direct type point light source backlight device of the present embodiment further includes an optical film having a condensing property on the light exit surface (A surface) side of the optical plate of the present embodiment. It is preferable from the viewpoint.
The optical film having the light condensing property is a film having a function of raising the light incident on the film in a direction directly above the film, and when the 550 nm monochromatic light is incident on the sheet at an incident angle of 60 degrees, the variable angle luminous intensity. A film in which the main peak angle of the light emission distribution measured with a meter (for example, GC5000L manufactured by Nippon Denshoku Industries Co., Ltd.) is 50 degrees or less is preferable. More preferably, the film has a main peak angle of 35 degrees to 45 degrees.
For example, a commercially available prism sheet, a diffusion sheet, a lens sheet, etc. are mentioned.
In particular, when the 550 nm monochromatic light is incident on the anti-light source surface (A surface) side of the optical plate at an incident angle of 60 degrees, the main peak angle of the light emission distribution measured by the goniophotometer is 35 degrees to 45 degrees. Arrangement pattern in which two optical films are arranged, or main peak angle of light distribution measured by a goniophotometer when monochromatic light of 550 nm is incident on the A side of the optical plate at an incident angle of 60 degrees An arrangement pattern in which one optical film having an angle of 35 to 45 degrees is arranged and a prism sheet is further arranged thereon is preferably used. As a more preferable arrangement pattern, a method in which two prism sheets each having a prism extending in one direction on the surface on the light exit surface (A surface) side are arranged orthogonally is preferable from the viewpoint of luminance uniformity.
The inclination angle formed by the base and side surfaces of the prism triangle extending in one direction formed on the surface of the prism sheet on the A surface side is more preferably 42 to 48 degrees from the viewpoint of luminance uniformity.
Also, the prism sheet is measured with a goniophotometer when monochromatic light of 550 nm is incident at an incident angle of 30 degrees on the A surface side of the optical plate and perpendicular to the triangular prism extending on the prism sheet surface. When the main peak angle of the emitted light distribution is −3 degrees to 3 degrees, it is effective for excellent luminance uniformity. Furthermore, the main peak angle is more preferably -1 to 1 degree.

[Use]
The optical plate in the present embodiment has a plurality of substantially triangular pyramid-shaped convex portions on the surface thereof (the side that becomes the light exit surface when used in combination with a light source), and the diffusing agent species included in the optical plate By adjusting the density and adjusting the total light transmittance, when used as an optical plate for a direct type point light source backlight having an LED light source having a light emission peak on the wide-angle side, particularly improvement in luminance uniformity, The darkness just above the LED can be eliminated. Therefore, according to the direct type point light source backlight using this, thinning of the backlight which cannot be achieved by the prior art is achieved, and a liquid crystal TV, an illumination device, or a signboard having a direct type point light source backlight device is achieved. It can be suitably used for digital signage.

Hereinafter, although a specific Example and a comparative example are given and demonstrated, this invention is not limited to these.
The main measured values in the examples were measured by the following methods.

(Light exit surface shape of optical plate)
The light exit surface side of the optical plate was observed with a Keyence laser microscope Generation II VK-9700, and the shape of the convex portion was observed.

(Refractive index)
(A) A 0.3 mm-thick sheet was produced using a transparent material (transparent resin) among the materials used for the lens layer, and the refractive index was determined using an Abbe refractometer in accordance with JIS K7142.

(Total light transmittance)
<Total light transmittance Tt_A (%) of optical plate when entering from surface A>
The total light transmittance Tt_A (%) of the optical plate when entering from the surface having the periodic structure (surface A) is measured by a method based on JIS K7105 using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. Asked.
<Total light transmittance Tt_B (%) when light enters from surface B>
The total light transmittance Tt_B (%) when entering from the surface opposite to the surface having the periodic structure (B surface) is compliant with JIS K7105 using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. Obtained by the method.

(Light peak angle)
The light peak angle of the backlight (LED) was measured with a spectroradiometer SR-3 manufactured by Topcon Corporation. Measurement conditions were such that the aperture angle was 1 °, and an ND filter (1/10) was added to the SR-3 camera. The distance between SR-3 and the LED was 1000 mm, the LED angle was swung in 1 degree increments of 0 to 85 degrees, the light emission distribution was measured, and the angle at which the luminance became maximum was taken as the LED peak angle.

(0 degree relative intensity)
The 0 degree relative intensity of the backlight (LED) was defined as the ratio (%) between the 0 degree luminance and the maximum luminance obtained by the same measurement method as that for the above peak angle.

(Half width)
The half-value width (mm) of one LED was made relative to the surface luminance distribution obtained by measuring the luminance with a two-dimensional surface luminance meter CA2000 manufactured by Konica Minolta, and the position at a luminance ratio of 50% was defined as the half-value width. At that time, the measurement range (mm) and the pixel range of the camera were made the same.

(Darkness just above LED)
The darkness directly above the LED is 100-Lc when the luminance ratio (%) directly above the LED is Lc, relative to the surface luminance distribution obtained by measuring with a two-dimensional luminance meter CA2000 manufactured by Konica Minolta. The darkness just above the LED was taken.
<7-1. Half width>
The visual level of the full width at half maximum is described below.
44 mm or more → Level where luminance unevenness cannot be seen at all 40 mm or more and 43 mm or less → Level where luminance unevenness is slightly visible 39 mm or less → Level where luminance unevenness is visible <7-2. Darkness just above LED>
Below, the visual level of the darkness just above LED is described.
4% or less → Level at which the darkness directly above the LED cannot be seen at all 5% → Level at which the darkness directly above the LED can be seen slightly 6% or higher → Level at which the darkness directly above the LED can be seen visually )
The evaluation was determined as follows using the half width and the darkness just above the LED.
◎: Half width of 44 mm or more and darkness of 4% or less just above the LED ○: Half width of 40 mm or more and darkness of 5% or less just above the LED, other than ◎ ×: Half value width of 39 mm or less or darkness just above the ED 6% or more

  Next, the manufacturing method of the press original plate required in order to manufacture the optical plate in an Example and a comparative example is demonstrated.

(Press plate 1)
99.75 parts by mass of a polystyrene resin (PS Japan, Stylon G9504) having a refractive index of 1.59, and 0.25 parts by mass of silicone-based crosslinked particles (Tospearl 120) having a refractive index of 1.43 and an average particle size of 2.0 μm. Were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press original plate 2)
99.70 parts by mass of polystyrene resin (PS Japan Co., Stylon G9504) with a refractive index of 1.59, and 0.30 parts by mass of silicone-based crosslinked particles (Tospearl 120) with a refractive index of 1.43 and an average particle size of 2.0 μm. Were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 3)
99.60 parts by mass of polystyrene resin (PS Japan, Stylon G9504) with a refractive index of 1.59, and 0.40 parts by mass of silicone-based crosslinked particles (Tospearl 120) with a refractive index of 1.43 and an average particle size of 2.0 μm. Were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 4)
99.00 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., Ltd., Stylon G9504) and acrylic crosslinked particles having a refractive index of 1.49 and an average particle size of 2.5 μm (manufactured by Sekisui Plastics Co., Ltd., Tech. 1.00 parts by mass of polymer MBX-2.5) was mixed with a Henschel mixer, melt-kneaded with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C., and pelletized.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press master 5)
98.50 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., Ltd., Stylon G9504) and acrylic crosslinked particles having a refractive index of 1.49 and an average particle size of 2.5 μm (manufactured by Sekisui Plastics Co., Ltd., Tech. Polymer MBX-2.5) 1.50 parts by mass was mixed with a Henschel mixer, melt-kneaded with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C., and pelletized.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 6)
98.14 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., Ltd., Stylon G9504), and acrylic crosslinked particles having a refractive index of 1.49 and an average particle size of 2.5 μm (manufactured by Sekisui Plastics Co., Ltd., Tech. 1.86 parts by mass of polymer MBX-5) was mixed with a Henschel mixer, melt-kneaded with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C., and pelletized.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 7)
99.98 parts by mass of a polystyrene resin having a refractive index of 1.59 (PS950, G9504), 0.02 of titanium oxide having a refractive index of 2.71 and an average particle size of 0.21 μm (RF-740, 0.02) Mass parts were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 8)
99.97 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan, G9504) and 0.03 of titanium oxide having a refractive index of 2.71 and an average particle diameter of 0.21 μm (RF-740, manufactured by Ishihara Sangyo) Mass parts were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 9)
99.95 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., G9504), 0.051 of titanium oxide having a refractive index of 2.71 and an average particle size of 0.21 μm (RF-740, manufactured by Ishihara Sangyo) 0.05 Mass parts were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 10)
99.95 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., Ltd., G9504) and a titanium oxide having a refractive index of 2.71 and an average particle size of 0.25 μm (manufactured by Ishihara Sangyo Co., Ltd., CR60-2) 0.05 Mass parts were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

(Press plate 11)
99.94 parts by mass of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan Co., Ltd., G9504), and titanium oxide having a refractive index of 2.71 and an average particle size of 0.21 μm (manufactured by Ishihara Sangyo Co., Ltd., RF-740) 0.06 Mass parts were mixed with a Henschel mixer, melt kneaded and pelletized with a twin screw extruder (TEM-58 manufactured by Toshiba Machine Co., Ltd.) at a resin temperature of 230 ° C.
The pellets were melt-kneaded again with a TEX-90 single-screw extruder and extruded from a 1000 mm wide T die to produce a 1.5 mm thick sheet.

Next, the LED of the LED point light source backlight used in Examples and Comparative Examples will be described.
(LED)
As the LEDs in Examples and Comparative Examples, LEDs with lens caps mounted on SharpLC46L5 having a light emission peak angle of ± 73 ° and a 0 degree relative intensity of 10% were used.

Next, the optical films used in Examples and Comparative Examples will be described.
(Optical film)
The optical films in Examples and Comparative Examples were those mounted on Sharp LC46L5 and arranged as they were mounted. Specifically, the following Lens cage was placed on the optical plate, the following Prism was placed thereon, and the following DBEF was further placed thereon.
(Lens⊥)
Lens ⊥ is a lens film made of PMMA or PET whose surface shape is a lens. The arrangement direction on the optical plate was arranged so that the lens shape extending in one direction of the lens film and the long side direction of the LED backlight unit were substantially perpendicular.
(Prism)
Prism is a prism film made of PET whose surface shape is a prism. The arrangement direction on the lens rod was arranged such that the prism shape extending in one direction and the long side direction of the LED backlight unit were substantially parallel.
(DBEF)
DBEF is a polarization reflection sheet.

Next, the reflection sheet used in Examples and Comparative Examples will be described.
(Reflective sheet)
The reflective sheet used in the examples and comparative examples was E6SR manufactured by Toray Industries, Inc., and was installed on the surface opposite to the surface on which the optical plate was installed when viewed from the LED.

[Example 1]
The press original plate 6 produced as described above is sandwiched between press dies shaped into a concave triangular pyramid shape, put into a press machine, under the conditions of a press plate temperature of 180 ° C. and a surface pressure of 100 kg / cm ² , Pressed for 30 minutes.
Thereafter, the press mold sandwiching the press original plate 6 was replaced with a water-cooled press machine and cooled for 10 minutes.
After cooling, a 1.5 mm thick optical plate shaped into a predetermined shape was taken out from the press mold.
The obtained optical plate has a mat shape in which the surface on the light incident surface side has a concavo-convex shape with an average inclination angle of 10 degrees, and a convex triangular pyramid with a regular bottom surface on which the surface on the light exit surface side is periodically formed Met.
Further, the inclination angle θ of the triangular pyramid of the convex portion of this optical plate was 57 degrees, and the height between the bottom surface and the top portion of the convex portion was 154 μm. Table 1 shows the results of measuring Tt_A and Tt_B for this optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Example 2]
It was produced by the same method as in Example 1 except that the press original plate produced as described above was changed to the press original plate 7.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

Example 3
It was prepared in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 8.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

Example 4
It was produced by the same method as in Example 1 except that the press original plate produced as described above was changed to the press original plate 9.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

Example 5
It was produced in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 10.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 1]
It was produced in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 1.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 2]
An optical plate was produced in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 2.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 3]
It was prepared in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 3.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 4]
It was produced in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 4.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 5]
It was prepared in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 5.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

[Comparative Example 6]
It was produced in the same manner as in Example 1 except that the press original plate produced as described above was changed to the press original plate 11.
Table 1 shows the result of measuring Tt_A and Tt_B for the obtained optical plate. Further, Table 1 shows the results of measuring the half-value angle and the darkness directly above the LED by mounting this optical plate on the LED backlight.
Further, Table 1 shows the results of measuring the half-value width and the darkness directly above the LED by mounting this optical plate on an LED backlight having a distance (BL thickness) from the optical plate to the reflection sheet of 8 mm.

  This application is based on the pamphlet of international publication 2011/030594, The content is taken in here as a reference.

The optical plate of the present invention can be suitably used in a point light source, in particular, a backlight in which a point light source having a light peak angle of ± 26 degrees to ± 85 degrees and a high light intensity of directly above light is arranged.
Since the point light source backlight provided with the optical plate of the present invention has the effect of reducing the thickness of the backlight while maintaining the luminance uniformity (particularly the elimination of the darkness directly above the LED), for example, the LED light source liquid crystal It is useful for a wide range of applications such as televisions, LED light source signs, and LED light source illumination.

B: Slope portion in the cross section of the convex portion C: A portion on the skirt side from B in the cross section of the convex portion.
D: A portion on the top side from C in the cross section of the convex portion.
α: Inner angle of the triangular base of the convex triangular pyramid shaped on the surface of the optical plate β: Inner angle of the triangular base of convex triangular pyramid shaped on the surface of the optical plate γ: Shaped on the surface of the optical plate Inner angle of bottom triangle of convex triangular pyramid shape

Claims (7)

An optical plate having a periodic structure on one side (A surface), which satisfies the following formulas (1) and (2).
54% ≦ Tt_A ≦ −Tt_B + 124% (1)
48% ≦ Tt_B ≦ 54% (2)
In the formula, Tt_A is measured by a method according to JIS K7105, the total light transmittance of the optical plate when entering from the surface having the periodic structure (A surface), and Tt_B is a method according to JIS K7105. It is the total light transmittance of the optical plate when light is incident from the surface (B surface) opposite to the surface having the periodic structure.   The optical plate according to claim 1, wherein the periodic structure has a convex triangular pyramid shape.   The optical plate according to claim 1, wherein the optical plate contains a diffusing agent.   The difference between the refractive index of the material constituting the optical plate and the refractive index of the diffusing agent is 0.75 or more, and the concentration of the diffusing agent contained in the optical plate is 0.010% by mass or more. And the optical plate of Claim 3 which is 0.055 mass% or less.   The difference between the refractive index of the material constituting the optical plate and the refractive index of the diffusing agent is 0.01 or more and 0.13 or less, and the concentration of the diffusing agent contained in the optical plate is 1 The optical plate according to claim 3, which is 0.55 mass% or more and 2.40 mass% or less. The optical plate according to any one of claims 1 to 5,
A direct type point light source backlight device including one or more point light sources disposed on a surface (B surface) opposite to a surface (A surface) having the periodic structure.   7. The direct type point light source back according to claim 6, wherein at least one of the point light sources is a point light source having a light peak angle of ± 26 ° or more and ± 85 ° or less, and 0 ° intensity is 50% or less. Light equipment.