JP2011123379A - Light beam control unit, direct backlight apparatus and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light beam control unit which enables coexistence of excellent luminance and luminance uniformity (in a front face and in a transverse visual field) to be achieved by desired backlight thickness and a less number of light sources without using a large number of optical films together in a direct backlight. <P>SOLUTION: The light beam control unit has a light diffusion plate 14 and a diffusion sheet 15. The light diffusion plate 14 has, on its surface, two or more projections each of which has an almost trigonal pyramid shape with a trigonal bottom face and has no retroreflection characteristic to visible light. In the diffusion sheet 15, a diffusion angle of emission light periodically changes along a predetermined direction in a sheet surface when a light beam is made incident vertically on the sheet surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light beam control unit including a light diffusing plate and a diffusion sheet, a backlight provided with a light source, and a direct type backlight device including the light beam control unit.

  In general, there are two types of backlights for liquid crystal displays, called edge light type backlights and direct type backlights, but for large display devices, direct type backlights that can realize high luminance at low cost. Many lights are used. The direct type backlight is generally designed on the basis of 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, there has been a demand for a light source shift to LED instead of a cold cathode tube from the viewpoint of environmental problems, light source life, power saving, and image quality improvement. 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. As an LED light source, an LED having the Lambertian distribution with the highest light intensity of the light directly above the LED is often used as the LED light source, and how to convert a light source with high directivity directly above the LED into a surface light source is large. It is a problem.

  On the other hand, in recent years, there has been a strong demand for liquid crystal displays to be thin and low in cost. As backlights, technologies for reducing light sources, reducing optical films, and diffusing light from a light source to a diffusion plate at a short distance are required. It has been.

  Conventionally, as a light diffusing technique for a direct type point light source, among four point light sources, four point light sources that form a convex quadrilateral having the smallest area and the shortest circumference are provided. There has been proposed an image forming position adjusting means for allowing each image of each point light source on the light exit surface of the light diffusing plate to be observed within a specific region of the light exit surface. In addition, a concave quadrangular pyramid shape having a different inclination angle has been proposed as the shape of the diffusion plate (see, for example, Patent Document 1).

  Similarly, a structure in which concave quadrangular pyramids are arranged obliquely on the light exit surface side of the diffuser is disclosed for the purpose of improving the light utilization efficiency (see, for example, Patent Document 2).

  Also, as a technique for reducing the unevenness of the light amount of the LED light source, a structure has been proposed in which a prism sheet in which a plurality of prisms having a corner cube shape are formed without gaps on the exit surface side of the light diffusing plate is disposed above the LED light source. (For example, see Patent Document 3).

  Furthermore, the concave / convex shape is recorded on the photosensitive medium by the speckle of the laser beam, and a mold for pattern transfer is manufactured. Using this mold, the concave / convex shape is formed on the surface of the light guide plate for the direct type large liquid crystal display device. An invention that forms a hologram light guide plate is disclosed (for example, Patent Document 4).

Pamphlet of International Publication No. 07/114158 US Pat. No. 7,334,920 JP-A-10-274947 Japanese Patent Laid-Open No. 2001-23422

  However, when the light diffusing plate having the concave inverted quadrangular pyramid shape described in Patent Document 1 on the exit surface side is used as a light diffusing plate with respect to a highly directional point light source having a Lambertian distribution, luminance unevenness reducing effect And has a big problem in luminance uniformity especially when viewed from an oblique direction.

  Also, the light diffusion plate having the concave quadrangular pyramid shape described in Patent Document 2 on the exit surface side has a small effect on improving the luminance uniformity in the front and oblique directions, as in Patent Document 1.

  Patent Document 3 discloses a structure in which a prism sheet having a thickness of 1 mm, in which a plurality of corner cube-shaped prisms made of acrylic resin are formed without gaps, is disposed above a point light source. However, there is no description regarding the optimum combination of the light output distribution of the point light source, the diffuse reflection characteristics of the diffusion film, and the surface shape of the light diffusion plate. In addition, since the disclosed prism sheet having a corner cube shape made of acrylic resin has a retroreflective characteristic, there is a problem that the luminance of a backlight configured in combination with a point light source is significantly reduced. .

  Further, Patent Document 4 discloses a hologram light guide formed so that the density of the unevenness forming the hologram is such that the portion where the light source is located is high and the density decreases as the distance from the light source increases. There is no description regarding the light output distribution of the point light source and the optimum combination with other light diffusion plates.

  In general, the backlight is intended to make the brightness uniform by using a plurality of optical sheets. However, all of the backlights described in Patent Documents 1 to 4 are optimized by using a single optical sheet. None of the documents describes an optimal combination of a plurality of optical sheets.

  As described above, in the conventional technology, a large number of light sources or a large number of optical films are used together in order to achieve excellent luminance and luminance uniformity (front and oblique view) at a desired backlight thickness. There was a need to do.

  The present invention solves the above-mentioned problems, and its purpose is to achieve a desired backlight thickness and a small number of light sources without using a large number of optical films in a direct type backlight using a light source. It is an object to provide a light beam control unit and a direct backlight device that can achieve both brightness and brightness uniformity (front and oblique visual fields).

  The light beam control unit of the present invention comprises a light diffusing plate having a plurality of substantially triangular pyramid-shaped convex portions having a triangular bottom surface on the surface and having no retroreflective property for visible light, and a light beam perpendicular to the sheet surface. A diffusion sheet in which a diffusion angle of outgoing light when incident is periodically changed along a predetermined direction in the sheet surface.

  Further, the characteristics of the light beam control unit can be further improved by adjusting the configurations of the light diffusion plate and the diffusion sheet.

  When the light beam control unit of the present invention is used, good luminance and luminance uniformity (front and oblique field of view) are exhibited, so that it is possible to reduce the number of light sources and optical films used for the backlight and to reduce the thickness of the backlight. .

It is a light emission distribution map of LED-1. It is a figure which shows the structure of the direct type | mold backlight apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the direct type | mold backlight apparatus which concerns on embodiment of this invention. (A)-(c) is a figure which shows the other example of a structure of the direct type | mold backlight apparatus which concerns on embodiment of this invention. It is a figure which shows the other example of a structure of the direct type | mold backlight apparatus which concerns on embodiment of this invention. It is a perspective view of an example of the convex triangular pyramid shape (triangular frustum shape) shaped on the light diffusing plate surface. It is a perspective view of an example of the convex triangular pyramid shape in which the vertex formed on the light diffusing plate surface is a curved surface shape. It is a perspective view of an example of the convex triangular pyramid shape formed on the light diffusing plate surface. It is the front view of the convex triangular pyramid shape shaped on the light diffusing plate surface, and its sectional drawing. It is a figure which shows the internal angle figure of the bottom triangle of the convex triangular pyramid shape shaped on the light diffusing plate surface. It is a layer block diagram (same layer, continuous layer, separate layer) of a light diffusing plate. FIG. 6 is a correlation diagram between the inclination angle θ of the convex triangular pyramid shape and the refractive index A of the resin forming the convex triangular pyramid shape. It is a correlation diagram of the convex triangular pyramid shape formed on the light diffusing plate surface and LED arrangement. It is a correlation diagram of the convex triangular pyramid shape formed on the light diffusing plate surface and LED arrangement. It is a correlation diagram of the convex triangular pyramid shape formed on the light diffusing plate surface and LED arrangement. It is a figure (plan view) showing an example of LED arrangement (grid arrangement) of a backlight. It is a figure (plan view) which shows an example of LED arrangement (staggered arrangement) of a backlight. (A), (b) is a figure which shows the projection area | region between the projection area | region of a light source, and a light source. (A), (b) It is a figure which shows the definition of the diffusion angle in the diffusion sheet which concerns on embodiment of this invention. It is a figure which shows distribution of the diffusion angle (aspect ratio) in the diffusion sheet of this invention. (A)-(f) is an example of the diffusion angle distribution figure which made the relative position in a sheet | seat surface a horizontal axis, and made the vertical axis | shaft the diffusion angle in the position in the said sheet | seat surface in the diffusion sheet of this invention. (A), (b) is a figure which shows the cross-section of the direct type | mold backlight apparatus which concerns on embodiment of this invention. (A) to (f) are examples of a diffusion sheet in which the aspect ratio changes from a projection area on the light source to a projection area between the light sources in a linear shape, a mixed shape of straight lines and curves, or a staircase shape. FIG. It is a figure which shows the structure of the direct type | mold backlight apparatus which concerns on embodiment of this invention. It is a figure which shows distribution with respect to the relative position in a sheet | seat surface of the diffusion angle in the diffusion sheet which concerns on embodiment of this invention. It is a correlation diagram of the convex triangular pyramid shape formed on the light diffusing plate surface and LED arrangement. It is the front view (convex triangular pyramid shape) by the side of the light emission surface of an example of the light diffusing plate in this invention. 3 is a plan view showing a region where the diffusion angle of the diffusion sheet 1 is high. FIG. It is a figure which shows the diffusion angle distribution of the diffusion sheet 1 on the line Y in FIG. It is a figure which shows the diffusion angle distribution of the diffusion sheet 1 on the line Y in FIG.

  The present invention will be specifically described below.

(Light control unit)
First, the light beam control unit according to the present invention will be described.

  The light beam control unit according to the present invention includes a light diffusing plate having a plurality of substantially triangular pyramid-shaped convex portions having a triangular bottom surface and a retroreflective property for visible light, and a light beam perpendicular to the sheet surface. A diffusion sheet in which a diffusion angle of outgoing light when incident is periodically changed along a predetermined direction in the sheet surface.

  The inventors of the present invention have intensively studied the arrangement of the optical sheet used in the direct type backlight device, and as a result, the combination of the specific light diffusing plate and the specific light diffusing sheet as described above has excellent luminance. And luminance uniformity (front and oblique visual field). Preferred embodiments of the light diffusion plate and diffusion sheet that can be used in the present invention will be described later.

(Direct type backlight device)
The backlight device according to the present invention includes a light source and a light control unit disposed above the light source. Further, the direct type backlight device according to the present invention can be incorporated in a liquid crystal display device as a device for supplying light to the liquid crystal display panel. In addition, the direct type backlight device can also be used as a lighting device.

(light source)
As a light source that can be used in the direct type backlight device of the present invention, for example, a linear light source such as a cathode ray tube (CCFL), or a point light source such as an LED (light emitting diode) or a laser can be used.

  Examples of the light source that can be preferably used include a point light source having a high light intensity directly above, for example, a light output distribution with a light peak intensity of −25 to 25 °.

  An LED light source having a light peak angle of −25 to 25 ° has a feature of high conversion efficiency to light energy and high luminance per current. Therefore, when such a point light source is used, high luminance is maintained. , Brightness uniformity can be improved. The light beam control unit according to the present invention has a diffuse reflection performance that diffuses and reflects light from a point light source over a wide range of angles and a light collection performance between the light sources, which cannot be achieved with conventional light diffusion plates. For this reason, by combining a point light source, particularly a point light source with a light peak angle of −25 to 25 ° and a strong light beam intensity, and the light control unit of the present invention, a direct type back having excellent luminance. Light can be realized.

  In particular, a point light source (LED light source) (FIG. 1) having a Lambertian type light emission distribution with a light peak angle of 0 degree and a half-value angle of 60 degrees is more preferably used. Conditions other than the above-mentioned light emission distribution are not particularly limited, for example, a type in which a yellow phosphor is excited by a blue LED, a one-chip type pseudo white LED in which green and red phosphors are excited by a blue LED; red / green / Examples include a multi-chip type that generates white light by combining blue LEDs, and a one-chip type pseudo white LED that combines a near-ultraviolet LED and a red / green / blue phosphor.

Next, an example of a direct type backlight device using the above-described light beam control unit according to the present invention will be described.
(Laminated structure of direct type backlight device)
2 and 3 are diagrams showing a schematic configuration of the direct type backlight device according to the embodiment of the present invention. The light beam control unit according to the present invention is basically disposed at least two light sources 11 and 12 and above the light sources 11 and 12 and diffuses the light from the light sources 11 and 12 according to the present invention. The structure which comprises the board 14 and the diffusion sheet 15 concerning this invention arrange | positioned above the said diffusion board 14 is taken.

  In addition, a reflection sheet 13 for reflecting light is used below the light sources 11 and 12. Moreover, if it has the said structure, you may arrange | position at least 1 optical sheet, a diffusion sheet, etc. further.

  As the whole light beam control unit, a plurality of light sources are used. As the light source, as shown in FIG. 2, a linear light source such as a cold cathode tube (CCFL) 11 or a point light source such as an LED (light emitting diode) 12 shown in FIG. 3 or a laser can be used. The arrangement of the light sources is arranged directly below the image display surface.

  As the reflection sheet 13, various materials can be used as long as they can reflect light. For example, a resin such as polyester or polycarbonate is foamed and fine air particles are put inside to form a sheet, a sheet formed by mixing two or more resins, and a resin layer with a different refractive index is laminated. The sheet | seat etc. which were done can be used. In addition, the reflective sheet 13 may have an uneven shape on the surface. As these, those having inorganic fine particles added to the surface can be used as necessary. Further, the reflection sheet 13 is preferably a white resin sheet having a diffuse reflectance of 90% or more, and most preferably a white resin sheet having a reflectance of 95% or more. The 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 ° using a spectrophotometer, for example, a spectrophotometer UV-2200 manufactured by Shimadzu Corporation. And it can obtain | require by calculating an average reflectance.

  The direct type backlight device according to the present invention can employ other arrangement configurations, for example, the arrangement configurations shown in FIGS. 4 (a) to 4 (c). 4 (a) to 4 (c) are diagrams showing other configurations of the direct type backlight device according to the embodiment of the present invention. For the direct type backlight device, a direct type LED may be used as a light source, and an arrangement configuration as shown in FIG. 5 can be adopted using the diffusion sheet 15 of the present invention.

  FIG. 4 (a) shows a surface enhancement in which a fine concavo-convex structure is formed on the surface between the light diffusion plate 14 of the present invention and the diffusion sheet 15 of the present invention arranged immediately above the light source in the configuration shown in FIG. A direct type backlight device in which a shaped diffusion sheet 16 is disposed and the surface-shaped diffusion sheet 16 is disposed immediately above the diffusion sheet 15 of the present invention is shown.

  Here, as the surface shaping type diffusion sheet 16, a sheet in which spherical beads of acrylic resin are coated on a sheet of polyester resin, triacetyl cellulose, polycarbonate or the like can be used.

  Moreover, as the surface shaping type | mold diffusion sheet 16, the sheet | seat by which the fine uneven structure by the ultraviolet curable resin was transcribe | transferred on sheets, such as a polyester-type resin, a triacetyl cellulose, or a polycarbonate can be used. Such a surface-shaped diffusion sheet 16 has a function of condensing the light diffused by the light diffusion plate 14 as well as the effect of diffusing and uniformizing the light. By using the surface-shaped diffusion sheet 16 in combination with the light beam control unit of the present invention, it is possible to reduce luminance unevenness, reduce the thickness of the light beam control unit, and reduce the number of light sources.

  FIG. 4B shows an optical sheet 17 having an arrayed prism arrangement structure above the light diffusion plate 14 of the present invention and the diffusion sheet 15 of the present invention arranged immediately above the light source in the configuration shown in FIG. 1 shows a direct type backlight device in which a surface-shaped diffusion sheet 16 having a fine concavo-convex structure formed on a surface thereof is arranged in this order. FIG. 4C shows a surface in which a fine concavo-convex structure is formed on the surface above the light diffusion plate 14 of the present invention and the diffusion sheet 15 of the present invention arranged immediately above the light source in the configuration shown in FIG. A direct type backlight device in which a shaping type diffusion sheet 16 and an optical sheet 17 having an arrayed prism arrangement structure are arranged is shown.

  As the optical sheet 17 having such an array-like prism arrangement structure, an optical sheet in which prism rows having a substantially triangular shape, a substantially trapezoidal shape, and a substantially elliptical shape are arrayed on the surface. A sheet can be used. A shape obtained by rounding the apex of the cross-sectional shape can also be preferably used from the viewpoint of improving scratch resistance. These prism sheets can be used in a form in which a prism array made of an ultraviolet curable resin is transferred onto a base material sheet such as polyester resin, triacetyl cellulose, or polycarbonate. Since such an optical sheet 17 exhibits retroreflectivity, it has a function of collecting incident light to the front. By using this optical sheet in combination with the light beam control unit of the present invention, it is possible to reduce luminance unevenness, reduce the thickness of the direct type backlight device, and reduce the number of light sources.

  FIG. 5 shows a surface shaping mold in which a fine concavo-convex structure is formed on the surface above the light diffusing plate 14 according to the present invention and the diffusion sheet 15 according to the present invention arranged in the structure shown in FIG. 1 shows a direct type backlight device in which a diffusion sheet 16 is arranged, an optical sheet 17 having an array of prism rows, and a reflective polarizing sheet 18 are arranged in this order.

(Light diffusion plate)
Next, the light diffusing plate used in the backlight device will be described. The light diffusing plate according to the present invention has a plurality of substantially triangular pyramid-shaped convex portions having a triangular bottom surface on the surface thereof from the viewpoint of luminance and luminance uniformity (front and perspective), and retroreflection for visible light. It has no characteristics, that is, visible light emitted from the point light source does not return to the point light source due to reflection by the light diffusion plate. In particular, when a light diffusing plate is used in a direct backlight device using a point light source and a diffuse reflector, light directly above the light source emitted from the point light source is diffusely reflected downward as much as possible by the light diffusing plate. It is necessary to diffusely reflect the light on the plate, but if the light diffuser has a retroreflective property, the light emitted from the point light source returns to the point light source again, so the luminance is greatly reduced and the luminance uniformity is impaired. It is. For this reason, by making the light diffusing plate have no retroreflective property with respect to visible light, the loss of light is reduced, and the luminance can be improved.

  Furthermore, when using a spectrophotometer, light having a wavelength of 450 to 750 nm is incident from the light incident surface side of the light diffusing plate at an incident angle inclined by 7 degrees with respect to the normal to the horizontal plane of the light diffusing plate. The average reflectance R is preferably 40% or more, more preferably 45% or more, further preferably 50% or more, and most preferably 55% or more. Here, the average reflectance R means an average value when the reflectance is obtained for each wavelength of 1 nm in the wavelength region of 450 to 750 nm.

  If the convex triangular pyramid shape of the convex portion is, for example, a convex substantially triangular pyramid whose bottom surface is a triangle, and the inclination angle θ of the side surface of the triangular pyramid is 57 degrees, the light incident point Light does not return and does not have retroreflectivity. On the other hand, when the substantially triangular pyramid shape of the convex portion has, for example, a retroreflective property having a corner cube shape (the inclination angle θ is 55 degrees), the light returns to the light exit point, and thus the reflectance. Is less than 40%, the luminance uniformity is impaired, and the luminance is greatly reduced.

  In addition, a light diffusing plate in which a diffusing agent is added to the material forming the convex portion and a light diffusing plate provided with a diffusing layer having a diffusing agent as described later do not have retroreflective properties with respect to visible light. Furthermore, the light diffusing plate having an inclined light incident surface of the light diffusing plate does not have a retroreflective property with respect to visible light, for example, even in a corner cube shape, the average inclination angle of the light incident surface of the light diffusing plate. U is set to 1 degree or more, preferably 5 degrees or more, or a diffusing agent is added to the light diffusion plate to control the total light transmittance T of the light diffusion plate to 85 to 95%, more preferably 87 to 93%. Thus, a light diffusing plate having no retroreflective property and a reflectance of 40% or more can be obtained. A method for measuring the total light transmittance T will be described later.

  The inclination angle θ with respect to the bottom surface of the substantially triangular pyramid side surface of the convex portion of the light diffusing plate in the present invention is preferably 50 to 62 degrees from the viewpoint of luminance and luminance uniformity (front and perspective). Most preferably, it is 60 degrees.

  The inclination angle θ can be obtained by observing the cross-sectional shape of the light diffusion plate using a laser microscope or SEM (electron microscope).

  In the present invention, the substantially triangular pyramid shape refers to a solid whose bottom surface is a triangle and whose top is a point or a triangle whose area is smaller than the bottom surface, and includes a so-called triangular frustum (FIG. 6).

  The side surface may be a flat surface or a curved surface, and when the top is a point, the apex may be pointed (FIG. 8) or curved surface (FIG. 7).

  In the substantially triangular pyramid shape, it is preferable that a straight line (center axis) connecting the apex (or the center of the triangle on the top) and the center of the triangle on the bottom is perpendicular to the plane, that is, not a diagonal triangular pyramid.

  In the present invention, the inclination angle θ is an angle formed by the side surface and the bottom surface of the convex portion.

  Even when a part of the side surface includes a curved surface, when the side surface includes a flat surface, the angle formed by the flat surface and the bottom surface is the inclination angle θ. When the side surfaces are all curved surfaces, the inclination angle θ is the largest angle among the angles formed between the tangential plane of the side surfaces and the bottom surface.

  When the substantially triangular pyramid shape is an oblique triangular pyramid, the inclination angle θ 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 light diffusing plate in the present invention is formed by periodically forming convex portions of the same shape having the substantially triangular pyramid shape on the surface thereof.

  From the viewpoint of brightness and brightness uniformity, the shape and arrangement of the convex portions of the light diffusion plate of the present invention preferably satisfy the following formulas (5) and (6).

(5) 0 ≦ c / b ≦ 0.20
(6) 0 ≦ d / b ≦ 0.50
Here, b, c, and d respectively pass the convex portion through the apex (or the center of the top triangle when the convex portion is a triangular frustum shape), and on one side of the triangle on the bottom surface of the convex portion. In the cross section cut by a vertical plane, the length of the projected line segment projected from the portion B where the angle θ ′ formed by the tangential plane of the one side surface of the convex portion and the bottom surface satisfies 50 to 62 degrees onto the horizontal plane, The length of the projection line segment which projected the part C in the skirt side on the horizontal plane, and the length of the projection line segment which projected the part D in the top side from B on the horizontal plane (FIG. 9).

  C includes the distance l × 1/2 between adjacent convex portions, and the top end of D is the apex of the convex portion (in the case of a triangular frustum shape, the top triangular shape is Center).

  In FIG. 9, a straight line segment is illustrated as the portion B, but the portion B may be a curve as long as θ ′ satisfies 50 to 62 degrees. For example, when the refractive index A of the material forming the convex portion is 1.59, the portion B may be a curve that continuously changes in the range of θ ′ = 52 to 62 °.

  From the viewpoint of further luminance enhancement, it is more preferable that 0.01 ≦ c / b ≦ 0.13 and 0 ≦ d / b ≦ 0.30, 0.01 ≦ c / b ≦ 0.06, and Most preferably, 0 ≦ d / b ≦ 0.20.

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

  In the substantially triangular pyramid shape, the sum b + c + d of b, c and d is preferably 5 to 200 μm from the viewpoint of luminance uniformity, moire, and manufacturing, preferably 10 to 150 μm, and preferably 15 to 120 μm. Most preferably it is.

  Moreover, it is preferable that the height (distance from a bottom face to the uppermost part) of a substantially triangular pyramid shape is 10-400 micrometers.

  The substantially triangular pyramid-shaped convex portion is preferably formed on the surface on the light exit surface side when used in combination with a light source, out of the two surfaces of the light diffusion plate.

  Hereinafter, in this specification, when used in combination with a light source, the surface closer to the light source is defined as the light incident surface, and the surface farther from the light source (opposite the light source) is defined as the light exit surface.

  A plurality of convex portions having a substantially triangular pyramid shape are provided on the surface of the light diffusion 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 viewpoints of luminance uniformity and productivity that the plurality of convex portions are arranged adjacently so that the opposing sides of the 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, when the inner angles are α, β, and γ, | α−β |, | β-γ |, and | γ-α | are each preferably 20 ° or less from the viewpoint of luminance uniformity, and 10 °. More preferably, it is more preferably 5 ° or less (FIG. 10). 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 portions provided on the surface of the light diffusing plate are preferably formed in a region of 70 area% or more of the horizontal plane of the light diffusing plate, from the viewpoint of luminance uniformity, and 80 area% or more. More preferably, it is formed at 90 area% or more, and most preferably at 95 area% or more.

  The light diffusing plate in the present invention is preferably composed of at least (a) a lens layer and (b) a diffusing layer from the viewpoint of luminance and luminance uniformity of front and perspective. (A) A lens layer is a layer in which the convex triangular pyramid shape is formed, and (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 may be formed from a plurality of layers.

  Said (a) and (b) may be the same layer, a continuous layer, or a separate layer (FIG. 11). Specifically, the same layer refers to a layer structure in which the substantially triangular pyramid is formed on the surface of (b) the diffusion layer, that is, the (a) layer is incorporated in the (b) layer. , (A) Lens layer and (b) Diffusion layer are in close contact and integrated layer structure. Separate layer is (a) Lens layer and (b) Diffusion layer exist as separate sheets. This is a configuration in which the sheets are physically stacked. 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 arranged between the layers.

  There is no limitation on the material constituting the convex portion ((a) lens layer) of the light diffusing plate in the present invention. For example, a resin having high light transmittance is preferably used. Specific examples 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; polystyrene Styrene resins such as styrene-acrylonitrile copolymer, styrene-methacrylic acid copolymer, methyl methacrylate-styrene copolymer, alphamethylstyrene copolymer; acrylic resins such as polymethyl methacrylate and polyethyl acrylate; methacryl Examples include acid ester resins and polycarbonate resins.

  There is no limitation in the material which comprises the (b) diffusion layer of the light diffusing plate in this invention, For example, the resin composition containing (transparent) resin and a spreading | diffusion agent is mentioned. The (b) diffusing layer has a total light transmittance T of 85 to 95% and a diffusivity S of 5 to 40%, so that brightness, luminance uniformity (front and perspective) and retroreflective properties are obtained. It is preferable from a viewpoint not to make it express, and it is most preferable that T is 87 to 93% and S is 10 to 30%. In particular, when (a) the convex portion formed on the lens layer has a triangular pyramid shape of θ = 55 degrees, (b) when the diffusivity S of the diffusion layer is less than 5%, the light diffusion plate has a retroreflection characteristic. The light emitted from the point light source returns to the point light source, and there is a problem that the luminance of the backlight is lowered. Therefore, it is preferable to adjust the values of θ and S so as not to exhibit such retroreflectivity. In addition, when the diffusion rate S of the (b) diffusion layer is larger than 40%, the luminance uniformity (front and perspective) tends to decrease.

  In addition, the total light transmittance T of the light diffusing plate is obtained by smoothing the surface by hot pressing with the (a) layer and the (b) layer overlapped, and then applying the hot press product to JIS K7105. Can be measured.

  As for the diffusion rate S of the (b) diffusion layer, the (a) layer and the (b) layer of the light diffusion plate are the same layer, and the (a) layer and the (b) layer are continuous layers. In this case, after smoothing the surface by hot pressing with the (a) layer and the (b) layer overlapped, using a goniophotometer (for example, GC5000L manufactured by Nippon Denshoku Industries Co., Ltd.), the transmission mode Then, the brightness of the transmitted light when light is incident at a light incident angle of 0 degree can be obtained by the following equation. When the (a) layer and the (b) layer are separate layers, the surface of the (b) layer press product can be measured in the same manner as described above after the surface is smoothed by hot pressing only the (b) layer. it can.

Diffusivity S = 100 × (L (20 degrees) + L (70 degrees)) / (L (5 degrees) × 2)
here,
L (5 degrees) is the luminance (cd / m ² ) of transmitted light emitted at an angle of 5 degrees,
L (20 degrees) is the luminance (cd / m ² ) of transmitted light emitted at an angle of 20 degrees,
L (70 degrees) is the luminance (cd / m ² ) of transmitted light emitted at an angle of 70 degrees,
It is.

  The material constituting the (b) diffusion layer of the light diffusing plate in the present invention is a resin 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. Compositions are preferred. 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, and alphamethylstyrene copolymer; acrylic resins such as polymethyl methacrylate and polyethyl acrylate A methacrylic ester resin, a polycarbonate resin and the like.

  Examples of the light diffusing agent include acrylic resin crosslinked fine particles, styrene resin crosslinked fine particles, silicone resin crosslinked fine particles, MS (methyl methacrylate / styrene copolymer) crosslinked fine particles, fluororesin fine particles, glass fine particles, silica fine particles, Examples thereof include calcium carbonate, barium sulfate, titanium oxide, alumina, talc, and mica, and these can be used alone or in combination. Examples of the shape of the light diffusing agent include true sphere, ellipse, indefinite shape, needle shape, plate shape, hollow shape, columnar shape, and cone shape.

  The average particle diameter of the light diffusing agent is preferably 1 to 20 μm, and most preferably 2 to 10 μm, from the viewpoint of luminance uniformity and easy manufacturing. The average particle size can be determined by a particle size distribution meter.

  The difference in refractive index between the resin constituting the diffusion layer (b) and the light diffusing agent is preferably 0.05 to 0.2 from the viewpoint of luminance uniformity and easy production, and is preferably 0.10 to 0.00. 16 is most preferred. For example, preferred light diffusing agents for polystyrene resins include acrylic crosslinked fine particles and silicone crosslinked fine particles.

  Furthermore, the addition amount of the light diffusing agent is 0.02 to 2% by weight with respect to the entire material (for example, the resin composition) constituting the diffusion layer (b) from the viewpoint of luminance uniformity and easy manufacture. It is preferred that it is 0.05 to 1% by weight.

  In the present invention, the thickness of the light diffusing plate is preferably 0.5 to 3.0 mm from the viewpoint of rigidity, optical properties (luminance, luminance uniformity), and backlight thickness, and 0.8 to 2.5 mm. It is preferable that it is 1.0-2.0 mm.

  In addition, when the (a) layer and the (b) layer of the light diffusion plate in the present invention are separate layers, the total thickness when the (a) layer and the (b) layer are superposed is the thickness of the light diffusion plate. To do.

  The light diffusing plate in the present invention 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 depends on the use and purpose. It can be selected appropriately.

  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 light diffusing plate is composed of five or less layers in view of ease of manufacture.

  You may mix | blend various additives with the light diffusing plate in this invention. 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 light diffusing plate according to the present invention is a surface opposite to the surface on which the substantially triangular pyramid-shaped convex portions are formed, that is, the light source from the viewpoint of luminance uniformity and rubbing with the indicator pin mounted on the backlight. In a preferred embodiment when used in combination, it is preferable to provide a concavo-convex shape on the surface that becomes the light incident surface (surface on the light source side).

  Specifically, the average inclination angle U of the light incident surface is preferably 1 to 30 ° from the viewpoint of not exhibiting luminance and luminance uniformity and retroreflective properties, and more preferably 3 to 25 °. 5 to 20 ° is most preferable. When the average inclination angle U of the light incident surface is less than 1 °, for example, if the inclination angle of the convex portion on the light exit surface side is 55 degrees, the light diffusion plate exhibits retroreflective characteristics. Therefore, for example, when a point light source is used, the light emitted from the point light source 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 °, the luminance uniformity tends to deteriorate.

  The average inclination angle U is obtained by observing a cross section of the diffuser plate with a laser microscope, and continuously averaging the average inclination angle of 1 μm width (inclination angle with respect to the horizontal plane of the light diffusion plate) with a width of 1000 μm in the longitudinal direction and the short direction. 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. When the (a) layer and the (b) layer are separate layers, it is preferable that the average inclination angle on the light incident surface side is within the above range for both the (a) layer and the (b) layer.

  As a method for producing a light diffusing plate in the present invention, a material constituting each layer of the light diffusing plate, for example, a resin composition containing a highly light-transmitting resin, is extruded from a die in a molten state, and has a desired shape. Melt molding method using a roll processed into a mold; Solution cast method in which a resin composition is extruded from a die in a state dissolved in a solvent and processed into a desired shape; Melt molding method; Solution Extrusion lamination method of laminating molten resin and dry lamination method of laminating solid films on solid film obtained by surface shaping by casting method; processed into a desired shape a plate extruded from a die in a molten state Examples include a method of hot press molding using a press mold; and a method of injection molding using a mold processed into a desired shape. Among these, the melt molding method is the most preferable molding method from the viewpoints of productivity and environmental suitability.

  When the light diffusing plate in the present invention is disposed above a point light source having a light peak angle of −25 to 25 ° and having high light intensity, the light from the point light source is spread over a wide angle. This is preferable because it exhibits a function of diffusing and reflecting (point light source side). Furthermore, the diffuser reflection of the light diffused and reflected by the light diffusing plate toward the light diffusing plate makes it possible to maintain the brightness uniformity of the front and perspective as a backlight.

  The light diffusing plate in the present invention is characterized in that the diffuse reflection property is remarkably higher than the performance of the conventional light diffusing plate. That is, in the conventional light diffusing plate, when the diffusibility is increased, the reflectivity is greatly reduced and both functions cannot be achieved.However, the light diffusing plate of the present invention has excellent diffuse reflectivity, Both reflectivity. In particular, when the light diffusing plate has a triangular pyramid-shaped convex portion formed of a material having a side surface inclination angle θ and a refractive index A satisfying the following expressions (1) and (2) (FIG. 12), The light can be condensed even in the dark portion between the light sources, and the effect of improving the luminance uniformity of the backlight is remarkably large.

(1) θ ≧ −40A + 115.2
(2) θ ≦ 25A + 22.25
Further, when the tilt angle θ and the refractive index A satisfy the following expressions (3) and (4) (FIG. 12), the backlight luminance, front luminance uniformity, and perspective luminance uniformity are further improved.

(3) θ ≧ −40A + 116.2
(4) θ ≦ 25A + 20.25
The refractive index A can be obtained by cutting and separating the part forming the convex part, creating a film having a smooth surface by hot pressing, and using an Abbe refractometer in accordance with JIS K7142.

  The refractive index A of the sample is determined by a transparent material (for example, transparent resin) among the materials forming the sample, and even if a light diffusing agent or the like is added, the refractive index 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, a transparent material (for example, a material forming the convex portion (for example, Only the transparent resin raw material) is formed into a film, and the refractive index A of the film is measured using an Abbe refractometer in the same manner as described above to obtain the refractive index A.

  Furthermore, in the direct type backlight using the point light source as described above, the triangular pyramid shape of the convex portion provided on the surface of the light diffusion plate used in the arrangement of the plurality of point light sources and the light control unit of the present invention. Exhibits a particularly excellent luminance uniformity when has a specific relationship.

  Specifically, a plurality of convex portions are periodically arranged on the surface of the light diffusing plate so that one side of the bottom triangle of adjacent convex portions is parallel to each other, and the plurality of point light sources are periodically arranged in a grid pattern. The point light source and the light diffusing plate are arranged such that at least one side of the bottom triangle of each convex portion of the light diffusing plate is parallel to a rectangular diagonal line constituting the lattice of the plurality of point light sources. From the viewpoint of luminance uniformity, it is preferable that the position is in a proper positional relationship (FIG. 13). The parallel positional relationship includes a deviation within ± 2 ° from the parallel.

  Here, the lattice means an arrangement of the vertices of the quadrangle when the plane is filled with a quadrangle so that the apexes coincide with the sides of the adjacent quadrangle. Examples of the quadrangle include a square, a rectangle, and a parallelogram.

  In addition, when the bottom triangle of the convex triangular pyramid of the diffuser plate is an isosceles triangle, the base of the bottom isosceles triangle of the convex part and the rectangular diagonal lines constituting the lattice of the point light source in a lattice arrangement are parallel to each other. It is more preferable from the viewpoint of luminance uniformity, and it is more preferable that the quadrangles constituting the lattice of the lattice arrangement are in a rhombus shape in which the bases of the isosceles triangles face each other (see FIG. 14). The parallel positional relationship includes a deviation within ± 2 ° from the parallel.

  Furthermore, when the bottom triangle of the diffusing plate convex triangular pyramid is a regular triangle, one side of the convex bottom regular triangle and the diagonal of the quadrangle constituting the lattice of the point light source in a lattice arrangement are parallel to each other. It is more preferable from the viewpoint of luminance uniformity, and it is most preferable that the quadrangles constituting the lattice of the lattice-like arrangement have a rhombus shape in which equilateral triangles face each other (FIG. 15). The parallel positional relationship includes a deviation within ± 2 ° from the parallel.

  It is preferable that the point light sources arranged in the direct type backlight of the present invention are arranged as uniformly as possible between the point light sources. Specifically, an arrangement method 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 on the screen, that is, the light diffusing plate (FIG. 16, squares constituting the grid: squares). Or rectangular), or an arrangement method in which point light sources are arranged in a staggered (grid) shape (triangular lattice shape) at equal intervals in the vertical and horizontal directions of the screen (FIG. 17, quadrangle constituting the lattice: rhombus shape). Can be adopted.

  In particular, it is more preferable to arrange the point light sources in a staggered manner from the viewpoint of improving luminance uniformity, and as shown in FIG. 17, the side of the backlight (light diffusing plate) of the point light sources arranged in a staggered manner. N1 / n2 is preferably 0.26 to 3.87, more preferably 0.35 to 2.82, when the distance between the light sources in the vertical direction and the vertical direction is n1 and n2. More preferably, it is 46 to 0.75, or 1.33 to 2.18, and most preferably 0.51 to 0.66, or 1.52 to 1.96.

  The light diffusing plate according to the present invention has a plurality of substantially triangular pyramid-shaped convex portions on the surface (preferably the side that becomes the light exit surface when used in combination with a light source), so that it is used for a direct type point light source backlight. When used as a light diffusing plate, the effect of improving luminance and luminance uniformity, in particular, improving luminance uniformity in the front direction and the perspective direction is exhibited. Therefore, in the direct type point light source backlight of the present invention, reduction of the number of point light sources, reduction of the optical film, and thinning of the backlight which cannot be achieved by the prior art are achieved, and the economic effect is great.

(Diffusion sheet)
Next, the diffusion sheet used in the backlight device will be described in detail with reference to the drawings.

  18A and 18B show the projection area between the light source and the projection area between the light sources. In FIG. 18, in order to explain the positional relationship with the light source, the diffusion plate in the light source control unit of the present invention is omitted. A plurality (at least two) of light sources are arranged. 18A shows a case where a linear light source such as a cold cathode fluorescent lamp (CCFL) 1 is used, and FIG. 18B shows an example where a point light source such as an LED (light emitting diode) 2 or a laser is used. . In FIGS. 18A and 18B, reference numeral 3 indicates a projection area immediately above the light source, and reference numeral 4 indicates a projection area between the light sources. FIGS. 18A and 18B show an example in which the entire area is divided into a projection area immediately above the light source and a projection area between the light sources. Further, it may be divided so as to provide an area other than the projection area between the light sources. In addition, the projection area between the light sources may not be adjacent to the projection area immediately above the light source, and may include an area located in the middle of the adjacent light sources.

  The diffusion sheet of the present invention is characterized in that the diffusion angle of outgoing light when a light beam is incident perpendicularly to the sheet surface periodically changes along a predetermined direction in the sheet surface. The period of the sheet diffusion angle is preferably matched to the period of the projection area composed of the area directly above the light source and the area between the light sources. Thereby, luminance unevenness can be reduced.

  FIG. 19A is a diagram showing the definition of the diffusion angle of the present invention. The “diffusion angle” in the present invention refers to an angle (FWHM: Full Width Half Maximum) that is twice the angle (half-value angle) at which the transmitted light intensity is attenuated to half the peak intensity. This diffusion angle is measured, for example, by a Far-Field Profiler LD8900 manufactured by Photon Co., Ltd., where the uneven surface of the diffusion sheet 15 is the incident surface, and the angular distribution of transmitted light intensity with respect to light incident in the normal direction of the uneven surface is measured. You can ask for it. Here, the normal direction of the diffusion sheet refers to the direction shown in FIG.

  In addition, as the diffusion sheet of the present invention, both an isotropic diffusion sheet capable of obtaining substantially the same diffusion angle regardless of the measurement direction and an anisotropic diffusion sheet having a different diffusion angle depending on the measurement direction can be used. An anisotropic diffusion sheet is, for example, a diffusion sheet having different diffusion angles when the diffusion angles are measured in two orthogonal directions.

  FIG. 20 is a diagram showing the distribution of the diffusion angle (aspect ratio) in the diffusion sheet of the present invention. In this diffusion sheet, the diffusion angle of the emitted light when a light beam is incident on the sheet surface perpendicularly changes periodically along a predetermined direction in the sheet surface. In the diffusion angle (aspect ratio) distribution diagram shown in FIG. 20, the horizontal position indicates the relative position within the sheet surface in a predetermined direction within the sheet surface, and the vertical axis indicates the diffusion angle at the relative position within the sheet surface. For In the diffusion sheet according to the present invention, there are a plurality of peak values of the diffusion angle (or aspect ratio) and bottom values of the diffusion angle (or aspect ratio) (one is shown in FIG. 20). The peak value refers to the value of the highest diffusion angle (or aspect ratio) in one period of the distribution of the diffusion angle (or aspect ratio), and the bottom value refers to 1 of the distribution of the diffusion angle (or aspect ratio). The value of the lowest diffusion angle (or aspect ratio) in the period.

  In the present invention, in such a diffusion angle distribution diagram, the arithmetic average value of the diffusion angles between the adjacent peak values and the bottom value is the arithmetic operation of the diffusion angles distributed between the adjacent peak value and the bottom value. It is preferably larger than the average value.

  Changes in the diffusion angle are strictly linear, curved if the arithmetic average value of the adjacent peak value and the bottom value is greater than the arithmetic average value of the diffusion angle distributed between the adjacent peak value and the bottom value, The shape may not be stepped, and may be a straight shape, a curved shape, a shape slightly deviated from the stepped shape, or a mixed shape of a straight line and a curved line due to variation in measurement of the diffusion angle. When transitioning from the region directly above the light source to the region between the light sources, the light incident angle with respect to that position increases linearly. Considering that the light reflected below the diffuser sheet and the light that passes obliquely with respect to the normal direction of the diffuser sheet increase as the incident angle increases, the transition from the upper light source region to the inter-light source region As it does so, the amount of light to be diffused is not linear and attenuates much more. In other words, if the diffusion sheet is larger than the arithmetic average value of the diffusion angles distributed between the adjacent peak value and the bottom value, it will attenuate the light to be diffused. In addition, luminance unevenness can be reduced. 21 (a) to 21 (f) are diagrams of diffusion angle distributions in the diffusion sheet of the present invention, in which the relative position in the sheet surface is the horizontal axis, and the diffusion angle at the position in the sheet surface is the vertical axis. It is an example. An example of a diffusion sheet in which the diffusion angle changes in a linear shape, a mixed shape of straight lines and curves, or a staircase shape from a projection region on the light source to a projection region between the light sources is shown.

  As for the diffusion angle in each region in the sheet, a region having a relatively high diffusion angle may be disposed immediately above the light source, and a region having a relatively low diffusion angle may be disposed immediately above the light source (FIG. 21 (c). ), (D)). Moreover, it is preferable that the diffusion angle between each area | region changes smoothly. In particular, a shape including a plurality of peak values continuous in a high diffusion angle region is preferable from the viewpoint of reducing luminance unevenness, and the shape is a linear shape or a downwardly convex curve shape or a mixed shape of a straight line and a downwardly convex curve. It is preferable (FIGS. 21 (c), (d), (f)). Further, there is a bottom value of the diffusion angle, and the diffusion angle distribution in the low diffusion angle region including the bottom value is preferably a downward convex curve with the bottom value being the minimum value from the viewpoint of reducing luminance unevenness. (FIGS. 21A to 21E).

  Here, the high diffusion angle region is an angle region that is ½ or more of the maximum FWHM, and the low diffusion angle region is an angle region that is ½ or less of the region maximum FWHM. The arithmetic average value is calculated from the peak value and the bottom value in the present invention using the distribution of the diffusion angle based on the above definition. In one cycle, the peak value and the bottom value are not limited to one, and a plurality of the same values may exist. For example, in FIG. 20, there are a plurality (two) of peak values in one high diffusion angle region.

  Further, the diffusion angle distributed between adjacent peak values and bottom values refers to the diffusion angle existing in the broken line section of FIG. That is, when there are a plurality of peak values, it means the diffusion angle existing in the section between the position corresponding to the adjacent bottom value and the position corresponding to the peak value.

  The diffusion angle of the diffusion sheet of the present invention is preferably controlled in the range of 0.1 to 120 degrees.

  Here, in order to further improve the uniformity of brightness, the difference in diffusion angle and the distribution state of the diffusion angle can be adjusted. In particular, when the distance between the light source and the diffusion sheet is reduced in order to reduce the thickness (FIG. 22 (a)), or when the distance between the light sources is increased (FIG. 22 (b)), the luminance unevenness increases. A larger difference in diffusion angle is preferred. The diffusion angle is preferably controlled in a range of 0.1 degrees to 100 degrees, and more preferably in a range of 0.1 degrees to 80 degrees, in order to obtain a high front luminance. . In particular, when the diffusion sheet is used in combination with an optical sheet having prism rows formed on the surface, the diffusion angle is formed to be in the range of 0.1 degrees to 70 degrees, and the diffusion angle difference is large. Is preferable from the viewpoint of eliminating uneven brightness and improving brightness.

  Moreover, it is preferable to control the minimum value of the diffusion angle of the diffusion sheet of the present invention in the range of 0.1 degrees or more and 40 degrees or less. Further, the minimum value of the diffusion angle is more preferably controlled from 0.1 degrees to 30 degrees, and most preferably from 0.1 degrees to 20 degrees, from the viewpoint of eliminating luminance unevenness. .

  The diffusion angle in the plane of the diffusion sheet of the present invention periodically changes along a predetermined direction in the plane, and the relative position in the sheet plane in the predetermined direction is taken on the horizontal axis, In the diffusion angle distribution diagram when the diffusion angle at the position is taken on the vertical axis, the difference between the maximum value and the minimum value of the diffusion angle is preferably 40 degrees or more and 80 degrees or less. By setting the diffusion angle difference to be 40 degrees or more, a sufficient difference in diffusion characteristics can be obtained, and it is possible to meet demands for eliminating high luminance unevenness in reducing the thickness of the direct type backlight device and reducing the number of light sources. In addition, since the diffusion angle difference is set to 80 degrees or less, and the amount of change in the diffusion characteristics with respect to the change in the position in the sheet surface is suppressed, the diffusion angle distribution can be finely controlled, thereby eliminating uneven brightness. Increases effectiveness. As a result, the difference in diffusion characteristics can be set within a preferable range, and a direct type backlight device with less luminance unevenness can be obtained. In particular, it is preferably used because it exhibits high luminance unevenness elimination performance when the liquid crystal display device is thinned and the number of light sources is reduced.

  Such a diffusion angle can be realized by having a large number of uneven structures on the surface of the diffusion sheet. The uneven structure is, for example, a structure in which a large number of protrusions are provided on the surface. The shape of the protrusions may be approximately conical, approximately spherical, approximately ellipsoidal, approximately lenticular lens, or approximately parabolic, and the protrusions may be regularly or irregularly arranged. It may be. Further, the protrusions may be connected by a continuous curved surface. Further, a pseudo random structure in which irregular irregularities are connected by a continuous curved surface can also be preferably used. This pseudo-random structure is preferably a fine three-dimensional structure characterized by non-planar speckles.

  Further, in the present invention, a large number of uneven structures may be provided on either the light exit surface or the light entrance surface of the diffusion sheet, and the surface side where the uneven structure is not provided is a smooth surface, an uneven surface, a mat surface. It may be. From the viewpoint of improving brightness and reducing unevenness in brightness, the light exit surface side is preferably an uneven surface, and the light entrance surface side is more preferably a smooth surface or a mat surface. In general, when a diffusion sheet is laminated, a very small amount of beads may be applied to the light incident surface within a range that does not impair optical characteristics in order to prevent damage. Such a case is also included in the smooth surface.

  The three-dimensional structure characterized by non-planar speckle is suitable for forming a fine concavo-convex structure of 10 μm or less, which was difficult by machining. In particular, the method of forming irregularities using non-planar speckle is a manufacturing method suitable for changing the diffusion angle in accordance with the region on the diffusion sheet. Also, an isotropic shape such as a microlens and an anisotropic shape such as a lenticular lens can be easily formed. This concavo-convex structure is preferably irregular in height and pitch from the viewpoint of suppressing moire.

  In the present invention, the aspect ratio of the concavo-convex structure is greatly related to suppression of luminance unevenness. Here, the aspect ratio is a value obtained by dividing the height of the concavo-convex structure by the pitch. The pitch means the distance from the top of a certain uneven structure to the top of the adjacent uneven structure. That is, the height and pitch of the concavo-convex structure are greatly related to suppressing luminance unevenness.

  In the present invention, in the aspect ratio distribution diagram in which the horizontal axis represents the relative position in the sheet surface in a predetermined direction within the sheet surface and the vertical axis represents the aspect ratio at the relative position in the sheet surface, the aspect ratio There are a plurality of peak values and a bottom value of the aspect ratio, and an arithmetic average value of diffusion angles between the adjacent peak values and the bottom value is between the adjacent peak value and the bottom value. It is characterized by being larger than the arithmetic average value of the distributed aspect ratio.

  The change in the aspect ratio is strictly linear, curved, if the arithmetic average value of the adjacent peak value and the bottom value is larger than the arithmetic average value of the aspect ratio distributed between the adjacent peak value and the bottom value, The shape may not be stepped, and may be a straight shape, a curved shape, a shape slightly deviated from the stepped shape, or a mixed shape of a straight line and a curved line due to variation in aspect ratio measurement. 23 (a) to 23 (f), diffusion in which the aspect ratio changes in a linear shape, a mixed shape of straight lines and curves, or a staircase shape from a projection region on the light source to a projection region between the light sources. An example of a sheet is shown.

  As for the aspect ratio of each region in the sheet, a region having a relatively high aspect ratio may be disposed immediately above the light source, or a region having a relatively low aspect ratio may be disposed directly above the light source (FIG. 23 ( c), (d)). Moreover, it is preferable that the uneven height between the regions changes smoothly. In particular, a shape including a plurality of peak values continuous in a high aspect ratio region is preferable from the viewpoint of reducing luminance unevenness, and the shape is a linear shape or a downwardly convex curve shape or a mixed shape of a straight line and a downwardly convex curve. It is preferable (FIGS. 23 (c), (d), (f)). Also, from the viewpoint of reducing luminance unevenness, there is a bottom value of the aspect ratio, and the aspect ratio distribution in the low aspect ratio region including the bottom value is a downward convex curve with the bottom value being a minimum value. (FIGS. 23A to 23E).

  Here, the high aspect ratio region is a region showing an aspect ratio of 1/2 or more of the maximum aspect ratio, and the low aspect region is a region showing an aspect ratio of 1/2 or less of the maximum aspect ratio. The arithmetic average value of the aspect ratio distributed between the peak value and the bottom value in the present invention is calculated using the aspect ratio distribution based on the above definition. For example, in FIG. 20, there are a plurality (two) of peak values in one high aspect ratio region.

  Also, the aspect ratio distributed between adjacent peak values and bottom values refers to the aspect ratio existing in the broken line section of FIG. That is, when there are a plurality of peak values, the aspect ratio exists in the section between the position corresponding to the adjacent bottom value and the position corresponding to the peak value.

  In the present invention, the shape in which the height of the concavo-convex structure changes while maintaining the value of the aspect ratio can be performed without changing the optical system, so that it is inexpensive and easy to manufacture a diffusion sheet. It is preferable from the viewpoint.

  In the present invention, it is preferable to use a shape in which the pitch of the concavo-convex structure changes while maintaining the value of the aspect ratio from the viewpoint that moiré is unlikely to occur when a high-definition liquid crystal is used.

  A diffusion sheet having this uneven structure on the surface and changing the diffusion angle according to the region on the diffusion sheet can be specifically manufactured as follows. First, a sub-master type in which a speckle pattern is formed so that the diffusion angle changes depending on the position by irradiating a photosensitive material or a photoresist with a laser beam through a lens or a mask in advance by interference exposure. By changing the distance and size between the members constituting the laser irradiation system and adjusting the size, shape and direction of the speckle pattern, the range of the diffusion angle can be controlled and the concavo-convex structure having different diffusion angles can be recorded. .

  In general, the range of the diffusion angle depends on the average size and shape of the speckle. If speckle is small, the angle range is wide. Moreover, the unit structure of the unevenness is not limited to an isotropic one, and an anisotropic one can be formed, or an uneven structure in which both are combined can be formed. If the speckle is an oval in the horizontal direction, the shape of the angular distribution is an oval in the vertical direction. In this way, a sub-master type in which the diffusion angle changes depending on the position is manufactured. A metal is deposited on the sub-master mold by a method such as electroforming, and a speckle pattern is transferred to the metal to produce a master mold. A speckle pattern is transferred to the light extraction surface of the light-transmitting resin layer by forming the light-transmitting resin layer with ultraviolet rays using the master mold. A detailed manufacturing method of the diffusion sheet in which the diffusion angle is changed depending on the position is disclosed in JP-T-2003-535472. All this content is included here. The diffusion angle may be controlled by changing the aspect ratio (height, pitch) of the concavo-convex structure.

  The unevenness height of the surface structure can be judged from, for example, the pitch, aspect ratio, surface roughness, etc. of the cross-sectional shape of the diffusion sheet observed with a scanning electron microscope. Further, the pitch, aspect ratio, surface roughness, and the like can also be read from an observation image of the diffusion sheet surface by a laser confocal microscope. For example, as the pitch is shorter, the aspect ratio is larger, or the surface roughness is larger, it can be considered that the unevenness height is higher.

  The uneven structure in the diffusion sheet of the present invention may be on the light exit surface side or the light entrance surface side of the sheet. The concavo-convex structure on the light exit surface side is preferable from the viewpoint that the luminance unevenness can be reduced while minimizing the decrease in luminance. Moreover, it is preferable that the concavo-convex structure is on the light incident surface from the viewpoint of easy alignment in the surface of the light source and the diffusion sheet.

  The surface opposite to the surface having the uneven structure may be a smooth surface, an uneven surface, a mat surface, or the like. From the viewpoint of improving luminance and reducing luminance unevenness, it is preferable that the surface opposite to the surface having the concavo-convex structure is a smooth surface. In general, when laminating diffusion sheets, a very small amount of beads may be applied to the surface opposite to the surface having the concavo-convex structure within a range not losing smoothness in order to prevent damage. Such a case is also included in the smooth surface.

  The diffusion angle of the diffusion sheet 15 of the present invention can be controlled in the range of 0.1 degrees to 120 degrees.

  The height of the unevenness is preferably controlled in the range of 0.1 μm to 20 μm from the viewpoint that moire does not occur even when the pitch of the uneven structure is 5 μm, even if the liquid crystal has a high definition (pixel narrowing).

  Furthermore, in the light beam control unit of the present invention, it is preferable that the period of the diffusion angle distribution of the diffusion sheet is equal to the period of the illuminance distribution on the light incident surface of the diffusion sheet. The illuminance distribution on the light incident surface of the diffusion sheet can be measured by, for example, EZContrastXL88 manufactured by ELDIM. Specifically, in the direct type backlight device provided with the diffusion sheet of the present invention, the omnidirectional luminance distribution is measured by setting the focal point of the device at a position where the light incident surface of the diffusion sheet is located, excluding the diffusion sheet. The measurement is performed by repeating the process of obtaining the integrated light intensity (Integrated Intensity) from the result in the in-plane measurement target range.

  FIG. 24 is a schematic view of an example of the direct type backlight device when viewed from obliquely above. In the direct-type backlight device shown in FIG. 24, the diffusion sheet 15 of the present invention is configured such that the diffusion angle is periodically distributed, and the direction in which the diffusion angle is periodically distributed is orthogonal to the longitudinal direction of the CCFL light source 11. It is arranged so that the direction to be matched.

  FIG. 25 is a view showing the interval between light sources and the diffusion angle distribution period of the diffusion sheet in the direct type backlight device of the present invention. In FIG. 24, since the period of the illuminance distribution on the light incident surface of the diffusion sheet is equal to the interval between the light sources, it is preferable that the diffusion angle distribution period in the diffusion sheet surface according to the present invention is substantially equal to the light source interval. In the illuminance distribution on the light incident surface of the diffusion sheet, when the illuminance in the region directly above the light source is high, it is preferable to dispose a high diffusion angle region of the diffusion sheet from the viewpoint of eliminating luminance unevenness. FIG. 25 shows an example of the diffusion angle distribution designed to correspond to the illuminance distribution on the light incident surface of the diffusion sheet. Next, examples carried out to clarify the effects of the present invention will be described, but the present invention is not limited to these examples.

  Below, it demonstrates based on a specific Example and a comparative example.

In addition, the main measured values in the following examples were measured by the following methods.
1. Light Emitting Surface Shape of Light Diffusing Plate 1-1 Surface Shape The light emitting surface side of the light diffusing plate was observed with a Keyence Laser Microscope Generation II VK-9700, and the shape of the convex portion was observed.
1-2 b, c, d value A section cut through a plane perpendicular to one side of the bottom triangle passing through the top of the convex or concave polygonal pyramid (or the bottom of the concave) is the same as 1-1. Observed and observed its shape.
1-3 Inclination angle θ (degree) with respect to the bottom surface (opening surface) of the side surface of the convex portion (concave portion)
In the same manner as in 1-2, cross-sectional observation of the light diffusing plate exit surface was performed, and the inclination angle (θ) formed by the side surface and the bottom surface was measured.
1-4 Angle F (degree) formed by one side of the bottom triangle of the convex portion and the diagonal of the quadrilateral that forms the lattice of the point light source
In the same manner as in 1-1, the triangular pyramid shape of the convex portion on the light exit surface side of the light diffusing plate is observed, and the angle formed by the diagonal lines of the quadrangle that forms the lattice-like arrangement with one side of the convex bottom triangle is F (degrees) was set (FIG. 26).
1-5 Interior angle (α, β, γ) of bottom triangle of convex part
Similarly to 1-1, the light exit surface side of the light diffusing plate was observed with a laser microscope, and the interior angles α, β, and γ of the bottom triangles of the convex portions were obtained (FIG. 10).
2. Total light transmittance T (%)
The light diffusion plate was press-molded to smooth the surface, and then the total light transmittance T was measured by a method based on JIS K7105 using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.
3. Average reflectance R (%)
Using a UV3150 spectrophotometer manufactured by Shimadzu Corporation, light having a wavelength of 450 to 750 nm is incident from the light incident surface side of the light diffusing plate at an incident angle inclined by 7 degrees from the normal to the horizontal surface of the light diffusing plate, and every 1 nm wavelength. The reflectance was obtained, and the average value was defined as the average reflectance R (%).

The average reflectance R (%) was obtained as a relative value with the average reflectance of barium sulfate as a standard plate as 100%. Further, when the surface shape of the light diffusing plate was a convex triangular pyramid, it was obtained by arranging in a spectrophotometer so that at least one side of the bottom triangle faces up and down.
4). Diffusion rate S (%)
After the light diffusing plate is press-molded and the surface is smoothed, the brightness of transmitted light of light incident at a light incident angle of 0 degree in the transmission mode is measured using a GC5000L variable angle photometer manufactured by Nippon Denshoku Industries Co., Ltd. And the diffusivity S was determined by the following formula.

Diffusivity S = 100 × (L (20 degrees) + L (70 degrees)) / (L (5 degrees) × 2)
here,
L (5 degrees) is the transmitted light intensity (cd / m ² ) emitted at an angle of 5 degrees,
L (20 degrees) is the transmitted light luminance (cd / m ² ) emitted at an angle of 20 degrees,
L (70 degrees) is the transmitted light intensity (cd / m ² ) emitted at an angle of 70 degrees,
It is.
5). Average inclination angle U (degrees) of convex / concave depression on diffuser light entrance surface
The light incident surface of the light diffusing plate is observed with a laser microscope, the cross-sectional shape is analyzed with a width of 1000 μm in the longitudinal direction and the short side of the diffusing plate, and an average inclination angle of 1 μm width (inclination angle with respect to the horizontal plane) is continuously continuous with a width of 1000 μm The average inclination angle in the longitudinal direction and the average inclination angle in the short direction were calculated, and the average value was calculated as the average inclination angle U.
6). Average LED distance P
When the area of a quadrangle composed of the four LEDs closest to each other is S, the square root √ (S) is defined as an average LED interval P (mm).
7). Average distance H between top of LED and light diffuser
The distance (mm) between the top of the LED mounted with the LED light source backlight and the light diffusing plate was measured for all the mounted LEDs, and the average value was defined as the average distance H between the top of the LED and the light diffusing plate.
8-1. Uneven brightness (front)
Evaluation was performed both visually and with a luminance meter. The visual evaluation is 0.5 meter directly above the center of the backlight. Specifically, the LED light source backlight is provided with a light diffusing plate and a predetermined optical film, the LED is turned on, and Konica Luminance was measured using a CA2000 from Minolta. The measurement was performed by placing the camera at a position 0.5 meters directly above the center of the LED light source backlight. The screen size of the LED light source backlight used in this example and the comparative example is 306 mm × 306 mm, and the luminance was measured at a resolution of 490 × 490 resolution in the center portion of 250 mm × 250 mm. Then, the luminance unevenness was calculated using the luminance data of the 250 mm × 250 mm portion. Specifically, in the unevenness enhancement mode of Konica Minolta software CA-S20w, when the number of unevenness detection pixels is 83, the S.D. D. The value was determined as a luminance unevenness measurement value.
8-2. Brightness unevenness (perspective)
Luminance unevenness was visually evaluated from a position 0.5 meters directly above the center of the backlight and 0.5 meters horizontally.

In addition, evaluation of the luminance unevenness of the front and perspective was according to the following criteria.
<Evaluation of uneven brightness>
A: Brightness unevenness value ≦ 1.0
Or a level at which no luminance unevenness can be visually observed ○: 1.0 ≦ luminance unevenness value ≦ 2.0
Or the level where the brightness unevenness is slightly visible ×: 2.0 ≦ brightness unevenness value
→ Level of visible brightness unevenness 9. Converted 46-inch LED count The value obtained by dividing the 46-inch size (573 mm × 1018 mm) by the occupied area P ² per LED was used as the converted 46-inch LED count.
10. Diffusion angle (FWHM)
The diffusion angle shown in this example is obtained by entering light from a surface having a fine concavo-convex structure. Angles measured with Inc's Far-field Profiler LD8900. For example, 5 degrees indicates that the FWHM in any direction is 5 degrees. The diffusion sheet described in the examples and comparative examples has a diffusion angle distribution in the sheet surface, and the diffusion angle distribution in the diffusion sheet surface is designed so as to correspond to the illuminance distribution from the light source. A region having a high diffusion angle of the diffusion sheet was disposed and used in a region having a high.

Next, the hot press original plate and the light diffusion light used when manufacturing the light diffusion plate used in this example and the comparative example will be described.
1). Press plate 1
99.97 parts by weight of a polystyrene resin having a refractive index of 1.59 (manufactured by PS Japan, Stylon G9504) and acrylic crosslinked particles having an average particle diameter of 5 μm (Techpolymer MBX-5, manufactured by Sekisui Plastics Co., Ltd.) 0.3 Weight 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. The press plate 1 had a total light transmittance T of 93% and a diffusivity S of 11%.
2). Light diffusion plate 1
The press original plate 1 is sandwiched between press dies shaped into a predetermined shape, put into a press machine, and pressed for 30 minutes under the conditions of a press plate temperature of 180 ° C. and a surface pressure of 100 kg / cm ^2. The sandwiched press mold was replaced with a water-cooled press machine and cooled for 10 minutes. After cooling, a 1.5 mm-thick light diffusing plate shaped into a predetermined shape was taken out from the press mold.

  The obtained light diffusing plate is a mat shape having a concave-convex shape with an average inclination angle of 10 degrees on the surface on the light incident surface side, and a convex triangular pyramid shape (regular three-dimensional shape) in which the light-emitting surface side surface is periodically formed. The shape was a truncated pyramid (see FIG. 27).

  Further, the inclination angle θ of the substantially triangular pyramid of the convex portion of the light diffusing plate is 54 degrees, and the cross-sectional shapes are 94 μm for the B portion, 1 μm for the C portion, 5 μm for the D portion, and the inner angles α, β, Each γ was 60 degrees.

Further, it was confirmed that this light diffusing plate had an average reflectance R of 53% and did not have retroreflective properties.
3). Light diffusion plate 2
The press original plate 1 is sandwiched between press dies shaped into a predetermined shape, put into a press machine, and pressed for 30 minutes under the conditions of a press plate temperature of 180 ° C. and a surface pressure of 100 kg / cm ^2. The sandwiched press mold was replaced with a water-cooled press machine and cooled for 10 minutes. After cooling, a 1.5 mm-thick light diffusing plate shaped into a predetermined shape was taken out from the press mold.

  The obtained light diffusing plate is a mat shape having a concave-convex shape with an average inclination angle of 10 degrees on the surface on the light incident surface side, and a convex triangular pyramid shape (regular three-dimensional shape) in which the light-emitting surface side surface is periodically formed. The shape was a truncated pyramid (see FIG. 27).

  Further, the inclination angle θ of the substantially triangular pyramid of the convex portion of the light diffusing plate is 60 degrees, and the cross-sectional shape is 94 μm for the B portion, 1 μm for the C portion, 5 μm for the D portion, and the inner angles α, β, Each γ was 60 degrees.

In addition, it was confirmed that this light diffusing plate had an average reflectance R of 57% and did not have retroreflection characteristics.
4). Light diffusion plate 3
DSF60 (manufactured by Asahi Kasei E-Materials): a light diffusing plate having a thickness of 1.5 mm, having a mat shape with an average inclination angle U of 10 degrees on both surfaces, a total light transmittance T of 58%, and a diffusivity S Was 83%, and the average reflectance R was 37%.
5). Light diffusion plate 4
DL216 (manufactured by Asahi Kasei E-materials): a light diffusing plate with a thickness of 1.5 mm, having a matte shape with an average inclination angle U of 10 degrees on one side and a linear lens shape on the other side, and the total light transmittance T is The diffuse reflectance S was 25% and the average reflectance R was 38%.

Next, the diffusion sheet used for a present Example and a comparative example is demonstrated.
1]. Diffusion sheet 1
In the diffusion sheet 1, the diffusion angle of the emitted light when a light beam is incident perpendicularly to the sheet surface changes in the plane, and the region having a high diffusion angle has an interval n1: 55.8 mm as shown in FIG. n2: It is arranged in a staggered pattern of 32.2 mm. Furthermore, the diffusion angle distribution of the diffusion sheet 1 on the line Y in FIG. 28 is as shown in FIG. The sheet thickness is 280 μm, and the sheet base material is PET.
2]. Diffusion sheet 2
In the diffusion sheet 2, the diffusion angle of the emitted light when a light beam is incident perpendicularly to the sheet surface changes in the plane, and the region where the diffusion angle is high has an interval n1: 55.8 mm as shown in FIG. n2: It is arranged in a staggered pattern of 32.2 mm. Furthermore, the diffusion angle distribution of the diffusion sheet 2 on the line Y in FIG. 28 is as shown in FIG. The sheet thickness is 270 μm, and the sheet base material is PET.
3]. Diffusion sheet 3
In the diffusion sheet 3, the diffusion angle of the emitted light when the light beam is incident perpendicularly to the sheet surface changes in the plane, and the region where the diffusion angle is high has an interval n1: 52.1 mm as shown in FIG. n2: It is arranged in a 30.1 mm staggered pattern. Further, the diffusion angle distribution of the diffusion sheet 3 on the line Y in FIG. 28 is as shown in FIG. The relative position in the figure is a value obtained by dividing the measured distance from the center of the region where the diffusion angle is high by the LED pitch n1 in the direction parallel to the line Y. The sheet thickness is 280 μm, and the sheet base material is PET.
4]. Diffusion sheet 4
In the diffusion sheet 4, the diffusion angle of the emitted light when a light beam is incident perpendicularly to the sheet surface changes in the plane, and the region where the diffusion angle is high has an interval n1: 37.2 mm as shown in FIG. n2: Arranged in a 21.5 mm staggered pattern. Further, the diffusion angle distribution of the diffusion sheet 4 on the line Y in FIG. 28 is as shown in FIG. The relative position in the figure is a value obtained by dividing the measured distance from the center of the region where the diffusion angle is high by the LED pitch n1 in the direction parallel to the line Y. The sheet thickness is 280 μm, and the sheet base material is PET.

  As the LED type in the light source part of the backlight in this example and the comparative example, a white LED (LM6-EWN1-03-N3 manufactured by CREE) having a light peak angle of 0 degrees manufactured by Cree was used (light emission distribution is shown in the figure). 1).

[Example 1]
As shown in FIG. 16, 104 white LEDs are mounted on the LED substrate (PCB) in a staggered arrangement (arrangement 1) with an LED interval of n1: 55.8 mm and n2: 32.2 mm (n1 / n2 = 0.0). 58 (see FIG. 17)), an LED light source backlight evaluation apparatus having a screen size of 320 × 320 mm was prepared. At this time, the average LED interval P was 30 mm. The corresponding number of converted 46-inch LEDs was 648.

  Next, on the LED substrate (PCB) on which the LED is mounted, Lumirror E6SL (manufactured by Toray) having a diffuse reflectance of 95% is attached as a reflective sheet with double-sided tape, and the distance h between the reflective sheet and the top of the LED h Was kept at 1.9 mm (see FIG. 11). Next, the light reflecting plate is fixed above the reflecting sheet so that the average distance H between the LED uppermost part and the light diffusing plate 1 is 30 mm, and the diffusing sheet 1 is disposed on the light diffusing plate 1, and the LED The light beam control unit 1 was configured on the top.

  Next, two diffusion sheets TDF-127 (manufactured by Toray Seishan) and DBEF-D400 (manufactured by 3M) are arranged in this order on the light beam control unit 1, and the direct type backlight 1 of Example 1 is disposed. Configured.

  The backlight was turned on by passing a current of 20 mA through one LED. Thereafter, the average distance H between the LED uppermost part and the light diffusing plate 1 was shortened by 1 mm, and the shortest distance with favorable front and oblique luminance unevenness was found to be 12 mm. In addition, when it shortened to 11 mm, it resulted in the brightness nonuniformity worsening. The luminance unevenness was measured after the LED was turned on and the backlight was aged for 1 hour.

[Example 2]
The light diffusion unit 2 was disposed on the light diffusion plate 2 to constitute the light beam control unit 2 on the LED. Next, the reflection sheet and the light diffusion plate 2 are fixed above the reflection sheet. Next, on the light control unit 2, two diffusion sheets TDF-127 (manufactured by Toray Seishan) and DBEF (manufactured by 3M) are attached. Arranged in order, a direct type backlight device 2 was configured. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet having favorable front and oblique luminance unevenness and the light diffusing plate 2 was found to be 11 mm. In addition, when it shortened to 10 mm, it resulted in that the brightness nonuniformity worsened.

[Example 3]
The light diffusion unit 1 is disposed on the light diffusion plate 1 to form the light beam control unit 3 on the LED. Next, the reflecting sheet and the light diffusing plate 1 are fixed above the reflecting sheet, and then two diffusing sheets TDF-127 (manufactured by Toray Seishan) are arranged on the light beam control unit 2 to constitute a direct type backlight device 3 did. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the light diffusing plate 2 was found to be 12 mm. In addition, when it shortened to 11 mm, it resulted in the brightness nonuniformity worsening.

[Example 4]
A light diffusing plate 1 was disposed on the diffusing sheet 1 to constitute a light beam control unit 4 on the LED. Next, the reflection sheet and the diffusion sheet 1 are fixed above the reflection sheet. Next, on the light control unit 4, two diffusion sheets TDF-127 (manufactured by Toray Seishan) and DBEF-D400 (manufactured by 3M) are attached. The direct type backlight device 4 was configured by arranging in this order. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the diffusion sheet 1 was found to be 13 mm. In addition, when it shortened to 12 mm, it resulted in that the brightness nonuniformity worsened.

[Example 5]
The light diffusion unit 1 was disposed on the light diffusion plate 1 to form a light beam control unit 5 on the LED. Next, the reflection sheet and the light diffusing plate 1 are fixed above the reflection sheet, and then on the light beam control unit 2, one diffusion sheet TDF-127 (manufactured by Toray Seyhan) and DBEF-D400 (manufactured by 3M) Are arranged in this order to constitute a direct type backlight device 5. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the light diffusing plate 1 was found to be 13 mm. In addition, when it shortened to 12 mm, it resulted in that the brightness nonuniformity worsened.

[Comparative Example 1]
On the light diffusion plate 1, two diffusion sheets TDF-127 (manufactured by Toray Seishan) and DBEF (manufactured by 3M) were arranged in this order, and the direct type backlight device 6 of Comparative Example 1 was configured.

  All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the light diffusing plate 1 was found to be 17 mm. In addition, when it shortened to 16 mm, it resulted in a brightness nonuniformity worsening.

[Comparative Example 2]
As the light diffusing plate, a light diffusing plate 3: DSF60 (manufactured by Asahi Kasei E-Materials) having an embossed surface with a total light transmittance of 58% is used. On the light diffusing plate 3, the diffusing sheet 1 and the diffusing sheet TDF-127 are used. Two sheets (manufactured by Toray Seishan) and DBEF (manufactured by 3M) were arranged in this order to constitute a direct type backlight device 7 of Comparative Example 2. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the light diffusing plate 3 was found to be 18 mm. In addition, when it shortened to 17 mm, it resulted in that the brightness nonuniformity worsened.

[Comparative Example 3]
As the light diffusing plate, a light diffusing plate 4: DL216 (manufactured by Asahi Kasei E-Materials) with a single-sided linear lens embossed with a total light transmittance of 72% of light incident on the lens surface is used. 1. Two diffusion sheets TDF-127 (manufactured by Toray Sehan) and DBEF-D400 (manufactured by 3M) were arranged in this order to constitute a direct type backlight device 8 of Comparative Example 2. All other conditions were the same as in Example 1, and luminance unevenness measurement was performed. The shortest distance between the reflection sheet with favorable front and oblique luminance unevenness and the light diffusing plate 4 was found to be 18 mm. In addition, when it shortened to 17 mm, it resulted in that the brightness nonuniformity worsened.

  Table 1 shows the evaluation results of the obtained optical control unit and direct type backlight device.

In Examples 1 and 2, it can be seen that luminance unevenness (front) and luminance unevenness (perspective) can be significantly improved as compared with Comparative Examples 1, 2, and 3.

  In Examples 3, 4 and 5, it can be seen that the luminance unevenness (front) and luminance unevenness (perspective) equivalent to those of Comparative Examples 1, 2, and 3 were achieved while suppressing H.

[Example 6]
When the luminance unevenness measurement was performed under the condition that the distance H between the LED uppermost part of the direct type backlight device 4 of Example 4 and the diffusion sheet 1 was 12 mm, the luminance unevenness was a result of x in both the front and diagonal directions. Therefore, while H is fixed at 12 mm, the average LED interval P is shortened by 1 mm from 30 mm, and the average interval P of the pattern of the diffusion angle of the diffusion sheet 1 (the calculation method is based on the calculation method of the average LED interval). ) Was also shortened by 1 mm (while maintaining the diffusion angle distribution of FIG. 29), the result was that the brightness unevenness was good at P = 28 mm (the diffusion sheet 1 was replaced with the diffusion sheet 3). The number of converted 46 inch LEDs corresponding to P = 28 mm was 744. The results are shown in Table 2.

[Example 7]
When the brightness unevenness measurement was performed under the condition that the distance H between the LED uppermost part of the direct type backlight device 5 and the light diffusing plate 1 was 12 mm, the brightness unevenness was indicated as x in both the front and diagonal directions.
Therefore, under the condition that H is fixed at 12 mm, the average LED interval P is shortened by 1 mm from 30 mm, and the average interval P of the pattern of the diffusion angle (the calculation method is based on the calculation method of the average LED interval) is also 1 mm. As a result of shortening (while maintaining the diffusion angle distribution of FIG. 29), the result was that the brightness unevenness was good at P = 28 mm (the diffusion sheet 1 was replaced with the diffusion sheet 3). The number of converted 46 inch LEDs corresponding to P = 28 mm was 744. The results are shown in Table 2.

[Comparative Example 4]
When the luminance unevenness measurement was performed under the condition that the distance H between the LED uppermost part of the direct type backlight device 6 and the light diffusing plate 1 was 12 mm, the luminance unevenness was indicated as x in both the front and diagonal directions.

  Therefore, when the average LED interval P was shortened by 1 mm from 30 mm under the condition that H was fixed at 12 mm, the brightness unevenness was good at P = 23 mm. The number of converted 46 inch LEDs corresponding to P = 23 mm was 1103. The results are shown in Table 2.

[Comparative Example 5]
When the brightness unevenness measurement was performed under the condition that the distance H between the LED uppermost part of the direct type backlight device 7 and the light diffusion plate 1 was 12 mm, the brightness unevenness was indicated as x in both the front and diagonal directions.
Therefore, under the condition that H is fixed at 12 mm, the average LED interval P is shortened by 1 mm from 30 mm, and the average interval P of the pattern of the diffusion angle (the calculation method is based on the calculation method of the average LED interval) is also 1 mm. When shortening (while maintaining the diffusion angle distribution of FIG. 29), P = 20 mm and the result of good luminance unevenness was obtained (the diffusion sheet 1 was replaced with the diffusion sheet 4). The number of converted 46-inch LEDs corresponding to P = 20 mm was 1458. The results are shown in Table 2.

[Comparative Example 6]
When the luminance unevenness was measured under the condition that the distance H between the LED uppermost part of the direct type backlight device 8 and the light diffusing plate 1 was 12 mm, the luminance unevenness was indicated as x in both the front and diagonal directions.
Therefore, under the condition that H is fixed at 12 mm, the average LED interval P is shortened by 1 mm from 30 mm, and the average interval P of the pattern of the diffusion angle (the calculation method is based on the calculation method of the average LED interval) is also 1 mm. When shortening (while maintaining the diffusion angle distribution of FIG. 29), P = 20 mm and the result of good luminance unevenness was obtained (the diffusion sheet 1 was replaced with the diffusion sheet 4). The number of converted 46-inch LEDs corresponding to P = 20 mm was 1458. The results are shown in Table 2.

In Examples 1, 5 and 6, it was possible to significantly reduce the number of point light sources used while achieving the same luminance unevenness (front) and luminance unevenness (perspective) as in Comparative Examples 4, 5, and 6. I understand that.

  Since the optical control unit of the present invention can realize remarkably excellent luminance and luminance uniformity (front and perspective) with a desired backlight thickness and a small optical film, for example, LED light source liquid crystal televisions, LED light source signs. It is useful for a wide range of applications such as LED light source illumination.

B: A portion satisfying (1 ′) and (2 ′) 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 convex triangular pyramid shaped bottom triangle shaped on the light diffusion plate surface β: Inner angle of the convex triangular pyramid shaped bottom triangle shaped on the light diffusion plate surface γ: Applied to the light diffusion plate surface Formed convex triangular pyramid shaped bottom triangle interior angle n1: LED staggered LED distance n2: LED staggered LED distance F: convex triangular pyramid shaped bottom triangle shaped on the light diffusion plate surface The angle between one side and the grid of the point light source 1,3 High diffusion angle region 2,4 Low diffusion angle region 11 CCFL (cold cathode tube)
12 LED (Light Emitting Diode)
DESCRIPTION OF SYMBOLS 13 Reflective sheet 14 Diffusion plate 15 Diffusion sheet 16 Lens sheet 17 Prism sheet 18 Reflective polarizing sheet

Claims (32)

A light diffusing plate having a plurality of convex portions having a substantially triangular pyramid shape whose bottom surface is a triangle and having no retroreflective property with respect to visible light;
A diffusion sheet in which a diffusion angle of emitted light when a light beam is incident perpendicularly to the sheet surface periodically changes along a predetermined direction in the sheet surface;
Light control unit with The light control unit according to claim 1, wherein the light diffusion plate satisfies the following condition (1):
Condition (1): The average reflectance R when light having a wavelength of 450 to 750 nm is incident at an incident angle inclined by 7 degrees with respect to the normal to the horizontal plane of the light diffusion plate from the light incident surface side is 40% or more. . The inclination angle θ with respect to the bottom surface of the substantially triangular pyramidal side surface of the light diffusing plate and the refractive index A of the material forming the convex portion satisfy the following formulas (1) and (2):
(1) θ ≧ −40A + 115.2
(2) θ ≦ 25A + 22.25
The light beam control unit according to claim 1 or 2.   The substantially triangular pyramid-shaped convex portion was cut along a plane perpendicular to one side of the triangle on the bottom surface of the convex portion, passing through its apex (or the center of the top triangle when the convex portion is a triangular frustum shape). 4. The light beam control unit according to claim 1, wherein, in a cross section, an angle θ ′ formed by a tangential plane of one side surface of the convex portion and a bottom surface is 50 to 62 °. 5. The light beam control unit according to claim 4, wherein the convex portion of the light diffusion plate satisfies the following formulas (5) and (6).
(5) 0 ≦ c / b ≦ 0.2
(6) 0 ≦ d / b ≦ 0.5
(Here, b, c, and d are one side of the triangle on the bottom surface of the convex part, passing through the convex part and passing through its apex (or the center of the top triangle when the convex part is a triangular frustum shape). In the cross section cut by a plane perpendicular to the length of the projected line segment projected from B, the length of the projection line B projected on the horizontal plane, the angle B ′ formed by the tangent plane of the side surface of the convex portion and the bottom surface satisfying 50 to 62 degrees The length of the projection line segment projected on the horizontal plane of the portion C on the hem side and the length of the projection line segment projected on the horizontal plane of the portion D on the top side of B.)   The light control unit according to claim 5, wherein the sum of b, c and d is 5 to 200 μm. The light diffusing plate is composed of at least (a) a lens layer and (b) a diffusing layer,
The (a) lens layer and (b) diffusion layer are either the same layer, a continuous layer, or a separate layer,
The light control unit according to claim 1, wherein the convex portion is formed on a surface of the lens layer (a).   The light control unit according to claim 7, wherein the (b) diffusion layer includes a transparent resin and a diffusing agent, has a total light transmittance T of 85 to 95% and a diffusion rate S of 5 to 40%. The light diffusing plate comprises only (a) a lens layer and (b) a diffusing layer,
The sum of the thicknesses of the (a) lens layer and (b) diffusion layer is 0.5 to 3.0 mm.
The light beam control unit according to claim 7 or 8. Of the diffusion sheet,
In the diffusion angle distribution diagram in which the horizontal position is the relative position in the sheet surface in the predetermined direction and the vertical axis is the diffusion angle at the relative position in the sheet surface, the peak value of the diffusion angle and the diffusion angle There are a plurality of bottom values, and the arithmetic average value of the diffusion angles between the adjacent peak values and the bottom value is distributed between the adjacent peak values and the bottom value. The light control unit according to claim 1, wherein the light control unit is larger than the value. Of the diffusion sheet,
In the diffusion angle distribution diagram in which the horizontal axis represents the relative position within the sheet surface in the predetermined direction and the vertical axis represents the diffusion angle at the relative position within the sheet surface, a plurality of peaks in one high diffusion angle region. The light control unit according to claim 1, wherein the light control unit includes a value.   The light beam control unit according to claim 11, wherein a diffusion angle distribution between adjacent peaks in the high diffusion angle region is linear.   12. The light beam control unit according to claim 11, wherein the diffusion angle distribution between adjacent peaks in the high diffusion angle region is a downwardly convex curve shape or a mixed shape of a curve and a straight line. Of the diffusion sheet,
In the diffusion angle distribution diagram in which the horizontal axis represents the relative position within the sheet surface in the predetermined direction and the vertical axis represents the diffusion angle at the relative position within the sheet surface, there is a bottom value of the diffusion angle, The light beam control according to any one of claims 1 to 9, wherein a diffusion angle distribution in a low diffusion angle region including a bottom value is a downwardly convex curve with the bottom value being a minimum value. unit.   The light beam control unit according to any one of claims 1 to 14, wherein a diffusion angle of diffused light emitted from the diffusion sheet is in a range of 0.1 ° to 120 °. The diffusion sheet is
A diffusion sheet in which an aspect ratio of a concavo-convex structure provided on a sheet surface periodically changes along a predetermined direction in the sheet surface, and a relative position in the sheet surface in the predetermined direction of the diffusion sheet In the aspect ratio distribution diagram in which the horizontal axis is taken and the aspect ratio at the relative position in the sheet surface is taken as the vertical axis, there are a plurality of peak values of the aspect ratio and bottom values of the aspect ratio, and the adjacent peaks The arithmetic average value of the diffusion angle between the value and the bottom value is larger than the arithmetic average value of the aspect ratio distributed between the adjacent peak value and the bottom value. The light beam control unit according to any one of 9. The diffusion sheet is
A diffusion sheet in which an aspect ratio of a concavo-convex structure provided on a sheet surface periodically changes along a predetermined direction in the sheet surface, and a relative position in the sheet surface in the predetermined direction of the diffusion sheet In the aspect ratio distribution diagram in which the horizontal axis is taken and the aspect ratio at the relative position in the sheet plane is taken as the vertical axis, a plurality of peak values are included in one high aspect ratio region. The light beam control unit according to any one of 9.   The light beam control unit according to claim 17, wherein the aspect ratio distribution between adjacent peaks in the high aspect ratio region is linear.   18. The light beam control unit according to claim 17, wherein the aspect ratio distribution between adjacent peaks in the high aspect ratio region is a downwardly convex curve shape or a mixed shape of a curve and a straight line. The diffusion sheet is
A diffusion sheet in which an aspect ratio of a concavo-convex structure provided on a sheet surface periodically changes along a predetermined direction in the sheet surface, and a relative position in the sheet surface in the predetermined direction of the diffusion sheet In the aspect ratio distribution diagram in which the horizontal axis represents the aspect ratio at the relative position in the sheet surface and the vertical axis represents the aspect ratio distribution in the low aspect ratio region including the bottom value and the bottom value of the aspect ratio. 10. The light beam control unit according to claim 1, wherein the light beam control unit has a downwardly convex curved shape having the bottom value as a minimum value. 11.   The light beam control unit according to any one of claims 16 to 20, wherein the light emitting unit has a shape in which the aspect ratio changes as the height of the uneven structure changes.   21. The light beam control unit according to claim 16, wherein the light beam control unit has a shape in which the aspect ratio changes as the pitch of the uneven structure changes.   The light control unit according to any one of claims 16 to 22, wherein the concavo-convex structure is a concavo-convex structure formed using a speckle pattern by interference exposure. Of the diffusion sheet,
The difference between the maximum value and the minimum value of the diffusion angle in a diffusion angle distribution diagram in which the horizontal axis represents the relative position in the sheet surface in the predetermined direction and the vertical axis represents the diffusion angle at the position in the sheet surface. The light beam control unit according to any one of claims 1 to 23, wherein the angle is not less than 40 degrees and not more than 80 degrees. Multiple light sources;
The light beam control unit according to any one of claims 1 to 24, disposed above the light source;
A reflective sheet disposed below the light source;
Direct-type backlight device with   The direct type backlight device according to claim 25, wherein the light source is an LED point light source.   The direct type backlight device according to claim 25 or 26, wherein the diffuse reflectance of the reflective sheet is 90% or more.   The direct type backlight device according to claim 26, wherein the plurality of point light sources are periodically arranged in a grid pattern. The plurality of point light sources are periodically arranged in a lattice pattern,
The plurality of convex portions of the light diffusing plate are periodically arranged so that one side of the triangle of the bottom surface of the adjacent convex portion is parallel to each other, and the plurality of point light sources and the light diffusing plate are Stacked so that one side of the triangle on the bottom surface of each convex portion of the light diffusing plate is parallel to the diagonal of the quadrangle that forms the lattice of the lattice arrangement of the point light sources,
The direct type backlight device according to claim 26. The plurality of convex portions have a substantially triangular pyramid shape whose bottom surface is an isosceles triangle,
The plurality of convex portions of the light diffusing plate are periodically arranged such that the bases of the isosceles triangles on the bottom surfaces of adjacent convex portions are parallel to each other, and the plurality of point light sources and the light diffusing plate are The bases of the isosceles triangles on the bottom surface of each convex portion of the light diffusing plate are stacked so as to be parallel to the diagonal lines of the quadrangle constituting the lattice of the lattice arrangement of the point light sources.
The direct type backlight device according to claim 29. A direct backlight device comprising a plurality of point light sources and the light beam control unit according to any one of claims 1 to 24,
The plurality of point light sources are periodically arranged in a lattice pattern,
The plurality of convex portions are periodically arranged such that one side of an equilateral triangle on the bottom surface of adjacent convex portions is parallel to each other, and the plurality of point light sources and the light diffusing plate are made of a light diffusing plate. Stacked so that one side of the equilateral triangle on the bottom surface of each convex part is parallel to the diagonal of the quadrangle constituting the lattice of the lattice arrangement of the point light sources,
Direct type backlight device.   A liquid crystal display device comprising: a liquid crystal display panel; and the direct type backlight device according to any one of claims 25 to 31 for supplying light to the liquid crystal display panel.