JP2012022272A - Light diffusion sheet and light source unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion sheet capable of reducing front luminance unevenness and oblique luminance unevenness.SOLUTION: A light diffusion sheet allows a diffusion angle of emission light to be periodically changed along a predetermined direction in a sheet plane when an incident beam is perpendicular to the sheet plane. In a diffusion angle distribution chart, in which the lateral axis represents a relative position in a sheet plane in a predetermined direction and the vertical axis represents a diffusion angle in the relative position in the plane, a plurality of peak values of the diffusion angle and a plurality of bottom values of the diffusion angel exist, an arithmetic average value of the diffusion angles between neighboring peak value and bottom value is larger than an arithmetic average value of the diffusion angles at all the points distributed between the neighboring peak value and bottom value, and the following conditions (a) to (c) are satisfied: (a) a bottom value of the diffusion angle of equal to or greater than 0.1° and smaller than 40°; (b) a peak value of the diffusion angle from 40° to 75°; and (c) a difference between the bottom value and the peak value from 20° to 70°.

Description

  The present invention relates to a diffusion sheet and a light source unit used for back lighting of a liquid crystal display device or the like.

  Currently, liquid crystal display devices are used in a wide range of fields such as mobile phones, PDA terminals, digital cameras, televisions, personal computer displays, and notebook computers. In a liquid crystal display device, for example, a light source unit such as a backlight unit is arranged behind a liquid crystal display panel, and an image is displayed by supplying light from the light source unit to the liquid crystal display panel. The light source unit used in such a liquid crystal display device is required not only to supply uniform light to the liquid crystal display panel but also to supply as much light as possible in order to make the display image easy to see. In other words, the light source unit is required to have optical characteristics such as excellent light diffusibility and high brightness.

  In the conventional light source unit, for example, in order to make the distribution of light incident on the liquid crystal display panel uniform over the entire panel, a method of imparting an uneven shape to the light guide plate or the diffusion plate has been used. As a method for imparting the concavo-convex shape, there are a method in which a resin is injection-molded using a mold, and a method in which a concavo-convex structure is processed into a roll with a diamond blade and is then extruded.

  Here, the mechanical unevenness forming method as described above has a problem that it takes a lot of time and the manufacturing cost is high. Moreover, in the above uneven | corrugated formation method, there existed a problem that the structure of about several dozen micrometers was a limit, and it was not easy to improve the uniformity of a shape.

  On the other hand, the concave / convex shape is recorded on the photosensitive medium by the speckle of the laser beam, a mold for pattern transfer is manufactured, and the surface of the light guide plate for the large liquid crystal display device of the direct type using this mold. An invention is disclosed in which irregularities are formed on a hologram light guide plate (see FIG. 41 of Patent Document 1).

  In addition, as a diffusion sheet having a high effect of reducing uneven brightness, a diffusion sheet in which a plurality of diffusion layers having different degrees of light diffusion in the plane are distributed, or a light diffusion angle in a light projection area is a projection area between light sources There has been proposed a diffusion sheet having a large number of concavo-convex structures on the light exit surface which are higher than the light diffusion angle in (see Patent Document 2 and Patent Document 3).

Japanese Patent Laid-Open No. 2001-23422 JP 2007-3852 A JP 2009-244846 A

  However, in recent years, liquid crystal display devices have been made thinner, and the distance between a light source and an optical sheet (such as the above-described hologram light guide plate, diffusion sheet) for diffusing the light source light has become shorter. A method of reducing the number of light sources of the light source unit is also used for cost reduction and power consumption reduction. Here, as compared with the conventional light source, the larger the ratio (p / h) of the light source pitch (p) and the light source-optical sheet distance (h), that is, the smaller h is (as shown in FIG. 19A). h ′) and / or p becomes larger (p ′ in FIG. 19B), the luminance unevenness of the backlight becomes more conspicuous. Here, luminance unevenness refers to the phenomenon in which the light and darkness derived from the intensity distribution of the light source illuminance can be seen in the screen, and “frontal luminance unevenness” when viewing the screen from the front and “oblique luminance when viewing from the diagonal. It can be divided into “unevenness”. If front luminance unevenness or oblique luminance unevenness occurs, it is not preferable for a liquid crystal display device. The conventional methods disclosed in the above-mentioned patent documents cannot sufficiently reduce the front luminance unevenness and the oblique luminance unevenness, and cannot always sufficiently cope with the thinning of the liquid crystal display device and the reduction in the number of light sources. There is.

  The present invention has been made in view of such a point, and an object thereof is to provide a diffusion sheet, a light source unit, and a liquid crystal display device that can reduce front luminance unevenness and oblique luminance unevenness.

The diffusion sheet of the present invention is 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, and the predetermined direction In the diffusion angle distribution diagram in which the horizontal axis represents the relative position in the sheet surface and the vertical axis represents the diffusion angle at the relative position in the sheet surface, the peak value of the diffusion angle and the bottom value of the diffusion angle There is a plurality, and the arithmetic average value of the diffusion angles between the adjacent peak value and the bottom value is the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak value and the bottom value. It is larger and satisfies the following conditions (a) to (c).
(A) The diffusion angle of the bottom value is 0.1 ° or more and less than 40 ° (b) The diffusion angle of the peak value is 40 ° or more and 75 ° or less (c) The difference between the bottom value and the peak value is 20 ° or more. 70 ° or less

  In the diffusion sheet of the present invention, it is preferable that one diffusion angle region includes a plurality of peaks in the diffusion angle distribution diagram, and the diffusion angle distribution between adjacent peaks in the high diffusion angle region is linear. .

  In the diffusion sheet of the present invention, the diffusion angle distribution diagram includes a plurality of peaks in one high diffusion angle region, and the diffusion angle distribution between adjacent peaks in the high diffusion angle region is a downward convex curve. Or it is preferable that it is a mixed shape of a curve and a straight line.

  In the diffusion sheet of the present invention, the peak value of the diffusion angle and the bottom value of the diffusion angle alternately and periodically, the arithmetic average of the diffusion angle at two points of the adjacent peak value and the bottom value The value is larger than the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak value and the bottom value, and the distribution of the diffusion angles includes the peak value and has a convex curve shape It is preferable that the first section and the second section in which the distribution of the diffusion angle includes the bottom value and has a downward convex curve shape.

  In the diffusion sheet of the present invention, it is preferable that the diffusion angle is generated by an uneven structure formed on the surface of the diffusion sheet.

  In the diffusion sheet of the present invention, the concavo-convex structure is preferably a concavo-convex structure formed by using a speckle pattern by interference exposure.

  The light source unit of the present invention includes two or more light sources and the diffusion sheet disposed above the light sources, and a standard deviation value in luminance unevenness when viewed from an oblique direction is 0.008 or less. It is preferable that

  In the light source unit of the present invention, the light source is preferably a linear light source.

  In the light source unit of the present invention, the light source is preferably a point light source.

  In the light source unit of the present invention, it is preferable that the period of the diffusion angle distribution of the diffusion sheet is substantially equal to the period of the illuminance distribution on the light incident surface of the diffusion sheet.

  In the light source unit of this invention, it is preferable to provide the diffusion plate which is arrange | positioned between the said diffusion sheet and the said light source, and contains a diffusing agent inside, and the reflection sheet arrange | positioned under the said light source.

  In the light source unit of the present invention, it is preferable to include a lens sheet disposed above the diffusion sheet.

  In the light source unit of the present invention, it is preferable that a prism sheet is provided above the diffusion sheet.

  In the light source unit of this invention, it is preferable to provide the reflective polarizing sheet arrange | positioned above the said diffusion sheet.

  The liquid crystal display device of the present invention comprises a liquid crystal display panel and the light source unit that supplies light to the liquid crystal display panel.

  According to the diffusion sheet, the light source unit, and the liquid crystal display device of the present invention, it is possible to reduce front luminance unevenness and oblique luminance unevenness.

(A), (b) is a top view which shows the area | region directly above the light source and the area | region between light sources which concern on embodiment of this invention. (A), (b) 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 an example of the diffusion angle distribution in the diffusion sheet which concerns on embodiment of this invention, and is explanatory drawing of concepts, such as a peak value, a bottom value, and an arithmetic mean value. (A)-(f) is a figure which shows distribution with respect to the relative position in the diffusion sheet surface of the diffusion angle of the diffusion sheet which concerns on embodiment of this invention. It is explanatory drawing of the high diffusion angle area | region and low diffusion angle area | region of the diffusion sheet which concerns on embodiment of this invention. It is explanatory drawing of the high diffusion angle area | region and low diffusion angle area | region of the diffusion sheet which concerns on embodiment of this invention. It is explanatory drawing of the high diffusion angle area | region and low diffusion angle area | region of the diffusion sheet which concerns on embodiment of this invention. (A), (b) is a figure which shows schematic structure of the light source unit which concerns on embodiment of this invention. (A), (b) is a figure which shows schematic structure of the light source unit which concerns on embodiment of this invention. (A), (b) is a typical perspective view which shows the structure of the light source unit which concerns on embodiment of this invention. It is a figure which shows distribution with respect to the relative position with the light source in the diffusion sheet surface of the diffusion angle in the diffusion sheet of the light source unit which concerns on embodiment of this invention. (A)-(c) is a figure which shows the other example of a structure of the light source unit which concerns on embodiment of this invention. (A)-(d) is a figure which shows the other example of a structure of the light source unit which concerns on embodiment of this invention. (A)-(d) is a figure which shows the other example of a structure of the light source unit which concerns on embodiment of this invention. (A), (b) is a figure which shows the other example of a structure of the light source unit which concerns on embodiment of this invention. It is a figure which shows arrangement | positioning of the LED light source used for the Example and comparative example of this invention. (A), (b) is a figure which shows the relationship between the diffusion angle of a diffusion sheet, and light source distance in the Example of this invention. (A)-(c) is a figure which shows the relationship between the diffusion angle of a diffusion sheet, and light source distance in the comparative example of this invention. (A), (b) is a cross-sectional schematic diagram which shows arrangement | positioning of the light source unit which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, in each drawing, unless otherwise specified, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawing, and the dimensional ratio in the drawing is not limited to the illustrated ratio.

  First, referring to FIGS. 1A and 1B, a projection area of a light source (hereinafter referred to as an area immediately above the light source) and a projection area between light sources (hereinafter referred to as an inter-light source area) of the diffusion sheet according to the present embodiment. ). FIGS. 1A and 1B are plan views showing a region immediately above the light source and a region between the light sources of the diffusion sheet according to the present embodiment. A plurality (at least two) of light sources are arranged. As the light source, a line light source such as a cold cathode fluorescent lamp (CCFL) 11 as shown in FIG. 1A, or a point light source such as an LED (light emitting diode) 12 or a laser as shown in FIG. 1B. Can be used. When three cold-cathode tubes 11 are arranged in parallel as light sources, a rectangular area in plan view along the line direction of the cold-cathode tubes 11 is a region A1 immediately above the light source, and a region between the light source regions A1 is a region between the light sources. A2. In addition, when a plurality of LEDs 12 are used as the light source, a region in a circular shape in plan view near the outer peripheral edge of each LED 12 is the region A1 directly above the light source, and a region between the regions A1 directly above the light sources is an inter-light source region A2. 1A and 1B show an example in which the entire area of the diffusion sheet 1 is divided into an area A1 immediately above the light source and an area A2 between the light sources, but the area A1 directly above the light source. The light source may be divided so as to provide an area other than the inter-light source area A2. In addition, the inter-light source region A2 may not be adjacent to the region A1 directly above the light source, and may include a region located in the middle of the adjacent light sources.

  In the diffusion sheet according to the present invention, the diffusion angle of the emitted light when a light beam enters perpendicularly to the diffusion sheet surface periodically changes along a predetermined direction in the diffusion sheet surface. When this diffusion sheet is disposed above the light source, it is preferable to match the period of the diffusion angle of the diffusion sheet with the projection area period composed of the region directly above the light source and the region between the light sources. Thereby, the front luminance unevenness and the oblique luminance unevenness can be reduced.

  In the present invention, the “diffusion angle” refers to an angle (FWHM: Full Width Half Maximum) that is twice the angle (half-value angle) at which the transmitted light intensity attenuates to half the peak intensity (see FIG. 2A). . This diffusion angle is, for example, a Gotonometric Radiometers Real-Time Far-Field Angular Profiles Model LD8900 (hereinafter referred to as LD8900) manufactured by Photon, and transmitted light with respect to light incident from the uneven surface side from the normal direction of the uneven surface of the diffusion sheet. It can be determined by measuring the angular distribution of intensity. Here, the normal direction of the diffusion sheet refers to the direction shown in FIG.

  Moreover, as the diffusion sheet according to 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. 3 is a diagram showing an example of the distribution of diffusion angles in the diffusion sheet according to the present invention. In this diffusion sheet, the diffusion angle of outgoing light when a light beam enters perpendicularly to the diffusion sheet surface periodically changes along a predetermined direction in the diffusion sheet surface. In the diffusion angle distribution diagram shown in FIG. 3, the horizontal axis represents the relative position within the diffusion sheet surface in a predetermined direction within the diffusion sheet surface, and the vertical axis represents the diffusion angle at the relative position within the diffusion sheet surface. In the diffusion sheet according to the present invention, there are a plurality of diffusion angle peak values and diffusion angle bottom values (one is shown in FIG. 3). The peak value refers to the highest diffusion angle value in one cycle of the diffusion angle distribution, and the bottom value refers to the lowest diffusion angle value in one cycle of the diffusion angle distribution.

  In the diffusion sheet according to the present invention, in such a diffusion angle distribution diagram, the arithmetic average value of the diffusion angles between the adjacent peak value and the bottom value is all distributed between the adjacent peak value and the bottom value. Greater than the arithmetic mean value of the diffusion angle at a point. The “all points” described here mean all the measurement points.

  Regarding the diffusion angle in the diffusion sheet, a region having a relatively high diffusion angle may be disposed in the region directly above the light source, or a region having a relatively low diffusion angle may be disposed in the region directly above the light source. Moreover, it is preferable that the diffusion angle between each area | region changes smoothly.

  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 at all points distributed between the adjacent peak value and the bottom value, the light to be diffused It is possible to reduce the luminance unevenness in accordance with the attenuation of. FIGS. 4A to 4F show examples of the diffusion sheet in which the diffusion angle is changed to a linear shape, a curved shape, or a mixed shape of a straight line and a curved line.

  In particular, a shape including a plurality of continuous peak values in the high diffusion angle region is preferable from the viewpoint of reducing luminance unevenness, and the shape is a straight line or a downwardly convex curve, or a mixture of a straight line and a downwardly convex curve. The shape is preferable (FIGS. 4D and 4F). Such a pattern is particularly effective when the light source is a linear light source. Also, from the viewpoint of reducing luminance unevenness, 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 a downward convex curve with the bottom value being the minimum value (see FIG. 4 (a)-(d)). In the example shown in FIG. 4C, the first interval D2 in which the diffusion angle distribution includes a peak value and has an upward convex curve shape, and the diffusion angle distribution includes a bottom value and the downward convex curve shape. And such a pattern is particularly effective when the light source is a point light source. For example, when an LED (light emitting diode) is used as the point light source, the diffusion angle in the diffusion sheet according to the present invention can be designed with respect to the illuminance distribution regardless of the light emission angle.

  Here, the high diffusion angle region is an angle region where the diffusion angle is larger than the arithmetic average value of the maximum value of the peak value and the minimum value of the bottom value, and the low diffusion angle region is the maximum value of the peak value of the diffusion angle. The angle area is smaller than the arithmetic average value of the minimum bottom value. The arithmetic average value of the peak value and the bottom value in the present invention is calculated using the distribution of diffusion angles 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. 3, 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 D1 in 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.

  In addition, “periodically” means that the repeated patterns are compared with each other, and the peak value corresponding to the same repetition and the displacement from the start point of the period giving the peak value, and the bottom value and the bottom value are given. If the displacement from the starting point of the cycle is within a range of ± 15% (preferably within 10%, more preferably within 5%) of the average value of all the repeated patterns, it periodically changes. Shall. The direction indicating the periodicity may be at least one in the diffusion sheet surface, and can be specified by creating a distribution of diffusion angles on the diffusion sheet surface. In the present invention, the diffusion angle of a plurality of repeated peak values is preferably such that the difference in the diffusion angles of all measured peak values is within 5 °, more preferably within 3 °, and within 2 °. Most preferably it is. The same applies to the bottom value.

  Next, arrangement examples of the high diffusion angle region and the low diffusion angle region of the diffusion sheet 1 according to the present embodiment will be described with reference to FIGS. 5-7 is explanatory drawing of the high diffusion angle area | region and low diffusion angle area | region of the diffusion sheet 1 which concerns on this Embodiment. In the example shown in FIG. 5, the high diffusion angle region A3 and the low diffusion angle region A4 alternately change in the cycle C in the x-axis direction within the surface of the diffusion sheet 1. The diffusion angle in the surface of the diffusion sheet 1 has a peak value in the vicinity of the virtual line L1 in each high diffusion angle region A3, and a bottom value in the vicinity of the virtual line L2 in each low diffusion angle region A4.

  In the example shown in FIG. 6, in the Y-axis direction within the diffusion sheet 1, the region A5 changes from the high diffusion angle region A3 to the low diffusion angle region A4 from one end side to the other end side of the diffusion sheet 1. And the region A6 that changes from the low diffusion angle region A4 to the high diffusion angle region A3 alternately changes in the period C. That is, in the example shown in FIGS. 5 and 6, the high diffusion angle region A3 and the low diffusion angle region A4 periodically change as shown in FIG. 4 in the x-axis direction in the surface of the diffusion sheet 1. Show. Such a pattern is preferably used for a line light source, but is also used for a point light source in some cases.

  FIG. 7 is a diagram illustrating an example in which the high diffusion angle region A3 and the low diffusion angle region A4 periodically exist in the x-axis direction and the y-axis direction in the surface of the diffusion sheet 1. In the example shown in FIG. 7, in the diffusion sheet 1 surface, circular high diffusion angle regions A3 exist in a lattice shape, and low diffusion angle regions A4 exist between the high diffusion angle regions A3. The diffusion angle in the surface of the diffusion sheet 1 has a peak value in the vicinity of the center point P1 of each high diffusion angle region A3, and a bottom value in the low diffusion angle region A4. Also in the example shown in FIG. 7, the diffusion angle changes as shown in FIG. 4 in the cross section of the diffusion sheet 1 in the x-axis direction or the y-axis direction. Such a pattern is preferably used for a point light source, but may be used for a line light source.

The diffusion sheet according to the present invention must satisfy the following conditions (a) to (c).
(A) Bottom value diffusion angle is 0.1 ° to less than 40 ° (b) Peak value diffusion angle is 40 ° to 75 ° (c) Difference between bottom value and peak value is 20 ° to 70 °

  In the diffusion sheet according to the present invention, (a) the diffusion angle of the bottom value is 0.1 ° or more makes it easy to produce the diffusion sheet, and if it is less than 40 °, the effect of suppressing luminance unevenness is improved. Further, from the viewpoint of suppressing the front and oblique luminance unevenness, the bottom value diffusion angle is preferably 1 ° or more and less than 30 °, and more preferably 5 ° or more and less than 25 °. (B) When the diffusion angle of the peak value is 40 ° or more, the luminance unevenness in the entire region within the diffusion sheet surface can be reduced, and when it is 75 ° or less, a specific dot or line shape on the light source. Can suppress unevenness. From the viewpoint of suppressing front and oblique luminance unevenness and preventing specific unevenness, the peak value diffusion angle is preferably 40 ° or more and 75 ° or less, and more preferably 50 ° or more and 70 ° or less. (C) When the difference between the bottom value and the peak value is 20 ° or more, the front unevenness can be effectively eliminated, and when it is 70 ° or less, the luminance unevenness when viewed from an oblique direction can be easily eliminated. .

  Thus, in the diffusion sheet according to the present invention, by setting the diffusion angle of the peak value to 40 ° to 75 °, specific unevenness on the light source can be suppressed, and the difference between the bottom value and the peak value can be suppressed. By setting the angle to 20 ° to 70 °, the diffusion angle difference between the high diffusion angle region and the low diffusion angle region can be suppressed. In this way, light that leaks from an intermediate region between the high diffusion angle region and the low diffusion angle region is suppressed by suppressing the specific unevenness on the light source and suppressing the diffusion angle difference between the high diffusion angle region and the low diffusion angle region. Since it is possible to suppress detection as oblique unevenness, oblique unevenness can be effectively reduced. From the viewpoint of suppressing front and oblique luminance unevenness and preventing specific unevenness from occurring, the difference between the bottom value and the peak value is preferably 20 ° or more and 60 ° or less, and more preferably 25 ° or more and 50 ° or less.

  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 substantially conical, approximately spherical, approximately ellipsoidal, approximately lenticular lens-shaped, or approximately parabolic, and the protrusions may be arranged irregularly or irregularly. It may be arranged. 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.

  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.

  The diffusion sheet according to the present invention may have a portion where the uneven shape as described above is arranged somewhere in the surface of the diffusion sheet and has a function of diffusing light. May exist.

  A diffusion sheet having such a concavo-convex structure on the surface of the diffusion sheet and in which the diffusion angle changes 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 photocurable resin layer by forming the photocurable 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-2003-525472 (International Publication No. 01/065469 pamphlet). Specifically, a light source, a mask provided with a size and shape variable opening provided in an optical path of light projected from the light source, a plate for recording a diffusion pattern generated by the light projected from the light source, Using a diffuser plate that diffuses light disposed between the mask and the plate, and a blocker provided between the diffuser plate and the plate to block part of the light, the size and shape of the mask opening and blocker, It is made by changing the diffusion degree of the diffusion plate and the distance between the constituent members.

A diffusion sheet is manufactured as follows, for example.
1. By making the mask opening shape vertically long, the shape of the bottom surface of the convex portion recorded on the plate is made into a horizontally long ellipse, and a region having a vertically long elliptical diffusivity (diffusing angles in two orthogonal directions are different) is formed. To do.
2. By making the mask opening shape square, the shape of the bottom surface of the convex portion recorded on the plate is isotropic, and a region showing isotropic diffusion ability (the diffusion angle is the same in all directions) is formed.

  If a periodic pattern is formed by combining the patterns 1 and 2, the diffusion sheet according to the present invention, that is, a diffusion sheet in which the diffusion angle periodically changes in the plane can be manufactured.

  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 be read from the 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 according to the present invention may be on the light exit surface side or the light entrance surface side of the diffusion 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 the luminance and reducing the luminance unevenness, it is preferable that the surface opposite to the surface having the concavo-convex structure is a smooth surface. In general, when a diffusion sheet is laminated, a very small amount of beads may be applied to the surface opposite to the surface having the concavo-convex structure as long as smoothness is not lost in order to prevent damage. Such a case is also included in the smooth surface.

  Next, an example of a light source unit using the diffusion sheet will be described. The light source unit according to the present embodiment basically includes a plurality (at least two) of light sources (line light source or point light source) and the diffusion sheet according to the present invention disposed above the light source. To do. A reflective sheet for reflecting light from the light source is preferably used below the light source. 8 and 9 show a schematic configuration of the light source unit shown in the present embodiment. FIGS. 8A and 8B are diagrams showing an example of a light source unit using a cold cathode fluorescent lamp (CCFL) as a line light source. FIGS. 9A and 9B show an LED (light emission) as a point light source. It is a figure which shows an example of the light source unit using a diode. Thus, it is preferable to use the reflection sheet 22 for reflecting light below the light source (cold cathode tube 21, LED 25). In this case, it is more preferable that the unevenness forming surface side of the diffusion sheet 23 is a light exit surface.

  As shown in FIG. 8A, a light source unit using a line light source is arranged under three cold cathode tubes 21 arranged in parallel and under the cold cathode tubes 21, and receives light from the cold cathode tubes 21. The reflective sheet 22 which reflects and the diffusion sheet 23 arrange | positioned above the cold cathode tube 21 are comprised. The light source unit may further include an optical sheet, a diffusion sheet, or the like as long as it has the above-described configuration. For example, a diffusion plate (optical sheet) is provided between the cold cathode tube 21 and the diffusion sheet 23. ) 24 (see FIG. 8B).

  As shown in FIG. 9A, a light source unit using a point light source includes a plurality of LEDs 25 arranged in parallel, a reflection sheet 22 that is disposed below the LEDs 25 and reflects light from the LEDs 25, and the LED 25. And a diffusion sheet 23 disposed above. Moreover, it can be set as the structure which provided the diffusion plate (optical sheet) 24 between LED25 and the diffusion sheet 23 similarly to the optical unit using a linear light source (refer FIG.9 (b)).

  In the light source unit according to the present embodiment, the standard deviation value in the luminance unevenness when viewed from an oblique direction is 0.008 or less. The luminance unevenness when viewed from an oblique direction is the standard deviation value calculated in the y direction in FIG. In the case of a point light source, an average value of standard deviation values calculated in two directions of the x-axis direction and the y-axis direction in FIG. As an example, a method for calculating a standard deviation value of a light source unit in the case of a point light source will be described below with reference to FIG.

  The luminance measurement range is a range of 120 mm in the x-axis direction including the center of the screen of the light source unit × 120 mm in the y-axis direction, and the measurement interval is 2 mm in both the x-axis direction and the y-axis direction (the measurement point is 61 points in the x-axis direction). X 61 points in the y-axis direction). First, the average luminance value of 61 points (120 mm) in the x-axis direction is determined with the y-axis direction fixed, and the average luminance value of each point is within ± 15.2 mm in the y-axis direction from each point. The luminance unevenness is obtained as the standard deviation of the value divided by the average value of the average luminance values. Here, 15.2 mm corresponds to a half value of the distance between the LEDs in the y-axis direction. Similarly, an average luminance value of 61 points (120 mm) in the y-axis direction is obtained, and a standard deviation of values obtained by dividing the luminance value of each point by a luminance average value for ± 20.8 mm in the x-axis direction from each point. The luminance unevenness is obtained as follows. Similarly, 20.8 mm is given by the half value of the distance between the LEDs in the x-axis direction. Finally, in the case of a linear light source, the standard deviation value in the y-axis direction, and in the case of a point light source, an average value of the standard deviation in the x-axis direction and the standard deviation in the y-axis direction (hereinafter referred to as SD). The luminance unevenness of the light source unit is assumed.

  The front luminance unevenness is obtained by measuring the luminance unevenness from the normal direction with respect to the screen, and the oblique luminance unevenness by measuring the luminance unevenness viewed from the 45 ° direction with respect to the X direction with respect to the screen. In the light source unit according to the present invention, the S.I. D. The value is 0.008 or less. If it exceeds 0.008, it can be identified as unevenness, and by setting it to 0.008 or less, uneven luminance unevenness can be suppressed.

  As the reflection sheet 22, 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 made into a sheet, and a sheet is formed by mixing two or more resins, and resin layers with different refractive indexes are laminated. Sheet, etc. can be used. In addition, the reflective sheet 22 may have an uneven shape on the surface. As these, those having inorganic fine particles added to the surface can be used as necessary.

  As the diffusion plate 24, various materials can be used as long as they can diffuse light. For example, polystyrene, acrylic resin, polycarbonate, cycloolefin polymer, or the like added with an organic polymer or inorganic fine particles having an effect of diffusing light can be used. These diffusers have the effect of diffusing light and making the light from the lower light source uniform. Further, the diffusing plate 24 may have an uneven shape on the surface. These may be added with an organic polymer or inorganic fine particles as necessary. A diffusion plate in which two or more components are mixed and stretched to form a sheet can also be used.

  The light source unit uses a plurality of light sources. As the light source, a linear light source such as a cold cathode fluorescent lamp (CCFL) 21 as shown in FIG. 8, a point light source such as an LED (light emitting diode) 25 and a laser as shown in FIG. 9 can be used. In this case, the light sources are arranged directly below the light incident surface and the light outgoing surface of the diffusion sheet 23.

  Further, as the diffusion sheet applicable to the light source unit, both an isotropic diffusion sheet that can obtain substantially the same diffusion angle regardless of the measurement direction and an anisotropic diffusion sheet that has 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.

  In the light source unit shown in the present embodiment, the period of the diffusion angle distribution of the diffusion sheet is made 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 light source unit provided with the diffusion sheet, the omnidirectional luminance distribution is measured with the apparatus focused on the position where the light incident surface of the diffusion sheet is located, excluding the diffusion sheet, and the integrated luminous flux amount is obtained from the result. It is measured by repeating (obtaining Integrated Intensity) in the in-plane measurement target range.

  In addition, the difference in the diffusion angle in the projection area (inter-light source area) between the light source projection area (the area directly above the light source) and the light source is designed within the above-mentioned range. Can be adjusted as appropriate so as to equalize.

  Next, the distribution of the diffusion angle in the light source unit according to the present embodiment will be described with reference to FIGS. FIGS. 10A and 10B are schematic perspective views showing the configuration of the light source unit according to the present embodiment. FIG. 11 is a diagram showing the distribution of the diffusion angle in the diffusion sheet of the light source unit shown in FIGS. 10A and 10B with respect to the relative position with the light source in the diffusion sheet surface.

  In the light source unit shown in FIG. 10A, three cold cathode fluorescent lamps (CCFL) 21 are arranged in parallel at a predetermined light source interval S1. The longitudinal direction of each cold cathode tube 21 is arranged along the Y-axis direction. The diffusion sheet 23 is disposed in the XY plane, and the Z-axis direction orthogonal to the diffusion sheet 23 is the light exit direction. In addition, FIG.10 (b) becomes a structure which added the diffusion plate 24 (optical sheet) to the structure of Fig.10 (a). The diffusion sheet 23 is arranged such that the diffusion angle is periodically distributed, and the direction in which the diffusion angle is periodically distributed coincides with the Y-axis direction orthogonal to the longitudinal direction of the cold cathode tube 21. The diffusion angle in the plane of the diffusion sheet 23 has a peak value near the imaginary line L5 and a bottom value near the imaginary line L6.

  10A and 10B, since the period C of the illuminance distribution on the light incident surface of the diffusion sheet 23 is equal to the interval between the adjacent cold cathode tubes 21, the diffusion angle distribution period in the surface of the diffusion sheet 23 is It is preferable that the light source interval S1 of the cold cathode tube 21 is substantially equal. In the illuminance distribution on the light incident surface of the diffusion sheet 23, when the illuminance in the region directly above the light source is high, it is preferable to arrange the high diffusion angle region of the diffusion sheet 23 from the viewpoint of eliminating luminance unevenness. FIG. 11 shows an example of the diffusion angle distribution designed to correspond to the illuminance distribution on the light incident surface of the diffusion sheet 23.

  A specific configuration example of the light source unit described in this embodiment will be described below. For example, the configuration shown in FIGS. 12A to 12C can be used as the configuration of the light source unit. Here, the CCFL that is a linear light source is illustrated, but the light source may be a point light source such as an LED as shown in FIGS. 13 (a) to 13 (d), for example.

  In the example shown in FIG. 12A, in the configuration shown in FIG. 8B, a fine uneven structure is formed on the surface between the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the cold cathode tube 21. The surface-shaped diffusion sheet 26 thus arranged is disposed, and the surface-shaped diffusion sheet 26 is disposed immediately above the diffusion sheet 23.

  Here, as the surface shaping type diffusion sheet 26, 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 26, 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 26 has a function of condensing the light diffused by the diffusion plate 24 as well as the effect of diffusing and uniformizing the light. By using the surface-shaped diffusion sheet 26 and the diffusion sheet 23 in combination, luminance unevenness can be reduced, and the light source unit can be made thinner and the number of light sources can be reduced.

  In the example shown in FIG. 12B, in the configuration shown in FIG. 8B, an optical element having an arrayed prism arrangement structure above the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the cold cathode tube 21. A sheet (hereinafter also referred to as “prism sheet”) 27 and a surface-shaped diffusion sheet 26 having a fine concavo-convex structure formed on the surface thereof are arranged in this order. In the example shown in FIG. 12C, in the configuration shown in FIG. 8B, a fine concavo-convex structure is formed on the surface above the diffusion plate 24 and the diffusion sheet 23 disposed immediately above the cold cathode tube 21. The formed surface-shaped diffusion sheet 26 and the prism sheet 27 are arranged in this order.

  As the prism sheet 27, an optical sheet in which prism rows having a substantially triangular shape, a substantially trapezoidal shape, and a substantially elliptical shape are arranged in an array shape on the surface can be used. A shape obtained by rounding the top of the cross-sectional shape can 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 a prism sheet 27 exhibits retroreflectivity, it has a function of collecting incident light to the front. By using this prism sheet in combination with the diffusion sheet according to the present embodiment, luminance unevenness can be reduced, and the light source unit can be made thinner and the number of light sources can be reduced.

  In the example shown in FIG. 13A, in the configuration shown in FIG. 9B, surface shaping in which a fine uneven structure is formed on the surface above the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the LED 25. A mold diffusion sheet 26, a prism sheet 27 having prism rows on the array, and a reflective polarizing sheet 28 are arranged in this order. In the example shown in FIG. 13B, in the configuration shown in FIG. 9B, surface shaping in which a fine uneven structure is formed on the surface above the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the LED 25. Two mold diffusion sheets 26 are disposed, and a reflective polarizing sheet 28 is disposed on the surface-shaped diffusion sheet 26. In the example shown in FIG. 13 (c), in the configuration shown in FIG. 9 (b), surface shaping in which a fine uneven structure is formed on the surface between the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the LED 25. A mold diffusion sheet 26 is disposed, and a surface-shaped diffusion sheet 26 having a fine uneven structure formed on the surface and a reflective polarizing sheet 28 are sequentially disposed above the diffusion sheet 23. In the example shown in FIG. 13 (d), in the configuration shown in FIG. 9 (b), a prism sheet 27 having a prism row on the array is arranged between the diffusion plate 24 and the diffusion sheet 23 arranged immediately above the LED 25. Furthermore, a surface-shaped diffusion sheet 26 and a reflective polarizing sheet 28 having a fine concavo-convex structure formed on the surface thereof are arranged above the diffusion sheet 23 in this order.

  As the reflective polarizing sheet 28, a sheet having a function of separating linearly polarized light from natural light or polarized light can be used. As a sheet | seat which isolate | separates linearly polarized light, the film etc. which permeate | transmit one of the linearly polarized light orthogonal to an axial direction, and reflect the other are mentioned, for example. Specifically, as the reflective polarizing sheet, a resin having a large birefringence retardation (polycarbonate, acrylic resin, polyester resin, etc.) and a resin having a small birefringence retardation (cycloolefin polymer, etc.) are alternately laminated. A sheet obtained by laminating and uniaxially stretching, a sheet having a structure in which several hundred layers of birefringent polyester resin are laminated (DBEF, manufactured by 3M), and the like can be used.

  In the example shown in FIG. 14A, in the configuration shown in FIG. 8A, a diffusion plate 24 is arranged between the cold cathode tube 21 and the diffusion sheet 23, and surface shaping is performed immediately above the diffusion sheet 23. A mold diffusion sheet 26 is disposed. In the example shown in FIG. 14B, in the configuration shown in FIG. 8A, the diffusion plate 24 and the surface-shaped diffusion sheet 26 are arranged in this order above the diffusion sheet 23.

  In the example shown in FIG. 14C, in the configuration shown in FIG. 8A, a diffusion plate 24 is disposed between the cold cathode tube 21 and the diffusion sheet 23, and an array-like prism is disposed above the diffusion sheet 23. The prism sheet 27 having the arrangement structure and the reflective polarizing sheet 28 are arranged in this order. Further, in the example shown in FIG. 14D, in the configuration shown in FIG. 8A, a diffusion plate 24 is disposed between the cold cathode tube 21 and the diffusion sheet 23, and a prism is disposed above the diffusion sheet 23. Two sheets 27 are arranged so that the prism arrangement directions thereof are orthogonal to each other, and the surface-shaped diffusion sheet 26 is arranged above the two sheets.

  In the example shown in FIG. 15A, in the configuration shown in FIG. 8A, a diffusion plate 24 is disposed between the cold cathode tube 21 and the diffusion sheet 23, and a surface shaping type is provided above the diffusion sheet 23. The diffusion sheet 26, the prism sheet 27, and the reflective polarizing sheet 28 are arranged in this order. In the example shown in FIG. 15B, in the configuration shown in FIG. 8A, the diffusion plate 24, the surface-shaped diffusion sheet 26, the prism sheet 27, and the reflective polarizing sheet are disposed above the diffusion sheet 23. 28 are arranged in this order.

  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.

  The diffusion angles shown in Examples 1 to 4 and Comparative Examples 1 to 3 are angles measured by the LD8900 after entering from a surface having a fine concavo-convex structure. For example, 5 ° indicates that the FWHM in any direction is 5 °. Regarding the diffusion angle distribution, FWHM was measured at intervals of 2 mm with respect to the x-axis direction and / or the y-axis direction of the diffusion sheet, and a diffusion angle distribution diagram was created. Hereinafter, the diffusion angle distributions of Example 2 and Example 3 are also measured in the same manner.

  In Examples 1 to 4 and Comparative Examples 1 to 3, what is not described as an optical sheet, that is, a reflection sheet, a diffusion plate, a surface-shaped diffusion sheet, an optical having an arrayed prism arrangement structure The sheet and the reflective polarizing sheet are respectively a white reflective sheet made of polyester resin (hereinafter abbreviated as RS) and a diffuser plate made of polystyrene and having a thickness of 1.5 mm and a diffusing agent concentration of 13000 ppm (hereinafter abbreviated as DP). A diffusion sheet (hereinafter abbreviated as DS) in which resin beads and a binder are coated on a PET substrate having a thickness of 250 μm, or a hemispherical lens is shaped by a UV curable resin on a PET substrate having a thickness of 250 μm. An optical sheet (hereinafter abbreviated as MLF), a prism array with an apex angle of 90 ° and a pitch of 50 μm on a PET substrate with a thickness of 250 μm is UV cured. An optical sheet (hereinafter abbreviated as “prism sheet”) and a reflective polarizing sheet (hereinafter abbreviated as “DBEF”; manufactured by 3M) were used.

  For Examples 1 to 4 and Comparative Examples 1 to 3, a white LED light source of 3.5 mm square and 2.0 mm height made by CREE was used as the light source of the light source unit. 133 LEDs were arranged in an arrangement as shown in FIG. 16 to produce a light source unit. Luminance and luminance unevenness were measured using a Konica Minolta two-dimensional color luminance meter (CA2000) at a distance of 70 cm from the light-emitting surface of the light source unit and measured in a range of 120 mm × 120 mm at the center of the light source unit. Was defined as luminance.

The luminance unevenness was an average value of values calculated in two directions of the x-axis direction and the y-axis direction. First, an average luminance value in the x-axis (120 mm) direction is obtained, and in the y-axis direction, luminance is obtained as a standard deviation of a value obtained by dividing the luminance value at each point by the average luminance value for ± 15.2 mm from each point. I asked for unevenness. Similarly, an average luminance value in the y-axis direction (120 mm) direction is obtained, and a standard deviation of values obtained by dividing the luminance value of each point by the average luminance value of ± 20.8 mm from each point in the x-axis direction. As a result, luminance unevenness was obtained. Finally, a value obtained by averaging the standard deviation in the x-axis direction and the standard deviation in the y-axis direction (SD value) was used as the luminance unevenness of the light source unit. Since the LED light source is a point light source, as shown in FIG. 1 (b), the diffusion angle distribution is distributed on a line (a broken line in FIG. 1 (b)) that maximizes the linear distance between adjacent light sources. Thought. Frontal luminance unevenness was measured from the normal direction to the screen. Oblique luminance unevenness was measured when viewed from a 45 ° direction in the x-axis direction with respect to the screen.
Here, the criterion for determining the front luminance unevenness was classified into two stages (◯, ×) as follows.
○: S. D. ≦ 0.005
X: 0.005 <S. D.
In addition, the criteria for determining the uneven luminance unevenness were classified into two levels (◯, ×) as follows.
○: S. D. ≦ 0.008
X: 0.008 <S. D.

Example 1
As shown in FIG. 13B, DP, the diffusion sheet of Example 1, DS, DS, and DBEF were arranged in this order above the light source to configure the light source unit of Example 1. In the diffusion sheet of Example 1, the diffusion angle of the projection area of the light source is 74 °, the diffusion angle of the projection area of the intermediate point between the light source and the light source is 19 °, and the diffusion angle changes as shown in FIG. The diffusion sheet used was used so that the uneven surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 19.0 mm. The front luminance unevenness and the oblique luminance unevenness in the light source unit of Example 1 were calculated by the above method. The results are shown in Table 1 below. Further, for the diffusion sheet of Example 1, the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value, and all the measurement points distributed between the continuous diffusion angle peak value and the diffusion angle bottom value. The arithmetic average value (Av2) of the diffusion angle is also shown in Table 1 below. In addition, Table 1 also describes whether or not the conditions (a) to (c) that are essential requirements of the present invention are satisfied.

(Example 2)
As shown in FIG. 13C, DP, DS, the diffusion sheet of Example 2, MLF, and DBEF were arranged in this order above the light source to configure the light source unit of Example 2. As the diffusion sheet of Example 2, the same sheet as that of Example 1 was used so that the concavo-convex surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 18.0 mm. The front luminance unevenness and the oblique luminance unevenness in the light source unit of Example 2 were calculated by the above method. The results are also shown in Table 1.

(Example 3)
As shown in FIG. 13D, DP, a prism sheet, the diffusion sheet of Example 3, DS, and DBEF were arranged in this order above the light source to configure the light source unit of Example 3. As the diffusion sheet of Example 3, the same sheet as that of Example 1 was used so that the concavo-convex surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 16.0 mm. The front luminance unevenness and the oblique luminance unevenness in the light source unit of Example 3 were calculated by the above method. The results are also shown in Table 1.

Example 4
As shown in FIG. 13B, the light source unit of Example 4 was configured by arranging DP, the diffusion sheet of Example 4, DS, DS, and DBEF in this order above the light source. In the diffusion sheet of Example 4, the diffusion angle of the projection area of the light source is 41 °, the diffusion angle of the projection area of the intermediate point between the light source and the light source is 10 °, and the diffusion angle changes as shown in FIG. The diffusion sheet used was used so that the uneven surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 21.0 mm. The front luminance unevenness and the oblique luminance unevenness in the light source unit of Example 4 were calculated by the above method. The results are also shown in Table 1. In addition, for the diffusion sheet of Example 4, the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value, and all the measurement points distributed between the continuous diffusion angle peak value and the diffusion angle bottom value. The arithmetic average value (Av2) of the diffusion angle is also shown in Table 1 below.

(Comparative Example 1)
As shown in FIG. 13 (b), DP, the diffusion sheet of Comparative Example 1, DS, DS, and DBEF were arranged in this order above the light source to constitute a light source unit of Comparative Example 1. In the diffusion sheet of Comparative Example 1, the diffusion angle of the projection area of the light source is 74 °, the diffusion angle of the projection area of the intermediate point between the light source and the light source is 19 °, and the diffusion angle changes as shown in FIG. The diffusion sheet used was used so that the uneven surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 19.0 mm. Front luminance unevenness and oblique luminance unevenness in the light source unit of Comparative Example 1 were calculated by the above method. The results are also shown in Table 1. Further, for the diffusion sheet of Comparative Example 1, the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value, and all the measurement points distributed between the continuous diffusion angle peak value and the diffusion angle bottom value. The arithmetic average value (Av2) of the diffusion angle is also shown in Table 1 below.

(Comparative Example 2)
As shown in FIG. 13B, DP, the diffusion sheet of Comparative Example 2, DS, DS, and DBEF were arranged in this order above the light source to constitute a light source unit of Comparative Example 2. In the diffusion sheet of Comparative Example 2, the diffusion angle of the projection area of the light source is 37 °, the diffusion angle of the projection area of the intermediate point between the light source and the light source is ° 1, and the diffusion angle changes as shown in FIG. The diffusion sheet used was used so that the uneven surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 21.0 mm. Front luminance unevenness and oblique luminance unevenness in the light source unit of Comparative Example 2 were calculated by the above method. The results are also shown in Table 1. For the diffusion sheet of Comparative Example 2, the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value, and all the measurement points distributed between the continuous diffusion angle peak value and the diffusion angle bottom value. The arithmetic average value (Av2) of the diffusion angle is also shown in Table 1 below.

(Comparative Example 3)
As shown in FIG. 13B, DP, the diffusion sheet of Comparative Example 3, DS, DS, and DBEF were arranged in this order above the light source to constitute a light source unit of Comparative Example 3. In the diffusion sheet of Comparative Example 3, the diffusion angle of the projection area of the light source is 82 °, the diffusion angle of the projection area of the intermediate point between the light source and the light source is 1 °, and the diffusion angle changes as shown in FIG. The diffusion sheet used was used so that the uneven surface became the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 19.0 mm. Front luminance unevenness and oblique luminance unevenness in the light source unit of Comparative Example 3 were calculated by the above method. The results are also shown in Table 1. Further, for the diffusion sheet of Comparative Example 3, the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value, and all the measurement points distributed between the continuous diffusion angle peak value and the diffusion angle bottom value. The arithmetic average value (Av2) of the diffusion angle is also shown in Table 1 below.

  From Table 1, the diffusion sheets of Examples 1 to 4 are distributed between the diffusion angle peak value and the diffusion angle bottom value in which the arithmetic average value (Av1) of the diffusion angle peak value and the diffusion angle bottom value continues. Is larger than the arithmetic average value (Av2) of the diffusion angles of all measurement points to be satisfied, and satisfies all the above-mentioned conditions (a) to (c), so that the front luminance unevenness and oblique luminance unevenness reducing ability is good, and the light source unit It can be seen that the number of light sources can be reduced or the distance between the light sources and the optical sheet can be shortened.

  The present invention is not limited to the embodiment described above, and can be implemented with various modifications. For example, the material, arrangement, shape, and the like of the members in the above embodiment are illustrative, and can be implemented with appropriate changes. Further, the light source unit can be configured by appropriately combining the configurations shown in the above embodiments. In addition, various modifications can be made without departing from the scope of the present invention.

  The present invention is effective for a diffusion sheet and a light source unit of a display device such as a liquid crystal display device.

1,23 Diffusion sheet 11,21 Cold cathode tube (CCFL)
12, 25 LED
22 Reflective sheet 24 Diffusion plate 26 Surface-shaped diffusion sheet 27 Prism sheet 28 Reflective polarizing sheet

Claims (15)

A diffusion sheet in which a diffusion angle of outgoing light when a light beam is incident perpendicularly to a sheet surface periodically changes along a predetermined direction in the sheet surface, and the relative in the sheet surface in the predetermined direction In a diffusion angle distribution diagram in which the position is taken on the horizontal axis and the diffusion angle at the relative position in the sheet surface is taken on the vertical axis, there are a plurality of peak values of the diffusion angle and bottom values of the diffusion angle, and the adjacent The arithmetic average value of the diffusion angles between the peak value and the bottom value is larger than the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak value and the bottom value, and the following (a ) To (c) satisfying the conditions.
(A) The diffusion angle of the bottom value is 0.1 ° or more and less than 40 ° (b) The diffusion angle of the peak value is 40 ° or more and 75 ° or less (c) The difference between the bottom value and the peak value is 20 ° or more. 70 ° or less   The diffusion angle distribution between the adjacent peaks in the high diffusion angle region includes a plurality of peaks in the high diffusion angle region in the diffusion angle distribution diagram. Diffusion sheet.   In the diffusion angle distribution diagram, a single high diffusion angle region includes a plurality of peaks, and the diffusion angle distribution between adjacent peaks in the high diffusion angle region is a downward convex curve shape or a mixed shape of a curve and a straight line. The diffusion sheet according to claim 1, wherein the diffusion sheet is provided.   The peak value of the diffusion angle and the bottom value of the diffusion angle alternately and periodically, and the arithmetic average value of the diffusion angles at two points of the adjacent peak value and the bottom value is the adjacent peak. A first interval that is larger than the arithmetic average value of the diffusion angles at all points distributed between the value and the bottom value, and the distribution of the diffusion angles includes the peak value and has an upward convex curve shape, and the diffusion angle 2. The diffusion sheet according to claim 1, wherein the distribution sheet has a second section including the bottom value and having a downward convex curve shape.   The diffusion sheet according to any one of claims 1 to 4, wherein the diffusion angle is generated by a concavo-convex structure formed on the surface of the diffusion sheet.   The diffusion sheet according to claim 5, wherein the uneven structure is an uneven structure formed using a speckle pattern by interference exposure.   A standard deviation value in luminance unevenness when viewed from an oblique direction, comprising two or more light sources and the diffusion sheet according to any one of claims 1 to 6 disposed above the light sources. Is 0.008 or less, The light source unit characterized by the above-mentioned.   The light source unit according to claim 7, wherein the light source is a linear light source.   The light source unit according to claim 7, wherein the light source is a point light source.   The light source unit according to any one of claims 7 to 9, wherein a period of the diffusion angle distribution of the diffusion sheet is substantially equal to a period of the illuminance distribution on the light incident surface of the diffusion sheet.   The diffusing plate that is disposed between the diffusing sheet and the light source and contains a diffusing agent therein, and a reflecting sheet that is disposed below the light source. The light source unit according to any one of the above.   The light source unit according to any one of claims 7 to 11, further comprising a lens sheet disposed above the diffusion sheet.   The light source unit according to any one of claims 7 to 12, further comprising a prism sheet disposed above the diffusion sheet.   The light source unit according to claim 7, further comprising a reflective polarizing sheet disposed above the diffusion sheet.   A liquid crystal display device comprising: a liquid crystal display panel; and the light source unit according to claim 7 for supplying light to the liquid crystal display panel.

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