JP2012058395A - Diffusion sheet, light source unit and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion sheet, a light source unit and a liquid crystal display device capable of suppressing frontal luminance unevenness and oblique luminance unevenness.SOLUTION: In a diffusion sheet of the present invention, in a diffusion angle distribution diagram in which the abscissa represents relative positions in a sheet surface and the ordinate represents diffusion angles at the relative positions in the sheet surface, there are a plurality of peak points indicating peak values of the diffusion angle and bottom points indicating bottom values of the diffusion angle, the arithmetic average value of the diffusion angles between the adjacent peak points and bottom points is larger than the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak points and bottom points, and if a point indicating a diffusion angle equal to the sum of the bottom values and three fifths of the value obtained subtracting the bottom values from the peak values is defined as b point, in an arbitrary cycle of the diffusion angle distribution diagram, the ratio d/c of the distance c of the cycle to the distance d between two adjacent b points across the bottom points satisfies 0.79≤d/c<0.90.

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 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 then extrusion is used.

  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. Further, the above-described unevenness forming method has a problem that the structure of about several tens of μm is the limit and it is not easy to improve the shape uniformity.

  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 become 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. 21A). h ′) and / or p becomes larger (p ′ in FIG. 21B), 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. For this reason, the conventional method cannot sufficiently reduce the front luminance unevenness and the oblique luminance unevenness, and there is a problem that the liquid crystal display device cannot be sufficiently reduced in thickness and the number of light sources.

  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.

  As a result of intensive studies in order to solve the problems of the related art relating to the diffusion sheet described above, the inventor has found that the above-described problems of the prior art can be solved by a diffusion sheet having a specific diffusion angle distribution. The invention has been completed. The present invention is as follows.

  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, In the diffusion angle distribution diagram in which the horizontal axis represents the relative position in the sheet surface in the direction and the vertical axis represents the diffusion angle at the relative position in the sheet surface, the peak point indicating the peak value of the diffusion angle and the diffusion There are a plurality of bottom points indicating the bottom value of the angle, and the arithmetic average value of the diffusion angles between the adjacent peak points and the bottom points is distributed between the adjacent peak points and the bottom points. It is larger than the arithmetic average value of the diffusion angles at all points, and is located between the peak point and the bottom point, and the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value Diffusion equal to the sum value When the point indicating the degree is b point, in any one cycle of the diffusion angle distribution diagram, the interval c of the cycle and the distance d between two adjacent b points across the bottom point The ratio d / c satisfies “0.79 ≦ d / c <0.90”.

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

  In the diffusion sheet of the present invention, the diffusion angle distribution map includes a plurality of peak points in one high diffusion angle region, and the diffusion angle distribution between adjacent peak points in the high diffusion angle region is downwardly convex. A curved shape or a mixed shape of a curved line and a straight line is preferable.

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

  In the diffusion sheet of the present invention, the diffusion angle is preferably generated by a concavo-convex structure formed on the sheet surface.

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

  The light source unit of the present invention comprises two or more light sources and the diffusion sheet disposed above the light sources.

  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 the present invention, it is preferable that the light source unit includes a diffusion plate disposed between the diffusion sheet and the light source and containing a diffusing agent therein, and a reflection sheet disposed below the 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 present invention, it is possible 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.

(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 point, a bottom point, and arithmetic average. (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. It is explanatory drawing of the diffusion angle 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. The arrangement pattern figure of the LED light source used for the Example and comparative example of this invention is shown. The arrangement pattern figure of the LED light source used for the Example and comparative example of this invention is shown. (A)-(c) is a figure which shows the relationship between the diffusion angle of the diffusion sheet which concerns on the Example of this invention, and light source distance. (A), (b) is a figure which shows the relationship between the diffusion angle of the diffusion sheet which concerns on the comparative example of this invention, and light source distance. (A), (b) is a cross-sectional schematic diagram which shows arrangement | positioning of a light source unit.

  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.

  The diffusion sheet according to the present invention is a diffusion sheet in which the diffusion angle of outgoing light when a light beam is incident perpendicularly to the sheet surface changes periodically along a predetermined direction in the sheet surface, It has a plurality of peak points indicating the peak value and bottom points indicating the bottom value of the diffusion angle, and the arithmetic average value of the diffusion angles between the adjacent peak points and the bottom point is the adjacent peak point and bottom point. It is larger than the arithmetic average value of the diffusion angles at all points distributed between and. In the diffusion sheet, the inventor is located between the peak point and the bottom point, and has a diffusion angle equal to the sum of the bottom value and 3/5 of the peak value minus the bottom value. The ratio d / c between the interval c of the diffusion angle cycle and the distance d between two adjacent b points across the bottom point is “0.79 ≦ d / c It has been found that by satisfying <0.90 ”, luminance unevenness can be effectively reduced. Below, the specific structure of a diffusion sheet is demonstrated.

  First, referring to FIGS. 1A and 1B, a projection area of a light source (hereinafter, also referred to as “light source area”) and a projection area between light sources (hereinafter, referred to as “light source”) of the diffusion sheet according to the present embodiment. , Also referred to as “inter-light source region”). FIGS. 1A and 1B are plan views showing a region directly 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 linear light source such as a cold cathode fluorescent lamp (CCFL) 101 as shown in FIG. 1A, or a point light source such as an LED (light emitting diode) 102 or a laser as shown in FIG. 1B. Can be used. When three cold-cathode tubes 101 are arranged in parallel as light sources, an area having a rectangular shape in plan view along the line direction of the cold-cathode tubes 101 in the vicinity of the cold-cathode tubes 101 becomes an area A1 immediately above the light source, and between the areas A1 directly above each light source Is the inter-light source region A2. When a plurality of LEDs 102 are used as the light source, a circular area in plan view near the outer peripheral edge of each LED 102 is the area A1 directly above the light source, and an area between the areas A1 immediately above the light sources is an inter-light source area A2. FIGS. 1A and 1B show an example in which the area of the entire diffusion sheet is divided into an area A1 immediately above the light source and an area A2 between the light sources. You may divide | segment so that areas other than area | region A2 between light sources may be provided. 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 embodiment, 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. 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, Phonon's Goniometric Radiometers Real-Time Far-Field Angular Profiles Model LD8900 (hereinafter referred to as “LD8900”), which is incident from the normal direction of the uneven surface of the diffusion sheet from the uneven surface side. It can be obtained by measuring the angular distribution of transmitted light intensity with respect to the measured light. Here, the normal direction of the diffusion sheet refers to the direction shown in FIG.

  In addition, as the diffusion sheet according to the present embodiment, 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 diffusion angle different 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 peak points indicating the peak value of the diffusion angle and bottom points indicating the bottom value of the diffusion angle (in FIG. 3, one peak point and two bottom points are shown). . 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 two diffusion angles of the adjacent peak point and the bottom point is all distributed between the adjacent peak point and the bottom point. Greater than the arithmetic mean value of the diffusion angle at a point. The “all points” described here mean all the measurement points.

  If the arithmetic average value of the two diffusion angles of the adjacent peak point and the bottom point is larger than the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak point and the bottom point, the change of the diffusion angle is as follows. Strictly, it does not have to be linear, curved, or stepped. Depending on the dispersion angle measurement, etc., the shape may be slightly different from linear, curved, or stepped, or a mixture of straight and curved. Good. On the diffusion sheet surface, 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 downward from the diffusion sheet and the light that passes obliquely with respect to the normal direction of the diffusion sheet increase as the incident angle increases, the transition from the region directly above the light source to the region between the light sources 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 has an arithmetic average value of the diffusion angles of two points, the adjacent peak point and the bottom point, that is larger than the arithmetic average value of the diffusion angles at all points distributed between the adjacent peak point and the bottom point. Therefore, it is possible to reduce luminance unevenness in accordance with attenuation of light to be diffused. 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 general, the arrangement of the diffusion angle in each region in the diffusion sheet surface is preferably a region with a relatively high diffusion angle directly above the light source. You may make it arrange | position the area | region which has a comparatively low diffusion angle in a diffusion sheet surface in an area | region with high illumination intensity. Moreover, it is preferable that the diffusion angle between each area | region changes smoothly.

  In particular, a shape including a plurality of continuous peak points 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 combination 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, there is a bottom point of the diffusion angle, and the distribution of the diffusion angle in the low diffusion angle region including the bottom point is a downward convex curve with the bottom value at the bottom point being a minimum value. (FIGS. 4A to 4D). FIG. 4C shows a first section D1 in which the distribution of the diffusion angle includes the peak point and has an upward convex curve shape, and the first section D1 in which the distribution of the diffusion angle includes the bottom point and has a downward convex curve shape. This 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 diffusion angle of the peak point and the bottom point in the diffusion sheet according to the present invention is calculated using the distribution of the diffusion angle based on the above definition. In one cycle, the number of peak points and bottom points is not limited to one, and a plurality of the same values may exist.

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

  In addition, “cyclically” means that the repeated patterns are compared with each other, the peak value of the peak point corresponding to the same repetition position, the interval between two adjacent peak points corresponding to the same repetition position, and , The bottom value of the bottom point corresponding to the same repetition position, and the interval between two adjacent bottom points corresponding to the same repetition position are within ± 15% (preferably within 10%, respectively) of the average value of all the repetition patterns. If it is within the range of more preferably 5% or less, it is assumed that it changes periodically. 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, with reference to FIGS. 5-7, the example of arrangement | positioning of the high diffusion angle area | region and low diffusion angle area | region of the diffusion sheet which concerns on this invention is demonstrated. 5 and 6 show that the high diffusion angle region A3 and the low diffusion angle region A4 periodically exist in the X-axis direction in the diffusion sheet surface, that is, the diffusion angle changes periodically as shown in FIG. It shows that. In the example shown in FIG. 5, the diffusion angle in the diffusion sheet surface has a peak value in the vicinity of the imaginary line L1 in each high diffusion angle region A3, and the bottom in the vicinity of the imaginary line L2 in each low diffusion angle region A4. Value. Further, in the example shown in FIG. 6, in the X-axis direction within the diffusion sheet surface, the diffusion sheet changes from the high diffusion angle region A4 to the low diffusion angle region A3 from one end side to the other end side in the Y axis direction. A region A5 and a region A6 that changes from the low diffusion angle region A3 to the high diffusion angle region A4 periodically exist from one end side to the other end side in the Y-axis direction of the diffusion sheet. 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 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 sheet surface. In the example shown in FIG. 7, circular high diffusion angle regions A3 exist in a lattice shape within the diffusion sheet surface, and low diffusion angle regions A4 exist between the high diffusion angle regions A3. The diffusion angle in the diffusion sheet surface 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 X-axis direction or Y-axis direction cross section of the diffusion sheet. Such a pattern is preferably used for a point light source, but may be used for a line light source.

  A diffusion sheet according to the present invention is a diffusion sheet in which 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, and in the predetermined direction In the diffusion angle distribution diagram in which the horizontal axis is the relative position in the sheet surface and the vertical axis is the diffusion angle at the relative position in the sheet surface, the peak point indicating the peak value of the diffusion angle and the bottom value of the diffusion angle are shown. There are a plurality of bottom points. Further, in the diffusion sheet according to the present invention, the arithmetic average value of the diffusion angles between the adjacent peak points and the bottom points is the arithmetic operation of the diffusion angles at all points distributed between the adjacent peak points and the bottom points. A point that is larger than the average value and is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the peak value minus the bottom value is b When the point is a point, the ratio d / c of the distance c between the interval c of the period and the two adjacent b points across the bottom point in any one period of the diffusion angle distribution diagram is “ 0.79 ≦ d / c <0.9 ”is satisfied. A diffusion sheet having a d / c value of 0.9 or more is very difficult to produce. When the value of d / c of the diffusion sheet is 0.79 or more, the luminance unevenness is effectively reduced. From the viewpoint of reducing luminance unevenness, the value of d / c is preferably 0.81 or more, and more preferably 0.82 or more.

  Hereinafter, the distribution of the diffusion angle of the diffusion sheet according to the present embodiment will be described in detail with reference to FIG. FIG. 8 is an explanatory diagram of the diffusion angle of the diffusion sheet according to the embodiment of the present invention. FIG. 8 is a diffusion angle distribution diagram in which the horizontal axis indicates the relative position in the sheet plane in a predetermined direction, and the vertical axis indicates the diffusion angle at the relative position in the sheet plane. In addition, the distribution of the diffusion angle of the diffusion sheet according to the present invention is indicated by a solid curve, and the distribution of the diffusion angle of a general diffusion sheet is indicated by a dashed line curve.

  As shown in FIG. 8, in the diffusion sheet according to the present invention, the diffusion angle is equal to the sum of the bottom value of the distribution curve of the diffusion angle and 3/5 of the value obtained by subtracting the bottom value from the peak value. When the point is b1 point, the ratio d1 / c between the distance d1 between two adjacent b1 points across the bottom point and the period interval c is “0.79 ≦ d1 / c <0.9. Is configured to satisfy. With this configuration, as shown in FIG. 8, the diffusion angle distribution curve has a shape in which the diffusion angle decreases sharply as the relative distance from the light source position increases (solid line). On the other hand, in a general diffusion sheet, a point showing a diffusion angle equal to the sum of the bottom value of the distribution curve of the diffusion angle and 3/5 of the value obtained by subtracting the bottom value from the peak value is defined as b2. Sometimes, the ratio d2 / c between the distance b2 between two adjacent b2 points across the bottom point and the interval c is “0.79> d2 / c”. For this reason, in the distribution curve of the diffusion angle, the diffusion angle decreases relatively gradually as the relative distance from the light source position increases (dashed line).

  In this way, the present inventor makes a predetermined point relatively close to the peak value relative to the bottom value of the distribution curve of the diffusion angle as b point, and two adjacent b points across the bottom value. By setting the ratio d / c (the width of the peak in the distribution curve of the diffusion angle) of the distance d between and the period interval c to a predetermined range (set to be relatively narrow), that is, It has been found that by controlling the diffusion angle so as to change steeply in the vicinity of the light source position (near the peak point), the front luminance unevenness and the oblique luminance unevenness can be reduced. This is based on the assumption that the relationship between the light source position and the luminance approximates the distribution curve of the diffusion angle as shown in FIG. 8, and the distribution curve of the diffusion angle is added to the relationship between the light source position and the luminance. This is considered to be because the light from the light source can be more effectively diffused between the light sources by approximation. Note that a point indicating a diffusion angle equal to the sum of the bottom value of the distribution curve of the diffusion angle and 3/5 of the value obtained by subtracting the bottom value from the peak value is defined as point b. This is because the difference in the peak width (d / c) in the diffusion angle distribution curve between the sheet and the sheet becomes clear, and the peak in the diffusion angle distribution curve between the sheet and the general diffusion sheet. Any value other than 3/5 may be used as long as the difference in width (d / c) can be shown. That is, if the distribution curve of the diffusion angle can be approximated to the relationship between the light source position and the luminance, the position in the distribution curve of the diffusion angle for specifying the width of the peak in the distribution curve of the diffusion angle is particularly limited. There is no.

  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. The pseudo-random structure is preferably a fine three-dimensional structure characterized by speckle patterns by interference exposure and non-planar speckles.

  In order to obtain favorable characteristics regarding the light diffusion performance, the height of the protrusions is preferably in the range of 1 μm to 15 μm, and the pitch is preferably in the range of 1 μm to 30 μm.

  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 only needs to have a portion exhibiting a function of diffusing light by arranging the uneven shapes as described above in any one of the sheet surfaces, and a portion that does not need to have a diffusion function, for example, an end portion In, there may be a portion where the sheet surface is smooth.

  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. In addition, the unit structure of the unevenness is not limited to an isotropic structure, and an anisotropic structure can be formed, and an uneven structure in which both are combined can be obtained. 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 this 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). 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.

The 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 sheet surface 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 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 the light source unit of the present invention using the diffusion sheet will be described. The light source unit according to the present embodiment basically includes a plurality (two or more) 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. 9A, 9B, 10A, and 10B show a schematic configuration of the light source unit shown in the present embodiment. FIGS. 9A and 9B are diagrams showing an example of a light source unit using a cold cathode fluorescent lamp (CCFL) 11 as a line light source. FIGS. 10A and 10B show an LED ( It is a figure which shows an example of the light source unit using the light emitting diode) 12. Moreover, it is preferable to use the reflection sheet 13 for reflecting light under the light source (the cold cathode tube 11 and the LED 12). In this case, it is more preferable that the unevenness forming surface side of the diffusion sheet 15 is a light exit surface.

  Further, if the optical unit has the above-described configuration, an optical sheet may be further provided. For example, a diffusion plate (optical sheet) is provided between the light source (cold cathode tube 11 and LED 12) and the diffusion sheet 15. ) 14 (see FIGS. 9B and 10B).

  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 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 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.

  As the diffusing plate 14, 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 diffusion plate 14 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) 11 as shown in FIGS. 9A and 9B, an LED (light emitting diode) 12 as shown in FIGS. 10A and 10B, A point light source such as a laser can be used. In this case, the light source (cold cathode tube 11, LED 12) is arranged directly below the light incident surface and light outgoing surface of the diffusion sheet 15.

  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 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.

  FIGS. 11A and 11B are schematic diagrams of an example of the light source unit when viewed from obliquely above. In the light source unit shown in FIG. 11A, three cold cathode fluorescent lamps (CCFL) 11 are arranged in parallel on the reflection sheet 13 with a predetermined light source interval S1. The longitudinal direction of each cold cathode tube 11 is disposed along the Y-axis direction. The diffusion sheet 15 is disposed in the XY plane, and the Z-axis direction orthogonal to the diffusion sheet 15 is the light exit direction. The diffusion sheet 15 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 11. The diffusion angle in the surface of the diffusion sheet 15 has a peak value near the virtual line L5 and a bottom value near the virtual line L6. 11A and 11B, FIG. 11B has a configuration in which a diffusion plate 14 (optical sheet) is added to the configuration of FIG. 11A.

  FIG. 12 is a diagram showing a light source interval and a diffusion angle distribution period of the diffusion sheet in the light source unit. 11A and 11B, since the period C of the illuminance distribution on the light incident surface of the diffusion sheet 15 is equal to the light source interval S1 between the adjacent cold cathode tubes 11, the diffusion angle distribution period in the surface of the diffusion sheet 15 is It is preferable that the distance between the light sources is substantially equal to S1. In the illuminance distribution on the light incident surface of the diffusion sheet 15, when the illuminance in the region directly above the light source is high, it is preferable to dispose the high diffusion angle region of the diffusion sheet 15 from the viewpoint of eliminating luminance unevenness. FIG. 12 shows an example of the diffusion angle distribution designed to correspond to the illuminance distribution on the light incident surface of the diffusion sheet 15.

  Moreover, the value of the diffusion angle from the light source (cold-cathode tube 11 and the region immediately above the light source of the LED 12 to the region between the light sources) can be adjusted in order to make the luminance uniform. The bottom value is preferably in the range of 11 ° or more and less than 40 °.

  Hereinafter, a specific configuration of the light source unit described in this embodiment will be described with an example.

  For example, the arrangement shown in FIGS. 13A to 13C can be adopted as the configuration of the light source unit. Here, the light source is a CCFL which is a line light source, but the light source may be a point light source such as an LED as shown in FIGS. 14 (a) to 14 (d), for example.

  In the example shown in FIG. 13A, in the configuration shown in FIG. 9B, a fine concavo-convex structure is formed between the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source (cold cathode tube 11). The surface-shaped diffusion sheet 16 formed in the above is disposed, and the surface-shaped diffusion sheet 16 is disposed immediately above the diffusion sheet 15.

  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 shaping type diffusion sheet 16 has a function of condensing the light diffused by the diffusion plate 14 as well as the effect of diffusing and uniformizing the light. By using the surface-shaped diffusion sheet 16 and the diffusion sheet 15 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. 13B, in the configuration shown in FIG. 9B, an array-like prism arrangement structure is provided above the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source (cold cathode tube 11). The optical sheet 17 (hereinafter referred to as “prism sheet”) and the surface-shaped diffusion sheet 16 are arranged in this order. In the example shown in FIG. 13C, in the configuration shown in FIG. 9B, the surface-shaped diffusion sheet 16 is disposed above the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source (cold cathode tube 11). And a prism sheet 17.

  As the prism sheet 17, 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 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 17 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 invention, 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. 14A, in the configuration shown in FIG. 10B, the surface-shaped diffusion sheet 16 is arranged above the diffusion plate 14 and the diffusion sheet 15 arranged just above the light source (LED 12). The prism sheet 17 and the reflective polarizing sheet 18 are arranged in this order. In the example shown in FIG. 14B, in the configuration shown in FIG. 10B, two surface-shaped diffusion sheets 16 are disposed above the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source (LED 12). The reflective polarizing sheet 18 is arranged in this order.

  In the example shown in FIG. 14C, in the configuration shown in FIG. 10B, a surface-shaped diffusion sheet 16 is arranged between the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source (LED 12). Above the diffusion sheet 15, a surface-shaped diffusion sheet 16 having a fine concavo-convex structure formed on the surface and a reflective polarizing sheet 18 are arranged in this order. In the example shown in FIG. 14D, in the configuration shown in FIG. 10B, a prism sheet 17 is arranged between the diffusion plate 14 and the diffusion sheet 15 arranged immediately above the light source, and above the diffusion sheet 15. The surface shaping type diffusion sheet 16 and the reflection type polarizing sheet 18 are arranged in this order.

  As the reflective polarizing sheet 18, 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. 15A, in the configuration shown in FIG. 9A, the diffusion plate 14 is disposed between the light source (cold cathode tube 11) and the diffusion sheet 15, and the surface directly above the diffusion sheet 15. A shaping type diffusion sheet 16 is arranged. In the example shown in FIG. 15B, in the configuration shown in FIG. 9A, the diffusion plate 14 and the surface-shaped diffusion sheet 16 are arranged in this order above the diffusion sheet 15.

  In the example shown in FIG. 15C, in the configuration shown in FIG. 9A, the diffusion plate 14 is disposed between the light source (cold cathode tube 11) and the diffusion sheet 15, and the prism is disposed above the diffusion sheet 15. The sheet 17 and the reflective polarizing sheet 18 are arranged in this order. In the example shown in FIG. 15D, in the configuration shown in FIG. 9A, a diffusion plate 14 is arranged between the light source (cold cathode tube 11) and the diffusion sheet 15, and further above the diffusion sheet 15. Two prism sheets 17 are arranged so that the prism arrangement directions are orthogonal to each other, and the surface-shaped diffusion sheet 16 is further disposed above the prism sheet 17.

  In the example shown in FIG. 16A, in the configuration shown in FIG. 9A, a diffusion plate 14 is disposed between the light source (cold cathode tube 11) and the diffusion sheet 15, and further above the diffusion sheet 15, A light source unit in which a surface-shaped diffusion sheet 16, a prism sheet 17, and a reflective polarizing sheet 18 are arranged in this order is shown. In the example shown in FIG. 16B, in the configuration shown in FIG. 9A, the diffusion plate 14, the surface-shaped diffusion sheet 16, the prism sheet 17, and the reflective polarizing sheet are disposed above the diffusion sheet 15. 18 are arranged in this order.

  The liquid crystal display device of the present embodiment includes a predetermined liquid crystal display panel and the light source unit of the present embodiment described above. For example, a liquid crystal display panel having a liquid crystal layer between two polarizing plates is provided above the light source unit of the present embodiment as shown in FIG.

  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 3 and Comparative Examples 1 and 2 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.

  In Examples 1 to 3 and Comparative Examples 1 and 2, there is no description as an optical sheet, that is, a reflective sheet, a diffuser plate, a surface-shaped diffusion sheet, a prism sheet, and a reflective polarizing sheet. A white reflective sheet (hereinafter abbreviated as RS) made of polyester resin, a diffuser plate (hereinafter abbreviated as DP) having a thickness of 1.5 mm and a diffusing agent concentration of 13000 ppm, and a PET substrate having a thickness of 250 μm An optical sheet (hereinafter abbreviated as MLF) and a reflective polarizing sheet (hereinafter abbreviated as DBEF; manufactured by 3M) were used in which a hemispherical lens was shaped with a UV curable resin.

  For Examples 1 to 3 and Comparative Examples 1 and 2, 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. Moreover, in Example 1, Example 2, and Comparative Example 1, 133 LEDs were arranged in an arrangement as shown in FIG. 17 to produce a light source unit. In Example 3 and Comparative Example 2, 67 LEDs were arranged in an arrangement as shown in FIG. 18 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 is an average value of values calculated in two directions of the X-axis direction and the Y-axis direction.

  In Example 1, Example 2, and Comparative Example 1, first, an average luminance value in the X-axis direction (120 mm) is obtained, and in the Y-axis direction, the luminance value of each point is ± 21.5 mm from each point. The brightness unevenness was obtained as the standard deviation of the value divided by the brightness average value. Similarly, the average luminance value in the Y-axis direction (100 mm) is obtained, and the standard deviation of the value obtained by dividing the luminance value of each point by the average luminance value of ± 37.25 mm from each point in the X-axis direction. Luminance unevenness was obtained. Finally, a value (SD value) obtained by averaging the standard deviation in the X-axis direction and the standard deviation in the Y-axis direction was used as the luminance unevenness of the light source unit.

  In Example 3 and Comparative Example 2, first, an average luminance value in the X-axis direction (120 mm) is obtained, and in the Y-axis direction, the luminance value at each point is a luminance average value for ± 15.2 mm from each point. The luminance unevenness was obtained as the standard deviation of the divided values. Similarly, the average luminance value in the Y-axis direction (100 mm) is obtained, and the standard deviation of the value 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. Luminance unevenness was obtained. Finally, a value (SD value) obtained by averaging the standard deviation in the X-axis direction and the standard deviation in the Y-axis direction 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. The oblique luminance unevenness was measured as the luminance unevenness viewed from the 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. <0.004
X: 0.004 ≦ S. D.
In addition, the criteria for determining the uneven luminance unevenness were classified into two levels (◯, ×) as follows.
○: S. D. <0.008
×: 0.008 ≦ 0.008

Example 1
As shown in FIG. 14B, DP, the diffusion sheet of Example 1, MLF, MLF, 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 in the region immediately above the light source is 88 °, the diffusion angle in the region between the light sources is 14 °, and the diffusion sheet having a varying diffusion angle as shown in FIG. The surface was used as a light emitting surface. Here, the distance h between the light incident surface of RS and DP was set to 29.0 mm. The luminance unevenness in the light source unit of Example 1 was calculated by the above method. The results are shown in Table 1 below. In addition, with respect to the diffusion sheet of Example 1, the arithmetic average value (Av1) of the diffusion angles between adjacent peak points and bottom points, and the diffusion angle arithmetic of all measurement points distributed between the adjacent peak points and bottom points. The average value (Av2) is also shown in Table 1 below. In addition, when the point that is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value is b point, The value of the ratio d / c between the interval c of the cycle and the distance d between two adjacent b points across the bottom point is also shown in any one cycle of the diffusion angle distribution diagram.

(Example 2)
As shown in FIG. 14B, DP, the diffusion sheet of Example 2, MLF, MLF, and DBEF were arranged in this order above the light source to configure the light source unit of Example 2. In the diffusion sheet of Example 2, the diffusion angle of the region immediately above the light source is 85 °, the diffusion angle of the region between the light sources is 13 °, and the diffusion angle is changed as shown in FIG. The surface was used as a light emitting surface. Here, the distance h between the light incident surface of RS and DP was set to 29.0 mm. The luminance unevenness in the light source unit of Example 2 was calculated by the above method. The results are shown in Table 1 below. In addition, with respect to the diffusion sheet of Example 2, the arithmetic average value (Av1) of the diffusion angles of adjacent peak points and bottom points and the diffusion angle arithmetic of all measurement points distributed between the adjacent peak points and bottom points. The average value (Av2) is also shown in Table 1 below. In addition, when the point that is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value is b point, The value of the ratio d / c between the interval c of the cycle and the distance d between two adjacent b points across the bottom point is also shown in any one cycle of the diffusion angle distribution diagram.

Example 3
As shown in FIG. 14B, DP, the diffusion sheet of Example 3, MLF, MLF, and DBEF were arranged in this order above the light source to configure the light source unit of Example 3. In the diffusion sheet of Example 3, the diffusion angle in the region immediately above the light source is 67 °, the diffusion angle in the region between the light sources is 17 °, and the diffusion sheet having a varying diffusion angle as shown in FIG. The surface was used as a light emitting surface. Here, the distance h between the light incident surface of RS and DP was set to 19.0 mm. The luminance unevenness in the light source unit of Example 3 was calculated by the above method. The results are shown in Table 1 below. In addition, with respect to the diffusion sheet of Example 3, the arithmetic average value (Av1) of the diffusion angles of the adjacent peak points and the bottom points and the arithmetic operation of the diffusion angles of all measurement points distributed between the adjacent peak points and the bottom points. The average value (Av2) is also shown in Table 1 below. In addition, when the point that is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value is b point, The value of the ratio d / c between the interval c of the cycle and the distance d between two adjacent b points across the bottom point is also shown in any one cycle of the diffusion angle distribution diagram.

(Comparative Example 1)
As shown in FIG. 14B, DP, the diffusion sheet of Comparative Example 1, MLF, MLF, and DBEF were arranged in this order above the light source to configure the light source unit of Comparative Example 1. The diffusion sheet of Comparative Example 1 has a diffusion angle of 88 ° in the region directly above the light source, a diffusion angle of 15 ° in the region between the light sources, and a diffusion sheet whose diffusion angle is changed as shown in FIG. The surface was used as a light emitting surface. Here, the distance h between the light incident surface of RS and DP was set to 29.0 mm. The luminance unevenness in the light source unit of Comparative Example 1 was calculated by the above method. The results are shown in Table 1 below. In addition, with respect to the diffusion sheet of Comparative Example 1, the arithmetic average value (Av1) of the diffusion angles of adjacent peak points and bottom points, and the diffusion angles of all measurement points distributed between the adjacent peak points and bottom points The average value (Av2) is also shown in Table 1 below. In addition, when the point that is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value is b point, The value of the ratio d / c between the interval c of the cycle and the distance d between two adjacent b points across the bottom point is also shown in any one cycle of the diffusion angle distribution diagram.

(Comparative Example 2)
As shown in FIG. 14B, DP, the diffusion sheet of Comparative Example 2, MLF, MLF, and DBEF were arranged in this order above the light source to configure the light source unit of Comparative Example 2. In the diffusion sheet of Comparative Example 2, the diffusion angle in the region immediately above the light source is 65 °, the diffusion angle in the region between the light sources is 18 °, and the diffusion angle is changed as shown in FIG. The surface was used as a light emitting surface. Here, the distance h between the light incident surface of RS and DP was set to 19.0 mm. The luminance unevenness in the light source unit of Comparative Example 2 was calculated by the above method. The results are shown in Table 1 below. In addition, with respect to the diffusion sheet of Comparative Example 2, the arithmetic average value (Av1) of the diffusion angles of the adjacent peak points and the bottom points and the arithmetic operation of the diffusion angles of all measurement points distributed between the adjacent peak points and the bottom points. The average value (Av2) is also shown in Table 1 below. In addition, when the point that is located between the peak point and the bottom point and shows a diffusion angle equal to the sum of the bottom value and 3/5 of the value obtained by subtracting the bottom value from the peak value is b point, The value of the ratio d / c between the interval c of the cycle and the distance d between two adjacent b points across the bottom point is also shown in any one cycle of the diffusion angle distribution diagram.

  From Table 1, in the diffusion sheets of Examples 1 to 3, all the measurement points in which the arithmetic average value (Av1) of the diffusion angles of the adjacent peak points and the bottom points are distributed between the adjacent peak points and the bottom points. Since it is larger than the arithmetic average value (Av2) of the diffusion angle and satisfies “0.79 ≦ d / c <0.90”, it can be understood that the front luminance unevenness and the oblique luminance unevenness can be effectively reduced. For this reason, it becomes possible to reduce the number of light sources of the light source unit, or to shorten the distance between the light source and the optical sheet.

  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.

11, 101 Cold cathode tube (CCFL)
12, 102 LED
DESCRIPTION OF SYMBOLS 13 Reflective sheet 14 Diffusion plate 15 Diffusion sheet 16 Surface shaping type diffusion sheet 17 Prism sheet 18 Reflective polarizing sheet A1 Area directly above light source A2 Area between light sources A3 High diffusion angle area A4 Low diffusion angle area

Claims (15)

  A diffusion sheet in which a diffusion angle of emitted light when a light beam is incident perpendicularly to a sheet surface periodically changes along a predetermined direction in the sheet surface, and the diffusion sheet in the sheet surface in the predetermined direction In the diffusion angle distribution diagram in which the relative 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, the peak point indicating the peak value of the diffusion angle and the bottom value indicating the bottom value of the diffusion angle There are a plurality of points, and the arithmetic average value of the diffusion angle between the adjacent peak point and the bottom point is distributed between the adjacent peak point and the bottom point. A diffusion angle that is greater than the average value and is located between the peak point and the bottom point and is equal to the sum of the bottom value and 3/5 of the peak value minus the bottom value And point b Then, within any one period of the diffusion angle distribution diagram, the ratio d / c between the period c and the distance d between two adjacent b points across the bottom point is “ A diffusion sheet satisfying 0.79 ≦ d / c <0.90 ”.   The diffusion angle distribution diagram includes a plurality of peak points in one high diffusion angle region, and a diffusion angle distribution between adjacent peak points in the high diffusion angle region is linear. The diffusion sheet described in 1.   In the diffusion angle distribution diagram, a plurality of peak points are included in one high diffusion angle region, and a diffusion angle distribution between adjacent peak points in the high diffusion angle region is a downward convex curve or a curve and a straight line. The diffusion sheet according to claim 1, wherein the diffusion sheet has a mixed shape.   The diffusion angle peak point and the diffusion angle bottom point alternately and periodically, and the arithmetic average value of the diffusion angle at two points of the adjacent peak point and the bottom point 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 point and the bottom point, and the distribution of the diffusion angles includes the peak point and has a convex convex shape, and the diffusion angle 2. The diffusion sheet according to claim 1, wherein the distribution sheet includes a second section including the bottom point and having a downwardly convex curved 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 sheet surface.   The diffusion sheet according to claim 5, wherein the uneven structure is an uneven structure formed using a speckle pattern by interference exposure.   A light source unit comprising two or more light sources and the diffusion sheet according to claim 1 disposed above the light sources.   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.   11. The apparatus according to claim 7, further comprising: a diffusion plate disposed between the diffusion sheet and the light source and containing a diffusing agent therein; and a reflection sheet disposed below the light source. The light source unit according to crab.   The light source unit according to claim 7, 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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