JP2010210828A - Diffusion sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion sheet which can reduce uneven brightness. <P>SOLUTION: Provided is the diffusion sheet in which light incident upon a sheet surface at a right angle is emitted, as emitted light, at a diffusion angle which periodically varies in a predetermined direction in the sheet surface. In a diffusion angle distribution diagram in which the abscissa represents relative positions in the sheet surface in the predetermined direction and the ordinate represents the diffusion angles at the relative positions in the sheet surface, a difference between a maximum value and a minimum value of the diffusion angles is 40° to 80°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a diffusion sheet 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 the 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 technique of injection molding of a resin using a mold, and a technique of processing a concavo-convex structure into a roll with a diamond blade and extrusion molding using the roll.

  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 (Patent Document 1 FIG. 41).

Japanese Patent Laid-Open No. 2001-23422

  However, in recent years, liquid crystal display devices have become thinner, and the distance between a light source and an optical sheet (such as a hologram light guide) for diffusing the light source light has become shorter. In order to reduce cost and power consumption, a method of reducing the number of light sources of the liquid crystal display device is also used. 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. 9A). h ′) and / or p becomes larger (p ′ in FIG. 9B), the luminance unevenness of the backlight becomes more conspicuous. However, in the conventional method disclosed in Patent Document 1, since the optimum distribution range of the diffusion angle is not defined, the luminance unevenness cannot be sufficiently reduced, and the liquid crystal display device can be made thinner and the light source can be reduced. It cannot cope with the reduction of the number.

  This invention is made | formed in view of this point, and it aims at providing the diffusion sheet which can reduce a brightness nonuniformity.

  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 within the sheet surface and the vertical axis represents the diffusion angle at the relative position within the sheet surface, the difference between the maximum value and the minimum value of the diffusion angle is 40 degrees. It is more than 80 degree | times, It is characterized by the above-mentioned.

  In the diffusion sheet of the present invention, in the diffusion angle distribution diagram, it is preferable that a diffusion angle in the entire region within the sheet surface is in a range of 0.1 degrees to 120 degrees.

  In the diffusion sheet of the present invention, it is preferable that the minimum value of the diffusion angle is in a range of 0.1 degrees to 40 degrees.

  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 uneven structure is preferably formed using a speckle pattern by interference exposure.

  The light source unit of the present invention preferably includes 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 this invention, it is preferable to provide the diffusion plate arrange | positioned under the said diffusion sheet and containing 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 diffusion plate which is arrange | positioned above the said diffusion sheet and contains a diffusing agent inside.

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

  The diffusion sheet according to the present invention is a diffusion sheet in which a diffusion angle of emitted light when a light beam is incident on the sheet surface perpendicularly changes periodically along a predetermined direction in the sheet surface, In the diffusion angle distribution diagram in which the horizontal axis represents the relative position in the sheet surface in the direction of the axis and the vertical axis represents the diffusion angle at the relative position in the sheet surface, the difference between the maximum value and the minimum value of the diffusion angle is Since it is 40 degrees or more and 80 degrees or less, it becomes possible to effectively use the difference in diffusion characteristics between the respective portions in the sheet surface, and a light source unit with less luminance unevenness can be provided.

It is a schematic diagram at the time of seeing the diffusion sheet which concerns on embodiment of this invention from the front. It is a schematic diagram at the time of seeing the diffusion sheet which concerns on embodiment of this invention from the front. (A), (b) It is a figure which shows the definition of the diffusion angle in the diffusion sheet which concerns on embodiment of this invention. (A)-(f) is a figure which shows distribution with respect to the relative position in a sheet | seat surface of the diffusion angle in the diffusion sheet which concerns on embodiment of this invention. (A), (b) is a figure which shows the structure of the light source unit which concerns on embodiment of this invention. It is a figure 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 in a sheet | seat surface of the diffusion angle in the diffusion sheet which concerns on embodiment of this invention. It 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 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 cross-section 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.
FIG. 1 is a schematic view when the diffusion sheet of the present invention is viewed from the front, and a high diffusion angle region 1 and a low diffusion angle region 2 are periodically present in the x-axis direction within the diffusion sheet surface. That is, the diffusion angle changes periodically. FIG. 2 is a schematic view of another form of the diffusion sheet of the present invention when viewed from the front, where the high diffusion angle region 3 and the low diffusion angle region 4 are in the x-axis direction and the y-axis direction within the sheet surface. In FIG. 5, it is periodically present, that is, the diffusion angle is periodically changed.

  FIG. 3A is a diagram showing the definition of the diffusion angle of the present invention. The “diffusion angle” in the present invention refers to an angle (FWHM: Full Width Half Maximum) that is twice the angle (half-value angle) at which the transmitted light intensity is attenuated to half the peak intensity. This diffusion angle is, for example, a goniophotometer (GC 5000L) manufactured by Nippon Denshoku Industries Co., Ltd., with the concavo-convex surface of the diffusion sheet 15 as the incident surface, and the transmitted light intensity with respect to the light incident in the normal direction of the concavo-convex surface Can be obtained by measuring the angular distribution of Here, the normal direction of the diffusion sheet refers to the direction shown in FIG.

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

  In the present invention, luminance unevenness is reduced by optimizing the diffusion angle so that the luminance is constant. 4 (a) to 4 (f) are diffusion angle distribution diagrams in the diffusion sheet of the present invention, in which the horizontal position is the relative position in the sheet surface and the vertical axis is the diffusion angle at the position in the sheet surface. It is an example. FIG. 4A to FIG. 4F show examples of diffusion sheets in which the diffusion angle changes in a linear shape, a mixed shape of straight lines and curves, or a staircase shape. The change in the diffusion angle does not have to be strictly linear, curved, or stepped, but may vary slightly from linear, curved, or stepped due to dispersion angle measurement variations, etc. It may be a shape. In particular, it is preferable that the diffusion angle changes smoothly in the plane of the diffusion sheet (FIGS. 4B, 4C, and 4F).

  The diffusion angle of the diffusion sheet of the present invention is preferably controlled in the range of 0.1 to 120 degrees. Here, in order to further improve the uniformity of brightness, the difference in diffusion angle and the distribution state of the diffusion angle can be adjusted. In particular, when the distance between the light source and the diffusion sheet is reduced in order to reduce the thickness (FIG. 9A), or when the interval between the light sources is increased (FIG. 9B), the luminance unevenness increases. A larger difference in diffusion angle is preferred. The diffusion angle is preferably controlled in a range of 0.1 degrees to 100 degrees, and more preferably in a range of 0.1 degrees to 80 degrees, in order to obtain a high front luminance. . In particular, when the diffusion sheet is used in combination with an optical sheet having prism rows formed on the surface, the diffusion angle is formed to be in the range of 0.1 degrees to 70 degrees, and the diffusion angle difference is large. Is preferable from the viewpoint of eliminating uneven brightness and improving brightness.

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

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

  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 speckles is a manufacturing method suitable for changing the diffusion angle in a region within the surface of 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.

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

  A diffusion sheet that has this uneven shape on the surface and changes the diffusion angle in a region within the surface of 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 diffusion angle can be controlled and the concavo-convex structure having different diffusion angles can be recorded.

  In general, the diffusion angle depends on the average size and shape of the speckle. If the speckle is small, the diffusion angle is large. Moreover, the unit structure of the unevenness is not limited to an isotropic one, and an anisotropic one can be formed, or an uneven structure in which both are combined can be formed. If the speckle is an oval in the horizontal direction, the shape of the angular distribution is an oval in the vertical direction. In this way, a sub-master type in which the diffusion angle changes depending on the position is manufactured. A metal is deposited on the sub-master mold by a method such as electroforming, and a speckle pattern is transferred to the metal to produce a master mold. A speckle pattern is transferred to the light extraction surface of the light-transmitting resin layer by forming the light-transmitting resin layer with ultraviolet rays using the master mold. A detailed manufacturing method of the diffusion sheet in which the diffusion angle is changed depending on the position is disclosed in JP-T-2003-525472. All this content is included here. The diffusion angle may be controlled by changing the pitch, height, and aspect ratio of the concavo-convex structure.

Next, a light source unit using the above-described diffusion sheet according to the present invention will be described.
FIGS. 5A and 5B are diagrams showing a schematic configuration of the light source unit according to the embodiment of the present invention. The light source unit according to the present invention basically has a configuration including at least two light sources 11 and 12 and a diffusion sheet 15 according to the present invention disposed above the light sources 11 and 12. Moreover, it is preferable that a reflection sheet 13 for reflecting light is used below the light sources 11 and 12. Therefore, if it has the said structure, you may arrange | position at least 1 optical sheet, a diffusion sheet, etc. further.

  Various reflection sheets 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. The reflection sheet may have a concavo-convex shape on the surface. As these, those having inorganic fine particles added to the surface can be used as necessary.

  The light source unit uses a plurality of light sources. As a light source, a linear light source such as a cold cathode tube (CCFL) 11 as shown in FIG. 5A, a point light source such as an LED (light emitting diode) 12 or a laser as shown in FIG. 5B is used. Can do. In this case, the light sources 11 and 12 are arranged directly below the light incident surface and the light outgoing surface of the diffusion sheet 15 according to the present invention.

  In addition, as the diffusion sheet that can be used in the present invention, 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 are used. Can do. An anisotropic diffusion sheet is, for example, a diffusion sheet having different diffusion angles when the diffusion angles are measured in two orthogonal directions.

  The light source unit of the present invention is characterized in that the period of the diffusion angle distribution of the diffusion sheet is equal to the period of the illuminance distribution on the light incident surface of the diffusion sheet. The illuminance distribution on the light incident surface of the diffusion sheet can be measured by, for example, EZContrastXL88 manufactured by ELDIM. Specifically, in the light source unit provided with the diffusion sheet of the present invention, the omnidirectional luminance distribution is measured by setting the focal point of the apparatus at the position where the light incident surface of the diffusion sheet is located, excluding the diffusion sheet, and the result It is measured by repeating the process of obtaining the integrated intensity from the in-plane measurement target range.

  FIG. 6 is a schematic diagram of an example of the light source unit when viewed from obliquely above. In the light source unit shown in FIG. 6, in the diffusion sheet 15 of the present invention, the diffusion angle is periodically distributed, and the direction in which the diffusion angle is periodically distributed and the direction orthogonal to the longitudinal direction of the CCFL light source 11 are arranged. They are arranged to match.

  FIG. 7 is a diagram showing a light source interval and a diffusion angle distribution period of the diffusion sheet in the light source unit of the present invention. In FIG. 6, since the period of the illuminance distribution on the light incident surface of the diffusion sheet is equal to the interval between the light sources, it is preferable that the diffusion angle distribution period in the diffusion sheet surface according to the present invention is substantially equal to the light source interval. In the illuminance distribution on the light incident surface of the diffusion sheet, when the illuminance in the region directly above the light source is high, it is preferable to dispose a high diffusion angle region of the diffusion sheet from the viewpoint of eliminating luminance unevenness. FIG. 7 shows an example of the diffusion angle distribution designed to correspond to the illuminance distribution on the light incident surface of the diffusion sheet.

  The light source unit according to the present invention can employ other arrangement configurations, for example, the arrangement configurations shown in FIGS. 8A to 8G, using the diffusion sheet of the present invention. FIGS. 8A to 8G are diagrams showing other configurations of the light source unit according to the embodiment of the present invention.

  FIG. 8A shows the configuration shown in FIG. 5A, in which a diffusion plate 14 is disposed between the light source 11 and the diffusion sheet 15 of the present invention, and the lens sheet 16 is directly above the diffusion sheet 15 of the present invention. The light source unit which arrange | positions is shown. FIG. 8B shows a light source unit in which the diffusion plate 14 and the lens sheet 16 are arranged in this order above the diffusion sheet 15 of the present invention in the configuration shown in FIG.

  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 diffusing plates 14 have the effect of diffusing light and making 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 the 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.

  As the lens sheet 16, a sheet in which spherical beads of acrylic resin are applied on a sheet of polyester resin, triacetyl cellulose, polycarbonate, or the like can be used. Further, the lens sheet 16 can be used in a form in which a fine concavo-convex structure made of an ultraviolet curable resin is transferred onto a base material sheet such as polyester resin, triacetyl cellulose, or polycarbonate. Such a lens sheet 16 has the function of condensing the light diffused by the diffusion plate, together with the effect of diffusing and uniformizing the light. By using these lens sheets 16 and the diffusion sheet 15 of the present invention in combination, it is possible to reduce luminance unevenness, reduce the thickness of the light source unit, and reduce the number of light sources.

  FIG. 8C shows a configuration shown in FIG. 5A in which a diffusion plate 14 is disposed between the light source 11 and the diffusion sheet 15 of the present invention, and an array-like structure is disposed above the diffusion sheet 15 of the present invention. A light source unit in which an optical sheet (hereinafter abbreviated as a prism sheet) 17 having a prism arrangement structure and a reflective polarizing sheet 18 are arranged in this order is shown. FIG. 8D shows a configuration shown in FIG. 5A in which a diffusion plate 14 is disposed between the light source 11 and the diffusion sheet 15 of the present invention, and a prism is disposed above the diffusion sheet 15 of the present invention. 2 shows a light source unit in which two sheets 17 are arranged so that the prism arrangement directions thereof are orthogonal to each other, and a lens sheet 16 is further arranged thereon.

  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 apex of the cross-sectional shape can also be preferably used from the viewpoint of improving scratch resistance. These prism sheets can be used in a form in which a prism array made of an ultraviolet curable resin is transferred onto a base material sheet such as polyester resin, triacetyl cellulose, or polycarbonate. Since such 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 of 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.

  FIG. 8E shows a configuration in which the diffusion plate 14 is disposed between the light source 11 and the diffusion sheet 15 of the present invention in the configuration shown in FIG. 5A, and the lens sheet 16 is disposed above the diffusion sheet 15 of the present invention. , A prism unit 17 and a reflective polarizing sheet 18 are shown in this order. FIG. 8 (f) shows the structure shown in FIG. 5 (a) in which the diffusion plate 14, the lens sheet 16, the prism sheet 17, and the reflective polarizing sheet 18 are arranged in this order above the diffusion sheet 15 of the present invention. The light source unit arranged by is shown.

  FIG. 8G shows a structure shown in FIG. 5B in which a diffusion plate 14 is disposed between the light source 12 and the diffusion sheet 15 of the present invention, and the lens sheet 16 is disposed above the diffusion sheet 15 of the present invention. 1 shows a light source unit in which a prism sheet 17, an anti-polarization-type polarizing sheet 18 are arranged in this order.

  These light source units can be used as a liquid crystal display device by supplying light to the liquid crystal display panel.

  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 angle shown in the examples is calculated from the result of measuring the angle distribution of the transmitted light intensity with respect to the light incident in the normal direction of the uneven surface, with the uneven surface of the diffusion sheet as the incident surface, measured with a goniophotometer. Yes. For example, 5 degrees indicates that the diffusion angle in any direction is 5 degrees.

  The diffusion sheet having a diffusion angle distribution in the sheet surface described in the examples and comparative examples, the diffusion angle periodically changes in one direction in the sheet surface, and further includes a light source unit including the diffusion sheet , The direction orthogonal to the longitudinal direction of the CCFL light source is matched with the direction in which the diffusion angle periodically changes. Moreover, the diffusion angle distribution in the surface of the diffusion sheet was designed so as to correspond to the illuminance distribution from the light source, and a region where the diffusion angle of the diffusion sheet was high was arranged and used in a region where the illuminance was high.

  In Examples 1 to 2 and Comparative Examples 1 to 3, for optical sheets that are not described in the examples, that is, for reflective sheets, diffuser plates, lens sheets, prism sheets, and reflective polarizing sheets, A white reflective sheet (hereinafter abbreviated as RS) made of a polyester resin, a polystyrene, and a 1.5 mm thick diffuser plate containing 13000 ppm of silicone fine particles having a particle size of 2 μm and a true specific gravity of 1.35 as a diffusing agent ( (Hereinafter abbreviated as DP), lens sheet (hereinafter abbreviated as DS) in which resin beads and binder are coated on a PET substrate having a thickness of 250 μm, apex angle 90 °, pitch on a PET substrate having a thickness of 250 μm Prism sheet (hereinafter abbreviated as “prism sheet”) in which a 50 μm prism array is formed of UV curable resin, reflective type Light sheet (hereinafter, DBEF made of abbreviated .3M Co., Ltd.) was used.

In Examples 1 to 3 and Comparative Examples 1 to 6, a CCFL light source having a diameter of 3.0 mmφ and a length of 710 mm was used as the light source of the light source unit. The CCFL light sources are arranged in parallel in the longitudinal direction, the distance between the RS and the center of the diameter of the light source is 3.8 mm, and 16 are arranged so that the distance p between the light sources is 23.7 mm. A light source unit was prepared. Luminance and luminance unevenness were measured using a Konica Minolta two-dimensional color luminance meter (CA2000) at a distance of 75 cm from the light source unit, and the average luminance value measured in the range of 20 mm × 190 mm in the center of the light source unit as luminance. did. The luminance unevenness is obtained as an average luminance value in the x-axis (20 mm) direction, and the standard deviation of the value obtained by dividing the luminance value of each point by the average luminance value of ± 11.8 mm from each point in the y-axis direction. Luminance unevenness was obtained.
Here, the judgment criteria for luminance unevenness were classified into the following three levels (◎, ○, ×).
A: S. D. ≦ 0.002
A: 0.002 <S. D. ≦ 0.004
X: 0.004 <S. D.

  Example 1 and Example 2 and Comparative Examples 1 to 3 were evaluated in a light source unit having a basic configuration as shown in FIG.

Example 1
As shown in FIG. 8E, DP, the diffusion sheet of the present invention, the DS, the prism sheet, and the DBEF were arranged in this order above the light source to constitute the light source unit of Example 1. The diffusion sheet of the present invention has a maximum diffusion angle value of 70 degrees, a minimum value of 1 degree, and a diffusion angle difference of 69 degrees. As shown in FIG. A diffusion sheet in which the diffusion angle is distributed was arranged so that the uneven surface becomes the light exit surface. Here, the distance h between the CCFL light source and the light incident surface of the DP was 4.5 mm. The luminance in the light source unit of Example 1 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 1 below.

(Example 2)
As shown in FIG. 8 (c), the diffusion plate formed with the lenticular lens, the diffusion sheet of the present invention, the prism sheet, and the DBEF are arranged in this order above the light source, and the light source unit of Example 2 is arranged. Configured. The diffusion plate used in Example 2 is made of polystyrene having a thickness of 1.5 mm, contains 2000 ppm of a diffusing agent inside, and a lenticular lens having a height of 130 μm and a pitch of 320 μm is parallel to the longitudinal direction of the CCFL light source. Many are formed in the direction. In the diffusion sheet of the present invention, the maximum value of the diffusion angle is 80 degrees, the minimum value of the diffusion angle is 40 degrees, and the diffusion angle difference is 40 degrees. As shown in FIG. A diffusion sheet having a smoothly distributed diffusion angle was disposed so that the uneven surface becomes the light exit surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion plate was 4.5 mm. The luminance in the light source unit of Example 2 was measured, and the luminance unevenness was calculated by the above method. The results are also shown in Table 1 below.

(Comparative Example 1)
As shown in FIG. 8E, a diffusion sheet having a concavo-convex structure characterized by a non-planar speckle on the surface, DS, a prism sheet, and DBEF are arranged in this order above the light source and compared. The light source unit of Example 1 was configured. The diffusion sheet used in (Comparative Example 1) has a maximum diffusion angle value of 40 degrees, a minimum value of 5 degrees, and a diffusion angle difference of 35 degrees. As shown in FIG. The diffusion angle is distributed smoothly in the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was 4.5 mm. The luminance in the light source unit of Comparative Example 1 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 1 below.

(Comparative Example 2)
As shown in FIG. 8E, a diffusion sheet having a concavo-convex structure characterized by a non-planar speckle on the surface, DS, a prism sheet, and DBEF are arranged in this order above the light source and compared. The light source unit of Example 2 was configured. The diffusion sheet used in Comparative Example 2 has a maximum diffusion angle value of 105 degrees, a minimum value of 20 degrees, and a diffusion angle difference of 85 degrees. As shown in FIG. The diffusion angle is distributed smoothly in the interior. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was 4.5 mm. The luminance in the light source unit of Comparative Example 2 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 1 below.

(Comparative Example 3)
As shown in FIG. 8E, a DP, a diffusion sheet having a concavo-convex structure formed using a speckle pattern by interference exposure, DS, a prism sheet, and DBEF are arranged in this order above the light source. Thus, the light source unit of (Comparative Example 3) was configured. The diffusion sheet used in Comparative Example 3 has a diffusion angle of 71 degrees in the entire region within the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was 4.5 mm. The luminance in the light source unit of Comparative Example 3 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 1 below.

  From Table 1, a light source unit having a DP / diffusion sheet / prism sheet / DBEF configuration shown in FIG. 8C or a diffusion plate / diffusion sheet / DS / prism sheet / DBEF configuration shown in FIG. In the diffusion sheet of the present invention, the uneven brightness was reduced compared to the case where the difference in diffusion angle was not in the range of 40 degrees to 80 degrees (Comparative Examples 1, 2, and 3). Furthermore, in the configuration of Comparative Example 3, when the distance h from the center of the CCFL light source diameter to the DP light incident surface is changed, the luminance equivalent to that of Examples 1 and 2 is obtained when h = 12.5. It became uneven. In the first and second embodiments, considering that h = 4.5, the distance h from the center of the CCFL light source diameter to the DP incident surface can be reduced by 8 mm compared to the first comparative example. (FIG. 9A), it can be seen that the light source unit can be thinned.

  Example 3 and Comparative Examples 4 to 6 were evaluated in a light source unit having a basic configuration as shown in FIG.

Example 3
As shown in FIG. 8 (f), the diffusion sheet, DP, DS, prism sheet, and DBEF of the present invention were arranged in this order above the light source to constitute the light source unit of Example 3. The diffusion sheet of the present invention has a maximum diffusion angle value of 70 degrees, a minimum value of 1 degree, and a diffusion angle difference of 69 degrees. As shown in FIG. A diffusion sheet in which the diffusion angle is distributed was disposed so that the uneven surface becomes the light exit surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was set to 9.1 mm. The luminance in the light source unit of Example 3 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 2 below.

(Comparative Example 4)
As shown in FIG. 8 (f), a diffusion sheet having a concavo-convex structure characterized by non-planar speckles on the surface, DP, DS, prism sheet, and DBEF are arranged in this order above the light source for comparison. The light source unit of Example 4 was configured. The diffusion sheet used in Comparative Example 4 has a maximum diffusion angle of 30 degrees, a minimum value of 0.1 degrees, and a diffusion angle difference of 30 degrees. As shown in FIG. The diffusion angle is distributed smoothly in the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was set to 9.1 mm. The luminance in the light source unit of Comparative Example 4 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 2 below.

(Comparative Example 5)
As shown in FIG. 8 (f), a diffusion sheet having a concavo-convex structure characterized by non-planar speckles on the surface, DP, DS, prism sheet, and DBEF are arranged in this order above the light source for comparison. The light source unit of Example 5 was configured. The diffusion sheet used in Comparative Example 5 has a maximum diffusion angle of 100 degrees, a minimum value of 0.1 degrees, and a diffusion angle difference of 100 degrees. As shown in FIG. The diffusion angle is distributed smoothly in the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was set to 9.1 mm. The luminance in the light source unit of Comparative Example 5 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 2 below.

(Comparative Example 6)
As shown in FIG. 8F, a diffusion sheet having a concavo-convex structure formed on the surface using a speckle pattern by interference exposure, DP, DS, prism sheet, and DBEF are arranged in this order above the light source. And the light source unit of the comparative example 6 was comprised. The diffusion sheet used in Comparative Example 6 has a diffusion angle of 71 degrees in the entire region. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was set to 9.1 mm. The luminance in the light source unit of Comparative Example 6 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 2 below.

  From Table 2, in the light source unit having the configuration of diffusion sheet / DP / DS / BEF / DBEF shown in FIG. 8 (f), the diffusion sheet of the present invention has a diffusion angle difference in the range of 40 degrees to 80 degrees. The brightness unevenness was reduced as compared with the cases not in the above (Comparative Examples 4, 5, 6). Further, in the configuration of Comparative Example 6, when the distance h from the center of the diameter of the CCFL light source to the diffusion sheet incident surface is changed, the luminance unevenness equivalent to that of Example 3 is obtained at h = 12.5. It became. In Example 3, considering that h = 9.5, the distance h from the center of the diameter of the CCFL light source to the light incident surface of the diffusion sheet can be reduced by 3 mm compared to Comparative Example 6. (FIG. 9A), it can be seen that the light source unit can be thinned.

In Example 4 and Comparative Examples 7 to 8, a CCFL light source having a diameter of 3.4 mmφ and a length of 710 mm was used as the light source of the light source unit. The CCFL light sources are arranged in parallel in the longitudinal direction, the distance between the RS and the center of the diameter of the light source is 3.8 mm, and eight are arranged so that the distance p between the light sources is 47.6 mm. A light source unit was prepared. Luminance and luminance unevenness were measured using a Konica Minolta two-dimensional color luminance meter (CA2000) at a distance of 75 cm from the light source unit, and the average luminance value measured in the range of 20 mm × 190 mm in the center of the light source unit as luminance. did. The luminance unevenness is obtained as an average luminance value in the x-axis (20 mm) direction, and in the y-axis direction, the standard deviation of the value obtained by dividing the luminance value of each point by the average luminance value of ± 23.8 mm from each point. Luminance unevenness was obtained.
Here, the judgment criteria for luminance unevenness were classified into the following three levels (◎, ○, ×).
A: S. D. ≦ 0.002
A: 0.002 <S. D. ≦ 0.004
X: 0.004 <S. D.

  Example 4 and Comparative Examples 7 to 8 were evaluated in a light source unit having a basic configuration as shown in FIG.

Example 4
As shown in FIG. 8E, DP, the diffusion sheet of the present invention, the DS, the prism sheet, and the DBEF are arranged in this order above the light source to constitute the light source unit of Example 4. The diffusion sheet of the present invention has a maximum diffusion angle value of 50 degrees, a minimum diffusion angle value of 1 degree, and a diffusion angle difference of 49 degrees. As shown in FIG. A diffusion sheet having a smoothly distributed diffusion angle was used so that the uneven surface becomes the light exit surface. Here, the distance h between the CCFL light source and the light incident surface of the DP was 14.5 mm. The luminance in the light source unit of Example 4 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 2 below.

(Comparative Example 7)
As shown in FIG. 8E, a diffusion sheet having a concavo-convex structure characterized by DP on the light source and a non-planar speckle on the surface, DS, prism sheet, DBEF are arranged in this order, and a comparative example Seven light source units were constructed. The diffusion sheet used in Comparative Example 7 has a maximum diffusion angle of 30 degrees, a minimum value of 0.1 degrees, and a diffusion angle difference of 30 degrees. As shown in FIG. The diffusion angle is distributed smoothly in the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was 14.5 mm. The luminance in the light source unit of Comparative Example 7 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 3 below.

(Comparative Example 8)
As shown in FIG. 8E, a diffusion sheet having a concavo-convex structure characterized by a DP above the light source and a non-planar speckle on the surface, DS, a prism sheet, and DBEF are arranged in this order. Eight light source units were constructed. The diffusion sheet used in Comparative Example 8 has a maximum diffusion angle value of 100 degrees, a minimum value of 0.1 degrees, and a diffusion angle difference of 100 degrees. As shown in FIG. The diffusion angle is smoothly distributed in the sheet surface. In addition, the said diffusion sheet was arrange | positioned so that an uneven surface may become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the diffusion sheet was 14.5 mm. The luminance in the light source unit of Comparative Example 8 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 3 below.

(Comparative Example 9)
As shown in FIG. 8E, a diffusion sheet having a concavo-convex structure characterized by DP above the light source and non-planar speckles on the surface, and a diffusion angle of 41 degrees over the entire region, DS , Prism sheet, and DBEF were arranged in this order to constitute a light source unit of Comparative Example 9. In addition, the said diffusion sheet was used so that an uneven surface might become a light emission surface. Here, the distance h between the CCFL light source and the light incident surface of the DP was 14.5 mm. The luminance and luminance unevenness in the light source unit of Comparative Example 9 were measured by the above method. The results are also shown in Table 3 below.

  From Table 3, in the light source unit having the configuration of DP / diffusion sheet / DS / prism sheet / DBEF shown in FIG. 8 (e), the diffusion sheet of the present invention has a diffusion angle difference in the range of 40 degrees to 80 degrees. As compared with the case where the difference is not present (Comparative Examples 7, 8, 9), the luminance unevenness could be reduced. Further, in the configuration of Comparative Example 9, when the center-to-center distance p of the CCFL light source diameter was changed, the luminance unevenness equivalent to Example 4 was obtained at p = 23.7. In Example 4, considering that p = 47.6, the center-to-center distance p of the diameter of the CCFL light source can be increased approximately twice as compared with Comparative Example 9 (FIG. 9B). As a result, it can be seen that the number of CCFL light sources can be reduced.

  In Example 5 and Example 6, Comparative Example 10 and Comparative Example 11, what is not particularly described as an optical sheet, that is, for a reflective sheet, a diffuser plate, a lens sheet, a prism sheet, and a reflective polarizing sheet, A white reflection sheet made of polyester resin (hereinafter abbreviated as RS), made of polystyrene, and containing 20000 ppm of silicone fine particles having a particle diameter of 2 μm and a true specific gravity of 1.35 as a diffusing agent (hereinafter referred to as 2.0 mm thick) Abbreviated as DP), a diffusion sheet (hereinafter abbreviated as DS) in which resin beads and a binder are coated on a 250 μm thick PET substrate, and an apex angle of 90 degrees and a pitch of 50 μm on a 250 μm thick PET substrate. Prism sheet (hereinafter abbreviated as “prism sheet”) in which prism rows are formed of UV curable resin, reflective polarizing sheet (Hereinafter abbreviated .3M manufactured by the DBEF) was used.

  Moreover, about Example 5, Example 6, Comparative Example 10, and Comparative Example 11, the white LED light source made from CREE 3.5mm square and 2.0mm in height was used as a light source of a light source unit. The distance between the centers of the light sources was set to 24.0 mm in the x-axis direction and the y-axis direction, and 10 rows were arranged in a grid and arranged to form a light source unit. Luminance and luminance unevenness were measured using a Konica Minolta 2-dimensional color luminance meter (CA2000), 70 cm away from the light source unit, and the average luminance value measured in the range of 120 mm × 120 mm in the center of the light source unit as luminance. did.

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 luminance unevenness is obtained as a standard deviation of values obtained by dividing the luminance value of each point by the average luminance value of ± 12 mm from each point in the y-axis direction. Asked. Similarly, the average luminance value in the y-axis (100 mm) direction is obtained, and the luminance unevenness is obtained as a standard deviation of values obtained by dividing the luminance value of each point by the average luminance value of ± 12 mm from each point in the x-axis direction. Asked. Finally, a 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, the distribution of diffusion angles on the x-axis and the y-axis was considered as shown in FIG.
Here, the judgment criteria for luminance unevenness were classified into the following three levels (◎, ○, ×).
A: S. D. ≦ 0.002
A: 0.002 <S. D. ≦ 0.004
X: 0.004 <S. D.

(Example 5)
As shown in FIG. 8 (g), DP, the diffusion sheet of the present invention, DS, the prism sheet, and DBEF were arranged in this order above the light source to constitute the light source unit of Example 5. The diffusion sheet of the present invention has a maximum diffusion angle of 70 °, a minimum diffusion angle of 10 °, and a diffusion angle difference of 60 °. As shown in FIG. 4B, the diffusion angle is smooth. A changing diffusion sheet was used so that the uneven surface becomes the light exit surface. Here, the distance h between the light incident surface of RS and DP was set to 16.0 mm. The luminance in the light source unit of Example 5 was measured, and the luminance unevenness was calculated by the above method. The results are shown in Table 4 below.

(Example 6)
As shown in FIG. 8G, DP, the diffusion sheet of the present invention, the DS, the prism sheet, and the DBEF were arranged in this order above the light source to constitute the light source unit of Example 6. The diffusion sheet of the present invention has a maximum diffusion angle of 50 °, a minimum diffusion angle of 5 °, and a diffusion angle difference of 45 °. As shown in FIG. 4B, the diffusion angle is smooth. A changing diffusion sheet was used so that the uneven surface becomes the light incident surface. Here, the distance h between the light incident surface of RS and DP was set to 16.0 mm. The luminance in the light source unit of Example 6 was measured, and the luminance unevenness was calculated by the above method. The results are also shown in Table 4 below.

(Comparative Example 10)
As shown in FIG. 8 (g), diffusion has a concavo-convex structure formed using DP above the light source and a speckle pattern formed by interference exposure on the surface, and the diffusion angle is 70 ° over the entire region. The sheet, DS, prism sheet, and DBEF were arranged in this order to configure the light source unit of Comparative Example 10. In addition, the said diffusion sheet was used so that an uneven surface might become a light emission surface. Here, the distance h between the light incident surface of RS and DP was set to 16.0 mm. The luminance in the light source unit of Comparative Example 10 was measured, and the luminance unevenness was calculated by the above method. The results are also shown in Table 4 below.

(Comparative Example 11)
As shown in FIG. 8 (g), diffusion has a concavo-convex structure formed using DP above the light source and a speckle pattern formed by interference exposure on the surface, and the diffusion angle is 50 ° over the entire region. The sheet, DS, prism sheet, and DBEF were arranged in this order, and the light source unit of Comparative Example 11 was configured. In addition, the said diffusion sheet was used so that an uneven surface may become a light-incidence surface. Here, the distance h between the light incident surface of RS and DP was set to 16.0 mm. The luminance in the light source unit of Comparative Example 11 was measured, and the luminance unevenness was calculated by the above method. The results are also shown in Table 4 below.

  From Table 4, in the light source unit having the configuration of DP / diffusion sheet / DS / prism sheet / DBEF shown in FIG. 8 (g), the diffusion sheet of the present invention has a diffusion sheet with a uniform diffusion angle over the entire region ( As compared with the configuration using Comparative Examples 10 and 11), the luminance unevenness could be reduced. Further, in the configurations of Comparative Examples 10 and 11, when the distance h between RS and DP was changed, the luminance unevenness equivalent to that in Examples 5 and 6 was obtained at h = 32.0. In Examples 5 and 6, considering that h = 16.0, compared to Comparative Examples 10 and 11, the distance h from the RS to the DP incident surface can be reduced to about half by 16 mm. It can be seen that the light source unit can be thinned.

  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. 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 of a display device such as a liquid crystal display device.

1,3 High diffusion angle region 2,4 Low diffusion angle region 11 CCFL (Cold cathode tube)
12 LED (Light Emitting Diode)
DESCRIPTION OF SYMBOLS 13 Reflective sheet 14 Diffusion plate 15 Diffusion sheet 16 Lens sheet 17 Prism sheet 18 Reflective polarizing sheet

Claims (14)

  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 a relative position in the sheet surface in the predetermined direction Is a diffusion angle distribution diagram in which the horizontal axis represents the diffusion angle at a position in the sheet surface and the vertical axis represents the diffusion angle, the difference between the maximum value and the minimum value of the diffusion angle is 40 degrees or more and 80 degrees or less. Characteristic diffusion sheet.   2. The diffusion sheet according to claim 1, wherein in the diffusion angle distribution diagram, the diffusion angle in the entire region is in a range of 0.1 degrees or more and 120 degrees or less.   The diffusion sheet according to claim 1 or 2, wherein a minimum value of the diffusion angle in the diffusion angle distribution diagram is 0.1 degrees or more and 40 degrees or less.   The diffusion sheet according to any one of claims 1 to 3, wherein the diffusion angle is generated by an uneven structure formed on the surface of the diffusion sheet.   The diffusion sheet according to any one of claims 1 to 4, wherein the concavo-convex structure is 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 6, wherein the light source is a linear light source.   The light source unit according to claim 6, wherein the light source is a point light source.   The light source unit according to any one of claims 6 to 8, 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.   10. The device according to claim 6, further comprising: a diffusion plate disposed below the diffusion sheet and containing a diffusing agent therein; and a reflection sheet disposed below the light source. The light source unit described.   The light source unit according to any one of claims 6 to 10, further comprising a lens sheet disposed above the diffusion sheet.   The light source unit according to claim 6, further comprising a prism sheet disposed above the diffusion sheet.   The light source unit according to any one of claims 6 to 12, further comprising a diffusion plate disposed above the diffusion sheet and containing a diffusing agent therein.   A liquid crystal display device comprising: a liquid crystal display panel; and the light source unit according to claim 6 for supplying light to the liquid crystal display panel.