JP2011081366A - Diffusion sheet, light source unit and liquid crystal display device - Google Patents

Abstract

To provide a diffusion sheet capable of suppressing luminance unevenness.
A diffusion sheet in which fine irregularities are provided unevenly on a surface, wherein a maximum portion (Ry) of the fine irregularities is 2 μm or less, and a maximum height (Ry) of the fine irregularities And a rough surface portion larger than 2 μm, and the flat portion provides a diffusion sheet existing so as to surround the rough surface portion.
[Selection] Figure 1

Description

  The present invention relates to an optical technique, and relates to a diffusion sheet, a light source unit, and a liquid crystal display device.

  Currently, liquid crystal display devices are used in a wide range of fields such as cellular phones, personal digital assistants (PDAs), digital cameras, televisions, personal computer displays, and notebook computers. In a liquid crystal display device, for example, a light source unit is disposed 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 the liquid crystal display device is required to supply not only uniform light to the liquid crystal display panel but also as much light as possible in order to make the display image easy to see. That is, the light source unit is required to have optical characteristics that are excellent in uniformity and can realize high luminance.

  In a conventional light source unit, a plurality of point light sources (for example, LEDs) or a plurality of line light sources (for example, CCFL: Cold Cathode Fluorescent Lamp) are usually used. In order to make the distribution of light uniform, for example, a light guide plate having a uniform concavo-convex structure on the entire surface, or an optical member made of a diffusion plate containing a diffusing agent inside, a diffusion sheet, a prism sheet, A combination with a plurality of optical sheets such as a reflective polarizing sheet has been used. However, in recent years, liquid crystal display devices have been required to be thinner and save power, and the thickness of the light source unit and the number of light sources have been reduced. Due to the reduction in the thickness of the light source unit and the reduction in the number of light sources, the amount of light flux emitted from the light source unit and the variation in the light vector are remarkably increased. For this reason, the conventional optical member having a uniform concavo-convex structure formed on the entire surface is not sufficiently effective in reducing luminance unevenness. In addition, a decrease in luminance is unavoidable with an optical member made of a diffusion plate containing a diffusing agent therein.

  In Patent Document 1, a mold for pattern transfer is manufactured by recording a concavo-convex structure on a photosensitive medium by speckle of a laser beam, and using the manufactured mold, a guide for a large liquid crystal display device of a direct type is disclosed. An invention for controlling the area density of a pattern of a hologram light guide plate having a concavo-convex structure formed on the surface of an optical plate is disclosed (see, for example, FIG. 41 of Patent Document 1). In Patent Document 1, the area density of the hologram pattern in the region corresponding to the position immediately above the light source on the surface of the light guide plate is made higher than the area density of the region corresponding to the position between the plurality of light sources, There is a description that luminance unevenness can be effectively reduced.

  Patent Document 2 discloses an invention in which, for example, a lens group or a prism array having different curvatures is formed on the surface of a diffusion sheet by transfer from a die cut by a cutting tool, and the degree of diffusion is changed in the plane. ing. Patent Document 2 describes an example in which uneven brightness can be reduced by disposing a wide diffusion region on a light source and a narrow diffusion region between a plurality of light sources.

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

  However, since all of the light guide plates disclosed in Patent Document 1 simply form a portion where the diffusion angle is changed in a band shape in the plane, the thickness of the light source unit is reduced and the number of light sources is reduced. There is a problem that it can not cope.

  In addition, the uneven structure on the surface of the diffusion sheet such as a lens group or a prism array that can be manufactured by the manufacturing method disclosed in Patent Document 2 has a discrete change and a low degree of design freedom. It is difficult to cope with variations in the light vector in the light source unit due to a decrease in the number of light sources and a decrease in the number of light sources. Further, since the lens group or the prism array has a size of several tens of μm or more and the arrangement thereof is regular, there is a problem that moire fringes are generated between the lens group and the prism array.

  The present invention has been made in view of such problems, and in a so-called light-saving model in which the thickness of the light source unit and the number of light sources are reduced, a diffusion sheet, a light source unit, and a liquid crystal capable of suppressing luminance unevenness An object is to provide a display device.

  According to a first aspect of the present invention, there is provided a diffusion sheet in which fine irregularities are provided unevenly on a surface, a flat portion having a maximum height (Ry) of the fine irregularities of 2 μm or less, and a maximum of the fine irregularities. And a rough surface portion having a height (Ry) larger than 2 μm, and the flat portion is a diffusion sheet existing so as to surround the rough surface portion.

According to a second aspect of the present invention, there is provided a diffusion sheet in which fine irregularities are provided unevenly on a surface, wherein an emission angle of light emitted from the surface is a horizontal axis, and an intensity of light emitted from the surface is longitudinal. In the light emission pattern distribution as an axis, the intensity of the emitted light is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM, which is twice the emission angle at which the intensity of the emitted light is half the peak intensity. The gist of the diffusion sheet is that the ratio FWTM / FWHM of the angle FWTM is 1.5 or more and 10 or less.

According to a third aspect of the present invention, there is provided a diffusion sheet in which fine irregularities are provided unevenly on a surface, wherein an emission angle of light emitted from the surface is a horizontal axis, and an intensity of light emitted from the surface is longitudinal. Diffusion pattern in which the integrated value of the intensity of light emitted in the direction of 30 ° or less from the normal direction of the surface is 50% to 99.5% with respect to the integrated value of the entire emitted light pattern The gist is the sheet.

According to a fourth aspect of the present invention, there is provided a diffusion sheet in which fine irregularities are provided unevenly on a surface, wherein an emission angle of light emitted from the surface is a horizontal axis, and an intensity of light emitted from the surface is longitudinal. In the light emission pattern distribution as the axis, x is the ratio (%) of the integral value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface to the integral value of the entire light emission pattern, and x of the emitted light. When y is a ratio FWTM / FWHM of an angle FWTM that is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM that is twice the emission angle at which the intensity is half the peak intensity The gist is a diffusion sheet characterized by satisfying the following formula (1).
y> 0.011x + 0.64 (where 50 <x <100, 1.5 <y ≦ 2.5) (1)

  According to a fifth aspect of the present invention, there is provided a light source unit comprising two or more light sources that emit light and the diffusion sheet according to any one of the first to fourth aspects of the present invention arranged in parallel with the light sources. It is a summary.

  The gist of a sixth aspect of the present invention is a liquid crystal display device comprising a liquid crystal display panel and the light source unit according to the fifth aspect of the present invention for supplying 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 suppress luminance unevenness of the screen.

It is sectional drawing which shows typically the structure of the flat part and rough surface part of the diffusion sheet which concern on the 1st Embodiment of this invention. It is a schematic diagram for demonstrating the incident angle of the light which injects into an optical sheet from the diagonal which concerns on the 1st Embodiment of this invention. It is a schematic diagram for demonstrating the difference of the average height of the flat part and rough surface part which concern on the 1st Embodiment of this invention. It is a top view for demonstrating the width | variety L of the rough surface part of the diffusion sheet which concerns on the 1st Embodiment of this invention. It is a typical 1st graph which shows the relationship between the emission angle of the emitted light of the diffusion sheet which concerns on the 1st Embodiment of this invention, and intensity | strength. It is a perspective view of the light source unit which concerns on the 2nd Embodiment of this invention. FIG. 3 is a layout view of LED light sources according to an embodiment of the present invention. It is a surface shape photograph of an example of the diffusion sheet which has a flat part / rough surface part structure. In the photograph, the long side is 100 μm and the short side is 75 μm. The ratio of height and width to height is 1: 1, and no enlargement / reduction in the z direction is performed. It is a surface shape photograph of an example of the sheet base material which does not have a flat part / rough surface part structure. In the photograph, the long side is 100 μm and the short side is 75 μm. The ratio of height and width to height is 1: 1, and no enlargement / reduction in the z direction is performed. It is a surface structure photograph of an example of a commercial diffusion sheet. 8 is a light emission pattern distribution with the horizontal axis representing the emission angle of light emitted from the surface and the vertical axis representing the intensity of light emitted from the surface for the diffusion sheets of FIGS. Both diffusion angles are 35 °. It is the light emission pattern distribution which made the intensity | strength of the light radiate | emitted from the surface the vertical axis | shaft about two examples of the diffusion sheet which concerns on this invention at the diffusion angle of 25 degrees. It is a surface shape photograph of an example of the sheet base material which does not have a flat part / rough surface part structure.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
The diffusion sheet according to the first embodiment relates to the first aspect described above, and as shown in FIG. 1, the diffusion sheet is provided with uneven unevenness on the surface, and has a maximum of the fine unevenness. A flat portion having a height (Ry) of 2 μm or less and a rough surface portion having a maximum height (Ry) of the fine irregularities of greater than 2 μm, and the flat portion is present so as to surround the rough surface portion. It is a diffusion sheet.
Examples of the structure composed of the flat portion and the rough surface portion as described above include a sea-island structure in which the flat portion is the sea and the rough surface portion is an island, and a structure in which this uneven structure is inverted. The cross sections of these structures are shown, for example, in the cross sectional view of FIG. 1 (a) or FIG. 1 (b).

  Here, on the surface of the diffusion sheet, both the flat portion and the rough surface portion have a structure in which fine irregularities are provided unevenly. The structure in which the fine unevenness is provided non-uniformly means that at least one of the shape, pitch, and height of the fine unevenness is not uniform. The fine unevenness means that the uneven structure is a regular shape such as a cylinder, a prism, or a hemisphere (including similar shapes), and the uneven structure is regularly arranged. .

A typical structure with non-uniform shapes, pitches, and heights has a continuous non-uniform wavy uneven structure as shown in FIGS. 8 and 9, which is a speckle pattern formed by interference exposure. It is a structure based on the three-dimensional structure formed by using. In addition to this, the spherical beads having a uniform shape on the surface are randomly embedded, that is, the structure in which the pitch and the height are not constant, as long as the requirements of FWTM / FWHM described later are satisfied. It falls into the category of the structure in which the fine irregularities are provided unevenly. Furthermore, the case where the height of the lenticular lens or the prism is irregular or the pitch is irregular is also a category of the embodiment of the present invention.

  Even if the uneven structure of the beads, the lenticular lens, or the prism structure is used, if any of the shape, height, and pitch is not uniform, the effects of suppressing the occurrence of moire and light unevenness can be exhibited. And the thing of the continuous uneven wave-like uneven structure as shown in FIG. 9 is remarkably excellent in those effects.

The maximum height (Ry) of the fine irregularities in the flat portion is 2 μm or less. The flat part may be completely flat, but it is not completely flat, and it is preferable that irregularities with Ry of 2 μm or less are formed unevenly. On the other hand, in the rough surface portion, the maximum height (Ry) of the fine irregularities is larger than 2 μm.
Further, in the flat portion, the ten-point average roughness (Rz) measured with a minimum width of 5 μm is preferably 1 μm or less. More preferably, it is 0.6 micrometer or less, More preferably, it is 0.3 micrometer or less. On the other hand, in the rough surface portion, the ten-point average roughness (Rz) measured with a minimum width of 5 μm is preferably 2 μm or more.

The maximum height (Ry) and average height and ten-point average roughness (Rz) of the fine irregularities of the rough surface portion / flat portion are, for example, an ultra-deep color 3D shape measuring microscope (VK-9500) manufactured by Keyence Corporation. It can be measured using an atomic force microscope (AFM).
FIG. 8 is a diagram showing a surface structure of a typical first embodiment, which has a non-uniform uneven structure and a rough surface portion surrounded by a flat portion. The portion of the mountain that appears black in the figure is the rough surface portion, and the portion of the valley that appears white corresponds to the flat portion.

On the other hand, FIG. 9 shows a structure that does not have a flat portion although it has a non-uniform uneven structure on the whole surface.
Even if the structure does not have a flat part as shown in FIG. 9, if the fine unevenness is non-uniform, it will be effective in preventing moire and screen uniformity, but the flat part is partially shown in FIG. If this structure is present, this portion has low diffusion, and the luminance can be improved without impairing the uniformity of the screen.

  As shown in FIG. 2, the diffusion sheet having a rough surface portion surrounded by a flat portion in the plane according to the first embodiment has incident light incident obliquely on the diffusion sheet from the light source as a normal direction of the emission surface. Therefore, the in-plane luminance can be improved. Here, the incident angle of light refers to an angle formed by incident light with respect to the normal line of the incident surface of the diffusion sheet. The diffusion sheet according to the first embodiment particularly efficiently launches light incident at an angle of 10 to 80 °. At the same time, the flat portion can transmit light from directly below in the normal direction. In this way, the flat part and the rough surface part are mixed on a minute scale, in other words, the low diffusion angle part and the high diffusion angle part are mixed on a minute scale, so that the entire surface is efficiently transmitted in the normal direction of the exit surface. The front luminance can be increased compared to the average diffusion angle of the entire sheet.

  In the diffusion sheet having the rough surface portion surrounded by the flat portion according to the first embodiment in the plane, the average height of the flat portion and the average height of the rough surface portion are different as shown in FIG. It is preferable. The difference is preferably 0.1 μm or more and less than 20 μm. In order to obtain a high light rising effect, that is, high luminance, the difference between the average height of the flat portion and the average height of the rough surface portion is preferably 0.5 μm to 20 μm, more preferably 1 μm to 15 μm, and more preferably 2 μm to 12 μm. More preferably, 3 μm to 10 μm is particularly preferable. In addition, in FIG. 3, although the case where the average height of a rough surface part is higher than the average height of a flat part is shown, the average height of a flat part may be higher than the average height of a rough surface part. However, the preferable difference in average height is the same.

  In the diffusion sheet having the rough surface portion surrounded by the flat portion in the plane according to the first embodiment, the width L of the rough surface portion surrounded by the flat portion is measured by the above-described ultra-deep color 3D shape measurement microscope. Image analysis is performed on the portion recognized as the rough surface portion as a result, the rough surface portion is recognized as a substantially elliptical shape, the length of the longest diameter of the substantially elliptical shape is obtained in each rough surface portion, and the average of the obtained 10 lengths Value. In order to obtain a high light rising effect, that is, high luminance, the width L shown in FIG. 4 of the rough surface portion surrounded by the flat portion is preferably 0.1 μm or more and less than 100 μm. The lower limit of the width L of the rough surface portion is more preferably 0.5 μm or more, and further preferably 1 μm or more. The upper limit of the width L of the rough surface portion is more preferably less than 50 μm, further preferably less than 10 μm, and particularly preferably less than 5 μm.

  The area ratio between the flat portion and the rough surface portion is preferably 5:95 to 50: 5 from the viewpoint of improving luminance while suppressing in-plane luminance unevenness. More preferably, the flat portion: rough surface portion = 5: 95 to 80:20, still more preferably, the flat portion: rough surface portion = 5: 95 to 70:30, and still more preferably, the flat portion: rough surface portion = 5: 95. ~ 60: 40, particularly preferably, flat part: rough surface part 5:95 to 50:50, and the optimum range is flat part: rough surface part = 5: 95 to 40:60.

In addition, the area of a flat part and a rough surface part is computed with the following method from the measurement result of a super-depth color 3D shape measurement microscope. The above-mentioned ultra-deep color 3D shape measurement microscope is used to divide a straight line drawn at an arbitrary position into adjacent sections with a width of 5 μm, measure the height of each measurement point in each section, and measure the maximum height ( Ry). This is obtained for 10 or more sections. The section where the maximum height (Ry) is greater than 2 μm is a rough surface portion, the section where Ry is 2 μm or less is a flat portion, and the number a of the sections that became the rough surface portion and the number b of the sections that became the flat portions are shown below. The ratio of each area is calculated | required by Formula (2) and Formula (3).
Rough surface area ratio (%) = a ² / (a ² + b ² ) × 100 (2)
Flat part area ratio (%) = b ² / (a ² + b ² ) × 100 (3)

  The flat portion / rough surface portion structure may be provided on the entire surface of the diffusion sheet according to the first embodiment, or may be provided partially. For example, a flat portion / rough surface portion structure may be partially provided in a region corresponding to the light source of the diffusion sheet. Alternatively, a flat portion / rough surface portion structure may be partially provided in a region corresponding to between the light sources. On the surface of the portion of the diffusion sheet that is not the flat portion / rough surface portion structure, fine unevenness that does not become the flat portion / rough surface portion structure may be provided, or fine unevenness may not be provided. The ratio of the area of the portion provided with the flat portion / rough surface portion structure to the total area of the diffusion sheet is preferably 30% or more, and 50% or more, from the viewpoint of expressing sufficient brightness enhancement ability. More preferably.

  The diffusion angle of light emitted from the diffusion sheet according to the first embodiment is preferably in the range of 0.1 ° to 120 °. In order to obtain a high luminance unevenness suppressing effect, the angle is preferably 20 ° or more and 100 ° or less, more preferably in the range of 20 ° to 80 °, more preferably in the range of 20 ° to 60 °, and still more preferably 25 °. It is in the range of -50 °, more preferably in the range of 25 ° -40 °, most preferably in the range of 25 ° -35 °. Here, as shown in FIG. 5, the light diffusion angle is a peak intensity when the distribution angle of the transmitted light intensity with respect to the emission angle is taken with the emission angle of the transmission diffused light as the horizontal axis and the intensity as the vertical axis. It means an angle (FWHM: Full Width at Half Maximum) that is twice the emission angle (half-value angle) that is half the intensity.

  The light diffusion angle is incident from the normal direction to the surface on which the flat portion / rough surface portion structure of the diffusion sheet is provided, for example, using a variable angle photometer (GC-5000L) manufactured by Nippon Denshoku Industries Co., Ltd. It can be obtained by measuring the distribution of the light intensity with respect to the outgoing angle of the transmitted light. Here, the normal line direction with respect to the diffusion sheet is a direction perpendicular to the surface or the bottom surface of the diffusion sheet, as described with reference to FIG.

  In addition, the light diffusion angle is determined by Photon. Inc. Far-field Profiler LD8900's measurement surface is a diffusion sheet with the flat / rough surface structure provided on the outside, and the bottom surface of the diffusion sheet is irradiated with a laser perpendicularly to emit the transmitted light. It can also be measured by obtaining the intensity distribution for.

  The diffusion sheet according to the first embodiment can be an isotropic diffusion sheet in which the FWHM has substantially the same diffusion angle regardless of the measurement direction in the measurement in the direction parallel to the sheet surface. However, it may be an anisotropic diffusion sheet having a different FWHM depending on the measurement direction, or may include both an isotropic diffusion portion and an anisotropic diffusion portion. Even in the case of an anisotropic diffusion sheet, the diffusion angle is preferably in the range of 0.1 ° to 120 ° as described above. More preferably, the range is 20 ° to 80 °, more preferably 20 ° to 60 °, more preferably 25 ° to 50 °, and even more preferably 25 ° to 40 °. Is in the range of 25 ° to 35 °.

  For example, even if a non-uniform rough surface portion structure is not provided in the diffusion sheet, even if spherical or elliptical spherical particles having a refractive index different from that of the base material are contained in the base material of the diffusion sheet, the angle is 0.1 ° or more and 120 °. A diffusion angle of less than 0 ° can be realized. However, the diffusion sheet having a non-uniform rough surface structure on the surface can reduce the thickness of the sheet. In addition, the diffusion angle can be easily controlled, and when incorporated in a light source unit, a remarkable effect of eliminating luminance unevenness even when the number of light sources is small is brought about.

  Further, the optical characteristics of the diffusion sheet according to the first embodiment are as follows: FWHM shown in FIG. 5 and an angle twice as large as the emission angle at which the intensity is 1/10 of the peak intensity (FWTM: Full Width at Tenth Maximum). FWTM / FWHM, which is the ratio of That is, FWTM more reflects the optical characteristics of the rough surface portion, and FWHM more reflects the optical characteristics of the flat portion, and can be summarized by the ratio FWTM / FWHM. In that case, it is preferably 1.5 or more and 10 or less in the present invention. A more preferred lower limit is 1.7 or more, and even more preferably 1.8 or more. A more preferred upper limit is 2.5 or less, and even more preferred is 2.4 or less. Within this range, the effect of improving the brightness is better exhibited. Note that FWTM can be measured in the same manner as FWHM.

For example, in the case of a commercially available diffusion sheet having the surface shape shown in FIG. 10 (D141 manufactured by Tsujiden Co., Ltd., in which beads having a hemispherical uniform shape are embedded on the surface), the value of FWTM / FWHM is 14. Become.
Moreover, in the light emission pattern of FIG. 11, the value of FWTM / FWHM of the diffusion sheet having the surface shape of FIG. 8 is 2.2, and the value of FWTM / FWHM of the diffusion sheet having the surface shape of FIG. 6.
Further, FIG. 12 shows a light emission pattern of diffusion sheets A and B having fine unevenness on the surface, which is different from that shown in FIG. Both are isotropic diffusions and the FWHM is 25 °. In this light emission pattern, the diffusion sheet A has a FWTM / FWHM value of 2.5, and the diffusion sheet B has a FWTM / FWHM value of 1.7.

  Further, in the diffusion sheet according to the first embodiment, in the light emission pattern distribution with the intensity of the light emitted from the surface as the vertical axis, the light emitted in a direction of 30 ° or less from the normal direction of the surface. It is preferable that the integrated value of intensity is 50 to 99.5% with respect to the integrated value of the entire light emission pattern. A more preferable lower limit is 70%, still more preferably 77%, more preferably 80%, and further more preferably 85%. A more preferred upper limit is 98%, and even more preferred is 95%. Within this range, the effect of improving the brightness is better exhibited. For this integrated value, a goniophotometer (GC-5000L) or Photon. It can be calculated from data measured with Inc's Far-field Profiler LD8900.

  FIG. 11 shows the light emission pattern of the diffusion sheet having the surface shape of FIG. 8 and the light emission pattern of the diffusion sheet having the surface shape of FIG. Both are isotropic diffusions and the FWHM is 35 °. In the diffusion sheet having the surface shape of FIG. 8, the integrated value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface is 87.6% with respect to the integrated value of the entire light emission pattern. On the other hand, in the light emission pattern of the diffusion sheet having the surface shape of FIG. 9, the ratio is 97.3%.

  Further, FIG. 12 shows a light emission pattern of diffusion sheets A and B in which fine irregularities are provided unevenly on the surface, which is different from that shown in FIG. Both are isotropic diffusions and the FWHM is 25 °. In the diffusion sheet A, the integral value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface is 92.1% with respect to the integral value of the entire light emission pattern. On the other hand, in the light emission pattern of the diffusion sheet B, the above ratio is 99.5%. Both are excellent in moire suppression and screen uniformity, but the effect of improving the brightness of sheet A is superior to that of sheet B.

  The flat portion / rough surface portion structure of the diffusion sheet according to the first embodiment may be provided on either the light incident surface or the light exit surface, or may be provided on both. However, from the viewpoint of improving luminance and reducing luminance unevenness, the flat portion / rough surface portion structure is preferably provided on the light exit surface, and the light incident surface is more preferably smooth. In general, when laminating diffusion sheets, a very small amount of beads may be applied to the light incident surface within a range not losing smoothness to prevent damage. Also in such a case, it is assumed that it is smooth.

Next, a method for manufacturing the diffusion sheet according to the first embodiment will be described. The manufacturing method of the diffusion sheet according to the first embodiment is as follows: 1) The surface shape of a flat / rough surface structure having suitable fine irregularities is calculated by simulation, and a surface shape master is manufactured by laser micromachining or the like. 2) A sheet base material having a convex portion that becomes a rough surface portion on the surface in advance, a resin is applied to a necessary portion of the sheet base material, a valley is filled, a resin layer is formed, and fine Method of controlling surface shape so as to have a flat part / rough surface part structure with unevenness 3) A sheet base material having non-uniform unevenness which becomes a flat part on the surface in advance is prepared, and a required part of the sheet base material Examples include a method of forming a portion to be a rough surface portion by shaping a resin and controlling the surface shape so as to have a flat portion / rough surface portion structure having fine irregularities. A combination of these methods can also be used.

  In the method 2), a sheet base material provided with a base uneven shape having the same size as the rough surface portion shape to be formed is prepared in advance. The base uneven shape is, for example, a shape in which a large number of irregularly shaped protrusions are provided on the surface. This shape is preferably a three-dimensional structure formed using a speckle pattern by interference exposure.

  A three-dimensional structure formed using a speckle pattern by interference exposure is suitable for forming a base irregularity shape of 20 μm or less, which has been difficult by machining. In particular, the method of forming the base uneven shape using the non-planar speckle is a suitable manufacturing method when the diffusion angle is changed according to 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. In addition, since the base uneven | corrugated shape formed by interference exposure becomes irregular in height and pitch, it has the effect of suppressing a moire and the 0th-order light.

  Further, a three-dimensional structure formed using a speckle pattern by interference exposure may be provided on the surface, and the diffusion angle may be changed within the surface. Specifically, such a sheet base material can be 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. The range and range of the speckle pattern is adjusted by changing the distance and size between the components that make up the laser irradiation system, and the range of the diffusion angle is controlled, and it varies depending on the uneven structure or position having an appropriate diffusion angle. An uneven structure having a diffusion angle can be recorded.

  In general, the range of the diffusion angle depends on the average size and shape of the speckle. If speckle is small, the angle range is wide. Moreover, the unit structure of the base uneven shape is not limited to an isotropic one, and an anisotropic one can be formed, or a base uneven shape in which both are combined can be formed. If the speckle is an oblong in the lateral direction, the shape of the angular distribution is an oblong in the longitudinal direction, and in this case, it has anisotropic diffusivity. 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 shaping master. The speckle pattern is transferred to the light extraction surface of the photocurable resin layer by forming the photocurable resin layer with ultraviolet rays using a shaping master. A detailed manufacturing method is disclosed in, for example, Japanese translations of PCT publication No. 2003-525472. The diffusion angle may be controlled by changing the pitch, height, and aspect ratio of the concavo-convex structure. If the diffusion angle is appropriately adjusted according to the distance from the light source and the intensity of the light source, the luminance unevenness can be satisfactorily eliminated and the luminance can be improved.

  Next, a resin is applied to the sheet base material to which the pattern has been transferred. As a method for applying the resin onto the sheet substrate, a method using a roll coater, a die coater, a bar coater, a spray, or the like can be used. Preferably, a spray and a die coater are used from the viewpoint of imparting a smooth change in the diffusion angle. Moreover, you may make it apply resin to the required location on a sheet | seat base material using a mask etc. Furthermore, a solvent may be added to the liquid that becomes the resin layer from the viewpoint of imparting a smooth change in the diffusion angle. The amount of the solvent added is appropriately adjusted according to the flat / rough surface structure to be formed. Generally, 1 part to 5000 parts of the solvent is added to 100 parts of the resin.

The sheet base material may be a light-transmitting base material made of a material such as resin or glass. In particular, the light transmittance of the base material alone is preferably 75% or more.
In this case, “light” is not particularly limited as long as it is visible light. For example, “light” is light emitted from a light source in a light source unit using the diffusion sheet of the present embodiment.
The light transmittance is obtained by, for example, using a UV-visible spectrophotometer (MPC-2200) manufactured by Shimadzu Corporation, setting a base material between a light source and a detector, and incident light intensity at 550 nm and After detecting the transmitted light intensity, it can be calculated by the following equation (4).
Light transmittance (%) = (transmitted light intensity at 550 nm) / (incident light intensity at 550 nm) × 100 (4)

Although the thickness of a base material is not specifically limited, Usually, it exists in the range of 50 micrometers-500 micrometers.
Examples of the resin material of the base material include polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, acrylic resins such as polymethyl methacrylate, thermoplastic resins such as polycarbonate resin, polystyrene resin and polymethylpentene resin, and polyester. Examples include resins obtained by curing an ionizing radiation curable resin composed of oligomers such as acrylate, urethane acrylate, epoxy acrylate, and / or acrylate monomers with electromagnetic radiation such as ultraviolet rays or electron beams.
As the glass, soda glass, borosilicate glass, or the like is used.

  After applying the resin to the sheet base material, the resin is cured by a method such as ultraviolet irradiation. The step of curing may be a method of curing by heat using a thermosetting resin or a method of curing by drying after dissolving the resin in a solvent, but from the viewpoint of workability and surface hardness, a curing step by ultraviolet irradiation Is preferred. By controlling the resin coating amount, the resin dilution amount, and the resin coating site, the flat portion / rough surface portion unevenness ratio, the flat portion / rough surface portion area ratio, and the fine unevenness roughness formed. Can be set to an appropriate value to obtain the required optical performance.

In the method 3), a sheet base material provided with a base uneven shape having the same size as the flat portion shape to be formed is prepared in advance. This can be obtained by the same method as 2) described above. The diffusion sheet according to the embodiment can be obtained by shaping an ultraviolet curable resin on the sheet using a master having a rough surface portion shape and forming an uneven shape on the rough surface portion.
In the above methods 2) and 3), by using a sheet substrate provided with one type of base irregularity shape, various types of diffusion sheets are formed by forming a flat portion by coating or forming a rough surface portion by shaping. There is a merit that it can be obtained.

  As another manufacturing method, after applying a resin to the sub-master before performing the above-described metal electroforming to obtain a desired pattern, this is subjected to metal electroforming as a sub-master to obtain a shaping master. There is also a way. Using the obtained metal shaping master, the optical pattern was transferred to the light extraction surface of the light transmissive resin layer by applying the ultraviolet light to the light transmissive resin layer in the same manner as described above. A diffusion sheet according to the form is obtained.

  In addition, it is also possible to use the sheet itself produced using the methods 2) and 3) as a diffusion sheet of the final product, and also to copy this surface shape and use it as a master. .

  In addition to a method of shaping an optical pattern on the surface of a substrate by a metal flat master or metal roll master, a metal mold having the shape of the optical pattern is manufactured, and injection molding is performed using the metal mold. Thus, it is also possible to manufacture a diffusion plate or a light guide plate on which the optical pattern is formed.

The diffusion sheet according to the first embodiment is a diffusion sheet according to the second aspect described above, in which fine irregularities are provided unevenly on the surface, and the emission angle of light emitted from the surface is plotted on the horizontal axis. In the light emission pattern distribution in which the intensity of light emitted from the surface is the vertical axis, the intensity is a peak with respect to the diffusion angle FWHM, which is twice the emission angle at which the intensity of the emitted light is half the peak intensity. Also included is a diffusion sheet in which the ratio FWTM / FWHM of the angle FWTM that is twice the emission angle that is 1/10 of the intensity is 1.5 or more and 10 or less.

As described above, the diffusion sheet having the surface shape of FIGS. 8 and 9 and the optical sheets A and B having the light emission pattern of FIG.
A more preferable lower limit value of the ratio FWTM / FWHM is 1.7 or more, and more preferably 1.8 or more. A more preferred upper limit is 2.5 or less, and even more preferred is 2.4 or less.

The diffusion sheet according to the first embodiment relates to the third aspect described above, and is a diffusion sheet in which fine irregularities are provided unevenly on the surface, and the horizontal axis indicates the emission angle of light emitted from the surface. And the integrated value of the intensity of the light emitted in the direction of 30 ° or less from the normal direction of the surface is the integrated value of the entire output pattern in the light emission pattern distribution with the intensity of the light emitted from the surface as the vertical axis. Also included is a diffusion sheet that is 60% to 99.5%.
As described above, the diffusion sheets having the surface shapes of FIGS. 8 and 9 and the optical sheets A and B having the light emission pattern of FIG. 12 are both within the range of the above formula.
A more preferred lower limit is 70%, still more preferably 77%, more preferably 80%, and even more preferably 85%. A more preferred upper limit is 98%, and even more preferred is 95%.

The diffusion sheet according to the first embodiment is the diffusion sheet according to the fourth aspect described above, in which fine irregularities are provided unevenly on the surface, and the emission angle of light emitted from the surface is plotted on the horizontal axis. And the ratio of the integral value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface to the integral value of the entire light emission pattern in the light emission pattern distribution having the light intensity emitted from the surface as the vertical axis (%) Is x, and the intensity of the emitted light is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM, which is twice the emission angle at which the intensity is half the peak intensity. When the ratio FWTM / FWHM of the angle FWTM is y, a diffusion sheet that satisfies the following formula (1) is also included.
y> 0.011x + 0.64 (where 50 <x <100, 1.5 <y ≦ 2.5) (1)
As described above, the diffusion sheets having the surface shapes of FIGS. 8 and 9 and the optical sheets A and B having the light emission pattern of FIG. 12 are both within the range of the above formula.
Further preferred is a range that satisfies the above formula (1) with 70 <x <99.5 and 1.5 <y ≦ 2.5.

(Second Embodiment)
The light source unit according to the second embodiment relates to the above-described fifth aspect. As shown in FIG. 6, two or more light sources 1 that emit light and a first light source that is arranged in parallel with the light sources. The diffusion sheet 3 according to the embodiment is provided. As the light source 1, as shown in FIG. 6A, a linear light source such as a cold cathode fluorescent lamp (CCFL) can be used. Alternatively, instead of the line light source 1, a point light source 2 such as an LED (light emitting diode) and a laser can be used as shown in FIG. In the example of FIG. 6, the light source 1 is arranged directly below the light incident surface and the light outgoing surface of the diffusion sheet 3 according to the first embodiment of the present invention.

  As shown in FIG. 6C, the light source unit according to the second embodiment has flatness and self-supporting property between the light source 1 and the diffusion sheet 3 according to the first embodiment of the present invention. In order to hold, a transparent plate or a diffusion plate 5 may be further provided. As the diffusing plate 5, 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 a diffusing agent such as an organic polymer or inorganic fine particles having an effect of diffusing light can be used.

  Further, the diffusing plate 5 may have an uneven structure on the surface. As the concavo-convex structure on the surface of the diffusion plate 5, an isotropic microlens, an anisotropic prismatic row, a lenticular lens, or the like may be provided on the surface. The cross section of the lenticular lens may not be a strict circular lens, but may be an elliptical shape or a shape in which an arc and a straight line are mixed. These may be added with an organic polymer or inorganic fine particles as necessary.

  Examples of the diffusion plate 5 include Delagras DL / DH series (manufactured by Asahi Kasei E-Materials Co., Ltd.), Zeonoa diffuser plate (manufactured by ZEON Corporation), and Microlens Brightness Film (manufactured by Bright View Technologies). Can be used. Alternatively, a diffusion plate in which two or more components are mixed and stretched to form a sheet may be used.

  The light source unit according to the second embodiment may further include a reflection sheet 4 disposed on the opposite side of the diffusion sheet 3 according to the first embodiment of the present invention with respect to the light source 1. As the reflection sheet 4, various materials can be used as long as they can reflect light. For example, a resin such as polyester and polycarbonate is made into a sheet by foaming fine air particles inside, a sheet made by mixing two or more resins, and a resin layer having a different refractive index. A laminated sheet or the like can be used. Further, the reflective sheet 4 may have an uneven structure on the surface. As the reflection sheet 4, a material with inorganic fine particles added to the surface can be used as necessary.

  The light source unit according to the second embodiment may further include a diffusion sheet 6 that receives light emitted from the diffusion sheet 3 according to the first embodiment of the present invention. The diffusion sheet 6 is preferably a diffusion plate having uniform diffusion performance in the plane. A plurality of diffusion sheets 6 may be arranged. As the diffusion sheet 6, a diffusion sheet having a surface coated with a plurality of beads as a diffusing agent, a diffusion sheet having a random concavo-convex shape provided on the surface, a light condensing diffusion sheet, and the like can be used.

  As the diffusion sheet having a plurality of beads coated on the surface, for example, an optical sheet in which beads having light diffusibility are wet coated on a substrate surface such as PET film, polycarbonate film, and polystyrene can be used. It is used for the purpose of reducing uneven brightness in the light plane. Examples of the light diffusing beads include acrylic beads, silica beads, barium sulfate, titanium oxide, and calcium silicate. Specifically, TDF-127 (trade name, manufactured by Toray Sehan Co., Ltd.), Opulse BS-080 (trade name, manufactured by Eiwa Co., Ltd.), D141 (trade name, manufactured by Tsujiden Co., Ltd.), etc. It can be used.

  As the diffusion sheet provided with a random uneven shape on the surface, for example, a PET film, a polycarbonate film, and a material having a random uneven shape formed on the substrate surface such as polystyrene can be used. It is used for the purpose of reducing the uneven brightness. Detailed manufacturing methods are also described in JP-A No. 2002-202508 and JP-A No. 2002-148416. For example, roll press-bonding is performed at the time of forming a sheet of an amorphous resin such as polycarbonate. It is obtained by making the surface of the roll random irregularities. As such a diffusion sheet, for example, Opulse PC-ES (trade name, manufactured by Eiwa Co., Ltd.) can be used.

  A diffusion sheet having a random uneven shape on the surface can be manufactured by, for example, a method described in JP-T-2003-525472. Specifically, a sub-master in which a speckle pattern is formed is manufactured by previously irradiating a photosensitive material or a photoresist with laser light through a lens or a mask by interference exposure. Next, a metal is deposited on the produced submaster by a method such as electroforming, and a speckle pattern is transferred to the metal to produce a master. Thereafter, the master is used to shape the photocurable resin layer with ultraviolet rays, and the speckle pattern is transferred to the light extraction surface of the photocurable resin layer. As the diffusion sheet having a random uneven shape on the surface, for example, LSD (Light Shaping Diffuser, manufactured by Lumit) can be used.

  A condensing diffusion sheet refers to an optical sheet in which a lens pattern is provided on the surface of a substrate such as a PET film, a polycarbonate film, and polystyrene, for example. Is used for the combined purpose of condensing light. The arrayed lens is provided, for example, by applying acrylic resin spherical beads on a sheet. Alternatively, it can be obtained by transferring a fine concavo-convex structure made of an ultraviolet curable resin onto a sheet of polyester resin, triacetyl cellulose, polycarbonate, or the like. In addition, it can also be manufactured by machining or etching. It does not have to be a strict circular lens, and may be elliptical or a shape in which arcs and straight lines are mixed. Examples of the condensing diffusion sheet include PTR733 (trade name, manufactured by Shinfa Intertech Co., Ltd.), UTE-21 (trade name, manufactured by Mirai Nanotech Co., Ltd.), and ML13MK (trade name, manufactured by SKC Haas Co., Ltd.). ) Etc. can be used.

  The light source unit according to the second embodiment may further include a prism sheet 7 that receives the light emitted from the diffusion sheet 3 as shown in FIG. The prism sheet 7 is an optical sheet in which an array-like prism pattern is provided on the surface of a base material such as a PET film, a polycarbonate film, and polystyrene, and is used mainly for the purpose of concentrating backlight light and improving luminance. It is done. The prism pattern does not have to be strictly a prism shape, but may have a shape having an R shape at the top, a wave film shape, or a downward prism shape.

  The prism sheet 7 includes, for example, Vicuity BEFIII (trade name, manufactured by 3M Corporation), Vicuity BEFII (trade name, manufactured by 3M Corporation), Vicuity RBEF (trade name, manufactured by 3M Corporation), LES-T2F. (Trade name, manufactured by LG Chemical Co., Ltd.), wave film W818 (trade name, manufactured by 3M Co., Ltd.), Diaart C (trade name, manufactured by Mitsubishi Rayon Co., Ltd.) and the like can be used. As the material of the prism sheet 7, acrylic photopolymer, polycarbonate, or the like is often used, but is not limited thereto.

  The light source unit according to the second embodiment may further include a reflective polarizing sheet 8 that receives light emitted from the diffusion sheet 3, as shown in FIG. 6 (e). The reflective polarizing sheet 8 has a function of separating linearly polarized light from natural light or polarized light. 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 8, a resin (polycarbonate, acrylic resin, polyester resin, etc.) having a large birefringence phase difference and a resin (cycloolefin polymer, etc.) having a small birefringence retardation are alternately used. 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 Co., Ltd.) and the like can be used.

The number and arrangement of the diffusion sheet 6, the prism sheet 7, and the reflective polarizing sheet 8 of the light source unit according to the second embodiment can be variously changed. For example, as shown in FIG. 6 (f), a plurality of diffusion sheets 6 may be arranged on the diffusion sheet 3, but the function of improving the brightness of the diffusion sheet according to the embodiment of the present invention is exhibited better. For this purpose, it is preferable to arrange the optical sheet from the light source side so that the diffusion plate / the diffusion plate according to the embodiment of the present invention / two commercially available diffusion sheets / reflection type change sheet is obtained. Furthermore, the diffusion sheet according to the embodiment of the present invention preferably changes the diffusion angle in accordance with the light intensity incident on the surface of the diffusion sheet. It is more preferable to control the optical characteristics of the diffusion sheet so as to change the diffusion angle with a positive correlation with the light intensity.
(Third embodiment)
A liquid crystal display device according to a third embodiment relates to the sixth aspect described above, and includes a liquid crystal display panel and a light source unit according to the second embodiment that supplies light to the liquid crystal display panel. .
It is possible to provide a high-quality liquid crystal display device by disposing a liquid crystal display panel above the light source unit according to the second embodiment described above and irradiating the liquid crystal display panel with light without uneven brightness. It becomes.

(Other embodiments)
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-described 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.

Next, the embodiment will be described more specifically with reference to examples and comparative examples. However, the embodiment is not limited to the following examples unless it exceeds the gist.
(Configuration example)
As the light source, LEDs of Lambertian type with light distribution characteristics are arranged in a staggered pattern as shown in FIG. A reflective sheet was disposed below the LED. Moreover, the diffusion plate was arrange | positioned above the light source so that the distance from a reflection sheet might be 40 mm. The diffusion plate is manufactured by Asahi Kasei E-Materials Co., Ltd., and contains 1.3% by weight of silicone fine particles having an average particle size of 2 μm and a true specific gravity of 1.35 in the base polystyrene, and the thickness is 1.5 mm. is there.

  Furthermore, the diffusion sheet which concerns on the Example of this invention was arrange | positioned on the said diffusion plate so that the said diffusion plate might be contact | connected. Above the diffusion sheet according to the embodiment of the present invention, two diffusion sheets (a diffusion sheet different from the diffusion sheet according to the embodiment of the present invention) and a reflective polarizing sheet are arranged, and in the configuration example Such a light source unit was obtained. TDF-127 made by Toray Sehan Co., Ltd. was used for the two diffusion sheets. In addition, DBEF manufactured by 3M Corporation was used for the reflective polarizing sheet.

  The area ratio of the flat portion / rough surface portion was determined by the following method. Using an ultra-deep color 3D shape measurement microscope (VK-9500) manufactured by Keyence Corporation, a straight line drawn at an arbitrary position is divided into adjacent sections with a width of 5 μm, and the height of the measurement points in each section is determined. The maximum height (Ry) in that section was measured for 10 sections or more. The section where the maximum height (Ry) is greater than 2 μm is a rough surface portion, the section where Ry is 2 μm or less is a flat portion, the number a of the sections that are rough surfaces and the number b of the sections that are flat portions are The ratio of each area was calculated | required by (2) and Formula (3).

Example 1
A sheet base material having a diffusing surface of a speckle pattern formed by interference exposure described in JP-T-2003-525472 on the surface of a 125 μm thick PET film and having a diffusion angle of 80 ° was prepared. Next, a urethane acrylate UV curable resin solution diluted with methanol was applied on top. The dilution ratio was 5% by weight of resin. The coating amount of the diluted UV curable resin solution was 0.1 ml / cm ² . After application, methanol was evaporated and cured by UV irradiation. As a result, a flat / rough surface structure having non-uniform fine irregularities was formed on the sheet substrate. The in-plane average diffusion angle of the obtained diffusion sheet was 49 °. Further, the area ratio of the flat portion to the rough surface portion was 8:92. Also, FWTM / FWHM is 1.6. In the light emission pattern distribution in which the intensity of light emitted from the surface is the vertical axis, the light output is an integral value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface. The ratio of the entire pattern to the integrated value was 84.1%. The average width of the rough surface portion was 1.8 μm. Furthermore, the light source unit which concerns on the structural example was produced using the obtained diffusion sheet. The luminance of the manufactured light source unit was 636 cd / m ² , and no luminance unevenness was visually observed.

(Example 2)
By the same manufacturing method as in Example 1, the uneven surface is provided with unevenness on the surface of the 125 μm-thick PET film, the diffusion angle is 25 °, and the area ratio of flat part: rough surface part is 11:89, FWTM / FWHM = 2.1, and in the light emission pattern distribution with the light intensity emitted from the surface as the vertical axis, the light output is an integral value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface. A diffusion sheet according to Example 2 having a ratio of 94.3% to the integral value of the entire pattern was produced. The average width of the rough surface portion was 3.8 μm. Furthermore, using the diffusion sheet according to Example 2, a light source unit according to a configuration example was produced. The luminance of the produced light source unit was 646 cd / m ² , and no luminance unevenness was visually observed.

(Example 3)
A diffusion sheet having a diffusive base of a speckle pattern formed by an interference exposure method described in JP-T-2003-525472 and having a diffusion angle of 57 ° was prepared on the surface of a PET sheet substrate having a thickness of 250 μm. FWTM / FWHM of this diffusion sheet is 1.6, and in the base uneven shape of the speckle pattern, when the rough surface portion is approximated by an ellipse, the adjacent rough surface portions are partially in contact with each other, and the width of the rough surface portion Could not be calculated. The ratio of the integrated value of the intensity of light emitted in the direction of 30 ° or less from the normal direction of the surface to the integrated value of the entire light output pattern was 82.2%. The surface shape by SEM is shown in FIG. Next, a light source unit according to a configuration example was manufactured using the prepared diffusion sheet. In the produced light source unit, no luminance unevenness was visually observed, and the luminance was 626 cd / m ² .

  The present invention can be used in the electrical industry and the like. Specifically, it can be used for a mobile phone, a personal digital assistant (PDA), a digital camera, a television, a display for a personal computer, a notebook computer, and the like.

DESCRIPTION OF SYMBOLS 1 Light source 3 The diffusion sheet which concerns on the Example of this invention 4 The reflection sheet 5 The diffusion plate 6 The diffusion sheet different from the diffusion sheet which concerns on the Example of this invention 7 Prism sheet 8 Reflective polarizing film

Claims (16)

A diffusion sheet in which fine irregularities are provided unevenly on the surface,
A flat portion having a maximum height (Ry) of the fine unevenness of 2 μm or less, and a rough surface portion having a maximum height (Ry) of the fine unevenness of greater than 2 μm,
The said flat part is a diffusion sheet which exists so that the said rough surface part may be surrounded.   The diffusion sheet according to claim 1, wherein a difference between an average height of the flat portion and an average height of the rough surface portion is 0.1 μm or more and less than 20 μm.   The diffusion sheet according to claim 1 or 2, wherein a width of the rough surface portion is 1 µm or more and less than 100 µm. The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
4. The diffusion angle according to claim 1, wherein a diffusion angle, which is an angle twice as large as an emission angle at which the intensity of the emitted light is half the peak intensity, is 0.1 degrees or more and 120 degrees or less. Diffusion sheet. The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
The ratio FWTM / FWHM of the angle FWTM that is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM that is twice the emission angle at which the intensity of the emitted light is half the peak intensity The diffusion sheet according to any one of claims 1 to 4, wherein is 1.5 or more and 10 or less. The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
The integrated value of the intensity of light emitted in a direction of 30 ° or less from the normal direction of the surface is 50% to 99.5% with respect to the integrated value of the light intensity of the entire light emission pattern. The diffusion sheet according to any one of 5. A diffusion sheet in which fine irregularities are provided unevenly on the surface,
The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
The ratio FWTM / FWHM of the angle FWTM that is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM that is twice the emission angle at which the intensity of the emitted light is half the peak intensity Is a diffusion sheet of 1.5 or more and 10 or less. A diffusion sheet in which fine irregularities are provided unevenly on the surface,
The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
A diffusion sheet in which an integrated value of the intensity of light emitted in a direction of 30 ° or less from a normal direction of the surface is 50% to 99.5% with respect to an integrated value of the entire emitted light pattern. A diffusion sheet in which fine irregularities are provided unevenly on the surface,
The horizontal axis represents the emission angle of light emitted from the surface,
In the light emission pattern distribution with the vertical axis representing the intensity of light emitted from the surface,
X is the ratio (%) of the integral value of the intensity of light emitted in the direction of 30 ° or less from the normal direction of the surface to the integral value of the entire light emission pattern,
The ratio FWTM / FWHM of the angle FWTM that is twice the emission angle at which the intensity is 1/10 of the peak intensity with respect to the diffusion angle FWHM that is twice the emission angle at which the intensity of the emitted light is half the peak intensity A diffusion sheet satisfying the following formula (1), where y is y.
y> 0.011x + 0.64 (where 50 <x <100, 1.5 <y ≦ 2.5) (1) Two or more light sources that emit light;
The diffusion sheet according to any one of claims 1 to 9, disposed in parallel with the light source,
A light source unit comprising: A diffusion plate disposed between the light source and the diffusion sheet and containing a diffusion agent;
A reflective sheet disposed on the opposite side of the diffusion sheet with respect to the light source;
The light source unit according to claim 10.   The light source unit according to claim 10, further comprising a lens sheet that receives the light emitted from the diffusion sheet.   The light source unit according to claim 10, further comprising a prism sheet that receives the light emitted from the diffusion sheet.   The light source unit according to claim 10, further comprising a reflective polarizing film that receives the light emitted from the diffusion sheet.   The light source unit according to claim 10 or 11, further comprising a second diffusion sheet containing a diffusing agent that receives the light emitted from the diffusion sheet. A liquid crystal display panel;
The light source unit according to any one of claims 12 to 15, which supplies light to the liquid crystal display panel;
A liquid crystal display device comprising: