JP2007003852A - Diffusion sheet, method for manufacturing diffusion sheet, backlight device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion sheet which is excellent in availability of light and has high reduction effect of brightness unevenness. <P>SOLUTION: The diffusion sheet 18 is formed of translucent materials and lens layers L1 to L3 are distributed and formed as a plurality of diffusion layers which have diffusion degrees of light different from one another in the plane of the diffusion sheet. A first lens layer L1 is located right above a light source 2, and second and third lens layers L2, L3 are located non-right above the light source 2. The first lens layer L1 has a diffusion degree larger than that of the third lens layer L3, and the third lens layer L3 has a diffusion degree larger than that of the second lens layer L2. According to the composition, on the right above position of the light source 2, light diffuses into a wide range and, therefore, the brightness is reduced and, on the non-right above position of the light source 2, light diffuses into a narrow range and, therefore, the reduction of brightness is suppressed. As the result, the in-plane brightness is made even on the emission side of the diffusion sheet 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diffusion sheet that diffuses and emits light from a surface light source, a manufacturing method thereof, and a backlight device and a liquid crystal display device including the diffusion sheet.

  Liquid crystal displays (LCDs) can be reduced in power consumption, size, and thickness compared to cathode ray tubes (CRTs), and are now available from small devices such as mobile phones and digital cameras. Widely used in large-size LCD TVs.

  The liquid crystal display device is classified into a transmission type, a reflection type, and the like. In particular, the transmission type liquid crystal display device includes a backlight unit in addition to a liquid crystal panel in which liquid crystal is sandwiched between glass substrates. There are two types of backlight units. As shown in FIG. 10A, a plurality of linear light sources (fluorescent tubes such as cold cathode tubes) 2 and a reflector 3 are provided immediately below the liquid crystal panel 1 to brighten the entire screen. There are a direct type backlight unit 4 and an edge light type backlight unit 7 in which a light source 2 is placed beside a liquid crystal panel 1 and a light guide plate 5 and a reflection sheet 6 are used together as shown in FIG. 10B.

  In each of the backlight units 4 and 7, a diffusion sheet 8 for reducing brightness unevenness and a brightness enhancement film 10 for improving the front brightness of the liquid crystal panel 1 may be used (the following patent document). 1), the backlight device 9 is configured to irradiate the liquid crystal panel 1 uniformly with light from the back side.

JP 2000-30515 A

  In general, in a liquid crystal display device including a direct type backlight unit, luminance unevenness is likely to occur because the light intensity differs between the vicinity of the light source and the other portions. Therefore, conventionally, a method has been adopted in which a milky white thick diffusion plate is inserted between the backlight unit and the diffusion sheet so that the backlight light is scattered and emitted and the in-plane variation of the light intensity is minimized.

  However, the use of a milky white thick diffuser greatly reduces the transmittance of light passing therethrough, and thus has the problem that the light utilization efficiency is poor and the brightness of the display is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a diffusion sheet, a diffusion sheet manufacturing method, a backlight device, and a liquid crystal display device that are excellent in light utilization efficiency and have a high luminance unevenness reduction effect.

  In solving the above problems, the diffusion sheet of the present invention is formed of a translucent material, and a plurality of diffusion layers having different light diffusion degrees are distributed in the plane. In particular, the plurality of diffusion layers include a plurality of first diffusion layers and a plurality of second diffusion layers having a light diffusion degree smaller than that of the first diffusion layers.

  The diffusion layer has a function of reducing luminance unevenness by diffusing and emitting incident light. Therefore, the first diffusion layer is formed on the surface portion corresponding to the position directly above the light source, and the second diffusion layer is distributed on the surface portion corresponding to the position not directly above the light source. As a result, the luminance is reduced because light is emitted with a high degree of diffusion in a portion near the light source, and the luminance is suppressed from being lowered because light is emitted with a small degree of diffusion in a portion far from the light source. Thereby, the in-plane luminance is made uniform regardless of the light source position, and the effect of reducing the in-plane luminance unevenness can be enhanced without requiring a milky white thick diffuser.

  The degree of light diffusion in each diffusion layer can be adjusted by the diffusion angle of light emitted from the diffusion layer. That is, in the present invention, the light diffusion angle in the first diffusion layer is larger than the light diffusion angle in the second diffusion layer. Here, the “diffusion angle” refers to an angle (FWHM: Full Width Half Maximum) that is twice the angle at which the luminance attenuates to half of the peak luminance (half-value angle).

  In addition, the diffusion sheet of the present invention can further form a third diffusion layer having a light diffusion degree smaller than that of the first diffusion layer and a light diffusion degree larger than that of the second diffusion layer. As a result, it is possible to improve the continuity in the plane of the light diffusion angle and further improve the effect of reducing luminance unevenness.

  The configuration of the diffusion layer is not particularly limited, and for example, it can be configured by a lens group formed on the sheet surface. And the diffusion angle in each diffusion layer can be changed by varying the curvature of the cross section of this lens group for each region. The shape of the lens can be circular or elliptical.

  The first and second diffusion layers are formed in a distribution corresponding to the arrangement form of the light sources. For example, in the case of a direct type backlight unit, since the light sources are regularly arranged in the plane, the first and second diffusion layers are also periodically formed on the sheet surface. For example, when the light source is a linear light source, the light sources are juxtaposed in a fixed direction at regular intervals. In this case, the first and second diffusion layers are alternately distributed and formed in a line shape on the sheet surface.

  The diffusion sheet of the present invention configured as described above includes a step of measuring an in-plane luminance distribution of a surface light source, a step of determining a diffusion degree that can equalize the in-plane luminance of the surface light source in each in-plane region, And a step of forming a plurality of diffusion layers having different diffusion degrees for each region on the surface of the diffusion sheet.

  Further, the backlight device of the present invention is a backlight device including a plurality of light sources and a diffusion sheet disposed on the plurality of light sources, and the diffusion sheet is formed at a position immediately above the light source. And a second diffusion layer formed at a position directly above the light source, wherein the first diffusion layer has a light diffusion degree greater than that of the second diffusion layer.

  Furthermore, the liquid crystal display device of the present invention is a liquid crystal display device comprising a plurality of light sources, a diffusion sheet disposed on the plurality of light sources, and a liquid crystal panel disposed above the diffusion sheet. The sheet has a first diffusion layer formed at a position directly above the light source and a second diffusion layer formed at a position not directly above the light source, and the first diffusion layer is more than the second diffusion layer. It is characterized by a high degree of light diffusion.

  As described above, according to the present invention, the in-plane brightness can be made uniform regardless of the light source position, and the effect of reducing the in-plane brightness unevenness can be enhanced without requiring a milky white thick diffuser. Is possible. Further, since a thick diffuser is not required, it is possible to increase the in-plane luminance by increasing the light use efficiency, and to reduce the thickness of the backlight device and the liquid crystal display device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a liquid crystal display device 20 according to an embodiment of the present invention. The liquid crystal display device 20 of the present embodiment includes a liquid crystal panel 1 sandwiched between a pair of polarizing plates 11a and 11b, a backlight unit 4, a prism sheet 10, and a diffusion sheet 18. The backlight unit 4, the prism sheet 10 and the diffusion sheet 18 constitute the backlight device 21 of the present invention.

  The backlight unit 4 includes a plurality of linear light sources 2 juxtaposed in parallel with each other in the same plane, and a reflecting plate 3 that reflects light from the linear light sources 2 toward the liquid crystal panel 1 side. It consists of a direct type of the configuration. In the present embodiment, the linear light source 2 is a cold cathode fluorescent lamp (CCFL). In the figure, the arrangement direction of the linear light sources 2 is the X direction, the extending direction (axial direction) of the linear light sources 2 is the Y direction, and the front direction of the liquid crystal panel 1 is the Z direction.

  The prism sheet 10 has a prism structure in which grooves having a triangular cross section (prism grooves) 12A are continuously formed on the surface side facing the liquid crystal panel 1, and is irradiated from the backlight unit 4 and is diffused. The light that has passed through is condensed.

  Next, the configuration of the diffusion sheet 18 according to the present invention will be described. FIG. 2 is a side view schematically showing the relationship between the diffusion sheet 18 and the backlight unit 4.

  The diffusion sheet 18 includes a sheet base 18S and a lens layer 18L formed of a plurality of microlenses having different shapes formed on the light emission surface of the sheet base 18S. The lens layer 18L is configured as a diffusion layer that diffuses and emits light from the backlight unit 4 toward the liquid crystal panel 1 side. The lens layer 18L has different light diffusion angles (diffuse degrees) depending on the shape of the micro lens.

  The sheet base material 18S is made of an optically transparent material such as polyester, polyethylene terephthalate, polybutylene terephthalate, polyethylene, polycarbonate, acrylic resin, polyvinyl chloride, polyurethane, silicone resin, or the like.

  As will be described later, when the diffusion sheet 18 is formed using a resin that absorbs and cures energy, an ultraviolet curable acrylate resin, an ultraviolet curable epoxy resin, an ultraviolet curable fluororesin, an amorphous In addition to a fluororesin, a transparent resin having a refractive index of about 1.3 to 1.6 such as a thermosetting epoxy resin or an isocyanate resin can be used.

  The lens layer 18L is formed by distributing a plurality of micro lens groups having different cross-sectional shapes. As shown in FIG. 2, the diffusion sheet 18 disposed immediately above the backlight unit 4 (Z direction) has a large diffusion angle when the lens layer 18 </ b> L is directly above the light source 2. The cross-sectional shape of each microlens periodically changes in the arrangement direction (X direction) of the linear light sources 2 so that the diffusion angle becomes small at the position immediately above.

  That is, a first lens group L1 composed of a plurality of microlenses having a large cross-sectional curvature (small curvature radius) is formed at a position directly above the linear light source 2, and a position corresponding to a position directly above the linear light source 2 is formed. Is formed with a second lens group L2 composed of a plurality of microlenses having a smaller cross-sectional curvature (larger curvature radius) than that of the first lens group L1.

  Further, the diffusion sheet 18 of the present embodiment has a third smaller curvature than the second lens group L2 between the first lens group L1 and the second lens group L2 and smaller than the first lens group L1. A lens group L3 is formed. The third lens unit L3 may be composed of microlenses having a uniform cross-sectional shape, or may be composed of a plurality of types of microlenses having different cross-sectional shapes as shown in the drawing.

  The configuration of the lens layer 18L is schematically shown in FIG. A is a plan view of the lens layer 18L, B is a cross-sectional view of the main part, and C is a cross-sectional view of the main part showing another configuration example.

  The lens layer 18L is formed by laying microlenses on the surface of the sheet base material 18S. The individual lens shapes of the lens groups L1 to L3 constituting the lens layer 18L are formed in an elliptical shape. In particular, with respect to the in-plane X direction, the third lens group L3 is larger than the second lens group L2, and the first lens group L1 is larger (longer diameter / shorter diameter) than the third lens group L3. Is formed to be large. Thereby, the lens layer 18L can have a large light diffusion angle in the order of the first lens group L1, the third lens group L3, and the second lens group L2.

  The size of the individual microlenses constituting each of the lens groups L1 to L3 is not particularly limited. As an example, the microlenses constituting the first lens unit L1 have a major axis of 20 μm or more and 200 μm or less and a major axis / minor axis of 3 or more and 6 or less with respect to the elliptical shape of the lens bottom surface.

  Each microlens is distributed and formed on the surface of the sheet base material 18S with a certain periodicity for each of the lens shape types. In the present embodiment, the first to third lens groups L1 to L3 are distributed in a line shape corresponding to the axial direction and the arrangement interval of the linear light sources 2 of the backlight unit 4, and the linear light sources The major axis direction of each microlens is oriented in the extending direction of 2.

  The individual microlenses constituting the lens layer 18L are formed in a convex shape with respect to the sheet base 18S as shown in FIG. 3B, but the microlenses are formed on the sheet base 18S as shown in FIG. 3C. May be formed in a concave shape, or a composite of these convex shape and concave shape.

The diffusion sheet 18 having the above-described configuration is, for example, ground in the circumferential direction and the axial direction of the transfer roll by grinding the transfer roll surface by continuously changing the cutting amount of the cutting tool in conjunction with the rotation of the transfer roll. Forming a plurality of concave microlens molds having different curvatures, applying and filling a resin that absorbs and cures energy on the transfer roll surface, applying energy to the resin and curing the microlens Through the step of forming a group. Alternatively, a method of pressing the sheet base material 18S using a press die in which a plurality of convex microlens dies are formed is also applicable.
Furthermore, a method (so-called melt extrusion method) in which a molten thermoplastic resin is directly dropped onto a transfer roll and a microlens is formed through a cooling and solidification process can be used.

  In the liquid crystal display device 20 of the present embodiment configured as described above, the light emitted from the backlight unit 4 enters the liquid crystal panel 1 via the diffusion sheet 18 and the prism sheet 10, and the liquid crystal panel 1 Image light is formed on the front side. In the figure, the linear light source 2, the lens group on the diffusion sheet 18, the prism groove 12A of the prism sheet 10 and the like are shown slightly exaggerated for easy understanding, and there is no correlation in size or the like.

  As described above, in the diffusion sheet 18 of the present embodiment, a plurality of diffusion layers, that is, lens layers 18L having different degrees of light diffusion in the plane are formed, and in particular, a portion corresponding to a position immediately above the linear light source 2 is formed. Since the first lens group L1 is disposed and the second lens group L2 is disposed at a position corresponding to a position not directly above the linear light source 2, light is emitted with a relatively wide diffusion angle at a position immediately above the linear light source 2. However, light is emitted with a relatively narrow diffusion angle at a position directly above the linear light source 2.

  As a result, light diffuses over a wide area in the region close to the linear light source 2 to reduce the luminance, and light diffuses into a narrow region in the region away from the linear light source 2 to increase the luminance. As a result, the in-plane light intensity distribution corresponding to the position of the linear light source 2 can be made uniform, and luminance unevenness can be reduced. In addition, the light transmissivity of the diffusion sheet 18 can increase the light transmittance and improve the in-plane luminance as compared with the conventional milky white and thick diffusion plate.

  In particular, in the present embodiment, since the third lens group L3 that diffuses the light with an intermediate diffusion angle is interposed between the first lens group L1 and the second lens group L2, each lens group. It becomes possible to change the diffusion angle of light almost continuously between the formation regions of L1 to L3. Thereby, it is possible to further enhance the effect of reducing luminance unevenness.

  On the other hand, the light diffused and emitted from the diffusion sheet 18 as described above is collected by the prism sheet 10 and is incident on the liquid crystal panel 1. According to the present embodiment, the elliptical microlenses constituting the lens layer 18L on the diffusion sheet 18 are oriented in the direction perpendicular to the prism groove 12A in the major axis direction, so as shown in FIG. Further, the light is incident on the prism sheet 10 with the diffusion angle Dy in the Y direction being smaller than the diffusion angle Dx in the X direction with respect to the optical axis L from the minute lens. Thereby, the condensing effect | action by the prism sheet 10 is heightened, and the improvement of in-plane brightness | luminance can be aimed at.

  As described above, according to the present embodiment, in-plane luminance unevenness that occurs in relation to the position of the linear light source 2 of the backlight unit 4 can be significantly improved. Moreover, since a milky white thick diffuser is not required, the in-plane luminance can be improved and the backlight device 21 and the liquid crystal display device 20 can be made thinner.

  Next, a method for manufacturing a diffusion sheet according to the present invention, particularly an optical design method for individual lens groups constituting the lens layer will be described.

  The method of manufacturing a diffusion sheet according to the present invention includes a step of measuring an in-plane luminance distribution of a surface light source, a step of determining a diffusion degree that can equalize the in-plane luminance of the surface light source in each in-plane region, and a diffusion sheet Forming a plurality of diffusion layers having different diffusion degrees for each in-plane region.

  The surface light source corresponds to the direct type backlight unit 4 having the above-described configuration, but may be an edge light type backlight unit. The in-plane luminance distribution of the surface light source is greatly related to the size of the light source, the number of arrangement, the arrangement interval, the emission intensity, and the like. The light source is not only a linear light source 2 such as a CCFL but also a point light source such as an LED (Light Emitting Diode).

  Next, based on the in-plane luminance distribution of the surface light source, the degree of light diffusion that can improve the luminance distribution and make the luminance uniform is determined for each region. Specifically, the light intensity is extremely different between the position just above the light source and the position just above the light source, so the diffusion degree is increased to reduce the brightness at the position directly above the light source, and the diffusion degree is decreased at the position directly above the light source. Suppresses a decrease in luminance. These diffusion degree settings are determined for each region in the plane. Note that the degree of diffusion can be determined using a computer simulation or the like.

  And the diffusion layer of the diffusion sheet surface is designed based on the diffusion degree of each area | region in the surface determined at the said process. Specifically, when the diffusion layer is configured by the lens layer 18L described above, microlenses having different cross-sectional shapes are distributed and arranged for each region, and a diffusion layer including a plurality of types of lens layers as a whole is formed. As described above, the diffusion sheet according to the present invention is manufactured.

  5 and 6 show another embodiment of the diffusion sheet according to the present invention. In each of the following embodiments, an example in which a point light source such as a light emitting diode (LED) is used as the light source of the backlight unit is shown, but it is of course applicable to a linear light source such as CCFL.

  The diffusion sheet 32 shown in FIG. 5A is composed of a transparent resin sheet mixed with fine particles that diffuse incident light within the layer. Raised layers 32A are respectively formed on the back surface side of the diffusion sheet 32 corresponding to the positions where the point light sources 31 that emit white light are disposed. The raised layers 32A differ depending on whether the raised layers 32A are formed or not. A plurality of diffusion layers are formed.

  That is, since the light intensity is greatly different between the position directly above the point light source 31 and the position not directly above, the layer thickness of the diffusion sheet 32 is made different between the position directly above the point light source 31 and the position not directly above. In the position directly above, the light scattering probability in the diffusion sheet 32 is increased to increase the light diffusion degree, and conversely, the light diffusion degree is decreased in the position not directly above the light source 31. By appropriately adjusting the formation range and formation height of the raised portions 32A, the in-plane luminance of the light emitted from the diffusion sheet 32 can be made uniform.

  The diffusion sheet 33 shown in FIG. 5B is made of a transparent resin sheet, and a prism groove 33A having an irregular shape is formed on the back side thereof corresponding to the arrangement site of the point light sources 31 that emit white light. Has been. A plurality of diffusion layers are formed by the formation positions and non-formation positions of the prism grooves 33A.

  In this example, the degree of diffusion of the emitted light is increased at a position immediately above the point light source 31 by refraction incident on the prism groove 33A as compared with a portion where the prism groove 33A is not formed. By appropriately adjusting the shape pattern such as the groove width and depth of the prism grooves 33A, the in-plane luminance of the light emitted from the diffusion sheet 33 can be made uniform.

  The diffusion sheet 34 shown in FIG. 5C is made of a transparent resin sheet, and on the back side thereof, prism grooves 34A are formed corresponding to the arrangement site of the point light sources 31 that emit white light, and the point light sources 31 are formed. A prism groove 34B is formed corresponding to the non-directly above position. The groove depth of the prism groove 34A is larger than the groove depth of the prism groove 34B.

  In this example, the position directly above the point light source 31 has a configuration in which the degree of diffusion of light due to light refraction is increased compared to the non-directly above position. By appropriately adjusting the groove pitch and groove depth of the prism grooves 34A and 34B, the in-plane luminance of the light emitted from the diffusion sheet 34 can be made uniform.

  The diffusion sheet 35 shown in FIG. 6D is composed of a transparent resin sheet mixed with fine particles that diffuse incident light within the layer. On the back side of the diffusion sheet 35, a raised portion 35G having a relatively small raised amount corresponding to the arrangement location of the point light source 31G that emits green light, and the arrangement site of the point light source 31R that emits red light. Corresponding to the bulging portion 35R, the bulging amount is relatively large. In the present embodiment, the surface of each RGB color light is obtained by varying the scattering emission probability of the light transmission part for each color according to the light emission intensity of the point light sources 31R, 31G, 31B that emit each color light of RGB. The internal luminance is made uniform.

  The diffusion sheet 36 shown in FIG. 6E has different color lights by making the groove shapes of the prism grooves 36G, 36B, and 36R formed on the back side of the transparent resin sheet different for each color point light source 31G, 31B, and 31R. In this example, the in-plane luminance is made uniform by varying the degree of diffusion. Also in this example, the same effect as described above can be obtained.

  And the diffusion sheet 37 shown to FIG. 6F each forms the coating film 37A containing a diffusion particle corresponding to the arrangement | positioning site | part of the point light source 31 which light-emits white light on the back surface side of a transparent resin sheet. Thus, a configuration example in which the in-plane luminance distribution is made uniform by improving the intensity distribution of the emitted light by changing the degree of diffusion of light between the position directly above and the position not directly above the point light source 31. Show.

  Examples of the present invention will be described below. In addition, this invention is not limited to this Example.

  In this example, the in-plane luminance distribution was measured using the diffusion sheet 18 having the configuration described in the first embodiment as a sample. 7 and 8 schematically show the measurement method. As the backlight, a direct type backlight unit for 32-inch LCD TV manufactured by Sony Corporation was used. Twenty light sources (cold-cathode tubes) are arranged horizontally with respect to the television at intervals of 25 mm. The sample was placed at a position 17 mm from the cold cathode tube, and the luminance directly above the tube and on the intermediate portion between the tube was measured with a luminance meter. For the luminance meter, “BM-9” manufactured by Topcon Corporation was used.

  9A and 9B show the luminance distributions of the wide diffusion part (lens layer L1) and the narrow diffusion part (lens layer L2) of the diffusion sheet in this example, respectively. For comparison, the same measurement was performed using a 6 mm thick milk resin diffuser (Comparative Example 1) and a general-purpose diffusion sheet (Comparative Example 2) with an isotropic angle of 38 °. The measurement results are shown in Table 1.

  As shown in Table 1, according to the diffusion sheet of this example, the brightness difference between the portion directly above the light source and the intermediate portion can be significantly reduced as compared with the isotropic diffusion sheet of Comparative Example 2. It is possible to improve the in-plane luminance distribution.

  Further, the milky white diffusion plate (Comparative Example 1) had a small luminance difference and was effective in reducing luminance unevenness, and the diffusion sheet of this example was also visually equivalent to Comparative Example 1. Furthermore, according to the present embodiment, the light use efficiency is higher than that of the first comparative example, and the luminance can be improved.

  The embodiment of the present invention has been described above. Of course, the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.

  For example, in the above embodiment, the lens layers L1 to L3 on the surface of the diffusion sheet are configured by elliptical microlenses. However, the shape (bottom surface) of these microlenses is not limited to an elliptical shape, and is, for example, a circular shape. May be.

  In the above embodiment, the prism sheet 10 is arranged on the light emission side of the diffusion sheet 18, but instead of this, a deflection separation element may be used.

It is a schematic block diagram of the liquid crystal display device 20 provided with the diffusion sheet 18 by embodiment of this invention. 3 is a schematic side view of a backlight device 21 for explaining the operation of the diffusion sheet 18. FIG. 2A and 2B are diagrams for explaining a diffusion sheet 18, wherein A is a plan view of the main part, B is a cross-sectional view of the main part, and C is a cross-sectional view showing another configuration example. FIG. 5 is a diagram illustrating a relationship between a lens layer 18L and the prism sheet 10. It is a schematic block diagram of the diffusion sheet explaining other embodiment of this invention. It is a schematic block diagram of the diffusion sheet explaining other embodiment of this invention. It is a figure explaining the measuring method of the luminance distribution by the Example of this invention. It is a luminance distribution image figure of a backlight unit. It is a figure which shows the luminance distribution of the wide diffusion site | part of the diffusion sheet by the Example of this invention, and a narrow diffusion site | part. It is a schematic block diagram of the backlight unit of the conventional liquid crystal display device, A shows a direct type and B shows an edge light type, respectively.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel, 2 ... Linear light source, 3 ... Reflecting plate, 4 ... Direct type backlight unit, 10 ... Prism sheet, 18, 32-37 ... Diffusion sheet, 18L ... Lens layer, 18S ... Sheet base material, 20 Liquid crystal display device 21 Backlight device 31, 31B, 31G, 31R Point light source L1-L3 Lens group

Claims (12)

A diffusion sheet formed of a light-transmitting material, wherein a plurality of diffusion layers having different degrees of light diffusion are formed in a plane. 2. The plurality of diffusion layers include a plurality of first diffusion layers and a plurality of second diffusion layers having a light diffusion degree smaller than that of the first diffusion layers. Diffusion sheet. The plurality of diffusion layers further include a plurality of third diffusion layers having a light diffusion degree smaller than that of the first diffusion layer and a light diffusion degree larger than that of the second diffusion layer. The diffusion sheet according to claim 2. 2. The diffusion sheet according to claim 1, wherein each diffusion layer has a lens group formed on a sheet surface, and a curvature of a cross section of the lens group is different for each diffusion layer. The diffusion sheet according to claim 4, wherein the shape of each lens constituting the lens group is circular or elliptical. The diffusion sheet according to claim 2, wherein the first and second diffusion layers are periodically formed on the sheet surface. The diffusion sheet according to claim 6, wherein the first and second diffusion layers are alternately distributed in a line shape on the sheet surface. A method for producing a translucent diffusion sheet disposed on the light emitting side of a surface light source,
Measuring an in-plane luminance distribution of the surface light source;
Determining the degree of diffusion in each in-plane region that can equalize the in-plane brightness of the surface light source;
Forming a plurality of diffusion layers having different diffusion degrees for each of the regions on the surface of the diffusion sheet. A method for producing a diffusion sheet, comprising: In a backlight device including a plurality of light sources and a diffusion sheet disposed on the plurality of light sources,
The diffusion sheet includes a first diffusion layer formed at a position directly above the light source, and a second diffusion layer formed at a position not directly above the light source, and the first diffusion layer is the first diffusion layer. A backlight device characterized in that the degree of light diffusion is larger than that of the diffusion layer 2. The backlight device according to claim 9, wherein the light source is a linear light source. The backlight device according to claim 9, wherein the light source is a point light source. In a liquid crystal display device comprising a plurality of light sources, a diffusion sheet disposed on the plurality of light sources, and a liquid crystal panel disposed above the diffusion sheet,
The diffusion sheet includes a first diffusion layer formed at a position directly above the light source, and a second diffusion layer formed at a position not directly above the light source, and the first diffusion layer is the first diffusion layer. A liquid crystal display device characterized in that the degree of light diffusion is larger than that of the second diffusion layer.

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