Light diffusion sheet, backlight unit, liquid crystal display device, information equipment, and method for manufacturing light diffusion sheet

Abstract

The light diffuser (43) has a plurality of recesses (22) formed into an approximately inverted polygonal pyramid or an approximately inverted polygonal truncated cone shape on at least the first surface (43a). The ridges (23) dividing the plurality of recesses (22) have a shape that is recessed between the intersections (23a) relative to a straight line connecting the intersections (23a) of the ridges (23). If the arrangement pitch of the plurality of recesses (22) is set to P and the size occupied by the curved portion of the top of the ridge (23) in the arrangement direction of the plurality of recesses (22) is set to Wr, the ratio Wr / P is less than 0.3. The maximum height difference d between the straight line connecting the intersections (23a) of the ridges (23) and the ridge (23) is greater than 1 μm and less than 10 μm.

Description

Technical Field

[0001] The present disclosure relates to a light diffuser, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing the light diffuser. Background Art

[0002] In recent years, liquid crystal displays (hereinafter referred to as LCDs) have become widely used as display devices in various information devices such as smartphones and tablet computers. The mainstream backlighting methods for LCDs are either side-lit, with the light source positioned directly below the back of the LCD panel or near the side of the LCD panel.

[0003] When a direct backlight is used, a light diffusion member (light diffusion plate, light diffusion sheet, light diffusion film) is used to eliminate the image of a light source such as an LED (Light Emitting Diode) on the light emitting surface and improve the in-plane brightness uniformity.

[0004] In the direct-type backlight disclosed in Patent Document 1, a light diffuser plate having multiple recesses in the shape of inverted polygonal pyramids (inverted pyramids) or inverted polygonal truncated pyramids is used to improve brightness uniformity. Patent Document 1 discloses the following technical details: In the laminated structure of the light diffuser plate and other optical films, to prevent wear and damage to the light diffuser plate and other optical films due to vibration during transportation, the opening edge of the inner side surface of the recess of the light diffuser plate is a curved surface with the center of curvature located on the side of the recess in the depth direction.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-117707 Summary of the Invention

[0006] -Technical problem to be solved by the invention-

[0007] However, in the direct-type backlight disclosed in Patent Document 1, damage to the light diffuser plate or other optical films cannot be sufficiently suppressed.

[0008] Therefore, an object of the present disclosure is to provide a light diffuser that improves brightness uniformity and is not easily damaged even when stacked.

[0009] -Technical solutions to technical problems-

[0010] In order to achieve the above-mentioned purpose, the light diffuser involved in the present disclosure has a plurality of recesses formed in the shape of an approximately inverted polygonal pyramid or an approximately inverted polygonal truncated cone on at least the first surface. The ridges dividing the plurality of recesses have a shape that is recessed between the intersections relative to the straight line connecting the intersections of the ridges. If the arrangement pitch of the plurality of recesses is set to P, and the size of the curved portion of the top of the ridge in the arrangement direction of the plurality of recesses is set to Wr, then the ratio Wr / P is less than 0.3. The maximum height difference d between the straight line and the ridge is greater than 1 μm and less than 10 μm.

[0011] According to the light diffuser involved in the present disclosure, a plurality of recesses formed in the shape of approximately inverted polygonal pyramids or approximately inverted polygonal truncated cones are provided on at least the first surface, thereby improving brightness uniformity. In order to prevent the ridges (opening edges of the recesses) that divide the recesses from becoming a cause of wear or damage, the ridges have a shape that is concave between the intersections of the ridges. Therefore, even if it is used overlapping with other optical sheets or other light diffusers, it is not easy to be worn or damaged. The size Wr of the curved portion at the top of the ridge in the arrangement direction of the recesses is suppressed to less than 30% of the arrangement pitch P of the recesses. Therefore, the top of the ridge can maintain a steep shape, so even if the ridge is concave between the intersections of the ridges, the brightness uniformity is not easily reduced. Since the maximum height difference d between the straight line connecting the intersections of the ridges and the ridge is set to be greater than 1μm, scratch resistance is improved, and since the maximum height difference d is set to be less than 10μm, it is possible to suppress the reduction of brightness uniformity.

[0012] It should be noted that in the light diffuser involved in the present disclosure, considering that it is difficult to form a geometrically strictly defined inverted polygonal pyramid or inverted polygonal truncated pyramid concave portion using ordinary shape transfer technology, the expressions "approximately inverted polygonal pyramid" or "approximately inverted polygonal truncated pyramid" are used, but these expressions of course also include shapes that are truly or essentially can be regarded as inverted polygonal pyramids or inverted polygonal truncated pyramids.

[0013] In the light diffusion sheet of the present disclosure, it is preferred that the ridges have a concave shape between all intersections of the ridges, but it is not necessary for the ridges to have a concave shape between all intersections. In other words, the ridges may not have a concave shape between some intersections.

[0014] In the present disclosure, a “light diffusion sheet” includes a plate-shaped “light diffusion plate” and a film-shaped “light diffusion film”.

[0015] In the present disclosure, an “optical sheet” refers to a sheet having various optical functions such as diffusing light, focusing light, refracting light, and reflecting light. A “light diffusion sheet” is a type of “optical sheet”.

[0016] In the light diffuser of the present disclosure, if the maximum height difference d is greater than or equal to 1.5 μm and less than or equal to 7 μm, scratch resistance and brightness uniformity can be further improved. In this case, if the maximum height difference d is greater than or equal to 2.5 μm and less than or equal to 5 μm, scratch resistance and brightness uniformity can be further improved.

[0017] In the light diffusion sheet according to the present disclosure, if the ratio Wr / P is 0.2 or less, the brightness uniformity can be further improved. In this case, if the ratio Wr / P is 0.1 or less, the brightness uniformity can be further improved.

[0018] As for the light diffuser involved in the present disclosure, if the arrangement spacing P is greater than 50 μm and less than 500 μm, and the angle formed by the wall surfaces of the multiple recesses (i.e., the inclined surfaces that are approximately inverted polygonal pyramids or approximately inverted polygonal truncated cones) and the sheet surface of the light diffuser is greater than 40 degrees and less than 65 degrees, the brightness uniformity can be improved.

[0019] In the light diffusion sheet according to the present disclosure, if the ridge lines are recessed into a substantially parabolic shape, a substantially arc shape, a substantially triangular shape, or a substantially trapezoidal shape between the intersection points, the scratch resistance can be improved.

[0020] In the light diffuser involved in the present disclosure, the multiple recesses may also be formed into an approximately inverted quadrangular pyramid shape or an approximately inverted quadrangular truncated pyramid shape. In this case, the ridge line may extend along the first direction and the second direction. The maximum height difference d may be the average value of the maximum height difference dx between the straight line and the ridge line in the first direction and the maximum height difference dy between the straight line and the ridge line in the second direction. The arrangement pitch P may be the average value of the arrangement pitch Px of the multiple recesses in the first direction and the arrangement pitch Py of the multiple recesses in the second direction. The dimension Wr may also be the average value of the dimension Wrx occupied by the curved portion of the top of the ridge line in the first direction and the dimension Wry occupied by the curved portion of the top of the ridge line in the second direction. In this way, it is easy to manufacture a light diffuser with excellent scratch resistance and brightness uniformity.

[0021] In the light diffusion sheet of the present disclosure, if the plurality of recesses are provided only on the first surface and the second surface is a matte surface, wear or damage on the second surface can be suppressed and brightness uniformity can be further improved.

[0022] The backlight unit according to the present disclosure is assembled in a liquid crystal display device, guides light emitted from a light source toward a display screen, and includes the light diffusion sheet according to the present disclosure between the display screen and a plurality of light sources.

[0023] According to the backlight unit according to the present disclosure, since it includes the light diffusion sheet according to the present disclosure, it is possible to improve brightness uniformity and suppress damage even when the light diffusion sheet and other optical sheets are stacked.

[0024] In the backlight unit of the present disclosure, if a reflective sheet is provided on the opposite side of the display screen from the light diffusion sheet, and the light source is arranged on the reflective sheet, the brightness uniformity will be further improved.

[0025] In the backlight unit disclosed herein, multiple (e.g., three or more) light diffusers may be stacked and positioned between the display screen and the light source. This further improves brightness uniformity. When three or more light diffusers are stacked, brightness uniformity is further improved if the light diffuser closest to the display screen contains a diffusing agent, while the other light diffusers are substantially free of diffusing agent.

[0026] The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure and a liquid crystal display panel.

[0027] According to the liquid crystal display device according to the present disclosure, including the backlight unit according to the present disclosure, it is possible to improve brightness uniformity and suppress damage even when a light diffusion sheet and other optical sheets are laminated.

[0028] The information equipment involved in the present disclosure includes the liquid crystal display device involved in the present disclosure.

[0029] According to the information equipment according to the present disclosure, including the liquid crystal display device according to the present disclosure, brightness uniformity can be improved, and even when a light diffusion sheet and other optical sheets are laminated, damage can be suppressed.

[0030] The manufacturing method of the light diffuser involved in the present disclosure is the manufacturing method of the light diffuser involved in the present disclosure, which uses extrusion molding to manufacture the light diffuser under the conditions of a line speed of greater than 10m / min and less than 30m / min and a compression line pressure of greater than 100kgf / cm and less than 500kgf / cm.

[0031] According to the manufacturing method of the light diffuser involved in the present disclosure, the dimension Wr of the curved portion of the ridge top in the arrangement direction of the recesses can be made less than 30% of the arrangement pitch P of the recesses, thereby manufacturing a light diffuser with a steep ridge top shape and excellent brightness uniformity.

[0032] According to the method for manufacturing a light diffuser sheet disclosed herein, the maximum height difference (d) between the straight line connecting the intersections of the ridges and the ridges can be made to be greater than 1 μm and less than 10 μm. In other words, a light diffuser sheet can be obtained in which the ridges are recessed between the intersections of the ridges and are elevated at the intersections. Therefore, even when the light diffuser sheet is stacked with other optical sheets, the ridges are unlikely to come into contact with the other optical sheets at the intersections, making them less susceptible to wear or damage. Furthermore, since the ridges only make point contact with the other optical sheets at the intersections, they are less susceptible to sliding, causing wear or damage. As a result, a light diffuser sheet with excellent scratch resistance can be manufactured.

[0033] According to the method for manufacturing a light diffuser sheet of the present disclosure, extrusion molding is adopted, and thus the light diffuser sheet of the present disclosure can be manufactured at low cost.

[0034] -Effects of the Invention-

[0035] According to the present disclosure, a light diffusion sheet can be provided that improves brightness uniformity and is not easily damaged even when stacked with other optical sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a cross-sectional view of a liquid crystal display device according to an embodiment;

[0037] Figure 2 is a cross-sectional view of a backlight unit according to an embodiment;

[0038] Figure 3 To express Figure 2 A top view of an example of light source arrangement in a backlight unit shown;

[0039] Figure 4 is a perspective view of a light diffusion sheet according to an embodiment;

[0040] Figure 5 A perspective view showing an enlarged view of a concave portion formed on a light diffusion sheet according to an embodiment;

[0041] Figure 6 1 is a schematic diagram showing an example of the shape of an X-direction ridge line that divides a concave portion in a light diffusion sheet according to an embodiment;

[0042] Figure 7 1 is a schematic diagram showing an example of the shape of a Y-direction ridge line that divides a concave portion in a light diffusion sheet according to an embodiment;

[0043] Figure 8 Schematic diagram showing an example of a change in the shape of a ridge line that defines a concave portion in a light diffusion sheet according to an embodiment;

[0044] Figure 9Schematic diagram showing a cross-sectional structure of a light diffusion sheet according to an embodiment when cut along a plane perpendicular to the sheet surface, the plane passing through the center of each of adjacent recesses in the X direction and the midpoint of a ridgeline between the recesses;

[0045] Figure 10 Schematic diagram showing a cross-sectional structure of a light diffusion sheet according to an embodiment when cut along a plane perpendicular to the sheet surface, the plane passing through the center of each of adjacent concave portions in the Y direction and the midpoint of a ridgeline between the concave portions;

[0046] Figure 11 The laser microscope is used to measure Figure 6 The diagram shows an example of the result of the shape and size of the X-direction ridgeline;

[0047] Figure 12 The laser microscope is used to measure Figure 7 FIG. 1 is a diagram showing an example of the results of the shape and size of the Y-direction ridgeline;

[0048] Figure 13 The laser microscope is used to measure Figure 9 An example of the result of the shape and size of the cross-sectional structure shown;

[0049] Figure 14 The laser microscope is used to measure Figure 10 An example of the result of the shape and size of the cross-sectional structure shown;

[0050] Figure 15 is a structural diagram of an apparatus for measuring the scratch resistance of a light diffuser sheet in an embodiment;

[0051] Figure 16 A diagram showing the shape of a regular quadrangular pyramid on a roller used for manufacturing a light diffusion sheet in an embodiment;

[0052] Figure 17 A diagram showing the shape of a regular square pyramid on a flat plate used to manufacture a light diffuser in a comparative example;

[0053] Figure 18 Graph showing the results of a scratch resistance test conducted on samples of each of Examples and Comparative Examples;

[0054] Figure 19 is a cross-sectional view of a backlight unit according to a modified example. DETAILED DESCRIPTION

[0055] (Implementation Method)

[0056] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the scope of the present disclosure is not limited to the following embodiments, and can be arbitrarily modified within the scope of the technical concept of the present disclosure.

[0057] Liquid Crystal Display Devices

[0058] like Figure 1 As shown, a liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the rear side of the liquid crystal display panel 5 with the first polarizing plate 6 interposed therebetween. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 disposed opposite each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) provided in a frame-like shape to seal the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0059] From the front ( Figure 1 The display screen 50a of the liquid crystal display device 50 viewed from above is in principle rectangular or square in shape, but is not limited thereto and may be any shape such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or an instrument panel.

[0060] In each sub-pixel corresponding to each pixel electrode of the liquid crystal display device 50, a voltage of a specified magnitude is applied to the liquid crystal layer 3 to change the orientation state of the liquid crystal layer 3, thereby adjusting the transmittance of light incident from the backlight unit 40 through the first polarizer 6 and allowing the light to be emitted through the second polarizer 7, so that the liquid crystal display device 50 displays an image.

[0061] The liquid crystal display device 50 of this embodiment can be used as a display device incorporated into various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals, portable game consoles, copiers, ticket vending machines, and automatic teller machines).

[0062] The TFT substrate 1, for example, includes: a plurality of TFTs arranged in a matrix on a glass substrate; an interlayer insulating film provided to cover each TFT; a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to corresponding ones of the plurality of TFTs; and an alignment film provided to cover each pixel electrode. The CF substrate 2, for example, includes: a black matrix arranged in a grid pattern on a glass substrate; a color filter including a red layer, a green layer, and a blue layer respectively provided between each grid of the black matrix; a common electrode provided to cover the black matrix and the color filter; and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is formed of, for example, a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties. The first polarizer 6 and the second polarizer 7, for example, each include: a polarizer layer having a unidirectional polarization axis and a pair of protective layers provided to sandwich the polarizer layer.

[0063] <Backlight unit>

[0064] like Figure 2 As shown, the backlight unit 40 of this embodiment includes a reflective sheet 41, a plurality of small light sources 42 arranged two-dimensionally on the reflective sheet 41, a laminate of first light diffusers 43 disposed above the plurality of small light sources 42, a second light diffuser 44 disposed above the laminate of first light diffusers 43, and a first prism sheet 45 and a second prism sheet 46 disposed sequentially above the second light diffuser 44. In this example, the laminate of first light diffusers 43 is formed by laminating two layers of first light diffusers 43 having the same structure. Although not shown, a polarizer may also be disposed above the second prism sheet 46.

[0065] The reflection sheet 41 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor-deposited film, or the like.

[0066] The type of the small light source 42 is not particularly limited, and it may be an LED element or a laser element. From the perspective of cost and productivity, it is preferred to use an LED element. In order to adjust the light emission angle characteristics of the LED element that becomes the small light source 42, a lens may be installed on the LED element. For example, Figure 3 As shown, a plurality of small light sources 42 composed of square LED elements with a side length of several mm can also be arranged in a two-dimensional array at regular intervals on the reflective sheet 41. When viewed from above, the small light sources 42 can be rectangular, in which case the length of one side can be greater than 10 μm (preferably greater than 50 μm) and less than 20 mm (preferably less than 10 mm, more preferably less than 5 mm).

[0067] There is no specific limit on the number of small light sources 42 that can be arranged. When multiple small light sources 42 are dispersed, they are preferably arranged regularly on the reflector 41. Regular arrangement refers to the arrangement following a certain regularity. For example, arranging the small light sources 42 at equal intervals is considered a regular arrangement. When the small light sources 42 are arranged at equal intervals, the distance between the centers of two adjacent small light sources 42 can be greater than 0.5 mm (preferably greater than 2 mm) and less than 20 mm.

[0068] Each first light diffuser 43 has a base material layer 21. A plurality of recesses 22 are provided on the first surface 43a of the first light diffuser 43 (the surface opposite to the small light source 42). The plurality of recesses 22 are formed in an approximately inverted polygonal pyramid shape or an approximately inverted polygonal truncated pyramid shape. In this example, the plurality of recesses 22 are formed in an approximately inverted square pyramid shape. Adjacent recesses 22 are divided by ridge lines 23. The arrangement pitch of the recesses 22 is, for example, greater than or equal to about 50 μm and less than or equal to about 500 μm. The angle formed by the wall surface of the recess 22 (the inclined surface of the approximately inverted polygonal pyramid shape or the approximately inverted polygonal truncated pyramid shape) and the sheet surface of the first light diffuser 43 (the imaginary mirror surface without the recess 22) is, for example, greater than or equal to 40 degrees and less than or equal to 65 degrees. In other words, the vertex angle of the recess 22 is, for example, greater than or equal to 50 degrees and less than or equal to 100 degrees. The second surface 43b of the first light diffuser 43 can be a mirror surface, but is preferably a matte surface in order to improve the diffusion property. Figure 4 The case where the recessed portions 22 formed in a substantially inverted square pyramid shape are arranged in a 5×5 matrix on the first surface 43 a of the first light diffusion sheet 43 is exemplified.

[0069] The base material layer 21 is formed, for example, from polycarbonate as a matrix resin. It preferably contains no diffusing agent, but may contain, for example, approximately 0.1 to 4% by mass of a diffusing agent relative to 100% by mass of the base material. Known materials can be used as appropriate as the diffusing agent. In this example, the first light diffusing sheet 43 comprises a single layer of the base material layer 21. However, the first light diffusing sheet 43 may alternatively comprise a two-layer or higher structure including a layer having the recessed portions 22 formed therein.

[0070] The second light diffuser 44 may have a matte surface on its first surface 44a (the surface facing the first prism sheet 45) and a concave portion formed into a mirrored surface or a substantially inverted square pyramid shape on its second surface 44b. The second light diffuser 44 is formed, for example, from a polycarbonate base material (matrix resin) and preferably contains a diffusing agent, for example, approximately 0.5 to 4% by mass of the diffusing agent relative to 100% by mass of the base material. The second light diffuser 44 may be formed, for example, by mixing 1 part by mass of a silicon composite powder (average particle size 2.0 μm) as a diffusing agent with 99 parts by mass of an aromatic polycarbonate resin.

[0071] The first prism sheet 45 and the second prism sheet 46 are each formed of a film having a plurality of adjacent grooves having an isosceles triangle cross-section. The portion between adjacent pairs of grooves forms a prism, and the vertex angle of the prism is approximately 90°. The grooves formed in the first prism sheet 45 and the grooves formed in the second prism sheet 46 are arranged so as to be orthogonal to each other. The first prism sheet 45 and the second prism sheet 46 can be formed integrally. For example, a PET (polyethylene terephthalate) film formed into a prism shape using a UV-curable acrylic resin can be used as the first prism sheet 45 and the second prism sheet 46.

[0072] Although not shown in the figure, when a polarizer is provided on the upper side of the second prism sheet 46, for example, a DBEF series polarizer manufactured by 3M can be used. The polarizer prevents light emitted from the backlight unit 40 from being absorbed by the first polarizer 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a.

[0073] <Detailed Structure of Light Diffuser>

[0074] exist Figure 2 In the example shown, a plurality of recesses 22 are formed on the first surface 43a of the first light diffuser 43 (the surface facing the small light sources 42). However, a plurality of other recesses similar to the recesses 22 may be formed on the second surface 43b of the first light diffuser 43 instead. Alternatively, not only are a plurality of recesses 22 formed on the first surface 43a of the first light diffuser 43, but a plurality of other recesses similar to the recesses 22 may also be formed on the second surface 43b of the first light diffuser 43.

[0075] The plurality of recesses 22 can be formed into a shape approximating an inverted polygonal pyramid or an inverted polygonal truncated cone. The plurality of recesses 22 can be arranged in a regular two-dimensional pattern. As the "inverted polygonal pyramid (truncated cone) shape," preferably, a triangular pyramid (truncated cone), a quadrangular pyramid (truncated cone), or a hexagonal pyramid (truncated cone) shape that can be arranged two-dimensionally without gaps is preferred. While a mold (metal roller) is used in the manufacturing process such as extrusion molding or injection molding to form the recesses 22, an inverted quadrangular pyramid (truncated cone) shape can be selected as the "inverted polygonal pyramid (truncated cone) shape" in consideration of the precision of the cutting operation on the surface of the mold (metal roller).

[0076] It should be noted that, considering the difficulty of forming geometrically strictly defined inverted polygonal pyramid or inverted polygonal truncated pyramid concaves using conventional shape transfer techniques, the terms "approximately inverted polygonal pyramid" or "approximately inverted polygonal truncated pyramid" are used. However, these terms naturally include shapes that are truly or substantially identifiable as inverted polygonal pyramids or inverted polygonal truncated pyramids. "Approximately" means capable of approximating to something. For example, "approximately a quadrangular pyramid" refers to a shape that can be approximated to a quadrangular pyramid. Within the inevitable shape variations caused by machining accuracy in industrial production, shapes that vary from "inverted polygonal pyramid" or "inverted polygonal truncated pyramid" are also included in "approximately inverted polygonal pyramid" or "approximately inverted polygonal truncated pyramid."

[0077] When the plurality of recesses 22 are regularly arranged two-dimensionally, the plurality of recesses 22 may be provided on the entire surface of the first light diffuser 43 without any gaps or at regular intervals (pitch).

[0078] The first light diffuser 43 can be composed of a base layer 21 that does not contain a diffusing agent, such as a base layer 21 formed of transparent polycarbonate. When a diffusing agent is contained in the base layer 21, the material of the diffusing agent is not particularly limited. Inorganic particles such as silicon dioxide, titanium oxide, aluminum hydroxide, and barium sulfate can be used; organic particles such as acrylate, acrylonitrile, silicone, polystyrene, and polyamide can be used. From the perspective of light diffusion effect, the particle size of the diffusing agent can be, for example, greater than 0.1 μm (preferably greater than 1 μm) and less than 10 μm (preferably less than 8 μm). From the perspective of the reflection and refraction effect brought about by the approximately inverted polygonal pyramid shape and the light diffusion effect brought about by the diffusing agent, the first light diffuser 43 preferably does not contain a diffusing agent. However, the material (matrix) forming the base layer 21 can also be set to 100% by mass, and the content of the diffusing agent can be set to, for example, greater than 0.1% by mass (preferably greater than 0.3% by mass) and less than 10% by mass (preferably less than 8% by mass). The difference between the refractive index of the diffusing agent and the refractive index of the matrix in the base layer 21 is 0.01 or greater, preferably 0.03 or greater, more preferably 0.05 or greater, further preferably 0.1 or greater, and most preferably 0.15 or greater. If the difference between the refractive index of the diffusing agent and the refractive index of the matrix in the base layer 21 is less than 0.01, the diffusion effect of the diffusing agent will be insufficient.

[0079] The resin forming the matrix of the base material layer 21 is not particularly limited as long as it is a material that allows light to pass through. For example, acrylate, polystyrene, polycarbonate, MS (methyl methacrylate / styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. can be used.

[0080] The thickness of the first light diffuser 43 is not particularly limited, and can be, for example, 3 mm or less (preferably 2 mm or less, more preferably 1.5 mm or less, and even more preferably 1 mm or less) and 0.1 mm or more. If the thickness of the first light diffuser 43 exceeds 3 mm, it is difficult to achieve a thinner LCD display. On the other hand, if the thickness of the first light diffuser 43 is less than 0.1 mm, it is difficult to achieve the effect of improving brightness uniformity.

[0081] When the first light diffuser 43 has a multilayer structure (for example, a first substrate layer and a second recess-forming layer), the thickness of the recess-forming layer is greater than the maximum depth of the recess 22. For example, in the case of a layer having a recess with a depth of 20 μm, the thickness of the layer is greater than 20 μm. The first light diffuser 43 may be composed of a structure of three or more layers including a substrate layer and a recess-forming layer. Alternatively, the first light diffuser 43 may be an optical sheet structure in which the substrate layer and the recess-forming layer are independent of each other, or a structure in which the substrate layer and the recess-forming layer are stacked, or the substrate layer and the recess-forming layer may be arranged separately.

[0082] <Method for Manufacturing Light Diffusing Sheet>

[0083] The following describes a method for manufacturing the first light diffuser 43. The method for manufacturing the first light diffuser 43 is not particularly limited, and may be, for example, extrusion molding or injection molding. When extruding the first light diffuser 43, for example, the line speed may be set to 10 m / min to 30 m / min, and the compression line pressure may be set to 100 kgf / cm to 500 kgf / cm.

[0084] The steps for manufacturing a single-layer light diffuser with a concave-convex surface using an extrusion molding method are as follows. First, pellet-shaped plastic particles to which a diffusing agent has been added (pellet-shaped plastic particles without a diffusing agent can also be mixed together) are put into a single-screw extruder and melted and kneaded while heating. After that, the molten resin extruded from the T-die is clamped between two metal rollers and cooled, then transported by guide rollers and cut into single flat sheets by a slicer to produce a diffuser. Here, the desired concave-convex shape can be given to the surface of the diffuser by clamping the molten resin with a metal roller whose surface shape is opposite to the desired concave-convex shape and transferring the opposite shape of the roller surface to the resin. Because the shape of the roller surface may not be 100% transferred to the resin, the shape of the roller surface can be designed by reverse calculation based on the degree of transfer.

[0085] When using the extrusion molding method to manufacture a double-layer light diffuser with a concave-convex surface, for example, after adding granular plastic particles required to form each layer into two single-screw extruders, the same steps as above are performed on each layer, and the produced sheets are stacked.

[0086] Alternatively, a double-layered light diffuser with a concavo-convex surface can be produced as follows. First, granular plastic particles required to form each layer are fed into two single-screw extruders, where they are melted and mixed while being heated. The molten resin forming each layer is then fed into a T-die, where it is stacked. The stacked molten resin extruded from the T-die is then clamped between two metal rollers and cooled. The stacked molten resin can then be conveyed using guide rollers and cut into single flat sheets using a slicer, thereby producing a double-layered light diffuser with a concavo-convex surface.

[0087] Alternatively, a light diffuser sheet can be manufactured using UV (ultraviolet) shape transfer, as described below. First, uncured UV-curable resin is filled onto a roller having a shape that is the inverse of the concave and convex shape to be transferred, and a substrate is then pressed against the resin. Next, while the roller filled with UV-curable resin and the substrate are integrated, the resin is irradiated with ultraviolet light to cure it. The sheet, to which the concave and convex shape has been shape-transferred using the resin, is then peeled from the roller. Finally, the sheet is irradiated with ultraviolet light again to completely cure the resin, thereby producing a diffuser sheet with a concave and convex surface.

[0088] <Characteristics of Light Diffusers>

[0089] Below, refer to Figures 5 to 10 The features of the first light diffusion sheet 43 of this embodiment will be described in detail.

[0090] like Figure 5 As shown, a plurality of recesses 22, for example, shaped approximately like an inverted square pyramid, are provided on the first surface 43a of the first light diffuser 43. The plurality of recesses 22 can be shaped approximately like an inverted square pyramid. The center 22a of each recess 22 is the deepest portion of the recess 22. The plurality of recesses 22 are arranged along mutually orthogonal X-directions (first direction) and Y-directions (second direction). Adjacent recesses 22 are separated by ridgelines 23. The ridgelines 23 extend along the X-directions and the Y-directions.

[0091] One of the characteristics of the first light diffuser 43 is that the ridges 23 have a shape that is recessed between the intersections 23a of the ridges 23 relative to the straight lines Lx and Ly connecting the intersections 23a. The maximum height difference d between the straight lines Lx and Ly connecting the intersections 23a and the ridges 23 should be 1 μm to 10 μm, preferably 1.5 μm to 7 μm, and more preferably 2.5 μm to 5 μm.

[0092] It should be noted that, in the first light diffuser 43, the ridges preferably have a concave shape between all the intersections 23a of the ridges, but the ridges 23 do not necessarily have a concave shape between all the intersections 23a. In other words, the ridges 23 may not have a concave shape between some of the intersections 23a.

[0093] Figure 6 It indicates that the direction along the sheet is viewed from the direction parallel to the sheet surface and perpendicular to the X direction. Figure 5 An example of the shape observed when the line Ax-Bx is the ridge line 23 extending in the X direction, Figure 7 Indicates the direction parallel to the sheet surface and perpendicular to the Y direction when viewed along Figure 5 An example of the shape observed when the line Ay-By is the ridge line 23 extending in the Y direction. Figure 6 As shown, the ridge line 23 has a shape that is recessed between the intersection points 23a relative to the straight line Lx connecting the intersection points 23a of the ridge lines 23 in the X direction. Assuming that the arrangement pitch of the recesses 22 in the X direction is Px, the ridge line 23 extending in the X direction has a lowest point 23b at a position that is Px / 2 (half the pitch) away from the intersection points 23a, and the distance from the straight line Lx to the lowest point 23b (maximum height difference) is dx. Figure 7 As shown, the ridge lines 23 have a shape that is recessed between the intersection points 23a relative to a straight line Ly connecting the intersection points 23a of the ridge lines 23 in the Y direction. Assuming that the arrangement pitch of the recesses 22 in the Y direction is Py, the ridge lines 23 extending in the Y direction have a lowest point 23b at a position Py / 2 (half the pitch) from the intersection points 23a, and the distance from the straight line Ly to the lowest point 23b (maximum height difference) is dy.

[0094] It should be noted that when the recess 22 is formed into an inverted quadrangular pyramid, the arrangement spacing Px of the recess 22 in the X direction is equal to the spacing (horizontal distance) between the intersection points 23a in the X direction, and the arrangement spacing Py of the recess 22 in the Y direction is equal to the spacing (horizontal distance) between the intersection points 23a in the Y direction.

[0095] The average value of the maximum height difference dx in the X direction and the maximum height difference dy in the Y direction is taken as the maximum height difference d. The maximum height difference d needs to be set to be greater than 1 μm and less than 10 μm, preferably greater than 1.5 μm and less than 7 μm, and more preferably greater than 2.5 μm and less than 5 μm.

[0096] The shape of the depression between the intersection points 23a of the ridge line 23 is not particularly limited, for example, Figure 8 As shown, the ridge line 23 may also be recessed into an approximately circular arc shape between the intersection points 23a relative to the straight line L connecting the intersection points 23a ( Figure 8 (A)), approximately parabolic shape ( Figure 8 (B)), approximately triangular shape ( Figure 8 (C)) or approximately trapezoidal shape ( Figure 8 (D)).

[0097] As another feature of the first light diffuser 43, when the arrangement pitch of the recesses 22 is set to P and the size of the curved portion at the top of the ridge 23 in the arrangement direction of the recesses 22 is set to Wr, the ratio Wr / P needs to be below 0.3, more preferably below 0.2, and further preferably below 0.1.

[0098] Figure 9 The first light diffuser 43 is shown along Figure 5 An example of a cross-sectional structure taken along line Cx-Dx. Figure 10 The first light diffuser 43 is shown along Figure 5 An example of a cross-sectional structure taken along the line Cy-Dy. Figure 9 The cross-sectional structure of the first light diffuser 43 is shown when the first light diffuser 43 is cut along a plane perpendicular to the sheet surface, the plane passing through the midpoint between the centers 22a of the concave portions 22 adjacent in the X direction and the intersection 23a of the ridge lines 23 between the concave portions 22. Figure 10 The cross-sectional structure of the first light diffuser 43 is shown when the surface perpendicular to the sheet surface passes through the midpoint between the centers 22a of the concave portions 22 adjacent in the Y direction and the intersection 23a of the ridges 23 between the concave portions 22.

[0099] exist Figure 9 In the cross-sectional structure shown, the spacing (horizontal distance) between the centers 22a of adjacent recesses 22 in the X direction is equal to the arrangement pitch Px of the recesses 22 in the X direction. The dimension occupied by the curved portion at the top of the ridge line 23 in the X direction is Wrx. The dimensions occupied by the straight portions of the wall surfaces (the slopes of the inverted quadrangular pyramids) of the adjacent recesses 22 sandwiching the ridge line 23 in the X direction are Wsx1 and Wsx2. In the X direction, the angle formed by the wall surfaces (the slopes of the inverted quadrangular pyramids) of the recesses 22 and the sheet surface is θx. The height from the center 22a of the recess 22 to the vertex (the midpoint between the intersection points 23a) of the ridge line 23 (ridge line 23 extending in the Y direction) is Hx.

[0100] exist Figure 10In the cross-sectional structure shown, the spacing (horizontal distance) between the centers 22a of adjacent recesses 22 in the Y direction is equal to the arrangement pitch Py of the recesses 22 in the Y direction. The dimension occupied by the curved portion at the top of the ridgeline 23 in the Y direction is Wry. The dimensions occupied by the straight portions of the wall surfaces (the slopes of the inverted quadrangular pyramids) of the adjacent recesses 22 sandwiching the ridgeline 23 in the Y direction are Wsy1 and Wsy2. In the Y direction, the angle formed by the wall surfaces (the slopes of the inverted quadrangular pyramids) of the recesses 22 and the sheet surface is θy. The height from the center 22a of the recess 22 to the vertex (the midpoint between the intersection points 23a) of the ridgeline 23 (ridgeline 23 extending in the X direction) is Hy.

[0101] It should be noted that when the recess 22 is formed in the shape of an inverted quadrangular pyramid, the average value of the arrangement spacing Px and the arrangement spacing Py is set to P, and the average value of the size Wrx and the size Wry is set to Wr, then the ratio Wr / P needs to be set to less than 0.3, preferably less than 0.2, and more preferably less than 0.1.

[0102] Figure 11 It is measured by laser microscope Figure 6 The shape and size of the X-direction ridgeline shown in the figure are examples of the results. Figure 12 It is measured by laser microscope Figure 7 An example of the results of the shape and size of the Y-direction ridgeline shown, Figure 13 It is measured by laser microscope Figure 9 An example of the results of the shape, size and angle of the cross-sectional structure shown, Figure 14 It is measured by laser microscope Figure 10 An example of the results of the shape, size and angle of the cross-sectional structure shown.

[0103] It should be noted that in Figure 11 、 Figure 12 In the measurement of the maximum value (maximum height difference) dx, dy of the distance between the straight lines Lx, Ly connecting the intersection points 23a of the ridge lines 23 and the ridge lines 23, the maximum value of the length of the perpendicular line drawn from the point on the ridge line 23 perpendicular to the straight lines Lx, Ly is set as dx, dy.

[0104] When measuring the arrangement pitches Px and Py, the horizontal distances between the intersections 23a in the X and Y directions are calculated as Px and Py, respectively. This makes it possible to easily and accurately calculate the arrangement pitches Px and Py even when measuring the horizontal distances between the intersections 23a.

[0105] <Effects of implementation>

[0106] As described above, the first light diffuser 43 of this embodiment has a plurality of recesses 22 formed in an approximately inverted polygonal pyramid shape or an approximately inverted polygonal truncated cone shape on at least the first surface 43a. The ridges 23 that divide the plurality of recesses 22 have a shape that is recessed between the intersections 23a relative to the straight line connecting the intersections 23a of the ridges 23. If the arrangement pitch of the plurality of recesses (22) is set to P, and the size occupied by the curved portion of the top of the ridge (23) in the arrangement direction of the plurality of recesses (22) is set to Wr, then the ratio Wr / P is less than 0.3. If the intersections 23a of the ridges 23 are connected to each other, the maximum height difference d with the ridge 23 is greater than 1 μm and less than 10 μm.

[0107] According to the first light diffuser 43 of this embodiment, a plurality of recesses 22 formed in the shape of approximately inverted polygonal pyramids or approximately inverted polygonal truncated cones are provided on at least the first surface 43a, thereby improving brightness uniformity. In order to prevent the ridges 23 (opening edges of the recesses 22) that divide the recesses 22 from causing wear or damage, the ridges 23 have a shape that is recessed between the intersections 23a of the ridges 23. Therefore, even when used overlapping with other optical sheets or other light diffusers, wear or damage is unlikely to occur. The dimension Wr of the curved portion at the top of the ridge 23 in the arrangement direction of the recesses 22 is suppressed to less than 30% of the arrangement pitch P of the recesses. Therefore, the top of the ridge 23 can maintain a steep shape, so even if the ridge 23 is recessed between the intersections 23a, brightness uniformity is unlikely to be reduced. Since the maximum height difference d between the straight line connecting the intersection points 23 a and the ridge line 23 is set to 1 μm or more, scratch resistance is improved, and since the maximum height difference d is set to 10 μm or less, a decrease in brightness uniformity can be suppressed.

[0108] In the first light diffuser 43 of this embodiment, if the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 is set to be greater than 1.5 μm and less than 7 μm, scratch resistance and brightness uniformity can be further improved. In this case, if the maximum height difference d is greater than 2.5 μm and less than 5 μm, scratch resistance and brightness uniformity can be further improved.

[0109] In the first light diffuser 43 of this embodiment, the arrangement pitch of the plurality of recesses 22 is denoted by P, and the dimension of the curved portion at the top of the ridge line 23 in the arrangement direction of the plurality of recesses 22 is denoted by Wr. If the ratio Wr / P is 0.2 or less, brightness uniformity can be further improved. In this case, if the ratio Wr / P is 0.1 or less, brightness uniformity can be further improved.

[0110] As for the first light diffuser 43 of this embodiment, if the arrangement pitch P of the multiple recesses 22 is greater than 50 μm and less than 500 μm, and the angle formed between the wall surfaces of the multiple recesses 22 (i.e., the inclined surfaces that are approximately inverted polygonal pyramids or approximately inverted polygonal truncated cones) and the sheet surface is greater than 40 degrees and less than 65 degrees, the brightness uniformity can be improved.

[0111] In the first light diffusion sheet 43 of this embodiment, if the ridge lines 23 are recessed into a substantially parabolic shape, a substantially circular arc shape, a substantially triangular shape, or a substantially trapezoidal shape between the intersection points 23 a , the scratch resistance can be improved.

[0112] In the first light diffuser 43 of this embodiment, the plurality of recesses 22 may be formed in a shape approximating an inverted quadrangular pyramid or an inverted quadrangular truncated pyramid. In this case, the ridge line 23 may extend in the X direction (first direction) and the Y direction (second direction). The maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 may be the average of the maximum height difference dx between the straight line and the ridge line 23 in the X direction and the maximum height difference dy between the straight line and the ridge line 23 in the Y direction. The arrangement pitch P of the plurality of recesses 22 may be the average of the arrangement pitch Px of the recesses 22 in the X direction and the arrangement pitch Py of the recesses 22 in the Y direction. The dimension Wr occupied by the curved portion at the top of the ridge line 23 in the direction in which the recesses 22 are arranged may be the average of the dimension Wrx occupied by the curved portion at the top of the ridge line 23 in the X direction and the dimension Wry occupied by the curved portion at the top of the ridge line 23 in the Y direction. This facilitates the manufacture of a light diffuser with excellent scratch resistance and brightness uniformity.

[0113] In the first light diffusion sheet 43 of this embodiment, if the plurality of recesses 22 are provided only on the first surface 43a and the second surface 43b is matte, wear or damage of the second surface 43b can be suppressed and brightness uniformity can be further improved.

[0114] The backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50 and guides light emitted by a light source 42 toward a display screen 50 a . The backlight unit 40 includes a first light diffusion sheet 43 of this embodiment between the display screen 50 a and the light source 42 .

[0115] According to the backlight unit 40 of this embodiment, the first light diffusion sheet 43 of this embodiment is included, so that luminance uniformity can be improved and damage can be suppressed even if the first light diffusion sheets 43 are stacked on each other or stacked on other optical sheets.

[0116] In the backlight unit 40 of this embodiment, if the reflective sheet 41 is disposed on the opposite side of the display screen 50 a from the first light diffusion sheet 43 and the light source 42 is arranged on the reflective sheet 41 , the brightness uniformity is further improved.

[0117] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and the liquid crystal display panel 5 .

[0118] According to the liquid crystal display device 50 of this embodiment and the information equipment including the liquid crystal display device 50, including the backlight unit 40 of this embodiment, it is possible to improve brightness uniformity and suppress damage even if the first light diffuser sheets 43 are stacked on each other or the first light diffuser sheets 43 are stacked on other optical sheets.

[0119] The light diffuser manufacturing method of this embodiment is a method for manufacturing the first light diffuser 43 of this embodiment, and the first light diffuser 43 is manufactured by extrusion molding under the conditions of a line speed of not less than 10m / min and not more than 30m / min and a compression line pressure of not less than 100kgf / cm and not more than 500kgf / cm.

[0120] According to the light diffuser manufacturing method of this embodiment, the dimension Wr of the curved portion at the top of the ridge line 23 in the arrangement direction of the recess 22 can be made less than 30% of the arrangement pitch P of the recess 22, thereby being able to manufacture a first light diffuser 43 having a steep shape at the top of the ridge line 23 and excellent brightness uniformity.

[0121] According to the light diffuser sheet manufacturing method of this embodiment, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 can be made to be greater than 1μm and less than 10μm. In other words, a first light diffuser sheet 43 can be obtained in which the ridge lines 23 are recessed between the intersections 23a and are partially elevated at the intersections 23a. Therefore, even if the first light diffuser sheets 43 are stacked on top of each other or with other optical sheets, the ridge lines 23 are unlikely to come into contact with other optical sheets at the intersections 23a, making them less susceptible to wear or damage. At the intersections 23a, the ridge lines 23 make point contact with other optical sheets, making them less susceptible to sliding and wear or damage. Consequently, a first light diffuser sheet 43 with excellent scratch resistance can be manufactured.

[0122] According to the method for manufacturing a light diffusion sheet of the present embodiment, since extrusion molding is adopted, the first light diffusion sheet 43 of the present embodiment can be manufactured at low cost.

[0123] (Example)

[0124] Hereinafter, the first light diffusion sheet 43 according to the embodiment will be described with reference to a comparative example.

[0125] <Measurement of the shape, size, and angle of the recess>

[0126] The shape of the concave portion 22 formed on the first light diffusion sheet 43 in each embodiment described below was observed using a laser microscope VK-100 manufactured by KEYENCE. Specifically, the following measurements were made: the cross-sectional shape of the ridge line 23 of the concave portion 22 formed in the shape of an inverted square pyramid ( Figure 6 、 Figure 7 、 Figure 9 、 Figure 10 cross-sectional shape shown); Figure 6 、 Figure 7 The maximum height differences dx and dy (the maximum value of the distance between the straight line connecting the intersection points 23a and the ridge line 23) and their average value d are shown; Figure 9 、 Figure 10 The heights Hx and Hy (the heights from the center 22a of the recess 22 to the apex of the ridge 23) and their average value H are shown; Figure 9 、 Figure 10 The dimensions Wrx and Wry shown (the dimensions of the curved portion of the top of the ridge line 23 in the X and Y directions) and their average value Wr; Figure 6 、 Figure 7 The arrangement pitches Px and Py of the recesses 22 (horizontal distances between the intersections 23a in the X and Y directions) and their average value P; the ratio Wr / P (unit: %) of the dimension Wr to the arrangement pitch P; and Figure 9 、 Figure 10 The angles θx and θy shown are angles formed between the wall surface (the slope of the inverted square pyramid) of the recessed portion 22 and the sheet surface of the first light diffusion sheet 43 in the X and Y directions.

[0127] <Measurement of optical properties>

[0128] As optical properties of the first light diffuser 43 in each of the examples described below, haze and light transmittance at a wavelength of 450 nm were measured. Haze was measured in accordance with JIS K-7105 using an HZ-2 tester manufactured by SUGA Testing Instruments Co., Ltd., with light incident from a surface (first surface 43 a) of the recessed portion 22 formed in the shape of an inverted square pyramid. Light transmittance at a wavelength of 450 nm was measured using a V-670 tester manufactured by JASCO Corporation, with light incident from a surface (first surface 43 a) of the recessed portion 22 formed in the shape of an inverted square pyramid.

[0129] <Evaluation of scratch resistance>

[0130] In the scratch resistance test of the first light diffuser 43 of each embodiment described below, Figure 15 The device shown. Figure 15As shown, the lower surface of the first light diffuser 43, serving as a fixed sample, was designated as the first surface 43a (the surface where the inverted square pyramid-shaped recess 22 was formed), and the upper surface of the first light diffuser 43, serving as a moving sample, was designated as the second surface 43b (matte surface). The moving sample and the fixed sample were stacked sequentially on a glass plate. A weight of 516 gf was placed from above on a circular area with a diameter of 20 mm. The moving sample was pulled at a speed of 10 mm / second for 100 mm. The degree of scratching on the friction surface between the moving sample and the fixed sample was visually inspected. Both the lower surface of the fixed sample (the surface where the inverted square pyramid-shaped recess 22 was formed) and the upper surface of the moving sample (matte surface) were inspected and evaluated.

[0131] The following criteria were used for inspection and evaluation.

[0132] AA: No scratches were visually observed, indicating a light diffusion sheet with very excellent scratch resistance.

[0133] A: Almost no scratches are visible to the naked eye, indicating that the light diffuser has excellent scratch resistance.

[0134] B: Scratches are slightly visible, and the light diffusion sheet has relatively excellent scratch resistance.

[0135] C: A few scratches are visible to the naked eye, and the light diffuser sheet is close to the lower limit of acceptable scratch resistance.

[0136] ×: Many scratches are clearly visible even with the naked eye, indicating that the light diffusion sheet has poor scratch resistance.

[0137] <Brightness and Brightness Uniformity Measurement>

[0138] The brightness and brightness uniformity of the first light diffuser 43 of each embodiment described below were measured by Figure 2 and Figure 3The backlight unit 40 shown in FIG. Specifically, two first light diffusers 43 are stacked on top of small light sources 42 (LED arrays) arranged in an array, with the first surface 43a having a recess 22 facing the light source 42. The recess 22 is an inverted square pyramid-shaped recess obtained in the later-described embodiment. A second light diffuser 44 is stacked on top of the stack of first light diffusers 43, with the second surface 44b, i.e., the mirror surface, facing the light source 42. The second light diffuser 44 is made of the same aromatic polycarbonate resin as in Example 18, described later, with the same composition and the same diffusing agent added thereto. The second light diffuser 44 has a thickness of 120 μm. One roller is a mirror-finished roller, and the other roller is a roller with a random matte surface (surface roughness Ra = 2.5 μm) similar to that in Example 1, described later. The same method as in Example 1 is used to manufacture the second light diffuser 44. In the second light diffuser 44, the surface roughness Ra of the matte surface (first surface 44a) is 1.6 μm, and the surface roughness Ra of the mirror surface (second surface 44b) is 0.4 μm. Two prism sheets 45 and 46 are arranged overlapping on the second light diffuser 44. Under the above configuration, brightness and brightness uniformity measurements were performed. It should be noted that an array with an LED pitch of 3 mm was used as the LED array, and a blue LED manufactured by Cree (product number XPGDRY-L1-0000-00501) was used as the LED (small light source 42).

[0139] In the measurement of brightness uniformity, first, Figure 3 In the LED array (six × six) shown, the cross-sectional brightness is obtained along the diagonal line L passing directly above the LED (small light source 42). Then, the mean and standard deviation of the cross-sectional brightness are calculated.

[0140] The brightness uniformity (%) was calculated according to the following formula: Brightness uniformity (%)=(average value of cross-sectional brightness)÷(standard deviation of cross-sectional brightness)×100.

[0141] The higher the value of the brightness uniformity obtained as described above, the more uniform the brightness.

[0142] The evaluation criteria for brightness uniformity are as follows.

[0143] AA: Brightness uniformity is 210% or higher, a level at which no brightness unevenness is visually visible, and this is a light diffuser that exhibits the most excellent uniformity.

[0144] A: The luminance uniformity is 200% or more and less than 210%. The luminance unevenness is almost invisible to the naked eye, and the light diffuser exhibits excellent uniformity.

[0145] B: The light diffuser has a luminance uniformity of 190% or more and less than 200%. Although slight luminance unevenness is visually observed, the light diffuser still exhibits a uniformity of acceptable level.

[0146] C: The luminance uniformity is 180% or more and less than 190%. Although luminance unevenness is visually observed, the light diffuser exhibits a minimum uniformity of an acceptable level.

[0147] X: The brightness uniformity is less than 180%, and the brightness unevenness is obvious when viewed visually, indicating a light diffuser with poor uniformity.

[0148] The evaluation criteria for brightness are as follows.

[0149] A: The average profile brightness is 3150cd / m 2 The above light diffuser.

[0150] B: The average brightness of the cross section is 3100cd / m 2 Above and less than 3150cd / m 2 light diffuser.

[0151] C: The average brightness of the profile is 3050cd / m 2 Above and less than 3100cd / m 2 light diffuser.

[0152] Overall Evaluation

[0153] Based on the results of the scratch resistance test and the evaluation results of the luminance uniformity, the first light diffusion sheet 43 of each example described below was comprehensively evaluated according to the following criteria.

[0154] AA: The light diffuser with all the evaluation results of the scratch resistance test and the evaluation results of the brightness uniformity test of both the inverted square pyramid surface and the matte surface being A or higher and having two or more AA results is the most excellent overall.

[0155] A: A light diffuser sheet with all the evaluation results of the scratch resistance test and the brightness uniformity test of both the inverted square pyramid surface and the matte surface being A or higher, and being the most excellent overall (except for the AA evaluation product).

[0156] B: A light diffusing sheet that is generally excellent, with all the evaluation results of the scratch resistance test and the evaluation results of the brightness uniformity test of both the inverted square pyramid surface and the matte surface being B or higher (except for products evaluated as AA and A).

[0157] C: The evaluation results of the scratch resistance test and the brightness uniformity test of both the inverted square pyramid surface and the matte surface are all C or higher, indicating that the light diffuser has overall performance that exceeds the minimum and is usable (however, AA, A, and B evaluation products are excluded).

[0158] ×: A light diffusion sheet with an overall poor evaluation of × in any one of the evaluation results of the scratch resistance test and the evaluation results of the brightness uniformity of both the inverted square pyramid surface and the matte surface.

[0159] <Example 1>

[0160] The manufacturing method of the first light diffuser 43 of Example 1 is as follows. First, an aromatic polycarbonate resin having a melt flow rate of 15 g / 10 min as measured according to ISO 1133 is fed into an extruder, melt-kneaded, and then extruded from a T-die. Then, a metal roller having a surface Figure 16 A roller with the shape shown in (A) and (B) ((B) is a cross-sectional view of (A) along line XY) (a regular square pyramid (i.e., a pyramid) with a height of 50 μm, a pitch of 100 μm, and a vertex angle of 90 degrees) was used. A roller with a randomly matte surface (surface roughness Ra = 2.5 μm) was used as the other roller. Molten resin extruded from a T-die was sandwiched between these two rollers, transferring the shape while cooling. In this way, a single-layer light diffuser sheet with a thickness of 180 μm was produced by extrusion molding. As shown in Table 1, one surface of this light diffuser sheet has a concave (inverted) pyramid shape, the depth of which is determined by the height of the regular square pyramid on the roller, and the other surface has a matte surface with a surface roughness of Ra = 1.67 μm. It should be noted that, as the molding conditions, as shown in Table 1, pressurization was performed at a line speed of 17 m / min and a compressive force (compression line pressure) between two rollers of 280 kgf / cm, and a light diffuser was obtained under resin temperature conditions (230 to 310°C) in which the shape transfer to the polycarbonate resin was good and the sheet was well peeled from the roller.

[0161]

Table 1

[0162]

[0163] The shape of the concave portion (inverted square pyramid) 22 formed on the first light diffusion sheet 43 of Example 1 produced as described above was observed using a laser microscope VK-100 manufactured by KEYENCE. Specifically, the following measurements were made: the cross-sectional shape of the ridgeline 23 of the concave portion 22 formed in the shape of an inverted square pyramid ( Figure 6 、 Figure 7 、 Figure 9 、 Figure 10 cross-sectional shape shown); Figure 6 、 Figure 7 The maximum height differences dx and dy (the maximum value of the distance between the straight line connecting the intersection points 23a and the ridge line 23) and their average value d are shown; Figure 9 、 Figure 10 The heights Hx and Hy (the heights from the center 22a of the recess 22 to the apex of the ridge 23) and their average value H are shown; Figure 9 、 Figure 10 The dimensions Wrx and Wry shown (the dimensions of the curved portion of the top of the ridge line 23 in the X and Y directions) and their average value Wr; Figure 6 、 Figure 7 The arrangement pitches Px and Py of the recesses 22 (horizontal distances between the intersections 23a in the X and Y directions) and their average value P; the ratio Wr / P (unit: %) of the dimension Wr to the arrangement pitch P; and Figure 9 、 Figure 10 The angles θx and θy shown are angles formed between the wall surface (the slope of the inverted square pyramid) of the recessed portion 22 and the sheet surface of the first light diffusion sheet 43 in the X and Y directions.

[0164] <Examples 2 and 3>

[0165] In the manufacturing method of the first light diffuser 43 of Example 2, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 54.6 μm, a spacing of 100 μm, and a vertex angle of 85 degrees was used as the roller in the shape of a regular tetrahedron among the two metal rollers. Except for this, as shown in Table 1, the same conditions as in Example 1 were adopted.

[0166] In the manufacturing method of the first light diffuser 43 of Example 3, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 59.6 μm, a spacing of 100 μm, and a vertex angle of 80 degrees was used as the roller in the shape of a regular tetrahedron among the two metal rollers. Except for this, as shown in Table 1, the same conditions as in Example 1 were adopted.

[0167] Comparative Examples 1 to 3

[0168] In Comparative Example 1, first, a 1 mm thick punching plate was produced using the same aromatic polycarbonate resin as in Example 1. Figure 17 A flat plate mold having the shape shown in (A) and (B) ((B) is a shape diagram observed from the line XY section direction of (A)) (a shape in which the valley portion of the pyramid is repaired into a curved surface with a curvature radius of 4.2 μm in the same regular quadrangular pyramid, i.e., pyramid shape as in Example 1), and a flat plate mold having the same random matte shape (surface roughness Ra = 2.5 μm) as in Example 1 on the surface, the two molds are used to clamp the stamping original plate, and the plate is placed in a stamping machine with a heating and cooling device, and the stamping plate temperature is 250°C and the pressure is 200 kg / cm 2Then, the pressing plate temperature was cooled to 20°C while maintaining the pressure, and the pressure was maintained until the resin plate was sufficiently cooled. The light diffuser sheet with a thickness of 180 μm shown in Table 1 was produced by compression molding.

[0169] In Comparative Example 2, after a stamping original plate was produced in the same manner as in Comparative Example 1, a flat plate mold was used in which the surface had a regular quadrangular pyramid, i.e., a pyramid, in the same shape as in Example 2, with the valley portion of the pyramid being trimmed into a curved surface with a curvature radius of 4.2 μm as in Comparative Example 1. In addition, under the same conditions as in Comparative Example 1, a light diffuser with a thickness of 180 μm as shown in Table 1 was produced by compression molding using a punching machine for heating, pressurizing, and cooling.

[0170] In Comparative Example 3, after a stamping original plate was produced in the same manner as in Comparative Example 1, a flat plate mold was used having a surface having a regular quadrangular pyramid, i.e., a pyramid, in the same shape as in Example 3, with the valley portion of the pyramid being trimmed into a curved surface with a curvature radius of 4.2 μm as in Comparative Examples 1 and 2. In addition, under the same conditions as in Comparative Examples 1 and 2, a light diffuser with a thickness of 180 μm as shown in Table 1 was produced by compression molding using a punching machine for heating, pressurizing, and cooling.

[0171] <Evaluation of Examples 1 to 3 and Comparative Examples 1 to 3>

[0172] For the first light diffuser 43 obtained in Examples 1 to 3, the shapes, sizes, angles, etc. of the various elements measured are shown in Table 2 together with Comparative Examples 1 to 3, and the measurement results of the optical properties, the results of the scratch resistance test, the evaluation results of the brightness and brightness uniformity, and the comprehensive evaluation results are shown in Table 3 together with Comparative Examples 1 to 3.

[0173]

Table 2

[0174]

[0175]

Table 3

[0176]

[0177] The results shown in Tables 2 and 3 show that in the first light diffusing sheets 43 formed with inverted square pyramid-shaped recesses 22 obtained in Examples 1 to 3, the maximum height difference d between the straight line connecting the intersections 23a and the ridgeline 23 was greater than 1.0 μm, and the ridgeline 23 had a shape that was approximately parabolic, concave between the intersections 23a. Therefore, even when used in a stacked manner, the ridgeline 23 was less susceptible to wear and damage, resulting in excellent results in scratch resistance testing.

[0178] On the other hand, in Comparative Examples 1 to 3, although a curved surface with a radius of curvature of approximately 4.2 μm was applied near the apex of ridge line 23, the maximum height difference d was 0 μm, and ridge line 23 had no concavity at all, with ridge line 23 being horizontal between intersections 23a. Consequently, scratches were caused by ridge line 23 during the scratch resistance test, resulting in poor scratch resistance.

[0179] In each of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, the ratio Wr / P was all 10% or less, and the steep shape of the top of the ridge line 23 was maintained, so that similarly good evaluation results were obtained for luminance uniformity.

[0180] As described above, in the comprehensive evaluation, Examples 1 to 3 were rated "C" and Comparative Examples 1 to 3 were rated "X".

[0181] <Examples 4 to 10 and Comparative Example 4>

[0182] In Examples 4 to 7, light diffusion sheets were produced by the same method as in Example 1 except that the line speed among the molding conditions was changed to 15 m / min to 4 m / min as shown in Table 4.

[0183] In Examples 8 to 10 and Comparative Example 4, light diffusion sheets were produced in the same manner as in Example 1 except that the compression line pressure between the two rolls in the molding conditions was changed to 180 kgf / cm to 40 kgf / cm as shown in Table 4.

[0184]

Table 4

[0185]

[0186] <Evaluation of Examples 4 to 10 and Comparative Example 4>

[0187] For the first light diffuser 43 obtained in Examples 4 to 10, the shapes, sizes, angles, etc. of the various elements measured are shown in Table 5 together with Comparative Example 4, and the measurement results of the optical properties, the results of the scratch resistance test, the evaluation results of the brightness and brightness uniformity, and the comprehensive evaluation results are shown in Table 6 together with Comparative Example 4.

[0188]

Table 5

[0189]

[0190]

Table 6

[0191]

[0192] The results shown in Tables 5 and 6 show that in the first light diffusing sheets 43 formed with inverted square pyramid-shaped recesses 22 obtained in Examples 4 to 10 and Comparative Example 4, the maximum height difference d between the straight line connecting the intersections 23a and the ridgeline 23 was greater than 1.0 μm, and the ridgeline 23 had a shape that was concave, approximately parabolic, between the intersections 23a. Therefore, even when used in overlapping positions, the ridgeline 23 was less susceptible to wear and damage, resulting in excellent results in scratch resistance testing.

[0193] In Examples 4 to 10, the ratio Wr / P was all 30% or less, and the steep shape of the top of the ridge line 23 was maintained, so that similarly good evaluation results were obtained for the luminance uniformity.

[0194] However, in Comparative Example 4, since the ratio Wr / P exceeds 30%, the steep shape of the top of the ridge line 23 cannot be maintained, resulting in poor luminance uniformity.

[0195] As described above, in the comprehensive evaluation, Examples 4 to 10 were rated "C" and Comparative Example 4 was rated "X".

[0196] <Examples 11 to 14>

[0197] In the manufacturing method of the first light diffuser 43 of Example 11, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 90.0 μm, a spacing of 180 μm, and a vertex angle of 90 degrees is used. Except for this, conditions substantially the same as those in Example 1 are used to produce a light diffuser with a thickness of 200 μm as shown in Table 7.

[0198]

Table 7

[0199]

[0200] In the manufacturing method of the first light diffuser 43 of Example 12, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 98.2 μm, a spacing of 180 μm, and a vertex angle of 85 degrees is used. Except for this, conditions substantially the same as those in Example 1 are used to produce a light diffuser with a thickness of 200 μm as shown in Table 7.

[0201] In the manufacturing method of the first light diffuser 43 of Example 13, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 107.3 μm, a spacing of 180 μm, and a vertex angle of 80 degrees is used as the roller in the shape of a regular tetrahedron among the two metal rollers. Except for this, conditions substantially the same as those in Example 1 are used to produce a light diffuser with a thickness of 200 μm as shown in Table 7.

[0202] In the manufacturing method of the first light diffuser 43 of Example 14, as the roller in the shape of a regular tetrahedron, a roller in the shape of a pyramid with a surface having a height of 117.3 μm, a spacing of 180 μm, and a vertex angle of 75 degrees is used. Except for this, conditions substantially the same as those in Example 1 are used to produce a light diffuser with a thickness of 200 μm shown in Table 7.

[0203] <Examples 15 to 17 and Comparative Example 5>

[0204] In Examples 15 to 17, the same rollers as in Example 13 were used, and as shown in Table 7, the line speed among the molding conditions was changed to 15 m / min to 11 m / min to produce light diffusing sheets having a thickness of 200 μm.

[0205] In Comparative Example 5, after a stamping original plate was produced in the same manner as in Comparative Example 1, a flat plate mold was used having a surface having a regular quadrangular pyramid, i.e., a pyramid, in the same shape as in Example 11, with the valley portion of the pyramid being trimmed into a curved surface with a curvature radius of 4.2 μm as in Comparative Example 1. In addition, under the same conditions as in Comparative Example 1, a light diffuser having a thickness of 200 μm as shown in Table 7 was produced by compression molding using a punching machine for heating, pressurizing, and cooling.

[0206] <Evaluation of Examples 11 to 17 and Comparative Example 5>

[0207] For the first light diffuser 43 obtained in Examples 11 to 17, the shapes, sizes, angles, etc. of the various elements measured are shown in Table 8 together with Comparative Example 5, and the measurement results of the optical properties, the results of the scratch resistance test, the evaluation results of the brightness and brightness uniformity, and the comprehensive evaluation results are shown in Table 9 together with Comparative Example 5.

[0208]

Table 8

[0209]

[0210]

Table 9

[0211]

[0212] The results shown in Tables 8 and 9 show that in the first light diffusing sheets 43 formed with inverted square pyramid-shaped recesses 22 obtained in Examples 11 to 17, the maximum height difference d between the straight line connecting the intersections 23a and the ridgeline 23 was greater than 2.5 μm, and the ridgeline 23 had a shape that was concave, approximately parabolic, between the intersections 23a. Therefore, even when used in overlapping applications, the ridgeline 23 was less susceptible to wear and damage, resulting in the best results among the examples in the scratch resistance test.

[0213] On the other hand, in Comparative Example 5, although a curved surface shape was imparted near the apex of ridge line 23, the maximum height difference d was 0 μm, and ridge line 23 had no concavity at all, with ridge line 23 having a horizontal shape between intersections 23a. Consequently, scratches were generated by ridge line 23 during the scratch resistance test, resulting in poor scratch resistance.

[0214] In Examples 11 to 17 and Comparative Example 5, the ratio Wr / P was all below 10%, maintaining a steeper top shape at the ridgeline 23, resulting in particularly good luminance uniformity evaluation results. In particular, in Examples 11 to 17, the maximum height difference d was below 5.0 μm, indicating no degradation in luminance uniformity due to the concave shape of the ridgeline 23 between the intersections 23 a.

[0215] As described above, in the comprehensive evaluation, Example 11 was rated "A", Examples 12 to 17 were rated "AA", which was the most excellent, and Comparative Example 5 was rated "X".

[0216] <Examples 18 to 23>

[0217] In Example 18, 1 part by mass of silicon composite powder (average particle size 2.0 μm) as a diffusing agent was pre-mixed with 99 parts by mass of the aromatic polycarbonate resin used in Example 1, and the mixture was put into an extruder for melt kneading. Except for this, the same conditions as in Example 1 were used to produce a light diffuser with a thickness of 180 μm as shown in Table 10.

[0218]

Table 10

[0219]

[0220] In Examples 19 to 23, the same method as in Example 18 was used, but the line speed in the molding conditions was changed to 15 m / min to 9 m / min as shown in Table 10, to produce light diffusing sheets having a thickness of 180 μm.

[0221] <Evaluation of Examples 18 to 23>

[0222] For the first light diffuser 43 obtained in Examples 18 to 23, the shapes, dimensions, and angles of the various elements measured are shown in Table 11, and the measurement results of optical properties, the results of the scratch resistance test, the evaluation results of brightness and brightness uniformity, and the comprehensive evaluation results are shown in Table 12.

[0223]

Table 11

[0224]

[0225]

Table 12

[0226]

[0227] The results shown in Tables 11 and 12 show that in the first light diffusing sheets 43 formed with inverted square pyramid-shaped recesses 22 obtained in Examples 18 to 23, the maximum height difference d between the straight line connecting the intersections 23a and the ridgeline 23 was greater than 1.6 μm, and the ridgeline 23 had a shape that was approximately parabolic, concave between the intersections 23a. Therefore, even when used in a stacked manner, the ridgeline 23 was less susceptible to wear and damage, resulting in excellent results in scratch resistance testing.

[0228] In Examples 18 to 23, the ratio Wr / P was within the range of 6 to 13%, and the steep shape of the top of the ridge line 23 was maintained, so that good evaluation results were obtained for the luminance uniformity.

[0229] In conclusion, Examples 18 to 23 were rated "C" in the comprehensive evaluation.

[0230] <Examples 24 to 27>

[0231] In Example 24, the aromatic polycarbonate resin used in Example 1 and the molding conditions shown in Table 13 were used, and a metal roller having a surface Figure 16 A roller having the shape shown in (A) and (B) (a regular quadrangular pyramid, i.e., a pyramid shape, with a height of 50 μm, a spacing of 100 μm, and a vertex angle of 90 degrees) was used, and a roller having a random matte surface (surface roughness Ra = 1.6 μm) was used as another roller to produce a light diffuser with a thickness of 120 μm as shown in Table 13.

[0232]

Table 13

[0233]

[0234] In Example 25, the same diffusing agent-containing aromatic polycarbonate resin and molding conditions shown in Table 13 as in Example 18 were used, and the same two metal rollers as in Example 24 were used to produce a light diffusing sheet having a thickness of 120 μm shown in Table 13.

[0235] In Example 26, the same aromatic polycarbonate resin as in Example 24 and the molding conditions shown in Table 13 were used, and as one of the two metal rollers, a roller having a surface having a height of 107.3 μm, a spacing of 180 μm, and a pyramid shape of a regular tetrahedron, i.e., a vertex angle of 80 degrees, used in Example 13 was used, and as the other roller, a roller having a surface having a random matte shape (surface roughness Ra = 2.0 μm) was used to produce a light diffuser having a thickness of 200 μm as shown in Table 13.

[0236] In Example 27, the same diffusing agent-containing aromatic polycarbonate resin and the molding conditions shown in Table 13 as in Example 25 are used, and as one of the two metal rollers, a roller having a surface having the same regular quadrangular pyramid or pyramid shape as in Examples 24 and 25 is used, and as the other metal roller, a roller having a surface having a random matte shape (surface roughness Ra = 2.0 μm) is used to produce a light diffuser with a thickness of 200 μm as shown in Table 13.

[0237] <Evaluation of Examples 24 to 27>

[0238] Table 14 shows the shapes, dimensions, and angles of the various elements of the first light diffuser 43 obtained in Examples 24 to 27. Table 15 shows the results of the optical property measurements, the scratch resistance test results, the brightness and brightness uniformity evaluation results, and the comprehensive evaluation results. Surface photographs of the samples after the scratch resistance test of Examples 24 to 27 and Comparative Example 1, specifically, the lower surface (inverted quadrangular pyramid surface) of the fixed sample and the upper surface (matte surface) of the moving sample, are shown. Figure 18 .

[0239]

Table 14

[0240]

[0241]

Table 15

[0242]

[0243] According to the results shown in Tables 14 and 15, in the first light diffuser sheets 43 having the inverted square pyramid-shaped recesses 22 obtained in Examples 24 to 27, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 is 2.7 μm or more, and the ridge line 23 has a shape that is concave in a nearly parabolic shape between the intersections 23a. Therefore, even when used in a stacked manner, wear or damage due to the ridge line 23 is unlikely to occur. Figure 18 As shown in FIG, not only the matte surface (upper surface of the moving sample) but also the inverted quadrangular pyramid surface (lower surface of the fixed sample) obtained good results in the scratch resistance test. On the other hand, in Comparative Example 1, as described above (see Table 2, etc.), the maximum height difference d is 0 μm, the ridge line 23 has no depression at all, and the ridge line 23 has a horizontal shape between the intersection points 23a. Therefore, as shown in FIG. Figure 18 As shown, on the inverted quadrangular pyramid surface (the lower surface of the fixed sample), damage due to the ridge line 23 was clearly generated in the scratch resistance test, and the scratch resistance was poor.

[0244] It should be noted that in Examples 24 and 25, since the first light diffuser 43 is relatively thin, a relatively large depression is generated at the ridgeline 23 . In Example 26, since the inverted quadrangular pyramid of the recess 22 is relatively large, a relatively large depression is generated at the ridgeline 23 .

[0245] In Examples 24 to 27, the ratio Wr / P was within the range of approximately 5 to 11%, and the steep shape of the top of the ridge line 23 was maintained, so that good evaluation results were obtained for the luminance uniformity.

[0246] As described above, in the comprehensive evaluation, Example 24 was rated "A", Examples 25 and 27 were rated "C", and Example 26 was rated the most excellent "AA".

[0247] (Other embodiments)

[0248] The above describes the embodiments of the present disclosure (including examples, the same below), but the present disclosure is not limited to the aforementioned embodiments, and various changes can be made within the scope of the present disclosure. In other words, the description of the aforementioned embodiments is essentially an example and is not intended to limit the present disclosure, its applicable objects or its uses. For example, the composition (layer structure, material, etc.) of the light diffuser is certainly not limited to the composition of the first light diffuser 43 of the aforementioned embodiment. Of course, the composition of the backlight source using the light diffuser and the liquid crystal display device including the backlight source are not limited to the composition of the backlight unit 40 and the liquid crystal display device 50 of the aforementioned embodiment.

[0249] For example, you can replace Figure 2 The backlight unit 40 of the aforementioned embodiment is a combination of two stacked first light diffusion sheets 43 and a second light diffusion sheet 44, as shown in FIG. Figure 19 As shown in the modified backlight unit 40, three first light diffusers 43 are stacked, or four or more first light diffusers 43 are stacked. It should be noted that when three or more first light diffusers 43 are stacked, from the perspective of balancing the reflection and refraction effects of the approximately inverted polygonal pyramid shape with the light diffusion effect of the diffusing agent, it is also possible to include a diffusing agent in the light diffuser 43 closest to the display screen 50a (i.e., the first prism sheet 45), while the other light diffusers 43 are substantially free of diffusing agent. This can further improve brightness uniformity.

[0250] -Explanation of symbols-

[0251] 1 TFT base

[0252] 2 CF substrate

[0253] 3 Liquid crystal layer

[0254] 5 LCD panel

[0255] 6. First polarizer

[0256] 7 Second polarizer

[0257] 21 base material layer

[0258] 22 recess

[0259] 22a Center

[0260] 23 Ridge

[0261] 23a Intersection

[0262] 23b Lowest point

[0263] 40 Backlight unit

[0264] 41 reflective sheet

[0265] 42 Small light sources

[0266] 43. First light diffuser

[0267] 43a Page 1

[0268] 43b Side 2

[0269] 44 Second light diffuser

[0270] 44a Page 1

[0271] 44b Side 2

[0272] 45 First Prism

[0273] 46 Second prism

[0274] 50 Liquid crystal display device

[0275] 50a Display screen.

Claims

1. A light diffuser having a plurality of concave portions on at least a first surface thereof, each of which is approximately inverted polygonal pyramidal or approximately inverted polygonal truncated pyramidal, characterized in that: The ridge lines that divide the plurality of recesses have a shape that is recessed between the intersection points relative to a straight line connecting the intersection points of the ridge lines. If the arrangement pitch of the plurality of concave portions is set to P, and the size of the curved portion of the top of the ridge line in the arrangement direction of the plurality of concave portions is set to Wr, then the ratio Wr / P is less than 0.3, A maximum height difference d between the straight line and the ridge line is greater than or equal to 1 μm and less than or equal to 10 μm.

2. The light diffuser according to claim 1, wherein: The maximum height difference d is greater than or equal to 1.5 μm and less than or equal to 7 μm.

3. The light diffuser according to claim 2, wherein: The maximum height difference d is greater than or equal to 2.5 μm and less than or equal to 5 μm.

4. The light diffuser according to any one of claims 1 to 3, wherein: The ratio Wr / P is less than 0.

2.

5. The light diffuser according to claim 4, wherein: The ratio Wr / P is less than 0.

1.

6. The light diffuser according to any one of claims 1 to 3, wherein: The arrangement pitch P is greater than or equal to 50 μm and less than or equal to 500 μm. An angle formed between the wall surfaces of the plurality of recesses and the sheet surface of the light diffusion sheet is greater than or equal to 40 degrees and less than or equal to 65 degrees.

7. The light diffuser according to any one of claims 1 to 3, wherein: The ridge lines are recessed into an approximately parabola shape, an approximately circular arc shape, an approximately triangular shape, or an approximately trapezoidal shape between the intersection points.

8. The light diffuser according to any one of claims 1 to 3, wherein: The plurality of recesses are formed in a shape approximately equal to an inverted quadrangular pyramid or an inverted quadrangular truncated pyramid. The ridge line extends along the first direction and the second direction, The maximum height difference d is the average value of the maximum height difference dx between the straight line and the ridge line in the first direction and the maximum height difference dy between the straight line and the ridge line in the second direction. The arrangement pitch P is an average value of the arrangement pitch Px of the plurality of concave portions in the first direction and the arrangement pitch Py of the plurality of concave portions in the second direction. The dimension Wr is an average of a dimension Wrx occupied by the curved portion of the top of the ridge line in the first direction and a dimension Wry occupied by the curved portion of the top of the ridge line in the second direction.

9. The light diffuser according to any one of claims 1 to 3, wherein: The plurality of recesses are provided only on the first surface, The second side is matte.

10. A backlight unit assembled in a liquid crystal display device to guide light emitted from a light source toward a display screen, characterized in that: The light diffusion sheet according to any one of claims 1 to 3 is included between the display screen and the light source.

11. The backlight unit according to claim 10, wherein: The reflective sheet is arranged on the opposite side of the display screen from the light diffusion sheet, and the light source is arranged on the reflective sheet.

12. The backlight unit according to claim 10, wherein: The light diffusion sheet is stacked in multiple layers and is arranged between the display screen and the light source.

13. The backlight unit according to claim 12, wherein: The light diffusion sheet is stacked in three or more layers and is arranged between the display screen and the light source.

14. The backlight unit according to claim 13, wherein: Among the three or more light diffusing sheets stacked together, the light diffusing sheet closest to the display screen contains a diffusing agent, and the other light diffusing sheets contain substantially no diffusing agent.

15. A liquid crystal display device, characterized in that: The invention comprises the backlight unit according to claim 10 and a liquid crystal display panel.

16. An information device, characterized in that: A liquid crystal display device comprising the liquid crystal display device according to claim 15.

17. A method for manufacturing a light diffuser, the light diffuser being the light diffuser according to any one of claims 1 to 3, characterized in that: The light diffusion sheet is manufactured by extrusion molding under the conditions of a line speed of 10 m / min to 30 m / min and a compression line pressure of 100 kgf / cm to 500 kgf / cm.

Images