Light Diffusing Sheet, Backlight Unit, Liquid Crystal Display Device, Information Equipment, and Method for Manufacturing Light Diffusing Sheet

Abstract

To provide a light diffusion sheet which hardly causes damage even when being stacked while improving luminance uniformity using a polycarbonate resin obtained from a biomass resource.SOLUTION: A light diffusion sheet 43 has a plurality of recesses 22 which contains a specific polycarbonate resin including a first structural unit derived from a dihydroxy compound or is formed into inverted polygonal pyramid or inverted truncated polygonal pyramid shapes, on at least a first surface 43a. Ridge lines 23 partitioning the plurality of recesses 22 have such shapes as to be recessed between intersections 23 of the ridge lines 23 with respect to straight lines connecting the intersections 23. When an array pitch of the plurality of recesses 22 is represented by P, and a dimension occupied by a curve part of tops of the ridge lines 23 in the array direction of the plurality of recesses 22 is represented by Wr, a ratio Wr / P is 0.3 or less. A maximum height difference d between the straight lines connecting the intersections 23a of the ridge lines 23, and the ridge lines 23 is 1 μm or more and 10 μm or less.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a light diffusion sheet, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing a light diffusion sheet. In particular, the present disclosure relates to a light diffusion sheet using a polycarbonate resin obtained from biomass resources and having excellent luminance uniformity and scratch resistance.

Background Art

[0002] Conventionally, in consideration of the environment, polycarbonate resins using ether group-containing diols typified by isosorbide, which is a plant-derived raw material, have been developed. Polycarbonate resins using isosorbide are known to be excellent in heat resistance, weather resistance, impact resistance, and scratch resistance, and are applied to, for example, interior and exterior parts of automobiles.

[0003] In recent years, liquid crystal display devices (hereinafter sometimes referred to as liquid crystal displays) have been widely used as display devices for various information devices such as smartphones and tablet terminals. As the backlight of a liquid crystal display, a direct-lit type in which a light source is disposed behind a liquid crystal panel or an edge-lit type in which a light source is disposed near the side surface of a liquid crystal panel is mainstream.

[0004] When a direct-lit backlight is adopted, a light diffusion member (light diffusion plate, light diffusion sheet, light diffusion film) is used to erase the image of a light source such as an LED (Light Emitting Diode) on the light emitting surface and improve the in-plane luminance uniformity.

[0005] In the direct-lit backlight disclosed in Patent Document 1, in order to improve the luminance uniformity, a light diffusion plate provided with a plurality of concave portions having an inverted pyramid shape or an inverted truncated pyramid shape is used. Patent Document 1 discloses that, in a laminated structure of a light diffusion plate and another optical film, in order to suppress wear and damage of the light diffusion plate and another optical film due to vibration during transportation, the inner surface of the concave portion of the light diffusion plate is a curved surface whose center of curvature is located on the depth direction side of the concave portion at the opening edge portion.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the direct-bottom backlight disclosed in Patent Document 1, damage to the light diffusion plate and other optical films cannot be sufficiently suppressed. Also, in liquid crystal displays and the like, products that consider the environment are required.

[0008] Therefore, an object of the present disclosure is to provide a light diffusion sheet that uses a polycarbonate resin obtained from biomass resources, improves luminance uniformity, and is less likely to be damaged even when laminated.

Means for Solving the Problems

[0009] In order to achieve the above object, the light diffusion sheet according to the present disclosure includes "a homopolymer polycarbonate resin composed of a first structural unit derived from a dihydroxy compound represented by the following formula (1)", or "the first structural unit and one or more second structural units derived from a dihydroxy compound selected from the group consisting of an aliphatic dihydroxy compound, an alicyclic dihydroxy compound, and an ether group-containing dihydroxy compound (excluding the dihydroxy compound represented by the following formula (1))".

[0010]

Chemical Formula

[0011] In the light diffusion sheet according to the present disclosure, the homopolymer polycarbonate resin includes not only "polymers that do not contain stereoisomers" but also "polymers that contain stereoisomers".

[0012] Further, the light diffusion sheet according to the present disclosure has at least a first surface with a plurality of recesses formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape. The ridge lines partitioning the plurality of recesses have a concave shape between the intersections of the ridge lines with respect to a straight line connecting the intersections of the ridge lines. When the arrangement pitch of the plurality of recesses is P and the dimension occupied by the curved portion of the top of the ridge line in the arrangement direction of the plurality of recesses is Wr, the ratio Wr / P is 0.3 or less. The maximum height difference d between the straight line and the ridge line is 1 μm or more and 10 μm or less.

[0013] According to the light diffusion sheet of the present disclosure, since at least the first surface has a plurality of recesses formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape, the luminance uniformity can be improved. In addition, where the ridge lines (the opening edges of the recesses) partitioning the recesses cause wear and damage, the ridge lines have a concave shape between the intersections of the ridge lines. Therefore, even when used in overlay with other optical sheets or other light diffusion sheets, wear and damage are less likely to occur. Further, the dimension Wr occupied by the curved portion of the top of the ridge line in the arrangement direction of the recesses is suppressed to 30% or less of the arrangement pitch P of the recesses. For this reason, since the top of the ridge line can maintain a steep shape, the luminance uniformity is less likely to decrease even when the ridge line is recessed between the intersections of the ridge lines. In addition, since the maximum height difference d between the straight line connecting the intersections of the ridge lines and the ridge line is 1 μm or more, the scratch resistance is improved, and since the maximum height difference d is 10 μm or less, a decrease in luminance uniformity can be suppressed. Furthermore, by using a polycarbonate resin obtained from biomass resources, a product considering the environment can be provided.

[0014] In the light diffusion sheet according to the present disclosure, considering that it is difficult to form geometrically precise inverted pyramids or truncated inverted pyramids by ordinary shape transfer techniques, the notations "substantially inverted pyramid" or "substantially truncated inverted pyramid" are used, but it goes without saying that these notations include shapes that can be regarded as true or substantially inverted pyramids or truncated inverted pyramids.

[0015] Also, in the light diffusion sheet according to the present disclosure, it is preferable that the ridge line is recessed between all intersections of the ridge lines, but it is not essential to have a shape in which the ridge line is recessed between all intersections. In other words, it is not necessary to have a shape in which the ridge line is not recessed between some intersections.

[0016] Also, in the present disclosure, the "light diffusion sheet" shall include a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film".

[0017] Also, in the present disclosure, the "optical sheet" means a sheet having various optical functions such as diffusion, light collection, refraction, and reflection, and the "light diffusion sheet" is one of the "optical sheets".

[0018] In the light diffusion sheet according to the present disclosure, when the maximum height difference d is 1.5 μm or more and 7 μm or less, both the scratch resistance and the luminance uniformity can be further improved. In this case, when the maximum height difference d is 2.5 μm or more and 5 μm or less, both the scratch resistance and the luminance uniformity can be further improved.

[0019] In the light diffusion sheet according to the present disclosure, when the ratio Wr / P is 0.2 or less, the luminance uniformity can be further improved. In this case, when the ratio Wr / P is 0.1 or less, the luminance uniformity can be further improved.

[0020] In the light diffusion sheet according to the present disclosure, when the array pitch P is 50 μm or more and 500 μm or less, and the angle formed by the wall surfaces of the plurality of recesses (that is, the inclined surfaces of the substantially inverted pyramid or substantially inverted truncated pyramid) and the sheet surface of the light diffusion sheet is 40 degrees or more and 65 degrees or less, the luminance uniformity can be improved.

[0021] In the light diffusion sheet according to the present disclosure, when the ridge line is recessed in a substantially parabolic shape, substantially arc shape, substantially triangular shape, or substantially trapezoidal shape between the intersections, the scratch resistance can be improved.

[0022] In the light diffusion sheet according to the present disclosure, the plurality of recesses may be formed in a substantially inverted quadrangular pyramid or substantially inverted truncated quadrangular pyramid. In this case, the ridge line may extend in the first direction and the second direction. Further, the maximum height difference d may be an 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. Further, the array pitch P may be an average value of the array pitch Px of the plurality of recesses in the first direction and the array pitch Py of the plurality of recesses in the second direction. Further, the dimension Wr may be an 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. By doing so, it becomes easy to manufacture a light diffusion sheet excellent in scratch resistance and luminance uniformity.

[0023] In the light diffusion sheet according to the present disclosure, when the plurality of recesses are provided only on the first surface and the second surface is a matte surface, the luminance uniformity can be further improved while suppressing wear and damage on the second surface.

[0024] The backlight unit according to the present disclosure is a backlight unit incorporated in a liquid crystal display device and guiding the light emitted from a light source toward a display screen, and includes the light diffusion sheet according to the present disclosure described above between the display screen and the light source.

[0025] According to the backlight unit related to the present disclosure, since the light diffusion sheet related to the present disclosure described above is provided, the luminance uniformity can be improved, and damage can be suppressed even when the light diffusion sheet and other optical sheets are laminated.

[0026] In the backlight unit related to the present disclosure, when the light source is disposed on the reflection sheet provided on the opposite side of the display screen as viewed from the light diffusion sheet, the luminance uniformity is further improved.

[0027] In the backlight unit related to the present disclosure, a plurality of (for example, three or more) light diffusion sheets may be laminated and disposed between the display screen and the light source. By doing so, the luminance uniformity is further improved. When three or more light diffusion sheets are laminated, if the light diffusion sheet closest to the display screen contains a diffusing agent and the other light diffusion sheets do not substantially contain a diffusing agent, the luminance uniformity is further improved.

[0028] The liquid crystal display device related to the present disclosure includes the backlight unit related to the present disclosure described above and a liquid crystal display panel.

[0029] According to the liquid crystal display device related to the present disclosure, since the backlight unit related to the present disclosure described above is provided, the luminance uniformity can be improved, and damage can be suppressed even when the light diffusion sheet and other optical sheets are laminated.

[0030] The information device related to the present disclosure includes the liquid crystal display device related to the present disclosure described above.

[0031] According to the information device related to the present disclosure, since the liquid crystal display device related to the present disclosure described above is provided, the luminance uniformity can be improved, and damage can be suppressed even when the light diffusion sheet and other optical sheets are laminated.

[0032] The manufacturing method of the light diffusion sheet according to the present disclosure is a method for manufacturing the light diffusion sheet according to the above-mentioned present disclosure, wherein the light diffusion sheet is extrusion-molded at a line speed of 10 m / min or more and 30 m / min or less and a compression line pressure of 100 kgf / cm or more and 500 kgf / cm or less.

[0033] According to the manufacturing method of the light diffusion sheet according to the present disclosure, the dimension Wr occupied by the curved portion of the ridge line top in the arrangement direction of the recesses can be made 30% or less of the arrangement pitch P of the recesses. Therefore, a light diffusion sheet with a steep shape at the ridge line top and excellent luminance uniformity can be manufactured.

[0034] Further, according to the manufacturing method of the light diffusion sheet according to the present disclosure, the maximum height difference d between the straight line connecting the intersections of the ridge lines and the ridge line can be made 1 μm or more and 10 μm or less. That is, a light diffusion sheet is obtained in which the ridge line is recessed between the intersections of the ridge lines and the intersection portion of the ridge lines is raised. Therefore, even when the light diffusion sheet and another optical sheet are laminated, the ridge line is less likely to contact the other optical sheet between the intersections of the ridge lines, so wear and damage are less likely to occur. At the intersections of the ridge lines, since it is in point contact with the other optical sheet, slipping occurs and wear and damage are less likely to occur. Therefore, a light diffusion sheet with excellent scratch resistance can be manufactured.

[0035] Further, according to the manufacturing method of the light diffusion sheet according to the present disclosure, since extrusion molding is used, the light diffusion sheet according to the above-mentioned present disclosure can be manufactured at low cost.

[0036] Further, according to the manufacturing method of the light diffusion sheet according to the present disclosure, since a polycarbonate resin obtained from biomass resources is used, a product considering the environment can be provided.

Effects of the Invention

[0037] According to the present disclosure, by using a polycarbonate resin obtained from biomass resources, it is possible to provide a light diffusion sheet that is less likely to be damaged even when laminated with other optical sheets while improving luminance uniformity.

Brief Description of the Drawings

[0038]

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Mode for Carrying Out the Invention

[0039] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments and can be arbitrarily changed within the scope of the technical idea of the present disclosure.

[0040] <Liquid Crystal Display Device> As shown in FIG. 1, the liquid crystal display device 50 of the present 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 back side of the liquid crystal display panel 5 via the first polarizing plate 6. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 provided to face 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 shape for enclosing the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0041] In principle, the shape of the display screen 50a of the liquid crystal display device 50 as viewed from the front (above in FIG. 1) is rectangular or square, but it is not limited thereto, and may be a shape in which the corners of the rectangle are rounded, an elliptical shape, a circular shape, a trapezoidal shape, or any arbitrary shape such as an instrument panel (instrument panel) of an automobile.

[0042] In the liquid crystal display device 50, in each sub-pixel corresponding to each pixel electrode, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3, and the light incident from the backlight unit 40 through the first polarizing plate 6 is adjusted in its transmittance and emitted through the second polarizing plate 7, whereby an image is displayed.

[0043] The liquid crystal display device 50 of the present embodiment is used as a display device incorporated in various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals, portable game machines, copy machines, ticket vending machines, automated teller machines, etc.).

[0044] The TFT substrate 1 includes, for example, a plurality of TFTs provided in a matrix on a glass substrate, an interlayer insulating film provided so as to cover each TFT, a plurality of pixel electrodes provided in a matrix on the interlayer insulating film and connected to the plurality of TFTs respectively, and an alignment film provided so as to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix provided in a grid pattern on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between the grids of the black matrix respectively, a common electrode provided so as to cover the black matrix and the color filter, and an alignment film provided so as to cover the common electrode. The liquid crystal layer 3 is composed of a nematic liquid crystal material containing liquid crystal molecules having electro-optical characteristics. The first polarizing plate 6 and the second polarizing plate 7 include, for example, a polarizer layer having a polarization axis in one direction, and a pair of protective layers provided so as to sandwich the polarizer layer.

[0045] <Backlight Unit> As shown in FIG. 2, the backlight unit 40 of this embodiment includes a reflection sheet 41, a plurality of small light sources 42 two-dimensionally arranged on the reflection sheet 41, a laminate of a first light diffusion sheet 43 provided above the plurality of small light sources 42, a second light diffusion sheet 44 provided above the laminate of the first light diffusion sheet 43, and a first prism sheet 45 and a second prism sheet 46 sequentially provided above the second light diffusion sheet 44. In this example, the laminate of the first light diffusion sheets 43 is formed by laminating two first light diffusion sheets 43 having the same structure. Although not shown, a polarizing sheet may be provided above the second prism sheet 46.

[0046] The reflection sheet 41 is composed of, for example, a white polyethylene terephthalate resin film, a silver vapor deposition film, or the like.

[0047] The type of the small light source 42 is not particularly limited, and for example, an LED element, a laser element, or the like may be used, and an LED element may be used from the viewpoints of cost, productivity, etc. In order to adjust the light emission angle characteristics of the LED element serving as the small light source 42, a lens may be attached to the LED element. For example, as shown in FIG. 3, a plurality of small light sources 42 each composed of an LED element with a side length of several millimeters may be arranged on the reflection sheet 41 in a two-dimensional array with a certain interval. The small light source 42 may have a rectangular shape in plan view, and in that case, the length of one side may be 10 μm or more (preferably 50 μm or more) and 20 mm or less (preferably 10 mm or less, more preferably 5 mm or less).

[0048] Also, the number of arrangements of the small light sources 42 is not particularly limited, but when a plurality of small light sources 42 are arranged dispersedly, it is preferable to arrange them regularly on the reflection sheet 41. Arranging regularly means arranging with a certain regularity, and for example, the case where the small light sources 42 are arranged at equal intervals corresponds to this. When the small light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent small light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0049] Each first light diffusing sheet 43 has a base material layer 21. A plurality of recesses 22 are provided on the first surface 43a of the first light diffusing sheet 43 (the surface facing the small light source 42). The plurality of recesses 22 are formed in a substantially inverted polygonal pyramid or a substantially inverted truncated polygonal pyramid shape. In this example, the plurality of recesses 22 are formed in a substantially inverted regular quadrangular pyramid shape. Adjacent recesses 22 are partitioned by ridge lines 23. The arrangement pitch of the recesses 22 is, for example, about 50 μm or more and about 500 μm or less. The angle formed by the wall surface of the recess 22 (the inclined surface of the substantially inverted polygonal pyramid or the substantially inverted truncated polygonal pyramid) and the sheet surface of the first light diffusing sheet 43 (the virtual mirror surface without the recesses 22) is, for example, 40 degrees or more and 65 degrees or less. In other words, the apex angle of the recess 22 is, for example, 50 degrees or more and 100 degrees or less. The second surface 43b of the first light diffusing sheet 43 may be a mirror surface, but in order to improve diffusibility, it is preferably a matte surface. FIG. 4 illustrates a state in which the recesses 22 formed in a substantially inverted regular quadrangular pyramid shape are arranged in a 5×5 matrix on the first surface 43a of the first light diffusing sheet 43.

[0050] The base material layer 21 is preferably composed of polycarbonate obtained from biomass resources as a base material (matrix resin) and does not contain a diffusing agent, but may contain, for example, about 0.1 to 4% by mass of a diffusing agent with respect to 100% by mass of the base material. Details of the matrix resin of the first light diffusing sheet 43 will be described later. Known materials can be appropriately used as the diffusing agent. In this example, the first light diffusing sheet 43 has a single-layer structure of the base material layer 21, but instead, it may have a structure of two or more layers including a layer in which the recesses 22 are formed.

[0051] The second light diffusing sheet 44 has a matte surface on the first surface 44a (the surface facing the first prism sheet 45), and may have a mirror surface or recesses formed in a substantially inverted regular quadrangular pyramid shape on the second surface 44b. The second light diffusing sheet 44 is, for example, composed of polycarbonate as a base material (matrix resin), preferably contains a diffusing agent, and may contain, for example, about 0.5 to 4% by mass of a diffusing agent with respect to 100% by mass of the base material. The second light diffusing sheet 44 is, for example, composed of mixing 1 part by mass of silicone composite powder (average particle diameter 2.0 μm) as a diffusing agent with respect to 99 parts by mass of an aromatic polycarbonate resin.

[0052] The first prism sheet 45 and the second prism sheet 46 are, for example, films in which a plurality of groove stripes with an isosceles triangle cross-section are formed adjacent to each other, and the apex angle of the prism sandwiched between a pair of adjacent groove stripes is formed to be about 90°. Here, each groove stripe formed on the first prism sheet 45 and each groove stripe formed on the second prism sheet 46 are arranged to be orthogonal to each other. The first prism sheet 45 and the second prism sheet 46 may be integrally formed. As the first prism sheet 45 and the second prism sheet 46, for example, a PET (polyethylene terephthalate) film with a prism shape formed using a UV-curable acrylic resin may be used.

[0053] Although illustration is omitted, when a polarizing sheet is provided on the upper side of the second prism sheet 46, as the polarizing sheet, for example, the DBEF series manufactured by 3M may be used. The polarizing sheet improves the luminance of the display screen 50a by preventing the light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50.

[0054] <Detailed configuration of the light diffusion sheet> In the example shown in FIG. 2, a plurality of recesses 22 are formed on the first surface 43a (the surface facing the small light source 42) of the first light diffusion sheet 43. Instead of this, or in addition to this, a plurality of other recesses similar to the recesses 22 may be formed on the second surface 43b of the first light diffusion sheet 43.

[0055] The plurality of recesses 22 may be formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape. The plurality of recesses 22 may be regularly two-dimensionally arranged. As the "inverted pyramid (truncated pyramid)", a triangular pyramid (truncated pyramid), a quadrangular pyramid (truncated pyramid), or a hexagonal pyramid (truncated pyramid) that can be two-dimensionally arranged without gaps is preferable. In the manufacturing process such as extrusion molding or injection molding when providing the recesses 22, a mold (metal roll) is used. Considering the accuracy of the cutting operation on the surface of this mold (metal roll), an inverted quadrangular pyramid (truncated pyramid) may be selected as the "inverted pyramid (truncated pyramid)".

[0056] In consideration of the fact that it is difficult to form geometrically precise inverted pyramids or frustums of inverted pyramids by ordinary shape transfer techniques, the notations "substantially inverted pyramid" or "substantially frustum of inverted pyramid" are used, but it goes without saying that these notations include shapes that can be regarded as true or substantially inverted pyramids or frustums of inverted pyramids. Also, "substantially" means that approximation is possible. For example, "substantially quadrangular pyramid" refers to a shape that can approximate a quadrangular pyramid. Also, shapes deformed from "inverted pyramid" or "frustum of inverted pyramid" within the range of inevitable shape variations due to processing accuracy in industrial production are also included in "substantially inverted pyramid" or "substantially frustum of inverted pyramid".

[0057] When a plurality of recesses 22 are regularly two-dimensionally arranged, the plurality of recesses 22 may be provided without gaps over the entire surface of the first light diffusing sheet 43, or may be provided at a constant interval (pitch).

[0058] The first light diffusion sheet 43 may be composed of a base material layer 21 that does not contain a diffusing agent, for example, a base material layer 21 made of clear polycarbonate. When the diffusing agent is contained in the base material layer 21, the material of the diffusing agent is not particularly limited. As inorganic particles, for example, silica, titanium oxide, aluminum hydroxide, barium sulfate, etc. may be used, and as organic particles, for example, acrylic, acrylonitrile, silicone, polystyrene, polyamide, etc. may be used. From the viewpoint of the light diffusion effect, the particle size of the diffusing agent may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less). The first light diffusion sheet 43 preferably does not contain a diffusing agent from the viewpoints of the effects of reflection and refraction by a substantially inverted pyramid shape and the light diffusion effect by the diffusing agent. However, assuming that the material (matrix) constituting the base material layer 21 is 100% by mass, the content of the diffusing agent may be, for example, 0.1% by mass or more (preferably 0.3% by mass or more) and 10% by mass or less (preferably 8% by mass or less). The difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 may be 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and most preferably 0.15 or more. When the difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 is less than 0.01, the diffusion effect by the diffusing agent becomes insufficient.

[0059] The thickness of the first light diffusion sheet 43 is not particularly limited, but may be, for example, 3 mm or less (preferably 2 mm or less, more preferably 1.5 mm or less, still more preferably 1 mm or less) and 0.1 mm or more. When the thickness of the first light diffusion sheet 43 exceeds 3 mm, it becomes difficult to achieve the thinning of the liquid crystal display. On the other hand, when the thickness of the first light diffusion sheet 43 is less than 0.1 mm, it becomes difficult to exhibit the effect of improving the luminance uniformity.

[0060] When the first light diffusion sheet 43 has a multilayer structure (for example, a base material layer of the first layer and a recess formation layer of the second layer), the thickness of the recess formation layer is greater than the maximum depth of the recess 22. For example, in the case of a layer provided with a recess having a depth of 20 μm, the thickness is made greater than 20 μm. The first light diffusion sheet 43 may be configured with a structure of three or more layers including a base material layer and a recess formation layer. Alternatively, the base material layer and the recess formation layer may be configured as independent sheets, and the two may be laminated or separately arranged.

[0061] <Matrix resin of the light diffusion sheet> As the matrix resin of the first light diffusion sheet 43, for example, a homopolymer polycarbonate resin composed of a first structural unit derived from a dihydroxy compound represented by the following formula (1) may be used.

[0062]

Chemical formula

[0063] Examples of the dihydroxy compound represented by the above formula (1) include isosorbide, isomannide, and isoidide, which are in a stereoisomeric relationship with each other and are represented by the following formula (2), formula (3), and formula (4), respectively. These may be used alone or in combination of two or more. That is, the homopolymer polycarbonate resin includes not only "polymers that do not contain stereoisomers" but also "polymers that contain stereoisomers".

[0064]

Chemical formula

[0065]

Chemical formula

[0066]

Chemical formula

[0067] Isosorbide is abundantly present as a plant-derived resource and is obtained by dehydrative condensation of sorbitol produced from various starches that are easily available, so it is easy to obtain and manufacture. In addition, the polycarbonate resin obtained by using isosorbide as the main raw material is excellent in moldability, heat resistance, impact resistance, surface hardness, and carbon neutrality, so it is suitable as the matrix resin material for the first light diffusing sheet 43.

[0068] Further, as the matrix resin of the first light diffusing sheet 43, a copolymer polycarbonate resin composed of a first structural unit derived from the dihydroxy compound represented by the above formula (1) and a second structural unit derived from one or more dihydroxy compounds selected from the group consisting of aliphatic dihydroxy compounds, alicyclic dihydroxy compounds, and ether group-containing dihydroxy compounds (excluding the dihydroxy compound represented by the above formula (1)) (hereinafter, may also be referred to as "other dihydroxy compounds") may be used. In terms of impact resistance, the copolymer polycarbonate resin containing the second structural unit is excellent.

[0069] The aliphatic dihydroxy compound may be a linear aliphatic dihydroxy compound or a branched-chain aliphatic dihydroxy compound, and for example, ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-heptanediol, 1,6-hexanediol, 1,10-decanediol, etc. may be used.

[0070] The alicyclic dihydroxy compound may be, for example, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, pentacyclopentadecanedimethanol, 2,6-decalindimethanol, 1,5-decalindimethanol, 2,3-decalindimethanol, 2,3-norbornanedimethanol, 2,5-norbornanedimethanol, 1,3-adamantanediethanol, etc.

[0071] The ether group-containing dihydroxy compound may be, for example, diethylene glycol, triethylene glycol, polyethylene glycol (molecular weight 150 to 2000), poly-1,3-propylene glycol, polytetramethylene glycol, or the like.

[0072] From the viewpoint of the heat resistance of the copolymer polycarbonate resin, as the "other dihydroxy compound", an alicyclic dihydroxy compound is preferable, and among the alicyclic dihydroxy compounds, cyclohexanedimethanol is preferable from the viewpoints of both heat resistance and impact resistance.

[0073] The content ratio of the second structural unit derived from the "other dihydroxy compound" in the copolymer polycarbonate resin is preferably 5 mol% or more, more preferably 20 mol% or more, particularly preferably 30 mol% or more, while preferably 50 mol% or less, more preferably 45 mol% or less, in the structural units derived from all the dihydroxy compounds in the polycarbonate resin. If the second structural unit derived from the "other dihydroxy compound" in the copolymer polycarbonate resin is too small, the impact resistance may be insufficient, and if it is too large, the heat resistance may be insufficient.

[0074] The polycarbonate resin serving as the matrix resin of the first light diffusion sheet 43 can be produced by a generally used method for producing a polycarbonate resin. The production method may be, for example, any of a solution polymerization method using phosgene and a melt polymerization method in which a carbonic acid diester and a dihydroxy compound are reacted, but a melt polymerization method in which the dihydroxy compound represented by the above formula (1) is reacted with a carbonic acid diester having lower toxicity to the environment in the presence of a polymerization catalyst is preferable.

[0075] The polycarbonate resin that serves as the matrix resin of the first light diffusion sheet 43 can also be produced by subjecting a dihydroxy compound represented by the above formula (1) and a carbonic acid diester such as diphenyl carbonate to a transesterification reaction. More specifically, a polycarbonate resin can be obtained by performing a transesterification reaction and removing by-products such as monohydroxy compounds out of the system. In this case, usually, melt polymerization is carried out by a transesterification reaction in the presence of a transesterification reaction catalyst.

[0076] <Method for manufacturing a light diffusion sheet> Hereinafter, the method for manufacturing the first light diffusion sheet 43 will be described. The method for manufacturing the first light diffusion sheet 43 is not particularly limited, and for example, an extrusion molding method, an injection molding method, or the like may be used. When extruding the first light diffusion sheet 43, for example, the line speed may be set to 10 m / min or more and 30 m / min or less, and the compression line pressure may be set to 100 kgf / cm or more and 500 kgf / cm or less.

[0077] The procedure for manufacturing a single-layer light diffusion sheet having an uneven shape on the surface using the extrusion molding method is as follows. First, pellet-shaped plastic particles added with a diffusing agent (optionally, pellet-shaped plastic particles not added with a diffusing agent may be mixed) are put into a single-screw extruder and melted and kneaded while heating. When manufacturing a light diffusion sheet not containing a diffusing agent, only pellet-shaped plastic particles not added with a diffusing agent are used. Then, the molten resin extruded by a T-die is sandwiched between two metal rolls and cooled, and then conveyed using guide rolls and cut into single-sheet flat plates by a sheet cutter to produce a diffusion sheet. Here, by sandwiching the molten resin using a metal roll having a shape with the desired uneven shape inverted on the surface, the inverted shape on the roll surface is transferred to the resin, so that the desired uneven shape can be imparted to the surface of the diffusion sheet. Also, since the shape transferred to the resin does not necessarily have 100% of the shape on the roll surface transferred, the shape of the roll surface may be designed by calculating backward from the transfer degree.

[0078] When manufacturing a light diffusing sheet with a two-layer structure having a concavo-convex shape on its surface using an extrusion molding method, for example, after putting pellet-shaped plastic particles necessary for forming each layer into each of two single-screw extruders, the same procedure as described above is carried out for each layer, and the produced sheets may be laminated.

[0079] Alternatively, a light diffusing sheet with a two-layer structure having a concavo-convex shape on its surface may be produced as follows. First, pellet-shaped plastic particles necessary for forming each layer are put into each of two single-screw extruders and melted and kneaded while being heated. Then, the molten resin for each layer is put into a single T-die, laminated in the T-die, and the laminated molten resin extruded by the T-die is sandwiched between two metal rolls and cooled. Then, the laminated molten resin is conveyed using guide rolls and cut into single-sheet flat plates by a sheet cutter machine, whereby a diffusing sheet with a two-layer structure having a concavo-convex shape on its surface may be produced.

[0080] Also, a light diffusing sheet may be manufactured as follows by shape transfer using UV (ultraviolet rays). First, an uncured ultraviolet curable resin is filled into a roll having an inverted shape of the concavo-convex shape to be transferred, and a base material is pressed against the resin. Next, while the roll filled with the ultraviolet curable resin and the base material are integrated, ultraviolet rays are irradiated to cure the resin. Next, the sheet having the concavo-convex shape shape-transferred by the resin is peeled off from the roll. Finally, the sheet is irradiated with ultraviolet rays again to completely cure the resin, and a diffusing sheet having a concavo-convex shape on its surface is produced.

[0081] <Features of the light diffusing sheet> Hereinafter, the features of the first light diffusing sheet 43 of the present embodiment will be described in detail with reference to FIGS. 5 to 10.

[0082] As shown in FIG. 5, a plurality of concave portions 22 formed, for example, in a substantially inverted regular square pyramid shape are provided on the first surface 43a of the first light diffusion sheet 43. The plurality of concave portions 22 may be formed in a substantially inverted regular square pyramid frustum shape. The center 22a of the concave portion 22 is the deepest part of the concave portion 22. The plurality of concave portions 22 are arranged along the X direction (first direction) and the Y direction (second direction) that are orthogonal to each other. Adjacent concave portions 22 are partitioned by ridge lines 23. The ridge lines 23 extend along the X direction and the Y direction.

[0083] As one of the features of the first light diffusion sheet 43, the ridge line 23 has a shape that is recessed between the intersection points 23a of the ridge line 23 with respect to the straight lines Lx and Ly connecting the intersection points 23a of the ridge line 23. Here, the maximum height difference d between the straight lines Lx and Ly connecting the intersection points 23a and the ridge line 23 needs to be 1 μm or more and 10 μm or less, more preferably 1.5 μm or more and 7 μm or less, and even more preferably 2.5 μm or more and 5 μm or less.

[0084] In addition, in the first light diffusion sheet 43, it is preferable that the ridge line has a recessed shape between all the intersection points 23a of the ridge line, but it is not essential that the ridge line 23 has a recessed shape between all the intersection points 23a. In other words, the ridge line 23 may not have a recessed shape between some of the intersection points 23a.

[0085] FIG. 6 shows an example of the shape of the ridge line 23 extending in the X direction along the Ax - Bx line in FIG. 5 when viewed from a direction parallel to the sheet surface and perpendicular to the X direction, and FIG. 7 shows an example of the shape of the ridge line 23 extending in the Y direction along the Ay - By line in FIG. 5 when viewed from a direction parallel to the sheet surface and perpendicular to the Y direction. As shown in FIG. 6, with respect to the straight line Lx connecting the intersections 23a of the ridge line 23 in the X direction, the ridge line 23 has a concave shape between the intersections 23a. Taking the arrangement pitch Px in the X direction of the recess 22, the ridge line 23 extending in the X direction has, for example, the lowest point 23b at a position of Px / 2 (half pitch) from the intersection 23a, and the distance (maximum height difference) from the straight line Lx to the lowest point 23b is dx. Also, as shown in FIG. 7, with respect to the straight line Ly connecting the intersections 23a of the ridge line 23 in the Y direction, the ridge line 23 has a concave shape between the intersections 23a. Taking the arrangement pitch Py in the Y direction of the recess 22, the ridge line 23 extending in the Y direction has, for example, the lowest point 23b at a position of Py / 2 (half pitch) from the intersection 23a, and the distance (maximum height difference) from the straight line Ly to the lowest point 23b is dy.

[0086] In addition, when the recess 22 is formed in an inverted regular square pyramid shape, the arrangement pitch Px in the X direction of the recess 22 is equal to the interval (horizontal distance) between the intersections 23a in the X direction, and the arrangement pitch Py in the Y direction of the recess 22 is equal to the interval (horizontal distance) between the intersections 23a in the Y direction.

[0087] Also, taking the average value of the maximum height difference dx in the X direction and the maximum height difference dy in the Y direction as the maximum height difference d, it is necessary to set the maximum height difference d to be 1 μm or more and 10 μm or less, preferably 1.5 μm or more and 7 μm or less, and more preferably 2.5 μm or more and 5 μm or less.

[0088] Also, the concave shape of the ridge line 23 between the intersections 23a is not particularly limited. For example, as shown in FIG. 8, with respect to the straight line L connecting the intersections 23a, the ridge line 23 may be concave in a substantially arc shape (FIG. 8(A)), a substantially parabolic shape (FIG. 8(B)), a substantially triangular shape (FIG. 8(C)), or a substantially trapezoidal shape (FIG. 8(D)) between the intersections 23a.

[0089] As another feature of the first light diffusion sheet 43, when the arrangement pitch of the recesses 22 is P and the dimension occupied by the curved portion at the top of the ridge line 23 in the arrangement direction of the recesses 22 is Wr, the ratio Wr / P needs to be 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

[0090] FIG. 9 shows an example of the cross-sectional configuration of the first light diffusion sheet 43 along the Cx-Dx line in FIG. 5, and FIG. 10 shows an example of the cross-sectional configuration of the first light diffusion sheet 43 along the Cy-Dy line in FIG. 5. Specifically, FIG. 9 shows the cross-sectional configuration when the first light diffusion sheet 43 is cut by a plane passing through the centers 22a of the recesses 22 adjacent to each other in the X direction and the midpoints between the intersection points 23a on the ridge line 23 located between the recesses 22 and perpendicular to the sheet surface. FIG. 10 shows the cross-sectional configuration when the first light diffusion sheet 43 is cut by a plane passing through the centers 22a of the recesses 22 adjacent to each other in the Y direction and the midpoints between the intersection points 23a on the ridge line 23 located between the recesses 22 and perpendicular to the sheet surface.

[0091] In the cross-sectional configuration shown in FIG. 9, the interval (horizontal distance) between the centers 22a of the recesses 22 adjacent to each other 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 inclined surfaces of the inverted square pyramids) of the recesses 22 adjacent to each other across the ridge line 23 in the X direction are Wsx1 and Wsx2. The angle formed between the wall surface (the inclined surface of the inverted square pyramid) of the recess 22 and the sheet surface in the X direction is θx. The height from the center 22a of the recess 22 to the apex (the midpoint between the intersection points 23a) of the ridge line 23 (the ridge line 23 extending in the Y direction) is Hx.

[0092] In the cross-sectional configuration shown in FIG. 10, the distance (horizontal distance) between the centers 22a of the 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 ridge line 23 in the Y direction is Wry. The dimensions occupied by the straight portions of the respective wall surfaces (the inclined surfaces of the inverted square pyramids) of the adjacent recesses 22 sandwiching the ridge line 23 in the Y direction are Wsy1 and Wsy2. The angle formed between the wall surface (the inclined surface of the inverted square pyramid) of the recess 22 and the sheet surface in the Y direction is θy. The height from the center 22a of the recess 22 to the apex (the midpoint between the intersection points 23a) of the ridge line 23 (the ridge line 23 extending in the X direction) is Hy.

[0093] In addition, when the recess 22 is formed as an inverted square pyramid, it is necessary to set the ratio Wr / P, where P is the average value of the arrangement pitch Px and the arrangement pitch Py, and Wr is the average value of the dimension Wrx and the dimension Wry, to 0.3 or less, preferably 0.2 or less, and more preferably 0.1 or less.

[0094] FIG. 11 shows an example of the results of measuring the shape and dimensions of the X-direction ridge line shown in FIG. 6 using a laser microscope. FIG. 12 shows an example of the results of measuring the shape and dimensions of the Y-direction ridge line shown in FIG. 7 using a laser microscope. FIG. 13 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 9 using a laser microscope. FIG. 14 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 10 using a laser microscope.

[0095] In addition, in FIGS. 11 and 12, in the measurement of the maximum values (maximum height differences) dx and dy of the distances between the straight lines Lx and Ly connecting the intersection points 23a of the ridge line 23 and the ridge line 23, the maximum values of the lengths of the perpendiculars drawn perpendicularly from the points on the ridge line 23 to the straight lines Lx and Ly were taken as dx and dy.

[0096] Also, in the measurement of the arrangement pitches Px and Py, the "horizontal distances between the intersection points 23a" in the X direction and the Y direction were obtained as Px and Py, respectively. By using this method of measuring the "horizontal distances between the intersection points 23a", the arrangement pitches Px and Py can be obtained easily and accurately.

[0097] <Effects of the Embodiment> As described above, the first light diffusion sheet 43 of the present embodiment includes "a homopolymer polycarbonate resin composed of a first structural unit derived from the dihydroxy compound represented by the above formula (1)", or "the first structural unit and an aliphatic dihydroxy compound, an alicyclic dihydroxy compound, and an ether group-containing dihydroxy compound (excluding the dihydroxy compound represented by the above formula (1)). A copolymer polycarbonate resin composed of one or more other structural units derived from dihydroxy compounds selected from the group consisting of".

[0098] Further, the first light diffusion sheet 43 of the present embodiment has at least on the first surface 43a a plurality of recesses 22 formed in a substantially inverted pyramid or a substantially inverted pyramid frustum shape. The ridge lines 23 partitioning the plurality of recesses 22 have a concave shape between the intersections 23a of the ridge lines 23 with respect to the straight line connecting the intersections 23a of the ridge lines 23. When the arrangement pitch of the plurality of recesses 22 is P and the dimension occupied by the curved portion of the top of the ridge line 23 in the arrangement direction of the plurality of recesses 22 is Wr, the ratio Wr / P is 0.3 or less. The maximum height difference d between the ridge line 23 and the straight line connecting the intersections 23a of the ridge lines 23 is 1 μm or more and 10 μm or less.

[0099] According to the first light diffusing sheet 43 of the present embodiment, since at least the first surface 43a has a plurality of concave portions 22 formed in a substantially inverted pyramid or substantially inverted truncated pyramid shape, the luminance uniformity can be improved. Further, where the ridge line 23 (the opening edge of the concave portion 22) partitioning the concave portion 22 causes wear and damage, the ridge line 23 has a shape that is recessed between the intersection points 23a of the ridge line 23. For this reason, even when used in overlap with other optical sheets or other light diffusing sheets, wear and damage are less likely to occur. Also, the dimension Wr occupied by the curved portion of the top of the ridge line 23 in the arrangement direction of the concave portions 22 is suppressed to 30% or less of the arrangement pitch P of the concave portions. For this reason, since the top of the ridge line 23 can maintain a steep shape, the luminance uniformity is less likely to decrease even when the ridge line 23 is recessed between the intersection points 23a. Further, since the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 is 1 μm or more, the scratch resistance is improved, and since the maximum height difference d is 10 μm or less, a decrease in luminance uniformity can be suppressed. Furthermore, by using a polycarbonate resin obtained from biomass resources, a product considerate of the environment can be provided.

[0100] In the first light diffusing sheet 43 of the present embodiment, when the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 is 1.5 μm or more and 7 μm or less, both the scratch resistance and the luminance uniformity can be further improved. In this case, when the maximum height difference d is 2.5 μm or more and 5 μm or less, both the scratch resistance and the luminance uniformity can be further improved.

[0101] In the first light diffusing sheet 43 of the present embodiment, when the arrangement pitch of the plurality of concave portions 22 is P and the dimension occupied by the curved portion of the top of the ridge line 23 in the arrangement direction of the plurality of concave portions 22 is Wr, when the ratio Wr / P is 0.2 or less, the luminance uniformity can be further improved. In this case, when the ratio Wr / P is 0.1 or less, the luminance uniformity can be further improved.

[0102] In the first light diffusion sheet 43 of the present embodiment, when the arrangement pitch P of the plurality of recesses 22 is 50 μm or more and 500 μm or less, and the angle formed by the wall surfaces of the plurality of recesses 22 (that is, the slopes of the substantially inverted pyramid or substantially inverted truncated pyramid) with the sheet surface is 40 degrees or more and 65 degrees or less, the luminance uniformity can be improved.

[0103] In the first light diffusion sheet 43 of the present embodiment, when the ridge line 23 is recessed in a substantially parabolic shape, substantially arc shape, substantially triangular shape, or substantially trapezoidal shape between the intersection points 23a, the scratch resistance can be improved.

[0104] In the first light diffusion sheet 43 of the present embodiment, the plurality of recesses 22 may be formed in a substantially inverted quadrangular pyramid or substantially inverted truncated quadrangular pyramid. In this case, the ridge line 23 may extend in the X direction (first direction) and the Y direction (second direction). Further, the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 may be the average value 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. Further, the arrangement pitch P of the plurality of recesses 22 may be the average value 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. Further, the dimension Wr occupied by the curved portion of the top of the ridge line 23 in the arrangement direction of the recesses 22 may be the average value of the dimension Wrx occupied by the curved portion of the top of the ridge line 23 in the X direction and the dimension Wry occupied by the curved portion of the top of the ridge line 23 in the Y direction. By doing so, it becomes easy to manufacture a light diffusion sheet excellent in scratch resistance and luminance uniformity.

[0105] In the first light diffusion sheet 43 of the present embodiment, when the plurality of recesses 22 are provided only on the first surface 43a and the second surface 43b is a matte surface, the luminance uniformity can be further improved while suppressing wear and damage on the second surface 43b.

[0106] The backlight unit 40 of the present embodiment is a backlight unit 40 incorporated in the liquid crystal display device 50 and guiding the light emitted from the light source 42 toward the display screen 50a, and includes the first light diffusion sheet 43 of the present embodiment between the display screen 50a and the light source 42.

[0107] According to the backlight unit 40 of the present embodiment, since the first light diffusion sheet 43 of the present embodiment is provided, the luminance uniformity can be improved, and even if the first light diffusion sheets 43 are laminated together or the first light diffusion sheet 43 and other optical sheets are laminated, damage can be suppressed.

[0108] In the backlight unit 40 of the present embodiment, when the light source 42 is disposed on the reflection sheet 41 provided on the opposite side of the display screen 50a as viewed from the first light diffusion sheet 43, the luminance uniformity is further improved.

[0109] The liquid crystal display device 50 of the present embodiment includes the backlight unit 40 of the present embodiment and the liquid crystal display panel 5.

[0110] According to the liquid crystal display device 50 of the present embodiment and the information device including the liquid crystal display device 50, since the backlight unit 40 of the present embodiment is provided, the luminance uniformity can be improved, and even if the first light diffusion sheets 43 are laminated together or the first light diffusion sheet 43 and other optical sheets are laminated, damage can be suppressed.

[0111] The method for manufacturing a light diffusion sheet of the present embodiment is a method for manufacturing the first light diffusion sheet 43 of the present embodiment, in which the first light diffusion sheet 43 is extrusion-molded at a line speed of 10 m / min or more and 30 m / min or less and a compression line pressure of 100 kgf / cm or more and 500 kgf / cm or less.

[0112] According to the method for manufacturing a light diffusion sheet of the present embodiment, the dimension Wr occupied by the curved portion of the top of the ridge line 23 in the arrangement direction of the recesses 22 can be made 30% or less of the arrangement pitch P of the recesses 22, so that the first light diffusion sheet 43 having a steep shape at the top of the ridge line 23 and excellent luminance uniformity can be manufactured.

[0113] Also, according to the method for manufacturing a light diffusion sheet of the present embodiment, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 can be set to 1 μm or more and 10 μm or less. That is, a first light diffusion sheet 43 is obtained in which the ridge line 23 is recessed between the intersections 23a and the portions of the intersections 23a are raised. Therefore, even when the first light diffusion sheets 43 are laminated or the first light diffusion sheet 43 and other optical sheets are laminated, the ridge line 23 is less likely to contact other optical sheets or the like between the intersections 23a, so wear and damage are less likely to occur. At the intersections 23a, since there is point contact with other optical sheets or the like, slippage occurs and wear and damage are less likely to occur. Therefore, the first light diffusion sheet 43 excellent in scratch resistance can be manufactured.

[0114] Also, according to the method for manufacturing a light diffusion sheet of the present embodiment, since extrusion molding is used, the first light diffusion sheet 43 of the present embodiment can be manufactured at low cost.

[0115] Also, according to the method for manufacturing a light diffusion sheet of the present embodiment, since a polycarbonate resin obtained from biomass resources is used, a product considering the environment can be provided.

[0116] (Example) Hereinafter, the first light diffusion sheet 43 according to the example will be described while making a comparison with a comparative example.

[0117] (Measurement of the shape, dimensions, and angle of the concave portion) Observation of the shape of the recess 22 formed in the first light diffusing sheet 43 of each of the embodiments described below was performed using a laser microscope VK-100 manufactured by Keyence Corporation. Specifically, the cross-sectional shape of the ridge line 23 of the recess 22 formed in an inverted regular square pyramid (the cross-sectional shapes shown in FIGS. 6, 7, 9, and 10), the maximum height differences dx and dy shown in FIGS. 6 and 7 (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, the heights Hx and Hy shown in FIGS. 9 and 10 (the height from the center 22a of the recess 22 to the apex of the ridge line 23) and their average value H, the dimensions Wrx and Wry shown in FIGS. 9 and 10 (the dimensions occupied by the curved portions at the top of the ridge line 23 in the X and Y directions) and their average value Wr, the arrangement pitches Px and Py of the recesses 22 shown in FIGS. 6 and 7 (the horizontal distance between the intersection points 23a in the X and Y directions) and their average value P, the ratio Wr / P of the dimension Wr to the arrangement pitch P (unit: %), and the angles θx and θy shown in FIGS. 9 and 10 (the angles formed between the wall surface of the recess 22 (the slope of the inverted regular square pyramid) and the sheet surface of the first light diffusing sheet 43 in the X and Y directions) were measured.

[0118] <Measurement of optical properties> As the optical properties of the first light diffusing sheet 43 of each of the embodiments described below, Haze and the light transmittance at a wavelength of 450 nm were measured. Haze was measured by irradiating light from the surface (the first surface 43a) having the recess 22 formed in an inverted regular square pyramid using an HZ-2 manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K-7105. Also, the light transmittance at a wavelength of 450 nm was measured by irradiating light from the surface (the first surface 43a) having the recess 22 formed in an inverted regular square pyramid using a V-670 manufactured by JASCO Corporation.

[0119] <Evaluation of scratch resistance> For the scratch resistance test of the first light diffusion sheet 43 in each of the embodiments described below, the apparatus shown in FIG. 15 was used. As shown in FIG. 15, the lower surface of the first light diffusion sheet 43 serving as a fixed sample was made the first surface 43a (the surface on which the inverted regular square pyramid-shaped recess 22 was formed), and the upper surface of the first light diffusion sheet 43 serving as a moving sample was made the second surface 43b (mat surface). The moving sample and the fixed sample were sequentially stacked on a glass plate. A weight of 516 gf was placed on a circular area with a diameter of 20 mm from above, and while pulling the moving sample at a pulling speed of 10 mm / second, it was moved 100 mm. The degree of damage to the friction surface between the moving sample and the fixed sample was visually inspected and judged. The inspection and judgment were performed on both the lower surface of the fixed sample (the surface on which the inverted regular square pyramid-shaped recess 22 was formed) and the upper surface of the moving sample (mat surface).

[0120] The evaluation in the inspection and judgment was carried out according to the following criteria. AA: No scratches can be seen visually, and it is a light diffusion sheet with extremely excellent scratch resistance. A: Almost no scratches can be seen visually, and it is a light diffusion sheet with considerably excellent scratch resistance. B: Slight scratches can be seen visually, and it is a light diffusion sheet with a certain degree of excellent scratch resistance. C: Some scratches can be seen visually, and it is a light diffusion sheet with scratch resistance close to the lower limit that can be barely tolerated. ×: Many scratches can be clearly seen visually, and it is a light diffusion sheet with poor scratch resistance.

[0121] <Measurement of luminance and luminance uniformity> The measurement of the luminance and luminance uniformity of the first light diffusion sheet 43 in each of the following examples was carried out with the configuration of the backlight unit 40 shown in FIGS. 2 and 3. That is, on the small light sources 42 (LED arrays) arranged in an array, two first light diffusion sheets 43 having the inverted regular square pyramid-shaped recesses 22 obtained in the following examples were stacked with the first surface 43a on which the recesses 22 were formed facing the light source 42 side. On the laminate of the first light diffusion sheets 43, 99 parts by mass of an aromatic polycarbonate resin having a melt mass flow rate measured in accordance with ISO1133 of 15 g / 10 min was blended with 1 part by mass of a silicone composite powder (average particle diameter 2.0 μm) as a diffusing agent, and a 120-μm-thick second light diffusion sheet 44 was stacked with the mirror surface 44b facing the light source 42 side. In the production of the second light diffusion sheet 44, a mirror roll was used for one roll, and a roll having the same random matte shape (surface roughness Ra = 2.5 μm) as in Example 1 described below on the surface was used for the other roll, and it was produced in the same manner as in Example 1. In the second light diffusion sheet 44, the surface roughness Ra on the matte surface (first surface 44a) side was 1.6 μm, and the surface roughness Ra on the mirror surface (second surface 44b) side was 0.4 μm. Two prism sheets 45 and 46 were stacked on the second light diffusion sheet 44. The luminance and luminance uniformity were measured with the above configuration. As the LED array, one with an LED pitch of 3 mm was used, and as the LED (small light source 42), a blue LED (product number XPGDRY-L1-0000-00501) manufactured by Cree was used.

[0122] In the measurement of the luminance uniformity, first, in the LED array (6 × 6) shown in FIG. 3, the cross-sectional luminance was obtained along the diagonal line L passing directly above the LED (small light source 42), and then the average value and standard deviation of this cross-sectional luminance were calculated. Luminance uniformity = (average value of cross-sectional luminance) ÷ (standard deviation of cross-sectional luminance) The luminance uniformity was obtained according to the above calculation formula. The higher the value of the luminance uniformity obtained in this way, the more uniform the luminance indicates.

[0123] The evaluation criteria for the luminance uniformity are as follows. AA: It is a light diffusing sheet that exhibits the best uniformity, with a luminance uniformity of 210 or more and no visible luminance unevenness by visual inspection. A: It is a light diffusing sheet that exhibits excellent uniformity, with a luminance uniformity of 200 or more and less than 210, and almost no visible luminance spots by visual inspection. B: It is a light diffusing sheet that exhibits a qualified level of uniformity, with a luminance uniformity of 190 or more and less than 200, and slightly visible luminance spots by visual inspection. C: It is a light diffusing sheet that exhibits the minimum qualified level of uniformity, with a luminance uniformity of 180 or more and less than 190, and visible luminance spots by visual inspection. X: It is a light diffusing sheet with poor uniformity, with a luminance uniformity of less than 180 and clearly visible luminance spots by visual inspection.

[0124] Also, the evaluation criteria for luminance are as follows. A: It is a light diffusing sheet with an average cross-sectional luminance value of 3150 cd / m 2 or more. B: It is a light diffusing sheet with an average cross-sectional luminance value of 3100 cd / m 2 or more and less than 3150 cd / m 2 C: It is a light diffusing sheet with an average cross-sectional luminance value of 3050 cd / m 2 or more and less than 3100 cd / m 2

[0125] <Comprehensive Evaluation> The comprehensive evaluation of the first light diffusing sheet 43 in each of the following examples was conducted based on the results of the scratch resistance test and the evaluation results of luminance uniformity, according to the following criteria. AA: It is a light diffusing sheet that is comprehensively the best, with all evaluation results of the scratch resistance test for both the reverse regular square pyramid surface and the matte surface and the evaluation results of luminance uniformity being A or more, and having two or more AA. A: It is a light diffusing sheet that is comprehensively the best (excluding AA-rated products), with all evaluation results of the scratch resistance test for both the reverse regular square pyramid surface and the matte surface and the evaluation results of luminance uniformity being A or more. ​​B: In the evaluation results of the scratch resistance tests for both the inverted regular square pyramid surface and the matte surface, and the evaluation results of the luminance uniformity, it is a comprehensively excellent light diffusing sheet with all values being B or higher (excluding AA and A-graded products). C: In the evaluation results of the scratch resistance tests for both the inverted regular square pyramid surface and the matte surface, and the evaluation results of the luminance uniformity, it is a usable light diffusing sheet with comprehensively having a performance of at least the minimum level with all values being C or higher (excluding AA, A, and B-graded products). ×: In the evaluation results of the scratch resistance tests for both the inverted regular square pyramid surface and the matte surface, and the evaluation results of the luminance uniformity, it is a comprehensively inferior light diffusing sheet with an × evaluation in any one or more of them.

[0126] <Example 1> The manufacturing method of the first light diffusing sheet 43 of Example 1 is as follows. First, a polycarbonate resin (Bioengineering Plastic DURABIO (registered trademark) D7340A, which is a plant-derived isosorbide from Mitsubishi Chemical Corporation and has a melt mass flow rate of 10 g / 10 min measured in accordance with ISO 1133) is fed into an extruder, melt-kneaded, and then the resin is extruded from a T-die. Thereafter, as one of the two metal rolls, a roll having the shape shown in FIGS. 16(A) and (B) ((B) is a shape view seen from the X-Y cross-sectional direction of (A)) (a pyramid shape of a regular square pyramid with a height of 50 μm, a pitch of 100 μm, and an apex angle of 90 degrees) on its surface is used, and as the other roll, a roll having a random matte shape (surface roughness Ra = 2.5 μm) on its surface is used. The molten resin extruded from the T-die is sandwiched between the two rolls and cooled while transferring the shape. As a result, as shown in Table 1, a single-layer light diffusing sheet with a thickness of 180 μm having a concave (inverted) pyramid shape with a depth depending on the height of the regular square pyramid on one surface and a matte surface with a surface roughness Ra = 1.68 μm on the other surface was created by an extrusion molding method. Note that as the molding conditions, as shown in Table 1, pressurization was performed so that the line speed was 15 m / min and the compression force (compression linear pressure) between the two rolls was 250 kgf / cm, and a light diffusing sheet was obtained under resin temperature conditions (220 to 260 °C) where the shape transfer to the polycarbonate resin was good and the peeling of the sheet from the roll was good.

[0127]

Table 1

[0128] The shape observation of the concave portion (inverted regular square pyramid) 22 formed on the first light diffusing sheet 43 of Example 1 produced as described above was performed using a laser microscope VK-100 manufactured by Keyence Corporation. Specifically, the cross-sectional shape of the ridge line 23 of the concave portion 22 formed in the inverted regular square pyramid (the cross-sectional shapes shown in FIGS. 6, 7, 9, and 10), the maximum height differences dx and dy shown in FIGS. 6 and 7 (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, the heights Hx and Hy shown in FIGS. 9 and 10 (the height from the center 22a of the concave portion 22 to the apex of the ridge line 23) and their average value H, the dimensions Wrx and Wry shown in FIGS. 9 and 10 (the dimensions occupied by the curved portions at the top of the ridge line 23 in the X and Y directions) and their average value Wr, the arrangement pitches Px and Py of the concave portions 22 shown in FIGS. 6 and 7 (the horizontal distance between the intersection points 23a in the X and Y directions) and their average value P, the ratio Wr / P of the dimension Wr to the arrangement pitch P (unit: %), and the angles θx and θy shown in FIGS. 9 and 10 (the angles formed between the wall surface of the concave portion 22 (the inclined surface of the inverted regular square pyramid) and the sheet surface of the first light diffusing sheet 43 in the X and Y directions) were measured.

[0129] <Examples 2 to 3> In the manufacturing method of the first light diffusing sheet 43 of Example 2, among the two metal rolls, as the roll having a regular square pyramid shape, a roll having a pyramid shape of a regular square pyramid with a height of 54.6 μm, a pitch of 100 μm, and an apex angle of 85 degrees on its surface was used. Except for this point, as shown in Table 1, the same conditions as in Example 1 were used.

[0130] In the manufacturing method of the first light diffusing sheet 43 of Example 3, among the two metal rolls, as the roll having a regular square pyramid shape, a roll having a pyramid shape of a regular square pyramid with a height of 59.6 μm, a pitch of 100 μm, and an apex angle of 80 degrees on its surface was used. Except for this point, as shown in Table 1, the same conditions as in Example 1 were used.

[0131] <Comparative Examples 1 to 3> In Comparative Example 1, first, a press original plate with a thickness of 1 mm was made using the same polycarbonate resin (DURABIO (registered trademark) D7340A) as in Example 1. Subsequently, a flat mold having the shape shown in Figs. 17(A) and (B) ((B) is a shape diagram seen from the X-Y cross-sectional direction of (A)) (in the shape of a regular square pyramid with the same shape as in Example 1, the valley portion of the pyramid is rounded into a curved surface shape with a curvature radius of 4.2 μm) on the surface, and a flat mold having a random matte shape (surface roughness Ra = 2 μm) similar to that in Example 1 on the surface were used. The press original plate was sandwiched between two molds and placed in a press machine equipped with a heating and cooling device. The press plate temperature was 240 °C, and the surface pressure was 200 kg / cm 2 and pressed for 20 minutes under these conditions. Then, while maintaining the pressure, the press plate temperature was cooled to 20 °C, and the pressure was held until the resin plate was sufficiently cooled, and a light diffusion sheet with a thickness of 180 μm shown in Table 1 was produced by the compression molding method.

[0132] In Comparative Example 2, after making a press original plate in the same manner as in Comparative Example 1, except for using a flat mold having the shape of a regular square pyramid with the same shape as in Example 2 and rounding the valley portion of the pyramid into a curved surface shape with a curvature radius of 4.2 μm on the surface in the same manner as in Comparative Example 1, heating, pressurization, and cooling in the press machine were performed under the same conditions as in Comparative Example 1, and a light diffusion sheet with a thickness of 180 μm shown in Table 1 was produced by the compression molding method.

[0133] In Comparative Example 3, after making a press original plate in the same manner as in Comparative Example 1, except for using a flat mold having the shape of a regular square pyramid with the same shape as in Example 3 and rounding the valley portion of the pyramid into a curved surface shape with a curvature radius of 4.2 μm on the surface in the same manner as in Comparative Examples 1 and 2, heating, pressurization, and cooling in the press machine were performed under the same conditions as in Comparative Examples 1 and 2, and a light diffusion sheet with a thickness of 180 μm shown in Table 1 was produced by the compression molding method.

[0134] <Evaluation of Examples 1 - 3 and Comparative Examples 1 - 3> Regarding the first light diffusion sheet 43 obtained in Examples 1 to 3, Table 2 shows the shape, dimensions, angles, etc. of each element obtained by measurement, together with Comparative Examples 1 to 3. Table 3 shows the measurement results of optical properties, the results of the scratch resistance test, the evaluation results of luminance and luminance uniformity, and the comprehensive evaluation results, together with Comparative Examples 1 to 3. In addition, surface photographs of the samples after the scratch resistance test in each of Examples 1 to 3 and Comparative Example 1, specifically, the lower surface (inverted square pyramid surface) of the fixed sample and the upper surface (mat surface) of the moving sample, are shown in Fig. 18.

[0135]

Table 2

[0136]

Table 3

[0137] From the results shown in Table 2 and Table 3, in the first light diffusion sheet 43 in which the inverted regular square pyramid-shaped recess 22 was formed and obtained in Examples 1 to 3, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 is 1.0 μm or more, and the ridge line 23 has a shape that is recessed approximately in a parabolic shape between the intersections 23a. Therefore, wear and damage caused by the ridge line 23 are less likely to occur even when used in layers. As a result, as shown in Fig. 18, good results were obtained in the scratch resistance test not only on the mat surface (upper surface of the moving sample) but also on the inverted square pyramid surface (lower surface of the fixed sample).

[0138] On the other hand, in Comparative Examples 1 to 3, although a curved surface shape with a radius of curvature of about 4.2 μm is provided near the apex of the ridge line 23, the maximum height difference d is 0 μm, there is no depression in the ridge line 23, and the ridge line 23 has a horizontal shape between the intersections 23a. Therefore, as shown in Fig. 18, scratches caused by the ridge line 23 occurred in the scratch resistance test on the inverted square pyramid surface (lower surface of the fixed sample), resulting in inferior scratch resistance.

[0139] Also, 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. Therefore, good evaluation results were obtained for the luminance uniformity.

[0140] From the above, for the comprehensive evaluation, Example 1 was "B", Example 2 was "A", and Example 3 was "AA", while Comparative Examples 1 to 3 were "×".

[0141] <Examples 4 to 6 and Comparative Example 4> In Examples 4 and 5, as shown in Table 1, a light diffusing sheet was produced in the same manner as in Example 1, except that the line speeds among the molding conditions were changed to 11 m / min and 4 m / min, respectively.

[0142] In Example 6 and Comparative Example 4, as shown in Table 1, a light diffusing sheet was produced in the same manner as in Example 1, except that the compression linear pressures between the two rolls were changed to 150 kgf / cm and 40 kgf / cm, respectively.

[0143] <Evaluation of Examples 4 to 6 and Comparative Example 4> Regarding the first light diffusing sheets 43 obtained in Examples 4 to 6, the shapes, dimensions, angles, etc. of each element obtained by measurement were shown in Table 2 together with Comparative Example 4, and the measurement results of the optical physical properties, the results of the scratch resistance test, the evaluation results of the luminance and the luminance uniformity, and the comprehensive evaluation results were shown in Table 3 together with Comparative Example 4.

[0144] From the results shown in Table 2 and Table 3, in the first light diffusing sheets 43 in which the reverse regular square pyramid-shaped recesses 22 were formed, obtained in Examples 4 to 6 and Comparative Example 4, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 was 1.0 μm or more, and the ridge line 23 had a shape that was recessed approximately in a parabolic shape between the intersections 23a. For this reason, wear and damage due to the ridge line 23 were less likely to occur even when used in layers, and thus good results were obtained in the scratch resistance test.

[0145] In Examples 4 to 6, since all of the ratios Wr / P were 30% or less and the steep shape of the top of the ridge line 23 was maintained, good evaluation results were obtained for the luminance uniformity.

[0146] However, in Comparative Example 4, since the ratio Wr / P exceeded 30%, the steep shape of the top of the ridge line 23 was not maintained, and the result for the luminance uniformity was poor.

[0147] From the above, for the comprehensive evaluation, Example 4 was "B", Examples 5 and 6 were "C", but Comparative Example 4 was "×".

[0148] <Examples 7 to 9 and Comparative Example 5> In the manufacturing method of the first light diffusion sheet 43 of Example 7, among the two metal rolls, as the roll with a regular square pyramid shape, except for using a roll having a pyramid shape of a regular square pyramid with a height of 90.0 μm, a pitch of 180 μm, and an apex angle of 90 degrees on the surface, a light diffusion sheet with a thickness of 200 μm shown in Table 4 was produced using substantially the same conditions as in Example 1.

[0149]

Table 4

[0150] In the manufacturing method of the first light diffusion sheet 43 of Example 8, among the two metal rolls, as the roll with a regular square pyramid shape, except for using a roll having a pyramid shape of a regular square pyramid with a height of 98.2 μm, a pitch of 180 μm, and an apex angle of 85 degrees on the surface, a light diffusion sheet with a thickness of 200 μm shown in Table 4 was produced using substantially the same conditions as in Example 1.

[0151] In the manufacturing method of the first light diffusion sheet 43 of Example 9, among the two metal rolls, as the roll with a regular square pyramid shape, except for using a roll having a pyramid shape of a regular square pyramid with a height of 107.3 μm, a pitch of 180 μm, and an apex angle of 80 degrees on the surface, a light diffusion sheet with a thickness of 200 μm shown in Table 4 was produced using substantially the same conditions as in Example 1.

[0152] In Comparative Example 5, after producing a press master plate in the same manner as in Comparative Example 1, a flat die having a surface with a shape in which the valley portion of the pyramid was rounded into a curved surface shape with a radius of curvature of 4.2 μm in the shape of a regular square pyramid having the same shape as in Example 7 was used, except that heating, pressurization, and cooling were performed with a press machine under the same conditions as in Comparative Example 1, and a light diffusing sheet having a thickness of 200 μm shown in Table 4 was produced by a compression molding method.

[0153] <Evaluation of Examples 7 to 9 and Comparative Example 5> Regarding the first light diffusing sheets 43 obtained in Examples 7 to 9, the shapes, dimensions, angles, etc. of the respective elements obtained by measurement are shown in Table 5 together with Comparative Example 5, and the measurement results of optical physical properties, the results of the scratch resistance test, the evaluation results of luminance and luminance uniformity, and the comprehensive evaluation results are shown in Table 6 together with Comparative Example 5.

[0154]

Table 5

[0155]

Table 6

[0156] From the results shown in Table 5 and Table 6, in the first light diffusing sheet 43 in which the concave portion 22 having an inverted regular square pyramid shape was formed and obtained in Examples 7 to 9, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 is 2.5 μm or more, and the ridge line 23 has a shape that is recessed approximately in a parabolic shape between the intersections 23a. For this reason, even when used in a stacked manner, wear and damage due to the ridge line 23 are less likely to occur, and as a result, the best result among the examples was obtained in the scratch resistance test.

[0157] On the other hand, in Comparative Example 5, although a curved surface shape is imparted near the apex of the ridge line 23, the maximum height difference d is 0 μm, there is no depression in the ridge line 23, and the ridge line 23 has a horizontal shape between the intersections 23a. For this reason, scratches due to the ridge line 23 occurred in the scratch resistance test, resulting in a poor result in terms of scratch resistance.

[0158] In Examples 7 to 9 and Comparative Example 5, the ratio Wr / P was 10% or less in all cases, and the top of the ridge line 23 was maintained in a steeper shape. Therefore, particularly good evaluation results were obtained for the luminance uniformity. In particular, in Examples 7 to 9, since the maximum height difference d was 5.0 μm or less, no decrease in luminance uniformity due to the shape in which the ridge line 23 was recessed between the intersections 23a was observed.

[0159] From the above, for the comprehensive evaluation, Examples 7 to 9 were the most excellent with "AA", while Comparative Example 5 was "×".

[0160] <Examples 10 to 12> In Example 10, using a polycarbonate resin (Bioengineering Plastic DURABIO (registered trademark) D5380A, which is a plant-derived isosorbide manufactured by Mitsubishi Chemical Corporation) having a melt mass flow rate of 5 g / 10 minutes measured in accordance with ISO 1133, 1 part by mass of a silicone composite powder (average particle diameter 2.0 μm) as a diffusing agent was premixed with 99 parts by mass of the polycarbonate resin and then charged into an extruder for melt kneading. Except for this point, the same two rolls as in Example 1 were used. As shown in Table 7, pressurization was performed such that the line speed was 17 m / min and the compression force (compression linear pressure) between the two rolls was 280 kgf / cm. A light diffusing sheet with a thickness of 180 μm was obtained under resin temperature conditions (220 to 260°C) where the shape transfer to the polycarbonate resin was good and the peeling of the sheet from the roll was good.

[0161]

Table 7

[0162] In Examples 11 and 12, using the same method as in Example 10, as shown in Table 7, the line speed among the molding conditions was changed to 15 m / min and 13 m / min, respectively, to produce a light diffusing sheet with a thickness of 180 μm.

[0163] <Evaluation of Examples 10 to 12> For the first light diffusion sheet 43 obtained in Examples 10 to 12, Table 8 shows the shape, dimensions, angles, etc. of each element obtained by measurement, and Table 9 shows the measurement results of optical physical properties, the results of the scratch resistance test, the evaluation results of luminance and luminance uniformity, and the comprehensive evaluation results.

[0164]

Table 8

[0165]

Table 9

[0166] From the results shown in Table 8 and Table 9, in the first light diffusion sheet 43 in which the inverted regular square pyramid-shaped recess 22 was formed and obtained in Examples 10 to 12, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 is 2.0 μm or more, and the ridge line 23 is recessed in a substantially parabolic shape between the intersections 23a. For this reason, wear and damage due to the ridge line 23 are less likely to occur even when used in an overlapping manner, and thus good results were obtained in the scratch resistance test.

[0167] Also, in Examples 10 to 12, the ratio Wr / P is within the range of 6 to 9%, and since the steep shape of the top of the ridge line 23 is maintained, good evaluation results were obtained for the luminance uniformity.

[0168] From the above, for the comprehensive evaluation, Example 10 was "B", and Examples 11 and 12 were "C".

[0169] (Other Embodiments) The embodiments of the present disclosure (including examples. The same shall apply hereinafter) have been described above. However, the present disclosure is not limited to the foregoing embodiments only, and various modifications are possible within the scope of the disclosure. That is, the description of the foregoing embodiments is essentially only illustrative and is not intended to limit the present disclosure, its applications, or its uses. For example, it goes without saying that the configuration of the light diffusion sheet (layer structure, material, etc.) is not limited to the configuration of the first light diffusion sheet 43 in the foregoing embodiment shown in FIG. 2. Also, it goes without saying that the backlight to which the light diffusion sheet is applied and the configuration of the liquid crystal display device including the backlight are not limited to the configurations of the backlight unit 40 and the liquid crystal display device 50 in the foregoing embodiment.

[0170] For example, instead of the combination of two laminated first light diffusion sheets 43 and the second light diffusion sheet 44 in the backlight unit 40 of the foregoing embodiment shown in FIG. 2, three laminated first light diffusion sheets 43 may be used as in the backlight unit 40 of the modified example shown in FIG. 19, or four or more first light diffusion sheets 43 may be laminated. In addition, when three or more first light diffusion sheets 43 are laminated, from the perspective of the trade-off between the reflection and refraction effects due to the substantially inverted pyramid shape and the light diffusion effect due to the diffusing agent, the light diffusion sheet 43 closest to the display screen 50a (that is, the first prism sheet 45) contains a diffusing agent, and the other light diffusion sheets 43 do not necessarily contain a diffusing agent substantially. Thereby, the luminance uniformity can be further improved.

Explanation of Reference Numerals

[0171] 1 TFT substrate 2 CF substrate 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizing plate 7 Second polarizing plate 21 Base material layer 22 Concave portion 22a Center 23 Ridge line 23a Intersection point 23b Lowest point 40 Backlight unit 41 Reflection sheet 42 Small light source 43 First light diffusion sheet 43a First surface 43b Second surface 44 Second light diffusion sheet 44a First surface 44b Second surface 45 First prism sheet 46 Second prism sheet 50 Liquid crystal display device 50a Display screen

Claims

1. A light-diffusing sheet having at least a first surface with a plurality of recesses formed in a substantially inverted pyramid or substantially inverted frustum of a pyramid shape, a homopolymer polycarbonate resin composed of a first structural unit derived from a dihydroxy compound represented by the following formula (1), or a copolymer polycarbonate resin composed of the first structural unit and a second structural unit derived from one or more dihydroxy compounds selected from the group consisting of an aliphatic dihydroxy compound, an alicyclic dihydroxy compound, and an ether group-containing dihydroxy compound (excluding the dihydroxy compound represented by the following formula (1)) containing, the ridge lines partitioning the plurality of recesses have a concave shape between the intersections with respect to a straight line connecting the intersections of the ridge lines, the top portions of the ridge lines are curved in the arrangement direction of the plurality of recesses, when the arrangement pitch of the plurality of recesses is P and the dimension occupied by the curved portions of the top portions of the ridge lines in the arrangement direction of the plurality of recesses is Wr, the ratio Wr / P is 0.3 or less, the maximum height difference d between the straight line and the ridge line is 1 μm or more and 10 μm or less, the ridge lines are recessed in a substantially parabolic shape, substantially arc shape, substantially triangular shape, or substantially trapezoidal shape between the intersections, light-diffusing sheet. 【Chemical 1】

2. the maximum height difference d is 1.5 μm or more and 7 μm or less The light-diffusing sheet according to claim 1.

3. the maximum height difference d is 2.5 μm or more and 5 μm or less The light-diffusing sheet according to claim 2.

4. the ratio Wr / P is 0.2 or less, The light-diffusing sheet according to any one of claims 1 to 3.

5. the ratio Wr / P is 0.1 or less, The light-diffusing sheet according to claim 4.

6. the arrangement pitch P is 50 μm or more and 500 μm or less, the angle formed by the wall surfaces of the plurality of recesses and the sheet surface of the light-diffusing sheet is 40 degrees or more and 65 degrees or less, The light-diffusing sheet according to any one of claims 1 to 3.

7. the plurality of recesses are formed in a substantially inverted quadrangular pyramid or substantially inverted frustum of a quadrangular pyramid shape, the ridge lines extend in a first direction and a 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 the average value of the arrangement pitch Px of the plurality of recesses in the first direction and the arrangement pitch Py of the plurality of recesses in the second direction, The dimension Wr is 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. The light diffusing sheet according to any one of claims 1 to 3.

8. The plurality of concave portions are provided only on the first surface. The second surface is a matte surface. The light diffusing sheet according to any one of claims 1 to 3.

9. A backlight unit incorporated in a liquid crystal display device for guiding light emitted from a light source toward a display screen, comprising the light diffusing sheet according to any one of claims 1 to 3 between the display screen and the light source. Backlight unit.

10. The light source is disposed on a reflective sheet provided on the opposite side of the display screen as viewed from the light diffusing sheet. The backlight unit according to claim 9.

11. The light diffusing sheet is disposed between the display screen and the light source by laminating a plurality of sheets. The backlight unit according to claim 9.

12. The light diffusing sheet is disposed between the display screen and the light source by laminating three or more sheets. The backlight unit according to claim 11.

13. Among the light diffusing sheets laminated with three or more sheets, the light diffusing sheet closest to the display screen contains a diffusing agent, and the other light diffusing sheets substantially do not contain a diffusing agent. The backlight unit according to claim 12.

14. The backlight unit according to claim 9, and a liquid crystal display panel. Liquid crystal display device.

15. An information device comprising the liquid crystal display device according to claim 14. Information device.

16. A method for manufacturing the light diffusing sheet according to any one of claims 1 to 3, wherein the light diffusing sheet is extrusion-molded at a line speed of 10 m / min or more and 30 m / min or less and a compression line pressure of 100 kgf / cm or more and 500 kgf / cm or less. Method for manufacturing a light diffusing sheet.

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