Diffusion sheets, backlight units, liquid crystal display devices, and information equipment

Abstract

To provide a diffusion sheet capable of improving luminance uniformity while avoiding deterioration in luminance on the entire screen, in a liquid crystal display device.SOLUTION: A diffusion sheet 43 is incorporated into a liquid crystal display device in which a plurality of light sources 42 is distributed and provided on the back side of a display screen. One surface of the diffusion sheet 43 has an uneven shape formed by a two-dimensional arrangement of concave parts that diffuse light. In a predetermined area R on one side of the diffusion sheet 43, a luminance improvement member 25 that suppresses the diffusion of light in the predetermined region R and improves a total light transmittance is provided so that the concave parts 22a of the uneven shape are at least partially filled.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a diffusion sheet, a backlight unit, a liquid crystal display device, and an information device.

Background Art

[0002] In recent years, as a display device for various information devices such as smartphones and tablet terminals, a liquid crystal display device (hereinafter sometimes referred to as a liquid crystal display) has been widely used. As a backlight for the liquid crystal display, a direct-lit type in which a light source is arranged behind the liquid crystal panel or an edge-lit type in which the light source is arranged near the side surface of the liquid crystal panel is the mainstream.

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

[0004] The direct-lit backlight disclosed in Patent Document 1 includes a prism sheet arranged on the light incident side of the liquid crystal display panel, a diffusion sheet, and a plurality of light sources such as LEDs, and the light source, the diffusion sheet, and the prism sheet are laminated in order from the back side.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, with conventional direct-lit backlights, a decrease in brightness may occur in areas between light sources (areas where no light sources are located) due to the thinning of the backlight (reducing the distance between the light source and the diffusion sheet, or the thickness of the diffusion sheet) and the reduction in the number of light sources to reduce costs.

[0007] In response to this, attempts have been made to improve brightness uniformity by using diffusion sheets with, for example, a concave pyramidal surface or diffusion sheets containing a large amount of diffusing agent, but these have not been able to sufficiently suppress the decrease in brightness in areas between light sources.

[0008] Furthermore, attempts have been made to eliminate brightness unevenness between light sources and the areas between them by printing white ink in the region directly above the light source on the diffusion sheet. However, in this case, the brightness of the region directly above the light source decreases, resulting in an unavoidable decrease in the overall brightness of the screen.

[0009] Therefore, the present disclosure aims to provide a diffusion sheet that can improve brightness uniformity while avoiding a decrease in brightness across the entire screen in a liquid crystal display device. [Means for solving the problem]

[0010] To achieve the above objective, the diffusion sheet according to the present disclosure is a diffusion sheet incorporated into a liquid crystal display device in which a plurality of light sources are dispersed on the back side of the display screen, wherein one surface of the diffusion sheet has an uneven shape, and a brightness-enhancing member is provided in a predetermined area on the one surface of the diffusion sheet such that the recesses of the uneven shape are at least partially filled, thereby improving the total light transmittance of the predetermined area.

[0011] According to the diffusion sheet of this disclosure, brightness-enhancing members are provided in predetermined areas of the diffusion sheet surface having an uneven shape, such as areas between light sources or sheet edges where brightness reduction is likely to occur, so as to fill in recesses at least partially, thereby improving the total light transmittance. As a result, the brightness of the predetermined area is increased, making it possible to improve brightness uniformity in a liquid crystal display device while avoiding a decrease in brightness across the entire screen. Therefore, the diffusion sheet of this disclosure can also accommodate further thinning of the backlight and reduction of the number of light sources.

[0012] In the diffusion sheet according to this disclosure, the brightness-enhancing member may be composed of transparent ink. In this case, the brightness of a predetermined area is increased by a simple method of printing transparent ink into the recesses of a predetermined area. In this case, if the transparent ink is a medium and the matrix resin constituting the diffusion sheet is polycarbonate, the total light transmittance of the predetermined area is improved simply by providing transparent ink in the recesses of the predetermined area. Furthermore, in this case, if the brightness-enhancing member is formed by dot printing of the transparent ink, it becomes easier to adjust the total light transmittance of the predetermined area. Moreover, in this case, if the area ratio of the transparent ink in the dot printing is 4% or more, the total light transmittance of the predetermined area can be significantly increased (for example, by about 10%).

[0013] In the diffusion sheet according to this disclosure, the refractive index difference between the diffusion sheet and the brightness-enhancing member may be 0.3 or less. In this way, the brightness of a predetermined region can be increased without being affected by light diffusion at the interface between the diffusion sheet and the brightness-enhancing member.

[0014] In the diffusion sheet relating to this disclosure, the diffusion sheet may contain a diffusion agent. Doing so further improves brightness uniformity.

[0015] In the diffusion sheet according to this disclosure, the recess may have a concave pyramidal shape. This further improves brightness uniformity.

[0016] In the diffusion sheet according to this disclosure, the other side of the diffusion sheet may have an embossed shape. This further improves brightness uniformity.

[0017] In the diffusion sheet according to this disclosure, the predetermined region on one surface of the diffusion sheet where the brightness-enhancing member is provided may be flatter than other regions on the same surface of the diffusion sheet where the brightness-enhancing member is not provided. In this way, the total light transmittance of the predetermined region can be improved compared to the other regions.

[0018] The backlight unit according to this disclosure is incorporated into a liquid crystal display device and guides light emitted from multiple light sources to the display screen side, and includes the aforementioned diffusion sheet between the display screen and the multiple light sources.

[0019] According to the backlight unit of this disclosure, since it is equipped with the aforementioned diffusion sheet, it is possible to improve brightness uniformity while avoiding a decrease in brightness across the entire screen.

[0020] In the backlight unit according to this disclosure, the brightness-enhancing member may be placed in the intermediate region between adjacent light sources among the plurality of light sources. This makes it possible to increase the brightness in the region between light sources where brightness reduction is likely to occur. In this case, the brightness-enhancing member may be provided in all the region between light sources on the diffusion sheet, or it may be provided in only a portion of the region between light sources on the diffusion sheet. Alternatively, the brightness-enhancing member may be provided in the entire region between light sources on the diffusion sheet, or it may be provided in only a portion of the region between light sources on the diffusion sheet.

[0021] In the backlight unit according to this disclosure, the distance between the plurality of light sources and the diffusion sheet may be 10 mm or less. This makes it possible to improve brightness uniformity even in configurations where brightness reduction is more likely to occur in areas between light sources.

[0022] In the backlight unit according to the present disclosure, the plurality of light sources may be LED elements. By doing so, even if the number of light sources is reduced, sufficient luminance across the entire screen can be obtained.

[0023] In the backlight unit according to the present disclosure, the plurality of light sources may be arranged regularly. By doing so, the luminance uniformity is further improved.

[0024] In the backlight unit according to the present disclosure, the plurality of light sources may be arranged on a reflection sheet provided on the opposite side of the diffusion sheet. By doing so, the luminance uniformity is further improved.

[0025] The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure described above and a liquid crystal display panel.

[0026] According to the liquid crystal display device according to the present disclosure, since it includes the backlight unit according to the present disclosure described above, it is possible to improve the luminance uniformity while avoiding a decrease in luminance across the entire screen.

[0027] The information device according to the present disclosure includes the liquid crystal display device according to the present disclosure described above.

[0028] According to the information device according to the present disclosure, since it includes the liquid crystal display device according to the present disclosure described above, it is possible to improve the luminance uniformity while avoiding a decrease in luminance across the entire screen.

Effects of the Invention

[0029] According to the present disclosure, in a liquid crystal display device, it is possible to improve the luminance uniformity while avoiding a decrease in luminance across the entire screen.

Brief Description of the Drawings

[0030] [Figure 1] It is a cross-sectional view of a liquid crystal display device according to an embodiment. [Figure 2] It is a cross-sectional view of a backlight unit according to an embodiment. [Figure 3] This is a cross-sectional view of the diffusion sheet according to the embodiment. [Figure 4] This figure shows how the brightness uniformity decreases in the diffusion sheet according to the comparative example. [Figure 5] This figure shows how brightness uniformity is improved in the diffusion sheet according to the embodiment. [Figure 6] This is a plan view of the diffusion sheet according to Modification Example 1. [Figure 7] This is a plan view of the diffusion sheet according to modified example 2. [Figure 8A] This is a cross-sectional view of the diffusion sheet according to Example 1. [Figure 8B] This is a cross-sectional view of the diffusion sheet according to Example 2. [Figure 8C] This is a cross-sectional view of the diffusion sheet according to Example 3. [Figure 8D] This is a cross-sectional view of the diffusion sheet according to Example 4. [Figure 8E] This is a cross-sectional view of the diffusion sheet according to Example 5. [Figure 8F] This is a cross-sectional view of the diffusion sheet according to Example 6. [Figure 9] This figure shows a cross-section of a recess formed in an inverted square pyramid. [Modes for carrying out the invention]

[0031] (Embodiment) Hereinafter, the diffusion sheet, backlight unit, liquid crystal display device, and information equipment according to the embodiments of this disclosure will be described with reference to the drawings. However, the scope of this disclosure is not limited to the embodiments described below and can be modified at will within the scope of the technical concept of this disclosure.

[0032] Figure 1 is an example of a cross-sectional view of a liquid crystal display device according to this embodiment, Figure 2 is an example of a cross-sectional view of a backlight unit according to this embodiment, and Figure 3 is an example of a cross-sectional view of a diffusion sheet according to this embodiment.

[0033] As shown in Figure 1, the liquid crystal display device 50 comprises 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 comprises a TFT substrate 1 and a CF substrate 2 arranged facing 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 the shape of a frame between the TFT substrate 1 and the CF substrate 2 to enclose the liquid crystal layer 3.

[0034] The shape of the display screen 50a of the liquid crystal display device 50, when viewed from the front (above in Figure 1), is generally a rectangle or a square, but is not limited to these. It may also be a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or any other shape such as the instrument panel of an automobile.

[0035] In the liquid crystal display device 50, an image is displayed by applying a predetermined voltage to the liquid crystal layer 3 at each subpixel corresponding to each pixel electrode to change the orientation state of the liquid crystal layer 3, and by adjusting the transmittance of the light incident from the backlight unit 40 through the first polarizing plate 6 and emitting it through the second polarizing plate 7.

[0036] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, personal information terminals, portable game consoles, photocopiers, ticket vending machines, ATMs, etc.).

[0037] The TFT substrate 1 comprises, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film provided to cover each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to each of the plurality of TFTs, and an alignment film provided to cover each pixel electrode. The CF substrate 2 comprises, for example, a black matrix arranged in a grid on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between each grid of the black matrix, a common electrode provided to cover the black matrix and the color filter, and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material containing liquid crystal molecules having electro-optic properties. The first polarizer plate 6 and the second polarizer plate 7 comprise, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers provided to sandwich the polarizer layer.

[0038] As shown in Figure 2, the backlight unit 40 comprises a reflective sheet 41, a plurality of small light sources 42 arranged two-dimensionally on the reflective sheet 41, a laminate of diffusion sheets 43 provided above the plurality of small light sources 42, a first prism sheet 44 and a second prism sheet 45 provided sequentially above the laminate of diffusion sheets 43, and a polarizing sheet 46 provided above the second prism sheet 45. In this example, the laminate of diffusion sheets 43 is constructed by laminating two layers of diffusion sheets 43 having the same structure.

[0039] The reflective sheet 41 is composed of, for example, a white polyethylene terephthalate resin film, a silver vapor-deposited film, or the like.

[0040] The type of miniature light source 42 is not particularly limited, but may be an LED element or a laser element, for example, and an LED element may be used from the viewpoint of cost, productivity, etc. The miniature light source 42 may have a rectangular shape when viewed from above, in which 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). When an LED is used as the miniature light source 42, multiple LED chips of several millimeters square may be arranged on the reflective sheet 41 at regular intervals. In addition, a lens may be attached to the LED to adjust the light emission angle characteristics of the LED that becomes the miniature light source 42.

[0041] Each diffusion sheet 43 has a diffusion layer 21 and an uneven surface layer 22 formed on the diffusion layer 21, as shown in Figure 3. The diffusion layer 21 is made of, for example, polycarbonate as the base material (matrix resin) and contains, for example, about 0.5 to 4% by mass of a diffusion agent 21a based on 100% by mass of the base material. Known materials can be used as the diffusion agent 21a as appropriate. The surface (bottom surface) 21b of the diffusion layer 21 opposite the uneven surface layer 22 may be a mirror surface, but may have an embossed shape as shown in Figure 3 in order to improve diffusion. The uneven surface layer 22 is made of, for example, clear polycarbonate, and recesses 22a in the shape of, for example, inverted (concave) pyramids are arranged in two dimensions on the surface of the uneven surface layer 22. The apex angle θ of the recesses 22a is, for example, 90°, and the arrangement pitch p of the recesses 22a is, for example, about 100 μm. The diffusion sheet 43 may be made of a single layer structure containing a diffusion agent and having an uneven surface. Thus, the diffusion sheet 43 is not limited to the form shown in Figure 3. For example, the diffusion sheet may be a single-layer structure with an uneven surface, or a structure of three or more layers including a layer with an uneven surface. Furthermore, the uneven surface layer is not limited to a two-dimensional arrangement of inverted pyramidal recesses as described above, but may be arranged with randomly placed recesses.

[0042] The first prism sheet 44 and the second prism sheet 45 are, for example, films in which multiple grooves with isosceles triangular cross-sections are formed adjacent to each other, and the apex angle of the prism sandwiched between adjacent pairs of grooves is formed to be approximately 90°. Here, each groove formed on the first prism sheet 44 and each groove formed on the second prism sheet 45 are arranged to be perpendicular to each other. The first prism sheet 44 and the second prism sheet 45 may be formed integrally. As the first prism sheet 44 and the second prism sheet 45, for example, a PET (polyethylene terephthalate) film may be used with a prism shape formed using a UV-curable acrylic resin.

[0043] For example, the DBEF series manufactured by 3M may be used as the polarizing sheet 46. The polarizing sheet 46 improves the brightness 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.

[0044] As shown in Figure 4, the light emitted from the miniature light source 42 is diffused by the uneven layer 22 and the diffusing agent 21a as it passes through the two-layer laminate of the diffusion sheet 43. As a result, the brightness is suppressed in the area directly above the miniature light source 42. However, if the backlight unit 40 is made thinner by reducing the distance between the miniature light source 42 and the diffusion sheet 43 or by reducing the thickness of the diffusion sheet 43, or if the number of miniature light sources 42 is reduced to reduce costs, a decrease in brightness will occur in areas such as the inter-light source region (area where no light source is placed) R, as shown in Figure 4. Note that in Figure 4 and Figure 5 described later, the light that has passed through the diffusion sheet 43 is indicated by an arrow, and the length of this arrow represents the intensity of the light, i.e., the brightness. Also, the diffusing agent 21a is not shown in Figures 4 and 5.

[0045] Therefore, in this embodiment, as shown in Figure 5, a brightness-enhancing member 25 is provided in the light-source region R on the surface of the uneven-shaped layer 22 of the upper diffusion sheet 43, such that the recesses 22a of the uneven-shaped layer 22 are filled, thereby improving the total light transmittance of the light-source region R. In other words, the total light transmittance of the light-source region R with the brightness-enhancing member 25 is higher than when the brightness-enhancing member 25 is not provided. The brightness-enhancing member 25 may be made of, for example, a transparent ink that can be dot-printed. The refractive index difference between the diffusion layer 21 and the uneven-shaped layer 22 constituting the diffusion sheet 43 and the brightness-enhancing member 25 is preferably small, but may be about 0.3 or less. For example, if the matrix resin of the diffusion layer 21 and the uneven-shaped layer 22 is polycarbonate, a medium may be used as the transparent ink for the brightness-enhancing member 25. As the medium, for example, either a UV-curing type or a thermosetting type may be used.

[0046] Other UV-curing resins such as urethane acrylate and acrylic resin may be used as the brightness-enhancing member 25. Specifically, UV-curing polyester acrylate, UV-curing epoxy acrylate, UV-curing polyol acrylate, etc. may be used as the acrylic resin. Alternatively, thermosetting resins such as phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, silicon resin, alkyd resin, polyimide, polyaminobismaleimide, casein resin, furan resin, and urethane resin may be used as the brightness-enhancing member 25.

[0047] In the example shown in Figure 5, the brightness-enhancing member 25 is provided so that the recess 22a in the light source region R is completely filled. However, the example is not limited to this, and the brightness-enhancing member 25 may be provided so that the recess 22a in the light source region R is at least partially filled.

[0048] Furthermore, in the example shown in Figure 5, the brightness-enhancing member 25 is provided in all inter-light source regions R of the diffusion sheet 43, but instead, the brightness-enhancing member 25 may be provided in only some inter-light source regions R of the diffusion sheet 43.

[0049] Furthermore, in the example shown in Figure 5, the brightness-enhancing member 25 is provided over the entire inter-light source region R in the diffusion sheet 43. Alternatively, the brightness-enhancing member 25 may be provided over only a portion of the inter-light source region R in the diffusion sheet 43.

[0050] According to the embodiment described above, a brightness-enhancing member 25 is provided in a predetermined area on the surface of the uneven-shaped layer 22 of the diffusion sheet 43, specifically in the area R between light sources where brightness reduction is likely to occur, such that the recesses 22a of the uneven-shaped layer 22 are at least partially filled, thereby improving the total light transmittance of the area R. As a result, the brightness of the area R is increased, making it possible to improve brightness uniformity in the liquid crystal display device 50 while avoiding a decrease in brightness across the entire screen. Therefore, the diffusion sheet 43 of this embodiment can also accommodate further thinning of the backlight and reduction of the number of light sources.

[0051] Furthermore, in this embodiment, if the brightness-enhancing member 25 is made of transparent ink, the brightness of a predetermined area can be increased by a simple method of printing transparent ink into the recesses 22a of a predetermined area. In this case, if the transparent ink is a medium and the matrix resin constituting the diffusion sheet 43 is polycarbonate, the total light transmittance of a predetermined area can be improved simply by providing transparent ink in the recesses 22a of a predetermined area. Also, in this case, if the brightness-enhancing member 25 is formed by dot printing of transparent ink, it becomes easier to adjust the total light transmittance of a predetermined area.

[0052] Furthermore, in this embodiment, if the refractive index difference between the diffusion sheet 43 (diffusion layer 21 and uneven-shaped layer 22) and the brightness-enhancing member 25 is 0.3 or less, the brightness of a predetermined area can be increased by the brightness-enhancing member 25 without being affected by light diffusion at the interface between the diffusion sheet 43 and the brightness-enhancing member 25.

[0053] Furthermore, in this embodiment, if the diffusion sheet 43 (diffusion layer 21) contains a diffusion agent 21a, the brightness uniformity is further improved.

[0054] Furthermore, in this embodiment, if the recesses 22a of the uneven-shaped layer 22 have a concave pyramidal shape, the brightness uniformity is further improved.

[0055] Furthermore, in this embodiment, if the surface 21b opposite to the uneven-shaped layer 22 of the diffusion sheet 43 (diffusion layer 21) has an embossed shape, the brightness uniformity is further improved.

[0056] Furthermore, in this embodiment, if a predetermined region (specifically, the inter-light source region R) on the surface of the uneven-shaped layer 22 of the diffusion sheet 43 where the brightness-enhancing member 25 is provided is flatter than other regions where the brightness-enhancing member 25 is not provided, the total light transmittance of the predetermined region can be further improved compared to the other regions.

[0057] Furthermore, the backlight unit 40 equipped with the diffusion sheet 43 of this embodiment can improve brightness uniformity while avoiding a decrease in brightness across the entire screen.

[0058] Furthermore, in the backlight unit 40, if the brightness-enhancing member 25 is placed in the intermediate region between adjacent light sources 42 among the multiple light sources 42, that is, in the inter-light source region R, the brightness of the inter-light source region R, where brightness reduction is likely to occur, can be increased.

[0059] Furthermore, in the backlight unit 40, even in configurations where the distance between the multiple light sources 42 and the diffusion sheet 43 is 10 mm or less, making it more likely for brightness reduction to occur in the inter-light source region R, the brightness enhancement member 25 can improve brightness uniformity.

[0060] Furthermore, if the backlight unit 40 has multiple light sources 42 that are LED elements, sufficient brightness can be obtained across the entire screen even if the number of light sources is reduced.

[0061] Furthermore, if multiple light sources 42 are arranged regularly in the backlight unit 40, the uniformity of brightness is further improved.

[0062] Furthermore, in the backlight unit 40, if multiple light sources 42 are arranged on a reflective sheet 41 provided on the opposite side of the diffusion sheet 43, the uniformity of brightness is further improved.

[0063] Furthermore, a liquid crystal display device 50 equipped with a backlight unit 40, or an information device equipped with a liquid crystal display device 50, can improve brightness uniformity while avoiding a decrease in brightness across the entire screen.

[0064] In this embodiment, the brightness-enhancing member 25 is provided in the region R between light sources, but the invention is not limited to this, and the brightness-enhancing member 25 may also be provided in a region such as the sheet edge where the brightness is relatively reduced in the backlight unit 40. For example, if a decrease in brightness occurs at the periphery of a rectangular display screen, the brightness-enhancing member 25 may be arranged along the periphery of the diffusion sheet 43 corresponding to the screen shape, as shown in Modification 1 in Figure 6. Alternatively, if a light source cannot be placed at the corner of a track-shaped display screen and a decrease in brightness occurs, the brightness-enhancing member 25 may be placed at the corner of the diffusion sheet 43, as shown in Modification 2 in Figure 7.

[0065] Furthermore, in this embodiment, the brightness-enhancing member 25 is provided on the surface of the uneven-shaped layer 22 of the upper diffusion sheet 43, but instead of this, or in addition to this, the brightness-enhancing member 25 may be provided on the surface of the uneven-shaped layer 22 of the lower diffusion sheet 43.

[0066] Furthermore, in this embodiment, the number of miniature light sources 42 is not particularly limited, but when multiple miniature light sources 42 are distributed, it is preferable to arrange them regularly on the reflective sheet 41. Arranging them regularly means arranging them according to a certain rule, for example, when the miniature light sources 42 are arranged at equal intervals. When the miniature light sources 42 are arranged at equal intervals, the distance between the centers of two adjacent miniature light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less. If the distance between the centers of two adjacent miniature light sources 42 is 0.5 mm or more, a phenomenon in which the brightness is lower in the region between adjacent miniature light sources 42 than in other regions (brightness unevenness) is likely to occur, so the usefulness of applying the brightness-enhancing member 25 increases.

[0067] Furthermore, in this embodiment, an uneven shape (recess 22a) is provided on the upper surface of the diffusion sheet 43 (the surface on the first prism sheet 44 side), but the uneven shape only needs to be provided on at least one surface of the diffusion sheet 43. That is, the uneven shape may be provided on the lower surface (the surface on the small light source 42 side) or on both sides (the upper and lower surfaces) of the diffusion sheet 43.

[0068] Furthermore, the uneven shape provided on the surface of the diffusion sheet 43 is not particularly limited, and may be, for example, a mat shape with random pitch, arrangement, shape, etc., or a shape in which multiple protrusions and recesses are regularly arranged in two dimensions.

[0069] Furthermore, the uneven surface of the diffusion sheet 43 may include a polygonal pyramid or a shape that can approximate a polygonal pyramid. Here, as the "polygonal pyramid," a triangular pyramid, a square pyramid, or a hexagonal pyramid that can be arranged without gaps on the surface of the diffusion sheet 43 is preferred. In addition, a mold (metal roll) is used in the manufacturing process such as extrusion molding or injection molding when creating the uneven surface of the diffusion sheet 43, and a square pyramid may be selected as the "polygonal pyramid" considering the precision of the cutting work on the surface of this mold (metal roll).

[0070] Examples of the shape of the convex portion include a hemisphere (upper half), a cone, a triangular pyramid, a square pyramid, a hexagonal pyramid, etc., and examples of the shape of the concave portion include a hemisphere (lower half), an inverted cone, an inverted triangular pyramid, an inverted square pyramid, an inverted hexagonal pyramid, etc.

[0071] Furthermore, examples of the shape of the convex portion include a roughly hemisphere (upper half), a roughly cone, a roughly triangular pyramid, a roughly square pyramid, a roughly hexagonal pyramid, etc., and examples of the shape of the concave portion include a roughly hemisphere (lower half), a roughly inverted cone, a roughly inverted triangular pyramid, a roughly inverted square pyramid, a roughly inverted hexagonal pyramid, etc. Here, "roughly" means that it is possible to approximate it, and for example, "roughly square pyramid" refers to a shape that can be approximated to a square pyramid. However, considering the precision required for industrial production, the convex and concave portions may also be deformed shapes from a roughly hemisphere (upper or lower half), a roughly cone (roughly inverted cone), a roughly triangular pyramid (roughly inverted triangular pyramid), or a roughly square pyramid (roughly inverted square pyramid), and there may be unavoidable variations in shape due to the processing precision required for industrial production.

[0072] When multiple protrusions and recesses are regularly arranged in a two-dimensional manner on the surface of the diffusion sheet 43, the multiple protrusions and recesses may be provided without gaps across the entire surface of the diffusion sheet 43, or they may be provided at regular intervals (pitch), or at random intervals.

[0073] Furthermore, in this embodiment, the material of the diffusion agent 21a contained in the diffusion sheet 43 (diffusion layer 21) is not particularly limited, but inorganic particles such as silica, titanium oxide, aluminum hydroxide, and barium sulfate may be used, and organic particles such as acrylic, acrylonitrile, silicone, polystyrene, and polyamide may be used.

[0074] The particle size of the diffusing agent 21a may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less) from the viewpoint of light diffusion effect.

[0075] Regarding the content of the diffusing agent 21a, from the viewpoint of light diffusion effect, the amount 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), with the material (matrix) constituting the diffusion layer 21 being 100% by mass. Alternatively, instead of the diffusion layer 21, a substrate layer that does not contain the diffusing agent 21a, such as a substrate layer made of clear polycarbonate, may be used.

[0076] The difference between the refractive index of the diffusing agent 21a and the refractive index of the matrix of the diffusion layer 21 may be 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and most preferably 0.15 or more. If the difference between the refractive index of the diffusing agent 21a and the refractive index of the matrix of the diffusion layer 21 is less than 0.01, the diffusion effect by the diffusing agent 21a will be insufficient.

[0077] The resin that forms the matrix of the diffusion layer 21 is not particularly limited as long as it is a light-transmitting material, but for example, acrylic, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. may be used.

[0078] The thickness of the diffusion sheet 43 in this embodiment 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, and even more preferably 1 mm or less) and 0.1 mm or more. If the thickness of the diffusion sheet 43 exceeds 3 mm, it becomes difficult to achieve a thinner liquid crystal display. On the other hand, if the thickness of the diffusion sheet 43 is less than 0.1 mm, it becomes difficult to achieve the aforementioned effect of improving brightness uniformity.

[0079] In the case of a multilayer structure (lower diffusion layer 21 and upper uneven-shaped layer 22) as in the diffusion sheet 43 of this embodiment, the thickness of the layer on which the uneven shape is provided (uneven-shaped layer 22) is greater than the maximum height or maximum depth of the uneven shape. For example, in the case of a layer on which a protrusion (or recess) with a height (or depth) of 20 μm is provided, the thickness is greater than 20 μm.

[0080] In this specification, "optical sheet" means a sheet having various optical functions such as diffusion, focusing, refraction, and reflection. As described above, the diffusion sheet 43 of this embodiment has a ridged layer 22 on a diffusion layer 21, but instead, the diffusion sheet 43 may be made of a single layer structure containing a diffusing agent and having a ridged shape on its surface. Alternatively, the diffusion sheet 43 may be made of a structure of three or more layers including a diffusion layer 21 and a ridged layer 22. Alternatively, the diffusion layer 21 and the ridged layer 22 may be made of separate diffusion sheets and stacked together, or they may be placed separately. In the latter case, the ridged layer 22 may be placed on the side of the small light source 42. Alternatively, the diffusion sheet 43 may be made of only the diffusion layer 21, and a ridged shape may be provided on the lower surface of the first prism sheet 44. In other words, an uneven surface is provided on one of the optical sheets constituting the backlight unit 40, and the brightness-enhancing member 25 may be provided such that the recesses of the uneven surface are at least partially filled in a predetermined region where the brightness of the optical sheet is relatively reduced.

[0081] The manufacturing method for the diffusion sheet 43 is not particularly limited, but for example, an extrusion molding method or an injection molding method may be used. The procedure for manufacturing a single-layer diffusion sheet having an uneven surface shape using the extrusion molding method is as follows. First, pellet-shaped plastic particles to which a diffusion agent has been added (a mixture of pellet-shaped plastic particles without a diffusion agent may also be used) are fed into a single-screw extruder and melted and kneaded while being heated. After that, the molten resin extruded by a T-die is cooled by being sandwiched between two metal rolls, then conveyed using guide rolls, and cut into a single sheet using a sheet cutter to produce a diffusion sheet. Here, by sandwiching the molten resin using metal rolls that have a shape on the surface that is an inverse of the desired uneven shape, the inverse shape of the roll surface is transferred to the resin, so that the desired uneven shape can be formed on the surface of the diffusion sheet. Also, the shape transferred to the resin is not necessarily a 100% transfer of the shape of the roll surface, so the shape of the roll surface may be designed by working backward from the degree of transfer.

[0082] When manufacturing a two-layer diffusion sheet with an uneven surface using the extrusion molding method, for example, pellet-shaped plastic particles necessary for forming each layer can be placed into each of two single-screw extruders, and then the same procedure as described above can be performed for each layer, after which the resulting sheets can be stacked.

[0083] Alternatively, a two-layer diffusion sheet with an uneven surface may be produced as follows: First, pellet-shaped plastic particles necessary for forming each layer are fed into each of two single-screw extruders, and the mixture is heated, melted, and kneaded. Then, the molten resin for each layer is fed into a single T-die, and the layers are laminated within the T-die. The laminated molten resin extruded by the T-die is then cooled by being sandwiched between two metal rolls. After that, the laminated molten resin is conveyed using guide rolls and cut into flat sheets using a sheet cutter to produce a two-layer diffusion sheet with an uneven surface.

[0084] Alternatively, the diffusion sheet 43 may be manufactured by shape transfer using UV (ultraviolet) light as follows: First, an uncured UV-curable resin is filled into a roll having an inverted shape of the uneven surface to be transferred, and the substrate is pressed against the resin. Next, with the roll filled with UV-curable resin and the substrate as one unit, the resin is cured by irradiating it with ultraviolet light. Next, the sheet on which the uneven surface has been transferred by the resin is peeled off the roll. Finally, the sheet is irradiated with ultraviolet light again to completely cure the resin, and a diffusion sheet with an uneven surface is produced.

[0085] Furthermore, in this embodiment, a direct-type backlight unit is used as the backlight unit 40, in which a plurality of small light sources 42 are distributed on the back side of the display screen 50a of the liquid crystal display device 50. Therefore, in order to miniaturize the liquid crystal display device 50, it is necessary to reduce the distance between the small light sources 42 and the diffusion sheet 43. However, if this distance is reduced, a phenomenon (brightness unevenness) is more likely to occur in which the brightness of the display screen 50a in the area located in the region between the distributed small light sources 42 is lower than in other parts.

[0086] In contrast, as mentioned above, using a diffusion sheet in which brightness-enhancing members 25 are provided in areas where brightness reduction occurs is useful in suppressing brightness unevenness. In particular, with an eye on the future thinning of small and medium-sized liquid crystal displays, the usefulness of this disclosure is expected to become even more pronounced when the distance between the small light source and the diffusion sheet is 15 mm or less, preferably 10 mm or less, more preferably 5 mm or less, even more preferably 2 mm or less, and ultimately 0 mm.

[0087] (Examples and Comparative Examples) The diffusion sheets for the examples and comparative examples will be described below with reference to the drawings. Figures 8A to 8F are cross-sectional views of the diffusion sheets for Examples 1 to 6, respectively.

[0088] As shown in Figures 8A to 8F, the diffusion sheets 43 according to Examples 1 to 6 have a 160 μm thick base layer 23 made of polycarbonate, with an uneven surface (opposite the light source) 23a having a concave pyramidal recess 24, and an embossed surface (light source side) 23b. The depth and arrangement pitch of the recesses 24 are 50 μm and 100 μm, respectively. Although not shown in the figures, the base layer 23 contains a diffusing agent.

[0089] Furthermore, as shown in Figures 8A to 8F, in the diffusion sheets 43 according to Examples 1 to 6, the aforementioned brightness-enhancing members 25 are provided in the recesses 24 by printing dots with a diameter of 80 μm on the surface 23a side of the substrate layer 23 using a transparent ink made of medium, with area ratios of 4%, 10%, 30%, 50%, 65%, and 100%, respectively. Here, "area ratio" is a parameter in the settings of the printing press that performs the dot printing, and does not necessarily correspond to the area ratio of the transparent ink on the surface 23a of the substrate layer 23. Note that dot printing with an area ratio of 100% is what is known as solid printing. In addition, although not shown in the figures, a diffusion sheet was prepared as "Comparative Example 1" using the same substrate layer 23 as the diffusion sheets 43 according to Examples 1 to 6, but without transparent ink dot printing (i.e., without the brightness-enhancing members 25).

[0090] Table 1 below shows the haze and total light transmittance (relative values ​​when the transmittance of Comparative Example 1 without dot printing is set to "1") for each of the diffusion sheets 43 according to Examples 1 to 6 and the diffusion sheet of Comparative Example 1, when light is incident perpendicularly from the back surface 23b side of the substrate layer 23, along with the area ratio of the dot printing. Here, the haze and total light transmittance of each diffusion sheet were measured with a haze meter HZ-2 manufactured by Suga Test Instruments Co., Ltd.

[0091] [Table 1]

[0092] As shown in Table 1, the total light transmittance increases as the area ratio of the dot printing of the transparent ink that forms the brightness-enhancing member 25 increases. On the other hand, even when the area ratio of the dot printing of the transparent ink that forms the brightness-enhancing member 25 increases, the decrease in haze (diffusivity) is suppressed. For example, in the solid printing of Example 6, the transmittance increased by 68% compared to the unprinted product of Comparative Example 1, while the decrease in haze was only 1.7%. Also, in the dot printing with an area ratio of 4% of Example 1, the transmittance increased significantly by 10% compared to the unprinted product of Comparative Example 1, while the decrease in haze was only 0.2%. In actual backlights, other optical films such as prism sheets are also laminated on top of these diffusion sheets, so the increase in total light transmittance does not directly translate to an increase in brightness. However, it goes without saying that the higher the total light transmittance, the higher the brightness. Therefore, by adjusting the area ratio of the dot printing, it is possible to easily form a brightness-enhancing member 25 with a total light transmittance corresponding to the degree of brightness reduction in the region where brightness reduction occurs. In other words, by first investigating the areas where brightness reduction occurs and the degree of brightness reduction, and then printing dots of transparent ink in those areas on the diffusion sheet 43 at an area ratio corresponding to the degree of brightness reduction to form the brightness-enhancing member 25, brightness uniformity can be improved.

[0093] Tables 2 and 3 show the measurement results for the arithmetic mean roughness Ra and maximum heights Rz and Ry of the surface 23a of the substrate layer 23 in the diffusion sheet (unprinted) of Comparative Example 1 and the diffusion sheet 43 (solid print) of Example 6, respectively.

[0094] [Table 2]

[0095] [Table 3]

[0096] The measurements of Ra, Rz, and Ry shown in Tables 2 and 3 were performed in accordance with JIS B0606-1994 using a contact-type surface roughness meter SJ-210 (manufactured by Mitutoyo). The measurement speed was set to 0.5 mm / s, the measurement distance to 4 mm, and the cutoff value λc to 0.8 mm. Measurements were performed at 10 different locations (N1 to N10) along the direction parallel to the arrangement direction of the recesses 24 formed in a roughly inverted square pyramid. The average and maximum values ​​of the measured values ​​of Ra, Rz, and Ry are also shown in Tables 2 and 3.

[0097] As shown in Figure 9, on the surface of the substrate layer 23, adjacent recesses (concave square pyramids) 24 are demarcated by edges 24a. Therefore, in the absence of the brightness-enhancing material 25 (printing), if the measurement cross-section passes through the valleys 24b of the recesses (concave square pyramids) 24, the surface becomes rough (Figure 9(A)). On the other hand, if the measurement cross-section deviates from the valleys 24b of the recesses (concave square pyramids) 24, the surface becomes smoother (Figure 9(B)). Thus, as shown in Tables 2 and 3, Ra, Rz, and Ry measurements were performed at multiple locations, and the surface roughness was evaluated based on the average and maximum values ​​of the measured values.

[0098] Compared to the average and maximum values ​​of Ra, Rz, and Ry for Comparative Example 1 (no printing) shown in Table 2, the average and maximum values ​​of Ra, Rz, and Ry for Example 6 (solid printing) shown in Table 3 are smaller. This indicates that by providing the brightness-enhancing member 25 (printing), the resin of the ink is filled into the recesses (concave square pyramids) 24, making the surface of the substrate layer 23 smooth.

[0099] While embodiments (including examples; hereinafter the same) of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the disclosure. In other words, the description of the embodiments described above is essentially illustrative and is not intended to limit the present disclosure, its applications, or its uses.

[0100] For example, in the embodiment described above, transparent ink was used as the brightness-enhancing member 25, but the invention is not limited to this. Any highly transparent material that can improve the total light transmittance by filling the recesses of the diffusion sheet 43 can be used as the brightness-enhancing member 25. As such a highly transparent material, for example, a white pigment consisting of inorganic substances such as alumina, titanium oxide, barium sulfate, zinc oxide, and calcium carbonate, or urea-based organic substances, dispersed in a vehicle (varnish: resin dissolved in a solvent) can be used. Furthermore, it goes without saying that the method for forming the brightness-enhancing member 25 is not limited to dot printing, and known pattern forming methods may also be used. [Explanation of Symbols]

[0101] 1 TFT substrate 2 CF boards 3. Liquid crystal layer 5. LCD display panel 6. First polarizing plate 7. Second polarizing plate 21 Diffusion layer 21a Diffusing agent 21b Bottom side 22 Concave and convex layer 22a Recess 23 Base material layer 23a surface 23b Back side 24 recesses 25 Brightness-enhancing material 40 Backlight Units 41 Reflective sheet 42 Small light source 43 Diffusion Sheet 44. First Prism Sheet 45. Second prism sheet 46 Polarizing Sheet 50 LCD display device 50a display screen

Claims

1. A diffusion sheet incorporated into a liquid crystal display device in which multiple light sources are dispersed on the back side of the display screen, One surface of the diffusion sheet has an uneven shape, The aforementioned uneven shape is formed by a two-dimensional arrangement of recesses that diffuse light. A brightness-enhancing member is provided in a predetermined area on one surface of the diffusion sheet, such that the recesses of the uneven shape are at least partially filled, thereby suppressing the diffusion of light in the predetermined area and improving the total light transmittance. The recess has a concave pyramidal shape, The diffusion sheet is positioned above the plurality of light sources. The predetermined region is the region between light sources where the plurality of light sources are not arranged, or the peripheral edge or corner of the diffusion sheet. Diffusion sheet.

2. The refractive index difference between the diffusion sheet and the brightness-enhancing member is 0.3 or less. The diffusion sheet according to claim 1.

3. The aforementioned diffusion sheet contains a diffusion agent. The diffusion sheet according to claim 1 or 2.

4. The other side of the diffusion sheet has an embossed shape. A diffusion sheet according to any one of claims 1 to 3.

5. The predetermined region on one surface of the diffusion sheet where the brightness-enhancing member is provided is flatter than other regions on the same surface of the diffusion sheet where the brightness-enhancing member is not provided. A diffusion sheet according to any one of claims 1 to 4.

6. The brightness-enhancing member is made of transparent ink. A diffusion sheet according to any one of claims 1 to 5.

7. The transparent ink is a medium, The matrix resin constituting the diffusion sheet is polycarbonate. The diffusion sheet according to claim 6.

8. A backlight unit incorporated into the liquid crystal display device, which guides light emitted from the plurality of light sources to the display screen side, The plurality of light sources, A diffusion sheet according to any one of claims 1 to 7 is provided above the plurality of light sources, The system comprises a prism sheet provided above the diffusion sheet, Backlight unit.

9. The brightness-enhancing member is positioned in the intermediate region between adjacent light sources among the plurality of light sources. The backlight unit according to claim 8.

10. The distance between the multiple light sources and the diffusion sheet is 10 mm or less. The backlight unit according to claim 8 or 9.

11. The aforementioned multiple light sources are LED elements. The backlight unit according to any one of claims 8 to 10.

12. The aforementioned multiple light sources are arranged regularly. The backlight unit according to any one of claims 8 to 11.

13. The aforementioned multiple light sources are arranged on a reflective sheet provided on the opposite side of the diffusion sheet. A backlight unit according to any one of claims 8 to 12.

14. A backlight unit according to any one of claims 8 to 13, Equipped with a liquid crystal display panel, LCD display device.

15. A liquid crystal display device according to claim 14, Information equipment.

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