WO2023281925A1 - 光拡散シート、バックライトユニット、液晶表示装置、情報機器、及び光拡散シートの製造方法 - Google Patents
光拡散シート、バックライトユニット、液晶表示装置、情報機器、及び光拡散シートの製造方法 Download PDFInfo
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- WO2023281925A1 WO2023281925A1 PCT/JP2022/020856 JP2022020856W WO2023281925A1 WO 2023281925 A1 WO2023281925 A1 WO 2023281925A1 JP 2022020856 W JP2022020856 W JP 2022020856W WO 2023281925 A1 WO2023281925 A1 WO 2023281925A1
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- Prior art keywords
- light diffusion
- diffusion sheet
- luminance
- brightness
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Classifications
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- F21—LIGHTING
- F21S—NON-PORTABLE LIGHTING DEVICES; SYSTEMS THEREOF; VEHICLE LIGHTING DEVICES SPECIALLY ADAPTED FOR VEHICLE EXTERIORS
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- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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- G02F1/1333—Constructional arrangements; Manufacturing methods
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- G02F1/133606—Direct backlight including a specially adapted diffusing, scattering or light controlling members
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- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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Definitions
- the present disclosure relates to a light diffusion sheet, a backlight unit, a liquid crystal display device, information equipment, and a method for manufacturing a light diffusion sheet.
- Liquid crystal display devices are widely used as display devices for various information devices such as smartphones and tablet terminals.
- a backlight for a liquid crystal display device a direct type in which a light source is arranged on the back surface of a liquid crystal panel or an edge light type in which a light source is arranged in the vicinity of a side surface of the liquid crystal panel is mainly used.
- a light diffusing member (light diffusing plate, light diffusing sheet, light diffusion film) is used.
- the thickness of the light diffusion sheet and the distance between the light source and the light diffusion sheet are reduced, and the number of light sources is reduced to reduce costs.
- the luminance may be lowered in regions where there is no such arrangement.
- An object of the present disclosure is to provide a light diffusion sheet that can improve luminance uniformity while avoiding a decrease in luminance over the entire screen in a liquid crystal display device.
- a light diffusion sheet according to the present disclosure is a light diffusion sheet incorporated in a liquid crystal display device in which a plurality of point light sources are dispersed on the back side of the display screen.
- At least the first surface of the light diffusion sheet according to the present disclosure has a light diffusion section provided with a plurality of concave portions arranged two-dimensionally, and a plurality of brightness enhancement sections flatter than the light diffusion section.
- the plurality of brightness enhancement portions are arranged in a gradation form such that the lower the brightness in the brightness distribution generated by the plurality of point light sources, the higher the arrangement density. be provided.
- the luminance improving portion that is flatter than the light diffusing portion is provided in a region where the luminance decreases in the luminance distribution when the concave portion provided in the light diffusing portion is formed over the entire surface of the sheet. .
- the luminance improving portion is arranged, light diffusibility is suppressed, and as a result, the proportion of straight light that travels straight perpendicularly to the sheet surface increases.
- the luminance improving portions are provided in a gradation such that the arrangement density increases in the luminance distribution described above as the luminance decreases in the region. Therefore, it becomes easy to adjust the area, density, etc. of the portion where the ratio of linear light is increased according to the luminance distribution described above, so that the luminance uniformity can be further improved.
- the low luminance region may be a region between adjacent point light sources among the plurality of point light sources. By doing so, it is possible to increase the luminance in the area between the point light sources and improve the luminance uniformity.
- the low luminance region may be a region directly above the plurality of point light sources. By doing so, it is possible to increase the luminance in the region immediately above the point light source and improve the luminance uniformity.
- the plurality of recesses are also formed in the placement region of the plurality of brightness enhancement portions, and the plurality of brightness enhancement portions are provided in the plurality of recesses of the placement region. It may be constructed from a transparent member.
- the brightness improving portion can be formed by providing the transparent member in the recessed portion of the predetermined region after forming the recessed portion on the entire surface of the sheet.
- each of the transparent members forming the plurality of brightness enhancement portions may fill at least one or more recesses among the plurality of recesses of the arrangement region.
- filling one or more recesses with one transparent member makes it easier to form the brightness improving portion than when a plurality of transparent members are provided in one recess.
- the plurality of recesses are not formed in the arrangement regions of the plurality of brightness enhancement portions, and the plurality of brightness enhancement portions are made of the same material as the light diffusion portion.
- the luminance improving portion can be formed by processing using, for example, a mold, a shaping roll, a laser, or the like, without performing a step of providing a transparent member in the concave portion.
- the plurality of concave portions may have an inverted polygonal pyramid shape, an inverted polygonal truncated pyramid shape, or a lower hemispherical shape. By doing so, the light diffusibility of the light diffusing portion can be improved.
- a backlight unit according to the present disclosure is a backlight unit that is incorporated in the liquid crystal display device and guides light emitted from the plurality of point light sources toward the display screen, wherein the display screen and the plurality of point light sources and the light diffusion sheet according to the present disclosure described above.
- the backlight unit according to the present disclosure since the light diffusion sheet according to the present disclosure is provided, it is possible to improve brightness uniformity while avoiding a decrease in brightness over the entire screen.
- the distance between the plurality of point light sources and the light diffusion sheet may be 2 mm or less. It is possible to improve the luminance uniformity even in such a configuration where the luminance distribution tends to vary with the conventional light diffusion sheet.
- the plurality of point light sources may be LED elements. In this way, even if the number of light sources is reduced, sufficient brightness can be obtained over the entire screen.
- the plurality of point light sources may be arranged on a reflecting member provided on the opposite side of the display screen when viewed from the light diffusion sheet. By doing so, the luminance uniformity is further improved.
- a liquid crystal display device includes the aforementioned backlight unit according to the present disclosure and a liquid crystal display panel.
- the backlight unit according to the present disclosure since the backlight unit according to the present disclosure is provided, it is possible to improve brightness uniformity while avoiding a decrease in brightness over the entire screen.
- the information equipment according to the present disclosure includes the above-described liquid crystal display device according to the present disclosure.
- the liquid crystal display device according to the present disclosure since the liquid crystal display device according to the present disclosure is included, it is possible to improve brightness uniformity while avoiding a decrease in brightness over the entire screen.
- a method for manufacturing a light diffusion sheet according to the present disclosure is a method for manufacturing a light diffusion sheet incorporated in a liquid crystal display device in which a plurality of point light sources are dispersed on the back side of the display screen. At least the first surface of the light diffusing sheet has a light diffusing portion in which a plurality of concave portions are provided two-dimensionally, and a plurality of brightness improving portions that are flatter than the light diffusing portion.
- a method for manufacturing a light diffusion sheet includes a step A of calculating a luminance distribution generated by the plurality of point light sources when the plurality of recesses are formed on the entire first surface; a step B of forming on the first surface; and the plurality of luminance improving portions are formed on the first surface in a gradation manner so that an arrangement density of the plurality of luminance improving portions increases as the luminance decreases in the luminance distribution calculated in the step A. and Step C of forming.
- a luminance improving portion that is flatter than the light diffusion portion is provided in a region where luminance decreases in the luminance distribution when the concave portion provided in the light diffusion portion is formed on the entire surface of the sheet.
- the luminance improving portions are provided in a gradation manner so that the arrangement density increases in areas with lower luminance in the luminance distribution described above. Therefore, it becomes easy to adjust the area, density, etc. of the portion where the ratio of linear light is increased according to the luminance distribution described above, so that the luminance uniformity can be further improved.
- the step B includes a step of forming the plurality of concave portions also in the arrangement region of the plurality of luminance improving portions, and the step C is performed after the step B. and forming the plurality of brightness enhancement portions by providing a transparent member in the plurality of recesses of the arrangement region.
- the brightness improving portion can be formed by providing the transparent member in the recessed portion of the predetermined region after forming the recessed portion on the entire surface of the sheet.
- the process B and the process C may be performed at the same time.
- the number of processes can be reduced by simultaneously performing the process B and the process C by processing using a mold, a shaped roll, a laser, or the like.
- FIG. 1 is a cross-sectional view of a liquid crystal display device according to an embodiment
- FIG. 4 is a cross-sectional view of the backlight unit according to the embodiment
- FIG. It is a sectional view of a light diffusion part of a light diffusion sheet concerning an embodiment. It is a perspective view of the light-diffusion part of the light-diffusion sheet which concerns on embodiment.
- FIG. 4 is a cross-sectional view of a brightness improving portion of the light diffusion sheet according to the embodiment
- FIG. 4 is a plan view showing the layout pattern of the luminance improving portions of the light diffusion sheet according to the embodiment
- FIG. 5 is a plan view showing an arrangement pattern of luminance improving portions of a light diffusion sheet according to a comparative example;
- FIG. 11 is a plan view showing an arrangement pattern of luminance improving portions of a light diffusion sheet according to a modification;
- FIG. 11 is a plan view showing an arrangement pattern of luminance improving portions of a light diffusion sheet according to a modification;
- FIG. 11 is a plan view showing an arrangement pattern of luminance improving portions of a light diffusion sheet according to a modification;
- 4 is a photograph showing a planar configuration of a light diffusion sheet according to an example. It is a figure which shows the surface shape of the light-diffusion sheet which concerns on an Example. It is a figure which shows the luminance distribution of the light-diffusion sheet which concerns on an Example. It is a figure which shows the luminance distribution of the light-diffusion sheet which concerns on a comparative example.
- the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, and a second polarizing plate attached to the upper surface of the liquid crystal display panel 5. 7 and a backlight unit 40 provided on the back side of the liquid crystal display panel 5 with the first polarizing plate 6 interposed therebetween.
- the liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 facing each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and the TFT substrate 1 and the CF substrate 2.
- a frame-shaped sealing material (not shown) is provided to seal the liquid crystal layer 3 between them.
- the shape of the display screen 50a of the liquid crystal display device 50 viewed from the front (upper side in FIG. 1) is, in principle, rectangular or square, but is not limited thereto, and may be a rectangular shape with rounded corners, an elliptical shape, a circular shape, or the like. Any shape such as a trapezoid or an automobile instrument panel (instrument panel) may be used.
- 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 . Thereby, the transmittance of the light incident from the backlight unit 40 through the first polarizing plate 6 is adjusted. The light whose transmittance has been adjusted is emitted through the second polarizing plate 7, and an image is displayed on the display screen 50a.
- the liquid crystal display device 50 of the present embodiment can be used for various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers and tablets, portable game machines, copiers, ticket vending machines, It is used as a display device incorporated in an automatic teller machine, etc.).
- information devices for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers and tablets, portable game machines, copiers, ticket vending machines, It is used as a display device incorporated in an automatic teller machine, etc.).
- 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, and a plurality of TFTs provided in a matrix on the interlayer insulating film. and an alignment film provided 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, and a black matrix and a color filter.
- a common electrode is provided to cover the filter, and an alignment film is provided to cover the common electrode.
- the liquid crystal layer 3 is made of a nematic liquid crystal material or the like containing liquid crystal molecules having electro-optical properties.
- the first polarizing plate 6 and the second polarizing plate 7 each include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers provided to sandwich the polarizer layer.
- the backlight unit 40 includes a reflecting member 41, a plurality of point light sources 42 arranged two-dimensionally on the reflecting member 41, and a sheet laminate provided above the plurality of point light sources 42. 100.
- the sheet laminate 100 has a light diffusion sheet 43 arranged on the side of the point light source 42, and a pair of prism sheets 44 and 45 provided on the upper side of the light diffusion sheet 43 (on the display screen 50a side).
- three light diffusion sheets 43 are laminated and provided in the backlight unit 40 .
- the light diffusing sheet 43 may be used by one sheet, by laminating two sheets, or by laminating four or more sheets. In particular, when the uniformity of luminance can be sufficiently increased by precisely arranging the point light sources 42, one light diffusion sheet 43 may be used.
- the pair of prism sheets 44 and 45 may be a lower prism sheet 44 and an upper prism sheet 45 whose prism stretching directions (directions in which prism ridgelines extend) are orthogonal to each other.
- the reflecting member 41 is made of, for example, a white film made of polyethylene terephthalate resin, a silver-deposited film, or the like.
- the type of the point light source 42 is not particularly limited, it may be, for example, an LED element, a laser element, or the like, and an LED element may be used from the viewpoint of cost, productivity, and the like.
- a lens may be attached to the LED element in order to adjust the light output angle characteristics of the LED element.
- the LED element (chip) may have a rectangular shape when viewed from above, in which case the length of one side is 10 ⁇ m or more (preferably 50 ⁇ m or more) and 20 mm or less (preferably 10 mm or less, more preferably 5 mm). below).
- the LED chips of several mm square may be two-dimensionally alternately arranged on the reflective sheet 41 at regular intervals.
- the center-to-center distance between two adjacent chips may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.
- the point light source 42 may be arranged on the sheet-shaped reflecting member 41 .
- the point light source 42 may be embedded in the reflecting member 41 so that only the light emitting portion of the point light source 42 (for example, the lens attached to the LED element) is exposed.
- the point light source 42 may be a white light source.
- the white light source may be composed of an LED element whose peak wavelength is in the blue region, an LED element whose peak wavelength is in the green region, and an LED element whose peak wavelength is in the red region.
- the point light source 42 may be a blue light source.
- the blue light is converted into light of an arbitrary color (for example, green or red) between the point light source 42 and the light diffusion sheet 43 or between the light diffusion sheet 43 and the lower prism sheet 44.
- a color conversion sheet may be provided.
- the color conversion sheet for example, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used.
- the light diffusion sheet 43 has a base layer 21 .
- the light diffusion sheet 43 (base material layer 21) has a first surface 21a that serves as a light emitting surface and a second surface 21b that serves as a light incident surface. That is, the light diffusion sheet 43 is arranged with the second surface 21 b facing the point light source 42 .
- the resin serving as the matrix of the base material layer 21 is not particularly limited as long as it is composed of a material that transmits light. Examples include acrylic, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, Polyethylene naphthalate, cellulose acetate, polyimide, and the like may also be used.
- the base material layer 21 may contain a diffusing agent and other additives, or may contain substantially no additives.
- Additives that can be contained in the base material layer 21 are not particularly limited. It may be organic particles such as polystyrene, polyamide, and the like.
- the thickness of the 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. If the thickness of the light diffusion sheet 43 exceeds 3 mm, it becomes difficult to reduce the thickness of the liquid crystal display device 50 . If the thickness of the light diffusion sheet 43 is less than 0.1 mm, it becomes difficult to make the brightness uniform.
- the light diffusion sheet 43 may be film-like or plate-like.
- a plurality of recesses 22 having an inverted quadrangular pyramid shape are arranged in a two-dimensional matrix.
- a portion of the light diffusion sheet 43 where the concave portion 22 is provided becomes a light diffusion portion 43A.
- the plurality of recesses 22 may be arranged along two directions orthogonal to each other. Adjacent recesses 22 are separated by ridgelines 111 .
- the ridgeline 111 extends along two directions in which the recesses 22 are arranged.
- the center 112 of the recess 22 (the apex of the inverted pyramid) is the deepest part of the recess 22 .
- the recesses 22 may be provided without gaps, or may be provided at predetermined intervals. Moreover, some recesses 22 may be arranged randomly to the extent that the light diffusion effect is not impaired.
- the apex angle ⁇ of the recesses 22 may be, for example, 90°, the arrangement pitch p of the recesses 22 may be, for example, 100 ⁇ m, and the depth of the recesses 22 may be, for example, 50 ⁇ m.
- the apex angle ⁇ of the recess 22 is a plane perpendicular to the surface on which the light diffusion sheet 43 is arranged, and is a pair of slopes that pass through the center of the recess 22 (apex 112 of the inverted pyramid) and face each other across the center. It is the angle formed by the cross-sectional lines of the slopes in the cross section (longitudinal cross section) that appears when cut across.
- the arrangement pitch p of the recesses 22 is the distance between the centers (the apexes 112 of the inverted pyramids) of the adjacent recesses 22 (the distance along the direction parallel to the arrangement surface of the light diffusion sheet 43). .
- inverted quadrangular pyramid means a true or substantially inverted quadrangular pyramid. It includes not only shapes that can be regarded as pyramids, but also “substantially inverted quadrangular pyramids”. "Substantially” means that it can be approximated, and "substantially inverted quadrangular pyramid” means a shape that can be approximated to an inverted quadrangular pyramid. A shape deformed from the "inverted quadrangular pyramid" within the range of unavoidable variations in shape due to processing accuracy in industrial production is also included in the "substantially inverted quadrangular pyramid".
- the recessed portion 22 in the shape of an inverted square pyramid is formed. The same is true when forming the concave portion 22 of other shape such as a hemisphere.
- the second surface 21b of the light diffusion sheet 43 may be, for example, a flat surface (mirror surface) or an embossed surface. Alternatively, the second surface 21b of the light diffusion sheet 43 may also be provided with an uneven shape in the same manner as the first surface 21a.
- the light diffusion sheet 43 may be configured with a single-layer structure of the base layer 21 having an uneven shape (recesses 22) on the first surface 21a.
- the light diffusing sheet 43 may have a two-layer structure of a substrate layer having flat surfaces on both sides and a layer having unevenness on one surface.
- the light diffusion sheet 43 may have a structure of three or more layers including a layer having unevenness on one surface.
- the first surface 21a of the light diffusion sheet 43 is used as the light emitting surface
- the second surface 21b is used as the light incident surface.
- 21b may be a light exit surface.
- the first surface 21a of the light diffusion sheet 43 has a light diffusion portion 43A provided with a plurality of concave portions 22, and moreover the light diffusion portion 43A It has a plurality of flat brightness enhancement portions 43B.
- the brightness enhancement portion 43B may be provided on at least one light diffusion sheet 43, for example, the light diffusion sheet 43 closest to the display screen 50a.
- the luminance improving portion 43B is provided in the low luminance region R of the luminance distribution generated by the point light source 42 when the concave portions 22 are formed on the entire first surface 21a of the light diffusion sheet 43.
- the low luminance region R may be, for example, a region (inter-light source region) between adjacent point light sources 42 .
- the luminance improving portion 43B may be composed of a transparent member 23 provided in the concave portion 22 of the low luminance region R, as shown in FIG. 5, for example. The details of the brightness enhancement unit 43B will be described later.
- the prism sheets 44 and 45 are made mainly of a transparent (for example, colorless and transparent) synthetic resin because they are required to transmit light rays.
- the prism sheets 44 and 45 may be integrally formed.
- the lower prism sheet 44 has a substrate layer 44a and a row of projections composed of a plurality of ridge prism portions 44b laminated on the surface of the substrate layer 44a.
- the upper prism sheet 45 has a substrate layer 45a and a row of projections composed of a plurality of ridge prism portions 45b laminated on the surface of the substrate layer 45a.
- the ridge prism portions 44b and 45b are laminated in stripes on the surfaces of the substrate layers 44a and 45a, respectively.
- the ridge prism portions 44b and 45b are triangular prisms whose back surfaces are in contact with the surfaces of the substrate layers 44a and 45a, respectively.
- the extension direction of the ridge prism portion 44b and the extension direction of the ridge prism portion 45b are orthogonal to each other.
- the lower limit of the thickness of the prism sheets 44 and 45 (the height from the back surface of the base material layers 44a and 45a to the vertices of the ridge prism portions 44b and 45b) is, for example, about 50 ⁇ m, more preferably about 100 ⁇ m. good.
- the upper limit of the thickness of the prism sheets 44 and 45 may be approximately 200 ⁇ m, more preferably approximately 180 ⁇ m.
- the lower limit of the pitch of the ridge prism portions 44b and 45b on the prism sheets 44 and 45 may be, for example, about 20 ⁇ m, more preferably about 25 ⁇ m.
- the upper limit of the pitch of the prismatic protrusions 44b and 45b on the prism sheets 44 and 45 may be, for example, approximately 100 ⁇ m, more preferably approximately 60 ⁇ m.
- the apex angles of the ridge prism portions 44b and 45b may be, for example, 85° or more and 95° or less.
- the lower limit of the refractive index of the ridge prism portions 44b and 45b may be, for example, 1.5, more preferably 1.55.
- the upper limit of the refractive index of the ridge prism portions 44b and 45b may be, for example, 1.7.
- Prism sheets 44 and 45 are formed by providing ridge prism portions 44b and 45b, which are shape-transferred using a UV curable acrylic resin, on substrate layers 44a and 45a made of, for example, PET (polyethylene terephthalate) film.
- substrate layers 44a and 45a made of, for example, PET (polyethylene terephthalate) film.
- the ridge prism portions 44b and 45b may be formed integrally with the base layers 44a and 45a.
- a polarizing sheet may be provided above the prism sheets 44 and 45 (on the display screen 50a side).
- the polarizing sheet prevents the light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a.
- the backlight unit 40 shown in FIG. 2 the light emitted from the point light source 42 is diffused by the concave portions 22 and the diffusion agent (not shown) when passing through the light diffusion sheet 43 .
- the backlight unit 40 is made thinner by reducing the distance between the point light source 42 and the light diffusion sheet 43 or the thickness of the light diffusion sheet 43, or the number of the point light sources 42 is reduced for cost reduction. If this occurs, the brightness will drop in the low brightness region R such as the region between the light sources (the region where no light source is arranged).
- a luminance improving portion 43B flatter than the light diffusing portion 43A provided with the concave portion 22 is provided in the inter-light source region R on the first surface 21a of the light diffusing sheet 43 of the uppermost layer.
- Arithmetic mean roughness Ra and maximum heights Rz and Ry (JISB0606-1994) of the luminance improving portion 43B are smaller than those of the light diffusing portion 43A.
- the surface of the luminance improving portion 43B may be smooth, or may have unevenness within a range in which the light diffusibility is lower than that of the light diffusing portion 43A.
- the luminance improving portion 43B may be composed of a transparent member 23 provided in the concave portion 22 of the low luminance region R, as shown in FIG. 5, for example.
- each of the transparent members 23 forming each luminance improving portion 43B may fill at least one or more concave portions 22 .
- filling one or more recesses 23 with one transparent member 23 makes it easier to form the brightness improving portion 43B than when a plurality of transparent members 23 are provided in one recess 22. can.
- the transparent member 23 may be a dot-printable transparent ink.
- the luminance improving portion 43B can be formed by a simple method of printing transparent ink.
- the difference in refractive index between the base layer 21 of the light diffusion sheet 43 and the transparent member 23 is preferably as small as possible, but may be about 0.3 or less. By doing so, the luminance of the low luminance region R can be increased without being affected by light diffusion at the interface between the base material layer 21 and the transparent member 23 .
- the transparent member 23 transparent ink
- the medium may for example be of the UV curable type or of the heat curable type.
- UV curable resin such as urethane acrylate and acrylic resin may be used.
- acrylic resin UV-curable polyester acrylate, UV-curable epoxy acrylate, UV-curable polyol acrylate, or the like may be used.
- the transparent member 23 may be made of, for example, phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, silicon resin, alkyd resin, polyimide, polyaminobismaleimide, casein resin, furan resin, urethane resin. You may use thermosetting resins, such as.
- the total light transmittance that is, the brightness
- the area ratio of the dot printing increases as the area ratio of the dot printing increases. Therefore, by adjusting the area ratio of dot printing, it is possible to easily realize the total light transmittance according to the degree of luminance reduction in the low luminance region R.
- the low-luminance region R and the degree of luminance reduction in the low-luminance region R are grasped, and transparent ink dots are formed in the low-luminance region R of the light diffusion sheet 43 at an area ratio corresponding to the degree of luminance reduction.
- color ink for example, white, yellow, or blue color ink
- a concentration range capable of maintaining the transparency necessary for improving brightness, thereby improving chromaticity and the like. Adjustments may be made. Also, particles such as a diffusing agent may be added to the transparent ink to adjust the diffusibility, refractive index, and the like.
- the transparent member 23 is not limited to transparent ink, and other highly transparent materials capable of increasing brightness by filling the recesses 22, such as alumina, titanium oxide, barium sulfate, zinc oxide, calcium carbonate, etc.
- a white pigment made of an inorganic substance or a urea-based organic substance dispersed in a vehicle (varnish: resin dissolved in a solvent) can also be used.
- the brightness improving portion 43B (the transparent member 23) is provided so as to completely fill the recess 22 of the low brightness region R. 43B may be provided.
- the brightness improving section 43B may be provided in all the low brightness regions R, or may be provided in some of the low brightness regions R.
- the brightness improving part 43B may be provided in the entire low brightness region R, or may be provided in a part of each inter-light source region R.
- the low luminance region R is an inter-light source region between adjacent point light sources 42 .
- the luminance uniformity can be improved by providing the luminance improving portion 43B in the inter-light-source region that becomes the low-luminance region R.
- FIG. The inter-light source area includes not only the area between the point light sources 42 adjacent to each other along the two directions in which the point light sources 42 are arranged, but also the area in the direction (diagonal direction) inclined with respect to the arrangement direction of the point light sources 42. It also includes areas between point light sources 42 that are adjacent along the line. If the center-to-center distance of the point light sources 42 such as LED elements is 0.5 mm or more, a phenomenon in which the brightness is reduced in the region between the light sources is likely to occur, so the usefulness of providing the brightness improving portion 43B increases.
- the brightness of the sheet edge area is usually relatively likely to decrease.
- the brightness improving portion 43B may be arranged along the periphery of the light diffusion sheet 43 corresponding to the shape of the display screen 50a.
- the luminance improving portion 43B may be arranged at the corner of the light diffusion sheet 43.
- the region directly above the point light source 42 in the light diffusion sheet 43 (hereinafter also referred to as the region directly above the light source) may become a low luminance region R.
- the uniformity of luminance can be improved by providing the luminance improving portion 43B in the area directly above the light source, which is the low luminance area R.
- the area immediately above the light source may be not only the projection area of the point light source 42 on the light diffusing sheet 43 but also an area including its neighborhood and periphery.
- the low-luminance region R is formed according to the luminance distribution (hereinafter, sometimes simply referred to as "luminance distribution") generated by the point light source 42 when the concave portion 22 is formed on the entire first surface 21a. is set as appropriate.
- the brightness improving portions 43B are provided in a gradation such that the arrangement density increases in the brightness distribution in areas with lower brightness.
- FIG. 6 shows an example of an arrangement pattern of the luminance improving portions 43B in the light diffusion sheet 43 of this embodiment.
- FIG. 6 shows an arrangement pattern of the luminance improving portion 43B when 2 ⁇ 2 unit light source regions each having four point light sources 42 each made up of LED elements are provided.
- the dot-shaped luminance improving portions 43B are provided in a gradation manner so that the arrangement density increases as the luminance decreases in the luminance distribution.
- the dot-shaped luminance improving portions 43B are formed by, for example, dot printing with transparent ink. As shown in FIG.
- only the light diffusing portion 43A is arranged in the center of each unit light source region, and the arrangement density of the luminance improving portions 43B increases toward the boundary of each unit light source region.
- the luminance improving portion 43B arranged in the vicinity of the boundary (where the luminance is lowest) of each unit light source region may be linear or solid.
- the dot-shaped brightness enhancement portions 43B and the line-shaped or solid brightness enhancement portions 43B may be mixed.
- shapes that can be recognized as granular shapes such as circles, triangles, squares, etc. are referred to as “dot shapes”, and shapes that can be recognized as linear shapes or wavy shapes are referred to as “line shapes”, and “dot shapes”.
- a shape other than “shape” and “line shape” and having a surface (two-dimensional spread) is referred to as "solid (meaning solid in solid printing) shape”.
- FIG. 7 shows an example of the arrangement pattern of the luminance improving portions 43B in the light diffusion sheet 43 according to the comparative example.
- the comparative example shown in FIG. 7 differs from the embodiment shown in FIG. 6 in that a solid luminance improving portion 43B is provided in the low luminance region R around the boundary of the unit light source regions.
- the solid brightness enhancement portion 43B is formed by solid printing with transparent ink. If the brightness improving portion 43B is provided in a solid shape as in the comparative example, it becomes difficult to adjust the area, density, etc. of the portion where the proportion of linear light is increased in accordance with the brightness distribution. Sex gets worse.
- the arrangement pattern of the luminance improving portions 43B is particularly limited. not.
- the luminance improving portion 43B may be provided in a linear shape such as a linear shape or a wavy line shape.
- the line width, length, line spacing, etc. are appropriately set according to the luminance distribution, for example, by adjusting the printing density of the transparent ink, and a plurality of lines having different dimensions may be used.
- the line-shaped brightness enhancement portions 43B and the dot-shaped or solid-shaped brightness enhancement portions 43B may be mixed.
- Both (a) and (b) of FIG. 8 illustrate the case where the inter-light source region between the adjacent point light sources 42 becomes the low luminance region R. As shown in FIG. That is, the arrangement density of the luminance improving portions 43B is high in the inter-light source region, and the arrangement density of the luminance improving portions 43B decreases toward the region directly above the light source.
- the arrangement pattern shown in (b) may also be used.
- the dot shape is not limited to circular, but may be triangular, quadrangular, hexagonal, or other shapes, or dots may have a plurality of different shapes.
- the dot size, dot spacing, and the like are appropriately set according to the luminance distribution, for example, by adjusting the print density of the transparent ink, and a plurality of dots having different sizes may be used.
- dot-shaped or reversed brightness enhancement portions 43B and line-shaped or solid brightness enhancement portions 43B may be mixed.
- FIGS. 9A and 9B both illustrate the case where the inter-light source region between the adjacent point light sources 42 is the low luminance region R. As shown in FIG. That is, the arrangement density of the luminance improving portions 43B is high in the inter-light source region, and the arrangement density of the luminance improving portions 43B decreases toward the region directly above the light source.
- the brightness enhancement portions 43B may be arranged in other geometric patterns, such as the ripple pattern shown in FIG. can be placed in
- the concave portion 22 is also formed in the arrangement region (low luminance region R) of the luminance improving portion 43B, and the luminance improving portion 43B is provided in the concave portion 22.
- 23 is exemplified.
- the concave portion 22 is not formed in the arrangement region (low luminance region R) of the brightness enhancement portion 43B, and the brightness enhancement portion 43B is made of the same material as the light diffusion portion 43A (for example, the base layer 21 ).
- the luminance improving portion 43B can be formed without performing the step of providing the transparent member 23 in the concave portion 22 by processing the base layer 21 using, for example, a mold, a shaped roll, a laser, or the like.
- a die, a shaping roll, a laser, or the like is used to form the shape of the light diffusion sheet 43 (base material layer 21) into a flat shape that becomes the concave portion 22 and the brightness improving portion 43B. A part can be provided.
- Step B includes a step of forming recesses 22 in the regions (low-brightness regions R) in which the brightness enhancement portions 43B are arranged
- Step C includes providing transparent members 23 in the recesses 22 of the low-brightness regions R after step B.
- the brightness improving portions 43B can be formed by providing the transparent members 23 in the concave portions 22 in predetermined regions.
- the luminance improving portion 43B can be formed by a simple method of printing the transparent ink.
- the use of transparent ink dot printing facilitates the adjustment of the total light transmittance.
- the method of forming the luminance improving portion 43B is not limited to dot printing, and other known pattern forming methods or the like may be used.
- the transparent member 23 is provided in the concave portion 22 using screen printing of transparent ink, for example, a patterning plate having an open low-luminance region R is placed on the ridgeline 111 shown in FIG. 4, and transparent ink is dropped onto the patterning plate. A squeegee may be used to smooth out the clear ink. As a result, the concave portion 22 of the low luminance region R is filled with the transparent member 23 up to the height of the ridge line 111, and the luminance improving portion 43B with a flat surface is formed.
- step C is separately performed after step B.
- the step A of calculating the luminance distribution may be performed between the step B and the step C. That is, after forming the concave portions 22 on the entire first surface 21a of the light diffusion sheet 43 in step B, the brightness distribution may be calculated in step A using the light diffusion sheet 43 in which the concave portions 22 are formed. . Alternatively, the brightness distribution may be calculated in step A using a dummy light diffusion sheet or simulation before step B is performed.
- the step C of forming the brightness improving portion 43B when processing using, for example, a mold, a shape roll, a laser, etc. is performed without printing the transparent ink, the step B and the step C must be performed at the same time. is possible, thereby reducing the number of steps.
- the step C is necessarily performed simultaneously with the step B of forming the light diffusing portion 43A.
- the step C may be performed simultaneously with the step B of forming the light diffusing portion 43A, or the step C may be performed together with the step B. may be performed separately.
- the brightness distribution may be calculated in the process A using a dummy light diffusion sheet or a simulation before the process.
- the method of shaping the concave portions 22 and the like in the light diffusion sheet 43 is not particularly limited, but for example, an extrusion molding method, an injection molding method, a laser processing method, or the like may be used.
- the procedure for manufacturing a single-layer light diffusion sheet having an uneven surface using an extrusion molding method is as follows. First, pellet-shaped plastic particles to which a diffusing agent has been added (along with pellet-shaped plastic particles to which no diffusing agent has been added may be mixed) are put into a single-screw extruder, heated and melted, knead. After that, the molten resin extruded by the T-die is sandwiched between two metal rolls, cooled, transported using guide rolls, and cut into flat plates by a sheet cutter to produce a light diffusion sheet. .
- the reverse shape of the roll surface is transferred to the resin. can be shaped into
- the shape transferred to the resin does not always correspond to the shape of the roll surface that is 100% transferred, the shape of the roll surface may be designed by calculating backward from the degree of transfer.
- pellet-shaped plastic particles necessary for forming each layer are supplied to each of two single-screw extruders. After charging, the same procedure as described above is performed for each layer, and each sheet thus produced may be laminated.
- a light diffusion sheet with a two-layer structure having an uneven surface may be produced as follows. First, pellet-like plastic particles necessary for forming each layer are put into each of two single-screw extruders, melted and kneaded while being heated. After that, the molten resin for each layer is put into one 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. After that, the laminated molten resin may be conveyed using guide rolls and cut into flat plates with a sheet cutter to produce a light diffusion sheet having a two-layer structure having an uneven surface.
- the light diffusion sheet may be manufactured as follows by shape transfer using UV (ultraviolet). First, a roll having an inverted shape of the uneven shape to be transferred is filled with an uncured UV curable resin, and the substrate is pressed against the resin. Next, in a state in which the roll filled with the ultraviolet curable resin and the substrate are integrated, the resin is cured by irradiating ultraviolet rays. Next, the sheet on which the concavo-convex shape has been shape-transferred by the resin is separated from the roll. Finally, the sheet is again irradiated with ultraviolet rays to completely harden the resin, thereby producing a light diffusion sheet having an uneven surface.
- UV ultraviolet
- the light diffusing sheet 43 of this embodiment is incorporated in a liquid crystal display device 50 in which a plurality of point light sources 42 are dispersedly provided on the back side of a display screen 50a.
- At least the first surface 21a of the light diffusion sheet 43 has a light diffusion portion 43A provided with a plurality of recesses 22 arranged two-dimensionally, and a plurality of brightness enhancement portions 43B flatter than the light diffusion portion 43A.
- the plurality of brightness enhancement portions 43B are arranged in a gradation manner so that the lower the brightness in the brightness distribution generated by the plurality of point light sources 42 when the plurality of concave portions 22 are formed on the entire first surface 21a, the higher the arrangement density becomes. be provided.
- the light diffusing sheet 43 of the present embodiment when the concave portions 22 provided in the light diffusing portion 43A are formed on the entire surface of the sheet, in the region where the luminance lowers in the luminance distribution, the luminance is improved flatter than that of the light diffusing portion 43A.
- a portion 43B is provided. At the location where the luminance improving portion 43B is arranged, light diffusibility is suppressed, and as a result, the proportion of straight light that travels straight perpendicularly to the sheet surface increases. As a result, it is possible to increase the brightness in the area where the brightness is lowered, so that it is possible to improve the uniformity of brightness while avoiding the decrease in brightness over the entire screen of the liquid crystal display device 50 . Therefore, the light diffusion sheet 43 of the present embodiment can further reduce the thickness of the backlight unit 40 and reduce the number of the point light sources 42 arranged.
- the luminance improving portions 43B are provided in a gradation manner so that the arrangement density increases in the luminance distribution in areas with lower luminance. Therefore, it becomes easy to adjust the area, density, etc. of the portion where the proportion of linear light is increased according to the luminance distribution, so that the luminance uniformity can be further improved.
- providing the luminance improving portions in a gradation pattern means changing the arrangement density of the luminance improving portions.
- the arrangement density of the luminance improving portions is the area ratio occupied by the luminance improving portions in a unit area.
- the area ratio is calculated based on "the area of one dot in the unit area" x "the number of dots in the unit area” (if there are multiple dot sizes, it is also taken into account).
- the area ratio is calculated based on "the area of one line in the unit area” x "the number of lines in the unit area” (when there are multiple line sizes, this is also taken into account).
- the area ratio is calculated based on "the area of one solid in the unit area” x "the number of solids in the unit area” (when there are multiple solid sizes, it is also taken into account).
- the arrangement density of the brightness enhancement portions provided in a gradation pattern varies from 100% (complete solid) to 0%.
- the range of arrangement density from 100% to 0% also includes 100% and 0%, but the maximum and minimum values of the arrangement density of the luminance enhancing portions need not always be 100% and 0%.
- a change in arrangement density may be a linear change or a curvilinear change.
- the change in arrangement density may be a unidirectional change (for example, 100% ⁇ 0%) such as a monotonous increase or a monotonous decrease, or a change accompanied by an increase or decrease (for example, 100% ⁇ 50% ⁇ 70% ⁇ 0% ).
- the “unit area” for representing the arrangement density of the brightness enhancement portions may be set arbitrarily.
- the low-luminance region R may be an inter-light source region between adjacent point light sources 42 . By doing so, it is possible to increase the luminance in the region between the light sources and improve the luminance uniformity.
- the low-luminance region R may be a light source region directly above the point light source 42 . By doing so, it is possible to increase the brightness in the area immediately above the light source and improve the brightness uniformity.
- the recessed portions 22 are also formed in the regions (low-luminance regions R) in which the brightness improving portions 43B are arranged, and the brightness improving portions 43B are provided in the recessed portions 22 of the low-luminance regions R. It may be composed of a transparent member 23 having a thickness. In this way, the brightness improving portion 43B can be formed by providing the transparent member in the recesses of the low brightness region R after forming the recesses 22 on the entire surface of the sheet. In this case, each of the transparent members 23 forming each luminance improving portion 43B may fill at least one or more concave portions 22 in the low luminance region R. Thus, one transparent member 23 filling one or more recesses 22 makes it easier to form the brightness improving portion 43B than the case where a plurality of transparent members 23 are provided in one recess 22. can.
- the concave portion 22 is not formed in the arrangement region (low luminance region R) of the brightness enhancement portion 43B, and the brightness enhancement portion 43B is made of the same material as the light diffusion portion 43A. may be In this way, the luminance improving portion 43B can be formed without performing the step of providing the transparent member 23 in the concave portion 22 by processing using, for example, a mold, a shaping roll, a laser, or the like.
- the concave portions 22 may have an inverted polygonal pyramid shape, an inverted polygonal truncated pyramid shape, or a lower hemispherical shape. By doing so, the light diffusibility of the light diffusing portion 43A can be improved.
- the backlight unit 40 of the present embodiment is incorporated in the liquid crystal display device 50, guides light emitted from the plurality of point light sources 42 to the display screen 50a side, and between the display screen 50a and the plurality of point light sources 42, The light diffusion sheet 43 of this embodiment is provided. Therefore, luminance uniformity can be improved while avoiding a decrease in luminance over the entire screen.
- the distance between the point light source 42 and the light diffusion sheet 43 is 2 mm. It may be below. It is possible to improve the luminance uniformity even in such a configuration where the luminance distribution tends to vary with the conventional light diffusion sheet. That is, the backlight unit 40 of this embodiment is a direct type backlight unit in which a plurality of point light sources 42 are dispersedly arranged on the back side of the display screen 50 a 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 point light source 42 and the light diffusion sheet 43.
- the distance between the point light source and the light diffusion sheet is set to 10 mm or less, more preferably 5 mm or less, still more preferably 2 mm or less, and ultimately 0 mm, in view of the future thinning of small and medium-sized liquid crystal display devices, It is believed that the usefulness of the light diffusion sheet 43 of this embodiment will become even more remarkable.
- the point light sources 42 may be LED elements. In this way, even if the number of light sources is reduced, sufficient brightness can be obtained over the entire screen.
- the point light source 42 may be arranged on the reflecting member 41 provided on the opposite side of the display screen 50a when viewed from the light diffusion sheet 43. By doing so, the luminance uniformity is further improved.
- the liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and the liquid crystal display panel 5, luminance uniformity can be improved while avoiding a decrease in luminance over the entire screen. . A similar effect can be obtained in an information device including the liquid crystal display device 50 of the present embodiment.
- the method for manufacturing the light diffusion sheet 43 of the present embodiment includes a step A of calculating the luminance distribution generated by the plurality of point light sources 42 when the plurality of recesses 22 are formed on the entire first surface 21a; on the first surface 21a, and a step of forming the luminance improving portions 43B on the first surface 21a in a gradation such that the lower the luminance in the luminance distribution calculated in the step A, the higher the arrangement density.
- the region where the luminance decreases in the luminance distribution is flatter than the light diffusing portion 43A.
- a brightness enhancement unit 43B is provided. At the location where the luminance improving portion 43B is arranged, light diffusibility is suppressed, and as a result, the proportion of straight light that travels straight perpendicularly to the sheet surface increases. As a result, it is possible to increase the brightness in the area where the brightness is lowered, so that it is possible to improve the uniformity of brightness while avoiding the decrease in brightness over the entire screen of the liquid crystal display device 50 . Therefore, it is possible to further reduce the thickness of the backlight unit 40 and reduce the number of the point light sources 42 arranged.
- the luminance improving portions 43B are provided in a gradation manner so that the arrangement density increases in areas with lower luminance in the luminance distribution. Therefore, it becomes easy to adjust the area, density, etc. of the portion where the proportion of linear light is increased according to the luminance distribution, so that the luminance uniformity can be further improved.
- step B includes a step of forming recesses 22 also in the region (low brightness region R) where the brightness enhancement portion 43B is arranged, and step C is performed after step B.
- a step of forming the luminance improving portion 43B by providing the transparent member 23 in the concave portion 22 of the low luminance region R may be included.
- the luminance improving portion 43B can be formed by providing the transparent member in the recessed portion 22 of the low luminance region R after forming the recessed portion 22 on the entire surface of the sheet.
- the process B and the process C may be carried out at the same time.
- the number of processes can be reduced by performing process B and process C at the same time by processing using a mold, shape roll, laser, or the like.
- FIG. 11 is a photograph showing a planar configuration of a part of the light diffusion sheet 43 according to the example, and FIG. ).
- the light diffusion sheet 43 of the example is composed of a base material layer 21 made of polycarbonate and having a thickness of 200 ⁇ m. and a brightness improving portion 43B flatter than the light diffusion portion 43A.
- the second surface 21b of the light diffusion sheet 43 is a flat surface.
- the light diffusing sheet 43 is formed by extruding the polycarbonate that serves as the base material layer 21, and two-dimensionally arraying concave pyramid-shaped concave portions 22 having a vertical angle of 90° and a depth of 50 ⁇ m on the entire surface of the first surface 21a at a pitch of 100 ⁇ m. and formed.
- the brightness improving portion 43B was formed by arranging the transparent member 23 made of transparent ink in a dot pattern on the first surface 21a using a patterning plate having openings with a diameter of 600 ⁇ m.
- the dot-shaped transparent members 23 are embedded across the plurality of recesses 22 respectively.
- the luminance improving portions 43B are arranged in the pattern shown in FIG.
- a light diffusing sheet 43 in which brightness improving portions 43B are arranged in the pattern shown in FIG. 7 was prepared.
- the luminance distribution along line VI-VI in FIG. 6 was measured.
- the luminance distribution along line VII-VII in FIG. 7 was measured.
- the sheet laminate 100 shown in FIG. was examined for luminance. Specifically, the sheet laminate 100 including the light diffusion sheet 43 is placed on the point light source 42 (LED array), and a transparent glass plate is placed thereon to prevent the sheets from floating.
- a two-dimensional color luminance meter UA-200 manufactured by Co., Ltd. the luminance in the vertical upward direction (the direction from the LED array toward the glass plate) was measured.
- 13 and 14 show luminance distributions obtained for the light diffusion sheet 43 of the example and the light diffusion sheet 43 of the comparative example, respectively.
- the luminance distribution of the solid line is the luminance distribution of the light diffusion sheet 43 on which the luminance improving portion 43B is formed
- the luminance distribution of the broken line is the luminance distribution of the light before forming the luminance improving portion 43B.
- 4 shows the luminance distribution of the diffusion sheet 43.
- the luminance improving portions 43B are provided in a gradation such that the arrangement density increases in the luminance distribution indicated by the dashed line in FIG. 13 as the luminance decreases (see FIG. 6). Therefore, it becomes easy to adjust the area, density, etc. of the portion where the proportion of linear light is increased in accordance with the luminance distribution shown by the dashed line in FIG. 13, so that excellent luminance uniformity can be obtained.
- a solid brightness improving portion 43B is provided in a region of low brightness in the brightness distribution indicated by the dashed line in FIG. 14 (see FIG. 7). For this reason, although the luminance improving effect of the luminance improving unit 43B can be obtained, fine adjustment of the area, density, etc. of the portion where the proportion of straight light is increased cannot be performed. Sex got worse.
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Abstract
Description
以下、実施形態に係る光拡散シート、バックライトユニット、液晶表示装置、情報機器、及び光拡散シートの製造方法について、図面を参照しながら説明する。尚、本開示の範囲は、以下の実施形態に限定されず、本開示の技術的思想の範囲内で任意に変更可能である。
図1に示すように、液晶表示装置50は、液晶表示パネル5と、液晶表示パネル5の下面に貼付された第1偏光板6と、液晶表示パネル5の上面に貼付された第2偏光板7と、液晶表示パネル5の背面側に第1偏光板6を介して設けられたバックライトユニット40とを備えている。
図2に示すように、バックライトユニット40は、反射部材41と、反射部材41に2次元状に配置された複数の点光源42と、複数の点光源42の上側に設けられたシート積層体100とを備える。シート積層体100は、点光源42の側に配置された光拡散シート43と、光拡散シート43の上側(表示画面50aの側)に設けられた一対のプリズムシート44及び45とを有する。
反射部材41は、例えば、白色のポリエチレンテレフタレート樹脂製のフィルム、銀蒸着フィルム等により構成される。
点光源42の種類は特に限定されないが、例えばLED素子やレーザー素子等であってもよく、コスト、生産性等の観点からLED素子を用いてもよい。LED素子の出光角度特性を調節するために、LED素子にレンズを装着してもよい。LED素子(チップ)は、平面視した場合に長方形状を有していてもよく、その場合、一辺の長さは10μm以上(好ましくは50μm以上)20mm以下(好ましくは10mm以下、より好ましくは5mm以下)であってもよい。数mm角のLEDチップは、2次元的に交互に一定の間隔で反射シート41に配置されてもよい。複数のLEDチップを等間隔で配置する場合、隣り合う2つのチップの中心間距離は、0.5mm以上(好ましくは2mm以上)20mm以下であってもよい。LED素子等の点光源42を規則的に配置することによって、輝度均一性が向上する。
光拡散シート43は、基材層21を有する。光拡散シート43(基材層21)は、光出射面となる第1面21aと、光入射面となる第2面21bとを有する。すなわち、光拡散シート43は、第2面21bを点光源42の方に向けて配置される。基材層21のマトリックスとなる樹脂は、光を透過させる材料で構成されていれば、特に限定されないが、例えば、アクリル、ポリスチレン、ポリカーボネート、MS(メチルメタクリレート・スチレン共重合)樹脂、ポリエチレンテレフタレート、ポリエチレンナフタレート、セルロールアセテート、ポリイミド等であってもよい。基材層21は、拡散剤その他の添加剤を含んでいてもよいし、或いは、実質的に添加剤を含有しなくてもよい。基材層21に含有可能な添加剤は、特に限定されないが、例えば、シリカ、酸化チタン、水酸化アルミニウム、硫酸バリウム等の無機粒子であってもよいし、例えば、アクリル、アクリルニトリル、シリコーン、ポリスチレン、ポリアミド等の有機粒子であってよい。
プリズムシート44及び45は、光線を透過させる必要があるので、透明(例えば無色透明)の合成樹脂を主成分として形成される。プリズムシート44及び45は、一体に形成されてもよい。下側プリズムシート44は、基材層44aと、基材層44aの表面に積層される複数の突条プリズム部44bからなる突起列とを有する。同様に、上側プリズムシート45は、基材層45aと、基材層45aの表面に積層される複数の突条プリズム部45bからなる突起列とを有する。突条プリズム部44b及び45bはそれぞれ、基材層44a及び45aの表面にストライプ状に積層される。突条プリズム部44b及び45bはそれぞれ、裏面が基材層44a及び45aの表面に接する三角柱状体である。突条プリズム部44bの延伸方向と突条プリズム部45bの延伸方向とは、互いに直交する。これにより、光拡散シート43から入射される光線を下側プリズムシート44によって法線方向側に屈折させ、さらに下側プリズムシート44から出射される光線を上側プリズムシート45によって表示画面50aに対して略垂直に進むように屈折させることができる。
図示は省略しているが、プリズムシート44及び45の上側(表示画面50aの側)に偏光シートを設けてもよい。偏光シートは、バックライトユニット40から出射された光が液晶表示装置50の第1偏光板6に吸収されることを防止することによって、表示画面50aの輝度を向上させる。
図2に示すバックライトユニット40において、点光源42から出射された光は、光拡散シート43を通過する際に、凹部22や拡散剤(図示省略)によって拡散される。これにより、例えば点光源42の直上領域での輝度が抑制される。しかし、点光源42と光拡散シート43との距離や光拡散シート43の厚みを削減するなどしてバックライトユニット40が薄型化されたり、或いは、コスト削減のために点光源42の数が減らされると、例えば光源間領域(光源が配置されていない領域)等の低輝度領域Rで輝度の低下が生じる。
本実施形態の光拡散シート43の製造方法では、光拡散部43Aに設ける凹部22が第1面21aの全体に形成された場合に点光源42によって生じる輝度分布を算出する工程Aと、光拡散部43Aを第1面21aに形成する工程Bと、工程Aで算出された輝度分布において輝度が低い領域ほど配置密度が高くなるように、輝度向上部43Bをグラデーション状に第1面21aに形成する工程Cとを実施する。
本実施形態の光拡散シート43は、表示画面50aの背面側に複数の点光源42が分散して設けられた液晶表示装置50に組み込まれる。光拡散シート43の少なくとも第1面21aは、2次元的に配列された複数の凹部22が設けられた光拡散部43Aと、光拡散部43Aよりも平坦な複数の輝度向上部43Bとを有する。複数の輝度向上部43Bは、複数の凹部22が第1面21aの全体に形成された場合に複数の点光源42によって生じる輝度分布において輝度が低い領域ほど配置密度が高くなるようにグラデーション状に設けられる。
以下、実施例について、図面を参照しながら説明する。図11は、実施例に係る光拡散シート43の一部分の平面構成を示す写真であり、図12は、実施例に係る光拡散シート43の一部分の表面形状(第1面21aの高さの変化)を示す図である。
以上、本開示についての実施形態(実施例を含む。以下同じ。)を説明したが、本開示は前述の実施形態のみに限定されず、開示の範囲内で種々の変更が可能である。すなわち、前述の実施形態の説明は、本質的に例示に過ぎず、本開示、その適用物或いはその用途を制限することを意図するものではない。
2 CF基板
3 液晶層
5 液晶表示パネル
6 第1偏光板
7 第2偏光板
21 基材層
21a 第1面
21b 第2面
22 凹部
23 透明部材
40 バックライトユニット
41 反射部材
42 点光源
43 光拡散シート
43A 光拡散部
43B 輝度向上部
44 下側プリズムシート
44a 基材層
44b 突条プリズム部
45 上側プリズムシート
45a 基材層
45b 突条プリズム部
50 液晶表示装置
50a 表示画面
100 シート積層体
111 稜線
112 凹部中心(逆ピラミッド頂点)
Claims (16)
- 表示画面の背面側に複数の点光源が分散して設けられた液晶表示装置に組み込まれる光拡散シートであって、
前記光拡散シートの少なくとも第1面は、2次元的に配列された複数の凹部が設けられた光拡散部と、前記光拡散部よりも平坦な複数の輝度向上部とを有し、
前記複数の輝度向上部は、前記複数の凹部が前記第1面の全体に形成された場合に前記複数の点光源によって生じる輝度分布において輝度が低い領域ほど配置密度が高くなるようにグラデーション状に設けられる
光拡散シート。 - 前記輝度が低い領域は、前記複数の点光源のうち隣り合う点光源同士の間の領域である
請求項1に記載の光拡散シート。 - 前記輝度が低い領域は、前記複数の点光源の直上領域である
請求項1に記載の光拡散シート。 - 前記複数の凹部は、前記複数の輝度向上部の配置領域にも形成されており、
前記複数の輝度向上部は、前記配置領域の前記複数の凹部に設けられた透明部材から構成される
請求項1~3のいずれか1項に記載の光拡散シート。 - 前記複数の輝度向上部を構成する前記透明部材はそれぞれ、前記配置領域の前記複数の凹部のうち少なくとも1つ以上の凹部を埋める
請求項4に記載の光拡散シート。 - 前記複数の凹部は、前記複数の輝度向上部の配置領域には形成されておらず、
前記複数の輝度向上部は、前記光拡散部と同じ材質で構成される
請求項1~3のいずれか1項に記載の光拡散シート。 - 前記複数の凹部は、逆多角錐形状、逆多角錐台形状又は下半球形状を有する、
請求項1~3のいずれか1項に記載の光拡散シート。 - 前記液晶表示装置に組み込まれ、前記複数の点光源から発せられた光を前記表示画面側に導くバックライトユニットであって、
前記表示画面と前記複数の点光源との間に、請求項1~7のいずれか1項に記載の光拡散シートを備える、
バックライトユニット。 - 前記複数の点光源と前記光拡散シートとの間の距離は、2mm以下である、
請求項8に記載のバックライトユニット。 - 前記複数の点光源は、LED素子である、
請求項8に記載のバックライトユニット。 - 前記複数の点光源は、前記光拡散シートから見て前記表示画面の反対側に設けられた反射部材に配置される
請求項8に記載のバックライトユニット。 - 請求項8~11のいずれか1項に記載のバックライトユニットと、
液晶表示パネルとを備える
液晶表示装置。 - 請求項12に記載の液晶表示装置を備える
情報機器。 - 表示画面の背面側に複数の点光源が分散して設けられた液晶表示装置に組み込まれる光拡散シートの製造方法であって、
前記光拡散シートの少なくとも第1面は、複数の凹部が2次元的に設けられた光拡散部と、前記光拡散部よりも平坦な複数の輝度向上部とを有し、
前記複数の凹部が前記第1面の全体に形成された場合に前記複数の点光源によって生じる輝度分布を算出する工程Aと、
前記光拡散部を前記第1面に形成する工程Bと、
前記工程Aで算出された前記輝度分布において輝度が低い領域ほど配置密度が高くなるように、前記複数の輝度向上部をグラデーション状に前記第1面に形成する工程Cとを備える
光拡散シートの製造方法。 - 前記工程Bは、前記複数の凹部を、前記複数の輝度向上部の配置領域にも形成する工程を含み、
前記工程Cは、前記工程Bの後に、前記配置領域の前記複数の凹部に透明部材を設けることによって、前記複数の輝度向上部を形成する工程を含む
請求項14に記載の光拡散シートの製造方法。 - 前記工程Bと前記工程Cとは、同時に実施される
請求項14に記載の光拡散シートの製造方法。
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CN202280045972.5A CN117597606A (zh) | 2021-07-07 | 2022-05-19 | 光扩散片材、背光单元、液晶显示装置、信息设备和光扩散片材的制造方法 |
EP22837346.0A EP4357664A1 (en) | 2021-07-07 | 2022-05-19 | Light diffusion sheet, backlight unit, liquid crystal display device, information apparatus, and method for manufacturing light diffusion sheet |
US18/405,444 US20240231149A9 (en) | 2021-07-07 | 2024-01-05 | Light diffusion sheet, backlight unit, liquid crystal display device, information apparatus, and method for manufacturing light diffusion sheet |
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JP2009238491A (ja) * | 2008-03-26 | 2009-10-15 | Dainippon Printing Co Ltd | 光学シートおよび面光源装置 |
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JP2011129277A (ja) | 2009-12-15 | 2011-06-30 | Toppan Printing Co Ltd | バックライトユニット及びディスプレイ装置 |
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US7108414B2 (en) * | 1995-06-27 | 2006-09-19 | Solid State Opto Limited | Light emitting panel assemblies |
KR20170066974A (ko) * | 2015-12-07 | 2017-06-15 | 삼성전자주식회사 | 광 확산판 및 이를 포함하는 디스플레이 장치 |
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JP2008003232A (ja) * | 2006-06-21 | 2008-01-10 | Fujifilm Corp | 光学シート及び光学シートの製造方法、バックライト、液晶表示装置 |
JP2008166057A (ja) * | 2006-12-27 | 2008-07-17 | Sony Corp | 面状光源装置、表示装置及び面状照明方法 |
JP2009238491A (ja) * | 2008-03-26 | 2009-10-15 | Dainippon Printing Co Ltd | 光学シートおよび面光源装置 |
JP2010277983A (ja) * | 2009-04-27 | 2010-12-09 | Toshiba Corp | 面状照明装置およびこれを備えた液晶表示装置 |
JP2011129277A (ja) | 2009-12-15 | 2011-06-30 | Toppan Printing Co Ltd | バックライトユニット及びディスプレイ装置 |
JP2012018880A (ja) * | 2010-07-09 | 2012-01-26 | Panasonic Corp | 面状照明装置、映像表示装置および光学シート |
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TW202303192A (zh) | 2023-01-16 |
US20240231149A9 (en) | 2024-07-11 |
CN117597606A (zh) | 2024-02-23 |
US20240134228A1 (en) | 2024-04-25 |
EP4357664A1 (en) | 2024-04-24 |
JP2023009400A (ja) | 2023-01-20 |
TWI836458B (zh) | 2024-03-21 |
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