JP2010231194A - Optical sheet, method for manufacturing the same, light source including optical sheet, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which ensures a uniform luminance distribution by improving luminance ratios at middle points between mutually juxtaposed linear light sources and at positions directly above the linear light sources, in a liquid crystal display panel, a method for manufacturing the same, a direct light source device, and a liquid crystal display device. <P>SOLUTION: In the optical sheet including a linear ridge-like lens group, the lens group includes unit lenses, each of which includes a curve (R1) and a curve (R2) at a prescribed ratio in a convex outer peripheral part of a cross-section perpendicular to a lengthwise direction of the unit lens, wherein angles (θ1) formed between tangent lines at all points on the curve (R1) and a base line are equal to or larger than 40° and angles (θ2) formed between tangent lines at all points on the curve (R2) and the base line are equal to or larger than 25° and equal to or smaller than 35°. Thereby the problem is solved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet, a method for manufacturing the optical sheet, a light source device including the optical sheet, and a display device.

  In recent years, a display device has been replaced by a liquid crystal display from a display using a cathode ray tube, and the screen has been enlarged. The light source of the liquid crystal display device includes an edge light type and a direct type, but a large type liquid crystal display device generally uses a direct type light source in which a plurality of cold cathode tubes are arranged as the light source.

  On the screen of a liquid crystal display device using a direct type light source, the portion where the cold-cathode tube is present is bright, while the portion where the cold-cathode tube is not present is relatively dark, resulting in uneven brightness. There is a problem of being reflected in. Therefore, by arranging various optical sheets between the cold cathode fluorescent lamp and the liquid crystal panel, light emitted from the cold cathode fluorescent lamp is uniformly diffused over the entire screen.

  Liquid crystal display devices are required to be further thinned. For this reason, the distance between the cold cathode fluorescent lamp and the screen has to be narrowed, and it has become difficult to sufficiently diffuse the light from the cold cathode fluorescent lamp. . Further, in order to reduce the cost, the number of cold cathode tubes is also reduced, and it is difficult to uniformly diffuse light from the cold cathode tubes as the interval between the cold cathode tubes is increased. Therefore, under such severe conditions, as a method of eliminating luminance unevenness and improving luminance, select an optical sheet with a lens as the optical sheet placed closest to the light source and adjust the lens shape. Has been done. Further, from the viewpoint of luminance, at least one prism sheet is selected as the second and subsequent optical sheets with respect to the direction from the light source to the liquid crystal panel. The problem in the combination of a plurality of optical sheets is that, in the first place, the portion where the cold-cathode tube is present is bright, but the portion where the cold-cathode tube is not present is relatively dark, and the unevenness of brightness is reduced. Secondly, it is also possible to eliminate new brightness unevenness caused by the low brightness portion near the cold cathode tube which is generated by using a diffusion sheet with a lens or a prism sheet.

  In order to make the luminance distribution uniform while preventing a reduction in illumination efficiency, for example, in the direct light source device disclosed in Patent Literature 1 and Patent Literature 2, a plurality of prism lenses having a triangular cross section are arranged in parallel. A prism sheet and a lenticular lens sheet in which a plurality of cylindrical lenses having a cylindrical convex surface are arranged in parallel are used as an alternative to the conventional optical sheet. The prism sheet and lenticular lens sheet have a smaller number of incident light beams that are repeatedly reflected and refracted compared to optical sheets using conventional light diffusing agents. Can be improved. However, although the prism sheet can improve the luminance, there is a limit to the uniform distribution thereof. Although the lenticular lens sheet can also increase the uniformity of the luminance distribution as compared to the prism sheet, it is difficult to completely eliminate the luminance unevenness under the severe cold cathode tube installation conditions as described above.

Japanese Patent Laid-Open No. 10-283818 JP 2004006256 A

  An optical sheet having lenses arranged in a straight bowl on the light exit surface is arranged at a position closest to the light source, and at least one prism is provided on the optical sheet arranged second or later in the direction from the light source to the liquid crystal panel. When a sheet or the like is used, the light diffusibility is enhanced by the effect of the prism, and the front luminance can be increased. Therefore, it is considered to be an optical sheet configuration for a light source that is optimal for thinning a liquid crystal television and reducing the number of cold cathode tubes.

  However, although such an optical sheet configuration can diffuse sufficient light between cold cathode tubes with originally low brightness, light with a small incident angle from the optical sheet to the prism sheet is optically reflected by the prism sheet. Since the sheet is returned to the sheet, a dark line is generated on the cold cathode tube. Even if the pattern of the cold-cathode tube can be erased, this dark line remains, resulting in new brightness unevenness.

  Further, for further cost reduction, it is required to reduce the number of optical sheets used in the light source device. Here, when the number of used optical sheets is reduced, it becomes more difficult to eliminate luminance unevenness, and a new problem has arisen that an image of a pin that supports the optical sheet appears in the backlight unit.

  An object of the present invention is to reduce luminance unevenness at an intermediate point between line light sources (for example, cold-cathode tubes) arranged in parallel with each other and directly above the line light source, and to be arranged second or later in the direction from the light source to the liquid crystal panel. It is to provide an optical sheet capable of obtaining a uniform luminance distribution by combination with the optical sheet, a method for manufacturing the optical sheet, a light source device including them, and a liquid crystal display device.

  As a result of intensive studies to solve the above problems and the problems of the prior art, the inventors have found that each unit lens in the lens group formed in a linear bowl shape on the surface of the optical sheet is perpendicular to its length direction. In the cross-sectional shape, when two curved portions having tangent angles within different specific ranges form the outer peripheral line of the convex portion at a specific ratio, the above problem is found and the invention is completed. It was. In order to describe the lens of the present invention and the surface shape of the lens, a cross-section (vertical cross-section) perpendicular to the linear heel direction (lens length direction) of the lens that is originally arranged in a linear ridge shape on the optical sheet The form will be described below (see FIG. 13).

  The first embodiment is an optical sheet having a convex lens group formed on the surface in the form of a straight bowl, and the lens group has a convex section outer peripheral line in a vertical cross-sectional shape with respect to the length direction of the unit lens. Is composed mainly of a curved portion, and an angle (θ1) between a tangent and a base line at all points on the curve is θ1 ≧ 40 °, and all on the curve The angle (θ2) formed between the tangent and the base line at the point includes a curved portion (R2) where 25 ° ≦ θ2 ≦ 35 °, and the base line of the unit lens shape of the curved portion (R1) The ratio of the total projected length (r1) to the total length of the base line is 25% to 60%, and the base of the total length (r2) projected onto the base line of the unit lens shape of the curved portion (R2). A unit lens having a ratio to the total line length of 25% to 60% (FIGS. 2 to 9) An optical sheet, comprising a.

  The second embodiment is a method for producing the optical sheet of the present invention, and the third embodiment is a light source device for a liquid crystal display device which essentially comprises the optical sheet of the present invention. The fourth embodiment is a display device including the light source device for a liquid crystal display device of the present invention.

  By using the form of the present invention described in the above solution, the luminance in the viewing angle direction in the region immediately above the cold cathode tube of the light source device and the luminance in the viewing angle direction in the intermediate region of the adjacent cold cathode tubes are obtained. Each can be adjusted independently, and in various apparatus settings (apparatus configuration, light source apparatus conditions, combinations with optical sheets other than the present invention), high brightness uniformity on the light-emitting surface side in the settings can be realized.

It is a schematic diagram which shows the structure of a display apparatus. It is explanatory drawing of an example of the unit lens surface shape design concept of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of this invention. It is explanatory drawing of an example of the unit lens surface shape of the optical sheet of a comparative example. It is explanatory drawing of arrangement | positioning of the support pin in the direct type light source device used in the Example. It is explanatory drawing of the name of each part of the optical sheet of this invention. It is explanatory drawing of an example of the matrix which faces directly for forming the surface shape used for the manufacturing method of this invention.

  The following description is made with reference to the drawings and the like, but the present invention is not limited to the embodiments of the drawings.

  Hereinafter, first, the physical configuration such as the surface shape of the optical sheet according to the present invention will be described, and then the chemical composition, the method of combining other sheets, the apparatus configuration, etc. will be described.

  In the present specification, the first optical sheet refers to an optical sheet arranged first in the direction from the light source to the liquid crystal panel, and the second and subsequent optical sheets are the second, third, and fourth, respectively. And the optical sheets in the order of arrangement (see FIG. 1). Further, the optical sheet closest to the front panel corresponds to the fourth optical sheet denoted by reference numeral 6 in FIG. If these optical sheets can achieve the purpose of installation (for example, improvement in luminance) without causing any hindrance (for example, significant increase in thickness and cost), there is no upper limit on the number of sheets.

<Surface shape of the optical sheet of the present invention>
In the optical sheet of the present invention, a convex lens group formed in a linear bowl shape on at least one side is formed. In the lens group, the convex portion outer peripheral line in the vertical cross-sectional shape with respect to the length direction of the unit lens is mainly composed of a curved portion, and the angle formed by the tangent line and the convex portion base line at all points on the curve ( A curve where θ1) is θ1 ≧ 40 °, and an angle (θ2) between the tangent line and the convex base line at all points on the curve is 25 ° ≦ θ2 ≦ 35 ° A ratio of the total length (r1) of the curved portion (R1) projected onto the base line of the unit lens shape to the total base line length is 25% to 60%, and the curved portion ( The unit lens has a ratio of the total length (r2) projected on the base line of the unit lens shape of R2) to the total length of the base line of 25% to 60%. And the surface shape as the whole lens shaping | molding surface of an optical sheet is comprised by arrange | positioning a unit lens substantially parallel. As for the arrangement of the unit lenses, the unit lenses may be arranged without a gap or may be arranged at intervals. In order to fully exhibit the optical performance of the unit lens, it is preferable not to leave a gap. However, as long as it does not affect the performance of the optical sheet as an assembly of unit lenses, an interval may be provided for ease of molding. In order to provide optical performance different from that of the unit lenses, the unit lenses may be spaced apart. In that case, the planar shape between the unit lenses may be a surface shape that achieves the object to be imparted at a sufficient interval to achieve the object to be imparted.

  In the optical sheet of the present invention, these surface shapes are set on the light exit surface side. On the other hand, the surface shape configuration on the light incident surface side of the optical sheet of the present invention is not particularly limited and can be appropriately selected from flat surfaces, embossed surfaces, mat surfaces, surfaces having optical elements such as lenses, etc. An embossed surface and a mat surface are preferably used from the viewpoints of preventing sticking, preventing sound noise, and exhibiting a light scattering effect.

<Unit lens structure>
In the lens group arranged in the shape of a straight bowl on the optical sheet of the present invention, the outer peripheral line of the convex part in the vertical cross-sectional shape with respect to the length direction of the unit lens is mainly composed of a curved part, and all points on the curved line The angle (θ1) formed between the tangent line and the convex portion base line at the angle (θ1) between the curved line portion (R1) where θ1 ≧ 40 ° and the tangent line and the convex portion base line at all points on the curve ( θ2) includes a curved portion (R2) where 25 ° ≦ θ2 ≦ 35 °, and the total length (r1) of the total length (r1) projected on the baseline of the unit lens shape of the curved portion (R1) The ratio is 25% to 60%, and the ratio of the total length (r2) projected on the base line of the unit lens shape of the curved portion (R2) to the total length of the base line is 25% to 60% at the same time. Has a unit lens to fill.

  The curved portion (R1) and the curved portion (R2) of the unit lens may be directly connected to form a convex outer peripheral line, or a straight portion, a tangent at a point on the curved line, and a convex portion base. The angle (θ3) formed with the line may be connected via a curved portion (R3) of 35 ° <θ3 <40 ° or θ3 <25 °. However, in order to increase the luminance uniformity, which is the object of the present invention, the ratio of the total length (r3) projected onto the convex base line of these curved portions (R3) to the total base line length is 40% or less. Is more preferable, and more preferably 20% or less.

[Curved part]
The curve referred to in the present invention includes a curve that is different from a straight line but has a small curvature that is substantially close to a straight line. The minimum structural unit defined in the present invention is in the order of microns, but when observed in the order of microns, for example, when a vertical section of an optical sheet is observed with an electron microscope, the curved portion defined in the present invention is In the case of a curve with a small curvature that is difficult to determine as a curve in that order, the determination is performed as follows, for example. That is, with respect to a straight line having a length A connecting two points on the curve with the shortest distance, the value of 100 × d / A is 1 when the shortest distance d between the point on the curve farthest from the straight line and the straight line is set. If larger, it is determined as a curve.

  The curved portion (R1) is preferably a part of a quadratic curve from the viewpoints of design easiness, workability, and optical performance, and may be a combination of one or two or more quadratic curves, and has a convex shape. They may be arranged symmetrically on the left and right of the part outer peripheral line or asymmetrically arranged. When the curved portion (R1) is a part of an ellipse, the eccentricity is preferably 0.50 to 0.95, more preferably 0.70 to 0.93, and more preferably 0.80 to 0.90. preferable.

  The curved part (R2) may be a part of a quadratic curve, like the curved part (R1), but the angle (θ2) between the tangent line and the convex part base line at all points on the curved line is In addition, the ratio of the total length (r2) projected on the convex portion base line to the total base line length is 25% to 60% while being a narrow tangent angle of 25 ° ≦ θ2 ≦ 35 °. Since it is necessary, it does not necessarily have to be a part of a quadratic curve, and may be composed of any one or two or more curves that satisfy the above conditions. Moreover, similarly to the curved portion (R1), it may be arranged symmetrically on the left and right of the convex portion outer peripheral line or may be arranged asymmetrically. The quadratic curve means an ellipse including a circle, a hyperbola, and a parabola.

  The ratio of the total length (r1) of the length projected onto the convex portion base line of the curved portion (R1) to the total base line length is preferably 25% to 60%. When the total (r1) is less than 25%, light diffusion to the intermediate portion of the cold-cathode tube row is reduced and the luminance in the viewing angle direction at the intermediate portion is lowered, making it difficult to eliminate luminance unevenness. On the other hand, when the total (r1) exceeds 60%, in order to increase the luminance in the viewing angle direction, when a commonly used optical sheet such as a prism sheet or a diffusion sheet with a lens is overlapped, The brightness of the upper region is lowered, and new brightness unevenness is caused. The total (r1) is more preferably 27% to 58%, still more preferably 30% to 55%.

  The ratio of the total length (r2) projected on the convex portion base line of the curved portion (R2) to the total base line length is preferably 25% to 60%. When the total (r2) is less than 25%, in order to increase the luminance in the viewing angle direction, when a commonly used optical sheet such as a prism sheet or a diffusion sheet with a lens is overlaid, The luminance of the area is lowered, and it becomes difficult to eliminate luminance unevenness. On the other hand, if the total (r2) exceeds 60%, light diffusion to the intermediate portion of the cold cathode tube array is reduced, and the luminance in the viewing angle direction at the intermediate portion is lowered, making it difficult to eliminate luminance unevenness. . The total (r2) is more preferably 27% to 58%, and further preferably 30% to 55%.

  The ratio of the total length (r1) projected on the convex portion base line of the curved portion (R1) to the total base line length is 25% to 60%, and is projected onto the convex portion base line of the curved portion (R2). By setting the ratio of the total length (r2) to the total length of the base line to be 25% to 60%, the light from the light source can be sufficiently diffused into the middle part of the cold cathode tube array, and the viewing angle in the middle part The luminance in the direction can be improved. In addition, in order to increase the luminance in the viewing angle direction, even when a commonly used optical sheet such as a prism sheet or a diffusion sheet with a lens is superposed, the luminance in the upper area of the cold cathode tube can be sufficiently secured, and the thickness is further reduced. Increasing the distance between the line light sources due to the closer distance between the line light source and the optical sheet and the reduction in the energy consumption of liquid crystal display devices and the reduction in the number of line light sources for cost reduction will become increasingly difficult. Even in liquid crystal display panels, it has become possible to eliminate the uneven brightness.

  Further, the ratio of the total length (r1) projected on the convex portion base line of the curved portion (R1) to the total base line length is 25% to 60%, and the convex portion base line of the curved portion (R2) As long as the ratio of the total length (r2) projected on the base line to the total length of the base line is 25% to 60%, these connection methods are left-right asymmetric even if the convex portion outer peripheral line is symmetrical. In addition, by adjusting these connection methods, higher-level luminance unevenness can be eliminated. Either of the setting positions of the curved portion (R1) and the curved portion (R2) may be close to the base portion. It is desirable from the viewpoint of formability that the curved portion (R1) is close to the base portion. From the viewpoint of moldability, it is preferable that the curved portion (R1) is close to the base portion, and the curved portion (R1) and the curved portion (R2) are symmetrical positions with respect to the center line of the unit lens.

[Ratio of height H to width P]
The ratio of the length (P) of the base portion and the height (H) from the base portion to the lens apex in the vertical sectional shape with respect to the length direction of the unit lens is the convex shape of the curved portion (R1) and the curved portion (R2). The ratio of the total length (r1) of the curved portion (R1) projected to the lens-shaped convex portion base line is 25% to 60% with respect to the total length of the base line. The ratio is not particularly limited as long as the ratio of the total length (r2) of R2) to the total length of the base line is 25% to 60%, but preferably H / P = 0.25 to 0.75. 3-0.6 are more preferable. When H / P is less than the above range, the composition ratio of the curved portion (R1) to the curved portion (R2) decreases, and it becomes difficult to sufficiently diffuse light into an intermediate region between adjacent cold cathode tubes. The brightness in the viewing angle direction in the region cannot be improved. On the other hand, when the above range is exceeded, the ratio of the curved portion (R1) of the curved portion (R2) decreases, and when the optical sheet such as a prism sheet or a diffusion sheet with a lens is overlaid, The luminance is insufficient, and it becomes difficult to eliminate the luminance unevenness. The length (P) and height (H) of the unit lens may be appropriately set according to desired characteristics, but usually the length (P) is 10 μm to 300 μm and the height (H) is 2.5 μm to 225 μm.

<Combination of unit lens structures>
[Disposition ratio of unit lenses on the optical sheet plane]
In the optical sheet of the present invention, the unit lens structure having the specific shape is an optimum shape for achieving high brightness uniformity. Therefore, usually other unit lens structures may be included. In order to exhibit preferable performance as the entire optical sheet, it is preferable that 50% by area or more of the entire optical sheet is composed of unit lenses having a specific shape defined in the present invention, and a structure of 70% by area or more is further included. A configuration of 90% by area or more is more preferable. Examples of the other lens structure include a lenticular shape and a prism shape. In the unit lens structure configuration of these optical sheets, the unit lens structure breakdown having a specific shape defined in the present invention may be a combination configuration of the same shape or a combination configuration of a plurality of types of shapes. I do not care. In addition, an aspect in which the lens group includes only unit lenses having a specific shape defined in the present invention is also preferable.

[Disposition method of planar unit lens of optical sheet]
In the optical sheet of the present invention, in the vertical cross section with respect to the length direction of the unit lens, it is preferable that the distance between the tops of the convex portion outer peripheral lines of adjacent unit lenses is 300 μm or less. When the distance exceeds 300 μm, the luminance uniformity in the viewing angle direction is lowered, or a moire pattern is likely to be generated depending on the combination with the optical sheet to be overlapped. The arrangement of the lens groups arranged in the shape of the straight saddle is not limited as long as the entire optical sheet has the arrangement ratio, and unit lenses having a specific shape defined in the present invention may be arranged at the above intervals. Other unit lens structures (for example, lenticular shape or prism shape) may be adjacent.

  In the optical sheet of the present invention, the configuration of the connecting portion between adjacent unit lenses is not particularly limited as long as the target optical performance is not affected. For example, when it is desired to achieve only the optical performance as designed for the unit lens with the entire optical sheet, ideally, the lowest part of the outer peripheral line of the convex part in the vertical cross section with respect to the length direction of the unit lens is the base line. It is preferable that the unit lenses are aligned, that is, the unit lenses are arranged without gaps.

  However, a gap may be provided between the unit lenses as long as the optical performance of the entire optical sheet is not affected. For example, in the step of transferring the lens shape of the optical sheet of the present invention, a slight gap is given so as to facilitate release after the lens shape transfer. With respect to the cross-sectional shape between the unit lenses given to the optical sheet of the present invention by this slight gap, any shape such as a straight line, a concave curve, or a V-shape can be used as long as the optical performance is not affected. The invention is synonymous with no gap.

  On the contrary, in order to assist the optical performance of the unit lens having a specific shape defined in the present invention, to strengthen, or to supplement other optical performance, the minimum unit of the adjacent unit lenses are separated from each other, In the meantime, a shape that exhibits an effect according to the purpose may be added.

<Configuration of optical sheet of the present invention>
[Transparent thermoplastic resin]
The thermoplastic resin constituting the optical sheet of the present invention is not particularly limited as long as it is transparent and has an appropriate strength as a main component of the optical sheet. For example, polycarbonate resin; acrylic resin such as polymethyl methacrylate; styrene resin such as polystyrene, polyvinyl toluene, and poly (p-methylstyrene); MS resin (copolymer of methyl methacrylate and styrene); norbornene resin Polyolefin resin; polyarylate resin; polyethersulfone resin and the like can be mentioned, and two or more kinds of mixed resins can be used. A polycarbonate resin, a styrene resin, or a norbornene resin is preferably used. Among these, polycarbonate resin is particularly preferable as a resin for an optical sheet because it is excellent in transparency, heat resistance, and workability and has a good balance. In addition, an ultraviolet absorber, a fluorescent brightening agent, a flame retardant, and the like may be included as necessary.

[Light diffusion layer]
The optical sheet of the present invention may be composed of only a transparent resin, but in order to adjust the light diffusibility, a light diffusing layer made of particles having a light diffusing ability may be provided. The light diffusing layer may be uniformly or randomly dispersed in the entire optical sheet, only the lens portion, the entire portion other than the lens portion, only the light exit surface layer, only the light entrance surface layer, or the intermediate layer. In the light diffusion layer, light diffusing particles (light diffusing agent) having a refractive index of 0.01 or more different from that of the transparent resin are dispersed in the thermoplastic resin, and the diffusion direction of the light diffusion by the lens And adjusting the diffusion ratio and the like, it is possible to further increase the luminance uniformity in the viewing angle direction. Here, when the number of optical sheets used in the light source device is reduced, there may be a problem that an image of pins supporting the optical sheet appears in the backlight unit. However, by providing the light diffusion layer in the optical sheet of the present invention, the support pin image can be erased even when the number of sheets used is reduced.

  The thickness of the optical sheet of the present invention can be adjusted as appropriate, and is not particularly limited, but can usually be about 0.3 mm or more and 10 mm or less. If the thickness is less than 0.3 mm, the light diffusing action may not be sufficiently exerted, or the rigidity may be insufficient to maintain the shape stability. On the other hand, if the thickness exceeds 10 mm, the entire apparatus to which the optical sheet of the present invention is applied. It is because there is a possibility that cannot be made compact. More preferably, it is 0.5 mm or more and 5 mm or less. Note that the thickness of the optical sheet is the sum of the thickness of the base and the lens height in FIG.

[Light diffusing agent]
Examples of the material of the light diffusing particles (fine particles) include (meth) acrylic resins, styrene resins, polyurethane resins, polyester resins, silicone resins, fluorine resins, and synthetic resins such as copolymers thereof. Glass; clay compounds such as smectite and kaolinite; inorganic oxides such as silica and alumina; and the like. Of these materials, (meth) acrylic resins, silicone resins, and silica are particularly suitable. As the light diffusing agent, any one of these exemplified materials, a single material mixture, a mixed material, and a mixed material mixture may be used. In the present application, (meth) acryl means acryl and / or methacryl.

  The particle size of the light diffusing particles is preferably 0.1 μm to 50 μm, more preferably 0.3 μm to 10 μm, and further preferably 0.5 μm to 5 μm. When the particle size of the light diffusing particles is out of the above range, there is a possibility that sufficient light diffusing properties cannot be exhibited. Here, the average particle diameter of the light diffusing particles is a volume-based median diameter measured by a particle size distribution measuring device (Coulter counter).

  The ratio between the thermoplastic resin and the light diffusing particles may be adjusted as appropriate. For example, if the light diffusing particles are added in an amount of 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. Good. If the light diffusing particles are less than 0.01 part by mass with respect to 100 parts by mass of the thermoplastic resin, the luminance leveling adjustment by the light diffusing agent cannot be sufficiently performed. On the other hand, when the amount exceeds 10 parts by mass, the transparency of the light diffusion layer is reduced and the transmitted light is reduced, which may reduce the luminance of the entire light source device.

  In the case where the optical sheet of the present invention needs to have higher anisotropic light diffusion performance as the optical performance, low crosslink density organic fine particles capable of exhibiting anisotropic light diffusibility during molding of the optical sheet are preferably used. Monomers used as raw materials for the low crosslink density organic fine particles include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, n -Butyl (meth) acrylate, iso-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, hydroxyethyl (meth) acrylate, (Meth) acrylates such as hydroxypropyl (meth) acrylate; styrenes such as styrene, p-methylstyrene, vinyltoluene, pt-butylstyrene; N-phenylmaleimide, N-cyclohexylmaleimide, N-benzyl Maleimides such as reimide; (meth) acrylamide, (meth) acrylamides such as N-methylol (meth) acrylamide; acrylonitriles such as (meth) acrylonitrile; N-vinylpyrrolidone; or two of these The above can be mixed and used.

  Examples of the crosslinking agent used as a raw material for the crosslinked organic fine particles include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) ) Acrylate, bishydroxyethyl bisphenol A polyfunctional (meth) acrylates such as di (meth) acrylate; radically polymerizable crosslinking agents such as divinyloxyethoxy (meth) acrylate, diallyl phthalate, allyl (meth) acrylate, divinylbenzene; Polyfunctional epoxy compounds such as bisphenol A diglycidyl ether, diethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether; Or a polyfunctional isocyanate compound such as N-methylol melamine or N-methylol benzoguanamine; or a mixture of two or more thereof. it can.

  The crosslink density of the crosslinked organic fine particles for producing anisotropic diffusion is preferably 0.001% or more and 0.12% or less. Such organic fine particles having a low crosslinking density are spherical or substantially spherical at the raw material stage, but are formed in an ellipsoidal shape or a rod shape at a predetermined position (layer, etc.) of the optical sheet due to heat, shearing force, etc. received during the optical sheet molding. When this shape is changed, anisotropic diffusivity is expressed. In addition, a crosslinking density is a numerical value calculated | required by following Formula (1).

Fn (c): number of functional groups of the crosslinking agent used for production of radical polymerized crosslinked fine particles, provided that Fn (c) ≧ 2
Mw (c): Molecular weight of the crosslinking agent used for the production of radical polymerized crosslinked fine particles W (c): Mass blending ratio (%) of the crosslinking agent used for the production of radical polymerized crosslinked fine particles
W (m): Mass blending ratio (%) of monomer used for production of radical polymerized crosslinked fine particles
However, W (m) + W (c) = 100

[Antioxidant]
An antioxidant may be further added to at least one of the organic fine particles including the low crosslink density organic fine particles of the present invention and the thermoplastic resin. Since the antioxidant can suppress coloring of the thermoplastic resin and organic fine particles due to oxidation and deterioration during thermoforming, the luminance of the light source device to which the optical sheet of the present invention is applied can be more reliably exhibited.

  A conventionally well-known thing can be used as antioxidant. For example, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] or octadecyl-3- (3,5-di-t-butyl-1-hydroxyphenyl) propionate Hindered phenolic antioxidants; tris (2,4-di-t-butylphenyl) phosphite and tris [2-[[2,4,8,10-tetra-t-butyldibenzo [d, f] [ Phosphorous antioxidants such as 1,3,2] dioxaphosphin-6-yl] oxy] ethyl] amine; thiodiethylenebis [3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate] and the like having no aromatic ring, pentaerythrityltetrakis (3-laurylthiopropionate) Sulfur-based antioxidants such as; lactone-based antioxidants such as the reaction product of 3-hydroxy-5,7-di-t-butyl-furan-2-one and o-xylene; Hydroxylamine antioxidants such as oxidation products of alkylamines; 3,4-dihydro-2,5,7,8-tetramethyl-2- (4,8,12-trimethyltridecyl) -2H-benzopyran- Vitamin E antioxidants such as 6-ol can be used.

  Although the usage-amount of antioxidant may be adjusted suitably, normally, what is necessary is just to add about 0.005 mass% or more and 0.3 mass% or less with respect to a thermoplastic resin.

<About optical sheet manufacturing method and optical sheet molded by the manufacturing method>
The optical sheet of the present invention can be manufactured using a matrix that faces the surface shape described in the claims of the present invention. The shape of the matrix is a shape for realizing the surface shape described in <Surface shape of the optical sheet of the present invention>, <Unit lens structure> and <Combination of unit lens structures> in the section of the description of the invention. That is, it is sufficient if the convex portions of these surface structures are concave and the concave portions are convex. In the present invention, the matrix of these structures is referred to as “a matrix facing directly to form the surface shape”. (See FIG. 14).

  The optical sheet of the present invention can be manufactured by a manufacturing process having the matrix. Specifically, a transparent thermoplastic resin or a transparent thermoplastic resin can be blended with fine particles having light diffusibility and obtained by known extrusion molding or injection molding. When a laminated body is used to adjust optical performance and other physical properties, for example, when a light diffusing layer is installed only on a specific layer such as a light incident side or a lens side, or for improving the light resistance of an optical sheet. In the case of installing an absorber blending layer or an antistatic layer for preventing dust from adhering to the optical sheet due to static electricity, the extrusion method is particularly preferable from the viewpoint of productivity. In particular, when molding a lens shape with a narrow pitch, it is particularly preferable to use the method described in International Application No. (PCT / JP2009 / 0666525).

  Whether or not a molded product according to the design of the present invention can be manufactured can be confirmed by obtaining r1, r2, etc. from the molded product. Specifically, a vertical cross-sectional shape with respect to the length direction of the unit lens is photographed with an electron microscope or the like, and an appropriate curve (may be a combination of two or more) is fitted to the outer peripheral line of the convex part, and the tangent line is the basis. It is possible to obtain from the range of the outer peripheral line in which the angle formed with the line is a predetermined angle.

  With these various manufacturing methods, the optical sheet manufactured so that the configuration of the sheet has the configuration described in <Configuration of optical sheet of the present invention> is the <surface shape of optical sheet of the present invention>, <unit lens It becomes an excellent optical sheet having substantially the same shape and optical and mechanical characteristics as the optical sheet having the lens shape described in “Structure> and <Combination of Unit Lens Structures”.

<Combination with the second optical sheet and other optical sheets>
The optical sheet of the present invention is preferably used as the first optical sheet in order to efficiently use its high optical performance adjustment capability in other optical sheets and apparatus settings. By using it as the first optical sheet, the effect of improving the luminance in the viewing angle direction in the intermediate region of the adjacent cold cathode tubes of the light source device and the luminance in the viewing angle direction in the region immediately above the cold cathode tube are improved. The effect can be utilized to the maximum. In addition, when used as the first optical sheet, as the other optical sheet, a prism sheet, a diffusion sheet, a diffusion sheet with a lens, a reflective polarizing film, etc. can be used, and the combination thereof is more suitable depending on the conditions of the light source device. In this case, as the optical sheet closest to the front panel, it is preferable to use a diffusion sheet or a diffusion sheet with a lens. In particular, the use of at least one prism sheet for the second and subsequent optical sheets eliminates dark lines generated near the cold cathode tube and achieves high brightness and brightness uniformity on the light exit surface immediately before the front panel. It becomes possible.

  Further, for further cost reduction, it is required to reduce the number of optical sheets used in the light source device. Here, when the number of used optical sheets is reduced, not only is the luminance unevenness more difficult to be solved, but also there is a problem that an image of pins that support the optical sheet appears in the backlight unit. That is, in the conventional optical sheet, a large number (four or more) of optical sheet groups are required to erase the pattern of the line light source. Pin image was never a problem. In the conventional optical sheet, when the number of sheets used is reduced, the pattern of the line light source cannot be erased, so that the support pin image cannot be recognized.

  However, since the optical sheet of the present invention exhibits excellent light diffusion performance when used in combination with a prism sheet, the pattern of the line light source can be erased even if the number of optical sheets used is reduced to three. Become. Thus, it has been found that the image of the support pin becomes noticeable for the first time when the number of sheets used is reduced to 3 using the optical sheet of the present invention. Here, when the optical sheet of the present invention has a light diffusing layer, in the direct type light source device, the performance of erasing the image of the support pins that support the optical sheet is also improved. Accordingly, when the optical sheet of the present invention has a light diffusing layer, it is also a preferable aspect to use only three sheets of the optical sheet, the prism sheet and the light diffusing sheet of the present invention.

  The optical sheet manufactured according to the present invention can diffuse light in a desired direction and, as a result, can maintain the uniformity of the light, so that the power consumption reduction and the manufacturing cost of the liquid crystal display device, which are in increasing demand, are increased. It is extremely useful industrially because it can contribute to the reduction in the thickness of the liquid crystal display device as it can exhibit high brightness while reducing. Therefore, by applying the optical sheet of the present invention and the direct light source device having the optical sheet to a liquid crystal display device or the like, it is possible to reduce power consumption and manufacturing cost. Furthermore, the liquid crystal display device can be made thin.

  Next, actual examples as examples of the present invention will be described in Tables 1, 2 and 3, but the present invention is not limited to these examples.

<Method for measuring surface of optical sheet>
Using polycarbonate as a raw material, an optical sheet having an embossed surface (arithmetic average roughness Ra = 2 to 6 μm) on the light incident surface and a linear rod-shaped lens group having various cross-sectional shapes on the light output surface was manufactured by extrusion molding. The cross-sectional shapes of the produced various optical sheets were confirmed using a scanning electron microscope. Table 1 shows the observation results of the surface shape.

<Evaluation of uneven brightness>
A white reflector is provided on the inner surface of a plastic case with an inner dimension of 690 mm, depth of 390 mm, and depth of 10 mm, and 19 cold cathode fluorescent tubes with a diameter of 3 mm are spaced 20.5 mm apart from the bottom of the reflector. The optical sheets of the present invention having various shapes were arranged on the direct type light source device arranged in parallel so that the lens processing surface was up and the longitudinal direction of the lens was parallel to the longitudinal direction of the cold cathode tube. On this optical sheet, a commercially available light diffusion sheet (CH273 manufactured by Hiroshige Kogyo (Suzhou) Co., Ltd.), prism sheet (BEF II 90/50 manufactured by Sumitomo 3M: apex angle 90 degrees, pitch 50 μm), micro lens sheet ( Made by Hiroshige Kogyo (Suzhou) Co., Ltd. ML24M: an optical sheet with a hemispherical convex lens group arranged finely on one surface) as shown in Table 2, and in each combination, the direct light source device The luminance unevenness was visually observed from a position 400 mm away from the center in the vertical direction. The brightness unevenness is evaluated in 10 stages, and the larger the value, the less the brightness unevenness, indicating that the lamp image of the cold cathode tube is not noticeable. The evaluation results are shown in Table 1.

<Support pin image, brightness unevenness evaluation>
In the test, a white reflector was provided on the inner surface of a plastic case with an inner width of 690 mm, a depth of 390 mm, and a depth of 25 mm, and 8 cold cathode fluorescent tubes with a diameter of 3 mm were spaced 45 mm apart from the bottom of the reflector. The direct type light source device in which the support pins are arranged as shown in FIG. 12 was used. On the direct type light source device, the optical sheets of the present invention of various shapes were arranged such that the lens processing surface was on top and the longitudinal direction of the lens was parallel to the longitudinal direction of the cold cathode tube. A prism sheet (BEF II 90/50: vertical angle 90 degrees, pitch 50 μm, manufactured by Sumitomo 3M) is placed on this optical sheet, and a microlens sheet (manufactured by Hiroshige Kogyo (Suzhou) Co., Ltd.) ML24M: one side An optical sheet in which hemispherical convex lens groups are finely arranged is placed on the surface. In each optical sheet group, the support pin image and the luminance unevenness were visually observed from a position 400 mm away from the center of the direct light source device in the vertical direction. As for the support pin image, a case where it can be visually confirmed is defined as “bad”, a portion which can be confirmed as “good”, and a case where it cannot be confirmed as “excellent”. The brightness unevenness is evaluated in 10 stages, and the larger the value, the less the brightness unevenness, indicating that the lamp image of the cold cathode tube is not noticeable. The evaluation results are shown in Table 3.

  Example 13 is an optical sheet in which the total (r1) and the total (r2) are within the specified range of the present invention, and a light diffusion layer is provided. When the optical sheet of Example 13 is used, the support pin image can be erased by the group of three optical sheets, and luminance unevenness is small.

  By using the form of the present invention, the first optical sheet capable of improving the luminance ratio at the intermediate point between the line light sources arranged in parallel to each other and / or directly above the cold cathode tube and obtaining a uniform luminance distribution, and Type light source devices and liquid crystal display devices can be provided, which are extremely useful in industry.

1: Cold cathode tube lamp 2: Reflective film 3: 1st optical sheet 4: 2nd optical sheet 5: 3rd optical sheet 6: 4th optical sheet 7: Front panel P: Lens part width H: Lens portion height θ1: Angle formed by the tangent of the curved portion R1 and the base line θ2: Angle formed by the tangent of the curved portion R2 and the base line R1: Curved portion R2 satisfying θ1 ≧ 40 °: 25 ° ≦ θ2 ≦ 35 ° Curve portions r1 and r2 that are: projection lengths to the base portions corresponding to the curve portions R1 and R2, respectively

Claims (12)

An optical sheet having a convex lens group formed in a linear bowl shape on the surface,
In the lens group, the convex portion outer peripheral line in the vertical cross-sectional shape with respect to the length direction of the unit lens is mainly composed of the curved portion, and an angle (θ1) formed between the tangent and the base line at all points on the curve. ) Is a curved line portion (R2) in which the angle (θ2) between the tangent line and the base line at all points on the curved line (R1) where θ1 ≧ 40 ° is 25 ° ≦ θ2 ≦ 35 ° )
The ratio of the total length (r1) projected on the base line of the unit lens shape of the curved portion (R1) to the total length of the base line is 25% to 60%, and the unit lens of the curved portion (R2) An optical sheet comprising a unit lens having a ratio of the total length (r2) projected onto the shape base line to the total base line length of 25% to 60%.   2. The optical sheet according to claim 1, wherein the unit lens contains the curved portion (R1) and the curved portion (R2) two by two.   The optical sheet according to claim 1 or 2, wherein the curved portion (R1) is a part of a quadratic curve.   The unit lens has a ratio (H / P) of the length (P) of the base line and the height (H) from the base line to the apex of the lens in the vertical cross-sectional shape with respect to the length direction. The optical sheet according to any one of claims 1 to 3.   An optical sheet comprising at least 50 area% of the entire light exit surface of the unit lens having the shape defined in any one of claims 1 to 4.   An optical sheet in which the lens group is composed only of unit lenses having the shape defined in any one of claims 1 to 4.   7. The lens group according to claim 1, wherein in the vertical cross-sectional shape with respect to the length direction of the unit lens, the distance between the tops of the convex portion outer peripheral lines of adjacent unit lenses is 300 μm or less. Optical sheet. The material constituting the optical sheet contains a thermoplastic resin and fine particles having an average particle diameter different from that of the thermoplastic resin of 0.1 μm to 50 μm,
The optical sheet according to any one of claims 1 to 7, wherein an amount of the fine particles is 0.01 to 10 parts by mass with respect to 100 parts by mass of the thermoplastic resin.   A method for producing an optical sheet, comprising using a master die facing to form the surface shape of the optical sheet according to claim 1.   An optical sheet manufactured by the manufacturing method according to claim 9.   A light source device for a display device comprising the optical sheet according to any one of claims 1 to 8 and a prism sheet.   A display device comprising the light source device for a display device according to claim 11.