JP2011169923A - Manufacturing method for optical sheet, light source unit including the optical sheet, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an optical sheet by which a first optical sheet having a variety of surface shapes and optical characteristics can be manufactured from one shaping roll, because reduction in the cost and thickness is requested for a display device using a directly-below type light source unit. <P>SOLUTION: In the method for manufacturing a first optical sheet, an optical sheet base material formed with cylindrical optical elements on the light-emitting surface with a pitch P of 200 μm or less, a height H of 200 μm or less, and an H/P value of 0.1 to 0.9 is stretched under the following condition: 100×(¾A-B¾)/((A+B)/2)≤10, wherein A is the brightness at a point directly above cold-cathode tube lamps on the optical sheet closest to a front panel, and B is the brightness at a center point of adjacent cold-cathode tube lamps on the optical sheet, when 2d<W is conditioned, wherein an interval between multiple cold-cathode tube lamps as a linear light source is W, and a distance between the optical sheet placed on the light source and the light source is d. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

In the present specification, the first optical sheet refers to an optical sheet disposed first in the direction from the light source to the liquid crystal panel, and the second optical sheet, the third optical sheet, and the fourth optical sheet. Indicates optical sheets arranged in the second, third and fourth positions, respectively (see FIG. 1). In addition, the optical sheet closest to the front panel corresponds to the third optical sheet denoted by reference numeral 5 in FIG.
The sheet original fabric in this specification refers to a sheet-like molded product of a thermoplastic resin before stretching.

  In recent years, the display device has been replaced by a liquid crystal display from a display using a cathode ray tube, and the screen has been enlarged.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 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 a light source.

  On the screen of a liquid crystal display device using a direct type light source, there is a problem that unevenness of brightness occurs such that the portion where the cold cathode tube exists is bright while the portion where it does not exist is relatively dark, and the cold cathode tube is reflected on the screen. is there. Therefore, by arranging a light diffusion plate 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.

  At the present stage, an optical sheet is employed between the light source unit and the front panel in order to further suppress uneven brightness and increase the light uniformity. As an optical sheet, a plurality of sheets such as a prism sheet as a second optical sheet and a microlens sheet as a third optical sheet are stacked on a light diffusion plate as a first optical sheet. . However, such a method requires a member cost corresponding to the number of sheets to be used, and these sheets are manually installed in a clean room, which requires labor costs.

  However, the liquid crystal display is required to be further thinned. For this reason, the distance between the cold cathode tube and the screen has to be reduced, and light cannot be sufficiently diffused. In order to reduce the cost, the number of cold cathode tubes is also reduced. As a result, luminance unevenness has become a larger problem, and thus a light diffusing plate having an excellent light diffusing action is desired.

  As an optical sheet for suppressing luminance unevenness and improving luminance, as a case of selecting a light diffusing plate of the first optical sheet, for example, in Patent Document 1, a prism portion is provided on at least one surface. An optical sheet having a dispersed phase dispersed in a continuous phase is disclosed. Since this dispersed phase has a refractive index different from that of the continuous layer, the light emitted from the cold cathode fluorescent lamp can be diffused in the plate surface direction, and the light is further diffused by the prism portion formed on the surface. Such a dispersed phase is incompatible with the continuous phase or hardly compatible with the continuous phase, and is deformed into a rugby ball shape when the sheet is drawn or uniaxially stretched, and is thus anisotropy. According to the embodiment, a polystyrene resin is added and dispersed in a polypropylene resin together with a compatibilizing agent, and then extruded at a draw ratio of about 3 times, so that the dispersed phase made of the polystyrene resin becomes a rugby ball shape. There is a description that it became.

  Similarly, as a case where a light diffusing plate is selected as the first optical sheet, Patent Document 2 can form a similar second solid pattern by stretching a sheet having the first surface shaping. Is disclosed.

JP 2007-20669 A JP 2007-137058 A

  An object of the present invention is to erase a lamp image that is a problem in a display device using a direct light source unit using a linear light source by using a first optical sheet. A display device using a direct light source unit is usually combined with a light source, an optical sheet, and a front panel of a liquid crystal display device. In this product development, the specifications of the front panel and light source are determined from the viewpoint of power consumption, circuit, and external design of the display device, and the optical sheet is selected. The selection and design of the optical sheet is required to satisfy optical performance requirements. In such an optical sheet, the first optical sheet plays a large role. In addition to the optical performance, the first optical sheet is required to maintain the synthesis of the entire direct light source and to have mechanical strength to support other optical sheets when combining a plurality of optical sheets. Moreover, since it is located closest to the light source, heat resistance and ultraviolet resistance are required.

  In recent years, there has been a demand for cost reduction in display devices using direct light source units. There is also a great need for thinning. The light source setting that meets these requirements is a condition of 2d <W where the distance between the light sources of adjacent linear light sources of the light source unit is W and the distance between the light source and the first optical sheet is d. There are many other design items for the light source and front panel, so there is little room for choice. However, there is much room for selection for optical sheets where optical design is a major design item. At least one optical sheet, that is, the first optical sheet is always used. Therefore, the influence of the cost of the first optical sheet on the cost of the entire liquid crystal display device is great. Under such circumstances, there is a problem in the manufacturing method in order to satisfy each performance required for the first optical sheet and create a sheet at low cost. Usually, a 1st optical sheet is manufactured by extrusion molding of the thermoplastic translucent resin which is the main component. Adjustment of basic plate shape such as thickness can be done by adjustment of molding machine, but surface shaping adjustment of optical elements such as mat, emboss, cylindrical lens etc. can also have options such as press and patterning after sheet molding However, from the viewpoint of economic efficiency, it is carried out by surface processing of the surface of the polishing roll because it is incorporated into the extrusion and batch process using the polishing roll subjected to surface processing. The surface processing of polishing rolls involves numerous steps, such as roll removal, pre-processing, fine processing with precision lathes, post-processing, and roll mounting adjustment, and this greatly affects the economics of the first optical sheet. Was exerting.

  The present invention has been made in view of the above problems, and provides an optical sheet manufacturing method capable of manufacturing a first optical sheet having various surface shapes and optical performances from a single polishing roll provided with a three-dimensional pattern for transfer. The task is to do.

  Based on the above problems, the inventors have intensively studied, as a result of extending the original optical sheet having a cylindrical optical element at least on the light exit surface in the cylinder direction thereof, in a direct light source unit using a linear light source, The first optical that can erase the lamp image on the optical sheet closest to the front panel in any optical sheet combination, any linear light source distance setting, any light source and first optical sheet distance setting The present invention was completed by finding that a sheet could be obtained. The solving means of the present invention will be described below.

  In the first optical sheet manufactured by the present invention, the interval between a plurality of cold-cathode tube lamps which are linear light sources is W, the distance between the optical sheet placed on the light source and the light source is d, and 2d <W When the above condition is satisfied, the cylinder is arranged at the closest position from the light source, and at least the light emitting surface has a pitch P of 200 μm or less, a height H of 200 μm or less, and a H / P value between 0.1 and 0.9. The optical elements must be shaped. In the arrangement of the first optical sheet alone or the combination of the second and third optical sheets, the sheet surface closest to the front panel has the condition (1) The brightness at a point immediately above the cold-cathode tube lamp is A When the brightness at the midpoint between adjacent cold-cathode tube lamps on the optical sheet is B, the first optical element is set so that 100 × (| A−B |) / ((A + B) / 2) ≦ 10. The sheet is produced by uniaxially stretching the sheet in the cylindrical direction.

  The thermoplastic resin used in the first optical sheet produced according to 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. Those that are excellent in transparency, heat resistance, and workability and that have a good balance are used. Since transparency and the like are naturally required for other sheets, they can be used as resins constituting other sheets. Further, light diffusing particles may be dispersed.

  The first optical sheet manufactured according to the present invention has a cylindrical lens group formed on at least one surface. The cylindrical lens in the present invention has a certain length and a cross-sectional shape such as an isosceles triangle or a semicircular kamaboko shape unlike a normal lens, and in this specification, this is a substantially triangular bowl shape or a substantially elliptic bowl shape, respectively. (See FIGS. 3 and 4). A lens capable of diffusing or condensing incident light within each fixed visual field. What is necessary is just to adjust the magnitude | size of a cylindrical lens suitably.

  The cylindrical lens on the first optical sheet manufactured according to the present invention may be formed between the adjacent cylindrical lenses formed in parallel to the entire first optical sheet. Adjacent without spacing to enhance. When the interval is set, adjustment for increasing the light diffusion efficiency of the interval portion, for example, adding light diffusing particles to the thermoplastic resin of the first optical sheet, finely increasing the light diffusion efficiency on the surface or back surface of the interval portion Make irregularities. The cylindrical lens may be formed up to the end, but the end may be left flat for fixing.

  The resin constituting the lens portion of the cylindrical lens on the first optical sheet manufactured according to the present invention can be the same as the thermoplastic resin used for the first optical sheet. In the first optical sheet, The resin of the lens portion and the portion other than the lens portion may be different, but usually the same resin. In the thermoplastic resin constituting the lens portion, light diffusing particles may be dispersed in the same manner as the thermoplastic resin constituting the lens portion. When the dispersed fine particles are optically anisotropic using cross-linked organic fine particles, the major axis direction is also substantially the same as the length direction of the cylindrical lens.

  When the first optical sheet manufactured according to the present invention is uniaxially stretched in the cylinder direction from the initial cylindrical lens shape and deformed, on the optical sheet closest to the front panel with each combination of the light source and the optical sheet under various conditions. 100 × (| A−B |) where A represents the luminance at a point immediately above the cold-cathode tube lamp and B represents the luminance at an intermediate point between adjacent cold-cathode tube lamps on the optical sheet. / ((A + B) / 2) ≦ 10 is satisfied.

  The manufacturing method of the present invention includes a step (A) of obtaining a first basic optical sheet by applying a cylindrical basic lens shape and a step (B) of uniaxially stretching the shape of the original in the cylinder direction. It is characterized by.

  In the previous stage of the step (A), a step of mixing the light diffusing particles may be included, or a step for functionalizing the surface (providing an ultraviolet resistant function and an antistatic function) may be included. The shape of the polishing roll for transferring the cylindrical shape used in the step (A) is 200 μm or less because the depth corresponds to the height H of the cylindrical lens, and the width corresponds to the width P of the cylindrical lens, and is 200 μm or less. Is preferably used. In the subsequent stage of the step (B), a step for functionalizing the surface of the optical sheet manufactured by the manufacturing method of the present application (providing an ultraviolet resistant function and an antistatic function) may be included.

  The direct type light source unit of the present invention includes the first optical sheet and the cold cathode tube, and the first optical sheet and the cold cathode tube so that the length direction of the cylindrical lens coincides with the length direction of the cold cathode tube. Is arranged.

  The display device of the present invention includes a direct light source unit manufactured according to the present invention.

  Since the optical sheet produced according to the present invention accurately transfers the shape of the polishing roll for transfer in step (A) in the production process, it is appropriately deformed in the stretching step in step (B). Demonstrate desired optical performance. Therefore, the optical sheet manufactured according to the present invention can reduce the number of cold-cathode tubes as light sources or change the distance between the light source and the first optical sheet (that is, the linear light source adjacent to the light source unit). Light is desired even if the light source condition does not change and the combination of the optical sheets changes, assuming that the interval between the light sources is W and the distance between the light source and the first optical sheet is d), or 2d <W. Therefore, the present invention is extremely useful in the industry as a device capable of exhibiting high luminance while reducing the manufacturing cost of the liquid crystal display device, which is in increasing demand.

The light source setting that meets the market demand for thinning and reduction in the number of lamps is an apparatus in which 2d <W when the distance between the light sources of adjacent linear light sources is W and the distance between the light source and the first optical sheet is d. It becomes a setting condition. Under these conditions, the luminance state on the optical sheet that is closest to the front panel finally is A, the luminance at the point immediately above the cold-cathode tube lamp is A, and the intermediate point between adjacent cold-cathode tube lamps on the optical sheet In the present invention, the first optical sheet capable of satisfying 100 × (| A−B |) / ((A + B) / 2) ≦ 10 can be supplied, where B is the luminance in the present invention. The first optical sheet will be described.
The explanation will be made with reference to the drawings. The present invention is not limited to the embodiments shown in the drawings. In the present specification, the first optical sheet refers to an optical sheet disposed first in the direction from the light source to the liquid crystal panel, and the second optical sheet, the third optical sheet, and the fourth optical sheet. Indicates optical sheets arranged in the second, third and fourth positions, respectively (see FIG. 1). The optical sheet closest to the front panel corresponds to the third optical sheet denoted by reference numeral 5 in FIG. The sheet raw fabric refers to a sheet-like molded product of a thermoplastic resin before stretching.

Hereinafter, the structure of the optical sheet according to the present invention will be described first, and then the manufacturing method thereof will be described.
<Optical sheet>
The thermoplastic resin constituting the first optical sheet according to the present invention is not particularly limited as long as it is transparent and has an appropriate strength as a main component of the first 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; poly An arylate resin; a polyethersulfone resin; a mixed resin of two or more of these can be used. A polycarbonate resin, a styrene resin, or a norbornene resin is preferably used. Among these, the polycarbonate resin is particularly preferable as the resin for the first optical sheet because it is excellent in transparency, heat resistance, and processability and has a good balance.

  The above thermoplastic resin has been exemplified as constituting the first optical sheet. However, since transparency and the like are naturally required for other sheets, they can also be used as resins constituting other sheets.

  The first optical sheet according to the present invention may be composed of only a transparent resin, but a light diffusion layer may be provided in order to adjust the light diffusion property. The light diffusing layer may be uniformly or randomly dispersed in the entire first 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. The light diffusion layer is one in which light diffusing particles are dispersed in a thermoplastic resin, and diffuses light in a predetermined direction.

  The thickness of the light diffusing layer 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 exhibited, or the rigidity may be insufficient to maintain the shape stability, whereas if it 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 about 0.5 mm or more and 5 mm or less.

  Examples of the material for the light diffusing particles include (meth) acrylic resins, styrene resins, polyurethane resins, polyester resins, silicone resins, fluorine resins, and synthetic resins such as copolymers thereof; glass; And 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.

  The amount of the fine particles used is preferably 0.1 parts by mass or more and 20 parts by mass or less, more preferably 0.2 parts by mass or more and 10 parts by mass with respect to 100 parts by mass of the thermoplastic resin constituting the first optical sheet. Or less. If the amount used is less than 0.1 parts by mass, the light incident on the first optical sheet may not be sufficiently diffused to exhibit the expected effect of containing fine particles. On the other hand, when the amount used exceeds 20 parts by mass, it may be difficult to extrude the first optical sheet, or the amount of transmitted light may be reduced to lower the luminance.

  The ratio of the thermoplastic resin and the light diffusing particles may be adjusted as appropriate. For example, the light diffusing particles are added in an amount of 0.1 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. do it. If the light diffusing particles are less than 0.1 parts by mass with respect to 100 parts by mass of the thermoplastic resin, there is a possibility that the luminance uniformity cannot be sufficiently improved. On the other hand, when it exceeds 5.0 parts by mass, the transparency of the light diffusion layer may be lowered, and the luminance itself may be lowered.

  When it is desired to add anisotropic diffusion performance as optical performance to the first optical sheet, crosslinked organic fine particles are preferably used. Monomers used as raw materials for the crosslinked organic fine particles include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and 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, hydroxypropyl (Meth) acrylates such as (meth) acrylate; styrenes such as styrene, p-methylstyrene, vinyltoluene, pt-butylstyrene; N-phenylmaleimide, N-cyclohexylmaleimide, N-benzylmale 1 type of maleimides such as amides; (meth) acrylamides such as (meth) acrylamide and 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 crosslinking density of the crosslinked organic fine particles for producing anisotropic diffusion is preferably 0.001% or more and 0.12% or less.

  The refractive index of the crosslinked organic fine particles according to the present invention is different from the refractive index of the thermoplastic resin constituting the light diffusion layer. When cross-linked organic fine particles having the same refractive index are used, light is not refracted, and the brightness uniformity cannot be sufficiently increased. However, on the other hand, since the refractive index of the resin differs depending on the type, the types of the resin constituting the crosslinked organic fine particles and the thermoplastic resin may be different. However, in order to exhibit the light diffusion anisotropy more reliably, it is preferable that the difference in refractive index between the thermoplastic resin and the crosslinked organic fine particles is 0.03 or more.

  An antioxidant may be further added to at least one of the crosslinked organic fine particles and the thermoplastic resin of the present invention. Since the antioxidant can suppress coloring of the crosslinked organic fine particles due to oxidation or deterioration during heat molding, the luminance of the backlight unit 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 the whole bridge | crosslinking organic fine particle.

  A cylindrical lens group is formed on at least one surface of the optical sheet of the present invention. The cylindrical lens in the present invention refers to a lens that has a certain length and a cross-sectional shape such as an isosceles triangle and a semicircular kamaboko shape unlike a normal lens, and that can diffuse or condense incident light in each fixed visual field. . The size of the cylindrical lens is not particularly limited as long as it is adjusted as appropriate. For example, the width is about 10 μm to 200 μm, the height is about 10 μm to 200 μm, and the length is the same as the length of the optical sheet or excluding the end. Can be the same as the length of the part. The cross-sectional shape is not particularly limited as long as it can diffuse light in the direction orthogonal to the lens length. For example, an isosceles triangle, a semicircle, a parabola, a lower part is a rectangle, and an upper part is a semicircle. . The apex angle of the isosceles triangle can be 60 ° or more and 120 ° or less. The central angle of the semicircle is not limited to 180 °, and may be adjusted so that light can be diffused in a certain direction.

  A plurality of cylindrical lenses may be formed on at least one surface of the optical sheet of the present invention, and the adjacent cylindrical lenses may be spaced apart from each other, but are preferably adjacent to each other without increasing the interval in order to increase the light diffusion efficiency. When the interval is set, adjustment for increasing the light diffusion efficiency of the interval portion, for example, adding light diffusing particles to the thermoplastic resin of the first optical sheet, finely increasing the light diffusion efficiency on the surface or back surface of the interval portion Make irregularities. The cylindrical lens may be formed up to the end, but the end may be left flat for fixing.

As the resin constituting the lens part of the cylindrical lens, the same resin as that constituting the first optical sheet can be used, and the resin other than the lens part and the lens part may be different. Use the same resin. In the thermoplastic resin constituting the lens portion, light diffusing particles may be dispersed in the same manner as the thermoplastic resin constituting the lens portion. When the dispersed fine particles are cross-linked organic fine particles and have optical anisotropy, the long axis direction is also substantially the same as the length direction of the cylindrical lens. In addition, a layer containing an ultraviolet absorber, a layer containing an antistatic agent, or both an ultraviolet absorber-containing layer and an antistatic agent-containing layer may be formed on at least the side opposite to the side on which the cylindrical lens is formed. . That is, a layer having an action other than the light dispersion action may be formed on at least one side of the light diffusion layer. Here, “at least one side” is not limited to the case where layers having different functions are formed directly on the light diffusion layer. For example, a plurality of layers such as an ultraviolet absorber-containing layer and an antistatic agent-containing layer Is intended to be laminated on one side of the light diffusion layer. Moreover, since there is no trouble even if it exists on both sides, this form is not excluded. These layers having different functions reduce the ultraviolet rays emitted from the illuminant to suppress the coloring of the optical sheet, or suppress the charging to suppress the decrease in luminance due to the adhesion of dust or extend the life of the electronic device. Or the like is added to the optical sheet of the present invention.

  Conventionally known UV absorbers and antistatic agents can be used. For example, as a UV absorber, a salicylic acid phenyl ester UV absorber; a benzophenone UV absorber; a triazine UV absorber; a benzotriazole UV absorber; a cyclic imino ester UV absorber; and a hindered phenol structure in the molecule Hybrid UV absorbers with hindered amine structures; low molecular UV absorbers such as triphenylcyanoacrylate UV absorbers, and high molecular UV light in which these low molecular UV absorbers are attached to the polymer An absorbent (for example, Halus Hybrid (registered trademark) manufactured by Nippon Shokubai Co., Ltd.) can be used.

  Antistatic agents include alkyl sulfonic acids, alkyl benzene sulfonic acids, olefinic sulfates such as Li, Na, Ca, Mg, and Zn salts thereof or metal salts thereof; anionic surface activity such as phosphate esters of higher alcohols. Agents; Cationic surfactants such as tertiary amines, quaternary ammonium salts, cationic acrylic ester derivatives, cationic vinyl ether derivatives; amphoteric salts of alkylamine betaines, amphoteric salts of alanine carboxylates or sulfonates, Amphoteric surfactants such as amphoteric salts of alkyl imidazolines; Nonionic surfactants such as fatty acid polyhydric alcohol esters, polyoxyethylene adducts of alkyl (amines); Polyamide elastomers such as polyether ester amides and polyester amides This Can. In addition, conductive resins such as polyvinyl benzyl type cationic resins and polyacrylic acid type cationic resins can also be used as an antistatic agent.

  Although the usage-amount of a ultraviolet absorber and an antistatic agent can be suitably adjusted according to each function, Usually, it is about 1-50 mass parts with respect to 100 mass parts of resin which comprises each layer.

  These layers having different functions may be obtained by bonding a sheet in which an ultraviolet absorber or an antistatic agent is uniformly dispersed in a thermoplastic resin similar to the light diffusion layer onto an optical sheet or the like by thermocompression bonding or an adhesive. Or you may dry or cool, after apply | coating the paste containing an ultraviolet absorber etc. on an optical sheet. Alternatively, a thermoplastic resin blended with a light diffusing agent and a thermoplastic resin blended with an ultraviolet absorber or an antistatic agent may be coextruded.

  The thickness of the layer having these different functions may be appropriately adjusted according to each function, etc., but can usually be about 1 to 50 μm.

  The size and shape of the optical sheet of the present invention are not particularly limited, and may be adjusted to the size and shape of the liquid crystal display device, for example.

<Combination with the second optical sheet and other sheets>
In order to further erase the lamp image or improve the luminance, a second optical sheet can be combined with the first optical sheet. The second optical sheet is preferably a lens sheet, a diffusion sheet, a reflective polarizing film, or a brightness enhancement film. Further, a third optical sheet and a fourth optical sheet can be combined to provide optical performance. The third optical sheet and the fourth optical sheet are preferably selected from a lens sheet, a diffusion sheet, a reflective polarizing film, and a brightness enhancement film, and at least one of these is selected depending on the desired optical performance. Alternatively, a plurality of arbitrary combinations can be selected. In particular, under the condition of W> 2d and when the value of W / 2d is greater than 1.5, the luminance unevenness is small when the other optical sheets are combined, and the overall luminance value is not reduced. It becomes easy to balance.
<Optical sheet manufacturing method>
The production method of the present invention is characterized by including a step (A) for obtaining a cylindrical basic lens shape to obtain an original optical sheet and a step (B) for uniaxially stretching the shape in the cylinder direction.

  In the previous stage of the step (A), a step of mixing the light diffusing particles may be included. The step of mixing the light diffusing particles is used when adjusting the optical performance (more light diffusion). As a method for dispersing the light diffusing particles in the thermoplastic resin, a general method can be used. For example, after the thermoplastic resin is heated to the melting temperature or higher and softened, the light diffusing particles may be added and sufficiently stirred and mixed.

  In addition, a step for functionalizing the surface (providing an ultraviolet resistant function, an antistatic function, and a color change prevention function) may be included. It is preferable to perform molding after dispersing functional components (UV absorber, UV stabilizer, antistatic agent, antioxidant) in the thermoplastic resin before molding. A general one can be used. For example, after the thermoplastic resin is heated to the melting temperature or higher and softened, the functional component is added and sufficiently stirred and mixed.

  As a method for dispersing in the thermoplastic resin, a general method can be used. For example, after the thermoplastic resin is heated to the melting temperature or higher and softened, the functional component is added and sufficiently stirred and mixed.

  Next, the sheet-shaped original fabric is molded in the step (A) in which a cylindrical basic lens shape is imparted to obtain an optical sheet original fabric. The molding method is not particularly limited, but an extrusion molding method is preferably used. That is, the dispersion is melted and extruded into a sheet to form an optical sheet original.

  The step of dispersing the light diffusing particles and functionalizing components in the transparent thermoplastic resin and the step (A) are integrated by heating and mixing raw materials such as the transparent thermoplastic resin with an extruder. It is also possible to carry out.

  A cylindrical lens group is formed on at least one surface of the obtained original optical sheet through step (A), and uniaxially stretched in the same direction as the length of the cylindrical lens in step (B). Any of these steps (A) and (B) may be performed first or simultaneously. That is, after forming a cylindrical lens and obtaining the optical sheet original fabric, it may be uniaxially stretched, or the optical sheet original fabric before cylindrical molding may be uniaxially stretched before forming a cylindrical lens, or a plurality of These polishing rolls may be used to simultaneously mold the optical sheet, form a cylindrical lens, and perform uniaxial stretching. When the uniaxial stretching is performed first, the uniaxial stretching is performed in the length direction of the cylindrical lens to be formed next, or the cylindrical lens is formed according to the uniaxially stretched direction.

When forming a cylindrical lens and uniaxial stretching simultaneously using a plurality of polishing rolls, for example, a groove for forming a cylindrical lens is formed in at least one of the first rolls, and used for the above-described sheet molding . Among the rolls, there are methods such as narrowing the gap between the final rolls to increase the pressure or adjusting the draw ratio by increasing the take-up speed of the sheet from the final roll.

  The stretching ratio, that is, (sheet thickness before stretching / sheet thickness after stretching) × 100 (%) is preferably 120% or more. This is because if the cross-linked organic particles are 120% or more as the light diffusing fine particles, the spherical or substantially spherical light dispersant can be more surely formed into an ellipsoid shape and can be oriented in the stretching direction. However, since the strength of the light diffusing plate may be lowered when it is stretched excessively, the stretch ratio is preferably 400% or less, more preferably 300% or less. The “sheet thickness before stretching” in the above formula when three rolls are used in the steps (A) and (B) may be the gap between the first roll and the second roll immediately after extrusion.

  The direct type light source unit of the present invention includes the optical sheet and the cold cathode tube, and the optical sheet and the cold cathode tube are arranged so that the cylinder direction of the lens on the optical sheet coincides with the length direction of the cold cathode tube. It is characterized by being.

  In the manufacturing process, the optical sheet manufactured according to the present invention accurately transfers the shape of the polishing roll for transfer to the optical sheet original in the process (A), while being appropriately deformed in the process (B). Therefore, the desired optical performance is exhibited. Therefore, the optical sheet manufactured according to the present invention does not change the number of cold cathode tubes that are light sources, the distance between the light source and the first optical sheet changes, or the light source condition does not change. Even if the combination changes, the light can be diffused in the desired direction, and as a result, the uniformity of the light can be maintained. It is extremely useful industrially as possible.

  Therefore, the manufacturing cost can be reduced by applying the light diffusing plate of the present invention and the direct light source unit having the light diffusing plate to a liquid crystal display device or the like.

  Next, as an embodiment of the present invention, an example will be given and described when the distance W between adjacent lamps is 30 mm, but the present invention is not limited to this example.

[Production Example 1]
100 parts of polycarbonate resin ("Iupilon E2000FN": manufactured by Mitsubishi Engineering Plastics), 0.01 part of phosphorous antioxidant ("Irgaphos 168": manufactured by Ciba Specialty Chemicals), oxazole-based fluorescent whitening agent (""UbitexOB" (manufactured by Ciba Specialty Chemicals Co., Ltd.) is supplied to a sheet extrusion molding machine having three polishing rolls with a vent and a gear pump, and an extrusion temperature of 290 ° C and a first roll temperature of 140 The first optical sheet was extruded through the optical sheet at a temperature of 2 ° C., a second roll temperature of 180 ° C., and a third roll temperature of 190 ° C. The first and second rolls are mirror rolls, and the third roll is a roll engraved with a substantially elliptical cylindrical lens having a lens pitch of 100 microns and a lens height of 60 microns (the direction of the lens ridge is a roll). The sculpture was used so as to be parallel to the rotation direction. Also, the plate thickness is adjusted to 2.0 mm at the outlet of the third roll, and then the peripheral speed of the take-up roll is higher than that of the third roll to be 1.5 mm. Thus, an optical sheet 1 stretched in a uniaxial direction with a thickness of 1.5 mm was obtained. The optical property evaluation results of the obtained optical sheet 1 are shown in Table 1.

[Production Example 2]
Same as Production Example 1 except that the thickness at the outlet of the third roll was 2.5 mm, and then the peripheral speed of the take-up roll was adjusted to be higher than that of the third roll to 1.5 mm. Thus, an optical sheet 2 finally stretched in a uniaxial direction with a thickness of 1.5 mm was obtained. The optical property evaluation results of the obtained optical sheet 2 are shown in Table 1.

[Production Example 3]
The third roll has a lens pitch of 200 microns, a lens height of 150 microns, and an apex (the deepest part of the engraving surface) with a radius of curvature of 10 microns. The thickness at the exit of the third roll is 2.5 mm, and the peripheral speed of the take-up roll is then made higher than that of the third roll to obtain a thickness that is parallel to the rotation direction of the roll. An optical sheet 3 that was finally stretched in a uniaxial direction with a thickness of 1.5 mm was obtained in the same manner as in Production Example 1 except that the thickness was adjusted to 1.5 mm. The optical property evaluation results of the obtained optical sheet 3 are shown in Table 1.

[Production Example 4]
Except for further adding 0.2 parts of silica fine particles ("Seahoster KE-P150" manufactured by Nippon Shokubai Co., Ltd.) as a light diffusing agent, it was finally stretched in a uniaxial direction of a thickness of 1.5 mm in the same manner as in Production Example An optical sheet 4 was obtained. The optical property evaluation results of the obtained optical sheet 4 are shown in Table 1.

[Production Example 5]
The film was finally stretched in a uniaxial direction of a thickness of 1.5 mm in the same manner as in Production Example 1 except that 0.5 part of PMMA-based fine particles (“Eposter MA1002” manufactured by Nippon Shokubai Co., Ltd.) was further added as a light diffusing agent. An optical sheet 5 was obtained. The optical property evaluation results of the obtained optical sheet 5 are shown in Table 1.

[Comparative Production Example 1]
A roll (engraved so that the direction of the lens ridge line is parallel to the rotation direction of the roll) engraved with an approximately elliptical cylindrical lens having a lens pitch of 300 microns and a lens height of 150 microns was used for the third roll. The optical sheet 6 finally stretched in a uniaxial direction with a thickness of 1.5 mm was obtained in the same manner as in Production Example 1. The optical property evaluation results of the obtained optical sheet 6 are shown in Table 1.

[Comparative Production Example 2]
A roll (engraved so that the direction of the lens ridge line is parallel to the rotation direction of the roll) engraved with an approximately elliptical cylindrical lens having a lens pitch of 100 microns and a lens height of 25 microns was used for the third roll. The optical sheet 7 finally stretched in a uniaxial direction with a thickness of 1.5 mm was obtained in the same manner as in Production Example 1. The optical property evaluation results of the obtained optical sheet 7 are shown in Table 1.

[Comparative Production Example 3]
An optical sheet 8 having flat surfaces was obtained in the same manner as in Production Example 1 except that a mirror roll was used as the third roll. The optical property evaluation results of the obtained optical sheet 8 are shown in Table 1.

[Comparative Production Example 4]
An optical sheet 9 having flat surfaces on both sides was obtained in the same manner as in Comparative Production Example 3 except that 0.2 part of silica fine particles (“Seahoster KE-P150” manufactured by Nippon Shokubai Co., Ltd.) was further added as a light diffusing agent. The optical property evaluation results of the obtained optical sheet 9 are shown in Table 1.

[Comparative Production Example 5]
An optical sheet 10 having both flat surfaces was obtained in the same manner as in Comparative Production Example 3 except that 0.5 part of silica fine particles (“Seahoster KE-P150”: Nippon Shokubai Co., Ltd.) was further added as a light diffusing agent. The optical property evaluation results of the obtained optical sheet 10 are shown in Table 1.

[Second optical sheet and third optical sheet]
The second and third optical sheets used in Examples and Comparative Examples are diffusion films are SKC, HAAS CH273 (DS in the table), and microlens sheets are SHINWHA (MLS in the table), manufactured by Intertec. SD743, the prism sheet is UTE30 (Pr-S in the table) manufactured by MN, Tech.

[Arrangement of optical sheet]
The 1st sheet | seat was arrange | positioned so that it might become 8 mm, 10 mm, 12 mm, and 15 mm from the light source center on the light source unit whose space | interval W of adjacent light sources is 30 mm. In an embodiment in which the second and third sheets are required, the first and second optical sheets are arranged as shown in FIG.

[Optical property evaluation]
Table 1 shows the results of measuring the luminance in the arrangement state of the optical sheet as examples and comparative examples.

According to the embodiment, when the first optical sheet having a specific shape is arranged on the surface under the condition of 2d <W, the luminance at a point immediately above the cold-cathode tube lamp on the optical sheet closest to the front panel is A, Assuming that the brightness at the midpoint between adjacent cold-cathode tube lamps on the optical sheet is B, a range of 100 × (| A−B |) / ((A + B) / 2) ≦ 10 is satisfied, and a lamp image is obtained. You can see that it can be erased. It should be noted that the lamp image can be similarly erased even when the optical sheet arranged in the present invention is used under the condition of the conventional condition 2d ≧ W.

  The optical sheet manufactured according to the present invention is appropriately transferred in the stretching process of the step (B) while accurately transferring the shape of the polishing roll for transfer to the optical sheet original in the process (A) in the manufacturing process. Since it is deformed, the desired optical performance is exhibited. Therefore, the optical sheet manufactured according to the present invention can reduce the number of cold-cathode tubes as light sources or change the distance between the light source and the first optical sheet (that is, the linear light source adjacent to the light source unit). Light is desired even if the light source condition does not change and the combination of the optical sheets changes, assuming that the interval between the light sources is W and the distance between the light source and the first optical sheet is d), or 2d <W. Therefore, the present invention is extremely useful in the industry as a device capable of exhibiting high luminance while reducing the manufacturing cost of the liquid crystal display device, which is in increasing demand.

Configuration of display device Arrangement relationship diagram of linear light source and first optical sheet Diagram of surface shape arrangement relation between linear light source and first optical sheet Surface shape of the first optical sheet

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cold cathode tube lamp 2 ... Reflective film 3 ... 1st optical sheet 4 ... 2nd optical sheet 5 ... 3rd optical sheet 6 ... Front panel

Claims (6)

An optical sheet original fabric in which a cylindrical optical element having a pitch P of 200 μm or less and a height H of 200 μm or less and an H / P value of 0.1 to 0.9 is formed on the light exit surface is as follows. Condition (1) for producing the first optical sheet, which is stretched so as to satisfy the condition (1)
On the optical sheet closest to the front panel when 2d <W, where W is the interval between the plurality of cold-cathode tube lamps that are linear light sources, and d is the distance between the optical sheet placed on the light source and the light source. 100 × (| A−B |) / ((A + B) where A is the luminance at a point immediately above the cold cathode tube lamp and B is the luminance at an intermediate point between adjacent cold cathode tube lamps on the optical sheet. / 2) The range is ≦ 10. The method for producing a first optical sheet according to claim 1, wherein the optical sheet original fabric contains light diffusing particles. The method for producing a first optical sheet according to claim 2, wherein the shape of the light diffusing particles is deformed by stretching. The first optical according to any one of claims 1 to 3, wherein the second optical sheet is one or more selected from the group consisting of a lens sheet, a diffusion sheet, a reflective polarizing film, and a brightness enhancement film. Sheet manufacturing method. A direct light source unit using the first optical sheet prepared by the manufacturing method according to claim 1. A display device using the direct type light source unit according to claim 5.

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