JP2010113814A - Downright backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a downright backlight that excels in color uniformity. <P>SOLUTION: The downright backlight has a light source, a laminated sheet including a laminated body with two kinds of resin layers with different refractive indices laminated, and a diffusion plate arrayed in that order, of which the laminate has two kinds of resin layers with different refraction indices alternately laminated in 100 layers or more, and that, with particles with a number average particle size of 1 μm or more and 10 μm or less contained by 0.01% by mass or more and 10% by mass or less with respect to the laminate as a whole. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a direct type backlight used as a back light source in a liquid crystal display device such as a monitor and a television.

  Liquid crystal display devices used for monitors and televisions are composed of a liquid crystal panel and a backlight. Such a liquid crystal display device is used for displaying large and high-definition images and moving images. Therefore, the backlight is required to have high brightness, and a direct type backlight that can be designed with a wide light source arrangement space and a large number of arrangements is currently mainstream.

  In recent years, the trend toward thinning of liquid crystal display devices has increased, and a thin design for direct type backlights has been required. In the thin design of the direct type backlight, it is common to reduce the distance between the reflector and the diffuser. At this time, the distance between the light source and the diffusing plate is also narrowed, and the light source is likely to be short of light quantity between the light source and the light intensity becomes lower than the surroundings when the light quantity is insufficient. Problem arises.

  Various technical proposals have been made regarding this problem. A half mirror is placed in the opening of the direct type backlight, and light is repeatedly reflected in the space surrounded by the side and bottom surfaces of the half mirror and the backlight to achieve a wide angle. There is known a technique for making light uniform within a casing by scattering the light into the casing (Patent Documents 1 and 2).

However, the conventional backlight configuration described in the second term of Patent Literature 1 and the fourth term of Patent Literature 2 is insufficient as a method for obtaining brightness. That is, since metal plating is used for the material of the half mirror, there is a problem that a part of the light is absorbed when the light is reflected on the surface of the metal plating, resulting in a decrease in luminance.
JP-A-6-250171 JP 2006-73449 A

  In order to solve this problem, there is a method in which a half mirror using the principle of interference reflection by a laminated structure of an optical wavelength level made of resin as a material that does not absorb light is disposed on the lower surface of the diffusion plate. Interference reflection is a phenomenon in which a large number of different light-transmitting media, that is, thin layers having different refractive indexes are stacked, and reflected light on the boundary surfaces interfere with each other and strengthen each other. In general, the reflectance of a multilayer film having a structure in which thermoplastic resins A and B are alternately laminated with a predetermined layer thickness is larger as the refractive index difference between the thermoplastic resin A and the thermoplastic resin B is larger. The greater the number, the higher the reflectivity. However, when this laminated sheet is used for a direct type backlight, each layer in the sheet surface does not have a completely uniform thickness, but the spectral intensity of transmitted light changes in the sheet surface according to the unevenness of the laminated thickness. There is a problem that the color of the transmitted light is non-uniform, and there is a problem that the color uniformity of the direct type backlight is impaired.

In order to achieve the above object, the direct type backlight of the present invention is:
A light source;
A laminated sheet including a laminate in which two types of resin layers having different refractive indexes are laminated;
The diffuser plate is arranged in this order,
Two or more types of resin layers having different refractive indexes are alternately laminated in the laminate, and particles having a number average particle diameter of 1 μm or more and 10 μm or less are 0.01% by mass or more based on the entire laminate. The content is 10% by mass or less.

  According to the direct type backlight configuration of the present invention, a direct type backlight excellent in color uniformity can be obtained.

  Hereinafter, the present invention will be described in detail.

  An example of the configuration of a liquid crystal display device using the direct type backlight of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of the backlight device cut in the vertical direction. The case of the backlight is covered with the reflecting plate 1 and has an opening on one side facing the liquid crystal panel 7, and the fluorescent lamp 2 is arranged inside the case. In the opening, a fluorescent lamp 2 as a light source, a laminated sheet 3, a diffusion plate 4, a diffusion sheet 5, a prism sheet 6, and a liquid crystal panel 7 are arranged in this order. Further, support pins 8 protrude from the lower part of the housing.

  The reflecting plate 1 is made of, for example, a white polyester sheet containing fine bubbles inside. This formation of fine bubbles is achieved by finely dispersing a high melting point incompatible polymer in a sheet base material, for example, polyester, and stretching (for example, biaxial stretching). During stretching, voids (bubbles) are formed around the incompatible polymer particles, and this exhibits a scattering effect on the light, so that it becomes white and high reflectance can be obtained. On the other hand, an important characteristic of a liquid crystal display is the degree of brightness of the screen. In particular, in a display with a large screen, if the light reflected by the reflecting plate is not sufficiently scattered, brightness unevenness occurs in the screen and a beautiful image cannot be obtained. In order to maintain the brightness uniformity of the screen, it is known that the reflected light is sufficiently diffusely reflected by adding inorganic particles to the surface of the white sheet for the reflector.

The laminated sheet 3 in the present invention includes a laminated body 16 having a structure in which two or more types of resin layers having different refractive indexes (hereinafter referred to as a resin layer A and a resin layer B) are alternately laminated. Yes. A structure in which a plurality of two types of resin layers are alternately laminated means that the resin layers A and B are periodically laminated in a regular arrangement of A (BA) n (n is a natural number). .
By incorporating the laminated sheet 3 into the direct type backlight with the above-described configuration, the light emitted from the fluorescent lamp 2 is repeatedly reflected in the casing by the interference reflection by the laminated sheet 3 and the reflection by the reflecting plate 1, and in a wide-angle manner. Scattered. At this time, a part of the light reaching the laminated sheet 3 is emitted to the diffusion plate 4 according to the light transmittance of the laminated sheet 3, but the light scattered in a wide angle inside the housing, that is, the light intensity is Since evenly distributed light is emitted, a direct type backlight with good luminance uniformity can be obtained. Further, since the laminated sheet 3 does not contain a metal, a bright direct type backlight without light absorption is obtained.

  The optimum combination of the resin layer A and the resin layer B is preferably such that the absolute value of the difference in refractive index between the resin layers is 0.05 or more from the viewpoint of producing a high reflectance by the optical interference phenomenon. The refractive index difference is more preferably 0.1 or more, and further preferably 0.12 or more. Here, when the resin layer is a stretched sheet, the refractive index is an in-plane refractive index, and the refractive index in the MD (Machine Direction) direction which is the running direction of the sheet and the TD (Transverse Direction) direction which is the sheet width direction. It is the average value of the refractive index. The refractive index is determined by measuring the refractive index of MD and TD using an Abbe refractometer after forming a particle-free single film under the same film forming conditions as the laminated sheet 3, and calculating the average refractive index of MD and TD. The value can be obtained by using the refractive index of the resin layer.

  Moreover, since the reflectance becomes higher as the number of layers increases, the number of resin layers A and resin layers B constituting the laminate 16 is 100 or more. Preferably each is 350 layers or more.

  The layer thickness of each constituent layer is preferably set according to the refractive index of the thermoplastic resin that constitutes each layer. For example, the refractive index of the thermoplastic resin forming the laminated structure is in the range of about 1.3 to 1.9, and the thickness of each layer in this case is in the range of 30 to 650 nm from the viewpoint of facilitating the use of optical interference. It is preferable to set the value. More preferably, it is 50-350 nm.

  The resin constituting the resin layers A and B is preferably a combination of polyethylene terephthalate and a copolyester. That is, it is preferable that the resin layer A is made of polyethylene terephthalate and the resin layer B is made of copolyester, or the resin layer A is made of copolyester and the resin layer B is made of polyethylene terephthalate.

  The polyethylene terephthalate constituting the resin layer of the laminate 16 is a condensation polymer of terephthalic acid and ethylene glycol. As an industrial production method of polyethylene terephthalate, as is known, transesterification of dimethyl terephthalate (DMT) and ethylene glycol (EG) (transesterification method), direct esterification of terephthalic acid (TPA) and EG (direct First, the first stage reaction in which TPA is a diglycol ester (referred to as bis-β-hydroxyethyl terephthalate (BHT)) and the BHT is subjected to condensation polymerization under high temperature and high vacuum. It is divided into the second stage reaction. In the transesterification reaction, a catalyst is required. In the first-stage reaction, known weak acid salts such as Ca, Ma, Mg, Zn are used. In the second-stage polycondensation reaction, antimony is used. A compound, a titanium oxide compound, a germanium compound, or the like can be used.

  The polyester constituting the resin layer of the laminate 16 is a polyester obtained by polymerization from a monomer mainly composed of an aromatic dicarboxylic acid or aliphatic dicarboxylic acid and a diol. Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyl Examples thereof include dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid, and the like. Examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid and ester derivatives thereof. Of these, terephthalic acid and 2,6 naphthalenedicarboxylic acid are preferred. These acid components may be used alone or in combination of two or more thereof, and further may be partially copolymerized with oxyacids such as hydroxybenzoic acid.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4- Hydroxyethoxyphenyl) propane, 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene, isosorbate, spiroglycol and the like. Of these, ethylene glycol is preferably used. These diol components may be used alone or in combination of two or more.

  The copolymer polyester constituting the resin layer of the laminate 16 is a polyethylene terephthalate copolymer, a polyethylene naphthalate copolymer, a polybutylene terephthalate copolymer, or a polybutylene naphthalate copolymer of the above polyesters. It is preferable to use a polymer, a copolymer of polyhexamethylene terephthalate, a copolymer of polyhexamethylene naphthalate, or the like. Moreover, as a copolymerization component, it is preferable that 1 or more types of the above-mentioned dicarboxylic acid component and diol component are respectively copolymerized.

  Furthermore, the copolyester constituting the resin layer of the laminate 16 preferably contains the same basic skeleton as that of polyethylene terephthalate from the viewpoint of achieving a highly accurate laminated structure. Here, the basic skeleton is a repeating unit constituting the resin. For example, in the case of polyethylene terephthalate, ethylene terephthalate is the basic skeleton. When the resin layer A and the resin layer B are resins containing the same basic skeleton, the lamination accuracy is high, and delamination at the lamination interface is less likely to occur.

  The copolyester constituting the resin layer of the laminate 16 is preferably a polyester comprising a cyclohexanedicarboxylic acid component and a spiroglycol component that are difficult to cause oriented crystallization. The polyester comprising a cyclohexanedicarboxylic acid component and a spiroglycol component refers to a copolyester obtained by copolymerizing spiroglycol and cyclohexanedicarboxylic acid, or a homopolyester, or a polyester obtained by blending them. In particular, a polyester having polyethylene terephthalate as a basic skeleton and copolymerized with a cyclohexanedicarboxylic acid component and a spiroglycol component is most preferable.

  The cyclohexanedicarboxylic acid component and the spiroglycol component are ethylene terephthalate polycondensates having a copolymerization amount of 5 mol% or more, respectively, from the viewpoint of lowering the refractive index and causing little change in physical properties due to heating or aging. preferable. Copolymerization of spiroglycol component and cyclohexanedicarboxylic acid component from the viewpoint of achieving high reflectivity by reducing the refractive index of copolyester with polyethylene terephthalate and reducing the refractive index of the copolymerized polyester. The amounts are more preferably 10 mol% or more and 20 mol% or more, respectively. More preferably, it is 30 mol% or more. If the amount of copolymerization is excessively increased, the compatibility between the resins will deteriorate, so that it will be difficult to achieve a laminated structure with high precision, and the amount of copolymerization will be 60 mol% or less from the viewpoint of easy peeling between layers. Preferably there is.

  The laminate 16 can be produced by the following method. For example, in the case of a laminated film of A (BA) n, thermoplastic resin is supplied from two units of an extruder A corresponding to the A layer and an extruder B corresponding to the B layer, and the polymer from each flow path is Laminate over 100 layers by using a multi-manifold type feed block and a square mixer, which are known laminating devices, or using only a comb type feed block, and then use the T-type die etc. Examples thereof include a method in which a sheet is melt-extruded and then cooled and solidified on a casting drum to obtain an unstretched film.

  The multi-manifold type feed block is a known feed block as described in Keiji Sawada “Latest Technology of Plastic Extrusion” (Rubber Digest Co., Ltd.) (1993). That is, before a plurality of resins are fed into the die body, they are merged in the feed block, and then sent to a single manifold of the die to widen and extrude the flow.

  Also, the square mixer is a publicly known unit having a merge portion that divides a polymer channel into two channels having a square cross-sectional area, and further joins the branched polymers so that they are stacked again in the thickness direction. It is a cylinder. By repeating this step, it is possible to obtain a multi-layered laminate. For example, an A / B / A3 layered laminate composed of two types of resins becomes a five-layered laminate when branched and merged once. In such a case, the number of layers can be expressed by (initial number of layers−1) × 2 to the nth power + 1. However, n means repeating one branching / merging n times. In addition, since the distribution ratio of the square mixer is usually branched into equal flow paths having an equal cross-sectional area of 1: 1, the same laminate is periodically formed. On the other hand, if the structure of the initial laminated body is an inclined structure, the laminated body after passing through the square mixer can maintain an inclined structure having a continuous layer thickness by making the distribution ratio non-uniform. The initial inclined structure before the square mixer can be achieved by inclining the pressure loss of each manifold in the multi-manifold type feed block corresponding to each layer having the inclined structure.

  From the above, when a multi-manifold type feed block and a square mixer are combined, for example, when a laminated body in 11 layers in a multi-manifold type feed block passes through the square mixer four times, 161 layers Can be obtained. Examples of a method for increasing the number of layers include a method of arranging a plurality of feed blocks in parallel, a method of increasing the number of square mixers, and a method of increasing the number of layers of the laminated flow obtained in the feed block. As the multi-manifold type feed block here, a type II feed block described in JP-A-2006-44212 is exemplified.

  However, when the manifold type feed block described above is used, the size of the apparatus increases, and it is difficult to obtain a multilayer laminated film that maintains high lamination accuracy because it passes through the square mixer a plurality of times. Therefore, in the matte film of the present invention, it is preferable to obtain a laminated structure using a comb type feed block having a large number of fine slits. Details of the comb type feed block are described in Japanese Patent Application Laid-Open No. 2005-352237. This feed block can easily form a laminate of up to 400 layers at a time by increasing the number of slits. Furthermore, if a square mixer is combined, a laminate of 1000 layers or more can be obtained. In order to achieve higher stacking accuracy, a stack of 800 layers or more can be easily obtained by arranging at least two fine slit members in parallel without using a square mixer. Details of the manufacturing method are described in JP-A-2005-352237.

  The transmittance of the laminated sheet 3 is preferably 20% or more and 50% or less. When the transmittance is 20% or more, when light is scattered at a wide angle in the housing, the light is absorbed by the reflecting plate 1 or the fluorescent lamp 2, or the light is lost to the back surface of the reflecting plate 1. Luminance can be increased because loss of light quantity is reduced. On the other hand, if it is 50% or less, the efficiency of repeated reflection of light in the housing is good, and the effect of improving the uniformity of light intensity by scattering light in a wide angle within the housing is enhanced, so that the luminance unevenness of the fluorescent tube is increased. Becomes difficult to see. The transmittance is more preferably 20% or more and 40% or less, and further preferably 20% or more and 30% or less. As a light source for measuring the transmittance, D65, C, A, F6, F10, a three-wavelength white LED, or the like is used. The transmittance in the present application is a measured value using a D65 light source. .

  Some of the plurality of resin layers 10 constituting the laminate 16 contain particles 9 inside as shown in FIG. Although the thickness of the resin layer 10 is not uniform within the sheet surface, there is a problem that the color uniformity of the transmitted light is caused by the occurrence of color unevenness of the transmitted light, but there are particles 9. As a result, light scattering occurs, and a function of increasing color uniformity is exhibited by creating a crossing of light paths crossing the stacked body 16 by light scattering and mixing the colors. Light scattering includes light scattering (Mie scattering and Rayleigh scattering) that occurs between the particles 9 and a medium having a different refractive index, and light scattering that depends on the surface shape. Therefore, the light transmitted through the laminated body 16 having the resin layer in which the particles 9 are present is more uniform in color within the sheet surface than the laminated body 16 having no resin layer in which the particles 9 are present. Are better. The particles 9 do not have to be present in all the resin layers, but the light diffusibility becomes stronger as the optical path length is longer. Therefore, the particles 9 are preferably present in 100 layers or more.

  In the present invention, from the viewpoint of imparting slidability, light diffusion effect or color uniformity without impairing interference reflection, the shape of the particles 9 includes aggregated particles, spherical particles, beaded particles, complex particles, Particle shapes such as scale-like particles can be used. In addition, as a material thereof, from the viewpoint of imparting easy slipperiness, polyolefin, modified polyolefin resin of silica, silicon oxide, aluminum silicate, polyimide resin, crosslinked or non-crosslinked polystyrene resin, crosslinked or non-crosslinked acrylic resin And various amide compounds such as stearic acid amide, oleic acid amide, and fumaric acid amide. From the viewpoint of suppressing the luminance non-uniformity and color non-uniformity of the backlight by imparting a light diffusion effect, silica, polyethylene, polypropylene, polylactic acid, norbornene-based alicyclic olefin, styrene acrylonitrile copolymer, poly 4-methylpentene 1, polyvinyl alcohol, ethylene / vinyl acetate copolymer, nylon 6, 11, 12, 66, polycarbonate, acrylic beads and the like are preferable. Moreover, these copolymers may be sufficient.

  The particles 9 in the present invention are preferably made of spherical silica or cross-linked polystyrene from the viewpoint of easy lubrication. Further, from the viewpoint of facilitating interference reflection, the number average particle diameter of the particles 9 is preferably 1 μm or less, and the content ratio with respect to the entire laminate 16 is preferably 0.1 mass% or less. More preferably, the number average molecular weight is 0.5 μm or less and the content is 0.05% by weight or less. More preferably, the number average molecular weight is 0.1 μm or less and the content is 0.01% by weight or less.

  On the other hand, from the viewpoint of imparting a light diffusion effect or a color uniformity effect, in particular, spherical silica, crosslinked polystyrene, poly 4-methylpentene 1, polymethyl methacrylate, polycarbonate, ethylene propylene copolymer, metallocene and Ziegler. Cyclic olefin copolymers which are copolymers of norbornene and ethylene copolymerized with a Natta catalyst, and cyclic polyolefins obtained by ring-opening metathesis polymerization of norbornene-based monomers and hydrogenation are preferred. From the viewpoint of facilitating interference reflection, the content of the particles is 10% by mass or less with respect to the entire laminate 16. Preferably it is 5 mass% or less, More preferably, it is 1 mass% or less. Further, from the viewpoint of facilitating color uniformity due to light diffusion, it is preferably 0.01% by mass or more, and more preferably 0.05% by weight or more. Further, from the viewpoint of improving color uniformity, the number average particle diameter of the particles 9 is 10 μm or less because it is difficult to cause interference reflection due to destruction of the layer if it is too large. Preferably it is 5 micrometers or less. More preferably, it is 2 μm or less. On the other hand, if it is too small, light scattering (Mie scattering, Rayleigh scattering) does not occur sufficiently, so that it is 1 μm or more.

  The relationship between the thickness t (nm) of the layer containing particles and the ratio r / t of the number average particle size r (nm) of the particles 9 is preferably 1 or more. When r / t is less than 1, since the particles 9 are buried in the layer, light scattering by the particles 9 does not occur sufficiently, which is not preferable from the viewpoint of color uniformity. More preferably, it is 5 or more. Furthermore, it is preferably 20 or more. On the other hand, r / t is preferably 100 or less. When r / t exceeds 100, since the particles 9 greatly collapse the laminate, interference reflection does not occur sufficiently and the transmittance increases, which is not preferable from the viewpoint of luminance uniformity.

  Further, an optical functional layer having other optical functions may be provided on the fluorescent lamp 2 side of the laminated sheet 3. The optical function includes ultraviolet absorption, light scattering, refraction, diffraction, etc., and the optical functional layer can be integrated with the multilayer laminated sheet 3 via an adhesive layer, and is a separate sheet from the laminated sheet 3. There may be. If there is an ultraviolet ray absorbing function, ultraviolet rays generated from the fluorescent lamp 2 can be substantially blocked, so that deterioration of the resin contained in the laminated sheet 3 and the diffusion plate 4 can be suppressed, and light resistance is improved. The light scattering, refraction, and diffraction functions can create more intersections of the light that is incident on and traverses the laminated sheet 3, so that not only the function of increasing the color uniformity is exhibited, but also interference occurs in the laminated sheet 3. Since the light reflected and returned to the lower side of the casing can be distributed in a wider angle, the function of improving the uniformity of light intensity in the casing is also exhibited.

  Further, a hard coat layer may be provided on the fluorescent lamp 2 side of the laminated sheet 3. Due to the presence of the hard coat layer, the tip of the support pin 8 that prevents the diffusion plate 4 from bending and the multilayer laminated sheet 3 rub against each other, and the rubbed portion appears darker than the surroundings as a shadow in the backlight illumination. Problems that impair the uniformity of luminance can be prevented.

  As the light source in the present invention, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a light emitting diode (LED), a laser diode (LD), or the like can be used. Light emitting diodes combine blue LED and yellow phosphor to emit blue light from the LED, then excite the phosphor with some light to obtain white by mixing blue and yellow, ultraviolet LED and multiple colors Combining phosphors (for example, red, green, and blue) to excite the phosphors with ultraviolet light to obtain a white color by mixing multiple colors (red, green, and blue); a single wavelength LED that has multiple colors (for example, red, green, and blue) Although there is one that obtains white color by mixing colors emitted separately and being emitted in a space, there is no particular limitation. In the present invention, since the light is repeatedly reflected and scattered at a wide angle in the casing, the light in the casing can be evenly distributed. Therefore, the backlight design has a single wavelength LED arranged in a plurality of colors (for example, red, green, and blue). Even in such a case, a direct type backlight having good color mixing and excellent color uniformity can be obtained.

  The diffusing plate 4 in the present invention is composed of, for example, a core layer in which a light diffusing material is dispersed and a surface layer in which beads for forming an ultraviolet absorber and a textured surface are dispersed. However, the surface layer is not limited to a satin surface, but may have a prism, lenticular shape, or the like, but is not particularly limited in the present invention. Furthermore, since the laminated sheet 3, the diffusion sheet 5, and the prism sheet 6 need to be arranged without bending or twisting, the diffusion plate 4 may be used as a support for the laminated sheet 3, the diffusion sheet 5, or the prism sheet 6. If the laminated sheet 3, the diffusion sheet 5, and the prism sheet 6 are not bent or twisted, the contact between the optical sheets or the contact between the optical sheet and the liquid crystal display panel does not occur, and uniform luminance illumination can be obtained. Moreover, it is preferable that the thickness of the diffusion plate 4 is 0.8 mm or more and 2 mm or less. When the thickness of the diffusing plate 4 is 0.8 mm or more, necessary rigidity is obtained and a function as a support is obtained. On the other hand, if the thickness is 2 mm or less, the backlight can be designed to be thin. The thickness of the diffusion plate 4 is more preferably 1 mm or more and 1.5 mm or less. The light incident on the diffusion plate 4 is further radiated by light scattering by the pear ground formed on the surface of the diffusion plate 4, refraction by the prism, or volume scattering by the light diffusion material existing inside the diffusion plate 4. The light is emitted with improved uniformity.

  Moreover, it is preferable that the lamination sheet 3 and the diffusion plate 4 have an integral structure through an adhesive layer. By doing so, there is no space such as an air layer at the interface between the laminated sheet 3 and the diffusing plate 4, and loss light that does not contribute to front luminance due to Fresnel reflected light or the like occurring at the interface can be caused to occur. High backlight illumination can be obtained. Furthermore, since the diffusion plate 4 and the laminated sheet 3 as a support are integrated, it is possible to prevent the laminated sheet 3 from being bent and twisted by a more excellent method.

  Furthermore, it is preferable that a material having substantially the same linear expansion as that of the laminated sheet 3 is integrated with the surface of the diffusion plate 4 opposite to the surface on which the laminated sheet 3 is disposed via an adhesive layer. By doing in this way, even if the diffuser plate 4 receives heat when the fluorescent lamp 2 is lit, warpage can be suppressed because substantially the same linear expansion material is adhered to both surfaces of the diffuser plate 4. The adhesive material constituting the adhesive layer is not particularly limited as long as it has translucency. For example, an acrylic pressure-sensitive adhesive, an ethylene vinyl acetate polymer pressure-sensitive adhesive, a hot-melt pressure-sensitive adhesive, and thermosetting A reactive adhesive, a cyanoacrylate adhesive that is a reactive adhesive, an epoxy adhesive, an ultraviolet curable resin, an electron beam curable resin, or the like can be used.

  The diffusion sheet 5 is composed of a transparent layer and a surface layer in which beads for forming a textured surface are dispersed. However, there are some which have a volume scattering function by including two or more materials having different refractive indexes in the core layer, but the invention is not particularly limited in the present invention. The light incident on the diffusion sheet 5 is emitted in a state in which the brightness and color uniformity are further improved by light scattering by the textured surface formed on the surface of the diffusion sheet 5.

  The prism sheet 6 is composed of a transparent layer and a surface layer on which a prism for condensing light in the front direction of the backlight is formed. The prism cross section is an isosceles triangle and the apex angle is approximately 90 °. The prism is on the liquid crystal panel side, and the prism ridge line is arranged in a relationship substantially parallel to the longitudinal direction of the fluorescent lamp 2. Alternatively, the prism ridge lines are arranged in a substantially parallel relationship with the horizontal when the liquid crystal display device is installed in use. Since the light incident on the prism sheet 6 is condensed in the front direction of the backlight by refraction by the prism, the front luminance is improved. Further, since the apex angle is approximately 90 °, the light incident on the prism sheet 6 substantially perpendicularly undergoes total reflection of 2 degrees or more and is retroreflected to the lower part of the backlight. The retroreflected light returns to the lower part and is reflected again to reach the prism sheet again. At this time, the number of light paths is increased, thereby further improving the uniformity of luminance and color. Accordingly, the light emitted from the prism sheet 6 has a high front luminance and is a backlight illumination excellent in luminance and color uniformity.

  As described above, the transmissive liquid crystal panel 7 is arranged on the direct type backlight including the reflecting plate 1, the fluorescent lamp 2, the multilayer laminated sheet 3, the diffusing plate 4, the diffusing sheet 5, and the prism sheet 6, thereby displaying a liquid crystal display. The device is configured.

  The members disposed between the diffusion plate 4 and the liquid crystal panel 7 are not limited to the diffusion sheet 5 and the prism sheet 6. The number of sheets, the type, and the order of superposition may be appropriately selected according to the luminance and luminance uniformity. The sheet may be a diffusion sheet having a bead coat layer on its surface, a prism sheet having a prism layer on its surface, or a hologram sheet having a hologram layer on its surface, and the base material may be a transparent resin layer or two or more different refractive indexes. A resin layer having a volume scattering function including a material may be used.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Evaluation method of effect]
[Evaluation method of color uniformity, tube unevenness and average brightness of direct type backlight]
The evaluation method using a direct type backlight is as follows.

A voltage was applied to light the fluorescent lamp of the backlight illumination device having a diagonal size of 32 inches, and aging was performed for 30 minutes or more in order to stabilize the light emission of the fluorescent lamp. Then, after normalizing the optical system and the backlight emission surface using a luminance meter installed vertically from the center of the emission area of the backlight illumination device, focus the lens and view the entire backlight illumination area. The picture was taken in the state of entering. The luminance meter used was CA-2000 manufactured by Konica Minolta. The setting conditions of the luminance meter were a wide-angle lens, a measurement distance of 90 cm, a number of measurement points of 490 × 490, and an output integration number of 4 for considering the influence of noise. Next, the image data was analyzed using data management software CA-S20w manufactured by Konica Minolta. The analysis process was performed after selecting the light emitting area of the backlight illumination device from the image and excluding unnecessary pixels from the analysis process.
The numerical value data of the chromaticity value X and chromaticity value Y of the effective pixel were obtained with the color space setting Lvxy. Next, the average value, the maximum value, and the minimum value of the chromaticity value X and the chromaticity value Y were calculated from the numerical data of the chromaticity value X and the chromaticity value Y by using spreadsheet software (Excel2003). Further, a value obtained by dividing the minimum value by the maximum value and multiplying by 100 was defined as color uniformity. The color uniformity values of the example and the comparative example were compared to compare the uniformity of the emission color of the backlight illumination device.
Further, the average value of the luminance data of the effective pixels is defined as the average luminance.

  Moreover, the brightness distribution data of the cross section orthogonal to the light source longitudinal direction was created by calculating the average value of the brightness data having a parallel relationship with the light source longitudinal direction using the spreadsheet software (Excel2003) from the brightness data of the effective pixels. . Take out the range data for one fluorescent lamp corresponding to the center of the backlight of this luminance distribution data, calculate the average luminance, divide each luminance value of this data group by the average luminance value, and calculate the minimum value from the maximum value The value obtained by subtraction was defined as the tube unevenness value.

[Measurement method of light transmittance]
The laminated sheet cut into a 50 mm square was measured three times in the MD direction and the TD direction with a haze meter NDH2000 (D65 light source) manufactured by Nippon Denshoku Industries Co., Ltd., and the average value was taken as the light transmittance.

[Measurement method of refractive index of each layer]
A particle-free single film was formed under the same film forming conditions as the laminated sheet 3. In this case, the unstretched film was formed by the same method up to casting. Next, a sample is cut out from the unstretched film to a size of 10 cm × 10 cm, stretched using a biaxial stretching apparatus (Toyo Seiki Co., Ltd.), and the obtained stretched film is attached to a 20 cm × 20 cm metal frame. Then, heat treatment was performed using a tunnel oven (manufactured by Taishin Manufacturing Co., Ltd.) to obtain a single film. In addition, when the heat treatment temperature at the time of film formation was a temperature at which the thermoplastic resin was melted, it was sandwiched by a support such as a polyimide film and subjected to heat treatment in a tunnel oven. A sample is cut out from the central portion of the obtained single film in the film width direction with a length of 4 × 3.5 cm in width, and the refractive index of MD and TD is obtained using an Abbe refractometer 4T manufactured by Atago Co., Ltd. It was. As a light source, a sodium D line wavelength of 589 nm was used. The average refractive index of MD and TD was taken as the refractive index of the matrix resin layer. As the immersion liquid, methylene iodide and a test piece having a refractive index of 1.74 were used.

[Average particle size]
The laminated sheet was cut with a microtome to prepare a cross section. Using a field emission scanning electron microscope JSM-6700F (manufactured by Jeol Co., Ltd.), select a magnification at which the particles can be sufficiently observed within a magnification range of 5000 to 40000 times. The particles were observed. By changing the observation location, the particle diameter was measured for 50 or more particles having a particle diameter of 0.5 μm or more, and the average value was taken as the number average particle diameter. The particle diameter to be measured is the major axis particle diameter of the particles.

  When the particles are agglomerated particles, only a part of the agglomerated particles can be confirmed by cross-sectional observation. Therefore, the surface of the film is exposed by plasma ion etching, and then Pt ion plating is performed on the surface. Agglomerated particles were observed. The particle diameter was measured on the long axis of a circle or ellipse circumscribing a lump of aggregated particles.

[Particle content]
A solvent that dissolves the resin but does not dissolve the inert particles was selected, the inert particles were centrifuged from the resin, and the particle mass ratio (% by mass) relative to the entire laminate was taken as the particle content. In the case of resin particles, the concentration was calculated from the mass fraction of the added amount.

[Example 1]
The configuration of the direct type backlight according to the first embodiment will be described with reference to FIG.
The diagonal area of the light emitting area of the backlight is 32 inches, the casing is covered with the reflecting plate 1 and only one surface is opened, and the fluorescent lamp 2 is arranged inside the casing. In the opening, the fluorescent lamp 2, the anisotropic diffusion sheet 12, the laminated sheet 3, the diffusion plate 4, the diffusion sheet 5, and the prism sheet 6 are arranged in this order. The laminated sheet 3 and the diffusion plate 4 are laminated without using an adhesive. Further, support pins 8 protrude from the lower part of the housing. Here, as the reflector 1, a white polyester sheet having a thickness of 0.26 mm and containing fine bubbles therein was used. Nineteen fluorescent tubes 2 were arranged at equal intervals using an external electrode fluorescent lamp (EEFL) having a diameter of 3 mm, and the interval between the fluorescent tubes was 20.4 mm. The distance from the surface of the reflector 1 to the center of the fluorescent lamp 2 was 3 mm. An anisotropic diffusion sheet 12 having a thickness of 0.14 mm and having a layer having a hologram pattern transferred on the surface of a transparent substrate was used. The hologram pattern is arranged in a parallel relationship such that the majority of the period is on the order of several μ and the shape in which the ridge lines extend linearly overlap each other without a gap, and the direction in which the ridge lines extend and the length of the fluorescent lamp 2 Arranged so that the directions are parallel. The distance from the surface of the reflector 1 to the surface of the anisotropic diffusion sheet 12 was 9.5 mm. The laminated sheet 3 has a thickness of 0.21 mm, and is a copolymerized polyethylene teite obtained by copolymerizing about 30 mol of cyclohexanedimethanol with an A layer made of polyethylene terephthalate containing 0.3% by mass of an agglomerated silica having an average particle diameter of 4 μm. A layer in which B layers made of phthalate were alternately laminated was used (the B layer was free of particles). The number of layers is 401 for the A layer and 400 for the B layer, and the layer thickness ratio of the A layer and the B layer is 1: 1. Therefore, the content of particles with respect to the entire stack is 0.15% by mass. And B layer have a refractive index difference of 0.065 after biaxial stretching and a light transmittance of 41%. The diffuser plate 4 used was RM851 manufactured by Sumitomo Chemical Co., Ltd., having a thickness of 2 mm and having two principal surfaces that are both pear ground. As the diffusion sheet 5, 188GM2 manufactured by Kimoto was used. The prism sheet 6 used was BEF III90 / 50T manufactured by Sumitomo 3M. The anisotropic diffusion sheet 12 and the multilayer laminated sheet 3 have a slightly smaller outer shape than the diffusion plate 4 in the outer peripheral range outside the evaluation area that does not affect the evaluation result, and only the outer peripheral portion of the outer shape is diffused with tape without using an adhesive layer. The plate 4 was fastened and arranged.

[Comparative Example 1]
As the lamination sheet 3, what does not contain particle | grains in the A layer in the lamination sheet 3 used in Example 1 was prepared. The light transmittance is 24%. In the direct type backlight device of Example 1, a direct type backlight was configured in the same manner as in Example 1 except that the laminated sheet 3 containing no particles was used.

[Comparative Example 2]
The direct type backlight is the same as in Example 1 except that the arrangement order of the diffusion plate and the laminated sheet is changed and the fluorescent lamp is changed to the anisotropic diffusion sheet, the diffusion plate, the laminated sheet, the diffusion sheet, and the prism sheet. Configured.

[Comparative Example 3]
The arrangement order of the diffusion plate, the diffusion sheet and the laminated sheet was changed, and it was changed to the anisotropic diffusion sheet, the diffusion plate, the diffusion sheet, the laminated sheet, and the prism sheet in the order from the fluorescent lamp, as in Example 1. A mold backlight was constructed.

[Comparative Example 4]
Same as Example 1 except that the order of arrangement of the diffusion plate, diffusion sheet, prism sheet and laminated sheet was changed to the order from fluorescent lamp to anisotropic diffusion sheet, diffusion plate, diffusion sheet, prism sheet, laminated sheet. Thus, a direct type backlight was constructed.

[Comparative Example 5]
The configuration of the backlight illumination device in Comparative Example 5 will be described with reference to FIG.
The diagonal area of the light emitting area of the backlight is 32 inches, the casing is covered with the reflecting plate 1 and only one surface is opened, and the fluorescent lamp 2 is arranged inside the casing. In the opening, the fluorescent lamp 2, the diffusion plate 4, the diffusion sheet 13, the prism sheet 6, the diffusion sheet 14, and the diffusion sheet 15 are arranged in this order. Further, support pins 8 protrude from the lower part of the housing. Here, the same reflector 1 as in Example 1 was used. The same fluorescent tube 2 as in Example 1 was used, and the number used, the arrangement interval, and the distance from the reflector 1 were also the same as in Example 1. The diffuser plate 4 was a prism diffuser plate that was 2 mm thick, one main surface was a satin surface, and the other was a prism surface, and was more expensive than the double-sided textured diffuser plate used in Example 1 and Comparative Example 1. The prism is a V-groove in which the ridge line extends in a straight line, and the direction in which the ridge line extends and the longitudinal direction of the fluorescent lamp 2 are parallel to each other, and the prism side is arranged in the direction opposite to the fluorescent lamp 2. The diffusion sheet 13 having a thickness of 0.16 mm was used. The prism sheet 6 was the same as in Example 1. The diffusion sheet 14 has a thickness of 0.16 mm. A diffusion sheet 15 having a thickness of 0.21 mm was used.
Comparative Example 2 is an example of a general configuration of a thin backlight mounted on a recent thin TV.

[Evaluation result of effect]
The effect evaluation results will be described with reference to Table 1.

  Comparison between Example 1 and Comparative Example 1 makes it possible to compare the case where particles are present in the resin layer constituting the laminated sheet 3 with the case where particles are not present. The values of color uniformity of chromaticity x and chromaticity y are both higher in Example 1, and when particles are present in the resin layer constituting the laminated sheet 3, the color uniformity of the direct type backlight is excellent. It was.

  Comparison between Example 1 and Comparative Example 5 shows a general configuration of a direct type backlight in the case where particles are present in the resin layer constituting the laminated sheet 3 and a thin backlight mounted on a recent thin TV. Comparison with a direct type backlight is possible. The value of the color uniformity of the chromaticity x is a difference of 1%, and the value of the color uniformity of the chromaticity y is the same as that of the comparative example 2. Therefore, when particles are present in the lamination of the laminated sheet 3, The color uniformity of the backlight illuminator is almost the same as the backlight illuminator mounted on a commercial TV, and it contains particles while using an inexpensive prism-shaped diffuser instead of an expensive prism diffuser. The decrease in color uniformity that occurred when using a non-laminated sheet was eliminated.

  By comparison between Example 1 and Comparative Examples 2 to 4, the arrangement position of the laminated sheet 3 can be compared. Since the brightness is higher as the arrangement position is closer to the light source, a bright backlight can be obtained when the laminated sheet is closer to the light source than the diffusion plate. This is presumably because when the number of optical members arranged between the laminated sheet and the reflecting plate increases, a light amount loss occurs in the reflected light component by the laminated sheet. Further, since the color uniformity value is higher as the arrangement position is closer to the light source, a backlight having excellent color uniformity can be obtained when the laminated sheet is closer to the light source than the diffusion plate. This is presumably because the transmitted light that has undergone the color mixing effect in the laminated sheet exhibits a further color mixing effect due to light scattering that occurs when the transmitted light passes through the member disposed on the upper side.

  The direct type backlight of the present invention is suitably used for a transmissive liquid crystal panel, but can be applied to other display devices that require a direct type backlight that requires color uniformity.

It is a typical sectional view showing one embodiment of a direct type backlight of the present invention. FIG. 2 is a schematic cross-sectional view showing particles present inside a laminated sheet. It is typical sectional drawing which shows the backlight structure of Example 1 and Comparative Example 1. It is typical sectional drawing which shows the backlight structure of the comparative example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reflector 2 Light source 3 Laminated sheet 4 Diffusion plate 5 Diffusion sheet 6 Prism sheet 7 Liquid crystal panel 8 Support pin 9 Particle 10 Resin layer 11 Sheet thickness direction 12 Anisotropic diffusion sheet 13 Diffusion sheet 14 Diffusion sheet 15 Diffusion sheet 16 Lamination sheet Laminated body constituting 3

Claims (4)

A light source;
A laminated sheet including a laminate in which two types of resin layers having different refractive indexes are laminated;
The diffuser plate is arranged in this order,
In the laminate, 100 or more layers of two types of resin layers having different refractive indexes are alternately laminated, and 0.01% by mass or more of particles having a number average particle diameter of 1 μm or more and 10 μm or less with respect to the entire laminate. Direct type backlight containing 10% by mass or less.   The direct type backlight according to claim 1, wherein the light transmittance of the laminated sheet is 50% or less.   The direct type backlight according to claim 1 or 2, wherein the laminated sheet and the diffusion plate are arranged via an adhesive layer.   A liquid crystal display device using the direct type backlight according to claim 1.

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