JP2008129546A - Light diffusion film, optical diffusion laminated film and optical member using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion film free from problems occurring in a stretch die when an inorganic acicular filler excellent in optical characteristics and orientation property is used, and free from problems such as limitation of the content of the filler when mixing into an adhesive layer. <P>SOLUTION: The light diffusion film comprises an isotropic transparent resin matrix, and an inorganic acicular filler dispersed as oriented in a given direction in the isotropic transparent resin matrix and having a refractive index different from that of the isotropic transparent resin matrix. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusing film suitable for use in an illuminating device such as a backlight of a liquid crystal display device and an optical member in which the light diffusing film is laminated.

Various optical elements are used in the liquid crystal display device. For example, a light reflecting element, a light diffusing element, a prism element, a polarizing element, etc. are widely used for the backlight.
Among these optical elements, light diffusing elements include those in which a spherical or irregular filler having a refractive index different from that of the base material is contained / dispersed in the base material, and a large number of fine particles in the resin layer on the film surface by the replica method. Known are those in which irregularities are formed, and a coating containing a spherical or irregular filler on one surface of a transparent film. When thin linear light is vertically incident on these light diffusing elements, the light image of the transmitted light generally has a circular shape as shown in FIG. In this specification, the state in which the diffusibility of transmitted light is diffused in a circular shape without depending on the azimuth angle is referred to as isotropic light diffusion in this specification.

In recent years, anisotropic light diffusing elements that are diffused in a specific direction instead of isotropic diffusion have been proposed as light diffusing elements. That is, when light is incident on the anisotropic light diffusing element, the optical image obtained from the transmitted light is not circular, but exhibits azimuth angle dependency such as linear or elliptical.
For example, the following patent documents are disclosed as such anisotropic light diffusing elements.
Patent Documents 1 and 2 disclose a projection screen in which fibrous particles or acicular particles are dispersed in a substrate and oriented in one direction.
Patent Documents 3 to 5 disclose a projection screen or a light diffusing sheet in which a rod-shaped resin having a refractive index different from that in a transparent matrix is oriented and dispersed in the same direction, and these have different refractive indexes. It is described that it can be produced by stretching a resin composition having a sea-island structure and deforming and orienting resin fine particles corresponding to the islands into a rod shape.
Patent Document 6 discloses an anisotropic diffusion sheet in which rod-shaped bubbles are oriented in one direction in parallel to the sheet surface instead of fibrous particles and resin fine particles.
Patent Document 7 discloses a method for producing a transmitted light scattering control film in which a condition in which a thermoplastic polymer resin film is uniaxially stretched is controlled to form a groove extending in a direction perpendicular to the stretching direction on the film surface. Has been.
Patent Document 8 discloses an anisotropic light-diffusing adhesive layer containing an adhesive and an acicular filler having a refractive index different from that of the adhesive (wherein the acicular filler is oriented and dispersed in substantially the same direction. Is disclosed.

JP 59-176734 A JP-A-8-327805 Japanese Patent Laid-Open No. 2-199444 JP-A-4-314522 JP-A-9-311205 JP 2002-98810 A JP-A-10-119125 WO2004 / 044629

In the above Patent Documents 1 to 7, a basic configuration is disclosed in which a rod-like material (including needles and fibers) having a refractive index different from that of the matrix is dispersed and oriented in the transparent matrix. The material of the rod-shaped material used there is not necessarily detailed.
Here, the candidate for the rod-shaped material includes an organic type and an inorganic type. The organic filler is typically a synthetic resin fiber, but generally has a refractive index close to that of a transparent matrix. Therefore, when the same weight is blended, the diffusibility is inferior compared to an inorganic filler. In addition, when a rod-shaped organic filler is used in advance among organic fillers, since the rigidity is low, especially those with a high aspect ratio become a fuzzy ball shape at the time of dispersion, and even when oriented, they cannot be bent and arranged in parallel. There is a problem. On the other hand, the inorganic filler has a higher refractive index than the organic matrix, so it has excellent light diffusibility and high rigidity. This is advantageous because it can be oriented in the following manner.
On the other hand, in the above-mentioned Patent Documents 1 to 7, the anisotropic light diffusing element is manufactured by stretching a resin sheet. Here, when the said extending | stretching process is applied to transparent resin containing an inorganic type filler, possibility that a space | gap will arise between an inorganic type filler and a matrix is high. In addition, since the inorganic acicular filler has high rigidity, there is a possibility that fine cracks are generated in the film by stretching. In particular, when the amount of the filler is large, there is a high possibility that such a defect will occur. Therefore, in order not to cause defects such as voids and cracks, advanced manufacturing techniques are required to optimize various parameters at the time of stretching along with the selection of materials.
As described above, in the case of the stretch type, a large-scale facility and a high-level manufacturing technique are required, and it is difficult to cope with small-scale production of varieties having different degrees of anisotropy and thickness of transmitted light. In this method, since it is necessary to disperse and orient the rod-shaped material or the rod-shaped material after stretching in the matrix resin in the molten state, the combinations of materials that can be used are extremely limited. The optical properties of the obtained anisotropic diffusion film are also limited. In other words, the matrix material that is suitable for the stretching process and that can disperse the acicular filler is limited, and may not satisfy the physical properties in the final application. Furthermore, in the case of producing by stretching, even if an isotropic matrix material is used, the obtained film becomes anisotropic.
Furthermore, Patent Document 8 discloses a pressure-sensitive adhesive layer exhibiting directional diffusion, which is prepared by dispersing and blending a needle-like filler in a pressure-sensitive adhesive composition. Since the adhesive layer is produced not by stretching but by a coating technique, there is no problem with the above-described stretching mold. However, if the blending of the filler is increased to improve the diffusibility, the adhesiveness decreases, and as a result There is another problem that it is difficult to obtain the above haze, and the application is limited.

  In view of the above circumstances, the present invention has no problems that may occur in the stretched mold when using inorganic needle fillers excellent in optical properties and orientation, and the content is limited when mixed in the adhesive layer. The purpose is to provide technology that does not have such problems.

  In light of the above problems, the present inventor is capable of small-scale production, has a wide range of material selection, can directly impart an anisotropic diffusion function to any substrate surface, and requires expensive equipment. Focusing on the coating technique as a simple and inexpensive manufacturing method, the present invention has been completed. In the present invention, what has been expressed by the term “anisotropic diffusion” until now will be expressed by “directional diffusion” which is considered more appropriate in the following sentence.

  The present invention (1) includes an isotropic transparent resin matrix and inorganic needles having a refractive index different from that of the isotropic transparent resin matrix that are oriented and dispersed in a certain direction within the isotropic transparent resin matrix. It is a light-diffusion film containing a filler.

  In the present invention (2), a resin composition comprising a transparent resin and an inorganic needle filler having a refractive index different from that of the transparent resin is dispersed in the transparent resin matrix with the inorganic needle filler oriented in a certain direction. It is the light-diffusion film obtained by coating so that it may.

  In the present invention (3), a resin composition containing a transparent resin and an inorganic needle filler having a refractive index different from that of the transparent resin is dispersed in the transparent resin matrix with the inorganic needle filler oriented in a certain direction. Thus, it is a light diffusion film in which inorganic needle-like fillers are oriented and dispersed in a certain direction within an isotropic transparent resin matrix obtained by coating.

  The present invention (4) is the light diffusion film according to any one of the inventions (1) to (3), wherein the inorganic needle filler is a whisker or glass fiber.

  The light diffusing film according to any one of the inventions (1) to (4), wherein the invention (5) further comprises a spherical filler having a refractive index different from that of the transparent resin matrix, which is dispersed in the transparent resin matrix. It is.

  The present invention (6) is the light diffusion film according to any one of the inventions (1) to (5), wherein the light diffusion film is a directional diffusion film.

  The present invention (7) is a light diffusion laminated film in which any one of the light diffusion films of the inventions (1) to (6) is laminated on a transparent substrate.

  The present invention (8) is the light diffusion laminated film of the invention (7), wherein the light diffusion film is directly laminated on the transparent substrate by a coating method.

  In the invention (9), any one of the light diffusing films of the inventions (1) to (6) or the light diffusing laminated film according to claim 7 or 8 is any one of transmission, reflection, polarization, refraction, and diffusion. It is the optical member laminated | stacked on the optical element with the function.

  This invention (10) is the optical member of the said invention (9) whose optical element which shows a permeation | transmission function is a transparent glass plate or a transparent resin plate.

  This invention (11) is the optical member of the said invention (9) whose optical element which shows a reflective function is a reflecting plate.

  This invention (12) is the optical member of the said invention (9) whose optical element which shows a polarization function is an absorption type polarizer.

  This invention (13) is the optical member of the said invention (9) whose optical element which shows a polarization function is a reflection type polarizer.

  The present invention (14) is the optical member according to the invention (9), wherein the optical element exhibiting a refractive function is a prism sheet.

  This invention (15) is the optical member of the said invention (9) whose optical element which shows a spreading | diffusion function is an isotropic diffusion film or a diffusion plate.

  The present invention (16) is the optical member according to any one of the inventions (9) to (15), wherein the light diffusion film is directly laminated on the optical element by a coating method. is there.

  According to the present invention, since the inorganic needle filler and the coating mold are combined, there is a problem in the film properties of the stretch mold while enjoying the merit of the inorganic needle filler that is excellent in light diffusibility and orientation. And the effect that the problem in film manufacture can be eliminated is produced. In particular, the following can be mentioned as specific effects by coating, for example. (1) The coater is generally less expensive than the stretching device. (2) The coating method is suitable for small-scale production because the production cost is low compared to stretching (small turning is effective). (3) Since an organic solvent is used, there is a wide selection of materials such as a transparent matrix, a needle-like filler, and other auxiliary agents. (4) Since the needle-like filler is oriented using the flow orientation and shear orientation at the time of coating, cracks observed in the stretching process do not occur. (5) Since the orientation of the filler is completed at the stage of the coating film containing the organic solvent, the transparent matrix is optically isotropic. (6) Since it is a coating film, it can be made thinner than a stretched film. (7) A directional diffusion layer can be provided by coating directly on another optical element. (8) By adjusting the thickness of the transparent substrate, films having various total thicknesses can be formed. The “organic solvent” in the description of the column is not necessarily used as described later, and may be, for example, a solvent-free system (therefore, “use an organic solvent” herein). And “contains an organic solvent” should be understood as the main point of “because it is in a viscosity state similar to a general paint”). Furthermore, even if the filler content is increased to improve the diffusibility, problems such as pressure-sensitive adhesive type (decrease in adhesiveness) do not occur, so it is easy to obtain a haze above a certain level, for various applications. The effect that it can respond is also produced.

Hereinafter, the present invention will be described in detail.
The light diffusing film of the present invention is characterized in that inorganic needle-like fillers having different refractive indexes are dispersed and oriented in one direction in an isotropic transparent resin matrix. Directional diffusion of incident light incident on the diffusion film can be shown. Here, the “isotropic transparent resin matrix” does not mean that the transparent resin used as a raw material is isotropic, but the transparent resin matrix portion in the obtained film (light diffusion film) is equal. It means that it is anisotropic. The directional light diffusion mechanism will be briefly described with reference to FIG. FIG. 1A is a diagram schematically showing a light diffusion film of the present invention and a diffusion state of transmitted light when thin linear light is vertically incident on the light diffusion film of the present invention, and FIG. It is a figure which shows typically the projection image of the transmitted light of a diffusion film. In FIG. 1, for the sake of convenience, the major axis direction of the needle filler is the x axis, the surface of the light diffusion film is the xy plane, and the thickness direction of the light diffusion film is the z axis.
As shown in FIG. 1, when linear light is vertically incident on the light diffusion film of the present invention, the incident light is refracted on the surface of a needle-like filler having a refractive index different from that of the transparent resin matrix. As a result, the amount of light diffusion to the surface orthogonal to the major axis direction of the needle-like filler and the vicinity thereof increases, and the diffused light exhibits directivity. That is, the projected image of the transmitted light has a linear shape or an elliptical shape extending in a direction orthogonal to the major axis direction of the needle-like filler.
In the present invention, it is essential that the needle fillers are oriented, but this does not necessarily mean that all the needle fillers are accurately oriented in one direction. Usually, in order to obtain a desired directional light diffusion function, the content of the inorganic needle filler and the degree of orientation are controlled. In addition to the needle-like filler, the optical characteristics can be adjusted by further containing a spherical filler or an irregular filler.

Hereinafter, the structure of the light-diffusion film of this invention is explained in full detail.
(Transparent resin matrix)
As the transparent resin matrix material of the light diffusion film of the present invention, a polymer resin having high optical transparency and physical strength as a light diffusion film can be used. Moreover, when laminating | stacking a light-diffusion film on a transparent base material or an optical element directly, high adhesiveness with a transparent base material or an optical element is calculated | required by this polymeric resin. Specific examples of usable polymer resins include acrylic resins, styrene resins, styrene-acrylic copolymers, polyurethane resins, polyester resins, epoxy resins, cellulose resins, vinyl acetate resins, and vinyl chloride-vinyl acetate copolymers. , Polyvinyl butyral resin, cycloolefin resin, norbornene resin and the like, and these can be used alone or as a mixture thereof. These polymer resins are usually used after being dissolved in an organic solvent, but it is also possible to introduce a thermosetting or photocuring system or to use a solvent-free material.

(Needle filler)
The needle-like filler used in the present invention is not particularly limited as long as it has a refractive index different from that of the transparent resin matrix and is a high-aspect ratio inorganic filler such as needle-like, rod-like, or fiber-like. When used for a device, a backlight for a liquid crystal display device or the like, a colorless or white one is preferable in order to prevent coloring of transmitted light. Here, as an aspect-ratio of a needle-like filler, 2-1000 are preferable and 10-300 are more preferable. When the aspect ratio is less than 2, it is difficult to sufficiently align the needle-like filler. When the aspect ratio is 1000 or more, the dispersibility is deteriorated due to the entanglement of the needle-like fillers, and a non-uniform surface with many aggregation defects is easily formed.

  Specifically, metal oxides such as titanium oxide, zirconium oxide, and zinc oxide, metal compounds such as boehmite, aluminum borate, calcium silicate, basic magnesium sulfate, calcium carbonate, and potassium titanate, and glass fiber are preferable. Used. Among these inorganic needle fillers, those called whiskers have a high aspect ratio and are sometimes marketed as reinforcing agents for plastic products, and can be suitably used in the present invention. In addition, about glass fiber, what is marketed with names, such as a chopped strand, a milled fiber, a cut fiber, can be used.

The size of the needle filler is preferably 2 to 5000 μm in the major axis and 0.1 to 30 μm in the minor axis, particularly preferably 10 to 300 μm in the major axis and 0.3 to 5 μm in the minor axis. When the major axis is less than 2 μm or more than 5000 μm, it is difficult to disperse and orient the needle filler in the transparent resin matrix, and the directional light diffusion function may not be stably expressed. Absent. On the other hand, if the minor axis is less than 0.1 μm, it is difficult to disperse and orient the needle-shaped filler well, and the directional light diffusion function may be deteriorated. If the minor axis exceeds 30 μm, the diffused light is not emitted. Since it becomes a thing with a strong glare, it is not preferable.
The needle-like filler used in the present invention is characterized by being an inorganic material. Compared to organic synthetic resin fibers, the needle-like filler generally has a high refractive index and thus has a superior directional light diffusion function and high rigidity. Therefore, it is excellent in dispersion and orientation.

(Spherical filler, irregular filler)
In the present invention, the spherical or amorphous filler that can be used in combination with the acicular filler is preferably colorless or white having a refractive index different from that of the transparent resin matrix.
Specifically, resin particles such as acrylic resin, polystyrene resin, styrene-acrylic copolymer resin, polyethylene resin, and epoxy resin are preferably used as the spherical filler.
Examples of the amorphous filler include inorganic white pigments such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide. In addition, the amorphous filler referred to in the present invention means that it does not show an obvious needle shape or sphere, and even if it has a certain crystal form, it cannot be substantially oriented in the resin matrix, For this reason, it does not contribute to directional diffusion.
The particle size (JIS B9921) of these fillers is 0.1 to 20.0 μm, preferably 1.0 to 10.0 μm. When the particle diameter is less than 0.1 μm, the light diffusibility is lowered, and when the particle diameter is more than 20.0 μm, the diffused light becomes strongly glaring.

(Transparent substrate)
The light diffusing film of the present invention can be directly laminated on a transparent substrate. As the transparent substrate usable here, the higher the transparency, the better, and the total light transmittance (JIS K7361). -1) is 80% or more, more preferably 85% or more, most preferably 90% or more, and the haze value (JIS K7136) is 3.0 or less, more preferably 1.0 or less, most preferably 0. .5 or less can be suitably used. A transparent plastic film, a glass plate, or the like can be used, but a plastic film is preferable because it is thin, light, difficult to break, and has excellent productivity. Specifically, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), polycarbonate (PC), polyarylate, polyimide (PI), aromatic polyamide, polysulfone (PS), polyethersulfone ( PES), cellophane, polyethylene (PE), polypropylene (PP), polyvinyl alcohol (PVA), cycloolefin resin and the like can be mentioned, and these can be used alone or in combination or further laminated. The thickness of the substrate is 1 μm to 5 mm, preferably 10 to 500 μm, more preferably 50 to 200 μm in consideration of the use and productivity.

  In the present invention, it is essential that there is a difference in refractive index between the transparent resin matrix and the needle-like filler, spherical filler, and amorphous filler, but in order to develop a good directional light diffusion function, a difference in refractive index is required. Is preferably 0.01 or more, and particularly preferably 0.05 or more. In addition, in this specification, the refractive index of a filler shall be measured based on the B method as described in JIS K-7142 (1996).

The content of the filler in the light diffusing film of the present invention is not particularly limited, and is appropriately designed according to desired optical characteristics, the size and specific gravity of the filler, the refractive index difference between the transparent resin matrix and the filler, etc. It is preferable that it is 0.1-80.0 mass% with respect to the total mass of a film, and it is especially preferable that it is 5-45 mass%. If the filler content is less than 0.1% by mass, the light diffusibility may be insufficient, and if it exceeds 80.0% by mass, the binding force may decrease and the filler may be peeled off. If the filler content exceeds a certain level, fine irregularities due to the filler will be generated on the surface of the coated surface, and the diffusion effect due to the surface irregularities is also a design matter for obtaining the final diffusion characteristics. I can do it. Thus, compared with the conventional adhesive type, more filler can be blended, so that the haze can be improved to about 90%.
Here, the content of the inorganic needle filler among the fillers is preferably 50% by mass or more, and more preferably 66.7% by mass or more with respect to the total mass of all fillers. Here, when the ratio of the inorganic needle filler is less than 50% by mass based on the total filler, it becomes difficult to sufficiently show directivity.

  Although the thickness of the light-diffusion film of this invention is not specifically limited, It is preferable that it is 5-100 micrometers, and it is especially preferable that it is 20-80 micrometers. If the thickness is less than 5 μm, there is a risk that sufficient haze and directional light diffusing function may not be realized. If the thickness exceeds 100 μm, further improvement in optical properties cannot be expected for the increased material cost, and the manufacturing efficiency is poor. Therefore, it is not preferable.

[Production method of light diffusion film]
The light diffusing film of the present invention is prepared by preparing a resin composition in which acicular fillers are dispersed in the transparent resin, and the acicular fillers are arranged in a certain direction on a transparent substrate, a release sheet, and various optical elements. After coating so as to be oriented, the solvent is dried and removed.

Here, in preparing the resin composition, an organic solvent such as ethyl acetate, acetone, methyl ethyl ketone, or toluene may be used to dissolve the transparent resin and disperse the filler. In addition to the above solvents, a solvent such as butyl acetate, methyl isobutyl ketone, or cyclohexanone may be added as necessary in order to improve coating suitability such as wettability, leveling properties, and drying properties. As described above, since means for mixing and dispersing the inorganic needle filler in the resin composition set to a viscosity suitable for coating by adding an organic solvent or the like is provided, (1) In the resin It is possible to greatly improve the dispersibility of the inorganic needle filler, and (2) it is possible to efficiently unravel the bundle-like inorganic needle filler.
In addition, in order to improve the dispersibility of the filler in the transparent resin, the filler surface is modified in advance by applying a dispersibility improver such as fats and oils, a surfactant, and a silane coupling agent to the filler surface. May be. In addition, this dispersibility improvement agent can also be mix | blended with a filler containing coating material instead of making it adhere to the surface of a filler. Furthermore, a coloring dye, a fluorescent dye, a thickener, a surfactant, a leveling agent, and the like can be added to the filler-containing coating as necessary.
Dispersion of the filler in the resin composition can be usually performed using various mixing / stirring devices such as a disperser, an agitator, a homogenizer, a ball mill, an attritor, a dispersing device, etc., but the shape of the acicular filler was maintained. In order to disperse as it is, it is preferable to use a device that generates a strong shearing force without using beads. The prepared resin composition is preferably defoamed in advance before being applied to the substrate.

The resin composition is applied by a coating method in which the flow orientation and shear orientation of the acicular filler in the resin composition are strongly promoted, so that the long axis of the acicular filler is substantially along the coating direction. It is possible to produce a light diffusion film oriented in a relatively easy manner. Specific coating methods include reverse coaters, gap coaters, comma coaters, die coaters, lip coaters, wire bar coaters, dip coaters, micro gravure coaters, roll coaters, and the like. The degree of orientation of the acicular filler can be adjusted by the size of the acicular filler, the viscosity of the filler-containing paint, the coating method, the coating speed, and the like. Further, the thickness of the light diffusion film can be easily adjusted by the WET coating thickness of the resin composition, the solid content concentration of the resin composition, and the like.
In addition, since the light-diffusion film of this invention is produced by coating in this way, optical anisotropy which generate | occur | produces at an extending process does not arise in transparent resin. That is, the transparent resin matrix itself has no phase difference and is isotropic, so that it basically does not disturb the polarization. Although directivity of light diffusion due to the orientation of the acicular filler is recognized, when the degree of diffusion is small, the light diffusion film as a whole has little depolarization, so it is inserted between two polarizing plates of a liquid crystal display device. It is also possible.
In the present invention, it is possible to obtain a light diffusion laminated film provided with a light diffusion film by directly coating a needle-like filler-containing paint on a transparent substrate. After coating and drying on a substrate such as metal or ceramics, it can be peeled off to form a single-layer light diffusion film. Furthermore, these light diffusing films and light diffusing laminated films can be laminated with optical elements having any of the functions of transmission, reflection, polarization, refraction, and diffusion (a needle-filler-containing paint is directly applied to the optical elements. You may work).
Here, a transparent glass plate and a transparent resin plate are mentioned as an optical element which shows a transmission function. In the liquid crystal display device, the former corresponds to the glass substrate of the liquid crystal cell, and the latter corresponds to the light guide plate. In addition, a reflecting plate is used as an optical element that exhibits a reflecting function, an absorbing polarizer or a reflecting polarizer is used as an optical element that exhibits a polarizing function, and a prism sheet is used as an optical element that exhibits a refractive function. Examples of the optical element shown include isotropic diffusion films or diffusion plates.
In addition to the usual “light-absorbing polarizing element” that transmits only specific polarized light and absorbs other light, the polarizing element transmits “light reflecting polarized light that transmits only specific polarized light and reflects other light”. Element ". As a light reflection type polarizing element, for example, two types of polyester resins (PEN and PEN copolymer) having different refractive indexes in the stretching direction when stretched are alternately laminated and stretched by several hundred layers by an extrusion molding technique. "DBEF" manufactured by 3M, or a cholesteric liquid crystal polymer layer and a quarter-wave plate, and the light incident from the side of the cholesteric liquid crystal polymer layer is separated into two circularly polarized beams that are opposite to each other. Nitto Denko's “Nipox” and Merck's “Transmax”, which are configured to convert the circularly polarized light that has been transmitted and reflected on the other side and transmitted through the cholesteric liquid crystal polymer layer into linearly polarized light by a quarter-wave plate, are commercially available. Yes. Any of these can be used by laminating with the light diffusion film of the present invention.

  The light diffusing film of the present invention can be directly laminated on the above transparent substrate and various optical elements by coating, but can also be laminated via an adhesive or an adhesive.

  The light diffusing film of the present invention can be produced relatively easily by preparing a filler-containing paint, coating and drying it as described above in the production process. In addition, the degree of directional diffusion of transmitted light can be adjusted by selecting filler type, size, blending ratio, thickness, and the degree of orientation of needle filler, etc., for liquid crystal display devices and liquid crystal display devices It can be suitably used for various optical devices such as a backlight.

[Application field of light diffusion film]
The light diffusing film of the present invention can be used for a backlight for a liquid crystal display device. In particular, as a light diffusing film for a direct type backlight using a cold cathode tube, a spatial luminance due to the shape of a light source can be used. It is effective in eliminating unevenness and making it uniform. Further, by arranging the LED array light on the surface where the light enters the light guide plate, it is possible to eliminate bright lines and dark lines. In addition to these effects, the number of members can be reduced and the thickness can be reduced. Furthermore, the use which expands a viewing angle using the visual recognition side of a liquid crystal display device is also considered. Furthermore, by arranging in combination with an optical element selected from a light guide plate, a light reflecting element, a light diffusing element, a prism element, a polarizing element, a phase difference element, and a viewing angle widening element, or by laminating both, It is expected to enhance functions or to express functions beyond simple combinations.

Next, examples and comparative examples according to the present invention will be described.
(Example)
An acrylic resin having a refractive index of 1.50 was selected as the transparent resin matrix, and a solution in which the total solid content concentration was 30% in a mixed solvent of methyl ethyl ketone and toluene was prepared. To 60 parts by mass of this acrylic resin solution, 40 parts by mass of aluminum borate whisker (major axis 10 to 30 μm, minor axis 0.5 to 1.0 μm, refractive index 1.60 to 1.63) is added as an acicular filler, Furthermore, 40 parts by mass of toluene was added as a diluent solvent, and the mixture was stirred with an agitator for 30 minutes to disperse the needle-like filler. To this dispersion, 0.7 part by mass of an isocyanate curing agent was added and mixed well to prepare a filler-containing adhesive composition.
This composition was applied onto a 75 μm-thick transparent PET film using an applicator and dried at 100 ° C. for 3 minutes to prepare a light diffusion laminated film of the present invention. The formed directional light diffusion film had a thickness of 19 μm.
As a result of observation with an optical microscope, it was confirmed that the needle-like filler was oriented so that the major axis was substantially along the coating direction. Moreover, when the obtained light-diffusion laminated | multilayer film is arrange | positioned in parallel with a space | interval of 10 cm from white paper, when light is vertically incident on the film from the laser pointer from above, it is orthogonal to the major axis direction of a needle-like filler. An elliptical light image extending in the direction was projected onto the paper (see FIG. 1).
Furthermore, the light diffusion laminated film of the present invention was irradiated with light from the normal direction with a goniophotometer, and the diffusion state of the transmitted light is shown in FIG. The dotted line here is measured in the direction in which the light diffuses over a wide range (corresponding to the y-axis direction in FIG. 1), and the solid line shows the case where the diffusion angle is narrow (see FIG. 1 corresponding to the x-axis direction).

  As described above, according to the present invention, it is possible to provide a film having a directional light diffusion function, and an optical layered body and an illumination device using the film. The light diffusing film of the present invention is relatively easy to manufacture, and the degree of directivity and thickness of transmitted light can be easily adjusted. In addition, by applying the directional light diffusion film of the present invention to an illumination device such as a backlight of a liquid crystal display device, it is possible to achieve uniform illuminance, elimination of bright lines and dark lines, reduction in the number of members, and reduction in thickness. it can.

FIGS. 1A and 1B are diagrams for explaining an anisotropic light diffusion mechanism of an anisotropic light diffusion adhesive laminated layer. FIGS. 2A and 2B are diagrams for explaining the reason why an anisotropic light diffusion function is not exhibited in a light diffusion adhesive layer using a spherical filler instead of a needle filler. FIGS. 3A and 3B are diagrams for explaining the anisotropic light diffusion mechanism of the anisotropic diffusion adhesive laminate of the example.

Claims (16)

  Light diffusion comprising an isotropic transparent resin matrix and inorganic needle fillers having a different refractive index from that of the isotropic transparent resin matrix, which are oriented and dispersed in a certain direction within the isotropic transparent resin matrix the film.   Coating a resin composition comprising a transparent resin and an inorganic needle filler having a refractive index different from that of the transparent resin so that the inorganic needle filler is oriented and dispersed in a certain direction within the transparent resin matrix. , A light diffusion film obtained.   Coating a resin composition comprising a transparent resin and an inorganic needle filler having a refractive index different from that of the transparent resin so that the inorganic needle filler is oriented and dispersed in a certain direction within the transparent resin matrix. A light diffusing film in which inorganic needle-like fillers are oriented and dispersed in a certain direction within an isotropic transparent resin matrix.   The light diffusion film according to claim 1, wherein the inorganic needle filler is a whisker or glass fiber.   The light-diffusion film as described in any one of Claims 1-4 which further contains the spherical filler of the refractive index different from the said transparent resin matrix currently disperse | distributed in the said transparent resin matrix.   The light diffusion film according to claim 1, wherein the light diffusion film is a directional diffusion film.   The light-diffusion laminated film in which the light-diffusion film as described in any one of Claims 1-6 is laminated | stacked on the transparent base material.   The light diffusion laminated film according to claim 7, wherein the light diffusion film is directly laminated on the transparent substrate by a coating method.   The light diffusing film according to any one of claims 1 to 6 or the light diffusing laminated film according to claim 7 or 8 is laminated on an optical element having any one of functions of transmission, reflection, polarization, refraction, and diffusion. Optical member.   The optical member according to claim 9, wherein the optical element exhibiting a transmission function is a transparent glass plate or a transparent resin plate.   The optical member according to claim 9, wherein the optical element exhibiting a reflecting function is a reflecting plate.   The optical member according to claim 9, wherein the optical element exhibiting a polarization function is an absorptive polarizer.   The optical member according to claim 9, wherein the optical element exhibiting a polarization function is a reflective polarizer.   The optical member according to claim 9, wherein the optical element exhibiting a refraction function is a prism sheet.   The optical member according to claim 9, wherein the optical element exhibiting a diffusion function is an isotropic diffusion film or a diffusion plate.   The optical member according to any one of claims 9 to 15, wherein the light diffusion film is directly laminated on the optical element by a coating method.

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