JP3743624B2 - Light diffusing layer, light diffusing sheet, optical element and display device - Google Patents

Description

実施例１ではバーコータにより、実施例２ではマイクログラビアコータにより塗工液を塗工しており、得られる光拡散層の微細凹凸形状表面の光沢度が入射方向により差があり、外光に対する表面拡散性に異方性が認められ、防眩機能と表示画像のコントラストのいずれも良好である。一方、比較例１では、必要量だけを外部からの力がかからないダイコータにより塗工液を塗工しており、得られる光拡散層の微細凹凸形状表面の光沢度は入射方向によって殆ど差がない。そのため表面拡散性に外光に対する表面拡散性が等方性であり、黒色表示時に表示画面が白ぼけにより、コントラストが低下している。
【図面の簡単な説明】
【図１】本発明の光拡散性シートの断面図の一例である。
【符号の説明】
１：透明基板
２：樹脂皮膜層
３：微粒子
４：光拡散層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light diffusing layer used for suppressing a reduction in screen visibility in a display device such as a liquid crystal display (LCD), an organic EL display device, and a PDP, and further a light diffusing layer having the light diffusing layer. The present invention relates to a light-sensitive sheet and an optical element provided with the light-diffusing sheet. Furthermore, the present invention relates to a display device on which the light diffusing sheet or the optical element is mounted. The display device can be effectively applied to a flat display device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image display device such as an LCD has an image visibility hindered by room lighting such as a fluorescent lamp, sunlight incident from a window, and an operator's shadow on a display device surface. Therefore, on the LCD surface, in order to improve the visibility of the image, the surface reflection light is diffused, regular reflection of external light is suppressed, and reflection of the external environment can be prevented (having anti-glare properties). A light diffusion layer having a concavo-convex structure is provided. As a method for forming the light diffusion layer, a method in which a resin film layer is formed by coating a resin in which fine particles are dispersed has become the mainstream because the structure can be easily refined and the productivity is good.
[0003]
However, if the anti-glare function of the light diffusing layer is enhanced to obtain a light diffusing layer having a high surface diffusibility, the entire surface of the light diffusing layer is strongly diffused and reflected, and the display screen becomes whitish when black is displayed. This causes a problem that the contrast of the display screen is lowered.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a light diffusing layer, a light diffusing sheet, and an optical element provided with the light diffusing layer while maintaining the antiglare property and having a good display screen contrast. Furthermore, it aims at providing the display apparatus with which the said light diffusable sheet or an optical element is mounted | worn.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by the light diffusion layer described below, and have completed the present invention.
[0006]
That is, according to the present invention, in the light diffusion layer composed of a resin film layer having a fine concavo-convex shape formed on the surface, the value of 60 ° glossiness (JIS-Z8741) of the surface of the fine concavo-convex shape varies depending on the incident direction. The light diffusion layer is characterized in that the maximum value (a) and the minimum value (b) of the degree satisfy the formula: (ab)> {(a + b) / 2} × 0.1.
[0007]
In the present invention, a general light diffusion layer having a fine uneven surface is isotropic in terms of surface diffusibility with respect to external light, and exhibits the same surface reflection behavior with respect to external light from any direction. Although it has a uniform anti-glare function, the anti-glare function of the light diffusing layer is required to diffuse strongly in the direction in which external light strikes the surface of the fine irregularities, while it strongly diffuses in a direction in which external light does not strike strongly. Since it is not required to do so, as a result of obtaining the knowledge that if the anti-glare function is increased and the surface diffusibility is increased, the contrast of the display screen is reduced, the gloss value is controlled to be different depending on the incident direction, The light diffusing layer has anisotropy in the surface diffusibility with respect to external light.
[0008]
By providing anisotropy to the surface diffusivity of the light diffusing layer in this way, it is possible to increase the diffusibility and suppress the surface reflection for light from above, which is likely to be strongly exposed to outside light, that is, to reduce the glossiness. On the other hand, diffusivity can be suppressed against external light reflection from the lateral direction where strong external light is not applied. In this way, the present invention improves the antiglare property against light from the direction in which external light is strongly applied while maintaining the contrast of the display image.
[0009]
The maximum value (a) and the minimum value (b) of the 60 ° glossiness of the fine uneven surface of the light diffusing layer are not particularly limited as long as the above formula is satisfied. The maximum value (a) and the minimum value (b) of the 60 ° glossiness are preferably in the range of 40 to 70, more preferably 30 to 53. When the difference (ab) between the maximum value (a) and the minimum value (b) of the 60 ° glossiness increases, the antiglare property decreases. The difference (ab) decreases to 10 or less, and further to 6 or less. It is preferable to adjust.
[0010]
In the light diffusing layer, it is preferable that the resin film layer contains fine particles, and the uneven surface shape of the resin film layer is formed of fine particles. The resin film layer is preferably formed of an ultraviolet curable resin.
[0011]
The gloss characteristics can be easily adjusted by using fine particles. In addition, the ultraviolet curable resin can efficiently form a resin film layer (light diffusion layer) by a simple processing operation by a curing treatment by ultraviolet irradiation.
[0012]
The present invention also relates to a light diffusing sheet, wherein the light diffusing layer is provided on at least one surface of a transparent substrate. The present invention also relates to an optical element, wherein the light diffusing layer or the light diffusing sheet is provided on one side or both sides of the optical element. The light diffusing layer of the present invention can be used for various applications as a light diffusing sheet provided on a transparent substrate. For example, it is used for an optical element.
[0013]
Furthermore, the present invention relates to a display device equipped with the light diffusing sheet or the optical element. The light diffusing sheet and the optical element of the present invention can be used for various applications, and are applied to, for example, a display device.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a light diffusing sheet in which a light diffusing layer 4 composed of a resin film layer 2 in which fine particles 3 are dispersed is formed on a transparent substrate 1, and the fine particles dispersed in the resin film layer 2. 3 forms an uneven shape on the surface of the light diffusion layer 4. In addition, in FIG. 1, although the case where the resin film layer 2 is one layer is shown, by separately forming a resin film layer containing fine particles between the resin film layer 2 and the transparent substrate 1, The light diffusion layer can also be formed by a plurality of resin film layers.
[0015]
Examples of the transparent substrate 1 include films made of transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Can be given. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides, etc. Examples thereof include films made of transparent polymers such as amide polymers. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Examples thereof include a film made of a transparent polymer such as a polymer, an epoxy-based polymer, and a blend of the aforementioned polymers. In particular, those having a small optical birefringence are preferably used.
[0016]
The thickness of the transparent substrate 1 can be appropriately determined, but is generally about 10 to 500 μm from the viewpoints of workability such as strength and handleability, and thin layer properties. 20-300 micrometers is especially preferable, and 30-200 micrometers is more preferable.
[0017]
As long as the resin film layer 2 having a fine concavo-convex structure surface is formed on the transparent substrate 1, the formation method is not particularly limited, and an appropriate method can be adopted. For example, the surface of the film used for forming the resin film layer 2 is previously roughened by an appropriate method such as sand blasting, embossing roll, chemical etching, etc. A method of forming the surface of the material itself for forming the resin film layer 2 in a fine concavo-convex structure is exemplified. Further, there is a method in which a resin film layer is separately applied on the resin film layer 2 and a fine concavo-convex structure is imparted to the surface of the resin film layer by a transfer method using a mold or the like. Further, as shown in FIG. 1, there is a method in which fine concavo-convex structure is imparted by dispersing fine particles 3 in the resin film layer 2. These fine concavo-convex structure forming methods may be formed as a layer in which two or more methods are combined to combine the fine concavo-convex structure surfaces in different states. Among the methods for forming the resin film layer 2, a method of providing the resin film layer 2 containing the fine particles 3 in a dispersed manner is preferable from the viewpoint of the formability of the surface of the fine concavo-convex structure.
[0018]
Hereinafter, a method for providing the resin film layer 2 by dispersing the fine particles 3 will be described. As the resin for forming the resin film layer 2, fine particles 3 can be dispersed, and a resin having sufficient strength and transparency as a film after the resin film layer is formed can be used without particular limitation. Examples of the resin include thermosetting resins, thermoplastic resins, ultraviolet curable resins, electron beam curable resins, and two-component mixed resins. An ultraviolet curable resin that can efficiently form a light diffusion layer by a processing operation is preferable.
[0019]
Examples of the ultraviolet curable resin include polyesters, acrylics, urethanes, acrylurethanes, amides, silicones, and epoxy resins, and include ultraviolet curable monomers, oligomers, polymers, and the like. . The UV curable resin preferably used includes, for example, those having an ultraviolet polymerizable functional group, and in particular, those containing an acrylic monomer or oligomer having 2 or more, particularly 3 to 6 functional groups. . Further, an ultraviolet polymerization initiator is blended in the ultraviolet curable resin.
[0020]
In addition, in formation of the resin film layer 2, additives, such as a leveling agent, a thixotropic agent, and an antistatic agent, can be contained. By forming a thixotropic agent (0.1 μm or less of silica, mica, etc.) in forming the resin film layer, the surface of the resin film layer (light diffusion layer) can be easily formed with a fine uneven structure by protruding particles. Can do.
[0021]
As the fine particles 3, those having transparency such as various metal oxides, glass, and plastic can be used without particular limitation. For example, inorganic fine particles that may be conductive such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, antimony oxide, polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, Examples thereof include crosslinked or uncrosslinked organic fine particles and silicone fine particles composed of various polymers such as benzoguanamine, melamine, and polycarbonate. Note that crushed silica powder or the like can be used as the inorganic fine particles such as silica, and bead particles are used as the organic fine particles. These fine particles 3 can be used by appropriately selecting one type or two or more types. The average particle diameter of the fine particles is adjusted and used according to the thickness of the resin film layer, but is usually about 1 to 10 μm, preferably 2 to 10 μm.
[0022]
The method for producing the light diffusing sheet is not particularly limited, and an appropriate method can be adopted. For example, a resin containing fine particles 3 (for example, an ultraviolet curable resin: a coating solution) is applied onto the transparent substrate 1, dried, and cured to form a concavo-convex shape whose surface has the glossiness. The light diffusion layer 4 is formed by the resin film layer 2 as shown. The coating solution may be diluted with a general solvent such as toluene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, isopropyl alcohol, ethyl alcohol, or can be applied as it is without dilution. .
[0023]
The coating method of the coating liquid is not particularly limited as long as it is a coating method that causes a difference in the glossiness of the fine uneven surface of the obtained light diffusion layer and causes anisotropy in diffusibility, As a coating method, it is preferable to employ a bar coater method using a Mayer bar or the like, or a micro gravure coater method.
[0024]
In the formation of the light diffusion layer 4, the average particle diameter and the ratio of the fine particles 3 contained in the coating liquid and the thickness of the resin film layer 2 are appropriately adjusted so that the surface has a fine uneven structure.
[0025]
The ratio of the fine particles 3 contained in the coating liquid is not particularly limited, but it is preferably 6 to 20 parts by weight with respect to 100 parts by weight of the resin in terms of antiglare properties and display image contrast. The thickness of the resin film layer 2 is not particularly limited, but is preferably about 2 to 10 μm, particularly 3 to 10 μm.
[0026]
A low refractive index layer having an antireflection function can be provided on the uneven surface of the resin film layer 2 that forms the light diffusion layer 4. The material of the low refractive index layer is not particularly limited as long as it has a refractive index lower than that of the resin film layer 2. For example, a low refractive index material such as fluorine-containing polysiloxane can be used. The thickness of the low refractive index layer is not particularly limited, but is preferably about 0.05 to 0.3 μm, particularly preferably 0.1 to 0.3 μm. An antireflection function can be imparted by the low refractive index layer, and irregular reflection on the surface of an image such as a display can be effectively suppressed.
[0027]
Further, an optical element can be bonded to the transparent substrate 1 of the light diffusing sheet of FIG. 1 (not shown).
[0028]
Examples of the optical element include a polarizer. The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include hydrophilic polymer films such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film, and two colors such as iodine and dichroic dye. Examples thereof include polyene-based oriented films such as those obtained by adsorbing an active substance and uniaxially stretched, polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer made of a dichroic material such as a polyvinyl alcohol film and iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.
[0029]
A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be produced, for example, by dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing polyvinyl alcohol film surface stains and anti-blocking agents by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven coloring by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0030]
The polarizer is usually used as a polarizing plate with a transparent protective film provided on one side or both sides. The transparent protective film is preferably excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like. As the transparent protective film, the same material as the above-described transparent substrate is used. The transparent protective film may be a transparent protective film made of the same polymer material on the front and back sides, or a transparent protective film made of a different polymer material or the like. When the light diffusing sheet is provided on one side or both sides of a polarizer (polarizing plate), the transparent substrate of the light diffusing sheet can also serve as a transparent protective film of the polarizer.
[0031]
In addition, the surface of the transparent protective film on which the polarizer is not adhered may be a hard coat layer, a sticking prevention layer or a treatment intended. Hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate. For example, a transparent protective film is applied to a cured film excellent in hardness, sliding properties, etc. with an appropriate ultraviolet curable resin such as acrylic or silicone. It can be formed by a method of adding to the surface of the film. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer. The hard coat layer, the anti-sticking layer and the like can be provided on the transparent protective film itself, or can be provided separately from the transparent protective film as an optical layer.
[0032]
As an optical element, in practical use, an optical film in which another optical element (optical layer) is laminated on the polarizing plate can be used. The optical layer is not particularly limited. For example, it can be used to form liquid crystal display devices such as reflectors, transflectors, retardation plates (including wavelength plates such as 1/2 and 1/4), and viewing angle compensation films. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate is further laminated with a reflecting plate or a semi-transmissive reflecting plate, an elliptical polarizing plate or a circular polarizing plate in which a retardation plate is further laminated on a polarizing plate, a polarizing plate A wide viewing angle polarizing plate in which a viewing angle compensation film is further laminated on a plate, or a polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate is preferable.
[0033]
A reflective polarizing plate is a polarizing plate provided with a reflective layer, and is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side). Such a light source can be omitted, and the liquid crystal display device can be easily thinned. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one surface of the polarizing plate via the transparent protective film or the like, if necessary.
[0034]
Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or a vapor deposition film made of a reflective metal such as aluminum on one surface of a transparent protective film matted as necessary.
[0035]
The reflection plate can be used as a reflection sheet in which a reflection layer is provided on an appropriate film according to the transparent film, instead of the method of directly applying to the transparent protective film of the polarizing plate. Since the reflective layer is usually made of metal, the usage form in which the reflective surface is covered with a transparent protective film, a polarizing plate or the like is used to prevent the reflectivity from being lowered by oxidation, and thus to maintain the initial reflectivity for a long time. In addition, it is more preferable to avoid a separate attachment of the protective layer.
[0036]
The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell, and displays an image by reflecting incident light from the viewing side (display side) when a liquid crystal display device is used in a relatively bright atmosphere. In a relatively dark atmosphere, a liquid crystal display device or the like that displays an image using a built-in light source such as a backlight built in the back side of the transflective polarizing plate can be formed. In other words, the transflective polarizing plate is useful for forming a liquid crystal display device of a type that can save energy of using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source even in a relatively dark atmosphere. It is.
[0037]
An elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on a polarizing plate will be described. A phase difference plate or the like is used when changing linearly polarized light to elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light. In particular, a so-called 1/4 wavelength plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light into circularly polarized light or changes circularly polarized light into linearly polarized light. A 1/2 wave plate (also referred to as a λ / 2 plate) is usually used to change the polarization direction of linearly polarized light.
[0038]
The elliptically polarizing plate is effectively used for black and white display without the above color by compensating (preventing) the coloration (blue or yellow) generated by the birefringence of the liquid crystal layer of the super twist nematic (STN) type liquid crystal display device. It is done. Further, the one in which the three-dimensional refractive index is controlled is preferable because it can compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which an image is displayed in color, and also has an antireflection function. Specific examples of the retardation plate include a birefringent film obtained by stretching a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, and polyamide. And an alignment film of a liquid crystal polymer, and a liquid crystal polymer alignment layer supported by a film. The retardation plate may have an appropriate retardation according to the purpose of use, such as those for the purpose of compensating for various wavelength plates or birefringence of the liquid crystal layer, viewing angle, and the like. What laminated | stacked the phase difference plate and controlled optical characteristics, such as phase difference, etc. may be used.
[0039]
The elliptical polarizing plate and the reflective elliptical polarizing plate are obtained by laminating a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination. Such an elliptically polarizing plate or the like can also be formed by sequentially laminating them sequentially in the manufacturing process of the liquid crystal display device so as to be a combination of a (reflective) polarizing plate and a retardation plate. An optical film such as a polarizing plate has an advantage that it can improve the manufacturing efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.
[0040]
The viewing angle compensation film is a film for widening the viewing angle so that the image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction rather than perpendicular to the screen. Examples of such a viewing angle compensation retardation plate include an alignment film such as a retardation film and a liquid crystal polymer, and a support in which an alignment layer such as a liquid crystal polymer is supported on a transparent substrate. A normal retardation film uses a birefringent polymer film uniaxially stretched in the plane direction, whereas a retardation film used as a viewing angle compensation film is biaxially stretched in the plane direction. Polymer films with birefringence, biaxially stretched films such as polymers with birefringence with a controlled refractive index in the thickness direction that are uniaxially stretched in the plane direction and also stretched in the thickness direction, etc. Used. Examples of the inclined alignment film include a film obtained by bonding a heat-shrinkable film to a polymer film and stretching or / and shrinking the polymer film under the action of the shrinkage force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. The raw material polymer for the phase difference plate is the same as the polymer described in the previous phase difference plate, preventing coloration due to a change in the viewing angle based on the phase difference by the liquid crystal cell and expanding the viewing angle for good visual recognition. An appropriate one for the purpose can be used.
[0041]
In addition, from the viewpoint of achieving a wide viewing angle with good visibility, an optical compensation position in which an alignment layer of a liquid crystal polymer, particularly an optically anisotropic layer composed of a tilted alignment layer of a discotic liquid crystal polymer, is supported by a triacetyl cellulose film. A phase difference plate can be preferably used.
[0042]
A polarizing plate obtained by bonding a polarizing plate and a brightness enhancement film is usually provided on the back side of a liquid crystal cell. The brightness enhancement film reflects linearly polarized light with a predetermined polarization axis or circularly polarized light in a predetermined direction and transmits other light when natural light is incident due to a backlight of a liquid crystal display device or the like or reflection from the back side. In addition, a polarizing plate in which a brightness enhancement film is laminated with a polarizing plate allows light from a light source such as a backlight to enter to obtain transmitted light in a predetermined polarization state, and reflects light without passing through the predetermined polarization state. The The light reflected on the surface of the brightness enhancement film is further inverted through a reflective layer provided behind the brightness enhancement film and re-entered on the brightness enhancement film, and a part or all of the light is transmitted as light in a predetermined polarization state. Luminance can be improved by increasing the amount of light that passes through the enhancement film and increasing the amount of light that can be used for liquid crystal display image display or the like by supplying polarized light that is difficult to be absorbed by the polarizer. That is, when light is incident through the polarizer from the back side of the liquid crystal cell without using a brightness enhancement film, light having a polarization direction that does not coincide with the polarization axis of the polarizer is almost polarized. It is absorbed by the polarizer and does not pass through the polarizer. That is, although depending on the characteristics of the polarizer used, approximately 50% of the light is absorbed by the polarizer, and the amount of light that can be used for liquid crystal image display or the like is reduced accordingly, resulting in a dark image. The brightness enhancement film allows light having a polarization direction that is absorbed by the polarizer to be reflected once by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflective layer or the like provided on the rear side thereof. Repeatedly re-entering the brightness enhancement film, and the brightness enhancement film transmits only the polarized light whose polarization direction is such that the polarization direction of the light reflected and inverted between the two can pass through the polarizer. Therefore, light such as a backlight can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.
[0043]
The brightness enhancement film has a characteristic of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayered thin film of dielectric material or a multilayered laminate of thin film films having different refractive index anisotropies. Such as a cholesteric liquid crystal polymer alignment film or an alignment liquid crystal layer that is supported on a film substrate, and reflects light of either left-handed or right-handed circular polarization and transmits other light. Appropriate things, such as a thing, can be used.
[0044]
Therefore, in the brightness enhancement film of the type that transmits linearly polarized light having the predetermined polarization axis as described above, the transmitted light is directly incident on the polarizing plate with the polarization axis aligned, thereby efficiently transmitting while suppressing absorption loss due to the polarizing plate. Can be made. On the other hand, in a brightness enhancement film of a type that emits circularly polarized light such as a cholesteric liquid crystal layer, it can be incident on the polarizer as it is, but from the viewpoint of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable to make it enter into a polarizing plate. Note that circularly polarized light can be converted to linearly polarized light by using a quarter wave plate as the retardation plate.
[0045]
A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a quarter-wave plate for light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superposing a retardation layer, for example, a retardation layer functioning as a half-wave plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.
[0046]
In addition, the cholesteric liquid crystal layer can also be obtained by reflecting circularly polarized light in a wide wavelength range such as a visible light region by combining two or more layers having different reflection wavelengths and having an overlapping structure. Based on this, transmitted circularly polarized light in a wide wavelength range can be obtained.
[0047]
Further, the polarizing plate may be formed by laminating a polarizing plate and two or more optical layers as in the above-described polarization separation type polarizing plate. Therefore, a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above-mentioned reflective polarizing plate or semi-transmissive polarizing plate and a retardation plate are combined may be used.
[0048]
Lamination of the light diffusive sheet to the optical element, and further lamination of various optical layers to the polarizing plate can be performed by a method of laminating them separately in the manufacturing process of a liquid crystal display device or the like. Those previously laminated are excellent in quality stability, assembly work, etc., and have the advantage of improving the manufacturing process of liquid crystal display devices and the like. For the lamination, an appropriate adhesive means such as an adhesive layer can be used. When adhering the polarizing plate and other optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.
[0049]
The light-diffusing sheet is provided on at least one surface of the optical element such as the polarizing plate or the optical film in which at least one polarizing plate is laminated, but the light-diffusing sheet is not provided. Can be provided with an adhesive layer for adhering to other members such as a liquid crystal cell. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.
[0050]
In addition to the above, in terms of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical properties and liquid crystal cell warpage due to differences in thermal expansion, etc., as well as formability of liquid crystal display devices with high quality and excellent durability An adhesive layer having a low moisture absorption rate and excellent heat resistance is preferred.
[0051]
The adhesive layer is, for example, natural or synthetic resins, in particular, tackifier resins, fillers or pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, etc. It may contain an additive to be added to the adhesive layer. Moreover, the adhesion layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.
[0052]
Attachment of the adhesive layer to an optical element such as a polarizing plate or an optical film can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. There is a method of attaching it directly on the optical element by an appropriate development method such as a casting method or a coating method, or a method of forming an adhesive layer on the separator according to the above and transferring it onto the optical element. can give. The pressure-sensitive adhesive layer can also be provided as an overlapping layer of different compositions or types in each layer. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.
[0053]
On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foamed sheet or metal foil, laminate thereof, silicone type or Appropriate conventional ones such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.
[0054]
In the present invention, the polarizer, the transparent protective film, the optical layer, and the like forming the optical element described above, and the adhesive layer and the like have, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, and a cyanoacrylate. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.
[0055]
The optical element provided with the light diffusion sheet of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical element, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except for the point which uses an element, and it can be based on the past. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.
[0056]
An appropriate liquid crystal display device such as a liquid crystal display device in which the optical element is arranged on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the optical element according to the present invention can be installed on one side or both sides of the liquid crystal cell. When optical elements are provided on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.
[0057]
Next, an organic electroluminescence device (organic EL display device) will be described. Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative and the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Alternatively, a structure having various combinations such as a laminate of such a light emitting layer and an electron injection layer composed of a perylene derivative or the like, or a laminate of these hole injection layer, light emitting layer, and electron injection layer is known. It has been.
[0058]
In organic EL display devices, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by recombination of these holes and electrons excites the phosphor material. Then, light is emitted on the principle that the excited fluorescent material emits light when returning to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.
[0059]
In an organic EL display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes must be transparent, and a transparent electrode usually formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is used as. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.
[0060]
In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.
[0061]
In an organic EL display device comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode While providing a polarizing plate on the side, a retardation plate can be provided between the transparent electrode and the polarizing plate.
[0062]
Since the retardation plate and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization action. In particular, the mirror surface of the metal electrode can be completely shielded by configuring the retardation plate with a quarter-wave plate and adjusting the angle between the polarization direction of the polarizing plate and the retardation plate to π / 4. .
[0063]
That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light becomes generally elliptically polarized light by the retardation plate, but becomes circularly polarized light especially when the retardation plate is a quarter-wave plate and the angle between the polarization direction of the polarizing plate and the retardation plate is π / 4. .
[0064]
This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again on the retardation plate. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.
[0065]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0066]
Example 1
100 parts by weight of an ultraviolet curable acrylic resin oligomer, 14 parts by weight of silica having an average particle diameter of 4 μm, 7 parts by weight of a benzophenone-based photopolymerization initiator, and a solvent (toluene) measured so that the solid content thereof is 30% by weight Were mixed to prepare a coating solution. This coating solution is applied to one side of a triacetyl cellulose film with a bar coater, dried at 120 ° C. for 5 minutes, and then cured by ultraviolet irradiation to form a resin film layer on the surface of a fine concavo-convex structure having a thickness of about 4 μm. A light diffusing sheet having the following characteristics was prepared.
[0067]
Example 2
100 parts by weight of an ultraviolet curable acrylic resin oligomer, 17 parts by weight of polystyrene beads having an average particle diameter of 3 μm, 5 parts by weight of a benzophenone-based photopolymerization initiator, and a solvent (toluene) measured so that its solid content is 40% by weight Were mixed to prepare a coating solution. This coating solution was applied to one side of a triacetyl cellulose film with a micro gravure coater, dried at 120 ° C. for 5 minutes, and then cured by ultraviolet irradiation to form a surface with a fine concavo-convex structure having a thickness of about 3 μm. A light diffusing sheet having a resin film layer was prepared.
[0068]
Comparative Example 1
In Example 1, a light diffusing sheet was produced in the same manner as in Example 1 except that the prepared coating solution was applied by a die coater.
[0069]
About the surface of the light diffusing layer of the light diffusing sheet obtained in the above-mentioned Examples and Comparative Examples, a gloss meter based on JIS-Z8741 (manufactured by Suga Test Instruments Co., Ltd., variable angle photometer UGV-5DP) was used. ° Gloss was measured. The glossiness was measured for the maximum value (a) and the minimum value (b) by changing the direction of light incidence. From these measured values, the difference between the maximum value (a) and the minimum value (b) (ab), {(a + b) / 2} × 0.1 was calculated. The results are shown in Table 1.
[0070]
The light diffusing sheets obtained in the examples and comparative examples are bonded to the surface of the liquid crystal display element (polarizing plate) and installed in a room with a brightness of 1000 lux illuminated by a fluorescent lamp from above. The anti-glare function of the reflected light of the fluorescent lamp reflected in the screen and the contrast of the displayed image were visually evaluated. The results are shown in Table 1.
[0071]
[Table 1]

The coating liquid is applied by a bar coater in Example 1 and by a microgravure coater in Example 2, and the glossiness of the fine uneven surface of the obtained light diffusion layer varies depending on the incident direction, and the surface against external light Anisotropy is observed in the diffusibility, and both the antiglare function and the contrast of the display image are good. On the other hand, in Comparative Example 1, the coating liquid is applied by a die coater in which only a necessary amount is not applied with an external force, and the glossiness of the surface of the fine concavo-convex shape of the obtained light diffusion layer has little difference depending on the incident direction. . Therefore, the surface diffusibility is isotropic with respect to the external light, and the contrast is lowered because the display screen is blurred at the time of black display.
[Brief description of the drawings]
FIG. 1 is an example of a cross-sectional view of a light diffusing sheet of the present invention.
[Explanation of symbols]
1: Transparent substrate
2: Resin film layer
3: Fine particles
4: Light diffusion layer

Claims (6)

In the light diffusion layer composed of a resin film layer having a fine concavo-convex shape formed on the surface, the 60 ° gloss value (JIS-Z8741) of the fine concavo-convex shape surface varies depending on the incident direction, and the maximum gloss value ( A light diffusing layer, wherein a) and the minimum value (b) satisfy the formula: (ab)> {(a + b) / 2} × 0.1. 2. The light diffusing layer according to claim 1, wherein the resin film layer contains fine particles, and the surface irregularities of the resin film layer are formed of fine particles. The light diffusion layer according to claim 1 or 2, wherein the resin film layer is formed of an ultraviolet curable resin. A light diffusing sheet according to claim 1, wherein the light diffusing layer is provided on at least one surface of the transparent substrate. An optical element, wherein the light diffusing layer according to any one of claims 1 to 3 or the light diffusing sheet according to claim 4 is provided on one side or both sides of the optical element. A display device equipped with the light diffusing sheet according to claim 4 or the optical element according to claim 5.

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