JP4410092B2 - Optical film, backlight system and liquid crystal display device - Google Patents

Description

  The present invention relates to an optical film in which a quarter wavelength plate, a linearly polarized light separating plate, and a linearly polarizing plate are laminated. Such an optical film is suitable as a luminance-enhancing polarizing plate, and is suitably used in a backlight system and a liquid crystal display device.

  Conventionally, in a liquid surface display device, a light source is disposed together with a liquid crystal cell in which linear polarizing plates are disposed on both sides. A linearly polarizing plate has a function of transmitting polarized light having a vibration plane parallel to the transmission axis as it is and absorbing polarized light having a vibration plane parallel to the absorption axis. The transmission axis and the absorption axis are orthogonal to each other. Is. As a light source, for example, a sidelight type backlight having a light guide plate that emits incident light from a side surface from one of upper and lower surfaces is known. A liquid crystal cell is disposed on the light emission surface side (upper side) of the light guide plate via a polarizing plate, and a reflection plate is provided on the lower side of the light guide plate. However, since the linear polarizing plate has a polarization characteristic that transmits only linearly polarized light having a specific vibration surface and absorbs other light, the amount of light that can be incident on the liquid crystal cell and used for display is the light emitted from the light guide plate. Of 45%, and theoretically does not exceed 50%. For this reason, the light use efficiency is poor and the improvement of the luminance of the liquid crystal display device or the like is hindered.

  Therefore, a linearly polarized light separating plate is generally provided between the linearly polarizing plate and the light guide plate as an element that extracts linearly polarized light from natural light. The linearly polarized light separating plate has a function of transmitting polarized light having a vibration surface parallel to the transmission axis while maintaining the vibration surface, and reflecting polarized light having a vibration surface parallel to the reflection axis. The axes are orthogonal to each other. The linearly polarized light separating plate is a birefringent dielectric thin film that separates natural light into reflected light and transmitted light consisting of linearly polarized light by a Brewster angle through a multilayer film in which dielectric thin films are superimposed. It is known that natural light is separated into reflected light and transmitted light composed of linearly polarized light through a multilayer film on which is superimposed.

  By aligning the transmission axis of this linearly polarized light separating plate with the transmission axis of the linearly polarizing plate, the light emitted from the light source is separated into reflected light and transmitted light composed of linearly polarized light by the linearly polarized light separating plate. A polarizing plate is also transmitted and used. On the other hand, the reflected light separated by the linearly polarized light separating plate is returned to the light source and reflected and inverted by the reflecting plate on the lower surface side so that the plane of vibration of the linearly polarized light is converted into linearly polarized light that can be transmitted through the linearly polarized light separating plate. Then, the light again enters the linearly polarized light separating plate and finally passes through the linearly polarizing plate. As a result, the outgoing light in a state where the inverted re-incident light of the reflected light is added to the initial transmitted light is obtained, and the light utilization efficiency is improved.

  However, in a sidelight type backlight, a condensing plate such as a diffuser plate or a prism sheet is usually used on the light guide plate for condensing, so that the linearly polarized light reflected by the linearly polarized light separating plate is The polarization state is disturbed by the diffusion plate and the light collecting plate. As a result, the reflected light from the linearly polarized light separating plate does not reach the reflecting plate in the state of polarization as it is, so that the light use efficiency is not sufficient. For this problem, it has been proposed to provide a quarter-wave plate on the light source side of the linearly polarized light separating plate (Patent Documents 1 and 2). By providing a quarter-wave plate, the linearly polarized light reflected by the linearly polarized light separating plate is made circularly polarized light, so that the surface reflection (polarization inversion) by the diffuser plate and the light collecting plate can be utilized to the maximum extent. The light utilization efficiency can be improved.

On the other hand, apart from the light utilization efficiency, the light transmitted through the linearly polarized light separating plate and the linearly polarizing plate has a problem that the hue becomes slightly yellow. This problem cannot be solved even when a quarter-wave plate is provided as described in the patent document.
Japanese Patent No. 3303278 Japanese Patent No. 3096851

  The present invention is an optical film in which a quarter-wave plate, a linearly polarized light separating plate, and a linearly polarizing plate are laminated in this order, and the light use efficiency is good, and the hue of transmitted light is neutral. It aims at providing the optical film which can be closely approached.

  Another object of the present invention is to provide a backlight system using the optical film, and further to provide a liquid crystal display device.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the following optical film, and have completed the present invention.

That is, the present invention is an optical film in which a quarter-wave plate, a linearly polarized light separating plate, and a linearly polarizing plate are laminated in this order,
The slow axis of the quarter-wave plate intersects the transmission axis of the linearly polarized light separating plate at an angle of 30 to 60 degrees, and the transmission axis of the linearly polarized light separating plate and the transmission axis of the linearly polarizing plate are formed. The angle is in the range of 0 ° ± 10 °,
The quarter-wave plate has an in-plane refractive index maximum direction as an X axis, a direction perpendicular to the X axis as a Y axis, and a film thickness direction as a Z axis, and the refractive index in each axial direction is nx. , Ny, nz, and the film thickness is d (nm),
Front phase difference (Δnd) at a wavelength of 550 nm: (nx−ny) × d is 70 to 95 nm,
And when the front phase differences (Δnd) at wavelengths of 400 nm, 550 nm, and 700 nm are λ (400), λ (550), and λ (700), respectively,
λ (400) / λ (550)> 1.1, λ (700) / λ (550) <1,
It is related with the optical film characterized by satisfying.

  In the optical film of the present invention, a quarter wavelength plate, a linearly polarized light separating plate, and a linearly polarizing plate are laminated in this order. Therefore, the linearly polarized light reflected by the linearly polarized light separating plate is circularly polarized light. Accordingly, surface reflection (polarization inversion) by the diffuser plate or the light collector can be used to the maximum, and the light use efficiency can be improved. Further, by using circularly polarized light, the influence of separation of p-polarized light and s-polarized light due to interface reflection at a deep angle can be reduced, and light utilization efficiency can be improved.

  In the present invention, a quarter wave plate having a front phase difference (Δnd) at a wavelength of 550 nm of 70 to 95 nm is used. The front phase difference (Δnd) has a phase difference value lower than a general quarter-wave plate front phase difference (Δnd): 100 to 180 nm. The quarter wave plate of the present invention has a large chromatic dispersion. As described above, λ (400) / λ (550)> 1.1, λ (700) / λ (550) ) <1 is satisfied. By using such a quarter-wave plate, it is possible to suppress the yellow hue and bring it closer to neutral by improving the utilization efficiency of light in the short wavelength region (blue light).

  The front phase difference (Δnd) of the quarter-wave plate at a wavelength of 550 nm is preferably 70 to 95 nm, more preferably 75 to 95 nm, and even more preferably 80 to 95 nm. The wavelength dispersion is λ (400) / λ (550)> 1.1, further λ (400) / λ (550)> 1.2, and further λ (400) / λ (550)>. 1.3 is preferable. Note that if the value of λ (400) / λ (550) becomes too large, the hue may be blue. Therefore, it is preferable that λ (400) / λ (550) <2. Also, λ (700) / λ (550) <1, further λ (700) / λ (550) <0.95, and further λ (700) / λ (550) <0.9. preferable. Note that if the value of λ (700) / λ (550) becomes too small, the hue may be blue. Therefore, it is preferable that λ (700) / λ (550)> 0.5.

  The 1/4 wavelength plate converts the linearly polarized light reflected by the linearly polarized light separating plate into circularly polarized light, and when it is reflected by the lower reflective plate of the light guide plate and enters the 1/4 wavelength plate again, In this case, it is considered that the vibration plane (polarization direction) of the linearly polarized light is converted into a state in which the linearly polarized light is easily transmitted. From this point, the optical axis of the quarter-wave plate is the polarization axis (polarization transmission axis or polarization reflection axis) of the linear polarization separation plate because the reflected light is converted into a state that allows easy transmission through the linear polarization separation plate. ), That is, it is preferably arranged so as to intersect at an angle of 30 to 60 degrees, further 35 to 55 degrees, particularly 40 to 50 degrees with respect to the polarization direction of the transmitted light or reflected light.

  In the optical film, the quarter-wave plate preferably satisfies an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) satisfying −1 <Nz <1.5. A quarter-wave plate having an Nz coefficient in the above range is preferable in that it prevents coloring of transmitted light. The Nz coefficient is preferably −0.8 <Nz <1.3, more preferably −0.5 <Nz <1.

  The present invention also relates to a backlight system comprising at least a light source arranged on the optical film.

  In the backlight system, the optical film is preferably used in the order of a quarter wavelength plate, a linearly polarized light separating plate, and a linearly polarizing plate from the light source side.

Further, as the backlight system, the light source is a sidelight type backlight having a light guide plate that emits incident light from the side surface from the upper surface,
On the lower side of the light guide plate, there is a reflector,
On the upper side of the light guide plate, a diffusion plate, a light collecting plate, and the optical film are preferably used in this order.

  The present invention also relates to a liquid crystal display device comprising at least a liquid crystal cell disposed on the optical film or the backlight system.

  The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of the optical film (A) of the present invention, in which a quarter-wave plate (1), a linearly polarized light separating plate (2), and a linearly polarizing plate (3) are laminated in this order. .

  FIG. 2 shows the optical axis (slow axis) direction a of the quarter-wave plate (1), the transmission axis direction b of the linearly polarized light separating plate (2), and the transmission axis direction c of the linearly polarizing plate (3). Show the relationship. On the quarter-wave plate (1), the transmission axis direction b of the linearly polarized light separating plate (2) is projected as the transmission axis direction b ′. The angle θ formed by the optical axis direction a and the transmission axis direction b is preferably 30 to 60 degrees as described above. The angle θ is a smaller angle formed by the optical axis direction a and the transmission axis direction b. The angle formed by the transmission axis direction b and the transmission axis c is preferably in the range of 0 ° ± 10 °.

  The quarter-wave plate (1) has a front phase difference (Δnd) at a wavelength of 550 nm, 70 to 95 nm, and as described above, λ (400) / λ (550)> 1.1, λ (700) Those having positive wavelength dispersion satisfying / λ (550) <1 can be used without any characteristic limitation. As the material of the quarter-wave plate (1), a transparent polymer material is preferably used.

  Examples of the polymer material include polycarbonate, polyolefin such as polyethylene and polypropylene, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyvinyl butyral, polymethyl vinyl ether, polyhydroxyethyl acrylate, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, Polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, polyallylsulfone, polyamide, polyimide, polystyrene, polyvinyl chloride, polyvinylidene chloride, cellulosic polymer, polyacrylic, epoxy or binary of these And various ternary copolymers, graft copolymers, and blends. The quarter-wave plate (1) is obtained by a method of stretching a polymer material film.

  The quarter wave plate (1) can be made of a liquid crystal material. A method for producing a quarter-wave plate using a liquid crystal material is, for example, a method of forming a liquid crystal polymer layer by applying a liquid crystal polymer or a liquid crystal monomer on an alignment substrate, curing after alignment, and a liquid crystal formed on a substrate film. For example, a method of transferring the polymer layer to an alignment substrate and aligning the polymer layer can be employed.

  The thickness of the quarter-wave plate (1) is appropriately determined so that the front phase difference (Δnd) is 70 to 95 nm, but is preferably about 1 to 500 μm from the viewpoint of flexibility and thinning. Furthermore, 5-400 micrometers, Furthermore, 10-300 micrometers is preferable.

  Examples of the linearly polarized light separating plate (2) include a grid-type polarizer, two or more multilayer thin film laminates of two or more materials having a difference in refractive index, vapor-deposited multilayer thin films having different refractive indexes used for beam splitters, etc. Two or more birefringent layer multilayer thin film laminates of two or more materials having refraction, two or more resin laminates using two or more resins having birefringence, stretched, orthogonally polarized light Examples include those that are separated by reflection / transmission in the axial direction.

  For example, phase difference expression such as polyethylene naphthalate, polyethylene terephthalate, materials that generate phase difference by stretching such as polycarbonate, acrylic resin typified by polymethyl methacrylate, norbornene resin typified by JSR Arton, etc. A resin obtained by uniaxially stretching a small amount of resin alternately as a multilayer laminate can be used. Specific examples of the linearly polarized light separating plate (2) include DBEF manufactured by 3M. The thickness of the linearly polarized light separating plate (2) is usually about 50 to 200 μm.

  The linearly polarizing plate (3) is usually called a polarizing plate, and a polarizer or one having a protective film on one side or both sides thereof is generally used.

  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 volatile substances and uniaxially stretched, polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer composed of a polyvinyl alcohol film and a dichroic material such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.

  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 such as potassium iodide which may contain boric acid, zinc sulfate, zinc chloride and the like. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing the polyvinyl alcohol film surface and anti-blocking agent by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven dyeing by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, or may be performed while dyeing, or may be performed with dyeing after iodine. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

  As a material for forming the transparent protective film provided on one side or both sides of the polarizer, a material excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like is preferable. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, styrene such as polystyrene and acrylonitrile / styrene copolymer (AS resin) -Based polymer, polycarbonate-based polymer and the like. Polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are also examples of polymers that form the transparent protective film. The transparent protective film can also be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylurethane, epoxy, and silicone.

  Moreover, the polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a substitution in the side chain And / or a resin composition containing a thermoplastic resin having unsubstituted phenyl and a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used.

  Although the thickness of a protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable.

  Moreover, it is preferable that a protective film has as little color as possible. Therefore, Rth = (nx−nz) · d (where nx is the refractive index in the slow axis direction in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a direction retardation value of −90 nm to +75 nm is preferably used. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  As the protective film, a cellulose polymer such as triacetyl cellulose is preferable from the viewpoints of polarization characteristics and durability. A triacetyl cellulose film is particularly preferable. In addition, when providing a protective film in the both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used. The polarizer and the protective film are usually in close contact with each other through an aqueous adhesive or the like. Examples of the water-based adhesive include an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl-based latex, a water-based polyurethane, and a water-based polyester.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, an antisticking treatment, or a treatment for diffusion or antiglare.

  The hard coat treatment is applied for the purpose of preventing scratches on the surface of the polarizing plate. For example, a transparent protective film with a cured film excellent in hardness, sliding properties, etc. by an appropriate ultraviolet curable resin such as acrylic or silicone is used. It can be formed by a method of adding to the surface of the film. The antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  Anti-glare treatment is applied for the purpose of preventing external light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, roughening by sandblasting or embossing. It can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a method or a compounding method of transparent fine particles. Examples of the fine particles to be included in the formation of the surface fine concavo-convex structure include a conductive material made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, or the like having an average particle diameter of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles, organic fine particles composed of a crosslinked or uncrosslinked polymer, etc. may be used. When forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle.

  The antireflection layer, antisticking layer, diffusion layer, antiglare 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.

  As for the lamination of the quarter wave plate (1), the linearly polarized light separating plate (2), and the linearly polarizing plate (3), any of the above-mentioned laminations may be placed on top of each other. From the viewpoint of utilization efficiency, each layer is preferably laminated using an adhesive or a pressure-sensitive adhesive. In that case, the adhesive or pressure-sensitive adhesive is transparent, has no absorption in the visible light region, and the refractive index is desirably as close as possible to the refractive index of each layer from the viewpoint of suppressing surface reflection.

  In each layer and (viscous) adhesive layer, particles are added to adjust the degree of diffusion as necessary to give isotropic scattering, UV absorbers, antioxidants, leveling during film formation A surfactant or the like can be appropriately added for the purpose of imparting property.

  It does not restrict | limit especially as an adhesive agent or an adhesive. For example, acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, natural rubber, synthetic rubber and other rubber-based polymers Can be appropriately selected and used. In particular, those excellent in optical transparency, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties and excellent in weather resistance, heat resistance and the like can be preferably used.

  The adhesive or pressure-sensitive adhesive can contain a crosslinking agent according to the base polymer. Examples of adhesives include natural and synthetic resins, in particular, tackifier resins, glass fibers, glass beads, metal powders, other inorganic powders, fillers, pigments, colorants, and antioxidants. An additive such as an agent may be contained. Further, it may be an adhesive layer containing fine particles and exhibiting light diffusibility.

  The adhesive and the pressure-sensitive adhesive are usually used as an adhesive solution having a solid content concentration of about 10 to 50% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent. As the solvent, an organic solvent such as toluene or ethyl acetate or a solvent such as water can be appropriately selected and used.

  The pressure-sensitive adhesive layer and the adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as an overlapping layer of different compositions or types. 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.

(Backlight system)
A backlight system can be constructed by arranging at least a light source on the optical film (A). The optical film (A) is preferably arranged from the light source side in the order of the quarter wavelength plate (1), the linearly polarized light separating plate (2), and the linearly polarizing plate (3).

  FIG. 3 shows a sidelight type backlight having a light guide plate (C) that emits incident light from the side surface from the upper surface as a light source. The sidelight-type backlight emits transmission light in the light guide plate to the upper surface side of the plate by diffusion, reflection, diffraction, interference, or the like. A light source (L) is provided on the side surface of the light guide plate (C). In FIG. 3, the lower side of the light guide plate (C) has a reflection plate (RF), and the upper side of the light guide plate (C) has a diffusion plate (D), a light collector (P), and an optical film (A). ) In this order. In FIG. 3, two light collecting plates (P) are used, but one light collecting plate (P) may be used.

  As the light guide plate (C), an appropriate one that emits incident light from the side surface from the upper surface can be used. Such a light guide plate is, for example, a transparent or semi-transparent resin plate provided with a diffuser in the form of dots or stripes on the upper surface (light emitting surface) or lower surface, or a concavo-convex structure on the lower surface of the resin plate, particularly from a prism array. And the like provided with a concavo-convex structure. The light guide plate is usually composed of a plate-like object having an upper surface, a lower surface facing the upper surface, and a light incident side surface including at least one side end surface between the upper and lower surfaces. The shape and thickness of the light guide plate are not particularly limited and can be determined as appropriate. The light-scattering light guide can be a wedge-type light guide.

  A light source (L) is disposed on one side of the light guide plate (C). The light source can be arranged on a plurality of side surfaces. The light source can be appropriately selected and used, and examples thereof include a linear light source such as a (cold, hot) cathode tube, a point light source such as a light emitting diode, or an array body such as a linear or planar shape. A cold cathode tube is particularly preferable from the viewpoint of low power consumption and durability.

  It is desirable to dispose a reflector (RF) on the lower side of the light guide plate serving as the light source (the side opposite to the liquid crystal cell arrangement surface). Preferably, a metal reflective layer can be attached. Such a reflective layer is effective in improving the emission efficiency by preventing the generation of leakage light from the lower surface on which the prism-shaped irregularities and the like are formed. It also functions as means for converting the polarization vibration plane of the reflected light by the linearly polarized light separating plate (2) layer.

  The metal reflective layer has a metal surface containing at least one kind of highly reflective metal made of aluminum, silver, gold, copper, chromium, or the like. The metal reflective layer having excellent adhesion to the light guide plate can be formed as a mixed coating layer of metal powder with a binder resin, or an attached layer of a metal thin film by a vapor deposition method or the like. An appropriate coat layer for the purpose of improving reflectivity, preventing oxidation, or the like can be provided on one or both surfaces of the metal reflective layer, if necessary.

  The light source can be provided with a light source holder. As the light source holder, a resin sheet or a metal foil provided with a highly reflective metal thin film is generally used. Further, the reflecting plate can be provided with a reflecting sheet along the lower surface of the light guide plate instead of or together with the reflecting plate.

  It is desirable to install an appropriate diffusion plate (D) between the optical film (A) and the light guide plate (C). The diffusing plate (D) scatters the reflected light beam in the vicinity of the light guide, and increases the light reuse efficiency. The diffusion plate (D) can be obtained by a method of embedding fine particles having different refractive indexes in a resin, in addition to a surface irregularity shape. The diffusion plate (D) may be sandwiched between the optical film (A) and the light guide plate (C), or may be bonded to the optical film (A).

  When the liquid crystal cell on which the optical film (A) is bonded is arranged close to the backlight, there is a risk that Newton's ring may occur in the gap between the film surface and the backlight, but the light guide plate side of the optical film (A) By arranging a diffusion plate having surface irregularities on the surface, generation of Newton rings can be suppressed.

  The light collecting plate (P) is for the purpose of controlling the direction of the emitted light, and appropriately selects a lens sheet that condenses light in the front direction, a prism sheet that converts the optical path of oblique light into the front direction, and the like. Can be used. In FIG. 3, the light collector (P) is provided between the optical film (A) and the light guide plate (D). The light collector (P) can be disposed on the linearly polarized light separating plate (2) or between the light guide plate (C) and the linearly polarized light separating plate (2). The light collector (P) can be arranged in two or more layers, in which case the prism sheet is arranged so that the arrangement direction of the prism array intersects with the upper and lower layers to control the light emission direction on the entire surface, It is also possible to achieve uniform brightness.

(Liquid crystal display device)
In the liquid crystal display device, various optical layers and the like are appropriately used according to a conventional method. Polarizers are arranged on both sides of the liquid crystal cell. The optical film (A) is applied to the light source side of the liquid crystal cell as shown in FIG. FIG. 3 is a cross-sectional view when the optical film (A) of FIG. 1 is applied to a liquid crystal display device. On both sides of the liquid crystal cell (LC), linear polarizing plates (3) are arranged so that their transmission axes are orthogonal.

  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. However, the optical film of the present invention is used. There is no particular limitation except for, and the conventional method can be applied. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  Furthermore, when forming the liquid crystal display device, as described above, appropriate components such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight are appropriately positioned. One layer or two or more layers can be arranged.

(Other materials)
In addition to the above, the optical layer laminated in practical use is not particularly limited. For example, one or more optical layers that may be used for forming a liquid crystal display device such as a reflective plate or a transflective plate are used. Can do. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflecting plate or a semi-transmissive reflecting plate is further laminated on an elliptical polarizing plate or a circular polarizing plate can be given.

  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 attached to one surface of the polarizing plate via a transparent protective layer or the like as necessary.

  Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or vapor-deposited film made of a reflective metal such as aluminum on one surface of a protective film matted as necessary. In addition, the protective film may include fine particles having a surface fine concavo-convex structure and a reflective layer having a fine concavo-convex structure thereon. The reflective layer having the fine concavo-convex structure has an advantage that incident light is diffused by irregular reflection to prevent directivity and glaring appearance and to suppress unevenness in brightness and darkness. Moreover, the protective film containing fine particles also has an advantage that incident light and its reflected light are diffused when passing through it and light and dark unevenness can be further suppressed. The reflective layer with a fine concavo-convex structure reflecting the surface fine concavo-convex structure of the protective film is transparently protected by an appropriate method such as a vapor deposition method such as a vacuum deposition method, an ion plating method, a sputtering method, or a plating method. It can be performed by a method of attaching directly to the surface of the layer.

  The reflective plate can be used as a reflective sheet in which a reflective layer is provided on an appropriate film according to the transparent film, instead of the method of directly imparting to the 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 protective film, a polarizing plate or the like is used to prevent a decrease in reflectance due to oxidation, and thus the long-term sustainability of the initial reflectance. More preferable is the point of avoiding the additional attachment of the protective layer.

  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.

  Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, like 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 transflective polarizing plate and a retardation plate are combined may be used.

  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 elliptical polarizing plate can be formed by sequentially laminating them 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 an elliptically polarizing plate has an advantage that it can improve the production efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.

  As the retardation plate, an appropriate retardation plate is used according to the purpose of use. As the retardation plate, a birefringent film formed by stretching a film made of an appropriate polymer such as polycarbonate, norbornene resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, polyamide, Examples thereof include an alignment film made of a liquid crystal material such as a liquid crystal polymer, and an alignment layer of the liquid crystal material supported by the film. The thickness of the retardation film (4) plate is usually preferably from 0.5 to 200 μm, particularly preferably from 1 to 100 μm.

  A retardation plate is laminated on a polarizing plate as a viewing angle compensation film and used as a wide viewing angle polarizing plate. The viewing angle compensation film is a film for widening the viewing angle so that an 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.

  As such a viewing angle compensation retardation plate, a birefringent film that has been biaxially stretched or stretched in two orthogonal directions, a bidirectionally stretched film such as a tilted orientation film, and the like are used. Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. The viewing angle compensation film can be appropriately combined for the purpose of preventing coloring or the like due to a change in viewing angle based on a phase difference caused by a liquid crystal cell or increasing the viewing angle for good viewing.

  In addition, from the viewpoint of achieving a wide viewing angle with good visibility, an optically compensated phase difference in which an optically anisotropic layer composed of a liquid crystal polymer alignment layer, particularly a discotic liquid crystal polymer gradient alignment layer, is supported by a triacetylcellulose film. A plate can be preferably used.

  In addition, the retardation plate can control two or more types of retardation plates to control optical characteristics such as retardation. (2) A retardation plate that functions as a λ / 4 plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a λ / 4 plate for light-colored light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method in which a phase difference layer, for example, a phase difference layer functioning as a λ / 2 plate is superimposed.

  The optical film (A) of the present invention can be provided with an adhesive layer or an adhesive layer. The pressure-sensitive adhesive layer can be used for adhering to a liquid crystal cell and also used for laminating optical layers. When adhering the optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics. As the adhesive layer or the adhesive layer, those exemplified above can be used.

  For the exposed surface such as 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 a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate ones according to the prior art, such as those coated with an appropriate release agent such as a long mirror alkyl type, fluorine type or molybdenum sulfide, can be used.

  In the present invention, each layer such as the optical element and the adhesive layer is made of an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. What gave the ultraviolet absorptivity by systems, such as a processing system, may be used.

  Hereinafter, the present invention will be specifically described with reference to examples.

  The front phase difference is defined by the refractive index nx and ny at 550 nm where the direction in which the in-plane refractive index is maximum is the X axis, the direction perpendicular to the X axis is the Y axis, and the refractive indexes in the respective axial directions are nx and ny. The front phase difference (Δnd): (nx−ny) × d is calculated from the value measured by the automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments, automatic birefringence meter KOBRA21ADH) and the thickness d (nm). did. From these, the Nz coefficient was calculated. Further, front phase differences (Δnd) at wavelengths of 400 nm, 550 nm, and 700 nm were measured, and λ (400) / λ (550) and λ (700) / λ (550) were calculated.

Example 1
(¼ wavelength plate)
A stretched polycarbonate film (thickness 30 μm) was used. The front phase difference (Δnd) was 90 nm, the wavelength dispersion was λ (400) / λ (550) = 1.14, λ (700) / λ (550) = 0.95, and the Nz coefficient was 1.

(Linear polarization separator)
DBEF manufactured by 3M was used.

(Linear polarizing plate)
A linear polarizing plate (TEG1465DU) manufactured by Nitto Denko Corporation was used.

(Optical film)
The angle formed by the optical axis (slow axis) of the quarter wavelength plate and the polarization axis (transmission axis) of the linear polarization separator is 45 degrees between the quarter wavelength plate and the linear polarization separator. It bonded together through the acrylic adhesive (Nitto Denko Co., Ltd. make, thickness 20 micrometers). Next, it is bonded via an acrylic pressure-sensitive adhesive (manufactured by Nitto Denko Corporation, thickness 20 μm) so that the polarization axis (transmission axis) of the linearly polarized light separating plate and the polarization axis (transmission axis) of the linear polarizing plate are in the same direction. The optical film of the present invention was obtained. The optical film was bonded to the glass plate with an acrylic pressure-sensitive adhesive (manufactured by Nitto Denko Corporation, thickness 20 μm) on the side of the linear polarizing plate. This was used as a sample. The configuration of the sample is a quarter wavelength plate, a linearly polarized light separating plate, a linearly polarizing plate, and a glass plate.

Example 2
(¼ wavelength plate)
The 1/4 wavelength plate used in Example 1 and the 1/1 wavelength plate are aligned and bonded via an acrylic adhesive (manufactured by Nitto Denko Corporation, thickness 20 μm). It was. The 1/1 wave plate is a stretched polycarbonate film (thickness 30 μm), the front phase difference (Δnd) is 590 nm, and the wavelength dispersion is λ (400) / λ (550) = 1.14, λ ( 700) / λ (550) = 0.95. The quarter-wave plate obtained by the pasting has a front phase difference (Δnd) of 90 nm, λ (400) / λ (550) = 1.42, λ (700) / λ (550) = 0.85. , Nz coefficient was 0.9.

(Optical film)
In Example 1, a sample was prepared in the same manner as in Example 1 except that the quarter wavelength plate obtained by bonding was used as the quarter wavelength plate.

Comparative Example 1
In Example 1, a sample was prepared in the same manner as in Example 1 except that the quarter wavelength plate was not used.

Comparative Example 2
In Example 1, a sample was prepared in the same manner as in Example 1 except that a stretched norbornene film (thickness: 30 μm) was used as the ¼ wavelength plate. A ZEONOR film manufactured by Nippon Zeon Co., Ltd. was used as the norbornene film. The front phase difference (Δnd) is 100 nm, and the wavelength dispersion is λ (400) / λ (550) = 1.00 and λ (700) / λ (550) = 1.01.

Comparative Example 3
In Example 1, a sample was prepared in the same manner as in Example 1 except that a stretched polycarbonate film (thickness 30 μm) having a front phase difference (Δnd) of 140 nm was used as the quarter-wave plate. .

Comparative Example 4
In Example 1, a sample was prepared in the same manner as in Example 1 except that a stretched polycarbonate film (thickness: 30 μm) having a front phase difference (Δnd) of 60 nm was used as the quarter-wave plate. .

Comparative Example 5
In Example 1, a sample was prepared in the same manner as in Example 1 except that the angle formed by the optical axis (slow axis) of the quarter-wave plate and the polarization axis (transmission axis) of the linearly polarized light separating plate was set to 65 degrees. It was created.

(Evaluation)
The samples obtained in Examples and Comparative Examples were placed on the following backlights, and the luminance enhancement rate and front hue were measured with a viewing angle measurement apparatus ELDIM manufactured by Ez-CONTRAST. The results are shown in Table 1. The luminance improvement rate (%) is a value indicating the luminance improvement rate with respect to 100% as the luminance when a sample in which only a linear polarizing plate is bonded to a glass plate is arranged. As the backlight, a sidelight type backlight system used in a general notebook personal computer (IBM Corporation, Think Pad) of reflector / light guide plate / diffusion plate / light collecting plate / light collecting plate was used.

表１から、実施例では、輝度向上率が高く、また色相もニュートラルになっていることが分かる。

From Table 1, it can be seen that in the examples, the luminance improvement rate is high and the hue is also neutral.

  Moreover, about Example 1 and the comparative example 1, the transmittance | permeability was measured by Ez-CONTRAST. The results are shown in FIG. The horizontal axis in FIG. 4 indicates the angle tilted from the front, and the vertical axis indicates the transmittance at that time. It can be seen that Example 1 shows higher luminance (transmittance). Moreover, the transmittance | permeability data for every direction of an evaluation sample are shown. It can be seen that the transmittance is stable from a deep angle in Example 1 and the light efficiency is improved at any angle.

It is an example of sectional drawing of the optical film (A) of this invention. It is an example of the conceptual diagram which shows each optical axis of the optical film (A) of this invention. It is an example of sectional drawing of the liquid crystal display device of this invention. 5 is a graph showing the transmittance of Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1/4 wavelength plate 2 Linearly polarized light separating plate 3 Linearly polarizing plate A Optical film C Light guide plate D Diffuser plate RF Reflector plate P Light collector LC Liquid crystal cell L Light source

Claims (6)

A quarter-wave plate, a linearly polarized light separating plate, and a linearly polarizing plate are optical films laminated in this order,
The slow axis of the quarter-wave plate intersects the transmission axis of the linearly polarized light separating plate at an angle of 30 to 60 degrees, and the transmission axis of the linearly polarized light separating plate and the transmission axis of the linearly polarizing plate are formed. The angle is in the range of 0 ° ± 10 °,
The quarter-wave plate has an in-plane refractive index maximum direction as an X axis, a direction perpendicular to the X axis as a Y axis, and a film thickness direction as a Z axis, and the refractive index in each axial direction is nx. , Ny, nz, and the film thickness is d (nm),
Front phase difference (Δnd) at a wavelength of 550 nm: (nx−ny) × d is 70 to 95 nm,
And when the front phase differences (Δnd) at wavelengths of 400 nm, 550 nm, and 700 nm are λ (400), λ (550), and λ (700), respectively,
λ (400) / λ (550)> 1.1, λ (700) / λ (550) <1,
An optical film characterized by satisfying The 1/4 wavelength plate has an Nz coefficient represented by Nz = (nx−nz) / (nx−ny),
The optical film according to claim 1 , wherein −1 <Nz <1.5 is satisfied. A backlight system comprising at least a light source disposed on the optical film according to claim 1 . The optical film according to claim 1 or 2, the light source side, 1/4-wavelength plate, linearly polarized separated plate, backlight system according to claim 3, characterized in that it is arranged in order of linear polarizing plate . The light source is a sidelight type backlight having a light guide plate that emits incident light from the side surface from the upper surface,
On the lower side of the light guide plate, there is a reflector,
The backlight system according to claim 3 or 4 , further comprising a diffusion plate, a light collecting plate, and the optical film according to claim 1 or 2 in this order on an upper side of the light guide plate. A liquid crystal display device comprising at least a liquid crystal cell in the optical film according to claim 1 or 2 or the backlight system according to any one of claims 3 to 5 .

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