JP4658383B2 - Manufacturing method of optical film, laminated polarizing plate using the same, and liquid crystal display device - Google Patents

Description

【００４７】
表１より、実施例１では、法線面を基準とした左右の斜め透過光の位相差の差が大きく、非対称性に優れると共に、面内での位相差のバラツキが小さく、品質も良好であった。これに対し、比較例１では、左右の斜め透過光の位相差に差がなくて通常の一軸延伸物の特性を示し、比較例２では、左右の斜め透過光の位相差の差が小さい上に、面内での位相差のバラツキが大きく、ロールとの接触による傷付きがあることがわかる。
【００４８】
【発明の効果】
以上説明したとおり、本発明の非対称な傾斜型位相差フィルムにより、その作用機構は不明であるが、液晶セルの複屈折に基づく視角による視認性の変化を広範囲の方位にわたり高度に補償でき、コントラストや白黒表示等の視認性に優れる液晶表示装置を得ることができる。また品質に優れる大面積の光学フィルムも容易に安定して形成することができる。よって、その工業的価値は大である。
【図面の簡単な説明】
【図１】本発明の光学フィルム（傾斜型位相差フィルム）の断面図である。
【図２】積層偏光板の構成例を示す断面図である。
【図３】本発明の製造方法を示す模式図である。
【符号の説明】
１ 光学フィルム（傾斜型位相差フィルム）
２ 接着（粘着）層
３ 偏光板
１１ 法線
１２ 斜め透過光
１３ 斜め透過光[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical film suitable for improving the display contrast of a liquid crystal cell, the viewing angle characteristics of a display color, and the like, in particular, a method for producing a tilted retardation film, a laminated polarizing plate using the same, and a liquid crystal display device.
[0002]
[Prior art]
TFT (Thin Film Transistor) type and MIM (Metal Insulator Metal) type liquid crystal display devices using twisted nematic (TN) type and super twisted nematic (STN) type liquid crystal cells, response speed, display contrast, etc. Although it is widely used as a display means for various devices such as OA equipment such as word processors and personal computers, the viewing angle (viewing angle), in particular, the decrease in contrast at an oblique viewing angle and the coloring of the screen As a result, there is a great demand for improvement in viewing angle characteristics. Conventionally, as a method for improving the viewing angle characteristics, a method of arranging a phase difference plate is known (Japanese Patent Laid-Open Nos. 4-229828 and 4-258923).
[0003]
[Problems to be solved by the invention]
However, when the retardation plate is used, it is difficult to improve the viewing angle characteristics in all directions, and there is a problem that the effect of improving the viewing angle characteristics in a specific direction is poor.
[0004]
On the other hand, there has also been proposed a method of arranging a retardation plate in which the main refractive index direction of the refractive index ellipsoid is inclined with respect to the normal direction so as to cope with the tilt of liquid crystal molecules (Japanese Patent Laid-Open No. 6-75116). Issue). However, there is a problem that it is difficult to form the retardation plate. There has also been proposed a method of arranging retardation plates having different three refractive indexes in the main axis direction obtained by obliquely cutting an extruded rod along the central axis (Japanese Patent Laid-Open No. 6-174920). However, there is a problem that it is difficult to obtain a liquid crystal display device having a necessary area.
[0005]
Furthermore, there is also proposed a method of arranging a retardation plate whose optical axis is inclined with respect to the normal direction, which is formed by stretching with a shearing force through rolls having different peripheral speeds (Japanese Patent Laid-Open No. 6-222213). ). However, since the shearing force and stretching orientation temperature that can be imparted are poor, the tilt angle of the optical axis is small, and the variation in the angle is large, so the effect of improving the viewing angle characteristics is poor, and contact scratches with the roll are likely to occur on the surface. There was a problem of lowering the display quality.
[0006]
In order to solve the above-mentioned conventional problems, the present invention can prevent deterioration of visibility in a liquid crystal display device due to a change in viewing angle in a wide range of directions, and manufacture an optical film capable of easily and stably forming a large-area product having excellent quality. It is an object to provide a method, a polarizing plate using the same, and a liquid crystal display device excellent in visibility such as contrast and black-and-white display in a wide viewing angle range.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an optical film manufacturing method of the present invention comprises a light-transmitting birefringent film, and optical films having different retardation values in obliquely transmitted light on the right and left sides with respect to the normal plane. A manufacturing method is characterized in that after the translucent resin is extruded into a film by a melt extrusion method, the film is cooled and cured by passing between two rolls having different surface hardnesses. In the method for producing an optical film of the present invention, it is preferable that a flat belt is attached to the roll.
[0008]
The method for producing an optical film of the present invention is characterized in that the optical film produced by the above method is further subjected to at least one treatment selected from a longitudinal uniaxial stretching treatment, a transverse uniaxial stretching treatment, and a thickness direction orientation treatment. And
[0009]
Next, the laminated polarizing plate of the present invention is characterized in that at least one optical film selected from the optical films produced by the above method and a polarizing plate are laminated via a pressure-sensitive adhesive. Thereby, a wide viewing angle polarizing plate is obtained.
[0010]
Furthermore, the liquid crystal display device of the present invention is characterized in that at least one optical film selected from the optical films produced by the above method is disposed on at least one side of the liquid crystal display cell.
[0011]
The liquid crystal display device of the present invention is characterized in that the laminated polarizing plate is disposed on at least one side of a liquid crystal display cell.
[0012]
Further, the liquid crystal display device of the present invention comprises at least one optical film (A) selected from the optical films produced by the above method and / or the laminated polarizing plate (B), and an in-plane refractive index of nx. , Ny (nx> ny) and the thickness direction refractive index is nz, at least one retardation plate (C) selected from retardation plates satisfying any of the following formulas (1) to (8): ).
nx> ny = nz (1)
nx = nz> ny (2)
nx = ny> nz (3)
nx = ny <nz (4)
nx>ny> nz (5)
nx>nz> ny (6)
nz>nx> ny (7)
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the production method according to the present invention, a translucent resin is extruded into a film by a melt extrusion method, and then the extruded film is passed between two rolls having different surface hardnesses to be cooled and cured to form an optical film (translucent film). Optical birefringent film), whereby an optical film excellent in display contrast of liquid crystal cells and viewing angle characteristics of display colors can be obtained. The manufactured optical film becomes a tilted phase difference film having characteristics in which the phase difference values in the oblique transmission light of the left and right objects with respect to the normal plane are different from each other.
[0014]
FIG. 1 is a diagram showing an example of the optical film of the present invention. As shown in FIG. 1, the optical film 1 of the present invention has the normal surface at an inclination angle (θ) of 40 degrees with respect to the normal surface 11 on one or both of the slow axis and the fast axis. The difference in phase difference due to birefringence in the left and right oblique transmitted lights 12, 13 is substantially different.
[0015]
As a method for producing an optical film, a translucent resin is extruded by, for example, a melt extrusion method such as a T-die method or an inflation method, and then the extruded film is placed under the two rolls having different surface hardness. What is necessary is just to cool and harden through. The cooling method is not particularly limited, and for example, it can be performed by pressurizing and cooling so as to be sandwiched between 200 mm diameter silicone rubber-coated rolls and 200 mm diameter metal roll caps.
[0016]
According to the manufacturing method of the present invention, the phase difference values based on the inclination angle with respect to the normal plane, that is, the phase difference values due to birefringence in the oblique transmitted light on the left and right of the normal plane are different from each other (asymmetric). The reason why the mold retardation film can be produced is as follows. As described in the prior art, a method of obtaining a retardation plate having an optical axis inclined with respect to the normal direction by stretching with shearing force through rolls having different peripheral speeds (Japanese Patent Laid-Open No. 6-222213). In this case, it is difficult to manage the peripheral speed, and it is difficult to maintain accuracy. However, in the present invention, in order to make up for such a defect, since the extruded film is sandwiched between rolls having different surface hardness, asymmetric deformation of the surface due to the difference in elastic modulus of the roll occurs, and the roll is rotated at a constant speed. Even so, it is considered that a shearing force is generated in the film at the roll contact portion.
[0017]
Further, in order to increase the adhesion force and increase the shearing force, a method of sandwiching a flat belt between rolls and sandwiching an extruded film therebetween may be used. The flat belt is not particularly limited as long as it is designed so that the deformation caused by the difference in the hardness of the roll is transmitted to the extruded film via the flat belt. The thickness, material, etc. of the belt are not particularly limited, and metal is preferable from the viewpoint of surface properties and thermal conductivity.
[0018]
The roll is not particularly limited as long as the surface hardness of the two rolls is different. For example, as described above, a combination of rolls having different surface materials, such as a combination of a roll coated with silicone rubber and a metal roll, can be used. Further, when a flat belt is mounted, it may be designed such that shear forces generated when a belt having different hardness is mounted on a roll of the same material and the roll is rotated at a constant speed are different from each other. The surface temperature of the roll, the diameter of the roll, the number of rotations of the roll, etc. are not particularly limited, and are appropriately set within a range in which the object of the present invention can be achieved.
[0019]
As described above, speed management is also facilitated by applying a shearing force between rolls having different surface hardness. Moreover, it becomes easy to control the magnitude of the shearing force by using a low-viscosity film immediately after melt extrusion or by applying a flat belt.
[0020]
The light-transmitting resin material used for forming the optical film of the present invention is not particularly limited, and an appropriate light-transmitting film material can be used, and a uniform film can be easily obtained during melt extrusion film formation. A resin material having a low melt viscosity is preferred. The light transmittance of the film is 70% or more, preferably 80% or more, particularly preferably 85% or more, and a light-transmitting film excellent in light transmittance is preferable. Among them, polycarbonate, polyarylate, polyethylene terephthalate, polyethersulfone, polyvinyl alcohol, polyolefins such as polyethylene or polypropylene, cellulose polymers, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyamide, polynorbornene, etc. A light film is preferably used.
[0021]
Moreover, in order to form the inclination type | mold phase difference film like this invention, the resin material extruded with moderate viscosity by the melt extrusion method etc. is preferable. Furthermore, it is preferably a film material that can be oriented by a stretching process or the like so that a uniaxially stretched film or a biaxially stretched film by a free end or a fixed end, a film orientated in the thickness direction, and the like can be easily formed. .
[0022]
In the present invention, the optical film after applying the shear stress described above may be subjected to a stretching process by an appropriate method such as a uniaxial stretching process or a biaxial stretching process to obtain an optical film (an inclined retardation film). it can.
[0023]
The thickness of the translucent film can be appropriately determined depending on the retardation characteristics of the target optical film. The phase difference can be obtained as the product (Δn × d) of the refractive index difference (Δn) of birefringence and the film thickness (d). Moreover, the general thickness of a translucent film thru | or an optical film is 5-500 micrometers, Preferably it is 10-350 micrometers, Most preferably, it is 20-200 micrometers.
[0024]
In the optical film of the present invention, due to birefringence in the obliquely transmitted light on the left and right of the normal line based on an inclination angle of 40 degrees with respect to the normal line on one or both of the slow axis and the fast axis. The difference in phase difference is preferably 10 nm or more from the viewpoint of the improvement of viewing angle characteristics. When the difference in phase difference is less than 10 nm, the effect of improving the viewing angle characteristics, particularly the effect of expanding the improvement azimuth, is poor. In addition, the difference between the maximum value and the minimum value of the phase difference of transmitted light (in the front direction) perpendicular to the film surface (in the front direction) is 10 nm or less, preferably 7 nm or less, from the viewpoint of preventing the occurrence of display unevenness and preventing the decrease in contrast The thing of 5 nm or less is especially preferable.
[0025]
The optical film of the present invention is preferably used for compensation of viewing angle characteristics due to birefringence of a liquid crystal cell as a single-layered product or the same type or different types of laminates. In practical use, a laminate with a polarizing plate, a laminate with a retardation plate, a laminate with a protective layer made of an isotropic transparent resin layer, a glass layer, or the like can be used in an appropriate form. . A laminate with a polarizing plate or the like can also be formed by sequentially laminating an optical film, a polarizing plate, etc. sequentially in the manufacturing process of the liquid crystal display device, but by previously laminating as described above, quality stability and There are advantages such as excellent laminating workability and the like, which can improve the manufacturing efficiency of the liquid crystal display device. In addition, suitable adhesion | attachment means, such as an adhesion layer, can be used for lamination | stacking.
[0026]
FIG. 2 illustrates a laminated polarizing plate (B) formed by bonding and laminating an optical film (tilted retardation film) 1 and a polarizing plate 3 with a pressure-sensitive adhesive 2 interposed therebetween. Here, as the polarizing plate, for example, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer partially saponified film, iodine and / or a dichroic dye. And a polarizing film composed of a polyene oriented film such as a dehydrated processed product of polyvinyl alcohol or a dehydrochlorinated processed product of polyvinyl chloride. The polarizing plate may have a transparent protective layer on one side or both sides of the polarizing film. For the lamination of the optical film and the polarizing plate, an appropriate bonding means such as a pressure-sensitive adhesive or an adhesive can be used. For example, a pressure-sensitive adhesive (pressure-sensitive adhesive) may be used.
[0027]
The polarizing plate may be a reflective type having a reflective layer. The reflective polarizing plate is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side) and displays a liquid crystal display that can omit the incorporation of a light source such as a backlight. It has an advantage that the display device can be easily thinned.
[0028]
The transparent protective layer may be suitably formed as a plastic coating layer or a laminate of a protective film, and is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, etc. Plastic or the like is preferably used. Examples include polyester resins, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, or acrylic, urethane, and acrylic urethane types. , Epoxy-type, silicone-type, etc. thermosetting or ultraviolet curable resins. The surface of the transparent protective layer may be formed in a fine concavo-convex structure by containing fine particles.
[0029]
Further, examples of the retardation plate (C) that may be laminated with the optical film or polarizing plate include polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, and polyamide. And a birefringent film formed by stretching a film made of an appropriate plastic. Further, it may be a birefringent film coated with a thin layer of a liquid crystal compound.
[0030]
The properties of the retardation plate are not particularly limited, and examples thereof include a uniaxially stretched film and a film oriented in the thickness direction. Retardation plates satisfying any of the above formulas (1) to (7) when the film in-plane refractive index is nx, ny (nx> ny), and the thickness direction refractive index is nz, alone or in combination Can be used. When the refractive index in the slow axis direction is nx, that in the fast axis direction is ny, and that in the thickness direction is nz, for example, a biaxially stretched film exhibiting characteristics such as nx>ny> nz, nx Appropriate retardation characteristics such as a uniaxially stretched optical ellipsoid showing characteristics such as = ny> nz and nx = ny <nz may be used.
[0031]
In the above, the adhesive (adhesive) used for laminating the optical film and the polarizing plate is not particularly limited. For example, acrylic, silicone, polyester, polyurethane, polyether, rubber, etc. An appropriate adhesive such as a transparent pressure-sensitive adhesive can be used. From the viewpoint of preventing changes in optical properties of optical films and the like, those that do not require a high-temperature process during curing and drying are preferable, and those that do not require a long curing process or drying time are desirable. Further, those which do not cause peeling or the like under heating or humidification conditions are preferably used.
[0032]
From this point, the weight average molecular weight obtained by polymerizing monomers such as butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic acid, and the like, glass transition An acrylic pressure-sensitive adhesive made of an acrylic polymer having a temperature of 0 ° C. or lower is particularly preferably used. An acrylic pressure-sensitive adhesive is also preferable from the viewpoint of excellent transparency, weather resistance, heat resistance, and the like. In addition, when laminating | stacking what has a different refractive index, the adhesive agent etc. which have a medium refractive index are used preferably from points, such as suppression of reflection loss.
[0033]
Adhesives include, for example, natural and synthetic resins, glass fibers and glass beads, fillers made of metal powder and other inorganic powders, pigments, colorants, antioxidants, etc. Appropriate additives can also be blended. Moreover, it can also be set as the adhesive layer which contains microparticles | fine-particles and shows light diffusibility.
[0034]
The above-described optical film, polarizing plate, and the like can be provided with an adhesive layer for bonding with other members such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed of an appropriate pressure-sensitive adhesive according to the conventional type such as acrylic. When the pressure-sensitive adhesive layer provided on the polarizing plate or the optical film is exposed on the surface, it is preferable to temporarily cover with a separator for the purpose of preventing contamination until the pressure-sensitive adhesive layer is put to practical use. The separator is formed by, for example, a method in which a release coat with an appropriate release agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide is provided on an appropriate thin leaf according to the above-described transparent protective film or the like. be able to.
[0035]
In addition, each layer such as the optical film, polarizing plate, retardation plate, transparent protective layer, and adhesive layer described above may be, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex salt compound. Ultraviolet absorbing ability can be provided by a method of treating with an ultraviolet absorber such as a compound.
[0036]
The liquid crystal display device using the optical film of the present invention can be formed according to a conventional method. That is, the liquid crystal display device is generally formed by assembling a liquid crystal cell, an optical film for optical compensation, and components such as a polarizing plate and an illumination system as needed, and incorporating a drive circuit. In the liquid crystal display device of the present invention, there is no particular limitation, except that the optical film of the present invention is used for optical compensation and is provided on at least one side of the liquid crystal cell, and it conforms to the conventional case.
[0037]
Therefore, an appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflecting plate used in an illumination system can be formed. In the case of a liquid crystal display device using a polarizing plate, the optical film for optical compensation is preferably disposed between the liquid crystal cell and the polarizing plate, particularly the polarizing plate on the viewing side, from the viewpoint of the compensation effect. In the arrangement, the laminated polarizing plate described above can also be used.
[0038]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0039]
Example 1
A transparent polycarbonate film having a thickness of 150 μm extruded from a T die by a melt extrusion method was cooled between metal endless belts each held by a metal roll having a diameter of 300 mm and a silicon roll to obtain an optical film. The outline is shown in FIG.
[0040]
(Comparative Example 1)
A transparent polycarbonate film having a thickness of 100 μm was passed between rolls having different peripheral speeds in an atmosphere of 160 ° C., and stretched 1.15 times to obtain an optical film.
[0041]
(Comparative Example 2)
A transparent polycarbonate film having a thickness of 100 μm was supplied between rolls having a drive system and sheared. One of the rolls had a surface temperature of 150 ° C. and a peripheral speed of 2.8 m / min, and the other had a surface temperature of 150 ° C. and a peripheral speed of 1.9 m / min.
[0042]
The following characteristics were examined for the optical films obtained in Examples and Comparative Examples. The results are shown in Table 1.
[0043]
(Phase difference)
Using an ADR-100XY made by Oak Co., the phase difference when tilted by ± 40 degrees in the front direction and slow axis direction was examined.
[0044]
(Phase difference variation)
The phase difference in the front direction within a 100 mm square was measured at 10 points at intervals of 10 mm, and the difference between the maximum value and the minimum value was obtained.
[0045]
(Scratches)
The appearance of the optical film was visually observed to check for scratches.
[0046]
[Table 1]

[0047]
From Table 1, in Example 1, the difference in the phase difference between the left and right oblique transmitted light with respect to the normal plane is large, the asymmetry is excellent, the variation in the phase difference in the plane is small, and the quality is also good. there were. In contrast, Comparative Example 1 shows the characteristics of a normal uniaxially stretched product with no difference in the phase difference between left and right oblique transmitted light, and Comparative Example 2 shows a small difference in phase difference between left and right oblique transmitted light. In addition, it can be seen that there is a large variation in the in-plane retardation, and there is a scratch due to contact with the roll.
[0048]
【The invention's effect】
As described above, the mechanism of operation of the asymmetric tilt-type retardation film of the present invention is unknown, but the change in visibility due to the viewing angle based on the birefringence of the liquid crystal cell can be highly compensated over a wide range of directions, and the contrast And a liquid crystal display device excellent in visibility such as monochrome display can be obtained. In addition, a large-area optical film having excellent quality can be easily and stably formed. Therefore, its industrial value is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an optical film (tilted retardation film) of the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration example of a laminated polarizing plate.
FIG. 3 is a schematic view showing the production method of the present invention.
[Explanation of symbols]
1 Optical film (tilt-type retardation film)
2 Adhesive (adhesive) layer 3 Polarizing plate 11 Normal 12 Obliquely transmitted light 13 Obliquely transmitted light

Claims (4)

It is made of a light-transmitting birefringent film and has a tilt angle of 40 degrees with respect to the normal plane on one or both of the slow axis and the fast axis, and the position in the obliquely transmitted light on the left and right of the normal plane. A method for producing a tilted retardation film having a phase difference of 10 nm or more, wherein a translucent resin (except for the case where the translucent resin is polysulfone) is extruded into a film by a melt extrusion method. Then, the film is passed between the flat belt and the flat belt (however, the flat belt is mounted on a plurality of rotating rolls, and the roll of one flat belt and the roll of the other flat belt are the surface hardness is different), the manufacturing method of the inclined retardation film for causing chill. The inclined retardation film produced by the method of claim 1, further longitudinal uniaxial stretching process, transverse uniaxial stretching process, the inclined phase, characterized in that performing at least one treatment selected from a thickness direction alignment treatment A method for producing a film . The method for producing an inclined retardation film according to claim 1 or 2 , wherein the two rolls having different surface hardness are a roll coated with silicone rubber and a metal roll. The translucent resin is made of polycarbonate, polyarylate, polyethylene terephthalate, polyethersulfone, polyvinyl alcohol, polyethylene or polypropylene, cellulosic polymer, polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyamide and polynorbornene. It is 1 or more selected from a group, The manufacturing method of the inclination type retardation film in any one of Claims 1-3 .

Images