JP2005156863A - Optical film for display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film that can be manufactured through a simple drawing operation, that has the capability of compensating various visual angle characteristics of liquid crystal displays such as VA, IPS, TN, STN, and OCB modes as well as being utilized as an antireflection coating, and that fulfills the relation of three-dimensional refractive indexes of nx>nz>ny. <P>SOLUTION: The retardation film comprises fine particles having at least one or more kinds of optical anisotropies and a transparent polymer, and fulfills the relation of nx>nz>ny, where nx, nz and ny are refractive indexes in the slow axis direction in the film surface, in the direction vertical to the slow axis, and in the thickness direction of the film, respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention comprises at least one kind of fine particles having optical anisotropy and a transparent polymer, the refractive index in the slow axis direction in the film plane is nx, the refractive index in the direction perpendicular thereto is ny, and the thickness of the film When the refractive index in the direction is nz, a retardation film that satisfies the relationship of nx> nz> ny and a display element comprising the same, and a retardation film that can be manufactured by a simple manufacturing process without requiring a special stretching method, and It is related with the display element which becomes.

  Liquid crystal displays are widely used as the most important display devices in the multimedia society, from mobile phones to computer monitors, notebook computers, and televisions. Many optical films are used for liquid crystal displays in order to improve display characteristics.

  In particular, the retardation film plays a major role in color tone compensation and viewing angle compensation. As the conventional retardation film, polycarbonate, cyclic polyolefin, and maleimide copolymer are used. These polymers are all polymers having positive birefringence.

  Here, the sign of birefringence is defined as shown below.

  The optical anisotropy of the polymer film molecularly oriented by stretching or the like can be represented by a refractive index ellipsoid shown in FIG. Here, the slow axis direction (stretching direction) in the film plane is the x-axis, the direction perpendicular thereto is the y-axis, the film thickness direction is the z-axis, and the respective refractive indexes are nx, ny, and nz.

  For example, the three-dimensional refractive index of polycarbonate is relatively large in the stretching direction and relatively small in the direction perpendicular to the stretching direction. Thus, the case where the refractive index in the stretching direction is relatively large is positive, and the case where the refractive index is small on the contrary is negative.

  Generally, when a polymer having positive birefringence is uniaxially stretched, the three-dimensional refractive index is nx> ny = nz, and in biaxial stretching, nx ≧ ny> nz. Here, in the case of uniaxial stretching, nx is the refractive index in the stretching direction (x direction: slow axis), ny is the refractive index in the direction perpendicular to the stretching direction (y direction), and nz is in the film thickness direction (z direction). Refractive index. In biaxial stretching, in the case of unbalanced biaxial stretching where the stretching ratio is x axis> y axis, the relationship of the three-dimensional refractive index is nx> ny> nz, and the stretching ratio is biaxial stretching where x axis = y axis. In this case, the three-dimensional refractive index is nx = ny> nz.

  On the other hand, in the uniaxial stretching of the polymer having negative birefringence, the three-dimensional refractive index is nz = ny> nx, and in the biaxial stretching, nz> ny ≧ nx. Here, in the case of uniaxial stretching, nx is the refractive index in the stretching direction (x direction), ny is the refractive index in the direction perpendicular to the stretching direction (y direction), and nz is the refractive index in the film thickness direction (z direction). . In biaxial stretching, in the case of unbalanced biaxial stretching where the stretching ratio is x-axis> y-axis, the relationship of the three-dimensional refractive index is nz> ny> nx, and the stretching ratio is x-axis = biaxial stretching where y-axis. The relationship of the three-dimensional refractive index is nz> ny = nx.

  As described above, the relationship between the positive and negative birefringence of the polymer and the three-dimensional refractive index can be controlled to some extent by the stretching method. However, with a general stretching method, it is not possible to obtain a film in which the refractive index in the z-axis direction is intermediate such that the relationship of the three-dimensional refractive index is nx> nz> ny.

  And it has been proposed that such a retardation film having a three-dimensional refractive index relationship of nx> nz> ny has a characteristic that the retardation is constant regardless of the viewing angle (for example, Patent Document 1). 2). Moreover, it is proposed that it is effective for the viewing angle compensation of a polarizing film (for example, refer nonpatent literature 1).

  However, as described above, in a normal stretching method such as uniaxial stretching or biaxial stretching, a retardation film having nx> nz> ny as a three-dimensional refractive index relationship cannot be obtained. A treatment method has been proposed in which a heat-shrinkable film is bonded to the laminate, and the laminate is heated and stretched to apply a shrinkage force in a direction (z-axis direction) perpendicular to the stretching direction of the polymer film (for example, Patent Document 3). , 4, 5). In this method, when the heat-shrinkable film shrinks, the components in the x-axis direction and the y-axis direction of the polymer chain are reduced, and the component in the z-axis direction is increased accordingly, so that nz is larger than ny. At the same time, nx is increased by stretching in the x-axis direction. In addition, a method of uniaxial stretching in a plane while applying an electric field to a polymer film has been proposed (see, for example, Patent Document 6). In this method, by applying an electric field, nz can be increased by increasing a component parallel to the electric field of the polymer chain.

  Further, optical materials such as optical films and optical adhesives using optically anisotropic fine particles have been proposed (see, for example, Patent Document 7 and Non-Patent Document 2).

Japanese Patent Laid-Open No. 02-160204

JP 2001-091743 A Jpn. J. et al. Appl. Phys. Vol. 41, p4553 (2002) Japanese Patent No. 2818983 JP 05-297223 A JP 05-323120 A Japanese Patent Laid-Open No. 06-088909 JP-A-11-293116 Polymer Society Annual Report, 2003, Vol. 52, no. 4, 748 pages

  However, the methods proposed in Patent Documents 3 to 6 have many problems such as requiring a very complicated manufacturing process. Further, those proposed in Patent Document 7 and Non-Patent Document 2 are substantially related to a zero birefringence (non-birefringence) material, and are actively used for retardation represented by retardation films. Etc. are not mentioned.

  Therefore, in the present invention, when the refractive index in the slow axis direction in the film plane is nx, the refractive index in the direction perpendicular thereto is ny, and the refractive index in the thickness direction of the film is nz, the relationship of nx> nz> ny is established. It is an object of the present invention to provide a retardation film that satisfies the requirements, a display element comprising the same, and a retardation film that can be produced by a simple production process without requiring a special stretching method and a display element comprising the retardation film.

  As a result of intensive studies on the above problems, the present inventor has found a retardation film composed of fine particles having optical anisotropy and a transparent polymer and having a specific relationship of three-dimensional birefringence, and completes the present invention. It came to.

  That is, the present invention comprises at least one kind of fine particles having optical anisotropy and a transparent polymer, the refractive index in the slow axis direction in the film plane is nx, the refractive index in the vertical direction is ny, and the film When the refractive index in the thickness direction is nz, the present invention relates to a phase difference film satisfying a relationship of nx> nz> ny and a display element comprising the same.

  The present invention is described in detail below.

  The retardation film of the present invention is composed of at least one kind of fine particles having optical anisotropy and a transparent polymer, and is a retardation film in which the relationship of three-dimensional refractive index satisfies nx> nz> ny. A retardation film made of a layer film is preferred. Here, nx represents the refractive index in the slow axis (x-axis) direction (orientation method) in the film plane, ny represents the refractive index in the direction perpendicular to it (y-axis), and nz represents the thickness of the film. The refractive index in the (z-axis) direction is shown.

  The retardation film of the present invention comprises a component having positive birefringence and a component having negative birefringence, and has a positive birefringence (nx> nz) as the retardation film (in the stretching direction). The refractive index difference between the normal light refractive index and the extraordinary light refractive index (hereinafter referred to as Δn) of the component having negative birefringence is positive birefringence. It is very large compared to the substantial Δn of the component having the property, and the relationship of the three-dimensional refractive index satisfies nx> nz> ny.

  The fine particles having optical anisotropy constituting the retardation film of the present invention may be any fine particles that belong to the category of fine particles having optical anisotropy, among which fine particles having negative optical anisotropy. In particular, a fine particle having negative optical anisotropy having a large Δn is preferable, and a phase difference satisfying a relationship of three-dimensional refractive index nx> nz> ny by a general alignment operation such as stretching is particularly preferable. Since the film can be easily obtained, it is preferably in the form of a rod, needle, spindle, or the like, and in that case, the phase difference film is excellent in retardation. And the ratio of the length perpendicular to the axial direction) is preferably 1.5 or more, more preferably 2 or more, and particularly preferably 3 or more. The particle diameter of the fine particles is preferably 1 μm or less, preferably 500 nm or less, particularly 200 nm, more preferably 100 nm or less, because it becomes a retardation film having high light transmittance and excellent transparency. .

  Examples of the fine particles include inorganic substances, organic crystals, especially acicular minerals, ceramics, and organic crystals. Specific examples include calcium carbonate such as calcite and aragonite; magnesium carbonate; zirconium carbonate; strontium carbonate; cobalt carbonate; manganese carbonate; talc;

  In addition, since the fine particles are effectively dispersed in the transparent polymer and become a retardation film having excellent light transmittance, the fine particles have been surface-treated with a binder having high dispersibility with respect to the transparent polymer. Is preferred. Examples of the surface treatment at that time include fatty acid treatment, alkylammonium treatment, epoxy resin treatment, silane treatment, and urethane treatment.

  The transparent polymer constituting the retardation film of the present invention may be any polymer as long as it belongs to the category of transparent polymers, such as polycarbonate; polyarylate; polysulfone; polyimide; polyetherimide; polyethylene terephthalate. Polyethylene naphthalate; acrylic resin; polynorbornene, hydrogenated ring-opening polymer of norbornene derivative, cyclic polyolefin resin such as polycyclohexane; maleimide resin; fluorene polyester resin; fluorene polycarbonate, etc. Among them, a transparent polymer having a glass transition temperature of 100 ° C. or higher is preferable because a retardation film having excellent heat resistance is obtained, a transparent polymer having a glass transition temperature of 120 ° C. or higher is particularly preferable, and a glass transition temperature of 130 ° C. or higher is more preferable. Akirasei polymer is preferred. Also, polycarbonate, cyclic polyolefin resin, and maleimide resin are preferable because of excellent optical properties.

  The retardation film of the present invention has a light transmittance of preferably 70% or more, particularly preferably 80% or more, and more preferably 85% or more, since the luminance when used in a liquid crystal display is increased. It is preferable.

  The retardation film of the present invention has a positive optical anisotropy (birefringence) as the retardation film itself because the three-dimensional refractive index relationship is nx> nz> ny. Specifically, the above-mentioned characteristics are satisfied by combining a component having positive optical anisotropy and a component having negative optical anisotropy. As the combination, fine particles having negative optical anisotropy and positive optical anisotropy are combined. There are combinations of transparent polymers having optical anisotropy, fine particles having positive optical anisotropy and transparent polymers having negative optical anisotropy, and among them, the availability of each component Since it is easier, a retardation film composed of fine particles having negative optical anisotropy and a transparent polymer having positive optical anisotropy is preferable. Examples of the transparent polymer having positive optical anisotropy include polycarbonate, cyclic polyolefin resin, and maleimide resin. Examples of fine particles having positive optical anisotropy include fine particles such as titania and yttrium vanarate. In the retardation film of the present invention, the Δn of the component having negative optical anisotropy is larger than the substantial Δn of the component having positive optical anisotropy. The relationship nx> nz> ny is achieved.

  When the retardation film of the present invention is produced, the retardation film having sufficient birefringence and stability and the film itself having a positive optical anisotropy can be obtained. Fine particles having anisotropy: transparent polymer having positive optical anisotropy = 0.1-50 wt%: preferably 99.9-50 wt%, particularly 1-30 wt%: 99- It is preferably composed of 70% by weight, more preferably 3 to 20% by weight: 97 to 80% by weight, and most preferably 5 to 15% by weight: 95 to 85% by weight.

  The retardation film of the present invention is obtained by forming a resin composition for a retardation film comprising, for example, fine particles having optical anisotropy and a transparent polymer, by a method such as solution casting, melt casting, and the like. It can be produced by biaxial stretching, preferably unbalanced biaxial stretching (stretching ratios in the x direction and y direction are different).

  As a method for producing a resin composition for a retardation film comprising fine particles having optical anisotropy and a transparent polymer, for example, a method of dissolving and homogenizing a transparent polymer in a dispersion of fine particles having optical anisotropy A method of dissolving and homogenizing a transparent polymer in a dispersion solution of fine particles having optical anisotropy, and then removing the solvent to form pellets, granulating, and powdering; making fine particles having optical anisotropy highly transparent And a method of compounding by dispersing in a molecular raw material monomer and polymerizing; a method of melting and kneading fine particles having optical anisotropy and a transparent polymer with an extruder, a roll, and the like.

  As the solution casting at the time of film formation, for example, a solution (hereinafter referred to as a dope) in which a resin composition for a retardation film comprising fine particles having optical anisotropy and a transparent polymer is dissolved in a solvent is referred to as a dope. And a method of removing the solvent by heating or the like to obtain a film. In this case, as a method for casting the dope on the support substrate, for example, a T-die method, a doctor blade method, a bar coater method, a roll coater method, a lip coater method or the like is used. Furthermore, industrially, the most common method is to continuously extrude the dope from the die onto a belt-like or drum-like support substrate. Examples of the support substrate used include a glass substrate; a metal substrate such as stainless steel or ferrotype; and a plastic substrate such as polyethylene terephthalate. In order to industrially continuously form a film having high surface properties and optical homogeneity, a metal substrate having a mirror-finished surface is preferably used. In the solution casting method, when forming a film having high transparency and excellent thickness accuracy and surface smoothness, the solution viscosity of the dope is a very important factor, and preferably 700 to 30000 cps. It is preferable that it is 1000-10000 cps. Moreover, the thickness of the film when formed into a film by the solution casting method is preferably 10 to 500 μm, and particularly preferably in the range of 40 to 300 μm because of excellent mechanical properties and productivity.

  In addition, as for melt casting at the time of film formation, for example, a resin composition for a retardation film composed of fine particles having optical anisotropy and a transparent polymer is melted in an extruder and extruded into a film form from a slit of a T die. Then, a molding method (hereinafter referred to as a T-die melt extrusion method) that is taken up while being cooled with a roll or air can be used. At this time, since the molten resin is shaped into a wide film in the T die, the dimensions of the film are mainly determined by the T die. The flow path in the T die may be optimized in accordance with the viscoelastic characteristics of the molten resin, and as a die, a straight manifold type, a coat hanger type, a fish tail type, a coat hanger manifold type, etc. are generally mentioned. Among these, when emphasizing the thickness accuracy of the obtained film, it is preferable to use a manifold type die. Moreover, the gap adjustment of the lip which is the exit part of molten resin is one of the important factors which determine the film thickness accuracy. The retardation film of the present invention has extremely strict thickness accuracy requirements. One reason is that the retardation is defined by the product of the birefringence of the medium through which light passes and the optical path length. Even if it is homogeneous, if the thickness of the retardation film is inhomogeneous, the retardation becomes inhomogeneous and the optical isotropy of the film becomes poor. However, it takes time to adjust the thickness of the lip accurately even if it takes an expert.In recent years, an automatic thickness control system using a computer has been introduced to improve not only the film thickness accuracy but also the yield. It contributes greatly. And, as such a method, there is a method of measuring the thickness of the film online, and automatically adjusting the gap of the lip and adjusting the speed of the gear pump based on the result, for example, JP-A-10-58518, As a method for automatically adjusting the lip proposed in Japanese Patent Application Laid-Open No. 2000-127226, for example, there are a heat bolt method, a robot method, a lip heater method, a piezoelectric element method, etc., and these methods are also added in the present invention. Can also be used.

  In addition, since the lip of the T die is the exit portion of the molten resin, if the lip portion that contacts the molten resin has irregularities, the irregularities are transferred to the film surface, and the shape is solidified by the cooling roll, so-called die line And so on. Therefore, it is desirable to reduce the surface roughness of the lip portion that comes into contact with the molten resin by a method such as electrolytic polishing. Further, even if the surface roughness of the lip portion is small, if the thermally decomposed resin adheres to the lip portion and becomes a so-called eye, unevenness is generated on the surface of the lip, which causes a die line. It is important to prevent the molten resin from adhering to the lip in order to prevent it from being easily observed. In the production method of the present invention, a lip coated with chromium or ceramic can be preferably used. Further, since the resin tends to stay at the edge portion of the lip that comes into contact with the molten resin, the edge of the lip is preferably as sharp as possible, and particularly preferably 0.1 mmR or less.

  In the T-die melt extrusion method, the molten resin (molten film) extruded from the slit of the T-die is brought into close contact with a cooling roll and cooled. Such a cooling roll and the first cooling roll when there are a plurality of cooling rolls are generally called a cast roll or a casting roll. And the surface of the 1st cooling roll which a molten film contacts is desired to have a small surface roughness for the same reason as the lip of the T die. In addition, when there are a plurality of cooling rolls, it is important to keep the rotation speed of the first cooling roll and the other cooling rolls constant. If the rotation speed is uneven, streaks in the width direction are formed on the film surface. May occur.

  And in order to cool the obtained film more efficiently, it is preferable to use a method of cooling the film wound around the first cooling roll from the opposite surface of the first cooling roll, such a method as Examples thereof include an air chamber method, a touch roll method, an air knife method, a rubber roll method, a cooling drum method, an ear press roll method, and an electrostatic peening method. As touch roll methods, touch rolls that can be elastically deformed are proposed in, for example, Japanese Patent Application Laid-Open No. 2002-36332, WO 97/28950, and Japanese Patent Application Laid-Open No. 11-235747. Thin films can be formed rather than using a touch roll, and these methods can also be employed in the present invention. In addition, by suppressing the film from the opposite surface of the first cooling roll with a touch roll, there is an effect of flattening the surface roughness or making it difficult to cause molecular orientation in the take-off direction, so these touch rolls should preferably be used. Can do. Of course, the cooling from the opposite surface of the first cooling roll is not particularly performed, and may be allowed to cool.

  Since the surface temperature of the cooling roll greatly affects the appearance of the resulting film, it is desirable to control the surface temperature of the cooling roll with an accuracy of 0.1 ° C. In this case, the glass transition temperature of the transparent polymer −40 It is preferable to set to ℃-+20 ℃, and in that case, pressurized water or oil is used as a medium for controlling the roll temperature. Note that oil temperature control is preferable because of excellent temperature control accuracy.

  A slitter for cutting both ends of the obtained film may be installed, and the slitter at that time is not limited. Among them, if the resulting film is hard and fine cracks are likely to occur on the fracture surface of the film, the generation of cracks is suppressed using a slitter called a shear cutter that presses and cuts the rotary blade from both sides of the film. It is preferable. There is no particular limitation on the winder for winding the obtained film, and it is preferable to use an accumulator facility for adjusting the balance between the take-up speed and the take-up speed.

  Then, the obtained film is biaxially stretched, preferably unbalanced biaxially stretched (with different stretch ratios in the x and y directions), so that the three-dimensional refractive index relationship satisfies nx> nz> ny. A film can be obtained. The stretching process at that time includes a process of continuously performing in the T-die melt extrusion process; a process of winding the optical film once and then subjecting the film to a stretching apparatus; Examples of the biaxial stretching method include a method of stretching with a tenter and a method of stretching in a tube shape and biaxial stretching is possible simultaneously or sequentially. As the stretching conditions, the retardation film hardly causes thickness unevenness, and the obtained retardation film is excellent in mechanical properties and optical properties. Therefore, the glass transition temperature of the transparent polymer is −20 ° C. to + 40 ° C. Under the stretching temperature condition in the temperature range of ° C., the stretching ratio is preferably in the range of 1.1 to 3 times, and the stretching ratio in the x direction and the y direction is preferably in the range of 1 to 100.

  The retardation film of this invention can adjust the phase difference according to the intended use. The retardation film for viewing angle compensation preferably has an in-plane retardation of 20 nm or more, particularly preferably 50 nm or more, and more preferably 100 nm or more. The retardation film for compensating the viewing angle of the polarizing plate preferably has an in-plane retardation of 100 to 500 nm, and the retardation film for a circularly polarizing film has an in-plane retardation of 100 to 200 nm. Preferably, the retardation film for the half-wave film has an in-plane retardation of 200 to 400 nm. The retardation film for viewing angle compensation for STN-LCD is a film. The in-plane retardation is preferably in the range of 50 to 1000 nm, and the retardation film for compensation of the liquid crystal display in VA mode or IPS mode is preferably in the range of in-plane retardation of 50 to 100 nm, particularly 100 to 400 nm. A range is preferred. The retardation of the retardation film of the present invention was measured at a measurement wavelength of 590 nm. As the retardation, in-plane retardation = (ny−nx) · d (d indicates the film thickness). , Out-of-plane phase difference = (nz−nx) · d.

  The retardation film of the present invention can be used as an elliptically polarizing plate by laminating and integrating with a polarizing plate, and can also be used as a circularly polarizing plate in pasting with a quarter wavelength retardation film. . Moreover, the retardation films of the present invention can be laminated with a retardation film having positive or negative birefringence. Furthermore, a polarizing plate formed by laminating and integrating the retardation film of the present invention on at least one side as a protective film for a polarizer made of polyvinyl alcohol / iodine can also be used. And it is also possible to set it as the liquid crystal element which used the retardation film of this invention as the plastic substrate. When laminating, it is also possible to laminate via an adhesive layer. As the adhesive at that time, a known water-soluble or oil-soluble adhesive can be used.

  In the retardation film of the present invention, it is preferable that an antioxidant is blended in order to increase the thermal stability of the retardation film itself or during film formation. Examples of the antioxidant include hindered phenol antioxidants, phosphorus antioxidants, and other antioxidants. These antioxidants may be used alone or in combination. And since an antioxidant effect | action improves synergistically, it is preferable to use together and use a hindered phenolic antioxidant and phosphorus antioxidant, for example, 100 weight part of hindered phenolic antioxidants in that case It is particularly preferable to use a phosphorous antioxidant mixed in an amount of 100 to 500 parts by weight. Moreover, as addition amount of antioxidant, 0.01-10 weight part is preferable with respect to 100 weight part of resin compositions for retardation films which comprise the retardation film of this invention, Especially 0.5-1 weight is preferable. The range of parts is preferred.

  Examples of the hindered phenol antioxidant include pentaerythritol-tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), thiodiethylene-bis (3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexane-1,6-diylbis (3 -(3,5-di-tert-butyl-4-hydroxyphenyl) propionamide), diethyl ((3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl) methyl) phosphate, 3,3 ' , 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-a, a ′, a ″-(mesitylene-2,4,6-triyl) tri-p-alkyl Sol, ethylenebis (oxyethylene) bis (3- (5-t-butyl-4-hydroxy-m-tolyl) propionate), hexamethylene-bis (3- (3,5-di-t-butyl-4-) Hydroxyphenyl) propionate), 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -Trione, 1,3,5-tris ((4-tert-butyl-3-hydroxy-2,6-xylyl) methyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H ) -Trione, 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, 3,9-bis (2- (3 -(3-t-butyl-4-hydroxy-5- Butylphenyl) propionyloxy) -1,1-dimethylethyl) -2,4,8,10-spiro (5,5) undecane.

  Examples of the phosphorus antioxidant include tris (2,4-di-t-butylphenyl) phosphite, bis (2,4-bis (1,1-dimethylethyl) -6-methylphenyl) ethyl ester Phosphoric acid, tetrakis (2,4-di-t-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, bis (2,4-di-t-butylphenyl) pentaerythritol Diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol-diphosphite, tetrakis (2,4-t- Butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, di-t-butyl-m-cresyl-phosphonite, etc. It is.

  In addition, a hindered amine light stabilizer may be used, and the hindered amine light stabilizer preferably has a molecular weight of 1,000 or more, particularly 1,500 or more, because it has an excellent thermal coloring suppression effect. Is preferred. Furthermore, the addition amount of the hindered amine light stabilizer is 0.01 to 1.5 parts by weight with respect to 100 parts by weight of the resin composition for retardation film because it is excellent in the effect of preventing thermal coloring and the light stabilization effect. It is preferably used, particularly 0.05 parts by weight to 1 part by weight, and more preferably 0.1 parts by weight to 0.5 parts by weight.

  Examples of the hindered amine light stabilizer include poly ((6-morpholino-s-triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene (( 2,2,6,6-tetramethyl-4-piperidyl) imino)) (molecular weight 1,600), poly ((6- (1,1,3,3-tetramethylbutyl) amino-1,3,5 Triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)) (Molecular weight 2,000-3,100), dibutylamine-1,3,5-triazine-N, N′-bis (2,2,6,6-tetramethyl-4-piperidyl) -1,6-hexa Methylenediamine and N- (2, , 6,6-tetramethyl-4-piperidyl) butylamine polycondensate (molecular weight 2,600-3,400), N, N′-bis (3-aminopropyl) ethylenediamine-2,4-bis (N— Butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -6-chloro-1,3,5-triazine condensate (molecular weight 2,000 or more), dimethyl succinate-1 -(2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine condensate (molecular weight 3,100 to 4,000) and the like, and these can be used as one or more kinds. .

  Furthermore, as an ultraviolet absorber, for example, an ultraviolet absorber such as benzotriazole, benzophenone, triazine, or benzoate may be blended as necessary.

  The retardation film of the present invention includes other polymers, surfactants, polymer electrolytes, conductive complexes, inorganic fillers, pigments, dyes, antistatic agents, antiblocking agents, lubricants and the like within the scope of the invention. It may be blended.

  The retardation film of the present invention is a retardation film composed of at least one kind of fine particles having optical anisotropy and a transparent polymer, and a three-dimensional refractive index relationship satisfying nx> nz> ny. The phase difference film can be produced by a simple stretching operation. The retardation film is useful for compensating the viewing angle characteristics of various liquid crystal displays such as VA mode, IPS mode, TN mode, STN mode, and OCB mode. Also, it can be used widely as it can be used as an antireflection film.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

  The evaluation measurement methods performed in the examples are shown below.

-Measurement of glass transition temperature of transparent polymer-
A differential scanning calorimeter (trade name DSC200, manufactured by Seiko Denshi Kogyo Co., Ltd.) was used to measure at a heating rate of 10 ° C./min.

-Measurement of total light transmittance of retardation film-
It measured based on JIS-K-7105.

-Evaluation of retardation and three-dimensional refractive index of retardation film-
Using a fully automatic birefringence meter (trade name KOBRA-21ADH, manufactured by Oji Scientific Instruments Co., Ltd.), measurement was performed under the condition of a measurement wavelength of 590 nm.

Example 1
Polycarbonate (manufactured by Teijin Chemicals, trade name Panlite; glass transition temperature 148 ° C.) 89.8 wt% and strontium carbonate fine particles surface-treated with an epoxy agent (average particle size 120 nm, average aspect ratio 6.0; Δn = − 1.5) 100 parts by weight of a mixture consisting of 10.2% by weight is dispersed in 400 parts by weight of methylene chloride and forcedly stirred with a stirrer (trade name Robin Mics, manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a homogeneous methylene chloride solution. It was.

  The obtained methylene chloride solution was cast on a mirror roll and dried to prepare a film having a thickness of 210 μm.

  The obtained film was unbalanced biaxially stretched at 154 ° C. in the x-axis direction twice and in the y-axis direction 1.6 times at 154 ° C. using a biaxial stretching device (manufactured by Imoto Seisakusho, model 16A1) to prepare a retardation film. The three-dimensional refractive index of the obtained retardation film is nx = 1.5838, ny = 1.5820, nz = 1.5825, and satisfies nx> nz> ny, and the total light transmittance is It was 88.5%. The in-plane retardation of the film was 118 nm.

Comparative Example 1
100 parts by weight of polycarbonate (manufactured by Teijin Chemicals, trade name Panlite; glass transition temperature 148 ° C.) was dispersed in 400 parts by weight of methylene chloride to obtain a uniform methylene chloride solution.

  The obtained methylene chloride solution was cast on a mirror roll and dried in the same manner as in Example 1 to prepare a 200 μm film.

  The obtained film was unbalanced biaxially stretched at 153 ° C. by 2 times in the x-axis direction and 1.6 times in the y-axis direction by a biaxial stretching apparatus (manufactured by Imoto Seisakusho, model 16A1) to prepare a retardation film. The three-dimensional refractive index of the obtained retardation film was nx = 1.5907, ny = 1.5774, nz = 1.5737, and nx> ny> nz. The total light transmittance was 88.4%.

It is a figure which shows the refractive index ellipsoid of the retardation film which shows positive optical anisotropy (birefringence).

Explanation of symbols

nx: Refractive index in the slow axis (stretching direction: x axis) direction.
ny: indicates the refractive index in the direction perpendicular to the stretching direction (y-axis).
nz: Refractive index in the thickness direction of the retardation film.

Claims (13)

It is composed of at least one kind of fine particles having optical anisotropy and a transparent polymer. The refractive index in the slow axis direction in the film plane is nx, the refractive index in the direction perpendicular thereto is ny, and the refractive index in the thickness direction of the film. Is a retardation film satisfying the relationship of nx> nz> ny, where nz is nz. The retardation film according to claim 1, wherein the retardation film is a single layer film. The retardation film according to claim 1, comprising at least one kind of fine particles having negative optical anisotropy and a transparent polymer having positive optical anisotropy. The retardation film according to any one of claims 1 to 3, wherein an in-plane retardation of the film measured at a measurement wavelength of 590 nm is 20 nm or more. The fine particles having negative optical anisotropy are in the form of rods, needles or spindles, the aspect ratio is 1.5 or more, and the average particle diameter is 500 nm or less. The retardation film described. 6. The retardation film according to claim 1, wherein the fine particles having negative optical anisotropy are one or more fine particles having negative optical anisotropy selected from the group consisting of minerals and ceramics. . The fine particles having negative optical anisotropy are fine particles having at least one kind of negative optical anisotropy selected from the group consisting of strontium carbonate, calcium carbonate, magnesium carbonate, cobalt carbonate and manganese carbonate. The retardation film according to claim 1. The retardation film according to claim 1, wherein the transparent polymer is a transparent polymer having a glass transition temperature of 100 ° C. or higher, and has a total light transmittance of 70% or more when formed into a film. . The transparent polymer is at least one kind of transparent polymer selected from the group consisting of polycarbonate, cyclic polyolefin, maleimide copolymer, and fumarate ester resin. The retardation film described. The method for producing a retardation film according to claim 1, wherein a film comprising at least one kind of fine particles having negative optical anisotropy and a transparent polymer is stretched unbalanced biaxially. A circular or elliptical polarizing plate, wherein the retardation film according to claim 1 and a polarizing plate are laminated and integrated. A retardation film according to claim 1, wherein the retardation film and a polarizer are laminated and integrated. A liquid crystal element, wherein the retardation film according to claim 1 is a plastic substrate.

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