JP2005156862A - Retardation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retardation film that is useful for compensation of the visual characteristics of a liquid crystal display having practical properties such as heat resistance and mechanical strength, that is composed of fine particles having negative optical anisotropy useful also as an optical film and a transparent polymer, and that particularly desirably has a three-dimensional refractive index fulfilling a relation of nx<ny≤nz or nx≤ny<nz. <P>SOLUTION: The retardation film is composed of: fine particles having at least one or more kinds of negative optical anisotropies and having particularly a shape of a bar, a needle or a spindle with an aspect ratio of ≥1.5 and an average grain size of ≤500 nm; and a transparent polymer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a retardation film composed of fine particles having negative optical anisotropy useful as an optical film for liquid crystal displays and a transparent polymer, particularly preferably a refractive index in the fast axis direction in the film plane is nx, Retardation film satisfying the relationship of nx <ny ≦ nz or nx ≦ ny <nz, where ny is the refractive index in the vertical direction and nz is the refractive index in the thickness direction of the film, and a manufacturing method thereof and a display element comprising the same Is.

  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 in liquid crystal displays 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 stretching direction in the film plane is the x-axis, the direction perpendicular thereto is the y-axis, the thickness direction of the film 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 becomes relatively large is called positive, and the case where the refractive index becomes small on the contrary is called negative. And as polymers having negative birefringence, there are acrylic resins and polystyrene, but they are not practically used because of their low heat resistance.

  However, since a polymer film exhibiting negative birefringence has a high z-axis refractive index and becomes an unprecedented retardation film, it is useful, for example, as a retardation film for compensating display angle characteristics of a display, heat resistance, etc. There is a strong market demand for a retardation film having negative birefringence that is practical. In order to increase the refractive index in the z-axis direction, a heat-shrinkable film is adhered to one or both sides of the polymer film, and the laminate is subjected to a heat-stretching process to a direction perpendicular to the polymer film stretching direction (z-axis direction ) Has been proposed (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). In this method, when the heat-shrinkable film is shrunk, 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 direction.

  In addition, a method of uniaxially stretching in a plane while applying an electric field to a polymer film has been proposed (see, for example, Patent Document 4). 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.

  Furthermore, optical materials such as optical films and optical adhesives using optically anisotropic fine particles have been proposed (see, for example, Patent Document 5 and Non-Patent Document 1).

Japanese Patent No. 2818983

JP 05-297223 A JP 05-323120 A Japanese Patent Laid-Open No. 06-088909 JP-A-11-293116 The Society of Polymer Science, Japan (2003), Vol. 52, no. 4, 748 pages

  However, the methods proposed in Patent Documents 1 to 4 have many problems such as requiring a very complicated manufacturing process. In addition, those proposed in Patent Document 5 and Non-Patent Document 1 are substantially related to zero birefringence (non-birefringence) materials, and are actively used for retardations represented by retardation films. Etc. are not mentioned.

  Therefore, the present invention is a retardation film excellent in heat resistance, and particularly preferably, the refractive index in the fast 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. In this case, an object of the present invention is to provide a retardation film satisfying a relationship of nx <ny ≦ nz or nx ≦ ny <nz, a manufacturing method thereof, and a display element comprising the same.

  As a result of intensive studies on the above problems, the present inventor has found that it can be applied as a retardation film by using fine particles having specific optical anisotropy, and has completed the present invention.

  That is, the present invention relates to a retardation film comprising at least one kind of fine particles having negative optical anisotropy and a transparent polymer, a method for producing the same, and a display device comprising the same.

  The present invention is described in detail below.

  The retardation film of the present invention comprises at least one kind of fine particles having negative optical anisotropy and a transparent polymer, and in particular, a retardation film having negative birefringence, progress in the film plane. When the refractive index in the phase axis direction 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, nx ≦ ny ≦ nz, especially nx <ny ≦ nz or nx ≦ ny <nz. A retardation film satisfying the relationship is preferable.

  The fine particles having negative optical anisotropy used in the present invention are the refractive index difference (ne−) between the refractive index of extraordinary light (hereinafter referred to as “ne”) and the refractive index of ordinary light (hereinafter referred to as “no”). no) is a fine particle that is negative (minus), and the fine particle may be any fine particle as long as it belongs to the category of fine particles having negative optical anisotropy. It is preferable to have an elongated shape such as a rod shape, a needle shape, a spindle shape, etc., because the resulting retardation film is excellent in controlling the orientation when it is produced and easily develops negative optical anisotropy. The ratio of the length in the axial direction to the length perpendicular to the axial direction is preferably 1.5 or more, more preferably 2 or more, and particularly preferably 3 or more. Further, the particle diameter of the fine particles is preferably 500 nm or less, more preferably 200 nm or less, and particularly preferably 100 nm or less in order to obtain a retardation film having high light transmittance and excellent transparency.

  Examples of the fine particles having negative optical anisotropy include inorganic substances, particularly minerals and ceramics. Specific examples include calcium carbonate such as calcite and aragonite; magnesium carbonate; zirconium carbonate; strontium carbonate; Cobalt carbonate; manganese carbonate can be mentioned, and it is preferable that the above-mentioned characteristics are satisfied.

  Since the fine particles are effectively dispersed in a transparent polymer and become a retardation film having excellent light transmittance, the fine particles may have been surface-treated with a binder having high dispersibility with respect to the transparent polymer. preferable. 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 that belongs to the category of transparent polymers, such as polycarbonate, polyarylate, polysulfone, polyimide, polyetherimide, polyethylene terephthalate. , Polyethylene naphthalate, acrylic resin, cyclic polyolefin resin, maleimide resin, and the like. Among them, a transparent polymer having a glass transition temperature of 100 ° C. or higher is preferable because it becomes a retardation film having excellent heat resistance. A glass transition temperature of 110 ° C. or higher is particularly preferable, a glass transition temperature of 120 ° C. or higher is more preferable, and a glass transition temperature of 130 ° C. or higher is most preferable. 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.

When producing the retardation film of the present invention, a retardation film having sufficient stability of birefringence can be obtained, so that the aspect ratio is 1.5 or more and the average particle diameter is 500 nm or less. The fine particles having negative optical anisotropy are preferably 0.1 to 50% by weight, particularly preferably 1 to 40% by weight, more preferably 3 to 30% by weight, most preferably 5 to 25% by weight and the transparent polymer. It is preferably 99.9 to 50% by weight, particularly preferably 99 to 60% by weight, more preferably 97 to 70% by weight, and most preferably 95 to 75% by weight. . In addition, the ease of developing birefringence generally required for optical films, etc. is expressed by a solid photoelastic coefficient, and a retardation film that is more excellent as a retardation film can be obtained. Therefore, the resin composition for retardation film preferably has a solid photoelastic coefficient of −1 * 10 ⁻¹² Pa or less, particularly preferably −5 * 10 ⁻¹² Pa or less, and further −10 * 10 ⁻¹² Pa or less is preferable. And when processing as a retardation film, the photoelastic coefficient in a rubber region is important, and as the resin composition for a retardation film, the photoelastic coefficient in a rubber region is −1 * 10 ⁻¹⁰ Pa or less. In particular, it is preferably −1 * 10 ⁻⁹ Pa or less, more preferably −5 * 10 ⁻⁹ Pa or less.

  The retardation film of the present invention is formed, for example, by forming a resin composition for a retardation film comprising fine particles having negative optical anisotropy and a transparent polymer by a method such as solution casting, melt casting, and the like. It can be produced by stretching the film uniaxially or biaxially or more.

  As a method for producing a resin composition for a retardation film comprising fine particles having negative optical anisotropy and a transparent polymer, for example, the transparent polymer is dissolved in a dispersion of fine particles having negative optical anisotropy. Method of homogenizing; Method of dissolving transparent polymer in fine particle dispersion with negative optical anisotropy and homogenizing, then removing solvent and pelletizing, granulating, powdering; Negative optical anisotropy A method in which fine particles having a property are dispersed in a raw material monomer of a transparent polymer and then polymerized; a method in which fine particles having a negative optical anisotropy and a transparent polymer are melt-kneaded with an extruder, a roll, or the like; Etc.

  As the solution casting at the time of film formation, for example, a solution (hereinafter referred to as a dope) in which a retardation film resin composition comprising fine particles having negative optical anisotropy and a transparent polymer is dissolved in a solvent is supported. An example is a method in which after casting on a substrate, heating or the like is performed to remove the solvent 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. In addition, the thickness of the film when formed into a film by the solution casting method is preferably 10 to 500 μm, particularly preferably 40 to 300 μm because of excellent mechanical properties and productivity.

  In addition, as melt casting at the time of film formation, for example, a resin composition for a retardation film composed of fine particles having negative optical anisotropy and a transparent polymer is melted in an extruder, and a film is formed from a slit of a T die. And a molding method (hereinafter referred to as a T-die melt extrusion method) that is taken out while being cooled with a roll or air. 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.

  And the obtained film can be used as the retardation film of the present invention by controlling the retardation by stretching uniaxially or biaxially as necessary. 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; Moreover, when extending | stretching to a uniaxial direction, it is more preferable when obtaining the stretched film with a uniform optical characteristic that the length of the film width direction is restrained so that it may not change in the middle of extending | stretching with respect to the length before extending | stretching. Examples of the uniaxial stretching method include a method of stretching with a tenter, a method of rolling and stretching with a calendar, a method of stretching between rolls, and the like. As a biaxial stretching method, for example, a method of stretching with a tenter, a tube shape There are methods such as inflating and stretching. As the stretching condition, unevenness in thickness is unlikely to occur, and a retardation film having excellent mechanical and optical properties is obtained. Therefore, a temperature range of −20 ° C. to + 40 ° C. with respect to the glass transition temperature of the transparent polymer. It is preferable to extend | stretch in the range of 1.1-3 times of draw ratio on the extending | stretching temperature conditions of these.

  The retardation of the retardation film of the present invention may be adjusted depending on the intended use, and for retardation compensation, the retardation film is preferably 20 nm or more, particularly preferably 50 nm or more. More specifically, the retardation film when used as a circular or elliptical polarizing film formed by laminating and integrating a retardation film and a polarizing plate is preferably 100 nm to 200 nm, and used as a half-wave film. The retardation film is preferably 200 nm to 400 nm, and the retardation film used for STN-LCD and the viewing angle compensation of the brightness enhancement film is preferably 50 nm to 1000 nm. The phase difference when the refractive index in the fast 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 is the in-plane phase difference = (ny− nx) · d (where d is the thickness) and out-of-plane retardation (nz−nx) · d, the retardation in the present invention means the out-of-plane direction of the film measured at a measurement wavelength of 589 nm. Refers to phase difference. The retardation film of the present invention preferably has a refractive index satisfying a relationship of nx <ny ≦ nz or nx ≦ ny <nz. The retardation film satisfying the relationship is, for example, for the above-described retardation film. It can be obtained by stretching a film made of the resin composition uniaxially or biaxially.

  The retardation film of the present invention can be laminated with a polarizing plate to form an elliptical polarizing plate. At that time, it is also possible to make a circularly polarizing plate by laminating with a quarter wavelength retardation film in particular, the circularly polarizing plate is a reflection type liquid crystal display, an antireflection film such as an organic EL display, It is also useful for brightness enhancement films. Furthermore, the retardation films of the present invention can be laminated with each other or with other retardation films. It is also possible to laminate a polarizer made of polyvinyl alcohol / iodine or the like to make a polarizing plate, or to make a liquid crystal element using the retardation film of the present invention as a plastic substrate. When laminating the retardation film of the present invention, it may be bonded through an adhesive layer, and a known water-soluble or oil-soluble adhesive can be used as the adhesive layer.

  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 below.

  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.

  According to the present invention, it is composed of fine particles having negative optical anisotropy and a transparent polymer that are also useful as an optical film useful for compensating visual characteristics of liquid crystal displays having practical properties such as heat resistance and mechanical strength. A retardation film, preferably a retardation film satisfying a relationship of nx ≦ ny ≦ nz, particularly nx <ny ≦ nz or nx ≦ ny <nz, can be provided.

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

-Measurement of number average molecular weight of transparent polymer-
It calculated | required as a standard polystyrene conversion value using the gel permeation chromatography (GPC) (The Tosoh Corporation make, brand name HLC-802A).

~ Measurement of glass transition temperature ~
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 solid photoelastic coefficient of resin composition for retardation film and photoelastic coefficient of rubber region-
The photoelastic coefficient (C) was measured by measuring the birefringence value (Δn) and stress (σ) at a take-up speed of 1% / s using an optical rheometer (trade name HRS-100, manufactured by Oak Seisakusho). Obtained from the equation.
C = Δn / σ
-Measurement of total light transmittance of retardation film-
It measured based on JIS-K-7105.

-Measurement 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.), the measurement was performed under conditions of a measurement wavelength of 589 nm.

Synthesis Example 1 (Production example of N-methylmaleimide / isobutene copolymer)
A 30 L autoclave equipped with a stirrer, nitrogen introduction tube, thermometer and deaeration tube was charged with 1.11 kg of N-methylmaleimide, 10 g of t-butylperoxypivalate, 7 kg of toluene and 3 kg of methanol, and purged several times with nitrogen and then liquefied. 1.68 kg of isobutene was charged and reacted at 60 ° C. for 6 hours. The obtained particles were centrifuged and dried to obtain 1.55 kg of an N-methylmaleimide / isobutene copolymer. The number average molecular weight of the obtained N-methylmaleimide / isobutene copolymer was 120,000, and the glass transition temperature was 159 ° C.

Example 1
95% by weight of N-methylmaleimide / isobutene copolymer (glass transition temperature 159 ° C.) having a number average molecular weight of 120,000 obtained by Synthesis Example 1 and surface treated with a silane coupling agent (average particle diameter 90 nm, An average aspect ratio of 4.5, ne-no = -0.17) 100 parts by weight of a mixture consisting of 5% by weight is dispersed in 400 parts by weight of chloroform and forced with a stirrer (trade name Robin Mics manufactured by Tokushu Kika Kogyo Co., Ltd.). Stir to obtain a homogeneous chloroform solution.

The obtained chloroform solution was cast on a mirror roll and dried to prepare a film having a thickness of 100 μm. Further, when the solid photoelastic coefficient of the resin composition for retardation film and the photoelastic coefficient of the rubber region were measured from the obtained film, the solid photoelastic coefficient = −6 * 10 ⁻¹² Pa, the rubber region The photoelastic coefficient was −3 * 10 ⁻⁹ Pa.

  The obtained film was stretched uniaxially with a width restriction of 1.5 times at 170 ° C. 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 is nx = 1.5367, ny = 1.5405, nz = 1.5405, satisfies nx <ny ≦ nz, and the total light transmittance is It was 91%. Further, the in-plane retardation ((ny−nx) · d) of the film was 253 nm, and the out-of-plane retardation ((nz−nx) · d) was 253 nm.

Example 2
94% by weight of N-methylmaleimide / isobutene copolymer having a number average molecular weight of 120,000 (glass transition temperature 159 ° C.) obtained by Synthesis Example 1 and strontium carbonate fine particles surface-treated with fatty acid (average particle size 95 nm, average aspect ratio) 3.8, ne-no = -0.15) 100 parts by weight of a mixture consisting of 5% by weight is dispersed in 400 parts by weight of chloroform and uniformly stirred with a stirrer (trade name Robin Mics, manufactured by Tokushu Kika Kogyo Co., Ltd.). A chloroform solution of was obtained.

The obtained chloroform solution was cast on a mirror roll and dried to prepare a film having a thickness of 100 μm. Further, when the solid photoelastic coefficient of the resin composition for retardation film and the photoelastic coefficient of the rubber region were measured from the obtained film, the solid photoelastic coefficient = −9 * 10 ⁻¹² Pa, the rubber region The photoelastic coefficient of the sample was −8 * 10 ⁻⁹ Pa.

  The obtained film was simultaneously biaxially stretched 1.5 times at 170 ° C. 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 is nx = 1.5398, ny = 1.5398, nz = 1.5422, satisfies nx ≦ ny <nz, and the total light transmittance is It was 91%. Further, the in-plane retardation ((ny−nx) · d) of the film was 0 nm, and the out-of-plane retardation ((nz−nx) · d) was 107 nm.

Example 3
Strontium carbonate fine particles (average particle size 120 nm, average aspect ratio 6.5, ne-no = −0) surface-treated with 86% by weight of polycarbonate (manufactured by Teijin Chemicals, trade name Panlite; glass transition temperature 149 ° C.) and epoxy agent .15) 14% by weight was melt-kneaded and pelletized at a kneading temperature of 270 ° C. using a twin-screw extruder (manufactured by Nippon Steel Works, trade name: TEX30). When the solid photoelastic coefficient of the obtained composition and the photoelastic coefficient of the rubber region were measured, the solid photoelastic coefficient = −5 * 10 ⁻¹¹ Pa, the photoelastic coefficient of the rubber region = −6 * 10 It was ⁻⁹ Pa.

  100 parts by weight of the obtained pellets were dispersed in 400 parts by weight of methylene chloride and forcibly stirred with a stirrer (trade name Robin Mics, manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a uniform methylene chloride solution.

  The obtained methylene chloride solution was cast on a mirror roll and dried to prepare a film having a thickness of 60 μm.

  The obtained film was stretched uniaxially with a width restriction of 1.3 times at 155 ° C. 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 is nx = 1.6138, ny = 1.6199, nz = 1.6199, satisfies nx <ny ≦ nz, and the total light transmittance is 87%. Further, the in-plane retardation ((ny−nx) · d) of the film was 281 nm, and the out-of-plane retardation ((nz−nx) · d) was 281 nm.

Comparative Example 1
N-methylmaleimide / isobutene copolymer having a number average molecular weight of 120,000 obtained in Synthesis Example 1 (glass transition temperature 159 ° C., photoelastic coefficient of solid = 5 * 10 ⁻¹² Pa, photoelastic coefficient of rubber region = 1 * 10 ⁻⁹ Pa) 100 parts by weight were dispersed in 400 parts by weight of chloroform to obtain a uniform chloroform solution.

  The obtained chloroform solution was cast on a mirror surface roll in the same manner as in Example 1 and dried to prepare a film having a thickness of 100 μm.

  The obtained film was stretched uniaxially in a width-constraint manner at 170 ° C. by a biaxial stretching apparatus (manufactured by Imoto Seisakusho, Model 16A1) to prepare a retardation film. The obtained three-dimensional refractive index of the retardation film was nx = 1.5394, ny = 1.5343, nz = 1.5343, nx> ny = nz, and the total light transmittance was 91%. It was. The in-plane retardation ((ny-nx) · d) of the film was −255 nm and the out-of-plane retardation ((nz−nx) · d) of −255 nm.

Comparative Example 2
100 parts by weight of polycarbonate (manufactured by Teijin Chemicals, trade name Panlite; glass transition temperature 149 ° C., solid photoelastic coefficient = 1 * 10 ⁻¹⁰ Pa, photoelastic coefficient of rubber region = 1 * 10 ⁻⁸ Pa) methylene chloride Dispersed in 400 parts by weight to obtain a uniform methylene chloride solution.

  The obtained methylene chloride solution was cast on a mirror roll in the same manner as in Example 3 and dried to prepare a film having a thickness of 40 μm.

  The obtained film was uniaxially stretched with a width restriction of 1.5 times at 155 ° C. by a biaxial stretching apparatus (manufactured by Imoto Seisakusho, Model 16A1) to prepare a retardation film. The obtained three-dimensional refractive index of the retardation film was nx = 1.5945, ny = 1.5737, nz = 1.5737, nx> ny = nz, and the total light transmittance was 87%. It was. The in-plane retardation ((ny-nx) · d) was −554 nm, and the out-of-plane retardation ((nz−nx) · d) was −554 nm.

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

Explanation of symbols

nx: Refractive index in the fast phase direction (stretching direction: x-axis).
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)

A retardation film comprising at least one kind of fine particles having negative optical anisotropy and a transparent polymer. 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. Retardation film. The fine particles having negative optical anisotropy are fine particles having one or more types of negative optical anisotropy selected from the group consisting of minerals and ceramics. Retardation film. The fine particles having negative optical anisotropy are fine particles having one or more types 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 total light transmittance is 70% or more. The transparent polymer is one or more types of polymers selected from the group consisting of polycarbonate, cyclic polyolefin, maleimide copolymer and fumarate ester resin. Phase difference film. The out-of-plane retardation measured at a measurement wavelength of 589 nm is 20 nm or more, the refractive index in the fast axis direction in the film plane is nx, the refractive index in the direction perpendicular to it is ny, and the refractive index in the thickness direction of the film is nz. The retardation film according to claim 1, wherein each of the relations satisfies nx <ny ≦ nz or nx ≦ ny <nz. 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 at least uniaxially. 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. It is characterized by comprising 0.1 to 50% by weight of fine particles having negative optical anisotropy having an aspect ratio of 1.5 or more and an average particle diameter of 500 nm or less and a transparent polymer of 99.9 to 50% by weight. A resin composition for a retardation film. The resin composition for retardation film according to claim 12, which has a solid photoelastic coefficient of −1 * 10 ⁻¹² Pa or less.

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