JP2007083471A - Optical film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having a delay phase axis and uniform retardation in the width direction of a cellulose ester type resin film used is the protective film of a liquid crystal display element, that is, a polarizing plate, for example, in the meaning of the extension of the visual field angle of a liquid crystal display device (LCD) operated in an IPS mode capable of realizing a display easy to see having a high contrast ratio over a wide range, and its manufacturing method. <P>SOLUTION: A cellulose ester type resin is extruded in a molten state from a casting die 4 by a melt flow casting film forming method and cooled and solidified by a first cooling drum 11 to form a non-stretched film while the non-stretched film is continuously stretched in its width direction while grasping both end parts of the film to manufacture the optical film. In this manufacturing method, the radius R of the cross-sectional area of the corner parts of the edges of the lip 5 on the web takeover side of a casting die 4 and the lip 6 on the non-takeover side thereof is set to 1-50 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used in various functional films such as a protective film for polarizing plates used for liquid crystal display devices (LCD), retardation films, viewing angle widening films, antireflection films used in plasma displays, and organic EL displays. The present invention relates to an optical film that can be used for various functional films, and a method for producing the same.

  A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, various optical films such as a polarizing film and a retardation film are used.

  By the way, the polarizing film of the polarizing plate used for a liquid crystal display device is laminated | stacked by using the optical film which consists of a cellulose-ester film as a protective film on the single side | surface or both surfaces of the polarizer which consists of a stretched polyvinyl alcohol film. The retardation film is used for the purpose of widening the viewing angle and improving the contrast. The retardation film is provided by stretching a film of polycarbonate, polymer having an alicyclic structure, cellulose ester, or the like. And a liquid crystal layer coated on a transparent substrate. Sometimes called an optical compensation film. When the slow axis of the retardation film is in the width direction, it is possible to perform roll-to-roll bonding with a polarizing plate, so that production efficiency can be significantly improved from conventional batch bonding.

  These optical films are required to have no optical defect and uniform retardation. In particular, the required quality is becoming stricter as monitors and TVs are becoming larger and higher definition.

  Optical film production methods are roughly classified into a solution casting film forming method and a melt casting film forming method. The former is a method in which a polymer is dissolved in a solvent, the solution is cast on a support, the solvent is evaporated, and further, if necessary, stretched to form a film. Although it has been widely adopted from the viewpoint of excellent film thickness uniformity, it has a problem such as an increase in size of equipment due to drying of the solvent. The latter is a method in which a polymer is heated and melted, cast onto a support, cooled and solidified, and further stretched as necessary to form a film, and since the solvent does not need to be dried, the equipment can be made relatively compact. However, there is a problem that the uniformity of the film thickness is inferior and uniform retardation cannot be obtained.

Conventionally, a method for producing an optical film by using a melt casting method has been proposed in, for example, Patent Documents 1 and 2 below.
Japanese Patent Application Laid-Open No. 10-10321 proposes a method of cooling a molten resin by sandwiching it on an arc with a cooling roll and an endless belt maintained at a uniform temperature in the width direction. According to the method of Patent Document 1, it is described that an optical film having a retardation of 20 nm or less and retardation unevenness within ± 5 nm can be obtained. Japanese Patent Laid-Open No. 2002-221312 proposes a method of cooling a molten resin by sandwiching it between two cooling drums. According to the method of Patent Document 2, it is described that an optical film having a film thickness unevenness of 5 μm or less, a retardation of 10 nm or less, and a retardation unevenness of 2 nm or less can be obtained.

  However, when a film obtained by stretching the film (unstretched film) obtained by the methods described in Patent Documents 1 and 2 in the width direction is observed under a crossed Nicol, the whole is not a uniform dark field. There was a problem that unevenness was recognized. This indicates that the retardation of the stretched film is not uniform, and if the retardation is uniform, the entire surface should be a dark field. Further, in these methods, the thickness profile in the width direction of the film is determined by the gap between the cooling roll and the endless belt and the gap between the cooling drums, and thus there is a problem that the thickness distribution in the width direction of the stretched film cannot be controlled. there were.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an optical film having a slow axis in the width direction of the film and having uniform retardation, and a method for producing the same.

  As a result of intensive studies in view of the above points, the inventor has melt-extruded a cellulose ester resin from a casting die by a melt casting film forming method, and is cooled and solidified by a cooling drum to form an unstretched film. Then, in the method for producing an optical film in which both ends of the unstretched film are gripped and stretched in the width direction of the film, the corner of the edge of the web take-up side lip and the web reverse take-up lip of the casting die is 1 μm. As described above, it has been found that the uniformity of the retardation of the cellulose ester resin film can be improved by setting it to 50 μm or less, and the present invention has been completed.

  In order to achieve the above object, the invention of claim 1 is characterized in that a cellulose ester resin is melt-extruded from a casting die by a melt casting film forming method, and cooled and solidified by a cooling drum to form an unstretched film. A method for producing an optical film that grips both ends of the unstretched film and stretches in the width direction of the film, and includes a cross-section at the corner of the edge of the web take-up side lip and the web take-off side lip of the casting die The radius R is 1 μm or more and 50 μm or less.

  Invention of Claim 2 is a manufacturing method of the optical film of said Claim 1, Comprising: Cellulose ester type resin is cellulose acetate, a cellulose propionate, a cellulose butyrate, a cellulose acetate propionate, a cellulose acetate butyrate It is at least one resin selected from the group consisting of rate, cellulose acetate phthalate, and cellulose phthalate.

  The invention of the optical film of claim 3 is characterized by being manufactured by the method of manufacturing an optical film according to claim 1 or 2.

  In the invention of claim 1, the cellulose ester resin is melt-extruded from a casting die by a melt casting film forming method, cooled and solidified by a cooling drum to form an unstretched film, and both end portions of the unstretched film are continuously formed. A method for producing an optical film that is gripped and stretched in the width direction of the film, wherein the radius R of the corner cross section of the edge of the web take-up side lip and web anti-take-off side lip of the casting die is 1 μm or more and 50 μm As described below, according to the method for producing an optical film of the present invention, it is possible to produce an excellent optical film with little retardation unevenness.

  Invention of Claim 2 is a manufacturing method of the optical film of said Claim 1, Comprising: Cellulose ester type resin is cellulose acetate, a cellulose propionate, a cellulose butyrate, a cellulose acetate propionate, a cellulose acetate butyrate And at least one compound selected from the group consisting of cellulose acetate phthalate and cellulose phthalate. According to the present invention, these cellulose ester resins have a small photoelastic coefficient and excellent optical properties. It exhibits the characteristics and produces an effect that it is possible to obtain a cellulose ester resin film suitable for a phase difference film with little dimensional change even under various conditions in the state of the film after film formation.

  Invention of Claim 3 was manufactured with the manufacturing method of the optical film of the said Claim 1 or 2, The optical film of this invention has an effect that it has a uniform retardation characteristic.

  By using such an optical film for a liquid crystal display device, there is an effect that a liquid crystal display device having good viewing angle characteristics can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

  The present invention relates to a method for producing an optical film that can be used particularly as a protective film for a polarizing plate of a liquid crystal display (LCD).

  FIG. 1 is a schematic flow sheet of an apparatus for carrying out the method for producing an optical film of the present invention.

  In the figure, the method for producing an optical film according to the present invention comprises mixing materials of a cellulose ester resin film, and then using the extruder 1 to melt and extrude from a casting die 4 onto a cooling drum (casting drum). A non-stretched film peeled off by a peeling roll 14 by sequentially circumscribing three cooling drums, a cooling drum 11, a second cooling drum 12, and a third cooling drum 13, in order to cool and solidify the unstretched film (web W). (Web W) is then stretched in the width direction by gripping both ends of the film (web W) by the stretching device 16.

  Here, the method of melt-extruding the cellulose ester resin from the casting die 4 onto the cooling drum and cooling and solidifying it on the cooling drum is called a melt casting film forming method. As the melt casting film forming method, there are a melt extrusion method such as a method using a casting die and an inflation method, a calendar method, a heat press method, an injection molding method, etc., but in the present invention, the thickness unevenness is small, A method using a casting die that can be easily processed to a thickness of about 50 to 500 μm and that can reduce film thickness unevenness and retardation unevenness is employed.

  The material of the cellulose ester resin film is preferably dried in advance. It is desirable to dry the moisture to 1000 ppm or less, preferably 200 ppm or less, using a vacuum or reduced pressure dryer or a dehumidifying hot air dryer.

  Cellulose ester resins and stabilizers are preferably mixed with a mixer before melting, but plasticizers, UV absorbers, and matting agents are also mixed with a mixer before melting. You can also keep it. As the mixer, a general mixer such as a V-type mixer, a conical screw type mixer, a horizontal cylindrical type mixer, or the like can be used.

  For example, the cellulose ester resin dried under hot air, vacuum or reduced pressure is melted at an extrusion temperature of about 200 to 300 ° C. using the extruder 1, and filtered through a leaf disk type filter 2 to remove foreign matters.

  When introducing into the extruder 1 from a supply hopper (not shown), it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere.

  When additives such as a plasticizer are not mixed in advance, they may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer 3.

  In the present invention, in addition to the method of directly forming a film using the extruder 1 after mixing the materials, it is also possible to form a film by once pelletizing and then melting the pellet with the extruder 1. Further, in a system in which a plurality of materials having different melting points are mixed, a so-called braided semi-melt is once produced at a temperature at which only a material having a low melting point is melted, and the semi-melt is put into the extruder 1. It is also possible to form a film. When using resins and additives that are susceptible to thermal decomposition, in order to reduce the number of times the resin is melted, a method of directly forming a film without producing pellets, A method of forming a film from is preferred.

  In the present invention, the extruder 1 used for film formation may be a single screw extruder or a twin screw extruder. In the case of forming a film directly without forming pellets from the material, it is preferable to use a twin-screw extruder because an appropriate degree of kneading is necessary. However, even with a single-screw extruder, the screw shape is a Maddock type, Unimelt type. By changing to a kneading type screw such as a mold or a dull mage, moderate kneading can be obtained and film formation becomes possible. In both the single screw extruder and the twin screw extruder, it is desirable to provide a vent port and remove gas from the vent port using a vacuum pump or the like. Once a pellet or braided semi-melt is produced, it may be a single screw extruder or a twin screw extruder.

  In the cooling process in the extruder 1 and after extrusion, it is preferable to reduce the oxygen concentration by replacing with an inert gas such as nitrogen gas or reducing the pressure.

  Although the preferable conditions for the melting temperature of the resin in the extruder 1 vary depending on the viscosity and discharge amount of the resin, the thickness of the sheet to be manufactured, etc., in general, the glass transition temperature (Tg) of the molding material is glass. The transition temperature (Tg) is preferably in the range of the glass transition temperature (Tg) + 100 ° C. or less. More preferably, the melting temperature is glass transition temperature (Tg) + 10 ° C. or higher and glass transition temperature (Tg) + 90 ° C. or lower. The melt viscosity at the time of extrusion is 10 to 100,000 poise, preferably 100 to 10,000 poise. The residence time of the resin in the extruder 1 is preferably short, and is within 5 minutes, more preferably within 3 minutes, and most preferably within 2 minutes. The residence time depends on the type of extruder and the extrusion conditions, but can be shortened by adjusting the material supply rate, L / D, screw rotation speed, screw groove depth, etc. It is.

  The screw shape, the number of rotations, and the like of the extruder 1 are appropriately selected depending on the viscosity, discharge amount, and the like of the resin. In the present invention, the shear rate in the extruder 1 is preferably 1 / second to 10000 / second, more preferably 5 / second to 1000 / second, and most preferably 10 / second to 100 / second. In order to prevent biting of the gear pump and reduce the main filter load, it is preferable to provide a prefilter on the exit side of the extruder 1.

  For example, a 50/80/100 mesh screen or a metal fiber sintered filter is preferably provided as necessary. It is preferable to use a type that can be changed online.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Moreover, it is preferable to provide the filter 2 downstream of the prefilter. A stainless fiber sintered filter is preferably used. Stainless steel fiber sintered filter is made by compressing the stainless fiber body after creating a complex intertwined state, and sintering and integrating the contact points. The density is changed according to the thickness and compression amount of the fiber, and the filtration accuracy Can be adjusted. It is preferable to use a multilayer body in which the filtration accuracy is repeated coarsely and densely multiple times. Further, it is preferable to adopt a configuration in which the filtration accuracy is sequentially increased or a method in which coarse and dense filtration accuracy is repeated, so that the filtration life of the filter can be extended and the accuracy of capturing foreign matters and gels can be improved. The filtration accuracy is preferably 0.5 μm or more and 50 μm or less.

  In the present invention, the material of the cellulose ester-based resin film is melt-extruded from the casting T die 4 using the extruder 1, and three of the first cooling drum 11, the second cooling drum 12, and the third cooling drum 13 are used. The outer drum is sequentially circumscribed on the cooling drum, and the surface is straightened and cooled and solidified to obtain an unstretched film.

  When the cooling drum with which the material extruded from the casting die 4 first contacts is the first cooling drum 11, it is preferable that the time until the material contacts the first cooling drum 11 from the casting die 4 is shorter. Within seconds, preferably within 5 seconds, and most preferably within 2 seconds. Further, the distance from the casting die 4 to the first cooling drum 11 is preferably 10 mm or more and 100 mm or less.

  The casting die 4 is an extrusion die that is used for forming a cellulose ester resin by extrusion-molding flat drawing. Here, the extruding flat stretch method film forming means that a molten polymer is extruded from a casting die 4 having parallel slits, formed into a film shape, and then successively or simultaneously in two longitudinal and lateral biaxial directions by a roll, a tenter or the like. It is a method of stretching and forming into a film. In the case of a cellulose ester resin, generally, a roll is provided with a peripheral speed difference and stretched 1.05-2.0 times in the longitudinal direction, and stretched 1.05-2.0 times in the transverse direction by a tenter. Then, the method of heat fixing is taken.

  In the optical film manufacturing method according to the present invention, the radius R of the corner cross section of the edge of the web take-up side lip 5 and / or the web anti-take-up side lip 6 of the casting die 4 is 1 μm or more and 50 μm or less. It is what has.

  By making the radius R of the corner cross section of the edge of the web take-up side lip 5 and / or the web anti-take-up side lip 6 of the casting die 4 to be 50 μm or less, it is possible to suppress the occurrence of deposits on the edge. The retardation can be made uniform. If the radius R of the cross section of the corner of the edge is less than 1 μm, the edge angle is likely to be damaged, and this causes uneven retardation, which is not preferable.

  In this embodiment, a third cooling drum 13 is arranged after the first cooling drum 11 and the second cooling drum 12 in order to improve the smoothness on both sides of the film.

  In the melt casting film forming method, when flaws or foreign matters adhere to the casting die 4, streak-like defects may occur. Such a defect is called a die line. In order to reduce surface defects such as a die line, the pipe from the extruder 1 to the casting die 4 has a structure in which the resin retention portion is minimized. It is preferable to do.

  In order to prevent adhesion of the resin, the surface roughness of the inner wall of the pipe is preferably small, and is preferably 0.3 s or less. It is preferable to buff the inner surface of the pipe with hard chrome plating.

  It is preferable to use the casting die 4 and the lip with as few scratches as possible. Since the volatile component is deposited from the resin around the casting die 4 and may cause a die line, it is preferable to suck the atmosphere containing the volatile component. Moreover, since it may precipitate also in apparatuses, such as an electrostatic application, it is preferable to apply alternating current or to prevent precipitation with another heating means.

  The casting die 4 is not particularly limited as long as it is used for producing a sheet or a film, but a coat hanger die is preferable. The lip portion gap t is preferably 0.1 mm or more and 2 mm or less, and the land portion length L is preferably 5 mm or more and 50 mm or less. L / t is preferably 10 or more.

  Assuming that the thickness of the resin immediately after adhering to the first cooling drum is h, t / h is 10 or less when the film thickness is 70 μm or more and less than 100 μm, and t or h is 50 μm or more and 70 μm or less. / H is 15 or less, and when it is less than 50 μm, t / h is preferably 20 or less. By setting t / h to the above value, the elongation of the ribbon can be suppressed and the retardation in the flow direction can be kept small.

  Thickness adjustment mechanisms include a heater type that adjusts the temperature by dividing in the width direction, a manual bolt type that adjusts the lip opening mechanically, or a lip opening adjustment that uses expansion and contraction of the bolts with a heater. It is preferable to use a heat bolt system or the like.

  The material of the casting die 4 is sprayed or plated with nickel, hard chrome, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide), etc. Buffing as surface processing, lapping using a # 1000 or higher grinding wheel, plane cutting using a diamond grinding wheel of # 1000 or higher (cutting direction is perpendicular to the resin flow direction), electrolytic polishing, electrolytic composite polishing, etc. And the like. A preferable material of the die lip is the same as that of the casting die 4. In order to prevent shark skin, it is important to reduce the friction between the lip and the resin. For this purpose, it is preferable to use, for example, a ceramic coating ((trade name K05MFC) manufactured by Dual Spiral Systems Inc. The surface accuracy of the die lip is preferably 0.5S or less, and more preferably 0.2S or less.

  In the present invention, the material extruded from the casting die 4 is cooled and surface-corrected by a cooling drum. When the cooling drum with which the material extruded from the casting die 4 first contacts is the first cooling drum 11, it is preferable that the time until the material contacts the first cooling drum 11 from the casting die 4 is shorter. Within seconds, preferably within 5 seconds, and most preferably within 2 seconds. The distance from the casting die 4 to the first cooling drum 11 is preferably 3 mm or more and 100 mm or less.

  The temperature of the resin immediately before closely contacting the first cooling drum 11 is preferably Tg or higher, and more preferably Tg + 50 ° C. or higher. By keeping the temperature of the resin high, the retardation in the flow direction generated by the elongation of the ribbon can be reduced. It is preferable to keep the temperature of the resin in the air gap immediately before the resin comes into close contact with the first cooling drum 11 from the casting die outlet. As the heat-retaining method, induction heating using a microwave, radiant heat heating using an infrared heater, or the like can be preferably used. As the infrared heater, an electric, gas, oil or steam far infrared ceramic heater can be used.

  As described above, the cellulose ester resin is melt-extruded from the casting die 4 onto the cooling drums 11, 12, and 13. The temperature of the cooling drum is adjusted by flowing a heat medium such as water or oil inside the cooling drum. It is preferable to adjust by.

  In the present invention, when the cellulose ester resin flows out from the casting die 4, it is preferable to attach a suction device in the vicinity of the casting die 4 in order to prevent contamination of the casting die 4 and the cooling drum with sublimates. The suction device needs to be treated such as heating with a heater so that the device itself does not become a place where the sublimate is attached. On the other hand, if the suction pressure is too large, film quality such as unevenness is affected. Conversely, if the suction pressure is too small, the sublimate cannot be sucked effectively.

  In the present invention, the film and the cooling drum are preferably in close contact. As a method for bringing the film and the cooling drum into close contact, pressing using a touch roll, an electrostatic contact method, an air knife, a decompression chamber, or the like can be used.

  One or more cooling drums may be used, but it is preferable that two or more cooling drums are provided in order to improve the smoothness on both surfaces of the film, and both surfaces are brought into contact with the cooling drum. Further, the cooling drum can be provided with cleaning equipment such as a cleaning roll. The temperature unevenness of the cooling drum is preferably 0.5 ° C. or less. Speed unevenness is O. 5% or less is preferable. The surface of the cooling drum can use hard chrome plating, but is not limited thereto. The surface roughness is preferably 0.1 s or less. As the material of the touch roll, a metal or a material obtained by winding a resin, rubber or the like around a metal roll can be used. Further, it is also possible to use a roll in which a resin, rubber or the like is wound around a metal roll and a metal is wound around the resin roll. Furthermore, a crown roll having a diameter changed as it goes from the center of the roll width to the roll side can also be used.

  Moreover, Tg or more is preferable and, as for the film temperature just before closely_contact | adhering to a touch roll, More preferably, it is Tg + 50 degreeC or more.

  In the present invention, a film-like cellulose ester-based resin in a molten state from the T die 4 is brought into close contact with the first cooling drum 11, the second cooling drum 12, and the third cooling drum 13 in order to be cooled and solidified while being conveyed, An unstretched cellulose ester resin film (web) is obtained. The cooled and solidified film (web) peeled from the third cooling drum 13 by the peeling roll 14 is guided to a stretching machine 16 through a dancer roll (film tension adjusting roll), where the film is stretched in the width direction. By this stretching, the molecules in the film are oriented.

  As a method of stretching the film in the width direction, a known tenter or the like can be preferably used. In particular, it is preferable to set the stretching direction to the width direction because lamination with the polarizing film can be performed in a roll form. By stretching in the width direction, the slow axis of the optical film made of the cellulose ester resin film becomes the width direction.

  On the other hand, the transmission axis of the polarizing film is also usually in the width direction. By incorporating a polarizing plate in which the transmission axis of the polarizing film and the slow axis of the optical film are parallel to each other into the liquid crystal display device, the display contrast of the liquid crystal display device can be increased and a good viewing angle can be obtained. Is obtained.

  As the stretching conditions in the stretching machine 16, the temperature and magnification can be selected so that desired retardation characteristics can be obtained. Usually, the draw ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually Tg to Tg + 50, where Tg is the glass transition temperature of the resin constituting the film. It is carried out in the temperature range of ° C, preferably Tg to Tg + 40 ° C. If the draw ratio is too small, the desired retardation may not be obtained. Conversely, if it is too large, the film may be broken. If the stretching temperature is too low, the film may break, and if it is too high, the desired retardation may not be obtained.

  The stretching in the width direction of the film is preferably performed under a controlled uniform temperature distribution. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

  The film may be stretched or shrunk in the length direction or the width direction for the purpose of reducing the retardation of the cellulose ester resin film F produced by the above method and reducing the dimensional change rate. In order to shrink in the length direction, for example, a method of contracting the film by temporarily clipping out the width stretching and relaxing in the length direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine. There is. The latter method can be performed by using a general simultaneous biaxial stretching machine and by using a pantograph method or a linear drive method to drive the clip portion in a smooth and gradually narrowing interval between adjacent clips in the longitudinal direction. it can. You may combine with extending | stretching of arbitrary directions (diagonal direction) as needed. The dimensional change rate of the optical film can be reduced by shrinking 0.5% to 10% in both the longitudinal direction and the width direction.

  The film thickness of the optical film varies depending on the purpose of use, but as a finished film, the film thickness range used in the present invention is 30 to 200 μm, and the recent thin tendency is preferably 40 to 120 μm, particularly 40 to A range of 100 μm is preferred. The average film thickness of the film can be adjusted by controlling the extrusion flow rate, the gap at the casting port of the casting die 4, the speed of the cooling drum, and the like so as to obtain a desired thickness.

  After slitting the edge of the film to a product width by the slitter 17 and cutting it off, the film is subjected to knurling (embossing) on both ends of the film by a knurling device comprising an embossing ring 18 and a back roll 19, and a winder 20 By taking up with, the sticking in an optical film (winding) F and generation | occurrence | production of an abrasion are prevented. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing. In addition, since the grip part of the clip of the both ends of a film is deform | transforming normally and cannot be used as a film product, it is cut out and reused as a raw material.

  The cellulose ester-based resin film stretched in the width direction obtained as described above has a fixed retardation with molecules oriented by stretching. Usually, the in-plane retardation (Ro) of the film is 20 to 200 nm, the thickness direction retardation (Rt) is 90 to 400 nm, the in-plane direction retardation (Ro) of the film is 20 to 100 nm, and the thickness direction retardation (Rt) is. It is preferable that it is 90-200 nm. The ratio of Rt to Ro: Rt / Ro is preferably 0.5 to 2.5, and particularly preferably 1.0 to 2.0.

In addition, when the refractive index Nx in the slow axis direction of the film, the refractive index Ny in the fast axis direction, the refractive index Nz in the thickness direction, and the film thickness of the film are d (nm),
Ro = (Nx−Ny) × d
Rt = {(Nx + Ny) / 2−Nz} × d
Represented as:

  The retardation variation is preferably as small as possible, and is usually within 15 nm, preferably 10 nm or less, more preferably 4 nm or less.

  The uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the width direction of the film, more preferably in the range of −1 to + 1 °, particularly −0. It is preferable that it is in the range of 0.5 to + 0.5 °.

  Thus, unlike the resin film molded by the solution casting film forming method, the cellulose ester-based resin film molded by the method for producing an optical film by the melt casting film forming method of the present invention has a thickness direction retardation ( Rt) is small, and there is also a feature that in-plane direction retardation (Ro) can be easily developed by stretching such a cellulose ester resin film. In addition, since there is no need to increase the draw ratio, the risk of breakage is small and stable production can be achieved.

  In the method for producing an optical film of the present invention, the cellulose ester resin is selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. It is preferably at least one resin selected from the inside.

  The degree of substitution of the acetyl group of the cellulose ester resin is preferably at least 1.5 or more because the resulting film has excellent dimensional stability. The method for measuring the substitution degree of the acyl group of the cellulose ester resin can be carried out in accordance with ASTM D-817-91. The molecular weight of the cellulose ester resin is preferably 50,000 to 300,000, particularly 60,000 to 200,000 as the number average molecular weight because the mechanical strength of the resulting film can be increased.

  The cellulose ester resin of the present invention may contain additives such as a plasticizer, an ultraviolet absorber, an antioxidant, a matting agent, an antistatic agent, a flame retardant, a dye and an oil agent for various purposes.

  Examples of the plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixyl phosphate, arylene bis (diaryl phosphate) Phosphate ester plasticizers such as esters, tricresyl phosphate, phthalate plasticizers such as diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate and di-2-ethylhexyl phthalate, triacetin, tributyrin, butyl Phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycol Glycolate ester plasticizers such as butyl phthalyl butyl glycolate, citric acid plasticizers such as tributyl acetyl citrate, dipropylene glycol benzoate, tripropylene glycol dibenzoate, 1,3-dibutylene glycol dibenzoate, Examples include polyhydric alcohol ester plasticizers such as tetraethylene glycol dibenzoate, trimethylolpropane triacetate, and trimethylolpropane tribenzoate, and trimellitic acid tris (2-ethylhexyl). You may use together 2 or more types of plasticizers among the above as needed. These addition amounts are preferably 1% to 30% with respect to the cellulose ester resin in view of the effect of the plasticizer and bleed out.

  In addition, polyester ether, polyester-urethane, polyester and the like can be preferably used because they can improve plasticity by blending.

  Polyester ethers include aromatic dicarboxylic acids or alicyclic dicarboxylic acids having 8 to 12 carbon atoms (eg terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid), 2 to 10 carbon atoms. Aliphatic glycols or alicyclic glycols (eg, ethylene diol, propylene diol, 1,4-butane diol, neopentyl glycol, 1,6-hexane diol, 1,4-cyclohexane dimethanol and 1,5-pentane diol ), Polyether glycols having 2 to 4 carbon atoms between the ether units (for example, polytetramethylene ether glycol, in particular 1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol and polytetramethylene ether). Copolyester ether) to component a glycol. The blending amount of the polyester ether is preferably 5 to 30% by weight with respect to the main resin. When the blending amount is within this range, a film exhibiting good plasticity can be obtained.

Examples of the polyester-urethane include polyester-urethane obtained by a reaction between polyester and diisocyanate. It has a repeating unit represented by the following general formula (1).

  In general formula (1), l represents 2, 3 or 4, m represents 2, 3 or 4, and n represents 1 to 100. R represents any of the structural units represented by structural unit formulas (2) to (7). In the structural unit formula (2), p represents 2 to 8.

  As the polyester constituting the polyester-urethane, the glycol component is ethylene glycol, 1,3-propanediol, or 1,4-butanediol, and the dibasic acid component is succinic acid, glutaric acid, or adipic acid. The polyester having a hydroxyl group at both ends and comprising a polymerization degree n of 1 to 100. A polyester having a molecular weight of 1,000 to 4,500 is particularly desirable.

  Examples of the diisocyanate component constituting the polyester-urethane include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and the like, p-phenylene diisocyanate, and triethylene diisocyanate. Examples thereof include aromatic diisocyanates such as range isocyanate, p, p'-diphenylmethane diisocyanate, and 1,5-naphthylene diisocyanate, and m-xylylene diisocyanate. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are preferable because they are excellent in compatibility with cellulose ester resins.

  The molecular weight of the polyester-urethane is preferably 2,000 to 50,000, more preferably 5,000 to 15,000. The synthesis of the polyester-urethane can be easily obtained by a conventional synthesis method in which the above polyester and diisocyanate are mixed and heated with stirring. In addition, the raw material polyester can be obtained by a conventional method, a corresponding dibasic acid, or a hot melt condensation method using a polyesterification reaction or transesterification reaction between these alkyl esters and glycols, or an acid chloride of these acids. It can be easily synthesized by appropriately adjusting the terminal group to be a hydroxyl group by any method of interfacial condensation with glycols.

  As for the compounding quantity of polyester-urethane, 5 to 30 weight% is preferable with respect to main resin. When the blending amount is within this range, a film exhibiting good plasticity can be obtained.

  The polyester is a polyester composed of polyethylene glycol and an aliphatic dibasic acid, and the average molecular weight is preferably 700 to 10,000.

Polyethylene glycol has the general formula HO— (CH ₂ CH ₂ —O) _n —H
(Where n is an integer). n is preferably 4 or less.

In addition, the aliphatic dibasic acid has the general formula HOOC-R-COOH
(Wherein R is an aliphatic divalent hydrocarbon group) represented by succinic acid, malonic acid, succinic acid, adipic acid, and the like, preferably having 9 or less carbon atoms.

  Polyesters can be synthesized by a conventional method using a polyesterification reaction between the dibasic acid or an alkyl ester thereof and a glycol, or a hot melt condensation method using a transesterification reaction, or an acid chloride of these acids and a glycol. It can be easily synthesized by any of the interfacial condensation methods.

  As for the compounding quantity of polyester, 5 to 30 weight% is preferable with respect to main resin. When the blending amount is within this range, a film exhibiting good plasticity can be obtained.

  As the antioxidant, hindered phenol compounds are suitable. Specific examples thereof include 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [ 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-tert-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadec -3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy Benzyl) benzene and tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination. In order to acquire the effect, the addition amount of these compounds is preferably 1 ppm to 1.0% by weight and particularly preferably 10 to 1000 ppm with respect to the cellulose ester resin.

  Examples of ultraviolet absorbers that can be used in the present invention include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloring is preferable. Further, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574, and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  As an ultraviolet absorber, from the viewpoint of preventing the deterioration of polarizers and liquid crystals, it is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, the absorption of visible light having a wavelength of 400 nm or more is small. Is preferred.

  Specific examples of useful UV absorbers in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-). Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2- Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydroxy) -3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy- A mixture of 5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate and the like can be mentioned, but not limited thereto. As commercially available products, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Specific examples of benzophenone compounds include 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy- 5-benzoylphenylmethane) and the like, but is not limited thereto.

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight with respect to the cellulose ester resin. If the amount used is too small, the ultraviolet absorption effect may be insufficient, and if it is too large, the transparency of the film may deteriorate. The ultraviolet absorber is preferably one having high heat stability.

In the present invention, it is preferable to add fine particles in order to impart slipperiness of the film. The fine particles used in the present invention may be either an inorganic compound or an organic compound as long as it has heat resistance during melting.
Examples of inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and Calcium phosphate or the like is preferable, and an inorganic compound containing silicon or zirconium oxide is more preferable. Among these, silicon dioxide is particularly preferably used because haze can be kept small. As specific examples of silicon dioxide, commercially available products having trade names such as Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600 (above, manufactured by Nippon Aerosil Co., Ltd.) are preferably used. it can.

  The optical film of the present invention is manufactured by the above-described optical film manufacturing method, and the optical film of the present invention has uniform retardation characteristics.

  And by using such an optical film for a liquid crystal display device, a liquid crystal display device having good viewing angle characteristics can be provided.

  The optical film obtained by the present invention can be formed into an elliptically polarizing plate by being bonded to at least one surface of a polarizing film.

  The polarizing film is a film that has been conventionally stretched by treating with a dichroic dye such as iodine a stretchable film such as a polyvinyl alcohol film. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose triacetate film having no anisotropy as a protective film to both sides thereof. The optical film obtained by the present invention may be prepared by bonding to the polarizing plate with the protective film, or may also be prepared by directly bonding to the polarizing film also serving as the protective film.

  In particular, since the optical film obtained according to the present invention has a slow axis in the width direction, it can be bonded between the polarizing film and long rolls without cutting, and the productivity of the polarizing plate is dramatically increased. Improve.

  A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

  Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and a liquid crystal display device is obtained using this.

  An image display device capable of realizing an easy-to-view display having a high contrast ratio over a wide range, particularly a liquid crystal display device operating in an IPS mode, includes a liquid crystal cell driven in an IPS mode comprising a pair of substrates sandwiching a liquid crystal layer, A liquid crystal display device having a pair of polarizing plates arranged orthogonally on both sides of a liquid crystal cell, wherein the cellulose ester resin film of the present invention is provided on the liquid crystal cell side of at least one polarizing plate It is.

  In addition, the cellulose ester resin film according to the present invention can also be used as a base material for an antireflection film or an optical compensation film.

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

Examples 1 and 2
Cellulose acetate propionate 100 parts by weight Degree of substitution of acetyl group 1.95 after vacuum drying at 60 ° C. for 24 hours,
Propionyl group substitution degree 0.7, number average molecular weight 75,000
Plasticizer
(1) 10 parts by weight of triphenyl phosphate
(2) Ethyl phthalyl ethyl glycolate 2 parts by weight UV absorber
(1) Tinuvin 109 0.5 part by weight
(2) Tinuvin 171 0.5 part by weight
(3) Tinuvin 326 0.3 part by weight Antioxidant 0.01 part by weight
(1) 2,6-di-t-butyl-p-cresol
(2) Pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-
4-hydroxyphenyl) propionate]
The mixture of the above materials was melt-mixed at 230 ° C. using a twin-screw extruder shown in FIG. 1 and pelletized. Using the pellets, the melt from the T-die 4 was melt extruded into a film on a cooling drum at a melting temperature of 250 ° C. and cooled and solidified to obtain an unstretched cellulose acetate propionate resin film (web).

  In Examples 1 and 2, two types of cellulose acetate were used by using casting dies having different radii R at the corner cross-sections at the edges of the web take-up lip 5 and the web take-off lip 6 of the casting die 4. A propionate resin film was obtained.

  Next, the cellulose acetate propionate resin film (web) peeled off by the peeling roll 14 is continuously introduced into the tenter 16 and stretched 1.5 times at 160 ° C. in the width direction, and then 3% in the width direction. Cooling to 30 ° C. while relaxing, then releasing from the clip, slitting the clip gripping part to the product width by the slitter 17 and cutting it off, then knurling by the knurling device comprising the embossing ring 18 and the back roll 19 Two types of cellulose acetate propionate films F having a width of 1.4 m and a film thickness of 80 μm were obtained by applying (embossing) to both ends of the film and winding the film with a winder 20.

  The R of the lip edge is measured by taking the tip R part with a silicone impression material (Matsukaze Dent Silicone V) and observing the R part with a digital microscope (VHX-200 manufactured by Keyence Corporation). It was.

  About the optical film obtained in Example 1 and 2, the uniformity of retardation was evaluated as follows. The obtained results are shown in Table 1.

  The glass transition temperature (Tg) of the cellulose acetate propionate film was 144 ° C.

(Uniformity of retardation)
The film obtained in Examples 1 and 2 is sandwiched between two polarizers arranged in a crossed Nicol state with a polarizing plate, that is, in an orthogonal state (crossed Nicol state), and light is applied from the outside of one polarizing plate, The other polarizing plate was visually observed from the outside, and the retardation uniformity was ranked according to the following criteria.

Rank Criteria A: No light transmission, uniform uniform dark field B: Partial streaky light / darkness is observed C: Comparative examples 1 and 2 in which strong streaky light / darkness is partially recognized
For comparison, the same procedure as in Examples 1 and 2 was performed. In Comparative Examples 1 and 2, a cellulose acetate propionate film was produced under conditions outside the scope of the present invention. That is, in Comparative Example 1, a casting die was used in which the radius R of the corner cross section of the edge of the web take-up side lip 5 of the casting die 4 was 63 μm, which was outside the scope of the present invention. In Comparative Example 2, a casting die was used in which the radius R of the corner cross section of the edge of the web take-up side lip 5 and the web anti-take-up side lip 6 of the casting die 4 was 80 μm which was outside the scope of the present invention. .

  In Comparative Examples 1 and 2, a cellulose acetate propionate film having a thickness of 80 μm was obtained in the same manner as in Example 1 except for these conditions.

About the obtained optical film, it carried out similarly to Example 1, evaluated the uniformity of retardation, and the obtained result was combined with following Table 1, and was shown.

  As is clear from the results in Table 1 above, in Examples 1 and 2 of the present invention, the cellulose acetate propionate film has a rating of rank A, and there is no light transmission and it is uniform throughout. A cellulose acetate propionate film as a good optical film having a dark field and little retardation unevenness could be produced.

  On the other hand, in Comparative Example 1, the cellulose acetate propionate film has an evaluation of rank B, and stripe-like light and darkness is partially recognized, the retardation property is not uniform, and is sufficient as an optical film. It was not usable. In Comparative Example 2, the cellulose acetate propionate film has an evaluation of rank C, a strong streak-like light and darkness is partially recognized, the retardation characteristics are not uniform, and it cannot be used as an optical film at all. It was a thing.

It is a general | schematic flow sheet which shows one Embodiment of the apparatus which enforces the manufacturing method of the optical film of this invention. It is an expanded cross-sectional view which shows the detail of a casting die.

Explanation of symbols

1: Extruder 2: Filter 3: Static mixer 4: Casting die (extrusion die)
5: Take-up lip 6: Anti-take-off lip 7: Corner cut portion 11: First cooling drum 12: Second cooling drum 13: Third cooling drum 14: Peeling roll 15: Dancer roll 16: Stretcher 17: Slitter 18 : Embossing ring 19: Back roll 20: Winding machine W: Web (film)
F: Optical film wound up

Claims (3)

  Cellulose ester resin is melt-extruded from a casting die by a melt casting film forming method, cooled and solidified by a cooling drum to form an unstretched film, and continuously gripped at both ends of the unstretched film. A method for producing an optical film stretched in a direction, characterized in that the radius R of the corner cross section of the edge of the web take-up side lip and the web counter take-up side lip of the casting die is 1 μm or more and 50 μm or less. A method for producing an optical film.   The cellulose ester resin is at least one resin selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. The method for producing an optical film according to claim 1, wherein:   An optical film manufactured by the method for manufacturing an optical film according to claim 1.

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