WO2008010361A1

WO2008010361A1 - Optical film, and its manufacturing method

Info

Publication number: WO2008010361A1
Application number: PCT/JP2007/061620
Authority: WO
Inventors: Kenichi Kazama
Original assignee: Konica Minolta Opto, Inc.
Priority date: 2006-07-18
Filing date: 2007-06-08
Publication date: 2008-01-24
Also published as: TW200821122A

Abstract

It is an object to provide an optical film used for a liquid crystal display device and other various display devices and its manufacturing method by use of melt flow casting method, wherein the optical film has improved uniformity in a width direction of retardation of the film and a superior optical characteristic. A touch roll (6) is provided with a pressure control unit and a retardation measuring device (20) is disposed on a film carrying way to measure retardation of the carrying film on an on-line basis. A retardation measured value signal is sent to the pressure control unit of the touch roll (6). A retardation value of the carrying film is controlled in the pressure control unit by adjusting the pressure of the touch roll (6) on a real time basis in accordance with the retardation measured value signal to make differences between the maximum and minimum values of the retardation of the carrying film always not more than 4 nm.

Description

Specification

Optical film and method for producing the same

Technical field

[0001] The present invention relates to an optical film produced by a melt casting film forming method, in particular, a protective film for a polarizing plate, a retardation film, a viewing angle widening film, a plasma display used in a liquid crystal display (LCD) and the like. The present invention relates to an optical film that can be used for various functional films such as antireflection films used, or various functional films used for organic EL displays, and a method for producing the same.

Background art

[0002] Liquid crystal display devices are widely used as monitors because they save space and energy compared to conventional CRT display devices. 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 a polarizing plate used in a liquid crystal display device is laminated on one or both sides of a polarizer made of a stretched polyvinyl alcohol record film using an optical film made of a cellulose ester film as a protective film. The retardation film is used for the purpose of widening the viewing angle and improving the contrast, and is provided with a retardation by stretching a film of polycarbonate, cyclic polyolefin resin, cellulose ester or the like. . Sometimes called an optical compensation film.

[0004] These optical films are required to have uniform retardation with no optical defects, and in particular, no phase axis variation. In particular, as monitors and TVs become larger and higher definition, these required qualities are becoming increasingly severe.

[0005] Optical film production methods are roughly classified into a melt casting film forming method and a solution casting film forming method. The former is a method in which a polymer is dissolved by heating and cast on a support, cooled and solidified, and further stretched as necessary to form a film. The latter is a solution in which the polymer is dissolved in a solvent to dissolve the solution. Is cast on a support, the solvent is evaporated, and the film is further stretched as necessary to form a film. [0006] In any film forming method, the molten polymer or polymer solution is cooled and solidified on a support. And after peeling from a support body, processes, such as drying and extending | stretching, are made | formed, while a polymer film is conveyed using a some conveyance roll.

[0007] The solution casting film forming method has a problem that the environmental load is large because a large amount of solvent is used. On the other hand, since the melt casting film forming method does not use a solvent, it can be expected to improve productivity and is preferable from the viewpoint of environmental protection.

[0008] Conventionally, an apparatus described in Patent Document 1 below has been proposed as a sheet-film forming apparatus using a melt casting film forming method.

Patent Document 1 discloses a sheet roll forming apparatus that introduces a sheet-like molten resin extruded from an extrusion molding machine between a main roll and a press roll (touch roll) and performs nipping molding. The main roll is composed of a highly rigid metal roll, and the Tatsuronole is fitted into the thin metal outer cylinder in the same axial center with a flexible thin metal outer cylinder and a cooling fluid flow space. A roll apparatus for forming a sheet 'film constituted by a double cylinder comprising a highly rigid metal inner cylinder is disclosed.

[0010] In Patent Document 1, the elastic deformation of the thin metal outer cylinder can be used to secure the contact length to the main roll in the same manner as in the rubber roll pressing method, whereby the holding pressure without a bank can be secured. It enables molding and diffused reflection of light with no residual strain. It produces an optically excellent resin film sheet without birefringence.

Patent Document 1: Japanese Patent No. 3194904

Disclosure of the invention

Problems to be solved by the invention

[0011] By the way, in general, when the range of force that changes the retardation of the film becomes wide due to the pressing pressure of the touch roll, it is difficult to maintain the uniformity in the width direction of the pressing pressure of the touch roll.

[0012] Since the pressure of the touch roll tends to be lowered at the center, Patent Document 1 discloses a technique for improving uniformity with a drum-shaped (crown) touch roll. However, if the temperature of the resin fluctuates during film formation, the roll temperature also fluctuates, and the roll deforms thermally, so that the crown amount deviates from the optimum value, the lateral direction distribution of the pressing pressure fluctuates, and the film retards. There was a problem that the dating could fluctuate.

[0013] An object of the present invention is to solve the above-mentioned problems of the prior art, improve the uniformity of the retardation of the film in the width direction, obtain an optical film having excellent optical characteristics, and The object is to provide a method of manufacturing by the melt casting method.

Means for solving the problem

[0014] In order to achieve the above object, the invention of claim 1 is characterized in that an amorphous thermoplastic resin is melted, extruded from a casting die onto a rotating support, and melted on the support. The resin is pressed on the surface of the support by pressing means, cooled and solidified to form a film, the film is peeled off from the support, transported by the transporting means, and then wound by a scraping device, and then optically formed by a melt casting film forming method. In the film manufacturing method, the retardation value of the film is measured by a retardation measuring device installed on the way of conveyance by the conveying means, and the support of the pressing means is based on the retardation value measured by the measuring device. The film is controlled in real time by adjusting the pressing force against the film so that the retardation value of the film falls within a predetermined range.

[0015] The invention of claim 2 is the method for producing an optical film of claim 1, wherein the retardance measuring instrument determines the retardation value of the film at a plurality of positions in the width direction. It is characterized by measuring.

[0016] The invention of claim 3 is the optical film manufacturing method of claim 1, wherein the difference between the maximum value and the minimum value of the retardation value measured by the retardation measuring device The pressing force of the pressing means against the support is adjusted in real time so that it becomes S4 nm or less.

In the above, the retardation value force may be any one of the in-plane direction retardation value and the thickness direction retardation value.

[0018] Further, in the method for producing an optical film according to the present invention, the width of the film when scraped is 1.

A thickness of 5 m or more and 4. Om or less is preferably 15 / im or more and 60 / im or less when the film is peeled off.

The invention of the optical film according to the present invention is manufactured by the above-described optical film manufacturing method, and has a maximum value and a minimum value of the retardation value in the width direction and the longitudinal direction of the film. It is characterized by a differential force of 4 nm or less.

The invention's effect

[0020] The invention of claim 1, wherein the amorphous thermoplastic resin is melted and extruded from a casting die onto a rotating support, and the molten resin on the support is pressed against the surface of the support. In the method for producing an optical film by a melt casting film forming method in which the film is pressed and solidified by cooling to form a film, the film is peeled off from the support, transported by a transporting means, and wound by a scraping device. The retardation value of the film is measured with a retardation measuring device installed on the way of conveyance by the means, and the pressing force of the pressing means against the support is adjusted in real time based on the retardation value measured by the measuring device. The retardation value of the film is controlled to be within a predetermined range. According to the present invention, the film retardation value in the width direction is controlled. Improved one property, an effect that it is possible to obtain an optical film excellent in optical properties.

[0021] The invention of claim 2 is the method for producing an optical film of claim 1, wherein the retardation measuring device calculates the retardation value of the film at a plurality of locations in the width direction. According to the present invention, it is possible to improve the uniformity in the width direction of the retardation of the film and to obtain an optical film having excellent optical characteristics.

[0022] The invention of claim 3 is the method of manufacturing an optical film according to claim 1, wherein the difference between the maximum value and the minimum value of the retardation value measured by the retardation measuring device. The pressing force of the pressing means against the support is adjusted in real time so that it becomes S4 nm or less.According to the present invention, the uniformity in the width direction of the retardation of the film is improved and the optical characteristics are improved. If an excellent optical film can be obtained, the effect is achieved.

[0023] The invention of the optical film according to the present invention is manufactured by the above-described optical film manufacturing method, and the difference between the maximum value and the minimum value of the retardation value in the width direction and the longitudinal direction of the film is 4 nm or less. According to the present invention, the uniformity in the width direction of the retardation of the film is improved, and the optical film is excellent in optical properties. Brief Description of Drawings

[0024] FIG. 1 is a schematic flow sheet showing one embodiment of an apparatus for carrying out the method for producing an optical film of the present invention. Explanation of symbols

[0025] 1 Extruder

2 Huino Letter

3 Static mixer

4 Casting die

5 First cooling roll

6 Tatsuchi Ronore

7 Second cooling roll

8 Third cooling roll

9 Peeling roll

10 Unstretched film

12 Stretching device

16 Scraper

F optical film

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to these.

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 device (LCD).

[0028] The film constituent material used preferably removes volatile components typified by moisture, solvent, and the like before film formation or during heating. As the removal method, a so-called known drying method can be applied, which can be performed by a heating method, a decompression method, a heating decompression method, or the like, and in air, dehumidified air, or an atmosphere selected with nitrogen as an inert gas. You can do it. When performing these known drying methods, it is preferable to carry out in a temperature range in which the film constituting material does not decompose. [0029] By drying before film formation, the generation of volatile components can be reduced, and the resin alone, or at least one mixture or compatible material other than the resin among the resin and the film constituent material. It can also be divided and dried. The drying temperature is preferably 80 ° C or higher. When a material having a glass transition temperature is present in the material to be dried, heating to a drying temperature higher than the glass transition temperature may cause the material to melt and become difficult to handle. It is preferable that it is below the glass transition temperature. When multiple substances have a glass transition temperature, the glass transition temperature with the lower glass transition temperature is used as a reference. The drying time is preferably 0.5 to 24 hours, more preferably 1 to 18 hours, and further preferably 1.5 to 12 hours. If the drying temperature is too low, the removal rate of volatile components will be low, and it will take too long to dry. In addition, the drying process may be divided into two or more stages. For example, the drying process includes a preliminary drying process for storing materials and a previous drying process performed immediately before film formation to one week before. May be.

[0030] Melt casting film forming methods are classified as molding methods that are heated and melted, and melt extrusion molding methods, press molding methods, inflation methods, injection molding methods, blow molding methods, stretch molding methods, and the like can be applied. Among these, the melt extrusion method is excellent for obtaining an optical film excellent in mechanical strength and surface accuracy. Hereinafter, the film production method of the present invention will be described by taking the melt extrusion method as an example.

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

[0032] Referring to the figure, in the method for producing an optical film according to the present invention, a film material such as a cellulose resin is mixed and then melted from the casting die 4 onto the first cooling roll 5 using the extruder 1. Extruding and circumscribing the first cooling roll 5, and further circumscribing a total of three cooling rolls, that is, the second cooling roll 7 and the third cooling roll 8, in order to cool and solidify the final roll 10. Next, the film 10 peeled off by the peeling roll 9 is then stretched in the width direction by gripping both ends of the film by the stretching device 12, and then scraped off by the scraping device 16. In addition, a touch roll 6 is provided for pressing the molten film against the surface of the first cooling roll 5 in order to correct the flatness. The touch roll 6 has an elastic surface and forms a two-piece with the first cooling roll 5. [0033] Here, the cooling roll 5 is defined as a roll that transports the film and has a longer contact time with the film out of the two rolls that press the film, and the touch roll 6 is the film that is pressed. It is defined as a roll in contact with the film from the opposite side of the cooling roll 5.

[0034] In the method for producing an optical film according to the present invention, the touch roll 6 is provided with a pressing force control unit (not shown), and a transport film retardation measuring device 20 is installed on the way of transporting the film. The retardation value is measured online, and the retardation measurement value signal from the measuring instrument 20 is transmitted to the pressing force control unit of the touch roll 6, and the control unit pushes the retardation value signal based on the retardation measurement value signal. The pressure is adjusted in real time, and the retardation value of the transport film is controlled to be within a predetermined range.

[0035] In the pressing force control unit of the touch roll 6, based on the retardation measurement value signal from the measuring device 20, the difference between the maximum value and the minimum value of the retardation of the transport film is always 4 nm or less. Calculate the pressing force of the molten film on the surface of the cooling roll 5 with the touch roll 6 and adjust the pressing force with the touch roll 6 in real time.

Here, the pressure adjustment between the first cooling roll 5 and the touch roll 6 can be performed by adjusting the position with a motor while measuring the pressing force between the first cooling roll 5 and the touch roll 6 using a pressure sensor, The pressure between the mouths can be controlled appropriately by adjusting the pressure of the air cylinder or hydraulic cylinder. In the pressing force control unit of the touch roll 6, the position adjustment by these motors and the pressure adjustment by the air cylinder or hydraulic cylinder may be performed based on the retardation measurement value signal from the measuring device 20.

In the present invention, as an air cylinder that adjusts the pressing force by the touch roll 6 in real time, for example, an air cylinder MBL-100 manufactured by SMC Corporation can be used.

[0038] Further, in the present invention, as the retardation measuring device 20 for measuring the retardation value of the transport film online, for example, Kobra_WX150K manufactured by Oji Scientific Instruments Co., Ltd., which uses a photoelectric tube without contact, can be used. it can.

[0039] The conveyance film retardation measuring device 20 may be installed on the upstream side or on the downstream side of the stretching device 12. [0040] Here, if the retardation value of the transport film measured on-line by the retardation measuring instrument 20 is either the in-plane direction retardation (Ro) value or the thickness direction retardation (Rt) value, the good quality is obtained. ,. Ro indicates in-plane retardation, the difference between the refractive index in the longitudinal direction MD in the plane and the refractive index in the width direction TD is multiplied by the thickness, and Rt indicates the thickness direction retardation. It is the difference between the refractive index (average of longitudinal MD and width TD) and the refractive index in the thickness direction multiplied by the thickness.

[0041] In the method for producing an optical film according to the present invention, the width of the film when scraped is 1.5 m or more and 4. Om or less, and the film length force is, for example, 1000 m or more and 2600 m or less. ,preferable.

[0042] In the method for producing an optical film according to the present invention, it is preferable that the thickness of the film at the time of scraping is 15 zm or more and 60 zm or less.

[0043] In the method for producing an optical film according to the present invention, the conditions for melt extrusion can be carried out in the same manner as those used for other thermoplastic resins such as polyesters. It is preferable to dry the material in advance. Desirably, the moisture should be dried to 100 ppm or less, preferably 200 ppm or less, using a vacuum or vacuum dryer or dehumidifying hot air dryer.

[0044] For example, a cellulose ester resin dried under hot air, vacuum or reduced pressure is melted at an extrusion temperature of about 200 to 300 ° C using an extruder 1, and filtered through a leaf disk type filter 2 or the like. Remove foreign material.

[0045] When introducing into the extruder 1 from a supply hopper (not shown), it is preferable to prevent oxidative decomposition and the like under an inert gas atmosphere under vacuum or reduced pressure.

[0046] If 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 Static Mixer 3.

In the present invention, the cellulose resin and other additives such as a stabilizer added as necessary are preferably mixed before melting. More preferably, the cellulose resin and the stabilizer are mixed first. Mixing may be performed by a mixer or the like, or may be performed in the cellulose resin preparation process as described above. When using a mixer, V-type mixer, conical screw type mixer, horizontal cylindrical type mixer, etc. A general mixer such as a heater or a ribbon mixer can be used. Mixing is preferably performed in an atmosphere of an inert gas such as dehumidified air or nitrogen gas.

[0048] After the film constituent materials are mixed as described above, the mixture may be directly melted and formed into a film using the extruder 1, but once the film constituent materials are pelletized, The pellets may be melted by the extruder 1 to form a film. In addition, when the film constituent material includes a plurality of materials having different melting points, a so-called braided semi-melt is once produced at a temperature at which only the material having a low melting point is melted, and the semi-melt is extruded 1 It is also possible to form a film by throwing it into the film. If the film component contains a material that is easily pyrolyzed, the film can be formed directly without producing pellets for the purpose of reducing the number of melting times, A method of forming a film from is preferred.

[0049] Various extruders available on the market can be used as the extruder 1. However, the extruder 1 may be a single screw extruder or a twin screw extruder which is preferable for a melt kneading extruder. When forming a film directly without making pellets from film constituent materials, it is preferable to use a twin-screw extruder because an appropriate degree of kneading is required, but even with a single-screw extruder, the screw shape is a Maddock type. By changing to a kneading type screw such as a unimelt type or a dull mage, an appropriate kneading can be obtained, so that it can be used. Full flight type screws and double flight type screws are also preferably used. When pellets or braided semi-melts are used as the film constituent material, they can be used with either single-screw extruders or twin-screw extruders.

[0050] In the extruder 1 and in the cooling step after extrusion, it is preferable to reduce the oxygen concentration by replacing with an inert gas such as nitrogen gas or reducing the pressure.

[0051] The preferable conditions for the melting temperature of the film constituent material in the extruder 1 vary depending on the viscosity and discharge amount of the film constituent material, the thickness of the sheet to be produced, etc., but generally the glass transition temperature Tg of the finoleme. On the other hand, it is Tg or more and Tg + 100 ° C or less, preferably Tg + 10 ° C or more and Tg + 90 ° C or less. The melt viscosity at the time of extrusion is 10 to 100,000 boise, preferably 100 to 10,000 boise. In addition, a shorter residence time of the film constituent material in the extruder 1 is preferably within 5 minutes, preferably within 3 minutes, and more preferably within 2 minutes. The residence time depends on the type of extruder 1 and the extrusion conditions, but it can be shortened by adjusting the material supply amount, L / D, screw rotation speed, screw groove depth, etc. Is possible. L / D is preferably 10 or more and 40 or less, more preferably 20 or more and 35 or less.

. The compression ratio is preferably 2 or more and 4 or less.

[0052] The shape, rotation speed, and the like of the screw of the extruder 1 are appropriately selected depending on the viscosity of the film constituting material, the discharge amount, and the like. In the present invention, the shear rate in the extruder 1 is 1 Z seconds to 100.

00 / sec, preferably 5 / sec to 1000 / sec, more preferably 10 / sec to 100Z sec.

[0053] The extruder 1 that can be used in the present invention is generally available as a plastic molding machine.

The film constituent material extruded from the extruder 1 is sent to the casting die 4 and extruded from the slit of the casting die 4 into a film shape. The casting die 4 is not particularly limited as long as it can be used to manufacture sheets and films. As the material of the casting die 4, hard chromium, chromium carbide, chromium nitride, titanium carbide, titanium carbonitride, titanium nitride, super steel, ceramic (tungsten carbide, aluminum oxide, chromium oxide), etc. are sprayed or plated. Buffing as surface processing, lapping using # 1000 or higher whetstone, #cutting using diamond whetstone of # 1000 or higher (cutting direction is perpendicular to resin flow direction), electrolytic polishing, electrolytic composite polishing, etc. And the like. A preferred material for the lip portion of the casting die 4 is the same as that of the casting die 4. The surface accuracy of the lip is preferably 0.5 S or less, more preferably 0.2 S or less.

[0055] The slit of the casting die 4 is configured such that the gap can be adjusted. The force is omitted in the drawing. Of the pair of lips forming the slit of the casting die 4, one is a flexible lip with low rigidity and easily deformed, and the other is a fixed lip. A number of heat bolts are arranged at a constant pitch in the width direction of the casting die 4, that is, in the length direction of the slit. Each heat bolt is provided with a block having a loaded electric heater and a cooling medium passage, and each heat bolt passes through each block vertically. The base of the heat bolt is fixed to the die body, and the tip is in contact with the outer surface of the flexible lip. While the block is always air-cooled, the input of the embedded electric heater is increased or decreased to raise or lower the temperature of the block, thereby thermally expanding and contracting the heat bolt, and displacing the flexible lip to adjust the film thickness. A thickness gauge is installed at the required location in the wake of the die, and the web thickness information detected by this is fed back to the control device. The thickness information is set by the control device. Compared with the information, the power of the heating element of the heat bolt by the correction control amount signal coming from the device

Alternatively, the ON rate can be controlled. The heat bolt may preferably be a cylinder having a length of 20 to 40 cm and a diameter of 7 to 20 mm, or a prism having a side of 5 to 20 mm. A plurality of, for example, several tens of heat bolts are preferably arranged at a pitch of 20 to 40 mm. Instead of a heat bolt, a gap adjustment member mainly composed of a bolt that adjusts the slit gap by moving it back and forth in the axial direction manually can be provided. The slit gap adjusted by the gap adjusting member is usually preferably 500 to 1500 μm.

In the present invention, preferred materials for the first cooling roll 5 and the second cooling roll 7 include carbon steel, stainless steel, resin, ceramics, and the like. The surface accuracy is preferably increased, and the surface roughness is set to 0.3 S or less, more preferably 0.1 S or less.

[0057] The thickness of the second cooling roll 7 is preferably 0.5 mm to 10 mm, more preferably 2 mm to 5 mm 3.

[0058] The fluctuation of the first cooling roll 5 and the second cooling roll 7 is preferably 100 μm or less, more preferably 50 / im or less, and the roundness of the cooling roll is preferably 100 / im or less. More preferably, it is 50 μΐη or less, and the cylindricity of the cooling roll is preferably 100 / im or less, more preferably 50 μm or less. A structure that can be kept warm by flowing warm water or oil inside the cooling roll is preferable. The difference between the maximum value and the minimum value of the surface temperature of the cooling roll is preferably within 2 degrees.

[0059] The gap between the first cooling roll 5 and the second cooling roll 7 can be adjusted by a motor while measuring the pressing force between the first cooling roll 5 and the second cooling roll 7 using a pressure sensor. The pressure between the chill rolls can be suitably controlled by adjusting the pressure of the air cylinder or hydraulic cylinder.

[0060] It is preferable to provide a suction device in the vicinity of the casting die 4 to remove the sublimate. It is preferable to take measures such as heating with a heater so that the suction device itself does not become a place where the sublimate adheres. In the present invention, if the suction pressure is too small, the sublimate cannot be sucked effectively, so it is necessary to set the suction pressure appropriately.

[0061] In the present invention, a film-like cellulose ester-based resin in a molten state is sequentially transferred from the T die 4 to the first roll (first cooling roll) 5, the second cooling roll 7, and the third cooling roll 8. Unstretched cellulose ester-based resin film that is cooled and solidified while being transported in close contact

Get ten.

In the embodiment of the present invention shown in FIG. 1, the uncooled and solidified film 10 peeled off from the third cooling roll 8 by the peeling roll 9 has a dancer roll (film tension adjusting tool) 11. Then, the film is guided to a stretching device 12, where the film 10 is stretched in the transverse direction (width direction). By this stretching, the molecules in the film are oriented.

[0063] 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 a polarizing film can be performed in a roll form. By stretching in the width direction, the slow axis of the optical film, which is a 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 into the liquid crystal display device a polarizing plate that is laminated so that the transmission axis of the polarizing film and the slow axis of the optical film are parallel, the display contrast of the liquid crystal display device can be increased and good A great viewing angle can be obtained.

[0065] The glass transition temperature Tg of the film constituting material can be controlled by varying the kind of the material constituting the film and the ratio of the constituting material. When a retardation film is produced as an optical film, Tg is preferably 120 ° C or higher, preferably 135 ° C or higher. In the liquid crystal display device, in the image display state, the temperature environment of the film changes due to the temperature rise of the device itself, for example, the temperature rise derived from the light source. At this time, if the Tg of the film is lower than the operating temperature of the film, the retardation value derived from the orientation state of the molecules fixed inside the film by stretching and the dimensional shape of the film will be greatly changed. . If the Tg of the film is too high, the temperature when the film constituent material is converted into a film increases, so that the energy consumption for heating increases, and the material itself may be decomposed and colored due to the film formation. Therefore, Tg is preferably 250 ° C or lower.

[0066] In addition, the stretching process may be carried out using known heat setting conditions, cooling, and relaxation treatment. The stretching process may be appropriately adjusted to have the characteristics required for the target optical film.

[0067] To achieve a function as a retardation film for widening the viewing angle of a liquid crystal display device In addition, the stretching process and the heat setting process are appropriately selected and performed.

[0068] After stretching, the end of the film is slit to the product width by slitter 13 and cut off, and then the Narka mouth (embombosinda cache) is filmed by a knurling device comprising embossing ring 14 and back roll 15. Apply to both ends and scrape off with scissor 16 to prevent sticking in optical film (original scissors) F and scratches.

[0069] According to the method of knurling, a metal ring having a concavo-convex pattern on its side surface can be caloeed by heating or pressing. Note that the gripping parts of the clips at both ends of the film are usually deformed and cannot be used as film products, so they are cut out and reused as raw materials.

[0070] When the retardation film is a polarizing plate protective film, the thickness of the protective film is preferably 15 to 6 Ozm. When the retardation film is thick, the polarizing plate after polarizing plate processing becomes too thick, and it is not particularly suitable for the purpose of thin and light in the liquid crystal display used for the notebook type personal computer and mopile type electronic equipment. On the other hand, if the retardation film is thin, it is difficult to develop retardation as a retardation film, and the moisture permeability of the film is increased, and the ability to protect the polarizer from humidity is reduced, which is not preferable.

[0071] The optical film according to the present invention is manufactured by the above-described method for manufacturing an optical film of the present invention, and has a maximum value and a minimum value of the retardation value in the width direction and the longitudinal direction of the film. The difference has 4nm or less. According to the optical film of the present invention, the uniformity of the film retardation in the width direction is improved, and the optical film is excellent in optical characteristics.

[0072] The optical film stretched in the width direction obtained as described above has a fixed-size 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 retardation (Ro) of the film is 20 to 100 nm, and the thickness direction retardation (Rt). Les, preferably 90-200nm. Also, the ratio of Rt to Ro: Rt / Ro is 0.5 to 2.5 force S, preferably 1.0 to 2.0.

[0073] 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) X d

Rt = {(Nx + Ny) / 2-Nz} Xd.

[0074] The variation in retardation is preferably as small as possible, usually within 15 nm, preferably 1 Onm or less, more preferably 4 nm or less.

[0075] The resin used in the present invention is preferably cellulose acetate, cellulose propionate, cenololose butyrate, cenololose acetate propionate, cenololose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate. It ’s not limited. The degree of substitution of the acetyl group of the cellulose ester is at least 1.5 or more, which is preferable because the strength S and the dimensional stability of the resulting film are excellent. As a method for measuring the degree of substitution of the acyl group of cellulose ester, it can be carried out according to ASTM D_817-91. The molecular weight of the cellulose ester is 50,000 to 300,000, especially 60,000 to 200,000 as the number average molecular weight. This is preferable because the mechanical strength of the resulting Finolem can be increased.

In the present invention, in the amorphous thermoplastic resin, 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 are used for various purposes. Can be included.

[0077] Examples of the plasticizer include triphenyl phosphate, tricresyl phosphate, credinole diphenyl phosphate, otachinoresi phenino rephosphate, diphen eno rebi eno rephosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl Phosphate plastic plastics such as phosphate, trixylinophosphate, arylene bis (diaryl phosphate) ester, tricresyl phosphate, jetyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, Phthalate ester plasticizers such as dibutyl phthalate and di-2-ethylhexyl phthalate, triacetin, tributyrin, ethinoreglycolate, butynolephthalinorebutinoleglycolate and other groups Ricoholenic acid esterolate plasticizer, citrate plasticizer such as tributyl acetyl citrate, dipropyleneglycol monorebenzoate, tripropyleneglycolinoresevenzoate, 1,3_dibutyleneglycolinoresevenzoate, tetraethyleneglycolenoresiate Benzoate, trimethylone lepronone Examples thereof include polyhydric alcohol ester plasticizers such as triacetate and trimethylolpropane tribenzoate, and trimellitic acid tris (2-ethylhexyl). If necessary, two or more of the above plasticizers may be used in combination. These addition amounts are preferably 1% to 30% with respect to the thermoplastic resin in view of the effect of the plasticizer and bleed out.

[0078] Polyester ether, polyester monourethane, polyester, and the like can also be preferably used because they can improve plasticity by blending.

[0079] Polyester ethers include aromatic dicarboxylic acids having 8 to 12 carbon atoms or alicyclic dicarboxylic acids (eg terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid), carbon Atom 2 to: 10 aliphatic glycols or cycloaliphatic glycols (eg, ethylene diol, propylene diol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexane Xanthodimethanol and 1,5-pentanediol), polyether glycols having 2 to 4 carbon atoms between ether units (eg, polytetramethylene ether glycolone, especially 1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol and polytetramethylene ether glycol Copolyester ether) to component a Lumpur are preferred. The blending amount of the polyester ether is preferably 5 to 30% by mass with respect to the main resin. By setting the blending amount within this range, a film exhibiting good plasticity can be obtained.

[0080] Examples of the polyester urethane include a polyester urethane obtained by a reaction between a polyester and a diisocyanate. It has a repeating unit represented by the following general formula (1).

[0081] [Chemical 1] H «» r ^

In the general formula (1), 1 represents 2, 3 or 4, m represents 2, 3 or 4, and n represents:! 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.

[0083] As the polyester constituting the polyester monourethane, the glycol component is ethylene glycolol, 1, propanediol, or 1,4 butanediol, and the dibasic acid component is succinic acid, dartaric acid, or adipic acid. The polyester having hydroxyl groups at both ends and having a polymerization degree n of 1 to 100. Polyester molecular weight of 1,000 to 4,500. S Particularly desirable.

[0084] The diisocyanate component constituting the polyester monourethane includes polymethylene isocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and p-phenylene diisocyanate. , Tolylene diisocyanate, p, p ^r —diphenylmethane diisocyanate, 1,5_naphthyl Aromatic diisocyanates such as diisocyanate, m-xylylene diisocyanate and the like. Of these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are preferable because they are excellent in compatibility with cellulose esters.

[0085] The molecular weight of polyester urethane is preferably 2,000 to 50,000 force S, more preferably 5,000 to 15,000 force S. The synthesis of polyester monourethane can be easily obtained by a conventional synthesis method in which the above polyester and disoocyanate 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 dallicols, or by using these acids. It can be easily synthesized by adjusting the terminal group to be a hydroxyl group by any one of the interfacial condensation methods of acid chloride and glycols.

[0086] The blending amount of the polyester-urethane is preferably 5 to 30% by mass with respect to the main resin. When the blending amount is within this range, a film exhibiting good plasticity can be obtained.

[0087] 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.

[0088] Polyethylene glycol has the general formula

HO— (CH 2 CH −0) — H (wherein n is an integer) n is preferably 4 or less

2 2 n

Good.

[0089] Aliphatic dibasic acids have the general formula

Oxalic acid, malonic acid, succinic acid, adipic acid and the like represented by HOOC—R—COOH (wherein R is an aliphatic divalent hydrocarbon group), preferably having 9 or less carbon atoms.

[0090] The polyester is synthesized by a conventional method, a polyesterification reaction of the above dibasic acid or an alkyl ester thereof with a dallicol, a hot melt condensation method by transesterification, or an acid of these acids. It can be easily synthesized by any of the methods of interfacial condensation between chloride and glycols.

[0091] The blending amount of the polyester is preferably 5 to 30% by mass with respect to the main resin. By setting the blending amount within this range, a film exhibiting good plasticity can be obtained. [0092] As the antioxidant, a hindered phenol compound is suitable, and specific examples thereof include 2,6 di-tert-butyl-cresol, pentaerythrityl-tetrakis [3- (3, 5- Di-tert-butyl-4-hydroxyphenyl) propionate], triethylene glycol monobis [3_ (3_t_butyl-1-5-methyl_4_hydroxyphenyl) propionate], 1,6-hexanediol 1-bis [3- (3,5-di-tert-butyl-1-hydroxyphenyl) propionate], 2,4_bis_ (n-octylthio) 1- 6_ (4-hydroxy-1,3,5-di- t-Butylanilino) _ 1, 3, 5, 5-triazine, 2, 2-thiodiethylenebis [3_ (3,5-di-t_butyl_4-hydroxyphenyl) propionate], octadecyl-3_ (3, 5 —Di_t_butyl _4-hydroxyphenyl) propione 1, 3, 5 _trimethylol 2, 4, 6 _tris (3,5-di-t_butyl _4-hydroxybenzyl) benzene and tris (3,5-di-tert-butyl 4- (Hydroxybenzyl) monoisocyanurate, etc. In particular, 2,6-di_t_butyl_p_cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and triethylene glycol monobis [3- (3- t-butyl 5-methyl 4-hydroxyphenol) propionate] is preferred. Also, for example, hydrazine-based metal deactivators such as N, N'-bis [3- (3,5-dibutyl 4-hydroxyphenyl) propionyl] hydrazine, tris (2,4-dibutyl butylphenyl) ) Phosphorite and other phosphorus processing stabilizers may be used in combination. In order to obtain the effect, the amount of these compounds added is preferably from 1 ppm to 1.0% by mass with respect to the thermoplastic resin. 10 to:! OOOOppm force S Especially preferred.

In the present invention, examples of the ultraviolet absorber that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, and nickel complex salts. Compounds can be mentioned, but benzotriazole compounds with less coloring are preferred. 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 preferably used.

[0094] As an ultraviolet absorber, from the viewpoint of preventing deterioration of a polarizer and a liquid crystal, it has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and from the viewpoint of liquid crystal display properties, it absorbs visible light having a wavelength of 400 nm or more. There are few les and things are preferred. [0095] Specific examples of UV absorbers useful in the present invention include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-1 3 ', 5'-di-1 t ert butylphenyl) benzotriazole, 2— (2 ′ —hydroxyl 3 ′ — tert butynol 5 ′ —methylphenyl) benzotriazole, 2_ (2 ′ —hydroxyl 3 ′, 5′-di-tert-butylphenyl) _ 5_ cloguchibenzotriazole, 2 _ {2 '—hydroxyl 3 ^r — (3, “, 5”, <“—tetrahydrophthalimidomethyl) 1 5 ′ —methylphenyl) benzotriazole, 2, 2-methylenebis (4— (1, 1, 3, 3, 3-tetramethylbutyl) _6 — (2H—benzotriazole-2-yl) phenol), 2— (2 ′ —hydroxy 1-3′-tert_butyl-1-5′—methylphenyl) _ 5_ Black mouth Benzotriazole, 2_ (2H— Nzotriazole _ 2 _yl)-6-(Straight and side chain dodecyl) _4_Methylphenol, Octyl _ 3 _ [3 _tert_Butyl _4-Hydroxy mono 5 _ (Black mouth 2H-Benzotriazole _ 2 _Inole) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl 4-hydroxy-5- (5 chlorotriethyl 2H benzotriazole 2-yl) phenyl] propionate Power S, not limited to these, and commercially available products such as TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba 'Specialty' Chemicals) can be preferably used. The

[0096] Specific examples of benzophenone compounds include 2,4 dihydroxybenzophenone, 2, 2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-1-methoxy-1-5-sulfobenzophenone, bis (2-methoxy (4) hydroxy (1-5) benzoyl methane), and the like.

[0097] The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by mass with respect to the thermoplastic resin, and more preferably 0.1 to 5% by mass. If the amount used is too small, the UV 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.

[0098] 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. For example, the inorganic compound includes a compound containing silicon, diacid Silicon fluoride, aluminum oxide, dinoleconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate are preferred, more preferably Inorganic compounds containing zirconium and zirconium oxide. Of 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 200 V, Aerosilore R972V, Aerosilore R972, R974, R812, 200, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.) are preferable. Can be used.

[0099] The optical film obtained by the present invention can be made into a circularly polarizing plate by being bonded to at least one surface of a polarizing film.

[0100] The polarizing film is a film that has been conventionally stretched, for example, a film that can be stretched and oriented, such as a polybutyl alcohol film, treated with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, in general, a cellulose triacetate film having no anisotropy as a protective film is attached to both sides to form a polarizing plate. The optical film obtained by the present invention may be prepared by bonding to the polarizing plate with the protective film, or may be prepared by directly bonding to the polarizing film also serving as the protective film.

[0101] In particular, since the optical film obtained by the present invention has a slow axis in the width direction, it can be bonded to a polarizing film between long rolls without cutting, and production of a polarizing plate Sexually improves.

[0102] A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides via a pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer) (to peel off the peelable sheet). It can also be easily attached to a liquid crystal cell or the like.

[0103] The polarizing plate thus obtained can be used in various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal cell in which liquid crystal molecules are substantially vertically aligned when no voltage is applied is preferable.

Example

[0104] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. It ’s not what you ’ll get.

[0105] Implementation

100 parts by weight of cellulose acetate propionate

(Acetyl group substitution degree 1.4, propionyl group substitution degree 1

(Total degree of acyl substitution, number average molecular weight 60000)

10 parts by weight of trimethylolpropane tribenzoate (plasticizer)

Additive (IRGANOX—XP—420 / FD) 1 part by mass

(Ciba Specialty Chemicals)

UV absorber Ti928 5 parts by mass

(Ciba Specialty Chemicals)

Matting agent (average particle size 0.3 z m silica fine particles) 0.1 parts by mass

(Seahoster KEP-30: manufactured by Nippon Shokubai Co., Ltd.)

The method for measuring the degree of substitution of an acyl group such as an acetyl group, propionyl group, or pentyl group was measured according to ASTM-D817-96.

[0106] After mixing the mixture of the above materials with a V-type mixer for 30 minutes, it was melted at 220 ° C with a twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) shown in Fig. 1 and was 4mm in length and diameter. A 3 mm cylindrical pellet was produced. At this time, nitrogen was also added to the extruder 1 inlet force to reduce the oxygen concentration.

[0107] Next, pellets were supplied to a single-screw extruder (GT-50, manufactured by Plastic Engineering Laboratory Co., Ltd.) 1 having a diameter of 50 mm, to which a T-die 4 was attached, to form a film. The set temperature of the extruder 1 was 250 ° C., and the T-die 4 was a coat hanger type.

[0108] T die 4 outlet force The temperature of the casting die 4 was set so that the temperature T1 of the extruded material was 250 ° C. The melt-extruded film was dropped into a gap formed by the first cooling roll 5 and the touch roll 6 so as to be in contact with the first cooling roll 5 and the touch roll 6 having a diameter of 350 mm whose temperature was adjusted to 100 ° C. at the same time. After finishing the first cooling roll 5 in close contact with the first cooling roll 5, it was pressed by the touch roll 6 after being transported around the circumference of the first cooling roll 5 having a central angle of 5 °. The entire width of the film, 1500 mm, was contacted at a pressure of 0.39 MPa. [0109] In the method for producing an optical film according to the present invention, the touch roll 6 is provided with a pressing force control unit (not shown), and the conveyance film retardation measuring device 20 is placed at a predetermined interval in the width direction while the film is being conveyed. Open two, install two units, measure the retardation values at two points with different width directions of the transport film online, and send the retardation measurement value signal from this measuring device 20 to the pressure control unit of Touch Roll 6 In the control unit, the pressing force by the touch roll 6 is adjusted in real time based on this retardation measurement value signal, and the retardation value of the transport film is controlled to be within a predetermined range.

[0110] In the pressing force control unit of the touch roll 6, based on the retardation measurement value signal from the measuring device 20, the difference between the maximum value and the minimum value of the retardation of the transport film is always 4 nm or less. Calculate the pressing force of the molten film on the surface of the cooling roll 5 with the touch roll 6 and adjust the pressing force with the touch roll 6 in real time.

[0111] In this example, the gap between the first cooling roll 5 and the touch roll 6 was controlled by adjusting the pressure of the air cylinder. In the pressure control unit of the touch roll 6, the pressure was adjusted by the air cylinder based on the retardation measurement value signal from the measuring device 20. Here, the air cylinder MBL-100 manufactured by SMC Corporation was used as the air cylinder, and the pressing force by the touch roll 6 was adjusted in real time.

[0112] Further, in this example, as the retardation measuring device 20 for measuring the retardation value of the transport film online, Kobra-WX150K manufactured by Oji Scientific Instruments Co., Ltd., which uses a photoelectric tube without contact, is used. The retardation measuring device 20 was installed between the stretching device 12 and the scraping device 16. In addition, the retardation value of the transport film measured online by the retardation measuring instrument 20 is the in-plane direction retardation (RoM direct).

[0113] The in-plane direction retardation (Ro) value of the transport film measured by the retardation measuring instrument 20 is 29.7 nm on the left side, 30.6 nm on the left side, and 30.6 nm on the right side. The difference between the maximum value and the minimum value of the in-plane direction retardation (Ro) value of the transport film was 4 nm or less.

[0114] The pressed film comes into contact with the circumferential portion of the first cooling roll 5 with a central angle of 150 °. The second cooling roll 7 and the third cooling roll 8 are brought into close contact with each other and cooled and solidified while being conveyed to obtain an unstretched cell mouth ester-based resin film 10.

In the embodiment of the present invention shown in FIG. 1, the cooled and solidified unstretched film 10 peeled from the third cooling roll 8 by the peeling roll 9 has a dancer roll (film tension adjusting tool) 11. Then, the film is guided to a stretching device 12, where the film 10 is stretched in the transverse direction (width direction). By this stretching, the molecules in the film are oriented.

[0116] After stretching, the end of the film is slit to the product width by slitter 13 and cut off, and then the Narka mouth (embombosinda cache) is filmed by a knurling device consisting of embossing ring 14 and back roll 15. Cellulose acetate propionate film F (original milling) F having a width of 1500 mm and a length of 2600 m was obtained by applying to both ends and scraping with a scraper 16. The extrusion amount and the number of rotations of the take-up roll were adjusted so that the thickness of the film F that had been scraped off was 40 μm.

[0117] Comparative Example 1

For comparison, the same operation as in Example 1 is performed, but the difference from Example 1 is that a transport film retardation measuring device 20 is installed, and the in-plane direction of the transport film is retarded (Ro). The force to measure the value on-line at two points This point is that the pressing force of the touch roll 6 was not controlled based on the in-plane direction retardation (Ro) value of this transport film.

As a result, in Comparative Example 1, the in-plane direction retardation (Ro) value of the transport film measured by the retardation measuring device 20 is 27.2 nm on the left side and Max force on the left side of the two points. · 7 nm, Min on the right side is 28.3 nm, Max on the right side is 37.2 nm, and the difference between the maximum and minimum in-plane retardation (Ro) values of the transport film is greater than 8 nm. It was a thing.

Thus, the cellulose acetate propionate film according to Example 1 of the present invention is

The difference between the maximum value and the minimum value of the in-plane retardation (Ro) value in the width direction and the longitudinal direction of the film is 4 nm or less, improving the uniformity of the film retardation in the width direction. Thus, the optical properties were excellent.

[0120] Example 2 Next, the present invention is carried out in the same manner as in the first embodiment, but the difference from the first embodiment is that the retardation value of the transport film measured online by the retardation measuring device 20 is used as the retardation value in the thickness direction. It is at the point where the (Rt) value was measured.

[0121] As a result, the thickness direction retardation (Rt) value of the transport film measured by the retardation measuring instrument 20 was 118. Onm on the left side and Max. Force 120.2 nm on the left side of the two points. The Min was 117.3 nm, and the right Max was 119.7 nm. In either case, the difference between the maximum and minimum thickness direction retardation (Rt) values of the transport film was 4 nm or less.

[0122] Comparative Example 2

For comparison, the same procedure as in Example 2 is performed, but the difference from Example 2 is that a transport film retardation measuring device 20 is installed and the transport film thickness direction retardation (Rt) value is set. The two points are measured online, but the pressing force of the touch roll 6 is not controlled based on the thickness direction retardation (Rt) value of the transport film.

[0123] As a result, in Comparative Example 1, the thickness direction retardation (Rt) value of the transport film measured by the retardation measuring instrument 20 is 26.4 of the left side Min is 116.4 nm, and the left side Ma X is 123. · 7 nm, right side Min is 114. 2 mm, right side Max is 122. 3 mm, both of which are the differential force between the maximum and minimum retardation (Rt) values in the thickness direction of the transport film \ 7 nm It was a big thing beyond.

Thus, in the cellulose acetate propionate film according to Example 2 of the present invention, the difference between the maximum value and the minimum value in the thickness direction retardation (Rt) in the width direction and the longitudinal direction was 4 nm. The film had the following characteristics, and improved uniformity in the width direction of the retardation of the film, and was excellent in optical characteristics.

Claims

The scope of the claims

[1] Amorphous thermoplastic resin is melted and extruded from a casting die onto a rotating support, the molten resin on the support is pressed against the surface of the support by pressing means, and cooled and solidified to form a finalem. In the method for producing an optical film by the melt casting film forming method, after peeling the film from the support, transporting it by a transporting means, and winding it by a scissoring device,

The retardation value of the film is measured with a retardation measuring device installed on the way of conveyance by the conveying means, and the pressing force of the pressing means against the support is measured based on the retardation value measured by the measuring device. Is adjusted in real time, and the retardation value of the film is controlled to be within a predetermined range.

[2] The method for producing an optical film according to [1], wherein the retardation measuring instrument measures a retardation value of the film at a plurality of positions in the width direction.

[3] The pressing force of the pressing means against the support is adjusted in real time so that the difference between the maximum value and the minimum value of the retardation value measured by the retardation measuring device is 4 nm or less. The method for producing an optical film according to claim 1.

[4] Retardation value force The method for producing an optical film according to any one of claims 1 to 3, wherein the retardation value is an in-plane direction retardation value or a thickness direction retardation value. .

[5] The optical according to any one of claims 1 to 3, wherein the width of the film at the time of wiping is 1.5 m or more and 4. Om or less. A method for producing a film.

[6] The optical device according to any one of claims 1 to 3, wherein the thickness of the film at the time of peeling is 15 μm or more and 60 μm or less. Film production method

[7] The maximum value of the retardation value produced by the method for producing an optical film according to any one of claims 1 to 3 and within the film width direction and the longitudinal direction. An optical film characterized in that the difference between the minimum value and the minimum value is 4 nm or less.