WO2012056665A1 - Method for producing optical film, optical film, polarizing plate using optical film, and display device - Google Patents

Abstract

The present invention cleans the surface of a support with high efficiency. A method for producing an optical film (F) in accordance with a melt-casting film formation process in which a resin melt is cast onto a support (5) involves: a first step of removing contamination on the surface of the support (5) by subjecting the exposed surface of the support (5) to atmospheric-pressure plasma irradiation, excimer ultraviolet irradiation, or laser irradiation during a period after peeling, from the support (5), the film (10) prepared from the cast resin melt until casting the resin melt onto the support (5) again; and a second step of further removing contamination on the surface of the support (5) by again subjecting the surface of the support (5) to atmospheric-pressure plasma irradiation, excimer ultraviolet irradiation, or laser irradiation, or by bringing a tangible article into contact with the surface of the support (5), after the first step.

Description

Manufacturing method of optical film, optical film, polarizing plate using optical film, and display device

The present invention provides an optical film that can be used for various functional films such as a protective film for a polarizing plate used in a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used in a plasma display. The present invention relates to a method, an optical film, a polarizing plate using the optical film, and a display device.

Conventionally, liquid crystal display devices have been used in televisions, large monitors, and the like due to improvements in image quality and high definition technology. In recent years, with an increase in size of a liquid crystal display device, it is required to widen the optical film, and with an increase in demand for the liquid crystal display device, a cost reduction of the optical film is required. That is, it is required to efficiently produce a wide optical film.

Optical film production methods are roughly classified into a melt casting film forming method and a solution casting film forming method. The former extrudes a resin melt obtained by heating and melting the resin from a casting die and casts it on a support such as a roll, and after cooling and solidifying, peels the obtained film from the support, and if necessary This is a method for producing an optical film by performing stretching or heat treatment. The latter is a film obtained by discharging a resin solution (dope) obtained by dissolving a resin in a solvent from a casting die onto a support such as an endless belt or drum, and evaporating the solvent by heating. Is peeled off from the support and subjected to stretching, heat treatment or the like as necessary to produce an optical film.

Patent Document 1 discloses a method for producing a film while irradiating the roll surface used for producing the film with ultraviolet rays with an excimer UV lamp to remove deposits on the roll surface. In Patent Document 2, an organic substance adhering to the surface of a support is removed by spraying dry ice, supplying oxygen radicals, irradiating ultraviolet rays or a laser, and removing the organic substance from the support by a casting film. It is disclosed that after the film is peeled off, the casting film is again formed on the surface of the support before being formed on the support.

JP 2003-89142 A JP 2008-207367 A

Since both the melt casting film forming method and the solution casting film forming method cast a resin melt or resin solution on the surface (circumferential surface) of the support, the obtained film is removed from the support. After peeling, there is a problem that, for example, cellulose ester-based resin or a decomposition product thereof, or an additive such as a plasticizer or an ultraviolet absorber or a contamination derived from the decomposition product remains on the surface of the support. . If dirt remains on the surface of the support, the peelability of the film decreases, the peel force increases, and the film is easily deformed. Alternatively, the shape of the dirt on the support surface is transferred to the film. Alternatively, dirt may be transferred to the film. As a result, variation in the crossed Nicols transmittance of the optical film and unevenness of the polarizing plate using the optical film occur.

Therefore, it is proposed to clean the support surface during use of the support. In addition, while the support is being used, while the optical film is manufactured using the support, more specifically, the film obtained by casting a resin melt or resin solution on the support is supported. This means that after peeling from the body, the operation of casting the resin melt or resin solution on the support again is repeated, that is, during the production of the optical film (during film formation).

In order to clean the support surface during production of the film (during use of the support), the film must be cleaned while the support surface is exposed. For that purpose, as disclosed in Patent Document 2, the surface of the support is cleaned after the film is peeled from the support and before the resin melt or the resin solution is cast again on the support. There is a need. For example, the diameter of the support (roll or drum) is 100 to 1000 mm, the film transport speed by the support is 50 to 200 m / min (0.83 to 3.33 m / sec), the resin melt or Assuming that the rotation angle of the support to the casting position of the resin solution is 90 ° (1/4 rotation), the time during which the support surface is exposed is approximately 0.025 to 0.9 seconds ( On the other hand, the time during which the support surface is coated with the resin melt or resin solution is approximately 0.075 to 2.7 seconds).

That is, even if the support surface is continuously cleaned while the support surface is exposed, the time at which a predetermined portion of the support surface can be cleaned at a time is at most about 1 second, It is relatively short. Therefore, it is difficult to completely remove the dirt from the support surface during that time, and a small amount of dirt is likely to remain on the support surface. If even a small amount of dirt remains on the surface of the support, the dirt accumulates on the surface of the support with the passage of time of use of the support. It will be necessary to stop and clean the entire support over time. This problem becomes more prominent as the film transport speed (rotational speed of the support) is increased by the support in order to increase the production speed of the optical film. Therefore, when manufacturing the film and cleaning the support surface in parallel, there is a demand for a technique capable of cleaning the support surface with high efficiency that has not been achieved in the past.

In the case of cleaning the support surface while producing an optical film, the present invention cleans the support surface with unprecedented high efficiency, removes most of the dirt in a relatively short time, and thus a film over a long period of time. The purpose is to enable high-speed production and continuous production.

One aspect of the present invention is a method for producing an optical film by a melt casting film forming method for casting a resin melt on a support or a solution casting film forming method for casting a resin solution. After peeling the film obtained from the resin melt or the resin solution from the support, the atmospheric pressure plasma is applied to the surface of the exposed support until the resin melt or the resin solution is cast on the support again. A first step of removing contamination on the surface of the support by irradiation, excimer ultraviolet irradiation or laser irradiation; and after the first step, the surface of the support is again exposed to atmospheric pressure plasma and excimer ultraviolet irradiation. Or a second step of further removing dirt on the surface of the support by performing laser irradiation or bringing a tangible object into contact with the surface of the support.

Another aspect of the present invention is an optical film manufactured by the above manufacturing method.

Still another aspect of the present invention is a polarizing plate characterized by using the optical film on at least one surface.

Still another aspect of the present invention is a display device using the optical film or the polarizing plate.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a schematic flow sheet showing a first embodiment of an apparatus for carrying out the method for producing an optical film of the present invention. FIG. 2 is a main part enlarged flow sheet of the manufacturing apparatus of FIG. FIG. 3 is a flow sheet showing a second embodiment of an apparatus for carrying out the method for producing an optical film of the present invention. FIG. 4 is a flow sheet showing a modification of the apparatus of FIG. FIG. 5 is an explanatory diagram for explaining the principle of an atmospheric pressure plasma irradiation apparatus used in the method for producing an optical film of the present invention. FIG. 6 is an explanatory diagram for explaining the principle of an excimer ultraviolet irradiation device used in the method for producing an optical film of the present invention.

Hereinafter, embodiments of the present invention will be described, but the present invention should not be construed as being limited to these embodiments.

The present inventor has repeatedly studied on the development of a technology capable of cleaning the support surface with high efficiency while manufacturing an optical film. As a result, high energy such as atmospheric pressure plasma irradiation, excimer ultraviolet irradiation, and laser irradiation is applied to the support surface. After irradiating the beam, the surface of the support is again irradiated with high energy rays, or when a tangible object such as a liquid or cloth is brought into contact with the surface of the support, the surface of the support is not contaminated with high efficiency. The invention was completed by finding that it was almost eliminated.

That is, the method for producing an optical film according to the present embodiment is a method for producing an optical film by a melt casting film forming method for casting a resin melt on a support or a solution casting film forming method for casting a resin solution. An exposed support after the film obtained from the cast resin melt or resin solution is peeled off from the support and before the resin melt or resin solution is cast again on the support. A first dirt removing step for removing dirt on the surface of the support by performing normal pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation on the surface of the substrate, and after the first dirt removing step, In addition, a second soil removing process is performed in which the dirt on the surface of the support is further removed by performing normal pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation again, or by bringing a tangible object into contact with the surface of the support. And, the has.

In the present embodiment, in addition to the first dirt removal step that has been conventionally performed, the second dirt removal step is further performed, so that the dirt on the support surface that has not been removed in the first dirt removal step (this In the dirt, the dirt that was decomposed by the high energy beam irradiation in the first dirt removing process but still adhered to the surface of the support is included). Even in a relatively short time, the dirt is removed with a high efficiency that has never been achieved.

As a method for removing the contamination on the support surface with high efficiency, for example, high energy beam irradiation such as atmospheric pressure plasma irradiation, excimer ultraviolet irradiation, laser irradiation and the like can be performed with increased output. However, the surface of the support is roughened, thereby reducing the peelability of the film. In this embodiment, instead of increasing the output of high energy beam irradiation, high energy beam irradiation is performed a plurality of times, or after high energy beam irradiation, by touching the support surface with a tangible object, Without increasing the output, dirt on the surface of the support is removed with high efficiency. Therefore, in this embodiment, the film peelability deterioration due to the rough surface of the support is avoided.

In this embodiment, the support is made of metal. As the metal support, for example, in the case of a belt, an endless belt made of stainless steel (SUS316, SUS304, etc.) is preferably used. For example, in the case of a cooling roll, a stainless steel drum is hard chrome plated. A roll can be preferably used.

In the method for manufacturing an optical film according to the present embodiment, the first step and the second step are performed in this order on the surface of the exposed support during use of the support, that is, during the manufacture of the optical film. Do. Thereby, in the case where the support surface is cleaned while manufacturing the optical film, the support surface can be cleaned with high efficiency unprecedented, and dirt can be almost removed in a relatively short time.

The normal pressure plasma irradiation can be performed using, for example, a normal pressure plasma irradiation apparatus as shown in FIG. Excimer ultraviolet irradiation can be performed using, for example, an excimer ultraviolet irradiation apparatus as shown in FIG. For the laser irradiation, for example, an irradiation apparatus such as a YAG laser, an argon laser, or an excimer laser can be used without any particular limitation.

In the present embodiment, the resin of the resin melt or resin solution is a thermoplastic resin, and particularly preferably a cellulose ester resin. This is because an optical film with high transparency is produced.

In this embodiment, the metal support is either a roll from which a resin melt is cast by a melt casting film forming method, an endless belt or a drum from which a resin solution is cast by a solution casting film forming method. It is. In the present embodiment, the optical film can be produced by a melt casting film forming method or a solution casting film forming method.

First, a method for producing an optical film by a melt casting method will be described. Melt casting film forming methods are classified into 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, in order to obtain an optical film excellent in mechanical strength and surface accuracy, the melt extrusion method is excellent. Hereinafter, the film production method of the present embodiment will be described by taking the melt extrusion method as an example.

In the method for producing an optical film by the melt casting film forming method of the present embodiment, the film constituent material to be used is mainly a pellet-shaped material, and is preferably dried before film formation. The moisture content of the pellets after drying is preferably 500 ppm or less, more preferably 200 ppm or less.

As the dryer, a dehumidifying hot air dryer, a ribbon type heat transfer vacuum dryer, a screw type heat transfer vacuum dryer, or the like can be preferably used, but is not limited thereto.

When using a vacuum dryer, the degree of vacuum is preferably 0.01 Pa or less, more preferably 0.03 Pa or less. The temperature is preferably 50 ° C. or higher and 150 ° C. or lower. More preferably, it is 80 degreeC or more and 120 degrees C or less. It is preferable to put nitrogen gas into the dryer during drying. When returning from the vacuum state to the atmospheric pressure, it is preferable to add dehumidified air or nitrogen gas.

When a dehumidifying hot air dryer is used, the dew point of the dehumidifying air is preferably −20 ° C. or lower, more preferably −40 ° C. or lower.

Pneumatic transportation is preferred as a method for transferring from the dryer to the extruder. The air used for transportation is preferably dehumidified. Pellets that are pneumatically transported from the dryer are placed in a hopper above the extruder, but there is a powder collector on the hopper to remove small debris and powder from the pellets that are transported along with the pellets Is preferred. In the collector, pellets and powder are separated by the force of air, and only the powder is removed. The hopper is preferably kept warm. The temperature is preferably 50 ° C. or higher and 150 ° C. or lower. More preferably, it is 80 degreeC or more and 120 degrees C or less. It is preferable to put dehumidified air into the hopper.

FIG. 1 is a schematic flow sheet showing the overall configuration of an apparatus for carrying out the method for producing an optical film by the melt casting method of the present invention, and FIG. 2 shows a cooling roll (5) from a casting die (4). It is an enlarged view of a part. Note that the implementation of the present invention is not limited to the process of the drawings shown below.

1 and 2, 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 a leaf disk type filter (2) Filter through to remove foreign matter.

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

When additives such as 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).

It is preferable that a resin such as a cellulose resin and other additives such as a stabilizer added as necessary are mixed before melting. Mixing may be performed by a mixer or the like, or as described above, mixing may be performed in a resin preparation process such as a cellulose resin. When a mixer is used, 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.

After the film constituent materials are mixed as described above, the mixture may be directly melted and formed into a film using an extruder (1), but once the film constituent materials are pelletized, the pellets May be melted with an extruder (1) to form a film. Further, 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 a material having a low melting point is melted, and the semi-melt is extruded (1). ) To form a film. If the film component contains a material that is easily pyrolyzed, in order to reduce the number of times of melting, a method of directly forming a film without producing pellets, A method of forming a film is preferred.

As the extruder (1), various commercially available extruders can be used, but a melt-kneading extruder is preferable, and a single-screw extruder or a twin-screw extruder may be used. When forming a film directly without producing pellets from film constituent materials, it is preferable to use a twin-screw extruder because an appropriate degree of kneading is required. However, 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, moderate kneading can be obtained, so that it can be used. When a pellet or braided semi-melt is once used as a film constituent material, it can be used in either a single screw extruder or a twin screw extruder.

In the extruder (1) and after the extrusion, the cooling step is preferably performed by substituting with an inert gas such as nitrogen gas or reducing the pressure to reduce the oxygen concentration.

Although 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., in general, the glass transition of the film (resin mixture) The temperature (Tg) 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 poise, preferably 100 to 10,000 poise. Further, the residence time of the film constituting material in the extruder (1) is preferably short, and is within 5 minutes, preferably within 3 minutes, more preferably within 2 minutes. The residence time depends on the type of the 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, and the like. Is possible.

The shape and rotation speed of the screw of the extruder (1) are appropriately selected depending on the viscosity and the discharge amount of the film constituting material. In this embodiment, the shear rate in the extruder (1) is 1 / second to 10,000 / second, preferably 5 / second to 1000 / second, more preferably 10 / second to 100 / second. As the extruder (1), an extruder generally marketed as a plastic molding machine can be used.

The film constituting material extruded from the extruder (1) is sent to the casting die (4) and extruded from the casting die (4) into a film shape.

The melt discharged from the extruder (1) is supplied to the casting die (4). The casting die (4) is not particularly limited as long as it is used for producing a sheet or a film. 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 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.

The preferred material of 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 0.5S or less, and more preferably 0.2S or less.

In the method for producing an optical film by the melt casting film forming method of the present invention, after mixing film materials such as cellulose resin, the resin melt from the die lip of the casting die (4) using the extruder (1). To form a cast film on the surface of the cooling roll (5).

In this embodiment, the cooling roll (5) as a metal support is a roll obtained by applying hard chrome plating to a stainless steel drum, and a melt casting film forming method is performed on the surface of the metal support (5). The thermoplastic resin melt in is cast.

As described above, the casting film is brought into contact with the first cooling roll (5), and is circumscribed by the first cooling roll (5), and further, the second cooling roll (7) and the third cooling roll (8). In total, three cooling rolls are circumscribed in order to cool and solidify to form a film (10).

In order to extrude the resin melt from the casting die (4) in the form of a film and to take out the extruded casting film (film), it is brought into close contact with at least two rotating bodies (cooling rolls) to form the film. To do.

Here, in order to correct the flatness, a touch roll (6) for sandwiching the molten film on the surface of the first cooling roll (5) is provided. The touch roll (6) has an elastic surface and forms a nip with the first cooling roll (5).

The embodiment of the present invention shown in FIG. 1 and FIG. 2 is different in that the cast film first contacts the surface of the first cooling roll (5) and the film contacts the surface of the touch roll (6). The embodiment which has shown is shown.

Although not shown, the cast film from the casting die (4) first contacts the surface of the first cooling roll (5) and the cast film contacts the surface of the touch roll (6). The point may be the same.

In this embodiment (melt casting film forming method), the cooling and solidifying temperature of the resin melt on the first cooling roll (5) is adjusted to 180 ° C. or lower.

Furthermore, in the embodiment of the present invention shown in FIGS. 1 and 2, the cooled and solidified film (10) peeled from the third cooling roll (8) by the peeling roll (9) is a dancer roll (film tension adjusting roll). Through (11), 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.

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.

After stretching, the end of the film is slit to a product width by a slitter (13) and cut off, and then knurled (embossed) by a knurling device comprising an embossing ring (14) and a back roll (15). By applying to both ends of the film and winding by the winding device (16), sticking in the optical film (original winding) (F) and generation of scratches 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.

In the method for producing an optical film of the present invention, various resins can be used as a film material. Among them, cellulose ester, particularly cellulose acylate is preferable.

Cellulose as a cellulose acylate raw material is not particularly limited, and examples thereof include cotton linter, wood pulp, and kefna. Moreover, you may mix and use the raw material cellulose obtained from these in arbitrary ratios. The cellulose acylate is preferably a cellulose acylate having an acetyl group or an acyl group having 3 to 22 carbon atoms. Examples of the acyl group having 3 to 22 carbon atoms include propionyl (C ₂ H ₅ CO—), n-butyryl (C ₃ H ₇ CO—), isobutyryl, valeryl (C ₄ H ₉ CO—), isovaleryl, Includes sec-valeryl, tert-valeryl, octanoyl, dodecanoyl, octadecanoyl and oleoloyl. Propionyl and butyryl are preferred. As the cellulose acylate, cellulose acetate is preferable, and cellulose triacetate is particularly preferable.

When the acylating agent for the acyl group is an acid anhydride or acid chloride, an organic acid (eg, acetic acid) or methylene chloride is used as the organic solvent as the reaction solvent.

Cellulose acylate preferably has a substitution degree of hydroxyl group of cellulose of 2.6 to 3.0. The degree of polymerization (average viscosity) of cellulose acylate is preferably 200 to 700, and particularly preferably 250 to 550.

These cellulose acylates are commercially available from Daicel Chemical Industries, Ltd., Courtles, Hoechst, and Eastman Kodak. Photographic grade cellulose acylate is preferably used. The water content of the cellulose acylate is preferably 2% by weight or less.

The β-1,4-bonded glucose unit constituting cellulose has free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with acetic acid or other acids. The degree of acyl substitution means the proportion of cellulose esterified at each of the 2-position, 3-position and 6-position (100% esterification is 1.00).

The cellulose acylate used in the present invention has a total acyl substitution degree of 2-position and 3-position of 1.70 to 1.95, and the acyl substitution degree of 6-position is 0.88 or more, It is obtained by blending cellulose acylate having a total acyl substitution degree at the 2nd and 3rd positions of 1.70 to 1.95 and an acyl substitution degree at the 6th position of less than 0.88. When the total of the 2- and 3-position acyl substitutions is 1.70 or less, the film is likely to absorb moisture and is susceptible to hydrolysis, so the durability of the film is lowered. In addition, the dimensional change due to humidity or the like becomes large. On the other hand, if it exceeds 1.95, the organicity of cellulose acylate increases, so the affinity with the solvent increases and the viscosity of the dope increases. Accordingly, the total of the 2- and 3-position acyl substitutions is preferably 1.70 to 1.95, and more preferably 1.75 to 1.88.

By the way, since the hydroxyl group at the 6-position is a primary hydroxyl group, unlike the hydroxyl groups at the 2- and 3-positions, it has been found that hydrogen bonding of the hydroxyl group is very likely to occur. Therefore, by setting the acyl substitution degree at the 6-position to 0.88 or more, the solubility in a solvent is remarkably improved, and it is possible to obtain a dope that is preferable in terms of casting suitability. The range of the degree of acyl substitution at the 6-position is preferably from 0.88 to 0.99, more preferably from 0.89 to 0.98 in view of synthesis suitability and the like. However, when the degree of acyl substitution at the 6-position is improved, there is a problem that the film strength is lowered, and it is difficult to achieve both. On the other hand, if the acyl substitution degree is less than 0.88, the solubility in a solvent is remarkably lowered, which is not preferable.

Further, a film made of cellulose acylate having a total acyl substitution degree at the 2nd and 3rd positions of 1.70 to 1.95 and an acyl substitution degree at the 6th position of 0.88 or more, In the roll state, an optical film in which a thin film is formed on a film made of cellulose acylate having a total acyl substitution degree of 1.70 to 1.95 and a acyl substitution degree of 6-position of less than 0.88. There has been a problem that flatness such as wrinkles and dents is liable to occur during storage, and the formed metal oxide layer is liable to crack, resulting in uneven film thickness.

It has been found that these problems can be solved by blending cellulose acylate. In addition, cellulose acylate having an acyl substitution degree at the 6-position of 0.88 or more desirably has a smaller number of carbon atoms in the acyl substituent from the viewpoint of film strength, and is preferably all acetyl groups. In JP-A-11-5851, the total of acetyl substituents at the 2nd, 3rd and 6th positions is 2.67 or more, and the total of the acetyl substituents at the 2nd and 3rd positions is 1.97 or less. Although cellulose acetate is described, the range in which the sum of the 2nd and 3rd positions exceeds 1.90 is a preferred range from the optical suitability of the film, and the casting suitability is described in this specification. The range described is more preferable.

The basic principle of the cellulose acylate synthesis method is described in Mita et al., Wood Chemistry pages 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method is a liquid phase acetylation method using an acetic anhydride-acetic acid-sulfuric acid catalyst. Specifically, a cellulose raw material such as wood pulp is pretreated with an appropriate amount of an organic acid, and then it is esterified by adding it to a pre-cooled acylated mixture to complete cellulose acylate (2nd, 3rd and 6th positions). The total degree of acyl substitution is approximately 3.00). The acylated mixed solution generally contains an organic acid as a solvent, an anhydrous organic acid as an esterifying agent, and sulfuric acid as a catalyst. The organic anhydride is usually used in a stoichiometric excess over the sum of the cellulose that reacts with it and the water present in the system. After completion of the acylation reaction, a neutralizing agent (for example, calcium, magnesium, iron, aluminum or zinc) is used for hydrolysis of excess organic anhydride remaining in the system and neutralization of a part of the esterification catalyst. Of carbonate, acetate or oxide).

Next, the obtained complete cellulose acylate is saponified and aged by maintaining it at 50 to 90 ° C. in the presence of a small amount of an acetylation reaction catalyst (generally, remaining sulfuric acid), and the desired degree of acyl substitution and The cellulose acylate having a polymerization degree is changed. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized with the neutralizing agent as described above, or water or dilute sulfuric acid without neutralization. A cellulose acylate solution is introduced into the cellulose acylate solution (or water or dilute sulfuric acid is introduced into the cellulose acylate solution) to separate the cellulose acylate, and the cellulose acylate is obtained by washing and stabilizing treatment.

In the usual cellulose acylate synthesis method, the acyl substitution degree at the 2nd or 3rd position is higher than the acyl substitution degree at the 6th position. Therefore, in order to make the total acyl substitution degree at the 2nd and 3rd positions 1.95 or less and the acyl substitution degree at the 6th position 0.88 or more, the above reaction conditions need to be specifically adjusted. . As specific reaction conditions, it is preferable to reduce the amount of the sulfuric acid catalyst and lengthen the time of the acylation reaction. When the amount of the sulfuric acid catalyst is large, the acylation reaction proceeds faster, but a sulfuric ester is formed between the cellulose and the cellulose according to the amount of the catalyst, and is released at the end of the reaction to form a residual hydroxyl group. Sulfate esters are more produced at the 6-position, which is highly reactive. Therefore, when there is much sulfuric acid catalyst, the acyl substitution degree of 6-position will become small. Therefore, in order to synthesize the cellulose acylate used in the present invention, it is necessary to extend the reaction time in order to reduce the amount of sulfuric acid catalyst as much as possible and compensate for the reduced reaction rate.

(Plasticizer)
The optical film of the present invention may contain the following plasticizer.

An ester plasticizer comprising a polyhydric alcohol and a monovalent carboxylic acid, and an ester plasticizer comprising a polyvalent carboxylic acid and a monohydric alcohol are preferred because of their high affinity with the cellulose ester.

An ethylene glycol ester plasticizer that is one of polyhydric alcohol esters: specifically, ethylene glycol alkyl ester plasticizers such as ethylene glycol diacetate and ethylene glycol dibutyrate, ethylene glycol dicyclopropylcarboxylate And ethylene glycol cycloalkyl ester plasticizers such as ethylene glycol dicyclohexylcarboxylate, and ethylene glycol aryl ester plasticizers such as ethylene glycol dibenzoate and ethylene glycol di-4-methylbenzoate. These alkylate groups, cycloalkylate groups, and arylate groups may be the same or different, and may be further substituted. Moreover, the mix of an alkylate group, a cycloalkylate group, and an arylate group may be sufficient, and these substituents may couple | bond together by the covalent bond. Further, the ethylene glycol part may be substituted, the ethylene glycol ester partial structure may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber, etc. It may be introduced into a part of the molecular structure of the additive.

Glycerin ester plasticizer that is one of polyhydric alcohol esters: Specifically, glycerol alkyl esters such as triacetin, tributyrin, glycerol diacetate caprylate, glycerol oleate propionate, glycerol tricyclopropylcarboxylate, glycerol Glycerin cycloalkyl esters such as tricyclohexylcarboxylate, glycerol aryl esters such as glycerol tribenzoate and glycerol-4-methylbenzoate, diglycerol tetraacetylate, diglycerol tetrapropionate, diglycerol acetate tricaprylate, diglycerol tetra Diglycerol alkyl esters such as laurate, diglycerol tetracyclobutylcarboxylate, diglycerol tetra Diglycerol cycloalkyl esters such as Russia pentyl carboxylate, diglycerin tetrabenzoate, diglycerin aryl ester such as diglycerin 3-methylbenzoate or the like. These alkylate groups, cycloalkylcarboxylate groups, and arylate groups may be the same or different, and may be further substituted. Moreover, the mix of alkylate group, a cycloalkyl carboxylate group, and an arylate group may be sufficient, and these substituents may couple | bond together by the covalent bond. Furthermore, the glycerin and diglycerin part may be substituted, the partial structure of the glycerin ester and the diglycerin ester may be part of the polymer or regularly pendant, and the antioxidant, acid scavenger, You may introduce | transduce into a part of molecular structure of additives, such as a ultraviolet absorber.

Specific examples of other polyhydric alcohol ester plasticizers include polyhydric alcohol ester plasticizers described in paragraphs 30 to 33 of JP-A No. 2003-12823.

These alkylate groups, cycloalkylcarboxylate groups, and arylate groups may be the same or different, and may be further substituted. Moreover, the mix of alkylate group, a cycloalkyl carboxylate group, and an arylate group may be sufficient, and these substituents may couple | bond together by the covalent bond. Furthermore, the polyhydric alcohol part may be substituted, and the partial structure of the polyhydric alcohol may be part of the polymer or regularly pendant, and may be an antioxidant, an acid scavenger, an ultraviolet absorber. May be introduced into a part of the molecular structure of the additive.

Among the ester plasticizers composed of the polyhydric alcohol and the monovalent carboxylic acid, alkyl polyhydric alcohol aryl esters are preferred. Specifically, the ethylene glycol dibenzoate, glycerin tribenzoate, diglycerin tetrabenzoate, Examples thereof include the exemplified compound 16 described in paragraph 32 of Kaikai 2003-12823.

Dicarboxylic acid ester plasticizer that is one of polyvalent carboxylic acid esters: Specifically, alkyl dicarboxylic acid alkyl such as didodecyl malonate (C1), dioctyl adipate (C4), dibutyl sebacate (C8), etc. Ester plasticizers, alkyl dicarboxylic acid cycloalkyl ester plasticizers such as dicyclopentyl succinate and dicyclohexyl adipate, and alkyl dicarboxylic acid aryl ester plasticizers such as diphenyl succinate and di-4-methylphenyl glutarate Dialkyl-1,4-cyclohexanedicarboxylate, didecylbicyclo [2.2.1] heptane-2,3-dicarboxylate, and the like, cycloalkyldicarboxylic acid alkyl ester plasticizers, dicyclohexyl-1,2- Cyclobutane deca Cycloalkyldicarboxylic acid cycloalkyl ester type plasticizers such as boxylate, dicyclopropyl-1,2-cyclohexyl dicarboxylate, diphenyl-1,1-cyclopropyldicarboxylate, di-2-naphthyl-1,4- Cycloalkyl dicarboxylic acid aryl ester plasticizers such as cyclohexane dicarboxylate, aryl dicarboxylic acid alkyl ester plasticizers such as diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, and di-2-ethylhexyl phthalate, dicyclopropyl Aryl dicarboxylic acid cycloalkyl ester plasticizers such as phthalate and dicyclohexyl phthalate, and aryl dicarboxylic acid esters such as diphenyl phthalate and di-4-methylphenyl phthalate Ruesuteru based plasticizers. These alkoxy groups and cycloalkoxy groups may be the same or different, may be mono-substituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, or these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. In addition, the partial structure of phthalate ester may be part of the polymer or regularly pendant to the polymer, and may be part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. It may be introduced.

Other polycarboxylic acid ester plasticizers include alkyl polycarboxylic acid alkyl esters such as tridodecyl tricarbarate and tributyl-meso-butane-1,2,3,4-tetracarboxylate. Plasticizers, alkylpolycarboxylic acid cycloalkyl ester plasticizers such as tricyclohexyltricarbarate, tricyclopropyl-2-hydroxy-1,2,3-propanetricarboxylate, triphenyl-2-hydroxy -1,2,3-propanetricarboxylate, tetra-3-methylphenyltetrahydrofuran-2,3,4,5-tetracarboxylate and other alkyl polyvalent carboxylic acid aryl ester plasticizers, tetrahexyl-1, 2,3,4-cyclobutanetetracarboxylate, te Cycloalkyl polycarboxylic acid alkyl ester plasticizers such as rabutyl-1,2,3,4-cyclopentanetetracarboxylate, tetracyclopropyl-1,2,3,4-cyclobutanetetracarboxylate, tricyclohexyl- Cycloalkyl polycarboxylic acid cycloalkyl ester plasticizers such as 1,3,5-cyclohexyl tricarboxylate, triphenyl-1,3,5-cyclohexyl tricarboxylate, hexa-4-methylphenyl-1,2 , 3,4,5,6-cyclohexylhexacarboxylate and other cycloalkyl polycarboxylic acid aryl ester plasticizers, tridodecylbenzene-1,2,4-tricarboxylate, tetraoctylbenzene-1,2, Ants such as 4,5-tetracarboxylate Polyvalent carboxylic acid alkyl ester plasticizer, aryl polyvalent carboxylic acid cycloalkyl such as tricyclopentylbenzene-1,3,5-tricarboxylate, tetracyclohexylbenzene-1,2,3,5-tetracarboxylate Aryl polyvalent carboxylic acids such as ester plasticizers triphenylbenzene-1,3,5-tetracartoxylate, hexa-4-methylphenylbenzene-1,2,3,4,5,6-hexacarboxylate Examples include aryl ester plasticizers. These alkoxy groups and cycloalkoxy groups may be the same or different, and may be monosubstituted, and these substituents may be further substituted. The alkyl group and cycloalkyl group may be mixed, or these substituents may be bonded together by a covalent bond. Furthermore, the aromatic ring of phthalic acid may be substituted, and a multimer such as a dimer, trimer or tetramer may be used. In addition, the partial structure of phthalate ester may be part of the polymer or may be regularly pendant to the polymer, and introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, UV absorbers, etc. May be.

Among the ester plasticizers composed of the polyvalent carboxylic acid and the monohydric alcohol, dialkyl carboxylic acid alkyl esters are preferable, and specific examples include the dioctyl adipate and tridecyl tricarbarate.

Further examples include phosphate ester plasticizers, carbohydrate ester plasticizers, and polymer plasticizers.

Phosphate ester plasticizers: specifically, phosphoric acid alkyl esters such as triacetyl phosphate and tributyl phosphate, phosphoric acid cycloalkyl esters such as tricyclobenthyl phosphate and cyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate And phosphoric acid aryl esters such as cresylphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, trinaphthyl phosphate, trixylyl phosphate, tris ortho-biphenyl phosphate. These substituents may be the same or different, and may be further substituted. Moreover, the mix of an alkyl group, a cycloalkyl group, and an aryl group may be sufficient, and substituents may couple | bond together by the covalent bond.

Also, alkylene bis (dialkyl phosphate) such as ethylene bis (dimethyl phosphate), butylene bis (diethyl phosphate), alkylene bis (diaryl phosphate) such as ethylene bis (diphenyl phosphate), propylene bis (dinaphthyl phosphate), phenylene bis (dibutyl phosphate) ), Arylene bis (dialkyl phosphate) such as biphenylene bis (dioctyl phosphate), phosphate esters such as arylene bis (diaryl phosphate) such as phenylene bis (diphenyl phosphate) and naphthylene bis (ditoluyl phosphate). These substituents may be the same or different, and may be further substituted. Moreover, the mix of an alkyl group, a cycloalkyl group, and an aryl group may be sufficient, and substituents may couple | bond together by the covalent bond.

Furthermore, the phosphate ester partial structure may be part of the polymer, or may be regularly pendant, and may be introduced into part of the molecular structure of additives such as antioxidants, acid scavengers, and UV absorbers. May be. Among the above compounds, phosphoric acid aryl ester and arylene bis (diaryl phosphate) are preferable, and specifically, triphenyl phosphate and phenylene bis (diphenyl phosphate) are preferable.

Next, the carbohydrate ester plasticizer will be described. The carbohydrate means a monosaccharide, disaccharide or trisaccharide in which the saccharide is present in the form of pyranose or furanose (6-membered ring or 5-membered ring). Non-limiting examples of carbohydrates include glucose, saccharose, lactose, cellobiose, mannose, xylose, ribose, galactose, arabinose, fructose, sorbose, cellotriose and raffinose. The carbohydrate ester refers to an ester compound formed by dehydration condensation of a hydroxyl group of a carbohydrate and a carboxylic acid. Specifically, it means an aliphatic carboxylic acid ester or an aromatic carboxylic acid ester of a carbohydrate. Examples of the aliphatic carboxylic acid include acetic acid and propionic acid, and examples of the aromatic carboxylic acid include benzoic acid, toluic acid, and anisic acid. Carbohydrates have a number of hydroxyl groups depending on the type, but even if a part of the hydroxyl group reacts with the carboxylic acid to form an ester compound, the whole hydroxyl group reacts with the carboxylic acid to form an ester compound. Also good. In the present invention, it is preferable that all of the hydroxyl groups react with the carboxylic acid to form an ester compound.

Specific examples of the carbohydrate ester plasticizer include glucose pentaacetate, glucose pentapropionate, glucose pentabtylate, saccharose octaacetate, saccharose octabenzoate, and of these, saccharose octaacetate is more preferred. preferable.

Polymer plasticizer: Specifically, aliphatic hydrocarbon polymer, alicyclic hydrocarbon polymer, polyethyl acrylate, polymethyl methacrylate, copolymer of methyl methacrylate and 2-hydroxyethyl methacrylate (For example, an arbitrary ratio between copolymer ratios 1:99 to 99: 1), vinyl polymers such as polyvinyl isobutyl ether, poly N-vinyl pyrrolidone, polystyrene, poly 4-hydroxystyrene, etc. Examples thereof include styrene-based polymers, polybutylene succinates, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyethers such as polyethylene oxide and polypropylene oxide, polyamides, polyurethanes, and polyureas. The number average molecular weight is preferably about 1,000 to 500,000, particularly preferably 5,000 to 200,000. If it is 1,000 or less, a problem occurs in volatility, and if it exceeds 500,000, the plasticizing ability is lowered, and the mechanical properties of the cellulose ester film are adversely affected. These polymer plasticizers may be a homopolymer composed of one type of repeating unit or a copolymer having a plurality of repeating structures. Two or more of the above polymers may be used in combination.

In addition, since the optical film of the present invention has an influence as an optical application when colored, the yellow degree (yellow index, YI) is preferably 3.0 or less, more preferably 1.0 or less. Yellowness can be measured based on JIS-K7103.

The plasticizer preferably removes impurities such as residual acids, inorganic salts, organic low molecules, etc. that are carried over from production or generated during storage, and more preferably has a purity of 99% or more, like the cellulose ester described above. is there. Residual acid and water are preferably 0.01 to 100 ppm, and when melt-forming cellulose resin, thermal deterioration can be suppressed, and film-forming stability, optical physical properties and mechanical properties of the film are improved. .

(Antioxidant)
In the optical film of the present invention, it is also preferable to use an antioxidant as the cellulose ester is decomposed not only by heat but also by oxygen in a high temperature environment where melt film formation is performed. .

The antioxidant useful in the present invention can be used without limitation as long as it is a compound that suppresses deterioration of the melt molding material due to oxygen, but among the useful antioxidants, phenolic compounds, hindered amine compounds, Examples thereof include phosphorus compounds, sulfur compounds, heat-resistant processing stabilizers, oxygen scavengers, etc. Among these, phenol compounds, hindered amine compounds, phosphorus compounds, and lactone compounds are particularly preferable.

The hindered amine compound (HALS) is described, for example, in US Pat. No. 4,619,956, columns 5 to 11 and US Pat. No. 4,839,405, columns 3 to 5. Thus, 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds are preferred. As a commercial item, LA52 (made by Asahi Denka Co., Ltd.) can be mentioned.

As the lactone compound, compounds described in JP-A-7-233160 and JP-A-7-247278 are preferable.

These stabilizers can be used singly or in combination of two or more, and the blending amount is appropriately selected within a range not impairing the object of the present invention, but is usually 0 with respect to 100 parts by weight of the cellulose ester. 0.001 to 10.0 parts by weight, preferably 0.01 to 5.0 parts by weight, more preferably 0.1 to 3.0 parts by weight.

By blending these compounds, it is possible to prevent coloring and strength reduction of the molded product due to heat and thermal oxidative degradation during melt molding without reducing transparency and heat resistance.

The addition amount of the antioxidant is usually 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the cellulose ester.

(Acid scavenger)
The acid scavenger is an agent that plays a role of trapping an acid (protonic acid) remaining in the cellulose ester brought in from the production. Further, when the cellulose ester is melted, the hydrolysis of the side chain is accelerated by moisture and heat in the polymer, and acetic acid and propionic acid are generated in the case of CAP. A compound having an epoxy structure, a tertiary amine, an ether structure, or the like may be used as long as it can be chemically bonded to an acid, but is not limited thereto.

Specifically, it preferably contains an epoxy compound as an acid scavenger described in US Pat. No. 4,137,201. Epoxy compounds as such acid scavengers are known in the art and are derived by condensation of diglycidyl ethers of various polyglycols, particularly about 8 to 40 moles of ethylene oxide per mole of polyglycol. Metal glycol compounds such as polyglycols, diglycidyl ethers of glycerol (eg, those conventionally used in and together with vinyl chloride polymer compositions), epoxidized ether condensation products, bisphenol A Diglycidyl ethers (ie, 4,4'-dihydroxydiphenyldimethylmethane), epoxidized unsaturated fatty acid esters (especially esters of alkyls of about 2 to 2 carbon atoms of fatty acids of 2 to 22 carbon atoms (eg Butyl epoxy stearate ), And various epoxidized long chain fatty acid triglycerides and the like (e.g., epoxidized vegetable oils and other unsaturated natural oils, which may be represented and exemplified by compositions such as epoxidized soybean oil, sometimes epoxidized natural) These are referred to as glycerides or unsaturated fatty acids and these fatty acids generally contain 12 to 22 carbon atoms)).

(UV absorber)
As an ultraviolet absorber, from the viewpoint of preventing deterioration of a polarizer or a display device with respect to ultraviolet rays, the ultraviolet absorber has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less. Less is preferred.

For example, salicylic acid ultraviolet absorbers (phenyl salicylate, p-tert-butyl salicylate, etc.) or benzophenone ultraviolet absorbers (2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, etc.), Benzotriazole UV absorber (2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di) -Tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-3'-dodecyl- 5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t rt-butyl-5 '-(2-octyloxycarbonylethyl) -phenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3'-(1-methyl-1-phenylethyl) -5'- (1,1,3,3-tetramethylbutyl) -phenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di- (1-methyl-1-phenylethyl) -phenyl) benzotriazole ), Cyanoacrylate ultraviolet absorbers (2'-ethylhexyl-2-cyano-3,3-diphenyl acrylate, ethyl-2-cyano-3- (3 ', 4'-methylenedioxyphenyl) -acrylate Etc.), triazine ultraviolet absorbers, compounds described in JP-A Nos. 58-185677 and 59-149350, nickel complex compounds Inorganic powder.

As the ultraviolet absorber according to the present invention, a benzotriazole-based ultraviolet absorber or a triazine-based ultraviolet absorber that is highly transparent and excellent in preventing deterioration of a polarizing plate or a liquid crystal element is preferable, and a spectral absorption spectrum is more appropriate. Benzotriazole ultraviolet absorbers are particularly preferred.

The conventionally known benzotriazole-based ultraviolet absorber particularly preferably used together with the ultraviolet absorber according to the present invention may be bisified, for example, 6,6′-methylenebis (2- (2H-benzo [d ] [1,2,3] triazol-2-yl))-4- (2,4,4-trimethylpentan-2-yl) phenol, 6,6'-methylenebis (2- (2H-benzo [d] And [1,2,3] triazol-2-yl))-4- (2-hydroxyethyl) phenol.

Further, in the present invention, it can be used in combination with a conventionally known ultraviolet absorbing polymer. The conventionally known UV-absorbing polymer is not particularly limited. For example, a polymer obtained by homopolymerizing R-UV A-93 (manufactured by Otsuka Chemical Co., Ltd.) and R-UV A-93 and other monomers are copolymerized. Examples thereof include polymers. Specifically, P ultraviolet rays A-30M obtained by copolymerization of R ultraviolet rays A-93 and methyl methacrylate at a ratio (weight ratio) of 3: 7, and P ultraviolet rays obtained by copolymerization at a ratio of 5: 5 (weight ratio). A-50M and the like. Furthermore, the polymer etc. which are described in Unexamined-Japanese-Patent No. 2003-113317 are mentioned.

As commercially available products, TINUVIN 109, TINUVIN 171, TINUVIN 360, TINUVIN 900, TINUVIN 928 (all manufactured by Ciba Specialty Chemicals), LA-31 (Manufactured by Asahi Denka Co., Ltd.) and R ultraviolet ray A-100 (manufactured by Otsuka Chemical Co., Ltd.) can also be 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 are not limited thereto.

In the present invention, the ultraviolet absorber is preferably added in an amount of 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and further preferably 1 to 5% by weight. Two or more of these may be used in combination.

(Viscosity reducing agent)
In the present invention, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity. The hydrogen bonding solvent is J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” that occurs between an electronegative atom and a covalently bonded hydrogen atom, that is, a bond having a large bonding moment and containing hydrogen, such as OH (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), FH (fluorine hydrogen bond), and an organic solvent that can arrange adjacent molecules. These have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin. In the melt casting film forming method performed in the present invention, the glass transition temperature of the cellulose resin used alone is used. In addition, the melting temperature of the cellulose resin composition can be lowered by the addition of a hydrogen bonding solvent, or the melt viscosity of the cellulose resin composition containing the hydrogen bonding solvent is lower than that of the cellulose resin at the same melting temperature. Can do.

Examples of the hydrogen bonding solvent include alcohols such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, t-butanol, 2-ethylhexanol, heptanol, octanol, nonanol, dodecanol, ethylene glycol, Propylene glycol, hexylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, hexyl cellosolve, glycerin, etc., ketones: acetone, methyl ethyl ketone, etc., carboxylic acids: for example formic acid, acetic acid, propionic acid, Butyric acid, etc., ethers: eg, diethyl ether, tetrahydrofuran, dioxane, etc., Pyrrolidones: eg, N-methyl Pyrrolidone, amines: for example, can be exemplified trimethylamine, pyridine, etc., and the like. These hydrogen bonding solvents can be used alone or in admixture of two or more. Among these, alcohol, ketone, and ether are preferable, and methanol, ethanol, propanol, isopropanol, octanol, dodecanol, ethylene glycol, glycerin, acetone, and tetrahydrofuran are particularly preferable. Furthermore, water-soluble solvents such as methanol, ethanol, propanol, isopropanol, ethylene glycol, glycerin, acetone and tetrahydrofuran are particularly preferred. Here, water-soluble means that the solubility in 100 g of water is 10 g or more.

(Retardation control agent)
In the optical film of the present invention, an alignment film may be formed to provide a liquid crystal layer, and a polarizing plate process may be performed in which a cellulose acylate film and a retardation derived from the liquid crystal layer are combined to provide an optical compensation capability. As the compound to be added for controlling the retardation, an aromatic compound having two or more aromatic rings as described in EP 911,656A2 can be used as a retardation control agent. . Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring. An aromatic heterocyclic ring is particularly preferred, and the aromatic heterocyclic ring is generally an unsaturated heterocyclic ring. Of these, compounds having a 1,3,5-triazine ring are particularly preferred.

(Matting agent)
In the optical film of the present invention, fine particles such as a matting agent can be added to impart slipperiness, and examples of the fine particles include inorganic compound fine particles and organic compound fine particles. The matting agent is preferably as fine as possible. Examples of the fine particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples thereof include inorganic fine particles such as magnesium silicate and calcium phosphate, and crosslinked polymer fine particles. Among these, silicon dioxide is preferable because it can reduce the haze of the film. In many cases, fine particles such as silicon dioxide are surface-treated with an organic material, but such a material is preferable because it can reduce the haze of the film.

Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like. The larger the average particle size of the fine particles, the greater the sliding effect, and the smaller the average particle size, the better the transparency. The average particle size of the secondary particles of the fine particles is in the range of 0.05 to 1.0 μm. The average particle diameter of the secondary particles of the fine particles is preferably 5 to 50 nm, more preferably 7 to 14 nm. These fine particles are preferably used in the cellulose acylate film in order to produce an unevenness of 0.01 to 1.0 μm on the surface of the cellulose acylate film. The content of the fine particles in the cellulose ester is preferably 0.005 to 0.3% by weight with respect to the cellulose ester.

Examples of the fine particles of silicon dioxide include Aerosil 200, 200V, 300, 972, 972V, 974, R202, R812, OX50, and TT600 manufactured by Nippon Aerosil Co., preferably Aerosil 200V, 972, 972V, 974, R202, R812. Two or more kinds of these fine particles may be used in combination. When using 2 or more types together, it can mix and use in arbitrary ratios. In this case, fine particles having different average particle sizes and materials, for example, Aerosil 200V and 972V can be used in a weight ratio of 0.1: 99.9 to 99.9: 0.1.

The presence of fine particles in the film used as the matting agent can be used for another purpose to improve the strength of the film. The presence of the fine particles in the film can also improve the orientation of the cellulose ester itself constituting the optical film of the present invention.

(Polymer material)
In the optical film of the present invention, polymer materials and oligomers other than cellulose ester may be appropriately selected and mixed. The polymer material or oligomer is preferably one having excellent compatibility with the cellulose ester, and the transmittance when formed into a film is preferably 80% or more, more preferably 90% or more, and further preferably 92% or more. The purpose of mixing at least one of polymer materials and oligomers other than cellulose ester includes meanings for controlling viscosity at the time of heating and melting and improving film physical properties after film processing.

Incidentally, in FIG. 2, the range is indicated by an arrow A around the cooling roll (5) as the metal support. This range (A) shows almost the entire circumference of the cooling roll (5) excluding the vicinity of the casting die (4). Moreover, the range is shown by the arrow B around the cooling roll (5) as a metal support body in FIG. This range (B) is the range from when the film obtained from the cast resin melt is peeled off from the cooling roll (5) until the resin melt is cast again on the cooling roll (5). Show. In this range (B), the surface of the cooling roll (5) is exposed.

In this embodiment, the diameter of the cooling roll (5) is 1000 mm, the film transport speed by the cooling roll (5) is 200 m / min (3.33 m / sec), and the resin melt is cast from the peeling position of the film. The rotation angle of the cooling roll (5) to the position, that is, the range (B) is 120 ° (one third rotation). Therefore, the time for which the surface of the cooling roll (5) is exposed is approximately 0.3 seconds. However, these numerical values are one specific example in the present embodiment, and needless to say, the numerical values may be appropriately changed according to the production speed or the like.

The range (B) is a high energy beam irradiation apparatus, that is, an atmospheric pressure plasma irradiation apparatus (40) shown in FIG. 5, an excimer ultraviolet irradiation apparatus (50) shown in FIG. 6, or a YAG laser irradiation apparatus (not shown). The range in which an argon laser irradiation apparatus or an excimer laser irradiation apparatus can be installed is shown. The high energy beam irradiation device is installed in this range (B), and the surface of the exposed cooling roll (5) is irradiated with normal pressure plasma while the cooling roll (5) is in use (during film production). Then, a first dirt removing step for removing dirt on the surface of the cooling roll (5) by performing excimer ultraviolet irradiation or laser irradiation is performed.

The execution time of the first dirt removing step depends on the time when the surface of the support (5) is exposed, the type of high energy ray irradiation, the output of the high energy ray irradiation, the type of dirt, the amount of dirt, and the like. However, from the viewpoint of necessary and sufficient time, for example, 0.01 to 0.3 seconds are preferable, 0.02 to 0.2 seconds are more preferable, and 0.03 to 0.1 seconds is more preferable.

In addition, the range (B) indicates a range in which the second dirt removing step is repeated after the first dirt removing step. That is, when the second dirt removing step is a step in which the surface of the cooling roll (5) is again subjected to normal pressure plasma irradiation, excimer ultraviolet ray irradiation, or laser irradiation, the high energy beam of the first dirt removing step. Another high energy ray irradiation apparatus is installed downstream of the irradiation apparatus (downstream in the rotation direction of the cooling roll (5)). Alternatively, when the second dirt removing step is a step of bringing a tangible object into contact with the surface of the cooling roll (5), the downstream side of the high energy ray irradiation device of the first dirt removing step (cooling roll (5) A device for bringing a tangible object into contact with the surface of the cooling roll (5) is installed on the downstream side in the rotation direction.

The execution time of the second dirt removing step is the time when the surface of the support (5) is exposed, the type of the first dirt removing step, the kind of tangible thing, the amount of tangible thing, the kind of dirt, the amount of dirt, etc. Depending on the above, it may vary in various ways and is not particularly limited. However, from the viewpoint of necessary and sufficient time, for example, 0.01 to 0.3 second is preferable, 0.02 to 0.2 second is more preferable, and 0 0.03 to 0.1 second is more preferable.

As a device for bringing a tangible object into contact with the surface of the cooling roll (5), for example, a liquid spraying device (such as an ultrasonic spray) for spraying a liquid on the surface of the cooling roll (5), or a cooling roll (5) Examples thereof include a cloth rubbing device for rubbing the surface with a cloth (nonwoven fabric or the like) (a device for pressing a silicon pad covered with a cloth against the surface of the cooling roll (5) with a predetermined pressing force).

Then, in the range (B) where the surface of the cooling roll (5) is exposed, the first dirt removal process is performed, and then the second dirt removal process is repeated, so that the first dirt is obtained. Dirt that has not been removed in the removal process (this dirt includes dirt that has been decomposed by high-energy ray irradiation in the first process but is still attached to the surface of the cooling roll (5)). Mostly removed with high efficiency by the dirt removal process. That is, when cleaning the surface of the cooling roll (5) while manufacturing the optical film, the surface of the cooling roll (5) can be cleaned with high efficiency unprecedented, and dirt can be almost removed in a relatively short time. .

FIG. 5 is an explanatory diagram for explaining the principle of the atmospheric pressure plasma irradiation apparatus (40). The atmospheric pressure plasma irradiation apparatus (atmospheric pressure plasma irradiation apparatus) (40) will be described in detail with reference to FIG.

In the atmospheric pressure plasma apparatus (40) used in the present invention, a reactive gas is changed to a plasma state by applying a high frequency voltage between opposing electrodes to discharge it, and a metal support (first cooling roll) (5 ) Is modified to form a dense and dense metal oxide film on the surface of the metal support (5).

In the atmospheric pressure plasma irradiation device (40), a method called a direct type or a planer type in which high-frequency power is applied between electrodes opposed to each other so as to sandwich a substrate to be processed, and a supply gas is converted into plasma, and a reactive gas are supplied. There are methods called a remote method and a downstream method in which plasma is generated between electrodes to which a high-frequency voltage is applied, and both methods can be used in the present invention. However, in the method for producing an optical film of the present invention, It is desirable to use the latter method for high energy surface treatment.

In FIG. 5, reference numerals (a) and (b) are counter electrodes of the atmospheric pressure plasma irradiation apparatus (40), reference numeral (g) is a reactive gas, and reference numeral (5) is a metal support.

Then, according to the atmospheric pressure plasma irradiation device (40), the reactive gas (g) is introduced between the counter electrodes (a) and (b) to which the high-frequency voltage is applied, and is converted into plasma, thereby forming a metal support. A fine metal oxide film is formed by spraying the surface of (5).

Here, in this embodiment, the cooling roll (5) as a metal support is a roll obtained by applying hard chrome plating to a stainless steel drum.

In the embodiment of the present invention, it is necessary to apply an electrode capable of maintaining a uniform glow discharge state by applying such a high power voltage to the atmospheric pressure plasma irradiation apparatus (40).

Such an electrode is preferably a metal base material coated with a dielectric. It is preferable to coat a dielectric on at least one side of the opposed application electrode and the ground electrode, and more preferably coat both of the opposed application electrode and the ground electrode with a dielectric. The dielectric is preferably an inorganic substance having a relative dielectric constant of 6 to 45. Examples of such a dielectric include ceramics such as alumina and silicon nitride, silicate glass, borate glass, and the like. Glass lining material and the like.

In addition, when a cellulose ester film, which is a transparent film base material, is placed between electrodes or transported between electrodes and exposed to plasma, the transparent film base material has a roll electrode specification that can be transported in contact with one electrode. In addition, the dielectric surface is polished and the electrode surface roughness Rmax (JIS B 0601) is 10 μm or less, so that the thickness of the dielectric and the gap between the electrodes can be kept constant. It is preferable because the discharge state can be stabilized, and further, the distortion and cracking due to the difference in thermal shrinkage and residual stress can be eliminated and the high-precision inorganic dielectric that is not porous can be coated to greatly improve the durability.

Further, the gap (d) between the blow-out slit for supplying and supplying plasma and the surface of the metal support (5) is preferably 0.5 to 6 mm, and more preferably 1 to 4 mm. If it is too close, there is a risk of contacting or damaging the surface of the metal support (5). If it is too far, the effect of modifying the surface becomes weak.

Various reactive gases (g) such as nitrogen, oxygen, argon, and helium can be used. Nitrogen is preferable from the viewpoints of environment, exhaust aftertreatment, and running cost. It is preferable to mix a small amount of oxygen. The mixing ratio of oxygen is preferably 2% by volume or less with respect to the volume of the source gas.

In addition, as a raw material gas (g) for forming the surface treatment layer, for example, an organic solvent vapor such as methylene chloride or alcohol, or a monomer gas such as acetylene is mixed with nitrogen or oxygen of the reactive gas of the atmospheric pressure plasma. May be introduced. The mixing ratio is preferably in the range of 0.2 to 20% by volume with respect to the total volume of nitrogen and oxygen.

When the source gas for forming the surface treatment layer is not mixed with the reactive gas of atmospheric pressure plasma, the source gas is sprayed on the surface of the casting film from the outside of the atmospheric pressure plasma irradiation device (40), It is also possible to carry out the reaction and form a film by feeding it under the atmospheric pressure plasma irradiation device (40).

In that case, the gas concentration around the atmospheric pressure plasma irradiation apparatus (40) is preferably in the range of 500 ppm to 100,000 ppm, more preferably 1,000 to 50,000 ppm.

Further, the air volume of the source gas of atmospheric pressure plasma is desirably 20 to 5000 L / min per 1 m of the effective width of plasma irradiation. Further, 40 to 2500 L / min is more preferable.

FIG. 6 is an explanatory diagram for explaining the principle of the excimer ultraviolet irradiation device (50). The excimer ultraviolet irradiation device (50) will be described with reference to FIG.

In FIG. 6, reference numeral (u) is an excimer ultraviolet lamp, reference numeral (r) is a reflector, reference numeral (p) is a purge gas, reference numeral (q) is quartz glass, and reference numeral (5) is a metal support.

In the present embodiment, the excimer ultraviolet lamp (u) shown in FIG. 6 is used to irradiate the surface of the metal support (5) mainly with ultraviolet light having a wavelength of 172 nm with a light quantity of 1 to 3,000 mJ / cm ^2. Is. Under such ultraviolet irradiation, oxygen contained in the purge gas (p) generates active oxygen and ozone, contributes to the modification of the surface of the metal support (5), and on the surface of the metal support (5). A dense metal oxide film is formed.

Further, if the gap (d) between the quartz glass (q) containing the excimer ultraviolet lamp (u) and the metal support (5) is too close, there is a risk of contact with or damage to the surface of the metal support (5). If it is too far, high energy of excimer ultraviolet rays is absorbed by oxygen or water in the atmosphere, and the effect of modifying the surface of the metal support (5) becomes weak. Further, 1 to 3 mm is more preferable.

In addition, when high energy ray irradiation is performed again in the second dirt removing step, it may be the same type of high energy ray irradiation as that in the first dirt removing step (for example, normal pressure plasma irradiation followed by normal pressure plasma irradiation). However, different types of high energy beam irradiation (for example, normal pressure plasma irradiation followed by excimer ultraviolet irradiation) may be used.

In the present embodiment, the contact of the tangible object with the surface of the cooling roll (5) in the second dirt removing step is preferably performed by spraying a liquid onto the surface of the cooling roll (5). Due to the collision of the liquid particles with the surface of the cooling roll (5), the dirt that has not been removed in the first dirt removing step is surely blown off and removed. Further, the surface of the cooling roll (5) is hardly damaged. In addition, as a liquid, the organic solvent (methylene chloride, alcohol, etc.) used for the resin solution of a solution casting film forming method is preferable, for example. This is because the tendency of the liquid to remain on the surface of the cooling roll (5) is small, and even if the liquid remains on the surface of the cooling roll (5) and mixes with the resin melt, there are few problems. The liquid spraying conditions (spraying amount, etc.) vary depending on the spraying time (the time during which the second step can be performed), the type of spraying device, the type of liquid, etc., for example, using an ultrasonic spray When methylene chloride is sprayed, the amount is about 1 to 10 ml / m ² per ^second .

In this embodiment, it is preferable that the contact of the tangible object with the surface of the cooling roll (5) in the second dirt removing step is to rub the surface of the cooling roll (5) with a cloth. Due to the friction of the surface of the cooling roll (5), the dirt that has not been removed in the first dirt removing step is surely wiped off and removed. Nonwoven fabric is preferred as the cloth. As a method of rubbing the surface of the cooling roll (5) with a cloth, for example, the silicon pad may be covered with a nonwoven fabric and pressed with a predetermined pressing force over the entire width of the surface of the cooling roll (5). At this time, the surface of the cooling roll (5) is pressed as uniformly as possible in the width direction.

As the nonwoven fabric, a nonwoven fabric using long fibers can be preferably used. As long fibers, cellulose is preferred. Examples of commercially available cleaning cloths (wiping tools) include “Bencot” series manufactured by Asahi Kasei Co., Ltd., and Bencot M-1, Bencott M-3, Bencott M-3II, and the like can be preferably used.

In this embodiment, the execution time of the first dirt removal step is set to 0.01 to 0.3 seconds from the viewpoint of necessary and sufficient time, but is not limited to this. In the present embodiment, the execution time of the second dirt removal step is set to 0.01 to 0.3 seconds from the viewpoint of necessary and sufficient time, but is not limited to this. .

In the present embodiment, in the range (B), the active oxygen species generator is provided upstream of the high energy beam irradiation device in the first step and / or the second step (upstream in the rotation direction of the cooling roll (5)). The atmospheric pressure plasma irradiation, the excimer ultraviolet irradiation or the laser irradiation in the first dirt removal step and / or the second dirt removal step is generated by this active oxygen species generator, and the cooling roll (5 ) In the presence of active oxygen species supplied to the surface. Strong decomposition effect of soil components by irradiation with high energy rays (breakage of chemical bond of soil components mainly composed of organic matter) and strong oxidation effect of soil components by active oxygen species (carbon dioxide of soil components composed mainly of organic matter) This is because the removal of dirt is promoted in synergy with the decomposition of water and other simple molecules. Here, the active oxygen species, for example, ozone _(O 3), nitrogen monoxide (NO), nitrogen dioxide (ONO), superoxide anion _{(O 2} ^-), superoxide anion radicals _(O 2 ^· -), A hydroxyl radical (HO.), Hydrogen peroxide (HOOH), etc. are mentioned.

In the present embodiment (melt casting film forming method), the temperature of the cooling roll (5) when performing the first dirt removing step and the second dirt removing step is preferably 180 ° C. or less, which will be described later. In the solution casting film forming method, the temperature of the endless belt (27) or the drum (26) when performing the first dirt removing step and the second dirt removing step is preferably −20 to 80 ° C. Generally, the cooling and solidification temperature of the resin melt on the cooling roll (5) in the melt casting film forming method is adjusted to 180 ° C. or less, and the endless belt (27) of the resin solution in the solution casting film forming method described later or Since the solvent evaporation temperature on the drum (26) is adjusted to −20 to 80 ° C., in any case, the first step and the second step can be performed during normal film formation. In particular, it is not necessary to cool or heat the supports (5), (26), (27). Further, the dirt removal effect of the first step and the stain removal effect of the second step are not lowered in the temperature range.

In the present embodiment, the dirt removal step is a combination of two. For example, high energy ray irradiation → high energy ray irradiation → high energy ray irradiation (the types of high energy rays may be the same or different from each other). Good), high energy beam irradiation → high energy beam irradiation → tangible object contact, high energy beam irradiation → tangible object contact → high energy beam irradiation, high energy beam irradiation → tangible object contact → tangible object contact, etc.

Next, a method for producing an optical film by the solution casting film forming method of the present invention will be described. In the case where the method for producing an optical film according to the present invention is based on a solution casting film forming method, the solution casting film forming method uses a dope (resin solution) in which a thermoplastic resin is dissolved in a solvent as a metal from a casting die. The method includes a step of casting on a rotating drum or a metal rotating endless belt (support) to form a cast film, and peeling the cast film from the support.

FIG. 3 is a flow sheet showing a specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method.

In the figure, first, in a dissolution vessel (21), for example, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and an additive such as a plasticizer or an ultraviolet absorber is added to the resin solution. (Dope) is prepared.

Next, the dope adjusted in the melting pot (21) is fed to the casting die (23) by a conduit through, for example, a pressurized metering gear pump (22), and is transferred infinitely, for example, from a rotationally driven stainless steel endless belt The dope is cast from the casting die (23) to the casting position on the metal support (27).

In the present invention, the stainless steel endless belt (27) as a metal support is an endless belt made of stainless steel (SUS316, SUS304, etc.), and is formed by solution casting on the surface of the metal support (27). A thermoplastic resin solution (dope) in a film method is cast.

For casting the dope by the casting die (23), there is a doctor blade method in which the film thickness of the cast dope film (web) is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. However, it is preferable to use a pressure die that can adjust the slit shape of the die part and easily make the film thickness uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

In addition, as a casting die (23), the pressure die which can adjust the slit shape of a nozzle | cap | die part and is easy to make a film thickness uniform is preferable. The casting die (23) is usually provided with a decompression chamber (not shown).

Here, the solid content concentration of the cellulose ester solution (dope) is preferably 15 to 30% by weight. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by weight, sufficient drying cannot be performed on the metal support (27), and a part of the dope film is on the metal support (27) during peeling. This leads to belt contamination and is not preferable. If the solid concentration exceeds 30%, the dope viscosity increases, filter clogging becomes faster in the dope adjustment process, or the pressure increases during casting on the metal support (27), and cannot be extruded. It is not preferable.

Next, the cast film cast as described above is brought into contact with a metal support (27) made of a rotationally driven endless belt. The endless belt-made metal support (27) is held by a pair of front and rear drums (25), (25) and a plurality of intermediate rolls (not shown), and is provided at both ends of the metal support (27). One or both of the drums (25) and (25) are provided with a driving device for applying tension (not shown) to the metal support (27), whereby the metal support (27) is tensioned and stretched. Used in the state.

Here, the width of the metal support (27) is preferably 1700 to 2500 mm, the casting width of the cellulose ester solution is preferably 1600 to 2400 mm, and the width of the film after winding is preferably 1400 to 2400 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

When an endless belt is used as the metal support (27), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and less than the boiling point of the solvent having the lowest boiling point in the mixed solvent. The film can be cast at a temperature, and more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. The temperature of the endless belt (27) is also preferably −20 to 80 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point. The peripheral speed of the metal support (27) is preferably 40 to 200 m / min.

As described above, the dope cast on the surface of the metal support (27) also increases the strength of the gel film (film strength) when drying is promoted until stripping.

In the system using an endless belt as the metal support (27), on the metal support (27), the web (29) has a film strength that can be peeled from the metal support (27) by the peeling roll (28). In order to dry and solidify, it is preferable to dry the amount of residual solvent in the web (29) to 150% by weight or less, and more preferably 80 to 120% by weight. The web temperature when peeling the web (29) from the metal support (27) is preferably 0 to 30 ° C. Further, immediately after the web (29) is peeled off from the metal support (27), the temperature once decreases rapidly due to solvent evaporation from the metal support (27) adhesion surface side, and vapor such as water vapor or solvent vapor in the atmosphere is volatilized. The web temperature at the time of peeling is more preferably 5 to 30 ° C. because the sex component is likely to condense.

Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(MN) / N} × 100

In the formula, M is the weight of the web at an arbitrary point in time, and N is the weight when a weight M is dried at 110 ° C. for 3 hours.

The dope film (web) (29) formed by the dope cast on the metal support (27) is heated on the metal support (27), and the release roll (28) is removed from the metal support (27). Until the web is peelable.

To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the metal support (27) by a liquid, a method of transferring heat from the front and back by radiant heat, etc. What is necessary is just to use in combination.

In the system using an endless belt for the metal support (27), the peeling tension when the metal support (27) and the web (29) are peeled off by the peeling roll (28) is measured as a peeling force as in JIS Z 0237. Peeling with a larger tension than the peeling force obtained in, but this may cause the peeling position to be taken downstream if the peeling tension is equal to the peeling force obtained by the JIS measurement method during high-speed film formation. Therefore, it is done at a high level for stabilization. However, even if the film is formed with the same peeling tension in the process, it is confirmed that the variation in the crossed Nicols transmittance (CNT) of the film is greatly reduced when the peeling force by the JIS measuring method is lowered.

The peeling tension value in the process is usually 50 to 250 N / m, but in the optical film produced according to the present invention, which is thinner than the conventional one, the web (29) Since the amount of residual solvent is large and easily stretches in the transport direction, the film tends to shrink in the width direction, and when drying and shrinkage overlap, the edge curls and folds, making it easy to wrinkle, so it can be peeled off. Peeling with a tension of up to 170 N / m is preferable, and peeling with a minimum tension of up to 140 N / m is more preferable.

In the present invention, after the web (29) is dried and solidified on the metal support (27) until it has a peelable film strength, the web (29) is peeled off by the peeling roll (28) and then stretched as described later. The web (29) is stretched in the process tenter (32).

Incidentally, in FIG. 3, a range is indicated by an arrow C around an endless belt (27) as a metal support. This range (C) shows almost the entire circumference of the endless belt (27) excluding the vicinity of the casting die (23). Further, FIG. 3 shows a range indicated by an arrow D around an endless belt (27) as a metal support. This range (D) shows the range from when the film obtained from the cast resin solution is peeled from the endless belt (27) until the resin solution is cast again on the endless belt (27). Yes. In this range (D), the surface of the endless belt (27) is exposed.

In the present embodiment, the time during which the surface of the endless belt (27) is exposed is approximately 0.3 seconds. However, this numerical value is one specific example in the present embodiment, and it is needless to say that the numerical value may be appropriately changed according to the production speed or the like.

The range (D) is a high energy beam irradiation apparatus, that is, an atmospheric pressure plasma irradiation apparatus (40) shown in FIG. 5, an excimer ultraviolet irradiation apparatus (50) shown in FIG. 6, or a YAG laser irradiation apparatus (not shown). The range in which an argon laser irradiation apparatus or an excimer laser irradiation apparatus can be installed is shown. The high energy beam irradiation device is installed in this range (D), and the surface of the exposed endless belt (27) is irradiated with normal pressure plasma while the endless belt (27) is in use (during film production). Then, a first dirt removing step for removing dirt on the surface of the endless belt (27) by performing excimer ultraviolet irradiation or laser irradiation is performed.

Further, the range (D) indicates a range in which the second dirt removing step is repeated after the first dirt removing step. That is, when the second dirt removal step is a step in which the surface of the endless belt (27) is again subjected to atmospheric pressure plasma irradiation, excimer ultraviolet ray irradiation, or laser irradiation, the high energy beam of the first dirt removal step. Another high energy beam irradiation device is installed downstream of the irradiation device (downstream in the traveling direction of the endless belt (27)). Alternatively, when the second dirt removing step is a step of bringing a tangible object into contact with the surface of the endless belt (27), the downstream side of the high energy beam irradiation device of the first dirt removing step (endless belt (27) A device for bringing a tangible object into contact with the surface of the endless belt (27) is installed on the downstream side in the traveling direction.

The high energy beam irradiation device used in the first dirt removing step and the device for bringing the tangible object into contact with the surface of the endless belt (27) used in the second dirt removing step are shown in FIGS. The same as described in the melt casting film forming method is used.

Then, in the range (D) where the surface of the endless belt (27) is exposed, the first dirt removal step is performed, and then the second dirt removal step is repeated, whereby the first dirt is removed. Dirt that has not been removed in the removal process (this dirt includes dirt that has been decomposed by high-energy ray irradiation in the first step but is still attached to the surface of the endless belt (27)). Mostly removed with high efficiency by the dirt removal process. That is, when cleaning the surface of the endless belt (27) while manufacturing the optical film, the surface of the endless belt (27) can be cleaned with high efficiency unprecedented, and dirt can be almost removed in a relatively short time. .

In addition, also in the manufacturing method of the optical film by this solution casting film-forming method, it is not restricted to the case where a dirt removal process is a combination of two, for example, high energy ray irradiation → high energy ray irradiation → high energy ray irradiation (high energy The types of lines may be the same or different from each other), high energy beam irradiation → high energy beam irradiation → tangible object contact, high energy beam irradiation → tangible object contact → high energy ray irradiation, high energy beam irradiation → tangible object contact → tangible object Contact may be used.

FIG. 4 is a flow sheet showing another specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. As a metal support, for example, stainless steel whose surface is subjected to hard chrome plating treatment The case where the steel rotational drive drum (26) is used is illustrated.

In the present invention, a thermoplastic resin solution (dope) in the solution casting film forming method is flowed on the surface of a stainless steel rotary drive drum (26) whose surface as a metal support is subjected to hard chrome plating. It is to extend.

Since the other points of the optical film manufacturing apparatus in FIG. 4 are the same as those in the optical film manufacturing apparatus in FIG. 3, the same components are denoted by the same reference numerals in the drawings.

Incidentally, in FIG. 4, a range is indicated by an arrow E around a stainless steel rotary drive drum (26) as a metal support. This range (E) shows almost the entire circumference of the drum (26) except the vicinity of the casting die (23). FIG. 4 shows a range indicated by an arrow F around a drum (26) as a metal support. This range (F) indicates a range from when the film obtained from the cast resin solution is peeled off from the drum (26) until the resin solution is cast again on the drum (26). In this range (F), the surface of the drum (26) is exposed.

In the present embodiment, the diameter of the drum (26) is 1000 mm, the film transport speed by the drum (26) is 200 m / min (3.33 m / sec), and from the film peeling position to the resin solution casting position. The rotation angle of the drum (26), that is, the range (F) is 60 ° (1/6 rotation). Therefore, the time for which the surface of the drum (26) is exposed is approximately 0.16 seconds. However, these numerical values are one specific example in the present embodiment, and needless to say, the numerical values may be appropriately changed according to the production speed or the like.

The range (F) is a high energy beam irradiation apparatus, that is, an atmospheric pressure plasma irradiation apparatus (40) shown in FIG. 5, an excimer ultraviolet irradiation apparatus (50) shown in FIG. 6, or a YAG laser irradiation apparatus (not shown). The range in which an argon laser irradiation apparatus or an excimer laser irradiation apparatus can be installed is shown. The high energy beam irradiation device is installed in this range (F), and the surface of the exposed drum (26) is exposed to atmospheric pressure plasma and excimer while the drum (26) is in use (during film production). A first dirt removing step for removing dirt on the surface of the drum (26) by performing ultraviolet irradiation or laser irradiation is performed.

Further, the range (F) indicates a range in which the second dirt removing step is repeated after the first dirt removing step. That is, when the second dirt removing step is a step in which atmospheric pressure plasma irradiation, excimer ultraviolet ray irradiation, or laser irradiation is performed again on the surface of the drum (26), high energy beam irradiation in the first dirt removing step is performed. Another high energy beam irradiation device is installed on the downstream side of the device (downstream in the rotation direction of the drum (26)). Alternatively, when the second dirt removing step is a step of bringing a tangible object into contact with the surface of the drum (26), the downstream side of the high energy beam irradiation device of the first dirt removing step (rotation of the drum (26)). A device for bringing a tangible object into contact with the surface of the drum (26) is installed on the downstream side in the direction.

Note that the high energy beam irradiation apparatus used in the first dirt removing step and the apparatus for bringing the tangible object into contact with the surface of the drum (26) used in the second dirt removing step are the melting points shown in FIGS. The same one as described in the casting film forming method is used.

Then, in the range (F) where the surface of the drum (26) is exposed, the first dirt removal process is performed, and then the second dirt removal process is repeated, thereby performing the first dirt removal process. Dirt that could not be removed in the process (this dirt includes dirt that was decomposed by high-energy radiation in the first process but still adhered to the surface of the drum (26)). Most of the process is removed with high efficiency. That is, when the surface of the drum (26) is cleaned while manufacturing the optical film, the surface of the drum (26) can be cleaned with high efficiency unprecedented, and dirt can be almost removed in a relatively short time.

In addition, also in the manufacturing method of the optical film by this solution casting film-forming method, it is not restricted to the case where a dirt removal process is a combination of two, for example, high energy ray irradiation → high energy ray irradiation → high energy ray irradiation (high energy The types of lines may be the same or different from each other), high energy beam irradiation → high energy beam irradiation → tangible object contact, high energy beam irradiation → tangible object contact → high energy ray irradiation, high energy beam irradiation → tangible object contact → tangible object Contact may be used.

Next, in the method for producing an optical film by the solution casting method of the present invention, a resin solution (dope) containing a resin such as cellulose ester resin as a main material, a plasticizer, a retardation adjusting agent, an ultraviolet absorber, At least one or more of fine particles and low molecular weight substances, and a solvent are included. Hereinafter, these will be described.

In the method for producing an optical film by the solution casting film forming method of the present invention, various resins can be used as the film material, and among them, cellulose ester is preferable.

Cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present invention are not impaired.

As an example of cellulose triacetate, the substitution degree of acetyl group is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

The cellulose used as a raw material of the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

In the present invention, the number average molecular weight of the cellulose ester is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 70,000 to 200,000 are preferable.

In the present invention, various additives can be added to the cellulose ester.

In the method for producing an optical film according to the present invention, it is preferable to use a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt).

In the present invention, reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of increasing the viewing angle of the liquid crystal display device operating in the IPS mode. In the present invention, such thickness direction retardation is used. The following are mentioned as an additive which reduces (Rt).

Generally, retardation of a cellulose ester film appears as the sum of retardation derived from a cellulose ester and retardation derived from an additive. Therefore, an additive for reducing the retardation of the cellulose ester is an additive that disturbs the orientation of the cellulose ester and is difficult to orient itself and / or has a small polarizability anisotropy. It is a compound that effectively reduces it. Therefore, as an additive for disturbing the orientation of the cellulose ester, an aliphatic compound is preferable to an aromatic compound.

Here, specific retardation reducing agents include, for example, polyesters represented by the following general formula (1) or (2).

Formula (1): B1- (GA-) mG-B1
Formula (2): B2- (GA-) nG-B2

In the above formula, B1 represents a monocarboxylic acid component, B2 represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

The monocarboxylic acid component represented by B1 is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, and the like can be used.

Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1-20 carbon atoms, and particularly preferably has 1-12 carbon atoms. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

Preferred monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecinic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

The monoalcohol component represented by B2 is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. More preferably, it has 1-20 carbon atoms, and particularly preferably has 1-12 carbon atoms.

Examples of the divalent alcohol component represented by G include the following, but the present invention is not limited thereto. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Examples include hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 , 2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol and triethylene glycol are preferred, and 1,3-propylene glycol and 1,4-butylene glycol are also preferred. Lumpur, 1,6-hexanediol, diethylene glycol is preferably used.

The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, etc. In particular, as aliphatic carboxylic acid, those having 4 to 12 carbon atoms, at least one selected from these are used. To do. That is, two or more dibasic acids may be used in combination.

The number of repetitions m and n in the general formula (1) or (2) is preferably 1 or more and 170 or less.

The weight average molecular weight of the polyester is preferably 20,000 or less, and more preferably 10,000 or less. In particular, polyesters having a weight average molecular weight of 500 to 10,000 have good compatibility with cellulose esters, and neither evaporation nor volatilization occurs during film formation.

Polyester polycondensation is performed by conventional methods. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or an alkyl ester thereof, for example, a methyl ester of dibasic acid and a glycol, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, it is preferable that polyester having a weight average molecular weight not so large is by direct reaction. Polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester, and after forming the film, a moisture permeability is small, and a cellulose ester film rich in transparency can be obtained.

The molecular weight adjustment method is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent compounds can be controlled by a method of blocking the molecular ends with a monovalent acid or monovalent alcohol. In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but during the polycondensation reaction, it is not distilled out of the system, but is stopped and such monovalent acid is removed from the reaction system. The one that is easy to accumulate is selected. These may be used in combination. In the case of direct reaction, the weight average molecular weight can also be adjusted by measuring the timing of stopping the reaction by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged, or can be adjusted by controlling the reaction temperature.

The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by weight based on the cellulose ester. It is particularly preferable to contain 5 to 15% by weight.

In the present invention, examples of the additive for reducing the thickness direction retardation (Rt) include the following.

The dope used for the production of the optical film of the present invention is mainly a cellulose ester, a polymer as an additive for reducing retardation (Rt) (a polymer obtained by polymerizing an ethylenically unsaturated monomer, an acrylic polymer), And an organic solvent.

In the present invention, in order to synthesize a polymer as an additive for reducing the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and a method that can make the molecular weight as uniform as possible by a method that does not increase the molecular weight too much. It is desirable to use it. Examples of such a polymerization method include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than usual polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a compound having a single thiol group and a secondary hydroxyl group as described in the publication, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferred.

In the present invention, monomers as monomer units constituting a polymer as an additive for reducing useful thickness direction retardation (Rt) are listed below, but are not limited thereto.

As the ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the thickness direction retardation (Rt) obtained by polymerizing an ethylenically unsaturated monomer, first, as a vinyl ester, for example, vinyl acetate, propionic acid, etc. Vinyl, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, Examples include vinyl crotonate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate.

Next, as acrylate esters, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2 Hydroxybutyl) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid esters include those of the acrylic acid ester was changed to methacrylic acid esters.

Furthermore, examples of the unsaturated acid include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid and the like.

The polymer composed of the monomer may be a copolymer or a homopolymer, and is preferably a homopolymer of vinyl ester, a copolymer of vinyl ester, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester.

In the present invention, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or methacrylic acid alkyl ester having no monomer unit having an aromatic ring or a cyclohexyl group.

Examples of the acrylate monomer having no aromatic ring and cyclohexyl group include, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-) , Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic (2-methoxyethyl), acrylic acid (2-ethoxyethyl), or the acrylic acid ester may include those obtained by changing the methacrylic acid ester.

The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by weight or more, and the methacrylic acid methyl ester monomer unit has 40% by weight or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both highly compatible with cellulose ester, excellent in productivity without evaporation and volatilization, and retainability as a protective film for polarizing plates The moisture permeability is small, and the dimensional stability is excellent.

In the present invention, an acrylic acid or methacrylic acid ester monomer having a hydroxyl group is not a homopolymer but a constituent unit of a copolymer. In this case, the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is preferably contained in the acrylic polymer in an amount of 2 to 20% by weight.

In the method for producing an optical film of the present invention, the dope composition contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 500 or more and 3000 or less as an additive for reducing the thickness direction retardation (Rt). Is preferred.

Moreover, in the manufacturing method of the optical film of this invention, dope composition is a cellulose ester and the weight average molecular weight 5,000 or more and 30,000 or less acrylic as an additive which reduces thickness direction retardation (Rt). It preferably contains a polymer.

In the present invention, the polymer as the additive for reducing the thickness direction retardation (Rt) has a weight average molecular weight of 500 or more and 3,000 or less, or the polymer has a weight average molecular weight of 5,000 or more and 30,000 or less. If so, the compatibility with the cellulose ester is good, and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester film after film formation is excellent, the moisture permeability is extremely low, and it exhibits excellent performance as a protective film for polarizing plates.

In the present invention, as an additive for reducing the thickness direction retardation (Rt), a polymer having a hydroxyl group in the side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. Examples include those substituted with methacrylic acid, preferably 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by weight, more preferably 2 to 10% by weight.

A polymer containing 2 to 20% by weight of the above-mentioned monomer unit having a hydroxyl group is, of course, excellent in compatibility with cellulose ester, retention, dimensional stability, and low moisture permeability. It is particularly excellent in adhesion with a polarizer as a protective film for a polarizing plate, and has an effect of improving the durability of the polarizing plate.

In the present invention, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate) is possible. A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization stopper having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a compound having one thiol group and a secondary hydroxyl group as described in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a polymerization catalyst using the compound and an organometallic compound in combination It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

In the present invention, the polymer having a hydroxyl group at the terminal and / or the polymer having a hydroxyl group in the side chain has the advantage of significantly improving the compatibility and transparency of the polymer with respect to the cellulose ester.

In the present invention, useful additives for reducing the thickness direction retardation (Rt) include, in addition to the above, an ester compound of diglycerin polyhydric alcohol and fatty acid described in JP-A No. 2000-63560, An ester or ether compound of a hexose sugar alcohol described in JP-A-2001-247717, a trialiphatic alcohol phosphate compound described in JP-A-2004-315613, and a general formula (1) described in JP-A-2005-41911 A phosphoric acid ester compound described in JP-A-2004-315605, a styrene oligomer described in JP-A-2005-105139, and a polymer of a styrene monomer described in JP-A-2005-105140. .

In the method for producing an optical film according to the present invention, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and has a main effect on dissolution. Organic) solvent or main (organic) solvent.

Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

In addition to the organic solvent, the dope preferably contains 1 to 40% by weight of an alcohol having 1 to 4 carbon atoms. After casting the dope onto the support, the solvent starts to evaporate and the alcohol ratio increases, so that the web (the dope film after the casting of the cellulose derivative dope on the support is called the web Is used as a gelling solvent that makes the web strong and makes it easy to peel off from the support, or when these ratios are small, dissolve the cellulose derivative of the non-chlorine organic solvent. There is also a role to promote.

Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

The most preferable solvent for dissolving a cellulose derivative, which is a preferable polymer compound satisfying such conditions, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethyl alcohol of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

The film according to the present invention includes a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles that impart slipperiness to the film (matting agent), an ultraviolet absorber that imparts an ultraviolet absorbing function, and deterioration of the film. You may contain the antioxidant etc. which prevent.

The plasticizer used in the present invention is not particularly limited. However, a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation can be used so as not to cause haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the condensate by hydrogen bonding or the like.

Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

The polyhydric alcohol used in the present invention is represented by the following general formula (3).

Formula (3): R1- (OH) n
(However, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.)

Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these.

Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

The monocarboxylic acid used in the polyhydric alcohol ester of the present invention is not particularly limited, and known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose derivative is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

Examples of preferable alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, and derivatives thereof.

Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and derivatives thereof, and benzoic acid is particularly preferable.

The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1,500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

The carboxylic acid used in the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

For phosphate plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, and the like can be used, but in the present invention, it is preferable that substantially no phosphate ester plasticizer is contained.

Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by weight, preferably 0.1% by weight, and particularly preferably not added.

These plasticizers can be used alone or in combination of two or more.

The amount of plasticizer used is preferably 1 to 20% by weight. It is more preferably 6 to 16% by weight, particularly preferably 8 to 13% by weight. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film Since the physical properties of the material deteriorate, it is not preferable.

It is preferable to add fine particles such as a matting agent to the cellulose derivative in the present invention in order to impart slipperiness. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

Examples of inorganic compound fine particles include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide, and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, 972, 972V, 974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

Examples of organic compound fine particles include fine particles of acrylic resin, silicone resin, fluorine compound resin, urethane resin, and the like.

The primary particle size of the fine particles is not particularly limited, but the final average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1 to 1.0 μm.

The average particle diameter of the fine particles refers to the average value of the lengths of the particles in the major axis direction when the cellulose ester film is observed with an electron microscope or an optical microscope. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for each film, and the number of particles in 100 μm ² whose major axis length is in the range of 0.05 to 5 μm for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film to aggregate. And controlling the particle size formed.

Here, if the average particle size of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or it may cause a failure in a wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

The fine particles are used by adding 0.04 to 0.5% by weight to the cellulose ester. Preferably, 0.05 to 0.3% by weight, more preferably 0.05 to 0.25% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

For dispersion of fine particles, it is preferable to treat a composition in which fine particles and a solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present invention is an apparatus that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. Further, at that time, those having a maximum reaching speed of 100 m / sec or more and those having a heat transfer speed of 100 kcal / hr or more are preferable.

Examples of such a high-pressure dispersion device include an ultra-high pressure homogenizer (trade name Microfluidizer) manufactured by Microfluidics Corporation, or a nanomizer manufactured by Nanomizer. A homogenizer etc. are mentioned.

In the present invention, the fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is allowed to flow on a support. A cellulose ester film is obtained which is formed by stretching and drying.

Here, the content ratio of the lower alcohol is preferably 50 to 100% by weight, more preferably 75 to 100% by weight.

Also, examples of lower alcohols preferably include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

The solvent other than the lower alcohol is not particularly limited, but it is preferable to use a solvent used at the time of forming a cellulose ester film.

Fine particles are dispersed in a solvent at a concentration of 1 to 30% by weight. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by weight, more preferably 10 to 20% by weight.

The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film, and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on a film made of the cellulose derivative.

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 preferably used.

As the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of a polarizer or liquid crystal and those having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. preferable.

Specific examples of UV absorbers useful 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- (straight 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- Examples include, but are not limited to, a mixture of 5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

Further, as commercially available ultraviolet absorbers, TINUVIN 109, TINUVIN 171, and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

In addition, specific examples of the benzophenone compounds that are ultraviolet absorbers that can be used in the present invention include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5- Examples thereof include, but are not limited to, sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

In the present invention, 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, based on the cellulose ester (cellulose derivative). If the amount of the UV absorber used is too small, the UV absorbing effect may be insufficient, and if the amount of the UV absorber used is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

As the ultraviolet absorber that can be used in the optical film of the present invention, the polymeric ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A Nos. 6-148430 and 2002-47357 is preferably used. be able to. In particular, it is represented by the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formulas (3), (6), and (7) described in JP-A-2002-47357. A polymer ultraviolet absorber is preferably used.

The antioxidant is generally referred to as an anti-degradation agent, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

As such an antioxidant, a hindered phenol compound is preferably used. For example, 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-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], oct Decyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-tert-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 processing stabilizer such as -butylphenyl phosphite may be used in combination.

The amount of these compounds added is preferably 1 ppm to 1.0% by weight, more preferably 10 to 1000 ppm by weight with respect to the cellulose derivative.

In addition, in the apparatus which implements the manufacturing method of the optical film of the present invention shown in FIG. 3 and FIG. 4, the stretching step is a film for a liquid crystal display device. A tenter method in which the film is fixed and stretched is preferable in order to improve the flatness and dimensional stability of the film.

The residual solvent amount of the web (film) (29) immediately before entering the tenter (32) in the stretching step is preferably 10 to 35% by weight.

The stretch ratio of the web in the tenter (32) in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%. Further, the temperature of the hot air blown from the hot air blowing slit port in the tenter (32) is 100 to 200 ° C., preferably 110 to 190 ° C., and more preferably 115 to 185 ° C.

It is preferable to provide a drying device (30) after the tenter (32) in the stretching step. In the drying device (30), the web (29) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web (29) is dried in the meantime. The film transport tension in the drying device (30) is affected by the properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, etc., but the film transport tension during drying is 10 to 300 N. / M width, and 20 to 270 N / m width is more preferable.

The means for drying the web (film) (29) is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity, for example, it is dried by the drying air (31) blown from the warm air inlet at the front portion of the bottom of the drying device (30), and is dried on the ceiling of the drying device (30). It is dried by exhaust air being discharged from the outlet of the rear portion. The temperature of the drying air (31) is preferably 40 to 160 ° C., more preferably 50 to 160 ° C. in order to improve the flatness and dimensional stability.

These steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

For example, a cellulose ester film that has finished the transport drying process is generally processed to form an emboss on the film by an embossing apparatus before the introduction to the winding process.

Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. For example, when the film thickness is 40 μm, the emboss height h 1 + h 2 (μm) is set to 2 to 12 μm. The emboss width is set to 5-30mm.

The film after drying is wound up by a winding device (33) to obtain the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film to be dried to 0.5% by weight or less, preferably 0.1% by weight or less.

The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. Use it properly.

The film may be joined to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

The optical film according to the present invention preferably has a width of 1200 to 2500 mm after winding.

In the present invention, the thickness of the cellulose ester film after drying is preferably in the range of 20 to 150 μm as the finished film from the viewpoint of thinning the liquid crystal display device. Here, the film thickness after drying refers to a film in which the amount of residual solvent in the film is 0.5% by weight or less.

Here, when the film thickness of the cellulose ester film after winding is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If the film thickness is too thick, the advantage of thinning the film becomes less than the conventional cellulose ester film. In order to adjust the film thickness, the dope concentration, the pumping amount, the slit gap of the die of the casting die, the extrusion pressure of the casting die, the speed of the support, etc. are controlled so as to obtain the desired thickness. Is good. Further, as a means for making the film thickness uniform, it is preferable that the film thickness detecting means is used to feed back and adjust the programmed feedback information to the respective devices.

In the process from immediately after casting through the solution casting film-forming method to drying, the atmosphere in the drying apparatus may be air, but may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

In the present invention, the cellulose ester film preferably has a moisture content of 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

In the present invention, the cellulose ester film desirably has a transmittance of 90% or more, more preferably 92% or more, and still more preferably 93% or more.

In addition, the optical film produced by the method of the present invention has a haze of 0.3 to 2.0 when three sheets are stacked. According to the optical film of the present invention, the haze of the film is very high. It is low and has optical characteristics excellent in transparency and flatness.

Here, the haze of the optical film may be measured, for example, using a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS K7105.

The tensile modulus in the machine direction (MD direction) of the cellulose ester film produced by the method for producing an optical film according to the present invention is 1500 MPa to 3500 MPa, and the tensile modulus in the direction perpendicular to the machine direction (TD direction) is It is preferably 3000 MPa to 4500 MPa, and the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the film is preferably 1.40 to 1.90.

Here, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the optical film is less than 1.40, the sag of the central portion becomes large in winding a film having a width exceeding 1650 mm, and Since sticking increases, it is not preferable. Further, when the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage after overheating in the polarizing plate occurs, or the backlight is heated by the heat of the backlight when incorporated in a liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JIS K7217 can be mentioned.

That is, using a tensile tester (TG-2KN, manufactured by Minebea), setting the sample at a chucking pressure: 0.25 MPa, a distance between marked lines: 100 ± 10 mm, and a pulling speed: 100 ± 10 mm / min Pull on. As a result, from the obtained tensile stress-strain curve, the elastic modulus calculation start point is 10N, the end point is 30N, and the tangent line drawn between them is extrapolated to calculate the elastic modulus.

In the optical film of the present invention, the in-plane retardation (Ro) defined by the following formula is 30 to 300 nm under the conditions of a temperature of 23 ° C. and a humidity of 55% RH, and the thickness direction retardation (Rt) is 23 ° C. and humidity. It is preferably 70 to 400 nm under the condition of 55% RH.

Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d

In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the film. The refractive index in the thickness direction (refractive index measured at a wavelength of 590 nm), d represents the thickness (nm) of the film.

The retardation values Ro and Rt can be measured using an automatic birefringence meter. For example, using KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), the wavelength can be obtained at 590 nm under the environment of temperature 23 ° C. and humidity 55% RH.

The optical film according to the present invention is manufactured by the above-described optical film manufacturing method, and the thickness of the film is preferably 30 to 200 μm.

The optical film according to the present invention has a film disposed between two polarizing plates orthogonal to each other, and the transmittance of the transmitted light having a wavelength of 600 nm is measured in a crossed Nicols state. The variation is 2 × 10 ⁻⁵ to 60 × 10 ⁻⁵ (%).

Here, it is preferable that the transmittance variation in the crossed Nicol state of the transmitted light having a wavelength of 600 nm of the optical film of the present invention is small, and if the transmittance variation exceeds 60 × 10 ⁻⁵ (%), the optical film is transparent. This is not preferable because the properties and flatness are deteriorated.

According to the invention of the optical film of the present invention, the release property (peelability) of the film or cast film (web) from the cooling roll or the surface of the support is improved, and a very smooth peelability is obtained. Since the fluctuation in the width direction of the position is reduced, the optical film is not deformed even in high-speed production, the variation in crossed Nicol transmittance is greatly reduced, and it has excellent transparency and flatness. It is possible to respond to the demand for conversion.

The optical film targeted by the present invention is a functional film used for various displays such as a liquid crystal display, a plasma display, and an organic EL display, particularly a liquid crystal display. A polarizing plate protective film, a retardation film, an antireflection film, It includes an optical compensation film such as a brightness enhancement film and a viewing angle expansion.

The optical film according to the present invention is preferably used for a liquid crystal display member, specifically a protective film for a polarizing plate. In particular, in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability, the optical film produced by the method of the present invention is preferably used.

By using the protective film for polarizing plate made of the optical film of the present invention, it is possible to provide a polarizing plate that is excellent in durability, dimensional stability, and optical isotropy, as well as being thinned. The polarizing plate uses an optical film produced by the method of the present invention on at least one surface.

By the way, the polarizing film is a film that has been conventionally stretched, for example, a film that can be stretched and oriented, such as a polyvinyl alcohol film, treated with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

The polarizing plate may be prepared by laminating the optical film produced by the method of the present invention as a retardation film, and the optical film produced by the method of the present invention is a retardation film and a protective film. Alternatively, it may be produced by directly bonding to a polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of the present invention. . 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).

The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. Is preferred.

Incidentally, the polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is immersed and stretched in an iodine solution and bonded to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. is there. The alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness.

The optical film produced by the method of the present invention includes a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optical anisotropic layer, a liquid crystal layer, an alignment layer, an adhesive layer, Various functional layers such as an adhesive layer and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

The polarizing plate obtained in this way does not visually observe unevenness in density, and can satisfactorily meet the demand for larger polarizing plates.

The polarizing plate thus obtained is provided on one side or both sides of the liquid crystal cell, and a liquid crystal display device is obtained using this.

In the present invention, the liquid crystal display device comprises two sheets comprising a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. It has a polarizing plate.

By using a protective film for a polarizing plate comprising an optical film produced by the method of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time. This display device is free from contrast reduction and shading unevenness, has excellent visibility, and can respond well to the demand for larger size.

The optical film produced by the method of the present invention can also be used as a base material for an antireflection film or an optical compensation film.

The technical features of this embodiment are summarized as follows.

The method for producing an optical film according to the present embodiment is a method for producing an optical film by a melt casting film forming method for casting a resin melt on a support or a solution casting film forming method for casting a resin solution. After the film obtained from the cast resin melt or resin solution is peeled from the support, the surface of the exposed support is exposed until the resin melt or resin solution is cast again on the support. Further, a first step of removing dirt on the surface of the support by performing atmospheric pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation, and after this first step, the surface of the support is again exposed to atmospheric pressure plasma. A second step of performing further irradiation, excimer ultraviolet irradiation or laser irradiation, or further removing dirt on the surface of the support by bringing a tangible object into contact with the surface of the support. It is a Irumu method of manufacturing.

According to this method for producing an optical film, when the support surface is cleaned while producing the optical film, the surface of the support is cleaned with high efficiency unprecedented, and dirt is almost removed in a relatively short time. Can do.

The reason is considered as follows. That is, in the manufacturing method according to the present embodiment, the first dirt removing step and the second dirt removing step are performed in this order on the surface of the support exposed during the production of the optical film. The first dirt removing step is to remove the dirt on the surface of the support by performing high energy ray irradiation, that is, atmospheric pressure plasma irradiation, excimer ultraviolet ray irradiation or laser irradiation. It corresponds to. Conventionally, the process is completed only by the first dirt removing step. In the present embodiment, in addition to the first dirt removal process, a second dirt removal process is further performed. In the second dirt removing step, after the first dirt removing step, high energy ray irradiation is performed again, or the tangible material is brought into contact with the support surface to further remove the dirt on the support surface. For this reason, dirt that has not been removed in the first dirt removing step (this dirt includes dirt that has been decomposed by high energy ray irradiation in the first process but is still attached to the support surface). It is considered that the second step is almost removed by overlapping.

In particular, this embodiment relates to a method for producing an optical film. And since the optical film has a polymer resin as a main component, dirt that has a polymer resin as a main component cannot be completely decomposed only by high-energy radiation irradiation that has been conventionally performed, or even if it can be decomposed, a low molecular weight molecule. It is considered that there are many cases where the dirt cannot be completely removed only by the high-energy radiation irradiation once because of the fact that it cannot be decomposed. Therefore, most of the dirt is supported by irradiating the high energy ray multiple times or by wiping off the dirt (decomposed matter and low molecular weight component as the main component) still adhering to the support surface after the high energy ray irradiation. It is considered to be removed from the body surface.

In addition, when high energy ray irradiation is performed again in the second step, it may be the same type of high energy ray irradiation as in the first step or may be different type of high energy ray irradiation.

In the said manufacturing method, it is preferable that the contact of the tangible thing to the support body surface in a 2nd process is spraying a liquid on the surface of a support body. Due to the collision of the liquid particles with the surface of the support, the dirt that has not been removed in the first step is reliably blown off and removed. Further, the support surface is hardly damaged. In addition, as a liquid, the organic solvent (methylene chloride, alcohol, etc.) used for the resin solution of a solution casting film forming method is preferable, for example. This is because there is little tendency for the liquid to remain on the surface of the support, and there are few problems even if the liquid remains on the surface of the support and is mixed with the resin melt or resin solution. The liquid spraying conditions (spraying amount, etc.) vary depending on the spraying time (the time during which the second step can be performed: about 1 second at the longest), the type of spraying device, the type of liquid, etc. When spraying methylene chloride using an ultrasonic spray, the amount is about 1 to 10 ml / m ² per ^second .

In the manufacturing method, the contact of the tangible object with the support surface in the second step is preferably rubbing the surface of the support with a cloth. By the friction of the surface of the support, the dirt that has not been removed in the first step is surely wiped off and removed. Nonwoven fabric is preferred as the cloth. As a method of rubbing the surface of the support with a cloth, for example, the silicon pad may be covered with a nonwoven fabric and pressed with a predetermined pressing force over the entire width of the surface of the support. At this time, the surface of the support is pressed as uniformly as possible in the width direction.

As the nonwoven fabric, a nonwoven fabric using long fibers can be preferably used. As long fibers, cellulose is preferred. Examples of commercially available cleaning cloths (wiping tools) include “Bencot” series manufactured by Asahi Kasei Co., Ltd., and Bencot M-1, Bencott M-3, Bencott M-3II, and the like can be preferably used.

In the manufacturing method, it is preferable that the atmospheric plasma irradiation, excimer ultraviolet irradiation or laser irradiation in the first step and / or the second step is performed in the presence of an active oxygen species. Strong decomposition effect of soil components by irradiation with high energy rays (breakage of chemical bond of soil components mainly composed of organic matter) and strong oxidation effect of soil components by active oxygen species (carbon dioxide of soil components composed mainly of organic matter) This is because the removal of dirt is promoted in synergy with the decomposition of water and other simple molecules. Here, the active oxygen species, for example, ozone _(O 3), nitrogen monoxide (NO), nitrogen dioxide (ONO), superoxide anion _{(O 2} ^-), superoxide anion radicals _(O 2 ^· -), A hydroxyl radical (HO.), Hydrogen peroxide (HOOH), etc. are mentioned.

In the production method, the temperature of the support when performing the first step and the second step is 180 ° C. or less in the melt casting film forming method and −20 to 80 ° C. in the solution casting film forming method. It is preferable. In general, the cooling and solidification temperature of the resin melt on the support in the melt casting method is adjusted to 180 ° C. or lower, and the solvent evaporation temperature on the support of the resin solution in the solution casting method is −20. Since the temperature is adjusted to ˜80 ° C., in any case, the first step and the second step can be performed during normal film formation, and it is not particularly necessary to cool or heat the support. Further, the dirt removal effect of the first step and the stain removal effect of the second step are not lowered in the temperature range.

In the above production method, the resin melt or resin solution resin is preferably a cellulose ester resin. A highly transparent optical film is produced.

In the manufacturing method, the support is preferably a roll, an endless belt, or a drum. The roll on which the resin melt is cast by the melt casting method and the surface of the endless belt or drum on which the resin solution is cast by the solution casting method are cleaned with high efficiency during the production of the optical film. Therefore, the peelability of the film does not deteriorate for a long time. Therefore, the optical film can be produced at high speed and continuously while the roll, endless belt, or drum is continuously used for a long time.

The optical film according to the present embodiment is an optical film manufactured by the manufacturing method. This optical film is not deformed even in high-speed production and continuous production over a long period of time, variation in crossed Nicols transmittance is suppressed, transparency and flatness are excellent, and it can respond well to the demand for wider optical films. Is.

The polarizing plate according to the present embodiment is a polarizing plate characterized by using the optical film on at least one surface. This polarizing plate does not have any unevenness in visual observation, and can satisfactorily meet the demand for larger polarizing plates.

The display device according to the present embodiment is a display device using the optical film or the polarizing plate. This display device is free from contrast reduction and shading unevenness, has excellent visibility, and can respond well to the demand for larger size.

According to this embodiment, since the peelability from the support of the film does not decrease over a long period of time, an optical film having optical properties excellent in transparency and flatness can be stably produced. It is possible to satisfactorily meet demands for thinning, widening and high quality of protective films for plates. Moreover, since high-speed production and continuous production of a film over a long time can be performed, an optical film can be produced efficiently.

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

[Test No. 1-26]
First, the manufacturing method of the optical film of this invention was implemented by the melt casting film forming method.

(Preparation of pellets)
100 weight of cellulose acetate propionate (acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, number average molecular weight 75000, temperature 130 ° C., dried for 5 hours, glass transition temperature Tg = 174 ° C.) Part 10 parts by weight of plasticizer (trimethylolpropane tris (3,4,5-trimethoxybenzoate)) 1 part by weight of antioxidant (IRGANOX-1010, manufactured by Ciba Specialty Chemicals) Antioxidant (Sumilizer GP, 1 part by weight of Sumitomo Chemical Co., Ltd. 0.05 parts by weight of silica particles (Aerosil 972V, manufactured by Nippon Aerosil Co., Ltd.) as a matting agent, and UV absorber (TINUVIN 360, manufactured by Ciba Specialty Chemicals) 5 parts by weight was added and mixed for 30 minutes in a V-type mixer filled with nitrogen gas. Then, it melt | dissolved at 240 degreeC using the biaxial extruder (PCM30, Ikegai Co., Ltd.) which attached the strand die | dye, and produced the cylindrical pellet of length 4mm and diameter 3mm. The shear rate at this time was set to 25 / second.

(Production of film)
Using the molten resin, a cellulose acetate propionate film having a thickness of 40 μm was produced as follows.

Film formation was performed with the manufacturing apparatus shown in FIG. Referring to the figure, the first cooling roll (5) and the second cooling roll (7) were made of stainless steel having a diameter of 1000 mm, and hard chrome plating was applied to the surface. Further, oil for temperature adjustment (cooling fluid) was circulated inside to control the roll surface temperature.

The elastic touch roll (6) had a diameter of 20 cm, the inner cylinder and the outer cylinder were made of stainless steel, and the outer cylinder surface was subjected to hard chrome plating. The wall thickness of the outer cylinder was 2 mm, and oil for cooling (cooling fluid) was circulated in the space between the inner cylinder and the outer cylinder to control the surface temperature of the elastic touch roll (6).

The obtained pellets (water content 50 ppm) were melted in a single screw extruder (1) and subjected to pressure filtration using a leaf disk type metal filter (2).

As the casting die (4), a casting die (4) having a lip clearance of 1.0 mm and a lip portion average surface roughness Ra of 0.01 μm was used. Further, silica fine particles as a slip agent were added from the hopper opening in the middle of the extruder so as to be 0.1 parts by weight.

The resin melt was melt extruded from the casting die (4) into a film at a melting temperature of 250 ° C.

And this test No. In Nos. 1 to 25, a casting film (web) was cast from the casting die (4) onto the surface of the first cooling roll (5) made of hard chrome plated stainless steel at a speed of 200 m / min. At this time, the cast film was brought into contact with the first cooling roll (5) having a surface temperature of 100 ° C. at a draw ratio of 10 to obtain a cast film having a thickness of 100 μm.

This test No. The glass transition temperature (Tg) of the cellulose acetate propionate film in 1 to 25 was 136 ° C., and the glass transition temperature of the cast film extruded from the casting die (4) was measured using a DSC6200 manufactured by Seiko Corporation. DSC method (in nitrogen, temperature rising temperature 10 ° C./min).

Furthermore, the cast film (film) was pressed on the first cooling roll (5) by the elastic touch roll (6) having a metal surface at a linear pressure of 10 kg / cm. The film temperature on the touch roll (6) side at the time of pressing was 180 ° C. ± 1 ° C. The surface temperature of the first cooling roll (5) was adjusted to 180 ° C.

The surface temperature of the second cooling roll (7) was 30 ° C. And the surface temperature of each roll of an elastic touch roll (6), a 1st cooling roll (5), and a 2nd cooling roll (7) is with respect to a rotation direction from the position where a cast film (film) contact | connects a roll first. The average value obtained by measuring the temperature of the roll surface at a position 90 ° before 10 points in the width direction using a non-contact thermometer was defined as the surface temperature of each roll.

The cooled and solidified film (10) peeled from the third cooling roll (8) by the peeling roll (9) is guided to a stretching device (12) through a dancer roll (film tension adjusting roll) (11), where the film ( 10) is stretched in the transverse direction (width direction). By this stretching, the molecules in the film are oriented.

After stretching, the end of the film is slit to a product width by a slitter (13) and cut off, and then knurled (embossed) by a knurling device comprising an embossing ring (14) and a back roll (15). It applied to the film both ends, and it wound up with the winding apparatus (16), and produced the cellulose acetate propionate film with a film thickness of 40 micrometers.

And during manufacture of such an optical film, after peeling the film (10) obtained from the cast resin melt from the 1st cooling roll (5), it is resin on the 1st cooling roll (5) again. Before casting the melt, the exposed surface of the first cooling roll (5) was subjected to the first dirt removing step and the second dirt removing step with the contents shown in Table 1. At this time, the time during which the surface of the cooling roll (5) was exposed was approximately 0.3 seconds. Then, during this 0.3 second, first, the first dirt removing step was performed for 0.1 second, and then the second dirt removing step was carried out for 0.1 second.

Here, the amount of reaction gas used in the atmospheric pressure plasma irradiation apparatus (40) was set to 1 m ³ per 1 m of irradiation width. The composition of the mixed gas (reactive gas) used for the plasma treatment was nitrogen: 99.8% by volume and oxygen: 0.2% by volume. The atmospheric pressure was 1.0 atm. As the atmospheric pressure plasma irradiation apparatus (40), the one shown in FIG. 5 was used.

The excimer ultraviolet irradiation device (50) is as shown in FIG. 6, and in the quartz glass (q) having a length of about 300 mm in the conveying direction of the cooling roll (5), the irradiance is 40 mW / cm ² . An apparatus containing four excimer ultraviolet lamps (u) having a Xe2 wavelength of 172 nm was used.

Excimer laser irradiation was performed as laser irradiation.

As the liquid spray, methylene chloride was sprayed on the surface of the first cooling roll (5) in an amount of 1 to 10 ml / m ² per second from a distance of 10 mm using an ultrasonic spray. As for cloth rubbing, “Bencot M-1” (cellulose wiping tool) manufactured by Asahi Kasei Co., Ltd. was pressed against the surface of the first cooling roll (5) with a predetermined pressure to rub the surface of the first cooling roll (5). . All were performed on the exposed surface of the cooling roll (5) rotating at a constant speed over the entire width of the cooling roll (5).

[Test No. 31-56]
Next, the method for producing the optical film of the present invention was carried out by a solution casting film forming method.

(Preparation of dope)
The following materials were put into a sealed container, heated and stirred, and completely dissolved and filtered to prepare a dope (resin solution). Silicon dioxide fine particles (Aerosil 972V) were added after being dispersed in ethanol.

(Dope composition)
100 parts by weight of cellulose triacetate (Mn = 148,000, Mw = 310,000, Mw / Mn = 2.1) 8 parts by weight of triphenyl phosphate 2 parts by weight of ethylphthalylethyl glycolate (plasticizer) Methylene chloride 440 parts by weight Ethanol 40 parts by weight Tinuvin 109 (UV absorber, manufactured by BASF Japan) 0.5 part by weight Tinuvin 171 (UV absorber, manufactured by BASF Japan) 0.5 part by weight Aerosil 972V (mat agent) As silica particles (manufactured by Nippon Aerosil Co., Ltd.)

(Production of film)
Using the dope, a cellulose triacetate film having a thickness of 40 μm was produced as follows.

Film formation was performed with the manufacturing apparatus shown in FIG. Referring to the figure, the filtered dope was cast in the form of a film on the surface of the endless belt (27) from a casting die (23) made of a coat hanger die at a dope temperature of 35 ° C.

And these test Nos. In Nos. 31 to 56, the dope was cast on the surface of a metal support (27) made of SUS316 and made of an endless belt polished to a super mirror surface.

Next, after the cast film was peeled off from the stainless steel endless belt (27), it was dried while being conveyed in a roll at 90 ° C., and the width in the width direction in the atmosphere at 100 ° C. when the residual solvent amount was 10%. The film is stretched 1.06 times, then the width is released, and drying is completed in a drying zone at 125 ° C. while being conveyed by roll, and a knurling process with a width of 10 mm and a height of 8 μm is applied to both ends of the film to obtain a film thickness of 40 μm. A cellulose triacetate film was prepared. The film width was 2000 mm, and the winding length was 3000 m.

And during manufacture of such an optical film, after peeling the film (10) obtained from the cast resin solution from the endless belt (27), the resin solution is cast again on the endless belt (27). In the meantime, the 1st dirt removal process and the 2nd dirt removal process were performed on the surface of the exposed endless belt (27) by the contents shown in Table 2. At this time, the time during which the surface of the endless belt (27) was exposed was approximately 0.3 seconds. Then, during this 0.3 second, first, the first dirt removing step was performed for 0.1 second, and then the second dirt removing step was carried out for 0.1 second.

Here, the amount of reaction gas used in the atmospheric pressure plasma irradiation apparatus (40) was set to 1 m ³ per 1 m of irradiation width. The composition of the mixed gas (reactive gas) used for the plasma treatment was nitrogen: 99.8% by volume and oxygen: 0.2% by volume. The atmospheric pressure was 1.0 atm. As the atmospheric pressure plasma irradiation apparatus (40), the one shown in FIG. 5 was used.

The excimer ultraviolet irradiation device (50) is as shown in FIG. 6, and in the quartz glass (q) having a length of about 300 mm in the conveying direction of the cooling roll (5), the irradiance is 40 mW / cm ² . An apparatus containing four excimer ultraviolet lamps (u) having a Xe2 wavelength of 172 nm was used.

Excimer laser irradiation was performed as laser irradiation.

As the liquid spray, methylene chloride was sprayed on the surface of the endless belt (27) in an amount of 1 to 10 ml / m ² per second from a distance of 10 mm using an ultrasonic spray. As for cloth rubbing, “Bencott M-1” (cellulose wiping material) manufactured by Asahi Kasei Co., Ltd. was pressed against the surface of the endless belt (27) with a predetermined pressure to rub the surface of the endless belt (27). Both were performed on the exposed surface of the endless belt (27) running at a constant speed over the entire width of the endless belt (27).

[Evaluation]
(Measurement of peel strength at the start of film formation and after 24 hours)
About each said test, regarding each cast film (it is a dope film | membrane or a web), based on JISZ0237, it peels 90 degree | times at the time of film forming start and 24 hours after film forming start (peeling speed: 300 mm). Per minute), and this was measured at the beginning of film formation (ie, the initial stage of use of the support, the beginning of film production) and 24 hours later, and the metal support (cooling roll in Test Nos. 1 to 26). (5) In Test Nos. 31 to 56, the minimum peeling force (lower limit peeling force: N / 100 mm) required for peeling the film from the surface of the endless belt (27) was set. The results are shown in Tables 1 and 2.

(Measurement of variation width of crossed Nicols (CNT) transmittance)
For the cellulose ester films obtained in all the above tests, using a polarizing film measuring apparatus (VAP-7070) manufactured by JASCO Corporation, at a measurement wavelength of 600 nm, the film width is 50 mm apart, and the longitudinal direction is Cross Nicol (CNT) transmittance is measured at intervals of 50 mm in a 300 mm section, and the difference between the average value of all data and the most dissimilar value is represented here as the variation width of cross Nicol (CNT) transmittance (× 10 ^{− 5} %). The results are shown in Tables 1 and 2.

(Polarization unevenness)
First, according to the method described below, a polarizing plate using the cellulose ester film obtained in all the tests as a protective film was prepared.

That is, a 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a polarizing film.

Step 1: The cellulose ester films obtained in all the above tests were each immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried. A protective film (made of polyethylene terephthalate) that can be removed again was attached to the surface provided with the antireflection film in advance for protection. Similarly, the cellulose ester film was immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

Step 2: The aforementioned polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by weight for 1 to 2 seconds.

Step 3: The excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and it was sandwiched between a cellulose ester film subjected to alkali treatment in Step 1 and a commercially available cellulose ester film, and laminated.

Step 4: The two rotating rolls were bonded together at a pressure of 20-30 N / cm ² and a speed of about 2 m / min. At this time, care was taken to prevent bubbles from entering.

Process 5: A polarizing plate having a structure in which a polarizing film and a cellulose ester film were bonded to each other was obtained by drying the sample prepared in Process 4 in a dryer at 80 ° C. for 2 minutes.

The polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD1525J, model name LA-1529HM) is carefully peeled off, and the polarizing plate produced as described above is aligned with the polarization direction. Pasted. Each liquid crystal display panel obtained in this way was visually observed by a plurality of evaluators to observe whitish unevenness when viewed from the front and oblique directions, and evaluated according to the following criteria. The results are shown in Tables 1 and 2.

Evaluation criteria for unevenness A: None of the evaluators could see any unevenness.
○: Although it may be faintly uneven depending on the evaluator, it is a level that can be used as a product.
(Triangle | delta): Although it was faint in many evaluators, the nonuniformity was seen.
X: Unevenness was seen in many evaluators.

As is clear from the results of Tables 1 and 2, the cast resin melt or the resin solution is used regardless of whether the optical film manufacturing method is a melt casting film forming method or a solution casting film forming method. After peeling the film obtained from the support, the surface of the exposed support is exposed to atmospheric pressure plasma, excimer ultraviolet irradiation, or until the resin melt or resin solution is cast again on the support. A first step of removing contamination on the surface of the support by performing laser irradiation; and after the first step, whether the surface of the support is again subjected to atmospheric pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation. Or, when the second step of further removing dirt on the surface of the support by bringing a tangible object into contact with the surface of the support, high-speed production of a film over a long period of time (24 hours), Continuous production However, the lower limit peel strength of the film hardly increases (the film peelability does not deteriorate), and the surface of the support is cleaned with high efficiency, and it is understood that the dirt is almost removed in a relatively short time. .

As a result, the deformation of the film was avoided, and the variation of the crossed Nicol (CNT) transmittance of the optical film caused by the deformation of the film and the unevenness of the polarizing plate using the optical film were satisfactorily suppressed.

In particular, in Tests 26 and 56 in which high energy rays were irradiated in the presence of active oxygen species, the lower limit peel strength of the film hardly increased even after 72 hours from the start of film formation.

This application is based on Japanese Patent Application No. 2010-241179 filed on Oct. 27, 2010, the contents of which are included in this application.

In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized as gaining. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

The present invention has wide industrial applicability in the technical fields of optical film manufacturing methods, optical films, polarizing plates using optical films, and display devices.

Claims (10)

1. A method for producing an optical film by a melt casting film forming method for casting a resin melt on a support or a solution casting film forming method for casting a resin solution,
   After peeling the film obtained from the cast resin melt or resin solution from the support, until the resin melt or resin solution is cast again on the support,
   A first step of removing contamination on the surface of the support by subjecting the exposed surface of the support to atmospheric pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation;
   After this first step, the surface of the support is soiled again by atmospheric pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation, or by bringing a tangible object into contact with the surface of the support. A second step of further removing
   A method for producing an optical film, comprising:
2. The method for producing an optical film according to claim 1, wherein the contact of the tangible object with the surface of the support in the second step is to spray a liquid onto the surface of the support.
3. The method for producing an optical film according to claim 1, wherein the contact of the tangible object with the surface of the support in the second step is rubbing the surface of the support with a cloth.
4. The atmospheric pressure plasma irradiation, excimer ultraviolet irradiation or laser irradiation in the first step and / or the second step is performed in the presence of an active oxygen species. Manufacturing method of the optical film.
5. The temperature of the support when performing the first step and the second step is 180 ° C. or less in the melt casting film forming method and −20 to 80 ° C. in the solution casting film forming method. Item 5. The method for producing an optical film according to any one of Items 1 to 4.
6. 6. The method for producing an optical film according to claim 1, wherein the resin melt or the resin in the resin solution is a cellulose ester resin.
7. 7. The method for producing an optical film according to claim 1, wherein the support is a roll, an endless belt, or a drum.
8. An optical film manufactured by the method for manufacturing an optical film according to any one of claims 1 to 7.
9. A polarizing plate using the optical film according to claim 8 on at least one surface.
10. A display device using the optical film according to claim 8 or the polarizing plate according to claim 9.

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