JP2008254223A - Optical film, its manufacturing method, polarization plate using optical film and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film reduced in the restriction of a film manufacturing condition, sharply widened in the selection range of the film manufacturing condition and made excellent in transparency and flatness in the manufacture of the optical film wherein the stain on the surface of a metal support is removed in a short time without applying a flaw or a water mark to the surface of the metal support, the surface releasability of the support is enhanced, the surface of the support is made hard to stain and inorganic matter such as Ca or the like is perfectly peeled in a short time by blowing an ultrasonic irradiation liquid against the surface of the support using a megasonic ultrasonic irradiator using a washing agent, its manufacturing method, a polarization plate using the optical film and a display device. <P>SOLUTION: In manufacturing the optical film, the surface of the metal support is washed by a washing apparatus using the washing agent, the liquid droplets remaining on the surface of the support is subsequently blown off by a liquid drainage device, the surface of the support is subjected to high energy surface treatment by an atmospheric pressure plasma device and a dope is subsequently cast over the surface of the support. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, liquid crystal display devices have come to be used in televisions and large monitors due to improvements in image quality and high definition technology. In particular, these liquid crystal display devices are costly due to their large size and efficient production. The demand for down and the like has become stronger in materials for liquid crystal display devices, and a wider optical film is required.

  In recent years, the demand for optical films has been increasing rapidly in response to the rapid growth of liquid crystal TVs, and there is a strong demand for improved productivity. As for the optical film formed by the solution casting method, the production speed can be increased because the amount of the solvent to be dried is small in the thin film.

  In general, in the solution film casting in which a resin solution (dope) containing a thermoplastic resin and an additive is cast on a metal support made of a rotationally driven stainless steel endless belt or the same drum, the type of vinegar, poor solvent However, when the weight ratio of the total solvent amount to the film solid content weight is around 60% by weight, there is a region where the peeling force of the film from the metal support increases and peeling becomes worse.

  In this region, the film cannot be peeled off smoothly from the metal support, accompanied by considerable flapping and peeling noise, and the film has a sharp step-like deformation extending in the width direction that occurs due to this flapping. In production, it was unavoidable to remove the condition, which was a restriction on the film.

  This poorly peeled area varies depending on the type of the dope material, that is, for example, the type of vinegar, the addition ratio of the poor solvent, the temperature of the film at the time of peeling, and the like. This region exists even in the case of the rolled film.

  In order to remove such a poor peeling region, for example, when trying to take film production conditions on the so-called high residual dissolution (high residual solvent amount) side of the web (film), particularly in a film having a film thickness of 40 μm or less, Even if the temperature of the drying air blown to dry the casting film on the metal support is lowered, the evaporation rate of methylene chloride, which is the solvent, cannot be greatly reduced, so that high residual melt peeling conditions cannot be achieved. was there.

  Therefore, in order to achieve high residual melt peeling, in addition to increasing the production rate of the film, in this case, post-drying is performed in order to increase the capacity of the solvent recovery facility or to reduce the amount of residual solvent in the product film to the limit. There was a problem that a large facility modification was required, such as extending the process.

  For this reason, normally, the manufacturing conditions of the optical film had to be set to the conditions on the low residual melt peeling side. However, in the case of low residual dissolution peeling conditions, the casting film enters the drying rate reduction period, so if the drying time on the support is not made very long, the residual dissolution cannot be lowered. There was a problem that the production speed had to be greatly reduced.

  As described above, conventionally, there is a problem that the metal support has a poorly peeled residual dissolution region, and thus there is a problem that a film has to be formed at a production rate significantly lower than the apparatus capability.

In addition, when shifting to the production conditions, when passing through this poorly peeled region, impurities in the dope, particularly calcium, magnesium and sulfuric acid traces derived from vinegared cotton, tend to adhere and accumulate on the belt surface, and these grow over time. When it comes, the unevenness is transferred to the film and appears as a whitish unevenness, streaks, or a belt-like pattern on the film, which is a big problem.
Japanese Patent Laid-Open No. 2003-55501 JP, 2003-128838, A In patent documents 1 and 2, in order to solve the above conventional subjects, the manufacturing method of the cellulose acylate film which adds exfoliation adjuvant to dope is indicated. Japanese Patent Laid-Open No. 2000-239403 discloses an apparatus-like improvement method for manufacturing an optical film, which is a solution casting film forming apparatus for casting having a specific surface roughness (Ra). A method for producing a cellulose acylate film formed using a metal support is disclosed. Japanese Patent Application Laid-Open No. 2002-264152 discloses a device improvement method for manufacturing an optical film, which is good by providing a continuous spiral groove on the surface of a metal support. A method is described in which accumulation of deposits and the like on the surface of a metal support is suppressed while maintaining peelability, and a smooth optical film is stably produced for a long period of time. In JP-A-2002-2894352, when a cellulose ester film is produced by a solution casting film-forming method, pure water is used in a method of cleaning an endless metal support surface that moves infinitely using a tool. Disclosed are a method for cleaning a metal support surface that includes an operation of wiping with a tool and an operation of wiping with an organic solvent included in the tool.

  However, the methods described in Patent Documents 1 and 2 have a problem that a sufficient effect cannot be obtained for the above-described web (film) peeling failure region.

  Further, in the methods described in Patent Documents 3 and 4, the accumulation of dirt on the surface of the metal support can be prevented, but the web (film) peeling failure region has not been eliminated.

  Furthermore, the wiping with the cleaning liquid described in Patent Document 5 can provide a certain degree of cleaning effect for plasticizers and UV agents, but cannot remove a substance such as calcium that is firmly fixed to the support surface. . Also, the cleaning time was very long, which was a problem. Moreover, depending on how to wipe, the surface of the metal support may be finely scratched, or a so-called watermark that remains in a ring shape on the trace of evaporation of the solvent detergent droplets may partially remain. was there.

  In the conventional cleaning method using a brush, which has been performed in the LCD panel cleaning process, the surface of the metal support for film formation is small but highly likely to be damaged. . In particular, in terms of pinholes on the surface of the metal support, the material for the film-forming endless belt or drum that can be used for an optical film is only SUS304 or SUS316 made of stainless steel, which is essentially an endless belt or drum. It can be said that these stainless steel materials are relatively soft materials and have a problem that they are easily damaged.

  The surface of the film by a scanning atomic force microscope (AFM) indicates that even if the number of scratches is in the order of nanometers, which cannot be confirmed by visual inspection, dirt accumulates in that area. It can be seen from the tracking of the change in the shape of the support surface transferred to the surface. For example, even if the dirt is removed by the brush, the dirt is accelerated by attaching a minute scratch.

  By the way, conventionally, in the production of an optical film having a film width of 1500 mm or more other than the above-described web (film) peeling failure region, the dope casting width on the metal support is 1700 mm or more. In manufacturing, variations in peelability in the width direction of the film appear as fluctuations in the peeling position. As a result, the retardation (Re) value and the like vary in the width direction and the longitudinal direction of the film. In liquid crystal panels that are becoming more and more precise year by year, such variations in the characteristics of the optical film, which in turn causes a decrease in the contrast of the liquid crystal panel and uneven density, have become a major problem. .

  An object of the present invention is to solve the above-mentioned problems of the prior art, and in an optical film manufacturing method by a solution casting film forming method, after cleaning a metal support surface on which a dope is cast using a cleaning agent, an air knife Blow off the droplets remaining on the surface with a liquid draining device, etc., and then irradiate with atmospheric pressure plasma, so that dirt can be removed in a short time without creating scratches or watermarks on the metal support surface. The mold releasability on the surface of the metal support can be improved, making it difficult for dirt to adhere, or even if dirt is attached, making the metal support surface difficult to get dirty, and using a cleaning agent Cleaning is a cleaning device that sprays ultrasonically applied liquid, especially called a megasonic cleaning agent.By spraying ultrasonically irradiated liquid onto the surface of a metal support, calcium, magnesium, or sodium Inorganic materials such as lithium can also be completely removed in a short time, which reduces the restrictions on film production conditions so far, greatly expands the range of film production conditions, and releases the film from the metal support. Improved moldability (peelability), extremely smooth peelability is obtained in the entire residual area of the peel, reducing fluctuations in the width direction of the peel position, and greatly varying retardation (Re) values It is possible to produce an optical film having optical characteristics with excellent transparency and flatness, and it is possible to increase the production speed and improve the productivity of the film. Optical film, manufacturing method thereof, polarizing plate using optical film, and display device capable of meeting demands for thinning, widening, and high quality of protective films for plates, etc. It is to provide a.

  In order to achieve the above object, an invention of claim 1 is a method for producing an optical film by a solution casting film forming method, wherein a resin solution (dope) containing a thermoplastic resin and an additive is applied on a metal support. To form a cast film (web), evaporate a part of the solvent, and then peel off from the metal support. The surface of the metal support is cleaned with a cleaning agent by a cleaning device. After cleaning, the droplet remaining on the surface of the metal support is blown off by a liquid draining device, and then subjected to high energy surface treatment by an atmospheric pressure plasma device, and then the dope is cast on the surface of the metal support. .

  Invention of Claim 2 is the manufacturing method of the optical film of Claim 1, Comprising: The washing | cleaning apparatus is a megasonic washing | cleaning apparatus which comprises the ultrasonic oscillator, and a liquid draining apparatus is an air knife, It is characterized by the above-mentioned. Yes.

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

  The invention of a polarizing plate according to a fourth aspect is characterized in that the optical film according to the third aspect is provided on at least one surface.

  The invention of the display device according to claim 5 is characterized by using the polarizing plate according to claim 4.

  The invention of claim 1 is a method for producing an optical film by a solution casting film-forming method, wherein a resin solution (dope) containing a thermoplastic resin and an additive is cast on a metal support to cast a film ( Forming a web), evaporating a part of the solvent, and then peeling off from the metal support. After cleaning the surface of the metal support with a cleaning agent using a cleaning device, According to the invention of claim 1, the remaining droplets are blown off by a liquid draining device such as an air knife, and then subjected to high energy surface treatment by an atmospheric pressure plasma device, and then the dope is cast on the surface of the metal support. After the surface of the metal support on which the dope is cast is washed with a cleaning agent, the remaining liquid on the surface is blown off by a liquid draining device such as an air knife, and then the metal support is irradiated with atmospheric pressure plasma. Scratches and Without having to make a Tamaku, it was able in a short time to stain removal. In addition, it is possible to improve the releasability of the surface of the metal support, and it becomes difficult for dirt to adhere, or it is easy to remove even if dirt is attached, and the surface of the metal support becomes difficult to get dirty. The restrictions on film production conditions are reduced, the range of film production conditions is greatly expanded, and the mold releasability (peelability) of the film from the metal support is improved. To produce an optical film having optical properties with excellent transparency and flatness, with reduced fluctuations in the width direction of the peeling position and greatly reduced variation in retardation (Re) value. Can increase production speed, improve film productivity, and in recent years demands for thinning, widening, and high quality of protective films for polarizing plates, etc. An effect that can be met.

  Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: The washing | cleaning apparatus is a megasonic washing | cleaning apparatus which comprises the ultrasonic oscillator, and a liquid draining apparatus is an air knife, According to the invention of Item 2, after the surface of the metal support on which the dope is cast is washed with a cleaning agent, the remaining droplets on the surface are blown off by a liquid draining device such as an air knife, and then the atmospheric pressure plasma irradiation is performed. As a result, the dirt could be removed in a short time without creating scratches or watermarks on the surface of the metal support. In addition, the mold releasability of the metal support surface can be improved, making it difficult for dirt to adhere, or even if dirt is attached, making the metal support surface difficult to get dirty, and using a cleaning agent. This cleaning device is called a megasonic, which is a cleaning device that sprays ultrasonically irradiated liquid. By spraying ultrasonically irradiated liquid onto the surface of a metal support, inorganic substances such as calcium, magnesium, and sodium are also removed in a short time. The film can be completely peeled off, thereby reducing the restrictions on the existing film production conditions, greatly expanding the selection range of film production conditions, and improving the film releasability (peelability) from the metal support. Improves and provides a very smooth peelability in the entire area of residual peeling, reduces fluctuations in the width direction of the peeling position, and varies the retardation (Re) value. Can be greatly reduced, and an optical film having optical properties with excellent transparency and flatness can be produced, and the production speed can be increased, so that the productivity of the film can be improved. There is an effect that it is possible to meet demands for thinning, widening, and high quality of protective films for polarizing plates in recent years.

  The invention of the optical film of claim 3 is manufactured by the method of claim 1 or 2, and according to the invention of claim 3, the releasability of the film from the metal support. (Removability) is improved, very smooth releasability is obtained in the entire remnant melting zone, and fluctuations in the width direction of the peeling position are reduced. Therefore, the optical film has a variation in retardation (Re) value. Is greatly reduced, and there is an effect that transparency and flatness are excellent.

  The invention of the polarizing plate according to claim 4 has an optical film excellent in transparency and flatness on at least one surface with greatly reduced variation in the retardation (Re) value according to claim 3. Therefore, according to the invention of claim 4, when the polarizing plate is incorporated in the liquid crystal panel, there is an effect that the liquid crystal panel is excellent in visibility without causing a decrease in contrast and uneven density.

  Since the invention of the display device of claim 5 uses a polarizing plate comprising an optical film having excellent optical properties without variation according to claim 4, according to the invention of claim 4, There is an effect that the liquid crystal panel is excellent in visibility without causing a decrease in contrast and uneven density.

  Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  The method for producing an optical film according to the present invention is a method for producing an optical film by a solution casting method, in which a resin solution (dope) containing a thermoplastic resin and an additive is cast on a metal support. After forming a film (web) and evaporating a part of the solvent, it includes a step of peeling from the metal support. After the surface of the metal support is cleaned with a cleaning agent by a cleaning device, the metal support The droplet remaining on the body surface is blown off by a liquid draining device such as an air knife, and then the surface of the metal support is modified by applying a high energy surface treatment by an atmospheric pressure plasma device, and the metal support after the modification The dope is cast on the surface.

  Here, a general bathtub-type ultrasonic apparatus can be used as the cleaning apparatus, but a megasonic cleaning apparatus including an ultrasonic oscillator is preferable because it can be compactly accommodated in the film forming apparatus. The liquid draining device is preferably an air knife.

  That is, in the method for producing an optical film according to the present invention, the surface of the metal support on which the dope is cast is washed with a cleaning agent, and then the remaining droplets on the surface are blown off as much as possible with a liquid draining device such as an air knife. Thereafter, the atmospheric plasma was irradiated to remove dirt in a short time without creating scratches or watermarks on the surface of the metal support. At the same time, the surface of the metal support has been modified by atmospheric pressure plasma irradiation, and the mold releasability (peelability) of the surface of the metal support has been improved, making it difficult for dirt to adhere or even if dirt is attached. It became easy and the metal support surface became difficult to get dirty.

  By the way, as for the contamination on the surface of the metal support, calcium and magnesium, which are considered to be residual impurities derived from the vinegar manufacturing process, when the raw material resin is cellulose, as well as dope additives such as plasticizers and UV agents. Organic salts such as sodium have been detected in the analysis. In particular, the calcium salt is hardly soluble in water as well as organic solvents, and is strongly fixed to the surface of the metal support, so that it can hardly be removed by conventional solvent wiping methods, physical polishing, Alternatively, since there is no choice but to dissolve and remove using a dilute aqueous solution of strong acid, it is difficult to maintain the cleaning time and the surface roughness of the support surface.

  In the method for producing an optical film according to the present invention, in cleaning using a cleaning agent, in particular, an ultrasonic irradiation liquid is sprayed on the surface of a metal support with a device called spraying the ultrasonic cleaning liquid called a megasonic. As a result, inorganic substances such as calcium, magnesium and sodium can be completely removed in a short time.

  According to the method for producing an optical film according to the present invention, the metal support surface is subjected to such a high-energy surface treatment, so that a poorly peeled residual solution region of a cast film, which has conventionally reduced the productivity of the film, is obtained. I was able to lose it.

  Furthermore, since the releasability (peelability) of the surface of the metal support has been improved, it becomes difficult for dirt to adhere, or it is easy to remove even if dirt is attached, and it has conventionally required a very long time. It was also possible to eliminate the need to clean the surface of the metal support with a solvent wipe.

  As described above, according to the method for producing an optical film according to the present invention, by eliminating a so-called peelable defect region of the metal support, the restrictions on the film production conditions so far are reduced, and the selection range of the film production conditions is greatly increased. As the film spreads, the releasability (peelability) of the film from the metal support is improved, and a very smooth peelability is obtained in the entire peeling residual melting zone, and the fluctuation in the width direction of the peeling position is reduced. The variation in retardation (Re) value is greatly reduced, and an optical film having optical properties excellent in transparency and flatness can be produced.

  Hereafter, the manufacturing method of the optical film by this invention is described in detail. The film can be produced by a solution casting method.

  FIG. 1 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. Note that the implementation of the present invention is not limited to the process of the drawings shown below.

  In the figure, first, in a dissolving pot (1), 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 vessel is fed to the casting die (3) by a conduit through, for example, a pressurized metering gear pump (2), and transferred infinitely, for example, a metal made of an endless belt made of, for example, a rotationally driven stainless steel. The dope is cast from the casting die (3) to the casting position on the support (7).

  In order to cast the dope by the casting die (3), 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, a pressure die that can adjust the slit shape of the die portion and can easily make the film thickness uniform is preferable. 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 (3), 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 (3) is usually provided with a decompression chamber (4).

  Here, it is preferable that the solid content concentration of the cellulose ester solution (dope) is 20 to 30% by weight. If the solid content concentration of the cellulose ester solution (dope) is less than 20% by weight, sufficient drying cannot be performed on the metal support (7), and a part of the dope film is on the metal support (7) during peeling. This leads to belt contamination and is not preferable. Also, if the solid content concentration exceeds 30%, the dope viscosity becomes high, filter clogging becomes faster in the dope adjustment process, or the pressure becomes high when cast onto the metal support (7), and cannot be extruded. It is not preferable.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the metal support (7), the belt metal support (7) includes a pair of front and rear drums (5) and (5) and a plurality of intermediate rolls (not shown). Omitted).

  One or both of the drums (5) and (5) at both ends of the rotary drive endless belt metal support (7) are provided with a drive device for applying tension to the belt metal support (7). Thus, the belt metal support (7) is used in a tensioned state.

  The width of the metal support (7) 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 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  Moreover, it is preferable that the peripheral speed of a metal support body (7) is 40-200 m / min.

  When an endless belt is used as the metal support (7), 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 temperature is more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  The dope cast on the surface of the metal support (7) as described above also increases the strength (film strength) of the gel film by promoting drying until stripping.

  In the system using an endless belt as the metal support (7), the film strength on which the web (9) can be peeled from the metal support (7) by the peeling roll (8) on the metal support (7). In order to dry and solidify until it becomes, it is preferable to dry to 150 weight% or less of the residual solvent amount in a web (9), and 80 to 120 weight% is more preferable. Moreover, as for the web temperature when peeling a web (9) from a metal support body (7), 0-30 degreeC is preferable. Further, immediately after the web (9) is peeled off from the metal support (7), the temperature once drops rapidly due to solvent evaporation from the metal support (7) contact surface side, and water vapor or solvent vapor in the atmosphere. For example, the web temperature at the time of peeling is more preferably 5 to 30 ° C. because volatile components are easily condensed.

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

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M is the weight of the web at an arbitrary time point, and N is the weight when the weight M is dried at 110 ° C. for 3 hours.

  The dope film (web) (9) formed by the dope cast on the endless belt metal support (7) is heated on the metal support (7), and then from the metal support (7). The solvent is evaporated until the web is peelable by the peeling roll (8).

  In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back surface of the metal support (7) by a liquid, a method of transferring heat from the front and back by radiant heat, and the like.

  In the system using an endless belt for the metal support (7), the peeling tension when peeling the metal support (7) and the web (9) with the peeling roll (8) is usually 50 N / m to 200 N. / M, but in the optical film produced according to the present invention, which is thinner than the conventional film, the amount of residual solvent of the web (9) is large at the time of peeling, and it tends to stretch in the transport direction. The film tends to shrink in the width direction, and when drying and shrinkage overlap, the end curls and folds, so that wrinkles are likely to occur. Therefore, it is preferable to peel at a minimum tension that can be peeled off to 170 N / m, more preferably. Is to peel at a minimum tension of ~ 140 N / m.

  In the present invention, the web (9) is dried and solidified on the metal support (7) until the web (9) has a peelable film strength, and then the web (9) is peeled off by the peeling roll (8). The web (9) is stretched in the process tenter (5).

  FIG. 2 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, a hard chrome plating treatment is applied to the surface. The case where the stainless steel rotation drive drum (6) was used is illustrated.

  The other points of the optical film manufacturing apparatus in FIG. 2 are the same as those of the optical film manufacturing apparatus in FIG.

  In the method for producing an optical film according to the present invention, the surface of the metal support (6) (7) is cleaned with the cleaning agent (cleaning solution) (14) by the cleaning device (15), and then the metal support (6). (7) The droplets remaining on the surface are blown off by a liquid draining device (17) such as an air knife, and then subjected to a high energy surface treatment by an atmospheric pressure plasma device (19), whereby a metal support (6) ( The surface of 7) is modified, and the dope is cast on the surface of the modified metal support (6) (7).

  Here, the cleaning device (15), the liquid draining device (17) such as an air knife, and the atmospheric pressure plasma device (19) according to the present invention are installed in any section of the metal support surface before casting the dope. 1 and 2 can be installed near the lower transition of a metal support (7) consisting of a stainless steel rotary drive drum (6) and a rotary drive stainless steel endless belt. is doing.

  In particular, it is preferable that the cleaning device is a megasonic cleaning device (15) including an ultrasonic oscillator, and the liquid draining device is an air knife (17).

  In the method for producing an optical film according to the present invention, the surface of the metal support (6) (7) on which the dope is cast is cleaned with a cleaning agent (cleaning solution) (14) by a cleaning device (15), and then an air knife. (17) A liquid draining device such as (17) blows off droplets remaining on the surface as much as possible, and then irradiates with atmospheric pressure plasma, so that no scratches or watermarks are formed on the surface of the metal support (6) (7). The dirt can be removed in a short time. In addition, since the releasability (peelability) of the surface of the metal support (6) (7) has been improved, it becomes difficult for dirt to adhere, or even if dirt is attached, the surface of the metal support is difficult to get dirty. became.

  In the method for producing an optical film according to the present invention, cleaning is performed using a cleaning agent, and in particular, the cleaning agent is called a megasonic cleaning device (15) for spraying a liquid irradiated with ultrasonic waves on a metal support surface. By spraying the ultrasonic irradiation liquid, inorganic substances such as calcium, magnesium and sodium can be completely removed in a short time.

  Next, the megasonic cleaning device (15) will be described in detail.

  As shown in FIG. 4, the megasonic cleaning device (15) supplies the cleaning liquid (14) and applies ultrasonic waves to the surfaces of the metal supports (6) and (7). The ultrasonic waves are emitted from an ultrasonic oscillator (u) provided in a cleaning nozzle that is an ultrasonic wave generation source, and the cleaning liquid (14) is also introduced into the cleaning nozzle and is used together with the ultrasonic wave to form a metal support ( 6) (7) Supplied to the surface.

  The ultrasonic frequency can be used for cleaning the support in a relatively low region of ˜100 kHz and in the megahertz order.

  The cleaning liquid (14) to be jetted is preferably ultrapure water, hydrogen water, ozone water, hydrogen peroxide water, subcritical water, supercritical water, magnetized water, or a mixture thereof.

  Moreover, it is desirable to install on the cleaned metal support (6) (7) surface so as not to be immersed in the cleaned cleaning liquid on the other plate surfaces thereafter.

  In the head having a cleaning nozzle at its tip, a vibrator (u) for applying ultrasonic waves to the cleaning liquid is provided as schematically shown in FIG. The impact force of ultrasonic waves is applied.

  As such a megasonic cleaning device (15), for example, model W-357LS-580 (manufactured by Honda Electronics Co., Ltd.) can be used.

  The distance between the nozzle tip and the substrate surface is preferably set in the range of about 0.5 to 5 times the slit gap of the nozzle, more preferably 1.5 to 3.0 times the gap. . If it is less than 0.5 times, the cleaning liquid after contacting the metal support (6) (7) tends to flow backward in the nozzle direction, and the distance between the nozzle tip and the substrate surface is 5 times. If it exceeds, the impact force of the cleaning liquid becomes weak, which is not preferable.

  Next, as shown in FIG. 5, following the cleaning by the megasonic cleaning device (15), the curtain-shaped gas (16) is blown from the slit-shaped nozzle, and the metal supports (6) (7). A liquid draining device (draining device) (17) for removing the liquid remaining on the surface is installed.

The liquid draining gas (16) that can be used for the liquid draining device (17) may be any gas as long as it can be drained and is not reactive with the metal supports (6) and (7). Air removed with a hepa filter or the like is preferable. Ejection pressure of the liquid removing gas (16) ^is preferably in the range of ^{0.5kg / cm 2 ~10kg / cm 2} .

  Further, as shown in FIG. 5, the angle θ of the blowing nozzle of the liquid draining device (17) is preferably in the range of 20 ° to 60 °. When the angle is less than 20 °, it is not preferable because the jetting pressure of the liquid-removing gas (16) applied to the film-forming support (u) decreases and the liquid breakage becomes worse. If θ exceeds 60 °, it is not preferable because it easily scatters to the surface after cleaning with the sprayed gas. Also, the drum casting drum (6) shown in FIG. 2 and the endless belt (7) shown in FIG.

  After the surface of the metal support (6) (7) on which the dope is cast is cleaned by the cleaning device (15) using the cleaning agent (cleaning solution) (14), the scattered droplets called watermarks are scattered. It is necessary to dry it without making spot spots that can be dried. In the solution casting film forming method, even if there are protrusions of the order of several tens of nanometers on the surface of the metal support, it is transferred to the film and appears as a failure that has been expanded by post-processing such as foreign matter failure and coating. It becomes a big problem.

  In order not to form such a droplet mark called a watermark, the liquid is drained to some extent by a liquid draining device such as an air knife (17) after the solution cleaning. Alternatively, a material for making droplets finer is necessary.

  In addition to the air knife (17), a method such as a water displacement drying method, an IPA vapor drying method, a Marangoni drying method, or the like may be employed for removing the droplets. This is an effective method particularly when water is used, and is a system in which water droplets are simply replaced with IPA and brought into the drying process.

  Next, the atmospheric pressure plasma apparatus will be described in detail.

  In the present invention, the atmospheric pressure plasma apparatus applies a high-frequency voltage between opposing electrodes to discharge, thereby bringing the reactive gas into a plasma state and exposing the surface of the metal support to the reactive gas in the plasma state. Thus, the surface of the metal support is modified.

  In the plasma device, a high frequency power is applied between the electrodes facing each other so that the substrate to be processed is sandwiched, and the supply gas is converted into plasma, and the reaction gas is converted into plasma through the electrodes to which the high frequency voltage is applied. In the non-film manufacturing method of the present invention, the latter downstream method is used for the high-energy surface treatment of the metal support surface.

  FIG. 3 is an explanatory diagram for explaining the principle of the atmospheric pressure plasma apparatus.

  In the figure, (a) and (b) are the counter electrodes of the reactor, (h) is the electrode length, (g) is the reactive gas, (w) is the solid dielectric gap, (i) is the air curtain and lamp device cooling Wind, (d) is a gap from the plasma spray slit to the support surface, (s) is a film-forming support, and (e) exhaust.

  As a simple structure of the atmospheric pressure plasma apparatus in FIG. 3, a reactive gas (g) is passed between the counter electrodes (a) and (b) of the reactor to which a high-frequency voltage has been applied to form a plasma, and a metal support (s ) Injecting and supplying high energy to the surface.

  In the present invention, the upper limit of the frequency of the high frequency voltage applied between the counter electrodes (a) and (b) of the reactor is preferably 150 MHz or less. Moreover, as a lower limit of the frequency of a high frequency voltage, Preferably it is 10 kHz or more, More preferably, it is 15 kHz or more.

Further, the lower limit value of the power supplied between the counter electrodes (a) and (b) of the reactor is preferably 1.2 W / cm ² or more, and the upper limit value is preferably 50 W / cm ² or less, and more preferably. Is 20 W / cm ² or less. Note that the voltage application area (/ cm ² ) in the electrode refers to the area in which discharge occurs.

  Further, the high frequency voltage applied between the counter electrodes (a) and (b) of the reactor may be an intermittent pulse wave or a continuous sine wave, but the effect of the present invention is enhanced. In order to obtain, it is preferable that it is a continuous sine wave.

  In the present invention, it is necessary to employ an electrode capable of applying such a high power voltage and maintaining a uniform glow discharge state in the plasma discharge processing apparatus.

  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. Furthermore, the dielectric surface and the gap between the electrodes can be kept constant by polishing the dielectric surface and setting the electrode surface roughness Rmax (JIS B 0601) to 10 μm or less. It is preferable that 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 non-porous, highly accurate inorganic dielectric can be coated to greatly improve the durability. .

  The distance between the discharge electrodes is preferably 0.5 mm to 20 mm, more preferably 0.5 mm to 5 mm, and particularly preferably 1 to 3 mm from the viewpoint of performing uniform discharge.

  Further, the gap (d) between the plasma blowing slit and the support surface 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 and damaging the support surface, and if it is too far away, the effect of modifying the support surface is weakened.

  Various reactive gases (g) can be used, but from the viewpoints of environment, exhaust after-treatment, and running cost, a mixture of a small amount of oxygen with nitrogen is preferable. The mixing ratio of oxygen is preferably 0.005 to 0.1% by volume with respect to the volume of the raw material gas.

  The gas flow rate is preferably 20 to 5000 L / min per 1 m of the effective width of plasma irradiation. Furthermore, 40 to 2000 L / min is more preferable.

  When there is much entrained air when the metal support (s) moves, the plasma gas flows and the concentration decreases. Moreover, since it will be in the solvent gas atmosphere evaporated from dope when using it in film forming, it is necessary to suppress those inflows.

  Therefore, it is preferable to install an air curtain or an air knife around the main body, and to install an exhaust duct for sucking exhaust gas and air or solvent gas to enter from the outside of the apparatus.

  Moreover, in an atmospheric pressure plasma apparatus, since there is a concern about damage such as roughening of the metal support surface due to induction current or arc discharge, it is desirable to use an apparatus having a shield mechanism. In particular, in solution casting film formation, even nm-order flaws on the surface of a metal support are transferred to the film, and therefore it is important to use an apparatus with such measures.

  An atmospheric pressure plasma apparatus is preferable if irradiation treatment is performed without taking time immediately after cleaning and draining the surface of the support, because high-energy surface treatment of plasma can be efficiently performed on the clean support surface after cleaning.

  In FIG. 1, the metal support (7) for casting the dope is made of, for example, stainless steel (SUS316 or SUS314). In FIG. 2, the metal support (6) for casting the dope is a stainless steel drum. The surfaces of the drums were subjected to hard chrome plating treatment, and the drums of which the three-dimensional surface roughness (Ra) by a scanning atomic force microscope (AFM) of the surfaces was polished to a super mirror surface with an average of 1.0 nm ( 6) or an endless belt (7) is used, and the following high energy surface treatment is performed on these surface sides.

  As described above, the cleaning device (15), the liquid draining device (17) such as an air knife, and the atmospheric pressure plasma device (19) according to the present invention can be used in any section of the metal support surface before casting the dope. Can be installed.

  According to the method of the present invention, by eliminating the so-called releasable defective region of the metal support (6) (7), restrictions on the film production conditions so far are reduced, and the selection range of the film production conditions is greatly expanded. The releasability (peelability) of the film from the metal supports (6) and (7) is improved, very smooth peelability is obtained in the entire peel residual melting zone, and the width direction of the peel position varies. In addition to reducing the variation of the retardation (Re) value, it is possible to produce an optical film having optical properties with excellent transparency and flatness, and to increase the production speed. Thus, it is possible to meet the recent demands for thinning, widening, and improving the quality of protective films for polarizing plates.

  Next, in the present invention, a resin solution (dope) for producing an optical film contains a resin such as cellulose ester resin as a main material, and includes a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and It contains at least one or more kinds of low molecular weight substances and a solvent.

  Hereinafter, these will be described.

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

  A 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 groups 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 direction 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 for 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 60000 to 300000, since the mechanical strength of the resulting film is strong. Furthermore, 70000-200000 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).

  In general, 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, as a specific retardation reducing agent, for example, a polyester represented by the following general formula (1) or (2) may be mentioned.

Formula (1) B _1- (GA-) mG-B ₁
Formula _{(2) B 2 - (G} -A-) nG-B 2
In the above formula, B ₁ represents a monocarboxylic acid component, B ₂ represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. . B ₁ , B ₂ , G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

Monocarboxylic acid component represented by B _1, not particularly limited, and may be known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid.

  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 1-12. 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 B ₂ is not particularly limited ,, and may be a known alcohol. 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. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12.

  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- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferable, and 1,3-propylene glycol, 1,4-butylene Call, 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 and the like, in particular, aliphatic carboxylic acid having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

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

  The weight average molecular weight of the polyester is preferably 20000 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.

  Polycondensation of polyester is carried out by a conventional method. 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 alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, 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 method for adjusting the molecular weight 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. Such polymerization methods 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 normal 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 ester, 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- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those 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 above monomers may be a copolymer or a homopolymer, and is preferably a vinyl ester homopolymer, a vinyl ester copolymer, 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 alkyl methacrylate 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 acid 2-methoxy-ethyl), 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 may contain 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). preferable.

  Moreover, in the manufacturing method of the optical film of this invention, dope composition contains a cellulose ester and the acrylic polymer of the weight average molecular weight 5000 or more and 30000 or less as an additive which reduces thickness direction retardation (Rt). Is preferred.

  In the present invention, if the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or if the polymer has a weight average molecular weight of 5000 or more and 30000 or less, Compatibility 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, a polymer having a hydroxyl group in the side chain can also be preferably used as an additive for reducing the thickness direction retardation (Rt). 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. The thing replaced by methacrylic acid can be mentioned, Preferably, it is 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.

  The polymer as described above containing 2 to 20% by weight of the monomer unit having the above hydroxyl group, of course, is 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). 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 terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. 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 an effect 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, for example, 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 No. 2004-315605, a styrene oligomer described in JP-A No. 2005-105139, and a polymer of a styrene monomer described in JP-A No. 2005-105140. .

  In the present invention, an additive for reducing the thickness direction retardation (Rt) can also be found by the following method.

  A dope formulation in which cellulose ester is dissolved in a mixed organic solvent composed of methyl acetate and acetone is formed on a glass plate and dried at 120 ° C./15 min to produce a cellulose ester film having a thickness of 80 μm. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt1.

  Next, 10% by weight of the polymer additive is added to the cellulose ester and dissolved in a mixed organic solvent composed of methyl acetate and acetone to prepare a dope formulation. A cellulose ester film with a film thickness of 80 μm is prepared in the same manner as above with this dope formulation. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt2.

And the relationship of retardation in the thickness direction of the above two cellulose ester films is Rt2 <Rt1
Then, it can be said that the polymer additive added to the cellulose ester is an additive for reducing the thickness direction retardation (Rt).

  In the present invention, the thickness direction retardation (Rt) of the cellulose ester is −10 nm to +10 nm, preferably −5 nm to +5 nm. Here, in either case where the thickness direction retardation (Rt) of the cellulose ester is smaller than −10 nm or larger than +10 nm, the viewing angle becomes narrow and the effect of the present invention does not appear.

  In the present invention, the in-plane retardation (Ro) of the cellulose ester is 0 nm to +5 nm, preferably 0 nm to +2 nm, more preferably 0 nm to +1 nm, and particularly preferably about 0 nm. Here, in either case where the in-plane retardation (Ro) is smaller than 0 nm or larger than +5 nm, the viewing angle becomes narrow and the effect of the present invention does not appear.

  The content of the additive for reducing the thickness direction retardation (Rt) described above is preferably 5 to 25% by weight based on the cellulose ester resin. If the content of the additive for reducing the thickness direction retardation (Rt) is less than 5% by weight, the effect of reducing the thickness direction retardation (Rt) of the film is not manifested. On the other hand, if the content of the additive for reducing the thickness direction retardation (Rt) exceeds 25% by weight, so-called bleed-out occurs and the stability in the film decreases, which is not preferable.

  In the present invention, the retardation value of the film is determined by measuring the three-dimensional refractive index at a wavelength of 590 nm using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). It can be calculated from Ny and Nz.

Ro = (Nx−Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
(In the formula, Nx, Ny, and Nz represent the refractive indexes in the principal axes x, y, and z, respectively, of the refractive index ellipsoid, and Nx, Ny represent the refractive index in the film in-plane direction, and Nz represents the thickness direction of the film. In addition, Nx ≧ Ny, and d represents the thickness (nm) of the film.
In the present invention, the cellulose ester film has an angle θ (radian) formed between the slow axis direction and the film forming direction and the retardation value (Ro) in the in-plane direction as shown below. It is preferably used as a cellulose ester film.

P ≦ 1-sin ² (2θ) sin ² (πRo / λ)
Here, P is 0.9999 or less.

  θ is the angle (° radians) formed between the slow axis direction in the film plane and the film forming direction (straight scale direction of the film). The wavelength of light is 590 nm, and π is the circumference.

  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, dimethyl sulfoxide, 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 on the metal support, the solvent starts to evaporate and the alcohol ratio increases, so the web (name of the dope film after casting the cellulose derivative dope on the metal support) Is used as a gelling solvent that makes the web strong and makes it easy to peel off from the metal support, or when these ratios are small, cellulose derivatives of non-chlorine organic solvents There is also a role to promote the dissolution of.

  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 (1).

Formula _{(1) R 1 - (OH} ) n
(However, R ₁ 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.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this invention, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. 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 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 preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or 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 1500, 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 for 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 a phosphate ester plasticizer is not substantially 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 the plasticizer used is preferably 1 to 20% by weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. 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.

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

  Examples of the fine particles of the inorganic compound 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, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

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

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

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. 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 it is important that the fine particles are finally combined with the cellulose ester in the film. It is to control the particle size formed by aggregation.

  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 the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the 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 the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, or a nanomizer manufactured by Nanomizer, and also a Manton Gorin type high-pressure dispersing device such as Izumi Food Machinery. 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 placed on a metal support. A cellulose ester film is obtained which is cast and dried to form a film.

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

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

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

  The fine particles are dispersed in the 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. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  As 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 useful UV absorbers in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-). Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2- Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy) 3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl -3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5 A mixture of-(5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

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

  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 this invention, the compounding quantity of these ultraviolet absorbers has the preferable range of 0.01 to 10 weight% with respect to a cellulose ester (cellulose derivative), and also 0.1 to 5 weight% is preferable. If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Further, as the ultraviolet absorber that can be used in the optical film of the present invention, the polymer ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-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.

  In general, the antioxidant is also referred to as a deterioration inhibitor, 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-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-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-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  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 the apparatus for carrying out the method for producing the optical film of the present invention shown in FIGS. 1 and 2, the stretching step is performed by clipping the side edges of the web (or film) (9) as 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.

  It is preferable that the residual solvent amount of the web (film) (9) immediately before entering the tenter (12) of the stretching step is 10 to 35% by weight.

  In the present invention, the stretch ratio of the web in the tenter (12) in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%. Moreover, the temperature of the warm air which blows out from the warm air blowing slit port in the tenter (12) is 100 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  It is preferable to provide a drying apparatus (10A) (10B) before and after the tenter (12) in the stretching step. In the drying apparatuses (10A) and (10B), the web (9) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web (9) is dried during the meandering. The film transport tension in the drying apparatus (10A) (10B) is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, etc. 30 to 300 N / width m, more preferably 40 to 270 N / width m.

  The means for drying the web (film) (9) 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 (11) blown from the hot air inlet at the front portion of the bottom of the drying device (10A) (10B), and the drying device (10A). It is dried by exhaust air being discharged from the exit of the rear part of the ceiling of (10B). The temperature of the drying air (11) is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or 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 to 30 mm.

  The film after drying is wound up by a winding device (13) 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 bonded to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  In the optical film according to the present invention, the width of the film after winding is preferably 1400 to 2500 mm.

  In this invention, the film thickness after drying of a cellulose-ester film has the preferable range of 20-150 micrometers as a finished film from a viewpoint of thickness reduction of a 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 in the die of the casting die, the extrusion pressure of the casting die, the speed of the metal support, etc. are controlled so as to obtain the desired thickness. It is good. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above 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 further preferably 93% or more.

  Moreover, the optical film manufactured 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 using, for example, a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS K6714.

  Moreover, the tensile elastic 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 to 3500 MPa, and the tensile elastic 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, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage after overheating on the deflecting plate occurs, or the backlight is heated by the heat of the backlight when incorporated in the 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 Co., Ltd.), a sample was set 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 a temperature of 23 ° C. It is preferable that it is 70-400 nm on the conditions of humidity 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 in an environment of a temperature of 23 ° C. and a humidity of 55% RH.

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

  By using the protective film for a polarizing plate comprising the optical film of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as thinning.

  By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, 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.

  By the way, a 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 alkali saponified, and a polyvinyl alcohol film is dipped in an iodine solution and stretched on both sides of a polarizing film prepared by 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.

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

  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 the protective film for polarizing plates made of the 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.

  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.

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

Example 1
(Preparation of dope)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. The silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 4 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxyphenyl)
-2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Aerosil R972V 0.1 part by weight Here, calcium (Ca), magnesium (Mg) remaining as impurities in cellulose triacetate The analysis method and measurement values are as follows.

(Analysis method)
After ashing 500 mg of vinegared cotton in an electric furnace (800 ° C., 1 hour), it was dissolved in nitric acid and finished to 50 ml, and all elements were qualitatively detected by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer). Quantification was performed on the elements.

(measured value)
Ca: 64 ppm
Mg: 12ppm
(Metal support)
As the metal support for casting the dope, an endless belt made of SUS316 and polished to a super mirror surface with an average of 1.0 nm in three-dimensional surface roughness (Ra) measured by a scanning atomic force microscope (AFM) was used. .

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

  The filtered dope was uniformly cast from a coat hanger die on an endless belt support made of SUS316 having a dope temperature of 35 ° C. and a surface temperature of 20 ° C. The temperature of the drying air is fixed at 30 ° C., and the drying time on the metal support is changed from 60 seconds to 120 seconds by changing the transport speed of the metal support, and the residual solvent amount of the casting film at the time of peeling is changed. Changed.

  After peeling from the endless belt support, the metal is dried while being conveyed in a roll at 90 ° C., and is stretched 1.06 times in the width direction in a 100 ° C. atmosphere when the residual solvent amount is 10%. The holding was released and drying was terminated in a drying zone at a temperature of 125 ° C. while being conveyed by a roll, to produce a cellulose ester film having a thickness of 40 μm. After film formation under these conditions for 24 hours, the support contact surface side of the obtained film was photographed with a scanning atomic force microscope (AFM), and the area ratio of stains on the support surface that appeared to be black spots was 9 0.7%.

  Next, the following cleaning process was performed while the metal support was transported at a speed of 0.5 m / min at a position where the metal support was horizontal.

  Pure water (14) as a cleaning liquid is supplied to the surface of the dirty metal support after 24 hours of film formation by a megasonic cleaning device (15) at a flow rate of 2 L / min / 10 cm width, Ultrasonic waves were applied from above from the ultrasonic transmitter (u). The oscillation frequency of the applied ultrasonic wave was output at 1 MHz. The gap from the slit of the pure water supply nozzle to the support surface was 3 mm, and the supply nozzle was perpendicular to the support.

The draining device (17) sprayed air (16) removed with a hepa filter from a nozzle with an installation angle of 45 degrees onto a support to which a cleaning liquid was adhered at an ejection pressure of 3 kg / cm ² .

  A downstream atmospheric pressure plasma irradiation device (19) is installed near the rear of the draining device (17), the length h of the counter electrode of the reactor is 30 mm, the solid dielectric gap w is 1 mm, and a high frequency oscillator is supplied. Plasma irradiation was performed under the condition that the power was 0.5 kW / electrode width 100 mm, and the gap d from the plasma injection slit to the support surface was 3 mm. The composition of the mixed gas (reactive gas) (18) used for the plasma treatment is shown below. The atmospheric pressure was 1.0 atm.

Nitrogen 99.98% by volume
Oxygen 0.02% by volume
Mixed gas flow rate 2m ³ / min / width m
Comparative Example For comparison, the surface of the metal support was wiped with a cleaning cloth soaked with pure water so as to gradually spread outward from the center in a circle, and then the pure water was dried. Before, it wiped off similarly with the cleaning cloth which included methylene chloride. Since the variation of wiping was seen by the workers, five workers were wiped by the above method and evaluated.

Example 2
Production of Polarizing Plate Using the optical film produced in Example 1, a polarizing plate was produced and evaluated according to the method described below.

  According to the following method, the polarizing plate of this invention which used the optical film as a protective film for polarizing plates was produced.

1. Production of Polarizing Film A long polyvinyl alcohol film having a thickness of 120 μm 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 at 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 long polarizing film.

  Subsequently, according to the following processes 1-5, the polarizing film and the optical film were bonded together and the polarizing plate was produced.

  Step 1: The long optical film produced in Example 1 was 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 pasted on the surface provided with the antireflection film for protection.

  Similarly, a long cellulose ester film (used as a substrate for an optical film) was immersed in a 2 mol / L sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

  Process 2: The above-mentioned long polarizing film was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and it was sandwiched between the optical film and the cellulose ester film that had been subjected to alkali treatment in Step 1, and then laminated.

Process 4: It bonded together at the speed | rate of about 2 m / min with the pressure of 20-30 N / cm < ² > with the two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The sample prepared in Step 4 was dried for 2 minutes in a dryer at 80 ° C. to prepare the polarizing plate 1 of the present invention.

(Evaluation of film unevenness due to transfer of substrate surface stains in long-term production)
The soiling of the metal support is caused by the adhesion of soiling components to the surface. In particular, the soiled state accumulates in a minute scratch portion (polishing marks) on the surface of the metal support in a granular manner, which is transferred to the film to form a dent. The film on which the dirt on the support has been transferred is scattered in the dents and looks whitish. The dirt on the surface of the support is irregularly shaped irregularities or streaks, making it very noticeable as a film and unusable as a product.

  AFM photographed the film at a 20 μm square with a scanning probe microscope (SPI3800N probe station multifunctional unit SPA-400) manufactured by Seiko Instruments. When the surface of the support becomes dirty, it has been confirmed that the area of the dent transferred to the film surface observed by AFM is increased, and the area occupied by black spots due to dirt transfer from the AFM image is occupied. The degree of progress of soiling of the support was evaluated by the ratio.

  When the support is contaminated and transferred to a film, it appears whitish, and when it is made into a liquid crystal panel, it may appear uneven depending on the projected image and viewing angle, and cannot be used as a product.

  There is the following relationship between the area ratio of black spots and the appearance of film unevenness. The film unevenness and the watermark due to the scattered liquid were visually evaluated. The visual evaluation was performed by spreading a film on an evaluation table with a black rubber cloth and irradiating it with a green lamp from an oblique direction.

The determination of unevenness is as follows. Also, if there is only one watermark, it can be used as a product because it is transferred and well understood as a dotted pattern on the film. Evaluation criteria for film irregularities and watermarks 1. Area ratio of 1% or less: No cloudiness unevenness can be visually observed. Area ratio 3% or less: When moving the film while visually moving,
Although the cloudiness is slightly faint, there is no problem as a product. Area ratio of 5% or less: White turbidity unevenness is seen slightly stronger visually,
Level that can be used as a product Area ratio of 7% or more: White turbidity unevenness can be seen at a glance. Cannot be used as a product (evaluation of polarizing plate)
It is a polarizing plate of the present invention in which 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 polarization direction is adjusted here, is a comparative example A polarizing plate was attached. About each liquid crystal display panel, the nonuniformity which looks whitish when it sees from the front and diagonally was visually observed by several evaluators.

Evaluation criteria for unevenness ○ None of the evaluators can see any unevenness △ Some evaluators may see slight unevenness, but the level that can be used as a product × Many evaluators have seen unevenness, but faintly Table 1 below The area ratio (%) of black spots after cleaning, the number of watermarks remaining after cleaning (pieces / m ² ), and the visual evaluation with a polarizing plate are collectively described.

  As is clear from the results in Table 1 above, when the cleaning method of Example 1 of the present invention is performed, there is no watermark and the conventional wiping method of the comparative example, despite the wet cleaning using the cleaning liquid. The fixed stains that could not be removed were removed almost completely in a short time.

  In addition, the liquid crystal display panel using the polarizing plate of the present invention is free from defects due to foreign matter, has no unevenness in reflected light, and has excellent display performance compared to the liquid crystal display panel using the polarizing plate of the comparative example. confirmed.

It is a flow sheet which shows the specific example of the apparatus which enforces the manufacturing method of the optical film of this invention. An example of an apparatus for carrying out the optical film manufacturing method of the present invention is shown in FIG. It is explanatory drawing for demonstrating the principle of the atmospheric pressure plasma apparatus used in the manufacturing method of the optical film of this invention. It is explanatory drawing for demonstrating the megasonic cleaning apparatus used in the manufacturing method of the optical film of this invention. It is explanatory drawing for demonstrating the liquid draining apparatus (water draining apparatus) used in the manufacturing method of the optical film of this invention.

Explanation of symbols

1: Melting pot 2: Pump 3: Casting die 4: Depressurization chamber 5: Front and rear winding drum 6: Rotary drive drum for casting (metal support)
7: Endless belt for casting (metal support)
8: peeling roll 9: web 10A: roll transport drying device 10B: roll transport drying device 11: hot air (dry air)
12: Tenter 13: Winder 14: Cleaning solution 15: Megasonic spray 16: High pressure air 17: Air knife (liquid draining device or draining device)
18: Reaction gas 19: Atmospheric pressure plasma irradiation device a: Counter electrode of reactor of atmospheric pressure plasma device b: Counter electrode of reactor of atmospheric pressure plasma device h: Electrode length g: Reaction gas w: Solid dielectric gap i: Air Curtain / lamp device cooling air d: gap from plasma spray slit to support surface s: film-forming support e: exhaust u: ultrasonic oscillator

Claims (5)

  A method for producing an optical film by a solution casting method, wherein a resin solution (dope) containing a thermoplastic resin and an additive is cast on a metal support to form a casting film (web), and a solvent. A step of evaporating a part of the metal support and peeling off from the metal support. After cleaning the surface of the metal support with a cleaning agent using a cleaning device, liquid droplets remaining on the surface of the metal support are drained. A method for producing an optical film, comprising: blowing off with an apparatus, and then performing a high energy surface treatment with an atmospheric pressure plasma apparatus, and then casting a dope on the surface of the metal support.   The method for producing an optical film according to claim 1, wherein the cleaning device is a megasonic cleaning device including an ultrasonic oscillator, and the liquid draining device is an air knife.   An optical film manufactured by the method according to claim 1.   A polarizing plate comprising the optical film according to claim 3 on at least one surface.   A display device comprising the polarizing plate according to claim 4.

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