WO2012026364A1 - Method for producing optical film, optical film, polarization plate, liquid crystal display device - Google Patents

Abstract

Disclosed is a method for producing an optical film by a solution casting film-forming method, wherein, in order to easily and reliably suppress the generation of a lateral step on the surface of the optical film, and reduce uneven film thickness in the longitudinal direction of the optical film, the method comprising a casting step wherein a resin solution is discharged from a die to form a casting ribbon, and the casting ribbon is attached onto a support to form a cast film on the support. In the casting step, a vibrator for applying vibration to the casting ribbon located between the die and the support is provided, and the vibration has a higher frequency than the peak frequency of the natural vibration of the casting ribbon.

Description

Optical film manufacturing method, optical film, polarizing plate, and liquid crystal display device

The present invention relates to an optical film manufacturing method, an optical film manufactured by the manufacturing method, a polarizing plate using the optical film as a transparent protective film, and a liquid crystal display device including the polarizing plate.

Conventionally, the demand for liquid crystal display devices (LCDs) has been expanded for applications such as liquid crystal televisions and personal computer liquid crystal displays. In recent years, as liquid crystal display devices have become larger, they can be used as large displays installed in streets and stores, and as displays for advertising in public places using display devices called digital signage. Is becoming more diverse.

The liquid crystal display device includes a liquid crystal cell having a configuration in which a transparent electrode, a liquid crystal layer, a color filter, and the like are sandwiched between glass plates, and two polarizing plates disposed on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell. Yes. The polarizing plate includes a polarizer (also referred to as a polarizing film or a polarizing film) and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer. As the transparent protective film, an optical film, usually an optical film made of a cellulose ester resin film such as cellulose triacetate is used.

A solution casting film forming method is known as an optical film manufacturing method. In the solution casting film forming method, a resin solution (dope) in which a resin is dissolved in a solvent is generally discharged from a die to form a casting ribbon, and this casting ribbon is attached to a support such as an endless belt or a drum. Casting process for forming a cast film (web) on the support, peeling process for peeling the formed cast film from the support, longitudinal direction and / or width direction of the peeled cast film (resin film) A stretching process for stretching the resin film, a heat treatment process for heat-treating the stretched resin film, a winding process for winding the heat-treated resin film as an optical film, and the like.

By the way, with the recent thinning of liquid crystal display devices, it is required to reduce the thickness of polarizing plates or transparent protective films. For this reason, the casting ribbon becomes thinner in the casting process, the casting ribbon becomes sensitive to vibration, and the undulation phenomenon is likely to occur. As a result, streaky horizontal steps extending in the width direction remain on the surface of the manufactured optical film, and film thickness unevenness in which the film thickness of the optical film periodically changes in the longitudinal direction is likely to occur.

In order to cope with this problem, for example, it has been proposed to suppress the vibration of the casting ribbon by suppressing the vibration of the support. However, since the support transports the casting film, there is a limit to the suppression of the vibration of the support.

Further, as disclosed in Patent Document 1, it has been proposed to cancel the vibration of the casting ribbon to reduce the film thickness unevenness by giving the casting ribbon vibration in the phase opposite to that of the casting ribbon. Yes. However, according to this technique, it is necessary to always operate a detection device for detecting the phase of vibration of the casting ribbon during the production of the film, which makes the film production apparatus large. Also, precise control without response delay is required.

JP 2008-279757 A

The present invention provides a method for producing an optical film by a solution casting film-forming method, which easily and reliably suppresses the occurrence of horizontal steps on the surface of the optical film, and the film thickness of the optical film changes periodically in the longitudinal direction. It is an object to reduce film thickness unevenness.

One aspect of the present invention is an optical device having a casting process in which a resin solution is discharged from a die to form a casting ribbon, and the casting ribbon is attached to a support to form a casting film on the support. A method for producing a film, wherein the casting step has a vibrator that vibrates the casting ribbon, and the vibrator is higher than a peak frequency of the natural vibration of the casting ribbon between the die and the support. A method for producing an optical film, characterized by applying a vibration of a frequency to a casting ribbon.

According to this method for producing an optical film, the occurrence of horizontal steps on the surface of the optical film is suppressed easily and reliably, and the film thickness unevenness in which the film thickness of the optical film periodically changes in the longitudinal direction is reduced.

The reason is considered as follows. First, the casting ribbon is fixed at one end by a die, but the other end is only fixed to the support and is not fixed, so one side is a free end system. Therefore, if vibration of a frequency different from the peak frequency of the natural vibration of the casting ribbon is applied to the casting ribbon, the state of the system changes, the attachment position of the casting ribbon to the support changes, and the die and the support The length of the casting ribbon in between changes. As a result, the applied vibration is not added to the natural vibration of the casting ribbon, but the natural vibration of the casting ribbon itself changes, and the low frequency that remains as a horizontal step on the surface of the manufactured optical film. The vibration of the vibration is attenuated or extinguished. Instead, the casting ribbon begins to vibrate at the applied frequency of vibration.

In that case, since a vibration with a frequency higher than the peak frequency of the natural vibration of the casting ribbon is given to the casting ribbon, the pitch of the undulation of the casting ribbon is shortened, the radius of curvature of the wave peak is reduced, and the wave Tends to be smoothed (leveled). That is, considering leveling by Laplace force, “P = P0 + (σ / 2R)” (P: pressure of resin solution, P0: atmospheric pressure (constant), σ: surface tension (constant) of resin solution, R: curvature. Therefore, the higher the frequency, the shorter the pitch, the smaller the radius of curvature R of the wave crest, and the higher the pressure P of the resin solution at the wave crest. Therefore, the difference between the pressure of the resin solution at the wave crest and the pressure of the resin solution at the wave trough increases, the force (leveling force) for smoothing the wave increases, and the wave is easily smoothed. It becomes a trend. As a result, the occurrence of lateral steps on the surface of the manufactured optical film is reliably suppressed, and the film thickness unevenness in which the film thickness of the optical film periodically changes in the longitudinal direction is reliably reduced.

And, according to the manufacturing method of the present invention, during the casting process, only giving the casting ribbon a vibration having a frequency higher than the peak frequency of the natural vibration of the casting ribbon, the peak frequency is measured in advance, The frequency of vibration to be applied can be determined in advance. Therefore, it is not necessary to always detect the peak frequency of the natural vibration of the casting ribbon or perform precise control during the production of the film, and it is possible to easily suppress the occurrence of horizontal steps on the surface of the optical film, Film thickness unevenness in which the thickness periodically changes in the longitudinal direction can be reduced. The natural vibration of the casting ribbon refers to the displacement of the contact point between the support and the casting ribbon.

For example, the natural vibration is measured by arranging two cameras in the vicinity of both end portions in the width direction of the discharge port of the die, and separately shooting the casting ribbon separately with the two cameras. From this, the vibration (frequency, amplitude) of the casting ribbon is detected, and the average value of the two vibrations (frequency, amplitude) obtained can be calculated.

“Peak frequency” means the data of the displacement (natural vibration) of the casting ribbon with respect to the time axis by frequency analysis using, for example, FFT (Fast Fourier Transform), etc. The frequency at which the peak value of vibration intensity appears when data is obtained.

In the production method of the present invention, the frequency of vibration applied to the casting ribbon is preferably 1 kHz to 100 kHz. Since the peak frequency of the natural vibration of the casting ribbon is usually about 700 Hz or less, it is higher than the peak frequency of the natural vibration of the casting ribbon by giving the casting ribbon a vibration having a frequency of 1 kHz or more. Is reliably applied to the casting ribbon. In addition, by applying vibration with a frequency of 100 kHz or less to the casting ribbon, heating of the casting ribbon is suppressed, and generation of a film on the surface of the casting ribbon is suppressed (the film is formed on the surface of the casting ribbon). When produced, the inside of the cast film becomes difficult to dry).

In the production method of the present invention, the amplitude of vibration applied to the casting ribbon is preferably 10 μm to 2000 μm. By applying vibration having an amplitude of 10 μm or more to the casting ribbon, the leveling force becomes sufficiently large, and it is possible to suppress the horizontal step due to the applied vibration from remaining. Further, by giving vibrations having an amplitude of 2000 μm or less to the casting ribbon, the casting ribbon is prevented from adhering to the lip portion of the die (the portion of the die that defines the discharge port), and the resin adheres to the lip portion. It is suppressed that it remains (if resin adhesion remains on the lip portion, a die line is generated on the casting ribbon and thus on the manufactured optical film).

In the production method of the present invention, it is preferable to vibrate the casting ribbon by vibrating the die with a vibrator. By vibrating the die, vibration is reliably applied to the casting ribbon whose one end is in contact with the die.

In the production method of the present invention, it is preferable to vibrate the casting ribbon by vibrating the support with a vibrator. By vibrating the support, vibration is reliably applied to the casting ribbon whose other end is in contact with the support.

In the production method of the present invention, it is preferable to vibrate the casting ribbon by vibrating the air around the casting ribbon with a vibrator. By vibrating the air around the casting ribbon, the casting ribbon is reliably vibrated.

Another aspect of the present invention is an optical film manufactured by the above-described manufacturing method. This optical film is capable of satisfactorily meeting the demand for thin optical films by suppressing the occurrence of horizontal steps on the surface and reducing film thickness unevenness in which the film thickness periodically changes in the longitudinal direction.

Yet another aspect of the present invention is a polarizing plate comprising a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer, the two transparent protective films At least one of the polarizing plates is an optical film produced by the method for producing an optical film of the present invention. In this polarizing plate, the occurrence of lateral steps on the surface of the transparent protective film is suppressed, the unevenness of the film thickness of the transparent protective film is reduced, and it is possible to satisfactorily meet the demand for thinning the polarizing plate.

Still another aspect of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell, and the two polarizing plates At least one of the liquid crystal display devices is a polarizing plate using the optical film of the present invention. In this liquid crystal display device, the occurrence of lateral steps on the surface of the transparent protective film in the polarizing plate is suppressed, and the film thickness unevenness in which the film thickness of the transparent protective film periodically changes in the longitudinal direction is reduced. It can cope with thinning well.

According to the present invention, film thickness unevenness in which the occurrence of lateral steps on the surface of the optical film is suppressed easily and reliably without performing precise control or the like, and the film thickness of the optical film periodically changes in the longitudinal direction. Was able to be reduced.

It is a schematic block diagram of the manufacturing apparatus of the belt-type optical film which concerns on embodiment of this invention. It is an enlarged view of the periphery of the casting ribbon between the die | dye and support body (endless belt) of the belt-type optical film manufacturing apparatus of FIG. (A) is an enlarged sectional view of a resin film or optical film obtained when the casting ribbon vibrates at a low frequency, and (B) is a resin film or optical film obtained when the casting ribbon vibrates at a high frequency. It is an expanded sectional view. It is a schematic block diagram of the manufacturing apparatus of the drum type optical film which concerns on other embodiment of this invention. It is an enlarged view of the periphery of the casting ribbon between the die | dye and support body (drum) of the drum type optical film manufacturing apparatus of FIG.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

<Optical film manufacturing equipment>
FIG. 1 is a schematic configuration diagram of an optical film manufacturing apparatus (belt type) 1 according to an embodiment of the present invention. The optical film manufacturing apparatus 1 a is for manufacturing an optical film by a solution casting film forming method, and includes a casting apparatus 10, a stretching apparatus 20, a heat treatment apparatus 30, and a winding apparatus 40.

The casting apparatus 10 includes a die (casting die) 11, an endless belt 12, and a peeling roller 13. The die 11 forms a casting ribbon 51 by discharging a resin solution (hereinafter also referred to as a dope) in which a resin is dissolved in a solvent, and the casting ribbon 51 is attached to an endless belt 12 as a support to endlessly. A cast film (web) 52 is formed on the belt 12. The endless belt 12 is wound around the support roll 12a and the support roll 12b and travels to convey the formed cast film 52 in the direction of the arrow in the figure. The peeling roller 13 peels the casting film 52 from the endless belt 12 and sends the peeled unstretched film 52 a to the stretching device 20.

The stretching device 20 transports the resin film 53 in the longitudinal direction (transport direction (machine direction: MD direction)) and / or the width direction (direction orthogonal to the transport direction) using a clip tenter, pin tenter, or the like while transporting the unstretched film 52a. (Transverse Direction: TD direction)).

The heat treatment apparatus 30 heats and heats (heats) the stretched film 53 to a predetermined temperature while conveying the stretched film 53.

Winding device 40 winds heat-treated stretched film 53 as an optical film in a roll shape.

In the present invention, in the embodiment, an optical film (that is, a cellulose triacetate film or a cellulose ester film) containing a cellulose ester resin such as cellulose triacetate (hereinafter sometimes simply referred to as cellulose ester) is produced as an optical film. . But not only this but the optical film containing an acrylic resin and a cellulose-ester resin may be manufactured, for example.

[Die]
The dope discharged from the die 11 is prepared, for example, by dissolving a cellulose ester resin such as cellulose triacetate in a solvent containing a good solvent for the cellulose ester resin using a dissolution vessel. The content of the cellulose ester resin in the resin solution is preferably 15% by mass to 30% by mass, for example.

For dissolving the cellulose ester resin, a method carried out at normal pressure, a method carried out below the boiling point of the solvent, a method carried out under pressure above the boiling point of the solvent, JP-A-9-95544, JP-A-9-95557, or Various dissolution methods such as a method using a cooling dissolution method as described in Kaihei 9-95538 and a method using a high pressure as described in Japanese Patent Application Laid-Open No. 11-21379 can be used. Among these, the method of pressurizing at a temperature equal to or higher than the boiling point of the solvent is preferable.

After the resin is dissolved in the solvent, the dope is filtered with a filter medium and defoamed. For the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 μm to 5 μm and a drainage time of 10 sec / 100 ml to 25 sec / 100 ml.

The dope is sent to the die 11 by a liquid feed pump such as a pressurized metering gear pump. The die 11 is preferably capable of adjusting the shape of the discharge port. Further, a pressure die that can easily make the film thickness of the casting ribbon 51 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 order to increase the film forming speed, two or more pressure dies may be arranged side by side, and the resin solution may be divided and discharged.

The discharge speed (moving speed of the casting ribbon 51) for discharging the resin solution from the die 11 is, for example, 20 m / min to 200 m in consideration of the balance with the transport speed of the casting film 52 by the endless belt 12 and productivity. / Min is preferable.

[Endless belt]
The endless belt 12 is a metal belt having a mirror-finished surface. The endless belt 12 is preferably made of stainless steel, for example, from the viewpoint of peelability of the cast film 52. From the viewpoint of effectively utilizing the width of the endless belt 12, the width of the casting film 52 in which the cast discharged from the die 11 is formed on the endless belt support is from 80% to the width of the endless belt 12. 99% is preferred.

The endless belt 12 travels to dry the casting film 52 while transporting the casting film 52 formed on the surface thereof. This drying is performed, for example, by a method of heating the back surface of the endless belt 12 by blowing a heater or heating air, a method of heating the casting film 52 on the endless belt 12 by blowing a heater or heating air, and the like. It is possible to select as appropriate. The temperature of the casting film 52 at the time of drying is preferably −5 ° C. to 70 ° C., more preferably 0 ° C. to 60 ° C. in consideration of the time required for evaporation of the solvent, the conveyance speed, productivity, and the like. If the temperature of the casting film 52 is too high, the casting film 52 tends to foam or the flatness of the casting film 52 tends to deteriorate.

When the heated air is blown, the wind pressure of the heated air is preferably 50 Pa to 5000 Pa in consideration of the uniformity of solvent evaporation and the like. The temperature of the heating air may be dried at a constant temperature, or may be sprayed in several steps in the traveling direction of the endless belt 12.

After the casting film 52 is formed on the endless belt 12, the time until the casting film 52 is peeled from the endless belt 12 varies depending on the film thickness of the optical film to be produced and the solvent used, but the endless belt 12. In view of the peelability from the film, it is preferably in the range of 0.5 minutes to 5 minutes.

The conveyance speed of the casting film 52 by the endless belt 12 is preferably about 50 m / min to 200 m / min, for example. The ratio (draft ratio) of the transport speed of the casting film 52 to the travel speed of the endless belt 12 is preferably about 0.8 to 1.2. When the draft ratio is within this range, the casting film 52 can be stably formed. For example, if the draft ratio is too large, there is a tendency to cause a phenomenon called neck-in in which the casting film 52 is reduced in the width direction, and if so, a wide film cannot be formed.

[Peeling roller]
The peeling roller 13 is in contact with the surface of the endless belt 12 in a pressurized state, and peels the dried casting film 52 from the endless belt 12. The peeling tension at the time of peeling is preferably in the range of 50 N / m to 400 N / m. The residual solvent ratio of the cast film 52 at the time of peeling is 30% to 200% by weight in consideration of peelability from the endless belt 12, transportability after peeling, physical properties of the optical film to be manufactured, and the like. It is preferable that

Here, the residual solvent ratio is defined by the following equation.

Residual solvent ratio (%) = {(mass before heat treatment of cast film−mass after heat treatment of cast film) / mass after heat treatment of cast film} × 100
Note that the heat treatment for measuring the residual solvent ratio is a heat treatment at 115 ° C. for 1 hour.

[Stretching device]
The stretching device 20 grips both side edges in the width direction of the resin film 53 which is the unstretched film 52a peeled from the endless belt 12 with a clip tenter, a pin tenter or the like, and holds the unstretched film 52a in the longitudinal direction (MD direction) and / Or extends in the width direction (TD direction).

Here, the stretch ratio in the TD direction of the unstretched film 52a is preferably about 15% to 30%. In general, when the stretching ratio is increased, the optical value of the optical film tends to be nonuniform. However, when the stretch ratio in the TD direction of the unstretched film 52a is 15% to 30%, the optical value of the optical film can be suppressed from becoming non-uniform. Therefore, an optical film having a uniform optical value and a wide width can be obtained. Moreover, when the width | variety of an optical film is wide, it is preferable also from the point of use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency.

Here, the stretching ratio in the TD direction is defined by the following equation.

Stretch ratio (%) in TD direction = {(length in the width direction after stretching at a predetermined position of the film−length in the width direction before stretching at a predetermined position of the film) / width direction before stretching at a predetermined position of the film Length} × 100
The length in the width direction of the film is a value measured with a C-type JIS grade 1 steel scale.

Also, the stretching ratio in the MD direction is defined by the following formula.

Stretching rate in MD direction (%) = {(Conveying speed of film after stretching−Conveying speed of film before stretching) / Conveying speed of film before stretching} × 100
[Heat treatment equipment]
The heat treatment apparatus 30 includes a plurality of transport rollers, and dries the stretched film 53 while transporting the resin film 53 between the rollers. In that case, you may dry using heating air, infrared rays, etc. independently, and you may dry using heating air and infrared rays together. It is preferable to use heated air from the viewpoint of simplicity. The drying temperature varies depending on the residual solvent ratio of the stretched film 53, but is appropriately selected depending on the residual solvent ratio in the range of 30 ° C to 180 ° C in consideration of drying time, shrinkage unevenness, stability of the amount of expansion and contraction, etc. And decide. Moreover, it may be dried at a constant temperature, or may be divided into two to four stages of temperature and divided into several stages of temperature.

[Winding device]
The winding device 40 winds the stretched film 53 stretched by the stretching device 20 and dried by the heat treatment device 30 to a necessary amount of length on a winding core. The temperature at the time of winding is preferably cooled to room temperature in order to prevent scratches and loosening due to shrinkage after winding. The winder to be used can be used without any particular limitation, and may be a commonly used one, such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. Can be wound up.

Here, the width of the optical film to be wound is preferably 1000 mm to 3000 mm. Such a wide optical film is preferable from the viewpoints of use in a large-sized liquid crystal display device, use efficiency of the optical film during polarizing plate processing, and production efficiency. The film thickness of the optical film is preferably 30 μm to 90 μm from the viewpoints of thinning the liquid crystal display device and stabilizing the production of the optical film. Here, the film thickness is an average film thickness. For example, a film thickness measuring instrument DH-150 manufactured by Tokyo Seimitsu Co., Ltd., a contact-type film thickness meter manufactured by Mitutoyo Co., Ltd., or the like is used. It is the value which measured the film thickness from 20 places to 200 places in the length direction and the width direction, and showed the average value of the measured value as a film thickness.

FIG. 2 is an enlarged view around the casting ribbon 51 between the die 11 and the endless belt 12 of the manufacturing apparatus 1 shown in FIG. In the figure, 11a is the lip portion of the die 11 (the portion of the die that defines the discharge port), 14 is the vibrator, 16 is the diaphragm, and L is the length of the casting ribbon 51. The distance between the discharge port of the die 11 and the surface of the endless belt 12 is appropriately adjusted within a range of about several tens of μm to several cm.

As shown in FIG. 2, in the present invention, a vibrator 14 is attached to the outer wall of the die 11. For this reason, when the vibrator 14 vibrates the die 11, vibration is given to the casting ribbon 51 discharged from the discharge port defined by the lip portion 11a. The vibrator 14 is disposed in the vicinity of the discharge port of the die 11. For this reason, the vibration generated by the vibrator 14 is efficiently transmitted to the casting ribbon 51. The vibrator 14 generates vibration so that the casting ribbon 51 undulates in the longitudinal direction (discharge direction).

The vibrator 14 can be used without any particular limitation, but preferably has a variable frequency (frequency) and / or amplitude. For example, an ultrasonic oscillator using an ultrasonic oscillator, a piezoelectric element, etc., a drive motor drive shaft with a half-moon eccentric weight attached, a drive motor drive shaft connected to the vibrator via a cam, etc. Those that generate vibration by moving the vibrator in a piston motion can be particularly preferably used from the viewpoint of versatility and installation.

The vibrator 14 discharges the dope from the die 11 to form a casting ribbon 51, and the casting ribbon 51 is attached to the endless belt 12 to form a casting film 52 on the endless belt 12. In the process, the casting ribbon 51 between the die 11 and the endless belt 12 is operated so as to vibrate.

In that case, the vibrator 14 is operated so as to give the casting ribbon 51 a vibration having a frequency higher than the peak frequency of the natural vibration of the casting ribbon 51. The peak frequency of the natural vibration of the casting ribbon 51 is usually about 700 Hz or less. Therefore, it is preferable to apply vibration with a frequency of, for example, 1 kHz or more to the casting ribbon 51.

When the peak frequency of the natural vibration of the casting ribbon 51 is relatively low, for example, 200 Hz, the moving speed of the casting ribbon 51 (resin solution discharge speed from the die 11) is 100 m / min (1666 mm / sec). If it is, the pitch of the wave produced in the casting ribbon 51 will become relatively long with about 8 mm. When the casting ribbon 51 vibrates at such a low frequency, as illustrated by a chain line in FIG. 3A, the curvature radius of the wave peak of the casting film 52 becomes large, and the wave tends to be smoothed. The force (leveling force) decreases and the waves tend not to be smoothed. As a result, the horizontal stage resulting from vibration remains on the surface of the stretched film 53, and the film thickness unevenness of the optical film increases.

In contrast, when the casting ribbon 51 is vibrated at a high frequency of 20 kHz, for example, the following phenomenon occurs. First, as shown in FIG. 2, the casting ribbon 51 is fixed at one end by the die 11, but the other end is only fixed to the endless belt 12 and is not fixed. One side is a free end system. Therefore, when vibration of a frequency (20 kHz) different from the peak frequency (200 Hz) of the natural vibration of the casting ribbon 51 is applied to the casting ribbon 51, the state of the system changes, and the casting ribbon 51 is attached to the endless belt 12. The contact position changes, and the length L of the casting ribbon 51 between the die 11 and the endless belt 12 changes. As a result, the applied vibration (high frequency vibration of 20 kHz) is not added to the natural vibration of the casting ribbon 51 (low frequency vibration of 200 Hz), and the natural vibration of the casting ribbon 51 itself changes. Low frequency vibrations that remain as horizontal steps on the surface of the stretched film 53 are damped or extinguished. Instead, the casting ribbon 51 begins to vibrate at a high frequency of 20 kHz.

When the casting ribbon 51 vibrates at 20 kHz, if the moving speed of the casting ribbon 51 (the discharge speed of the resin solution from the die 11) is 100 m / min (1666 mm / sec), the wave generated in the casting ribbon 51 Is as short as about 0.08 mm. When the casting ribbon 51 vibrates at such a high frequency, as illustrated by a chain line in FIG. 3B, the radius of curvature of the wave peak of the casting film 52 becomes small, and the wave is to be smoothed. The force (leveling force) increases and the wave tends to be smoothed. As a result, it is suppressed that the horizontal stage resulting from a vibration remains on the surface of the stretched film 53, and the film thickness nonuniformity of an optical film is reduced.

Moreover, since the vibration exciter 14 is operated during the casting process and vibrations having a frequency higher than the peak frequency of the natural vibration of the casting ribbon 51 are only given to the casting ribbon 51, the By analyzing the frequency of the displacement data using, for example, FFT (Fast Fourier Transform) or the like, the peak frequency can be measured in advance, and the frequency of vibration to be applied can be determined in advance. Therefore, it is not necessary to always detect the peak frequency of the natural vibration of the casting ribbon 51 or perform precise control during the production of the film, and it is possible to easily and reliably suppress the occurrence of horizontal steps on the surface of the optical film, It becomes possible to reduce film thickness unevenness that periodically changes in the longitudinal direction of the film.

The frequency of vibration applied to the casting ribbon 51 (the frequency of vibration generated by the vibrator 14) is not particularly limited as long as it is higher than the peak frequency of the natural vibration of the casting ribbon 51. For example, 1 kHz to 100 kHz Is preferable, and 2 kHz to 20 kHz is more preferable. By giving the casting ribbon 51 a vibration having a frequency of 1 kHz or more, the casting ribbon 51 is reliably given a vibration having a frequency higher than the peak frequency of the natural vibration of the casting ribbon 51 (usually about 700 Hz or less). Can do. On the other hand, by applying vibration having a frequency of 100 kHz or less to the casting ribbon 51, heating of the casting ribbon 51 can be suppressed, and generation of a film on the surface of the casting ribbon 51 can be suppressed. Therefore, when a film | membrane produces | generates on the surface of the casting ribbon 51, the malfunction that the inside of the casting film 52 becomes difficult to dry is avoided.

Further, the amplitude of vibration applied to the casting ribbon 51 (the amplitude of vibration generated by the vibrator 14) is not particularly limited, but is preferably 10 μm to 2000 μm, and more preferably 100 μm to 1000 μm, for example. By applying vibration having an amplitude of 10 μm or more to the casting ribbon 51, the leveling force for smoothing the wave becomes sufficiently large, and it is suppressed that the horizontal stage due to the applied vibration remains. On the other hand, by giving vibration having an amplitude of 2000 μm or less to the casting ribbon 51, the casting ribbon 51 is suppressed from adhering to the lip portion 11a of the die 11, and the resin adhesion to the lip portion 11a is suppressed from remaining. . Therefore, the problem that resin adhesion remains on the lip portion 11a and a die line is generated in the casting ribbon 51 and thus the manufactured optical film is avoided.

In the present invention, as shown in FIG. 2, the vibrator 14 is provided on the die 11 side. That is, the die 11 is used as a vibration source. As a result, the die 11 is vibrated by the vibrator 14, so that the casting ribbon 51 whose one end is in contact with the die 11 is reliably vibrated.

Note that, as indicated by a dotted line in FIG. 2, the vibrators 14 may be provided at both ends of the shaft core (not shown) of the support roll 12B. That is, the endless belt 12 may be a vibration source. Also by this, the endless belt 12 vibrates by vibrating the support roll 12 </ b> B with the vibrator 14, and vibration is reliably applied to the casting ribbon 51 whose other end is in contact with the endless belt 12.

Similarly, as shown by a dotted line in FIG. 2, the diaphragm 16 is disposed on the back side of the casting ribbon 51 (upstream side of the endless belt 12), and the vibrator 14 is attached to the diaphragm 16. Thus, the casting ribbon 51 may be vibrated by vibrating the air around the casting ribbon 51 with the diaphragm 16. That is, the diaphragm 16 is used as a vibration source. This also vibrates the casting ribbon 51 reliably by vibrating the air around the casting ribbon 51. In the illustrated example, the diaphragm 16 is disposed on the back side of the casting ribbon 51, but may be disposed on the front side of the casting ribbon 51 (downstream of the travel of the endless belt 12) depending on the situation. . A speaker can also be used as a set of the diaphragm 16 and the vibrator 14.

When the diaphragm 16 is disposed on the back side of the casting ribbon 51, the diaphragm 16 may be incorporated in a negative pressure chamber (not shown). The negative pressure chamber is provided on the back side of the casting ribbon 51 in order to suppress the impact of the air accompanying the endless belt 12 (entrained wind) hitting the back surface of the casting ribbon 51 as the endless belt 12 travels. It is a device that generates a negative pressure on the back side of the ribbon 51.

As means for applying vibration to the casting ribbon 51, a vibration exciter is disposed on the die, a vibration exciter is disposed near the end of the casting ribbon 51 of the endless belt, and a vibration exciter is provided on the back side of the casting ribbon 51. One of these or a combination of two or more thereof can be used.

Of these, using the die 11 and the endless belt 12 as the vibration source provides better results than using the diaphragm 16 as the vibration source. It is considered that high frequency vibration is more efficiently transmitted to the casting ribbon 51 when the die 11 and the endless belt 12 are used as the vibration source.

In the case where the support is the endless belt 12, better results can be obtained by using the die 11 as a vibration source than using the endless belt 12 as a vibration source. This is probably because the high frequency vibration is more efficiently transmitted to the casting ribbon 51 when the die 11 is used as the vibration source. Conversely, when the support is a drum, better results can be obtained when the drum is used as the vibration source than when the die 11 is used as the vibration source. It is considered that high frequency vibration is more efficiently transmitted to the casting ribbon 51 when the drum is used as the vibration source.

<Other embodiments>
FIG. 4 is a schematic configuration diagram of an optical film manufacturing apparatus (drum type) according to the optical film manufacturing method of the present invention. FIG. 5 is an enlarged view of the periphery of the casting ribbon between the die and the drum of the manufacturing apparatus (drum type) shown in FIG. In the figure, reference numeral 18 denotes a drum support cylinder. The optical film manufacturing apparatus 1b also manufactures an optical film by a solution casting film forming method. The only difference from the manufacturing apparatus 1a shown in FIGS. 1 and 2 is that the endless belt is changed to a drum, and the others are the same. Only parts different from the manufacturing apparatus shown in FIGS. 1 and 2 will be described.

In this figure, the casting apparatus 10 includes a drum 17 instead of the endless belt 12 as a support. The drum 17 rotates to convey the formed cast film 52 in the direction of the arrow in the figure. The drum 17 is a metal drum having a mirror-finished surface. The drum 17 is preferably made of, for example, stainless steel from the viewpoint of peelability of the cast film 52. Other symbols are the same as those in FIGS.

In the optical film manufacturing apparatus 1b shown in this figure, the vibrator 14 is provided at both ends of the shaft core (illustrated) of the drum 17. That is, the drum 17 is used as a vibration source. For this reason, the high frequency vibration generated by the vibrator 14 is efficiently transmitted to the casting ribbon 51. The vibrator 14 generates vibration so that the casting ribbon 51 undulates in the longitudinal direction (discharge direction).

<Method for producing optical film>
By using the optical film manufacturing apparatus 1 a having the configuration shown in FIG. 1 and the optical film manufacturing apparatus 1 b shown in FIG. 4, the casting solution 51 is formed by discharging the resin solution from the die 11. In the endless pelt 12 or the drum 17 to form the casting film 52 on the endless pelt 12 or the drum 17. A method of manufacturing an optical film capable of giving the casting ribbon 51 a vibration having a frequency higher than the peak frequency of the natural vibration of the casting ribbon 51 between the endless pelt 12 and the drum 17 can be implemented.

And the optical film manufactured by such a manufacturing method suppresses the occurrence of a horizontal step on the surface, reduces the film thickness unevenness that periodically changes in the longitudinal direction, and meets the demand for thinning the optical film. It can respond.

<Optical film>
In the production apparatus shown in FIGS. 1 to 5, as a representative example, an optical film containing a cellulose ester resin such as cellulose triacetate is produced.

In the production apparatus shown in FIG. 1 to FIG. 5, for example, a thermoplastic resin composed of cellulose ester resin or the like is dissolved in a mixed solvent of a good solvent and a poor solvent using a dissolution vessel, and a plasticizer or an ultraviolet absorber is added thereto. The dope is prepared by adding such additives.

Next, the dope adjusted by the melting pot is fed to the casting die 11 by a conduit through, for example, a pressurized metering gear pump, and is transported infinitely, for example, an endless belt 12 made of, for example, rotationally driven stainless steel, or a support comprising a drum 17 The dope is cast from the casting die 11 at a casting position on the body.

For example, when a thermoplastic resin solution in which cellulose ester is dissolved in a solvent is used as the dope, the solid content concentration in the dope is preferably 15% by mass to 30% by mass. If the solid content concentration of the dope is less than 15% by mass, sufficient drying cannot be performed on the endless belt 12 or the drum 17, and a part of the dope film remains on the endless belt 12 or the drum 17 at the time of peeling, This is not preferable because it leads to endless belt contamination or drum contamination. When the solid content concentration exceeds 30% by mass, the dope viscosity increases, the filter clogging becomes faster in the dope adjustment process, or the pressure increases when cast onto the endless belt 12 or the drum 17 and cannot be extruded. Therefore, it is not preferable.

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

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

As an example of cellulose triacetate, the substitution degree of acetyl group is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane 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 of the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

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

Various additives can be blended with the cellulose ester used in the present invention.

In the method for producing an optical film of the present invention, a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt) can be used.

When the cellulose ester film is used for widening the viewing angle of a liquid crystal display device operating in the IPS mode, it is important to reduce the thickness direction retardation (Rt), but such thickness direction retardation (Rt) is reduced. The following are mentioned as an additive.

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

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

Formula (1): B1- (GA-) mG-B1
Formula (2): B2- (GA-) nG-B2
In the above formula, B1 represents a monocarboxylic acid component, B2 represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

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

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

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

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

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

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

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

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

The weight average molecular weight of the polyester is preferably 20000 or less, and more preferably 10,000 or less. In particular, a polyester having a weight average molecular weight of 500 to 10,000 has good compatibility with a cellulose ester, and neither evaporation nor volatilization occurs in film formation.

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

The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by mass with respect to the cellulose ester. In particular, the content is preferably 5 to 15% by mass.

Examples of additives that reduce the thickness direction retardation (Rt) include the following.

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 it is desirable to use a method that can align the molecular weight as much as possible without increasing the molecular weight. . Examples of such a polymerization method include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than usual polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as described in the publication, or a polymerization catalyst in which the compound and an organometallic compound are used in combination. Although preferably used in the form, the method described in the publication is particularly preferable.

Although the monomer as a monomer unit which comprises the polymer as an additive which reduces useful thickness direction retardation (Rt) is mentioned below, it is not limited to this.

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

Next, as acrylate esters, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2 Hydroxybutyl) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid 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, the acrylic polymer refers to a homopolymer or a copolymer of acrylic acid or methacrylic acid alkyl ester having no monomer unit having an aromatic ring or a cyclohexyl group.

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

The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by mass or more, and the methacrylic acid methyl ester monomer unit has 40% by mass 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, it is preferable that the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is contained in an acrylic polymer in an amount of 2% by mass to 20% by mass.

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

In the method for producing an optical film of the present invention, the dope composition contains a cellulose ester and an acrylic polymer having a weight average molecular weight of 5000 or more and 30000 or less as an additive for reducing the thickness direction retardation (Rt). It is preferable.

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, the cellulose ester Is compatible with the material, and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester film after film formation is excellent, the moisture permeability is extremely low, and it exhibits excellent performance as a protective film for polarizing plates.

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

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

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

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

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

The content of the additive for reducing the thickness direction retardation (Rt) described above is preferably 5% by mass to 25% by mass with respect to the cellulose ester resin. If the content of the additive for reducing the thickness direction retardation (Rt) is less than 5% by mass, 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 mass, so-called bleed-out occurs and the stability in the film decreases, which is not preferable.

In the method for producing an optical film of the present invention, an organic solvent having good solubility for the cellulose derivative is referred to as a good solvent.

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

In addition to the organic solvent, the dope preferably contains 1% to 40% by weight of an alcohol having 1 to 4 carbon atoms. These are gels that, after casting the dope onto the support, the solvent begins to evaporate and the proportion of alcohol increases, making the web gel, making the web strong and easy to peel off from the support When used as a solvating solvent, or when the proportion of these is small, it also has a role of promoting the dissolution of a cellulose derivative of a non-chlorine organic solvent.

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 methylene chloride: ethyl alcohol ratio 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 optical film of the present invention includes a plasticizer that imparts processability, flexibility, and moisture resistance to the optical film, a fine particle (matting agent) that imparts slipperiness to the optical film, an ultraviolet absorber that imparts an ultraviolet absorption function, optical You may contain the antioxidant etc. which prevent deterioration of a film.

The plasticizer used in the present invention is not particularly limited, but a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation so as not to generate haze, bleed out or volatilize from the optical film. It preferably has a functional group capable of interacting with the polycondensate of the above by a hydrogen bond 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 embodiment is represented by the following general formula (3).

Formula (3): R ^1- (OH) n
In the formula, 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.

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

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

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

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

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

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

The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 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 in the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

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

For phosphate plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, and the like can be used. In this embodiment, 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 mass, preferably 0.1% by mass, 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% by mass to 20% by mass. 6 mass% to 16 mass% is further more preferable, and 8 mass% to 13 mass% is particularly preferable. If the amount of the plasticizer used is less than 1% by mass 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 mass, 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 used 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 inorganic compound fine particles include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide, and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

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

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

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

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

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

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

Fine particles are used by adding 0.04% by mass to 0.5% by mass with respect to the cellulose ester. Preferably, 0.05% by mass to 0.3% by mass, and more preferably 0.05% by mass to 0.25% by mass is used. When the amount of fine particles added is 0.04% by mass 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 mass, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

For dispersion of fine particles, it is preferable to treat a composition in which fine particles and a solvent are mixed with a high-pressure dispersion apparatus. A high-pressure dispersion device is a device 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 μm 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 include an ultra-high pressure homogenizer (trade name, microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other examples include a Manton Gorin type high-pressure dispersing device such as a homogenizer manufactured by Izumi Food Machinery. Can be mentioned.

In the present invention, the fine particles are dispersed in a solvent containing 25% by mass to 100% by mass of a lower alcohol, and then mixed with a dope obtained by dissolving a cellulose ester (cellulose derivative) in a solvent, and the mixed solution is placed on a support. To obtain a cellulose ester film characterized by being formed by drying.

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

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

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

Fine particles are dispersed in a solvent at a concentration of 1% by mass to 30% by mass. 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% by mass to 25% by mass, and more preferably 10% by mass to 20% by mass.

The ultraviolet absorbing function of the optical 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 the optical 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 preferred. Further, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are preferably used.

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 for use 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-butyl Phenyl) -5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2 -Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy -3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (straight and side chain dodecyl) -4-methylphenol, Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy- Examples include, but are not limited to, a mixture of 5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

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

In addition, specific examples of the benzophenone compounds that are UV absorbers that can be used in the present embodiment include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-methoxy-5. -Sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane) and the like can be mentioned, but are not limited thereto.

In the present invention, the blending amount of these ultraviolet absorbers is preferably in the range of 0.01% by mass to 10% by mass and more preferably in the range of 0.1% by mass to 5% by mass with respect to the cellulose ester (cellulose derivative). . 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.

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

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

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

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

In the present invention, the cellulose ester film as the finally produced optical film has a moisture content of preferably 0.1% to 5%, more preferably 0.3% to 4%, and more preferably 0.5% to 2%. % Is more preferable.

In the present invention, the cellulose ester film as the finally produced optical film desirably has a transmittance of 90% or more, more preferably 92% or more, and further preferably 93% or more.

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

The optical film of the present invention can be particularly preferably used as a protective film for a polarizing plate for a large liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

<Polarizing plate>
When using the optical film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

On the other surface, the optical film of the present invention may be used, or another protective film for polarizing plate may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4FR-4, KC4FR-3, KC4FR-3, KC4FR-4 -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound.

As an adhesive used for the adhesive layer, an adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the adhesive layer is used. Preferably, a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded is suitably used.

Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

The pressure-sensitive adhesive may be a one-component type or a type in which two or more components are mixed before use.

The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The concentration of the pressure-sensitive adhesive liquid may be appropriately determined depending on the film thickness after adhesion, the coating method, the coating conditions, and the like, and is usually 0.1% by mass to 50% by mass.

The polarizing plate of the present invention includes a polarizer and a transparent protective film disposed on the surface of the polarizer, and the transparent protective film is the optical film of the present invention. A polarizer is an optical element that emits incident light by converting it into polarized light.

As the polarizing plate, for example, a completely saponified polyvinyl alcohol aqueous solution is used on at least one surface of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution. What stuck the film is preferable. Further, the optical film of the present invention may be laminated on the other surface of the polarizer, or another transparent protective film for polarizing plate may be laminated. As another transparent protective film for polarizing plate, for example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto Co., Ltd.) Etc. are preferably used. Or you may use resin films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

As described above, the polarizing plate uses the optical film of the present invention as a protective film laminated on at least one surface side of the polarizer. In that case, when the said optical film functions as a phase difference film, it is preferable to arrange | position so that the slow axis of the optical film of this invention may be substantially parallel or orthogonal to the absorption axis of a polarizer.

Further, as a specific example of the polarizer, for example, a polyvinyl alcohol polarizing film can be mentioned. Polyvinyl alcohol polarizing films include those obtained by dyeing iodine on polyvinyl alcohol films and those obtained by dyeing dichroic dyes. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used.

The polarizer is obtained as follows, for example. First, a film is formed using a polyvinyl alcohol aqueous solution. The obtained polyvinyl alcohol film is uniaxially stretched and then dyed or dyed and then uniaxially stretched. And preferably, a durability treatment is performed with a boron compound.

The film thickness of the polarizer is preferably 5 μm to 40 μm, more preferably 5 μm to 30 μm, and even more preferably 5 μm to 20 μm.

When laminating a cellulose ester resin film on the surface of a polarizer, it is preferable to bond the cellulose ester resin film with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol. Moreover, in the case of resin films other than a cellulose ester-type resin film, it is preferable to carry out the adhesive process to a polarizing plate through a suitable adhesion layer.

The polarizing plate as described above uses the optical film of the present invention as a transparent protective film, so that the deformation of the optical film is sufficiently suppressed. For example, when applied to a liquid crystal display device, the contrast Improvement of image quality of the liquid crystal display device such as improvement of the above can be realized. In addition, since the optical film of the present invention applied as a transparent protective film of a polarizing plate also suppresses dimensional changes due to changes in humidity, for example, when applied to a liquid crystal display device, so-called corner unevenness is also suppressed. it can.

Thus, the polarizing plate of the present invention is a polarizing plate comprising a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer, and the two transparent protective films At least one of them is a polarizing plate characterized by being the optical film of the present invention. In this polarizing plate, the occurrence of lateral steps on the surface of the transparent protective film is suppressed, and the unevenness of the film thickness that periodically changes in the longitudinal direction of the transparent protective film is reduced. To get.

<Liquid crystal display device>
By incorporating a polarizing plate in which the optical film of the present invention is bonded as a protective film for a liquid crystal polarizing plate into a liquid crystal display device, various liquid crystal display devices having excellent visibility can be produced. It is preferably used for liquid crystal display devices for outdoor use such as devices and digital signage. The polarizing plate according to the present embodiment is bonded to the liquid crystal cell via the adhesive layer or the like.

The polarizing plate of the present invention includes various types such as a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), and an IPS type (including an FFS type). It is preferably used in a drive type LCD. In particular, in a large-screen display device having a screen size of 30 or more, particularly 30 to 54, there is no white spot in the periphery of the screen and the effect is maintained for a long time.

In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even after long hours of viewing.

The liquid crystal display device of the present invention includes a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates is the polarizing plate. Note that the liquid crystal cell is a cell in which a liquid crystal substance is filled between a pair of electrodes, and by applying a voltage to the electrodes, the alignment state of the liquid crystal is changed and the amount of transmitted light is controlled. In such a liquid crystal display device, since the optical film of the present invention in which deformation is sufficiently suppressed is used as the transparent protective film for the polarizing plate by using the polarizing plate of the present invention, the contrast and the like are high. An improved high-quality liquid crystal display device is obtained. Moreover, since what used the optical film of this invention by which the dimensional change by the humidity change was suppressed was used for the polarizing plate as a transparent protective film, generation | occurrence | production of what is called a corner nonuniformity can also be suppressed.

As described above, the liquid crystal display device of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell. In the liquid crystal display device, at least one of the polarizing plates is the polarizing plate of the present invention. In this liquid crystal display device, the occurrence of horizontal steps on the surface of the transparent protective film in the polarizing plate is suppressed, and the film thickness unevenness that periodically changes in the longitudinal direction of the transparent protective film is reduced, thereby making the liquid crystal display device thinner. It can respond well.

Hereinafter, the present invention will be described in more detail through examples, but the present invention is not limited to these examples.

<Optical film production test>
[Preparation of dope]
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. 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 Silicon dioxide fine particles (Aerosil R972V) 0.1 part by weight And, using the above dope, Thus, an optical film (cellulose triacetate film) was produced.

[Test 1]
The prepared dope was cast uniformly on an endless belt made of stainless steel at 22 ° C. and a width of 2 m using an apparatus similar to the belt-type optical film manufacturing apparatus 1 shown in FIG. On the endless belt, the solvent was evaporated until the residual solvent ratio of the cast film reached 60% by mass, and the cast film was peeled from the endless belt with a peel tension of 100 N / m.

Here, a small vibrator unit manufactured by Nippon Alex Co., Ltd. was used as the vibrator, and this was attached in the vicinity of the discharge port of the die. Then, the dope was discharged from the die to form a casting ribbon, and the vibrator was operated during the casting process in which the casting ribbon was attached to the endless belt to form a casting film on the endless belt. As shown in Table 1, the frequency of vibration generated by the vibrator was set to 1 kHz, and the amplitude of vibration generated by the vibrator was set to 5 μm. The moving speed of the casting ribbon (discharge speed of the dope from the die) was set to 100 m / min (1666 mm / sec) (the pitch of waves generated on the casting ribbon: 1.666 mm). The distance between the die outlet and the surface of the endless belt was adjusted to 8 mm. When the peak frequency of the natural vibration of the casting ribbon was measured in advance, it was 200 Hz. The natural vibration of the casting ribbon had an amplitude of 6 μm.

As for the natural vibration of the casting ribbon, two cameras are installed in the vicinity of the widthwise ends of the discharge port of the die, and the image data obtained by continuously shooting the casting ribbon separately with the two cameras. The value obtained from the average value of the two obtained amplitudes is shown. The peak frequency of the natural vibration indicates a value obtained by performing frequency analysis on the data obtained when obtaining the natural vibration by FFT.

The peeled unstretched film is stretched 1.1 times (stretching ratio: 10%) in the longitudinal direction (MD direction) and 1.2 times (stretching ratio: 20%) in the width direction (TD direction) using a clip tenter. However, it was dried at 70 ° C. for 10 seconds.

After stretching, relaxation was performed at 130 ° C. for 5 minutes, and then drying was completed while conveying a heat treatment apparatus at 120 ° C. and 140 ° C. with a plurality of rollers, slitting to 1.5 m width, and 10 mm width at both ends of the stretched film. An optical film (cellulose triacetate) that can be used as, for example, a protective film for a liquid crystal polarizing plate, is subjected to a knurling process of 5 μm and wound on a core having an initial tension of 220 N / m and a final tension of 110 N / m and an inner diameter of 15.24 cm. Film) was obtained.

The manufactured optical film had a residual solvent ratio of 0.01%, a film thickness of 40 μm, and a winding length of 4000 m.

[Tests 2 to 8]
An optical film was produced in the same manner as in Test 1 except that the amplitude of vibration generated by the vibrator was changed to the values shown in Table 1.

[Tests 9 to 16]
As shown in Table 1, an optical film was produced in the same manner as in Tests 1 to 8, except that the vibrator was attached to the endless belt side (belt support plate).

[Tests 17 to 24]
As shown in Table 1, optical films were produced in the same manner as in Tests 1 to 8, except that the vibrator was attached to the diaphragm disposed on the back side of the casting ribbon.

[Test 25]
As shown in Table 1, an optical film was produced in the same manner as in Test 1 except that the casting ribbon was not vibrated with a vibrator during the casting process.

[Tests 26 to 32]
An optical film was produced in the same manner as in Test 1 except that the frequency of vibration generated by the vibrator and the amplitude of vibration generated by the vibrator were changed to the values shown in Table 2. Test 27 is the same as test 2.

[Tests 33 to 39]
As shown in Table 2, an optical film was produced in the same manner as in Tests 26 to 32 except that the vibrator was attached to the endless belt side (belt support plate). Test 34 is the same as test 10.

[Tests 40 to 46]
As shown in Table 2, an optical film was produced in the same manner as in Tests 26 to 32 except that the vibrator was attached to the diaphragm disposed on the back side of the casting ribbon. The test 41 is the same as the test 18.

[Tests 51 to 58]
As shown in Table 3, an optical film was produced in the same manner as in Tests 1 to 8, except that an apparatus similar to the drum-type optical film production apparatus 1 shown in FIG. 4 was used. When the peak frequency of the natural vibration of the casting ribbon was measured in advance, it was 500 Hz.

[Tests 59 to 66]
As shown in Table 3, optical films were produced in the same manner as in Tests 51 to 58 except that the vibrator was attached to the drum side (drum support cylinder).

[Tests 67 to 74]
As shown in Table 3, an optical film was produced in the same manner as in Tests 51 to 58 except that the vibrator was attached to the diaphragm disposed on the back side of the casting ribbon.

[Test 75]
As shown in Table 3, an optical film was produced in the same manner as in Test 51 except that the casting ribbon was not vibrated with a vibrator during the casting process.

[Tests 76 to 82]
An optical film was produced in the same manner as in Test 51 except that the frequency of vibration generated by the vibrator and the amplitude of vibration generated by the vibrator were changed to the values shown in Table 4. Test 77 is the same as test 52.

[Tests 83 to 89]
As shown in Table 4, optical films were produced in the same manner as in Tests 76 to 82 except that the vibrator was attached to the drum side (drum support cylinder). The test 84 is the same as the test 60.

[Tests 90 to 96]
As shown in Table 4, an optical film was produced in the same manner as in Tests 76 to 82 except that the vibrator was attached to the diaphragm disposed on the back side of the casting ribbon. Test 91 is the same as test 68.

<Evaluation method>
The following evaluation was implemented about the optical film manufactured by each test 1-46 and 51-96. The results are shown in Tables 1 to 4.

[Main evaluation: Horizontal unevenness]
The thickness of the manufactured optical film was measured with a film thickness meter (film thickness measuring instrument DH-150, manufactured by Tokyo Seimitsu Co., Ltd.), and “horizontal unevenness (%) = (maximum value and minimum value of unevenness of thickness unevenness and Of difference / average film thickness) × 100 ”was evaluated and evaluated according to the following criteria. That is, the horizontal unevenness (%) is a value obtained by dividing the difference between the maximum value and the minimum value of the unevenness of the thickness unevenness of the optical film by the average film thickness of the optical film. The thickness of the optical film was continuously measured in the length direction, and the pitch of periodic thickness unevenness and the maximum value, minimum value, and average value (average film thickness) of thickness unevenness were read from the chart.

◎: Less than 0.4% ○: 0.4% or more and less than 0.6% △: 0.6% or more and less than 0.8% ×: 0.8% or more Manufactured in tests 1 to 24, 51 to 74 The following evaluation was implemented about the optical film. The results are shown in Tables 1 and 3.

[Sub-evaluation: Resin adhesion]
The lip part of the die was visually observed after film production, and whether or not the casting ribbon adhered to the lip part and the resin adhesion remained was evaluated according to the following criteria.

○: Resin adhesion could not be confirmed visually ×: Resin adhesion could be confirmed visually Test 27 to 32, 34 to 39, 41 to 46, 77 to 82, 84 to 89, 91 to 96 The following evaluation was performed on the film. The results are shown in Tables 2 and 4.

[Sub-evaluation: film formation]
The cast ribbon was imaged with a camera during film production, and whether or not a film was formed on the surface of the cast ribbon was evaluated according to the following criteria.

○: A film was not formed on the surface of the casting ribbon. △: A sign of film formation was seen on the surface of the casting ribbon. X: A film was formed on the surface of the casting ribbon.

<Consideration of results>
[Table 1]
As is apparent from Table 1, an endless belt is used as a support, and in the casting process, a vibration having a frequency of 1 kHz higher than the peak frequency 200 Hz of the natural vibration of the casting ribbon between the die and the endless belt is cast. The optical films of Tests 1 to 24 produced by the above were excellent in the horizontal unevenness as the main evaluation of less than 0.8%.

On the other hand, in the casting process, the optical film of Test 25 manufactured without giving vibration to the casting ribbon was inferior in the horizontal unevenness of 0.8% or more, which is the main evaluation.

Of Tests 1 to 8 using a die as a vibration source, Tests 2 to 7 in which the amplitude of vibration applied to the casting ribbon was 10 μm to 2000 μm were more excellent with a horizontal step unevenness of less than 0.6%. It was. Furthermore, in Tests 4 and 5 in which the amplitude of vibration applied to the casting ribbon was 100 μm and 1000 μm, the horizontal unevenness was less than 0.4%, which was further excellent.

On the other hand, among tests 9 to 16 using an endless belt as a vibration source, tests 11 to 14 in which the amplitude of the vibration applied to the casting ribbon was 50 μm to 1500 μm were more excellent with a horizontal unevenness of less than 0.6%. It was. Furthermore, in Tests 12 and 13, in which the amplitude of vibration applied to the casting ribbon was 100 μm and 1000 μm, the lateral unevenness was further excellent at less than 0.4%.

Furthermore, among tests 17 to 24 using the diaphragm as a vibration source, tests 20 and 21 in which the amplitude of vibration applied to the casting ribbon was 100 μm and 1000 μm were more excellent with a horizontal unevenness of less than 0.6%. It was.

When an endless belt is used as a support, generally, tests 1 to 8 using a die as a vibration source and tests 9 to 16 using an endless belt as a vibration source are more than tests 17 to 24 using a diaphragm as a vibration source. The main evaluation result was good. In general, tests 1 to 8 using a die as a vibration source performed better than the tests 9 to 16 using an endless belt as a vibration source.

Furthermore, Tests 1 to 7, 9 to 15, and 17 to 23 in which the amplitude of vibration applied to the casting ribbon was 2000 μm or less were excellent because the resin adhesion, which is a sub-evaluation, could not be confirmed. On the other hand, Tests 8, 16, and 24, in which the amplitude of vibration applied to the casting ribbon was 2500 μm, were inferior because the resin adhesion as a sub-evaluation could be confirmed.

[Table 2]
As is apparent from Table 2, an endless belt is used as the support, and in the casting process, a vibration having a frequency of 1 kHz to 150 kHz higher than the peak frequency 200 Hz of the natural vibration of the casting ribbon between the die and the endless belt is passed. The optical films of Tests 27 to 32, 34 to 39, and 41 to 46, which were produced by giving to the ribbon, were excellent with the horizontal unevenness as the main evaluation being less than 0.8%.

On the other hand, an endless belt is used as a support, and in the casting process, a vibration having a frequency of 0.1 kHz lower than the peak frequency 200 Hz of the natural vibration of the casting ribbon between the die and the endless belt is given to the casting ribbon. In the optical films of Tests 26, 33, and 40 manufactured in this manner, the horizontal unevenness as the main evaluation was inferior to 0.8% or more.

Further, when the die was used as the vibration source, tests 28 and 29 in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz were more excellent in the result of horizontal unevenness. When an endless belt was used as the vibration source, tests 35 to 38 in which the frequency of vibration applied to the casting ribbon was 2 kHz to 100 kHz had a more excellent result of lateral unevenness. Furthermore, in the tests 35 and 36 in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz, the result of the horizontal unevenness was further excellent. When the vibration plate was used as the vibration source, the tests 42 and 43 in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz were more excellent in the result of horizontal unevenness.

When an endless belt is used as a support, generally, tests 27 to 32 using a die as a vibration source and tests 34 to 39 using an endless belt as a vibration source are more than tests 41 to 46 using a diaphragm as a vibration source. The main evaluation result was good. In general, tests 27 to 32 using a die as a vibration source gave better main evaluation results than tests 34 to 39 using an endless belt as a vibration source.

Furthermore, Tests 27 to 31, 34 to 38, and 41 to 45, in which the frequency of vibration applied to the casting ribbon was 100 kHz or less, were excellent with no film formation as a secondary evaluation. On the other hand, Tests 32, 39, and 46, in which the frequency of vibration applied to the casting ribbon was 150 kHz, were inferior due to the formation of a film as a sub-evaluation.

[Table 3]
As is apparent from Table 3, a drum is used as the support, and in the casting process, the casting ribbon is given a vibration having a frequency of 1 kHz, which is higher than the peak frequency 500 Hz of the natural vibration of the casting ribbon between the die and the drum. The optical films of Tests 51 to 74 manufactured as described above were excellent with the horizontal unevenness as the main evaluation being less than 0.8%.

On the other hand, in the casting process, the optical film of Test 75 manufactured without giving vibration to the casting ribbon was inferior to 0.8% or more in the horizontal unevenness as the main evaluation.

Of tests 51 to 58 using a die as a vibration source, tests 53 to 56 in which the amplitude of the vibration applied to the casting ribbon was 50 μm to 1500 μm were more excellent, with the horizontal step unevenness being less than 0.6%. It was. Furthermore, in Tests 54 and 55 in which the amplitude of vibration applied to the casting ribbon was 100 μm and 1000 μm, the horizontal step unevenness was even less than 0.4%.

On the other hand, among the tests 59 to 66 using the drum as the vibration source, the tests 60 to 65 in which the amplitude of the vibration applied to the casting ribbon was 10 μm to 2000 μm were more excellent with the horizontal unevenness being less than 0.6%. It was. Furthermore, in Tests 62 and 63 in which the amplitude of vibration applied to the casting ribbon was 100 μm and 1000 μm, the horizontal step unevenness was further excellent at less than 0.4%.

Furthermore, among the tests 67 to 74 using the diaphragm as a vibration source, the tests 70 and 71 in which the amplitude of the vibration applied to the casting ribbon was 100 μm and 1000 μm were more excellent with the horizontal unevenness being less than 0.6%. It was.

When the drum is used as the support, the tests 51 to 58 using the die as the vibration source and the tests 59 to 66 using the drum as the vibration source are generally more evaluated than the tests 67 to 74 using the vibration plate as the vibration source. The result was good. In general, the tests 59 to 66 using the drum as the vibration source performed better than the tests 51 to 58 using the die as the vibration source.

Furthermore, the tests 51 to 57, 59 to 65, and 67 to 73 in which the amplitude of vibration applied to the casting ribbon was 2000 μm or less were excellent because the resin adhesion, which is a sub-evaluation, could not be confirmed. On the other hand, tests 58, 66, and 74 in which the amplitude of vibration applied to the casting ribbon was 2500 μm were inferior because the resin adhesion, which is a sub-evaluation, was confirmed.

[Table 4]
As is apparent from Table 4, a drum is used as the support, and in the casting process, vibrations having a frequency of 1 kHz to 150 kHz higher than the peak frequency 500 Hz of the natural vibration of the casting ribbon between the die and the drum are cast. The optical films of Tests 77 to 82, 84 to 89, and 91 to 96 produced by the above-described method were excellent in the horizontal unevenness as the main evaluation of less than 0.8%.

On the other hand, using a drum as a support, in the casting process, the casting ribbon was produced by applying a vibration at a frequency of 400 Hz lower than the peak frequency of 500 Hz of the natural vibration of the casting ribbon between the die and the drum. The optical film Nos. 76, 83, and 90 were inferior in the horizontal unevenness as the main evaluation of 0.8% or more.

Further, when the die was used as the vibration source, the test 78 to 81 in which the frequency of the vibration applied to the casting ribbon was 2 kHz to 100 kHz was superior in the result of the horizontal unevenness. Furthermore, in the tests 78 and 79 in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz, the result of horizontal unevenness was further excellent. When the drum was used as the vibration source, tests 85 and 86, in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz, were more excellent in the results of lateral unevenness. When the vibration plate was used as the vibration source, the tests 92 and 93 in which the frequency of vibration applied to the casting ribbon was 2 kHz and 20 kHz were more excellent in the result of the horizontal unevenness.

In the case where a drum is used as the support, the tests 77 to 82 using the die as the vibration source and the tests 84 to 89 using the drum as the vibration source are generally more evaluated than the tests 91 to 96 using the vibration plate as the vibration source. The result was good. In general, the tests 84 to 89 using the drum as the vibration source performed better than the tests 77 to 82 using the die as the vibration source.

Furthermore, Tests 77 to 81, 84 to 88, and 91 to 95, in which the frequency of vibration applied to the casting ribbon was 100 kHz or less, were excellent because there was no film formation as a secondary evaluation. On the other hand, Tests 82, 89, and 96, in which the frequency of vibration applied to the casting ribbon was 150 kHz, were inferior due to the formation of a film, which was a secondary evaluation.

DESCRIPTION OF SYMBOLS 1 Optical film manufacturing apparatus 10 Casting apparatus 11 Die 11a Lip part 12 Support body (endless belt)
13 Peeling roller 14 Exciter 16 Diaphragm 17 Support (drum)
18 Drum support cylinder 20 Stretching device 30 Heat treatment device 40 Winding device 51 Casting ribbon 52 Casting membrane (web)
53 Resin film L Ribbon length

Claims (9)

1. An optical film manufacturing method comprising a casting step of discharging a resin solution from a die to form a casting ribbon, and contacting the casting ribbon to a support to form a casting film on the support. ,
   The casting step includes a vibrator that vibrates a casting ribbon between the die and the support,
   The said vibration is a frequency higher than the peak frequency of the natural vibration of the said casting ribbon, The manufacturing method of the optical film characterized by the above-mentioned.
2. The method for producing an optical film according to claim 1, wherein the frequency is 1 kHz to 100 kHz.
3. 3. The method for producing an optical film according to claim 1, wherein the amplitude of the vibration is 10 μm to 2000 μm.
4. The method for producing an optical film according to any one of claims 1 to 3, wherein the vibrator vibrates the casting ribbon by vibrating the die.
5. The method for producing an optical film according to any one of claims 1 to 4, wherein the vibrator vibrates the casting ribbon by vibrating the support.
6. The method for producing an optical film according to any one of claims 1 to 5, wherein the vibrator vibrates the casting ribbon by vibrating the air around the casting ribbon.
7. An optical film manufactured by the manufacturing method according to any one of claims 1 to 6.
8. A polarizing plate comprising a polarizer and two transparent protective films disposed on both sides of the polarizer so as to sandwich the polarizer,
   The polarizing plate, wherein at least one of the two transparent protective films is the optical film according to claim 7.
9. A liquid crystal display device comprising a liquid crystal cell and two polarizing plates arranged on both sides of the liquid crystal cell so as to sandwich the liquid crystal cell,
   A liquid crystal display device, wherein at least one of the two polarizing plates is the polarizing plate according to claim 8.

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