WO2009101929A1

WO2009101929A1 - Optical film, process and apparatus for producing the same, polarizer employing optical film, and display

Info

Publication number: WO2009101929A1
Application number: PCT/JP2009/052202
Authority: WO
Inventors: Seiichi Iida
Original assignee: Konica Minolta Opto, Inc.
Priority date: 2008-02-12
Filing date: 2009-02-10
Publication date: 2009-08-20
Also published as: JPWO2009101929A1

Abstract

The failure in optical films which is caused by pressing is diminished, and the condensation caused by a plasticizer or impurity-containing water is prevented. Transfer failures in optical films are diminished. The desire for higher quality in optical films is met. An optical film is provided which can be produced continuously and stably with high productivity. Also provided are a process and apparatus for producing the optical film, a polarizer, and a display. The process for producing optical film is based on the solution casting film formation method. At the time when a web is separated from a support, the web has a residual solvent content regulated to 60-160 mass%. The surfaces of rolls (8) and (9) conveying the web (10) which has been separated from the support (7) are irradiated with a plasma or excimer UV to conduct a high-energy surface treatment. A treated surface film is thus formed on the surfaces of the conveyor rolls (8) and (9) to remove adherent substances such as a plasticizer or to prevent the condensation caused by a plasticizer or impurity-containing water.

Description

Optical film, manufacturing method and manufacturing apparatus thereof, polarizing plate using optical film, and display device

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

Conventionally, a liquid crystal display device (LCD) can be directly connected to an IC circuit with low voltage and low power consumption, and can be thinned, so that it is widely used as a display device for a word processor, a personal computer or the like. .

By the way, the basic structure of this LCD is one in which polarizing plates are provided on both sides of the liquid crystal cell. Since the polarizing plate allows only light with a polarization plane in a certain direction to pass, it plays an important role in visualizing changes in the orientation of the liquid crystal due to the electric field in the LCD, and the performance of the polarizing plate greatly depends on the performance of the polarizing plate. The A polarizing plate consists of a polarizer and a protective film laminated on both sides of the polarizer. And as a protective film of such a polarizing plate, the cellulose-ester film (henceforth only a film) is widely used. In addition to the polarizing plate protective film, it is known to use an optical film such as a retardation film, a viewing angle widening film, an antireflection film, or the like for a liquid crystal display device. Optical films are used. As materials for the optical film, materials other than cellulose ester are also known.

These optical films have been produced exclusively by the solution casting film forming method. When manufacturing an optical film with a solution casting film forming apparatus, there are roughly two dope casting methods. One is a belt casting method in which an endless belt as a support is wound between a pair of drums, and the other is a drum casting method in which the rotating drum itself is a support.

The present invention relates to an optical film manufacturing method using both the belt casting method and the drum casting method.

With the recent increase in screen size, there is a demand for a film with a wide film width and a long roll length. Conventionally, in the optical film manufacturing method by the solution casting film forming method, the web contains a large amount of solvent, so it is very soft and is damaged by the web roll immediately after peeling due to some cause (pressed failure) ) And transfer of dirt on the roll to the film (transfer failure) is more susceptible to melt film formation. It has been found that the optical film in which these failures occur becomes a serious defect when converted into a polarizing plate.

On the other hand, in the solution casting film forming method, adhesion of foreign matter on the roll near the peeling due to a film during casting, scattering of plasticizer, or the like may occur. Efforts have been made to remove the causal agent, but the situation is still not sufficient, and various attempts have been made to deal with it.

Here, patent documents relating to cleaning of the transport roll after the web is peeled from the support in the conventional solution casting method include the following.
JP 2002-292658 A JP 2006-256184 A JP 2002-86474 A JP 2005-225031 A JP 2001-62911 A JP 2001-139709 A JP 2001-341196 A JP 2003-89142 A

The conventional methods described in Patent Documents 1 to 4 make it difficult for a plasticizer or the like to adhere to a roll. However, if a solution casting film is formed over a long period of time, precipitation of the plasticizer and the like can be suppressed. However, there is a problem that some dirt remains on the surface of the roll near the peeling, and the quality of the optical film is deteriorated. Therefore, in order to clean a roll soiled with accumulated organic or inorganic substances, the film-forming line is temporarily stopped to wipe away the dirt on the roll, and the deposits have been removed. However, such a roll dirt removing operation has a problem that the working efficiency is poor and the productivity of the optical film is greatly reduced.

Further, the methods described in Patent Documents 5 to 8 relate to the melt casting film forming method, not the solution casting film forming method. However, the roll surface is attached by irradiating the roll with plasma or excimer UV. The kimono is to be removed.

However, once an additive such as a foreign substance or a plasticizer adheres to the roll of the web, it takes a very long time to decompose and remove it even when irradiated with plasma or excimer UV. For this reason, there is a problem that the productivity is also greatly reduced.

The object of the present invention is to solve the above-mentioned problems of the prior art and increase the production speed of an optical film such as a cellulose ester film. The optical film can reduce the occurrence of failure of the optical film due to foreign matter on the surface of the web transport roll, and can increase the productivity (increase the production amount) of high-quality optical films. It is in trying to provide a manufacturing method.

In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that the casting of a thermoplastic resin dope is cast from an endless support on which an endless transition of a thermoplastic resin dope is carried out by a solution casting film forming method. A method for producing an optical film comprising: evaporating a solvent on a body to form a web; then peeling the web from a support; transporting and drying the peeled web; and winding the resulting film. The amount of residual solvent of the web when peeling the web from the support is 60 to 160% by mass, and the surface of the web transport roll after peeling the web from the support is irradiated with plasma or excimer UV for high energy. A surface treatment is performed, and a surface treatment film is formed on the surface of the transport roll.

This plasma is preferably irradiated under normal pressure. This is because a normal modification of the manufacturing process is not necessary at normal pressure.

The invention according to claim 2 is the method for producing an optical film according to claim 1, wherein the plasma treatment or the excimer UV treatment is performed in the presence of at least the solvent vapor, and the surface treatment is performed. It is a process for forming a film.

A third aspect of the invention is a method for producing an optical film according to the first or second aspect of the invention, in which the plasma treatment or excimer UV treatment comprises the vapor of the solvent, and the plasma treatment or excimer. It is characterized in that the irradiation is performed in the presence of both gases used for UV treatment to form a surface treatment film.

The invention of claim 4 is the method for producing an optical film according to any one of claims 1 to 3, wherein the solvent is 1,3-dioxolane, tetrahydrofuran, methyl ethyl ketone. And at least one of acetone, methyl acetate and methylene chloride.

The invention of claim 5 is the method for producing an optical film according to any one of claims 1 to 4, wherein the distance between the web transport roll and the high energy wave irradiation device. Is characterized by being 0.5 to 20 mm.

The invention of claim 6 is an apparatus for producing an optical film, in which a dope of a thermoplastic resin is cast from a casting die onto an endless support that moves infinitely, and the solvent is evaporated on the support. After the web is formed, the web is peeled from the support, the peeled web is transported and dried, and the resulting film is wound up. The optical film manufacturing apparatus peels the web from the support. The residual solvent amount of the web during the process is 60 to 160% by mass, and the surface of the web transport roll after the web is peeled off from the support is irradiated with plasma to perform high energy surface treatment, or the same It is characterized by having an excimer UV irradiation device that irradiates the surface with excimer UV and performs high energy surface treatment.

The invention of the optical film according to claim 7 is characterized by being manufactured by the method of manufacturing an optical film according to any one of claims 1 to 5.

The invention of the polarizing plate according to claim 8 is characterized in that the optical film according to claim 7 is used as a protective film for a polarizing plate on at least one surface of both surfaces of the polarizing film. It is said.

The invention of the display device according to claim 9 is characterized by using the polarizing plate according to claim 8.

The invention of claim 1 is a method for producing an optical film by a solution casting film forming method, wherein the amount of residual solvent of the web when peeling the web from the support is 60 to 160% by mass, The surface of the web transport roll after peeling off the support is subjected to high-energy surface treatment by irradiating with plasma or excimer UV, and a solvent evaporated from the web is used as a material (that is, generated by a decomposition product of the solvent). A surface treatment film is formed on the surface of the transport roll. According to the first aspect of the invention, not only can the foreign matter adhered to the roll surface be removed, but also the formation of a surface treatment film on the roll surface can reduce adhesion of the film plasticizer and the like to the roll surface. Can do. In addition, it is possible to prevent condensation due to water containing a plasticizer or impurities, and even if the production speed of an optical film such as a cellulose ester film is increased, the adhesion of foreign matter on the surface of the web transport roll, and the optical film resulting therefrom It is possible to greatly reduce the occurrence of transfer failure and optical film pressing failure due to foreign matter on the surface of the web conveyance roll, and it is possible to increase the productivity (increase the production amount) of high-quality optical films. There is an effect.

The invention according to claim 2 is the method for producing an optical film according to claim 1, wherein the plasma treatment or the excimer UV treatment is performed in the presence of at least a solvent vapor, and the surface treatment film According to the second aspect of the invention, when the plasma or excimer UV is irradiated in the presence of solvent vapor, the peelability of the film is improved (the peel strength is reduced). did. Moreover, since the increase in carbon atoms was observed on the surface of the metal support after the treatment by XPS (X-ray photoelectron spectrometer) as compared with that before the treatment, the pure water contact angle using the solvent vapor as a raw material By forming a monolayer treatment film such as an amorphous hydrocarbon that reduces the adhesion, it is considered that the adhesion force of foreign matter or the like to the surface of the transport roll could be reduced. Also, as a secondary effect, the web with a high residual solvent amount is soft, so it has adhesiveness itself, and stress due to adhesive force is applied when it comes off in contact with the transport roll, so optical properties such as retardation There was a problem that the fluctuation of the increase was increased due to high-speed conveyance, but with this method, the adhesive force to the web conveyance roll was reduced, and the peeling force of the casting film was reduced. It is considered that the peeling stress applied to the film could be reduced even when the optical thin film was transported at high speed.

In addition, regarding the formation of the surface treatment film by the plasma apparatus and the excimer UV apparatus in the presence of such solvent vapor, the mechanism is not sufficiently elucidated at present, but the film is very thin of amorphous hydrocarbon. It is thought that is formed.

As for the possibility that the physical shape of the metal support surface has changed, the surface roughness Ra is scanned before and after irradiating plasma or excimer UV onto a plate with a super mirror polished surface such as SUS304 or SUS316. It is unlikely that the surface of the metal body is rough or, on the contrary, the metal body is smoothed and the peelability of the film has changed due to the fact that it has not changed by measurement with a scanning atomic force microscope (hereinafter referred to as AFM). It is considered a thing.

A third aspect of the invention is a method for producing an optical film according to the first or second aspect of the invention, wherein the plasma treatment or excimer UV treatment comprises solvent vapor, and plasma treatment or excimer UV. Irradiation in the presence of both of the gases used for the treatment is a treatment for forming a surface treatment film. According to the invention of claim 3, similarly, the peeling force of the casting film is reduced, As a result, even when the optical thin film is transported at a high speed, the peeling stress applied to the film can be reduced.

The invention of claim 4 is the process for producing an optical film according to any one of claims 1 to 3, wherein the solvent is 1,3-dioxolane, tetrahydrofuran, methyl ethyl ketone, It contains at least one of acetone, methyl acetate, and methylene chloride. According to the invention of claim 4, the surface treatment film can be effectively formed by plasma treatment or excimer UV treatment. The peeling force of the stretched film is reduced, so that the peeling stress applied to the film can be reduced even when the optical thin film is conveyed at high speed.

The invention of claim 5 is the method for producing an optical film according to any one of claims 1 to 4, wherein the distance between the web transport roll and the high energy wave irradiation device is According to the invention of claim 5, there is no risk that the web transport roll and the high energy wave irradiation device are in contact with each other and the surface of the web transport roll is damaged. Since the effect of modifying the surface of the transport roll is not weakened too much, it is possible to meet the demand for higher quality of the optical film and to achieve continuous and high productivity.

The invention of claim 6 is an apparatus for producing an optical film, in which a dope of a thermoplastic resin is cast from a casting die onto an endless support that moves infinitely, and the solvent is evaporated on the support. After the web is formed, the web is peeled from the support, the peeled web is transported and dried, and the resulting film is wound up. The optical film manufacturing apparatus peels the web from the support. The residual solvent amount of the web during the process is 60 to 160% by mass, and the surface of the web transport roll after the web is peeled off from the support is irradiated with plasma to perform high energy surface treatment, or the same An excimer UV irradiating device for irradiating the surface with excimer UV to perform high-energy surface treatment. According to the invention of claim 6, an optical film such as a cellulose ester film Even if the production speed is increased, the adhesion of foreign matter on the surface of the web transport roll after peeling, the transfer failure of the optical film due to this, and the occurrence of a pressing failure of the optical film due to foreign matter on the surface of the web transport roll As a result, it is possible to reduce the amount of the optical film, and it is possible to increase the productivity (increase the production amount) of the optical film with good quality.

Further, according to the present invention, in the continuous production of an optical film by the solution casting film forming method, the surface treatment film is formed on the surface of the web conveyance roll by plasma treatment or excimer UV treatment, thereby peeling from the web conveyance roll. The effect of improving the productivity of the optical film by increasing the production conditions of the optical film by enabling the film formation in the so-called high residual solvent amount region of the web while suppressing the haze of the optical film. Play.

Furthermore, according to the present invention, the surface of the web transport roll is subjected to plasma treatment or excimer UV treatment to form a surface treatment film, and the surface treatment film reduces foreign matter adhesion on the surface of the web transport roll, thereby providing an optical film. Reduces the occurrence of pressing failure, heats the roll surface by high energy irradiation with plasma or excimer UV irradiation, and raises the surface temperature, thereby preventing condensation due to plasticizer or water containing impurities, optical film The transfer failure can be reduced, thereby satisfying the demand for higher quality of the optical film and continuous and stable higher productivity.

The invention according to claim 7 is manufactured by the method for manufacturing an optical film according to any one of claims 1 to 5. According to the optical film of the seventh aspect, there is no transfer failure or pressing failure, and there is an effect that the optical film has excellent optical characteristics.

The invention of the polarizing plate according to claim 8 is characterized in that the optical film according to claim 7 is used as a protective film for a polarizing plate on at least one surface of both surfaces of the polarizing film. According to the polarizing plate of the eighth aspect of the invention, an optical film excellent in transparency and flatness is used as a polarizing plate protective film on at least one surface of the polarizing film. Therefore, when this polarizing plate is incorporated in a liquid crystal panel, the liquid crystal panel does not cause a decrease in contrast or uneven density, and has an effect of excellent visibility.

The invention of the display device according to claim 9 uses the polarizing plate including the optical film having the excellent optical characteristics according to claim 8, and therefore the claim 9. According to the display device of the present invention, there is an effect that the liquid crystal panel is excellent in visibility without causing a decrease in contrast or unevenness in density.

It is a flow sheet which shows embodiment of the apparatus which enforces the manufacturing method of the optical film of this invention. It is a flow sheet which shows the modification of the apparatus of FIG. It is explanatory drawing for demonstrating the principle of the plasma apparatus used in the manufacturing method of the optical film of this invention. It is explanatory drawing for demonstrating the principle of the excimer UV apparatus used in the manufacturing method of the optical film of this invention.

Explanation of symbols

1: Melting pot 2: Pump 3: Casting die 4: Depressurization chamber 5: Front and rear winding drum 6: Rotation drive drum (support)
7: Endless belt (support)
8: Web conveyance roll 9: Web conveyance roll 10: Web 11: Tenter 12: Roll conveyance drying device 13: Winder 14: Hot air (drying air)
18: Reaction gas supply pipe 19: Plasma irradiation device a: Electrode b: Electrode g: Reaction gas d: Gap from plasma spray slit to web conveyance roll surface e: Exhaust u: Excimer UV lamp of excimer UV device r: Reflection Plate p: Purge gas i: Air curtain / lamp device cooling air q: Quartz glass

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

The method for producing an optical film according to the present invention is obtained by casting a dope of a thermoplastic resin from a casting die onto an endless support that moves infinitely by a solution casting film forming method, evaporating a solvent on the support, After the web is formed, the web is peeled off from the support, the peeled web is transported and dried, and the resulting film is wound up. When the web is peeled off from the support The residual solvent amount of the web is 60 to 160% by mass, and the surface of the web transport roll after the web is peeled off from the support is subjected to high energy surface treatment by irradiating with plasma or excimer UV. A surface treatment film is formed on the surface. By forming a surface treatment film on the surface of the transport roll with the peeled web, adhesion of a plasticizer or the like to the roll surface is reduced, or a plasticizer is used. Or also it is intended to prevent condensed by water containing impurities.

Here, when the residual solvent amount of the web when peeling the web from the support is less than 60% by mass, a part of the web may be peeled off in the middle, and the residual solvent amount exceeds 160% by mass. In such a case, a peeling failure occurs and the web may be broken.

The method for producing an optical film of the present invention reduces contamination and condensation on the surface of the web conveyance roll by forming a surface treatment film on the surface of the web conveyance roll used for the production of the optical film by plasma treatment or excimer UV treatment. However, the distance between the energy wave irradiation device (plasma irradiation device or excimer UV irradiation device) and the surface of the web transport roll as the object to be cleaned is 0.5 to 20 mm, preferably 1.0. ~ 15 mm. If it is too close, there is a risk of damage to the surface of the transport roll due to contact, and if it is too far away, the effect of modifying the surface of the transport roll is weakened.

As a specific method of high energy surface treatment, what is called an excimer UV or plasma downstream or jet type is effective.

In the case of plasma, various gases can be used, but a mixed gas of nitrogen and a small amount of oxygen is preferable from the viewpoint of environment, exhaust aftertreatment, and running cost. The gas flow rate is desirably 20 to 5000 L / min per 1 m of the effective width of plasma irradiation. Furthermore, 40 to 1000 L / min is more preferable.

Also, under conditions where ozone is generated, such as plasma using excimer UV or oxygen gas, it is desirable to install a suction exhaust duct around the body.

The atmosphere for cleaning the surface of the web transport roll by irradiating with ultraviolet rays is preferably a clean oxygen atmosphere in which dust and the like are not suspended. An exhaust device is attached to the enclosure between the roll and the ultraviolet lamp, and fresh air is always supplied. It is more preferable to supply.

By irradiating the surface of the web transport roll where the film is transported during film formation with ultraviolet rays or plasma waves, a surface treatment film can be formed on the surface of the web transport roll to prevent adhesion and accumulation of dirt. Heating by high energy irradiation can prevent condensation of water and plasticizer containing impurities on the roll surface, and drastically reduce the number of times film formation is interrupted to clean dirt adhered to the web transfer roll surface. In addition, the productivity of the optical film can be improved.

In the irradiation of the present invention, the irradiation shape is preferably a long axis with respect to the roll width direction. That is, by taking the irradiation diameter long in the roll width direction, it is advantageous because the entire irradiation area can be gained by rotating the roll.

In the present invention, the organic deposit is mainly derived from a plasticizer and produces various organic compounds generated in the process. Furthermore, sublimates, oils and fats, dust, etc. contained in the air are also included.

In the present invention, the inorganic deposit is mainly derived from a stainless steel support, and produces various inorganic compounds generated in the process. In addition, sublimates and dust contained in the air are also included.

If necessary, an ultraviolet absorber, an antioxidant, an antistatic agent, a lubricant, a nucleating agent, a release agent, and the like are added to the thermoplastic resin used in the present invention as long as the object of the present invention is not impaired. Can do.

By producing an optical film by the solution casting film forming method, organic deposits accumulate on the surface of the web transport roll over time, causing the optical film to be pushed and broken, or water or plasticizer containing impurities on the roll surface. Condensation of the optical film occurs, resulting in a transfer failure of the optical film. By performing plasma treatment or excimer UV treatment on the surface of the web transport roll by the method of the present invention, a surface treatment film is formed on the surface of the web transport roll, and adhesion of dirt Accumulation can be prevented, and the surface of the web transport roll can be kept clean by heating the surface of the web transport roll by high energy irradiation to prevent condensation of water and plasticizers containing impurities.

Using the above-described production method of the present invention, a high-quality cellulose ester film free from pressing failure and transfer failure can be produced with high productivity.

According to the manufacturing method of the optical film of the present invention, even if the production rate of the optical film such as a cellulose ester film is increased, the adhesion of the foreign matter on the surface of the web transport roll, and the transfer failure of the optical film due to this, Occurrence of a pressing failure of the optical film due to foreign matter on the surface of the web conveying roll can be greatly reduced, and high-quality optical film with high quality (increase in production volume) can be achieved.

In continuous production of optical films by the solution casting method, the surface of the web transport roll is formed by plasma treatment or excimer UV treatment to increase the peelability of the surface of the web transport roll. The film can be formed in a so-called high residual solvent amount region of the web while suppressing the haze of the film, and the production conditions of the optical film are expanded, so that the productivity of the optical film is improved.

Furthermore, the surface of the web transport roll is subjected to plasma treatment or excimer UV treatment to form a surface treatment film, and the surface treatment film reduces adhesion of foreign matter on the surface of the web transport roll after peeling, thereby pressing the optical film. Reduces the occurrence of failure, heats the roll surface by high energy irradiation with plasma or excimer UV irradiation, raises the surface temperature, prevents condensation due to plasticizer or water containing impurities, transfer failure of optical film As a result, it is possible to meet the demand for high quality optical films and to achieve continuous and stable high productivity.

Furthermore, in the method for producing an optical film of the present invention, it is preferable to perform high energy surface treatment with a plasma apparatus or an excimer UV apparatus in the presence of a reaction gas used for the plasma apparatus or a purge gas used for the excimer UV apparatus.

According to the method for producing an optical film of the present invention, it is possible to eliminate a defect in peeling that is observed when a residual solvent in a web at the time of peeling is in a certain range, which is seen in a solution casting film forming method. Enables film formation in the residual solvent amount area, reduces the restrictions on film production conditions so far, greatly expands the selection range of film production conditions, and releases the film from the surface of the web transport roll (peelability) ) Is improved, and a very smooth peelability can be obtained in the entire residual peel zone.

FIG. 1 is a flow sheet showing a specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. Note that the implementation of the present invention is not limited to the process of the drawings shown below.

In the figure, first, in a dissolving pot (1), for example, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and an additive such as a plasticizer or an ultraviolet absorber is added to the resin solution. (Dope) is prepared.

Next, a support made of, for example, a rotationally driven stainless steel endless belt, in which the dope adjusted in the melting pot is fed to the casting die (3) by a conduit through, for example, a pressurized metering gear pump (2) and transferred infinitely. (7) The dope is cast from the casting die (3) to the upper casting position.

The dope casting by the casting die (3) includes a doctor blade method in which the film thickness of the cast web is adjusted with a blade, or a reverse roll coater method in which the web is adjusted with a reverse rotating roll. A method using a pressure die that can adjust the slit shape of the part and easily make the film thickness uniform is preferable. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

In addition, as the casting die (3), a pressure die that can adjust the slit shape of the die part and easily make the film thickness uniform is preferable. The casting die (3) is usually provided with a decompression chamber (4).

Here, the solid content concentration of the cellulose ester solution (dope) is preferably 15 to 30% by mass. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by mass, sufficient drying cannot be performed on the support (7), and a part of the dope film remains on the support (7) during peeling. This is not preferable because it leads to belt contamination. Moreover, when the solid content concentration exceeds 30%, the dope viscosity is increased, filter clogging is accelerated in the dope adjustment process, or pressure is increased during casting on the support (7), and it is not preferable to extrude. Absent.

In the illustrated film forming apparatus having a rotationally driven endless belt as the support (7), the belt support (7) is held by a pair of front and rear drums (5) and (5) and a plurality of intermediate rolls (not shown). Has been.

One or both of the drums (5) and (5) at both ends of the rotary drive endless belt support (7) are provided with a drive device for applying tension (not shown) to the belt support (7). Thus, the belt support (7) is used in a tensioned state.

The width of the metal support (7) is preferably 1700 to 2400 mm, the casting width of the cellulose ester solution is preferably 1600 to 2500 mm, and the width of the film after winding is preferably 1400 to 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

When an endless belt is used as the support (7), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and a mixed solvent having a temperature lower than the boiling point of the lowest boiling solvent. Further, the range of 5 ° C. to the boiling point of the solvent −5 ° C. is more preferable. At this time, it is necessary to control the ambient atmospheric humidity above the dew point. The peripheral speed of the support (7) is preferably 40 to 200 m / min.

As described above, the dope cast on the surface of the support (7) also increases the strength of the gel film (film strength) by promoting the drying until peeling.

In the system using an endless belt as the metal support (7), the film strength on which the web (10) can be peeled from the metal support (7) by the peeling roll (8) on the metal support (7). Therefore, the amount of residual solvent in the web (10) is preferably dried to 60 to 160% by mass, more preferably 80 to 130% by mass. The web temperature when peeling the web (10) from the metal support (7) is preferably 0 to 30 ° C. Further, immediately after the web (10) is peeled off from the metal support (7), the temperature once drops rapidly due to the solvent evaporation from the metal support (7) contact surface side, and water vapor or solvent vapor in the atmosphere. The web temperature at the time of peeling is more preferably 5 to 30 ° C. because volatile components such as these are easily condensed.

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

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

The web (10) formed by the dope cast on the support (7) is heated on the support (7), and the solvent is evaporated until the web can be peeled from the support (7).

To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the support (7) with a liquid, a method of transferring heat from the front and back by radiant heat, and the like. Can be used.

FIG. 1 shows a plasma irradiation apparatus (19) for performing high-energy surface treatment by irradiating plasma on the surface of the web transport rolls (8) and (9), and a reaction gas supply pipe for supplying a reaction gas thereto. (18) is shown.

After the web (10) is dried and solidified on the support (7) until it has a peelable film strength, the web (10) is peeled off from the support (7), and then a tenter (11 ).

FIG. 2 is a flow sheet showing another specific example of an apparatus for carrying out the method for producing an optical film of the present invention by a solution casting film forming method. As a support, for example, stainless steel whose surface is subjected to hard chrome plating treatment. The case where the steel rotational drive drum (6) is used is illustrated.

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

The apparatus for producing an optical film of the present invention is cast from a casting die (3) on an endless support composed of a rotating endless belt (7) or a rotating drum (6) that allows infinite transition of a thermoplastic resin dope, After evaporating the solvent on the supports (6) and (7) to form the web (10), the web (10) is peeled from the support (7), and the peeled web (10) is removed with a transport roll. The residual solvent of the web when the web (10) is peeled off from the support (6) (7), which is constituted by a solution casting film forming apparatus for transporting and further drying the web (10) to produce an optical film. High energy surface treatment is performed by irradiating the surface of the web transport roll (8) (9) after the web (10) is peeled from the support (6) (7) with plasma. Applying plasma irradiation device, or the same surface By irradiating excimer UV those comprising an excimer UV irradiation apparatus for applying a high energy surface treatment.

In the plasma device, a high frequency power is applied between the electrodes facing each other so as to sandwich the substrate to be processed, and the supply gas is converted into plasma, and the reaction gas is converted into plasma through the electrodes to which the high frequency voltage is applied. In the method for producing an optical film of the present invention, the latter downstream method is preferably used for the high energy surface treatment of the cast film surface.

FIG. 3 is an explanatory diagram for explaining the principle of the plasma apparatus. In the figure, (a) and (b) are the counter electrodes of the reactor, (g) is the reactive gas, (d) is the gap from the plasma spray slit to the surface of the web transfer roll (8) (9), (i) Is the air curtain wind, and (e) is the exhaust.

The plasma apparatus introduces a reactive gas (g) between the counter electrodes (a) and (b) to which a high-frequency voltage is applied, passes it into plasma, and forms plasma on the surface of the web transport rolls (8) and (9). A surface treatment layer is formed on the surface of the web transport rolls (8) and (9) by injecting and supplying a chemical gas and performing high energy treatment.

Next, an excimer UV apparatus that can be used in the method for producing an optical film of the present invention will be described.

FIG. 4 is an explanatory diagram for explaining the principle of the excimer UV apparatus. In the figure, (u) is an excimer UV lamp, (r) is a reflector, (p) is a purge gas, (i) is an air curtain / lamp device cooling air, (d) is a web transport from the excimer UV lamp (u). The gap to the roll (8) (9) surface, (e) is the exhaust.

In this embodiment, using the excimer UV lamp (u) shown in FIG. 4, the surface of the web transport roll (8) (9) is mainly irradiated with ultraviolet rays having a wavelength of 172 nm with a light quantity of 1 to 3,000 mJ / cm ^2. In addition, irradiation is performed.

Under such ultraviolet irradiation, oxygen contained in the purge gas (p) generates active oxygen and ozone and contributes to the modification of the surface of the web transport rolls (8) (9). Further, a raw material gas for generating a surface treatment film such as an organic solvent vapor such as methylene chloride or alcohol, or a monomer gas such as acetylene may be mixed with the purge gas (p) and introduced. When these raw material gases are not mixed with the purge gas (p), these raw material gases may be entrained on the surface of the casting film and sent under the excimer UV device to perform reaction and surface treatment layer formation.

Measures to maintain cleanliness are an issue when bringing these high-energy surface treatment devices into film-forming lines for optical applications. In particular, it is important to take measures for maintaining the cleanliness in a plasma apparatus having a structure in which dust generated is discharged into the line.

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

As the film material, various resins can be used, 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.

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

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

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

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

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

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

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

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

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

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

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

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

The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like, in particular, aliphatic carboxylic acids having at least one selected from those having 4 to 12 carbon atoms 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, polyesters having a weight average molecular weight of 500 to 10,000 have good compatibility with cellulose esters, and neither evaporation nor volatilization occurs during film formation.

Polyester polycondensation is performed by conventional methods. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or 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.

In the present invention, examples of the additive for reducing the thickness direction retardation (Rt) include a polymer obtained by polymerizing an ethylenically unsaturated monomer and an acrylic polymer.

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 compound having a single thiol group and a secondary hydroxyl group as described in the publication, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferred.

Although the monomer as a monomer unit which comprises the polymer as an additive which reduces useful thickness direction retardation (Rt) is mentioned below, this invention 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, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or methacrylic acid alkyl ester having no monomer unit having an aromatic ring or a cyclohexyl group.

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

The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by 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, the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is preferably contained in the acrylic polymer in an amount of 2 to 20% by 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 to 20% by mass, more preferably 2 to 10% by mass.

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

In the present invention, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate) is possible. A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization stopper having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a compound having one thiol group and a secondary hydroxyl group as described in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a polymerization catalyst using the compound in combination with an organometallic compound, 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 to 25% by mass relative 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 according to the present invention, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and has a main effect on dissolution. Organic) solvent or main (organic) solvent.

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

The dope preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. 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 ratio of methylene chloride: ethyl alcohol of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

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

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

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

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

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

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

Formula (3) 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 of the present invention is not particularly limited, and known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

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

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

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

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

The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 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, but in the present invention, it is preferable that substantially no phosphate ester plasticizer is contained.

Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by 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 plasticizer used is preferably 1 to 20% by mass. It is more preferably 6 to 16% by mass, particularly preferably 8 to 13% by mass. 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.

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

Examples of inorganic compound fine particles include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide, and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, 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 to 5.0 μm. More preferably, it is 0.1 to 1.0 μm.

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

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

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

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

The above fine particles are used by adding 0.04 to 0.5 mass% with respect to the cellulose ester. Preferably, 0.05 to 0.3% by mass, more preferably 0.05 to 0.25% by mass is added. 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. The high-pressure dispersion apparatus used in the present invention is an apparatus that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube.

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

Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name, Microfluidizer) manufactured by Microfluidics Corporation, or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing devices such as Izumi Food Machinery. Examples thereof include a homogenizer.

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

Here, the content ratio of the lower alcohol is preferably 50 to 100% by mass, and more preferably 75 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 at the time of forming a cellulose ester film.

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

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

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

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

Specific examples of UV absorbers useful in the present invention include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert- Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) ) -5-chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2- Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy) -3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (straight and side chain dodecyl) -4-methylphenol, Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy- Examples include, but are not limited to, a mixture of 5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

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

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

In the present invention, the blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 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 to 1000 ppm by mass relative to the cellulose derivative.

In addition, in the apparatus which implements the manufacturing method of the optical film of the present invention shown in FIG. 1 and FIG. 2, as for the film for the liquid crystal display device, the stretching step is a clip or the like on both side edges of the web (or film) (10). A tenter method in which the film is fixed and stretched is preferable in order to improve the flatness and dimensional stability of the film.

The residual solvent amount of the web (film) (10) immediately before entering the tenter (11) in the stretching step is preferably 10 to 35% by mass.

The stretch ratio of the web in the tenter (11) in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%. The temperature of the hot air blown from the hot air blowing slit port in the tenter (11) is 100 to 200 ° C., preferably 110 to 190 ° C., more preferably 115 to 185 ° C.

It is preferable to provide a drying device (12) after the tenter (11) in the stretching step. In the drying device (12), the web (10) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web (10) is dried in the meantime. The film transport tension in the drying apparatus (10) is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, etc. The film transport tension during drying is 30 to 300 N. / M width, and 40 to 270 N / m width is more preferable.

The means for drying the web (film) (10) is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the drying air (14) blown from the hot air inlet at the front portion of the bottom of the drying device (12), and is dried on the ceiling of the drying device (12). It is dried by exhaust air being discharged from the outlet of the rear portion. The temperature of the drying air (14) is preferably 40 to 160 ° C., more preferably 50 to 160 ° C. in order to improve the flatness and dimensional stability.

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

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

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

The film after drying is wound up by a winding device (13) to obtain the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film to be dried to 0.5% by mass or less, preferably 0.1% by mass or less.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Ro = (nx−ny) × d
Rt = {(nx + ny) / 2−nz} × d
In the formula, Ro is the retardation value in the film plane, Rt is the retardation value in the film thickness direction, nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is the film. (Refractive index is measured at a wavelength of 590 nm), d represents the thickness (nm) of the film.

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

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

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

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

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

The polarizing plate may be prepared by laminating the optical film produced by the method of the present invention as a retardation film, and the optical film produced by the method of the present invention is a retardation film and a protective film. Alternatively, it may be produced by directly bonding to a polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. The water-soluble polymer adhesive is preferably a completely saponified polyvinyl alcohol aqueous solution. Furthermore, a long polarizing plate can be obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of the present invention. . A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). Or the like can be easily attached).

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

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

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

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

The liquid crystal display device includes a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and two polarizing plates each including a transparent protective layer disposed on both sides thereof. It is what you have.

By using a protective film for a polarizing plate comprising an optical film produced by the method of the present invention, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

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

Examples of the present invention will be described below, but the present invention is not limited thereto.
Example 1
(Preparation of dope)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.
(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 4 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxyphenyl) -2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Aerosil R972V 0.1 part by weight The web after the dope was cast and peeled from the support The rolls to be transported were hard chrome plated on the surface and polished to a super mirror surface.
(Production of cellulose triacetate film)
Using the above dope, a cellulose triacetate film was produced as follows.

Film formation was performed using the manufacturing apparatus shown in FIG. Referring to the figure, the filtered dope is uniformly flown from a casting die (3) made of a coat hanger die on a support (7) made of SUS316 endless belt at a temperature of 20 ° C. at a dope temperature of 35 ° C. The cast film (web) (10) was formed. The drying air temperature on the support (7) was kept constant at 30 ° C., and the drying speed of the web (10) on the support (7) was changed to 60 seconds by changing the conveying speed of the support (7). Until 120 seconds, the amount of residual solvent of the web (10) at the time of peeling was changed.

After peeling the web (10) from the support (7), it is dried while being transported by transport rolls (8) and (9) in an atmosphere at a temperature of 90 ° C. When the residual solvent amount is 10% by the tenter (11) The web (10) was stretched 1.06 times in the width direction in an atmosphere at a temperature of 100 ° C., then the width was released, and drying was terminated in the drying zone (12) at a temperature of 125 ° C. while being conveyed by rolls. Both ends of the film were knurled with a width of 10 mm and a height of 8 μm to prepare a cellulose triacetate film having a thickness of 40 μm. The film width was 1300 mm, and the winding length was 1500 m.

And in this Example, by carrying out high energy surface treatment to the web conveyance roll (8) (9) after peeling with a plasma apparatus (19) as follows, the web conveyance roll (8) (9) A surface treatment film was formed on the surface.
(Plasma treatment)
During film formation, plasma irradiation treatment was performed under the condition that the gap (d) from the plasma injection slit of the plasma device (19) to the surface of the web transport rolls (8) and (9) was 2 mm.

The amount of reaction gas used was 1 m ³ per 1 m of irradiation width. The composition of the mixed gas (reactive gas) used for the plasma treatment is described below. The atmospheric pressure was 1.0 atm.

Nitrogen 99.0% by volume
Oxygen 1.0% by volume
Mixed gas flow rate 2m ³ / min
The solvent gas concentration around the plasma device was 4000 ppm of methylene chloride and 2000 ppm of ethanol in the vicinity of the surface of the peeling roll (8) before entering the plasma device.

In this example, the residual solvent amount of the web (10) when the web (10) was peeled from the support (7) was set to 68% by mass.

The cellulose triacetate film was wound on a winder with a final residual solvent amount of 0.2% by mass.
Example 2
Although it carries out similarly to the case of the said Example 1, the point different from the case of the said Example 1 differs in the amount of residual solvents of the web (10) at the time of peeling a web (10) from a support body (7) being 140 masses. %.
Examples 3 and 4
This is carried out in the same manner as in the first and second embodiments. However, the difference from the first and second embodiments is that an excimer UV apparatus shown in FIG. 4 is used instead of the plasma apparatus shown in FIG. It is in the point which performed UV processing.

That is, the following excimer UV treatment was performed on the surfaces of the web transport rolls (8) and (9).
(Excimer UV treatment)
An apparatus in which four Xe ₂ wavelength 172 nm excimer UV lamps having an irradiance of 40 mW / cm ² in quartz glass (q) having a length of about 300 mm in the conveyance direction of the support is placed from the quartz glass surface of the lamp. The gap (d) to the surface of the web transport rolls (8) and (9) was 1 mm, and the surface of the web transport rolls (8) and (9) was irradiated with excimer UV light.

In addition, the solvent vapor | steam density | concentration of the circumference | surroundings of an excimer UV apparatus was methylene chloride 4000ppm and ethanol 2000ppm in the vicinity of the surface of the peeling roll (8) before entering an excimer UV apparatus.
Comparative Examples 1 to 4
This is carried out in the same manner as in Examples 1 to 4, but the difference from Examples 1 to 4 is that the web (10) is peeled off from the support (7) on the surface of the web transport roll. (10) Residual solvent amount.

In Examples 1 to 4 and Comparative Examples 1 to 4 described above, a cellulose triacetate film was continuously formed for 2 weeks under the above-mentioned conditions, and a film prepared 1 day after the start of film formation and 2 weeks later In order to evaluate the difference between the two films, the film was pressed and observed for failure / foreign matter / dirt and evaluated. Moreover, the surface state of the web conveyance rolls (8) and (9) after 1 day of film formation and after 2 weeks of film formation was visually observed and evaluated. The obtained evaluation results are shown in Table 1 below.
(Observation and evaluation of pressed failure, foreign matter and dirt)
The cellulose triacetate film samples prepared in Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention were cut out to a length of 1 m in the longitudinal direction with a full width, and this film sample was transmitted with light on the Schaukasten with a loupe. The presence and size of the pressed failure / foreign matter / dirt was observed and evaluated according to the following criteria.

AA: Pushed failure / foreign matter / dirt was almost free. A: Pushing failure / foreign matter / dirt with a size of 50 μm or more was not.
0 to 10 specimens were observed with a size of less than 50 μm. B: There was no pressed failure, foreign matter, or dirt with a size of 50 μm or more.
11 to 30 specimens with a size of less than 50 μm were observed. C: 1 to 10 pressed faults / foreign particles / stains with a size of 50 μm or more were observed, and 31 to 50 specimens with a diameter of 50 μm or less were observed. D: 50 μm 11-30 pressed faults / foreign matters / stains with the above size were observed, and 51 or more with 50 μm or less were observed (visual observation and evaluation of the surface state of the web transport roll)
A: The surface of the web transport roll is clean. B: White haze slightly enters the surface of the web transport roll. C: The entire surface of the web transport roll becomes white. D: The surface of the web transport roll is greenish blue due to rust caused by corrosion. Next, in Examples 1 to 4 and Comparative Examples 1 to 4 described above, a cellulose triacetate film produced 1 day after the start of film formation and a cellulose triacetate film produced 2 weeks later were used as follows. Each polarizing plate was produced, and the deterioration level of the film was judged from the number of bright spots of each polarizing plate. The obtained evaluation results are shown in Table 1 below.
(Preparation of polarizing plate)
The cellulose triacetate films obtained in Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention were immersed in a 2 mol / l sodium hydroxide aqueous solution at a temperature of 60 ° C. for 2 minutes, washed with water, and then at a temperature of 100 ° C. Was dried for 10 minutes to prepare a protective film for a polarizing plate subjected to alkali saponification treatment.

On the other hand, a 120 μm thick polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 4 times at a temperature of 50 ° C. to produce a polarizing film. .

Next, the polarizing plate protective films were bonded to both sides of the polarizing film by using a completely saponified polyvinyl alcohol 5% aqueous solution as an adhesive, respectively, to prepare various polarizing plates.
(Evaluation of number of shine spots on polarizing plate)
Next, these polarizing plate samples were cut out to a size of 25 cm × 25 cm, and five samples were prepared for each sample, and two polarizing plates for shining spot observation (not shown) having a size of 30 cm × 30 cm were placed in a crossed Nicols state. The polarizing plate sample is inserted between the polarizing plates for shining spot observation, and the number of shining spots appearing on the dark surface due to foreign matter etc. of the polarizing plate sample is observed. Based on the value of The obtained results are shown in Table 1 below.

A: No shine spots were observed B: 1-5 small shine spots were observed C: 6-30 small shine spots were observed D: 31-50 shine spots were observed E: Shine spots More than 51 were observed

As is clear from the results in Table 1 above, according to Examples 1 to 4 of the present invention, the surface of the web transport rolls (8) and (9) was irradiated with the plasma wave or the excimer UV wave that is the feature of the present invention. By forming the respective surface treatment films, there was little adhesion of dirt to the surface of the web transport rolls (8) and (9), and the surfaces of the web transport rolls (8) and (9) could be kept clean.

And according to Examples 1 to 4 of the present invention, it is possible to stably produce a high-quality cellulose triacetate film having a good surface smoothness with little failure, foreign matter, and dirt pushed by the cellulose triacetate film over a long period of time. did it. In addition, according to the cellulose triacetate films of Examples 1 to 4, the number of bright spots on the polarizing plate was very small.

Further, in Examples 1 to 4 according to the present invention, the surface of the web transport rolls (8) and (9) is subjected to high energy surface treatment, so that the surface of the web transport rolls (8) and (9) is less likely to be whitish. Thus, the effect of slowing the soiling speed of the web transport rolls (8) and (9) was also obtained. As a result, the cleaning cycle of the surfaces of the web transport rolls (8) and (9) can be lengthened, and the film productivity can be improved.

On the other hand, according to Comparative Examples 2 and 4, since the amount of residual solvent is too high, it is not possible to prevent the adhesion of dirt to the web transport roll, and it is pushed by a large number of cellulose triacetate films. Foreign matter and dirt were observed, and the number of bright spots on the polarizing plate was observed, which could not be used as an optical film such as a protective film for a polarizing plate. Furthermore, according to Comparative Examples 2 and 4, the cleaning of the surface of the web transport roll was required after one week. On the other hand, in Comparative Examples 1 and 3, good results were obtained with respect to the pressed failure / foreign matter / dirt. However, since the residual solvent amount was too low, a part of the web was removed from the support (7) on the way. Troubles that peel off frequently occur, and not only the web transportability is very inferior, but also the web breaks and the productivity is sometimes lowered.

Claims

A thermoplastic resin dope is cast from a casting die onto an endless support that infinitely transfers a thermoplastic resin dope by a solution casting film forming method, and a solvent is evaporated on the support to form a web. Is a method for producing an optical film, in which the peeled web is transported and dried, and the resulting film is wound up, wherein the residual solvent amount of the web when the web is peeled from the support is 60 to 160. The surface of the web transport roll after the web is peeled off from the support is subjected to high energy surface treatment by irradiating with plasma or excimer UV, and a surface treatment film is formed on the surface of the transport roll. A method for producing an optical film, comprising:
The method for producing an optical film according to claim 1, wherein the plasma treatment or excimer UV treatment is a treatment for forming a surface treatment film by irradiating at least in the presence of the vapor of the solvent.
The plasma treatment or excimer UV treatment is a treatment for forming a surface treatment film on the surface of the transport roll by irradiation in the presence of both the vapor of the solvent and a gas used for the plasma treatment or excimer UV treatment. The method for producing an optical film according to claim 1 or claim 2.
The solvent according to any one of claims 1 to 3, wherein the solvent includes at least one of 1,3-dioxolane, tetrahydrofuran, methyl ethyl ketone, acetone, methyl acetate, and methylene chloride. The manufacturing method of the optical film of description.
The optical film production according to any one of claims 1 to 4, wherein a distance between the web transport roll and the high energy wave irradiation device is 0.5 to 20 mm. Method.
Casting the dope of the thermoplastic resin from the casting die onto an endless support that moves indefinitely, evaporating the solvent on the support to form a web, then peeling the web from the support, An apparatus for producing an optical film, which transports and dries a web and winds up the obtained film, wherein the amount of residual solvent of the web when peeling the web from the support is 60 to 160% by mass, A plasma irradiation apparatus for irradiating plasma on the surface of the web conveyance roll after peeling from the support to perform high energy surface treatment, or an excimer UV irradiation apparatus for irradiating the surface with excimer UV to perform high energy surface treatment. An apparatus for producing an optical film, comprising:
An optical film manufactured by the method for manufacturing an optical film according to any one of claims 1 to 5.
A polarizing plate comprising the optical film according to claim 7 as a protective film for a polarizing plate, on at least one of both surfaces of the polarizing film.
A display device using the polarizing plate according to claim 8.