JP2011115969A - Optical film manufacturing method, optical film, polarizing plate, and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film excellent in planar properties and little in orientation angle deviation, which improves the adhesion between a support and a cast film and suppresses air incorporation in a casting process, and to provide the optical film produced by the method, a polarizing plate using the optical film, and a display. <P>SOLUTION: In the casting process, before a resin solution is cast, activation treatment is applied on the surface of a support to make the surface energy of the surface of the support in contact with both ends in the width direction of the cast film, higher than the surface energy of the surface of the support in contact with the middle part in the width direction of the cast film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical film manufacturing method, an optical film, a polarizing plate, and a display device.

  In recent years, liquid crystal display devices have come to be used in televisions and large monitors due to improvements in image quality and high definition technology. In particular, these liquid crystal display devices are costly due to their large size and efficient production. Due to the demand for down, etc., the optical film is required to be wider, thinner and faster.

  As a method for producing an optical film, a solution containing a resin (hereinafter also referred to as a dope) is cast on a support from a casting die to form a casting film. A solution casting film forming method is used in which after the solvent is dried to some extent, the cast film is peeled off from the support, dried, and then wound up to produce an optical film.

  However, as the production speed of optical films is increased, the film thickness is reduced, and the width is increased, air (bubbles) is mixed between the support and the cast film when the cast film is formed on the support. In addition, the mixed portion causes poor planarity and film thickness on the film surface. Further, by reducing the pressure reduction of the pressure reducing device as the speed increases, the outside atmosphere of the pressure reducing device is sucked together with the accompanying air, and fluttering of the end portion is generated when the casting film is cast from the support. This fluttering causes uneven support landing points in the width direction at the time of casting, and the length of the casting ribbon is different at the width, so that the orientation angle deviation of the film becomes large and the optical performance deteriorates. It has become.

  With respect to such a problem, in Patent Document 1, electrostatic adhesion is applied between the dope cast from the casting die and the support to increase the adhesion between the casting film and the support, and air mixing is prevented. Methods for preventing it have been proposed.

  Further, Patent Document 2 proposes a method for preventing air from being mixed by providing a decompression chamber on the back surface of the casting die (upstream in the conveyance direction of the support) so that the casting film is in close contact with the support. Yes. However, in the method of providing the decompression chamber of Patent Document 2, the ears (both ends in the width direction) of the casting film flutter due to the air flow toward the decompression chamber, causing a conveyance failure in the subsequent process, and the conveyance direction. Thickness unevenness occurred. As a countermeasure against fluttering at the ear when a decompression chamber is provided, in Patent Document 3, a solvent is dropped on the ear of the casting film immediately after flowing down from the casting die to make the ear hard to shake. A method for preventing fluttering has been proposed.

Japanese Patent No. 4268286 JP 2002-337174 A JP 2003-181857 A

  However, in the method of Patent Document 1, it is necessary to reduce the oxygen concentration around the casting die so that the vaporized solvent does not explode due to electrostatic application. There is a problem that it takes time and work efficiency is lowered. Further, according to the method of Patent Document 3, as the film is made thinner and the production speed is increased in recent years, the effect of suppressing the fluttering is reduced, and the amount of the liquid dropped onto the ear part has to be increased. When the amount of the dropped liquid is increased, drying of the ear portion on the support becomes insufficient, and there is a problem that a peeling residue occurs at the time of peeling from the support, causing a film thickness defect and a foreign matter failure.

  Therefore, in view of the above-mentioned problems, the object of the present invention is that there is no risk of explosion when forming a casting film on the support, and by suppressing the flutter of the ear due to decompression, the support and A method for producing an optical film that improves adhesion with a casting film, suppresses air mixing, has excellent flatness, and has a small orientation angle deviation, an optical film produced by the production method, and the optical film. It is to provide a polarizing plate and a display device.

  The problems of the present invention can be solved by the following means.

1. A casting step of casting a resin solution on the surface of the support to form a casting film;
In the method for producing an optical film having a step of peeling the cast film from the support,
Before casting the resin solution, the surface energy of the surface of the support that is in contact with both ends in the width direction of the casting film is the surface energy of the surface of the support that is in contact with the center in the width direction of the casting film. A method for producing an optical film, comprising subjecting the surface of the support to an activation treatment so as to be higher than that.

  2. 2. The method for producing an optical film as described in 1 above, wherein the activation treatment is performed by atmospheric pressure plasma irradiation or excimer UV irradiation.

3. After performing the activation treatment,
The surface energy of the surface of the support in contact with both widthwise ends of the cast film is γse,
The difference Δγ (= γse−γsc) is in the range of 0.1 to 60 mN / m, where γsc is the surface energy of the surface of the support that is in contact with the widthwise center of the cast film. The method for producing an optical film as described in 1 or 2 above.

  4). Respective widths from both ends in the width direction of the casting film in contact with the surface of the support having a surface energy higher than the surface energy of the surface of the support in contact with the center in the width direction of the casting film, 4. The method for producing an optical film as described in any one of 1 to 3, wherein the width of the cast film is in a range of 0.05 Wr to 0.25 Wr, where Wr is Wr.

  5. 5. The method for producing an optical film according to any one of 1 to 4, wherein the support is one of an endless belt, a drum, and a roll.

  6). 6. An optical film produced by the method for producing an optical film according to any one of 1 to 5 above.

  7). A polarizing plate having the optical film according to 6 on at least one surface.

  8). 8. A display device using the polarizing plate described in 7 above.

  According to the present invention, in the method for producing an optical film by the solution casting film forming method, before casting the resin solution on the support, the surface energy of the surface of the support contacting the both ends in the width direction of the casting film is obtained. However, by applying an activation treatment to the surface of the support so that it is higher than the surface energy of the surface of the support in contact with the center in the width direction of the casting film, it is possible to prevent air from being mixed in the casting process. Can do. As a result, film edge fluttering during casting of the film from the support is also suppressed, so that the orientation angle deviation of the film can be reduced, and the production of an optical film having optical properties with excellent flatness A method, an optical film, a polarizing plate, and a display device can be provided.

It is a block diagram which shows 1st Embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method in this invention. It is a top view for demonstrating the area | region where the activation process area | region of the surface of a metal support body and the both ends of a casting film overlap. It is a block diagram which shows 2nd Embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method in this invention. It is explanatory drawing for demonstrating the principle of the atmospheric pressure plasma apparatus used in the manufacturing method of the optical film of this Embodiment. It is explanatory drawing for demonstrating the principle of the excimer UV apparatus used in the manufacturing method of the optical film of this Embodiment.

  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 embodiment is a method for producing an optical film by a solution casting film forming method, in which a resin solution (dope) is cast on a support to form a casting film (web). And a step of separating the solvent from the support after evaporating a part of the solvent, and before casting the resin solution, the surface energy of the support in contact with both ends in the width direction of the cast film An activation treatment is applied to the surface of the support so that the surface energy is higher than the surface energy of the support in contact with the central portion in the width direction of the film, and the resin solution is cast onto the surface of the support subjected to the activation treatment. To do.

  According to the method for producing an optical film according to the present embodiment, before casting the resin solution, the support is subjected to an activation treatment for increasing the surface energy of the surface of the support in contact with both ends in the width direction of the cast film. By applying to the surface, it was possible to prevent air from being mixed into the web during casting, which had previously reduced film productivity, and to suppress flutter during casting.

  Moreover, by suppressing fluttering during casting, the width of the casting ribbon became uniform, and the orientation angle deviation of the film could be reduced.

  This is because the dope is cast on the support after performing an activation treatment to increase the surface energy of the surface of the support that is in contact with both ends in the width direction of the casting film. This is considered to be because the adhesion (wet contact) between the substrate and the support surface was further improved. In this case, activation is performed so that the surface energy of the surface of the support in contact with both ends of the casting film in the width direction and the surface energy of the support in contact with the center in the width direction of the casting film have the same surface energy. Then, the length of the casting ribbon is shortened, but the difference in the length of the casting ribbon between the center portion and the end portion caused by the fluttering due to the inflow air at the end of the decompression chamber does not change, and the orientation angle deviation is not eliminated. .

  As the activation treatment for increasing the surface energy of the surface of the support that is in contact with both ends in the width direction of the cast film, it is preferable to perform treatment by atmospheric pressure plasma irradiation or excimer UV irradiation. By performing such a treatment, it is preferable that the surface energy of the surface of the support in contact with both ends in the width direction of the cast film can be appropriately increased.

  In addition, the surface energy of the surface of the support that is in contact with both ends in the width direction of the casting film after the activation treatment is γse, and the surface energy of the surface of the support that is in contact with the center in the width direction of the casting film Is preferably γsc, the difference Δγ (= γse−γsc) is preferably in the range of 0.1 to 60 mN / m. By making such a range, the adhesion of the both ends of the support is improved, the width of the casting ribbon is made uniform, and the optically superior orientation angle deviation is smaller even under high speed and wide production. A film can be produced.

  Further, when the width of the cast film obtained by casting the resin solution on the surface of the support is Wr, the support having a surface energy higher than the surface energy of the support in contact with the center in the width direction of the cast film. The width from both ends in the width direction of the cast film in contact with the surface is preferably in the range of 0.05 Wr to 0.25 Wr, respectively. By setting it as such a range, while improving the liquid-contact property in the both ends of a support body, peeling from a support body can be performed more stably.

  The surface energy of the support can be calculated by measuring the contact angle with water, nitromethane, and methylene iodide, and using these values, the Young Forks equation can be used. Specifically, it can be measured using a contact angle meter manufactured by Kyowa Interface Science Co., Ltd.

  FIG. 1 is a configuration diagram showing a first embodiment of an optical film manufacturing apparatus 100 for performing an optical film manufacturing method by a solution casting film forming method in the present invention. In the first embodiment, a case where an endless belt is used as the metal support is illustrated. Note that the present embodiment is not limited to the configuration of the drawings shown below.

  In FIG. 1, first, in a dope tank 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 thereto to prepare a dope. .

  Next, the dope adjusted in the dope tank 1 is fed to the casting die 3 through a liquid feeding pump 2 by a conduit, and flows to a casting position on a metal support 7 made of, for example, a rotationally driven endless belt. The dope 1 a is cast from the rolling die 3.

  For casting the dope 1a with the casting die 3, the doctor blade method in which the film thickness of the cast film (also referred to as web) 1b is adjusted with a blade, or the reverse roll coater with a reverse rotating roll. However, it is preferable to use a pressure die that can adjust the slit shape of the die portion and easily make the film thickness uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  On the upstream side of the casting die 3 in the support moving direction, an activation processing apparatus 200 for performing an activation treatment for increasing the surface energy is disposed on the surfaces of the both ends in the width direction of the surface of the metal support 7. .

  By the activation treatment apparatus 200, the surface energy of the surface of the metal support 7 in contact with the width direction both ends of the casting film 1b is more than the surface energy of the surface of the metal support 7 in contact with the width direction center of the casting film 1b. The surface of the metal support 7 is subjected to an activation treatment so as to be higher.

  FIG. 2 illustrates an activation processing region, which is a region where the surface energy of the surface of the metal support 7 is increased, and a region where both ends of the casting film 1b overlap. It is the top view which looked at the circumference of casting die 3 from the upper part. An activation region having a width Wk is formed on the surface of both ends in the width direction of the metal support 7 by the activation processing apparatus 200, and then a casting film having a casting width Wr is formed by the casting die 3. At this time, the width of Wrk overlaps with the activation region Wk from both ends S of the casting film Wr and from S to the center of the casting film.

  The activated region Wk may be processed so as to show a uniform surface energy value, or may be processed so as to have a non-uniform value, and a metal support that is in contact with both ends S in the width direction of the casting film 1b. The surface of the metal support 7 may be activated so that the surface energy of the surface of the metal support 7 becomes higher than the surface energy of the surface of the metal support 7 in contact with the widthwise central portion T of the casting film 1b. In the present embodiment, the vicinity of both ends of the support is activated by the activation processing apparatus. However, the vicinity of the center may be activated by the activation processing apparatus, and both ends S in the width direction of the casting film 1b. The surface energy of the surface of the metal support 7 in contact with the surface of the metal support 7 may be higher than the surface energy of the surface of the metal support 7 in contact with the center portion T in the width direction of the casting film 1b.

  Further, a decompression chamber may be provided on the upstream side of the casting die 3 so that the casting film is in close contact with the support.

  Here, the solid content concentration of the dope is preferably 15 to 30% by mass. If the solid content concentration of the dope is less than 15% by mass, sufficient drying cannot be performed on the metal support 7, and a part of the web may remain on the metal support 7 at the time of peeling, leading to belt contamination. Therefore, it is not preferable. If the solid content concentration of the dope exceeds 30%, the dope viscosity increases, filter clogging becomes faster in the dope preparation process, or the pressure increases when cast onto the metal support 7 and cannot be extruded. It is not preferable.

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

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

  The width of the metal support 7 is preferably 1700 to 2500 mm, the casting width of the dope is 1200 to 2400 mm, and the width of the film 9 after winding is preferably 1100 to 2500 mm. Thereby, the optical film for liquid crystal display devices with a wide width | variety can be manufactured with the film forming method using the metal support body 7. FIG.

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

  When a rotationally driven endless belt is used as the metal support 7, the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and the boiling point of the solvent having the lowest boiling point in the mixed solvent. The film can be cast at a temperature lower than 5 ° C., and more preferably in the range of 5 ° C. to the boiling point of the solvent−5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  As described above, the strength of the web 1b cast on the surface of the metal support 7 is increased by promoting the drying until peeling.

  In the system using a rotationally driven endless belt as the metal support 7, the web 1 b is dried and solidified on the metal support 7 until the web 1 b has a film strength that can be peeled from the metal support 7 by the peeling roll 8. Therefore, it is preferable to dry the residual solvent amount in the web 1b to 150% by mass or less, and more preferably 80 to 120% by mass. Moreover, as for the web temperature when peeling the web 1b from the metal support body 7, 0-30 degreeC is preferable. Further, immediately after the web 1b is peeled off from the metal support 7, the temperature once drops rapidly due to solvent evaporation from the side in close contact with the metal support 7, and volatile components such as water vapor and solvent vapor in the atmosphere are condensed. Since it is easy to do, the web temperature at the time of peeling has more preferable 5-30 degreeC.

  Here, the residual solvent amount of the web 1b can be expressed by the following equation.

Residual solvent amount (% by mass) = {(MN) / N} × 100
In the formula, M is the mass of the web 1b at an arbitrary time point, and N is the mass when the mass M is dried at 110 ° C. for 3 hours.

  The web 1b formed by the dope 1a cast on the metal support 7 is heated on the metal support 7, and the solvent is evaporated until the web 1b can be peeled from the metal support 7 by the peeling roll 8.

  For evaporating the solvent, there are a method of blowing air from the web 1b side, a method of transferring heat from the back surface of the metal support 7 by liquid, a method of transferring heat from the front and back by radiant heat, etc. Can be used.

  In the system using a rotationally driven endless belt for the metal support 7, the peeling tension when peeling the web 1 b from the metal support 7 by the peeling roll 8 is based on the peeling force obtained by peeling force measurement like JISZ0237. Although it is peeled off with a large tension, this may stabilize the peeling position when the peeling tension is made equal to the peeling force obtained by the JIS measurement method during high-speed film formation. Therefore, it is going high. However, even if the film is formed with the same peeling tension in the process, it is confirmed that the variation in the crossed Nicols transmittance (CNT) of the film is greatly reduced when the peeling force by the JIS measuring method is lowered.

  As the peeling tension value in the process, peeling is usually performed at 50 N / m to 250 N / m. However, in the optical film produced according to the present embodiment, which is made thinner than the conventional one, the web is peeled off at the time of peeling. Since the amount of residual solvent 1b is large and the film tends to stretch in the transport direction, the film tends to shrink in the width direction. When drying and shrinkage overlap, the end curls and folds, so that wrinkles tend to occur. Therefore, it is preferable to peel at a minimum tension that can be peeled to 170 N / m, and more preferably, peel at a minimum tension of 140 N / m.

  In the present embodiment, after drying and solidifying until the web 1b has a peelable film strength on the metal support 7, the web 1b is peeled off by a peeling roll 8, and then the web is stretched in a tenter 12 in a stretching process described later. 1b is stretched to form a film 9.

  FIG. 3 is a block diagram showing a second embodiment of an optical film manufacturing apparatus 100 for performing an optical film manufacturing method by a solution casting film forming method in the present invention. In the second embodiment, as the metal support 6, for example, a case of using a rotationally driven drum made of stainless steel whose surface is subjected to hard chrome plating is illustrated.

  The other points of the optical film manufacturing apparatus 100 in FIG. 3 are the same as those in the case of the optical film manufacturing apparatus 100 in FIG. 1 described above. Omitted.

  In the manufacturing method of the optical film of the first and second embodiments, the surface of the metal support 6 or 7 is subjected to atmospheric pressure plasma treatment or treatment at both ends shown in FIG. 2 before casting the dope 1a. The surface of the metal support 6 or 7 is activated by excimer UV treatment to increase the surface energy, the dope 1a is cast on the surface, and both ends of the cast film (dope) 1b are activated. It overlaps with the area that has been subjected to.

  Here, the place where the activation process by the atmospheric pressure plasma process or the excimer UV process is performed is the case where the dope 1a is cast on the metal support 6 or 7 and is formed into a film in FIG. 1 and FIG. This is performed in the section indicated by “A”. That is, the surface of the metal support 6 or 7 is so-called exposed while the web 1b is peeled from the metal support 6 or 7 by the peeling roll 8, and then the dope 1a is cast again from the casting die 3. It is limited to the section.

  Next, in the first and second embodiments, as an example of the surface treatment apparatus 200 for performing the activation treatment for increasing the surface energy, the atmospheric pressure plasma apparatus 20 used for the atmospheric pressure plasma treatment is described in detail. Explained.

  The atmospheric pressure plasma apparatus 20 according to the present embodiment applies a high-frequency voltage between opposing electrodes and discharges it to bring the reactive gas into a plasma state, and the surface of the metal support is changed to the reactive gas in the plasma state. By exposing, a region having a high surface energy is formed on the surface of the metal support.

  In an atmospheric pressure plasma apparatus, a high frequency voltage is applied to a reactive gas by a method called a direct method or a planar method in which high-frequency power is applied between electrodes arranged so as to sandwich a substrate to be processed, and a supply gas is converted into plasma. There is a system called a remote system or a downstream system which introduces between the added electrodes and turns into plasma, and any system can be used in the present invention.

  FIG. 4 is an explanatory diagram for explaining the principle of the atmospheric pressure plasma apparatus 20.

  4, a and b are counter electrodes of the atmospheric pressure plasma apparatus 20, g is a reactive gas, d is a gap from a blowing slit h for spraying plasma to the surface of the metal support s, and s is an object of film formation. A metal support h, h, is a blow-out slit for supplying plasma.

  As a simple structure of the atmospheric pressure plasma apparatus in FIG. 4, a reactive gas g is introduced between the counter electrodes a and b to which a high-frequency voltage is applied, is converted into plasma, and is sprayed and supplied to the surface of the metal support s. Increase energy.

  In the present embodiment, it is necessary to employ electrodes a and b that can apply a high power voltage and maintain a uniform glow discharge state in the atmospheric pressure plasma apparatus 20.

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

  In addition, when a cellulose ester film, which is a transparent film base material, is placed between electrodes or transported between electrodes and exposed to plasma, the transparent film base material has a roll electrode specification that can be transported in contact with one electrode. Furthermore, the dielectric surface and the gap between the electrodes can be kept constant by polishing the dielectric surface and setting the electrode surface roughness Rmax (JIS B 0601) to 10 μm or less. It is preferable that the discharge state can be stabilized, and further, the distortion and cracking due to the difference in thermal shrinkage and residual stress can be eliminated and the non-porous, highly accurate inorganic dielectric can be coated to greatly improve the durability. .

  In addition, the gap d between the blowing slit h that performs plasma supply and the surface of the metal support s is preferably 0.5 to 6 mm, and more preferably 1 to 4 mm. If it is too close, there is a risk of contacting or damaging the surface of the metal support (s), and if it is too far away, the effect of increasing the surface energy becomes weak.

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

  Further, from the outside of the atmospheric pressure plasma apparatus 20, the raw material gas is sprayed on the surface of the metal support (s), and the gas is entrained on the surface of the metal support (s) and sent to the bottom of the atmospheric pressure plasma apparatus 20 to activate it. Processing may be performed.

  In that case, the concentration of the source gas around the atmospheric pressure plasma apparatus 20 is preferably in the range of 500 ppm to 100,000 ppm, and more preferably 1000 to 50,000 ppm.

Further, the air volume of the source gas of the atmospheric pressure plasma is desirably 2 × 10 ^{−2 to} 5 m ³ / min per 1 m of the effective width of the plasma irradiation. Furthermore, 4 × 10 ^{−2 to} 2.5 m ³ / min is more preferable.

  Moreover, in the atmospheric pressure plasma apparatus 20, since there is a concern about damage such as roughening of the surface of the metal support (s) due to induced current or discharge, it is desirable to use an apparatus having a shield mechanism. In particular, in film formation by the solution casting film formation method, even nm-order flaws on the surface of the metal support (s) are all transferred to the film, and therefore it is important to use an apparatus with such measures.

  Next, in the first and second embodiments, an excimer UV apparatus 30 used for excimer UV processing will be described in detail as an example of the surface processing apparatus 200 for performing surface activation processing.

  FIG. 5 is an explanatory diagram for explaining the principle of the excimer UV device (30).

  In FIG. 5, u is an excimer UV lamp, q is quartz glass covering the excimer UV lamp u, p is a purge gas, d2 is a gap from the quartz glass q to the surface of the metal support s, and s is a metal support.

In the present embodiment, the excimer UV lamp u shown in FIG. 4 is used to irradiate the metal support s mainly with ultraviolet light having a wavelength of 172 nm with a light quantity of 1 to 3000 mJ / cm ² .

  Further, if the gap d2 between the quartz glass q and the metal support s is too close, there is a risk of contacting and damaging the surface of the metal support s, and if it is too far away, the excimer UV is highly exposed to oxygen and water in the atmosphere. Since energy will be absorbed and the effect of the activation process of the surface of the metal support body s will become weak, 0.5-4 mm is preferable, Furthermore, 1-3 mm is more preferable.

  When the surface treatment apparatus 200 for activating the surface of the metal support s, such as the atmospheric pressure plasma apparatus 20 or the excimer UV apparatus 30 described above, is brought into a film production line for optical use, the degree of cleanliness is maintained. Countermeasures are an issue. In particular, in the atmospheric pressure plasma apparatus 20 having a structure in which dust generated is discharged into the film-forming line, measures for maintaining cleanliness are important.

  In FIG. 1, the metal support 7 for casting the dope 1a is an endless belt made of, for example, stainless steel (SUS316 or SUS304). In FIG. 3, the metal support 6 for casting the dope 1a is, for example, stainless steel. A drum made of hard chrome plating on the surface of a drum or roll. In the present embodiment, the metal support 6 or 7 whose surface is polished to an ultra-mirror surface is used, and the activation treatment is performed on both ends of the surface side shown in FIG.

  According to the method of the present embodiment, the surface of both ends in the width direction of the metal support is subjected to an activation treatment for increasing the surface energy, and the surfaces of both ends in the width direction of the support subjected to the activation treatment are subjected to the activation treatment. By casting the resin solution so that both ends in the width direction of the casting film are applied, mixing of air in the casting process can be prevented. This also suppresses edge flutter when casting the film from the support, so the orientation angle deviation of the film can be reduced, and an optical film having excellent optical properties with transparency and flatness is produced. can do. Further, since stable casting properties can be obtained, the production speed can be increased and the productivity of the film can be improved. As a result, the manufacturing method of an optical film, an optical film, a polarizing plate, and a display apparatus which can respond to the request | requirement of thin film, widening, and quality improvement of the protective film for polarizing plates etc. in recent years can be provided.

  In the present invention, the orientation angle deviation of the optical film is, for example, a phase difference measuring device (trade name KOBRA-WR) manufactured by Oji Scientific Instruments Co., Ltd., for example, 100 mm from both ends of the film, and the orientation angle at the center of the film width. The difference between the maximum value and the minimum value was taken as the deviation.

  In this Embodiment, dope 1a for manufacturing an optical film contains resin, such as a cellulose ester resin, as a main material, These are a plasticizer, a retardation adjusting agent, a ultraviolet absorber, microparticles | fine-particles, and a low molecular weight substance. It contains at least one of these substances and a solvent.

  Hereinafter, these will be described.

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

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

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

  Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester used for this Embodiment, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

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

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

  In the method for producing an optical film according to the present embodiment, 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 embodiment, reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of expanding the viewing angle of a liquid crystal display device operating in an IPS (In-Plane-Switching) mode. However, in the present embodiment, examples of the additive for reducing such thickness direction retardation (Rt) include the following.

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

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

General formula (1) B1- (GA-) mG-B1
General 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.

  There is no restriction | limiting in particular as a monocarboxylic acid component represented by B1, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used.

  Examples of preferable monocarboxylic acid include the following, but the present embodiment is not limited to this.

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

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

The monoalcohol component represented by 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. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12.

  Examples of the divalent alcohol component represented by G include the following, but the present embodiment is not limited to this. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferred, and 1,3-propylene glycol, 1,4-butylene glycol 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 acid having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

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

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

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

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent acids or alcohols can be controlled by a method of blocking the molecular ends with monovalent acids or monovalent alcohols. 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 mass average molecular weight can also be adjusted by measuring the timing at which the reaction is stopped 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.

  It is preferable to contain 1-40 mass% of polyester represented by the said General formula (1) or (2) with respect to a cellulose ester. It is particularly preferable to contain 5 to 15% by mass.

  In this Embodiment, the following are further mentioned as an additive which reduces thickness direction retardation (Rt).

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

  In this embodiment, 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 the molecular weight can be adjusted as much as possible by a method that does not increase the molecular weight too much. It is desirable to use the method. Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as described in the publication, or a polymerization catalyst in which the compound and an organometallic compound are used in combination. The method described in the publication is particularly preferable.

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

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

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

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

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

  In this embodiment, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or alkyl methacrylate having no monomer unit having an aromatic ring or a cyclohexyl group.

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

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by 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 embodiment, an acrylic acid or methacrylic acid ester monomer having a hydroxyl group is not a homopolymer but a constituent unit of a copolymer. In this case, it is preferable that the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is contained in an acrylic polymer in an amount of 2 to 20% by mass.

  In the method for producing an optical film of the present embodiment, the dope composition comprises a cellulose ester and an acrylic polymer having a mass average molecular weight of 500 or more and 3,000 or less as an additive for reducing thickness direction retardation (Rt). It is preferable to contain.

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

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

  In this Embodiment, the polymer which has a hydroxyl group in a side chain can also be preferably used as an additive which reduces thickness direction retardation (Rt). The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. 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.

  Those containing 2 to 20% by mass of the monomer unit having the hydroxyl group as described above, of course, have 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 embodiment, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

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

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

  Moreover, in this Embodiment, the additive which reduces thickness direction retardation (Rt) can be found also with the following method.

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

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

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

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

  In the present embodiment, the in-plane retardation (Ro) of the cellulose ester is 0 nm to +5 nm, preferably 0 nm to +2 nm, more preferably 0 nm to +1 nm, and particularly preferably about 0 nm. Here, in either case where the in-plane retardation (Ro) is smaller than 0 nm or larger than +5 nm, the viewing angle is narrowed, and the effect of the present embodiment does not appear. In the optical film of the present embodiment, the in-plane direction retardation (Ro) defined by the following formula is 30 to 300 nm and the thickness direction retardation (Rt) is 23 at a temperature of 23 ° C. and a humidity of 55% RH. It is preferable that it is 70-400 nm on the conditions of (degreeC) and humidity 55% RH.

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

  In this embodiment, the retardation value of the film is 590 nm at a wavelength of 590 nm under an environment of a temperature of 23 ° C. and a humidity of 55% RH using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments). A three-dimensional refractive index measurement can be performed and calculated from the obtained refractive indexes Nx, Ny, and Nz.

Ro = (Nx−Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
(In the formula, Nx, Ny, and Nz represent the refractive indices in the principal axes x, y, and z directions of the refractive index ellipsoid (refractive index is measured at a wavelength of 590 nm), respectively, and Nx and Ny are refractive in the film in-plane direction. (Nz represents the refractive index in the thickness direction of the film, Nx ≧ Ny, and d represents the thickness (nm) of the film.)
In the present embodiment, the cellulose ester film has an angle θ (radian) formed between the slow axis direction and the film forming direction and a retardation value (Ro) in the in-plane direction, and particularly a protective film for a polarizing plate. It is preferably used as a cellulose ester film.

P ≦ 1-sin2 (2θ) sin2 (πRo / λ)
Here, P is 0.9999 or less, θ is an angle (° radians) formed between the slow axis direction in the film plane and the film forming direction (straight direction of the film), and λ is the above Nx, Ny, Nz , Θ, the wavelength of light in the three-dimensional refractive index measurement is 590 nm, and π is the circumference.

  In the method for producing an optical film according to the present embodiment, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and exhibits a main effect on dissolution, and an organic solvent used in a large amount among them is used. It is called the main (organic) solvent or the main (organic) solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride 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. After the dope is cast on a metal support, the alcohol starts to evaporate and the ratio of the alcohol increases, thereby making the web gel, making the web strong and easy to peel off from the metal support. It is also used as a gelling solvent, and when these ratios are small, it also has a role of promoting the dissolution of the cellulose derivative of the 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 is not toxic. 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: ethanol of 95: 5 to 80:20. Alternatively, a mixed solvent having a methyl acetate: ethanol ratio of 60:40 to 95: 5 is also preferably used.

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

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

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

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

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

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

Formula (3) R1- (OH) n
(However, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.)
Examples of preferred polyhydric alcohols include, but are not limited to, the following.

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

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this Embodiment, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but are not limited thereto.

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

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

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

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

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

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

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

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl 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 this embodiment, 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 less than 0.1% by mass, and particularly preferably not added. . These plasticizers can be used alone or in combination of two or more.

  As for the usage-amount of a plasticizer, 1-20 mass% is preferable. 6-16 mass% is further more preferable, Most preferably, it is 8-13 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 This is not preferable because the physical properties of the resin deteriorate.

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

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

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

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

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

As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for one 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 determined 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 after being 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. And controlling the particle size formed by aggregation.

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

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

  For the dispersion of the fine particles, it is preferable to treat a composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present embodiment is an apparatus that creates special conditions such as high shear and high-pressure conditions 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 4.1840 × 10 ⁵ J / 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 those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  In the present embodiment, 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 mixture is used as a metal support. A cellulose ester film is obtained which is cast on and dried to form a film.

  Here, as a content rate of a lower alcohol, Preferably it is 50-100 mass%, More preferably, it is 75-100 mass%.

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

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

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by 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 embodiment 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 coloration is preferred. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

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

  Specific examples of ultraviolet absorbers useful in the present embodiment include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert). -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butyl Phenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2 -Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2'-hydride) Xy-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.

  Moreover, as a commercial item of an ultraviolet absorber, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Japan) can be preferably used.

  Further, as specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in this embodiment, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy- Examples thereof include, but are not limited to, 5-sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

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

  Moreover, the ultraviolet absorber which can be used for the optical film of this Embodiment is the polymer ultraviolet absorber (or ultraviolet-absorbing polymer) of Unexamined-Japanese-Patent No. 6-148430 and 2002-47357. It can be preferably used. In particular, the polymer ultraviolet absorber represented by the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formula (3) 67 described in JP-A-2002-47357. Are preferably used.

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid-based plasticizer. Therefore, the antioxidant is preferably contained in the film. .

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

  The amount of these compounds added is preferably 1 ppm to 1.0% by mass and more preferably 10 to 1,000 ppm by mass with respect to the cellulose derivative.

  In the apparatus for carrying out the method for producing the optical film shown in FIGS. 1 and 3, the stretching step is a tenter for stretching the film 1b by fixing both side edges of the web 1b with clips or the like. The method is preferable for improving the flatness and dimensional stability of the film.

  The residual solvent amount of the web 1b immediately before entering the tenter 12 in the stretching process is preferably 10 to 35% by mass.

  In the present embodiment, the stretch ratio of the web 1b in the tenter 12 in the stretching process is 1.03 to 2 times, preferably 1.05 to 1.8 times, and further 1.05 to 1.6 times. It is desirable that Moreover, the temperature of the hot air blown out from the hot air blowing slit port in the tenter 12 is 100 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C. Here, the web 1b after being stretched by the tenter 12 is referred to as a film 9.

  It is preferable to provide a drying device (10) before or after the tenter 12 in the stretching step, or one of them. In the drying apparatus (10), the film 9 is meandered by a plurality of transport rolls arranged in a staggered manner as viewed from the side, and the film 9 is dried in the meantime. Further, 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., but the film transport tension during drying is 0.3. It is -3N / 10mm, and 0.4-2.7N / 10mm is more preferable.

  The means for drying the film 9 is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, a microwave, 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 (11a) blown from the hot air inlet at the rear part of the ceiling of the drying device (10), and is dried at the bottom of the drying device (10). The exhaust air (11b) is discharged from the outlet of the front portion to be dried. The temperature of the drying air (11a) is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or 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 subjected to a process of forming an emboss on the film by an embossing apparatus (not shown) in the previous stage of introduction into 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 h1 + h2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The film 9 which has been dried is wound up by a winding device (13) to obtain the original roll of the optical film. The residual solvent amount of the film 9 that finishes drying is 0.5% by mass or less, and preferably 0.1% by mass or less, whereby the film 9 with good dimensional stability can be obtained.

  The winding method of the film 9 may be a generally used winder, and there are methods for controlling 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. Should be used properly.

  The film 9 may be joined to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  In the optical film according to the present embodiment, the width of the film after winding is preferably 1100 to 2500 mm.

  In this Embodiment, the film thickness after drying of a cellulose-ester film has the preferable range of 20-150 micrometers as a finished film from a viewpoint of thickness reduction of a liquid crystal display device. Here, “after drying” means a film dried to a state where the amount of residual solvent in the film 9 is 0.5 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. To adjust the film thickness, control the dope concentration, pump feed volume, slit gap of the die of the casting die, extrusion pressure of the casting die, and the moving speed of the metal support to achieve the desired thickness. It is good to do. 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, or 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 embodiment, the cellulose ester film has a moisture content of preferably 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

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

  Further, the tensile modulus in the machine direction (MD direction) of the cellulose ester film produced by the method of producing an optical film according to the present embodiment is 1,500 MPa to 3,500 MPa, the direction perpendicular to the machine direction (TD direction). The tensile elastic modulus of the film is preferably 3,000 MPa to 4,500 MPa, and the ratio of the TD direction elastic modulus / MD direction elastic modulus 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 when winding a film having a width exceeding 1,650 mm, and the winding core Since sticking of a film 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 occurs after heating on the deflecting plate, or the backlight is heated by the heat of the backlight when incorporated in the liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

  As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JISK7217 can be mentioned.

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

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

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

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

  The polarizing plate may be prepared by laminating the optical film produced by the method of the present embodiment as a retardation film, or the optical film produced by the method of the present embodiment may be prepared as a retardation film. Alternatively, the protective film may be used as a direct attachment to the 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. As this water-soluble polymer adhesive, a completely saponified polyvinyl alcohol aqueous solution is preferably used. Furthermore, a long polarizing plate is 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 embodiment. Can do. A polarizing plate is a sticking type in which a peelable sheet is laminated on one side or both sides of a peelable sheet via a pressure sensitive adhesive layer (for example, an acrylic pressure sensitive adhesive layer). It can be easily attached to a cell or the like.

  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. It is preferable to use for.

  By the way, a polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is bonded to both surfaces of a polarizing film produced by immersing and stretching in an iodine solution 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 this embodiment 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, and an adhesive layer. Various functional layers such as a layer, an adhesive layer, and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

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

  In the present embodiment, 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 transparent protective layers disposed on both sides thereof. It has two polarizing plates.

  By using a protective film for a polarizing plate made of an optical film produced by the method of the present embodiment, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. it can. 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 embodiment can also be used as a base material for an antireflection film or an optical compensation film.

  Hereinafter, the present embodiment will be described more specifically by way of examples, but the present invention is not limited to these.

(Examples 1-9)
In this example, the optical film manufacturing apparatus of FIG. 1 was used, and the atmospheric pressure plasma apparatus 20 was used as an apparatus for performing the activation treatment.
(Preparation of dope)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered. The filtration was performed through a sintered metal filter (capture particle size = 10 microns) after filtration by a filter press. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate 100 parts by mass (Mn = 148000, Mw = 310000, Mw / Mn = 2.1)
Triphenyl phosphate 8 parts by mass Ethylphthalyl ethyl glycolate 2 parts by mass Methylene chloride 440 parts by mass Ethanol 40 parts by mass Tinuvin 109 (manufactured by Ciba Japan) 0.5 part by mass Tinuvin 171 (manufactured by Ciba Japan) 0.5 parts by mass Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by mass (metal support)
As a metal support for casting the dope 1a, an endless belt made of stainless steel (SUS316) and polished to a super mirror surface was used.
(Activation process)
The surface of the metal support was subjected to activation treatment in Examples 1 to 9 described later. The activation treatment was performed in advance in section A of FIG. 1 before casting the dope 1a on the support. The metal support temperature when the activation treatment was performed on the surface of the metal support was adjusted to 10 ° C.

An atmospheric pressure plasma apparatus 20 was used as the activation processing apparatus. Under the condition that the gap d from the blowing slit h to the surface of the metal support 7 of the atmospheric pressure plasma apparatus 20 is 2 mm, the metal support 7 is passed under the atmospheric pressure plasma apparatus 20 while being conveyed. The body surface was activated. By adjusting the output of the atmospheric pressure plasma apparatus 20, the surface of the support (see T in FIG. 2) in contact with the center of the film that has not been activated, and the support in contact with the end of the film that has been activated. The surface energy difference from the surface (see S in FIG. 2) was adjusted to the value shown in Table 1. Moreover, the width Wrk which overlaps with the active region Wk with a high surface energy by an atmospheric pressure plasma apparatus and the both ends of a casting film was made into Table 1, and it was set as the manufacturing conditions of the optical film of Examples 1-9. Further, the surface energy in the activation region Wk was set to a uniform surface energy having the same value.
(Production of cellulose ester film)
Using the above-described dope 1a, a cellulose ester film having a film thickness of 30 μm was produced as follows.

  The filtered dope 1a is uniformly cast from a coat hanger die on a metal support 7 made of an endless belt made of SUS316 subjected to surface treatment under the conditions shown in Examples 1 to 6 described above at a dope temperature of 35 ° C. did. The temperature of the wind for drying the web 1b was constant at 30 ° C.

After peeling from the metal support 7, it was dried while being rolled in an atmosphere of 90 ° C, and after stretching by 1.06 times in the width direction in an atmosphere of 100 ° C when the residual solvent amount was 10%, the width The holding was released and drying was completed in a 125 ° C. drying zone while being conveyed by rolls, and cellulose ester films of Examples 1 to 9 having a film thickness of 30 μm, a width of 2400 mm, and a length of 6000 m were produced.
(Comparative Example 1)
As Comparative Example 1, a cellulose ester film was produced in the same manner as in Example 4 except that the activation treatment by the atmospheric pressure plasma treatment apparatus in Example 4 was not performed.
(Comparative Example 2)
As Comparative Example 2, the width of the activation treatment by the atmospheric pressure plasma treatment apparatus in Example 4 was applied to the entire width of the metal support, and the width Wrk = Wr / 2 of the portion overlapping the casting film was set. A cellulose ester film was produced in the same manner as in Example 4.
(Comparative Example 3)
As Comparative Example 3, the width of the activation process by the atmospheric pressure plasma processing apparatus in Example 4 was applied to the central part of the metal support, not applied to both ends, and the width Wr / 3 of the central part of the casting film. A cellulose ester film was produced in the same manner as in Example 4 except that they overlapped.
(Evaluation)
In the evaluation of the mixing of bubbles in the films of Examples 1 to 9 and Comparative Examples 1 to 3, the foam of 100 μm or more was measured until the dope flowed down from the casting die 3 and peeled with respect to the total length and width of the film. Was optically detected and evaluated. If even one of them was detected, it was assumed that bubbles were mixed. Moreover, about the full width of the change angle deviation of the film of Examples 1-9 and Comparative Examples 1-3 from the beginning of film winding, the phase difference measuring apparatus (brand name KOBRA-WR) made by Oji Scientific Instruments Co., Ltd. The difference between the maximum and minimum values was taken as the deviation. These evaluation results are shown in Table 1, and were comprehensively evaluated. Comprehensive evaluation is that the generation of bubbles is not recognized and the orientation angle deviation is 0.3 ° or less at level 4, and the one with more than 0.3 ° and less than 0.8 ° is level 3, 0.8. Levels exceeding .degree. To .about.1.5.degree. Were designated level 2, and those exceeding 1.5.degree. Level 0 was defined as the presence of bubbles. Levels 1 and below are not levels that can be used as products.

  From the results in Table 1, when Examples 1 to 9 and Comparative Examples 1 to 3 are compared, the surface energy of the surface of the support that is in contact with both ends in the width direction of the casting film is reduced before the resin solution is cast. By applying an activation treatment to the surface of the support so as to be higher than the surface energy of the surface of the support in contact with the central portion in the width direction of the stretched film, bubbles can be prevented from being mixed, and the orientation angle deviation can be prevented. It can be seen that an optical film having a small optical unevenness can be produced. Moreover, when Examples 1-3 and 9 are compared, the surface energy of the surface of the support body which contacts the width direction both ends of a casting film is more than the surface energy of the surface of the support body which contacts the width direction center part of a casting film. It can be seen that a high range of 0.1 to 60 mN / m is preferable. Furthermore, when Examples 4-8 are compared, from the width direction both ends of the casting film which contact | connects the surface of the support body which has surface energy higher than the surface energy of the surface of the support body which contact | connects the width direction center part of a casting film It can be seen that each of the widths is preferably in the range of 0.05 Wr to 0.25 Wr, where the width of the cast film is Wr.

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

Step 1: The long optical film produced in Example 1 was immersed in a 2 × 10 ³ mol / m ³ sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried. The optical film produced in Example 1 was previously provided with an antireflection film on one side, and a protective film (made of polyethylene terephthalate) that could be removed again was attached to the surface for protection.

Similarly, a long cellulose ester film (used as a base material for an optical film) was immersed in a 2 × 10 ³ mol / m ³ sodium hydroxide solution at 50 ° C. for 90 seconds, then washed with water and dried.

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

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

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

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

  Similarly, using the long optical films prepared in Examples 2 to 9 and Comparative Examples 1 to 3, the polarizing plates of Examples 2 to 9 and the polarizing plates of Comparative Examples 1 to 3 of the present embodiment are used. Produced.

(Production of liquid crystal display panel)
The polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD 1525J, model name LA-1529HM) was carefully peeled off, and the polarizing plates of Examples 1 to 9 and Comparative Examples 1 and 2 described above. A liquid crystal display panel was manufactured by pasting the polarizing plates of the polarizing plates with the polarization direction aligned.

(Visual evaluation of polarizing plate)
Each liquid crystal display panel produced in this way was visually evaluated by a plurality of evaluators by visually observing unevenness that appeared whitish when viewed from the front and oblique directions. In the panels of Examples 1 to 9, no unevenness was observed, but in Comparative Examples 1 to 3, unevenness was observed.

  As described above, according to the present invention, in the method of manufacturing an optical film by the solution casting film forming method, before casting the resin solution, the surface of the support in contact with both ends in the width direction of the casting film. By applying an activation treatment to the surface of the support so that the surface energy of the support is higher than the surface energy of the support in contact with the center in the width direction of the casting film, the air (bubbles) in the casting process Mixing can be suppressed, fluttering of the film during casting due to air mixing can be reduced, and the orientation angle deviation of the optical film can be reduced. Moreover, the optical film which has the optical characteristic excellent in planarity can be manufactured. Thereby, the manufacturing method of an optical film, an optical film, a polarizing plate, and a display apparatus which can respond to the request | requirement of thin film formation, width expansion, and quality improvement, such as a protective film for polarizing plates, can be provided.

  In addition, the manufacturing method of the optical film according to the present invention, the optical film, the polarizing plate, and the detailed configuration and detailed operation of each component constituting the display device can be appropriately changed without departing from the spirit of the present invention. is there.

1 Dope tank 1a Dope (resin solution)
1b Web (casting membrane)
2 Liquid feed pump 3 Casting die 4 Depressurization chamber 5 Drum 6 Metal support (drum)
7 Metal support (endless belt)
DESCRIPTION OF SYMBOLS 8 Peeling roll 9 Film 10 Drying apparatus 11 Drying air 12 Tenter 13 Winding apparatus 20 Atmospheric pressure plasma apparatus 30 Excimer UV apparatus 100 Optical film manufacturing apparatus 200 Surface treatment apparatus A Section for film formation treatment a, b Electrode g Reaction gas d Blowout Gap between slit and metal support surface h Blowing slit s Metal support p Purge gas r Reflector u Excimer UV lamp d2 Gap between quartz glass and metal support surface q Quartz glass

Claims (8)

A casting step of casting a resin solution on the surface of the support to form a casting film;
In the method for producing an optical film having a step of peeling the cast film from the support,
Before casting the resin solution, the surface energy of the surface of the support that is in contact with both ends in the width direction of the casting film is the surface energy of the surface of the support that is in contact with the center in the width direction of the casting film. A method for producing an optical film, comprising subjecting the surface of the support to an activation treatment so as to be higher than that. The method for producing an optical film according to claim 1, wherein the activation treatment is performed by atmospheric pressure plasma irradiation or excimer UV irradiation. After performing the activation treatment,
The surface energy of the surface of the support in contact with both widthwise ends of the cast film is γse,
The difference Δγ (= γse−γsc) is in the range of 0.1 to 60 mN / m, where γsc is the surface energy of the surface of the support that is in contact with the widthwise center of the cast film. The method for producing an optical film according to claim 1 or 2. Respective widths from both ends in the width direction of the casting film in contact with the surface of the support having a surface energy higher than the surface energy of the surface of the support in contact with the center in the width direction of the casting film, 4. The method for producing an optical film according to claim 1, wherein the width of the cast film is in a range of 0.05 Wr to 0.25 Wr, where Wr is Wr. The method for producing an optical film according to any one of claims 1 to 4, wherein the support is any one of an endless belt, a drum, and a roll. 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 6 on at least one surface. A display device comprising the polarizing plate according to claim 7.

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