JP2014223758A - Production method of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve irregular film thickness in a process of forming a film by flow-casting a dope onto a belt between two drums, by suppressing vibration of the belt near a rear wall of a pressure reduction chamber even when film forming speed is increased, so as to suppress irregular intensity of an entrained wind and to suppress vibration of a flow-cast ribbon by the entrained wind.SOLUTION: A dope is cast from a flow-cast die 3 onto a belt 6 between two drums 5, 7. A pressure reduction chamber 4 is disposed on an upstream side along the moving direction of the belt 6 with respect to the flow-cast die 3 so as to give a 0.3 to 3 mm gap between the belt 6 and the chamber; and at least one support roll 11 is disposed to support the belt 6 from an inner circumference surface side. When a direction from the center position of a rear wall 4a of the pressure reduction chamber 4 toward the downstream side is defined as a positive direction while a direction toward the upstream side is defined as a negative direction, the first support roll 11a is positioned in such a manner that the center of the contact range between the support roll and the belt 6 along the moving direction of the belt 6 is present in a range from +100 mm to -300 mm with reference to the center position of the rear wall 4a.

Description

  The present invention relates to an optical film manufacturing method for forming an optical film by a solution casting method.

  Various optical films (for example, a transparent protective film for protecting the polarizing element of the polarizing plate) are disposed in the image display region of the liquid crystal display device. As such an optical film, for example, a resin film having excellent transparency such as a cellulose ester film is used.

  Such an optical film is often produced as a long resin film by, for example, a solution casting (film formation) method. Specifically, the solution casting method is obtained by casting a resin solution (dope) obtained by dissolving a transparent resin, which is a raw material resin, in a solvent, onto a traveling support and drying it to a peelable extent. In this method, the obtained web (dope film) is peeled from the support, and the peeled web is transported by a transport roller, and dried, stretched, or the like to form a long resin film.

  The solution casting method includes a belt-type film forming method in which a dope is cast on a support made of a rotationally driven stainless steel endless belt, or a drum type film-forming in which a dope is cast on a stainless steel rotationally driven drum. There are laws.

  In the belt-type film forming method, as shown in FIG. 5, an annular endless belt wound around two rolls 105 and 107 is used as the support 106. Then, the dope adjusted in the melting pot 101 is fed to the casting die 103 through the pressurization type fixed gear pump 102, and the dope is cast from the casting die 103 onto the support 106 wound around the roll 107. . At this time, the pressure reducing mechanism 104 is disposed upstream of the casting die 103 in the moving direction of the support 106, and the pressure reducing mechanism 104 decompresses the space upstream of the casting die 103 while casting. A dope is cast from the die 103 onto the support 106. The dope cast on the support 106 becomes a web 109 as a cast film having a self-supporting property after drying, and is peeled from the support 106 by a peeling roll 108. On the other hand, the drum-type film forming method is the same as the belt-type film forming method except that a drum-like support is used as the support 106 instead of the endless belt. Such a belt type film forming method and a drum type film forming method are disclosed in, for example, Patent Document 1.

  In recent years, there is a demand to separately adjust the temperature of the support at the dope casting position and the web peeling position. In this regard, for example, in Patent Document 2, the dope is cast on a belt between two rolls on which the belt is stretched, and the support is cooled by cooling the roll between web drying and peeling. On the other hand, the support is heated between peeling and casting. By cooling the support before peeling, the time required from drying to peeling can be shortened, so that the production efficiency can be improved.

  By the way, it was found that when a dope was cast on a belt between two rolls (drums) as in Patent Document 2 to produce a film, horizontal thickness unevenness occurred. This is because the belt vibration at the casting position becomes larger than before due to the separation of the casting position from the drum (where the belt is stretched), and the dope (flowing) until the belt lands on the belt from the casting die. This is thought to be because the ribbon is shaken at the landing point.

  As a method of suppressing the thickness unevenness, for example, a method of suppressing belt vibration by arranging a roll that supports the inner peripheral surface of the belt immediately below the casting position can be considered. However, as a result of various studies, in the high-speed film formation by high-speed running of the belt, the above method is insufficient to suppress the film thickness unevenness, and the cause of the fluctuation of the casting ribbon is the belt vibration at the casting position. It was found that factors other than were dominant.

  When factors other than belt vibration at the casting position were examined, the accompanying wind (air flow in the vicinity of the belt surface) generated as the belt moved increased as the belt moved faster. It hit the ribbon and rocked before landing, and it was found that this was the main factor causing uneven film thickness.

  As a countermeasure against accompanying air, conventionally, a method has been proposed in which a decompression chamber is arranged upstream of the casting die to suck the accompanying air (see, for example, Patent Document 1). However, in the film forming method in which the dope is cast on the belt between the two drums, the effect of improving the film thickness unevenness is not sufficient even if the gap between the decompression chamber and the belt is narrowed to reduce the inflow of the accompanying air. There wasn't. This is because the gap between the rear wall and the belt (the cross-sectional area of the entrained air flow) slightly fluctuates due to belt vibration in the vicinity of the rear wall on the upstream side of the decompression chamber, thereby causing the entrainment to flow into the gap. It is thought that the strength of the wind is generated and the casting ribbon is vibrated. Therefore, in order to sufficiently obtain the effect of improving the film thickness unevenness, it is necessary to suppress the vibration of the casting ribbon due to the strength of the accompanying wind.

Japanese Patent Laying-Open No. 2010-253723 (see FIGS. 1 and 5) Japanese Patent Laying-Open No. 2012-196858 (see claim 1, FIG. 2, etc.)

  In view of the above-described circumstances, the object of the present invention is to form a dope on a belt between two drums to form a film and increase the film forming speed. An optical film manufacturing method capable of sufficiently suppressing the unevenness of the film thickness by suppressing the unevenness of the accompanying wind and suppressing the vibration of the casting ribbon due to the accompanying wind, thereby providing a sufficient effect of improving the film thickness unevenness. There is to do.

  The above object of the present invention is achieved by the following configurations.

1. A method for producing an optical film comprising casting a dope from a casting die on a moving support, and forming an optical film by a solution casting method in which the casting film is peeled off from the support,
The support is a belt stretched between two drums,
The dope is cast on the belt between the two drums;
A decompression chamber is arranged upstream of the casting die in the moving direction of the belt so that a gap with the belt is 0.3 to 3 mm,
Arranging at least one support roll to support the belt from the inner peripheral surface side;
In the moving direction of the belt, the center position of the rear wall portion on the upstream side of the decompression chamber is used as a reference, the direction toward the downstream side in the moving direction of the belt with respect to the reference is positive, and the direction toward the upstream side is When negative,
One of the support rolls is a first support roll, and the center of the contact range with the belt in the moving direction of the belt is in a range of +100 mm to −300 mm with respect to the center position of the rear wall portion. A method for producing an optical film, comprising:

  2. Another support roll is arranged as a second support roll directly below the casting die through the belt, and the dope discharged from the casting die is within a range where the belt comes into contact with the second support roll. 2. The method for producing an optical film as described in 1 above, wherein the optical film is landed.

  3. The first support roll is positioned such that a center of a contact range with the belt in a moving direction of the belt is in a range of +30 mm to −100 mm with respect to a center position of the rear wall portion. 3. The method for producing an optical film as described in 1 or 2 above.

  4). A partition plate that extends in the width direction of the casting film and separates the interior of the decompression chamber into a plurality of spaces and communicates the plurality of spaces only through a gap with the belt is provided in the decompression chamber. 4. The method for producing an optical film as described in any one of 1 to 3 above, wherein

  5. Any one of 1 to 3 above, wherein a structure for controlling the air flow in the decompression chamber during decompression is provided in the decompression chamber so as to extend in the width direction of the casting film. The manufacturing method of the optical film of description.

  6). 6. The method for producing an optical film according to any one of 1 to 5, wherein the moving speed of the belt is 80 m / min to 200 m / min.

  According to the above manufacturing method, the dope is cast from the casting die on the belt between the two drums. At this time, a decompression chamber is arranged on the upstream side of the casting die so that the gap with the belt is as narrow as 0.3 to 3 mm, and the accompanying air generated as the belt moves to the decompression chamber. Inflow is reduced.

  Here, one of the support rolls that support the belt from the inner peripheral surface side is +100 mm (100 mm on the downstream side) to −300 mm (300 mm on the upstream side) with respect to the center position of the rear wall portion on the upstream side of the decompression chamber. Since it is located within the range, belt vibration in the vicinity of the rear wall of the decompression chamber can be suppressed by the support roll even when the film forming speed is increased. As a result, minute fluctuations in the gap between the rear wall portion of the decompression chamber and the belt can be suppressed, and unevenness of the accompanying air flowing into the gap can be suppressed. As a result, the vibration of the casting ribbon due to the unevenness of the accompanying wind can be suppressed, so that the effect of improving the film thickness unevenness can be sufficiently obtained.

It is explanatory drawing which shows the structure of the outline of the manufacturing apparatus of the optical film which concerns on embodiment of this invention. It is explanatory drawing which expands and shows the principal part of the said manufacturing apparatus. It is explanatory drawing which shows the structure different from FIG. 1 of the pressure reduction chamber which the said manufacturing apparatus has. It is explanatory drawing which shows other structure of the said pressure reduction chamber. It is explanatory drawing which shows the schematic structure of the manufacturing apparatus of the conventional optical film.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not limited to these. In the present specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B.

[Points of the present invention]
As a result of extensive studies by the present inventor, minute belt vibration occurs at the gap position between the decompression chamber and the belt, and the minute fluctuation of the gap area thereby creates the strength of the inflowing wind. Was found to be causing quality failure. That is, it has been found that the gap between the vacuum chamber and the belt needs to be kept constant while being at a minimum.

  In addition, the inventor arranges a roll (support roll) that supports the belt from the back just below or near the rear wall (back plate) of the decompression chamber, thereby suppressing belt vibration and making the gap constant. It was found that the film thickness unevenness can be suppressed. And based on such knowledge, it came to derive the manufacturing method of the optical film shown below.

  That is, the method for producing an optical film of the present embodiment includes the above-described support in solution casting in which a dope containing a polymer and a solvent is cast from a casting die on a traveling belt-like support and then peeled off as a film. As a body, a belt stretched between two drums is used, and the dope is cast on a belt between the two drums, and a gap with the belt is 0.3 to 3 mm on the upstream side of the casting die. The decompression chamber is installed so that the at least one support roll is disposed to support the back surface of the belt, and one of the support rolls is disposed directly below or near the decompression chamber. Is. More specifically, in the belt conveyance direction (movement direction), when the center position of the rear wall (back plate) of the decompression chamber is the reference (0 mm) and the belt conveyance direction is positive, the belt of the support roll The center of the wrap position (contact area with belt, contact range) is in the range of +100 mm to −300 mm.

  According to this configuration, it is possible to suppress the belt vibration just under the back plate of the decompression chamber and keep the gap area constant. This is because the vibration of the belt is reduced at the portion where the tension is most applied in contact with the support roll. The closer the belt wrap area where the support roll and belt contact, the closer to the back plate, the greater the effect of restraining the entrained wind.Therefore, after narrowing the gap between the decompression chamber and the belt, By setting the thickness within the range of +100 mm to −300 mm, a thickness unevenness failure can be suppressed.

  It should be noted that the installation range of the support roll is wider in the negative direction than in the positive direction with respect to the belt conveyance direction, because of the film peeling, the vibration is considered to propagate from the upstream side of the decompression chamber, This is because the gap area of the back plate, which is the rear wall portion of the decompression chamber, is stabilized when a support roll is installed on the upstream side to suppress vibration. However, if possible, it is preferable to dispose the support roll directly under the back plate as much as possible.

  In the above manufacturing method, it is preferable that a support roll different from the support roll directly under the decompression chamber is directly under the casting position. And it is preferable that the dope (casting ribbon) from the casting die lands within the belt wrap range of the support roll immediately below the casting position. As described above, it is considered that there are two causes of thickness unevenness: (1) belt vibration at the casting ribbon landing point, and (2) entrained wind that shakes the casting ribbon before landing. This is because a further effect can be expected by performing the two measures simultaneously. Usually, the distance from the casting position to the rear wall of the decompression chamber is 300 mm or more, but the support roll installed just below the decompression chamber and the support roll installed just below the casting position are not in contact with each other. It is preferable to determine the mutual roll diameter and arrangement position.

  Further, the position of the support roll immediately below the decompression chamber is the belt wrap position of the support roll when the center position of the rear wall of the decompression chamber in the belt conveyance direction is a reference (0 mm) and the belt conveyance direction is positive. More preferably, the center of is in the range of +30 mm to -100 mm.

  In addition, the optical film manufacturing method of the present embodiment is a known technique for improving the decompression chamber itself, specifically, a partition plate described in Japanese Patent No. 4400768 and a windshield described in Japanese Patent Application Laid-Open No. 2008-221760. It can be used in combination with conventional techniques such as structures. Since the manufacturing method of the present embodiment (control of the accompanying air by the support roll) operates at the inlet of the accompanying air upstream of the decompression chamber, the manufacturing method of this embodiment is used and the downstream side of the inlet Incorporating conventional improvement measures (partition plates, airflow control wind-shielding structures, etc.) into these can further increase their effects.

  Furthermore, in the manufacturing method of the optical film of this embodiment, it is preferable that the moving speed of a support body (belt) is 80 m / min-200 m / min. This is because unevenness in thickness, which is a subject of the present invention, becomes apparent as the speed of film formation increases, and is thus more effective during high-speed production.

  Hereinafter, the manufacturing method and manufacturing apparatus of the optical film of this embodiment will be described more specifically.

[Optical film manufacturing equipment]
FIG. 1 is an explanatory diagram showing a schematic configuration of the optical film manufacturing apparatus of the present embodiment. This manufacturing apparatus manufactures an optical film by a solution casting method, and includes a casting apparatus 10, a stretching apparatus 20, a drying apparatus 30, and a winding apparatus 40.

  The casting apparatus 10 includes a casting die 3, an endless belt 6 that is a support, and a peeling roll 8. Dissolve the raw material resin in the solvent in the melting pot 1, and add various additives such as plasticizers, matting agents, UV absorbers, antioxidants, etc. as necessary, and prepare the resin solution (dope). A web (casting film) 9 is formed by discharging from the casting die 3 through the pump 2 and casting on the moving (running) belt 6 (casting process).

  The belt 6 is stretched by a pair of drums 5 and 7, and the dope is cast on the belt 6 between the drums 5 and 7. At this time, the decompression chamber 4 is arranged on the upstream side of the casting die 3 in the moving direction of the belt 6, and the dope is added onto the belt 6 while decompressing the space upstream of the casting die 3 by the decompression chamber 4. Is casting. Thus, the accompanying air generated as the belt 6 moves is sucked and reduced in the decompression chamber 4 so as to suppress the vibration of the dope (casting ribbon) before landing on the belt 6 as much as possible.

  The web 9 formed by casting the dope onto the belt 6 is conveyed by the running of the belt 6 and is dried to some extent on the belt 6 by blowing warm air during the conveyance. The peeling roll 8 peels the conveyed web 9 from the belt 6 and sends it to the stretching device 20.

  The stretching device 20 uses a clip tenter, a pin tenter, or the like while transporting the peeled web 9 (resin film) by various transport means such as a transport roll (not shown), for example, in the longitudinal direction (Machine Direction: MD direction)) and / or the width direction (transverse direction (TD direction)).

  The drying device 30 evaporates the solvent by heating to a predetermined temperature while conveying the stretched resin film. The winding device 40 winds the dried resin film as an optical film F in a roll shape.

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

(Dissolution)
The resin solution discharged from the casting die 3 is prepared by, for example, dissolving a cellulose ester resin such as cellulose triacetate in a solvent containing a good solvent for the cellulose ester resin by using the dissolving pot 1. The content of the cellulose ester resin in the resin solution is preferably 15 to 30% by mass, for example.

  For dissolving the cellulose ester resin, a method carried out at normal pressure, a method carried out below the boiling point of the solvent, a method carried out under pressure above the boiling point of the solvent, JP-A-9-95544, JP-A-9-95557, Various dissolution methods can be used, such as a method performed by a cooling dissolution method as described in Kaihei 9-95538 and a method performed at a high pressure as described in Japanese Patent Application Laid-Open No. 11-21379. Among these, the method of pressurizing at a temperature equal to or higher than the boiling point of the solvent is preferable. After the resin is dissolved in the solvent, the resin solution is filtered through a filter medium and defoamed. In the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

(Casting die)
The resin solution is sent to the casting die 3 by a pump 2 for feeding liquid such as a pressurized metering gear pump. The casting die 3 is preferably one in which the shape of the discharge port can be adjusted. The casting die 3 is preferably a pressure die that can easily make the thickness of the web 9 uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  Regarding the angle of the casting die 3, when the surface of the support (belt) is set to 0 °, the angle of the lip gap serving as a discharge flow path stands up (inclined) with respect to the support in the range of 45 ° to 90 °. It is preferable to install in the range of 55 ° to 75 °. Outside this range, even if it was possible to effectively prevent the adherence of the lips to the lip tip (attachment due to dripping), the dope would contact the lip tip during discharge and flow onto the surface of the product film in the casting direction. Vertical streaks appear, which may reduce the quality.

  The discharge speed for discharging the resin solution from the casting die 3 is preferably, for example, about 30 m / min to 200 m / min in consideration of the balance with the conveyance speed of the web 9 by the belt 6 and the productivity, for example, 80 m It is more preferable that the speed is about 200 to 200 m / min.

  The casting width of the dope by the casting die 3 is preferably 80 to 99% of the width of the belt 6 from the viewpoint of effectively utilizing the width of the belt 6, for example, 1000 mm to 2500 mm. By doing so, it can contribute to widening of the optical film, and can contribute to enlargement of the protective film, the polarizing plate, and thus the liquid crystal display device.

(belt)
The belt 6 is a metal belt having a mirror-finished surface. The belt 6 is preferably made of, for example, stainless steel from the viewpoint of the peelability of the web 9. As the belt 6 rotates the drums 5 and 7, the upper traveling portion and the lower traveling portion move horizontally in opposite directions, and the web 9 cast and supported by the upper traveling portion from the casting die 3 is supported. It is conveyed halfway along the curved transition portion from the lower traveling portion to the upper traveling portion.

  In order to suppress vibration and meandering of the belt 6, at least one support roll 11 that supports the belt 6 between the drums 5 and 7 from the back surface side (inner peripheral surface side) is provided. The support roll 11 is disposed so as to be substantially parallel to the drums 5 and 7. The support roll 11 may be a metal roll whose surface is subjected to a treatment such as hard chrome plating, and the friction force with the metal belt 6 is increased to suppress the slip, and the wear powder is avoided by avoiding contact between metals. In order to reduce generation, a rubber lining or a resin lining may be provided on the surface. In the present embodiment, the support roll 11 includes a first support roll 11a positioned corresponding to the decompression chamber 4 and a second support toll 11b positioned corresponding to the casting die 3. Will be described later.

  The web 9 is dried to some extent on the belt 6 during conveyance. This drying is generally performed by, for example, a method in which warm air is blown from above the belt 6, a method in which warm air is blown on the back surface of the belt 6, and a heater is disposed above the belt 6. It is performed by a method of heating, a method of heating by arranging a heater on the back surface of the belt 6, and the like can be appropriately selected and combined as necessary.

  The temperature of the web 9 at the time of drying is preferably −5 to 70 ° C. and more preferably 0 to 60 ° C. in consideration of the time required for evaporation of the solvent, the conveyance speed, productivity, and the like. If the temperature of the web 9 is too high, the web 9 tends to foam or the flatness of the web 9 tends to deteriorate.

  When blowing warm air, the wind pressure is preferably 50 to 5000 Pa in consideration of the uniformity of solvent evaporation and the like. Further, the blowing of warm air may be performed with the temperature of the warm air being constant, or may be performed in several steps in the running direction of the belt 6. The temperature of the warm air is preferably about 20 to 60 ° C., for example.

  The time from the formation of the web 9 on the belt 6 to the peeling of the web 9 from the belt 6 varies depending on the film thickness of the optical film to be produced and the solvent used, but the peelability from the belt 6 is taken into consideration. In the range of 0.5 to 5 minutes.

  The conveyance speed of the web 9 by the belt 6 (that is, the moving speed of the belt 6) is more preferably a high speed range of, for example, about 80 m / min to 200 m / min from the viewpoint of contributing to high-speed production of the optical film. Moreover, it is preferable that the ratio (draft ratio) of the conveyance speed of the web 9 by the belt 6 to the discharge speed of the resin solution from the casting die 3 is about 0.8 to 3.0. If the draft ratio is within this range, the web 9 can be formed stably. If the draft ratio is too large, a phenomenon called neck-in in which the web 9 contracts in the width direction tends to occur, which makes it difficult to manufacture a wide optical film.

(Peeling roll)
The peeling roll 8 is in contact with the surface of the belt 6 in a pressurized state, and peels the dried web 9 from the belt 6. The peeling tension at the time of peeling is preferably in the range of 20 to 400 N / m. In addition, the residual solvent amount of the web 9 at the time of peeling is preferably 30 to 200% by mass in consideration of peelability from the belt 6, transportability after peeling, physical properties of the optical film to be manufactured, and the like. .

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

(Stretching device)
The stretching device 20 holds the resin film in the longitudinal direction (MD direction) and / or the width direction by gripping both ends in the width direction of the resin film as the web 9 peeled from the belt 6 with a clip tenter, a pin tenter, or the like. Stretch in (TD direction).

  The stretching ratio in the TD direction of the resin film is preferably about 0 to 50%. In general, when the stretching ratio is increased, the optical value of the optical film tends to be nonuniform. By setting the stretching ratio to 0 to 50%, it is possible to suppress the optical value of the optical film from becoming nonuniform, and it is possible to obtain a wide optical film having a uniform optical value. Moreover, when the width | variety of an optical film is wide, it is preferable also from the point of use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency.

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

Moreover, the draw ratio in the MD direction is defined by the following equation.
Stretching rate in MD direction (%) = {(Conveying speed of film after stretching−Conveying speed of film before stretching) / Conveying speed of film before stretching} × 100

(Drying device)
The drying device 30 includes a plurality of transport rolls, passes the resin film in a meandering manner by each transport roll, and dries the resin film therebetween. At that time, the resin film may be dried using heated air, infrared rays or the like alone, or may be dried using heated air and infrared rays in combination. From the viewpoint of simplicity, it is preferable to use heated air. The drying temperature varies depending on the amount of residual solvent in the resin film, but may be appropriately selected and determined in the range of 30 to 180 ° C. in consideration of drying time, shrinkage unevenness, stability of the amount of stretching, and the like. Further, the resin film may be dried at a constant temperature, or may be dried in several steps (for example, 2 to 4 steps).

(Winding device)
The winding device 40 winds the resin film stretched by the stretching device 20 and dried by the drying device 30 as an optical film F to a winding core with a necessary length. The temperature at the time of winding is preferably cooled to room temperature (for example, 20 ° C.) in order to prevent scratches or loosening due to shrinkage after winding. The equipment used for winding can be used without any particular limitation and may be generally used. Winding methods such as constant tension method, constant torque method, taper tension method, program tension control method with constant internal stress, etc. Can be rolled up.

  Here, the width of the optical film F to be wound is preferably, for example, 1000 mm to 2500 mm. Such a wide optical film is preferable from the viewpoints of use in a large liquid crystal display device, use efficiency of the film during polarizing plate processing, and production efficiency. Further, the film thickness of the optical film F is preferably 15 μm to 60 μm, for example, from the viewpoint of contributing to thinning (thinning) of the polarizing plate and the liquid crystal display device and stabilizing production of the film. Here, the film thickness is an average film thickness. For example, the film thickness measuring device DH-150 manufactured by Tokyo Seimitsu Co., Ltd., a contact-type film thickness meter manufactured by Mitutoyo Co., Ltd., or the like is used. The film thickness is measured at 20 to 200 locations in the longitudinal direction and the width direction, and the average value of the measured values is shown as the film thickness.

  The film thickness deviation in the width direction and the longitudinal direction of the optical film F is 0.1 μm from the viewpoint that the good flatness of the optical film F is reliably maintained and the optical characteristics of the optical film F are further improved. It is preferable that it is -1.5micrometer.

[Details of decompression chamber and support roll]
FIG. 2 is an explanatory view showing an enlarged main part of the above-described optical film manufacturing apparatus. A gap t between the rear wall 4a of the decompression chamber 4 and the belt 6 is 0.3 to 3 mm. The rear wall portion 4a of the decompression chamber 4 refers to a wall portion located at the most upstream end (rear end) of the decompression chamber 4 in the moving direction of the belt 6.

  If the gap t is too wide, the accompanying air flowing into the gap t increases as the belt 6 travels, and this accompanying air shakes the casting ribbon, resulting in increased thickness unevenness. Therefore, the narrower the gap t, the better. However, if the gap is too narrow, the surface of the belt 6 and the surface of the decompression chamber 4 (the bottom surface of the rear wall 4a) come into contact with each other, and the surface of the belt 6 is damaged and the optical film is damaged. It cannot be obtained satisfactorily (for example, the shape of the scratch is transferred to the film surface). From the above points, it is preferable to arrange the decompression chamber 4 so that the gap t is within the above range.

  Further, in the present embodiment, in order to make the gap between the decompression chamber 4 and the belt 6 constant and eliminate the unevenness of the entrained wind flowing from there, the belt 6 may be directly under the rear wall 4a of the decompression chamber 4 or its The first support roll 11a is arranged in the vicinity so as to suppress the vibration of the belt 6 directly below or in the vicinity of the rear wall portion 4a.

  Here, in the moving direction of the belt 6, the center position of the rear wall portion 4a of the decompression chamber 4 is set as a reference (0 mm), and the direction toward the downstream side in the moving direction of the belt 6 is positive with respect to this reference, and the upstream side The direction toward is negative. In the present embodiment, the center of the belt wrap range (contact range with the belt 6) R1 in the moving direction of the belt 6 is set within the range of +100 mm to −300 mm with the center of the rear wall 4a as the reference. It is positioned to be. FIG. 2 shows a case where the center of the belt wrap range R1 of the first support roll 11a is at a position of 0 mm, that is, coincides with the reference position.

  By arranging the first support roll 11a as described above, even when the belt 6 is traveling at a high speed in order to perform high-speed film formation, the vibration of the belt 6 immediately below or near the rear wall 4a of the decompression chamber 4 Thus, the gap t (or the cross-sectional area of the flow path) can be kept constant. Thereby, it becomes possible to sufficiently suppress the strength unevenness of the accompanying wind flowing from the gap t, and it is possible to sufficiently suppress the thickness unevenness failure by suppressing the vibration of the casting ribbon due to the accompanying wind.

  The effect of suppressing the unevenness of the accompanying wind is higher as the center of the belt wrap range R1 of the first support roll 11a approaches the position of the rear wall 4a (directly below), so the center of the belt wrap range R1 is +30 mm to −100 mm. If it is in the range, the thickness unevenness failure can be further suppressed.

  Since the above-described thickness unevenness failure becomes apparent as the film formation speed increases, the manufacturing method of the present embodiment is more effective during high-speed production. That is, when the moving speed of the belt 6 is as high as 80 m / min to 200 m / min, the above-described manufacturing method of the present embodiment that suppresses thickness unevenness is very effective.

  In the present embodiment, the installation range of the first support roll 11a is wider in the negative direction (upstream side) than in the positive direction (downstream side) with respect to the center position of the rear wall 4a. The reason is as follows.

  As shown in FIG. 1, the web 9 is peeled from the belt 6 further upstream of the decompression chamber 4, and the vibration of the belt 6 accompanying this peeling is directed toward the decompression chamber 4 (that is, from the upstream side). Propagating. For this reason, even if the first support roll 11a is displaced upstream from the center position (reference) of the rear wall 4a of the decompression chamber 4, vibration is efficiently suppressed, and the rear wall 4a and the belt 6 The gap area between the two can be stabilized. For this reason, the installation range of the 1st support roll 11a is taken wide in the negative direction. In order to ensure that the gap area is minimized and stabilized, it is preferable to position the first support roll 11a directly below the rear wall 4a.

  Moreover, in this embodiment, as shown in FIG. 2, the other support roll is arrange | positioned as the 2nd support roll 11b directly under the casting die 3 via the belt 6. As shown in FIG. The dope discharged from the casting die 3 is landed in a range (belt wrap range R2) of the belt 6 that contacts the second support roll 11b. By doing in this way, it becomes possible to suppress the vibration of the belt 6 at the casting position by the second support roll 11b so that the casting ribbon is not shaken at the landing point. Therefore, by using the second support roll 11b together with the first support roll 11a, it becomes more effective in suppressing the thickness unevenness failure.

[Other configuration of decompression chamber]
FIG. 3 is an explanatory view showing another configuration of the decompression chamber 4 described above. As shown in the figure, a partition plate 4 b may be provided in the decompression chamber 4. The partition plate 4 b extends in the width direction of the web 9 to separate the inside of the decompression chamber 4 into a plurality of spaces S 1 and S 2, and communicates the plurality of spaces S 1 and S 2 only through gaps with the belt 6. In addition, the structure which provides the partition plate 4b in the pressure reduction chamber 4 is also disclosed by patent 4400768, for example.

  When the partition plate 4b is not provided, when the pressure is reduced in the decompression chamber 4, a flow of wind directly from the vicinity of the casting ribbon toward the suction port 4c is generated, which causes the casting ribbon to shake. However, by providing the partition plate 4b upright with respect to the belt 6, air in the space S1 is sucked from the suction port 4c through the gap between the partition plate 4b and the belt 6 and the space S2 during decompression. Is done. That is, there is no flow of wind directly from the vicinity of the casting ribbon toward the suction port 4c. As a result, it is possible to reduce the vibration of the casting ribbon caused by the suction air and the accompanying film thickness unevenness. That is, it is possible to reduce the influence of the wind blown into the casting ribbon by the partition plate 4b while reducing the unevenness of the accompanying wind by making the gap between the rear wall 4a of the decompression chamber 4 and the belt 6 minimum and constant. This is possible, and the effect of suppressing film thickness unevenness is further increased.

  FIG. 4 is an explanatory view showing still another configuration of the decompression chamber 4. As shown in the figure, a structure 4 d for controlling the airflow in the decompression chamber 4 during decompression may be provided in the decompression chamber 4 so as to extend in the width direction of the web 9. In addition, the structure which provides the structure 4d in the decompression chamber 4 is also disclosed by Unexamined-Japanese-Patent No. 2008-221760, for example.

  By arranging the structure 4d in the decompression chamber 4 in this way and controlling the airflow in the decompression chamber 4 at the time of decompression, the vortex flows at the time of decompression on the downstream side inside the decompression chamber 4 (that is, in the vicinity of the casting ribbon). Can be prevented from occurring. As a result, it is possible to reduce the occurrence of film thickness unevenness due to vibration of the casting ribbon caused by the vortex. Therefore, the effect of suppressing the film thickness unevenness can be further increased by using the installation of the first support roll 11a in the present embodiment and the installation of the structure 4d in the decompression chamber 4 together.

  The installation position of the structure 4d in the decompression chamber 4 may be a position where generation of vortex flow can be suppressed, may be in the vicinity of the casting ribbon, or directly below the suction port 4c. Alternatively, other positions may be used. Moreover, the cross-sectional shape of the structure 4d may be a shape that can control the airflow, may be a triangle, or may be another shape such as a quadrangle or a circle.

[About optical film materials]
In the method for producing an optical film by the solution casting method 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 invention are not impaired.

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

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

  In the present embodiment, the number average molecular weight of the cellulose ester is preferably in the range of 20,000 to 300,000, and more preferably in the range of 40,000 to 200,000, in that the mechanical strength of the film obtained is strong.

  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, a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt) can be used.

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

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

  The dope preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. These are gels that, after casting the dope onto the support, the solvent begins to evaporate and the proportion of alcohol increases, making the web gel, making the web strong and easy to peel off from the support It also serves as a solvating solvent or promotes dissolution of cellulose derivatives.

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

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

  The film 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, and deterioration of the film. You may contain the antioxidant etc. which prevent this.

  The plasticizer used in the present embodiment is not particularly limited, but is a cellulose derivative or a reactive metal compound capable of hydrolysis 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 by hydrogen bonding or the like.

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

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

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

The polyhydric alcohol used in this embodiment is represented by the following general formula (3).
Formula (3): R1- (OH) n
In the formula, R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.

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

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

  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 the present invention is not limited thereto.

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

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

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

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

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferable because it is less likely to volatilize, and a lower molecular weight is preferable 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 the phosphate ester plasticizer is not substantially contained.

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

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

  The amount of the plasticizer used is preferably 1 to 20% by mass, more preferably 6 to 16% by mass, and particularly preferably 8 to 13% by mass. If the amount of the plasticizer used is less than 1% by mass with respect to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. 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, 972, 972V, 974, 202, 812, 805, OX50, and TT600 manufactured by Nippon 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.

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

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

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

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

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

  The fine particles are used by adding 0.04 to 0.8 mass% with respect to the cellulose ester. Preferably, 0.05 to 0.5 mass%, more preferably 0.05 to 0.35 mass% is added and used. When the amount of fine particles added is less than 0.04% by mass, 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 0.8% by mass, the coefficient of friction on the film surface will be too low and winding deviation will occur during winding, or the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

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

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

  Examples of the high-pressure dispersion 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 examples include a Manton Gorin type high-pressure dispersion device such as Izumi Food Machinery. Examples thereof include a homogenizer.

  In this embodiment, fine particles are dispersed in a solvent containing 25 to 100% by mass of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is allowed to flow on a support. And is dried to form a cellulose ester film.

  Here, as a content rate of a lower alcohol, Preferably it is 25-100 mass%, More preferably, it is 50-100 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.

  In this embodiment, examples of the ultraviolet absorber that can be used include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. However, a benzotriazole-based compound with little coloring is preferable. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

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

  In this embodiment, specific examples of useful UV absorbers 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'-hydro Cis-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy 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 of which can be obtained commercially from BASF Japan) can be preferably used.

  Further, specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in the present embodiment include 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-methoxy-5. -Sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane) and the like can be mentioned, but are not limited thereto.

  In the present embodiment, the blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass with respect to the cellulose ester (cellulose derivative). If the amount of the UV absorber used is too small, the UV absorbing effect may be insufficient, and if the amount of the UV absorber used is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Moreover, as an ultraviolet absorber which can be used for the optical film of this embodiment, the polymeric ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357 is used. It can be preferably used. In particular, it is represented by the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formulas (3), (6), and (7) described in JP-A-2002-47357. A polymer ultraviolet absorber is preferably used.

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

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

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

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

  In the present embodiment, the cellulose ester film as the finally produced optical film desirably has a transmittance of 88% or more, more preferably 90% or more, and further preferably 92% or more.

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

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

〔Polarizer〕
When using the optical film which concerns on this embodiment as a transparent protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back surface side of the optical film according to the present embodiment, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  The polarizing plate which concerns on this embodiment is equipped with a polarizer and the transparent protective film arrange | positioned on the surface of the said polarizer, and the said transparent protective film is the said optical film. The polarizer is an optical element that emits incident light by converting it into polarized light.

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

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

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

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

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

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

  The optical film of the present embodiment is manufactured by suppressing unevenness in film thickness due to strong and weak unevenness of the accompanying wind, suppressing occurrence of lateral steps, having good flatness, and excellent optical characteristics. . Therefore, a high quality polarizing plate is realizable by applying such an optical film to the transparent protective film of a polarizing plate.

<Liquid crystal display device>
By incorporating a polarizing plate in which the optical film according to this embodiment is bonded as a protective film for a liquid crystal polarizing plate into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. In particular, the polarizing plate is preferably used for a liquid crystal display device for outdoor use such as a large-sized liquid crystal display device or digital signage. The polarizing plate according to the present embodiment is bonded to the liquid crystal cell via an adhesive layer or the like.

  The polarizing plate according to the present embodiment is a reflective, transmissive, transflective LCD or TN, STN, OCB, HAN, VA (PVA, MVA), IPS (including FFS). It is preferably used in LCDs of various drive systems such as. In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time. In addition, there is little color unevenness, glare and wavy unevenness, and there is an effect that eyes are not tired even during long-time viewing.

〔Example〕
Examples of the present embodiment will be described below, but the present invention is not limited to these.

<Example 1>
(Preparation of dope)
The following materials were put into a sealed container, heated, stirred and completely dissolved, and filtered to prepare a dope.

<Dope composition>
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 1 part by weight AEROSIL 200V 0.1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight

(Manufacture of cellulose ester film)
Next, the cellulose-ester film as an optical film was manufactured using the optical film manufacturing apparatus shown in FIG. As the belt 6 for casting the dope, an endless belt made of SUS316 and polished to a super mirror surface with a three-dimensional surface roughness (Ra) of 1.0 nm on average by a scanning atomic force microscope (AFM) was used. .

  Subsequently, the dope filtered as described above is uniformly cast on the belt 6 at a temperature of 25 ° C. by the casting die 3 made of a coat hanger die to form a web 9 on the belt 6. did. At this time, a plurality of support rolls 11 supporting the belt 6 were installed on the back surface side of the belt 6, and one of them (the first support roll 11 a) was installed on the upstream side of the casting die 3. It was arranged directly under the decompression chamber 4. At that time, in the movement direction of the belt 6, when the center position of the rear end portion 4a of the decompression chamber 4 is set as a reference (0 mm) and the belt movement direction is positive, the belt wrap range R1 of the first support roll 11a. The 1st support roll 11a was installed so that a center may become a position of -200 mm from the said reference | standard. The moving speed of the belt 6 was 100 m / min, and the degree of vacuum in the vacuum chamber 4 was −500 Pa.

  In this way, the web 9 formed on the belt 6 was dried on the belt 6 with a drying air kept constant at a temperature of 40 ° C. while being conveyed on the belt 6, and then peeled off from the belt 6 by the peeling roll 8. Thereafter, after stretching 1.1 times in the width direction in an atmosphere of 100 ° C. when the residual solvent amount is 10% by the stretching device 20, the width is released and the roll is transported by the drying device 30 at 125 ° C. Drying was terminated, and winding was performed by the winding device 40. The obtained cellulose triacetate film (optical film F) had a film thickness of 40 μm, a film width of 2000 mm, and a film winding length of 3000 m.

<Example 2>
In Example 2, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is located at −280 mm from the above reference. The rest is the same as in the first embodiment.

<Example 3>
In Example 3, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is at a position of −120 mm from the reference. The rest is the same as in the first embodiment.

<Example 4>
In Example 4, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is at a position of −80 mm from the reference. The rest is the same as in the first embodiment.

<Example 5>
In Example 5, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is at a position of −50 mm from the reference. The rest is the same as in the first embodiment.

<Example 6>
In Example 6, an optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 was 20 mm from the above reference. The rest is the same as in the first embodiment.

<Example 7>
In Example 7, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is 50 mm from the reference. The rest is the same as in the first embodiment.

<Example 8>
In Example 8, the optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is 80 mm from the reference. The rest is the same as in the first embodiment.

<Comparative Example 1>
In Comparative Example 1, an optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is at a position of −320 mm from the reference. The rest is the same as in the first embodiment.

<Comparative example 2>
In Comparative Example 2, an optical film was manufactured by installing the first support roll 11a so that the center of the belt wrap range R1 is at a position of 120 mm from the reference. The rest is the same as in the first embodiment.

(Evaluation method)
<Horizontal evaluation>
It was visually observed whether or not horizontal steps (thickness unevenness in the longitudinal direction of the optical film) extending in the width direction occurred in the manufactured optical film, and evaluated according to the following criteria. The results are shown in Table 1.

<Evaluation criteria>
A: The horizontal row cannot be confirmed.
B: The horizontal stage can be confirmed, and the pitch is less than 3 mm.
C: The horizontal stage can be confirmed, and the pitch is 3 mm or more.

  From Table 1, in Examples 1-8, the evaluation result of horizontal stage unevenness is A or B, and it turns out that the film thickness nonuniformity (horizontal stage nonuniformity) of the optical film manufactured can be reduced. In the first to eighth embodiments, the belt 6 is driven at a high speed by positioning the first support roll 11a so that the center of the belt wrap range R1 is within the range of +80 mm to −280 mm from the reference. Even in this case, the vibration of the belt 6 immediately below or near the rear wall portion 4a of the decompression chamber 4 is suppressed by the first support roll 11a, whereby the gap between the rear wall portion 4a and the belt 6 becomes constant. This is considered to be because the unevenness of the accompanying wind flowing from the gap is suppressed, and the vibration of the casting ribbon due to the accompanying wind is suppressed. In particular, in Examples 4 to 6, the evaluation result of the horizontal unevenness is A. This is because the first support roll 11a approaches the position immediately below the rear wall 4a of the decompression chamber 4 in the moving direction of the belt 6. Thus, it is considered that the effect of suppressing the vibration of the belt 6 and suppressing the unevenness of the accompanying wind is increased, and the effect of suppressing the vibration of the casting ribbon is increased.

  On the other hand, in Comparative Examples 1 and 2, the evaluation result of the horizontal unevenness is C. In Comparative Examples 1 and 2, since the center of the belt wrap range R1 is too far from the reference position, when the belt 6 is run at a high speed, the belt lap range R1 is located immediately below or near the rear wall 4a of the decompression chamber 4. It is considered that the vibration of the belt 6 cannot be efficiently suppressed by the first support roll 11a, and as a result, the vibration of the casting ribbon is caused by the unevenness of the accompanying wind.

  In addition, between Example 8 (first support roll position: 80 mm) and Comparative Example 2 (first support roll position: 120 mm), and Example 2 (first support roll position: -280 mm) and Comparative Example 1 ( The first support roll position: −320 mm) is considered to be the boundary of the first support roll position that can suppress the occurrence of the horizontal stage. Therefore, if the first support roll 11a is positioned so that the center of the belt wrap range R1 is within the range of +100 mm to −300 mm from the above reference, it is considered that the occurrence of a horizontal step can be suppressed.

  Further, between Example 6 (first support roll position: 20 mm) and Example 7 (first support roll position: 50 mm), and Example 4 (first support roll position: −80 mm) and Example 3 ( The first support roll position: −120 mm) is considered as the boundary of the first support roll position at which the horizontal evaluation result A is obtained. Therefore, if the first support roll 11a is positioned so that the center of the belt wrap range R1 is within the range of +30 mm to −100 mm from the above reference, it is considered that the occurrence of the horizontal stage can be further suppressed.

<Example 9>
In the ninth embodiment, as shown in FIG. 2, a second support roll 12a is further disposed directly below the casting die 3 via the belt 6, and the belt 6 is within the belt wrap range R2 of the second support roll 11b. The dope discharged from the casting die 3 was landed to produce an optical film. The rest is the same as in the first embodiment.

<Example 10>
In Example 10, as shown in FIG. 3, the partition plate 4b was disposed in the decompression chamber 4 to produce an optical film while decompressing. The rest is the same as in the first embodiment.

<Example 11>
In Example 11, as shown in FIG. 4, the structure 4d was placed in the decompression chamber 4 to produce an optical film while decompressing. The rest is the same as in the first embodiment.

  Table 2 shows the horizontal evaluation results for Examples 1 and 9 to 11.

  From Table 2, in Examples 9-11, compared with Example 1, the evaluation result of a horizontal stage goes up 1 rank and is set to A. Therefore, in addition to the first support roll 11a, it can be said that the occurrence of the horizontal stage can be further suppressed by arranging any one of the second support roll 11b, the partition plate 4b, and the structure 4d.

  In addition, although the above demonstrated the manufacturing method of the optical film as a protective film for polarizing plates used for a liquid crystal display device (LCD, liquid crystal display), the manufacturing method mentioned above is retardation film used for a liquid crystal display device, The present invention can also be applied to the production of various functional films such as a viewing angle widening film and an antireflection film used for a plasma display.

  The present invention can be used, for example, for the production of various functional films such as a protective film for a polarizing plate used in a liquid crystal display device, a retardation film, a viewing angle widening film, and an antireflection film used in a plasma display.

3 Casting die 4 Depressurization chamber 4a Rear wall 4b Partition plate 4d Structure 5 Drum 6 Belt (support)
7 drum 9 web (casting film)
11 support roll 11a first support roll 11b second support roll F optical film

Claims (6)

A method for producing an optical film comprising casting a dope from a casting die on a moving support, and forming an optical film by a solution casting method in which the casting film is peeled off from the support,
The support is a belt stretched between two drums,
The dope is cast on the belt between the two drums;
A decompression chamber is arranged upstream of the casting die in the moving direction of the belt so that a gap with the belt is 0.3 to 3 mm,
Arranging at least one support roll to support the belt from the inner peripheral surface side;
In the moving direction of the belt, the center position of the rear wall portion on the upstream side of the decompression chamber is used as a reference, the direction toward the downstream side in the moving direction of the belt with respect to the reference is positive, and the direction toward the upstream side is When negative,
One of the support rolls is a first support roll, and the center of the contact range with the belt in the moving direction of the belt is in a range of +100 mm to −300 mm with respect to the center position of the rear wall portion. A method for producing an optical film, comprising:   Another support roll is arranged as a second support roll directly below the casting die through the belt, and the dope discharged from the casting die is within a range where the belt comes into contact with the second support roll. The method for producing an optical film according to claim 1, wherein landing is performed.   The first support roll is positioned such that a center of a contact range with the belt in a moving direction of the belt is in a range of +30 mm to −100 mm with respect to a center position of the rear wall portion. The manufacturing method of the optical film of Claim 1 or 2.   A partition plate that extends in the width direction of the casting film and separates the interior of the decompression chamber into a plurality of spaces and communicates the plurality of spaces only through a gap with the belt is provided in the decompression chamber. The method for producing an optical film according to claim 1, wherein the optical film is produced.   4. The structure according to claim 1, wherein a structure for controlling an air flow in the decompression chamber during decompression is provided in the decompression chamber so as to extend in a width direction of the casting film. A method for producing the optical film according to claim 1.   The method for producing an optical film according to any one of claims 1 to 5, wherein the moving speed of the belt is 80 m / min to 200 m / min.

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