JP6015552B2 - Manufacturing method of optical film - Google Patents

Description

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

  In recent years, liquid crystal display devices such as notebook personal computers, televisions, large monitors, and the like have been developed to be thinner and lighter, larger screens, and higher definition. Along with this, the demand for thinner, wider and higher quality protective films for polarizing plates of liquid crystal display devices has become stronger. Further, as the cost of optical films is reduced, a technique for increasing the film forming speed is required.

  In the solution casting (film forming) method, which is one of the methods for forming an optical film, it is well known that the casting process of casting a dope on a traveling support is rate limiting (slow speed). In this casting process, an accompanying wind is generated. The accompanying air refers to the air flow in the vicinity of the support surface generated by the travel of the support. Therefore, if the moving speed of the support is increased in order to increase the film forming speed, the wind speed of the accompanying air and the strength tends to increase. Therefore, the dope discharged from the casting die is likely to vibrate due to the collision of the accompanying wind before landing on the support. As a result, film thickness unevenness (horizontal stage) occurs in the optical film, and the problem that the flatness of the optical film is impaired is more likely to occur.

  One countermeasure for suppressing the influence of the accompanying wind on such a dope (particularly, a casting ribbon until landing on the support) is disclosed in Patent Document 1, for example. In Patent Document 1, a decompression chamber is arranged upstream of the casting die in the moving direction of the support, and the space on the upstream side of the casting ribbon is decompressed by this decompression chamber, so that the accompanying air is sucked and removed. I am doing so.

  However, the countermeasures for sucking and removing the accompanying air in the decompression chamber have the following problems. That is, as the moving speed of the support increases as the production speed increases, the negative pressure in the decompression chamber needs to be increased. If the negative pressure is excessively increased, the casting ribbon is vibrated by the suction air to the decompression chamber this time, resulting in an increase in film thickness unevenness. In addition, there is a limit to increasing the negative pressure in the decompression chamber.

  On the other hand, recently, as in Patent Document 2, by installing a moving body that moves (rotates) in the direction opposite to the moving direction of the support body around the decompression chamber, the accompanying wind does not greatly change. A method for suppressing the influence on the casting ribbon has also been proposed. However, although this method has a certain effect in the suppression of the accompanying wind, it actively generates a reverse wind to collide with the accompanying wind. There is a concern that the influence of the wind may reach the peeling part of the film (web) on which the dope is dried to some extent on the support, and peeling unevenness occurs due to the vibration of the web at the peeling part, which appears as film thickness unevenness. The Therefore, it is desirable to be able to reduce the influence of the accompanying wind without positively generating a reverse wind for canceling the accompanying wind by the moving body.

  The conventional production speed and product film thickness were not particularly problematic, but the further increase in speed caused an increase in the entrained wind, which resulted in an increase in the amount of air to be collided and the thinning of the casting ribbon. It became clear that the product defect of the film thickness nonuniformity became obvious by becoming easy to vibrate.

JP 2002-144357 A (see paragraphs [0008] to [0015], FIG. 1 and the like) JP 2012-171177 A (refer to claim 1, FIG. 2, etc.)

  In view of the above circumstances, the object of the present invention is to increase the film forming speed in the solution casting method, without increasing the negative pressure of the decompression chamber, and to reverse the accompanying wind. An optical film manufacturing method capable of suppressing the influence of the accompanying air on the casting ribbon without being actively generated by the moving body and thereby suppressing the occurrence of film thickness unevenness is provided. There is.

  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,
A decompression chamber is arranged upstream of the casting die in the moving direction of the support,
Arranging a stationary air shielding member made of at least one structure upstream of the decompression chamber,
In the case where the wind shield member is composed of one structure, the narrowest distance between the rear wall portion on the upstream side of the decompression chamber and the structure is set to L (mm), while there are a plurality of wind shield members. In the case of the above structure, the narrowest interval between the structure disposed in close contact with the rear wall portion and another structure disposed further upstream is defined as L (mm).
When the narrowest distance between the support and the wind shielding member is H (mm),
0 mm <L ≦ 50 mm and 0 mm <H ≦ 20 mm
The manufacturing method of the optical film characterized by the above-mentioned.

2. The support body when the surrounding wind that flows through the flow path formed at the narrowest interval L collides with the support-side-side accompanying air flowing between the support body and the wind shielding member when the support body moves. When the collision angle of the surrounding wind from the direction perpendicular to the direction is 0 °, and the direction in which the collision angle increases toward the downstream side of the moving direction of the support with respect to 0 ° is positive,
2. The optical film according to 1 above, wherein the direction of the synthetic vector of the peripheral wind when passing through the lowermost surface of the flow path on the support side is within a range of −30 ° to 80 °. Method.

3. 0 mm <L ≦ 10 mm and 0 mm <H ≦ 5 mm
3. The method for producing an optical film as described in 1 or 2 above.

4). When the wind shield member is the first wind shield member,
From the above 1, the second wind-shielding member made of at least one structure is disposed outside the side wall portion of the decompression chamber at a predetermined interval from the decompression chamber and the support. 4. A method for producing an optical film according to any one of 3 above.

  5. 5. The method for producing an optical film according to any one of 1 to 4, wherein a gap between the decompression chamber and the support is smaller than a gap between the wind shielding member and the support.

  6). 6. The method for producing an optical film as described in any one of 1 to 5, wherein the moving speed of the support is from 80 m / min to 200 m / min.

  According to the above manufacturing method, the accompanying wind generated along with the movement of the support is converted into the surrounding wind (wind passing through the flow path with the narrowest interval L) and the support-side accompanying wind (narrowest) by the stationary wind shielding member. The wind passing through the channel with the interval H) and then colliding them to reduce the entire accompanying wind. At this time, since the range of the narrowest interval L and the narrowest interval H is appropriately defined, it is possible to reliably reduce the accompanying wind by causing the peripheral wind to collide with the accompanying wind on the support side. As a result, even when the film forming speed is increased in the solution casting method, the influence of the entrained air on the casting ribbon is suppressed without increasing the negative pressure in the decompression chamber, thereby suppressing the occurrence of film thickness unevenness. can do. In addition, since the stationary wind shielding member is used without using the moving body, there is no need to worry about the influence of the wind in the direction opposite to the accompanying wind generated when the moving body is used. In the present specification, “disposing the windshield member and making it stand still” means that the windshield member is kept fixed without being moved or rotated during the production of the optical film. Represents that. The wind-shielding member may be installed so as to be movable in the film transport direction or orthogonal direction for position adjustment, etc., and the wind-shielding member must be moved before or after the production of the optical film. Is not excluded.

  That is, according to the manufacturing method described above, even when high-speed film formation is performed, the moving body positively generates the reverse wind for canceling the accompanying wind without increasing the negative pressure in the decompression chamber. Without the influence of the accompanying wind on the casting ribbon, it is possible to suppress the occurrence of film thickness unevenness.

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 shows the other structure of the said manufacturing apparatus. It is sectional drawing which expands and shows a part of said decompression chamber while showing the casting die and decompression chamber of the said manufacturing apparatus. It is sectional drawing of the 1st wind-shielding member arrange | positioned in the rear wall part of the said pressure reduction chamber, and its upstream. It is explanatory drawing which shows the flow of the wind around the said 1st wind-shielding member. It is sectional drawing which shows the other structure of the said 1st wind shielding member. It is sectional drawing which shows the other structure of the said 1st wind shielding member. It is sectional drawing which shows the other structure of the said 1st wind shielding member. It is sectional drawing which shows the other structure of the said 1st wind shielding member. It is sectional drawing which shows the other structure of the said 1st wind shielding member. It is explanatory drawing for demonstrating the direction of the surrounding wind produced by the said 1st wind-shielding member. It is explanatory drawing which shows the direction in each position of the flow-path bottom surface of the said surrounding wind. It is explanatory drawing which shows the synthetic | combination vector which synthesize | combined the direction in each position of the flow-path bottom surface of the said surrounding wind. It is a perspective view which shows the other structure of the principal part of the said manufacturing apparatus.

  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.

[Optical film manufacturing equipment]
FIG. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus used in the present embodiment. The optical film manufacturing method of the present embodiment uses a solution casting method in which a dope containing a polymer and a solvent is cast from a casting die on a traveling support and then peeled off as a film. Hereinafter, the manufacturing method will be described in more detail.

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

  Next, the dope adjusted in the melting pot 1 is fed to the casting die 3 by a conduit through a pressurized metering gear pump 2, and cast on a support 6 made of a rotationally driven stainless steel endless belt that is infinitely transported. The dope is cast from the casting die 3 at a position, thereby forming a web 9 as a casting film on the support 6. At this time, the pressure reducing mechanism 4 is arranged on the upstream side in the moving direction of the traveling support 6 with respect to the casting die 3, and the pressure reducing mechanism 4 causes the upstream side of the casting die 3 (particularly the casting die 3). The dope is cast on the support 6 from the casting die 3 while reducing the space on the upstream side of the casting ribbon from the support 6 to the support 6.

  Further, on the upstream side of the decompression chamber 4, a wind shielding member 21 (see FIG. 4) for reducing the accompanying air (air flow in the vicinity of the surface of the support 6) generated with the movement of the support 6. The details of the wind shielding member 21 will be described later.

  The dope is cast by the casting die 3 using a doctor blade method in which the film thickness of the cast web is adjusted by a blade, a method by a reverse roll coater in which the film thickness is adjusted by a reverse rotating roll, There is a method using a pressure die. Among them, a method using a pressure die is preferable because the slit shape of the base portion can be adjusted and the film thickness can be easily made uniform. The pressure die includes a coat hanger die and a T die, and any of them can be preferably used.

  The support 6 is held by a pair of front and rear drums 5 and 5 and a plurality of intermediate rolls (not shown). One or both of the drums 5 and 5 are provided with a driving device (not shown) for applying tension to the support body 6, whereby the support body 6 is used in a tensioned state.

  The width of the support 6 is preferably 1000 to 3000 mm, and the width of the film after winding is preferably 1000 to 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  In the case of using an endless belt as the support 6, the belt temperature during film formation is 0 ° C. to less than the boiling point of the solvent in a general temperature range, but the mixed solvent is less than the boiling point of the lowest boiling solvent. In particular, the range of 5 ° C. to the boiling point of the solvent −5 ° C. is more preferable. At this time, it is necessary to control the ambient atmospheric humidity above the dew point. In addition, it is preferable that the moving speed of the support body 6 is 80 m / min-200 m / min.

  The dope cast on the support 6 in this way also increases the strength of the gel film (film strength) by promoting drying until stripping.

  On the support 6, since the web 9 is dried and solidified until the film strength becomes detachable from the support 6 by the peeling roll 8, the residual solvent amount in the web 9 is preferably 200% by weight or less, 120% by weight is more preferred. Moreover, it is preferable that the web temperature when peeling the web 9 from the support body 6 is 0-30 degreeC. Further, immediately after the web 9 is peeled off from the support 6, the temperature once drops rapidly due to solvent evaporation from the contact surface side with the support 6, and volatile components such as water vapor and solvent vapor in the atmosphere tend to condense. Therefore, the web temperature during peeling is more preferably 5 to 30 ° C.

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

  The web 9 formed by the dope cast on the support 6 is heated on the support 6, and the solvent is evaporated until the web can be peeled from the support 6 by the peeling roll 8.

  In order to evaporate the solvent, there are a method in which air is blown from the web side, a method in which heat is transferred from the back surface of the support 6 by liquid, a method in which heat is transferred from the front and back by radiant heat, and the like. That's fine.

  The peeling tension when peeling the support 6 and the web 9 by the peeling roll 8 is larger than the peeling force obtained by measuring the peeling force as in JIS Z 0237. If it is equivalent to the peel force obtained by the measurement method, the peel position may be taken downstream, so it is increased for stabilization. In addition, even if it forms into a film with the same peeling tension in a process, if the peeling force by a JIS measuring method falls, it has also been confirmed that the variation in the cross nicols permeability (CNT) of a film reduces significantly.

  The peeling tension value in the process is usually 20 to 400 N / m. However, in the optical film produced by making the film thinner than before, the residual solvent amount of the web 9 is large at the time of peeling, and it is easy to extend in the conveying direction. For this reason, the film tends to shrink in the width direction, and when drying and shrinkage overlap, the end curls and folds, so that wrinkles are likely to occur. For this reason, it is preferable that peeling tension is the minimum tension which can peel -300N / m, More preferably, it is minimum tension-200N / m.

  After drying and solidifying until the web 9 has a peelable film strength on the support 6, the web 9 is peeled off by the peeling roll 8, and then the web 9 is stretched in the tenter 10 in the stretching step.

  In the stretching step, a tenter system in which both side edges of the web 9 are fixed with clips or the like and stretched is preferable as the liquid crystal display device film in order to improve the flatness and dimensional stability of the film.

  The residual solvent amount of the web 9 immediately before entering the tenter 10 in the stretching step is preferably 5 to 50% by weight, and more preferably 10 to 35% by weight. Moreover, the stretch ratio of the web in the tenter 10 in the stretching process is 3 to 100%, preferably 5 to 80%, and more preferably 5 to 60%.

  Moreover, the temperature of the warm air blown from the warm air blowing slit port in the tenter 10 is 70 to 200 ° C, preferably 110 to 190 ° C, and more preferably 115 to 185 ° C.

  It is preferable to provide the drying apparatus 11 after the tenter 10 in the stretching step. In the drying device 11, the web 9 is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, and the web 9 is dried in the meantime. Further, the film transport tension in the drying device 11 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 10 to 400 N / m. The width is more preferably 20 to 300 N / m.

  The means for drying the web 9 is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the point of simplicity. For example, the web 9 can be dried by blowing the drying air 12 from the hot air inlet of the drying device 11 and exhausting the exhaust air from the outlet of the drying device 11, so that the optical film F can be obtained. The temperature of the drying air 12 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 conveyance drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  For the optical film F that has finished the transport drying process, before introducing it into the winding process, in order to prevent winding slippage and blocking (sticking between films) in the winding process, at the end of the optical film F It is preferable to form an embossed portion having a large number of irregularities.

  Next, the film in which the embossed portion has been formed is taken up by the take-up device 13 to obtain the original roll of the optical film F. By setting the residual solvent amount of the film at the end of drying to 0.5% by weight or less, preferably 0.1% by weight or less, a film having good dimensional stability can be obtained.

  The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. Use it properly. The film may be bonded to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape. The optical film F preferably has a width of 1000 to 2500 mm after winding.

  The film thickness after drying of a resin film such as cellulose ester is preferably in the range of 15 to 100 μm as a finished film from the viewpoint of thinning the liquid crystal display device. Here, the film thickness after drying means the film thickness when the amount of residual solvent in the film is 0.5% by weight or less.

  If the film thickness of the optical film after winding is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. On the other hand, if the film thickness is too thick, the advantage of thinning the film over conventional resin films such as cellulose ester is lost. In adjusting the film thickness, the dope concentration, the pumping amount, the slit gap of the die of the casting die 3, the extrusion pressure of the casting die 3, the speed of the support 6 and the like are adjusted so as to obtain a desired thickness. It is good to control. 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.

  FIG. 2 is an explanatory view showing another configuration of the optical film manufacturing apparatus. As shown in the figure, a drum-like support 7 can be used instead of the belt-like support 6 as a casting support. The support 7 is a stainless steel rotary drive drum having a hard chrome plated surface. Even when such a support 7 is used, an optical film can be produced in the same manner as when the support 6 is used.

[About wind shield]
FIG. 3 is a cross-sectional view showing the casting die 3 and the decompression chamber 4 of the above-described optical film manufacturing apparatus, and a part of the decompression chamber 4 being enlarged. When the inventor conducted an air flow analysis around the decompression chamber 4 during the movement of the support body 6 by 3D fluid simulation (FLOW-3D), the gap between the rear wall portion 4a of the decompression chamber 4 and the support body 6 was analyzed. It was found that the wind was blowing from a very wide angle. Note that the rear wall portion 4 a of the decompression chamber 4 refers to a wall portion located at the most upstream end (rear end) of the decompression chamber 4.

  Therefore, in the present embodiment, as shown in FIG. 4, the wind shielding member 21 (first wind shielding member) is disposed in a stationary state on the upstream side of the rear wall portion 4 a of the decompression chamber 4. At this time, the wind shielding member 21 is positioned away from the rear wall portion 4a so as to satisfy the range of the narrowest interval L described later, and is separated from the support 6 so as to satisfy the range of the narrowest interval H described later. Position. Here, it is assumed that the wind-shielding member 21 is composed of a single plate-like structure 31.

  In this way, by arranging the wind shielding member 21 on the upstream side of the decompression chamber 4, as shown in FIG. 5, the wind blown into the gap between the rear wall portion 4 a and the support 6 when the support 6 is moved (entrained) Wind) is divided into two by the wind shielding member 21 into the support side accompanying wind W1 flowing near the surface of the support 6 and the surrounding wind W2 other than the support side accompanying wind W1, and then the direction of the surrounding wind W2 is changed. It can be made to collide with the support body side accompanying wind W1. That is, the wind-shielding member 21 sends the support-side accompanying wind W1 into the flow path with the narrowest interval H, and sends the peripheral wind W2 into the flow path with the narrowest interval L, so that the gap between the rear wall portion 4a and the support 6 is reduced. In the vicinity, the surrounding wind W2 can collide with the support-side accompanying wind W1 from a different direction. As a result, the support-side accompanying wind W1 is weakened or extinguished by the peripheral wind W2, and the entire accompanying wind blown into the gap between the rear wall portion 4a and the support 6 is reduced.

  Therefore, in the solution casting method, even when the moving speed of the support 6 is increased (even when the film forming speed is increased), the entrained wind casting ribbon is not increased without increasing the negative pressure of the decompression chamber 4. The influence on can be suppressed. As a result, the film thickness unevenness (occurrence of horizontal steps) of the optical film can be suppressed, and the flatness of the optical film can be ensured. In addition, since the film thickness unevenness can be suppressed with a simple configuration in which the wind shielding member 21 is arranged on the upstream side of the decompression chamber 4, the cost is low.

  Moreover, in the structure which reduces an accompanying wind using a moving body like the past, the wind of the reverse direction to the flow of an accompanying wind which arises by the movement (rotation) of a moving body reaches the peeling roll 8, and there There is a concern that film thickness unevenness may occur due to uneven peeling of the web 9. In the present situation where film formation is speeding up and thinning, it can be a risk to generate wind by a moving body. However, in the present embodiment, the windbreak member 21 is stopped and the accompanying wind accompanying the movement of the support 6 is separated and collided by the windshield member 21 to reduce the accompanying wind. There is no need to worry about the effect of the reverse wind.

  That is, according to the manufacturing method of the present embodiment, even when high-speed film formation is performed, the moving body positively applies the reverse wind for canceling the accompanying air without increasing the negative pressure of the decompression chamber 4. Without generating, the influence of the accompanying wind on the casting ribbon can be suppressed, and the occurrence of film thickness unevenness can be suppressed. In particular, since the thickness unevenness failure becomes obvious as the film formation speed increases, the film thickness unevenness can be suppressed when the moving speed of the support 6 is as high as 80 m / min to 200 m / min. The method of the embodiment is very effective. In addition, even when an ultra-thin film is formed at a high speed, it is possible to avoid the occurrence of optical film quality failure, demand for a thinner and higher quality protective film for liquid crystal polarizing plates, and improved productivity. Can also respond.

  Here, when the narrowest distance L between the rear wall portion 4a of the decompression chamber 4 and the wind shielding member 21 (structure 31) is 0 mm, the flow of the ambient wind W2 between the rear wall portion 4a and the wind shielding member 21 is reduced. Since no road is formed and the surrounding wind W2 cannot collide with the support-side accompanying wind W1, it is not preferable. On the other hand, when the narrowest interval L exceeds 50 mm, wind turbulence occurs in the flow path, and the amount of the surrounding wind W2 that collides with the support-side accompanying wind W1 is weakened. Therefore, it is desirable that the narrowest interval L (mm) is 0 mm <L ≦ 50 mm. Further, in order to further increase the air volume of the peripheral wind W2, it is desirable to further narrow the narrowest interval L. From such a viewpoint, the narrowest distance L (mm) is more preferably 0 mm <L ≦ 10 mm.

  On the other hand, if the narrowest distance H between the support 6 and the wind shielding member 21 is 0 mm, the surface of the support 6 and the surface of the wind shielding member 21 come into contact with each other, and the surface of the support 6 is damaged and the optical film. Cannot be obtained satisfactorily (for example, the shape of the scratch is transferred to the film surface), which is not preferable.

  Further, when the wind shield member 21 is arranged, if the gap between the support 6 and the wind shield member 21 is narrow, the wind speed of the wind passing therethrough increases, and the pressure around it decreases as the wind speed increases. Do (Bernoulli's theorem). Therefore, if there is another flow path guided to the gap, the wind is drawn through the flow path. In the present embodiment, the wind-shielding member 21 separates the support-side accompanying wind W1 and the surrounding wind W2, and aims to cause the surrounding wind W2 to flow only from a specific flow path and collide with the support-side accompanying wind W1. . Since the surrounding wind W2 is drawn on the same principle as that of the aspirator, there is no problem even if the height of the wind shielding member 21 is large as shown in FIG. 6, but the narrowest distance H between the support 6 and the wind shielding member 21 is In order to reliably realize the pull-in of the ambient wind W2, it is preferable not to exceed 20 mm, and more preferable not to exceed 5 mm.

  In summary, it can be said that the narrowest interval H (mm) is preferably 0 mm <H ≦ 20 mm, and more preferably 0 mm <H ≦ 5 mm.

  FIG. 7 is a cross-sectional view showing another configuration of the wind shielding member 21. The structure 31 constituting the wind shielding member 21 may be cylindrical (roll shape). Even in this case, by arranging the structure 31 such that the narrowest interval L and the narrowest interval H are within the above range, the effect of the above-described embodiment can be obtained. The structure 31 may have an elliptic cylinder shape or other shapes.

  8 to 10 are cross-sectional views showing still other configurations of the wind shielding member 21. The wind shielding member 21 may be composed of a plurality of structures 31 and 32. In this case, each of the structures 31 and 32 may have a plate shape (cuboid shape) or a triangular prism shape. When such a wind shielding member 21 is disposed upstream of the decompression chamber 4, one structure 31 of the wind shielding member 21 is disposed in close contact with the rear wall portion 4 a of the decompression chamber 4, and the other structure 32 is disposed. The structure 31 may be disposed on the upstream side of the structure 31 with the narrowest distance L from the structure 31.

  Thus, even when the wind-shielding member 21 is composed of a plurality of structures 31 and 32, the structures 31 and 32 are arranged so as to ensure the flow path with the narrowest interval L through which the peripheral wind W2 passes as described above. By disposing, the surrounding wind W2 can collide with the support-side accompanying wind W1 to reduce the accompanying wind.

[Direction of the surrounding wind during a collision]
FIG. 11 is an explanatory diagram for explaining the direction of the surrounding wind W2 that collides with the support-side accompanying wind W1. When the support 6 moves, the peripheral wind W2 flowing through the flow path formed at the narrowest interval L collides with the support-side accompanying wind W1 flowing between the support 6 and the wind shielding member 21. The collision angle of the surrounding wind W2 from the direction perpendicular to 6 is set to 0 °. The direction in which the collision angle increases toward the downstream side in the moving direction of the support 6 with respect to 0 ° is positive (the direction in which the collision angle increases toward the upstream side with respect to 0 ° is negative). ). In this case, the direction of the combined vector P of the peripheral wind W2 when the peripheral wind W2 passes through the lowermost surface (virtual surface) S on the support 6 side of the flow path formed at the narrowest interval L is −30 °. It is desirable to be within the range of ˜80 °. In addition, about the direction of the synthetic | combination vector P, it can obtain | require by the analysis by 3D fluid simulation (FLOW-3D).

  Here, the synthetic vector P is considered because the case where a columnar structure 31 as shown in FIG. That is, the direction of the vector in the traveling direction of the peripheral wind W2 in the flow path formed at the narrowest interval L is one direction (uniformly downward) when the plate-like structure 31 is used as the wind shielding member 21. When the columnar structure 31 is used as the wind shielding member 21, it changes depending on the position passing through the lowermost surface S as shown in FIG. For this reason, as shown in FIG. 13, a combined vector P obtained by combining vectors in the traveling direction of the peripheral wind W2 on the lowermost surface S is considered.

  When the direction of the composite vector P at the lowermost surface S of the flow path of the peripheral wind W2 is less than −30 ° (increases to the negative side), the direction of the peripheral wind W2 approaches the direction of the support-side accompanying wind W1. The effect of reducing the accompanying wind due to the collision of the wind W2 is reduced. In addition, it is difficult to form a flow path in which the direction of the composite vector P exceeds 80 ° because the structure of the wind shielding member 21 is complicated. Therefore, the wind shielding member 21 is configured and arranged so that the direction of the composite vector P falls within the range of −30 ° to 80 °, thereby reliably obtaining the effect of reducing the accompanying wind due to the collision and the effect. Can be easily obtained using the wind shielding member 21.

  When the gap between the decompression chamber 4 and the support 6 is t1 (mm) and the gap between the wind shielding member 21 and the support 6 is t2 (mm), when t1 <t2, the flow path of the surrounding wind W2 The lowermost surface S coincides with the lowermost surface of the wind shielding member 21, and the lowermost surface S coincides with the lowermost surface of the decompression chamber 4 at t 1 ≧ t 2. However, normally, the decompression chamber 4 is disposed as close as possible to the support 6 in order to enhance the effect of decompression. If the newly installed wind shield member 21 requires the same severe positional accuracy (with respect to the support 6) as the decompression chamber 4, the effect of simply installing the wind shield member 21 and reducing the accompanying wind is reduced. . Therefore, especially in the case of t1 <t2, the method of the present embodiment that reduces the accompanying wind using the wind shielding member 21 is very effective.

[Other configurations]
FIG. 14 is a perspective view showing another configuration of the main part of the optical film manufacturing apparatus. As shown in the figure, on the outside of the side wall 4b of the decompression chamber 4, there is a wind shielding member 41 (second wind shielding member) made of at least one structure 51 at a predetermined interval from the decompression chamber 4 and the support 6. ) May be placed stationary. The side wall 4b of the decompression chamber 4 is a wall located at both ends of the decompression chamber 4 in the casting width direction.

  In addition, in the same figure, illustration of the wind-shielding member 21 mentioned above is abbreviate | omitted for convenience. The wind shield member 41 is common to the wind shield member 21 in that it includes at least one structure 51. Therefore, the arrangement (the narrowest intervals L and H) and the configuration of the wind shield member 21 shown in FIGS. 7 and 8 can be applied to the wind shield member 41 as well.

  In addition to the accompanying air flowing from the upstream side of the decompression chamber 4, there are also winds that are drawn from the surroundings into the chamber due to the decompression of the decompression chamber 4. By arranging the wind shield member 41 outside the side wall portion 4b of the decompression chamber 4 in a stationary state, the wind that flows in from the gap between the side wall portion 4b and the support body 6 during decompression is based on the same principle as the wind shield member 21. Can be reduced. Thereby, the vibration of the casting ribbon due to the reduced pressure can be suppressed, and the film thickness unevenness can be further suppressed.

[About optical film materials]
In the method for producing an optical film by the solution casting method, the dope containing a resin such as cellulose ester as a main material is added to at least one of a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and a low molecular weight substance. Substances and solvents. Hereinafter, these will be described.

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

  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 triacetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. The cellulose ester used in this embodiment may contain other substituents.

  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 retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

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

  The number average molecular weight of the cellulose ester is preferably in the range of 20,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 40000-200000 are preferable. Various additives can be blended in the cellulose ester.

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

  Reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of widening the viewing angle of the liquid crystal display device operating in the IPS mode, but such an additive for reducing the thickness direction retardation (Rt). The following may be mentioned as:

  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, the 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, an aliphatic compound is preferable to an aromatic compound as an additive for disturbing the orientation of the cellulose ester.

  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 represents that they were 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 preferred monocarboxylic acids include, but are not limited to, the following.

  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 invention is not limited thereto. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are 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 adipine. Acids, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like, in particular, as aliphatic carboxylic acids, those having 4 to 12 carbon atoms, at least one selected from these use. That is, two or more dibasic acids may be used in combination.

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

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

  Polycondensation of polyester is 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 alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, it is preferable that polyester having a weight average molecular weight not so large is by direct reaction. Polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester, and after forming the film, a moisture permeability is small, and a cellulose ester film rich in transparency can be obtained.

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

  The polyester represented by the general formula (1) or (2) is preferably contained in an amount of 1 to 40% by weight based on the cellulose ester. It is particularly preferable to contain 5 to 15% by weight.

  Examples of the additive for reducing the thickness direction retardation (Rt) include the following.

  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 order to synthesize a polymer as an additive for reducing the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can align the molecular weight as much as possible without increasing the molecular weight. . Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a compound having a single thiol group and a secondary hydroxyl group as described in the publication, or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. In particular, the method described in the publication is preferable.

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

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

  Next, as acrylate 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-hydroxy) Rokishibuchiru) 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.

  An acrylic polymer (simply called an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or methacrylic acid alkyl ester having no monomer unit having an aromatic ring or a cyclohexyl group.

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

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by weight or more, and the methacrylic acid methyl ester monomer unit has 40% by weight or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both highly compatible with cellulose esters, 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 case of an acrylic acid or methacrylic acid ester monomer having a hydroxyl group, it is not a homopolymer but a constituent unit of a copolymer. In this case, the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is preferably contained in the acrylic polymer in an amount of 2 to 20% by weight.

  In the method for producing an optical film by the solution casting method, the dope composition has a cellulose ester and a weight average molecular weight of 500 or more and 3000 or less, or a weight average molecular weight of 5000 or more as an additive for reducing thickness direction retardation (Rt). It is preferable to contain 30000 or less acrylic polymer.

  If the weight average molecular weight of the polymer as an additive for reducing the thickness direction retardation (Rt) is 500 or more and 3000 or less, or the polymer has a weight average molecular weight of 5000 or more and 30000 or less, the compatibility with the cellulose ester is good. It is good and does not evaporate or volatilize 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.

  As an additive for reducing the thickness direction retardation (Rt), a polymer having a hydroxyl group in the side chain can also be preferably used. The monomer unit having a hydroxyl group is the same as the monomer described above, but is preferably acrylic acid or methacrylic acid ester. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. The thing replaced by methacrylic acid can be mentioned, Preferably it is 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by weight, more preferably 2 to 10% by weight.

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

  Moreover, it is preferable to have a hydroxyl group at least at one terminal of the main chain of the polymer. The method for making the main chain terminal have a hydroxyl group is not particularly limited, but a method using a radical polymerization initiator having a hydroxyl group such as azobis (2-hydroxyethylbutyrate), a method such as 2-mercaptoethanol, etc. A method of using a chain transfer agent having a hydroxyl group, 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, JP-A No. 2000-128911 or JP-A No. 2000-344823 There is a method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as described in the gazette, or a polymerization catalyst in which the compound and an organometallic compound are used in combination, and in particular, the method described in the gazette Is preferred.

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

  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 No. 2000-63560, JP-A No. 2001-247717 Hexose sugar alcohol ester or ether compound described in JP-A No. 2004-315613, phosphate trialiphatic alcohol ester compound described in JP-A No. 2004-315613, and general formula (1) described in JP-A No. 2005-41911 Compounds, phosphate ester compounds described in JP-A No. 2004-315605, styrene oligomers described in JP-A No. 2005-105139, and polymers of styrene monomers described in JP-A No. 2005-105140.

  In the method of producing an optical film by the solution casting method, an organic solvent having good solubility in the cellulose derivative is called a good solvent, and has 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 And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

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

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

  The most preferable solvent for dissolving the 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.

  Optical films produced by the solution casting method include plasticizers that give the film processability, flexibility, and moisture resistance, fine particles that give the film slipperiness (matting agent), and UV absorption that gives the UV absorption function. An antioxidant or an antioxidant that prevents deterioration of the film may be contained.

  The plasticizer used in the solution casting method is not particularly limited, but a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation so as not to cause 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 solution casting method 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 polyhydric alcohol ester, 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 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

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

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

  For phosphate plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate and the like can be used, but 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 weight, preferably 0.1% by weight, and particularly preferably not added.

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

  The amount of the plasticizer used is preferably 1 to 20% by weight. 6 to 16% by weight is further preferable, and 8 to 13% by weight is particularly preferable. If the amount of the plasticizer used is less than 1% by weight relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by weight, the plasticizer bleeds out from the film, and the film This is not preferable because the physical properties of the resin deteriorate.

  In order to impart slipperiness to the cellulose derivative in the solution casting method, 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 taken for each cross-sectional photograph. Count. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

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

  Here, when 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% by weight to the cellulose ester. Preferably, 0.05 to 0.5% by weight, more preferably 0.05 to 0.35% by weight is added. When the amount of fine particles added is 0.04% by weight or less, the film surface roughness becomes too smooth and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by weight, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat the composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion device used in the solution casting method 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 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 solution casting method, fine particles are dispersed in a solvent containing 25 to 100% by weight of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixed solution is placed on a support. The cellulose ester film is formed by casting and drying.

  Here, the content ratio of the lower alcohol is preferably 25 to 100% by weight, more preferably 50 to 100% by weight.

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

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

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by weight. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by weight, more preferably 10 to 20% by weight.

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

  Examples of ultraviolet absorbers that can be used in the solution casting method 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 useful UV absorbers include 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzo Triazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5 Chlorobenzotriazole, 2- (2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl) benzotriazole, 2,2-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy-3'-tert) Butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (straight and side chain dodecyl) -4-methylphenol, octyl-3- [3 -Tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy-5- (5-chloro) -2H-benzotriazol-2-yl) phenyl] propionate and the like, but not limited thereto.

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

  Specific examples of benzophenone compounds that are ultraviolet absorbers that can be used in the solution casting method include 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).

  The blending amount of these ultraviolet absorbers is preferably in the range of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight, based on 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 a solution casting method, the polymer ultraviolet absorber (or ultraviolet absorbing polymer) described in JP-A-6-148430 and JP-A-2002-47357 is disclosed. 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 display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

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

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

  The optical film of this embodiment is manufactured by the above-described optical film manufacturing method, and the film thickness is preferably in the range of 15 to 100 μm as a finished film from the viewpoint of thinning the liquid crystal display device. .

  The optical film targeted in this embodiment is a functional film used for various displays such as liquid crystal displays, plasma displays, and organic EL displays, particularly liquid crystal displays, and includes a polarizing plate protective film, a retardation film, and an antireflection film. In addition, an optical compensation film such as a brightness enhancement film and a viewing angle expansion is included.

  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 that is excellent in durability, dimensional stability, and optical isotropy as well as being thinned.

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

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

  The polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is 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 the present 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 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 irradiation 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.

  The liquid crystal display device here is a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. It has a polarizing plate.

  In addition, since the polarizing plate here uses an optical film excellent in flatness on at least one side, when the polarizing plate is incorporated in a liquid crystal panel, the contrast of the liquid crystal panel is reduced and the density unevenness occurs. There is no, and it is excellent in visibility.

  In addition, since the display device here uses a polarizing plate having an optical film having excellent flatness, it does not cause a decrease in contrast or unevenness of density of the liquid crystal panel, and has excellent visibility. It is what.

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

〔Example〕
Hereinafter, examples of the present embodiment will be described, but the present invention is not limited thereto.

<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

  Next, a cellulose triacetate film was produced using the production apparatus shown in FIG. As the support 6 for casting the dope, an endless belt polished to a super mirror surface with an average of 1.0 nm of three-dimensional surface roughness (Ra) measured by a scanning atomic force microscope (AFM) is used. It was.

  Subsequently, the filtered dope was uniformly cast on a support 6 having a dope temperature of 30 ° C. and a temperature of 25 ° C. by a casting die 3 made of a coat hanger die.

  Further, when the web 9 is formed on the support 6, the decompression chamber 4 opened downward is disposed as a means for reducing the pressure from the upstream side of the casting so that the web 9 is formed in close contact with the support 6. In addition, as shown in FIG. 5, a wind shielding member 21 is installed on the upstream side of the decompression chamber 4. At this time, the wind shielding member 21 was a plate-like structure extending in the casting width direction, and was erected vertically with respect to the support 6.

  In this embodiment, the moving speed of the support 6 is set to 100 m / min, the narrowest distance L between the decompression chamber 4 and the wind-shielding member 21 is set to 30 mm, and the narrowest distance H between the support 6 and the wind-shielding member 21 is set. The pressure in the decompression chamber 4 was -500 Pa. Further, since the plate-like wind shielding member 21 is erected vertically with respect to the support 6, the peripheral wind flowing through the flow path with the narrowest interval L becomes the support side-side accompanying air flowing through the flow path with the narrowest interval H. The angle at the time of collision was 0 °.

  In this way, the web 9 formed on the support 6 is dried on the support 6 with a drying air constant at a temperature of 30 ° C. while being transported on the support 6, and then peeled off from the support 6 by the peeling roll 8. 10, after stretching 1.1 times in the width direction in an atmosphere of 100 ° C. when the residual solvent amount is 10%, release the width holding, and finish drying with the drying device 11 at 125 ° C. while carrying the roll, It wound up with the winding device 13. The film thickness of the obtained optical film (cellulose triacetate film) was 30 μm, the film width was 2000 mm, and the film winding length was 3000 m.

<Example 2>
In Example 2, the optical film was manufactured by setting the narrowest distance H between the support 6 and the wind shielding member 21 to 20 mm. The rest is the same as in the first embodiment.

<Example 3>
In Example 3, the optical film was manufactured by setting the narrowest distance L between the decompression chamber 4 and the wind shielding member 21 to 50 mm. The rest is the same as in the first embodiment.

<Example 4>
In Example 4, the optical film was manufactured by setting the narrowest distance L between the decompression chamber 4 and the wind shield member 21 to 12 mm and the narrowest distance H between the support 6 and the wind shield member 21 to 8 mm. The rest is the same as in the first embodiment.

<Example 5>
In Example 5, the optical film was manufactured by setting the narrowest distance L between the decompression chamber 4 and the wind-shielding member 21 to 8 mm and the narrowest distance H between the support 6 and the wind-shielding member 21 to 4 mm. The rest is the same as in the first embodiment.

<Comparative Example 1>
In Comparative Example 1, an optical film was manufactured by setting the narrowest distance L between the decompression chamber 4 and the wind shielding member 21 to 60 mm and the narrowest distance H between the support 6 and the wind shielding member 21 to 25 mm. The rest is the same as in the first embodiment.

<Comparative example 2>
In Comparative Example 2, an optical film was manufactured by setting the narrowest distance H between the support 6 and the wind shielding member 21 to 25 mm. The rest is the same as in the first embodiment.

<Comparative Example 3>
In Comparative Example 3, an optical film was manufactured by setting the narrowest distance L between the decompression chamber 4 and the wind shielding member 21 to 60 mm. The rest is the same as in the first embodiment.

(Evaluation method)
About the optical film manufactured in Examples 1-5 and Comparative Examples 1-3, evaluation of the horizontal stage unevenness used as the parameter | index of film thickness nonuniformity was performed as follows. The thickness of the manufactured optical film was measured with a film thickness meter (film thickness measuring device DH-150 manufactured by Tokyo Seimitsu Co., Ltd.), and “horizontal unevenness (%) = (maximum and minimum unevenness of thickness unevenness and Difference / average film thickness) × 100 ”, and the lateral unevenness was evaluated according to the following criteria. That is, the horizontal unevenness (%) is a value obtained by dividing the difference between the maximum and minimum unevenness of the optical film thickness unevenness by the average film thickness of the optical film, and the optical film thickness unevenness in the length direction. Continuous measurement was performed, and the pitch of periodic thickness unevenness and the maximum value, minimum value, and average value (average film thickness) of thickness unevenness were read from the chart, and the horizontal unevenness was evaluated based on the following criteria. Table 1 shows the evaluation results at that time.
◎: Transverse unevenness is less than 0.4% ○: Transverse unevenness is 0.4% or more and less than 0.6% △: Transverse unevenness is 0.6% or more and less than 0.8% ×: Transverse unevenness is 0 .8% or more

  From Table 1, it can be seen that in Examples 1 to 5, the evaluation results of the horizontal unevenness are ◎ or ◯, respectively, and the film thickness unevenness (horizontal unevenness) of the manufactured optical film can be reduced. In Examples 1 to 5, the narrowest distance L and the narrowest distance H when the wind shielding member 21 is arranged satisfy 0 mm <L ≦ 50 mm and 0 mm <H ≦ 20 mm. When the body 6 moves, the surrounding wind flowing through the flow path with the narrowest interval L is surely collided with the support-side accompanying wind flowing through the flow path with the narrowest interval H, thereby reducing the entire accompanying wind, and thereby the casting ribbon This is thought to be due to the fact that it was possible to suppress vibration. In particular, in Example 5, the effect of reducing the unevenness in film thickness is the highest. This is because the narrowest interval L and the narrowest interval H further satisfy 0 mm <L ≦ 10 mm, 0 mm <H ≦ 5 mm, This is considered to be because the effect of reducing the accompanying wind due to the collision with the surrounding wind becomes higher.

  On the other hand, in Comparative Examples 1-3, the evaluation result of horizontal unevenness is x. In Comparative Examples 1 to 3, the narrowest interval L and the narrowest interval H when the wind shielding member 21 is arranged do not satisfy at least one of 0 mm <L ≦ 50 mm and 0 mm <H ≦ 20 mm, and the accompanying wind Since the effect of separating the support side entrained wind and the surrounding wind and causing them to collide with each other is weak, the accompanying wind cannot be reduced, and as a result, vibration of the casting ribbon due to the accompanying wind occurs. it is conceivable that.

  Next, an optical film was manufactured by changing the direction of the peripheral wind on the lowermost surface of the flow path having the narrowest interval L created by the wind shielding member 21, and the same horizontal unevenness was evaluated.

<Example 6>
In Example 6, as shown in FIG. 8, the wind shielding member 21 is composed of two structures 31 and 32, and one structure 31 is disposed in close contact with the rear wall 4 a of the decompression chamber 4. The structure 32 is arranged on the upstream side of one structure 31. At this time, the direction of the surrounding wind (the direction of the combined vector) on the lowermost surface of the flow path with the narrowest interval L made of the structures 31 and 32 is 45 ° in the definition of the angle shown in FIG. In the state where the structures 31 and 32 were configured and arranged, the support 6 was moved to manufacture an optical film. Other conditions including the narrowest intervals L and H are the same as those in the first embodiment.

<Example 7>
In the seventh embodiment, the support 6 is moved in a state in which the structures 31 and 32 are configured and arranged so that the direction of the surrounding wind flowing through the narrowest distance L formed by the structures 31 and 32 is 60 °. To produce an optical film. Other than that is the same as Example 6.

<Example 8>
In Example 8, in the state where the structures 31 and 32 are configured and arranged so that the direction of the surrounding wind flowing through the narrowest distance L formed by the structures 31 and 32 is −30 °, the support 6 is The optical film was manufactured by moving. Other than that is the same as Example 6.

<Example 9>
In Example 9, in the state where the structures 31 and 32 are configured and arranged so that the direction of the surrounding wind flowing through the narrowest distance L formed by the structures 31 and 32 is −40 °, the support 6 is The optical film was manufactured by moving. Other than that is the same as Example 6.

  Table 2 shows the evaluation results of horizontal unevenness for Examples 1 and 6 to 9.

  From Table 2, it can be seen that in Examples 1 and 6 to 8, the evaluation of the horizontal unevenness is good (◯), and the film thickness unevenness can be reduced. As in Examples 1 and 6 to 8, when the direction of the surrounding wind is −30 ° or more, the surrounding wind can be efficiently collided with the accompanying wind on the support side, thereby efficiently moving the accompanying wind. It is thought that it can be reduced.

  Note that the closer the direction of the surrounding wind is to 90 °, the more the surrounding wind collides with the support-side accompanying wind from the front. Therefore, it is considered that the effect of reducing the accompanying wind increases. It is practically difficult to construct and arrange the wind-shielding member 21 so as to be at an angle. In the embodiment, the direction of the surrounding wind is only 60 degrees in the positive direction, but the wind shielding member 21 can be configured and arranged until the direction of the surrounding wind is 80 degrees. . Therefore, if the direction of the surrounding wind is −30 ° to 80 °, it can be said that the accompanying wind can be efficiently collided with the support-side accompanying wind and the accompanying wind can be efficiently reduced.

  Further, in Example 9, the evaluation result of the horizontal unevenness is Δ, but it does not change that the film thickness unevenness can be reduced by colliding the peripheral wind with the support-side accompanying air. Based on the evaluation results of Examples 1 and 6 to 9, it is estimated that the same evaluation as in Example 9 can be obtained when the direction of the surrounding wind is larger than −90 ° and smaller than −30 °.

<Example 10>
In Example 10, an optical film was manufactured by arranging the wind shielding member 41 on the outside of the side wall portion 4 b of the decompression chamber 4. At this time, the interval between the wind shield member 41 and the decompression chamber 4 and the interval between the wind shield member 41 and the support 6 were made to coincide with the narrowest interval L and the narrowest interval H of the wind shield member 21, respectively. Other conditions are the same as in the first embodiment.

  As for Example 10, the same horizontal unevenness as described above was evaluated. As a result, a higher evaluation result (◎) than that of Example 1 was obtained. By arranging the wind shield member 41, the wind shield member 41 can reduce the wind flowing in from the gap between the side wall 4b and the support 6 when the decompression chamber 4 is decompressed, and the vibration of the casting ribbon due to the decompression can be reduced. This is thought to be due to suppression.

  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.

DESCRIPTION OF SYMBOLS 3 Casting die 4 Depressurization chamber 4a Rear wall part 4b Side wall part 6 Support body 7 Support body 9 Web (casting film)
21 Wind shield member (first wind shield member)
31 Structure 32 Structure 41 Wind-shielding member (second wind-shielding member)
51 Structure F Optical film W1 Support side accompanying wind W2 Ambient wind

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,
A decompression chamber is arranged upstream of the casting die in the moving direction of the support,
Arranging a stationary air shielding member made of at least one structure upstream of the decompression chamber,
In the case where the wind shield member is composed of one structure, the narrowest distance between the rear wall portion on the upstream side of the decompression chamber and the structure is set to L (mm), while there are a plurality of wind shield members. In the case of the above structure, the narrowest interval between the structure disposed in close contact with the rear wall portion and another structure disposed further upstream is defined as L (mm).
When the narrowest distance between the support and the wind shielding member is H (mm),
0 mm <L ≦ 50 mm and 0 mm <H ≦ 20 mm
The manufacturing method of the optical film characterized by the above-mentioned. The support body when the surrounding wind that flows through the flow path formed at the narrowest interval L collides with the support-side-side accompanying air flowing between the support body and the wind shielding member when the support body moves. When the collision angle of the surrounding wind from the direction perpendicular to the direction is 0 °, and the direction in which the collision angle increases toward the downstream side of the moving direction of the support with respect to 0 ° is positive,
2. The optical film according to claim 1, wherein a direction of a synthetic vector of the peripheral wind when passing through the lowermost surface of the flow path on the support side is within a range of −30 ° to 80 °. Production method. 0 mm <L ≦ 10 mm and 0 mm <H ≦ 5 mm
The method for producing an optical film according to claim 1 or 2, wherein: When the wind shield member is the first wind shield member,
2. The second wind-shielding member made of at least one structure is disposed outside the side wall portion of the decompression chamber at a predetermined interval from the decompression chamber and the support, and is stationary. 4. A method for producing an optical film according to any one of items 1 to 3.   5. The method of manufacturing an optical film according to claim 1, wherein a gap between the decompression chamber and the support is smaller than a gap between the wind shielding member and the support.   The method for producing an optical film according to claim 1, wherein a moving speed of the support is 80 m / min to 200 m / min.

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