JP7063380B2 - Optical film manufacturing method - Google Patents

Description

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

An optical film is used for a circular polarizing plate for preventing external light reflection of an organic EL (Electro-Luminescence) display device, which is also called an OLED (Organic light-Emitting Diode), and a polarizing plate of a liquid crystal display device. Conventionally, cellulosic resins (for example, triacetyl cellulose (also referred to as TAC)) are mainly used as the optical film. However, in recent years, with the spread of mobile devices, the diversification of usage and the demand for thin films have increased. There is an increasing need for a film having excellent resistance to water such as moisture permeability even in a thin film. TAC having high moisture permeability is difficult to use in a thin film in mobile devices, and recently, cycloolefin resins (hereinafter referred to as cycloolefin resins). COP) has come to be used. COP has low moisture permeability and is excellent in water resistance even in a thin film, and is suitable for use in a thin film in a mobile device.

By the way, as a typical method for producing an optical film, a melt casting film forming method (melt film forming method) and a solution casting film forming method (cast film forming method) are known. When an optical film is formed by the melt casting method, it is difficult to add an additive (for example, a matte agent) to the optical film (because the additive is scorched at high temperature), and it is difficult to make a thin film (difficult to control the film thickness). For reasons such as, the degree of freedom in designing optical films is low. Further, since it is difficult to mix the matting agent as described above, the slipperiness of the optical film is poor, and there still remains a problem that the upper and lower films stick to each other when wound.

Therefore, the inventors of the present application have studied the formation of an optical film containing COP (hereinafter, also referred to as COP film) by a solution casting film forming method having a relatively high degree of freedom in film design. Then, it was found that in the film formation of the optical film containing COP, even larger curl occurs after the casting film is peeled off from the support than in the film formation of the optical film containing TAC (hereinafter, also referred to as TAC film). rice field. The details of the reason why such curl occurs will be described later.

Various measures have been conventionally proposed for curls generated by the solution casting film forming method. For example, in Patent Document 1, the temperature outside the width end of the flow film after peeling from the support is controlled to T to T + 30 ° C, where the boiling point of the main solvent is T ° C. The width of the hand end is prevented from curling. Further, in Patent Document 2, the cast film is peeled off from the support, the cast film is dried, and then the end portion of the curled film is cut immediately before being wound as a film. At the same time, by heating the cut portion to a predetermined temperature and then cutting the cut portion, the flatness of the cut portion and the cutting condition of the cut portion are improved. Further, in Patent Documents 3 and 4, after the casting film is peeled off from the support, the curl portion of the width hand end portion of the casting film is sandwiched between nip rolls and heated to reduce the curl of the width hand end portion. I am doing it.

Japanese Unexamined Patent Publication No. 2003-175523 (see Claims 1 and 2, paragraphs [0005] to [0010], FIGS. 1, 2, etc.) Japanese Unexamined Patent Publication No. 2003-71783 (see claims 1 to 3, paragraphs [0003], [0004], [0011], [0018], FIG. 1 and the like). JP-A-2010-23312 (see claims 1 to 4, paragraphs [0006] to [0008], FIGS. 3, 4, etc.) Japanese Patent No. 4390254 (see claims 1, 9, 10, paragraphs [0005], [0011], [0051], FIGS. 2, 3, etc.)

However, Patent Documents 1 and 2 only propose measures against curling in film formation of a film containing a cellulosic resin. Since the degree of curl generated during film formation differs greatly between the cellulosic resin and COP (details will be described later), the methods proposed in Patent Documents 1 and 2 are applied to the film formation of COP film. However, it is considered that the effect of reducing curl cannot be sufficiently obtained. In particular, in Patent Document 2, the curled width hand end portion is only cut before winding, and in this case, when the curl of the cast film is large after peeling from the support, during the subsequent transportation. When the cast film is held by the roll (when the transport direction is changed by contact with the outer peripheral surface of the roll), the cast film is prone to wrinkles and cracks, which may lead to poor transport. be.

Further, in the method of correcting the shape of the end portion by niping and heating the end portion of the cast film as in Patent Documents 3 and 4, when the cast film contains a large amount of solvent, the cast film is formed. There is no escape for the solvent to evaporate from (because the end of the cast film is sandwiched between the two rolls). In this case, the foaming film may be deformed due to foaming in the casting film, and a clip error or the like may occur in the subsequent transport, and there is a concern that the transport may become unstable. Therefore, it is desired to reduce the curl by heating the cast film by a method other than the nip.

Also, if the width end of the casting film is heated to reduce curl, the width end will become too dry and hard, and when the casting film is held by the roll during subsequent transportation. There is a concern that the end of the width will crack and the transportation will be hindered. Further, if the heating temperature of the cast film after peeling is too high, the heated portion is softened too much and becomes twisted, which may cause wrinkles and breakage during transportation. Therefore, in order to reduce the curl of the flow film, it is desired to appropriately control the heating position and the heating temperature of the flow film when heating the flow film.

The problem described above also occurs when an optical film is formed by a solution casting film forming method using not only COP but also a resin different from the cellulosic resin (for example, a polyimide resin). obtain.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to support an optical film by a solution casting film forming method using a resin different from a cellulosic resin. By heating the cast film after peeling from the body by a method other than nip and appropriately controlling the heating position and heating temperature, the curl of the width end of the cast film is reduced and the transport is stable. It is an object of the present invention to provide the manufacturing method of the optical film which can secure the property.

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

The method for producing an optical film according to one aspect of the present invention includes a casting step of casting a dope containing a resin different from a cellulose-based resin and a good solvent onto a support to form a casting film, and the support. The peeling step of peeling the cast film from the support, the transport step of transporting the cast film peeled from the support by a roll, and the stretching or drying of the cast film conveyed by the roll to form an optical film. A method for producing an optical film including a stretching / drying step, wherein in the transporting step, a heating target region which is a part of the casting film peeled off from the support in the width direction is covered with the casting film. It is heated by a heat source that is not in contact with the above, and the width end portion of the heating target region is from the position corresponding to the width end portion before peeling of the cast film with respect to the entire width of the cast film. It is located inside the width by a distance of P%, the P is 1% or more and 20% or less, and when the boiling point of the good solvent is T ° C., the surface temperature of the heating target region at the time of heating. Is T + 40 ° C to T + 110 ° C.

Even when the optical film is formed by the solution casting film formation method using a resin different from the cellulosic resin, the transport is stable while reducing the curl at the width end of the casting film after peeling from the support. Sex can be ensured.

It is explanatory drawing which shows the schematic structure of the optical film manufacturing apparatus which concerns on embodiment of this invention. It is a flowchart which shows the flow of the manufacturing process of the said optical film. It is an enlarged view of the transport part of the said manufacturing apparatus. It is explanatory drawing which shows typically the principle that the curl is generated in the cast film after peeling from the support of the said manufacturing apparatus. It is explanatory drawing which shows the relative positional relationship between a casting film and a heat source in the said transport part. It is explanatory drawing which shows typically the principle of reducing the curl of a casting film by heating. It is explanatory drawing which shows the other structure of the said transport part. It is explanatory drawing which shows the other structure of the said transport part. It is explanatory drawing which shows the other structure of the said heat source.

An embodiment of the present invention will be described below with reference to the drawings. In this specification, when the numerical range is expressed as A to B, the numerical range includes the values of the lower limit A and the upper limit B. The present invention is not limited to the following contents.

FIG. 1 is an explanatory diagram showing a schematic configuration of the optical film manufacturing apparatus 20 of the present embodiment. Further, FIG. 2 is a flowchart showing the flow of the manufacturing process of the optical film. The method for producing an optical film of the present embodiment is a method for producing an optical film by a solution casting film forming method, and as shown in FIG. 2, a stirring preparation step (S1), a casting step (S2), and a peeling step. (S3), a transfer step (S4), a stretching step (S5), a drying step (S6), a cutting step (S7), an embossing step (S8), and a winding step (S9) are included. Hereinafter, each step will be described with reference to FIGS. 1 and 2.

(S1; stirring preparation step)
In the stirring preparation step, at least the resin and the solvent are stirred in the stirring tank 1a of the stirring device 1 to prepare a dope to be cast on the support 3 (endless belt). As the resin, for example, a cycloolefin resin (COP) can be used. As the solvent, a mixed solvent of a good solvent and a poor solvent can be used. The good solvent refers to an organic solvent having the property of dissolving the resin (solubility), and includes 1,3-dioxolane, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, methylene chloride (dichloromethane, methylene chloride), and the like. Tetrahydrofuran and the like correspond to this. On the other hand, the poor solvent refers to a solvent that does not have the property of dissolving the resin by itself, and corresponds to methanol, ethanol, or the like.

The resin constituting the dope is not limited to the above COP, and may be a resin other than the cellulosic resin. Examples of such resins include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acetate resins, polyether sulfone resins, polycarbonate resins (PC), polyamide resins, and polyimide resins. Examples thereof include a polyolefin resin, a (meth) acrylic resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polystyrene resin, a polyvinyl alcohol resin, a polyarylate resin, and a polyphenylene sulfide resin.

(S2; hypersalivation process)
In the casting step, the dope prepared in the stirring preparation step is sent to the casting die 2 by a conduit through a pressurized metering gear pump or the like, and is transferred indefinitely on the support 3 made of a rotary drive stainless steel endless belt. Dope is spread from the casting die 2 at the casting position. Then, the support 3 transports while supporting the flowed dope (flowing dope). As a result, the flow film (web) 5 is formed on the support 3.

The belt-shaped support 3 is held by a pair of rolls 3a and 3b and a plurality of rolls (not shown) located between them. One or both of the rolls 3a and 3b is provided with a drive device (not shown) for applying tension to the support 3, whereby the support 3 is used in a tensioned state. The support 3 may be composed of a rotating drum.

In the casting step, the casting film 5 is heated on the support 3 and the solvent is evaporated from the support 3 until the casting film 5 can be peeled off by the peeling roll 4. To evaporate the solvent, there are a method of blowing wind from the web side, a method of transferring heat from the back surface of the support 3 with a liquid, a method of transferring heat from the front and back surfaces by radiant heat, and the like, which are used individually or in combination as appropriate. Just do it.

(S3; peeling step)
In the above casting step, the casting film 5 is dried and solidified or cooled and solidified on the support 3 until the casting film 5 has a peelable film strength, and then in the peeling step, the casting film 5 has self-supporting property. It is peeled off by the peeling roll 4 while it is left in place.

The amount of residual solvent in the cast film 5 on the support 3 at the time of peeling is preferably in the range of 10% by mass to 120% by mass depending on the strength of the drying conditions, the length of the support 3, and the like. It is more preferably in the range of 10% by mass to 60% by mass, further preferably in the range of 15% by mass to 55% by mass, further preferably in the range of 20% by mass to 50% by mass, and 25% by mass. Most preferably, it is in the range of ~ 45% by mass. When peeling at a time when the amount of residual solvent is larger, if the casting film 5 is too soft, the flatness at the time of peeling is impaired, and wrinkles and vertical streaks are likely to occur due to the peeling tension. The amount of residual solvent is determined. The amount of residual solvent is defined by the following formula.

Residual solvent amount (mass%) = (mass before heat treatment of web-mass after heat treatment of web) / (mass after heat treatment of web) × 100
Here, the heat treatment when measuring the residual solvent amount means that the heat treatment is performed at 115 ° C. for 1 hour.

(S4; transport process)
In the transfer step, the cast film 5 peeled off from the support 3 is transferred to the tenter 6 by the transfer unit 11. Here, FIG. 3 is an enlarged view of the transport unit 11. The transport unit 11 includes at least one roll (transport roll), and FIG. 3 shows three rolls 11, 12, and 13. In the transport step, the cast film 5 is transported by rolls 11 to 13, and a part of the cast film 5 in the width direction is locally heated by a heat source 15 that is not in contact with the cast film 5. The details of heating the flow film 5 by the heat source 15 will be described later.

(S5; stretching step)
In the stretching step, the cast film 5 peeled off from the support 3 is stretched in the transport direction and / or the width direction by the tenter 6. In the stretching step, a tenter method in which both side edges of the casting film 5 are fixed with clips or the like and stretched is preferable in order to improve the flatness and dimensional stability of the film. In the tenter 6, drying may be performed in addition to stretching.

(S6; drying step)
The cast film 5 stretched by the tenter 6 is dried by the drying device 7. In the drying device 7, the cast film 5 is transported by a plurality of transport rolls arranged in a staggered pattern when viewed from the side surface, and the cast film 5 is dried between them. The drying method in the drying device 7 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, a heating roll, microwaves, or the like. From the viewpoint of simplicity, a method of drying the cast film 5 with hot air is preferable. The flow film 5 is dried by the drying device 7 and then conveyed as an optical film toward the winding device 10.

The drying step of S6 may be performed separately before and after the stretching step of S5. That is, after the transport step of S4, the stretching step and the drying step may be performed in this order, and the drying step (first drying step), the stretching step and the drying step (second drying step) may be performed in this order. It may be done. Therefore, it can be said that the method for producing an optical film of the present embodiment includes a stretching / drying step (S5, S6) in which the casting film 5 is stretched or dried to form an optical film after the transport step of S4. ..

(S7; cutting process, S8; embossing process)
A cutting portion 8 and an embossing portion 9 are arranged in this order between the drying device 7 and the winding device 10. In the cutting portion 8, a cutting step is performed in which both ends in the width direction are cut by a slitter while the formed optical film is conveyed. In the optical film, the portion remaining after cutting both ends constitutes a product portion to be a film product. On the other hand, the portion cut from the optical film is collected by a shooter and reused as a part of the raw material for film formation.

After the cutting step, both ends of the optical film in the width direction are embossed (nerling) by the embossing portion 9. The embossing process is performed by pressing a heated embossing roller against both ends of the optical film. Fine irregularities are formed on the surface of the embossed roller, and by pressing the embossed roller against both ends of the optical film, the irregularities are formed on both ends. By such embossing, winding misalignment and blocking (sticking between films) in the next winding process can be suppressed as much as possible.

(S9; winding process)
Finally, the optical film having been embossed is wound by the winding device 10 to obtain the original winding (film roll) of the optical film. That is, in the winding step, a film roll is manufactured by winding the optical film around the winding core while conveying it. As a method for winding the optical film, a commonly used winder may be used, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method with a constant internal stress. Should be used properly. The winding length of the optical film is preferably 1000 to 7200 m. Further, the width at that time is preferably 500 to 3200 mm, and the film thickness is preferably 30 to 150 μm.

[About the principle of curl generation]
Next, the principle that curl occurs after the casting film 5 is peeled from the support 3 and the reason why the curl becomes larger when COP is used than that of the cellulosic resin will be described.

FIG. 4 schematically shows the principle that curl is generated in the cast film 5 after peeling from the support 3. For convenience of explanation below, in the flow film 5 formed on the support 3, the surface on the support 3 side is also referred to as the B surface, and the surface on the opposite side (air side) from the support 3 is A. Also called a surface.

Immediately after the dope is poured onto the support 3, the solvent does not evaporate and remains sufficiently. Therefore, the resin (polymer) in the dope is used on both the B-side and the A-side of the casting film 5. It is in a state of being relatively free to move. Drying progresses as the dope is transported on the support 3, that is, the solvent evaporates, but the A-plane side of the casting film 5 on the support 3 is in contact with the air rather than the B-plane side. Therefore, the solvent is easy to evaporate (the B-side side is blocked from the air by the presence of the support 3 so that the solvent is hard to evaporate). Therefore, on the support 3, more solvent remains on the B-plane side than on the A-plane side of the casting film 5.

On the other hand, there is a difference in the drying rate of the solvent on the support 3 due to the difference in the contained resin between the dope containing COP and the dope containing TAC. Specifically, the dope containing COP has a slower drying rate of the solvent on the support 3 than the dope containing TAC. Therefore, on the support 3, the cast film 5 containing COP has more solvent remaining on the B-plane side than the cast film containing TAC (here, the content ratio of the resin and the solvent in the dope). , The thickness and width of the casting film are the same for COP and TAC).

When the flow film 5 is peeled off from the support 3, the solvent remaining on the B surface side due to the contact of the B surface side (the side in contact with the support 3) of the flow film 5 with air after the peeling. Evaporates rapidly, and as a result, volume shrinkage occurs on the B-plane side of the casting film 5. At this time, since the casting film 5 containing COP has more solvent remaining on the B-plane side than the casting film containing TAC, volume shrinkage occurs more. As a result, the cast film 5 containing COP causes more curl after peeling from the support 3 than the cast film containing TAC. In particular, since the flow film 5 containing COP is weaker and more easily bent than the flow film containing TAC, the generated curl will be prominently displayed at the width end portion of the flow film 5.

[About heating of the flow film in the transport process]
Next, a method for reducing the curl of the cast film 5 after peeling and ensuring the transport stability of the cast film 5 will be described.

FIG. 5 is an explanatory diagram showing the relative positional relationship between the flow film 5 and the heat source 15 in the above-mentioned transport unit 11. Although the figure shows the arrangement of the heat source 15 on the one end side in the width direction of the flow film 5, the same arrangement is made on the other end side. The heat source 15 is composed of a blower that locally heats the flow film 5 by blowing hot air onto the flow film 5. The heat source 15 is arranged vertically above the film surface (film surface) of the flow film 5 in a non-contact manner with the flow film 5, and heats the flow film 5 by blowing hot air vertically downward. do.

Here, in the present embodiment, the widthmost end E0 of the casting film 5 is not targeted for heating, and the region inside the width of the width end E0 is defined as the heating target region R, and this heating target. By heating the region R with the heat source 15, the cast film 5 is locally heated in the width direction. The width end E1 of the heating target region R of the flow film 5 is the entire width of the flow film 5 from the position corresponding to the width end E0 before peeling (before curling) of the flow film 5. It is located inside the width by a distance of P% with respect to W (mm), and in the present embodiment, P is a value of 1% or more and 20% or less. That is, the width end portion E1 of the heating target region R is within the range of 0.01 W or more and 0.20 W or less from the width end portion E0 before peeling to the inside of the width. As the range of the total width W, for example, 1000 to 2000 (mm) can be considered.

In order to reduce the curl at the end of the flow film 5 caused by the above principle, after the flow film 5 is peeled from the support 3, the width end of the flow film 5 is heated, but P is 1%. When the flow film 5 is heated so as to be less than, the width end portion E1 of the heating target region R coincides with or becomes very close to the width end portion E0 of the flow film 5. In this case, the width when the end of the width E0 or its vicinity becomes too dry and hard, and the cast film 5 is held by a roll (for example, a roll 14 or a roll in the drying device 7) during the subsequent transportation. There is a possibility that the vicinity of the end of the hand E0 may crack and interfere with transportation. On the other hand, when the flow film 5 is heated so that P exceeds 20% after the flow film 5 is peeled off from the support 3, the width end portion E1 of the heating target region R becomes the width of the flow film 5. Since the area R to be heated is moved away from the curl portion as it moves away from the end end portion E0, it becomes difficult to effectively reduce (correct) the curl of the width hand end portion of the casting film 5 by heating.

Here, FIG. 6 schematically shows the principle of reducing the curl of the cast film by heating. A resin is an aggregate of long chain-shaped macromolecules, and the macromolecules are intricately entangled with each other by an intramolecular interaction. By heating the curled portion of the casting film, the thermal motion of the molecules in the heated region is increased, so that the molecular spacing is widened and the intermolecular bonding force between the polymers is weakened. During the transfer of the flow film, the flow film is pulled in the transport direction and stress (tension) acts, and this stress acts in the direction of flattening the flow film. Therefore, it is possible to reduce curl by heating during the transport of the cast film.

Further, in the present embodiment, when the boiling point of the good solvent contained in the dope is T ° C., the surface temperature of the heating target region R when heated by the heat source 15 is T + 40 ° C. to T + 110 ° C. For example, when methylene chloride is used as a good solvent, the boiling point T of methylene chloride is 39 ° C., so that the surface temperature of the region R to be heated is in the range of 79 ° C. to 149 ° C. When toluene is used as a good solvent, the boiling point T of toluene is 110 ° C., so that the surface temperature of the region R to be heated is in the range of 150 ° C. to 220 ° C.

When the surface temperature of the heating target region R at the time of heating is a high temperature exceeding T + 110 ° C., the curl is reduced by heating, but the cast film 5 itself becomes so soft that it cannot maintain the flatness (wrinkles). Wrinkles occur, which deteriorates transportability (stable transport becomes impossible). On the other hand, at a low temperature of T + 40 ° C. or lower, the amount of heat that disturbs the resin orientation is not applied to the heating target region R, so that the effect of reducing curl is weak, especially when a large curl is generated as in COP. Has a very weak curl reduction effect due to heating.

Therefore, as in the present embodiment, when the cast film 5 after peeling from the support 3 is heated by the heat source 15, the heating position (particularly the position of the widthmost end E1 of the heating target region R) and the heating temperature. Even when a resin (for example, COP) whose volume shrinkage on the support side (B surface) of the cast film 5 is larger than that of the cellulosic resin after peeling from the support 3 is used as the resin. It is possible to manufacture an optical film having excellent transport stability while reducing curl due to the volume shrinkage.

Further, since the heat source 15 is arranged in a non-contact manner with the cast film 5 and the cast film 5 is heated in a non-contact manner, the inconvenience of heating by niping the cast film 5 does not occur. That is, even when the cast film 5 contains a large amount of solvent, the solvent can be evaporated without being trapped inside when the cast film 5 is heated by the heat source 15 after peeling, whereby the cast film 5 can be vaporized. It is possible to prevent foam deformation. Therefore, it is possible to reduce the occurrence of clip mistakes and the like due to the deformation of the casting film 5 in the subsequent transport, and it is possible to reduce the instability of the transport.

The preferable range of P is 3% or more and 8% or less. That is, if the width end portion E1 of the heating target region R is within the range of 0.03 W or more and 0.08 W or less inside the width hand from the width end portion E0 before peeling, the effect of reducing curl can be obtained. Obtained more effectively. Further, the preferable range of the surface temperature of the heating target region R at the time of heating is T + 70 ° C. to T + 110 ° C.

The position of the end portion E2 on the side opposite to the width end portion E1 (the width center side of the casting film 5) in the heating target region R is not particularly specified, but it is located on the width center side too much. Then, it becomes close to the product part (the part that remains as a product when the width end part is finally cut off), and the disorder of orientation due to heating may affect the product part and lead to deterioration of the quality of the product part. .. In addition, the width of the portion whose orientation is disturbed by heating becomes wide, and the width that can be used as the product part in the cast film 5 may also become narrow. Therefore, the position of the end portion E2 on the width center side of the heating target region R is from the position corresponding to the width end portion E0 before peeling (before curling) of the cast film 5. It is located inside the width by a distance of Q% with respect to the total width W (mm), and Q is preferably a value of 30% or less, more preferably a value of 25% or less. It is even more preferable that the value is 20% or less.

By the way, in the peeling step of S3 described above, if the amount of the residual solvent at the time of peeling the casting film 5 from the support 3 is too large, a large amount of the solvent on the B surface side of the casting film 5 evaporates after the peeling. Volume shrinkage increases. Therefore, in the transfer step of S4, it becomes difficult to obtain the effect of reducing curl by heating with the heat source 15 described above. Further, if the amount of residual solvent at the time of peeling is too small, the amount of curl caused by evaporation of the solvent after peeling is originally small, so that the method of the present embodiment for reducing curl by heating with the heat source 15 is low in effectiveness. Become. From the above, from the viewpoint of effectively and surely reducing curl by the method of the present embodiment, the amount of residual solvent at the time of peeling of the cast film 5 from the support 3 is 15% by mass to 55% by mass. It is desirable, and more preferably 20% by mass to 50% by mass.

Further, in the transfer step of S4, the heating target region R may be heated by the heat source 15 while applying stress so that the width end portion of the cast film 5 that curls after peeling from the support 3 becomes flat. .. For example, just by transporting the cast film 5 as described above, stress can be applied to the cast film 5 so that the width end portion becomes flat due to the tension in the transport direction. Further, by increasing the wind pressure of the hot air blown from the heat source 15, stress can be applied to the cast film 5 so that the width end portion becomes flat. By heating the heating target region R while applying stress to the cast film 5 in this way, both stress and heating act to reduce curl, so that large curl can be efficiently reduced.

FIG. 7 shows another configuration of the transport unit 11. The heat source 15 may heat the heating target region R by blowing hot air from a direction inclined inward by an angle θ with respect to the direction perpendicular to the flow film 5. In this case, since the hot air is blown from the diagonal direction to the spreading film 5 (heating target region R) so as to go from the inside of the width to the outside of the width, the stress of flattening the width end of the spreading film 5 is applied. Can be added. Therefore, even by blowing such hot air, the heating target region R can be heated while applying stress to the width end portion of the flow film 5, and curl can be efficiently reduced.

In particular, the above angle θ is preferably 20 ° to 40 °. Within the above angle range, both stress application to the width hand end portion of the flow film 5 and heating of the heating target region R can be performed satisfactorily, and the curl reduction effect can be further enhanced. It becomes.

FIG. 8 shows still another configuration of the transport unit 11. The heat source 15 may heat the heating target region R on a roll. The roll may be any of rolls 12, 13 and 14 in FIG. 3, but roll 13 is shown as an example in FIG. In this case, the width end of the flow film 5 is moved by contacting the roll 13 with respect to the flow film 5, that is, by moving the flow film 5 along the peripheral surface of the roll 13. A stress to flatten can be applied. Therefore, even in this case, it is possible to efficiently reduce the curl by heating the heating target region R while applying stress to the width end portion of the casting film 5. Further, by using the methods of FIGS. 7 and 8 together, the curl reduction effect can be further enhanced.

As described above, since the heat source 15 heats the heating target region R of the cast film 5 by blowing hot air, heating by non-contact with the cast film 5 can be surely realized.

Further, FIG. 9 shows another configuration of the heat source 15. The heat source 15 may heat the heating target region R of the cast film 5 by irradiating with infrared rays (IR). Even in this case, it is possible to reliably realize heating by non-contact with the flow film 5 by irradiation with infrared rays.

In the present embodiment, the resin (resin included in the dope) used for producing the optical film may contain a cycloolefin-based resin (COP) or a polyimide-based resin (PI). When forming a film using COP or PI, curl occurs after peeling due to the slower drying rate of the solvent on the support 3 than when forming a film using a cellulosic resin (for example, TAC). It occurs greatly. Therefore, when COP or PI is used as the resin, the method of the present embodiment, which reduces curl by non-contact heating by the heat source 15, is very effective.

〔Additive〕
In the film formation of the optical film, an additive may be added to the dope as needed. Additives include plasticizers, UV absorbers, retardation modifiers, antioxidants, antioxidants, release aids, surfactants, dyes, fine particles and the like. In the present embodiment, additives other than the fine particles may be added at the time of preparing the dope, or may be added at the time of preparing the fine particle dispersion.

〔Example〕
Hereinafter, specific examples of the diagonally stretched film in the present embodiment will be described with reference to comparative examples. The present invention is not limited to the following examples.

<Manufacturing of optical film 1>
An optical film 1 made of a cycloolefin resin film (COP film) was produced by the following production method (solution casting film forming method).

<< Manufacture of cycloolefin resin pellets >>
In a nitrogen atmosphere, 1.2 parts by mass of 1-hexene, 0.15 parts by mass of dibutyl ether, and 0.30 parts by mass of triisobutylaluminum were placed in a reactor at room temperature and mixed with 500 parts by mass of dehydrated cyclohexane, and then 45 ° C. Tricyclo [4.3.0.12.5] deca-3,7-diene (dicyclopentadiene, hereinafter abbreviated as DCP) 13 parts by mass, 8-methyl-8-methoxycarbonyltetracyclo [4] 4.0.12, 5.17,10] Dodec-3-ene (hereinafter abbreviated as MMT) 87 parts by mass of a norbornene-based monomer mixture and tungsten hexachloride (0.7% toluene solution) 40 parts by mass And were continuously added and polymerized over 2 hours. 1.06 parts by mass of butyl glycidyl ether and 0.52 parts by mass of isopropyl alcohol were added to the polymerization solution to inactivate the polymerization catalyst and stop the polymerization reaction.

Next, 270 parts by mass of cyclohexane was added to 100 parts by mass of the reaction solution containing the obtained ring-opening polymer, and 5 parts by mass of a nickel-alumina catalyst (manufactured by JGC Catalysts and Chemicals Co., Ltd.) was added as a hydrogenation catalyst. In addition, the mixture was pressurized to 5 MPa with hydrogen, heated to a temperature of 200 ° C. with stirring, and then reacted for 4 hours to obtain a reaction solution containing 20% of the DCP / MMT ring-opening polymer hydrogenated polymer.

After removing the hydrogenation catalyst by filtration, a soft polymer (manufactured by Kuraray Co., Ltd .; Septon 2002) and an antioxidant (manufactured by Chivas Specialty Chemicals Co., Ltd .; Irganox 1010) are added to the obtained solutions, respectively. And dissolved (in each case, 0.1 part by mass per 100 parts by mass of the polymer). Next, the solvent cyclohexane and other volatile components were removed from the solution using a cylindrical concentrated dryer (manufactured by Hitachi, Ltd.), and the hydrogenated polymer was extruded from the extruder in a molten state in a strand shape. After cooling, it was pelletized and recovered. When the copolymerization ratio of each norbornene-based monomer in the polymer was calculated from the residual norbornene composition (by gas chromatography method) in the solution after the polymerization, DCP / MMT / = 13/87 was almost equal to the charged composition. rice field. The ring-opening polymer hydrogenated product had a weight average molecular weight (Mw) of 89000, a molecular weight distribution (Mw / Mn) of 2.5, a hydrogenation rate of 99.9%, and a Tg of 161 ° C.

The obtained cycloolefin resin pellets of the ring-opening polymer hydrogenated product were dried at 70 ° C. for 2 hours using a hot air dryer in which air was passed to remove water.

<< Production of fine particles 1 >>
The polymer particle aggregate produced in the following production example was produced as fine particles 1.

<Manufacturing of seed particles>
1000 g of deionized water was placed in a polymer equipped with a stirrer and a thermometer, 200 g of methyl methacrylate and 6 g of t-dodecyl mercaptan were charged therein, and the mixture was heated to 70 ° C. while being replaced with nitrogen under stirring. The internal temperature was kept at 70 ° C., 20 g of deionized water in which 1 g of potassium persulfate was dissolved was added as a polymerization initiator, and then the mixture was polymerized for 10 hours. The average particle size of the polymer particles in the obtained emulsion was 0.44 μm.

<Manufacturing of polymer particles>
In a polymerizer equipped with a stirrer and a thermometer, 800 g of deionized water in which 3 g of polyoxyethylene tridecyl ether ammonium sulfate was dissolved was placed therein, and 144 g of methyl acrylate, 22 g of styrene and 34 g of ethylene glycol dimethacrylate were added thereto as a monomer mixture. , A mixture with 1 g of azobisisobutyronitrile was added as a polymerization initiator. Then, the mixed solution was added to T.I. A dispersion was obtained by stirring with a K homomixer (manufactured by Tokushu Kagaku Kogyo Co., Ltd.).

Further, 60 g of the above emulsion containing the seed particles was added to the dispersion liquid, and the mixture was stirred at 30 ° C. for 1 hour to allow the seed particles to absorb the monomer mixture. Then, the absorbed monomer mixture was polymerized by heating at 50 ° C. for 5 hours under a nitrogen stream, and then cooled to room temperature (about 25 ° C.) to obtain a slurry containing polymer particles. The average particle size of the obtained polymer particles (organic fine particles) was 0.3 μm.

<Manufacturing of aggregates of polymer particles>
After cooling, 50 g of Snowtex O-40 (manufactured by Nissan Chemical Industries, Ltd .: solid content 40% as colloidal silica (inorganic powder), particle size: 0.02-0.03 μm) was added to the obtained slurry, and T.I. The mixture was stirred with a K homomixer (manufactured by Tokushu Kagaku Kogyo Co., Ltd.) for 10 minutes. This slurry was spray-dried under the following conditions with a spray dryer (model: atomizer take-up method, model number: TRS-3WK) manufactured by Sakamoto Giken Co., Ltd. as a spray dryer to obtain a polymer particle aggregate. The average particle size of the polymer particle aggregate was 30 μm.
Supply rate: 25 ml / min
Atomizer rotation speed: 11000 rpm
Air volume: 2m ³ / min
Slurry inlet temperature of spray dryer: 130 ° C
Polymer particle aggregate outlet temperature: 70 ° C

<< Preparation of fine particle dispersion liquid 1 >>
1.0 part by mass of fine particles 1 and 100 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes and then dispersed with manton golin to obtain a fine particle dispersion liquid 1.

<< Preparation of dope >>
Then, the main dope 1 having the following composition was prepared. First, methylene chloride, ethanol and toluene were added to the pressurized dissolution tank. Next, the cycloolefin resin pellets prepared above and the additive (LA-F70) were charged into the pressure dissolution tank with stirring. Next, the fine particle dispersion 1 prepared above was added, and the mixture was heated to 60 ° C. and completely dissolved while stirring. The heating temperature was raised from room temperature at 5 ° C./min, dissolved in 30 minutes, and then lowered at 3 ° C./min.

The viscosity of the obtained solution was 7000 cp and the water content was 0.50%. This was filtered using SHP150 manufactured by Roki Techno Co., Ltd. at a filtration flow rate of 300 L / m ² · h and a filtration pressure of 1.0 × 10 ⁶ Pa to obtain a main dope 1.

<Composition of main dope 1>
Cycloolefin resin pellet 100 parts by mass Methylene chloride (boiling point 39 ° C) 270 parts by mass Ethanol 20 parts by mass Additive (ADEKA STAB LA-F70 (manufactured by ADEKA Corporation))
3 parts by mass Fine particle dispersion liquid 1 30 parts by mass

《Film formation》
Then, using an endless belt casting device, the main dope 1 was uniformly cast on a support made of a stainless steel belt at a temperature of 31 ° C. and a width of 1800 mm. At this time, the temperature of the support was controlled to 28 ° C. The transport speed of the support was set to 20 m / min.

On the support, the solvent was evaporated until the amount of residual solvent in the casting film was 35% by mass. Then, the cast film was peeled off from the support at a peeling tension of 128 N / m. Then, in the transporting step of transporting the peeled film with a large number of rolls, a heat source was used to heat the width end portion of the cast film between the rolls.

At this time, as a heat source, a blower for blowing hot air was used, and the heat source was arranged at a position where the distance between the hot air outlet and the flow film was 30 mm. The size of the hot air outlet was 30 mm in the direction along the width of the flow film and 200 mm in the direction along the length. Then, from the position where the width end of the heating target region of the flow film corresponds to the width end of the flow film before peeling (before curling), the entire width of the flow film before peeling Hot air was blown from the heat source perpendicularly (from above) to the cast film (heated area) so as to be located on the inner side of the width by 8% to heat the heated area. When the surface temperature of the area to be heated at this time was measured using a non-contact infrared sensor, it was 80 ° C. The size of the hot air outlet of the heat source in the width direction is 30 mm, and since hot air is blown onto the flow film from vertically above, the position on the center side of the width of the area to be heated is the width of the flow film before peeling. It is clear that the distance from the position corresponding to the end of the hand is 30% or less of the total width of the cast film before peeling.

In the transport step, after heating the cast film with a heat source as described above, the cast film is stretched 1.2 times in the transport direction at 120 ° C. with a tenter, and then 1 in the width direction under the condition of 150 ° C. . Stretched 1 times. Then, the end portion sandwiched between the tenter clips was slit, and then the film was wound to obtain an optical film 1 having a film thickness of 60 μm.

<Manufacturing of optical film 2>
When the cast film is heated in the transport process, the spread before peeling is performed from the position where the width end of the heating target area of the cast film corresponds to the width end of the cast film before peeling. Optical Film 2 was produced.

<Manufacturing of optical film 3>
When the cast film is heated in the transport process, the spread before peeling is performed from the position where the width end of the heating target area of the cast film corresponds to the width end of the cast film before peeling. Optical in the same manner as in the production of the optical film 1, except that the area to be heated is heated by blowing hot air from the heat source perpendicular to the cast film so that it is located 20% of the entire width of the film. Film 3 was produced.

<Manufacturing of optical film 4>
When the cast film is heated in the transport process, the spread before peeling is performed from the position where the width end of the heating target area of the cast film corresponds to the width end of the cast film before peeling. Optical Film 4 was made.

<Manufacturing of optical film 5>
When the cast film is heated in the transport process, the spread before peeling is performed from the position where the width end of the heating target area of the cast film corresponds to the width end of the cast film before peeling. Optical in the same manner as in the production of the optical film 1, except that the area to be heated is heated by blowing hot air from the heat source perpendicular to the cast film so that it is located 25% of the entire width of the film. Film 5 was made.

<Manufacturing of optical film 6>
The optical film 6 was produced in the same manner as the optical film 1 except that the widthmost end of the casting film was heated in the transport step. That is, when the cast film is heated, the width end of the heating target area of the cast film corresponds to the width end of the flow film before peeling, from the position corresponding to the width end of the flow film before peeling. The optical film is similar to the production of the optical film 1 except that the area to be heated is heated by blowing hot air from the heat source perpendicular to the flow film so that it is located on the inner side of the width by 0% of the entire width of the film. 6 was produced.

<Manufacturing of optical film 7>
The optical film 7 was produced in the same manner as the optical film 1 except that the flow film was not heated by the heat source in the transfer step.

<Manufacturing of optical film 8>
In the transfer step, the optical film 8 was produced in the same manner as the optical film 1 except that the cast film was heated so that the surface temperature of the heating target region was 95 ° C.

<Manufacturing of optical film 9>
In the transfer step, the optical film 9 was produced in the same manner as the optical film 1 except that the cast film was heated so that the surface temperature of the heating target region was 150 ° C.

<Manufacturing of optical film 10>
Preparation of optical film 1 except that toluene (boiling point 110 ° C.) was used instead of methylene chloride in the preparation of the dope and the cast film was heated so that the surface temperature of the heating target region was 150 ° C. in the transport step. The optical film 10 was produced in the same manner as above.

<Manufacturing of optical film 11>
The optical film 11 was produced in the same manner as the optical film 1 except that polyimide (PI) was used instead of COP in the preparation of the dope. The polyimide was synthesized as follows.

2,2-Bis (3,4-dicarboxyphenyl) -1,1,1, in a 4-necked flask equipped with a dry nitrogen gas introduction tube, a cooler, a Dean-Stark aggregator filled with toluene, and a stirrer. 25.59 g (57.6 mmol) of 3,3,3-hexafluoropropane dianhydride was added to N, N-dimethylacetamide (134 g), and the mixture was stirred under a nitrogen stream at room temperature. To it, 19.2 g (60 mmol) of 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl was added, and the mixture was heated and stirred at 80 ° C. for 6 hours. Then, the outside temperature was heated to 190 ° C., and the water generated by imidization was azeotropically distilled off together with toluene. After continuing heating, refluxing and stirring for 6 hours, no water was observed. Subsequently, the mixture was heated for 7 hours while distilling off toluene, and after distilling off toluene, methanol was added and reprecipitated to obtain a polyimide represented by the following formula.

<Manufacturing of optical film 12>
In the transfer step, the optical film 12 was produced in the same manner as the optical film 11 except that the cast film was heated so that the surface temperature of the heating target region was 150 ° C.

<Manufacturing of optical film 13>
In the transfer step, the optical film 13 was produced in the same manner as the optical film 1 except that the cast film was heated so that the surface temperature of the heating target region was 70 ° C.

<Manufacturing of optical film 14>
In the transport step, the optical film 14 was produced in the same manner as the optical film 1 except that the cast film was heated so that the surface temperature of the heating target region was 160 ° C.

<Evaluation>
(Curl amount)
Using a laser displacement meter, measure the warp height of the end due to curl from the reference surface (position of the center of the width) inside the flow film in the width direction before entering the tenter, and use it as the following evaluation standard. The amount of curl was evaluated based on this.
"Evaluation criteria"
⊚: The amount of curl is 3 mm or less.
◯: The curl amount is larger than 3 mm and 7 mm or less.
X: The curl amount is larger than 7 mm and 14 mm or less.
XX: The amount of curl is larger than 14 mm.

(End twist)
By heating the flow film more than necessary due to heating in the transport process, it is judged from the appearance whether wrinkles are generated on the width end of the flow film, and the end is twisted based on the following evaluation criteria. Was evaluated.
"Evaluation criteria"
⊚: No edge twist has occurred.
◯: There is almost no twist at the edges.
Δ: A slight twist at the end is seen, but it is within the range where there is no problem.
×: There is a problem because the edge is twisted considerably.

(Transportability)
The appearance of the flow film was evaluated based on the following evaluation criteria.
⊚: Transport is very stable.
◯: Some wrinkles are generated during transportation, but the transportation is stable.
Δ: Wrinkles are generated during transportation, but there is no major problem in transportation.
X: Clipping error due to curl, cracking at the end, or breakage due to wrinkles during transportation has occurred, and the transportation is unstable.

Tables 1 and 2 show the evaluation results of the produced optical films 1 to 14.

From Tables 1 and 2, in the production of the optical films 5 to 7, 13 and 14, the curl amount is not reduced and the transport is unstable. In the production of the optical film 7, since the end portion of the cast film peeled from the support is not heated, the curl of the end portion cannot be reduced. Then, since the cast film is conveyed with the curl remaining, it is considered that a clip error occurs in the subsequent tenter and the transfer becomes unstable. In the production of the optical film 6, the curl portion inside the width end portion of the cast film after peeling is heated, and the curl portion inside the width end portion cannot be efficiently heated, so that the curl amount can be reduced. It is considered that the end of the width is too dry and the end is cracked in the subsequent transportation, so that the transportation becomes unstable. In the production of the optical film 5, since the portion of the cast film after peeling that is too far inward from the end of the width is heated, even if the curl of the end can be reduced, the effect is small, and as a result. , It is considered that the transport is unstable due to a clip error in the tenter due to curl.

In the production of the optical film 13, the surface temperature of the heated region of the cast film after peeling is as low as 70 ° C., the curl reduction effect due to heating is low, and clipping errors due to curling occur and the transport is unstable. It is thought that it has become. In the production of the optical film 14, the surface temperature of the heated region of the cast film after peeling is as high as 160 ° C., so that the end portion of the cast film is softened and wrinkles are generated, which is caused by wrinkles in the subsequent transportation. It is considered that the transport is unstable due to the breakage. In the production of the optical film 14, the curl amount could not be measured due to the softening of the end portion.

On the other hand, in the production of the optical films 1 to 4, 8 to 12, the curl amount, the edge twist, and the transportability are all good (the evaluation is ⊚, ◯, or Δ). In the production of the optical films 1 to 4, 8 to 12, when the heating target region, which is a part of the casting film peeled off from the support in the width direction, is heated, the width end portion of the heating target region is formed. It is located inside the width by P% of the total width of the flow film from the position corresponding to the end of the width before peeling of the flow film, and P is 1% or more and 20% or less. The heating target region is heated so that the surface temperature is T + 40 ° C. to T + 110 ° C., where the boiling point of the good solvent is T ° C. In this way, since the heating position and heating temperature are appropriately controlled for the cast film, the flow after peeling is performed even when COP or PI is used as the resin, that is, even when a cellulosic resin is used. It is possible to effectively reduce curl while suppressing the occurrence of twisting at the edges of the rolled film, which enables stable transport without clip mistakes due to curl or breakage due to wrinkles. Conceivable.

In particular, in the production of the optical films 1 and 4, the curl amount is effectively reduced, and the transport is very stable. Therefore, it is desirable that P is 3% or more and 8% or less. I can say.

<Manufacturing of optical film 15>
The optical film 15 was produced in the same manner as the optical film 1 except that the solvent was evaporated on the support until the amount of the residual solvent in the cast film reached 10% by mass.

<Manufacturing of optical film 16>
The optical film 16 was produced in the same manner as the optical film 1 except that the solvent was evaporated on the support until the amount of the residual solvent in the cast film reached 60% by mass.

<Manufacturing of optical film 17>
The optical film 17 was produced in the same manner as the optical film 1 except that the solvent was evaporated on the support until the amount of the residual solvent in the cast film reached 20% by mass.

<Manufacturing of optical film 18>
The optical film 18 was produced in the same manner as the optical film 1 except that the solvent was evaporated on the support until the amount of the residual solvent in the casting film reached 50% by mass.

The produced optical films 15 to 18 were evaluated for curl amount, edge twist, and transportability based on the same evaluation criteria as described above. Table 3 shows the evaluation results of the produced optical films 15-18.

From Table 3, if the residual solvent amount of the cast film at the time of peeling is 10% by mass to 60% by mass, peeling from the support is possible without impairing the effect of reducing the curl amount. In particular, when the residual solvent amount of the cast film at the time of peeling is 20% by mass to 50% by mass, it can be said that the peeling can be performed while greatly obtaining the effect of reducing the curl amount.

Here, since the curl amount is 6 mm when the residual solvent amount is 10% by mass and the curl amount is 5 mm when the residual solvent amount is 20% by mass, the residual solvent amount is 15% by mass between them. From the above, it can be inferred that the effect of reducing the curl amount is high. Similarly, when the residual solvent amount is 60% by mass, the curl amount is 6 mm, and when the residual solvent amount is 50% by mass, the curl amount is 5 mm, so that the residual solvent amount is 55% by mass between them. If it is as follows, it can be inferred that the effect of reducing the curl amount is high. From this, it can be said that the preferable range of the residual solvent amount of the cast film at the time of peeling is 15% by mass to 55% by mass.

Further, since the curl amount is 5 mm when the residual solvent amount is 20% by mass and the curl amount is 4 mm when the residual solvent amount is 35% by mass, the residual solvent amount is 25% by mass or more between them. However, it can be inferred that the effect of reducing the amount of curl is even higher. Similarly, when the residual solvent amount is 50% by mass, the curl amount is 5 mm, and when the residual solvent amount is 35% by mass, the curl amount is 4 mm. Therefore, the residual solvent amount is 45% by mass between them. Below, it can be inferred that the effect of reducing the curl amount is higher. From this, it can be said that the more preferable range of the residual solvent amount of the cast film at the time of peeling is 25% by mass to 45% by mass.

<Manufacturing of optical film 19>
In the transport process after peeling the cast film from the support, the area to be heated is from the direction inclined by 20 ° inward in the width with respect to the direction perpendicular to the casting film (direction inclined by 70 ° with respect to the horizontal plane). The optical film 19 was produced in the same manner as the optical film 1 except that the heat source was tilted and arranged so that the film 1 could be heated. Regarding the position of the heat source in the width direction, the position of the width end portion of the heating target region (the position of 8% of the total width from the width end portion of the cast film before peeling) is the position of the optical film 1. The position of the heat source was slightly shifted inward by the width so that the position was the same as that at the time of production (even in the production of the following optical film, when the heat source is tilted, the position is shifted in the same manner).

<Manufacturing of optical film 20>
In the transport process after peeling the cast film from the support, the area to be heated is tilted by 40 ° inward in the width with respect to the direction perpendicular to the cast film (direction tilted by 50 ° with respect to the horizontal plane). The optical film 20 was produced in the same manner as the optical film 1 except that the heat source was tilted and arranged so that the film 1 could be heated.

<Manufacturing of optical film 21>
Similar to the production of the optical film 1, except that when the cast film after peeling from the support is conveyed by at least one roll, the area to be heated is heated from vertically above by a heat source on one of the rolls. The optical film 21 was produced.

<Manufacturing of optical film 22>
In the transport process after peeling the cast film from the support, the area to be heated is tilted by 40 ° inward in the width with respect to the direction perpendicular to the cast film (direction tilted by 50 ° with respect to the horizontal plane). The optical film 22 was produced in the same manner as the optical film 21 except that the heat source was tilted and arranged so that the film 21 could be heated.

<Manufacturing of optical film 23>
In the transport process after peeling the cast film from the support, the optical film 22 is used except that the cast film is irradiated with infrared rays as a heat source for heating the cast film and the heating target area is heated. The optical film 23 was produced in the same manner as in the production of.

The produced optical films 19 to 23 were evaluated for curl amount, edge twist, and transportability based on the same evaluation criteria as described above. Table 4 shows the evaluation results of the produced optical films 19 to 23.

In Table 4, it can be seen from the comparison of the optical films 1, 19 and 20 that the curl amount is reduced as the heat source is tilted inward from the vertical direction. This is because by tilting the heat source from the vertical direction to the inside of the width, the force (wind pressure) of the hot air blown diagonally to the flow film acts as a stress to flatten the end of the width (curl part). Conceivable. In particular, hot air is blown onto the heating target area from a direction inclined by 20 ° to 40 ° inward with respect to the direction perpendicular to the flow film (direction inclined by 50 ° to 70 ° with respect to the horizontal plane) to heat the region. It can be said that this is desirable in order to surely obtain the curl reduction effect.

Further, by comparing the optical film 1 and the optical film 21, and the optical film 20 and the optical film 22, the width end of the casting film is heated when the casting film is located between the rolls. However, it can be said that the effect of reducing curl is higher when the film is heated when it is located on the roll. It is believed that heating the flow film when it is located on the roll puts stress on the flow film to flatten the width hand end (when held by the roll) when in contact with the roll.

In particular, in the production of the optical film 22, the amount of curl is the smallest. It is considered that this is because the tilted arrangement of the heat source and the heating on the roll are used in combination in the transfer process, and the effect of reducing the curl amount is the highest.

Further, in the production of the optical film 23, the effect of reducing the curl amount is slightly inferior to that in the production of the optical film 22. It is considered that this is because the infrared irradiation does not hold down the flow film like the blowing of hot air, that is, the stress for flattening the width end is not applied to the flow film. However, even with infrared irradiation, a very high curl amount reduction effect is obtained, and it can be said that it is effective as a means for heating the end portion of the flow film.

〔others〕
The method for manufacturing the optical film of the present embodiment described above can be expressed as follows.

1. 1. A casting step of casting a dope containing a resin different from the cellulose-based resin and a good solvent onto a support to form a casting film, a peeling step of peeling the casting film from the support, and the support. A method for producing an optical film, comprising a transporting step of transporting the cast film peeled from the body by a roll and a stretching / drying step of stretching or drying the cast film conveyed by the roll to obtain an optical film. There,
In the transfer step, the area to be heated, which is a part of the cast film peeled off from the support in the width direction, is heated by a heat source that is not in contact with the cast film.
The width end of the heating target region enters the inside of the width by a distance of P% with respect to the total width of the flow film from the position corresponding to the width end before peeling of the flow film. In the same position
The P is 1% or more and 20% or less.
When the boiling point of the good solvent is T ° C,
A method for producing an optical film, wherein the surface temperature of the heating target region at the time of heating is T + 40 ° C. to T + 110 ° C.

2. 2. The method for producing an optical film according to 1 above, wherein in the peeling step, the amount of residual solvent at the time of peeling the cast film is 15% by mass to 55% by mass.

3. 3. The transfer step is characterized in that the heating target region is heated by the heat source while applying stress so that the width end portion of the cast film that curls after peeling from the support is flattened. The method for producing an optical film according to 1 or 2.

4. 3. The method for producing an optical film according to 3, wherein the heat source heats the heating target region from a direction inclined inward by an angle θ with respect to a direction perpendicular to the flow film.

5. 4. The method for manufacturing an optical film according to 4, wherein the angle θ is 20 ° to 40 °.

6. The method for producing an optical film according to any one of 3 to 5, wherein the heat source heats the heating target region on the roll.

7. The method for producing an optical film according to any one of 1 to 6, wherein the heat source heats the heating target region by blowing hot air.

8. The method for producing an optical film according to any one of 1 to 6, wherein the heat source heats the heating target region by irradiating the heat source with infrared rays.

9. The method for producing an optical film according to any one of 1 to 8 above, wherein the resin contains a cycloolefin resin or a polyimide resin.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to this, and can be extended or modified without departing from the gist of the invention.

The method for producing an optical film of the present invention can be used when an optical film is produced by a solution casting film forming method using a resin different from a cellulosic resin.

3 Support 5 Hypersalivation film 13 Roll 15 Heat source E0 Hypersalivation film width end E1 Heating target area Width end R Heating target area

Claims (9)

A casting step of casting a dope containing a resin different from the cellulose-based resin and a good solvent onto a support to form a casting film, a peeling step of peeling the casting film from the support, and the support. A method for producing an optical film, comprising a transporting step of transporting the cast film peeled from the body by a roll and a stretching / drying step of stretching or drying the cast film conveyed by the roll to obtain an optical film. There,
In the transfer step, the area to be heated, which is a part of the cast film peeled off from the support in the width direction, is heated by a heat source that is not in contact with the cast film.
The width end of the heating target region enters the inside of the width by a distance of P% with respect to the total width of the flow film from the position corresponding to the width end before peeling of the flow film. In the same position
The P is 1% or more and 20% or less.
When the boiling point of the good solvent is T ° C,
A method for producing an optical film, wherein the surface temperature of the heating target region at the time of heating is T + 40 ° C to T + 110 ° C. The method for producing an optical film according to claim 1, wherein in the peeling step, the amount of residual solvent at the time of peeling the casting film is 15% by mass to 55% by mass. Claim 1 or 2 in which, in the transfer step, the heating target region is heated by the heat source while applying stress so that the width end portion of the cast film that curls after peeling from the support is flattened. The method for manufacturing an optical film according to the above. The method for producing an optical film according to claim 3, wherein the heat source heats the heating target region from a direction inclined inward by an angle θ with respect to a direction perpendicular to the casting film. The method for manufacturing an optical film according to claim 4, wherein the angle θ is 20 ° to 40 °. The method for producing an optical film according to any one of claims 3 to 5, wherein the heat source heats the heating target region on the roll. The method for producing an optical film according to any one of claims 1 to 6, wherein the heat source heats the heating target region by blowing hot air. The method for producing an optical film according to any one of claims 1 to 6, wherein the heat source heats the heating target region by irradiating with infrared rays. The method for producing an optical film according to any one of claims 1 to 8, wherein the resin contains a cycloolefin resin or a polyimide resin.

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