CN112020413B

CN112020413B - Method for manufacturing optical film

Info

Publication number: CN112020413B
Application number: CN201980028121.8A
Authority: CN
Inventors: 川野友辉; 中岛新之助
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2018-04-26
Filing date: 2019-01-23
Publication date: 2022-04-29
Anticipated expiration: 2039-01-23
Also published as: WO2019207863A1; JP7063380B2; KR20200130448A; KR102407022B1; CN112020413A; JPWO2019207863A1

Abstract

In a transporting process of the casting film (5) peeled from the support (3), a heating target region (R) which is a part of the casting film (5) peeled from the support (3) in the transverse direction is heated by a heat source (15) which is not in contact with the casting film (5). The widthwise endmost portion (E1) of the heating target region (R) is located at: the cast film (5) is advanced laterally inward from a position corresponding to the widthwise outermost edge (E0) of the cast film (5) before peeling by a distance of P% of the full width W of the cast film (5), and P is 1% or more and 20% or less. When the boiling point of a good solvent contained in the dope cast on the support (3) is T ℃, the surface temperature of the heating target region (R) is T + 40-T +110 ℃.

Description

Method for manufacturing optical film

Technical Field

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

Background

An optical film is used for a circular polarizing plate for preventing reflection of external light in an Organic EL (Electro-Luminescence) display device, which is also called an OLED (Organic light-Emitting Diode), and a polarizing plate in a liquid crystal display device. Conventionally, as the optical film, a cellulose resin (for example, triacetyl cellulose (also referred to as TAC)) has been mainly used, but in recent years, due to the spread of mobile devices, the use diversification and the demand for films have been increased, and even films with high moisture permeability, films with excellent durability against water such as moisture permeability have become necessary.

However, as typical methods for producing optical films, a melt casting film formation method (melt film formation method) and a solution casting film formation method (cast film formation method) are known. When an optical film is formed by a melt-casting film-forming method, the optical film has a low degree of freedom in design because it is difficult to incorporate an additive (e.g., a matting agent) into the optical film (the additive is burnt at a high temperature), and it is difficult to form a thin film (the film thickness is difficult to control). Further, since the matting agent is difficult to be mixed as described above, the optical film has poor sliding properties, and problems such as adhesion between the upper and lower films during winding still remain.

Therefore, the present inventors have made studies on the film formation of an optical film including COP (hereinafter, also referred to as a COP film) by a solution casting film-forming method having a relatively high degree of freedom in film design. Thus, it is known that: in the film formation of an optical film including COP, after peeling of a casting film from a support, a curl larger than that in the film formation of an optical film including TAC (hereinafter also referred to as a TAC film) occurs. The reason for the occurrence of such curling will be described in detail later.

Various measures have been proposed to cope with curling that occurs in the solution casting film forming method. For example, in patent document 1, the boiling point of the main solvent is T ℃, and the temperature outside the lateral end portion of the cast film peeled from the support is controlled to T +30 ℃, thereby preventing the lateral end portion of the cast film from curling. In patent document 2, the end of the film with the curl is cut immediately before winding as a film after the cast film is peeled from the support and dried. Further, by heating the cutting portion to a predetermined temperature and cutting the same, the planarity of the cutting portion and the cutting condition of the cutting portion are improved. In

patent documents

3 and 4, after the cast film is peeled from the support, the curled portion of the lateral end portion of the cast film is nipped and heated by nip rolls, thereby reducing the curling of the lateral end portion.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2003-175523 (see claims 1-2, paragraphs [0005] to [0010], FIGS. 1 and 2, etc.)

Patent document 2: japanese patent laid-open No. 2003-71783 (see claims 1 to 3, paragraphs [0003], [0004], [0011], [0018], FIG. 1, etc.)

Patent document 3: japanese patent laid-open No. 2010-23312 (see claims 1 to 4, paragraphs [0006] to [0008], FIGS. 3 and 4, etc.)

Patent document 4: japanese patent No. 4390254 (see

claims

1, 9, 10, paragraphs [0005], [0011], [0051], FIGS. 2, 3, etc.)

Disclosure of Invention

Problems to be solved by the invention

However,

patent documents

1 and 2 both have been limited to proposing measures against curling in the formation of films containing cellulose-based resins. The cellulose-based resin and COP are considered to have a greatly different degree of curling generated during film formation (details will be described later): even if the methods proposed in

patent documents

1 and 2 are applied to the film formation of COP films, the effect of reducing curling cannot be sufficiently obtained. In particular, in patent document 2, only the lateral end portion where the curl is generated is cut before winding, and if the curl of the cast film is large after peeling from the support body, when the cast film is wound around a roll in the course of subsequent conveyance (when the conveyance direction is changed by contact with the outer peripheral surface of the roll), wrinkles or cracks are likely to be generated in the cast film, and conveyance failure may occur.

In addition, as in

patent documents

3 and 4, in the method of correcting the shape of the edge portion by swaging and heating the edge portion of the casting film, when the casting film contains a large amount of solvent, the escape place of the solvent that is to evaporate from the casting film disappears (since the edge portion of the casting film is sandwiched by 2 rollers). In this case, the casting film is deformed by foaming in the casting film, and a clamping error (クリップミス) may occur in the subsequent conveyance, and the conveyance may become unstable. Therefore, it is desirable to reduce the curl by heating the casting film by a method other than the nip.

Further, if the widthwise outermost end portion of the casting film is heated to reduce the curl, the widthwise outermost end portion is excessively dried and hardened, and there is a fear that the widthwise outermost end portion is broken to cause a trouble in conveyance when the casting film is wound around a roll in the course of subsequent conveyance. Further, if the heating temperature of the cast film after peeling is too high, the heated portion is excessively softened to warp, and wrinkles may occur to cause breakage during conveyance. Therefore, in order to reduce the curl of the casting film, it is desirable to appropriately control the heating position and the heating temperature of the casting film when the casting film is heated.

The above-described problems can similarly occur not only in COP but also in the case of forming an optical film by a solution casting film forming method using a resin (for example, a polyimide resin) different from a cellulose resin.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing an optical film, which can reduce curling at the lateral ends of a cast film and ensure transport stability by heating the cast film peeled from a support by a method other than pressing when an optical film is formed by a solution casting film-forming method using a resin different from a cellulose-based resin, and by appropriately controlling the heating position and the heating temperature.

Means for solving the problems

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

A method for producing an optical film according to an aspect of the present invention is a method for producing an optical film including the steps of: 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 cast film, a peeling step of peeling the cast film from the support, a conveying step of conveying the cast film peeled from the support by a roller, and a stretching/drying step of stretching or drying the cast film conveyed by the roller to form an optical film, wherein in the conveying step, a heating target region which is a part in a transverse direction of the cast film peeled from the support is heated by a heat source which is not in contact with the cast film, a transverse direction outermost end portion of the heating target region is located at a position which is located at a distance of P% of a full width of the cast film from a position corresponding to the transverse direction outermost end portion of the cast film before peeling to the cast film to the transverse direction inner side, the P being 1% to 20%, when the boiling point of the good solvent is T ℃, the surface temperature of the heating target region during heating is T +40 ℃ to T +110 ℃.

ADVANTAGEOUS EFFECTS OF INVENTION

Even when an optical film is formed by a solution casting film-forming method using a resin different from the cellulose-based resin, curling of the lateral end portion of the cast film after peeling from the support is reduced, and transport stability is ensured.

Drawings

Fig. 1 is an explanatory view showing a schematic configuration of an apparatus for manufacturing an optical film according to an embodiment of the present invention.

Fig. 2 is a flowchart showing a flow of the above-described optical film manufacturing process.

Fig. 3 is an enlarged view of a conveying section of the manufacturing apparatus.

Fig. 4 is an explanatory view schematically showing the principle of occurrence of curling in the cast film after peeling from the support of the above-described manufacturing apparatus.

Fig. 5 is an explanatory view showing a relative positional relationship between the casting film and the heat source in the above-described conveying section.

Fig. 6 is an explanatory view schematically showing a principle of reducing the curl of the casting film by heating.

Fig. 7 is an explanatory view showing another configuration of the conveying unit.

Fig. 8 is an explanatory view showing still another configuration of the conveying unit.

Fig. 9 is an explanatory view showing another configuration of the heat source.

Detailed Description

An embodiment of the present invention will be described below with reference to the drawings. In the present specification, when a numerical range is represented by a to B, the numerical range includes values of a lower limit a and an upper limit B. The present invention is not limited to the following.

Fig. 1 is an explanatory diagram showing a schematic configuration of an optical film manufacturing apparatus 20 according to the present embodiment. Fig. 2 is a flowchart showing a flow of the optical film manufacturing process. The method for manufacturing an optical film according to the present embodiment is a method for manufacturing an optical film by a solution casting film forming method, and includes, as shown in fig. 2, a stirring preparation step (S1), a casting step (S2), a peeling step (S3), a conveying step (S4), a stretching step (S5), a drying step (S6), a cutting step (S7), an embossing step (S8), and a winding step (S9). The respective steps will be described below with reference to fig. 1 and 2.

(S1; stirring preparation Process)

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 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 is an organic solvent having a property of dissolving the resin (solubility), and corresponds to 1, 3-dioxolane, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, methylene chloride (methylene chloride), toluene, or the like. On the other hand, the poor solvent is a solvent which does not have a property of dissolving the resin alone, and methanol, ethanol, or the like corresponds thereto.

The resin constituting the dope is not limited to the COP described above, and may be any resin other than the cellulose 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, polyimide resins, polyolefin resins, (meth) acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyacrylate resins, and polyphenylene sulfide resins.

(S2; casting Process)

In the casting step, the dope prepared in the stirring preparation step is fed to the casting die 2 by a pipe by a pressure type fixed-displacement gear pump or the like, and the dope is cast from the casting die 2 to a casting position on the support 3 constituted by a rotationally driven stainless steel endless belt which is endlessly transferred. Then, the support 3 is conveyed while holding the cast dope (casting dope). Thereby, the casting film (web) 5 is formed on the support 3.

The belt-like support body 3 is held by a pair of rollers 3a and 3b and a plurality of rollers (not shown) positioned therebetween. One or both of the rollers 3a and 3b is provided with a driving device (not shown) for applying tension to the support body 3, and the support body 3 is used in a tensioned state by applying tension thereto. The support body 3 may be constituted by a drum.

In the casting process, the casting film 5 is heated on the support 3, and the solvent is evaporated until the casting film 5 can be peeled from the support 3 by the peeling roller 4. When the solvent is evaporated, there are a method of blowing air from the web side, a method of transferring heat from the back surface of the support 3 by passing a liquid therethrough, a method of transferring heat from the front surface and the back surface by radiant heat, and the like, and they may be used singly or in combination as appropriate.

(S3; peeling step)

In the casting step, the cast film 5 is peeled by the peeling roller 4 in a state of having self-supporting property in the peeling step after the cast film 5 has been dried and solidified or cooled and solidified on the support 3 until the cast film 5 has a peelable film strength.

The amount of the residual solvent of the casting film 5 on the support 3 at the time of peeling is preferably in the range of 10 to 120 mass%, more preferably in the range of 10 to 60 mass%, further preferably in the range of 15 to 55 mass%, further preferably in the range of 20 to 50 mass%, and most preferably in the range of 25 to 45 mass%, depending on the strength of the drying condition, the length of the support 3, and the like. When the peeling is performed at a timing when the amount of the residual solvent is larger, if the casting film 5 is too soft, flatness is impaired at the time of peeling, and wrinkles and vertical streaks due to the peeling tension are likely to occur, and therefore the amount of the residual solvent at the time of peeling is determined at an economical speed and at a good quality. The residual solvent amount is defined by the following formula.

The residual solvent amount (% by mass) is (mass before heat treatment of web-mass after heat treatment of web)/(mass after heat treatment of web) × 100

The heat treatment for measuring the amount of the residual solvent means a heat treatment performed at 115 ℃ for 1 hour.

(S4; conveying step)

In the transport step, the casting film 5 peeled from the support 3 is transported to the tenter 6 by the transport section 11. Fig. 3 is an enlarged view of the conveying unit 11. The conveying section 11 includes at least 1 roller (conveying roller), and in fig. 3, 3

rollers

11, 12, and 13 are shown. In the conveying step, the casting film 5 is conveyed by the rollers 11 to 13, and a part of the casting film 5 in the transverse direction is locally heated by the heat source 15 which is not in contact with the casting film 5. The heating of the casting film 5 by the heat source 15 will be described in detail later.

(S5; drawing step)

In the stretching step, the casting film 5 peeled from the support 3 is stretched in the transport direction and/or the transverse direction by the tenter 6. In the stretching step, a tenter method in which both side edge portions of the cast film 5 are fixed by clips or the like and stretched is preferable because flatness and dimensional stability of the film are improved. In the tenter 6, drying may be performed in addition to stretching.

(S6; drying step)

The casting film 5 stretched by the tenter 6 is dried by the drying device 7. In the drying device 7, the casting film 5 is conveyed by a plurality of conveying rollers arranged alternately in side view, and the casting film 5 is dried therebetween. The drying method using the drying device 7 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, heated rolls, microwaves, or the like. From the viewpoint of simplicity, a method of drying the casting film 5 with hot air is preferable. The casting film 5 is dried by the drying device 7 and then conveyed to the winding device 10 as an optical film.

The drying step of S6 may be performed separately before and after the stretching step of S5. That is, after the conveyance step of S4, the stretching step and the drying step may be sequentially performed, or the drying step (1 st drying step), the stretching step, and the drying step (2 nd drying step) may be sequentially performed. Therefore, the method for producing an optical film according to the present embodiment can be said to include a stretching/drying step (S5, S6) of forming an optical film by stretching or drying the casting film 5 after the transport step of S4.

(S7; cutting step, S8; embossing step)

Between the drying device 7 and the winding device 10, a cutting unit 8 and an embossing unit 9 are disposed in this order. In the cutting section 8, a cutting step is performed in which the optical film to be formed is conveyed while both ends in the transverse direction are cut by a slitter. In the optical film, the remaining portions of the both end portions after cutting constitute product portions to be film products. On the other hand, the cut portion from the optical film is recovered by an ejector (シュータ) and reused as a part of the raw material in film formation.

After the cutting step, embossing (knurling) is performed on both ends of the optical film in the transverse direction by the embossing portion 9. In the case of embossing, the embossing is performed by pressing the heated embossing roller against both end portions of the optical film. Fine irregularities are formed on the surface of the emboss roller, and irregularities are formed on both end portions of the optical film by pressing the emboss roller against the both end portions. Such embossing can suppress winding displacement and blocking (adhesion between films) as much as possible in the subsequent winding step.

(S9; winding Process)

Finally, the embossed optical film is wound by the winding device 10 to obtain a raw roll (film roll) of the optical film. That is, in the winding step, the optical film is wound around the winding core while being conveyed, thereby producing a film roll. As a method for winding the optical film, a method for controlling tension, such as a generally used winding method, a constant torque method, a constant tension method, a gradual tension method, a programmed tension control method in which an internal stress is constant, and the like can be used, and these methods can be used in different ways. The roll length of the optical film is preferably 1000-7200 m. In this case, the width is preferably 500 to 3200mm, and the film thickness is preferably 30 to 150 μm.

[ mechanism for occurrence of curling ]

Next, the reason why the curl is generated after the cast film 5 is peeled from the support 3 and the curl is increased when COP is used as compared with a cellulose-based resin will be described.

Fig. 4 schematically shows the principle of occurrence of curling in the cast film 5 after peeling from the support 3. For the sake of convenience of the following description, in the casting film 5 formed on the support 3, the surface on the support 3 side is also referred to as "B surface", and the surface on the opposite side (air side) to the support 3 is also referred to as "a surface".

Immediately after casting the dope on the support 3, the solvent is not evaporated and remains sufficiently, and therefore the resin (polymer) in the dope moves relatively freely on both the B surface side and the a surface side of the casting film 5. As the dope is transported on the support 3, drying proceeds, that is, the solvent evaporates, and the side a of the casting film 5 on the support 3 is closer to the air than the side B (the side B is blocked from the air by the presence of the support 3, and therefore the solvent is difficult to evaporate). Therefore, a large amount of solvent remains on the B surface side of the support 3 as compared with the a surface side of the casting film 5.

On the other hand, for the cement including COP and the cement including TAC, a difference occurs in the drying speed of the solvent on the support 3 due to the difference in the resin content. Specifically, the drying speed of the solvent on the support 3 is slow in the dope containing COP compared with the dope containing TAC. Therefore, on the support 3, the casting film 5 including the COP has more solvent remaining on the B surface side than the casting film including the TAC (wherein the COP and the TAC are the same in terms of the content ratio of the resin and the solvent in the dope, the film thickness and the casting width of the casting film).

If the casting film 5 is peeled from the support 3, the solvent remaining on the B surface side (the side in contact with the support 3) of the casting film 5 rapidly evaporates because the B surface side is in contact with air after the peeling, and as a result, volume shrinkage occurs on the B surface side of the casting film 5. At this time, the casting film 5 including the COP has more solvent remaining on the B surface side than the casting film including the TAC, and thus the volume shrinkage largely occurs. As a result, the casting film 5 including COP largely curls after being peeled from the support 3 as compared with the casting film including TAC. In particular, the casting film 5 containing COP is not stiff and is easily bent as compared with the casting film containing TAC, and thus the occurrence of curl is remarkably exhibited at the widthwise end portion of the casting film 5.

[ heating of casting film in conveying Process ]

Next, a method for reducing the curl of the cast film 5 after the peeling and ensuring the transport stability of the cast film 5 will be described.

Fig. 5 is an explanatory view showing a relative positional relationship between the casting film 5 and the heat source 15 in the above-described conveying section 11. In the figure, the arrangement of the heat source 15 is shown on one end side in the transverse direction of the casting film 5, and the same arrangement is also shown on the other end side. The heat source 15 is constituted by a blower device for locally heating the casting film 5 by blowing hot air to the casting film 5. The heat source 15 is disposed vertically above the film surface (film surface) of the casting film 5 so as not to contact the casting film 5, and heats the casting film 5 by blowing hot air vertically downward.

Here, in the present embodiment, the widthwise endmost portion E0 of the casting film 5 is not taken as an object of heating, but a region located laterally inward with respect to the widthwise endmost portion E0 is taken as an object-of-heating region R, which is heated by the heat source 15, thereby causing the casting film 5 to be locally heated in the widthwise direction. The widthwise outermost end E1 of the region R to be heated of the cast film 5 is located at a position that is a distance of P% of the full width w (mm) of the cast film 5 from the position corresponding to the widthwise outermost end E0 before the cast film 5 is peeled (before curling), and P is a value of 1% to 20% in the present embodiment. That is, the widthwise outermost end E1 of the heating target region R is in the range of 0.01W to 0.20W from the widthwise outermost end E0 before peeling to the widthwise inner side. The range of the full width W may be, for example, 1000 to 2000 (mm).

In order to alleviate the curl of the end portion of the casting film 5 generated according to the principle described above, after the casting film 5 is peeled from the support 3, the widthwise end portion of the casting film 5 is heated, and if the casting film 5 is heated so that P becomes less than 1%, the widthwise endmost portion E1 of the heating target region R coincides with or is very close to the widthwise endmost portion E0 of the casting film 5. In this case, the widthwise outermost end E0 or the vicinity thereof is dried excessively and hardened, and the vicinity of the widthwise outermost end E0 may be broken when the casting film 5 is wound around a roll (for example, the roll 14 or a roll in the drying device 7) during the subsequent conveyance, thereby causing a trouble in the conveyance. On the other hand, after the casting film 5 is peeled from the support 3, if the casting film 5 is heated in such a manner that P exceeds 20%, the widthwise endmost portion E1 of the heating target region R is away from the widthwise endmost portion E0 of the casting film 5, and the heating target region R is away from the curled portion, so that it becomes difficult to effectively alleviate (correct) the curl of the widthwise end portion of the casting film 5 by heating.

Among them, fig. 6 schematically shows a principle of alleviating the curl of the casting film by heating. The resin is an aggregate of long chain-like polymers, and the polymers are intricately entangled with each other by intermolecular interaction. By heating the curled portion of the casting film, the thermal movement of molecules in the heated region becomes large, and therefore the molecular spacing becomes wide and the intermolecular bonding force between the high molecules becomes weak. In the conveyance of the casting film, the casting film is stretched in the conveyance direction, and a stress (tension) acts in a direction in which the casting film becomes flat. Therefore, by heating in the conveyance of the casting film, it becomes possible to reduce the curl.

In the present embodiment, when the boiling point of the good solvent contained in the dope is T ℃, the surface temperature of the heating target region R using the heat source 15 at the time of heating is T +40 to T +110 ℃. For example, when dichloromethane is used as the good solvent, since dichloromethane has a boiling point T of 39 ℃, the surface temperature of the heating target region R is in the range of 79 ℃ to 149 ℃. In addition, when toluene is used as a good solvent, the boiling point T of toluene is 110 ℃, and therefore the surface temperature of the heating target region R is in the range of 150 to 220 ℃.

If the surface temperature of the heating target region R at the time of heating is a high temperature exceeding T +110 ℃, the curling is reduced by heating, but the casting film 5 itself is softened to such an extent that the flatness is no longer maintained (becomes warped), and wrinkles are generated, so that the transportability is deteriorated (stable transportation is no longer possible). On the other hand, if the surface temperature is low at T +40 ℃ or lower, the effect of reducing the curl is weak because heat is not applied to the heating target region R to such an extent that the orientation of the resin is disturbed, and particularly, in the case where the curl is largely generated as in COP, the effect of reducing the curl by heating becomes very weak.

Therefore, as in the present embodiment, when the casting film 5 peeled from the support 3 is heated by the heat source 15, by appropriately controlling the heating position (particularly, the position of the widthwise outermost end E1 of the region to be heated R) and the heating temperature, even when a resin (for example, COP) is used as the resin, which has a larger volume shrinkage than the cellulose-based resin on the support side (B-side) of the casting film 5 after peeling from the support 3, the curl due to the volume shrinkage can be reduced, and an optical film having excellent transport stability can be produced.

In addition, since the heat source 15 is disposed in non-contact with the casting film 5 to heat the casting film 5 in non-contact, a disadvantage when the casting film 5 is swaged to be heated does not occur. That is, even when the casting film 5 contains a large amount of solvent, the solvent can be evaporated without being confined inside when the casting film 5 after peeling is heated by the heat source 15, and thus foaming deformation of the casting film 5 can be prevented. Therefore, occurrence of a nip error or the like due to deformation of the casting film 5 can be reduced in the subsequent conveyance, and the conveyance can be reduced from becoming unstable.

The preferable range of P is 3% to 8%. That is, the effect of reducing curl is more effectively obtained as long as the widthwise outermost end E1 of the heating target region R is in the range of 0.03W or more and 0.08W or less laterally inward from the widthwise outermost end E0 before peeling. The preferable range of the surface temperature of the heating target region R during heating is T +70 to T +110 ℃.

The position of the end E2 on the opposite side of the widthwise outermost end E1 in the region to be heated R (the widthwise central side of the casting film 5) is not particularly limited, but if the end is located excessively on the widthwise central side, the end is close to the product portion (the portion remaining as a product when the widthwise end is finally cut), and the disturbance of the orientation by heating may also affect the product portion and deteriorate the quality of the product portion. Further, the width of the portion in which the orientation is disturbed by heating may be widened, and the width of the cast film 5 that can be used as a product portion may be narrowed. Therefore, the position of the widthwise central side end E2 of the region to be heated R is located at a position that is located inward in the widthwise direction by a distance of Q% of the full width w (mm) of the casting film 5 from the position corresponding to the widthwise outermost end E0 before the peeling (before curling) of the casting film 5, and Q is preferably a value of 30% or less, more preferably a value of 25% or less, and still more preferably a value of 20% or less.

However, in the peeling step of S3 described above, if the amount of residual solvent is too large when the casting film 5 is peeled from the support 3, a large amount of solvent evaporates on the B surface side of the casting film 5 after the peeling, and the volume shrinkage becomes large. Therefore, in the conveying step of S4, it becomes difficult to obtain the effect of reducing curl by the above-described heating using the heat source 15. Further, if the amount of the residual solvent at the time of peeling is too small, the amount of curl due to evaporation of the solvent after peeling is originally small, and therefore the effectiveness of the technique of the present embodiment in which the curl is reduced by heating with the heat source 15 is reduced. From the above, the amount of the residual solvent at the time of peeling the casting film 5 from the support 3 is preferably 15 to 55 mass%, more preferably 20 to 50 mass%, from the viewpoint of effectively and reliably reducing the curl by the technique of the present embodiment.

In the transport step of S4, the heating target region R may be heated by the heat source 15 while applying stress so that the lateral end portion of the cast film 5 curled after being peeled from the support 3 becomes flat. For example, even if the casting film 5 is merely conveyed as described above, the casting film 5 can be stressed with the tension in the conveying direction to make the lateral end portions flat. In addition, by increasing the wind pressure of the hot wind ejected from the heat source 15, stress can also be applied to the casting film 5 so that the lateral end portions become flat. By heating the region R to be heated while applying stress to the casting film 5 in this way, both stress and heating act on the reduction of the curl, and therefore, it is possible to efficiently reduce a large curl.

Fig. 7 shows another configuration of the conveying unit 11. The heat source 15 may heat the region R to be heated by jetting hot air from a direction inclined at an angle θ to the laterally inner side with respect to the direction perpendicular to the casting film 5. In this case, since the hot air is jetted from the oblique direction to the casting film 5 (heating target region R) from the laterally inner side to the laterally outer side, stress for flattening the lateral end portion of the casting film 5 can be applied. Therefore, by such hot air blowing, the heating target region R can be heated while applying stress to the lateral end portion of the casting film 5, and the curl can be reduced efficiently.

In particular, the angle θ is preferably 20 ° to 40 °. If the angle is within the above range, both the application of stress to the lateral end portion of the casting film 5 and the heating of the region to be heated R can be satisfactorily performed, and the effect of reducing curling can be further improved.

Fig. 8 shows still another configuration of the conveying unit 11. The heat source 15 may heat the heating target region R on the roller. The rollers may be the

rollers

12, 13, and 14 shown in fig. 3, and fig. 8 shows the roller 13 as an example. In this case, with the casting film 5, by the contact with the roller 13, that is, by the casting film 5 moving along the circumferential surface of the roller 13, the stress to flatten the widthwise end portion of the casting film 5 can be applied. Therefore, even in this case, it is possible to heat the region R to be heated while applying stress to the lateral end portions of the casting film 5, thereby efficiently reducing the curl. Further, by using the techniques of fig. 7 and 8 together, the curl reduction effect can be further improved.

As described above, since the heating target region R of the casting film 5 is heated by ejecting hot air from the heat source 15, heating by non-contact with the casting film 5 can be reliably realized.

Fig. 9 shows another configuration of the heat source 15. As the heat source 15, the heating target region R of the casting film 5 can be heated by irradiating Infrared Rays (IR). Even in this case, heating by non-contact with the casting film 5 can be reliably achieved by irradiation of infrared rays.

In the present embodiment, the resin (resin contained in the paste) used for the production of the optical film may include a cycloolefin-based resin (COP) or a polyimide-based resin (PI). In the case of film formation using COP or PI, curling occurs greatly after peeling because the drying rate of the solvent on the support 3 is slow compared to the case of film formation using a cellulose-based resin (e.g., TAC). Therefore, when COP or PI is used as the resin, the method of the present embodiment in which the curl is reduced by non-contact heating using the heat source 15 is very effective.

[ additives ]

In the production of the optical film, additives may be added to the dope as necessary. Examples of the additives include plasticizers, ultraviolet absorbers, retardation regulators, antioxidants, deterioration inhibitors, release aids, surfactants, dyes, and fine particles. In the present embodiment, additives other than the fine particles may be added at the time of preparation of the cement or at the time of preparation of the fine particle dispersion.

[ examples ]

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

< production 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 formation method).

Production of pellets of cycloolefin resin

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 put into a reactor at room temperature and mixed under a nitrogen atmosphere, and then 13 parts by mass of tricyclo [4.3.0.12, 5] deca-3, 7-diene (dicyclopentadiene, hereinafter abbreviated as DCP), 13 parts by mass of 8-methyl-8-methoxycarbonyltetracyclo [4.4.0.12, 5.17, 10] dodec-3-ene (hereinafter abbreviated as MMT) and 40 parts by mass of tungsten hexachloride (0.7% toluene solution) were continuously added thereto at 45 ℃ over 2 hours and polymerized. 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 deactivate the polymerization catalyst and stop the polymerization reaction.

Then, to 100 parts by mass of the obtained reaction solution containing the ring-opened polymer, 270 parts by mass of cyclohexane was added, and 5 parts by mass of a nickel-alumina catalyst (manufactured by Nikki-Kasei Co., Ltd.) as a hydrogenation catalyst was further added, and the mixture was pressurized to 5MPa with hydrogen, heated to 200 ℃ with stirring, and then reacted for 4 hours to obtain a reaction solution containing 20% DCP/MMT ring-opened polymer hydrogenated polymer.

After the hydrogenation catalyst was removed by filtration, a soft polymer (manufactured by strain クラレ; セプトン 2002) and an antioxidant (manufactured by strain チバスペシャリティ and ケミカルズ; イルガノックス 1010) were added to the obtained solution, respectively, and dissolved (each 0.1 part by mass per 100 parts by mass of the polymer). Then, cyclohexane and other volatile components as a solvent were removed from the solution using a cylindrical concentrating dryer (manufactured by hitachi corporation), and the hydrogenated polymer was extruded in a molten state from an extruder into a strand shape, cooled, and pelletized for recovery. The copolymerization ratio of each norbornene-based monomer in the polymer was calculated from the composition of the residual norbornene in the solution after polymerization (by gas chromatography), and the result was DCP/MMT/═ 13/87, which was substantially equal to the feed composition. The hydrogenated ring-opened polymer had a weight-average molecular weight (Mw) of 89000, a molecular weight distribution (Mw/Mn) of 2.5, a hydrogenation ratio of 99.9% and a Tg of 161 ℃.

The obtained cycloolefin resin pellets of the ring-opened polymer hydride were dried at 70 ℃ for 2 hours by using a hot air dryer through which air was passed, and water was removed.

Production of Fine particles 1

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

Manufacture of seeds

1000g of deionized water was placed in a polymerization reactor equipped with a stirrer and a thermometer, 200g of methyl methacrylate and 6g of t-dodecyl mercaptan were charged therein, and the mixture was heated to 70 ℃ while exchanging nitrogen with stirring. While the internal temperature was maintained at 70 ℃, 20g of deionized water containing 1g of potassium persulfate as a polymerization initiator was added thereto, and the mixture was polymerized for 10 hours. The average particle diameter of the polymer particles in the obtained emulsion was 0.44. mu.m.

Production of Polymer particles

800g of deionized water in which 3g of ammonium polyoxyethylene tridecyl ether sulfate was dissolved was placed in a polymerization vessel equipped with a stirrer and a thermometer, and a mixture of 144g of methyl acrylate, 22g of styrene, 34g of ethylene glycol dimethacrylate, and 1g of azobisisobutyronitrile as a polymerization initiator was placed therein. Next, the mixture was stirred with an T.K homomixer (manufactured by Special machine industries, Ltd.) to obtain a dispersion.

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

Production of aggregate of Polymer particles

After cooling, 50g of スノーテックス O-40 (manufactured by Nissan chemical industries, Ltd.: as colloidal silica (inorganic powder), 40% solid content, particle size: 0.02 to 0.03 μm) was added to the resulting slurry, and the mixture was stirred for 10 minutes using a T.K homomixer (manufactured by Special machine industries, Ltd.). The slurry was spray-dried under the following conditions using a spray dryer (model: Atomizer Take-up system, model: TRS-3WK) manufactured by Sabbon research, Inc., as a spray dryer to obtain a polymer particle aggregate. The average particle diameter of the polymer particle assembly was 30 μm.

Feeding speed: 25 ml/min

Rotating speed of the atomizer: 11000rpm

Air volume: 2m³Per minute

Slurry inlet temperature of spray dryer: 130 deg.C

Polymer particle aggregate exit temperature: 70 deg.C

Preparation of Fine particle Dispersion 1

Microparticle 1 was dispersed in マントンゴーリン after stirring and mixing 1.0 part by mass of microparticle 1 and 100 parts by mass of methylene chloride for 50 minutes with a dissolver.

Preparation of mucilage

Next, a master syrup 1 having the following composition was prepared. First, methylene chloride, ethanol, and toluene were added to a pressure dissolution tank. Next, the cycloolefin resin pellets produced as described above and the additive (LA-F70) were put into a pressure dissolution tank while being stirred. Next, the fine particle dispersion liquid 1 prepared above was charged, heated to 60 ℃, and completely dissolved while stirring. The heating temperature was increased from room temperature at 5 ℃ per minute, dissolved for 30 minutes, and then decreased at 3 ℃ per minute.

The resulting solution had a viscosity of 7000cp and a water content of 0.50%. The filtrate was subjected to filtration at a flow rate of 300L/m using SHP150 (manufactured by KAISH corporation) ロキテクノ²H, filtration pressure 1.0X 10⁶Filtering under Pa to obtain main mucilage 1.

Composition of main mucilage 1

Film making

Next, the main dope 1 was uniformly cast on a support made of a stainless steel band at a temperature of 31 ℃ and a width of 1800mm using an endless belt casting apparatus. At this time, the temperature of the support was controlled to 28 ℃. The transport speed of the support was set to 20 m/min.

On the support, the solvent was evaporated until the amount of the residual solvent in the casting film became 35 mass%. Next, the casting film was peeled from the support with a peeling tension of 128N/m. Then, in a conveying step of conveying the peeled film by a plurality of rollers, the lateral end portion of the casting film is heated between the rollers using a heat source.

In this case, as the heat source, a blower for blowing hot air was used, and the heat source was disposed at a position where the distance between the hot air outlet and the cast film became 30 mm. The dimensions of the hot air outlet were 30mm in the transverse direction and 200mm in the longitudinal direction of the casting film. Then, hot air is blown perpendicularly (from the vertically upper side) from a heat source to the casting film (heating target region) to heat the heating target region so that the widthwise outermost end portion of the heating target region of the casting film is located at a position which is located inward in the widthwise direction by 8% of the entire width of the casting film before peeling (before curling) from a position corresponding to the widthwise outermost end portion of the casting film before peeling. The surface temperature of the heating target region at this time was measured by a non-contact infrared sensor, and the result was 80 ℃. The dimension in the transverse direction of the hot air outlet of the heat source was 30mm, and the position on the transverse center side of the heating target region was clearly a position away from the position corresponding to the transverse outermost end of the cast film before peeling by a distance of 30% or less of the total width of the cast film before peeling in order to eject hot air to the cast film from vertically above.

In the transporting process, after the casting film was heated by the heat source as described above, the casting film was stretched 1.2 times in the transporting direction at 120 ℃ and, secondly, 1.1 times in the width direction at 150 ℃ by using a tenter. Then, the end portion held by the tenter clips was slit and then wound to obtain an optical film 1 having a film thickness of 60 μm.

< production of optical film 2 >

An optical film 2 was produced in the same manner as the production of the optical film 1 except that hot air was blown perpendicularly from a heat source to the cast film to heat the region to be heated so that the widthwise outermost end portion of the region to be heated of the cast film was located at a position that entered only 1% of the full width of the cast film before peeling from a position corresponding to the widthwise outermost end portion of the cast film before peeling toward the widthwise inner side when the cast film was heated in the transport step.

< production of optical film 3 >

An optical film 3 was produced in the same manner as the production of the optical film 1 except that hot air was blown perpendicularly from a heat source to the cast film to heat the region to be heated so that the widthwise outermost end portion of the region to be heated of the cast film was located at a position that entered only 20% of the full width of the cast film before peeling from a position corresponding to the widthwise outermost end portion of the cast film before peeling toward the widthwise inner side.

< production of optical film 4 >

An optical film 4 was produced in the same manner as the production of the optical film 1 except that hot air was blown perpendicularly from a heat source to the cast film to heat the region to be heated so that the widthwise outermost end portion of the region to be heated of the cast film was located at a position that entered only 3% of the full width of the cast film before peeling from a position corresponding to the widthwise outermost end portion of the cast film before peeling toward the widthwise inner side.

< production of optical film 5 >

An optical film 5 was produced in the same manner as the production of the optical film 1 except that hot air was blown perpendicularly from a heat source to the cast film to heat the region to be heated so that the widthwise outermost end portion of the region to be heated of the cast film was located at a position that entered only 25% of the full width of the cast film before peeling from a position corresponding to the widthwise outermost end portion of the cast film before peeling toward the widthwise inner side.

< production of optical film 6 >

An optical film 6 was produced in the same manner as the optical film 1 except that the widthwise outermost end portion of the cast film was heated in the transport step. That is, the optical film 6 was produced in the same manner as the production of the optical film 1 except that hot air was blown perpendicularly from a heat source to the cast film to heat the region to be heated so that the widthwise outermost end portion of the region to be heated of the cast film was located at a position that entered only 0% of the full width of the cast film before peeling from a position corresponding to the widthwise outermost end portion of the cast film before peeling toward the widthwise inner side when the cast film was heated.

< production of optical film 7 >

An optical film 7 was produced in the same manner as the optical film 1 except that the casting film was not heated by the heat source in the transport step.

< production of optical film 8 >

An optical film 8 was produced in the same manner as the optical film 1 except that the cast film was heated in the transport step so that the surface temperature of the heating target region became 95 ℃.

< production of optical film 9 >

The optical film 9 was produced in the same manner as the optical film 1 except that the cast film was heated in the transport step so that the surface temperature of the heating target region became 150 ℃.

< production of optical film 10 >

An optical film 10 was produced in the same manner as in the production of the optical film 1, except that toluene (boiling point 110 ℃) was used instead of methylene chloride, and the cast film was heated so that the surface temperature of the heating target region became 150 ℃ in the transport step.

< production of optical film 11 >

An 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.

In a 4-neck flask equipped with a dry nitrogen introduction tube, a condenser, a Dean-Stark condenser filled with toluene, and a stirrer, 25.59g (57.6mmol) of 2, 2-bis (3, 4-dicarboxyphenyl) -1, 1, 1, 3, 3, 3-hexafluoropropane dianhydride was added to N, N-dimethylacetamide (134g), and the mixture was stirred at room temperature under a nitrogen stream. 19.2g (60mmol) of 4, 4 '-diamino-2, 2' -bis (trifluoromethyl) biphenyl was added thereto, and the mixture was stirred with heating at 80 ℃ for 6 hours. Then, the external temperature was heated to 190 ℃ to azeotropically distill off water generated with imidization together with toluene. Heating, refluxing and stirring were continued for 6 hours, and as a result, water was not produced. Subsequently, the mixture was heated for 7 hours while toluene was distilled off, and after toluene was distilled off, methanol was added thereto and reprecipitation was carried out to obtain a polyimide represented by the following formula.

[ solution 1]

< production of optical film 12 >

An optical film 12 was produced in the same manner as the optical film 11 except that the cast film was heated in the transport step so that the surface temperature of the heating target region became 150 ℃.

< production of optical film 13 >

An optical film 13 was produced in the same manner as the optical film 1 except that the cast film was heated in the transport step so that the surface temperature of the heating target region became 70 ℃.

< production of optical film 14 >

An optical film 14 was produced in the same manner as the optical film 1 except that the cast film was heated in the transport step so that the surface temperature of the heating target region became 160 ℃.

< evaluation >

(curl amount)

The warp height of the end portion due to the curl was measured from a reference surface (position of the widthwise central portion) on the inner side in the widthwise direction of the cast film before entering the tenter using a laser displacement meter, and the curl amount was evaluated based on the following evaluation criteria.

Reference to evaluation

Very good: the curl amount is 3mm or less.

O: the curl amount is larger than 3mm and is 7mm or less.

X: the curl amount is larger than 7mm and not more than 14 mm.

X: the curl amount is larger than 14 mm.

(end warping)

Whether or not the casting film is excessively softened by heating in the transport step and wrinkles are generated at the lateral end portions of the casting film is judged by the appearance, and the end portion warpage is evaluated based on the following evaluation criteria.

Reference to evaluation

Very good: no end warping occurred at all.

O: end warping hardly occurs.

And (delta): the end portion was found to be warped to a small extent, but to a range without problems.

X: end warping occurs considerably, with problems.

(transportability)

The conveyance property of the cast film was evaluated for appearance based on the following evaluation criteria.

Very good: the transport is very stable.

O: some wrinkles were generated in the delivery, but the delivery was stable.

And (delta): wrinkles are generated in the conveyance, but there is no great obstacle to the conveyance.

X: a clamping error due to curling, a breakage of an end portion, or a breakage due to a wrinkle during conveyance occurs, and conveyance is unstable.

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

From tables 1 and 2, it can be seen that: in the production of the optical films 5 to 7, 13 and 14, the amount of curling is not reduced and the conveyance is unstable. In the production of the optical film 7, the cast film peeled from the support is not heated at the end portion, and therefore, the curl at the end portion cannot be reduced. Further, it is considered that: since the cast film is conveyed in a state where the curl remains, a nipping error occurs in the subsequent tenter, and the conveyance becomes unstable. In the production of the optical film 6, it is considered that: since the widthwise outermost end portion of the cast film after the peeling is heated, the curled portion inside the widthwise outermost end portion cannot be efficiently heated, and thus, where the effect of reducing the amount of curling is small, the widthwise outermost end portion is excessively dried, and the end portion is broken in the subsequent conveyance, and the conveyance becomes unstable. In the production of the optical film 5, it is considered that: since the portion of the cast film peeled off from the widthwise outermost end portion to the inner side is heated to an excessive extent, even if the curling of the end portion can be reduced, the effect is small, and as a result, a nip error in the tenter due to the curling occurs, and the conveyance becomes unstable.

In the production of the optical film 13, it is considered that: the surface temperature of the heating target region of the cast film after peeling was 70 ℃, and excessively decreased, the effect of reducing curling due to heating was low, a pinching error due to curling occurred, and conveyance became unstable. In the fabrication of the optical film 14, it is considered that: the surface temperature of the heating target region of the cast film after peeling was too high, 160 ℃, and therefore, the end portion of the cast film was softened to generate wrinkles, and breakage due to wrinkles occurred during the subsequent conveyance, and the conveyance became unstable. In the production of the optical film 14, the amount of curl could not be measured due to softening of the end portions.

In the production of the optical films 1 to 4 and 8 to 12, the curl amount, the end warp, and the conveyance property were all good (evaluated as "excellent", "good", or "Δ"). In the production of the optical films 1 to 4 and 8 to 12, when a heating target region, which is a part in the transverse direction of the cast film peeled from the support, is heated, the transverse outermost end of the heating target region is located at a position that is located at a distance of P% of the entire width of the cast film from a position corresponding to the transverse outermost end of the cast film before peeling to the transverse inner side, P is 1% or more and 20% or less, the boiling point of the good solvent is T ℃, and the heating target region is heated so that the surface temperature is T +40 ℃ to T +110 ℃. It is considered that, since the heating position and the heating temperature are appropriately controlled for the cast film as described above, even when COP or PI is used as the resin, that is, even when a cellulose-based resin is used, the occurrence of warp at the end portion of the cast film after peeling can be suppressed, and the curl can be effectively reduced, whereby there is no pinching error due to the curl or breakage due to wrinkles, and the conveyance can be stably performed.

In particular, in the production of the

optical films

1 and 4, since the amount of curling is effectively reduced and the conveyance is very stably performed, it can be said that P is preferably 3% or more and 8% or less.

< production of optical film 15 >

An optical film 15 was produced in the same manner as the production of the optical film 1, except that the solvent was evaporated on the support until the amount of the residual solvent in the casting film became 10% by mass.

< production of optical film 16 >

An optical film 16 was produced in the same manner as the production of the optical film 1, except that the solvent was evaporated on the support until the amount of the residual solvent in the casting film became 60% by mass.

< production of optical film 17 >

An 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 casting film became 20% by mass.

< production of optical film 18 >

An optical film 18 was produced in the same manner as the production of the optical film 1, except that the solvent was evaporated on the support until the amount of the residual solvent in the casting film became 50% by mass.

The optical films 15 to 18 were evaluated for the amount of curling, end warping, and transportability based on the same evaluation criteria as described above. The results of evaluation of the manufactured optical films 15 to 18 are shown in table 3.

From table 3 it follows: when the residual solvent amount of the casting film at the time of peeling is 10 to 60 mass%, the effect of reducing the curl amount is not impaired, and peeling from the support becomes possible. In particular, if the residual solvent amount of the casting film at the time of peeling is 20% by mass to 50% by mass, it can be said that the effect of reducing the amount of curl is largely obtained and peeling can be performed.

Among them, since the amount of curl is 6mm when the amount of residual solvent is 10% by mass and 5mm when the amount of residual solvent is 20% by mass, it can be estimated that: if the residual solvent content is 15 mass% or more of the total amount, the effect of reducing the amount of curling is high. Similarly, since the amount of curl is 6mm when the amount of residual solvent is 60 mass% and 5mm when the amount of residual solvent is 50 mass%, it can be estimated that: if the residual solvent content is 55 mass% or less, the effect of reducing the amount of curling is high. From this, it can be said that the preferable range of the residual solvent amount of the casting film at the time of peeling is 15 to 55 mass%.

In addition, since the amount of curl is 5mm when the amount of residual solvent is 20 mass%, and 4mm when the amount of residual solvent is 35 mass%, it can be estimated that: if the residual solvent amount is 25% by mass or more of the amount, the effect of reducing the curl amount is higher. Similarly, since the amount of curl is 5mm when the amount of residual solvent is 50 mass% and 4mm when the amount of residual solvent is 35 mass%, it can be estimated that: if the residual solvent amount is 45 mass% or less, the effect of reducing the curl amount is higher. From this, it can be said that a more preferable range of the residual solvent amount of the casting film at the time of peeling is 25% by mass to 45% by mass.

< production of optical film 19 >

An optical film 19 was produced in the same manner as the production of the optical film 1, except that the heat source was disposed obliquely so that the region to be heated could be heated from a direction inclined by only 20 ° toward the laterally inner side with respect to the direction perpendicular to the cast film (direction inclined by 70 ° with respect to the horizontal plane) in the transport step after the cast film was peeled from the support. The position of the heat source in the transverse direction was shifted slightly to the transverse inner side so that the position of the transverse outermost end of the heating target region (the position from the transverse outermost end of the cast film before peeling to 8% of the full width) was the same as that at the time of manufacturing the optical film 1 (in the case of inclining the heat source in the following manufacturing of the optical film, the heat source was similarly shifted).

< production of optical film 20 >

An optical film 20 was produced in the same manner as the production of the optical film 1, except that the heat source was disposed obliquely so that the region to be heated could be heated from a direction inclined by only 40 ° toward the laterally inner side with respect to the direction perpendicular to the cast film (direction inclined by 50 ° with respect to the horizontal plane) in the transport step after the cast film was peeled from the support.

< production of optical film 21 >

An optical film 21 was produced in the same manner as the production of the optical film 1 except that the heating target region was heated from vertically above by a heat source on an arbitrary roll while the cast film peeled from the support was conveyed by at least 1 roll.

< production of optical film 22 >

An optical film 22 was produced in the same manner as the production of the optical film 21, except that the heat source was disposed obliquely so that the region to be heated could be heated from a direction inclined by only 40 ° toward the laterally inner side with respect to the direction perpendicular to the cast film (direction inclined by 50 ° with respect to the horizontal plane) in the transport step after the cast film was peeled from the support.

< production of optical film 23 >

An optical film 23 was produced in the same manner as the production of the optical film 22 except that in the transport step after the cast film was peeled from the support, the infrared heater was used as a heat source for heating the cast film, and infrared light was irradiated to the cast film to heat the region to be heated.

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

In table 4, from a comparison of the

optical films

1, 19, 20, it is known that: the amount of curl is reduced as the heat source is inclined laterally inward from the vertical direction. This is believed to be due to: by inclining the heat source from the vertical direction to the laterally inner side, the force (wind pressure) of the hot wind jetted from the oblique direction to the cast film acts as stress for flattening the lateral end portion (curled portion). In particular, it is preferable to reliably obtain the effect of reducing curling in the case of heating by ejecting hot air to the region to be heated from a direction inclined by only 20 ° to 40 ° laterally inward with respect to the direction perpendicular to the cast film (a direction inclined by 50 ° to 70 ° with respect to the horizontal plane).

In addition, by comparing the optical film 1 with the optical film 21, and the optical film 20 with the optical film 22, it can be said that the effect of reducing curling when heating is performed when the casting film is placed on the roller is higher for the widthwise end portion of the casting film than when heating is performed when the casting film is placed between the roller and the roller. It is considered that the reason is: if the casting film is heated while being on the roller, stress that flattens the widthwise end portion at the time of contact with the roller (at the time of nipping the roller) is applied to the casting film.

In particular, the amount of curl is minimal in the fabrication of the optical film 22. This is believed to be due to: in the conveying step, the oblique arrangement of the heat source is used in combination with the heating on the roller, and the effect of reducing the curl amount is the highest.

In addition, in the production of the optical film 23, the effect of reducing the amount of curl is slightly inferior to that in the production of the optical film 22. This is believed to be due to: in the irradiation of infrared rays, there is no pressing of the casting film by the jetting of hot air, that is, no stress to flatten the widthwise end portion is applied to the casting film. However, even when the infrared ray is irradiated, a very high effect of reducing the curl amount is obtained, and it can be said that the method is effective as a means for heating the edge portion of the casting film.

[ others ]

The method for producing an optical film according to the present embodiment described above can be expressed as follows.

1. A method for producing an optical film, comprising the steps of: a casting step of casting a dope containing a resin different from the cellulose-based resin and a good solvent on a support to form a casting film, a peeling step of peeling the casting film from the support, a conveying step of conveying the casting film peeled from the support by a roller, and a stretching/drying step of stretching or drying the casting film conveyed by the roller to form an optical film,

in the transporting step, a heating target region which is a part of the casting film peeled from the support in the transverse direction is heated by a heat source which is not in contact with the casting film,

the transverse extreme end of the heating target area is located at the following positions: a position which is located laterally inward from a position corresponding to a laterally outermost end of the cast film before peeling by a distance of P% of the total width of the cast film,

the content of P is 1% to 20%,

when the boiling point of the good solvent is T ℃, the surface temperature of the heating target region during heating is T +40 ℃ to T +110 ℃.

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

3. The method of manufacturing an optical film according to 1 or 2, wherein in the transporting step, the heating target region is heated by the heat source while applying stress so that a lateral end portion of the cast film curled after being peeled from the support becomes flat.

4. The method of manufacturing an optical film according to the above 3, wherein the heat source heats the region to be heated in a direction inclined by an angle θ inward in a lateral direction with respect to a direction perpendicular to the cast film.

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

6. The method for producing an optical film according to any one of the above 3 to 5, wherein the heat source heats the region to be heated on the roller.

7. The method of manufacturing an optical film according to any one of 1 to 6, wherein the heat source heats the region to be heated by injecting hot air.

8. The method of manufacturing an optical film according to any one of 1 to 6, wherein the heat source heats the region to be heated by irradiating infrared rays.

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

The embodiments of the present invention have been described above, but the scope of the present invention is not limited to the above, and the present invention can be implemented by expanding or changing the scope without departing from the gist of the present invention.

Industrial applicability

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 cellulose-based resin.

Description of reference numerals

3 support body

5 casting film

13 roller

15 heat source

Transverse extreme end of E0 casting film

E1 heating the transverse extreme end of the target area

R heating target region

Claims

1. A method for manufacturing an optical film, comprising the steps of: a casting step of casting a dope containing a resin different from a cellulose-based resin and a good solvent on a support to form a casting film, a peeling step of peeling the casting film from the support, a conveying step of conveying the casting film peeled from the support by a roller, and a stretching/drying step of stretching or drying the casting film conveyed by the roller to form an optical film,

the widthwise endmost portions of the heating target region are located at the following positions: a position which is located laterally inward from a position corresponding to a laterally outermost end of the cast film before peeling by a distance of P% of the full width of the cast film,

the P% is 1% or more and 20% or less,

2. The method of manufacturing an optical film according to claim 1, wherein in the peeling step, a residual solvent amount at the time of peeling of the casting film is 15% by mass to 55% by mass.

3. The method of manufacturing an optical film according to claim 1 or 2, wherein in the transporting step, the heating target region is heated by the heat source while applying stress so that a lateral end portion of the cast film curled after being peeled from the support becomes flat.

4. The method of manufacturing an optical film according to claim 3, wherein the heat source heats the region to be heated from a direction inclined by only an angle θ to a laterally inner side with respect to a direction perpendicular to the casting film.

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

6. The method for manufacturing an optical film according to claim 3, wherein the heat source heats the heating target region on the roller.

7. The method of manufacturing an optical film according to claim 1 or 2, wherein the heat source heats the heating target region by jetting hot air.

8. The method of manufacturing an optical film according to claim 1 or 2, wherein the heat source heats the heating target region by irradiating infrared rays.

9. The method for manufacturing an optical film according to claim 1 or 2, wherein the resin comprises a cycloolefin-based resin or a polyimide-based resin.