WO2014188993A1

WO2014188993A1 - Method for producing optical film

Info

Publication number: WO2014188993A1
Application number: PCT/JP2014/063179
Authority: WO
Inventors: 達希萩原
Original assignee: コニカミノルタ株式会社
Priority date: 2013-05-24
Filing date: 2014-05-19
Publication date: 2014-11-27
Also published as: JP6264373B2; JPWO2014188993A1

Abstract

The objective of the present invention is to provide a method for producing an optical film, which is a method for producing an optical film that has a reduced thickness and an increased width, and wherein the generation of scratches due to conveyance rollers and the occurrence of optical unevenness are reduced by suppressing abrupt increase in the stretching stress during stretching in the MD direction and by increasing the orientation of a resin in the film. A method for producing an optical film according to the present invention, wherein an optical film having a film thickness within the range of 10-40 μm and a width of 1.4 m or more is produced by a solution casting method, is characterized in that a web separated from a cast supporting body is preliminarily stretched in the MD direction at a stretch ratio within the range of from 1.01-1.10 times, and is then subjected to main stretching in the MD direction.

Description

Manufacturing method of optical film

The present invention relates to a method for producing an optical film. More specifically, the present invention relates to a method for manufacturing a thinned and widened optical film, and relates to a method for manufacturing an optical film in which generation of scratches and optical unevenness is reduced.

In recent years, liquid crystal display devices such as liquid crystal televisions tend to be thinner and larger, and accordingly, an optical film generally used as a member such as a polarizing plate protective film is also required to be thinner and wider. ing.

Conventionally, as a means for thinning a melt film-forming film, it is known to increase the total draw ratio in the longitudinal direction and the width direction, and as a means to widen the width, particularly to increase the draw ratio in the width direction. .
However, an optical film obtained by stretching a film produced by the solution casting method in the longitudinal direction (hereinafter referred to as the MD direction) or the width direction (hereinafter referred to as the TD direction) at a higher draw ratio than the conventional film. Since the stretching stress increases abruptly in the initial stage of stretching, scratches due to friction of the transport roller or the like are likely to occur during the manufacturing process. In particular, when the film is stretched at a high stretching ratio in the MD direction, the film easily slips on the transport roller immediately before stretching, and the scratches are likely to occur.

Further, by performing stretching at a high stretching ratio, the stretching stress applied to the film is likely to be nonuniform, and optical unevenness due to disorder of the orientation of the thermoplastic resin in the film is likely to occur.

Disclosed is a method for producing a cellulose acylate film in which the orientation of the thermoplastic resin of the optical film is eliminated by stretching in the MD direction in a high residual solvent state and then in the TD direction in a low residual solvent state. (For example, refer to Patent Document 1).

Japanese Patent No. 4277575

However, the draw ratio described in the Examples of Patent Document 1 is at most about 7% in the MD direction and about 10% in the TD direction, and this method has a small draw ratio, which contributes to widening and thinning. Furthermore, with the technique disclosed in Patent Document 1, it is difficult to eliminate the disorder of the orientation of the thermoplastic resin in the film, which is easily caused by stretching at a high stretching ratio as in the present invention.

Production conditions for reducing the stretching stress applied to the film while increasing the stretching ratio in the MD direction include methods such as increasing the stretching temperature and increasing the amount of residual solvent during stretching. Therefore, the necessary physical properties as an optical film cannot be obtained.

As another method, it is considered that the method of performing stretching a plurality of times by reducing the stretching ratio performed at one time can suppress a rapid increase in stretching stress without reducing the orientation of the thermoplastic resin. However, there is a problem that a long apparatus is required and the production cost is greatly increased.

Therefore, it is possible to reduce the occurrence of scratches and optical unevenness caused by the transport roller by suppressing the rapid increase in stretching stress and increasing the orientation of the thermoplastic resin in the film without requiring the introduction of large equipment. There is a need for a method for producing optical films.

The present invention has been made in view of the above-described problems and circumstances, and a solution to the problem is a method for producing a thinned and widened optical film, and the stretching stress is rapidly increased during stretching in the MD direction. It is intended to provide a method for producing an optical film that suppresses a significant increase and enhances the orientation of a thermoplastic resin in the film and reduces the occurrence of scratches and optical unevenness caused by a transport roller.

In order to solve the above-mentioned problems, the present inventor is a method for producing a thinned and widened optical film in the process of examining the cause of the above-mentioned problem, and a specific stretching at the time of stretching in the MD direction. By performing pre-stretching of magnification and then performing main stretching, the rapid increase in stretching stress is suppressed, and the orientation of the thermoplastic resin in the film is enhanced. The present inventors have found that a method for producing an optical film with reduced can be obtained.

That is, the above-mentioned problem according to the present invention is solved by the following means.

1. An optical film manufacturing method for manufacturing an optical film having a thickness in a range of 10 to 40 μm and a width of 1.4 m or more by a solution casting method, wherein a web peeled from a casting support is MD A method for producing an optical film, wherein the film is pre-stretched in a range of 1.01 to 1.10 times as a stretching ratio in the direction, and further stretched in the MD direction.

2. 2. The method for producing an optical film according to item 1, wherein the main stretching is performed in a range of 1.15 to 2.50 times as a stretching ratio.

3. The pre-stretching is performed within the range of 20 to 100% by mass of the residual solvent represented by the following formula of the web at the start of stretching, and the main stretching is performed at a residual solvent amount of 1 to 30% by mass at the start of stretching. The method for producing an optical film according to item 1 or 2, wherein the method is performed within a range of%.

Residual solvent amount (% by mass) = {(mass before heat treatment of web−mass after heat treatment of web) / (mass after heat treatment of web)} × 100
However, the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

4. When the glass transition temperature of the optical film is Tg (° C.), the preliminary stretching is performed at a temperature within the range of (Tg-100) to (Tg-20) ° C., and the main stretching is performed (Tg-10) to (T The method for producing an optical film according to any one of Items 1 to 3, wherein the method is performed at a temperature within a range of Tg + 100) ° C.

5. The method for producing an optical film according to any one of Items 1 to 4, wherein a stretch span of the preliminary stretching is 2 m or less, and a stretch span of the main stretching is 2 m or more.

6. 6. The pre-stretching and main stretching in the MD direction, followed by stretching in the range of 1.3 to 3.0 times in the TD direction, according to any one of items 1 to 5 Manufacturing method of optical film.

7). The thermoplastic resin used for the optical film is selected from any of cellulose acylate, acrylic resin, and a resin in which cellulose acylate and acrylic resin are mixed. The manufacturing method of the optical film of one term.
8). The method for producing an optical film according to claim 7, wherein the thermoplastic resin used for the optical film is an acrylic resin.

A method for producing an optical film that has been thinned and widened by the above-described means of the present invention, wherein a rapid increase in stretching stress is suppressed during stretching in the MD direction, and the orientation of the thermoplastic resin in the film By increasing the ratio, it is possible to provide a method for producing an optical film in which the generation of scratches and the occurrence of optical unevenness by the transport roller is reduced.

The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

As described above, with the thinning and enlargement of polarizing plates and liquid crystal display devices, there is a demand for optical films that are high quality and thin film / wide, but thin films that are stretched at a high draw ratio in the MD and TD directions. / A widened optical film is likely to be scratched due to friction of a transport roller or the like in the manufacturing process, particularly when the stretching stress increases rapidly in the initial stage of stretching in the MD direction. In addition, the stress applied to the film during stretching is likely to be non-uniform in a wide film, and optical unevenness due to uneven orientation of the thermoplastic resin is likely to occur, which has been a factor hindering high production. In particular, the scratches are likely to occur when the web slips on the transport roller immediately before stretching when stretching in the MD direction.

The inventor presumed that the cause of the sudden increase in the stretching stress in the initial stage of stretching was due to the entanglement of the resin chains of the thermoplastic resin.
Compared to the melt casting method, the solution casting method has the advantage that even a high molecular weight thermoplastic resin that easily increases the elastic modulus of the film can be cast, whereas the high molecular weight thermoplastic resin is a resin chain-to-resin chain. Since there are many entanglement points, stress concentration is likely to occur, and the resin is difficult to stretch during stretching. This difficulty in stretching the resin is considered to be the cause of increasing the stress during stretching. In addition, increasing the stretching ratio in the MD direction and increasing the stretching speed in order to reduce the film thickness and increase the production also cause the stretching stress to increase synergistically.

According to the inventor's study, by performing a low-strength pre-stretching under specific conditions before the main stretching, the entanglement points between the resin chains are effectively loosened and reduced, and then the main stretching is performed at a high magnification. Even when the resin chains are stretched, stress points due to the entanglement between the resin chains are less likely to occur because the entanglement points between the resin chains are reduced in the previous step. Therefore, the rapid increase in stretching stress can be suppressed, and further weak orientation can be given by pre-stretching, so that the orientation of the resin is easily aligned by main stretching, and the occurrence of scratches and optical unevenness can be reduced. Inferred. Furthermore, since the pre-stretching is a low-magnification stretching, the resin is not strong enough to inhibit the resin orientation during the main stretching, but the entanglement points between the resin chains are reduced, so that the MD direction. It is presumed that the effect of the main stretching and stretching in the TD direction can be enhanced, retardation unevenness of the film width can be suppressed, and uniform optical characteristics can be imparted.

The schematic diagram which shows an example of the manufacturing apparatus which enforces the manufacturing method of the optical film of this invention

The method for producing an optical film of the present invention is a method for producing an optical film in which an optical film having a thickness of 10 to 40 μm and a width of 1.4 m or more is produced by a solution casting method. The web peeled from the stretched support is pre-stretched within a range of 1.01 to 1.10 times in the MD direction, and further stretched in the MD direction. This feature is a technical feature common to the inventions according to claims 1 to 8.

If the draw ratio of the preliminary drawing is within the above range, there is no resin orientation strong enough to affect the resin orientation control in the main drawing, and the resin chains are easily loosened sufficiently.

As an embodiment of the present invention, from the viewpoint of manifesting the effects of the present invention, it is preferable that the main stretching is performed within a range of 1.15 to 2.50 times as a draw ratio from the viewpoint of thinning. Since the entanglement points between the resin chains are reduced by the preliminary stretching according to the present invention, even if the main stretching is performed at a high stretching ratio as in the above range, a low stretching stress can be maintained, and scratches caused by the transport roller. And the occurrence of optical unevenness can be reduced.
Further, the preliminary stretching is performed within the range of 20 to 100% by mass of the residual solvent at the start of stretching, and the main stretching is performed within the range of 1 to 30% by mass of the residual solvent at the start of stretching. Further, the preliminary stretching is performed at a temperature within the range of (Tg-100) to (Tg-20) ° C. when the glass transition temperature of the optical film is Tg, and the main stretching is performed at (Tg-10) to Performing within the range of (Tg + 100) ° C. is preferable because it suppresses a rapid increase in stretching stress, increases the orientation of the resin in the film, and reduces the occurrence of scratches and optical unevenness due to the transport roller.

Also, if the residual solvent amount and the stretching temperature during the pre-stretching are within the above ranges, there is no strong resin orientation that affects the orientation control of the resin in the main stretching, and the resin chains are also easily loosened.

Furthermore, if the temperature at the time of pre-stretching is within the above range, the drying speed of the solvent is high, the possibility of foaming due to volatilization of the solvent is low, and a special heating device is not required, so that the productivity is improved.

The stretching span of the preliminary stretching is preferably 2 m or less. From the viewpoint of equipment, it is preferable that the stretch span is as small as possible. However, if the span is too short, it becomes difficult to place the stretch span. Here, the stretching span refers to a length in which the film is stretched in the MD direction, and specifically refers to a length in which the film is conveyed to the rollers in a non-contact manner, that is, a distance between the rollers. In addition, when a clip tenter or the like is used for stretching, it means the interval between the clips.

The stretching span of the main stretching is preferably 2 m or more. This is because if the stretching span is short with respect to the film width, the width shrinkage is restricted, and there is a concern that uniform stretching cannot be performed.

In the method for producing an optical film of the present invention, the film is preliminarily stretched in the MD direction, followed by main stretching, and then stretched in the range of 1.3 to 3.0 times in the TD direction for thinning and widening. It is preferable from the viewpoint of obtaining a thin film and a wide optical film. Moreover, the elasticity modulus of MD direction of a film and TD direction improves by extending | stretching to a TD direction, and it is preferable.

Further, the thermoplastic resin used for the optical film is selected from any of cellulose acylate, acrylic resin, and a resin in which cellulose acylate and acrylic resin are mixed. From the viewpoint of obtaining. Furthermore, since the effect of the present invention is more easily manifested when the thermoplastic resin is an acrylic resin, it is suitable for application to an acrylic resin film.

Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In the present application, “˜” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

<< Outline of Manufacturing Method of Optical Film of the Present Invention >>
The method for producing an optical film of the present invention is a method for producing an optical film in which an optical film having a thickness of 10 to 40 μm and a width of 1.4 m or more is produced by a solution casting method. The web peeled from the extended support is pre-stretched in the range of 1.01 to 1.10 times in the MD direction, and further stretched in the MD direction. By adopting such a production method, An optical film in which the occurrence of scratches and optical unevenness due to the transport roller is reduced by suppressing the sudden increase in stretching stress and enhancing the orientation of the resin in the film during stretching in the MD direction. It is to provide. Hereinafter, the optical film manufactured by the manufacturing method of the optical film of the present invention is referred to as “the optical film of the present invention” in the present application.

“Preliminary stretching” as used in the present invention refers to a low-magnification stretching operation performed before “main stretching” for stretching at a high magnification, and specifically, a range of 1.01 to 1.10 times in the MD direction. This is the stretching performed inside.

<Optical film manufacturing equipment>
First, the manufacturing apparatus used for implementing the manufacturing method of the optical film of this invention is demonstrated.

FIG. 1 is a schematic view showing an example of a production apparatus for carrying out the method for producing an optical film of the present invention.

As shown in FIG. 1, the optical film manufacturing apparatus 1 according to this embodiment includes a casting apparatus 101, a preliminary stretching apparatus 102 in the MD direction, a main stretching apparatus 103 in the MD direction, and stretching in the TD direction. The apparatus 104, the drying apparatus 105, and the winding apparatus 106 are provided, and the film (web) 3 formed by the casting apparatus 101 is transported, and preliminary stretching is performed in the MD direction by the preliminary stretching apparatus 102. Then, the main stretching apparatus 103 performs high-stretching in the MD direction in the same manner. Further, if necessary, the film is stretched in the TD direction by a stretching device 104 in the TD direction, dried (heat treated) by a drying device 105, and wound as an optical film by a winding device 106. The web 3 may be dried by disposing a drying device between the first stretching device 102 and the second stretching device 103.

Here, the cast film (web) refers to a film in which a dope in which a resin, an additive or the like is dissolved is cast on a cast support, formed into a film, and peeled.

[Casting device]
The casting apparatus 101 is a metal endless belt having a mirror-finished surface (a metal cylindrical drum having a mirror-finished surface instead of an endless belt) 101a as a support, and a resin solution. The die 101b for casting the (dope) 2 on the endless belt 101a, the heating device 101c for removing the solvent from the dope 2 cast on the endless belt 101a, and the endless belt 101a were formed. And a peeling roller 4 for peeling the web 3 from the endless belt 101a. The endless belt 101a is wound around a driving roller 101a1 and a driven roller 101a2, and can travel in the direction of an arrow in the figure. The peeling roller 4 is disposed at an end portion on the side where the dope 2 is cast on the endless belt 101a. The casting apparatus 101 includes a casting process in which the resin solution (dope) 2 is cast on the endless belt 101a, and a casting film (web) 3 of the dope 2 formed on the endless belt 101a is peeled from the endless belt 101a. The peeling process to perform is performed.

When the dope 2 is cast on the endless belt 101a from the die 101b, the dope 2 gels on the endless belt 101a to form a cast film (web) 3. The web 3 formed on the endless belt 101 a is peeled from the endless belt 101 a by the peeling roller 4. Here, the thickness of the web 3 on the endless belt 101a can be changed to various values so that the thickness of the optical film wound up by the winding device 106 becomes a predetermined thickness. The thickness of the web 3 on the endless belt 101a is adjusted according to the casting amount of the dope 2, the traveling speed of the endless belt 101a, and the like.

The heating device 101c includes a drying box 101c1, a first heating air supply device 101d disposed in the drying box 101c1, a second heating air supply device 101e, and an exhaust port 101f. The first heating air supply device 101d and the second heating air supply device 101e include heating air supply pipes 101d1 and 101e1 and headers 101d2 and 101e2, respectively.

The temperature of the web 3 on the endless belt 101a on the first heating air supply device 101d side and the temperature of the web 3 on the endless belt 101a on the second heating air supply device 101e side are based on the time required for evaporation of the solvent, respectively. In consideration of the determined traveling speed of the endless belt 101a, the degree of dispersion of fine particles in the dope 2, productivity, etc., for example, a range of −5 ° C. to 70 ° C. is preferable, and a range of 0 ° C. to 60 ° C. is more preferable. .

The wind pressure of the heating air supplied from the first heating air supply device 101d and the second heating air supply device 101e is, for example, 50 to 50 in consideration of the uniformity of evaporation of the solvent, the degree of dispersion of the fine particles in the dope 2, and the like. A range of 5000 Pa is preferred.

The first heating air supply device 101d and the second heating air supply device 101e may supply only the heating air having a constant temperature, or stepwise the heating air having a plurality of temperatures along the traveling direction of the endless belt 101a. You may supply.

The heating device 101c shown in FIG. 1 is for removing the solvent by heating the web 3 with heating air, but is not limited to this, for example, a device for heating the web 3 with an infrared heater, or the back surface of the endless belt 101a. It is also possible to heat the web 3 from the back side by spraying heated air.

The time from casting the dope 2 on the endless belt 101a to peeling the web 3 from the endless belt 101a varies depending on the thickness of the manufactured optical film, the type of solvent, etc., but the endless belt 101a For example, the range of 0.5 to 5 minutes is preferable in consideration of good peelability from the surface.

The endless belt 101a preferably has a mirror-finished surface, and for example, a metal endless belt whose surface is plated with stainless steel or casting is preferably used. The width of the endless belt 101a varies depending on the size of the optical film to be manufactured, but is preferably in the range of 1700 mm to 2700 mm, for example. The width for casting the dope 2 is preferably in the range of 80 to 99% of the width of the endless belt 101a, for example.

[Preliminary stretching equipment]
The preliminary stretching device 102 includes an outer box 102a having a dry air intake port 102c and a discharge port 102b, and a stretching device 102d placed in the outer box 102a. The preliminary stretching apparatus 102 stretches the web 3 peeled from the endless belt 101a in the MD direction.

In the stretching device 102d, the web 3 can be stretched in the MD direction by making a difference in peripheral speed between the transport rollers. Note that the drying air inlet 102b and the outlet 102c may be reversed. Although the case where heating air is used is shown as the solvent removing means in the pre-stretching apparatus 102, the solvent removing means is not particularly limited, and other examples include means for heating with an infrared heater, for example.

The drying in the pre-stretching apparatus 102 may be performed at a constant temperature, or may be divided into three to four stages of temperature and may be divided into several stages of temperature.

For the stretching in the MD direction, a conventionally known method, typically a heater heating method and an oven heating method, can be used.

The heater heating method is a method in which a heater installed between a low-speed roller group and a high-speed roller group instantaneously raises the temperature to a stretching temperature and stretches with a relatively short stretching span.

Width shrinkage due to stretching is reduced as the stretching span is shortened. Therefore, in order to obtain a wide film, the distance between the low speed roller group and the high speed roller group is preferably as short as possible.

Specifically, it is preferable that the stretching span is 2 m or less, and the conveying roller is installed, and more preferably within the range of 0.2 to 1.5 m. From the viewpoint of equipment, it is preferable that the stretch span is as small as possible. Here, the stretching span refers to a length in which the film is stretched in the MD direction, and specifically refers to a length in which the film is conveyed to the rollers in a non-contact manner, that is, a distance between the rollers.

In the low-speed roller group, it is preferable to preheat to a temperature as close as possible to the stretching temperature as long as film adhesion and scratches do not occur.

The inside of the pre-stretching apparatus 102 is preferably a floating that is stretched while being transported in a non-contact manner while the film is floated so that the hot air blown from nozzles arranged above and below the film passage does not come into contact with the nozzle. Note that the upstream side from the entrance and the downstream side from the exit of the prestretching apparatus 102 are generally held and conveyed by a suction roller and a guide roller at a holding angle capable of stably conveying the film.

The heater heating method is advantageous in that the amount of width shrinkage can be kept small, which is advantageous for forming a wide film, and that it can be installed in a relatively small space. The oven heating method has high uniformity of optical characteristics. In addition, there are advantages such as less scratches and adhesion failure. The MD stretching method is appropriately selected in consideration of materials to be used and necessary physical properties.

[Main stretching device]
The stretching device 103 includes an outer box 103a having a dry air intake port 103c and a discharge port 103b, and a stretching device 103d placed in the outer box 103a. The main stretching apparatus 103 performs a stretching process in which the web 3 stretched by the preliminary stretching apparatus 102 is stretched at a higher stretch ratio in the MD direction. The stretching device 103d is not particularly limited. From the viewpoint of versatility and ease of operation, the stretching device 103d includes, for example, a low-speed roller group and a high-speed roller group as conveyance rollers similar to the pre-stretching device, and the peripheral speed of the roller. By providing a difference, an apparatus that stretches the web 3 in the MD direction may be used, and other stretching apparatuses include a clip tenter and a pin tenter, and can be selected and used as necessary. In the present embodiment, the main stretching step is preferably a method of stretching the web 3 that has been dried to some extent by making a difference in peripheral speed between the conveying rollers, or a method and apparatus of stretching by a clip tenter.

The present stretching device 103 has a dry air intake port 103c and a discharge port 103b. This may be reversed. Although the case where heated air is used as the solvent removing means in the stretching apparatus 103 is shown, the solvent removing means is not particularly limited, and other examples include means for heating with an infrared heater, for example.

Also in the main stretching, it is preferable to select and use a heater heating method and an oven heating method as in the pre-stretching, but the stretching span of the main stretching is preferably 2 m or more. This is because if the stretching span is short with respect to the film width, the width shrinkage is restricted, and there is a concern that uniform stretching cannot be performed. The drawing span is preferably in the range of 2 to 4 m in view of designing the equipment compactly, and more preferably in the range of 2.5 to 3.5 m.

The drying conditions in the stretching apparatus 103 vary depending on the residual solvent amount of the web 3 at the start of stretching by the second stretching apparatus 103, but taking into consideration drying time, shrinkage unevenness, stability of the amount of stretching, and the like. In addition, it achieves reasonable stretching, and at a constant temperature from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids in the manufactured optical film, and ensuring elastic modulus and optical properties. It may be dried, or may be divided into three to four stages of temperature and dried in several stages.

[TD stretcher]
The TD stretching device 104 includes an outer box 104a having a dry air intake port 104c and a discharge port 104b, and a TD stretching device 104d placed in the outer box 104a. The TD stretching device 104 performs a stretching process of additionally stretching the web 3 stretched by the stretching device 103 in the TD direction. The TD stretching device 104d is preferably a tenter stretching device, and the tenter to be used is not particularly limited, and examples thereof include a clip tenter and a pin tenter from the viewpoint of versatility and ease of operation. Can be selected and used. In particular, it is preferable to use a clip tenter.

The dry air intake 104c and the discharge port 104b may be reversed. Although the case where heated air is used as the solvent removal means in the TD stretching apparatus 103 is shown, the solvent removal means is not particularly limited, and other examples include means for heating with an infrared heater, for example.

The drying conditions in the TD stretching device 104 vary depending on the residual solvent amount of the web 3 at the start of stretching by the TD stretching device 104, but considering the drying time, shrinkage unevenness, stability of the stretch amount, etc. Also, it can be stretched without difficulty and dried at a constant temperature from the viewpoint of ensuring good dryness, flatness and film thickness uniformity without voids in the manufactured optical film, and ensuring elastic modulus and optical properties. Alternatively, it may be divided into three to four stages of temperature and may be dried in several stages of temperature.

[Drying equipment]
The drying device 105 includes a drying box 105a having a drying air intake port 105c and a discharge port 105b, an upper conveyance roller 105d that conveys the web 3, and a lower conveyance roller 105e. The drying apparatus 105 performs a heat treatment step of drying the web 3 stretched in the MD direction in the pre-stretching, main stretching, and TD directions. The upper conveyance roller 105d and the lower conveyance roller 105e are a set of upper and lower, and are composed of a plurality of sets. The number of transport rollers disposed in the drying device 105 varies depending on the drying conditions, the drying method, the length of the optical film 8 to be manufactured, and the like, and is appropriately set. The upper conveyance roller 105d and the lower conveyance roller 105e are free rotation rollers that are not rotated by a drive source. In addition, a transport roller that freely rotates is not used between the drying device 105 and the winding device 106, but usually one to several transport drive rollers (rollers that are rotationally driven by a drive source). Requires installation. Basically, the purpose of the driving roller for conveyance is to convey the web 3 by its drive, so the conveyance of the web 3 and the rotation of the driving roller are synchronized by nip, suction (air suction), or the like. With the mechanism.

The drying device 105 may dry using heated air, infrared light, or the like alone, or may dry using heated air and infrared light in combination. It is preferable to use heated air from the viewpoint of simplicity. FIG. 1 shows a case where heated air is used. The drying temperature varies depending on the amount of residual solvent in the web at the time of entering the drying process, but considering the drying time, unevenness of shrinkage, stability of the amount of expansion and contraction, etc., for example, the residual solvent in the range of 30 to 180 ° C. What is necessary is just to select suitably and decide by quantity. Further, it may be dried at a constant temperature, or may be divided into three to four stages of temperature and may be divided into several stages of temperature.

The amount of residual solvent in the web 3 after the drying process in the drying apparatus 104 is 0.01 to 0.5% by mass in consideration of the load of the drying process (heat treatment process), the dimensional stability during storage and the expansion / contraction rate. The range of is preferable. In the present embodiment, when the web 3 formed by the casting apparatus 101 is gradually removed of the solvent by the drying apparatus 105 and the total residual solvent amount becomes, for example, 2% by mass or less, the web 3 is called the optical film 8. There is.

[Winding device]
The winding device 106 winds the optical film 8 having a predetermined residual solvent amount in a roll shape around the core to a required length by the drying device 105. The temperature at the time of winding is preferably cooled to room temperature in order to prevent scratches and loosening due to shrinkage after winding. The winder to be used can be used without any particular limitation, and may be a commonly used one, such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. Can be wound up.

<Method for producing optical film>
According to the optical film manufacturing apparatus 1 as shown in FIG. 1, the casting step of casting the resin solution 2 on the metal support 101a and the web 3 formed on the support 101a are removed from the support 101a. A peeling step for peeling, a pre-stretching step for pre-stretching the peeled web 3 in the MD direction, a main stretching step for main stretching in the MD direction, and a TD stretching step for stretching in the TD direction as necessary, and stretching The manufacturing method of the optical film by the solution casting method is provided, which includes a heat treatment step for drying the web 3 and a winding step for winding the dried web 3 as an optical film. Such a method for producing an optical film by the solution casting method is capable of using a high molecular weight resin capable of increasing the elastic modulus, viewpoints of suppression of coloring, suppression of foreign matter defects, suppression of optical defects such as die lines, and the like. To a preferable method for producing an optical film.

In the present embodiment, in consideration of the use of the manufactured optical film 8 as a thin film, and from the viewpoint of preventing curling, wrinkles, etc. of the manufactured optical film 8, the optical film having a thickness in the range of 10 to 40 μm. Is to be manufactured. In order to control the film thickness within the above range, it is preferable to carry out by setting the film thickness before stretching by the casting amount at the time of dope casting and the stretching ratio.

In addition to the contents described above, further explanation will be given below.

[Dissolution process]
The dissolving step is a step of dissolving a thermoplastic resin and other additives in an organic solvent mainly containing a good solvent for the thermoplastic resin while stirring the thermoplastic resin and other additives to form a dope, or a thermoplastic resin solution. Depending on the case, it is the process of mixing dope which is a main solution by mixing other additive solutions.

For the dissolution of the thermoplastic resin, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557 Alternatively, various dissolution methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using a high pressure as described in JP-A-11-21379 can be used. The method of pressurizing at a boiling point or higher is preferred.

The total thermoplastic resin in the dope is preferably in the range of 10 to 45% by mass. After the additive is added and dissolved and dispersed in the dope during or after dissolution, the solution is filtered with a filter medium, defoamed, and sent to the next step with a liquid feed pump.

For the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

In this method, a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml is used for the aggregate remaining at the time of particle dispersion and the aggregate generated when the main dope is added. Only the aggregate can be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

If necessary, remove large agglomerates with a filter from the acrylic particle charging pot described later, and send the liquid to the stock pot. Thereafter, the acrylic particle additive liquid is added from the stock kettle to the main dope dissolving kettle.

Thereafter, the main dope is filtered by a main filter, and an ultraviolet absorbent additive solution or the like may be further added in-line thereto.

In many cases, the main dope may contain about 10 to 50% by weight of recycled material. Since the return material contains an additive, in that case, it is preferable to control the amount of additive added in accordance with the amount of return material added.

The return material is a product obtained by finely pulverizing an optical film, which is produced when an optical film is formed, and is obtained by cutting off both sides of the film, or an optical film original that has been speculated out by scratches, etc. .

Also, a thermoplastic resin, and optionally pelletized by kneading additives may be preferably used.

(Dope solvent)
A solvent useful for forming a dope when the optical film of the present invention is produced by a solution casting method is, for example, an organic solvent. As such an organic solvent, any organic solvent can be used without limitation as long as it can simultaneously dissolve a thermoplastic resin and other additives.

For example, as a chlorinated organic solvent, methylene chloride (methylene chloride) and as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone Ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3 -Hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Methylene chloride, methyl acetate, ethyl acetate, and acetone can be preferably used.

In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the web gels, facilitating peeling from the metal support, and when the proportion of alcohol is small, the dissolution of the thermoplastic resin in a non-chlorine organic solvent system is promoted. There is also a role.

In particular, a dope composition in which a thermoplastic resin and an additive are dissolved at least 10 to 45 mass% in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. It is preferable that
Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

[Casting process]
A description will be given with reference to FIG. 1 again. In the casting process, the dope is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump), and is supported by an endless metal belt such as a stainless steel belt or a rotating metal drum. This is a step of casting a dope from a pressure die slit to a casting position on the body.

¡Pressure dies that can adjust the slit shape of the die base and make the film thickness uniform are preferred. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

(Solvent evaporation process during casting process)
This is a step of heating the web on the support and evaporating the solvent.

To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of −5 to 100 ° C. More preferably, it is in the range of 40 to 70 ° C.

From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 0.5 to 5 minutes.

[Peeling process]
A peeling process is a process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

The temperature at the peeling position on the metal support is preferably in the range of 0 to 40 ° C, more preferably in the range of 5 to 30 ° C.

When the web 3 formed on the endless belt 101a is peeled from the endless belt 101a, the residual solvent amount of the web 3 (the residual solvent amount of the web 3 at the time of peeling) is the peelability and peeling of the web 3 from the endless belt 101a. In consideration of the transportability of the subsequent web 3, the retention by the tenter during stretching, the appearance and optical characteristics of the produced optical film, for example, the range of 20 to 100% by mass is preferable, and the range of 35 to 90% by mass is preferable. The range is more preferable, and the range of 45 to 80% by mass is further preferable.

The amount of residual solvent at the time of peeling of the web on the metal support at the time of peeling is in the range of 20 to 150% by mass depending on the strength of drying conditions, the length of the metal support, etc. in addition to the reasons described above. However, if the web is too soft, the flatness at the time of peeling is impaired, and slippage and vertical stripes due to peeling tension are likely to occur. Therefore, the amount of residual solvent at the time of peeling is determined.

The amount of residual solvent in the web is defined by the following formula.

Also, due to the tension acting on the web 3 when peeling the web 3 from the endless belt 101a (peeling tension), and the tension acting on the web 3 when transporting the web 3 after peeling (conveying tension), The web 3 is stretched in the conveyance direction (MD direction) of the web 3. From the viewpoint of controlling stretching here, the peel tension and the transport tension are preferably in the range of 20 to 400 N / m, for example.

The peeling tension when peeling the metal support from the film is preferably at a tension of 200 N / m or less when wrinkles are likely to occur at the time of peeling, and more preferably in the range of the minimum tension that can be peeled to 175 N / m. Then, it is preferable to peel in the range of the minimum tension to 150 N / m, but it is particularly preferable to peel in the range of the minimum tension to 100 N / m.

In the present invention, the temperature at the peeling position on the metal support is preferably in the range of −5 to 70 ° C., more preferably in the range of 0 to 60 ° C., and in the range of 15 to 60 ° C. Most preferred.

[Pre-stretching step in MD direction]
The pre-stretching according to the present invention is characterized in that it is performed within a range of 1.01 to 1.10 times in the MD direction. Within this range, there is no orientation of the resin that is so strong as to affect the orientation control of the resin in the main stretching, and the resin chains are also easily loosened. When the pre-stretching is performed at a ratio exceeding 1.10 times, the resin chains are surely loosened, but the orientation is likely to be non-uniform, and the non-uniformity of the orientation of the resin is likely to be expanded by the main stretching. It is necessary.

The draw ratio in the MD direction in the preliminary first stretching step is obtained by the formula “stretch ratio in the MD direction in the preliminary stretching step = web transport speed after the pre-stretching process / web transport speed before the pre-stretching process”.
The web conveyance speed during pre-stretching according to the present invention is preferably 10 to 100 m / min, more preferably 15 to 100 m / min in terms of productivity and breaking. Among these, from the viewpoint of effectively loosening the entanglement of the resin chains of the thermoplastic resin, it is particularly preferable to carry out in the range of 20 to 80 m / min.

In the present invention, when the web peeled from the casting support is stretched in the MD direction by the pre-stretching step and the main stretching step, the preferred stretching ratio is as described above. The product value of the magnification is preferably in the range of 1.5 to 2.5 times. By performing stretching within the above range, it is preferable from the viewpoint of expression of the effect of the present invention and uniform stretching treatment, and the product value is particularly preferably in the range of 1.5 to 2.0 times. preferable.

The pre-stretching temperature is preferably a temperature within the range of (Tg-100) to (Tg-10) ° C., where Tg (° C.) is the glass transition temperature of the optical film. ) To (Tg−20) ° C. is more preferable. If the stretching temperature is within the above range, there is no orientation of the resin that is strong enough to affect the orientation control of the resin in the main stretching, and the resin chain is also easily loosened.

The glass transition temperature Tg (° C.) of the film was measured at a rate of temperature increase of 20 ° C./min using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer) and determined according to JIS K7121 (1987). The intermediate glass transition temperature (Tmg).

Further, the residual solvent amount of the web 3 when the web 3 is started to be stretched by the prestretching apparatus 102 (the residual solvent amount of the web 3 at the start of stretching by the prestretching apparatus 102) The residual solvent amount (% by mass) represented by the formula is preferably within the range of 20 to 100% by mass, more preferably within the range of 21 to 80% by mass, and particularly preferably 30 to 80% by mass. Range.

If the amount of residual solvent is within the above range, there is no strong resin orientation that affects the orientation control of the resin in the main stretching, and the resin chain is also easily loosened.

[Main stretching process in the MD direction]
The stretching ratio of the main stretching is preferably in the range of 1.15 to 2.50 times from the viewpoint of thinning. Since the entanglement between the resin chains is effectively loosened by the pre-stretching according to the present invention, even if the main stretching is performed at a high stretching ratio as in the above range, it can be kept at a low stretching stress and depends on the transport roller. Generation of scratches and optical unevenness can be reduced.

Here, the draw ratio in the MD direction in the main stretching process is determined by the formula “stretch ratio in the MD direction in the main stretching process = web transport speed after the main stretching process / web transport speed before the main stretching process”.
The web conveyance speed during the main stretching according to the present invention is preferably 10 to 100 m / min, more preferably 15 to 100 m / min in terms of productivity and breaking.

Further, the amount of residual solvent at the time of the main stretching may be within a range of 1 to 30% by mass, and it can be stretched at a desired stretching ratio without foaming during heating, and has flatness and optical properties. An optical film with high uniformity can be obtained. The residual solvent amount is preferably in the range of 3 to 18% by mass.

Further, when the glass transition temperature of the optical film is Tg (° C.), performing the main stretching within the range of (Tg−10) to (Tg + 100) ° C. suppresses a rapid increase in stretching stress, In addition, the orientation of the resin in the film can be increased, and the occurrence of scratches and optical unevenness by the transport roller can be reduced, which is preferable. Preferably, it is in the range of Tg to (Tg + 80) ° C.

The stretching stress during the main stretching process is preferably in the range of 1 to 10 MPa, and the stretching stress is preferably in the range of 2 to 5 MPa while reducing the occurrence of scratches and uniforming the thermoplastic resin. This is particularly preferable from the viewpoint of promoting proper orientation.

The stretching stress can be measured by the following method.

<Evaluation of stretching stress>
The following measurement is performed using a Tensilon tester (ORICTEC, RTC-1225A).

The optical film was cut out at 120 mm (MD: longitudinal direction) × 10 mm (TD: lateral direction), and the sample was left in an environment of 23 ± 2 ° C. and 55 ± 5% RH for 24 hours, and then 23 ° C./55%. The film is pulled in the MD direction at a chuck length of 50 mm and a speed of 50 mm / min in a thermostatic chamber held in RH, and the tensile load at that time is divided by the film cross-sectional area (that is, film width × film thickness). Directional stretching stress is required.

[TD stretching step]
As a preferred embodiment of the present invention, after pre-stretching and main-stretching in the MD direction, stretching in the range of 1.3 to 3.0 times in the TD direction may reduce the thickness and width of the optical film. Therefore, it is also preferable from the viewpoint of increasing the elastic modulus in the MD direction and TD direction of the optical film. More preferably, it is in the range of 1.5 to 2.5 times from the viewpoint of maintaining physical properties such as elastic modulus as an optical film.

Here, the stretching ratio in the TD direction is determined by the formula “stretching ratio in the TD direction in the TD stretching process = web width after the TD stretching process / web width before the TD stretching process”. The width of the web is a value measured with a C-type JIS grade 1 steel scale.

In the TD stretching step, when a tenter stretching apparatus is used, it is preferable to use an apparatus that can independently control the holding position of the film by the tenter on the left and right. It is also preferable to create compartments with intentionally different temperatures to improve planarity. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

In the TD stretching process, the stretching operation may be performed in multiple stages. Biaxial stretching also includes stretching in one direction and contracting the other while relaxing the tension.

The residual solvent amount of the web immediately before the web is conveyed to the TD stretching device 104 is preferably less than 20% by mass, and more preferably in the range of 1 to 10% by mass. If it is in the said range, planarity and optical uniformity can be improved and it is preferable.

The temperature during stretching in the TD direction is specifically preferably within the range of (Tg-10) to (Tg + 100) ° C. when the glass transition temperature of the optical film is Tg (° C.). , (Tg-5) to (Tg + 100) ° C. is preferable.

In the stretching process in the TD direction, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the TD stretching process is preferably within ± 5 ° C., and ± 2 It is more preferably within 1 ° C., and further preferably within 1 ° C.
The web conveyance speed during stretching in the TD direction according to the present invention is preferably in the range of 15 to 200 m / min, and more preferably in the range of 15 to 180 m / min in terms of productivity and breaking.

[Heat treatment process]
The heat treatment step is a step of drying (heat treatment) while alternately passing the stretched web through rollers arranged in a drying apparatus.

The drying means is generally to blow hot air on both sides of the web, but there is also a means to heat by applying microwaves instead of wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from a residual solvent amount of about 10% by mass or less. Throughout the whole, the drying is preferably carried out in the range of approximately 30 to 250 ° C., particularly preferably in the range of 40 to 160 ° C.

[Winding process]
The winding process is a process in which the amount of residual solvent in the web becomes 2% by mass or less and is wound as an optical film by a winder, and the dimensional stability is achieved by setting the residual solvent amount to 0.05% by mass or less. Can be obtained. In particular, it is preferable to take up in the range of 0.00 to 0.05% by mass.

As a winding method, a generally used method may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

The optical film of the present invention is preferably a long film. Specifically, the optical film has a thickness of about 100 m to 5000 m, and is usually in the form of a roll. The width of the film is 1.4 m or more, which is necessary for obtaining a wide optical film, preferably 1.6 to 3 m, and more preferably 1.8 to 3 m.

The film thickness of the optical film of the present invention is characterized by being in the range of 10 to 40 μm in consideration of the use as a protective film for a thin polarizing plate, more preferably 15 to 35 μm, and 20 It is particularly preferable that the thickness is 35 μm. When the film thickness is within the above range, it is possible to meet the demand for thinning, and to satisfy physical properties required for an optical film.

The optical film manufactured by the method as described above is an optical film having low hygroscopicity, high transparency, and excellent weather resistance.

≪Material for optical film≫
Hereinafter, various materials used for the optical film of the present invention will be described.

<Thermoplastic resin>
The optical film of the present invention contains a thermoplastic resin. Here, the “thermoplastic resin” refers to a resin that becomes soft when heated to the glass transition temperature or melting point and can be molded into a desired shape.

The thermoplastic resin used in the present invention is preferably manufactured easily and optically transparent.

The term “transparent” as used in the present invention means that the total light transmittance of visible light is 60% or more, preferably 80% or more, and particularly preferably 90% or more.

Although it will not specifically limit if it has said property, For example, cellulose acylate type resins, such as a cellulose (di, tri) acetate, a cellulose acetate propionate, a cellulose acetate butyrate, Acrylic type, such as a polymethylmethacrylate Resin, Polyester resin such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polypropylene terephthalate, polyphenylene sulfide, polyphenylene oxide, polycaprolactone, polycarbonate resin, norbornene resin, monocyclic cyclic olefin resin, cyclic conjugated diene series Resins, vinyl alicyclic hydrocarbon resins, and cyclic polyolefin resins such as hydrides thereof, polyarylate resins, polysulfones (also polyether sulfones) Resin), polyethylene, polypropylene, ABS resin, polylactic acid, cellophane, polyvinylidene chloride, polyvinyl alcohol, ethylene vinyl alcohol, syndiotactic polystyrene resin, norbornene resin, polymethylpentene, polyether ketone, polyether ketone Examples thereof include polyamide resins such as imide and nylon, fluorine resins, polyarylate, thermoplastic elastomer, and silicone. Among them, a cellulose acylate resin (hereinafter also referred to as cellulose acylate), an acrylic resin (hereinafter also referred to as acrylic resin), or a mixed resin thereof can improve the strength of the film and adjust optical properties. ,preferable.

Particularly, since acrylic resin has a slightly lower hardness than other resins, scratches are likely to occur. However, the use of the production method of the present invention greatly improves the generation of scratches.

[Cellulose acylate]
The optical film of the present invention preferably contains cellulose acylate as a main component, and is suitable as an optical film for polarizing plate protective films and retardation films. A main component means that the content rate of the cellulose acylate in the said optical film is 55 mass% or more. Preferably it is 70 mass% or more.

The cellulose acylate according to the present invention preferably has an acyl group having 2 to 4 carbon atoms. Examples of the acyl group having 2 to 4 carbon atoms include an acetyl group, a propionyl group, and a butanoyl group.

The β-1,4-bonded glucose unit constituting cellulose has free hydroxy groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by acylating part or all of these hydroxy groups with an acyl group. The total acyl group substitution degree means the ratio in which all the hydroxy groups of cellulose located at the 2nd, 3rd and 6th positions are acylated per one glucose unit (100% acylation has a degree of substitution of 3). .

Examples of preferred acyl groups include acetyl, propionyl, butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, Examples thereof include an isobutanoyl group, a tert-butanoyl group, a cyclohexanecarbonyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, and a cinnamoyl group. Among these, an acetyl group, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a tert-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and an acetyl group is particularly preferable. A propionyl group and a butanoyl group (when the acyl group has 2 to 4 carbon atoms);

Specific cellulose acylates include at least selected from cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose acetate propionate benzoate, cellulose propionate, and cellulose butyrate. One type is preferable.

Among these, more preferred cellulose acylates are cellulose (di, tri) acetate, cellulose acetate propionate and cellulose acetate butyrate, and particularly preferred cellulose acylates are cellulose (di, tri) acetate and cellulose acetate propioate. Nate.

As the cellulose triacetate, those having an average degree of acetylation (bound acetic acid amount) in the range of 54.0 to 62.5% are preferably used, and more preferably, the average degree of acetylation is in the range of 58.0 to 62.5%. Of cellulose triacetate.

Cellulose diacetate preferably has an average degree of acetylation (bound acetic acid amount) in the range of 51.0% to 56.0%. Commercially available products include L20, L30, L40, and L50 manufactured by Daicel Corporation, and Ca398-3, Ca398-6, Ca398-10, Ca398-30, and Ca394-60S manufactured by Eastman Chemical Japan Co., Ltd. .

Cellulose acetate propionate or cellulose acetate butyrate has an acyl group having 2 to 4 carbon atoms as a substituent, the substitution degree of acetyl group is X, and the substitution degree of propionyl group or butyryl group is Y Those satisfying the following formulas (I) and (II) are preferred.

Formula (I) 2.0 ≦ X + Y ≦ 2.95
Formula (II) 0 ≦ X ≦ 2.5
Among them, it is preferable that 1.9 ≦ X ≦ 2.5 and 0.1 ≦ Y ≦ 0.9.

The method for measuring the degree of substitution of the acyl group can be measured according to ASTM-D817-96.

The weight average molecular weight Mw of the cellulose acylate is preferably in the range of 80000 to 300000, more preferably in the range of 120,000 to 200000, from the viewpoint of controlling the elastic modulus and stretching stress. Within the above range, it is easy to control the elastic modulus by stretching during solution casting film formation, and it is easy to control the stress during break stretching of the film.

The number average molecular weight (Mn) of the cellulose acylate is preferably in the range of 30,000 to 150,000 because the obtained cellulose acylate film has high mechanical strength. Further, cellulose acylate having a number average molecular weight of 40,000 to 100,000 is preferably used.

The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) of the cellulose acylate is preferably in the range of 1.4 to 3.0.

The weight average molecular weight Mw and number average molecular weight Mn of the cellulose acylate were measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 500 to 1000000 13 calibration curves were used. Thirteen samples are used at approximately equal intervals.

The raw material cellulose of cellulose acylate used in the present invention may be wood pulp or cotton linter, and wood pulp may be softwood or hardwood, but softwood is more preferable. A cotton linter is preferably used from the viewpoint of peelability during film formation. Cellulose acylates made from these can be used in appropriate mixture or independently.

For example, the ratio of cellulose acylate derived from cotton linter: cellulose acylate derived from wood pulp (conifer): cellulose acylate derived from wood pulp (hardwood) is 100: 0: 0, 90: 10: 0, 85: 15: 0, 50. : 50: 0, 20: 80: 0, 10: 90: 0, 0: 100: 0, 0: 0: 100, 80:10:10, 85: 0: 15, 40:30:30 it can.

The cellulose acylate according to the present invention can be produced by a known method. Generally, cellulose is esterified by mixing cellulose as a raw material, a predetermined organic acid (such as acetic acid or propionic acid), an acid anhydride (such as acetic anhydride or propionic anhydride), and a catalyst (such as sulfuric acid). The reaction proceeds until the triester is formed. In the triester, the three hydroxy groups of the glucose unit are substituted with an organic acid acyl acid. When two types of organic acids are used at the same time, a mixed ester type cellulose acylate such as cellulose acetate propionate or cellulose acetate butyrate can be produced. Next, cellulose acylate having a desired degree of acyl substitution is synthesized by hydrolyzing cellulose triester. Thereafter, cellulose acylate is completed through steps such as filtration, precipitation, washing with water, dehydration, and drying.

The cellulose acylate according to the present invention has a pH of 6 when charged in 20 ml of pure water (electric conductivity 0.1 μS / cm or less, pH 6.8) and stirred in a nitrogen atmosphere at 25 ° C. for 1 hr. The electric conductivity is preferably in the range of 1 to 100 μS / cm.

Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

〔acrylic resin〕
The optical film of the present invention is preferably a film containing an acrylic resin. In the present invention, the acrylic resin is a polymer of acrylic acid ester or methacrylic acid ester, and includes copolymers with other monomers.

Therefore, the acrylic resin used in the present invention includes a methacrylic resin. The resin is not particularly limited, but a resin having a methyl methacrylate unit content in the range of 50 to 99% by mass and other monomer units copolymerizable therewith is preferably in the range of 1 to 50% by mass. .

Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 alkyl carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, and amides such as acryloylmorpholine and N, N-dimethylacrylamide. Vinyl monomer having a group, methacrylic acid ester or acrylic acid ester having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion, α, β-unsaturated acid such as acrylic acid or methacrylic acid, maleic acid, Examples include unsaturated group-containing divalent carboxylic acids such as fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, and α and β-unsaturated nitriles such as acrylonitrile and methacrylonitrile. Alternatively, two or more monomers can be used in combination.

In addition, the acrylic resin of the present invention may have a ring structure, specifically, a lactone ring structure, a glutaric anhydride structure, a glutarimide structure, an N-substituted maleimide structure and a maleic anhydride structure, a pyran ring. Structure is mentioned.

Specific examples of the alkyl acrylate having 1 to 18 carbon atoms are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate n-butyl acrylate, s-butyl acrylate, t-butyl acrylate, isopentyl acrylate, Examples thereof include neopentyl acrylate, t-pentyl acrylate, and 2-ethylhexyl acrylate.

Specific examples of the alkyl methacrylate having 1 to 18 carbon atoms include ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, isopentyl methacrylate, neopentyl Examples include methacrylate, t-pentyl methacrylate, 2-ethylhexyl methacrylate, and the like.

Preferably, isopropyl acrylate, t-butyl acrylate, isopropyl methacrylate, t-butyl methacrylate and the like can be mentioned.

Specific examples of the vinyl monomer having an amide group include acrylamide, N-methylacrylamide, N-butylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, acryloylmorpholine, N-hydroxyethylacrylamide, acryloylpyrrolidine, Acryloylpiperidine, methacrylamide, N-methylmethacrylamide, N-butylmethacrylamide, N, N-dimethylmethacrylamide, N, N-diethylmethacrylamide, methacryloylmorpholine, N-hydroxyethylmethacrylamide, methacryloylpyrrolidine, methacryloylpiperidine, N-vinylformamide, N-vinylacetamide, vinylpyrrolidone and the like can be mentioned. Preferably, acryloylmorpholine, N, N-dimethylacrylamide, N-butylacrylamide, and vinylpyrrolidone are used.

Specific examples of the methacrylic acid ester or acrylic acid ester having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion include, for example, cyclopentyl acrylate, cyclohexyl acrylate, methyl cyclohexyl acrylate, trimethylcyclohexyl acrylate, Norbornyl acrylate, norbornyl acrylate, cyano norbornyl acrylate, isobornyl acrylate, bornyl acrylate, menthyl acrylate, fentyl acrylate, adamantyl acrylate, dimethyladamantyl acrylate, tricycloacrylate [5.2 .1.0 ^2,6 ] dec-8-yl, tricyclo [5.2.1.0 ^2,6 ] dec-4-methyl acrylate, cyclodecyl acrylate, cyclopentyl methacrylate, cyclohex methacrylate Sil, methyl cyclohexyl methacrylate, trimethyl cyclohexyl methacrylate, norbornyl methacrylate, norbornyl methyl methacrylate, cyano norbornyl methacrylate, phenyl norbornyl methacrylate, isobornyl methacrylate, bornyl methacrylate, menthyl methacrylate, methacryl Fentyl acid, adamantyl methacrylate, dimethyladamantyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] dec-8-yl methacrylate, tricyclo [5.2.1.0 ^2,6 ] decyl methacrylate 4-methyl, cyclodecyl methacrylate, dicyclopentanyl methacrylate and the like.

Preferably, isobornyl methacrylate, dicyclopentanyl methacrylate, dimethyladamantyl methacrylate and the like can be mentioned.

Examples of the N-substituted maleimide include N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, Ni-propylmaleimide, N-butylmaleimide, Ni-butylmaleimide, Nt-butylmaleimide, N-laurylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, N-phenylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, N- (4-bromophenyl) phenylmaleimide, N -(2-methylphenyl) maleimide, N- (2-ethylphenylmaleimide), N- (2-methoxyphenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide, N- (4-benzylphenyl) Maleimide, N- (2,4,6-tribromoph Yl) maleimide and the like.

Preferably, N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide and the like can be mentioned.

These monomers are commercially available.

The acrylic resin used in the acrylic resin-containing film according to the present invention has a weight average molecular weight (Mw) in the range of 100,000 to 1,000,000 from the viewpoint of mechanical strength as a film and fluidity when producing the film. Preferably, it is in the range of 300,000 to 500,000.

The weight average molecular weight of the acrylic resin according to the present invention can be similarly measured by the gel permeation chromatography.

The method for producing the acrylic resin in the present invention is not particularly limited, and any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. The polymerization temperature may be 30 to 100 ° C. for suspension or emulsion polymerization and 80 to 160 ° C. for bulk or solution polymerization. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

Commercially available acrylic resins can be used as the acrylic resin according to the present invention. For example, Delpet 60N, 80N (above, manufactured by Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (above, manufactured by Mitsubishi Rayon Co., Ltd.), Parapet HR-S (manufactured by Kuraray Co., Ltd.) ) And the like. Two or more acrylic resins can be used in combination.

[Film mixed with acrylic resin and cellulose acylate]
The optical film of the present invention is also preferably used as a thermoplastic resin by mixing an acrylic resin and cellulose acylate. In the case of mixing, the mixing mass ratio of the acrylic resin and the cellulose acylate is preferably in the range of acrylic resin: cellulose acylate = 95: 5 to 50:50, and preferably in the range of 90:10 to 70:30. The stretching stress during stretching is easy to control, and the orientation of the thermoplastic resin is also easy.

The acrylic resin can be appropriately selected from the aforementioned acrylic resins. As a cellulose acylate, it can select from the above-mentioned cellulose acylate suitably, and it is preferable to use a cellulose triacetate or a cellulose acetate propionate especially.

In the optical film of the present invention, it is preferable that an acrylic resin and cellulose acylate are contained in a compatible state. The physical properties and quality required as an optical film can be supplemented with each other by dissolving different resins.

Whether or not the acrylic resin and cellulose acylate are in a compatible state can be determined, for example, based on the glass transition temperature Tg.

For example, when the glass transition temperatures of the two resins are different, when the two resins are mixed, there are two or more glass transition temperatures of the mixture because there is a glass transition temperature of each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which becomes the glass transition temperature of the compatible resin.

The total mass of the acrylic resin and cellulose acylate in the optical film of the present invention is preferably 55% by mass or more of the total mass of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. It is.

<Additives>
As additives, it is also preferable to contain additives such as plasticizers, ultraviolet absorbers, antioxidants, deterioration inhibitors, peeling aids, surfactants, dyes, and fine particles.

In particular, it is preferable to contain the following sugar ester or the following polycondensed ester.

[Sugar ester]
The optical film of the present invention preferably contains a sugar ester other than cellulose acylate because the effect of aligning and aligning the thermoplastic resin in a desired direction by stretching is preferable. In particular, it is preferable to use from the viewpoint of effectively loosening the entanglement of the resin chain due to pre-stretching in the MD direction.

The sugar ester used in the present invention is preferably a sugar ester in which at least one pyranose ring or furanose ring is 1 to 12 and all or part of the OH groups in the structure are esterified.

The sugar ester used in the present invention is a compound containing at least one of a furanose ring and a pyranose ring, and may be a monosaccharide or a polysaccharide having 2 to 12 sugar structures linked together. The sugar ester is preferably a compound in which at least one OH group of the sugar structure is esterified. In the sugar ester used in the present invention, the average ester substitution degree is preferably within the range of 4.0 to 8.0, and more preferably within the range of 5.0 to 7.5.

The sugar ester applicable to the present invention is not particularly limited, and examples thereof include sugar esters represented by the following general formula (A).

Formula (A)
(HO) _m -G- (OC (= O) -R ² ) _n
In the general formula (A), G represents a monosaccharide or disaccharide residue, R ² represents an aliphatic group or an aromatic group, and m is directly bonded to the monosaccharide or disaccharide residue. N is the total number of — (O—C (═O) —R ² ) groups directly bonded to the monosaccharide or disaccharide residue, 3 ≦ m + n ≦ 8, and n ≠ 0.

The sugar ester having the structure represented by the general formula (A) is a single kind of hydroxy group (m) and-(O—C (═O) —R ² ) groups in which the number (n) is fixed. It is difficult to isolate as a compound, and it is known that a compound in which several components different in m and n in the formula are mixed is obtained. Therefore, the performance as a mixture in which the number of hydroxy groups (m) and the number of — (O—C (═O) —R ² ) groups (n) are changed is important. In the case of the optical film of the present invention, Sugar esters having an average ester substitution degree in the range of 5.0 to 7.5 are preferred.

In the above general formula (A), G represents a monosaccharide or disaccharide residue. Specific examples of monosaccharides include allose, altrose, glucose, mannose, gulose, idose, galactose, talose, ribose, arabinose, xylose, lyxose, and the like.

Specific examples of the compound having a monosaccharide residue of the sugar ester represented by the general formula (A) are shown below, but the present invention is not limited to these exemplified compounds.

Specific examples of the disaccharide residue include trehalose, sucrose, maltose, cellobiose, gentiobiose, lactose, and isotrehalose.

Specific examples of the compound having a disaccharide residue of the sugar ester represented by the general formula (A) are shown below, but the present invention is not limited to these exemplified compounds.

In the general formula (A), R ² represents an aliphatic group or an aromatic group. Here, the aliphatic group and the aromatic group may each independently have a substituent.

In general formula (A), m is the total number of hydroxy groups directly bonded to the monosaccharide or disaccharide residue, and n is directly bonded to the monosaccharide or disaccharide residue. And the total number of — (O—C (═O) —R ² ) groups. Further, it is necessary that 3 ≦ m + n ≦ 8, and it is preferable that 4 ≦ m + n ≦ 8. Further, n ≠ 0. When n is 2 or more, the — (O—C (═O) —R ² ) groups may be the same as or different from each other.

The aliphatic group in the definition of R ² may be linear, branched or cyclic, and preferably has 1 to 25 carbon atoms, more preferably 1 to 20 carbon atoms. Those of ˜15 are particularly preferred. Specific examples of the aliphatic group include, for example, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, tert-butyl, amyl, iso-amyl, tert-amyl, n- Examples include hexyl, cyclohexyl, n-heptyl, n-octyl, bicyclooctyl, adamantyl, n-decyl, tert-octyl, dodecyl, hexadecyl, octadecyl, didecyl and the like.

The aromatic group in the definition of R ² may be an aromatic hydrocarbon group or an aromatic heterocyclic group, and more preferably an aromatic hydrocarbon group. The aromatic hydrocarbon group preferably has 6 to 24 carbon atoms, more preferably 6 to 12 carbon atoms. Specific examples of the aromatic hydrocarbon group include rings such as benzene, naphthalene, anthracene, biphenyl, and terphenyl. As the aromatic hydrocarbon group, a benzene ring, a naphthalene ring, and a biphenyl ring are particularly preferable. As the aromatic heterocyclic group, a ring containing at least one of an oxygen atom, a nitrogen atom or a sulfur atom is preferable. Specific examples of the heterocyclic ring include, for example, furan, pyrrole, thiophene, imidazole, pyrazole, pyridine, pyrazine, pyridazine, triazole, triazine, indole, indazole, purine, thiazoline, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline, Examples of each ring include isoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole, benzimidazole, benzoxazole, benzthiazole, benzotriazole, and tetrazaindene. As the aromatic heterocyclic group, a pyridine ring, a triazine ring, and a quinoline ring are particularly preferable.

Next, preferred examples of the sugar ester represented by the general formula (A) are shown below, but the present invention is not limited to these exemplified compounds.

A sugar ester may contain two or more different substituents in one molecule, contains an aromatic substituent and an aliphatic substituent in one molecule, and contains two or more different aromatic substituents. Two or more different aliphatic substituents contained in one molecule can be contained in one molecule.

It is also preferable to contain a mixture of two or more sugar esters. It is also preferable to simultaneously contain a sugar ester containing an aromatic substituent and a sugar ester containing an aliphatic substituent.

<Synthesis Example: Synthesis Example of Sugar Ester Represented by Formula (A)>
Below, an example of the synthesis | combination of the sugar ester which can be used suitably for this invention is shown.

Four-headed Kolben equipped with a stirrer, reflux condenser, thermometer and nitrogen gas inlet tube, 34.2 g (0.1 mol) of sucrose, 180.8 g (0.8 mol) of benzoic anhydride, pyridine 379.7 g (4.8 mol) of each were charged, and the temperature was raised while bubbling nitrogen gas from a nitrogen gas inlet tube under stirring, and esterification was carried out at 70 ° C. for 5 hours. Next, the inside of the Kolben was depressurized to 4 × 10 ² Pa or less, and after excess pyridine was distilled off at 60 ° C., the inside of the Kolben was depressurized to 1.3 × 10 Pa or less and the temperature was raised to 120 ° C. Most of the acid and benzoic acid formed were distilled off. Then, 1 L of toluene and 300 g of a 0.5% by mass sodium carbonate aqueous solution were added, and the mixture was stirred at 50 ° C. for 30 minutes, and then allowed to stand to separate a toluene layer. Finally, 100 g of water was added to the separated toluene layer, and after washing with water at room temperature for 30 minutes, the toluene layer was separated, and toluene was distilled off at 60 ° C. under reduced pressure (4 × 10 ² Pa or less). A mixture of compounds A-1, A-2, A-3, A-4 and A-5 was obtained. Analysis of the resulting mixture by HPLC and LC-MASS revealed that A-1 was 7% by mass, A-2 was 58% by mass, A-3 was 23% by mass, A-4 was 9% by mass, A-5 Was 3% by mass, and the average ester substitution degree of the sugar ester was 6.57. A part of the obtained mixture was purified by silica gel column chromatography to obtain 100% pure A-1, A-2, A-3, A-4 and A-5, respectively.

The addition amount of the sugar ester is preferably in the range of 0.1 to 20% by mass, more preferably in the range of 1 to 15% by mass with respect to the thermoplastic resin.

The optical film of the present invention preferably contains the following ester (polycondensation ester).

[Polycondensed ester]
The optical film of the present invention preferably uses an ester other than a sugar ester as one of the plasticizers.

The ester other than the sugar ester applicable to the present invention is not particularly limited, but it is preferable to use a polycondensed ester having a structure represented by the following general formula (1).

The polycondensed ester is preferably contained in the range of 1 to 20% by mass and more preferably in the range of 2 to 15% by mass in the optical film of the present invention due to its plastic effect.

General formula (1)
B _3- (G ₂ -A) _n -G ₂ -B ₄
In the general formula (1), B ₃ and B ₄ each independently represent an aliphatic or aromatic monocarboxylic acid residue or a hydroxy group. G ₂ represents an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms. A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms. n represents an integer of 1 or more.

In the present invention, the polycondensed ester is a polycondensed ester containing a repeating unit obtained by reacting a dicarboxylic acid and a diol, A represents a carboxylic acid residue in the polycondensed ester, and G ₂ represents an alcohol residue. To express.

The dicarboxylic acid constituting the polycondensed ester is an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid or an alicyclic dicarboxylic acid, preferably an aromatic dicarboxylic acid. The dicarboxylic acid may be one type or a mixture of two or more types. In particular, it is preferable to mix aromatic and aliphatic.

The diol constituting the polycondensed ester is an aromatic diol, an aliphatic diol or an alicyclic diol, preferably an aliphatic diol, more preferably a diol having 1 to 4 carbon atoms. The diol may be one type or a mixture of two or more types.

Among them, it is preferable to include a repeating unit obtained by reacting at least a dicarboxylic acid containing an aromatic dicarboxylic acid and a diol having 1 to 8 carbon atoms, and a dicarboxylic acid containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid; More preferably, it contains a repeating unit obtained by reacting with a diol having 1 to 8 carbon atoms.

Both ends of the polycondensed ester molecule may or may not be sealed.

Specific examples of the alkylene dicarboxylic acid constituting A in the general formula (1) include 1,2-ethanedicarboxylic acid (succinic acid), 1,3-propanedicarboxylic acid (glutaric acid), 1,4-butanedicarboxylic acid. Divalent groups derived from (adipic acid), 1,5-pentanedicarboxylic acid (pimelic acid), 1,8-octanedicarboxylic acid (sebacic acid) and the like are included. Specific examples of the alkenylene dicarboxylic acid constituting A include maleic acid and fumaric acid. Specific examples of the aryl dicarboxylic acid constituting A include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid, 1,4-benzenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and the like. Can be mentioned.

A may be one type or two or more types may be combined. Among them, A is preferably a combination of an alkylene dicarboxylic acid having 4 to 12 carbon atoms and an aryl dicarboxylic acid having 8 to 12 carbon atoms.

G ₂ in the general formula (1) is a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms, a divalent group derived from an aryl glycol having 6 to 12 carbon atoms, or a carbon atom. It represents a divalent group derived from oxyalkylene glycol of 4 to 12.

Examples of the divalent group derived from an alkylene glycol having 2 to 12 carbon atoms in G ₂ include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, , 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (Neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-di-) Methylol heptane), 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanedio , 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc. Divalent groups are included.

Examples of divalent groups derived from aryl glycols having 6 to 12 carbon atoms in G ₂ include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxy Divalent groups derived from benzene (hydroquinone) and the like are included. Examples of the divalent group derived from oxyalkylene glycol having 4 to 12 carbon atoms in G are derived from diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol and the like. Divalent groups are included.

G ₂ may be a single type or a combination of two or more types. Among these, G ₂ is preferably a divalent group derived from an alkylene glycol having 2 to 12 carbon atoms, more preferably 2 to 5, and most preferably 2 to 4.

B ₃ and B ₄ in the general formula (1) are each a monovalent group derived from an aromatic ring-containing monocarboxylic acid or an aliphatic monocarboxylic acid, or a hydroxy group.

The aromatic ring-containing monocarboxylic acid in the monovalent group derived from the aromatic ring-containing monocarboxylic acid is a carboxylic acid containing an aromatic ring in the molecule, and not only those in which the aromatic ring is directly bonded to a carboxy group, Also included are those in which an aromatic ring is bonded to a carboxy group via an alkylene group or the like. Examples of monovalent groups derived from aromatic ring-containing monocarboxylic acids include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, and normal propyl benzoic acid. , Monovalent groups derived from aminobenzoic acid, acetoxybenzoic acid, phenylacetic acid, 3-phenylpropionic acid and the like. Of these, benzoic acid and p-toluic acid are preferable.

Examples of monovalent groups derived from aliphatic monocarboxylic acids include monovalent groups derived from acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid and the like. Is included. Among these, a monovalent group derived from an alkyl monocarboxylic acid having 1 to 3 carbon atoms in the alkyl portion is preferable, and an acetyl group (a monovalent group derived from acetic acid) is more preferable.

The weight average molecular weight of the polycondensed ester used in the present invention is preferably in the range of 500 to 3000, more preferably in the range of 600 to 2000. The weight average molecular weight can be measured by the gel permeation chromatography (GPC).

Hereinafter, although the specific example of the polycondensation ester which has a structure represented by General formula (1) is shown, it is not limited to this.

Hereinafter, a specific synthesis example of the polycondensation ester described above will be described.

<Polycondensed ester P1>
180 g of ethylene glycol, 278 g of phthalic anhydride, 91 g of adipic acid, 610 g of benzoic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst were charged into a 2 L four-necked flask equipped with a thermometer, a stirrer, and a slow cooling tube. The temperature is gradually raised with stirring until reaching 230 ° C. in a nitrogen stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted ethylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P1. The acid value was 0.20 and the number average molecular weight was 450.

<Polycondensed ester P2>
251 g of 1,2-propylene glycol, 244 g of phthalic anhydride, 103 g of adipic acid, 610 g of benzoic acid, 0.191 g of tetraisopropyl titanate as an esterification catalyst, 2 L four-neck equipped with thermometer, stirrer, and quick cooling tube The flask is charged and gradually heated with stirring until it reaches 230 ° C. in a nitrogen stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,2-propylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P2. The acid value was 0.10 and the number average molecular weight was 450.

<Polycondensed ester P3>
1,4-butanediol (330 g), phthalic anhydride (244 g), adipic acid (103 g), benzoic acid (610 g), tetraisopropyl titanate (0.191 g) as an esterification catalyst, 2 L four-neck equipped with a thermometer, stirrer, and slow cooling tube The flask is charged and gradually heated with stirring until it reaches 230 ° C. in a nitrogen stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,4-butanediol was distilled off at 200 ° C. under reduced pressure to obtain a polycondensed ester P3. The acid value was 0.50 and the number average molecular weight was 2000.

<Polycondensed ester P4>
251 g of 1,2-propylene glycol, 354 g of terephthalic acid, 610 g of benzoic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst were charged into a 2 L four-necked flask equipped with a thermometer, a stirrer, and a quick cooling tube. The temperature is gradually raised with stirring until it reaches 230 ° C. in an air stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,2-propylene glycol was distilled off at 200 ° C. under reduced pressure to obtain a polycondensed ester P4. The acid value was 0.10 and the number average molecular weight was 400.

<Polycondensed ester P5>
251 g of 1,2-propylene glycol, 354 g of terephthalic acid, 680 g of p-troyl acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst are charged into a 2 L four-necked flask equipped with a thermometer, stirrer, and slow cooling tube. The temperature is gradually raised with stirring until it reaches 230 ° C. in a nitrogen stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,2-propylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P5. The acid value was 0.30 and the number average molecular weight was 400.

<Polycondensed ester P6>
180 g of 1,2-propylene glycol, 292 g of adipic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst were charged into a 2 L four-necked flask equipped with a thermometer, a stirrer, and a slow cooling tube, in a nitrogen stream. The temperature is gradually raised while stirring until 200 ° C is reached. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,2-propylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P6. The acid value was 0.10 and the number average molecular weight was 400.

<Polycondensed ester P7>
180 g of 1,2-propylene glycol, 244 g of phthalic anhydride, 103 g of adipic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst were charged into a 2 L four-necked flask equipped with a thermometer, stirrer, and quick cooling tube. The temperature is gradually raised with stirring until it reaches 200 ° C. in a nitrogen stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted 1,2-propylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P7. The acid value was 0.10 and the number average molecular weight was 320.

<Polycondensed ester P8>
251 g of ethylene glycol, 244 g of phthalic anhydride, 120 g of succinic acid, 150 g of acetic acid, and 0.191 g of tetraisopropyl titanate as an esterification catalyst were charged into a 2 L four-necked flask equipped with a thermometer, a stirrer, and a slow cooling tube, and nitrogen The temperature is gradually raised with stirring until it reaches 200 ° C. in an air stream. The dehydration condensation reaction was carried out while observing the degree of polymerization. After completion of the reaction, unreacted ethylene glycol was distilled off under reduced pressure at 200 ° C. to obtain a polycondensed ester P8. The acid value was 0.50 and the number average molecular weight was 1200.

[Plasticizer]
The optical film of the present invention can contain other plasticizers as necessary for obtaining the effects of the present invention.

The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or an ester plasticizer. Agent, acrylic plasticizer and the like.

Of these, when two or more plasticizers are used, at least one is preferably a polyhydric alcohol ester plasticizer.

(Polyhydric alcohol ester)
The optical film of the present invention preferably contains a polyhydric alcohol ester represented by the following general formula (2).

General formula (2)
B ₁ -GB ₂
In the general formula (2), B ₁ and B ₂ each independently represent an aliphatic or aromatic monocarboxylic acid residue. G represents an alkylene glycol residue having a straight chain or branched structure having 2 to 12 carbon atoms.

In the general formula (2), G represents a divalent group derived from an alkylene glycol having a linear or branched structure having 2 to 12 carbon atoms.

Examples of the divalent group derived from an alkylene glycol having 2 to 12 carbon atoms in G include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1, 3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol ( Neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylol) Heptane), 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanedio , 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc. A divalent group can be mentioned. Two or more types of alkylene glycol can be preferably used in combination.

In the general formula (2), B ₁ and B ₂ are each independently a monovalent group derived from an aromatic ring-containing monocarboxylic acid or an aliphatic monocarboxylic acid.

Examples of monovalent groups derived from aliphatic monocarboxylic acids include monovalent groups derived from acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid and the like. Is included. Among these, a monovalent group derived from an alkyl monocarboxylic acid having 1 to 10 carbon atoms in the alkyl portion is preferable, and an acetyl group (a monovalent group derived from acetic acid) is more preferable.

Specific examples of polyhydric alcohol esters applicable to the present invention are shown below, but the present invention is not limited to these exemplified compounds.

The polyhydric alcohol ester having a structure represented by the general formula (2) used in the present invention is preferably contained in the range of 0.5 to 5% by mass with respect to the optical film. The content is more preferably in the range, and particularly preferably in the range of 1 to 2% by mass.

The polyhydric alcohol ester having the structure represented by the general formula (2) used in the present invention can be synthesized according to a conventionally known general synthesis method.

(Phosphate ester)
The optical film of the present invention can use a phosphate ester. As phosphoric acid esters, triaryl phosphoric acid esters, diaryl phosphoric acid esters, monoaryl phosphoric acid esters, aryl phosphonic acid compounds, aryl phosphine oxide compounds, condensed aryl phosphoric acid esters, halogenated alkyl phosphoric acid esters, halogen-containing condensed phosphoric acid Examples thereof include esters, halogen-containing condensed phosphonic acid esters, and halogen-containing phosphorous acid esters.

Specific phosphoric acid esters include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloro) Propyl) phosphate, tris (tribromoneopentyl) phosphate, and the like.

(Esters of glycolic acid)
In the present invention, glycolic acid esters (glycolate compounds) can be used as one kind of polyhydric alcohol esters.

The glycolate compound applicable to the present invention is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used.

Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl Ethyl glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl Glycolate, butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl Lil ethyl glycolate and the like, preferably ethyl phthalyl ethyl glycolate.

[Ultraviolet absorber]
The optical film of the present invention preferably contains an ultraviolet absorber from the viewpoint of improving light resistance. The ultraviolet absorber is intended to improve light resistance by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably in the range of 2 to 30%, more preferably 4 It is in the range of -20%, more preferably in the range of 5-10%.

The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, and particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers.

For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, There are tinuvins such as tinuvin 928, and these are all commercially available products from BASF Japan and can be preferably used. Of these, halogen-free ones are preferred.

In addition, a discotic compound such as a compound having a 1,3,5-triazine ring is also preferably used as the ultraviolet absorber.

The optical film of the present invention preferably contains two or more ultraviolet absorbers.

Also, as the ultraviolet absorber, a polymeric ultraviolet absorber can be preferably used, and in particular, a polymer type ultraviolet absorber described in JP-A-6-148430 is preferably used. Moreover, it is preferable that the ultraviolet absorber does not have a halogen group.

The method of adding the UV absorber can be added to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane or a mixed solvent thereof. Or you may add directly in dope composition.

For inorganic powders that do not dissolve in organic solvents, use a dissolver or sand mill in organic solvents and cellulose acylate (cellulose acetate) to disperse them before adding them to the dope.

The amount of the UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc., but when the optical film has a dry film thickness of 10 to 40 μm, it is 0.5 to 10% by mass relative to the optical film. The range is preferably 0.6 to 4% by mass.

〔Antioxidant〕
Antioxidants are also referred to as deterioration inhibitors. When an organic electroluminescence display device or the like is placed in a high humidity and high temperature state, the optical film may be deteriorated.

The antioxidant has a role of delaying or preventing the optical decomposition due to, for example, the residual solvent amount of halogen in the optical system, phosphoric acid of the phosphoric acid plasticizer, etc., and therefore, in the optical film of the present invention. It is preferable to contain.

As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], oct Decyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

The amount of these compounds to be added is preferably in the range of 1 ppm to 1.0%, more preferably in the range of 10 to 1000 ppm, in terms of mass ratio with respect to the optics.

[Fine particles (matting agent)]
The optical film of the present invention may further contain fine particles (matting agent) as necessary in order to improve the slipperiness of the surface.

The fine particles may be inorganic fine particles or organic fine particles. Examples of inorganic fine particles include silicon dioxide (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, Examples include magnesium silicate and calcium phosphate. Among these, silicon dioxide and zirconium oxide are preferable, and silicon dioxide is more preferable in order to reduce the increase in haze of the obtained film.

Examples of the fine particles of silicon dioxide include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Seahoster KE-P10, KE-P30, KE-P50, KE-P100 (manufactured by Nippon Shokubai Co., Ltd.) and the like are included. Among them, Aerosil R972V, NAX50, Seahoster KE-P30 and the like are particularly preferable because they reduce the coefficient of friction while keeping the turbidity of the resulting film low.

The primary particle diameter of the fine particles is preferably in the range of 5 to 50 nm, more preferably in the range of 7 to 20 nm. A larger primary particle size has a larger effect of increasing the slipperiness of the resulting film, but the transparency tends to decrease. Therefore, the fine particles may be contained as secondary aggregates having a particle diameter in the range of 0.05 to 0.3 μm. The size of the primary particles or the secondary aggregates of the fine particles is determined by observing the primary particles or secondary aggregates with a transmission electron microscope at a magnification of 500 to 2 million times, and 100 particles of primary particles or secondary aggregates. It can obtain | require as an average value of a diameter.

The content of the fine particles is preferably in the range of 0.05 to 1.0% by mass, more preferably in the range of 0.1 to 0.8% by mass with respect to the thermoplastic resin forming the optical film. preferable.

<Physical properties of optical film>
The moisture permeability of the optical film of the present invention is preferably in the range of 300 to 1800 g / m ² · 24 h at 40 ° C. and 90% RH, more preferably in the range of 400 to 1500 g / m ² · 24 h, and 40 to 1300 g / m ^2. -The range of 24 h is particularly preferred. The moisture permeability can be measured according to the method described in JIS Z 0208.

The visible light transmittance of the optical film of the present invention is preferably 90% or more, and more preferably 93% or more.

The haze of the optical film of the present invention is preferably less than 1%, particularly preferably 0 to 0.1%.

<Applications of optical films>
The optical film of the present invention is preferably a functional film used for various display devices such as a liquid crystal display, a plasma display, and an organic EL display. Specifically, the optical film of the present invention is a polarizing plate protective film for liquid crystal display devices, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an enlarged viewing angle, etc. Or an optical compensation film. Typically, the optical film of the present invention is a polarizing plate protective film, a retardation film, or an optical compensation film.

[Polarizing film]
The optical film of the present invention is preferably used as a polarizing plate protective film that is bonded to at least one surface of a polarizer.

The retardation value of the polarizing plate protective film is obtained by the following formula, and the retardation value Ro in the in-plane direction is preferably in the range of 0 to 100 nm, more preferably in the range of 0 to 50 nm. The retardation value Rt is preferably in the range of −400 to 400 nm, more preferably in the range of −300 to 300 nm.

Formula (i): Ro = (n _x −n _y ) × d (nm)
Formula (ii): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
(Wherein, Ro represents a plane retardation value of the film, Rt represents the retardation value in the thickness direction of the film. Further, d represents the thickness of the optical film (nm), n _x is represents the maximum refractive index in the plane of the film, also referred to as a slow axis direction of the refractive index .n _y represents a refractive index in the direction perpendicular to the slow axis in the film plane, n _z is the film in the thickness direction (All are measured values at a wavelength of 590 nm.)
The retardation value can be obtained at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH using, for example, KOBRA-WIS / RT (Oji Scientific Instruments).

[Optical compensation film]
Since liquid crystal displays use anisotropic liquid crystal materials and polarizing plates, there is a problem of viewing angle that even when good display is obtained when viewed from the front, display performance is degraded when viewed from an oblique direction. . Therefore, a viewing angle compensator is necessary to improve the performance of the liquid crystal display. The average refractive index distribution of the liquid crystal cell is larger in the cell thickness direction and smaller in the in-plane direction. Therefore, the viewing angle compensator must cancel this anisotropy. In other words, it is effective that the viewing angle compensation plate has a refractive index smaller than that in the in-plane direction, that is, a so-called negative uniaxial structure. The optical film of the present invention can be an optical compensation film having such a function.

When the optical film of the present invention is used for a VA mode liquid crystal cell, a total of two optical films may be used, one on each side of the cell (two-sheet type), or one of the upper and lower sides of the cell. An optical film may be used only on the side (single sheet type).

In the optical film of the present invention, the retardation value Ro in the in-plane direction represented by the above formula is preferably within a range of 20 to 150 nm at a measurement wavelength of 590 nm in an environment of 23 ° C. and 55% RH. A range of 30 to 130 nm is more preferable. The retardation value Rt in the thickness direction is preferably in the range of 50 to 350 nm and more preferably in the range of 100 to 270 nm at a measurement wavelength of 590 nm in an environment of 23 ° C. and 55% RH.

The optical film of the present invention has a slow axis or a fast axis in the film plane, and an angle θ1 formed by the slow axis or the fast axis and the film forming direction axis is −1 ° or more and + 1 ° or less. Preferably, it is more preferably −0.5 ° or more and + 0.5 ° or less. θ1 can be defined as an orientation angle, and θ1 can be measured using an automatic birefringence meter KOBRA-WIS / RT (Oji Scientific Instruments). An optical film in which θ1 satisfies the above relationship increases the brightness of a display image of a liquid crystal display device including the same, suppresses or prevents light leakage, and faithfully reproduces color in a color liquid crystal display device.

<Polarizing plate>
The polarizing plate using the optical film of the present invention is preferably produced by laminating the optical film of the present invention on one surface of the polarizer using an active energy ray-curable adhesive.

It should be noted that the optical film of the present invention may be used on the other surface of the polarizer constituting the polarizing plate, and other optical films are preferably bonded. Examples of such other optical films include commercially available cellulose ester films (for example, Konica Minoltak KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC4UY, KC4UY, KC4UY, KC4UY, , KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UAKC, KC4UAH, KC6UAH, Konica Minolta, Fujitac T40UZ, Fujitac T60UZ, Fujitac T80UZ, Fujitac TD80U FUJIFILM Corporation etc.) is preferably used.

[Polarizer]
A polarizer, which is a main component of the polarizing plate, is an element that allows only light having a plane of polarization in a certain direction to pass through. A typical polarizer currently known is a polyvinyl alcohol polarizing film. The polyvinyl alcohol polarizing film includes those obtained by dyeing iodine on a polyvinyl alcohol film and those obtained by dyeing a dichroic dye.

As the polarizer, a polarizer obtained by forming a polyvinyl alcohol aqueous solution into a film and dyeing it by uniaxial stretching or dyeing and then uniaxially stretching and then preferably performing a durability treatment with a boron compound may be used. The thickness of the polarizer is preferably in the range of 5 to 30 μm, and particularly preferably in the range of 10 to 20 μm from the viewpoint of thinning.

Further, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. is 1 to 4 mol%, the degree of polymerization is 2000 to 4000, and the degree of saponification is 99.0 to 99.99 mol%. The ethylene-modified polyvinyl alcohol is also preferably used. Among these, an ethylene-modified polyvinyl alcohol film having a hot water cutting temperature of 66 to 73 ° C. is preferably used. A polarizer using this ethylene-modified polyvinyl alcohol film is excellent in polarizing performance and durability, and has little color unevenness, and is particularly preferably used for a large liquid crystal display device.

[Photocurable adhesive]
The bonding of the optical film of the present invention and the polarizer is not particularly limited, but can be performed using a completely saponified polyvinyl alcohol adhesive, a photocurable adhesive, or the like. It is preferable to use a photocurable adhesive from the viewpoint that the obtained adhesive layer has a high elastic modulus and can easily suppress deformation of the polarizing plate.

Preferred examples of the photocurable adhesive include (α) cationic polymerizable compound, (β) photocationic polymerization initiator, and (γ) a wavelength longer than 380 nm, as disclosed in JP 2011-08234 A. And a photo-curable adhesive composition containing each component of a photosensitizer exhibiting maximum absorption in the light of (δ) and a naphthalene-based photosensitization aid. However, other photocurable adhesives may be used.

Hereinafter, an example of a method for producing a polarizing plate using a photocurable adhesive will be described. The polarizing plate includes (1) a pretreatment step for easily adhering the surface of the optical film to which the polarizer is bonded, and (2) at least one of the adhesive surfaces of the polarizer and the optical film. (3) a bonding step of bonding the polarizer and the optical film through the obtained adhesive layer, and (4) a polarizer and the optical film through the adhesive layer. It can manufacture by the manufacturing method including the hardening process which hardens an adhesive bond layer in the bonded state. What is necessary is just to implement the pre-processing process of (1) as needed.

(Pretreatment process)
In the pretreatment step, an easy adhesion treatment is performed on the adhesion surface of the optical film with the polarizer. When bonding an optical film to both surfaces of a polarizer, an easy adhesion process is performed on the adhesive surface of each optical film with the polarizer. Examples of the easy adhesion treatment include corona treatment and plasma treatment.

(Adhesive application process)
In the adhesive application step, the photocurable adhesive is applied to at least one of the adhesive surfaces of the polarizer and the optical film. When the photocurable adhesive is directly applied to the surface of the polarizer or the optical film, the application method is not particularly limited. For example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. Moreover, after casting a photocurable adhesive between a polarizer and an optical film, the method of pressurizing with a roller etc. and spreading uniformly can also be utilized.

(Bonding process)
Thus, after apply | coating a photocurable adhesive agent, it uses for a bonding process. In this bonding step, for example, when a photocurable adhesive is applied to the surface of the polarizer in the previous application step, an optical film is superimposed thereon. When a photocurable adhesive is applied to the surface of the optical film in the previous application step, a polarizer is superimposed thereon. In addition, when a photocurable adhesive is cast between the polarizer and the optical film, the polarizer and the optical film are superposed in that state. In the case where the optical film is bonded to both surfaces of the polarizer, and the photocurable adhesive is used on both surfaces, the optical film is superimposed on the both surfaces of the polarizer via the photocurable adhesive. Usually, in this state, both sides (if the optical film is superimposed on one side of the polarizer, the polarizer side and the optical film side, and if the optical film is superimposed on both sides of the polarizer, The film is pressed with a roller or the like from the film side). As the material of the roller, metal, rubber or the like can be used. The rollers arranged on both sides may be made of the same material or different materials.

(Curing process)
In the curing step, the active energy ray is irradiated to the uncured photocurable adhesive to cure the adhesive layer containing the epoxy compound or the oxetane compound. Thereby, the overlapped polarizer and the optical film are bonded via the photocurable adhesive. When bonding an optical film to the single side | surface of a polarizer, you may irradiate an active energy ray from either a polarizer side or an optical film side. Moreover, when bonding an optical film on both surfaces of a polarizer, an active energy ray is applied from either one of the optical films in a state where the optical film is superimposed on both surfaces of the polarizer via a photocurable adhesive. It is advantageous to irradiate and simultaneously cure the photocurable adhesive on both sides.

As the active energy rays, visible rays, ultraviolet rays, X-rays, electron beams and the like can be used, and since they are easy to handle and have a sufficient curing rate, electron beams or ultraviolet rays are generally preferably used.

Any appropriate conditions can be adopted as the electron beam irradiation conditions as long as the adhesive can be cured. For example, in the electron beam irradiation, the acceleration voltage is preferably in the range of 5 to 300 kV, more preferably in the range of 10 to 250 kV. If the acceleration voltage is less than 5 kV, the electron beam may not reach the adhesive and may be insufficiently cured. If the acceleration voltage exceeds 300 kV, the penetrating force through the sample is too strong and the electron beam rebounds, causing an optical film or polarized light. There is a risk of damaging the child. The irradiation dose is in the range of 5 to 100 kGy, more preferably in the range of 10 to 75 kGy. When the irradiation dose is less than 5 kGy, the adhesive becomes insufficiently cured, and when it exceeds 100 kGy, the optical film and the polarizer are damaged, resulting in a decrease in mechanical strength and yellowing, thereby obtaining predetermined optical characteristics. Can not.

Arbitrary appropriate conditions can be employ | adopted for the irradiation conditions of an ultraviolet-ray, if it is the conditions which can harden the said adhesive agent. Preferably the dose of ultraviolet rays in the range of 50 ~ 1500mJ / cm ² in accumulated light amount, and even more preferably in the range of within the range of 100 ~ 500mJ / cm ^2.

In the polarizing plate obtained as described above, the thickness of the adhesive layer is not particularly limited, but is usually in the range of 0.01 to 10 μm, and preferably in the range of 0.5 to 5 μm.

<Liquid crystal display device>
The liquid crystal display device in which the optical film of the present invention is used preferably includes a polarizing plate having the optical film of the present invention. Specifically, the polarizing film disposed in at least one of the liquid crystal cells includes the optical film of the present invention, and the film on the liquid crystal cell side of the polarizing plate is the optical film of the present invention.

In the liquid crystal display device of the present invention, it is preferable that the polarizing plate is bonded to one or both surfaces of the liquid crystal cell via an adhesive layer.

In addition to the antiglare layer or the clear hard coat layer, the polarizing plate protective film used on the surface side of the liquid crystal display device of the present invention preferably has an antireflection layer, an antistatic layer, an antifouling layer, and a backcoat layer. .

The optical film and polarizing plate of the present invention can be used for liquid crystal display devices of various drive systems such as STN, TN, OCB, HAN, VA (MVA, PVA), IPS, OCB. In particular, it is preferably used for a VA (MVA, PVA) type liquid crystal display device. In particular, even when used in a liquid crystal display device having a large screen of 30 type or more, coloring during black display due to light leakage can be reduced and visibility such as front contrast can be improved. Thus, the liquid crystal display device of the present invention is excellent in various visibility.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
A cellulose acylate film used as an optical film was produced by the following method.

<Preparation of optical film 101>
<Preparation of in-line additive solution>
10 parts by mass of Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd., average particle diameter of 16 nm, apparent specific gravity of 90 g / liter) and 90 parts by mass of methanol were stirred and mixed with a dissolver for 30 minutes, and then dispersed with Manton Gorin. A fine particle dispersion was obtained.

Into the obtained fine particle dispersion, 88 parts by mass of dichloromethane was added with stirring, and the mixture was diluted by stirring and mixing with a dissolver for 30 minutes. The obtained solution was filtered through a polypropylene wind cartridge filter TCW-PPS-1N manufactured by Advantech Toyo Co., Ltd. to obtain a fine particle dispersion dilution.

15 parts by mass of Tinuvin 928 (manufactured by BASF Japan Ltd.) and 100 parts by mass of dichloromethane were put into a sealed container, heated and stirred to completely dissolve, and then filtered. To the obtained solution, 36 parts by mass of the fine particle dispersion diluted solution was added with stirring, and further stirred for 30 minutes, and then 6 parts by mass of cellulose triacetate (acetyl group substitution degree 2.85, Mw = 152000, Mn = 90000). , Mw / Mn = 1.7) was added with stirring, and the mixture was further stirred for 60 minutes. The obtained solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to obtain an in-line additive solution. The filter medium having a nominal filtration accuracy of 20 μm was used.

<Preparation of dope 1>
The following components were put into a sealed container and completely dissolved with heating and stirring. The obtained solution was prepared as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration at 24 gave the main dope.

(Main dope composition)
Cellulose acetate propionate (manufactured by Eastman Chemical Co., Ltd., product name CAP482-20, acetyl group substitution degree 0.26, propionyl group substitution degree 2.5, total acyl group substitution degree 2.76, weight average molecular weight Mw 240000)
86 parts by mass Polyhydric alcohol ester (compound represented by formula (2)): Exemplified compound 2-10 2 parts by mass Sugar ester; BzSc (benzylsucrose: Compound a- described in Chemical formula 3
1 to a-4 mixture), average degree of ester substitution = 5.5 7 parts by mass Polycondensation ester: Polycondensation ester having a structure represented by the general formula (1): P8 5 parts by mass Dichloromethane 430 parts by mass Methanol 11 Part by mass 100 parts by mass of the main dope and 2.5 parts by mass of the in-line additive solution were sufficiently mixed with an in-line mixer (Toray static in-tube mixer Hi-Mixer, SWJ) to obtain a dope 1.

The obtained dope 1 was uniformly cast on a stainless steel band support using a belt casting apparatus shown in FIG. 1 under the conditions of a dope temperature of 35 ° C. and a width of 1.6 m. On the stainless steel band support, the solvent in the obtained dope film was evaporated until the residual solvent amount reached 100% by mass to obtain a web, and then the web was peeled from the stainless steel band support. The resulting web was further dried at 35 ° C.

Thereafter, the film was stretched in the MD direction at a stretching ratio of 1.02 times at 80 ° C. by the preliminary stretching apparatus 102 shown in FIG. At that time, the residual solvent amount of the web at the start of stretching was 30% by mass.

Next, the film was stretched in the MD direction at 160 ° C. at a stretching ratio of 1.60 times by the main stretching apparatus 103 shown in FIG. At that time, the residual solvent amount of the web at the start of stretching was 12% by mass.

Next, the web was stretched in the TD direction at a stretching ratio of 1.60 times by the TD stretching apparatus 104 shown in FIG. At that time, the residual solvent amount of the web at the start of stretching was 8% by mass.

Thereafter, the obtained film was dried at 125 ° C. for 15 minutes while being conveyed by a number of rollers in the drying apparatus, then slit to 1.8 m width, and the height of the convex portion was 10 μm at both ends in the width direction. The long optical film 101 having a width of 1.8 m, a length of 4000 m, and a film thickness of 30 μm was produced.

The glass transition temperature of the optical film was 145 ° C.

<Preparation of optical films 102 to 114>
In the production of the optical film 101, as shown in Table 1, the draw ratio, temperature, residual solvent amount and stretch span during preliminary stretching in the MD direction, and the stretch ratio, temperature, residual solvent amount during main stretching in the MD direction. Optical films 102 to 114 were produced in the same manner except that the stretch span was changed and the total draw ratio and film thickness were changed.

≪Evaluation≫
(Measurement of stretching stress)
The following measurements were performed using a Tensilon tester (ORITC Corporation, RTC-1225A).

The optical film was cut out at 120 mm (MD direction) × 10 mm (TD direction), and the sample was allowed to stand for 24 hours in an environment of 23 ± 2 ° C. and 55 ± 5% RH, and then kept at 23 ° C. and 55% RH. The film is pulled in the MD direction at a chuck length of 50 mm and a speed of 50 mm / min in the tank, and the tensile load in that direction is divided by the film cross-sectional area (that is, the film width × film thickness) to obtain the stretching stress in the MD direction. Asked.

[Scratch evaluation method]
Spread the film sampled in a strip of 1m in the MD direction on a flat evaluation table with a black lacquer cloth, irradiate the green lamp diagonally, and visually observe the scratches on the surface of the film. Evaluated by criteria.

◎: Scratches are not visible ○: Slight scratches are visible but there is no problem in performance △: Scratches are visible ×: Multiple scratches are visible [Evaluation method of optical unevenness in TD direction]
In order to evaluate the optical properties of the film, the retardation value (Rt) and in-plane retardation value (Ro) in the thickness direction of the film were measured using an automatic birefringence meter measuring device (KOBRA-WIS / RT, Oji Measurement). Measured at a wavelength of 590 nm under an environment of a temperature of 23 ° C. and a relative humidity of 55% RH.

Measured at intervals of 100 mm in the width direction of the film except for 50 mm each on both ends of the film. The difference between the maximum value and the minimum value of the width measurement points of in-plane retardation was calculated as ΔRo.

〔Comprehensive evaluation〕
A: There is no generation of scratches and ΔRo is 0.4 nm or less as optical unevenness. ○: There is generation of weak scratches, or ΔRo is 1.0 n as optical unevenness.
△: Generation of weak scratches and ΔRo as optical unevenness is 4.0 nm or less Δ: Generation of scratches can be visually recognized, and ΔRo is 5.0 nm or more as optical unevenness ×: Multiple scratches are visually recognized As an optical film, ΔRo is 5.0 nm or more as optical unevenness, the evaluation result of ◯ △ is within practical limits, and ◯ to ◎ indicate that the optical film is more excellent.

From the results in Table 1, the optical film No. It can be seen that Nos. 101 to 112 are excellent optical films as a result of pre-stretching according to the present invention having low stretching stress and low generation of scratches and optical unevenness. Among them, the optical films 101 to 106 in which the draw ratio, temperature, residual solvent amount, and draw span are in the preferred ranges in relation to each claim showed excellent characteristics.

Example 2
<Preparation of acrylic resin / cellulose acylate mixed optical film 201>
According to the following method, the optical film 201 which mixedly contains acrylic resin / cellulose acylate was produced as an optical film.

(Preparation of dope 2)
The following components were put into a sealed container and completely dissolved with heating and stirring. The obtained solution was prepared as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration at 24 gave the main dope.

(Preparation of main dope)
Acrylic resin: Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd., acrylic resin Mw: 280000) 90 parts by mass Cellulose ester (cellulose acetate propionate acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree) 2.5
6, Mw = 200000) 10 parts by mass Acrylic fine particles (C1) 2 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass <Preparation of acrylic fine particles (C1)>
A reactor with a reflux condenser with an internal volume of 60 liters was charged with 38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate and heated to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. The effect of oxygen was virtually eliminated. A single unit consisting of 0.36 g of ammonium persulfate (APS) and 1657 g of methyl methacrylate (MMA), 21.6 g of n-butyl acrylate (BA) and 1.68 g of allyl methacrylate (ALMA) after stirring for 5 minutes. The body mixture was added all at once, and after the detection of the exothermic peak, the mixture was further held for 20 minutes to complete the polymerization of the innermost hard layer.

Next, 3.48 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 8105 g of BA, 31.9 g of polyethylene glycol diacrylate (PEGDA: molecular weight 200), and 264.0 g of ALMA was applied for 120 minutes. The mixture was continuously added and held for an additional 120 minutes after completion of the addition to complete the polymerization of the soft layer.

Next, 1.32 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 2106 g of MMA and 201.6 g of BA was continuously added over 20 minutes, and held for another 20 minutes after the addition was completed. Polymerization of the outermost hard layer 1 was completed.

Next, 1.32 g of APS was added, and after 5 minutes, a monomer mixture consisting of 3148 g of MMA, 201.6 g of BA, and 10.1 g of n-OM was continuously added over 20 minutes, and the addition was completed. Later held for another 20 minutes. Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost hard layer 2.

A small amount of the polymer latex thus obtained was collected, and the flat particle size was determined by the absorbance method, which was 0.10 μm. The remaining latex was put into a 3% by mass sodium sulfate warm aqueous solution, salted out and coagulated, and then dried after repeated dehydration and washing to obtain acrylic fine particles (C1) having a three-layer structure.

100 parts by mass of the main dope was sufficiently mixed with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ) to obtain a dope 2.

The obtained dope 2 was uniformly cast on a stainless steel band support using a belt casting apparatus shown in FIG. 1 under the conditions of a dope temperature of 35 ° C. and a width of 1.6 m. On the stainless steel band support, the solvent in the obtained dope film was evaporated until the residual solvent amount reached 100% by mass to obtain a web, and then the web was peeled from the stainless steel band support. The resulting web was further dried at 35 ° C.

Thereafter, the film was stretched in the MD direction at a stretching ratio of 1.05 times at 80 ° C. by the preliminary stretching apparatus 102 shown in FIG. The residual solvent amount of the web at the start of stretching at that time was 30% by mass.

Thereafter, the obtained film was dried at 125 ° C. for 15 minutes while being conveyed by a number of rollers in the drying apparatus, then slit to 1.8 m width, and the height of the convex portion was 10 μm at both ends in the width direction. The long acrylic resin / cellulose acylate mixed film 201 having a width of 1.8 m, a length of 4000 m, and a film thickness of 30 μm was produced.

The acrylic resin / cellulose acylate mixed optical film had a Tg of 120 ° C.

<Production of acrylic resin / cellulose acylate mixed optical films 202 to 213>
In preparation of the acrylic resin / cellulose acylate mixed film 201, as shown in Table 2, the draw ratio at the time of pre-stretching in the MD direction, the temperature, the residual solvent amount and the stretch span, and the draw ratio at the time of main stretching in the MD direction Acrylic resin / cellulose acylate mixed optical films 202 to 213 were prepared in the same manner except that the temperature and the amount of residual solvent were changed, and the total draw ratio and film thickness were changed.

Using the obtained acrylic resin / cellulose acylate mixed optical films 201 to 213, the same evaluation as in Example 1 was performed, and the results are shown in Table 2.

From the results in Table 2, acrylic resin / cellulose acylate mixed optical film No. which is the optical film of the present invention. Nos. 201 to 211 are excellent optical films as a result of pre-stretching according to the present invention having low stretching stress and low generation of scratches and optical unevenness.

Example 3
<Production of acrylic resin-containing optical film 301>
An optical film 301 containing an acrylic resin was produced according to the following method.

(Preparation of fine particle dispersion)
10 parts by mass of Aerosil 972V (manufactured by Nippon Aerosil Co., Ltd., primary average particle size: 16 nm, apparent specific gravity of 90 g / L) and 90 parts by mass of ethanol were stirred and mixed with a dissolver for 30 minutes, and then high pressure disperser Manton Gorin Was used to prepare a fine particle dispersion.

(Preparation of inline additive solution)
15 parts by weight of Tinuvin 928 (manufactured by BASF Japan) and 100 parts by weight of dichloromethane as an ultraviolet absorber and 100 parts by weight of dichloromethane were put into a sealed container, and heated and stirred to completely dissolve, followed by filtration. To the obtained solution, 36 parts by mass of the fine particle dispersion diluted liquid was added with stirring, and further stirred for 30 minutes, and then 6 parts by mass of acrylic resin: Dianal BR85 (Mitsubishi Rayon, Mw: 280000) was added. The mixture was further stirred for 60 minutes with stirring, and the resulting solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to obtain an in-line additive solution. It was.

(Preparation of dope 3)
The following components were put into a sealed container and completely dissolved with heating and stirring. The obtained solution was prepared as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. Filtration at 24 gave the main dope.

<Composition of main dope>
Acrylic resin: Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd., acrylic resin Mw: 280000) 100 parts by weight Acrylic fine particles (C1) 2 parts by weight Methylene chloride 360 parts by weight Ethanol 15 parts by weight 100 parts by weight of main dope and 2.5 parts by weight Part of the in-line additive solution was thoroughly mixed with an in-line mixer (Toray static type in-tube mixer Hi-Mixer, SWJ) to obtain a dope 3.

The obtained dope 3 was uniformly cast on a stainless steel band support using a belt casting apparatus shown in FIG. 1 under the conditions of a dope temperature of 35 ° C. and a width of 1.6 m. On the stainless steel band support, the solvent in the obtained dope film was evaporated until the residual solvent amount reached 100% by mass to obtain a web, and then the web was peeled from the stainless steel band support. The resulting web was further dried at 35 ° C.

Thereafter, the film was stretched in the MD direction at a stretching ratio of 1.07 times at 80 ° C. by the preliminary stretching apparatus 102 shown in FIG. At that time, the residual solvent amount of the web at the start of stretching was 30% by mass.

Thereafter, the obtained film was dried at 125 ° C. for 15 minutes while being conveyed by a number of rollers in the drying apparatus, then slit to 1.8 m width, and the height of the convex portion was 10 μm at both ends in the width direction. A long acrylic resin-containing optical film 301 having a width of 1.8 m, a length of 4000 m, and a film thickness of 30 μm was produced.

In addition, Tg of the said acrylic resin containing optical film was 115 degreeC.

<Preparation of acrylic resin-containing optical films 302-312>
In the production of the acrylic resin-containing optical film 301, as shown in Table 3, the draw ratio, temperature, residual solvent amount and stretch span during preliminary stretching in the MD direction, and the stretch ratio and residual solvent during main stretching in the MD direction Acrylic resin-containing optical films 302 to 312 were produced in the same manner except that the amount was changed and the total draw ratio and film thickness were changed.

Using the obtained acrylic resin-containing optical films 301 to 312, the same evaluation as in Example 1 was performed, and the results are shown in Table 3.

From the results shown in Table 3, the acrylic resin-containing optical films 301 to 310, which are the optical films of the present invention, have a low stretching stress and suppress the occurrence of scratches and optical unevenness by performing preliminary stretching according to the present invention. It can be seen that it is a comprehensively excellent optical film.

According to the method for producing an optical film of the present invention, an optical film in which generation of scratches and optical unevenness by a transport roller is reduced can be produced, and the optical film is suitably used for a polarizing plate, a liquid crystal display element, and the like. .

DESCRIPTION OF SYMBOLS 1 Optical film manufacturing apparatus 2 Dope (resin solution)
3 Web (casting membrane)
4 peeling

roller

5, 6, 7 guide roller 8 optical film 101 casting apparatus 101a metal support (endless belt)

101b Die

101c Heating device 101d First heating air supply device 101e Second heating air supply device 101f Exhaust port 102 Pre-stretching device in MD direction (first stretching device)
102d Stretching device 103 Main stretching device in MD direction (second stretching device)
103d Stretching device 104 Stretching device in the TD direction (TD stretching device)
104d Stretching device 105 Drying device 106 Winding device 106a Rolled optical film wound up

Claims

An optical film manufacturing method for manufacturing an optical film having a thickness in a range of 10 to 40 μm and a width of 1.4 m or more by a solution casting method, wherein a web peeled from a casting support is MD A method for producing an optical film, wherein the film is pre-stretched in a range of 1.01 to 1.10 times as a stretching ratio in the direction, and further stretched in the MD direction.
2. The method for producing an optical film according to claim 1, wherein the main stretching is performed within a range of 1.15 to 2.50 times as a stretching ratio.
The pre-stretching is performed within the range of 20 to 100% by mass of the residual solvent represented by the following formula of the web at the start of stretching, and the main stretching is performed at a residual solvent amount of 1 to 30% by mass at the start of stretching. The method for producing an optical film according to claim 1, wherein the method is performed within a range of%.
Residual solvent amount (% by mass) = {(mass before heat treatment of web−mass after heat treatment of web) / (mass after heat treatment of web)} × 100
However, the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.
When the glass transition temperature of the optical film is Tg (° C.), the preliminary stretching is performed at a temperature within the range of (Tg-100) to (Tg-20) ° C., and the main stretching is performed (Tg-10) to (T The method for producing an optical film according to any one of claims 1 to 3, wherein the method is performed at a temperature within a range of Tg + 100) ° C.
The method for producing an optical film according to any one of claims 1 to 4, wherein a stretching span of the preliminary stretching is 2 m or less and a stretching span of the main stretching is 2 m or more.
The pre-stretching in the MD direction and the main stretching, followed by stretching in the range of 1.3 to 3.0 times in the TD direction, according to any one of claims 1 to 5 Manufacturing method of optical film.
The thermoplastic resin used for the optical film is selected from any one of cellulose acylate, acrylic resin, and a resin in which cellulose acylate and acrylic resin are mixed. The method for producing an optical film according to one item.
The method for producing an optical film according to claim 7, wherein the thermoplastic resin used for the optical film is an acrylic resin.