JP2015202627A - Method for manufacturing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film, by which a film having a retardation Re in an in-plane direction and a retardation Rth in a thickness direction, both small and uniform, and having a uniform thickness can be efficiently manufactured.SOLUTION: The method for manufacturing an optical film includes: a molten resin film forming step of extruding a thermoplastic resin in a molten state and continuously molding a molten resin film 101; and a cooling step of continuously guiding the molten resin film 101 to a cast roll 130, conveying the molten resin film 101 along a conveyance passage on a peripheral surface of the cast roll 130 by rotation of the cast roll 130 so as to cool the molten resin film 101 to obtain a cured film, and releasing the obtained cured film from the cast roll 130. The cooling step includes reducing a pressure in a specific space and controlling a temperature of the cured film to Tg or lower upon releasing the cured film.

Description

  The present invention relates to a method for producing an optical film.

  One method for producing a resin film is a melt extrusion method. In the melt extrusion method, the molten resin is usually formed into a film by extruding a molten thermoplastic resin from a die. Thereafter, the molded film-shaped molten resin is cooled and cured to produce a desired film. According to the melt extrusion method, a long film can be produced efficiently.

  The application of such a melt extrusion method to the production of optical films has also been studied (Patent Documents 1 to 3). For example, as a constituent element such as a polarizing plate protective film and a resin film substrate as an alternative to a conventionally used glass substrate, use in a display device such as a liquid crystal display device has been studied.

  The cooling of the molten resin film in the melt extrusion method is generally performed by extruding the molten resin film onto the peripheral surface of a support such as a cast roll, transferring heat from the molten resin film to the support, and gradually increasing the temperature of the molten resin film. It is done by lowering.

JP-A-2005-99097 JP 2009-166325 A JP 2008-302524 A

  When manufacturing an optical film, it is required to strictly control characteristics such as thickness and retardation of the obtained optical film. In particular, an optical film used for certain applications such as a polarizing plate protective film and a resin film substrate has both a very small and uniform value for both the in-plane retardation Re and the thickness retardation Rth. May be required. When such an optical film is produced by a melt extrusion method, it is difficult to make both Re and Rth as desired small and uniform values and to make the film thickness uniform.

  Accordingly, an object of the present invention is to provide an optical film that can efficiently produce a film having both a small and uniform both in-plane retardation Re and thickness-direction retardation Rth and a uniform thickness. It is in providing the manufacturing method of.

The present inventor has studied to solve the above problems, and in particular, has focused on the process of cooling the molten resin film on the peripheral surface of the cast roll. As a result, it was found that birefringence, particularly Rth, is likely to occur due to dimensional constraints of the molten resin on the cast roll. The present inventor further examined that a space on the outer surface of the molten resin film was reduced in pressure, and a large gap was provided between the molten resin film and the cast roll, so that a part on the peripheral surface of the cast roll was obtained. The film is slowly cooled only in this area, and then the film is separated from the cast roll at a temperature lower than the glass transition temperature, so that the birefringence is sufficiently relaxed, and the generation of birefringence after cooling is also possible. As a result, both the in-plane retardation Re and the thickness retardation Rth are both small and uniform, and a film with a uniform thickness can be produced even if the production line speed is increased. I found out that I can. The present invention has been completed based on these findings.
That is, the present invention is as follows.

[1] A molten resin film forming step of extruding a thermoplastic resin having a glass transition temperature of Tg (° C.) in a molten state and continuously forming the molten resin film, and continuously introducing the molten resin film to a cast roll The molten resin film is conveyed along the conveyance path on the peripheral surface of the cast roll by the rotation of the cast roll, the molten resin film is cooled to be a cured film, and the obtained cured film is removed from the cast roll. A method for producing an optical film, including a cooling step for separating,
The cooling step includes
In at least a part of the area (A) in the conveying path on the peripheral surface, the space close to the outer surface of the molten resin film is depressurized, and the temperature of the cured film when the cured film is detached is Tg The manufacturing method of an optical film including controlling the temperature of the outer surface of the said molten resin film, the said cured film, or both of these as follows.
[2] A chamber that is provided along the section (A) and has an opening that opens toward the molten resin film and surrounds the space adjacent to the outer surface of the molten resin film. The method for producing an optical film according to [1], wherein the method is performed with a decompressor comprising:
[3] The method for producing an optical film according to [1] or [2], comprising heating the outer surface of the molten resin film in at least a part of the conveyance path on the peripheral surface.
[4] The method for producing an optical film according to any one of [1] to [3], wherein the production rate is 100 m / min or more.
[5] The method for producing an optical film according to any one of [1] to [4], wherein the thermoplastic resin is an alicyclic polyolefin resin.

  According to the method for producing an optical film of the present invention, it is possible to efficiently produce a film in which both the in-plane retardation Re and the thickness retardation Rth are small and uniform, and the thickness is uniform. it can.

FIG. 1: is a side view which shows typically 1st embodiment of operation of the optical film manufacturing apparatus for enforcing the manufacturing method of the optical film of this invention, and the manufacturing method of the optical film of this invention using the same. is there. FIG. 2 is a side view schematically showing an example of a cooling process in the method of manufacturing an optical film of the present invention using the cooling device 200 in the optical film manufacturing apparatus shown in FIG. FIG. 3 is a perspective view schematically showing the positional relationship of the components of the cooling device 200 shown in FIG. FIG. 4 shows the outer surface of the molten resin film at various points on the transport path on the peripheral surface of the cast roll 130 in the manufacturing process of the present embodiment example and the comparative example performed using the apparatus shown in FIGS. It is a graph which shows the result of having measured the change of temperature with the infrared radiation thermometer. FIG. 5 is a perspective view schematically showing an example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. FIG. 6 is a cross-sectional view of the adjuster of the example of FIG. 5 taken along a plane along line A5. FIG. 7 is a perspective view schematically showing another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. FIG. 8 is a cross-sectional view of the adjuster of the example of FIG. 7 cut along a plane along line A7. FIG. 9 is a perspective view schematically showing still another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. FIG. 10 is a cross-sectional view of the adjuster of the example of FIG. 9 taken along a plane along line A9. FIG. 11 is a perspective view schematically showing still another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. 12 is a cross-sectional view of the adjuster of the example of FIG. 11 cut along a plane along the line A11. FIG. 13: is a perspective view which shows typically another example of the regulator which can be used in the cooling process of the manufacturing method of the optical film of this invention. FIG. 14 is a cross-sectional view of the regulator of the example of FIG. 13 cut along a plane along line A13.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and exemplifications, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

[1.1. First Embodiment: Overview]
The method for producing an optical film of the present invention includes a molten resin film forming step of continuously forming a molten resin film by extruding a resin having a glass transition temperature of Tg (° C.) in a molten state, and continuously forming the molten resin film on a cast roll. Cooling, the molten resin film is conveyed along the conveying path on the peripheral surface of the cast roll by rotating the cast roll, the molten resin film is cooled to be a cured film, and the obtained cured film is separated from the cast roll. Process.

  FIG. 1: is a side view which shows typically 1st embodiment of operation of the optical film manufacturing apparatus for enforcing the manufacturing method of the optical film of this invention, and the manufacturing method of the optical film of this invention using the same. is there. In the first embodiment shown in FIG. 1, the optical film manufacturing apparatus 10 includes a molten resin film forming apparatus 110 and a cooling device 200 provided downstream of the molten resin film forming apparatus 110. The molten resin film molding apparatus 110 includes an extrusion molding machine 111 and a die 112, and the cooling apparatus 200 includes a cast roll 130, a decompressor, and a temperature controller (not shown in FIG. 1). The optical film manufacturing apparatus 10 further includes an automatic birefringence meter 141 and a film thickness meter 142 that are provided downstream of the cooling device 200 and measure properties of the obtained optical film. The obtained optical film is a roll. 151 is wound up.

[1.2. First Embodiment: Molten Resin Film Forming Process]
In the operation of the optical film manufacturing apparatus 10, the resin that is the material of the optical film is melted in the extruder 111 and supplied to the die 112 through a polymer filter and a gear pump (not shown) as necessary. Resin is discharged from the lip portion of the die 112, whereby the resin is extruded as a molten resin film 101, and the molten resin film 101 is continuously formed. The temperature inside the extruder 111 and the temperature of the die 112 can be adjusted as appropriate, whereby the molten resin film 101 can be extruded from the die 112 at a desired temperature. In the molten resin film forming step, a molten resin film having a plurality of layers can be coextruded, but usually a molten resin film having one layer is extruded to produce a single layer optical film.

  The extrusion temperature at the time of extruding the molten resin film can be appropriately adjusted to a temperature at which both the in-plane direction retardation Re and the thickness direction retardation Rth are small and a film having a uniform thickness can be achieved. Specifically, the extrusion temperature is preferably Tg + 60 ° C. or higher, more preferably Tg + 100 ° C. or higher, while preferably Tg + 150 ° C. or lower, more preferably Tg + 140 ° C. or lower.

[1.3. First embodiment: cooling step]
The molten resin film 101 obtained in the molten resin film forming step is continuously led to the cast roll 130 of the cooling device 200. The cast roll 130 rotates about the shaft 131, whereby the molten resin film 101 is conveyed along the conveyance path on the peripheral surface of the cast roll, and at the same time, the molten resin film 101 is cooled. A part of the heat of the molten resin film 101 is also dissipated into the surrounding air, but most of the heat is transmitted to the cast roll 130, thereby achieving cooling of the molten resin film 101. By such cooling, the molten resin film 101 becomes a cured film 102 and is conveyed in the direction of arrow A1. The cured film 102 is measured by an automatic birefringence meter 141 and a film thickness meter 142 as necessary, and then wound by a winder to form a roll 151 of an optical film as a product.

  In the production method of the present invention, the molten resin film extruded in a molten state is gradually cooled and gradually cured in the cooling step. In the present application, for convenience of explanation, the molten resin film is called `` cured film '' that is cured to the extent that it can be removed from the cast roll as a result of cooling, and the film from immediately after being extruded to just before reaching the cured film, It is called “molten resin film” without distinction. Further, the molten resin film and the subsequent cured film may be collectively referred to simply as “film”.

  FIG. 2 is a side view schematically showing an example of a cooling process in the method of manufacturing an optical film of the present invention using the cooling device 200 in the optical film manufacturing apparatus shown in FIG. 1, and FIG. It is a perspective view which shows typically the positional relationship of the component of the cooling device 200 shown in FIG.

  In 1st embodiment shown in FIG. 2, the cast roll 130 of the cooling device 200 is arrange | positioned so that the molten resin film 101 may be conveyed along the conveyance path | route on the surrounding surface. In the present application, the conveyance path on the peripheral surface refers to a path from a position where the cast roll receives the film to a position where the film separates from the cast roll, among the conveyance paths of the molten resin film. In one embodiment, the path from the start point position 211 to the end point position 214 is a transport path on the circumferential surface.

  The distance between the two positions in the transport path on the peripheral surface is the line connecting one position and the cast roll axis and the other position and the cast roll axis in a cross section perpendicular to the cast roll axis. It can be expressed by the angle formed by the line. Further, the actual distance can be calculated from the angle and the diameter of the cast roll. In the following description, such an angle with respect to the start position and end position of a certain area may be simply referred to as the angle of the area. Moreover, the angle of the whole conveyance path | route on the surrounding surface of a cast roll is called a holding angle. In the first embodiment shown in FIG. 2, the holding angle of the cast roll 130 is an angle indicated by θh. The distance between the two positions in the transport path on the peripheral surface can also be expressed by the time required for the molten resin film to move the distance. For example, when the molten resin film 101 passes from the start point position 211 to the end point position 214 on the peripheral surface of the cast roll 130 in 1.3 seconds, the distance from the start point position 211 to the end point position 214 is 1.3. It can be expressed as a distance in seconds. Further, the actual distance can be calculated from the time and the moving speed of the peripheral surface of the cast roll.

  In the cooling step, the film is usually conveyed on a conveyance path on the peripheral surface in a state where it is pinned by a cast roll. In the first embodiment shown in FIGS. 2 and 3, the pinning of the molten resin film 101 can be performed by a known method such as electrostatic pinning or pinning with a roller. The electrostatic pinning can be performed by applying static electricity to the end of the molten resin film before the molten resin film 101 reaches the cast roll 130. Specifically, static electricity is applied to the end portion of the molten resin film 101 at a position indicated by an arrow A31 in FIG. 3, so that when the molten resin film 101 approaches the cast roll 130, only the end portion is static. It is possible to achieve electrostatic pinning by operating to adhere to the cast roll 130 by action.

  The molten resin film 101 is usually pinned to the cast roll 130 only at the end portion in the width direction, and therefore the inner surface of the molten resin film 101 is conveyed in a state of being in contact with the cast roll 130 at the end portion. On the other hand, when the molten resin film 101 is normally conveyed by the cast roll 130, the molten resin film 101 is conveyed with the surrounding air, and therefore, air is provided between the cast roll 130 and the molten resin film 101 in the direction indicated by the arrow A 22. Flows in. Therefore, the molten resin film 101 is transported in a state where the inner surface and the peripheral surface of the cast roll 130 are separated via the air layer at a portion other than the end portion in the width direction. In the present application, the “inside” surface of the molten resin film refers to the surface on the cast roll side of both surfaces of the molten resin film, and the “outside” surface refers to the surface opposite to the cast roll. In the present application, the temperature of the molten resin film is a temperature on the outer surface unless otherwise specified.

  In the cooling step in the production method of the present invention, an area (A) is set in the conveyance path on the peripheral surface, and the space close to the outer surface of the molten resin film in the area (A) is decompressed. The area (A) is set in at least a part of the conveyance path on the circumferential surface, but is usually set at a location close to the starting point position of the conveyance path on the circumferential surface. The start point position of the area (A) may coincide with the start point position of the transport path on the peripheral surface, but may be shifted upstream or downstream from the start point position of the transport path on the peripheral surface. The starting point position of the section (A) is preferably in the range of θa + 15 ° to θa-15 °, and more preferably in the range of θa + 10 ° to θa-10 °. Moreover, it is preferable that the length on the conveyance path | route of an area (A) is 50 mm-1000 mm, and it is more preferable that it is 300 mm-450 mm. In the first embodiment shown in FIG. 2, the start point position of the section (A) is the same position as the start position 211 of the conveyance path on the circumferential surface, and the section of the angle θa to the position 212 downstream from the section (A) Is set.

  In the first embodiment shown in FIGS. 2 and 3, the decompression is performed by the decompressor 220. The decompressor 220 is provided along the area (A), has an opening opened toward the molten resin film 101 over the area (A), and surrounds a space close to the outer surface of the molten resin film 221. And an air guide tube 222 communicating with the space and a space outside the chamber 221.

  By deriving a certain amount of air from the chamber 221 of the decompressor 220 through the air guide tube 222 in the direction of the arrow A21, the space close to the outer surface of the molten resin film in the area (A) can be decompressed. . When such pressure reduction is performed, the molten resin film 101 is sucked in the direction of the pressure reducer 220, so that the thickness of the air layer between the inner surface of the molten resin film 101 and the cast roll 130 reduces the pressure reduction. Thicker compared to when not done.

  Since such pressure reduction is normally performed at a location close to the starting point position of the conveyance path on the circumferential surface, the thickness of the air layer becomes the thickest at the starting point position of the conveyance path on the circumferential surface, and the molten resin film 101 is downstream. When moving to, the air layer gradually becomes thinner. Further, since the molten resin film 101 is normally pinned to the cast roll 130 only at the end in the width direction, the thickness of the air layer is the thickest at the center in the film width direction and zero at the pinned end. become. In the cooling process, by reducing the pressure and increasing the thickness of the air layer, the heat transfer from the molten resin film 101 to the cast roll 130 becomes more gradual. Thereby, the cooling rate of the molten resin film 101 becomes gentler in a part of the conveyance path on the peripheral surface.

  The preferred air layer thickness may vary depending on other manufacturing conditions, and can be adjusted as appropriate to achieve an appropriate thickness. However, as an example, the width at the starting point of the transport path on the peripheral surface The value at the center of the direction is preferably 60 μm to 360 μm, and more preferably 80 μm to 140 μm.

  The pressure in the chamber 221 of the decompressor 220 in the cooling step can be appropriately adjusted so that the thickness of the air layer between the inner surface of the molten resin film 101 and the cast roll 130 becomes a desired thickness. As an example, the difference between the atmospheric pressure and the pressure in the chamber is preferably 1 kPa to 100 kPa, and preferably 5 kPa to 15 kPa.

  In the cooling step in the production method of the present invention, the temperature of the outer surface of the film is further controlled so that the temperature of the cured film when the cured film is detached is Tg or less. The temperature can be controlled only by adjusting the degree of decompression and the temperature of the cast roll, but in addition, in at least a part of the transport path on the peripheral surface, the molten resin film is controlled. It is also possible to further heat the outer surface and thereby control the temperature.

  In the first embodiment shown in FIGS. 2 and 3, the temperature is controlled by adjusting the temperature of the cast roll 130 and the temperature of the space near the outer surface of the molten resin film downstream of the decompressor 220. This is performed by adjusting the temperature with the temperature controller 230 provided in an area to be adjusted using the temperature controller (hereinafter, this area may be referred to as “zone (B)”). In this example, the area (B) is a downstream area adjacent to the area (A), that is, set in the range of the angle θb from the position 212 to the position 213. The sum of θa and θb is adjusted to be 2/3 of the holding angle θh, and the position 213 is 3/2 from the starting point position in the transport path on the circumferential surface. The temperature controller 230 is provided along the area (B), has an opening that opens toward the molten resin film 101 over the area (B), and surrounds a space adjacent to the outer surface of the molten resin film. 231 and an air guide tube 232 communicating with the space and a space outside the chamber 231.

  By introducing air from a blower (not shown) that introduces temperature-controlled air into the chamber 231 through the air guide tube 232, the temperature of the outer surface of the molten resin film in the area (B) is It can be adjusted to the desired temperature. There is no particular restriction on the temperature range of the air introduced into the temperature controller. When rapid cooling is required, ambient air can be cooled and air having a temperature lower than room temperature can be introduced. However, in many cases, Tg is higher than room temperature, and preferable air temperature is usually Is higher than room temperature. In addition to the decompression operation, by adjusting the temperature of the outer surface of the molten resin film in the area (B) and the temperature of the cast roll 130 in combination, the film is detached from the cast roll 130 at the position 214. The temperature can be controlled so that the temperature of the film is equal to or lower than Tg.

  In the first embodiment shown in FIGS. 2 and 3, the area downstream of the section (B) is an area where cooling is performed without using a temperature controller (hereinafter, this section may be referred to as “section (C)”. ) And relatively rapid cooling. In this example, the section (C) is set to a range of the angle θc from the position 213 to the end point position 214 of the conveyance path on the circumferential surface.

  In the manufacturing method of the present invention, by performing the specific pressure reduction and temperature control described above in the cooling step, both the in-plane direction retardation Re and the thickness direction retardation Rth are small and uniform, In addition, it is possible to efficiently produce a film having a uniform thickness. The reason why such an effect can be obtained is presumed to be due to the mechanism described below according to the study of the present inventors. However, the present invention is not limited by the following estimation.

  The matter presumed as the mechanism by which the effect of the present invention is obtained will be described by taking the result obtained in the embodiment of the present invention as an example. FIG. 4 shows the outer surface of the molten resin film at various points on the transport path on the peripheral surface of the cast roll 130 in the manufacturing process of the present embodiment example and the comparative example performed using the apparatus shown in FIGS. It is a graph which shows the result of having measured the change of temperature with the infrared radiation thermometer. Details of the operations in the examples and comparative examples will be described later.

In FIG. 4, the horizontal axis indicates the position of the measurement point as an elapsed time with the position 211 as zero. That is, it shows the time for a certain point of the molten resin film to reach the measurement point after passing through the position 211. The vertical axis indicates the temperature of the outer surface of the molten resin film measured at the measurement point. Therefore, this graph shows how the temperature at a certain point of the molten resin film changes with the passage of time after passing through the position 211. In FIG. 4, times t ₂₁₁ , t ₂₁₃ and t ₂₁₄ correspond to positions 211, 213 and 214, respectively.

Comparative Example 1 shown in FIG. 4 is an example in which the optical film was manufactured without performing the decompression operation. In Comparative Example 2, since the temperature of the cast roll 130 was set higher than that in Example 1, time t ₂₁₄ was set. In this example, the film temperature is higher than Tg. On the other hand, Example 1 is an example in which pressure reduction and temperature control defined in the present invention were performed.

In Example 1, since the pressure reduction specified in the present invention was performed in the cooling process, the cooling rate of the molten resin film 101 was more moderate in the vicinity of the upstream in the transport path on the peripheral surface than in Comparative Example 1. It has become. Whereby the molten resin film 101 is kept a longer time temperature higher than Tg, so that the temperature T ₁ of the film as it passes through the position 213 has a temperature higher than Tg. In Example 1, further, the molten resin film 101 is rapidly cooled after passing through the position 213 by temperature control, becomes Tg or less at t ₂ which is earlier than t ₂₁₄ , and therefore when the film is separated from the cast roll 130. temperature _{T 3} has a lower Tg temperature.

  When the cooling step is performed under such conditions, it is presumed that the birefringence relaxation is sufficiently achieved, and the occurrence of birefringence after cooling is reduced, thereby obtaining the effects of the present invention. That is, in the molten resin film forming step, the molten resin film extruded from the die is subjected to a physical load such as pulling before being conveyed to the cast roll, and thereby birefringence can be imparted. In the process, the birefringence can be relaxed by maintaining the temperature for a sufficiently long time Tg or more. However, when such a film having a high temperature of Tg or higher leaves the cast roll, it is subjected to a load again in the subsequent conveyance process, and thereby birefringence can be imparted. Therefore, by controlling the temperature so that the temperature is lower than Tg when the film is released from the cast roll, the film after the release can be made in a state that is not easily affected by the load. The expression of birefringence can be suppressed.

  As exemplified in Example 1 shown in FIG. 4, in the production method of the present invention, temperature control is performed so that the surface temperature outside the molten resin film becomes Tg or more at a position 2/3 from the upstream of the holding angle. It is preferable to carry out. By performing such temperature control, relaxation of the birefringence of the molten resin film can be sufficiently achieved. In the example of FIG. 4, at a position 2/3 from the upstream of the holding angle, control such that the temperature of the molten resin film is Tg or more and the film temperature is Tg or less before the film is detached is indicated by an arrow A41. And a curve passing through the arrow A42. Such temperature control is performed by performing a decompression operation, further heating the zone (B) as necessary, thereby slowing the cooling upstream, and adjusting the temperature of the cast roll. This can be achieved by performing relatively rapid cooling in (C). In particular, the production of uniform Re, Rth, and film thicknesses can be efficiently performed by combining the decompression operation and the heating in the section (B). Specifically, if the air layer is excessively thick so as to obtain the effect of reduced pressure, there is a possibility that problems such as unevenness in the Re, Rth and thickness of the film and peeling of the film from the cast roll may occur. However, such unevenness and defects can be reduced by performing heating in combination with reduced pressure.

  Simply holding the molten resin film in a temperature range higher than Tg for a long time means that, for example, a cast roll having a very large diameter is used, or the rotation speed of the cast roll is extremely low without performing a decompression operation. Can also be achieved. However, when such cooling is performed, there are disadvantages such as the cost of installing the equipment for cooling, the inability to use the existing equipment, and the extremely low cooling rate. As a result, efficient production cannot be performed. On the other hand, by performing the decompression operation defined in the present invention, even if an existing device such as a die, a pinning device and a cast roll is used in an existing arrangement, a high-quality optical film can be manufactured. Can be performed efficiently.

The upper limit of the temperature T ₁ of the passing through the upstream from the 2/3 position of the molten resin film embracing angle is not particularly limited, from the viewpoint of achieving a sufficiently achieved by and subsequent rapid cooling the relaxed, preferably Is Tg + 50 ° C. or lower, more preferably Tg + 45 ° C. or lower.

The time required for the molten resin film to pass through the position 2/3 from the upstream of the holding angle after passing the starting point position 211 of the conveyance path (the value of _{t213 in} the example of FIG. 4) is preferably 0.8 seconds. More preferably, it is 1.2 seconds or more. By making the said time more than the said minimum, the value of Re and Rth can be made smaller and uniform, and the variation in film thickness can be further reduced. On the other hand, from the viewpoint of manufacturing efficiency, the upper limit of the time can be, for example, 2.5 seconds or less.

  The diameter of the cast roll used for the cooling step can be preferably 350 mm to 1200 mm, more preferably 600 mm to 900 mm. Cast rolls having a diameter less than or equal to the upper limit can be obtained and installed at a relatively low cost, and are widely used in existing film production equipment, so that inexpensive production can be realized. Moreover, the time required for relaxation can be easily ensured by having a diameter equal to or greater than the lower limit.

  In the production method of the present invention, the production rate of the film is preferably 50 m / min or more, and more preferably 100 m / min or more. Here, the film production speed refers to the film conveyance speed at which the cooling process is finished and the film is released from the cast roll. In the manufacturing method of the present invention, even when manufacturing at such a high speed, both the in-plane direction retardation Re and the thickness direction retardation Rth are small and uniform, and the thickness is uniform and high quality. The optical film can be manufactured. In addition, in the operation of manufacturing the optical film, the conveyance speed by the cast roll is faster than the discharge speed of the molten resin film from the die, and thus birefringence may be imparted to the molten resin film. According to the production method of the present invention, even when such an operation is performed, the birefringence can be relaxed satisfactorily and a high-quality optical film can be produced.

  The temperature of the cast roll in the cooling step can be appropriately adjusted to a range suitable for bringing the temperature of the molten resin film into a desired range in cooperation with other operations. Specifically, the temperature of the cast roll is preferably Tg-50 ° C or higher, more preferably Tg-30 ° C or higher, while preferably Tg-10 ° C or lower, more preferably Tg-20 ° C or lower. In many cases, Tg is higher than room temperature, which is the ambient temperature of the cooling device, and the preferable cast roll temperature is higher than room temperature. Therefore, in the normal cooling step, the operation is performed with the cast roll heated by an appropriate heating device (not shown).

  The temperature of the film in the cooling process can be measured by a temperature sensor. Specifically, as the temperature sensor, an infrared radiation thermometer (for example, product name “IT2-50” manufactured by Keyence Corporation) can be used. Based on the temperature measured by the temperature sensor, it is possible to control the temperature by appropriately adjusting the degree of heating by the temperature controller and, if necessary, the degree of pressure reduction and the temperature of the cast roll.

[1.4. First Embodiment: Structure of Pressure Reducer and Temperature Controller]
In the first embodiment shown in FIGS. 2 to 3, each of the decompressor 220 and the temperature controller 230 has an opening that opens toward the molten resin film 101, and is a space close to the outer surface of the molten resin film. A chamber (221 or 231) surrounding the space and an air guide tube (222 or 232) communicating with the space and a space outside the chamber. Thus, since the pressure reducer and the temperature controller can have a common structure, a plurality of devices including such a chamber and a conduit are provided around the cast roll, for example, a part of which is used as the pressure reducer. By using another part as a temperature controller, the position and length of the area (A), the area (B), etc. can be adjusted as necessary.

  FIG. 5 is a perspective view schematically showing an example of an apparatus (hereinafter simply referred to as “regulator”) that can be used as a decompressor or a temperature controller in the cooling step of the method for producing an optical film of the present invention. FIG. 6 is a cross-sectional view of the adjuster of the example of FIG. 5 taken along a plane along line A5. The adjuster 500 shown in FIG. 5 and FIG. 6 is shown in FIG. 2 to FIG. 3 by appropriately changing the specific shape of each part such as the edges 512C and 514C as needed to fit the use location. In the first embodiment, it can be used as a pressure reducer or a temperature controller.

  5 and 6, the adjuster 500 includes a chamber constituted by a top plate 511, side plates 512 and 514, a bottom plate 513 and a back plate 515. Edge portions 511C and 513C of the top plate 511 and the bottom plate 513 have a linear shape. Further, the side plates 512 and 514 may have a shape in which the shape of the edges 512C and 514C is adapted to the shape of the peripheral surface of the cast roll 130. By having such a shape, the regulator 500 can be used as a device that is installed close to the molten resin film 101 and surrounds a space close to the outer surface of the molten resin film 101 in the cooling process.

  Further, the regulator 500 has one air guide tube 521. By leading air from the regulator 500 through the air conduit 521, the regulator 500 can be used as a decompressor. On the other hand, the regulator 500 can be used as a temperature regulator by receiving air from a blower (not shown) that introduces temperature-adjusted air through the air guide pipe 521 and introducing it into the regulator 500. it can. Thereby, pressure reduction of the space close to the outer surface of the molten resin film in the area corresponding to the opening defined by the edges 511C to 514C, or the temperature of the outer surface of the molten resin film can be adjusted. .

[1.5. Process after cooling process]
In the production method of the present invention, an optional step can be performed as necessary after the cooling step. For example, at an arbitrary stage after the cooling process and before winding the film, the cured film is conveyed in order by circumscribing one or more rolls following the cast roll, thereby further cooling, embossing, etc. Any of the following steps can be performed. Further, in addition to or in place of the automatic birefringence meter 141 and the film thickness meter 142 shown in FIG. 1, various measuring devices can be provided on the conveyance path to measure the film properties in-line. . Alternatively, the optical film may be drawn from the roll body of the obtained optical film, a part of the film may be cut out, and the measurement may be performed for evaluation using the sample as a sample.

  Further, in the cooling step, by pinning the film end, the end of the film is cooled relatively rapidly as compared with other portions, and is easily subjected to dimensional constraints. As a result, the in-plane direction retardation Re and the thickness direction retardation Rth tend to be larger at the film edge than at other portions. Such a film edge part can be cut | disconnected as needed, and the remaining center part can be made into the optical film which is a product.

[2. (Modification)
The above-described embodiment may be further modified and implemented.
For example, in the first embodiment described above, the zone for heating (B) has its upstream end adjacent to zone (A) and its downstream end coincides with the range of 2/3 of the holding angle. However, the mode of setting the heating area is not limited to this. For example, the upstream of the section (B) may overlap with the downstream of the section (A). Further, the downstream end of the section (B) may be upstream or downstream of the position 2/3 of the holding angle.

In the first embodiment described above, one decompressor and one temperature controller are provided, but two or more decompressors may be provided, and two or more temperature controllers are provided. Also good.
Further, the surface of the cast roll 130 is usually mirror-finished in many cases. For example, when the surface is not in contact with the molten resin or the temperature is not transferred, the surface of the cast roll 130 has a satin finish. In this case, the heat exchange rate of the resin film can be further improved. For this reason, there exists an effect that manufacture of a resin film becomes still simpler by the element which adjusts the heat exchange of a resin film increasing.

[2.1. (Modification: adjuster)
The regulator (pressure reducer or temperature regulator) used in the production method of the present invention and the apparatus of the present invention is not limited to those illustrated in FIGS. 2 to 3 and FIGS. You may have.

  FIG. 7 is a perspective view schematically showing another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. FIG. 8 is a cross-sectional view of the adjuster of the example of FIG. 7 cut along a plane along line A7. The regulator 700 shown in FIGS. 7 and 8 is different from the regulator 500 shown in FIGS. 5 and 6 in that a rectifying plate 741 is provided in the chamber. The rectifying plate 741 may have a net-like structure, a structure having a large number of through holes penetrating in the thickness direction, a structure having a large number of slits, and the like. By providing such a rectifying plate in the chamber, it is possible to introduce a gas whose pressure is reduced or temperature is evenly distributed over the entire opening of the regulator.

  FIG. 9 is a perspective view schematically showing still another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. FIG. 10 is a cross-sectional view of the adjuster of the example of FIG. 9 taken along a plane along line A9. The regulator 900 shown in FIGS. 9 and 10 differs from the regulator 500 shown in FIGS. 5 and 6 in that it has a plurality of air guide tubes 921 to 928 instead of one air guide tube 521. As described above, by providing a plurality of air guide tubes and deriving air from each of the air guide tubes to the outside of the regulator at an equal flow rate, it is possible to uniformly reduce the pressure over the entire opening of the regulator. Alternatively, the gas can be introduced to equalize the temperature across the opening of the regulator by introducing air that is regulated to the same temperature from each conduit into the chamber.

  Or, for example, when the regulator is used as a pressure reducer, if it is desired to derive different flow rates from different parts of the chamber, such different flow rates are derived from each of the plurality of conduits. You can also. More specifically, for example, in the case where the air layer between the cast roll and the molten resin film tends to be thicker at the center than at the end in the width direction of the molten resin film, the air guide tubes 921, 924, 925 and 928 are provided. Thus, a relatively large flow rate of airflow can be derived from the air flow channels, while a relatively small flow rate of airflow can be derived from the air guide tubes 922, 923, 926, and 927, thereby reducing the difference in the thickness of the air layer.

  Or, for example, when using a regulator as a temperature regulator, if it is desired to regulate different parts of the chamber to different temperatures, a plurality of types adjusted to different temperatures from each of the plurality of conduits It is also possible to introduce an air stream of Thereby, a temperature gradient can be provided, or conversely, a non-uniform temperature distribution can be made uniform.

  FIG. 11 is a perspective view schematically showing still another example of a regulator that can be used in the cooling step of the method for producing an optical film of the present invention. 12 is a cross-sectional view of the adjuster of the example of FIG. 11 cut along a plane along the line A11. The regulator 1100 shown in FIGS. 11 and 12 includes a plurality of air guide tubes 1021 to 1028 instead of one air guide tube 521, and a partition wall extending in parallel with the upper surface plate 511 and the lower surface plate 513 in the chamber. It differs from the regulator 500 shown in FIG.5 and FIG.6 by the point which has 1051. FIG. The partition wall 1051 separates the space in the regulator 1100 into two spaces: an upper space communicating with the outside via the upper air guide tubes 1021 to 1024 and a lower space communicating with the outside via the lower air guide tubes 1025 to 1028. To do.

  The upper stage and conduits 1021 to 1024 of the regulator 1100 chamber and the lower stage and conduits 1025 to 1028 of the regulator 1100 can be used as separate regulators if necessary. For example, the upper stage can be used as a decompressor and the lower stage can be used as a temperature controller. In the middle of performing the manufacturing method of the present invention in this aspect, if it is determined that decompression is necessary in a wider area, the operating conditions can be changed so that the lower stage is also used as a decompressor. .

  FIG. 13: is a perspective view which shows typically another example of the regulator which can be used in the cooling process of the manufacturing method of the optical film of this invention. FIG. 14 is a cross-sectional view of the regulator of the example of FIG. 13 cut along a plane along line A13. The regulator 1300 shown in FIGS. 13 and 14 includes a plurality of air guide tubes 1321 to 1328 instead of one air guide tube 521, and a partition wall 1361 extending in parallel with the side plates 512 and 514 in the chamber. It differs from the regulator 500 shown in FIGS. 5 and 6 in that it has 1363. The partition walls 1361 to 1363 include a space in the regulator 1300 that communicates with the outside through the air guide tubes 1321 and 1325, a space that communicates with the outside through the air guide tubes 1322 and 1326, and a space that communicates with the outside through the air guide tubes 1323 and 1327, The air guide tubes 1324 and 1328 are separated into four spaces communicating with the outside.

  The pressure or temperature of the air flow derived or introduced through the conduits 1321 and 1325, the pressure or temperature of the air stream derived or introduced through the conduits 1322 and 1326, the pressure or temperature of the air stream derived or introduced through the conduits 1323 and 1327, and By independently adjusting the pressure or temperature of the airflow derived or introduced through the trachea 1324 and 1328, the pressure or temperature in the chamber can be variously adjusted. Thereby, a pressure or temperature gradient can be provided, or conversely, an uneven pressure or temperature distribution can be made uniform.

  The regulator used in the manufacturing method of the present invention is not limited to the mechanism described above, and may be based on a mechanism based on another principle. For example, the temperature controller may include a heating element and / or an endothermic body that are close to the outer surface of the molten resin film, and the temperature may be adjusted by the generation of heat and / or the endotherm.

  Examples of the heating element include a heating element that generates heat by resistance heating or the like when energized, and a heating element that generates heat conducted from a fluid heat medium such as water or oil heated by another heat source. On the other hand, as an example of the endothermic body, an endothermic body that is cooled by a fluid refrigerant such as water that is cooled as necessary to lower the ambient temperature can be given.

  A temperature controller including such a heating element and / or an endothermic body may have a chamber surrounding a range corresponding to any of a plurality of areas, but does not have such a chamber and melts. You may provide only the heat generating body and / or endothermic body which adjoin to the outer surface of the resin film.

  As another temperature controller of another mechanism, there is a temperature controller that does not have a chamber and has a structure such as a nozzle that blows hot or cold air on a molten resin film.

  Furthermore, the adjuster may be a combination of a plurality of mechanisms described above. For example, the regulator may be provided with both a mechanism for deriving air and a heating element in the chamber so that pressure reduction and heating can be performed simultaneously in the same area.

[3. Optical film materials]
In the production method of the present invention, as the resin that can be used as the material of the optical film, various thermoplastic resins that can be molded by a melt extrusion method can be used.

  Examples of thermoplastic resins include polyester resins (polyethylene terephthalate, polybutylene terephthalate, etc.), polyolefin resins (polyethylene, polypropylene, ethylene-propylene copolymers, alicyclic polyolefin resins, etc.), polycarbonate resins, cellulose ester resins, acrylics Examples include resins (polymethyl methacrylate, polyacrylonitrile, acrylonitrile-styrene copolymers, etc.) and other resins (polystyrene, polyvinyl chloride, etc.). Among these, polyolefin resins are more preferable, and alicyclic polyolefin resins are particularly preferable from the viewpoint of satisfying the balance of quality such as mechanical properties, heat resistance, and transparency required for a film for a display device such as a liquid crystal display device.

  The alicyclic polyolefin resin is a resin containing an alicyclic polyolefin polymer having an alicyclic structure in one or both of the main chain and the side chain. Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene) structure. Among these, from the viewpoint of mechanical strength and heat resistance, a cycloalkane structure and a cycloalkene structure are preferable, and a cycloalkane structure is particularly preferable.

  The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more per alicyclic structure. The number is preferably 20 or less, particularly preferably 15 or less. When the number of carbon atoms constituting the alicyclic structure falls within the above range, properties such as mechanical strength, heat resistance, and film formability are highly balanced, which is preferable.

  The proportion of the structural unit having an alicyclic structure in the alicyclic polyolefin polymer may be appropriately selected according to the purpose of use, preferably 55% by weight or more, more preferably 70% by weight or more, particularly preferably. 90% by weight or more. By keeping the proportion of the structural unit having an alicyclic structure in the alicyclic polyolefin polymer within the above range, the transparency and heat resistance of the optical film can be improved.

  Examples of alicyclic polyolefin polymers include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrides thereof. Can be mentioned. Among these, norbornene-based polymers are preferable because of their good transparency and moldability.

  Examples of the norbornene polymer include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening polymer of a monomer having a norbornene structure and an arbitrary monomer, or a hydride thereof; norbornene An addition polymer of a monomer having a structure, an addition polymer of a monomer having a norbornene structure and an arbitrary monomer, or a hydride thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used. Here, the (co) polymer means a polymer and a copolymer.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7. -Diene (common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . ^{17, 10} ] dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent in the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. Moreover, these substituents may be the same or different and a plurality may be bonded to the ring. Furthermore, the monomer which has a norbornene structure may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the kind of the polar group include a hetero atom or an atomic group having a hetero atom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfone group.

  Examples of the optional monomer capable of ring-opening copolymerization with a monomer having a norbornene structure include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; and cyclic conjugates such as cyclohexadiene and cycloheptadiene. Dienes and derivatives thereof; and the like. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  A ring-opening polymer of a monomer having a norbornene structure and a ring-opening copolymer of an arbitrary monomer copolymerizable with a monomer having a norbornene structure include, for example, a known opening of a monomer. It can be obtained by polymerization in the presence of a ring polymerization catalyst.

  Examples of optional monomers that can be addition copolymerized with a monomer having a norbornene structure include α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, and 1-butene, and derivatives thereof; cyclobutene and cyclopentene. And cycloolefins such as cyclohexene and derivatives thereof; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene; and the like. These monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, α-olefin is preferable and ethylene is more preferable.

  An addition polymer of a monomer having a norbornene structure and an addition copolymer of an arbitrary monomer copolymerizable with a monomer having a norbornene structure are, for example, known addition polymerization catalysts for monomers. Can be obtained by polymerization in the presence of.

  Hydrogenated product of a ring-opening polymer of a monomer having a norbornene structure, a hydrogenated product of a ring-opening copolymer of a monomer having a norbornene structure and an arbitrary monomer capable of ring-opening copolymerization thereof, Hydrogenated products of addition polymers of monomers having a norbornene structure, and hydrogenated products of addition polymers of monomers having a norbornene structure and any monomer copolymerizable therewith, have these weights. For example, a known hydrogenation catalyst containing a transition metal such as nickel or palladium is mixed into the combined solution, and the carbon-carbon unsaturated bond is preferably hydrogenated by 90% or more.

Among norbornene-based polymers, as structural units, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.1 ^2,5 ] decane- It has a 7,9-diyl-ethylene structure, the content of these structural units is 90% by weight or more with respect to the entire structural unit of the norbornene polymer, and the content ratio of X and the content of Y It is preferable that the ratio to the ratio is 100: 0 to 40:60 in terms of a weight ratio of X: Y. By using such a norbornene-based polymer, it is possible to obtain an optical film having no dimensional change over a long period of time and excellent optical property stability.

  The molecular weight of the alicyclic polyolefin polymer can be appropriately selected according to the purpose of use. The weight average molecular weight (Mw) of the alicyclic polyolefin polymer is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight average molecular weight is in such a range, the mechanical strength and molding processability of the optical film are highly balanced, which is preferable. Here, the weight average molecular weight is a value in terms of polyisoprene or polystyrene measured by gel permeation chromatography using cyclohexane (toluene when the sample polymer is not dissolved) as a solvent.

  The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the alicyclic polyolefin polymer is preferably 1.0 or more, more preferably 1.1 or more, particularly preferably 1.2 or more. Preferably 10.0 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less. By making molecular weight distribution more than the lower limit of the said range, the productivity of a polymer can be improved and cost can be reduced. Further, by making the amount lower than the upper limit value, it is possible to reduce the amount of the low molecular component and reduce the component having a short relaxation time, so that it becomes possible to reduce the alignment relaxation at the time of high temperature exposure.

  The resin constituting the optical film may contain any component other than the above-described polymer as long as the effects of the present invention are not significantly impaired. Examples of optional components include antioxidants, heat stabilizers, light stabilizers, UV absorbers, antistatic agents, dispersants, chlorine scavengers, flame retardants, crystallization nucleating agents, reinforcing agents, and antiblocking agents. , Antifogging agents, mold release agents, pigments, organic or inorganic fillers, neutralizing agents, lubricants, decomposition agents, metal deactivators, antifouling agents, and antibacterial agents. One of these may be used alone, or two or more of these may be used in combination at any ratio. However, the amount of the optional component is within a range not impairing the effects of the present invention, and is usually 50 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, particularly 100 parts by weight of the polymer. The amount is preferably 10 parts by weight or less. The lower limit is zero.

  The glass transition temperature of the resin constituting the optical film can be appropriately selected according to the purpose of use, and is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and preferably 250 ° C. or lower. A resin film having a glass transition temperature in such a range is less susceptible to deformation and stress during use at high temperatures, and is excellent in durability.

[4. Optical film)
The thickness of the optical film obtained by the production method of the present invention can be appropriately adjusted according to the purpose of use, and is preferably 10 μm to 1000 μm, more preferably 10 to 80 mm.

  Although the dimension of an optical film does not have a restriction | limiting in particular, Usually, it can be set as a elongate optical film. Thereby, efficient manufacture can be performed. “Long” refers to a material having a length of at least 5 times the width, preferably 10 times or more, and specifically wound into a roll. It has a length that can be stored or transported. The dimension in the width direction of the optical film can be appropriately adjusted according to the purpose of use, and can be preferably 300 to 3000 mm, more preferably 900 to 2300 mm.

The optical film obtained by the production method of the present invention can have small variations in film thickness. As an index of the variation in film thickness, for example, the film thickness is measured at measurement points aligned in a grid pattern in the width direction and the length direction of the film, and the difference between the maximum value and the minimum value can be adopted. Such grid-like measurement points are set at three intervals of 60 mm intervals over the range of about 70% of the film width from the central portion in the film width direction in the film width direction, and 10 to 100 mm intervals in the film length direction. sell. The variation in the film thickness is preferably 1 μm or less, more preferably 0.1 μm or less. The film thickness can be measured using a film thickness meter (for example, RC-1 ROTARY CALIPER manufactured by Meisho Co., Ltd.).
The optical film obtained by the production method of the present invention can have both in-plane direction retardation Re and thickness direction retardation Rth small and uniform. Specifically, Re can be preferably 2 nm or less, more preferably less than 1 nm. Rth can be preferably 5 nm or less, more preferably less than 1 nm. As Re and Rth, values measured at a wavelength of 590 nm using an automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-21ADH) can be adopted.

  The optical film preferably has a total light transmittance of 85% to 100%, more preferably 90% to 100%. The light transmittance can be measured using a spectrophotometer (manufactured by JASCO Corporation, ultraviolet-visible near-infrared spectrophotometer “V-570”) in accordance with JIS K0115.

  The specific application of the optical film is not particularly limited, and can be used for various applications requiring low and uniform Re and Rth. For example, as a component such as a polarizing plate protective film and a resin film substrate as an alternative to a conventionally used glass substrate, it can be used in a display device such as a liquid crystal display device in various devices such as a television receiver and a mobile phone. .

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the scope of the claims of the present invention and its equivalent scope. The operations described below were performed in an environment of normal temperature and pressure unless otherwise specified.

<Example 1>
Production of an optical film using an optical film production apparatus schematically shown in FIG. 1 (including a molten resin film forming apparatus 110 schematically shown in FIG. 1 and a cooling apparatus 200 schematically shown in FIGS. 1 to 3). Was done.

(1-1. Molten resin film forming step)
As a resin for the material of the optical film, a norbornene polymer (hydrogenated product of a ring-opening polymer of a norbornene monomer, trade name “ZEONOR (registered trademark)”, manufactured by Nippon Zeon Co., Ltd., glass transition temperature (Tg) is 140 ° C. ) Pellets were prepared. In a single-screw extruder (manufactured by Nippon Steel Works) 111 having a cylinder inner diameter of 90 mm and an L / D (length / diameter) of 32, this pellet was melted at a barrel temperature of 280 ° C. to obtain a molten resin. This molten resin is supplied to a T die 112 having a die temperature of 280 ° C. through a polymer filter and a gear pump (not shown), led to spread in a film shape inside the T die, and discharged from the lip portion of the T die 112. Thus, a molten resin film 101 having a width of 340 mm was continuously formed.

(1-2. Cooling step)
The cooling process was performed using the cooling device 200 schematically shown in FIGS. In the cooling device 200, a cast roll having a diameter of 900 mm was used. Of the transport path starting point position 211 to the ending point position 214 on the peripheral surface of the cast roll 130, the area from the starting point position 211 to the position 212 is the area (A), and the downstream area is the area from the position 212 to the position 213. Area (B) and the area downstream from position 213 to position 214 were set as area (C). The angle θa of the area (A) is 45 °, the angle θb of the area (B) is 135 °, and the angle θc of the area (C) is 90 °, so the holding angle (area (A), area (B) and area ( The overall angle C) h of C) was 270 °. A decompressor 220 including a chamber 221 and a conduit 222 is disposed along the area (A), and a temperature controller 230 including the chamber 231 and the conduit 232 is disposed along the section (B). Both the chamber 221 of the decompressor 220 and the chamber 231 of the temperature controller 230 have an opening that opens toward the molten resin film 101 and are disposed so as to surround a space close to the outer surface of the molten resin film.

  Static electricity was applied to the molten resin film 101 obtained in the step (1-1) continuously at the end indicated by the arrow A31 in FIG. 3 and led to the cast roll 130 of the cooling device 200. When the molten resin film 101 reached the rotating cast roll 130, the end thereof was electrostatically pinned and adhered to the cast roll 130. By rotating the cast roll 130 about the shaft 131, the molten resin film 101 was conveyed along the conveyance path on the peripheral surface of the cast roll 130, and the molten resin film was cooled to obtain a cured film. The obtained cured film 102 was guided to be detached from the cast roll 130 at the position 214 (cooling step).

  In the cooling step, the surface temperature of the cast roll 130 was adjusted to 100 ° C. The rotational speed (moving speed of the peripheral surface) of the cast roll 130 was 1667 mm / second. Therefore, the molten resin film 101 passed from the start point position 211 to the end point position 214 on the peripheral surface of the cast roll 130 in about 1.3 seconds.

  In the cooling process, a certain amount of air was led out from the chamber 221 of the decompressor 220 in the direction of arrow A21 through the air guide tube 221 in the area (A). Thereby, the space close to the outer surface of the molten resin film in the area (A) is decompressed, and the thickness of the air layer between the cast roll 130 and the molten resin film 101 at the position 211 is 0.1 mm ( Value in the center of the film width direction).

  In the cooling step, in the zone (B), air whose temperature is adjusted is introduced into the chamber 231 of the temperature controller 230 in the direction of the arrow A22 through the air guide tube 232, whereby the molten resin film in the zone (B). 101 was warmed. The heating conditions are set as appropriate, whereby in the cooling step, the surface temperature of Tg or higher is maintained until the molten resin film 101 reaches the position 213, and the obtained cured film 102 is cast at the position 214 at the cast roll 130. The temperature at the time of releasing from the temperature became Tg or less.

(1-3. Winding)
The cured film 102 detached from the cast roll 130 in the cooling step was wound up by a winder to obtain an optical film roll 151.

<Comparative Example 1>
In the step (1-2), an optical film was manufactured in the same manner except that the air was not led out from the decompressor 220. The thickness of the air layer between the cast roll 130 and the molten resin film 101 at the position 211 was a maximum of 0.05 mm (value at the center in the film width direction).

<Comparative Example 2>
In the step (1-2), except that the temperature of the cast roll was changed to 120 ° C., the same operation was performed to obtain an optical film roll.

[Evaluation of the obtained film]
Example 1, Comparative Example 1 and Comparative Example 2 are performed by changing production conditions in the production of a series of optical films, and as a result, rolls of continuous long optical films produced under a plurality of production conditions. was gotten. The film is unwound from the roll, and the in-plane direction retardation is determined by the following method for each rear part (the one manufactured most recently) of the films obtained under the manufacturing conditions of Example 1, Comparative Example 1 and Comparative Example 2. Re, thickness direction retardation Rth, and film thickness were measured.

  Re and Rth were measured at a wavelength of 590 nm using an automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-21ADH). The film thickness was measured using a film thickness meter (manufactured by Meisho Co., Ltd., RC-1 ROTARY CALIPER). The measurement positions were 15 measurement points of 5 columns × 3 rows. Specifically, from the obtained optical film having a width of 340 mm, from one edge in the width direction of the sample, a row (1) at a position of 50 mm, a row (2) at a position of 110 mm, a row at a position of 170 mm (3 ), 230 mm position column (4) and 290 mm position column (5), respectively, the last row (a) of the sample, 10 mm before the last row (b), and 100 mm from the last portion Measurements were taken in the previous row (c). The measurement results in Example 1, Comparative Example 1 and Comparative Example 2 are shown in Tables 1 to 3, respectively.

  In Tables 1 to 3, the unit of thickness is μm, and the units of Re and Rth are nm.

[Change in temperature]
In the manufacturing process of the example and the comparative example, the change in the temperature of the outer surface of the molten resin film at various points on the conveyance path on the peripheral surface of the cast roll 130 was measured with an infrared radiation thermometer (manufactured by Keyence Corporation, product name “ The result of measurement by “IT2-50”) is shown in FIG.
In FIG. 4, the measurement results in Example 1, Comparative Example 1, and Comparative Example 2 are shown by lines plotted with diamonds, lines plotted with triangles, and lines plotted with squares, respectively.

In FIG. 4, the horizontal axis indicates the position of the measurement point as an elapsed time with the position 211 as zero. That is, it shows the time for a certain point of the molten resin film to reach the measurement point after passing through the position 211. The vertical axis indicates the temperature of the outer surface of the molten resin film measured at the measurement point. Therefore, this graph shows how the temperature at a certain point of the molten resin film changes with the passage of time after passing through the position 211. In FIG. 4, times t ₂₁₁ , t ₂₁₃ and t ₂₁₄ correspond to positions 211, 213 and 214, respectively.

  As shown in FIG. 4, in Comparative Example 1, since the pressure reduction operation was not performed, the temperature of the molten resin film was rapidly cooled by the cast roll, and the temperature of the molten resin film decreased to Tg or less before reaching the position 213. It was. As a result, as shown in Table 2, both Re and Rth were large values.

  In Comparative Example 2, although the temperature of the molten resin film when reaching the position 213 was equal to or higher than Tg, the temperature was higher than Tg when the temperature reached the position 214. As a result, as shown in Table 3, both Re and Rth were large values.

For these, in Example 1, a temperature T ₁ of the temperature is above the Tg of the molten resin film when it reaches the position 213, and the corresponding position upstream from the position 214 (in t ₂ in FIG. 4 The temperature of the molten resin film reached Tg at a position where the cast roll was separated from the cast roll at position 214 at a temperature lower than Tg. Thereby, the birefringence of the film is sufficiently relaxed in the cast roll, and the addition of anisotropy after the release from the cast roll is small. As a result, as shown in Table 1, both Re and Rth are small and uniform. A film was obtained.

DESCRIPTION OF SYMBOLS 10 Optical film manufacturing apparatus 110 Molten resin film forming apparatus 101 Molten resin film 111 Extruder 112 Die 130 Casting drum 141 Automatic birefringence meter 142 Film thickness meter 151 Optical film roll 200 Cooling device 211 Starting point of conveyance path on circumferential surface Position 212 Position of transfer path on peripheral surface 213 Position 3/2 from start position in transfer path on peripheral surface 214 End point position of transfer path on peripheral surface 220 Decompressor 221 Chamber 222 Air guide tube 230 Temperature controller 231 Chamber 232 Air guide tube 500 Controller (pressure reducer or temperature controller)
511 Top plate 511C Edge of top plate 512 Side plate 512C Edge of side plate 513 Bottom plate 513C Edge of bottom plate 514 Side plate 514C Edge of side plate 515 Back plate 521 Induction tube 700 Regulator (pressure reducer or temperature) Regulator)
741 Rectifying plate 900 Controller (pressure reducer or temperature controller)
921-928 Air guide tube 1100 Controller (pressure reducer or temperature controller)
1021-1028 Air duct 1051 Partition 1300 Regulator (pressure reducer or temperature regulator)
1321 to 1328 Air guide tubes 1361 to 1363 Partition θa Angle of section (A) θb Angle of section (B) θc Angle of section (C)

Claims (5)

A thermoplastic resin having a glass transition temperature of Tg (° C.) is extruded in a molten state, and a molten resin film forming step for continuously forming a molten resin film, and the molten resin film is continuously guided to a cast roll, and the cast Cooling that conveys the molten resin film along a conveyance path on the peripheral surface of the cast roll by rotating the roll, cools the molten resin film to form a cured film, and releases the obtained cured film from the cast roll A process for producing an optical film comprising the steps of:
The cooling step includes
In at least a part of the area (A) in the conveying path on the peripheral surface, the space close to the outer surface of the molten resin film is depressurized, and the temperature of the cured film when the cured film is detached is Tg The manufacturing method of an optical film including controlling the temperature of the outer surface of the said molten resin film, the said cured film, or both of these as follows.   The reduced pressure is provided along the section (A), has an opening that opens toward the molten resin film, and includes a chamber that surrounds the space adjacent to the outer surface of the molten resin film. The manufacturing method of the optical film of Claim 1 performed with a container.   The manufacturing method of the optical film of Claim 1 or 2 including heating the said outer surface of the said molten resin film in the at least one part area in the conveyance path | route on the said surrounding surface.   The manufacturing method of the optical film of any one of Claims 1-3 whose manufacturing speed is 100 m / min or more.   The method for producing an optical film according to claim 1, wherein the thermoplastic resin is an alicyclic polyolefin resin.

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