JP2005172940A - Optical film and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film not only whose residual phase difference is small in a wide range in both of a transverse direction and a flow direction but also whose dispersion of optical axis is little and which is made of a noncrystalline thermoplastic resin, and a manufacturing method therefor. <P>SOLUTION: The temperature of a film which is extruded from a die installed at an extruding machine and is made of the noncrystalline thermoplastic resin is controlled to a glass transition temperature Tg+80°C or higher at the point immediately before the contact with a cooling roll to control the temperature variation in the transverse direction and the flow direction within 3°C and the film is produced while the film is pressed to the cooling roll in tight contact therewith by an elastic roll which is within 100 μm in the eccentricity deflection during rotation, has a length of 85 to 95% of the total width of the film, and is subjected to temperature control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical film used in optical applications, display fields, and the like, and more specifically to a method for producing the same, and more specifically, a long optical film obtained by extrusion molding and having small optical distortion (birefringence) and optical axis deviation, and It relates to the manufacturing method.

  In recent years, there has been a demand for optical films that are excellent in transparency, have a small residual phase difference, and have no optical axis misalignment in the field of optical applications and displays. However, when an optical film is produced by melt extrusion, distortion tends to remain due to deformation when the film in a semi-molten state is drawn on a cooling roll during film formation. This distortion remains optically as a phase difference. When the residual phase difference is large, it often becomes a problem when used as an optical film. For example, when used for a polarizer protective film laminated on both surfaces in order to protect the polarizer of the polarizing plate, the polarization performance is degraded due to the residual retardation.

  In addition, since the deformation direction is not necessarily uniform, there has been a problem that the direction of the optical axis, that is, the slow axis based on the residual phase difference varies. If the directions of the optical axes are not aligned, the same problem as when the phase difference is high is caused even if the residual phase difference is low. In general, when the residual phase difference is 1 nm or more, the variation of the optical axis cannot be ignored, and when the phase difference is 3 nm or less, the allowable optical axis variation is about 10 ° or less.

  Patent Document 1 discloses a film having a residual retardation of 3 nm or less made of a thermoplastic resin having positive birefringence and a thermoplastic resin having negative birefringence as an optical film having a small residual retardation. However, there is no description regarding the optical axis, and the quality is not always satisfactory.

As means for reducing this optical distortion, the present inventors have proposed that an amorphous thermoplastic resin extruded into a sheet from a die attached to an extruder, where Tg is the glass transition temperature of the amorphous thermoplastic resin. When the film made of is closely attached to the cooling roll, a low residual phase difference was realized by controlling the film temperature immediately before the contact point with the cooling roll (see Patent Document 2). Also, by pressing the film against the cooling roll with a touch roll or air chamber, etc., the adhesion of the film to the cooling roll is promoted, and the contact point of the film with respect to the cooling roll is stabilized over the entire surface. It succeeded in making it into +/- 10 degrees or less (refer patent document 3). Furthermore, in Japanese Patent Application No. 2002-308807, an invention has been proposed in which 80% or more of the entire width of the film extruded from the die is set to a low phase difference to suppress the optical axis shift. However, optical films are usually used in scrolls from the viewpoint of efficiency, and although it is important to stabilize the optical properties in the flow direction, a clear technology has not been established, which has been a major problem.
JP 2002-328232 A JP 2003-131006 A JP 2003-131036 A

  An object of the present invention is to provide an amorphous thermoplastic resin that not only has a small residual phase difference in a wide range in both the width direction and the flow direction, but also has a small optical axis variation in view of the current state of the prior art described above. It is providing the optical film which consists of, and its manufacturing method.

  The optical film according to the invention described in claim 1 of the present application is an optical film obtained by extrusion molding of an amorphous thermoplastic resin, and has a thickness of 100 μm or less over a length of at least 100 m and over 80% of the entire surface. The residual phase difference is 3 nm or less, and the optical axis variation is 10 ° or less in terms of a deviation angle with respect to the flow direction of the film.

  The amorphous thermoplastic resin used in the optical film according to the present invention is a polymer that maintains an amorphous state that hardly takes a crystal structure, and its Tg is not particularly limited because it varies depending on the resin, but is generally 100 ° C. or higher. Preferred are norbornene resins, polycarbonates, polymethyl methacrylates, polyacetals, olefin-maleimide resins, polysulfone, polyethersulfone, polyarylate, polyvinyl chloride and the like.

  Among these resins, norbornene-based resins are preferable because they are excellent in transparency and heat resistance, have a low intrinsic birefringence, and a low photoelastic coefficient. By taking advantage of these advantages of the norbornene resin, it is possible to obtain an optical film having a small residual retardation and little optical axis variation. Examples of norbornene resins include ring-opening polymers of norbornene monomers, addition polymers, addition polymers of norbornene monomers and other olefins, and modified products of these polymers. These norbornene resins may be used alone or in combination of two or more.

  The norbornene-based monomer is not particularly limited as long as it has a norbornene ring, but since a molded product excellent in heat resistance, low linear expansion coefficient, etc. is obtained, a tricyclic or higher polycyclic norbornene-based monomer is used. It is preferable to use it.

  Specific examples of the norbornene-based monomer include bicyclics such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene and dihydroxypentadiene; tetracyclics such as tetracyclododecene; pentacyclics such as cyclopentadiene trimer. A heptacycle such as tetracyclopentadiene; an alkyl such as methyl, ethyl, propyl, butyl, an alkenyl such as vinyl, an alkylidene such as ethylidene, an aryl such as phenyl, tolyl, and naphthyl; and an ester thereof Group other than carbon and hydrogen, such as group, ether group, cyano group, halogen atom, alkoxycarbonyl group, pyridyl group, hydroxyl group, carboxylic acid group, amino group, hydroxyl group-free, silyl group, epoxy group, acrylic group, methacryl group Examples thereof include substituted groups having a so-called polar group. Among these, an ester group and a hydroxyl group-free are preferable. These monomers are used alone or in combination of two or more. Tricyclic, tetracyclic, and pentacyclic monomers are preferred because they are easily available, have excellent reactivity, and have excellent heat resistance of the resulting resin molded product.

  There are commercially available norbornene resins such as ZEONOR and ZEONEX from Nippon Zeon, Arton from JSR, APPEL from Mitsui Chemicals, and TOPAS from TICONA.

  The ring-opening polymer of the norbornene-based monomer is obtained by ring-opening polymerization of the norbornene-based monomer by a known method, and may be a homopolymer of norbornene-based monomers, or between different types of norbornene-based monomers. It may be a copolymer or a copolymer of a norbornene monomer and a cyclic olefin monomer other than the norbornene monomer.

  Examples of addition polymers of norbornene monomers and other olefins include copolymers of norbornene monomers and cyclic olefins other than α-olefins or norbornene monomers. As the α-olefin, an α-olefin having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms, and a monocyclic olefin having 5 to 12 carbon atoms can be used.

  Of the norbornene-based resins, the ring-opening polymer has double bonds remaining in the molecule, and if the monomer has two or more double bonds, even if it is an addition polymer, Since heavy bonds remain, it is desirable from the viewpoint of durability to saturate these double bonds by hydrogenation.

  In the present invention, the residual phase difference needs to be 3 nm or less. A film having a residual retardation of 3 nm or less is suitable for optical applications such as optical discs and liquid crystal displays. In particular, in the case of a liquid crystal display, for example, a film for protecting a polarizer used for an original film of a retardation plate or a polarizing plate is required to have a particularly low retardation, and the optical film according to the present invention has a residual level. Since the phase difference is very small, it is particularly effectively used for such applications.

  In the present invention, the optical axis refers to the direction of the slow axis based on the phase difference. In the case of melt extrusion film formation, since the film is deformed in the take-up direction and the molecules are oriented, the optical axis is usually directed in the resin flow direction (MD). Accordingly, in the present invention, the variation is evaluated by the deviation of the optical axis with respect to the MD, but the deviation angle at this time is an absolute angle. In the optical film, when the optical axis variation is 10 ° or less with respect to the MD, the phase difference direction is relatively uniform. Therefore, when the optical film according to the present invention is used for optical applications, the yield rate is increased. be able to. Moreover, it is preferable from a viewpoint of manufacturing efficiency to satisfy the above optical characteristics over 80% or more of the entire surface of the extruded film. In addition, the stable production of the optical characteristics in the flow direction is very effective from the viewpoint of manufacturing efficiency and shortening of the inspection process. In particular, when an optical film is used for protecting a polarizer, when the polarizer is a long roll, continuous bonding is possible, which is very effective.

  The entire film surface in the present invention refers to the entire width of the film after the resin extruded from the mold has been drawn, cooled on a cooling roll and solidified. Further, the thickness of the film is preferably as thin as possible in order to reduce the overall thickness when used in a liquid crystal display device or the like, and is set to 100 μm or less, more preferably 80 μm or less, and further preferably 60 μm or less. Is done.

  Although the manufacturing method of the optical film which concerns on invention of this application is not specifically limited, It can manufacture according to the manufacturing method described in Claim 3. The method for producing an optical film according to claim 3, wherein the film made of an amorphous thermoplastic resin extruded from a die attached to an extruder is brought into close contact with a cooling roll and taken up while being cooled and solidified. The temperature of the film immediately before the contact point with the cooling roll is controlled to the glass transition temperature Tg + 80 ° C. or more of the resin, the temperature variation in the width direction and the flow direction is controlled to within 3 ° C. The film is pressed against the cooling roll by a temperature-controlled elastic roll having a length of 100 μm or less and having a length of 85 to 95% with respect to the entire width of the film.

  By setting the film temperature immediately before the contact with the cooling roll of the film extruded from the die to Tg + 80 ° C. or higher, even if the film is deformed from the amorphous thermoplastic resin in this state, the stress generated in the resin is extremely small. As a result, the occurrence of optical distortion is suppressed, so that the phase difference remaining in the film can be 3 nm or less.

  This is because the amorphous thermoplastic resin is less likely to generate an internal stress when it is deformed as the temperature of the resin becomes higher than that of the crystalline thermoplastic resin. Therefore, when the resin is deformed during film formation, the internal stress of the resin generated by appropriate temperature control is reduced, and the occurrence of a residual phase difference can be suppressed. Further, the film temperature variation immediately before the contact point with the cooling roll needs to be 3 ° C. or less in both the width direction and the flow direction, and preferably 1 ° C. or less. The temperature variation in the film flow direction represents temperature fluctuations with time in the film forming process.

The specific method of setting the film temperature immediately before the contact point with the cooling roll to Tg + 80 ° C. or higher is not particularly limited, and examples thereof include a method of controlling the mold temperature at a high temperature. In this case, if the mold temperature is raised too much, it may deteriorate depending on the resin, so by adopting a temperature condition that does not cause thermal deterioration, it is possible to reliably obtain an optical film that can satisfy the residual retardation. Can do. Further, a method of narrowing the air gap may be used. In this case, the size of the air gap may be set taking into account the thickness accuracy of the die line and film. Furthermore, a method of keeping or heating the air gap portion from the mold outlet to the cooling roll is also conceivable. Any means known in the art may be employed as the means for maintaining or heating.
On the other hand, as a specific method of setting the film temperature variation immediately before the contact point with the cooling roll to 3 ° C. or less, for example, the temperature control accuracy of the mold temperature is increased, or the production of the vicinity of the die, the vicinity of the roll, the air gap, etc. A method of eliminating disturbance as much as possible by covering the membrane with a hood is conceivable.

  In the optical film manufacturing method of the present invention, when the molten resin from the die is pulled down and brought into close contact with the cooling roll, the roll surface is elastic in order to press against the cooling roll made of a metal roll to stabilize the contact. It is necessary to apply a uniform force in the width direction using the touch roll having

  Usually, when a sheet is stamped and formed, the molten resin is passed between two pairs of rolls to form a film and sandwiched, so that the rolls are required to have a robust structure made of a material that can withstand the pressure. . However, if both the cooling roll and the touch roll are rigid metal rolls, they cannot absorb the subtle thickness unevenness of the resin, resulting in insufficient adhesion between the roll and the film, resulting in thickness unevenness and flare. It is not suitable for the production of optical films. Therefore, in the present invention, an elastic roll is used as the touch roll.

As the elastic roll, a material in which the outer circumference of a metal shaft core made of carbon steel, stainless steel, aluminum or the like is coated with an elastic material is suitably used. Any elastic material may be used as long as it has a smooth surface and is flexible, and examples thereof include silicone rubber and fluororubber, and a plurality of materials may be laminated in multiple layers. Furthermore, in the case of a multilayer, it is sufficient that at least one of them is flexible. For example, the inner layer may be made of an elastic material, and a metal sleeve or the like may be attached to the outermost surface. In particular, a metal is a preferable material because the surface smoothness can be excellent. Examples of the material of the metal sleeve include carbon steel, stainless steel, nickel manufactured by electroforming, and the like. Further, the surface thereof may be plated with chromium or the like.
When a metal sleeve is used, the thickness of the metal sleeve only needs to be flexible enough to allow the cooling roll and the film to adhere to each other when a predetermined pressure is applied, and the flexibility varies depending on the type of metal. There is no particular limitation. For example, when electroformed nickel is used, it may be appropriately selected within a range of about 100 μm to 1 mm.

  By the way, generally an elastic roll is inferior to the eccentric runout accuracy at the time of rotation compared with a metal roll. When the eccentric runout exceeds 100 μm, the pressure at the time of pinching fluctuates, and the phase difference in the flow direction and the optical axis deviation fluctuate. Therefore, the eccentric runout of the elastic roll is 100 μm or less, preferably 50 μm or less, more preferably Needs to be 30 μm or less. In order to suppress the eccentric runout, it is important to increase the accuracy in polishing the elastic coating material in the elastic roll manufacturing process.

  In the production method of the present invention, the width of the elastic roll needs to be 85 to 95% with respect to the entire width of the film. If it is less than 85%, it is difficult to satisfy the optical characteristics of the formed film at 80% or more of the total width, and the product efficiency decreases. Conversely, if it exceeds 95%, the thickness of the end of the extruded film is increased. Therefore, the effect of stabilizing the contact at the full width of the elastic roll becomes small, and it becomes difficult to satisfy the optical characteristics at 80% or more of the full width.

  In general, since the roll temperature greatly affects the residual phase difference and the optical axis, both the cooling roll and the touch roll need to be temperature-controlled in the present invention. Therefore, it is preferable that each roll has an axial core part having a structure that can be adjusted to an appropriate temperature. The temperature adjusting means preferably used is an electric heating method in which a sheathed heater is incorporated in the shaft core portion to heat the roll, an induction heating method in which the roll is heated by electromagnetic induction action by an induction heat generating coil, and provided in the shaft core portion. For example, a heat medium circulation heating method in which a heat medium for temperature control is circulated through the flow path to indirectly heat the roll. A particularly preferable method is a heat medium circulation heating method, and this heat medium may be a gas, but is preferably a liquid such as water or oil. Preferable examples of the heat medium flow path include those having a spiral structure of two or four inside.

  When the variation in roll temperature varies in the width direction, distortion can occur in the width direction, which not only causes variations in phase difference but also causes variations in the optical axis. In addition, if the average temperature changes with time, the amount of strain applied to the film during film formation is different, so there is a possibility that the magnitude of the residual phase difference is different, and the roll temperature is 5 ° C. or less in the width direction, preferably 1 ° C. or less. It is necessary to control the average temperature over time to 5 ° C. or lower, preferably 3 ° C. or lower.

In the method for producing an optical film according to the present invention, the average temperature of the elastic roll and the cooling roll is preferably in the range of the glass transition temperature Tg to Tg-100 ° C. of the resin, although it varies depending on the resin used.

The shape of the elastic roll is usually a cylindrical shape, but there is no problem even if the central portion has a slightly thick crown shape. The outer diameters of the elastic roll and the cooling roll are not particularly limited and may be the same, or one of them may be larger than the other.
The pressure of the elastic roll only needs to be equal to or higher than the pressure at which the cooling roll and the film are completely adhered to each other, and may be appropriately set depending on the viscosity of the resin.
The hardness of the elastic roll only needs to be flexible enough to allow the cooling roll and the film to adhere to each other when a predetermined pressure is applied. For example, in the case of silicone rubber, it may be 30 to 90 degrees on Shore A.

  According to the optical film of the present invention, since the residual phase difference and the optical axis deviation are stably small over a length of 100 m or more, even when used as a protective film for a polarizer, for example, It can be combined, and a significant improvement in productivity can be expected. Moreover, according to the manufacturing method of this invention, while the width efficiency of such an optical film can be raised significantly, it can produce continuously and stably in a length direction.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
A thermoplastic saturated norbornene resin (trade name “ZEONOR 1600”, manufactured by Nippon Zeon Co., Ltd., Tg = 168 ° C.) as an amorphous thermoplastic resin is supplied to an L / D = 32 single-screw extruder and attached to the extruder. The film was extruded from a T-die having a mold lip width of 1800 mm and a mold temperature of 310 ° C. onto a cooling roll having a roll diameter of 350 mm adjusted to 140 ° C. to produce a film having a thickness of 40 μm and a width of 1710 mm.
At this time, the air gap is 65 mm, and as a contact stabilization device for the film cooling roll, a metal core is coated with a silicone rubber having a shore hardness of 70 degrees with a thickness of 5 mm, and further a 50 μm chrome plating is applied to a 200 μm thick electric current. An elastic touch roll having a roll diameter of 250 mm and a roll width of 1600 mm, in which the periphery of silicone rubber was coated with a cast nickel sleeve, was temperature-controlled at 120 ° C. and used at a touch pressure of 2 kgf / cm. The eccentric touch roll had an eccentric runout of 70 μm, and the film temperature variation just before the contact with the cooling roll was in the range of 250.9 to 252.0 ° C.

  The eccentric runout of the roll was measured as follows. That is, a roundness measuring machine (trade name “Dial Gauge 2109S-10”, manufactured by Mitutoyo Corporation) is set on a stand fixed in the vicinity of the roll, and the measuring needle is brought into contact with the normal direction of the roll. The difference between the maximum value and the minimum value of the measured values obtained when rotating was defined as the eccentric shake. The measurement was performed at a total of three locations about 20 cm inside from the center in the roll width direction, and the average value was adopted.

  The obtained film is up to 500 m every 100 m, with 25 mm pitch from the center of the film to both ends (only the pitch at the extreme end in the width direction is 27 mm each), and 80% of the total width is 53 points in total, and the flow direction of each point A total of 159 residual phase differences and optical axis variations were measured at a pitch of 50 cm, and the average and maximum residual phase differences and the maximum optical axis deviation were shown in Table 1. In addition, the phase difference and the optical axis were measured with 590 nm light using a birefringence measuring apparatus (trade name “KOBRA-21ADH” manufactured by Oji Scientific Instruments).

(Example 2)
A film was produced in the same manner as in Example 1 except that an elastic touch roll having an eccentric runout of 40 μm was used. The film temperature variation just before the contact point with the cooling roll was in the range of 250.9 to 252.0 ° C. The evaluation results similar to those in Example 1 are shown in Table 1.

(Comparative Example 1)
A film was produced in the same manner as in Example 1 except that an elastic touch roll having a roll width of 1300 mm and an eccentric runout of 150 μm was used. The film temperature variation just before the contact point with the cooling roll was in the range of 250.9 to 252.0 ° C. The evaluation results similar to those in Example 1 are shown in Table 1.

(Comparative Example 2)
A film was produced in the same manner as in Example 1 except that an elastic touch roll having a roll width of 1700 mm and an eccentric runout of 65 μm was used. The film temperature variation just before the contact point with the cooling roll was in the range of 250.9 to 252.0 ° C. The evaluation results similar to those in Example 1 are shown in Table 1.

(Comparative Example 3)
A film was produced in the same manner as in Example 1 except that the airflow was disturbed by intentionally blowing air around the mold and the roll. At this time, the film temperature variation just before the contact point with the cooling roll was in the range of 242 ° C to 250 ° C. The evaluation results similar to those in Example 1 are shown in Table 1.

In addition, the measurement of film temperature variation measured the data which measured the maximum temperature and the minimum temperature at the time of extruding 500m in the state which separated the touch roll prior to extrusion of Example 1, Example 1, 2, Comparative Example 1, 2. Was substituted. Further, prior to the extrusion of Comparative Example 3, data obtained by measuring the maximum temperature and the minimum temperature when the touch roll was pushed out with a distance of 500 m was used as the data of Comparative Example 3.

Claims (3)

  An optical film obtained by extruding an amorphous thermoplastic resin, having a thickness of 100 μm or less over a length of at least 100 m, a residual retardation of 3 nm or less over 80% of the entire surface, and an optical axis variation in the direction of flow of the film The optical film which is 10 degrees or less in the gap angle with respect to.   The optical film according to claim 1, wherein the amorphous thermoplastic resin is a norbornene resin.   An optical film manufacturing method in which a film made of an amorphous thermoplastic resin extruded from a die attached to an extruder is brought into close contact with a cooling roll and then cooled and solidified. The temperature is controlled to the glass transition temperature Tg + 80 ° C. or more of the resin, the temperature variation in the width direction and the flow direction is controlled to within 3 ° C., and the eccentric runout during rotation is within 100 μm. The method for producing an optical film according to claim 1, wherein the film is pressed against and adhered to the cooling roll with a temperature-controlled elastic roll having a length of 95%.