JP5410136B2 - Film production method, film, polarizing plate, and liquid crystal display film - Google Patents

Description

  The present invention relates to a method for producing a film. Moreover, it is related with the film manufactured by the manufacturing method, the polarizing plate using this film, and the film for liquid crystal display plates.

  In recent years, various films have been developed with the rise of the liquid crystal display market. For example, Patent Document 1 and Patent Document 2 describe a method of creating a film in which the optical axis is inclined by applying a shearing force to the film by passing a thermoplastic resin between two rolls having different peripheral speeds. ing.

Patent Document 3 discloses a laminate by coextruding a resin material made of a resin (a) having a positive intrinsic birefringence value and a resin material made of a resin (b) having a negative intrinsic birefringence value. And a step of uniaxially stretching the obtained laminate, and the melt viscosities of the resin (a) and the resin (b) measured at 250 ° C. and a shear rate of 180 sec ⁻¹ are both 300 to 2, respectively. 000 Pa · s, and a method for producing a laminated retardation film in which the difference in melt viscosity between the resin (a) and the resin (b) is 1,500 Pa · s or less is disclosed.

JP 2007-38646 A JP 2003-25414 A JP 2004-163684 A

  By the way, this inventor is examining the method of obtaining the film which expressed the in-plane retardation (Re) by pinching a thermoplastic resin and applying a high linear pressure. In this method, it was difficult to develop sufficient in-plane retardation (Re) when the film thickness was 60 μm or less.

  The present invention has been made in view of such circumstances, and can achieve high in-plane retardation (Re) even with a thin film having a film thickness of 60 μm or less, and an optically inclined film. An object of the present invention is to provide a production method and a film thereof.

  In order to achieve the above object, the method for producing a film of the present invention is a method for producing a film having at least a core layer and two skin layers on the outer layer of the core layer, and is a thermoplastic film that becomes the core layer. A step of melt-extruding a first composition containing a resin, a second composition and a third composition containing a thermoplastic resin to be a skin layer from a die, and the melt-extruded melt A step of forming a film by continuously pressing between a first clamping surface and a second clamping surface constituting the pressure device, and a pressure applied to the melt by the pressure device is 20 to 500 MPa, Tg of said 1st composition is 0.5 to 50 degreeC lower than Tg of said 2nd composition and said 3rd composition, It is characterized by the above-mentioned.

  The core layer is composed of a thermoplastic resin composition having a glass transition temperature (Tg) lower than that of the skin layer, and a linear pressure of 20 to 500 MPa is applied to the melt of the thermoplastic resin composition, thereby providing a predetermined thin film. In-plane retardation (Re) can be expressed. The reason is that the Tg of the core layer is lower than the Tg of the skin layer, so that even if the skin layer is cooled by the first clamping surface and the second clamping surface, the core layer is stretched and deformed, and a predetermined in-plane letter is formed. It is considered that the foundation (Re) is expressed.

  The skin layer is a layer located on both outer sides of the core layer, and means a layer in contact with the first clamping surface and the second clamping surface. Therefore, another layer may be included between the core layer and the skin layer. For example, the present invention includes a case where an adhesive layer is provided between the core layer and the skin layer.

  In the method for producing a film of the present invention, in the above invention, the moving speed of the first clamping surface and the second clamping surface for clamping the melt is made different from each other, whereby 3000 to 30000 N per 1 m width of the melt. It is preferable to apply a shearing force of

  By making the moving speeds of the first and second clamping surfaces different from each other, a shearing force can be applied to the formed film, so that a film having a large optically inclined structure can be produced. . In the present invention, the second clamping surface is defined as a surface having a low moving speed.

  In the method for producing a film of the present invention, in the invention described above, it is preferable that the first clamping surface and the second clamping surface for clamping the melt are constituted by a pair of rolls arranged to face each other.

  Since the first clamping surface and the second clamping surface are constituted by a pair of rolls arranged to face each other, pressure can be easily applied to the melt.

  In the method for producing a film of the present invention, in the invention described above, it is preferable that the second composition and the third composition have the same composition.

  By making the composition of the second composition and the third composition the same, a film having a three-layer structure can be formed by two extruders. Further, by making the front and back resin compositions the same, it is possible to prevent appearance defects such as warping of the film.

  In the method for producing a film of the present invention, in the above invention, it is preferable that the second composition and the third composition are supplied from one extruder to the die.

  When the composition of the second composition and the third composition is the same, the second composition and the third composition can be fed from one extruder to the die. Thereby, manufacturing equipment can be simplified.

  In the method for producing a film of the present invention, in the above invention, the thickness of the skin layer is preferably 2% or more and 90% or less of the total film thickness.

  By setting the thickness of the skin layer to 2% or more and 90% or less of the total film thickness, it is possible to improve the in-plane retardation (Re) expression and the release property from the roll even if the film thickness is reduced. .

When the flow rate of the melt extruded from the die is 2.5 to 30 kg / cm ² per die discharge port area and the film forming speed is 3 m / min or more, the expression of Re is improved, and the target Re can be expressed. Here, the film forming speed refers to the moving speed of the second pressing surface.

  In the method for producing a film of the present invention, in the above invention, the pair of rolls are preferably metal rolls. By using a pair of metal rolls, a relatively large linear pressure can be applied to the melt.

  In the method for producing a film of the present invention, in the above invention, the arithmetic average height Ra of the pair of rolls is 100 nm or less, and the length of the melt of the portion sandwiched between the pair of rolls is less than 0 mm. It is preferably 2 mm or less.

  The smoothness and film haze of a film become favorable because arithmetic average height Ra of a pair of roll shall be 100 nm or less. Moreover, it becomes possible to apply a big linear pressure to a molten material by making the length of the molten material pinched | interposed into 2 mm or less larger than 0 mm.

  When the arithmetic average height Ra of the pair of rolls is 100 nm or less, scratches on the surface of the film can be prevented. Moreover, it becomes possible to apply a big linear pressure to a molten material by making the length of a molten material larger than 0 mm and 2 mm or less.

  In the method for producing a film of the present invention, in the above invention, the thermoplastic resin is at least selected from cyclic olefin copolymers, cellulose acylates, polycarbonates, styrene copolymers, and acrylic copolymers. One type is preferable.

  The film of the present invention is manufactured by any one of the above manufacturing methods.

The film of the present invention is a film having at least a core layer and two skin layers on the outer layer of the core layer, wherein the Tg of the composition forming the core layer forms the skin layer. Measured from a direction inclined by + 40 ° and retardation Re [0 °] at a wavelength of 550 nm measured from the normal line within a plane including the film tilt direction and the film normal line, 0.5 ° C. to 50 ° C. lower than the Tg of the film Retardation Re [+ 40 °] and retardation Re [−40 °] measured from a direction inclined by −40 ° with respect to the normal line satisfy both the following relational expressions (I) and (II): It is characterized by.
80 nm ≦ Re [0 °] ≦ 300 nm (I)
60 nm ≦ | Re [+ 40 °] −Re [−40 °] | ≦ 300 nm (II)
The film having the above-described optical characteristics can realize sufficient optical compensation when used in a liquid crystal display of ECB mode, OCB mode, and TN mode.

  Moreover, the polarizing plate of this invention is characterized by including the said film. Furthermore, the film for liquid crystal display of the present invention is characterized by containing the film.

  According to the present invention, even in the case of a thin film having a film thickness of 60 μm or less, in-plane retardation (Re) can be realized. In addition, an optically inclined film can be realized.

It is a whole block diagram which shows an example of the manufacturing apparatus of an optical film. It is sectional drawing which shows the structure of an extruder. It is a block diagram in the case of carrying out the longitudinal stretch and the lateral stretch of the manufactured film. It is a graph which shows the relationship between the peripheral speed ratio of a roll, and | Re [+ 40 °] −Re [−40 °] |. It is a table | surface which shows the test conditions and a result of an Example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described with reference to the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment can be used. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims.

  In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to”.

<Film production method>
The method for producing a film of the present invention is a method for producing a film having at least a core layer and two skin layers on the outer layer of the core layer, the first composition containing a thermoplastic resin to be the core layer And a step of melt-extruding the second composition and the third composition containing the thermoplastic resin to be the skin layer from the die, and the melt-extruded melt into the first sandwiching device constituting the sandwiching device A step of continuously pressing between the pressing surface and the second pressing surface to form a film, and the pressure applied to the melt by the pressing device is 20 to 500 MPa, and the Tg of the first composition Is lower by 0.5 ° C. to 50 ° C. than the Tg of the second composition and the third composition.

  FIG. 1 is a block diagram showing an example of a production apparatus for carrying out the method for producing a thermoplastic resin film of the present invention.

  As shown in FIG. 1, a manufacturing apparatus 10 includes an extruder 14 that melts a first composition 12 (hereinafter, also referred to as “thermoplastic resin composition”) containing a thermoplastic resin that serves as a core layer, Extruder 14 ′ for melting the second composition 12 ′ containing the thermoplastic resin to be the skin layer and the second composition 12 ″ to contain the thermoplastic resin for the other skin layer An extruder 14 ″, a die 16 for discharging the molten thermoplastic resin composition 12, 12 ′, 12 ″ into a film, and a high-temperature molten film 12A discharged from the die 16 (hereinafter referred to as “melt”). A plurality of casting rolls 18, 20, 22 for cooling in multiple stages, a touch roll 28 disposed opposite to the casting roll 18, and a peeling for peeling the film 12 </ b> B from the last casting roll 22. Provided with Lumpur 24, a winder 26 for winding the cooled film 12B, the.

  A supply process part is the process of forming the composition containing a thermoplastic resin and supplying to a film forming process. FIG. 2 is a cross-sectional view showing a configuration of the extruder 14 as an example of a supply unit. The extruders 14 ′ and 14 ″ have substantially the same configuration as the extruder 14. As shown in the figure, a single screw 38 having a flight 36 attached to a screw shaft 34 is provided in the cylinder 32 of the extruder 14. The single screw 38 is rotated by a motor (not shown). A hopper (not shown) is attached to the supply port 40 of the cylinder 32. Then, the thermoplastic resin composition is supplied from the hopper into the cylinder 32 through the supply port 40.

  Inside the cylinder 32, in order from the supply port 40 side, a supply unit (region indicated by A) for quantitatively transporting the thermoplastic resin composition supplied from the supply port 40, and a compression unit for kneading and compressing the thermoplastic resin composition (Area indicated by B) and a measuring section (area indicated by C) for measuring the kneaded and compressed thermoplastic resin composition. The thermoplastic resin composition melted by the extruder 14 is continuously sent from the discharge port 42 to the die 16.

  The screw compression ratio of the extruder 14 is preferably set to 1.5 to 4.5, and the ratio L / D of the cylinder length to the cylinder inner diameter is preferably set to 20 to 70. Here, the screw compression ratio is represented by the volume ratio between the supply unit A and the metering unit C, that is, the volume per unit length of the supply unit A ÷ the volume per unit length of the metering unit C. Is calculated using the outer diameter d1 of the screw shaft 34, the outer diameter d2 of the screw shaft 34 of the measuring section C, the groove diameter a1 of the supply section A, and the groove diameter a2 of the measuring section C. The extrusion temperature is preferably 190 to 300 ° C. Furthermore, in order to prevent the molten resin from being oxidized by residual oxygen, it is also preferable to carry out the inside of the extruder in an inert (nitrogen or the like) air flow or while evacuating using an extruder with a vent.

  The thermoplastic resin compositions 12, 12 ′, 12 ″ melted by the extruders 14, 14 ′, 14 ″ are transferred to the die 16 via the pipes 44, 44 ′, 44 ″ (see FIG. 1). Then, the film is discharged from the die discharge port in the form of a film. The fluctuation of the discharge pressure discharged from the die 16 is preferably within a range of 10%.

Moreover, it is preferable that the flow rate of the melt 12A extruded from the die 16 is 2.5 to 30 kg / cm ² per die discharge port area, and the film forming speed is 3 m / min or more. The film forming speed is preferably 4 m / min or more, and more preferably 5 m / min or more. When the film forming speed is low, the time for cooling by roll touch becomes long, and therefore the Re expression tends to be lowered. Here, the film forming speed refers to the moving speed of the second pressing surface.

  The die 16 separately receives the molten first thermoplastic resin composition 12, the molten second thermoplastic resin composition 12 ′, and the molten third thermoplastic resin composition 12 ″. 3 or more pockets are provided. The die 16 further includes three or more slits for transporting the thermoplastic resin composition in each pocket portion, a joining portion of the thermoplastic resin composition connected to each slit, and a discharge port formed continuously to the joining portion. I have. By discharging the thermoplastic resin compositions 12, 12 ', 12' 'from the die 16, a core layer and a melt 12A having two skin layers on the outer layer of the core layer are formed.

  In the present invention, the Tg of the first thermoplastic resin composition 12 is 0.5 ° C. to 50 ° C. lower than the Tg of the second thermoplastic resin composition 12 ′ and the third thermoplastic resin composition 12 ″. . For a melt 12A composed of the first thermoplastic resin composition 12, the melted second thermoplastic resin composition 12 ′, and the melted third thermoplastic resin composition 12 ″, A linear pressure of 20 to 500 MPa is applied by the casting roll 18 and the touch roll 28. At this time, when the Tg of the second thermoplastic resin composition 12 ′ and the third thermoplastic resin composition 12 ″ are different, the Tg temperature of the first thermoplastic resin composition 12 is 12 ′. It is necessary that the temperature is 0.5 ° C. to 50 ° C. lower than the Tg of the lower of 12 ″.

  In this way, the core layer is composed of a thermoplastic resin layer having a glass transition temperature (Tg) lower than that of the skin layer, and a linear pressure of 20 to 500 MPa is applied to the melt, thereby providing a predetermined in-plane with a thin film. Retardation (Re) can be expressed. The reason is that the Tg of the core layer is lower than that of the skin layer, so that the second thermoplastic resin layer 12 ′ and the third thermoplastic resin composition 12 ″ to be the skin layer are separated by the casting roll 18 and the touch roll 28. It is considered that the first thermoplastic resin composition 12 that becomes the core layer even when cooled is extended and deformed to exhibit a predetermined in-plane retardation (Re).

  The skin layer is a layer located on both outer sides of the core layer, and means a layer in contact with the first clamping surface and the second clamping surface. Therefore, another layer may be included between the core layer and the skin layer. For example, the present invention includes a case where an adhesive layer is provided between the core layer and the skin layer.

  Further, the core layer can be easily deformed by increasing the temperature of the casting roll 18 and the touch roll 28. Thereby, in-plane retardation (Re) is easily developed. Further, since the skin layer has a Tg higher than that of the core layer, the peelability of the film can be improved even if the temperature of the casting roll 18 and the touch roll 28 is increased.

  The temperature T [° C.] of the melt 12A immediately after being extruded from the discharge port of the die 16 preferably satisfies Tg + 60 ° C. ≦ T ≦ Tg + 140 ° C. with respect to Tg of the skin layer. The temperature T of the melt 12 </ b> A immediately after being extruded from the discharge port of the die 16 can be measured by a contact thermometer or a non-contact thermometer. Tg [° C.] means the glass transition temperature of the thermoplastic resin composition 12 and can be measured, for example, using a scanning differential calorimeter (DSC) according to the following procedure.

  The thermoplastic resin composition 12 was placed in a measurement pan of a scanning differential calorimeter (DSC), and this was heated from 30 ° C. to 300 ° C. at 10 ° C./min in a nitrogen stream (1st-run), then 30 The temperature is cooled to -10 ° C / min to ℃, and the temperature is raised again from 30 ° C to 300 ° C at 10 ° C / min (2nd-run). The temperature at which the baseline starts to deviate from the low temperature side at 2nd-run can be calculated as the glass transition temperature Tg of the thermoplastic resin composition 12.

  When the second thermoplastic resin composition 12 ′ and the third thermoplastic resin composition 12 ″ have the same composition, an extruder can be shared. Thereby, manufacturing equipment can be simplified.

  The first composition containing the thermoplastic resin to be the core layer, the second composition and / or the third composition containing the thermoplastic resin to be the skin layer are the Tg of the first composition. However, as long as it is lower by 0.5 ° C. to 50 ° C. than the Tg of the second composition and the third composition, either the same kind of polymers or different kinds of polymers may be used. Here, the same type of polymer has a solubility parameter difference (SP value) of less than 1.0, preferably less than 0.3, and the different polymer has a solubility parameter difference of 1.0 or more, preferably 2.0 or more. From the viewpoint of the peel strength of each layer of the film, it is preferable to use the same kind of polymer. On the other hand, when different types of polymers are laminated, the second composition and / or the third composition layer, which becomes the skin layer after film formation, is peeled off, although the thickness is extremely thin. It is also possible to obtain a film having an optical inclination with Re. In addition, the first composition containing the thermoplastic resin to be the core layer and the second composition and / or the third composition containing the thermoplastic resin to be the skin layer should have a small difference in melt viscosity. Specifically, the difference in zero shear rate is preferably 1000 Pa · s or less, more preferably 500 Pa · s or less, and particularly preferably 200 Pa · s or less. When the melt viscosities differ greatly, an appearance defect due to uneven elongation ratio at the interface of each layer occurs when sandwiched between rolls during film formation, which is not preferable.

  Further, the present invention comprises a first composition containing a thermoplastic resin to be a core layer and a second composition and / or a third composition containing a thermoplastic resin to be a skin layer. The Tg of the layer between the core layer and the skin layer may have a gradient. It is also possible to control the Re expression and the optical tilt when sandwiched by this Tg gradient. For example, by increasing the Tg of the second composition to be higher than the Tg of the third composition, the expression of Re on the film surface side of the third composition is increased more than the film surface side of the second composition. It is also possible to increase the angle of optical tilt.

  Further, from the viewpoint of reducing the influence of disturbance such as the fluctuation of the bank due to the flow of the surrounding air and the heat radiation to the surroundings of the resin composition, the gap between the discharge port of the die 16, the casting roll 18 and the touch roll 28. In addition, a shielding member surrounding the melt 12A may be provided.

  In this case, by enclosing a gas having a lower thermal conductivity than air inside the shielding member, heat conduction from the outside air can be suppressed, the resin temperature of the bank can be increased, and the disturbance received by the molten resin The influence of can be reduced. Examples of the gas that can be enclosed in the shielding member include argon and carbon dioxide.

  In the film forming process section, the melt 12A formed by the supply means is continuously sandwiched between the first sandwiching surface and the second sandwiching surface constituting the sandwiching device at a linear pressure of 20 to 500 MPa. Is formed. In FIG. 1, the first clamping surface and the second clamping surface constituting the clamping device are configured by a touch roll 28 and a casting roll 18.

  The linear pressure due to the first clamping surface and the second clamping surface is set in the range of 20 to 500 MPa, and is preferably set to 25 to 400 MPa. More preferably, it is 30-250 MPa. Thus, the 1st thermoplastic resin composition which becomes a core layer by extruding the melt 12A from the narrow pinching part between the touch roll 28 and the casting roll 18 while giving a large linear pressure in the above range. Elongation deformation occurs in the object 12, and high retardation is developed in the flow direction (in-plane direction) and the thickness direction. Thereby, for example, the film 12B having an in-plane retardation (Re) at a wavelength of 550 nm of 40 nm or more can be formed. The direction of the slow axis of the film 12B formed by the touch roll 28 and the casting roll 18 is substantially the same as the film transport direction.

  In the present embodiment, the length of the melt 12A pinched by the pinching device is adjusted to be greater than 0 mm and less than 2 mm. By setting the length of the melt 12A to be greater than 0 mm and less than 2 mm, the expression of Re is enhanced, and the target Re can be obtained.

  The nip pressure of the clamping device is determined by pressing the pressure measurement film “Prescale” manufactured by Fuji Film Co., Ltd. at the nip point to develop color, and then determining the degree of color development by using the prescale dedicated densitometer FPD-305 and the prescale dedicated pressure. It can be obtained by converting into a pressure value using a converter FPD-306. In addition, the length of the melted portion of the sandwiched portion was determined as the width in the transport direction in which the prescale was colored.

  The touch roll 28 has a configuration capable of pressing the melt 12 </ b> A supplied from the discharge port of the die 16 against the casting roll 18 by an unillustrated air cylinder, hydraulic cylinder, or the like.

  In addition, the elastic roll (for example, the rubber roll by which the surface was coat | covered with the metal described in Unexamined-Japanese-Patent No. 2003-25414) used conventionally is deform | transformed when a high pressure is given, Since the contact area with the resin composition 12 increases, it is difficult to apply the high linear pressure as described above.

  For this reason, it is preferable to use a roll having a Shore hardness of 45 HS or more as the touch roll 28 and the casting roll 18. A more preferable Shore hardness is 50 HS or more, and further preferably 60 HS or more. Here, the shore hardness can be obtained from an average value of values measured at 5 points in the roll width direction and at 5 points in the circumferential direction using the method of JIS Z 2246.

  In order to achieve the Shore hardness, the material of the two rolls is preferably a metal, more preferably stainless steel, and a roll whose surface is plated is also preferred. On the other hand, a rubber roll or a metal roll lined with rubber is preferably used because it has large surface irregularities and is easily scratched on the surface of the film.

  From the viewpoint of forming a film having a smooth surface, the surfaces of the casting roll 18 and the touch roll 28 preferably have an arithmetic average roughness Ra of 100 nm or less, more preferably 50 nm or less, and 25 nm or less. Is more preferable.

  As for the touch roll 28, for example, Japanese Patent Laid-Open Nos. 11-31263, 2002-36332, 11-235747, WO 97/28950, 2004-216717, JP The thing of 2003-145609 gazette can be utilized.

  The distance (air gap) between the discharge port of the die 16 and the bank is preferably set within 200 mm from the viewpoint of reducing the influence of the external air flow.

  In addition, it is preferable that the moving speed of the first pressing surface and the moving speed of the second pressing surface are different from each other. By providing the peripheral speed difference, a shearing force can be applied to the melt 12A, so that an optically inclined film 12B can be formed.

  In the present embodiment, the touch roll 28 (corresponding to the “first pressing surface”) and the casting roll 18 (corresponding to the “second pressing surface”) are moved (rotated) at different speeds (peripheral speeds). preferable. By providing a peripheral speed difference between the touch roll 28 and the casting roll 18, a shearing force can be applied to the melt 12 </ b> A at the pinching portion to form an optically inclined film. In particular, since a skin layer having a Tg higher than the Tg of the core layer is provided on the outer layer of the core layer, application of shearing force is facilitated. Thereby, the optically inclined film can be easily formed.

  When providing the above-mentioned peripheral speed difference, it is preferable to rotate the touch roll 28 at a peripheral speed larger than that of the casting roll 18. When the touch roll 28 is slower than the casting roll 18, a bank is formed on the touch roll 28 side, so that the contact time between the casting roll 18 and the melt 12A is shortened. For this reason, the cooling of the melt 12A becomes insufficient, the melt 12A becomes difficult to peel off from the touch roll 28, and a striped surface defect along the width direction of the film may occur. By rotating the touch roll 28 at a higher peripheral speed than the casting roll 18, it is possible to prevent striped surface defects along the width direction of the film.

  The peripheral speed ratio of the two rolls is preferably 0.6 to 0.99, and more preferably 0.75 to 0.98. Here, the peripheral speed ratio of the two rolls means the peripheral speed of the slow roll / the peripheral speed of the fast roll.

  The smaller the peripheral speed ratio of the two rolls (that is, the larger the peripheral speed difference), the larger the absolute value of the difference between Re [40 °] and Re [−40 °] of the film F obtained, If the speed ratio is too small, the surface of the resulting film is easily damaged. When the peripheral speed ratio of the two rolls is set within the above range, a film having a smooth surface and an optically inclined optical axis can be formed.

  In addition to the combination of two rolls having different peripheral speeds as shown in FIG. 1 (touch roll 28 and casting roll 18), the clamping apparatus having different speeds on the first clamping surface and the second clamping surface, Examples thereof include a combination of a roll and a touch belt having different speeds described in Japanese Patent Application Laid-Open No. 2000-219752.

  FIG. 4 shows | Re [+ 40 °] −Re [− when assuming that the peripheral speed ratio of the two rolls and the refractive index ellipsoid are uniformly inclined when the resin temperature is high and low. 40 °] |. As shown in FIG. 4, the change in | Re [+ 40 °] −Re [−40 °] | due to the change in the peripheral speed ratio is suppressed when the resin temperature is higher than when the resin temperature is low. Therefore, | Re [+ 40 °] −Re [−40 °] | can be stably manufactured by increasing the resin temperature.

  Furthermore, it is preferable to use a roll having a large diameter. Specifically, it is preferable to use two rolls having a diameter of 350 to 600 nm, more preferably 350 to 500 nm. When a roll having a large diameter is used, the contact area between the melt 12A and the roll becomes wide, and the time for shearing becomes longer. Therefore, a film having a large difference between Re [+ 40 °] and Re [−40 °] It can manufacture, suppressing the variation. The diameters of the two rolls may be the same or different.

  The two rolls may be driven or driven independently, but are preferably driven independently in order to suppress variations.

  As described above, it is possible to form an optically tilted film by rotating two rolls at different peripheral speeds. Further, the difference between Re [+ 40 °] and Re [−40 °] In order to enlarge, you may make a difference in the surface temperature of two rolls. A preferable temperature difference is 5 ° C to 80 ° C, more preferably 20 ° C to 80 ° C, and further preferably 20 ° C to 60 ° C. At that time, the temperature of the two rolls is Tg−70 ° C. to Tg + 20 ° C., more preferably Tg−50 ° C. to Tg + 10 ° C., more preferably Tg−40 ° C. to Tg + 5 ° C., using the glass transition temperature Tg of the resin. Set. Such temperature control can be achieved, for example, by flowing a temperature-controlled liquid or gas inside the touch roll 28.

  Further, as shown in FIG. 1, after forming the film in this way, in addition to the casting roll 18 and the touch roll 28 which are two rolls through which the film-like melt is passed, two casting rolls 20 and 22 are provided. It is preferred to use and cool the film. The casting roll is usually arranged so as to touch the most upstream side (closer to the die) of the casting roll 18. In general, it is relatively common to use three casting rolls as shown in FIG. 1, but this is not restrictive. The distance between the plurality of casting rolls is preferably 0.3 mm to 300 mm, more preferably 1 mm to 100 mm, and still more preferably 3 mm to 30 mm between the surfaces.

  The film 12B cooled and solidified in the casting roll 22 having the above-described configuration is peeled from the casting roll 22 by the peeling roll 24 shown in FIG.

  Further, it is preferable to trim both ends of the processed film. The portion cut off by trimming may be crushed and used again as a raw material. Further, it is also preferable to perform a thickness increasing process (knurling process) on one or both ends. The height of the unevenness due to the thickness increasing process is preferably 1 μm to 50 μm, more preferably 3 μm to 20 μm. Thickening processing may be convex on both sides or convex on one side. The width of the thickness increasing process is preferably 1 mm to 50 mm, more preferably 3 mm to 30 mm. Thickening processing can be performed at room temperature to 300 ° C. It is also preferable to attach a lami film on one side or both sides before winding. The thickness of the laminated film is preferably 5 μm to 100 μm, more preferably 10 μm to 50 μm. The material is not particularly limited, such as polyethylene, polyester, and polypropylene.

  As shown in FIG. 3, the film 12 </ b> B produced as described above is preferably subjected to longitudinal stretching and lateral stretching, and may further be combined with shrinkage treatment. The longitudinal stretching is performed after the longitudinal stretching or a combination of the lateral stretching and the longitudinal shrinkage treatment. The former is suitable for developing a high Rth, and the latter is suitable for developing a low Rth.

  When the transverse stretching and the longitudinal shrinkage treatment are performed in combination, the longitudinal shrinkage may be performed during the transverse stretching, may be performed after the transverse stretching, or may be performed both. Further, longitudinal stretching may be combined before or after the transverse stretching or both. Further, after the film 12B is manufactured by the melt film-forming process, the film may be wound up after the longitudinal stretching process and the lateral stretching process are continuously performed without being wound around the winder 26 once. The winding tension when winding is preferably 2 kg / m width to 50 kg / m width, and more preferably 5 kg / m width to 30 kg / m width.

  In the present invention, longitudinal stretching may be performed alone or in combination with lateral stretching. The longitudinal stretching may be performed either before or after the lateral stretching, but is more preferably performed before the lateral stretching. In addition, the longitudinal stretching may be performed in one stage or may be performed in multiple stages.

Longitudinal stretching can be achieved by installing two pairs of nip rolls and heating the gap between them so that the peripheral speed of the nip roll on the outlet side is higher than the peripheral speed of the nip roll on the inlet side. Under the present circumstances, the expression of the retardation of the thickness direction can be changed by changing the space | interval (L) between nip rolls, and the film width (W) before extending | stretching. When L / W exceeds 2 and is 50 or less (long span stretching), Rth can be reduced, and when L / W is 0.01 or more and 0.3 or less (short span stretching), Rth can be increased. In the present invention, any of a long span stretching, a short span stretching, and a region between them (intermediate stretching = L / W is more than 0.3 and 2 or less) may be used. Short span stretching is preferred. Further, when aiming at high Rth, it is more preferable to use short span stretching, and when aiming at low Rth, it is distinguished from long span stretching.

  The preferred stretching temperature for these longitudinal stretching is (Tg-10 ° C) to (Tg + 50) ° C, more preferably (Tg-5 ° C) to (Tg + 40) ° C, and more preferably (Tg) to (Tg + 30) ° C. is there. A preferable draw ratio is 2% to 200%, more preferably 4% to 150%, and still more preferably 6% to 100%.

  The transverse stretching can be performed using a tenter. That is, the film is stretched by gripping both ends in the width direction with clips and widening in the lateral direction. At this time, the stretching temperature can be controlled by sending wind at a desired temperature into the tenter. The stretching temperature is preferably Tg-10 ° C or higher and Tg + 60 ° C or lower, more preferably Tg-5 ° C or higher and Tg + 45 ° C or lower, and further preferably Tg or higher and Tg + 30 ° C or lower. A preferable draw ratio is 10% or more and 250% or less, more preferably 20% or more and 200% or less, and further preferably 30% or more and 150% or less. The draw ratio here is defined by the following formula.

Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / (Length before stretching)
<Film>
The film produced by the film production method of the present invention contains a thermoplastic resin, and has a retardation Re [0 °] at a wavelength of 550 nm measured from the normal line in a plane including the film tilt direction and the film normal line. And retardation Re [+ 40 °] measured from a direction inclined + 40 ° and retardation Re [−40 °] measured from a direction inclined −40 ° with respect to the normal line are expressed by the following relational expression (I ) And (II) are both satisfied.
80 nm ≦ Re [0 °] ≦ 300 nm (I)
60 nm ≦ | Re [+ 40 °] −Re [−40 °] | ≦ 300 nm (II)
In the film of the present invention, | Re [+ 40 °] −Re [−40 °] | is 60 to 300 nm, preferably 70 to 250 nm, and more preferably 80 to 200 nm. The film of the present invention has an in-plane retardation Re [0 °] of 80 to 300 nm, more preferably Re [0 °] of 80 to 250 nm, and still more preferably 80 to 200 nm.

  Further, the film of the present invention preferably has a thickness direction retardation Rth of 40 to 500 nm, more preferably 40 to 350 nm, and still more preferably 40 to 300 nm.

  A film having | Re [+ 40 °] −Re [−40 °] | and Re (0 °) in the above range and Rth in the above range can be produced by the production method of the present invention described above. When an optical film having such optical characteristics is used for optical compensation of a liquid crystal display such as a TN mode, an ECB mode, and an OCB mode, it contributes to an improvement in viewing angle characteristics and achieves a wide viewing angle. Can do.

  The thickness of the film for optical use of the present invention is not particularly limited, but when used for a liquid crystal display or the like, it is preferably 15 μm or more and 200 μm or less, and 20 μm or more and 100 μm or less from the viewpoint of thinning. More preferably, it is 25 μm or more and 60 μm or less. In the production method of the present invention, the Tg of the first composition has a core layer lower by 0.5 ° C. to 50 ° C. than the Tg of the second composition and the third composition. Such a thin film can be produced, which is one of the differences from the prior art. The thickness of the skin layer may be 2% or more and 90% or less of the total film thickness from the viewpoint of improving in-plane retardation (Re) and improving peelability from the roll when the film thickness is reduced. preferable. If the thickness of the skin layer is 2% or more, a uniform layer can be formed, so that the peelability from the roll can be improved and the optical properties can be made uniform. By making it 90% or less, the expression of in-plane retardation (Re) of a thin film can be improved.

  The layer thicknesses of the second composition and the third composition, which are the skin layers, are preferably equal from the viewpoint of curl of the film, but the pressure-clamping surface temperature is differentiated in order to impart an optically inclined structure. In some cases, the in-plane retardation (Re) and the optically tilted structure can be more effectively formed by changing the layer thickness ratio of the second composition and the third composition. For example, the expression of in-plane retardation (Re) is further improved by making the thickness of the skin layer on the lower roll temperature side thinner than the thickness of the skin layer on the higher roll temperature side.

  Variations in Re [0 °], Re [+ 40 °], and Re [−40 °] appear as display unevenness when used in a liquid crystal display. Therefore, the variation is preferably as small as possible. It is preferably ± 3 nm, and more preferably within ± 1 nm. Similarly, the variation in the angle of the slow axis also causes display unevenness. Therefore, the variation is preferably as small as possible, specifically within ± 1 °, preferably within ± 0.5 °. Is more preferable, and ± 0.25 ° is particularly preferable. The direction of the slow axis of the film depends on the production method of the film described later. For example, when a resin exhibiting positive intrinsic birefringence is passed through two rolls, the slow axis is the same as the longitudinal direction of the film.

  The optical characteristic value can be measured by the following method.

  In this specification, in the invention of the film, Re [0 °], Re [+ 40 °] and Re [−40 °] of the film are measured using KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments), Retardation value phase difference at a wavelength of 550 nm (at an inclination angle of 0 °) measured from the normal direction in a plane including the following inclination direction and film normal, tilted by 40 ° toward the inclination direction with respect to the normal Retardation value phase difference (at an inclination angle of 40 degrees) measured from a different direction and a letter (at an inclination angle of -40 degrees) measured from a direction inclined 40 ° to the opposite side of the inclination direction with respect to the normal line It is a measurement representing the retardation value phase difference.

Here, the inclination direction was determined by the following method.
(1) The slow axis direction in the film plane is 0 °, the fast axis direction in the film plane is 90 °, and the temporary tilt direction is set in increments of 0.1 ° between 0 ° and 90 °.
(2) Re [+ 40 °] and Re [−40 in the plane including each provisional tilt direction and film normal
[°] and | Re [+ 40 °] −Re [−40 °] |
(3) The direction in which | Re [+ 40 °] −Re [−40 °] | is maximized is determined as the tilt direction.

  In this specification, the “direction inclined by θ ° from the film normal” is defined as a direction inclined in the film surface direction by θ ° from the normal direction to the inclination direction. That is, the normal direction of the film surface is a direction with an inclination angle of 0 °, and an arbitrary direction within the film surface is a direction with an inclination angle of 90 °.

  In the present specification, Rth of the film is calculated by KOBRA21ADH or WR in the tilt direction.

  In addition, variations in Re [0 °], Re [+ 40 °], and Re [−40 °] can be measured by the following method. Sampling is performed at arbitrary 10 or more positions apart from each other by 2 mm or more in the center of the film, and Re [0 °], Re [+ 40 °] and Re [−40 °] are measured by the above method. The difference between the minimum values is the variation of Re [0 °], Re [+ 40 °], and Re [−40 °]. In the present invention, the average value of the above 10 points is Re [0 °], Re [+ 40 °], and Re [−40 °].

  When the film-like measurement object to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth is calculated by the following method.

  Rth is an in-plane slow axis (determined by KOBRA 21ADH or WR) as an inclined axis (rotation axis) (if there is no slow axis, the film-like object to be measured is an arbitrary in-plane The direction of rotation is the rotation axis), and light having a wavelength of 550 nm is incident on the normal direction of the film-like object to be measured in steps of 10 degrees from −50 ° to + 50 ° from the normal direction. Then, 11 retardation values are measured, and KOBRA 21ADH or WR is calculated based on the retardation value, the assumed value of the average refractive index, and the input film thickness value.

  In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.

  Retardation value from two inclined directions with the slow axis as the rotation axis (in the absence of the slow axis, the in-plane arbitrary direction of the film-like object to be measured is the rotation axis). Rth can be calculated from the following formulas (I) and (II) based on the measured value, the assumed value of the average refractive index, and the input film thickness value.

Formula (II)
Rth = {(nx + ny) / 2−nz} × d
In the formula, Re [θ] represents a retardation value in a direction inclined by an angle θ from the normal direction.

  In formula (I), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the direction perpendicular to nx and ny. Refractive index is represented, d represents a film thickness.

  In the case where a film-like measurement object to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a measurement object without a so-called optical axis, Rth is determined by the following method. Calculated.

  Rth is the Re in 10 degree steps from −50 ° to + 50 ° with respect to the film normal direction with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis). Measured 11 points with light having a wavelength of 550 nm incident from the inclined direction, and KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed average refractive index, and the input film thickness value. To do.

  In the above measurement, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, INC) and catalogs of various optical compensation films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical compensation films are as follows: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49) Polystyrene (1.59). The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

  Note that the measurement wavelengths of Re [θ °], Rth, and refractive index are values at a measurement wavelength of 550 nm unless otherwise specified.

  The thermoplastic resin used in the present invention is not particularly limited as long as it has the above-mentioned optical characteristics. However, when it is produced using a melt extrusion method, it is preferable to use a material having good melt extrusion moldability. In, cyclic olefins, cellulose acylates, polycarbonates, polyesters, transparent polyethylene, polyolefins such as transparent polypropylene, polyarylates, polysulfones, polyethersulfones, maleimide copolymers, transparent nylons, It is preferable to select transparent fluororesins, transparent phenoxys, polyetherimides, polystyrenes, acrylic copolymers, and styrene copolymers. One kind of the resin may be contained, or two or more kinds of the resins different from each other may be contained. Among these, cellulose acylates, cyclic olefin resins obtained by addition polymerization, polycarbonates, styrene copolymers, and acrylic copolymers are preferable.

  In particular, cellulose acylates that exhibit positive intrinsic birefringence, and cyclic olefin resins and polycarbonates obtained by addition polymerization, when the shear deformation is added by two rolls, the slow axis faces the MD direction. A film of | Re (40 °) −Re (−40 °) |> 0 can be produced with the longitudinal direction as the tilt direction.

  In addition, acrylic and styrene copolymers exhibiting negative intrinsic birefringence, when processed as described above, have a slow axis in the TD direction and a longitudinal direction in the tilt direction, and | Re (40 °) − A film with Re (−40 °) |> 0 can be produced.

  When this film is applied to a liquid crystal display device as a viewing angle compensation film, the positive or negative intrinsic birefringence resin is appropriately selected in consideration of the characteristics of the liquid crystal display device and the convenience of polarizing plate processing. Can be used.

  Examples of the cyclic olefin copolymers that can be used in the present invention include resins obtained by polymerization of norbornene-based compounds. It may be a resin obtained by any polymerization method of ring-opening polymerization and addition polymerization.

  Examples of the addition polymerization and the resin obtained thereby include, for example, Japanese Patent No. 3517471, Japanese Patent No. 3559360, Japanese Patent No. 3867178, Japanese Patent No. 3871721, Japanese Patent No. 3907908, Japanese Patent No. 3945598, and Japanese Translation of PCT International Publication No. 2005-527696. JP-A-2006-28993, JP-A-2006-11361, International Publication WO 2006/004376, International Publication WO 2006/0307077, and the like. Among these, those described in Japanese Patent No. 3517471 are particularly preferable.

  Examples of the ring-opening polymerization and the resin obtained thereby include WO 98/144499, pamphlet, patent 30605532, patent 3220478, patent 373046, patent 334027, patent 3428176, patent. Examples described in Japanese Patent No. 3687231, Japanese Patent No. 3873934, and Japanese Patent No. 3912159. Of these, those described in International Publication WO 98- / 14499 pamphlet and Japanese Patent No. 30605532 are particularly preferable.

  Among these cyclic olefins, those obtained by addition polymerization are preferable from the viewpoints of birefringence and melt viscosity. For example, “TOPAS # 6013” (manufactured by Polyplastics) can be used.

  Examples of cellulose acylates that can be used in the present invention include any cellulose acylate in which three hydroxyl groups in a cellulose unit are at least partially substituted with acyl groups. The acyl group (preferably an acyl group having 3 to 22 carbon atoms) may be either an aliphatic acyl group or an aromatic acyl group. Among them, cellulose acylate having an aliphatic acyl group is preferable, those having an aliphatic acyl group having 3 to 7 carbon atoms are more preferable, those having an aliphatic acyl group having 3 to 6 carbon atoms are more preferable, and carbon number More preferably has 3 to 5 aliphatic acyl groups. A plurality of these acyl groups may be present in one molecule. Examples of preferred acyl groups include acetyl, propionyl, butyryl, pentanoyl, hexanoyl and the like. Among these, cellulose acylate having one or more selected from acetyl group, propionyl group and butyryl group is more preferable, and more preferable one has both acetyl group and propionyl group. Cellulose acylate (CAP). CAP is preferable in terms of easy resin synthesis and high stability of extrusion molding.

When producing an optical film by a melt extrusion method such as the method of the present invention, the cellulose acylate used preferably satisfies the following formulas (S-1) and (S-2). Cellulose acylate satisfying the following formula has a low melting temperature and improved meltability, and is therefore excellent in melt extrusion film formation.
Formula (S-1) 2.0 ≦ X + Y ≦ 3.0
Formula (S-2) 0.25 <= Y <= 3.0
In the formula, X represents the degree of substitution of the acetyl group with respect to the hydroxyl group of cellulose, and Y represents the sum of the degree of substitution of the acyl group with respect to the hydroxyl group of cellulose. The “degree of substitution” in the present specification means the total of the ratio of substitution of hydrogen atoms of hydroxyl groups at the 2-position, 3-position and 6-position of cellulose. When the hydrogen atoms of all hydroxyl groups at the 2nd, 3rd and 6th positions are substituted with acyl groups, the degree of substitution is 3.

Furthermore, it is more preferable to use a cellulose acylate that satisfies the following formula:
2.3 ≦ X + Y ≦ 2.95
1.0 ≦ Y ≦ 2.95
It is more preferable to use a cellulose acylate that satisfies the following formula.
2.7 ≦ X + Y ≦ 2.95
2.0 ≦ Y ≦ 2.9
There is no restriction | limiting in particular about the mass average polymerization degree and number average molecular weight of cellulose acylates. In general, the mass average degree of polymerization is about 350 to 800, and the number average molecular weight is about 70000 to 230,000. The cellulose acylates can be synthesized using acid anhydrides or acid chlorides as acylating agents. In the industrially most general synthesis method, cellulose obtained from cotton linter, wood pulp, etc. is converted into organic acids (acetic acid, propionic acid, butyric acid) corresponding to acetyl groups and other acyl groups, or their acid anhydrides (anhydrous anhydride). A cellulose ester is synthesized by esterification with a mixed organic acid component containing acetic acid, propionic anhydride, and butyric anhydride). As a method for synthesizing cellulose acylate satisfying the above formulas (S-1) and (S-2), the Technical Report of the Japan Society of Invention (Public Technical Number 2001-1745, published on March 15, 2001, Japan Society of Invention) 7 Pp. 12 to 12, JP-A-2006-45500, JP-A-2006-241433, JP-A-2007-138141, JP-A-2001-188128, JP-A-2006-142800, JP-A-2007. Reference can be made to the method described in Japanese Patent No. 98917.

  Examples of the polycarbonates usable in the present invention include polycarbonate resins having a bisphenol A skeleton, which are obtained by reacting a dihydroxy component and a carbonate precursor by an interfacial polymerization method or a melt polymerization method. Those described in 2006-277914, JP-A-2006-106386, and JP-A-2006-284703 can be preferably used. For example, “Taflon MD1500” (manufactured by Idemitsu Kosan Co., Ltd.) can be used as a commercial product.

  Examples of the styrene copolymer that can be used in the present invention include styrene-acrylonitrile resins, styrene-acrylic resins, and multi-component (binary, ternary, etc.) copolymer polymers thereof. Among these, styrene maleic anhydride resin is preferable from the viewpoint of film strength.

In the styrene maleic anhydride resin, the mass composition ratio of styrene and maleic anhydride is preferably styrene: maleic anhydride = 95: 5 to 50:50, and styrene: maleic anhydride = 90: 10 to 70. : 30 is more preferable. In order to adjust the intrinsic birefringence, hydrogenation of a styrene resin can be preferably used.
Examples of the styrene maleic anhydride resin include “Daylark D332” manufactured by Nova Chemical Co., Ltd.

  The acrylic copolymer of the present invention is a resin obtained by polymerizing styrene and acrylic acid, methacrylic acid and derivatives thereof, and derivatives thereof, and is not particularly limited as long as the effects of the present invention are not impaired.

  Among these resins, those containing 30 mol% or more of MMA units (monomer) among all monomers constituting the resin are preferable. In addition to MMA, at least one of a lactone ring unit, a maleic anhydride unit, and a glutaric anhydride unit More preferably, for example, the following units can be used.

(1) Acrylic resin containing a lactone ring unit JP2007-297615, JP2007-63541, JP2007-70607, JP2007-100044, JP2007-254726, JP2007-254727, JP2007- 261265, JP2007-293272, JP2007-297619, JP2007-316366, JP2008-9378, JP2008-76764, and the like can be used. Among these, the resin described in JP-A-2008-9378 is more preferable.

(2) Acrylic resins containing maleic anhydride units JP2007-113109, JP2003-292714, JP6-279546, JP2007-51233 (acid-modified vinyl described herein), JP2001-270905, JP-A-2002-167694, JP-A-2000-302988, JP-A-2007-111110, JP-A-2007-11565 can be used. Among these, the one described in JP-A-2007-113109 is more preferable. A commercially available maleic acid-modified MAS resin (for example, Delpet 980N manufactured by Asahi Kasei Chemicals Corporation) can also be preferably used.

(3) Acrylic resin containing glutaric anhydride units JP2006-241263, JP2004-70290, JP2004-70296, JP2004-126546, JP2004-163924, JP2004-291302, JP 2004-292812, JP 2005-314534, JP 2005-326613, JP 2005-331728, JP 2006-131898, JP 2006-134882, JP 2006-206881, JP 2006-241197, JP 2006-2006. 283013, JP 2007-118266, JP 2007-176982, JP 2007-178504, JP 2007-197703, JP 2008-74918, WO 2005/105918, and the like can be used. Of these, the one described in JP-A-2008-74918 is more preferable.

  The glass transition temperature (Tg) of these resins is preferably 106 ° C. or higher and 170 ° C. or lower, more preferably 110 ° C. or higher and 160 ° C. or lower, and further preferably 115 ° C. or higher and 150 ° C. or lower.

  As a commercial product, “Delpet 980N” (manufactured by Asahi Kasei Chemicals Corporation) can be used.

  The optical film of the present invention may contain a material other than the thermoplastic resin, but one or more of the thermoplastic resins as a main component (the most content ratio among all the materials in the composition). In the aspect which means a high material and contains 2 or more types of the said resin, it is preferable to contain as the content ratio of those sum total being higher than the content rate of each other material. Examples of materials other than the thermoplastic resin include various additives, and examples thereof include a stabilizer, an ultraviolet absorber, a light stabilizer, a plasticizer, fine particles, and an optical adjusting agent.

(Stabilizer)
The optical film of the present invention may contain at least one stabilizer. The stabilizer is preferably added before or when the thermoplastic resin is heated and melted. The stabilizer has effects such as preventing oxidation of the film constituting material, capturing an acid generated by decomposition, and suppressing or inhibiting a decomposition reaction caused by radical species caused by light or heat. Stabilizers are useful for suppressing the occurrence of alterations such as coloring and molecular weight reduction and the generation of volatile components due to various decomposition reactions including unresolved decomposition reactions. Even at the melting temperature for forming a resin film, the stabilizer itself is required to function without being decomposed. Typical examples of stabilizers include phenol-based stabilizers, phosphorous acid-based stabilizers (phosphite-based), thioether-based stabilizers, amine-based stabilizers, epoxy-based stabilizers, and lactone-based stabilizers. Stabilizers, amine stabilizers, metal deactivators (tin stabilizers) and the like are included. These are described in JP-A-3-199201, JP-A-5-1907073, JP-A-5-194789, JP-A-5-271471, JP-A-6-107854, and the like. Then, it is preferable to use at least one or more of a phenol-based or phosphorous acid-based stabilizer. Among phenolic stabilizers, it is particularly preferable to add a phenolic stabilizer having a molecular weight of 500 or more. Preferable phenolic stabilizers include hindered phenolic stabilizers.

These materials are readily available as commercial products and are sold by the following manufacturers. From Ciba Specialty Chemicals, Irganox 1076, Irganox 1010, Irganox 3113, Irganox 245, Irganox 1135, Irganox 1330, Irganox 259, Irganox 565, Irganx 565, Irganx 565, Ir35x10 Moreover, it can obtain from Asahi Denka Kogyo Co., Ltd. as ADK STAB AO-50, ADK STAB AO-60, ADK STAB AO-20, ADK STAB AO-70, and ADK STAB AO-80. Furthermore, from Sumitomo Chemical Co., Ltd., it can obtain as Sumilizer BP-76, Sumilizer BP-101, Sumilizer GA-80. In addition, it is also possible to obtain as Sinox 326M and Sinox 336B from Sipro Kasei Co., Ltd.

  Moreover, as said phosphorous acid type stabilizer, the compound as described in [0023]-[0039] of Unexamined-Japanese-Patent No. 2004-182979 can be used more preferably. Specific examples of the phosphite ester stabilizer include JP-A-51-70316, JP-A-10-306175, JP-A-57-78431, JP-A-54-157159, Examples thereof include compounds described in Japanese Utility Model Laid-Open No. 55-13765. Furthermore, as other stabilizers, the materials described in detail on pages 17 to 22 of the Japan Institute of Invention Disclosure Bulletin (Public Technical No. 2001-1745, issued March 15, 2001, Japan Society of Invention) are preferably used. be able to.

  The phosphite stabilizer is useful to have a high molecular weight in order to maintain stability at high temperature, has a molecular weight of 500 or more, more preferably a molecular weight of 550 or more, and particularly a molecular weight of 600 or more. Is preferred. Furthermore, at least one substituent is preferably an aromatic ester group. The phosphite ester stabilizer is preferably a triester, and is desirably free of impurities such as phosphoric acid, monoester and diester. When these impurities are present, the content is preferably 5% by mass or less, more preferably 3% by mass or less, and particularly 2% by mass or less. Examples thereof include compounds described in JP-A No. 2004-182979, [0023] to [0039], and JP-A Nos. 51-70316, 10-306175, and JP-A Nos. The compounds described in JP-A-57-78431, JP-A-54-157159, and JP-A-55-13765 can also be mentioned. Preferable specific examples of the phosphite stabilizer include the following compounds. However, phosphite ester stabilizers that can be used in the present invention are not limited to these.

  These are commercially available from Asahi Denka Kogyo Co., Ltd. as ADK STAB 1178, 2112, PEP-8, PEP-24G, PEP-36G, HP-10, and Sandostab P-EPQ from Clariant. Is possible. Furthermore, a stabilizer having phenol and phosphite in the same molecule is also preferably used. These compounds are further described in detail in JP-A-10-273494. Examples of the compounds are included in the examples of the stabilizer, but are not limited thereto. As a typical commercial product, Sumitizer GP is available from Sumitomo Chemical Co., Ltd. These are commercially available from Sumitomo Chemical Co., Ltd. as Sumilizer TPL, TPM, TPS, TDP. Also available from Asahi Denka Kogyo Co., Ltd. as ADK STAB AO-412S.

  The stabilizers can be used alone or in combination of two or more, and the blending amount thereof is appropriately selected within a range not impairing the object of the present invention. Preferably, the addition amount of the stabilizer is preferably 0.001 to 5% by mass, more preferably 0.005 to 3% by mass, and still more preferably 0.01 to 0% with respect to the mass of the thermoplastic resin. 0.8% by mass.

(UV absorber)
The optical film of the present invention may contain one type or two or more types of ultraviolet absorbers. From the viewpoint of preventing deterioration, the ultraviolet absorbent is preferably excellent in the ability to absorb ultraviolet light having a wavelength of 380 nm or less and has little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of transparency. Examples include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Particularly preferred ultraviolet absorbers are benzotriazole compounds and benzophenone compounds. Among these, a benzotriazole-based compound is preferable because unnecessary coloring with respect to the cellulose mixed ester is small. These are disclosed in JP-A-60-235852, JP-A-3-199201, 5-1907073, 5-194789, 5-271471, 6-107854, 6-118233, 6 -148430, 7-11056, 7-11055, 7-11056, 8-29619, 8-239509, and JP-A-2000-204173.
The addition amount of the ultraviolet absorber is preferably 0.01 to 2% by mass of the thermoplastic resin, and more preferably 0.01 to 1.5% by mass.

(Light stabilizer)
The optical film of the present invention may contain one or more light stabilizers. Light stabilizers include hindered amine light stabilizer (HALS) compounds, more specifically, US Pat. No. 4,619,956, columns 5-11 and US Pat. No. 4,839. 2,405, 2,2,6,6-tetraalkylpiperidine compounds, or their acid addition salts or complexes of them with metal compounds. These are commercially available from Asahi Denka as ADK STAB LA-57, LA-52, LA-67, LA-62, LA-77, and TINUVIN 765, 144 from Ciba Specialty Chemicals. .

  These hindered amine light stabilizers can be used alone or in combination of two or more. These hindered amine light stabilizers may of course be used in combination with additives such as plasticizers, stabilizers, UV absorbers, etc., or may be introduced into a part of the molecular structure of these additives. Good. The blending amount is determined within a range not impairing the effects of the present invention, and is generally about 0.01 to 20 parts by mass, preferably 0.02 to 15 parts per 100 parts by mass of the thermoplastic resin. About mass parts, and particularly preferably about 0.05 to 10 mass parts. The light stabilizer may be added at any stage of preparing the melt of the thermoplastic resin composition, for example, at the end of the melt preparation process.

(Plasticizer)
The optical film of the present invention may contain a plasticizer. The addition of a plasticizer is preferable from the viewpoint of film modification such as improvement of mechanical properties, imparting flexibility, imparting water absorption resistance, and reducing moisture permeability. Further, when the optical film of the present invention is produced by a melt film-forming method, the purpose is to lower the melting temperature of the film constituting material by adding a plasticizer rather than the glass transition temperature of the thermoplastic resin to be used. It will be added for the purpose of lowering the viscosity at the same heating temperature than the added thermoplastic resin. For the optical film of the present invention, for example, a plasticizer selected from a phosphoric acid ester derivative and a carboxylic acid ester derivative is preferably used. Further, a polymer obtained by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of 500 to 10,000 described in JP-A-2003-12859, an acrylic polymer, an acrylic polymer having an aromatic ring in the side chain, or cyclohexyl An acrylic polymer having a group in the side chain is also preferably used.

(Fine particles)
The optical film of the present invention may contain fine particles. Examples of the fine particles include fine particles of inorganic compounds and fine particles of organic compounds, and any of them may be used. The average primary particle size of the fine particles contained in the thermoplastic resin in the present invention is preferably 5 nm to 3 μm, more preferably 5 nm to 2.5 μm, more preferably 10 nm to 2.0 μm from the viewpoint of keeping haze low. More preferably. Here, the average primary particle size of the fine particles is determined by observing the thermoplastic resin with a transmission electron microscope (magnification of 500,000 to 1,000,000 times) and determining the average value of the primary particle sizes of 100 particles. The addition amount of the fine particles is preferably 0.005 to 1.0% by mass with respect to the thermoplastic resin, more preferably 0.01 to 0.8% by mass, and further preferably 0.02 to 0%. 4% by mass.

(Optical adjusting agent)
The optical film of the present invention may contain an optical adjusting agent. Examples of the optical adjusting agent include a retardation adjusting agent, for example, those described in JP-A Nos. 2001-166144, 2003-344655, 2003-248117, and 2003-66230. Can be used. By adding an optical adjusting agent, in-plane retardation (Re) and thickness direction retardation (Rth) can be controlled. A preferable addition amount is 0 to 10% by mass, more preferably 0 to 8% by mass, and further preferably 0 to 6% by mass.

(Method for adjusting Tg (glass transition temperature))
Regarding, for example, “TOPAS # 6013” (manufactured by Polyplastics), which is one of cyclic olefins, the glass transition temperature can be changed by changing the copolymer composition ratio of ethylene and norbornene.

  The glass transition temperature can be adjusted by blending resins having different glass transition temperatures. However, in the case of resins having greatly different compositions, the compatibility is poor and there is a risk that a single Tg will not be obtained. Therefore, it is preferable to blend resins having similar compositions and different glass transition temperatures.

  Moreover, Tg can be lowered by the plasticizer. For example, as described in JP-A-5-147980, as the plasticizer, monocyclic, bicyclic and tricyclic aromatic hydrocarbons are preferable. Specifically, Nisseki-Highsol-SAS-LH, Nisseki-Highsol -SAS-296, Aromi * 200P (sold from Nippon Petrochemical Co., Ltd.), Sunthene450 (manufactured by Sun Oil), Diana process oil AH-58 (manufactured by Idemitsu Kosan Co., Ltd.), and the like can be used.

  The Tg of cellulose acetate can be adjusted by using a phosphoric acid ester derivative, a carboxylic acid ester derivative or the like as a plasticizer. Examples of phosphate ester derivatives include triphenyl phosphate, tricresyl phosphate, phenyl diphenyl phosphate, and the like. Examples of the carboxylic acid ester derivatives include phthalic acid esters and citric acid esters. Examples of the phthalic acid ester derivatives include dimethyl phthalate, diethyl phthalate, dicyclohexyl phthalate, dioctyl phthalate, and diethyl hexyl phthalate. Can include acetyltriethyl citrate and acetyltributyl citrate.

  In addition, butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, triacetin, trimethylolpropane tribenzoate, alkylphthalylalkyl glycolate, and the like can also be mentioned. The amount of these compounds added is preferably in the range of 0.5% by mass to less than 20% by mass with respect to the resin in which the plasticizer constitutes the film.

  Examples of plasticizers for polycarbonate resins include aliphatic esters such as dioctyl sebacate, dioctyl adipate, diisononyl adipate, diisodecyl adipate, aromatic esters such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diisodecyl phthalate, dicyclohexyl phthalate, poly ( Plasticizers such as aliphatic polyesters such as 1,4-adipate), phosphate esters such as tricresyl phosphate, triphenyl phosphate, and phosphorus trichloride can be used.

  As a plasticizer for acrylic resin, polybasic compounds such as monocarboxylic acid esters of alkylene ether glycol, dibasic acid esters such as phthalic acid esters and adipic acid esters, citric acid esters, trimellitic acid esters, and pyromellitic acid esters Acid esters and phosphate esters can be used.

<Polarizing plate>
The present invention also relates to a polarizing plate having a polarizer and the film of the present invention. Examples of the polarizing plate of the present invention include a polarizing plate formed on the surface of a polarizing film for the purpose of two functions of a protective film and viewing angle compensation, or a composite polarizing plate laminated on a protective film such as TAC. Point to.

  As the polarizing film, for example, a polarizing film obtained by dyeing a polyvinyl alcohol film with iodine and stretching the film is used.

  It is preferable that a protective film is also attached to the other surface of the polarizing film, and the protective film may be the film of the present invention. Moreover, the various films conventionally used as a protective film of a polarizing plate, such as a cellulose acylate film and a cyclic polyolefin polymer film, can be used.

  The optical film and polarizing plate of the present invention can be used for liquid crystal display devices in various modes. Preferably, it can be used for a TN (twisted nematic), OCB (optically compensatory bend), or ECB (electrically controlled birefringence) mode liquid crystal display device, and more preferably for a TN or ECB mode liquid crystal display.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

  In the optical film manufacturing apparatus 10 shown in FIG. 1, a first thermoplastic resin composition 12 that becomes a core layer, a second thermoplastic resin composition 12 ′ that becomes a skin layer, and a third thermoplastic resin composition. An optical film was produced by forming a film 12B having birefringence by sandwiching a melt 12A of a thermoplastic resin 12A melt-extruded from a die 16 with a touch roll 28 and a casting roll 18. The optical properties of the obtained optical film were evaluated.

Production Example 1 Production of Cyclic Olefin Copolymer Pellets Pellets of “TOPAS # 6013” manufactured by Polyplastics were used as the cyclic olefin copolymer. “TOPAS # 6013” indicates positive intrinsic birefringence. The glass transition point of the resin was 136 ° C.

[Production Example 2] Production of cellulose acylate pellets Cellulose acetate cellulose acetate acetate propionate (CAP) was produced according to the method described in Example 1 of JP-A-2006-348123, and pelletized according to a conventional method. did. The composition of the CAP used is a positive intrinsic birefringence with an acetylation degree of 0.15, a propionylation degree of 2.60, a total acyl substitution degree of 2.75, and a number average polymerization degree of DPn = 118. The glass transition point of the resin was 137 ° C.

[Production Example 3] Production of polycarbonate pellets As polycarbonate, "Taflon MD1500" pellets made by Idemitsu Kosan Co., Ltd. were used. “Taflon MD1500” exhibits positive intrinsic birefringence. The glass transition point of the resin was 14.5 ° C.

[Production Example 4] Production of acrylic resin pellets As the acrylic resin, pellets of "Delpet 980N" manufactured by Asahi Kasei Chemicals Corporation, which is a styrene-acrylic copolymer, were used. “Delpet 980N” indicates negative intrinsic birefringence. The glass transition point of the resin was 123 ° C.

[Example 1]
(Production of film)
Using pellets of cyclic olefin copolymer TOPAS # 6013, drying is performed at 100 ° C. for 2 hours or more (water content 100 ppm or less), and the A layer is discharged at a discharge resin temperature of 260 ° C. using a φ30 mm single screw extruder. 0.35 kg / hour, B layer using a single screw extruder of φ50 mm, discharge resin temperature 260 ° C., discharge amount 6.3 kg / hour, C layer using a single screw extruder of φ30 mm, discharge resin temperature Melt extrusion was performed at 260 ° C., a discharge rate of 0.35 kg / hour, and a total discharge rate of layers A to C of 7 kg / hour. At this time, a screen filter (mesh size # 200), a gear pump, and a leaf disk filter (filtration accuracy 5 μm) are arranged in this order between the extruder and the die, and these are connected by a melt pipe and laminated in multiple layers using a feed block. This was extruded from a hanger coat type die having a width of 450 mm and a lip gap of 0.4 mm under the conditions shown in Table 1. Thereafter, a melt (molten resin) was extruded just in the center of the portion sandwiched between the cast roll and the chill roll. At this time, a cylinder was set on the most upstream side metal cast roll (chill roll) having a width of 1800 mm and a diameter of 400 mm so as to achieve the touch pressure shown in Table 1 below, and an HCr having a width of 200 mm and a diameter of 350 mm. A plated metal touch roll was brought into contact. The touch pressure was measured by sandwiching a prescale (manufactured by Fuji Film Co., Ltd.) between two rolls in the absence of melt, and the value was taken as the pressure applied to the melt during film formation. The roll temperature at the time of pressure measurement was 25 ° C., and the roll speed was 5 m / min. Using these rolls, the touch roll speed, the chill roll speed, and the peripheral speed ratio were set to the conditions shown in Table 1 below to form a film. The temperature of the touch roll and chill roll was set to Tg-15 ° C. of the outer layer (A layer, C layer), and the distance between the die and the melt landing point was set to 130 mm. The atmosphere of the film forming apparatus was 25 ° C. and 60%.

  Then, after trimming both ends (5 cm each of the total width) immediately before winding, a thickness increasing process (knurling) with a width of 10 mm and a height of 7 μm was applied to both ends. The film forming width was 200 mm, and the film was wound up by 500 m at a film forming speed of 10 m / min (chill roll speed). The thickness of the film after film formation was 30 μm, and the film of Example 1 was produced.

[Examples 2 to 26, Comparative Examples 1 and 2]
Optical films of Examples and Comparative Examples were obtained in the same manner as in Example 1 except that the resin used and the film forming conditions were changed as described in Table 1 below.

  In Example 21, the A layer was discharged using a single screw extruder of φ30 mm, the discharge amount was 0.35 kg / hour, the B layer was discharged using a φ50 mm single screw extruder, the discharge amount was 6.3 kg / hour, C Using a single screw extruder with a φ30 mm layer, the discharge rate was 0.35 kg / hour, and the total discharge rate of the A to C layers was 7 kg / hour. Example 22 was a single screw extruder with a φ30 mm layer A. Using a single screw extruder with a discharge rate of 0.21 kg / hour, B layer φ50 mm, a discharge rate of 6.3 kg / hour, using a single screw extruder with φ30 mm C layer, a discharge rate of 0.49 kg In Example 26, using a single screw extruder having a diameter of φ30 mm, a discharge resin temperature of 270 ° C., a discharge amount of 1.2 kg / hour, Using a single screw extruder of φ50 mm for layer B, the discharge resin temperature is 260 ° C., Using a single screw extruder with a discharge amount of 6.0 kg / hour and a C layer of φ30 mm, each discharge resin temperature is 270 ° C., the discharge amount is 1.2 kg / hour, and the total discharge amount of the A to C layers is 8.4 kg / hour. Under the conditions described above, melt extrusion was performed.

<Result>
With a composition having a specific Tg difference between the resins used for the outer layer (A layer, C layer) and the core layer (B layer), even when the film thickness is as thin as 30 μm, Re [0 °] and | Re [+ 40 ° ] -Re [-40 [deg.]] Was well expressed. On the other hand, when there is no Tg difference between the resins used for the outer layer (A layer, C layer) and the core layer (B layer), Re [0 °] and | Re [+ 40 °] −Re [−40] []] Was extremely small and the optical compensation performance was poor. On the other hand, when the Tg difference was too large, the expression of Re [0 °] and | Re [+ 40 °] −Re [−40 °] was good, but the heat resistance of the film was inferior.

  FIG. 5 shows film production conditions, (thermoplastic resin composition components, Tg of each layer, difference in Tg, linear pressure (nip) for Examples (1-26) and Comparative Examples (1-2) of the present invention. Pressure), shear force per meter, speed ratio of the first and second clamping surfaces, thickness ratio of the skin layer in the film, discharge rate per die unit area, film forming speed, roll type, roll surface properties Nip width, film thickness) and optical properties of the film (difference between Re [0 °], Re [40 °] −Re [−40 °], film heat resistance, film haze, comprehensive evaluation) and Are summarized in a list.

<Evaluation method>
Regarding the heat resistance of the film, after performing a dry thermo treatment at 80 ° C. for 100 hours, the deformation rate is within 0.3% for both MD and TD, and at least one is 0.3 to 0.5%. In some cases, Δ, and in the case where at least one exceeds 0.5%, ×. Regarding film haze, a case where it was 0.3% or less was evaluated as ◯, a case where it exceeded 0.3% and 1.0% or less was evaluated as Δ, and a case where it exceeded 1.0% was evaluated as ×. Regarding the overall evaluation, both the heat resistance and the film haze of the film are evaluated as ◯, and Re [0 °] is 90 to 300 nm, ◎, Re [0 °] is 80 to 90 nm, or the film A case where any one of heat resistance and film haze evaluation is Δ, and Re [0 °] is less than 80 nm, or any one of film heat resistance and film haze evaluation is × evaluation When there was x, it was set as x.

  From the table of FIG. 5, Examples 1 to 26 satisfying the conditions that the Tg of the core layer is 0.5 ° C. to 50 ° C. lower than the Tg of the skin layer and the nip pressure is 20 MPa to 500 MPa are all evaluated as ○ Got.

  On the other hand, in Comparative Example 1, since the difference in Tg between the core layer and the skin layer was 0, the overall evaluation was x. Since the difference of Tg of the core layer and the skin layer was 70 degreeC larger than 50 degreeC in the comparative example 2, evaluation of the heat resistance of a film and comprehensive evaluation were x.

DESCRIPTION OF SYMBOLS 10 ... Manufacturing apparatus, 12, 12 ', 12' '... Thermoplastic resin composition, 12A ... Melt, 12B ... Film, 14, 14', 14 "... Extruder, 16 ... Die, 18, 20, 22 DESCRIPTION OF SYMBOLS ... Casting roll, 24 ... Stripping roll, 26 ... Winding machine, 28 ... Touch roll, 34 ... Screw shaft, 36 ... Flight, 38 ... Single screw, 40 ... Supply port, 42 ... Discharge port, 44 ... Piping,

Claims (12)

A method for producing a film having at least a core layer and two skin layers on the outer layer of the core layer,
A step of melt-extruding a first composition containing a thermoplastic resin to be a core layer, a second composition containing a thermoplastic resin to be a skin layer, and a third composition from a die;
The melt-extruded melt is continuously sandwiched between a first sandwiching surface and a second sandwiching surface constituting the sandwiching device to form a film, and added to the melt by the sandwiching device. The pressure applied is 20 to 500 MPa,
The Tg of the first composition is, rather low the second composition and Tg than 0.5 ° C. to 50 ° C. of the third composition,
The film is characterized in that a shearing force of 3000 to 30000 N per 1 m width of the melt is imparted by making the moving speeds of the first clamping surface and the second clamping surface for clamping the melt different from each other . Production method. The method for producing a film according to claim 1, wherein the first pressing surface and the second pressing surface for pressing the melt are configured by a pair of rolls arranged to face each other. The method for producing a film according to claim 1 or 2 , wherein the second composition and the third composition have the same composition. The method for producing a film according to claim 3 , wherein the second composition and the third composition are supplied to the die from one extruder. The method for producing a film according to any one of claims 1 to 4 , wherein the thickness of the skin layer is 2% or more and 90% or less of the entire film thickness. The method for producing a film according to any one of claims 3 to 5 , wherein the pair of rolls are metal rolls. The arithmetic average height Ra of the pair of rolls is not more 100nm or less and, according to any of claims 3-6 the length of the melt to be pinched by the pair of rolls is less than greater 2mm than 0mm Film manufacturing method. Wherein the thermoplastic resin is a cyclic olefin copolymers, cellulose acylates, polycarbonates, styrene copolymers, to any one of claims 1 to 7 at least one selected from an acrylic copolymer The manufacturing method of the film of description. Film characterized by being manufactured by the method according to any one of claims 1-8. A film having at least a core layer and two skin layers on the outer layer of the core layer, wherein the Tg of the composition forming the core layer is 0.5 than the Tg of the composition forming the skin layer Retardation Re [+40] measured from a direction inclined by + 40 ° and a retardation Re [0 °] at a wavelength of 550 nm measured from the normal line in a plane including a film inclination direction and a film normal line And a retardation Re [−40 °] measured from a direction inclined by −40 ° with respect to the normal line satisfy both the following relational expressions (I) and (II).
80 nm ≦ Re [0 °] ≦ 300 nm (I)
60 nm ≦ | Re [+ 40 °] −Re [−40 °] | ≦ 300 nm (II) A polarizing plate comprising the film according to claim 9 . A film for a liquid crystal display panel, comprising the film according to claim 9 .

Images