JP5083774B2 - Film production method - Google Patents

Description

  The present invention relates to a method for producing an optical film used for a film, particularly a liquid crystal display device or the like.

  Polymer films (hereinafter referred to as “films”) are widely used as optical films because of their features such as excellent light transmission, flexibility, and reduction in weight. Among them, a TAC film formed from cellulose acylate, particularly cellulose triacetate (hereinafter referred to as TAC) having an average degree of acetylation of 57.5% to 62.5% is a photograph because of its toughness and flame retardancy. It is used as a film support for photosensitive materials. Moreover, since the TAC film is excellent in optical isotropy among polymer films, it is used as an optical film such as a protective film for a polarizing plate of a liquid crystal display device, an optical compensation film (for example, a viewing angle widening film). ing.

  Main film production methods include a melt extrusion method and a solution casting method. The melt extrusion method is a method in which a polymer is heated and dissolved as it is, and then extruded with an extruder to produce a film, which has features such as high productivity and relatively low equipment cost. However, it is difficult to adjust the accuracy of the film thickness, and fine streaks (die lines) can be formed on the film, which is not suitable for the optical film manufacturing method. On the other hand, in the solution casting method, after a cast film formed by casting a polymer solution containing a polymer and a solvent (hereinafter referred to as a dope) on a support has self-supporting properties, This is a method in which this is peeled off from the support to form a wet film, and the wet film is sufficiently dried and wound up as a film. This solution casting method is superior in isotropy and thickness uniformity of optical properties as compared to the melt extrusion method, and can obtain a film with less contained foreign substances. Therefore, as a method for producing a film, particularly an optical film, A solution casting method is employed.

In order to adjust the optical characteristics of the film, or to suppress the occurrence of wrinkles and tarmi, the wet film is dried and the both ends of the wet film in the width direction (hereinafter referred to as ears) are held with clips or the like. A tenter that extends in the width direction is known (for example, Patent Document 1).
JP 2004-160831 A

  However, when a film that has been stretched by a tenter is transported using a roller or the like, there are frequent failures that cause scratches on the surface of the film. In addition, when a film that has been stretched by a tenter is wound around a take-up roller, the film cannot be taken up evenly in the width direction of the film. As a result, a band-like mark is formed on the surface of the film taken up by the take-up roller. Many troubles occurred (hereinafter referred to as black belt failure), and the film wound on the winding roller collapsed.

  As a result of intensive studies, the inventor has found that by performing a predetermined treatment after the stretching treatment with a tenter, it is possible to suppress the occurrence of scratches on the surface of the film, black belt failure, and collapse. An object of this invention is to provide the manufacturing method of the film which manufactures a film, suppressing the generation | occurrence | production of the crack of a film surface, a black belt failure, and winding collapse.

The present invention includes a thermoplastic resin, gripping the ears at both ends of the long film in the width direction, and stretching the film in the width direction, and among the films that have undergone the stretching process In the product part excluding the ear part, when the temperature at both ends in the width direction is Te and the temperature at the center part in the width direction is Tc, the equation (1) is satisfied, and the temperature distribution of the product part is The distribution in the width direction of the amount by which the product portion contracts in the longitudinal direction due to the stretching after the distribution is such that the temperature gradually decreases from both ends in the width direction toward the center portion in the width direction, A grip releasing step of releasing the gripping of the ear portion so as to suppress the contraction in the longitudinal direction of the product portion caused by the temperature distribution.
Formula (1) 0 (° C.) <Te−Tc (° C.) ≦ 80 (° C.)

In the grip release step, when the glass transition temperature of the thermoplastic resin is Tg (° C.), the grip of the ear portion is released for the film satisfying the formulas (2) and (3). preferable.
Formula (2) 25 (° C.) ≦ Te (° C.) ≦ Tg−10 (° C.)
Formula (3) 25 (° C.) ≦ Tc (° C.) ≦ Tg−10 (° C.)

  In the grip releasing step, it is preferable that the both end portions in the width direction of the product portion are heated and the center portion in the width direction of the product portion is cooled, and then the grip of the ear portion is released. Further, in the grip releasing step, after the film is cooled by a cooling air having a distribution that increases in speed from both ends in the width direction toward the center in the width direction, the grip of the ear portion is released. It is preferable to do.

  It is preferable that the thermoplastic resin is cellulose acylate. The thermoplastic resin is preferably a saturated norbornene resin.

  It is preferable to perform the stretching step and the grip releasing step after the film wound on the winding core is taken out from the winding core. Also, a film forming step of forming a film on the support by discharging a dope containing the thermoplastic resin and a solvent onto the support, and the film having self-supporting properties from the support. It is preferable to perform the stretching step and the grip releasing step on the film peeled off from the support.

  According to the present invention, the film that has undergone the stretching process of grasping the ears at both ends in the width direction of the long film and extending in the width direction satisfies Expression (1), and the ears are removed from the film. Variation in the width direction of the amount of shrinkage of the product part in the longitudinal direction due to the stretching after the temperature distribution of the product part is made such that the temperature gradually decreases from the both ends in the width direction toward the center part in the width direction. In order to release the above-mentioned grip of the film so as to suppress the shrinkage in the longitudinal direction of the product portion due to the temperature distribution, the film is manufactured while suppressing the occurrence of scratches, black belt failure and collapse on the film surface. Can do.

(Offline stretching device)
As illustrated in FIG. 1, the offline stretching apparatus 10 includes a supply unit 11, a tenter unit 12, a heat relaxation unit 13, a cooling unit 14, and a winding unit 15. The supply unit 11 stores a film 20 that is manufactured by a solution casting method described later and is wound into a roll and wound around the core 21. The film 20 taken up by the winding core 21 is sent to the tenter unit 12 by the supply roller 22, and then sequentially sent to the heat relaxation unit 13, the cooling unit 14, and the winding unit 15. Predetermined processing is performed.

  As shown in FIGS. 2 and 3, the tenter unit 12 grips both end portions (hereinafter referred to as “ear portions”) 20 a of the film 20 and conveys the film 20 in the direction Z <b> 1, while the width direction Z <b> 2 of the film 20. The extending | stretching process which extends | stretches is performed. Details of the configuration of the tenter unit 12 and the stretching process will be described later.

  As shown in FIG. 1, an ear clip device 25 is provided between the tenter unit 12 and the thermal relaxation unit 13. The ear clip device 25 cuts the ear portion 20a (see FIG. 3) of the film 20. The cut ear is cut into small pieces by the cut blower 26. The cut ear portion is sent to the crusher 27 by an air feeding device (not shown) and crushed into chips.

  A number of rollers 28 are provided in the heat relaxation unit 13, and the film 20 is conveyed to the cooling unit 14 by these rollers 28. Moreover, in the thermal relaxation part 13, dry wind is sprayed with respect to the film 20 in conveyance. In the cooling unit 14, the film 20 is cooled to a predetermined temperature. The cooled film 20 is sent to the winding unit 15. A winding roller 30 and a press roller 31 are provided in the winding unit 15, and the film 20 is wound around the winding roller 30 while being pressed by the press roller 31.

(Tenter part)
As shown in FIGS. 2 and 3, the tenter unit 12 is partitioned into a preheating area 36, an extension area 37, a relaxation area 38 and a cooling area 39 in order from the upstream side in the direction Z <b> 1. The relaxation area 38 may be omitted.

  The tenter unit 12 includes a clip 40, rails 41 and 42, a duct 43, and an air supply unit 45. The rails 41 and 42 are installed on both sides of the transport path of the film 20, and the rails 41 and 42 are separated by a predetermined rail width. This rail width is constant at the width L1 in the preheating area 36, gradually increases from the width L1 to the width L2 in the extending area 37 in the direction Z1, and in the relaxation area 38, from the width L2 to the width L3 in the direction Z1. The cooling area 39 has a constant width L3.

  A chain (not shown) is movably attached along the rails 41 and 42. The plurality of clips 40 are attached to the entire chain at a predetermined interval. In FIG. 3, only a part of the clip 40 is shown to avoid complication of the drawing. The chain meshes with sprockets 48 and 49. As the sprockets 48 and 49 rotate, the clip 40 moves along the rails 41 and 42. On the upstream side in the Z1 direction of the preheating area 36, grip start means (not shown) for starting gripping of the ear portion of the film 20 by the clip 40 is provided, and on the downstream side in the Z1 direction of the cooling area 39, the film by the clip 40 is provided. A grip releasing means (not shown) for releasing the grip of the 20 ears is provided. As the clip 40 moves along the rails 41 and 42, the film 20 is conveyed in the Z2 direction, sequentially passes through the areas 36 to 39, and predetermined processing is performed in the areas 36 to 39.

  As shown in FIGS. 2 and 4, the duct 43 is provided above the transport path of the film 20. The interval between the duct 43 and the transport path of the film 20 is substantially constant. On the lower surface of the duct 43, slits 53 are formed so as to extend in the Z2 direction, and a plurality of the slits 53 are provided at predetermined intervals in the Z1 direction. Further, the inside of the duct 43 is partitioned into first to fourth air supply chambers 43 a to 43 d by a partition plate 54. In FIG. 2, a plurality of slits 53 are provided in the first and second air supply chambers 43a and 43b, and one slit 53 is provided in the third and fourth air supply chambers 43c and 43d. However, the first supply chamber 43a and the second supply chamber 43b may be provided with one slit 53, and the third supply chamber 43c and the fourth supply chamber 43d may be provided with a plurality of slits 53.

  The air supply unit 45 supplies air to the first to fourth supply chambers 43 a to 43 d of the duct 43. The air supplied to the first to fourth supply chambers 43a to 43d is adjusted to a temperature within a predetermined range by a temperature controller (not shown). The air in the first to fourth supply chambers 43 a to 43 d becomes wind 56 to 59 and is blown against the film 20 passing through the areas 36 to 39 through the slits 53.

  In the cooling area 39, a pair of heating devices 63 are provided between the transport path of the film 20 and the duct 43 upstream of the sprocket 49 in the Z1 direction. The pair of heating devices 63 have a heat generating portion 64 on the lower surface, and are provided at both ends in the Z2 direction on the transport path of the film 20. Further, the distance between the heat generating portion 64 and the transport path of the film 20 is substantially constant. Here, if the part of the film 20 excluding the ear part 20a is the product part 20b, the product end part 20e on both sides in the Z2 direction of the product part 20b passing through the cooling area 39 is opposed to the heat generating part 64. The portion of the product portion 20b excluding the product end portion 20e, that is, the product central portion 20c faces the slit 53 (see FIG. 2) of the duct 43. The product end portion 20e refers to a region in which the length in the Z2 direction is 5% or more and 10% or less of the length in the Z2 direction of the entire product portion 20b.

  Next, the operation of the present invention will be described. As shown in FIG. 1, the supply roller 22 sends the film 20 that has been rolled up and taken up by the winding core 21 to the tenter unit 12. As shown in FIG. 3, the film 20 sent to the tenter unit 12 is sent to the preheating area 36. On the upstream side in the Z1 direction of the preheating area 36, the clip 40 traveling along the rails 41 and 42 grips the ear portion 20a of the film 20 by gripping start means (not shown). The clip 40 travels in the Z1 direction while grasping the ear portion 20a, so that the film 20 sequentially passes through the preheating area 36, the stretching area 37, the relaxation area 38, and the cooling area 39 from the upstream side in the Z1 direction. The film 20 that has passed through the tenter unit 12 is cut at the ear part 20a by the ear-cutting device 25, and the product part 20b becomes the film 20, and is sent to the winding part 15 through the heat relaxation part 13 and the cooling chamber 14.

  As shown in FIG. 2, the air supplied to the duct 43 by the air supply unit 45 becomes wind 56 to 59 through the slit 53 and blows against the film 20 passing through the areas 36 to 39. It is done. Thereby, the temperature of the film 20 in the preheating area 36 and the extending | stretching area 37 rises until it becomes in a predetermined range. In the relaxation area 38 and the cooling area 39, the temperature of the film 20 decreases until it falls within a predetermined range.

  As shown in FIG. 3, the film 20 passes through the preheating area 36 with the length in the Z2 direction being L1. Thereafter, in the stretching area 37, the film 20 is stretched. By the stretching process, the film 20 is given a tension in the Z2 direction, and the length in the Z2 direction gradually increases from L1 to L2. The residual solvent amount of the film 20 passing through the stretching area 37 is preferably 0% by weight or more and 3% by weight or less. The amount of residual solvent in the film 20 is determined by taking the sample film from the target film, x is the weight of the sample film at the time of collection, and y is the weight after drying the sample film {(xy) / y} × 100.

  In the relaxation area 38, the film 20 is subjected to a relaxation process. The stress remaining in the film 20 is removed by the relaxation treatment, and the length of the film 20 in the Z2 direction gradually decreases from L2 to L3. Thereafter, the film 20 passes through the cooling area 39 with the length in the Z2 direction being L3. The width L3 is preferably not less than 500 mm and not more than 4000 mm. The residual solvent amount of the film 20 that passes through the cooling area 39 is preferably 0 wt% or more and 3 wt% or less.

  As shown in FIG. 4, the heat generating unit 64 is heated to a predetermined temperature under the control of a control unit (not shown). Of the film 20 passing through the cooling area 39, the product end 20 e is heated by the heat generating part 64 provided in the heating device 63. On the other hand, in the film 20 that passes through the cooling area 39, the product center portion 20 c is cooled by the wind 59. Thereafter, gripping by the clip 40 is released by gripping release means (not shown).

  As shown in FIG. 5A, in the stretching area 37, the necking phenomenon occurs in the film 20 by the stretching process, and the shrinkage amount X1 in the Z1 direction of the film 20 before and after the stretching process is caused by the clip 20 as indicated by the dotted line C1. The distance increases from the both ends of the gripped Z2 direction toward the central portion that is not gripped by the clip 40. On the other hand, the shrinkage amount X2 in the Z1 direction before and after the clip 40 is released increases as the temperature of the film 20 increases, and decreases as the temperature of the film 20 decreases. Therefore, the temperature distribution in the Z2 direction is substantially uniform. When the gripping of the clip 40 (see FIG. 3) is released in this state, the contraction amount X2 becomes substantially constant in the Z2 direction. As a result, the product end 20e extends in the Z1 direction compared to the product center 20c. (Hereinafter referred to as “ear extension”).

  When the film 20 in the state of extending the ears is guided to the thermal relaxation portion 13 or the like, the center portion of the film 20 comes into contact with the peripheral surface of the roller 28, but both ends of the film 20 come into contact with the peripheral surface of the roller 28. As a result, the holding force on the circumferential surface of the roller 28 is reduced, and as a result, the roller 28 idles or the both ends of the film 20 flutter on the circumferential surface of the roller 28. Will occur. In addition, when the film 20 in the state of extending the ears is guided to the winding unit 15, only the central portion in the Z1 direction of the film 20 is wound, so that the wound film 20 has a band-like mark. A so-called black belt failure occurs, and in addition, it becomes difficult to wind both ends in the Z1 direction with a sufficient tension, and as a result, the roll is likely to collapse.

In the present invention, in the film 20 before releasing the grip of the clip 40, the temperature of the product center portion 20 c is set to Tc and the temperature of the product end portion 20 e is set to Te by the duct 43 and the heating device 63 provided in the cooling area 39. When satisfying the formula (1), the temperature distribution of the product portion 20b is set to be a distribution that becomes lower from the both end portions in the Z2 direction toward the central portion.
Formula (1) 0 (° C.) <Te−Tc (° C.) ≦ 80 (° C.)

  In the film 20 having such a temperature distribution, by releasing the gripping of the clip 40, the shrinkage amount X2 of the product portion 20b is caused by this temperature distribution, that is, in the Z2 direction, as shown in FIG. It becomes small as it goes to the center from both ends. In the present invention, since the clip 40 is released after the temperature distribution of the product portion 20b is adjusted to a predetermined distribution, the fluctuation in the Z2 direction of the shrinkage amount X1 due to the stretching process is caused by the temperature distribution. Since the shrinkage amount X2 can be suppressed, that is, the ear elongation of the film 20 can be suppressed, and the occurrence of scratches on the surface of the film 20, black belt failure, and collapse caused by the ear elongation can be suppressed.

  When the value of (Te−Tc) is less than 0 ° C., it is not preferable because ear elongation occurs. Further, when the value of (Te−Tc) exceeds 80 ° C., the length Lc becomes longer than the length Le, which is not preferable. Therefore, the lower limit of (Te−Tc) is preferably 2 ° C. or higher, and more preferably 5 ° C. or higher. Moreover, it is preferable that the upper limit of (Te-Tc) is 60 degrees C or less, It is more preferable that it is 40 degrees C or less, It is still more preferable that it is 30 degrees C or less.

  The temperature distribution of the film 20 immediately before the clip 40 is released may be determined according to the stretching ratio ER in the stretching process or the relaxation ratio RR in the relaxation process. The stretch ratio ER (%) is represented by (L2-L1) / L1 × 100, and the relaxation ratio RR (%) is represented by (L3-L2) / L2 × 100. The stretching ratio ER is preferably greater than 0% and not greater than 400%. The relaxation rate RR is preferably greater than 0% and 10% or less.

  In the film 20, if the length in the direction Z1 in the vicinity of the center portion in the Z2 direction in the product center portion 20c is Lc, and the length in the direction Z1 in the vicinity of the center portion in the Z2 direction in the product end portion 20e is Le, The value of Le is preferably 0.98 or more and 1.02 or less. The value of Lc / Le is more preferably 0.99 or more and 1.01 or less, more preferably 0.995 or more and 1.005 or less, and 0.998 or more and 1.002 or less. Is more preferable. When the value of Lc / Le is less than 0.98 or more than 1.02, the film 20 is in an ear stretched state, and the surface of the film 20 is scratched, black belt failure and roll-down are not preferable.

  In the film 20 before being introduced into the tenter unit 12, the length Lc takes a first point on the product center 20c and a second point that is separated from the first point by x in the direction Z1. Sometimes, in the film 20 sent out from the tenter unit 12, the distance in the direction Z1 between the first point and the second point. In the same manner as the length Lc, the length Le is also separated from the first point on the product end 20e by x in the direction Z1 on the product end 20e in the film 20 before being introduced into the tenter unit 12. In the film 20 sent out from the tenter unit 12 when the second point is taken, the distance in the direction Z1 between the first point and the second point.

Moreover, in the film 20 just before releasing the clip 40, it is preferable to satisfy the expressions (2) to (3). Furthermore, the upper limit of the temperatures Tc and Te is preferably (Tg-10) ° C. or lower, and (Tg-30) ° C. or lower, in order to maintain the retardation Re and Rth adjusted by the stretching treatment. More preferably, it is more preferably (Tg-40) ° C. or less, and particularly preferably (Tg-50) ° C. or less. Retardation Re is expressed by | n1-n2 | · d, where n1 and n2 are the refractive indexes in the Z1 and Z2 directions of the film, and d is the film thickness. The retardation Rth is represented by {(n1 + n2) / 2−n3} · d, where n3 is the refractive index in the thickness direction of the film.
Formula (2) 25 (° C.) ≦ Te (° C.) ≦ Tg−10 (° C.)
Formula (3) 25 (° C.) ≦ Tc (° C.) ≦ Tg−10 (° C.)

  Although the duct 43 is provided above the transport path of the film 20, it may be provided below the transport path of the film 20 or may be provided above and below the transport path of the film 20. When the duct 43 is provided below the conveyance path of the film 20, a slit 53 is provided on the upper surface of the duct 43, and a heating device having a heat generating part on the upper surface may be provided between the duct 43 and the conveyance path of the film 20. Good.

  In the above embodiment, a pair of heating devices 63 are provided, but the present invention is not limited to this, and a plurality of heating devices 63 are arranged in the Z2 direction, and from the both ends of the product portion 20b in the Z2 direction toward the center, The temperature of the heat generating part 64 may be lowered. Further, the heat generating portions 64 may be arranged so that the clearance between the heat generating portions 64 and the film 20 increases from both ends in the Z2 direction toward the center, and the temperatures of these heat generating portions 64 may be made substantially uniform.

  In the above embodiment, the product end portion 20e is heated using the heating device 63, but the present invention is not limited to this, and the temperature of the product portion 20b becomes a distribution that decreases from the both end portions in the Z2 direction toward the central portion. Any method may be used as long as it can be used. For example, when the slit is provided so as to face the entire product portion 20b, a part of the slit facing the product end portion 20e may be closed with a wind shielding member. Moreover, you may provide a slit so that only the product center part 20c may be opposed.

  In the above embodiment, the temperature distribution of the product portion 20b in the film 20 is made lower as it goes from the both end portions in the Z2 direction toward the central portion. However, the present invention is not limited to this, and the film fed from the tenter portion 12 is used. 20, when carrying out roller conveyance or winding without cutting the ear part 20 a, the temperature distribution of the film 20 is lowered from the both end parts in the Z2 direction toward the central part, The grip may be released.

  In the above embodiment, in order to adjust the temperature of the film 20 in each of the areas 36 to 39, the winds 56 to 59 in which the temperature is adjusted within a predetermined range are applied to the film 20, but the present invention is not limited to this. Alternatively, the air may be applied to the film 20 with the air 56 to 59 having the temperature and gas dew point adjusted within a predetermined range to adjust the temperature of the film 20 and the solvent may be evaporated from the film 20.

  In the above embodiment, the wind 59 is applied only to the product center portion 20c, but the wind 59 may be applied to the product center portion 20c and the product end portion 20e. For example, in the duct 43 shown in FIG. 2, a partition plate is provided in the fourth supply chamber 43d, and a plurality of supply chambers are provided in the Z1 direction. And an air blower is provided in each air supply chamber. A blower provided in each air supply chamber is adjusted by a control unit (not shown) so that the wind speed distribution of the wind 59 increases from both ends of the film 20 in the Z2 direction toward the center. Since the speed of the wind 59 that hits the product part 20b becomes a distribution that increases as it goes from the both ends of the Z2 direction to the center part, the temperature distribution of the product part 20b decreases as it goes from the both ends of the Z2 direction to the center part. After the distribution is reached, the gripping of the clip 40 may be released.

  The present invention can be applied to the solution casting method performed in the solution casting equipment 80 shown in FIG. In addition, about the apparatus and member same as the said embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted. The solution casting apparatus 80 includes a stock tank 81, a casting chamber 82, a pin tenter 112, a tenter unit 12, a drying chamber 83, a cooling chamber 14, and a winding unit 15.

  The stock tank 81 includes a stirring blade 81b that is rotated by a motor 81a and a jacket 81c, and a dope 91 that is a raw material for the film 20 is stored therein. The dope 91 in the stock tank 81 is adjusted so that the temperature becomes substantially constant by the jacket 11c. Also, the rotation of the stirring blade 81b keeps the dope 91 in a uniform quality while suppressing the aggregation of polymers and the like. doing. A gear pump 92 and a filtration device 93 are installed downstream of the stock tank 81, and the dope 91 is sent to the casting die 95 via these.

  In the casting chamber 82, a casting die 95, a casting drum 96 as a support, a peeling roller 97, temperature control devices 98 and 99, and a decompression chamber 100 are installed. The casting drum 96 is rotated in the A1 direction about the shaft 96a by a driving device (not shown). The dope 91 is discharged from the casting die 95 toward the circumferential surface of the rotating casting drum 96, and a casting film 103 is formed on the circumferential surface of the casting drum 96.

  The temperature in the casting chamber 82 and the casting drum 96 is set to a temperature at which the casting film 103 is easily cooled and solidified (gelled) by the temperature control devices 98 and 99. Then, while the casting drum 96 rotates about 3/4, the casting film 103 reaches a gel strength having self-supporting properties, and is peeled off from the casting drum 96 by the peeling roller 97 to become a wet film 104. .

  The decompression chamber 100 is arranged on the upstream side in the A1 direction with respect to the casting die 95, and maintains the inside of the decompression chamber 100 at a negative pressure. As a result, the back side of the casting bead (the surface that comes into contact with the circumferential surface of the casting drum 96 later) is reduced to a desired pressure, and the influence of the accompanying wind generated by the casting drum 96 rotating at high speed is reduced. Then, a stable casting bead is formed between the casting die 95 and the casting drum 96, and the casting film 103 with little film thickness unevenness is formed.

  The material of the casting die 95 is formed of a material having a high corrosion resistance against a mixed solution such as an electrolyte aqueous solution, dichloromethane or methanol, and a low coefficient of thermal expansion. It is preferable to use a finishing precision of the wetted surface of the casting die 95 with a surface roughness of 1 μm or less and a straightness of 1 μm / m or less in any direction.

  The peripheral surface of the casting drum 96 is chrome-plated and has sufficient corrosion resistance and strength. Further, the temperature control device 99 circulates the heat transfer medium through the casting drum 96 in order to keep the temperature of the peripheral surface of the casting drum 96 at a desired temperature. The heat transfer medium is maintained at a desired temperature, and the temperature of the peripheral surface of the casting drum 96 is maintained at the desired temperature by passing through the heat transfer medium flow path in the casting drum 96.

  The width of the casting drum 96 is not particularly limited, but it is preferable to use a casting drum having a width in the range of 1.1 to 2.0 times the casting width of the dope. The material of the casting drum 96 is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength. The chromium plating treatment applied to the peripheral surface of the casting drum 96 is preferably so-called hard chromium plating with a Vickers hardness of Hv 700 or more and a film thickness of 2 μm or more.

  In the casting chamber 82, a condenser (condenser) 109 for condensing and recovering the evaporated organic solvent and a recovery device 110 for recovering the condensed and liquefied solvent are provided. The organic solvent condensed and liquefied by the condenser 109 is recovered by the recovery device 110. The recovered solvent is regenerated by a regenerator and then reused as a dope preparation solvent.

  On the downstream side of the casting chamber 82, a crossover part 111, a pin tenter 112, and a tenter part 12 are installed in this order. In the transfer section 111, the wet film 104 is introduced into the pin tenter 112 using the transport roller 113. The pin tenter 112 has a large number of pin plates that pass through and hold both ends of the wet film 104, and the pin plates travel on a track. During the traveling, the drying air is sent to the wet film 104, and the wet film 104 is dried while traveling to become the film 20.

  The wet film 104 is preferably dried with a pin tenter 112 until the residual solvent amount is 0.1 wt% or more and 10 wt% or less. The cast film 103 is peeled off when the residual solvent amount is in the range of 150 wt% or more and 320 wt% or less, and dried by the pin tenter 112 until the residual solvent amount falls within the above range, whereby cellulose acylate molecules in the tenter section 12 are obtained. Is more effectively controlled. That is, the effect of controlling the direction of the slow axis, the effect of increasing Re and Rth, and the effect of improving optical unevenness in the stretching process in the tenter unit 12 are enhanced. However, in the present invention, drying with the pin tenter 112 may not be performed until the residual solvent amount falls within the above range. That is, the wet film 104 having a residual solvent amount higher than 10% by weight may be fed into the tenter unit 12.

  In the drying chamber 83, the film 20 is dried by applying a drying air of 50 ° C. or more and 200 ° C. or less to the film 20. In the drying chamber 83, it is preferable to dry the film 20 until the residual solvent amount becomes 0.01 wt% or more and 5 wt% or less.

  Although the tenter unit 12 is provided between the pin tenter 112 and the drying chamber 83, the present invention is not limited to this, and the tenter unit 12 may be provided between the cooling chamber 14 and the winding unit 15. The tenter unit 12 may be provided both between the 112 and the drying chamber 83 and between the cooling chamber 14 and the winding unit 15.

  The film 20 of the present invention is not limited to the film obtained by the solution casting method as described above, but also includes a film obtained by the melt casting method.

(polymer)
Hereinafter, the polymer used when preparing the dope 91 in the present invention will be described. It is preferable to use a thermoplastic resin as the polymer. Moreover, as a thermoplastic resin, it is preferable to use a cellulose acylate, cyclic polyolefin, etc., for example.

(Cellulose acylate)
As the cellulose acylate, cellulose triacetate (TAC) is particularly preferable. Among the cellulose acylates, the substitution degree of the acyl group to the hydroxyl group of cellulose is represented by the following formulas (I) to (III), and A and B represent the substitution degree of the acyl group with respect to the hydrogen atom in the hydroxyl group of cellulose. , A is the degree of substitution of the acetyl group, and B is the degree of substitution of the acyl group having 3 to 22 carbon atoms. In addition, it is preferable that 90 weight% or more of TAC is a particle | grain of 0.1-4 mm. However, the polymer that can be used in the present invention is not limited to cellulose acylate.
(I) 2.5 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9

  Glucose units having β-1,4 bonds constituting cellulose have free hydroxyl groups at the 2nd, 3rd and 6th positions. Cellulose acylate is a polymer obtained by esterifying some or all of these hydroxyl groups with an acyl group having 2 or more carbon atoms. The degree of acyl substitution means the ratio at which the hydroxyl group of cellulose is esterified at each of the 2-position, 3-position and 6-position (the substitution degree is 1 in the case of 100% esterification).

  The total degree of acylation substitution, that is, the value of DS2 + DS3 + DS6 is preferably 2.00 to 3.00, more preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88. Further, the value of DS6 / (DS2 + DS3 + DS6) is preferably 0.28, more preferably 0.30 or more, and particularly preferably 0.31 to 0.34. Here, DS2 is a ratio in which the hydrogen of the hydroxyl group at the 2-position in the glucose unit is substituted by an acyl group (hereinafter referred to as “acyl substitution degree at the 2-position”), and DS3 is the hydroxyl group at the 3-position in the glucose unit. The hydrogen is substituted with an acyl group (hereinafter referred to as “acyl substitution degree at the 3-position”), and DS6 is the ratio of the hydrogen at the 6-position hydroxyl group substituted with an acyl group (hereinafter referred to as “acyl substitution degree at the 3-position”). "The 6-position acyl substitution degree").

  Only one type of acyl group may be used in the cellulose acylate of the present invention, or two or more types of acyl groups may be used. When two or more kinds of acyl groups are used, it is preferable that one of them is an acetyl group. The sum of the degree of substitution of hydroxyl groups at the 2nd, 3rd and 6th positions by acetyl groups is DSA, and the sum of the degree of substitution of the hydroxyl groups at the 2nd, 3rd and 6th positions by acyl groups other than acetyl groups When DSB is DSB, the value of DSA + DSB is preferably 2.22 to 2.90, and particularly preferably 2.40 to 2.88.

  The DSB is preferably 0.30 or more, particularly preferably 0.7 or more. Further, 20% or more of DSB is preferably a substituent of a hydroxyl group at the 6-position, more preferably 25% or more, further preferably 30% or more, and particularly preferably 33% or more. Further, the DSA + DSB value at the 6-position of the cellulose acylate is 0.75 or more, more preferably 0.80 or more, and particularly preferably cellulose acylate of 0.85 or more. By using it, a dope with better solubility can be produced. In particular, when a non-chlorine organic solvent is used, a dope having excellent solubility, low viscosity and excellent filterability can be produced.

  Cellulose, which is a raw material for cellulose acylate, may be obtained from either linter or pulp.

  The acyl group having 2 or more carbon atoms of cellulose acylate in the present invention may be an aliphatic group or an aryl group, and is not particularly limited. For example, cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, aromatic alkylcarbonyl ester and the like may be mentioned, and each may further have a substituted group. Preferred examples of these include propionyl group, butanoyl group, pentanoyl group, hexanoyl group, octanoyl group, decanoyl group, dodecanoyl group, tridecanoyl group, tetradecanoyl group, hexadecanoyl group, octadecanoyl group, iso-butanoyl group , T-butanoyl group, cyclohexanecarbonyl group, olenoyl group, benzoyl group, naphthylcarbonyl group, cinnamoyl group and the like. Among these, a propionyl group, a butanoyl group, a dodecanoyl group, an octadecanoyl group, a t-butanoyl group, an oleoyl group, a benzoyl group, a naphthylcarbonyl group, a cinnamoyl group, and the like are more preferable, and a propionyl group and a butanoyl group are particularly preferable. It is.

  Solvents for preparing the dope include aromatic hydrocarbons (eg, benzene, toluene, etc.), halogenated hydrocarbons (eg, dichloromethane, chlorobenzene, etc.), alcohols (eg, methanol, ethanol, n-propanol, n-butanol, Diethylene glycol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl acetate, ethyl acetate, propyl acetate, etc.) and ethers (eg, tetrahydrofuran, methyl cellosolve, etc.).

  Among the above halogenated hydrocarbons, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. From the viewpoint of physical properties such as solubility of TAC, peelability of cast film from the support, mechanical strength and optical properties of the film, one or several kinds of alcohols having 1 to 5 carbon atoms are mixed in addition to dichloromethane. It is preferable. The content of alcohol is preferably 2 to 25% by weight, more preferably 5 to 20% by weight, based on the entire solvent. Examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, and n-butanol, but methanol, ethanol, n-butanol, or a mixture thereof is preferably used.

  Recently, a solvent composition that does not use dichloromethane has been studied for the purpose of minimizing the impact on the environment. In this case, an ether having 4 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and an alcohol having 1 to 12 carbon atoms are preferable. Sometimes used. For example, a mixed solvent of methyl acetate, acetone, ethanol, and n-butanol can be mentioned. These ethers, ketones, esters and alcohols may have a cyclic structure. In addition, a compound having two or more functional groups of ether, ketone, ester, and alcohol (that is, —O—, —CO—, —COO—, and —OH) can also be used as a solvent.

  Details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148, and these descriptions can also be applied to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, UV absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents, release accelerators and the like. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516], and these descriptions can also be applied to the present invention.

(Cyclic polyolefin)
A particularly preferred cyclic polyolefin will be described. The cyclic polyolefin in the present invention is a polymer having a cyclic olefin structure. Examples thereof include (1) a norbornene-based polymer, (2) a monocyclic olefin polymer, and (3) a cyclic conjugated diene. Polymers, (4) vinyl alicyclic hydrocarbon polymers, and hydrides of (1) to (4). A polymer preferable for the present invention further includes an addition (co) polymer cyclic polyolefin containing at least one repeating unit represented by the following chemical formula 2 and at least one repeating unit represented by the chemical formula 1. Is an addition (co) polymer cyclic polyolefin. Further, a ring-opening (co) polymer containing at least one cyclic repeating unit represented by Chemical formula 3 can also be suitably used.

In each formula in Chemical Formulas 1 to 3, m represents an integer of 0 to 4. R ^{1 to} R ⁶ are a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, and X ^{1 to} X ³ and Y ^{1 to} Y ³ are a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, and a halogen atom. , a hydrocarbon group having 1 to 10 carbon atoms substituted with a halogen ^{_{atom, - (CH 2) n COOR}} 11, - (CH 2) n OCOR 12, - (CH 2) n NCO, - (CH 2) n NO ₂ , — (CH ₂ ) _n CN, — (CH ₂ ) _n CONR ¹³ R ¹⁴ , — (CH ₂ ) _n NR ¹³ R ¹⁴ , — (CH ₂ ) _n OZ, — (CH ₂ ) _n W, or (—CO) ₂ O and (—CO) ₂ NR ¹⁵ composed of X ¹ and Y ¹ or X ² and Y ² or X ³ and Y ³ are shown. R ^{11 to} R ¹⁵ are a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, Z is a hydrocarbon group or a hydrocarbon group substituted with halogen, and W is SiR ¹⁶ _p D _3-p (R ¹⁶ is A hydrocarbon group having 1 to 10 carbon atoms, D is a halogen atom —OCOR ¹⁶ or —OR ¹⁶ , p is an integer of 0 to 3), and n is an integer of 0 to 10.

By introducing a polarizable large functional group in a substituent ^{X 1 ~X 3, Y 1 ~Y} 3, it is possible to increase the thickness direction retardation of the film (Rth), in-plane retardation ( The expression of Re) can be increased. A film having high Re and Rth expression can increase the Re value and the Rth value by stretching the film during the film production process.

  Norbornene-based addition (co) polymers are disclosed in JP-A-10-7732, JP-T 2002-504184, US2004229157A1, WO2004 / 070463A1, and the like. It can be obtained by addition polymerization. If necessary, it can also be obtained by addition polymerization of a norbornene-based polycyclic unsaturated compound and the following diene compound. Examples of the diene compound include conjugated dienes, non-conjugated dienes, and linear diene compounds. Examples of the conjugated diene compound include ethylene, propylene, butene, butadiene, and isoprene. An example of the non-conjugated diene compound is ethylidene norbornene. Examples of the linear diene compound include acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, acrylic acid ester, methacrylic acid ester, maleimide, vinyl acetate, and vinyl chloride. The norbornene-based addition (co) polymer is marketed by Mitsui Chemicals, Inc. under the trade name of Apel, and there are a plurality of grades having different glass transition temperatures (Tg). They are APL8008T (Tg70 degreeC), APL6013T (Tg125 degreeC), APL6015T (Tg145 degreeC) etc., for example. In addition, pellets such as TOPAS 8007, 6013, 6015, etc. are sold as products by Polyplastics Co., Ltd. Further, Appear 3000 is sold by Ferrania.

Norbornene polymer hydrides are disclosed in JP-A-1-240517, JP-A-7-196736, JP-A-60-26024, JP-A-62-19807, JP-A-2003-115767, JP-A-2004-309799. As disclosed in various publications such as No. 1, etc., it is prepared by addition polymerization or metathesis ring-opening polymerization of a polycyclic unsaturated compound and then hydrogenation. In the norbornene-based polymer used in the present invention, R ^{5 to} R ⁶ are preferably a hydrogen atom or —CH ₃ , X ³ and Y ³ are preferably a hydrogen atom, Cl, —COOCH ₃ , and other groups are appropriately selected. . This norbornene-based resin is sold under the trade name Arton G or Arton F by JSR Corporation, and from Zeon Corporation, Zeonor ZF14, ZF16, Zeonex 250 or Zeonex. It is commercially available under the trade name 280, and the above can be used in the present invention.

  The solvent is not particularly limited as long as it can dissolve the cyclic polyolefin, that is, a good solvent. Preferable examples include chlorinated compounds such as dichloromethane and chloroform, and compounds selected from chain hydrocarbons having 3 to 12 carbon atoms, cyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, and ethers. The ester, ketone and ether may have a cyclic structure. Examples of chain hydrocarbons having 3 to 12 carbon atoms include hexane, octane, isooctane and decane. Examples of cyclic hydrocarbons having 3 to 12 carbon atoms include cyclopentane, cyclohexane and derivatives thereof. Examples of the aromatic hydrocarbon having 3 to 12 carbon atoms include benzene, toluene, xylene and the like. Examples of the ester having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone. Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, and phenetole. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, and 2-butoxyethanol. The preferable boiling point of the organic solvent is 35 ° C. or more and 150 ° C. or less. In the present invention, a mixture of two or more compounds can be used as a solvent for adjusting dope physical properties such as drying property and viscosity. Further, when the mixture is used as a solvent, the mixture is a so-called poor solvent. May be added.

  When a mixture of a good solvent and a poor solvent is used as the dope solvent, the poor solvent may be appropriately selected according to at least one of the type of polymer used and the type of good solvent. For example, when a chlorinated organic solvent is used as the good solvent, alcohol can be preferably used. The alcohol may have any of a linear, branched, and cyclic structure, and among them, a saturated aliphatic hydrocarbon is preferable. The alcohol may be any of primary to tertiary. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol and cyclohexanol. In addition, as alcohol, a fluorine-type alcohol is also used. Examples thereof include 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like. Of the poor solvents, monohydric alcohols are particularly effective because they have an effect of reducing peeling resistance. The peeling resistance is a peeling force when peeling the cast film from the support. Particularly preferred alcohols vary depending on the good solvent to be selected, but considering the drying load, alcohols having a boiling point of 120 ° C. or lower are preferred, monohydric alcohols having 1 to 6 carbon atoms are more preferred, and alcohols having 1 to 4 carbon atoms Can be particularly preferably used. A particularly preferred mixed solvent for preparing a dope of cyclic polyolefin is a combination in which dichloromethane is the main solvent and one or more alcohols selected from methanol, ethanol, propanol, isopropanol, or butanol are poor solvents.

  Experiments 1 to 10 were performed under the following conditions, and the presence or absence of the effect of the present invention was examined. Each experiment will be described in detail in Experiment 1. For Experiments 2 to 10, descriptions of the same conditions as in Experiment 1 are omitted.

(Experiment 1)
A predetermined solid content was appropriately added to a predetermined solvent and dissolved by stirring to prepare a dope A. The prescription of dope A is as follows.
Cellulose triacetate (substitution degree 2.8) 89.3% by weight
Plasticizer A (triphenyl phosphate) 7.1% by weight
Plasticizer B (biphenyldiphenyl phosphate) 3.6% by weight
80% by weight of solid content (solute) with a composition ratio of dichloromethane
Methanol 13.5 wt%
n-butanol 6.5% by weight
The dope A was prepared by appropriately adding to a mixed solvent consisting of The TAC concentration of the dope was adjusted to be about 23% by weight. The dope is filtered with a filter paper (Toyo Filter Paper Co., Ltd., # 63LB), further filtered with a sintered metal filter (Nippon Seisen Co., Ltd. 06N, nominal pore size 10 μm), and further filtered with a mesh filter, and then a stock tank Put it in.

  The cellulose triacetate used here has a residual acetic acid content of 0.1% by weight or less, a Ca content of 5 ppm, a Mg content of 42 ppm, a Fe content of 0.5 ppm, free acetic acid of 40 ppm, It contained 15 ppm of sulfate ion. The degree of substitution of the acetyl group with respect to the hydrogen at the 6-position hydroxyl group was 0.91. Further, 32.5% of all acetyl groups were acetyl groups in which the hydrogen of the hydroxyl group at the 6-position was substituted. Moreover, the acetone extraction part which extracted this TAC with acetone was 8 weight%, and the weight average molecular weight / number average molecular weight ratio was 2.5. The obtained TAC had a yellow index of 1.7, a haze of 0.08, and a transparency of 93.5%. This TAC is synthesized using cellulose collected from pulp as a raw material. Moreover, the glass transition temperature Tg of this TAC was 145 degreeC.

  A solution casting method was performed using this dope A to obtain a film 20. The obtained film 20 was stretched in the tenter unit 12 using the offline stretching apparatus 10 shown in FIG. The width of the film 20 before stretching was 1500 mm. In the preheating area 36, the temperature of the film 20 was maintained at 150 ° C. to 180 ° C., and in the stretching area 37, the film 20 was stretched in the Z2 direction while maintaining the temperature of the film 20 at 180 ° C. to 200 ° C. The draw ratio ER was 30%. Next, in the relaxation area 38, relaxation treatment was performed while maintaining the temperature of the film 20 at 150 ° C. to 200 ° C. The relaxation rate RR was 5%. After that, in the cooling area 39, the heating device 63 and the duct 43 distributed the temperature of the product portion 20b so as to increase from both ends in the Z2 direction toward the center. The temperature Tc of the product center portion 20c was 70 ° C., and the temperature Te of the product end portion 20e was 88 ° C. Further, regarding the film 20 sent out from the tenter unit 12, the value of Lc / Le was 0.999.

(Experiments 2 to 10)
In Experiments 2 to 10, in the cooling area 39, the temperature Tc of the product center portion 20c, the temperature Te of the product end portion 20e, and the values of Lc / Le were set to the values shown in Table 1, as in Experiment 1. did. For Experiments 6 and 10, dope B was used instead of dope A.

Next, the dope B will be described. The cyclic polyolefin A was stirred and dissolved in a solvent to obtain a dope B. The components of the dope B are as follows.
Cyclic polyolefin A 100% by weight
Solid content (solute) consisting of 84% by weight of dichloromethane
10% by weight of methanol
n-butanol 6% by weight
The dope B was prepared by appropriately adding to a mixed solvent consisting of The dope is filtered with a filter paper (Toyo Filter Paper Co., Ltd., # 63LB), further filtered with a sintered metal filter (Nippon Seisen Co., Ltd. 06N, nominal pore size 10 μm), and further filtered with a mesh filter, and then a stock tank Put it in.

  Cyclic polyolefin A is a compound obtained by the following method. 100 parts by weight of purified toluene and 100 parts by weight of norbornenecarboxylic acid methyl ester were charged into the reaction kettle. Next, ethylhexanoate-Ni 25 mmol% (to monomer) dissolved in toluene, tri (pentafluorophenyl) boron 0.225 mol% (to monomer) and triethylariminium 0.25 mol% (to monomer) dissolved in toluene were added. The reaction kettle was charged. The reaction was allowed to proceed for 18 hours at room temperature with stirring. After completion of the reaction, the reaction mixture was poured into excess ethanol to form a polymer precipitate. The precipitate was purified and dried by vacuum drying at 65 ° C. for 24 hours to obtain cyclic polyolefin A.

  The obtained cyclic polyolefin A was dissolved in tetrahydrofuran and measured for the molecular weight by gel permeation chromatography. The number average molecular weight in terms of polystyrene was 79,000 and the weight average molecular weight was 205,000. The refractive index of the obtained polymer A measured with an Abbe refractometer was 1.52. Further, the glass transition temperature Tg of the cyclic polyolefin A was 138 ° C.

(Evaluation)
The following evaluation was performed about the obtained film.

1. Evaluation of the presence or absence of scratches The surface of the obtained film 20 was visually observed, and the presence or absence of scratches was evaluated based on the following criteria.
A: Scratches could not be confirmed on the surface of the film.
○: Only scratches with no practical problem were confirmed on the film surface.
X: The crack of the grade which cannot be used as a product on the surface of the film was confirmed.

2. Evaluation of strip mark The film 20 wound up in a roll shape was visually observed, and the presence or absence of the strip mark was evaluated based on the following criteria.
A: A band trace could not be confirmed.
○: Only band-like traces having no practical problem were confirmed.
X: A strip-shaped mark that could not be used as a product was confirmed.

3. Evaluation of ΔRe The variation amount ΔRe of the in-plane retardation Re of the film 20 before the introduction of the tenter portion and the in-plane retardation Re of the film 20 after being sent out from the tenter portion are measured. Based on the evaluation.
A: ΔRe was 2 nm or less.
X: ΔRe was larger than 2 nm.

The method for measuring the in-plane retardation Re is as follows. The film 20 was cut to 70 mm × 100 mm, conditioned for 2 hours at a temperature of 25 ° C. and a humidity of 60% RH, and measured with an automatic birefringence meter (KOBRA21DH Oji Scientific Co., Ltd.) from the vertical direction at 632.8 nm. It calculated according to the following formula from the extrapolation value of the foundation value.
Re = | n1-n2 | × d
n1 is the refractive index of Z1, n2 is the refractive index in the Z2 direction, and d is the thickness (film thickness) of the film.

4). Evaluation of ΔRth The amount of retardation Rth in the thickness direction of the film 20 before the introduction of the tenter portion and the amount of variation ΔRth in the thickness direction retardation Rth of the film 20 after being sent out from the tenter portion were measured. Evaluation was based on criteria.
○: ΔRth was 2 nm or less.
X: ΔRth was larger than 2 nm.

The measuring method of the thickness direction retardation Rth is as follows. The film 20 was cut into 30 mm × 40 mm, conditioned at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours, and measured with an ellipsometer (M150 manufactured by JASCO Corporation) at 632.8 nm from the vertical direction, and the film surface It calculated according to the following formula from the extrapolated value of the retardation value measured in the same manner while tilting.
Rth = {(n1 + n2) / 2−n3} × d
n3 represents the refractive index in the thickness direction.

  Evaluation results 1 to 4 in Experiments 1 to 10 are shown in Table 1. In Table 1, the evaluation result 1 represents the evaluation result of the presence or absence of scratches, the evaluation result 2 represents the evaluation result of the band-shaped trace, the evaluation result 3 represents the evaluation result of ΔRe, and the evaluation result 4 represents the ΔRth. Represents the evaluation result.

It is the schematic which shows an offline extending | stretching apparatus. It is a side view which shows the outline | summary of a tenter part. It is a top view which shows the outline | summary of a tenter part. It is a top view which shows the outline | summary of the duct provided in a tenter part, and a heating apparatus. (A) is explanatory drawing which shows the shrinkage amount X1 of the Z1 direction of the film resulting from a necking phenomenon. (B) is explanatory drawing which shows a mode that the fluctuation | variation in the Z2 direction of the shrinkage amount X1 is suppressed by the shrinkage amount X2 resulting from a temperature distribution. It is the schematic which shows a solution casting apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Off-line extending | stretching apparatus 12 Tenter part 20 Film 20a Ear part 20b Product part 20c Product center part 20e Product end part 37 Extension area 39 Cooling area 43 Duct 53 Slit 56-59 Wind 63 Heating device 64 Heat generating part

Claims (8)

A stretching process that includes a thermoplastic resin, grips the ears at both ends in the width direction of the long film, and stretches the film in the width direction;
In the product part excluding the ear part in the film that has undergone the stretching process, when the temperature at both ends in the width direction is Te and the temperature at the center part in the width direction is Tc, the formula (1) is satisfied. The amount of shrinkage of the product part in the longitudinal direction due to the stretching after the temperature distribution of the product part is made such that the temperature gradually decreases from the both ends in the width direction toward the center part in the width direction. A grip release step of releasing the grip of the ear portion so as to suppress the fluctuation in the width direction by contraction in the longitudinal direction of the product portion due to the temperature distribution;
A method for producing a film, comprising:
Formula (1) 0 (° C.) <Te−Tc (° C.) ≦ 80 (° C.) In the grip release step, when the glass transition temperature of the thermoplastic resin is Tg (° C.), the grip of the ear portion is released for the film satisfying the formulas (2) and (3). The method for producing a film according to claim 1.
Formula (2) 25 (° C.) ≦ Te (° C.) ≦ Tg−10 (° C.)
Formula (3) 25 (° C.) ≦ Tc (° C.) ≦ Tg−10 (° C.)   2. The grip releasing step includes heating the both ends of the product part in the width direction and cooling the center part in the width direction of the product part, and then releasing the grip of the ear part. 2. The method for producing a film according to 2.   In the grip releasing step, after the film is cooled by a cooling air having a distribution that increases in speed from both ends in the width direction of the product portion toward the center in the width direction, the grip of the ear portion is released. The method for producing a film according to claim 1 or 2.   The method for producing a film according to claim 1, wherein the thermoplastic resin is cellulose acylate.   The method for producing a film according to any one of claims 1 to 4, wherein the thermoplastic resin is a saturated norbornene resin.   The method for producing a film according to claim 1, wherein the stretching step and the grip releasing step are performed after the film wound on the winding core is taken out from the winding core. A film forming step of discharging a dope containing the thermoplastic resin and a solvent to a support to form a film on the support;
A peeling step of peeling off the film that has become self-supporting from the support,
The method for producing a film according to any one of claims 1 to 6, wherein the stretching step and the grip releasing step are performed on the film peeled off from the support.

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