JP2006306052A - Method of forming film from solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a film having a desired front surface retardation. <P>SOLUTION: A dope 21 is obtained by dissolving a solute, such as TAC, etc. in a solvent mixture which contains a methylene chloride as a principal component. The surface temperature of a casting drum 31 is regulated to -10°C. The dope 21 is cast on the casting drum 31 from a casting die 30, and a cast film 39 is formed. The cast film 39 is cooled and gelated. The cast film 39 is stripped off from the cast drum 31, and a wet film 60 having the amount of content solvent of 150 wt.% is obtained. A wind of 70°C is supplied to the wet film 60 in a passage section 50. Extension relaxation is performed while the wet film 60 having the amount of content solvent of 70 wt.% is heated at 120°C with a tenter type drier 13, and a film 52 is obtained. The film 52 having the amount of the content solvent of 5 wt.% is dried at 140°C in a drying room 15. The film 52 is rolled with a winding roller 58. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solution casting method, and more particularly to a solution casting method for producing a film preferably used for an optical film such as a polarizing plate protective film and an optical compensation film used in a liquid crystal display device.

  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 photographic photosensitive material because of its toughness and flame retardancy. It is used as a film support. Further, since the TAC film is excellent in optical isotropy, it is used for a polarizing plate protective film, an optical compensation film (for example, a viewing angle widening film, etc.) of a liquid crystal display device whose market is expanding in recent years. Yes.

The TAC film is usually produced by a solution casting method. The solution casting method can produce a film having excellent physical properties such as optical properties as compared with other production methods such as a melt casting method. In the solution casting method, a polymer solution (hereinafter referred to as a dope) is prepared by dissolving a polymer in a mixed solvent containing dichloromethane or methyl acetate as a main solvent. The dope is cast on a support by forming a casting bead from a casting die to form a casting film. After the cast film has a self-supporting property on the support, it is peeled off from the support as a film (hereinafter, this film is referred to as a wet film), dried and wound up as a film (for example, (Refer nonpatent literature 1.).
Japan Society for Invention and Innovation Public Technical Bulletin No. 2001-1745

  In recent years, highly functional films such as a VA (vertically aligned) compensation film and an OCB (optically compensated bend) WV support have been used. These highly functional films require refractive index anisotropy in the direction perpendicular to the casting direction (MD direction) (casting width direction; TD direction). Until now, in order to develop refractive index anisotropy in the TD direction, stretching in the TD direction has been performed, and films having desired values have been manufactured.

  However, when producing the high-functional film, it takes time to dry the cast film on the cast band, and a load for improving productivity is generated. That is, since it becomes necessary to dry the cast film on the casting band until the stretching in the TD direction becomes possible, the productivity is lowered. Therefore, a casting drum is used as the support instead of the casting band.

  In addition, stretching of the wet film peeled off from the support in the TD direction is usually performed with a tenter dryer. When a wet film is stretched in the TD direction with a tenter dryer, there are restrictions such as slow axis control of the film. That is, it is necessary to gradually stretch the wet film in the TD direction so that the slow axis does not increase. Therefore, the production speed of the film is limited, which is a factor that hinders productivity improvement.

  In addition, when a wet film is stretched in the TD direction with a tenter dryer, the chain to which the tenter clip is connected stretches, and after a certain period of time has elapsed, the tenter dryer is stopped and maintenance such as replacement is required. It may be. Further, even if the tenter clip deteriorates, maintenance such as stopping the operation of the tenter dryer and replacing the tenter clip is necessary. As described above, the stretching of the wet film by the tenter dryer in the TD direction places a heavy load on the equipment, particularly the tenter dryer, and there is a problem in stabilizing the production of the high-functional film.

  An object of the present invention is to provide a solution casting method capable of stably and continuously producing a film having a birefringence in a desired direction.

  As a result of intensive studies by the present inventor, the cast film on the casting drum is cooled and gelled, and then heated when it contains a desired solvent when transporting the wet film, so that the main chain of the polymer is oriented. To crystallize the film. Thereby, it discovered that a film will have a birefringence in a specific direction.

  The casting film is cooled by a casting drum (for example, −15 ° C. to 0 ° C.) to form a cross-linking point that is a seed of crystal and gel. The cast film which has been cooled and gelled is peeled off as a wet film from a casting drum as a support. In order to convey at this time, drawing (tension) in the casting direction (MD direction) is required. By applying tension, the main chain of the polymer is promoted to be oriented in the MD direction.

  When the wet film having a crosslinking point in the polymer is heated, the polymer main chain is oriented in the casting direction to promote crystallization of the film. The inventor of the present invention shows that the birefringence of the film is expressed in the direction perpendicular to the polymer main chain orientation (MD direction; casting width direction) by the orientation of the polymer main chain in the casting direction. I found it. That is, the present inventors have found that a film having optical characteristics having a birefringence in the MD direction can be obtained by heat-crystallization of a wet film in which the polymer main chain is oriented in the MD direction. Furthermore, the present inventor has also found that the orientation of the polymer main chain occurs at a lower temperature in the state of a wet film containing a large amount of solvent.

  The solution casting method of the present invention is a method in which a dope containing a polymer and a solvent is cast from a casting die onto a support to form a gelled casting film, and the casting film has a self-supporting property. Then, in the method for producing a cellulose acylate film, the cast film is peeled off from the support as a film and dried, and the main chain of the polymer is oriented in the casting direction.

  The drying is a case where the film is dried while being transported by a plurality of rollers after the film is peeled off from the support, and the content of the solvent based on the dry weight of the film is 65% by weight or more and 80% by weight. % Or less, the film surface temperature of the film is preferably 110 ° C. or more and 140 ° C. or less. When the drying is performed while gripping both edges of the film with gripping means, and the amount of solvent contained on the basis of the dry amount of the film is 60% by weight or more and 80% by weight or less, the film of the film The surface temperature is preferably 110 ° C. or higher and 140 ° C. or lower. More preferably, the temperature at which the film is heated is substantially constant while the width of the gripping means is substantially changing.

  The drying is a case where the film is dried while being conveyed by a plurality of rollers after being dried by the gripping means, and the content of the solvent on the basis of the dry amount of the film is 1% by weight or more and 8% by weight or less. In this case, the film surface temperature of the film is preferably 100 ° C. or higher and 220 ° C. or lower. The front retardation Re (nm) of the film is preferably -3 nm or less. The polymer is preferably cellulose acylate.

  According to the solution casting method of the present invention, a dope containing a polymer and a solvent is cast on a support from a casting die to form a gelled casting membrane, and the casting membrane has a self-supporting property. In the method for producing a cellulose acylate film, after the casting film is peeled off from the support as a film and dried, the main chain of the polymer is oriented in the casting direction. A film suitable for an optical functional film having (Re) of −3 nm or less can be produced.

The solution casting method of the present invention, when performing the solution casting method,
(1) The drying is a case where the film is dried while being transported by a plurality of rollers after the film is peeled off from the support, and the content of the solvent based on the dry weight of the film is 65% by weight. When the content is 80% by weight or less, the film surface temperature of the film is 110 ° C. or more and 140 ° C. or less.
(2) In the case where the drying is performed while gripping both edges of the film with gripping means, and the content of the solvent on the dry basis of the film is 60 wt% or more and 80 wt% or less, The film surface temperature of a film shall be 110 degreeC or more and 140 degrees C or less.
(3) The case where the film is dried while being conveyed by a plurality of rollers after the drying is performed by the gripping means, and the content of the solvent on the basis of the dry amount of the film is 1% by weight or more. The film surface temperature of the film is set to 100 ° C. or more and 220 ° C. or less when the content is not more than wt%.
Therefore, no special equipment is required, and by using a casting drum as the support, high-speed film formation is possible.

  Since the front retardation Re (nm) of the film produced by the solution casting method of the present invention is -3 nm or less, it is preferably used for those requiring a film having birefringence such as VA type and OCB type. .

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments listed here.

[material]
As the cellulose acylate, it is preferable to use a cellulose acylate in which the degree of substitution of the hydroxyl group of cellulose satisfies all of the following formulas (I) to (III). Hereinafter, cellulose acylate satisfying the following formula is referred to as TAC.
(I) 2.5 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9
In the formula, A and B represent the substitution degree of the acyl group to the hydrogen atom of the hydroxyl group of cellulose, A is the substitution degree of the acetyl group to the hydrogen atom of the hydroxyl group of cellulose, and B is the carbon to the hydrogen atom of the hydroxyl group of cellulose. It is a substitution degree of an acyl group having 3 to 22 atoms. In addition, it is preferable to use particles having 90% by mass or more of TAC of 0.1 mm to 4 mm. The polymer used in the present invention is not limited to cellulose acylate. The cellulose acylate may be obtained from either linter cotton or pulp cotton, but is preferably obtained from linter cotton.

  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.). In the present invention, the dope means a polymer solution or dispersion obtained by dissolving or dispersing a polymer in a solvent.

  Among these, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and dichloromethane is most preferably used. One kind of alcohol having 1 to 5 carbon atoms in addition to dichloromethane from the viewpoint of physical properties such as solubility of TAC, peelability of cast film from the support, mechanical strength of the film, and optical properties of the film It is preferable to mix several kinds. 2 mass%-25 mass% are preferable with respect to the whole solvent, and, as for content of alcohol, 5 mass%-20 mass% are more preferable. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like, but methanol, ethanol, n-butanol or a mixture thereof is preferably used.

  Recently, a solvent composition not using dichloromethane has been proposed in order to minimize the influence on the environment. Ethers having 4 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and alcohols having 1 to 12 carbon atoms are preferably used. Usually, these are used in an appropriate mixture. 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. 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 the solvent.

  Details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148. These descriptions are also applicable to the present invention. In addition, 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, The details are described in paragraphs [0196] to [0516] of JP-A-2005-104148.

[Dope production method]
First, a dope is manufactured using the raw material. First, the solvent is sent to the dissolution tank. Next, the TAC is fed into the dissolution tank while measuring. Thereafter, the additive solution prepared in advance is fed to the required amount dissolution tank. In addition to the method of sending the additive as a solution, for example, when the additive is liquid at room temperature, it is also possible to send the additive to the dissolution tank in the liquid state. Further, when the additive is solid, it can be fed into the dissolution tank using a hopper or the like. When a plurality of types of additives are added, a plurality of types of additives can be dissolved in the additive solution. Alternatively, a solution in which an additive is dissolved can be put in each of a plurality of additive solution tanks, and sent to the dissolution tank through independent pipes.

  The order of putting in the dissolution tank is not limited to the solvent (used in the meaning including the case of the mixed solvent), TAC, and additive. For example, a preferred amount of solvent can be fed after the TAC is metered into the dissolution tank. Further, the additive does not necessarily need to be put in the dissolution tank in advance, and can be mixed in a mixture of TAC and a solvent (hereinafter, these mixtures are also referred to as dope) in a later step.

  The dissolution tank is provided with a jacket and a first stirring blade that is rotated by a motor. Furthermore, it is preferable that the 2nd stirring blade rotated with a motor is attached. The first stirring blade is preferably an anchor blade, and the second stirring blade is preferably a dissolver type. It is preferable to adjust the temperature in the melting tank within a range of −10 ° C. to 55 ° C. by flowing a heat transfer medium through the jacket. By appropriately selecting and rotating the first stirring blade and the second stirring blade, a swelling liquid in which TAC is swollen in a solvent is obtained.

  The swelling liquid is sent to the heating device by a pump. The heating device is preferably a jacketed pipe, and preferably has a configuration capable of pressurizing the swelling liquid. The dope is obtained by dissolving TAC or the like in a solvent under heating or pressure heating conditions of the swelling liquid. In this case, it is preferable to carry out a method for preparing a dope by heating the swelling liquid to a temperature in the range of 40 ° C. to 120 ° C. (hereinafter referred to as a heating dissolution method). Moreover, the cooling dissolution method which cools a swelling liquid to the temperature of -100 degreeC--30 degreeC can also be performed. TAC can be sufficiently dissolved in a solvent by appropriately selecting the heating dissolution method and the cooling dissolution method. After the temperature of the dope is set to about room temperature with a temperature controller, the dope is filtered to remove impurities in the dope. It is preferable that the average pore diameter of the filtration filter of the filtration device is 100 μm or less. The filtration flow rate is preferably 50 L / hr or more.

  By the way, the method of once preparing a swelling liquid as mentioned above, and making dope with a swelling liquid after that requires time so that the density | concentration of TAC is raised, and a problem may arise in the point of cost. In that case, it is preferable to prepare a dope having a concentration lower than the target TAC concentration, and then perform a concentration step for preparing a dope having the target concentration. When performing such a method, the dope filtered by the filtration device is sent to the flash device. A part of the solvent in the dope is evaporated in a flash apparatus. The evaporated solvent is made liquid by a condenser and then recovered by a recovery device. The recovered solvent is regenerated and reused as a dope preparation solvent by a regenerator. This reuse is effective in terms of cost.

  The concentrated dope is extracted from the flash unit by a pump. Furthermore, it is preferable to perform a bubble removal process to remove bubbles generated in the dope. Any known method may be applied to remove bubbles, for example, an ultrasonic irradiation method. Thereafter, the dope is fed to a filtration device to remove foreign matters. In addition, it is preferable that the temperature of dope at the time of filtration is 0 degreeC-200 degreeC. By these methods, a dope having a TAC concentration of 5% by mass to 40% by mass, preferably 10% by mass to 30% by mass, and most preferably 15% by mass to 25% by mass can be produced.

  Regarding the dope material, raw material, additive dissolution method and addition method, filtration method, defoaming and other dope production methods in the solution casting method for obtaining a TAC film, see [0517 of JP-A-2005-104148. ] To [0616] paragraphs in detail. These descriptions are also applicable to the present invention.

[Solution casting method]
FIG. 1 shows a film production line 10. The film production line 10 includes a filtration device 11, a casting chamber 12, and a tenter dryer 13. Further, an ear clip device 14, a drying chamber 15, a cooling chamber 16 and a winding chamber 17 are arranged.

  The stock tank 20 contains a dope 21 prepared by the above method. A stirring blade 23 that is rotated by a motor 22 is attached. The dope 21 is always made uniform by rotating the stirring blade 23. The stock tank 20 is connected to the filtration device 11 via a pump 24. Additives such as a plasticizer and an ultraviolet absorber can be mixed into the dope 21 in the stock tank 20. In addition, a jacket 25 is attached to the stock tank 20 so that the temperature of the dope 21 can be adjusted.

The material of the casting die 30 is preferably a precipitation hardening stainless steel. It is preferable to use a material having a thermal expansion coefficient of 2 × 10 ⁻⁵ (° C. ⁻¹ ) or less. Moreover, what has a corrosion resistance substantially equivalent to the product made from SUS316 by the forced corrosion test by electrolyte aqueous solution can also be used. Further, a material having corrosion resistance that does not cause pitting (opening) at the gas-liquid interface even when immersed in a mixed solution of dichloromethane, methanol, and water for 3 months is used. Furthermore, it is preferable that the casting die 30 is manufactured by grinding a material that has passed one month or more after casting. This prevents the dope from flowing uniformly in the casting die 30 and prevents streaks and the like from occurring in the casting film described later.

  It is preferable to use a liquid contact surface finishing accuracy of the casting die 30 of 1 μm or less in terms of surface roughness and a straightness of 1 μm / m or less in any direction. The slit clearance that can be adjusted in the range of 0.5 mm to 3.5 mm by automatic adjustment is used. About the corner | angular part of the liquid-contact part of the lip tip of the casting die 30, R uses 50 micrometers or less over the full width of a slit. Moreover, it is preferable to use what was adjusted so that the shear rate in the casting die 30 may be set to 1 (1 / sec)-5000 (1 / sec).

  The width of the casting die 30 is not particularly limited, but it is preferable to use a casting die having a width of about 1.01 to 1.3 times the width of the final product. Further, during film formation, it is preferable to attach a temperature controller to the casting die 30 so as to be maintained at a predetermined temperature. The casting die 30 is preferably a coat hanger type. Furthermore, it is more preferable to provide a thickness adjusting bolt (heat bolt) at a predetermined interval in the width direction of the casting die 30 and attach an automatic thickness adjusting mechanism using the heat bolt. The heat bolt is preferably formed by setting a profile according to the amount of pump 24 (preferably a high precision gear pump) according to a preset program. Further, feedback control may be performed by an adjustment program based on a profile of a thickness meter (for example, an infrared thickness meter) (not shown) in the film production line 10. It is preferable that the thickness difference between any two points except the casting edge is adjusted within 1 μm, and the maximum difference in the width direction thickness is adjusted to 3 μm or less. Moreover, it is preferable to use the one whose thickness accuracy is adjusted to ± 1.5 μm or less.

More preferably, a cured film is formed at the lip tip of the casting die 30. A method for forming the cured film is not particularly limited, and examples thereof include ceramic coating, hard chrome plating, and a nitriding method. When ceramics are used as the cured film, those that can be ground, have low porosity, are not brittle, have good corrosion resistance, have good adhesion to the casting die 30, and have no adhesion to the dope are preferable. Specific examples include tungsten carbide (WC), Al ₂ O ₃ , TiN, Cr ₂ O _{3 and the} like, but it is particularly preferable to use WC. The WC coating can be performed by a thermal spraying method.

  In order to prevent the dope flowing out to the slit end of the casting die 30 from locally drying and solidifying, it is preferable to attach a solvent supply device (not shown) to the slit end. Solvent that solubilizes the dope (for example, a mixed solvent of 86.5 parts by mass of dichloromethane, 13 parts by mass of methanol, and 0.5 parts by mass of n-butanol). It is preferable to supply to. It is preferable to supply each side of the end portion in a range of 0.1 mL / min to 1.0 mL / min because it is possible to prevent foreign matters from being mixed in the cast film. In addition, it is preferable to use a pump having a pulsation rate of 5% or less for supplying the liquid.

  A casting drum 31 as a support is provided below the casting die 30. The casting drum 31 is rotated by a driving device (not shown). Further, a heat transfer medium circulation device 32 is attached to the casting drum 31 in order to set the surface temperature of the casting drum 31 to a predetermined value. A heat transfer medium flow path (not shown) is formed in the casting drum 31, and the temperature of the casting drum 31 is set to a predetermined value by passing through the heat transfer medium held at a predetermined temperature. Can be held at the value of

  The width of the casting drum 31 is not particularly limited, but it is preferable to use a casting drum having a width in the range of 1.05 to 1.5 times the casting width of the dope. It is preferable to use a surface polished to have a surface roughness of 0.05 μm or less. The material is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength.

  The casting die 30, the casting drum 31, etc. are housed in the casting chamber 12. In the casting chamber 12, a temperature adjustment facility 33 is attached to keep the temperature in the casting chamber 12 at a predetermined value. It is preferable that the temperature of the casting chamber 12 is 10 ° C to 30 ° C. In addition, a condenser (condenser) 34 for condensing and recovering the volatile organic solvent is provided. A recovery device 35 for recovering the condensed and liquefied solvent is also provided. The organic solvent condensed and liquefied by the condenser 34 is recovered by the recovery device 35. The solvent is regenerated by a regenerator (not shown) and then reused as a dope preparation solvent. Further, a decompression chamber 36 is attached to the casting die 30 in order to adjust the pressure of the back surface portion of the casting bead that is formed when casting. A decompression device 37 is attached to the decompression chamber 36 so that the degree of decompression can be adjusted.

  The crossover unit 50 is provided with a blower 51. Further, an ear clip device 14 is provided downstream of the tenter dryer 13. A crusher 53 that finely cuts the waste at the side end (referred to as an ear) of the cut film 52 is connected to the ear clip device 14.

  The drying chamber 15 is provided with a number of rollers 54. An adsorption recovery device 55 is provided for adsorbing and recovering the solvent gas generated by evaporation. Further, a humidity control chamber (not shown) may be provided between the drying chamber 15 and the cooling chamber 16. A forced static elimination device (static elimination bar) 56 for adjusting the charged voltage of the film 52 to be in a predetermined range (for example, −3 kV to +3 kV) is preferably provided downstream of the cooling chamber 16. In FIG. 1, the forced static eliminating device 56 is illustrated on the downstream side of the cooling chamber 16, but is not limited to this position. Furthermore, in this embodiment, it is preferable that a knurling application roller 57 for applying knurling to both edges of the film 52 by embossing is appropriately provided on the downstream side of the forced static elimination device 56. The winding chamber 17 includes a winding roller 58 for winding the film 52 and a press roller 59 for controlling the tension during the winding.

  Next, an example of a method for producing a film using the film production line 10 as described above will be described below. The dope 21 is always made uniform by the rotation of the stirring blade 23. The dope 21 may be mixed with additives such as a plasticizer and an ultraviolet absorber during the stirring. A heat transfer medium is supplied into the jacket 25, and the temperature of the dope 21 is adjusted to 25 ° C to 35 ° C.

The dope 21 is sent to the filtration device 11 by the pump 24 and filtered. Thereafter, as shown in FIG. 2, a casting bead 38 is formed from the casting die 30 and cast on the casting drum 31.
The speed fluctuation of the casting drum 31 is preferably 3% or less, and the meandering in the width direction that occurs when the casting drum 31 rotates once is preferably 3 mm or less. The casting drum 31 immediately below the casting die 30 is preferably adjusted so that the positional fluctuation in the vertical direction is 500 μm or less. Further, the temperature of the casting chamber 12 is preferably set to 10 ° C. to 30 ° C. by the temperature control equipment 33. The solvent evaporated in the casting chamber 12 is recovered by the recovery device 35 and then regenerated and reused as a dope preparation solvent.

  A casting bead 38 is formed from the casting die 30 to the casting drum 31, and a casting film 39 is formed on the casting drum 31. The surface temperature of the casting drum 31 is adjusted by supplying a heat transfer medium. In the present invention, the surface temperature of the casting drum 31 is preferably −10 ° C. or more and 10 ° C. or less in order to gel the casting film 39. The temperature of the dope 21 at the time of casting is preferably 30 ° C to 35 ° C. The casting film 39 is cooled to form a crosslinking point which is a crystal seed, and the gelation of the casting film is promoted.

  In order to stabilize the casting bead, the support contact surface (hereinafter referred to as the casting bead back surface) of the casting bead is adjusted to a desired pressure value by the decompression chamber 36. Although it is preferable to depressurize the casting bead back surface in the range of (atmospheric pressure −2000 Pa) to (atmospheric pressure −10 Pa), it is not limited to this range. Further, it is preferable that a jacket (not shown) is attached to the decompression chamber 36 and the temperature is controlled so that the internal temperature is kept at a predetermined temperature. The temperature of the decompression chamber 36 is not particularly limited, but is preferably set to be equal to or higher than the condensation point of the organic solvent used. Further, it is preferable to attach a suction device (not shown) to the edge portion of the casting die 30 in order to maintain the desired shape of the casting bead. The edge suction air volume is preferably in the range of 1 L / min to 100 L / min.

  The crossing part 50 provided with many rollers 62 is conveyed. It is preferable that the solvent content on the basis of the dry amount of the wet film 60 immediately before being transported to the transfer section 50 is 100 wt% or more and 200 wt% or less. When the solvent content is less than 100% by weight, the rigidity of the wet film 60 may be too high, and the orientation of the polymer constituting the wet film 60 may be difficult to occur. On the other hand, if it exceeds 200% by weight, conveyance failure may occur. In the crossover part 50, the drying of the wet film 60 is advanced by sending the drying air of desired temperature from the air blower 51. FIG. At this time, the temperature of the drying air is preferably 20 ° C. or higher and 250 ° C. or lower, more preferably 30 ° C. or higher and 200 ° C. or lower, and most preferably 40 ° C. or higher and 100 ° C. or lower. By setting it as the said temperature range, the surface temperature (henceforth film surface temperature) of the wet film 60 will be 20 to 50 degreeC.

  In the crossover portion 50, the drawing speed (tension in the casting direction) is applied to the wet film 60 by making the rotation speed of the downstream roller 62 faster than the rotation speed of the upstream roller 62. The tension in the casting direction is preferably stretched in the range of 1% to 20% in the casting direction of the wet film 60. If the stretching is less than 1%, sufficient draw tension may not be imparted to the wet film 60, and the orientation of the polymer main chain may be difficult to occur. Moreover, when it extends beyond 20%, there exists a possibility that the defect that the wet film 60 may burst may arise.

  By thus heating the wet film 60 and applying tension in the casting direction, the wet film 60 is oriented in the casting direction of the polymer main chain, and crystallization proceeds. As the crystallization proceeds, the wet film 60 has a birefringence in a direction perpendicular to the main chain orientation in the plane.

  The wet film 60 is sent from the transfer section 50 to the tenter dryer 13. The solvent content on the dry basis of the wet film 60 immediately before being sent to the tenter dryer 13 is preferably 50% by weight or more and 150% by weight or less. In the tenter dryer 13, the wet film 60 is dried while being transported while being gripped by gripping means such as a clip. Further, it is possible to stretch the wet film 60 in the casting width direction (in some cases, the casting direction in some cases) while drying the wet film 60 inside the tenter dryer 13. While the wet film 60 is being dried, the film surface temperature of the wet film 60 is preferably in the range of 110 ° C. or higher and 140 ° C. or lower. By following the above conditions, the polymer main chain can be stretched in the casting width direction without being disturbed by the orientation in the casting direction.

  When the tenter dryer 13 extends the wet film 60 in the casting width direction, it is preferable to keep the drying temperature of the dryer for drying the wet film 60 substantially constant.

  The wet film 60 is sent out as a film 52 after being dried to a predetermined residual solvent amount by the tenter dryer 13. Both end portions of the film 52 are cut by the ear clip device 14. The cut film is sent to the crusher 53 by a cutter blower (not shown). The side edges of the film are crushed by the crusher 53 into chips. It is advantageous in terms of cost to reuse this chip for dope preparation. In addition, although the process of cut | disconnecting the both edges of this film can also be abbreviate | omitted, it is preferable to carry out in either from the said casting process to the process of winding up the said film.

  Next, the film 52 is sent to the drying chamber 15 where a number of rollers 54 are provided. The solvent content based on the dry weight of the film 52 immediately before being sent to the drying chamber 15 is preferably 1% by weight or more and 10% by weight or less, more preferably 1% by weight or more and 8% by weight or less. If the solvent content is less than 1% by weight, the drying of the film 52 proceeds too much, and the orientation of the main chain of the polymer may not occur. On the other hand, if it exceeds 10% by weight, there is a possibility that a conveyance failure such as reflection from the roller 54 may occur.

  As for the temperature in the drying chamber 15, the film surface temperature of the film 52 is preferably 100 ° C. or higher and 220 ° C. or lower, and more preferably 120 ° C. or higher and 200 ° C. or lower. When the film surface temperature of the film 52 is less than 100 ° C., it may be difficult to volatilize the residual solvent in the film 52 and it may be difficult to align the polymer. Moreover, when it exceeds 220 degreeC, there exists a possibility that a deformation | transformation may arise in the film 52. FIG. In this case, the temperature in the drying chamber 15 is not particularly limited as long as the film surface temperature of the film 52 is in the above range, but is preferably in the range of 50 ° C to 160 ° C. The solvent (solvent gas) volatilized in the drying chamber 15 is adsorbed and recovered by the adsorption recovery device 55. The air from which the solvent component has been removed by the adsorption recovery device 55 is blown again as dry air inside the drying chamber 15.

  By setting the drying conditions of the film 52 within the above range in the drying chamber 15, the crystallization of the film 52 proceeds with the crystal seeds generated in the casting film 39 when the gel is first cooled and gelled. The progress of crystallization occurs when the main chain of the polymer is oriented in the casting direction. Thereby, a birefringence is generated in the casting width direction orthogonal to the casting direction in the plane.

  When a preliminary drying chamber (not shown) is provided between the ear-clipping device 14 and the drying chamber 15 and the film 52 is preliminarily dried, a change in the shape of the film 52 due to a rapid increase in the film temperature in the drying chamber 15 can be suppressed.

  The film 52 is cooled to approximately room temperature in the cooling chamber 16. A humidity control chamber (not shown) may be provided between the drying chamber 15 and the cooling chamber 16. Air adjusted to a desired humidity and temperature is blown onto the film 52 in the humidity control chamber. Thereby, generation | occurrence | production of the curling of the film 52 and the winding defect at the time of winding can be suppressed.

  The forced neutralization device (static neutralization bar) 56 sets the charged voltage while the film 52 is being conveyed to a predetermined range (for example, −3 kV to +3 kV). Although the example provided in the downstream of the cooling chamber 16 is shown in FIG. 1, it is not limited to the position. Furthermore, it is preferable to provide a knurling roller 57 and to impart knurling to both edges of the film 52 by embossing. In addition, it is preferable that the unevenness | corrugation of the knurled location is 1 micrometer-200 micrometers.

  Finally, the film 52 is taken up by the take-up roller 58 in the take-up chamber 17. At this time, it is preferable to wind the sheet while applying a desired tension with the press roller 59. More preferably, the tension is gradually changed from the start to the end of winding. The film 52 to be wound is preferably at least 100 m in the longitudinal direction (conveying direction). Further, the width direction is preferably 600 mm or more, and more preferably 1400 mm or more and 1800 mm or less. The present invention is also effective when it is larger than 1800 mm. The thickness of the film can also be applied when producing a thin film having a thickness of 15 μm to 100 μm.

In the present invention, the cast film 39 is cooled and gelled. Thereby, crystal seed is generated in the casting film 39. After that, by applying tension in the casting direction at at least one of the crossover part 50, the tenter dryer 13 or the drying chamber 15, the polymer main chain is oriented in the casting direction with the crystal seed as a starting point. Crystallization is allowed to proceed. As a result, the front retardation of the film 52 can be set to −3 nm or less, and can be set to −5 nm or less by selecting more experimental conditions, and can be −10 nm or less by selecting the most experimental conditions. It becomes possible to do. The front retardation Re is calculated by the following formula.
Re (nm) = (nx−ny) × d
In the formula, nx is the refractive index in the slow axis direction (MD direction in this example) in the film 52 plane, ny is the refractive index in the fast axis direction (TD direction in this example) in the film 52 plane, d (nm) is the film thickness of the film 52.

The orientation of the polymer main chain of the film 52 can be estimated by measuring the speed of sound wave transmission. The method for measuring the sound transmission speed is not particularly limited, but one specific example is given. Two oscillators (transmitting oscillator, receiving oscillator) are generated, the receiving oscillator generates a longitudinal wave (ultrasonic pulse), and the time T (μ) until the receiving oscillator receives the longitudinal wave is calculated. taking measurement. In the present invention, SST-110 (Nomura Corporation) is used as the measuring device. The film 52 as a sample is temperature-controlled at 25 ° C. and 55% RH for 2 hours. The transmission speed C (km / s) is calculated by the following formula.
C (km / s) = L1 (km) / T (s)
The transmission speed is measured five times while changing the mounting position of the two vibrators, and the average value is regarded as the transmission speed C. If there are molecules randomly arranged, the transmission speed is slowed because the progress of the sound wave is hindered. Therefore, if the transmission speed C is high, it can be determined that the orientation of the polymer molecules in the film 52 is excellent. The sound wave transmission speed is referred to as a sound speed value in the following description.

  The sound velocity values in the transport direction (MD direction) and the casting width direction (TD direction) of the film 52 are not particularly limited. As a specific example, the sound velocity value in the MD direction is preferably 2.0 km / sec or more and 3.0 km / sec or less. The sound velocity value in the TD direction is preferably 2.0 km / sec or more and 3.0 km / sec or less.

  In the present invention, the front retardation (Re) of the film 52 is -3 nm or less by the ratio of the sound velocity value in the MD direction and the sound velocity value in the TD direction (MD / TD; hereinafter referred to as the sound velocity value ratio). Can be judged. In the present invention, the sound velocity value ratio (MD / TD) is preferably 1.0 or more and 1.2 or less.

  In the solution casting method of the present invention, when casting dopes, two or more kinds of dopes are simultaneously laminated or sequentially laminated. Furthermore, you may combine both casting. When performing simultaneous lamination and co-casting, a casting die to which a feed block is attached may be used, or a multi-manifold casting die may be used. It is preferable that at least one of the thickness of the layer on the air surface side and the thickness of the layer on the support side is 0.5% to 30% of the thickness of the entire film of the film composed of multiple layers by co-casting. Furthermore, when performing simultaneous lamination co-casting, it is preferable that the high-viscosity dope is wrapped with the low-viscosity dope when casting the dope from the die slit to the support. Moreover, when performing simultaneous lamination co-casting, it is preferable that the dope contacting the outside of the casting bead formed from the die slit to the support has a higher alcohol composition ratio than the inner dope.

  From casting die, vacuum chamber, support structure, co-casting, peeling method, stretching, drying conditions for each process, handling method, curl, winding method after flatness correction, solvent recovery method, film recovery method The details are described in paragraphs [0617] to [0889] of JP-A-2005-104148. These descriptions are also applicable to the present invention.

[Performance / Measurement method]
(Curl degree / thickness)
The performance of the wound cellulose acylate film and the measurement method thereof are described in paragraphs [0112] to [0139] of JP-A-2005-104148. These are also applicable to the present invention.

[surface treatment]
It is preferable that at least one surface of the cellulose acylate film is surface-treated. The surface treatment is preferably at least one of vacuum glow discharge treatment, atmospheric pressure plasma discharge treatment, ultraviolet irradiation treatment, corona discharge treatment, flame treatment, acid treatment or alkali treatment.

[Functional layer]
(Antistatic, hardened layer, antireflection, easy adhesion, antiglare)
At least one surface of the cellulose acylate film may be undercoated.

  Furthermore, it is preferable to use the cellulose acylate film as a base film as a functional material provided with another functional layer. The functional layer is preferably provided with at least one layer selected from an antistatic layer, a cured resin layer, an antireflection layer, an easy adhesion layer, an antiglare layer and an optical compensation layer.

The functional layers preferably contain at least one surfactant 0.1mg / m ² ~1000mg / m ² containing. Further, the functional layers preferably contain at least one sort of plasticizers in the 0.1mg / m ² ~1000mg / m ² containing. Further, the functional layers preferably contain at least one sort of matting agents in the 0.1mg / m ² ~1000mg / m ² containing. Further, the functional layers preferably contain at least one sort of antistatic agents 1mg / m ² ~1000mg / m ² containing. In addition to the above, the method for applying a surface treatment functional layer for realizing various functions and properties on the cellulose acylate film is described in paragraphs [0890] to [1087] of JP-A-2005-104148. Detailed conditions and methods are also described. These are also applicable to the present invention.

(Use)
The cellulose acylate film is particularly useful as a polarizing plate protective film. A liquid crystal display device is produced by usually providing two polarizing plates each having a cellulose acylate film bonded to a polarizer in a liquid crystal layer. However, the arrangement position of the liquid crystal layer and the polarizing plate is not limited and may be any known position. Japanese Patent Application Laid-Open No. 2005-104148 describes TN type, STN type, VA type, OCB type, reflection type, and other examples in detail as a liquid crystal display device. This method can also be applied to the present invention. The publication also describes a cellulose acylate film provided with an optically anisotropic layer, and a cellulose acylate film provided with antireflection and antiglare functions. Furthermore, the use as an optical compensation film is also described as a biaxial cellulose acylate film imparting moderate optical performance. This can also be used as a polarizing plate protective film. These descriptions are also applicable to the present invention, and details are described in paragraphs [1088] to [1265] of JP-A-2005-104148.

In addition, the cellulose triacetate film (T
AC film) can be obtained. The TAC film can be used as a polarizing plate protective film or a base film for a photographic photosensitive material. Furthermore, it can also be used as an optical compensation film for improving the viewing angle dependency of a liquid crystal display device for television applications. In particular, it is effective for applications that also serve as a protective film for a polarizing plate. Therefore, not only the conventional TN mode but also IP
It is also used for S mode, OCB mode, VA mode and the like. Moreover, you may comprise a polarizing plate using the said film for polarizing plate protective films.

  Examples are given below, but the present invention is not limited thereto. The description will be made in detail in Experiment 1. With respect to Experiments 2 to 15 and Experiments 16 to 20 as comparative examples according to the present invention, the experimental conditions and results are collectively shown in Table 1 later.

The parts by weight of the raw materials used in Experiment 1 are shown below.
[composition]
Cellulose triacetate (substitution degree 2.84, viscosity average polymerization degree 306, water content 0.2% by weight, viscosity 6% by weight in dichloromethane solution 315 mPa · s, average particle diameter 1.5 mm with standard deviation 0.5 mm Some powders) 100 parts by weight dichloromethane (first solvent) 320 parts by weight methanol (second solvent) 83 parts by weight 1-butanol (third solvent) 3 parts by weight plasticizer A (triphenyl phosphate) 7.6 parts by weight Plasticizer B (diphenyl phosphate) 3.8 parts by weight UV agent a: 2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole 0.7 part by weight UV agent b: 2 ( 2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) -5-chlorobenzotriazole 0.3 part by weight of citric acid ester mixture (citric acid, monoethyl Chill ester, diethyl ester, triethyl ester mixture) 0.006 parts by weight fine particles (silicon dioxide (average particle size 15 nm), Mohs hardness about 7) 0.05 parts by weight

[Cellulose triacetate]
The cellulose triacetate used here has a residual acetic acid content of 0.1% by mass or less, a Ca content of 58 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 mass%, and the weight average molecular weight / number average molecular weight ratio was 2.5. The obtained TAC has a yellow index of 1.7, a haze of 0.08, a transparency of 93.5%, a Tg (glass transition temperature; measured by DSC) of 160 ° C., and a crystallization calorific value of It was 6.4 J / g. This TAC is synthesized using cellulose collected from cotton as a raw material. In the following description, this is called cotton raw material TAC.

  The plurality of solvents were mixed and stirred well in a 4000 L stainless steel dissolution tank having a stirring blade to obtain a mixed solvent. In addition, as each raw material of a solvent, that whose water content is 0.5 mass% or less was used. Next, TAC flaky powder was gradually added from the hopper. The TAC powder is put into a dissolution tank, and is initially a dissolver type eccentric agitator that stirs at a peripheral speed of 5 m / sec, and a condition in which the center axis has an anchor blade and agitates at a peripheral speed of 1 m / sec. Dispersed for 30 minutes. The temperature at the start of dispersion was 25 ° C., and the final temperature reached 48 ° C. Further, the additive solution prepared in advance was fed to the additive tank so that the total amount was 2000 kg. After finishing the dispersion of the additive solution, the high speed stirring was stopped. Then, the peripheral speed of the anchor blade was set at 0.5 m / sec, and the mixture was further stirred for 100 minutes to swell the TAC flakes to obtain a swelling liquid. Until the end of swelling, the inside of the dissolution tank was pressurized to 0.12 MPa with nitrogen gas. The inside of the dissolution tank at this time was kept in a state where there was no problem in terms of explosion prevention because the oxygen concentration was less than 2 vol%. The amount of water in the swelling liquid was 0.3% by mass.

  The swelling liquid was sent from the dissolution tank to the jacketed pipe using a pump. The swelling liquid was heated to 50 ° C. with a jacketed pipe, and further heated to 90 ° C. under a pressure of 2 MPa to completely dissolve. The heating time at this time was 15 minutes. Next, the temperature of the dissolved liquid was lowered to 36 ° C. with a temperature controller, and the solution was passed through a filtration apparatus having a filter medium having a nominal pore diameter of 8 μm to obtain a dope (hereinafter referred to as “pre-concentration dope”). At this time, the primary pressure in the filtration device was 1.5 MPa, and the secondary pressure was 1.2 MPa. The filters, housings and pipes exposed to high temperatures were made of Hastelloy (trade name) alloy and had excellent corrosion resistance, and were equipped with a jacket for circulating a heat transfer medium for heat insulation and heating.

The pre-concentration dope thus obtained was flash evaporated in a flash device at 80 ° C. and normal pressure, and the evaporated solvent was recovered by a condenser. The solid concentration of the dope after flashing was 22.5% by mass. The condensed solvent was recovered with a recovery device to be reused as a dope preparation solvent. Then, after regenerating with a regenerator, the solution was sent to a solvent tank. Distillation and dehydration were performed in the recovery device and the regeneration device. The flash tank of the flash device was provided with a stirrer having an anchor blade on the stirring shaft, and the dope flashed at a peripheral speed of 0.5 m / sec was stirred by the stirrer to perform defoaming. The temperature of the dope in this flash tank was 25 ° C., and the average residence time of the dope in the tank was 50 minutes. The shear viscosity measured by collecting this dope at 25 ° C. was 450 Pa · s at a shear rate of 10 (sec ⁻¹ ).

  Next, bubble removal was performed by irradiating the dope with weak ultrasonic waves. Thereafter, the filter was passed through the pump while being pressurized to 1.5 MPa using a pump. In the filtration apparatus, first, a sintered fiber metal filter having a nominal pore diameter of 10 μm was passed, and then a sintered fiber filter having a same pore diameter of 10 μm was passed. Respective primary pressures were 1.5 MPa and 1.2 MPa, and secondary pressures were 1.0 MPa and 0.8 MPa. The dope temperature after filtration was adjusted to 36 ° C., and the dope 21 was fed into a 2000 L stainless steel stock tank 20 and stored. The stock tank 20 had a stirrer provided with a stirring blade (anchor blade) 23 on the central axis, and was constantly stirred at a peripheral speed of 0.3 m / sec. In addition, when the dope was prepared from the dope before concentration, no problem such as corrosion occurred at all in the wetted part of the dope. The dope produced by the above method is referred to as dope A.

  A film was produced using the film production line 10 shown in FIG. The temperature of the dope 21 in the stock tank 20 was adjusted. Thereafter, the high-precision gear pump 24 was sent to the filtration device 11. The gear pump 24 has a function of increasing the pressure on the primary side of the pump 24, and sends the liquid by performing feedback control on the upstream side of the gear pump 24 with an inverter motor so that the pressure on the primary side becomes 0.8 MPa. . A gear pump 24 having a volume efficiency of 99.2% and a discharge rate variation rate of 0.5% or less was used. The discharge pressure was 1.5 MPa. Then, the dope 21 that passed through the filtration device 11 was fed to the casting die 30.

  A casting die 30 having a width of 1.8 m was used. Further, casting was performed by adjusting the flow rate of the dope 21 at the discharge port of the casting die 30 so that the film thickness of the dried film was 80 μm. The casting width of the dope 21 from the discharge port of the casting die 30 was 1700 mm. In order to adjust the temperature of the dope 21 to 36 ° C., the casting die 30 was provided with a jacket (not shown).

  The casting die 30 and the piping were all kept at 36 ° C. during film formation. The casting die 30 was a coat hanger type die. The casting die 30 was provided with thickness adjusting bolts at a pitch of 20 mm and equipped with an automatic thickness adjusting mechanism using heat bolts. The heat bolt can set a profile corresponding to the liquid feed amount of the gear pump 24 by a preset program, and is fed back by an adjustment program based on a profile of an infrared thickness meter (not shown) installed in the film production line 10. The thing which has the performance which can also be controlled was used. In the film excluding the edge 20 mm, the thickness difference between two arbitrary points 50 mm apart was within 1 μm, and the thickness variation in the width direction was adjusted to 3 μm / m or less. The overall thickness was adjusted to ± 1.5% or less.

  A decompression chamber 36 is provided on the upstream side of the casting die 30 in the support moving direction. The degree of decompression of the casting bead back surface by the decompression chamber 36 was adjusted so that the decompression of the casting bead back surface was 300 Pa lower than the atmospheric pressure.

The material of the casting die 30 was a precipitation hardening type stainless steel, and the material had a coefficient of thermal expansion of 2 × 10 ⁻⁵ (° C. ⁻¹ ) or less. In a forced corrosion test with an aqueous electrolyte solution, the material had a corrosion resistance substantially equivalent to that of SUS316. Further, even when immersed in a mixed solution of dichloromethane, methanol and water for 3 months, it had corrosion resistance that did not cause pitting (opening) at the gas-liquid interface. The finishing accuracy of the liquid contact surface of the casting die 30 was 1 μm or less in terms of surface roughness, the straightness was 1 μm / m or less in any direction, and the slit clearance was adjusted to 1.5 mm. About the corner | angular part of the liquid-contact part of the lip tip of the casting die 30, what was processed so that R might be set to 50 micrometers or less over the full width of a slit was used. The shear rate of the dope 21 inside the casting die 30 was in the range of 1 (1 / sec) to 5000 (1 / sec). Further, a WC (tungsten carbide) coating was performed on the lip end of the casting die 30 by a thermal spraying method to provide a cured film.

  Furthermore, in order to prevent the dope 21 flowing out from being locally dried and solidified at the discharge port of the casting die 30, a mixed solvent for solubilizing the dope 21 and the both-law side ends of the casting bead are provided. Each 0.5 ml / min was supplied to the interface with the discharge port. The pulsation rate of the pump supplying the mixed solvent was 5% or less. A jacket (not shown) was attached to make the internal temperature of the decompression chamber 36 constant at a predetermined temperature. A heat transfer medium adjusted to 35 ° C. was supplied into the jacket. The edge suction device can adjust the edge suction air volume so as to be in the range of 1 L / min to 100 L / min, and in the present embodiment, this is in the range of 30 L / min to 40 L / min. Adjusted appropriately.

  A casting drum 31 having a diameter of 3 m and a width of 1.5 m was used as a support. The surface material of the casting drum 31 is chrome-plated and has sufficient corrosion resistance and strength. Moreover, it grind | polished so that the surface roughness might be 0.05 micrometer or less. A liquid flow path was formed in the casting drum 31. A heat transfer medium circulation device 32 for supplying the heat transfer medium to the liquid flow path was attached. The surface temperature of the casting drum 31 was kept at −10 ° C. or lower. Further, when the casting drum 31 makes one rotation, the variation in the closest distance between the lip of the casting die 30 and the casting drum 31 (usually the position where the dope is cast) is 500 μm or less. did. The casting drum 31 was installed in the casting chamber 12 having wind pressure fluctuation suppressing means (not shown). The dope 21 was cast on the casting drum 31 from the casting die 30 so that the film thickness after drying was 80 μm.

The casting drum 31 preferably has no surface defects, has no pinholes of 30 μm or more, has no pinholes of 10 μm to 30 μm, 1 pin / m ² or less, and has 2 pinholes of less than 10 μm / m ^2. The following were used.

  The temperature of the casting chamber 12 was kept at 35 ° C. using the temperature control equipment 33. The cast film 39 was dried by sending dry air. The saturation temperature of the drying wind was around −8 ° C. The oxygen concentration in the dry atmosphere on the casting drum 31 was kept at 5 vol%. In order to maintain this oxygen concentration at 5 vol%, the air was replaced with nitrogen gas. Further, in order to condense and recover the solvent in the casting chamber 12, a condenser (condenser) 34 was provided, and its outlet temperature was set to -10 ° C.

  A wind shield (not shown) is installed so that dry air does not directly hit the casting bead and casting film 39 for 5 seconds after casting, and the static pressure fluctuation in the immediate vicinity of the casting die 30 is ± 1 Pa or less. Suppressed. When the solvent ratio in the casting film 39 reached 120% by weight on a dry basis, the film was peeled off as the wet film 60 while being supported by the peeling roller 61 from the casting drum 31. The solvent content on the basis of the dry weight is a value calculated by {(xy) / y} × 100, where x is the film weight at the time of sampling and y is the weight after drying the sampling film. It is. The stripping speed (stripping roller draw) was adjusted to 4% with respect to the speed of the casting drum 31 in order to suppress stripping failure and apply tension in the casting direction. The solvent gas generated by the drying was condensed and liquefied by a condenser 34 at −10 ° C. and recovered by a recovery device 35. The recovered solvent was adjusted so that the water content was 0.5% or less. The drying air from which the solvent was removed was heated again and reused as drying air.

  The wet film 60 was conveyed through the roller 62 of the crossover part 50. Tension was applied in the casting direction of the wet film 60 by increasing the rotational speed of the roller 62 at the crossover portion 50 and increasing the speed of the downstream roller. The solvent content based on the dry weight of the wet film 60 when transported to the transfer section 50 was 100% by weight. The film surface temperature of the wet film 62 was 20 ° C. ± 10 ° C. The film surface temperature was measured using a non-contact type surface thermometer. In the crossover portion 50, dry air was blown from the blower 51 to the wet film 60. The blowing temperature was adjusted as appropriate between 30 ° C and 100 ° C. A roller 62 made of Teflon (registered trademark) was used.

  Thereafter, the wet film 60 was sent to the tenter dryer 13. The solvent content on the dry basis of the wet film 60 when it was sent to the tenter dryer 13 was 70% by weight. The wet film 60 sent to the tenter dryer 13 was transported through the drying zone of the tenter dryer 13 while being fixed at both ends with clips, and was dried by drying air during this time. The clip was cooled by supplying a heat transfer medium at 20 ° C. The clip was conveyed by a chain, and the speed fluctuation of the sprocket was 0.5% or less. The drying air temperature in the tenter dryer 13 was adjusted to 120 ° C. The film surface temperature of the wet film 60 was in the range of 120 ° C. ± 20 ° C. Furthermore, the drying air temperature was kept constant at 130 ° C. while the wet film 60 was stretched or relaxed. The gas composition of the drying air was set to a saturated gas concentration at −10 ° C. The tenter dryer 13 was also stretched in the width direction while being conveyed.

  When the width of the wet film 60 before stretching was 100%, the film was stretched so that the width after stretching was 108%, and then relaxed to 105%. The stretching ratio in the tenter dryer 13 is any two at a difference of 10% or less between each of the substantial stretching ratios at any two points at a position 10 mm or more away from the biting start position by the clip and at a distance of 20 mm. The difference in the stretching ratio of points was 5% or less. The ratio of the length from the clip clamping start position to the clamping release position with respect to the length from the inlet to the outlet of the tenter dryer 13 was 90%. The solvent evaporated in the tenter dryer 13 was condensed and liquefied at a temperature of −10 ° C. and recovered. A condenser (condenser) was provided for condensation recovery, and the outlet temperature was set to -8 ° C. The condensed solvent was reused after adjusting the water content to 0.5% by mass or less. And it sent out from the tenter type dryer 13 as the film 52.

Then, the ear-cutting device 14 cuts off both ends of the film 52 within 30 seconds from the outlet of the tenter dryer 13. Ears 50 mm on both sides were cut with an NT-type cutter, and the cut ears were blown to a crusher 53 with a cutter blower (not shown) and crushed into chips of about 80 mm ² on average. This chip was used again as a raw material for dope production together with TAC flakes as a raw material for dope preparation. The oxygen concentration in the drying atmosphere of the tenter dryer 13 was maintained at 5 vol%. Note that the air was replaced with nitrogen gas in order to maintain the oxygen concentration at 5 vol%. Before drying at a high temperature in the drying chamber 15 described later, the film 52 was preheated in a predrying chamber (not shown) supplied with 100 ° C. drying air.

  The film 52 was dried at high temperature in the drying chamber 15. The solvent content based on the dry amount of the film 52 immediately before being put into the drying chamber 15 was 5% by weight. A drying air of 143 ° C. was supplied into the drying chamber 15 from a blower (not shown), and the film surface temperature of the film 52 was adjusted to a range of 140 ° C. ± 40 ° C. The conveying tension of the film 52 by the roller 54 was set to 100 N / m, and the film was dried for about 10 minutes until the residual solvent amount finally reached 1% by weight on the dry basis. The wrap angle of the roller 54 (film winding center angle) was 90 degrees and 180 degrees. The material of the roller 54 was made of aluminum or carbon steel, and the surface thereof was subjected to hard chrome plating. As the roller 54, a roller having a flat surface shape and a roller matted by blasting were used. All film position fluctuations due to the rotation of the roller 54 were 50 μm or less. The roller deflection at a tension of 100 N / m was selected to be 0.5 mm or less.

  The solvent gas contained in the drying chamber 15 was removed by adsorption using the adsorption / recovery device 55. The adsorbent used here was activated carbon, and desorption was performed using dry nitrogen. The recovered solvent was reused as a dope preparation solvent with the water content adjusted to 0.3 mass% or less. The drying air contains plasticizers, UV absorbers and other high-boiling substances in addition to the solvent gas, so these were removed by a cooler and pre-adsorber to be removed by cooling and used for recycling. And adsorption / desorption conditions were set so that VOC (volatile organic compound) in the outdoor exhaust gas was finally 10 ppm or less. Moreover, the solvent amount collect | recovered by a condensation method among all the evaporation solvents was 90 mass%, and most of the remainder was collect | recovered by adsorption collection.

  The dried film 52 was conveyed to a first humidity control chamber (not shown). A drying air of 110 ° C. was supplied to the transition portion between the drying chamber 15 and the first humidity control chamber. Air having a temperature of 50 ° C. and a dew point of 20 ° C. was supplied to the first humidity control chamber. Further, the film 52 was conveyed to a second humidity control chamber (not shown) that suppresses the curling of the film 52. In the second humidity control chamber, air of 90 ° C. and humidity of 70% was directly applied to the film 52.

  The film 52 after humidity control was cooled to 30 ° C. or lower in the cooling chamber 16, and then subjected to ear cutting at both ends again with an ear cutting device (not shown). The charged voltage of the film 52 being conveyed was adjusted by installing a forced charge removal device (charge removal bar) 56 so that the voltage was always in the range of −3 kV to +3 kV. Further, knurling was applied to both ends of the film 52 by a knurling roller 57. The knurling is imparted by embossing from one side of the film 52, the width for imparting the knurling is 10 mm, and the pressure applied by the knurling roller so that the height of the unevenness is 12 μm higher than the average thickness of the film 52 on average. It was set.

  Then, the film 52 was conveyed to the winding chamber 17. The air conditioning of the winding chamber 17 was maintained at a room temperature of 28 ° C. and a humidity of 70%. Inside the winding chamber 17, an ion wind static eliminating device (not shown) was also installed so that the charged voltage of the film 52 was −1.5 kV to +1.5 kV. The product width of the film (thickness 40 μm) 52 thus obtained was 1475 mm. The diameter of the winding roller 58 was 169 mm. The tension pattern was such that the winding start tension was 300 N / m and the winding end was 200 N / m. The total winding length was 4000 m. The variation range of winding deviation at the time of winding (sometimes referred to as the oscillating width) was ± 5 mm, and the winding deviation period with respect to the winding roller 58 was 400 m. The pressing pressure of the press roller 59 against the take-up roller 58 was set to 50 N / m.

The temperature of the film 52 at the time of winding was 23 ° C., the water content was 1.0% by weight, and the residual solvent amount was 1% by weight. The average drying rate was 20% by weight / min on the basis of the dry weight throughout the entire process. There was no winding looseness, no wrinkles, and no slippage occurred in the impact test at 10G. The roll appearance was also good.

  The film roll of the film 52 was stored in a storage rack at 25 ° C. and 55% RH for 1 month and further examined in the same manner as described above. As a result, no significant change was observed. Further, no adhesion was observed in the roll. In addition, after the film 52 was formed, no casting film 39 was left on the casting drum 31.

Measurement of sound velocity value The sound velocity value was measured using an SST-110 type sound velocity measuring device manufactured by Nomura Corporation. The film 52 was conditioned at 25 ° C. and 55% RH for 2 hours. Two vibrators (transmitting vibrator and receiving vibrator) were contacted in the MD direction of the film 52 at intervals of 150 mm. The measurement was performed 5 times and the average time was used. The sound velocity value in the MD direction was 2.59 km / sec.

  The sound velocity value in the TD direction was also measured and calculated in the same manner as in the TD direction, and was 2.28 km / sec. The sound speed ratio (= MD / TD) was 1.136.

Measurement of Front Retardation (Re) The film 52 was cut into 70 mm × 100 mm, conditioned for 2 hours at a temperature of 25 ° C. and a humidity of 60% RH, and 632 by an automatic birefringence meter (KOBRA21DH Oji Scientific Co., Ltd.). The extrapolation value of the retardation value measured from the vertical direction at 8 nm was calculated according to the following formula.
Re (nm) = (nx−ny) × d
nx is the refractive index in the slow axis direction (MD direction in Experiment 1), ny is the refractive index in the fast axis direction (TD direction in Experiment 1), and d is the film thickness (nm) of the film 52.
As a result of measurement, it was −9.8 nm and was a good product (◯). In addition, in this invention, the thing below -3 nm was made into the non-defective product ((circle)), and the thing exceeding -3 nm was evaluated as inferior goods (x).

It is the schematic of the film manufacturing line for enforcing the solution casting method concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Film production line 13 Tenta dryer 15 Drying chamber 21 Dope 50 Transition part 52 Film

Claims (7)

A dope containing a polymer and a solvent is cast on a support from a casting die to form a gelled casting film,
In the method for producing a cellulose acylate film, the cast film is peeled off as a film from the support after the cast film has a self-supporting property, and dried.
A solution casting method, wherein the polymer main chain is oriented in the casting direction. The drying is a case where the film is dried while being transported by a plurality of rollers after the film is peeled off from the support,
When the amount of solvent contained on the dry basis of the film is 65 wt% or more and 80 wt% or less,
The solution film-forming method according to claim 1, wherein the film surface temperature of the film is 110 ° C. or more and 140 ° C. or less. When the drying is performed while gripping both edges of the film with gripping means,
When the amount of solvent contained on the dry basis of the film is 60 wt% or more and 80 wt% or less,
3. The solution casting method according to claim 1, wherein the film surface temperature of the film is 110 ° C. or more and 140 ° C. or less.   4. The solution casting method according to claim 3, wherein the temperature at which the film is heated is substantially constant while the width of the gripping means is substantially changed. After the drying is performed by the gripping means, the film is dried while being conveyed by a plurality of rollers,
When the amount of solvent contained on the dry basis of the film is 1 wt% or more and 8 wt% or less,
5. The solution casting method according to claim 1, wherein a film surface temperature of the film is 100 ° C. or more and 220 ° C. or less.   6. The solution casting method according to claim 1, wherein a front retardation Re (nm) of the film is set to -3 nm or less.   The solution casting method according to any one of claims 1 to 6, wherein the polymer is cellulose acylate.

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