JP4841273B2 - Solution casting method - Google Patents

Description

  The present invention relates to a solution casting method.

  A cellulose acylate film, particularly a TAC film formed from cellulose triacetate (hereinafter referred to as TAC) having an average degree of acetylation of 57.5% to 62.5%, is photographic sensitive because of its toughness and flame retardancy. Widely used as a film support for materials. 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 more excellent physical properties such as optical properties than other production methods such as a melt casting method. In the solution casting method, a polymer solution (hereinafter referred to as a dope) in which a polymer is dissolved in a solvent is prepared. The solvent is often a mixture mainly composed of dichloromethane, methyl acetate, or the like. Then, the dope is cast on a support by forming a casting bead from a casting die to form a casting film. After the cast membrane becomes self-supporting on the support, the cast membrane is peeled off as a film from the support. Since the film when peeled off contains a solvent, it is hereinafter referred to as a wet film. The wet film is also dried while being stretched and relaxed in the casting width direction by a tenter dryer. Thereby, the flatness of the surface of the wet film can be improved. And the dried film is wound up (for example, refer nonpatent literature 1).

  However, when tension is applied in the width direction of the wet film with a tenter dryer, a bowing phenomenon occurs. It is known that due to this phenomenon, the direction of the slow axis differs in the casting width direction. Recently, in relation to the improvement in quality of liquid crystal display devices such as the contrast ratio and screen brightness, the demand for variation in the width direction of the slow axis direction of optical films has become increasingly severe, and improvement is desired. Yes. In particular, in a protective film for a polarizing plate, there is a strong demand for increasing accuracy in the slow axis direction. For the protective film of the polarizing plate, it is also required to set the in-plane retardation value to a very low value (0 nm to 5 nm) in order to prevent the ellipticalization of linearly polarized light, and the longitudinal direction of the film This is because the molecules cannot be uniformly oriented in either the width direction or the width direction.

  As a technique for preventing the occurrence of the bowing phenomenon, a method of performing biaxial stretching in the production of a polyester film by a melt film forming method has been well studied, and various improved methods have been proposed (for example, see Patent Document 1). ). However, in solution casting, the elastic modulus of the film changes according to the amount of residual solvent, so it is very difficult to control bowing.

  As a means for preventing the occurrence of the bowing phenomenon in the solution casting method, (1) the temperature of the edge is made higher than the center of the wet film. (2) Increase the amount of solvent at the edge of the wet film from the center. (3) A method of providing zones with different temperatures in the tenter dryer has been proposed (see, for example, Patent Document 2).

In addition, a method of making the direction of the slow axis uniform by setting the change in the amount of solvent in the film in the section holding both ends of the film with a tenter dryer to 25% by weight or less has also been proposed (for example, (See Patent Document 3).
Japan Society for Invention and Innovation Public Technical Bulletin No. 2001-1745 JP 2004-034536 A JP 2002-296422 A JP 2004-314529 A

  However, in the method described in Patent Document 2, it is necessary to provide a number of zones with different heating conditions in the stretching zone of the tenter dryer. It is also necessary to perform precise temperature control in the casting width direction of the wet film. Therefore, there arises a problem that the equipment cost increases due to factors such as the number of heating means, an increase in the number of control devices, and a complicated structure. Further, as the wet film is further dried in the tenter dryer, the flatness of the wet film is improved and the birefringence characteristics of the wet film are also changed. However, the technique described in Patent Document 3 has a problem that the flatness and birefringence characteristics cannot always be adjusted to the desired ranges because the amount of wet film dried by the tenter dryer is limited.

  An object of this invention is to provide the solution casting method which can manufacture the film by which generation | occurrence | production of the bowing phenomenon was suppressed, without using special equipment.

  As a result of intensive studies by the present inventors, it has been found that the occurrence of bowing occurs at the time of changing the width of stretching and relaxation in the width direction of the wet film during the drying of the wet film in the tenter dryer. We found that Boeing occurs when the width change speed is high. Therefore, in the present invention, the occurrence of bowing is suppressed by slowing the changing speed of the width of the wet film. It has also been found that bowing is likely to occur immediately after the entrance of the tenter drier. The wet film before being put into the tenter dryer is not tensioned in the width direction. Accordingly, it has been found that when the wet film is conveyed to a tenter dryer and both edges are gripped, tension is applied in the width direction of the wet film and bowing is likely to occur. The inventor has also found that the influence of the application of tension immediately after the tenter dryer entrance is about five times as frequent as the relaxation step performed later. Therefore, according to the present invention described below, it is possible to suppress the occurrence of bowing due to the tension at the tenter dryer inlet and the occurrence of bowing when relaxing the wet film.

  According to the method of the present invention, it is not necessary to change the drying conditions (for example, temperature) in the width direction of the wet film. Moreover, there is no possibility that the drying amount of the solvent in the wet film is limited in the tenter type dryer. Furthermore, it has also been found that the slow axis accuracy can be improved by changing the stretching pattern.

The solution casting method of the present invention includes a casting film forming step in which a dope containing cellulose acylate and a solvent is cast on a support to form a casting film, and the casting film is dried. In the solution film-forming method having a stripping step for stripping off as a film and a gripping drying step for gripping both ends of the film and drying while transporting the film, the gripping drying step starts gripping, and the width of the film is increased A first width holding step for holding, a stretching step for stretching the film in the width direction to enlarge it after the first width holding step , a relaxation step for reducing the width of the film after the stretching step, and a relaxation step And a second width holding step for holding the width until the grip is released. The width of the film at the start of gripping is La, and the film when 0.1 minute has elapsed from the start of gripping When the width is Lb And the relaxation relaxation rate per unit time in the step Y; {(Lb-La) / La} stretch rate X calculated by the × 100 (% unit); and (in% / min), but the 5X + Y <1 condition it that is configured as characterized in satisfying. Name your, per unit time the relaxation rate Y, hereinafter referred to as the relaxation rate Y. In the stripping step, it is preferable that the cast film having a residual solvent amount of 20% by weight to 250% by weight is stripped, and in the gripping drying step, the film is dried until it becomes 14% by weight to 17% by weight.

The stretching ratio X (%) is preferably 1.0% or less, and more preferably 0.50% or less. The relaxation rate Y (% / min) arbitrary preferred to 5.0% / min or less.

According to the solution casting method of the present invention, prior SL is generated in the time of stretching and bowing phenomenon upon relaxation suppression of the film, the surface of the state, that surface is good and plane retardation (Re) of the desired A film that is in range can be obtained. The film is preferably used for an optical film.

In addition to the above method,
(1) The stretch ratio X (%) of the film is 1.0% or less.
(2) The relaxation rate Y (% / min) is set to 5.0% / min or less.
Satisfying at least one of the above conditions further increases the effect of suppressing the bowing phenomenon, further improves the surface shape, and makes it easier to control the in-plane retardation (Re) to be in a desired range. .

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

[material]
In the present embodiment, cellulose acylate is used as the polymer, and triacetyl cellulose (TAC) is particularly preferable as the cellulose acylate. Among cellulose acylates, those in which the substitution degree of the acyl group with respect to the hydrogen atom of the hydroxyl group of cellulose satisfies all of the following formulas (I) to (III) are more preferable. In the following formulas (I) to (III), A and B represent the substitution degree of the acyl group with respect to the hydrogen atom of the hydroxyl group of cellulose, A represents the substitution degree of the acetyl group, and B represents 3 to 3 carbon atoms. 22 is the substitution degree of the acyl group. However, the polymer 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 constituting cellulose and having β-1,4 bonds 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 of the hydroxyl group of cellulose esterified at each of the 2-position, 3-position and 6-position (100% esterification has a substitution degree of 1).

The total acylation substitution degree, that is, 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, DS6 / (DS2 + DS3 + DS6) is preferably 0.28 or more, more preferably 0.30 or more, and particularly preferably 0.31 to 0.34. Here, DS2 is the degree of substitution of the hydroxyl group at the 2-position of the glucose unit with an acyl group (hereinafter also referred to as “degree of acyl substitution at the 2-position”), and DS3 is the degree of substitution of the hydroxyl group at the 3-position with an acyl group (hereinafter, referred to as “acyl group”). DS6 is the substitution degree of the hydroxyl group at the 6-position with an acyl group (hereinafter also referred to as “acyl substitution degree at the 6-position”).

  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. When the sum of the substitution degrees by the hydroxyl groups at the 2nd, 3rd and 6th positions is DSA, and the sum of the substitution degree by an acyl group other than the acetyl group at the 2nd, 3rd and 6th hydroxyl groups is DSB, the value of DSA + DSB is More preferably, it is 2.22 to 2.90, and particularly preferably 2.40 to 2.88. The DSB is 0.30 or more, particularly preferably 0.7 or more. Further, 20% or more of DSB is a substituent at the 6-position hydroxyl group, more preferably 25% or more is a substituent at the 6-position hydroxyl group, more preferably 30% or more, and particularly 33% or more is a 6-position hydroxyl group. It is preferable that it is a substituent. Furthermore, the cellulose acylate having a substitution degree of 6-position of cellulose acylate of 0.75 or more, further 0.80 or more, and particularly 0.85 or more can be mentioned. A preferable dope can be produced by using these cellulose acylates. In particular, when a non-chlorine organic compound is used as a solvent, a good dope can be produced. Furthermore, a dope having a low viscosity and good filterability can be produced.

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

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

  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. The content of the alcohol is preferably 2% by weight to 25% by weight and more preferably 5% by weight to 20% by weight with respect to the whole solvent. 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.

  By the way, recently, for the purpose of minimizing the influence on the environment, studies have been conducted on the solvent composition when dichloromethane is not used. For this purpose, ethers having 4 to 12 carbon atoms, 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 preferably used. These may be used in combination as appropriate. 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.

  The details of cellulose acylate are described in paragraphs [0140] to [0195] of JP-A-2005-104148. 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, etc. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516], and these can also be applied to the present invention.

[Dope production method]
First, a dope is manufactured using the above raw materials. The dope production line includes a solvent tank for storing the solvent, a mixing tank for mixing the solvent and TAC, a hopper for supplying TAC, and an additive tank for storing the additive. ing. Furthermore, a heating device for heating the swelling liquid described later, a temperature controller for adjusting the temperature of the prepared dope, and a filtration device are provided. Further, a recovery device for recovering the solvent and a regeneration device for regenerating the recovered solvent are provided. The dope production line is connected to the film production line 10 via the stock tank 11.

  First, the valve is opened and the solvent is sent from the solvent tank to the mixing tank. Next, it is put in the hopper, but sent to the mixing tank while being weighed. The additive solution (mainly containing the plasticizer) is fed from the additive tank to the mixing tank by opening and closing the valve. In addition to the method of feeding the additive as a solution, for example, when the additive is liquid at room temperature, it can be fed into the mixing tank in the liquid state. Further, when the additive is solid, a method of feeding into the mixing tank using a hopper or the like is also possible. When a plurality of types of additives are added, a solution in which a plurality of types of additives are dissolved can be placed in the additive tank. Alternatively, a solution in which an additive is dissolved can be put in each of a plurality of additive tanks and sent to the mixing tank through independent pipes.

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

  The mixing tank is provided with a jacket that wraps the outer surface thereof and a first stirrer that is rotated by a motor. Furthermore, it is preferable that the 2nd stirrer rotated by a motor is attached. The first stirrer is preferably provided with anchor blades, and the second stirrer is preferably a dissolver type eccentric stirrer. The temperature of the mixing tank is adjusted by flowing a heat transfer medium inside the jacket, and a preferable temperature range is -10 ° C to 55 ° C. By appropriately selecting and using the types of the first stirrer and the second stirrer, a swelling liquid in which TAC is swollen in a solvent is obtained.

  Next, the swelling liquid is sent to a heating device by a pump. The heating device is preferably a jacketed pipe, and further preferably has a configuration capable of pressurizing the swelling liquid. By using such a heating apparatus, the dope is obtained by dissolving the solid content in the swelling liquid under heating conditions or under pressure heating conditions. Hereinafter, this method is referred to as a heating dissolution method. In this case, the temperature of the swelling liquid is preferably 50 ° C to 120 ° C. 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 dope is brought to about room temperature with a temperature controller, the impurities contained in the dope are removed by filtration with a filtration device. The filtration filter used in the filtration device preferably has an average pore diameter of 100 μm or less. The filtration flow rate is preferably 50 L / hr or more. The dope 12 after filtration is sent to the stock tank 11 in the film production line 10 and stored therein.

  By the way, as described above, the method of once preparing the swelling liquid and then using the swelling liquid as a dope increases the time required as the concentration of TAC is increased, which may be problematic in terms of manufacturing cost. . In that case, it is preferable to prepare a dope having a concentration lower than the target concentration and then perform a concentration step for obtaining the target concentration.

  By the above method, the dope 12 having a TAC concentration of 5 wt% to 40 wt% can be manufactured. More preferably, the TAC concentration is in the range of 15% by weight to 30% by weight, and most preferably in the range of 17% by weight to 25% by weight. The concentration of the additive (mainly a plasticizer) is preferably in the range of 1% by weight to 20% by weight when the total solid content in the dope is 100% by weight. In addition, from the [0517] paragraph of Unexamined-Japanese-Patent No. 2005-104148 about the manufacturing methods of dope, such as the raw material in the solution casting method which obtains a TAC film, a raw material, the additive dissolution method and addition method, a filtration method, and defoaming. [0616] The paragraph is detailed. These descriptions are also applicable to the present invention.

[Solution casting method]
Next, a method for producing a film using the dope 12 obtained above will be described. FIG. 1 is a schematic view showing a film production line 10. However, the present invention is not limited to the film production line as shown in FIG. The film production line 10 includes a stock tank 11, a casting die 13, a casting band 16 stretched around rotating rollers 14 and 15, a tenter dryer 17, and the like. Further, an ear-cutting device 20, a drying chamber 21, a cooling chamber 22, a winding chamber 23, and the like are arranged.

  An agitator 31 that is rotated by a motor 30 is attached to the stock tank 11. The stock tank 11 is connected to a pipe 34 including a pump 32 and a filtration device 33. Further, a static mixer 35 is attached and connected to the casting die 13.

  The stock tank 40 stores a matting agent solution 41. The matting agent solution 41 includes a solvent, a polymer, an additive, and the like constituting the dope 12 and is prepared so as to be easily mixed with the dope 12. The stock tank 40 is connected to a pipe 43 provided with a pump 42. The matting agent used in the present invention is not particularly limited, but silica, alumina and the like are preferably used. The concentration is not particularly limited, but is preferably in the range of 0.01% by weight to 0.50% by weight.

  The stock tank 45 stores an ultraviolet absorbent solution 46. The ultraviolet absorber solution 46 includes a solvent, a polymer, an additive, and the like constituting the dope 12 and is prepared so as to be easily mixed with the dope 12. The stock tank 45 is connected to a pipe 48 provided with a pump 47. The pipe 48 is connected to a pipe 43 through which the matting agent liquid 41 is fed. A static mixer 49 is attached to the pipe 48. Further, the pipe 48 is connected to the pipe 34 through which the dope 12 is fed downstream of the static mixer 49. In addition, although the ultraviolet absorber used for this invention is not specifically limited, A benzotriazole type, a benzophenone type, etc. are used preferably. Further, the concentration is not particularly limited, but is preferably in the range of 0.1% by weight to 3.0% by weight.

  The matting agent solution 41 passes through the pipe 43 and is mixed with the ultraviolet absorbent solution 46. Thereafter, the mixture is uniformly mixed and stirred by the static mixer 49. Hereinafter, the mixed and stirred liquid is referred to as an additive liquid.

  The additive solution is mixed with the dope 12 that is fed through the pipe 34. Thereafter, the mixture is stirred by the static mixer 35 to become a uniform liquid. Hereinafter, this liquid is referred to as casting dope.

As a material of the casting die 13, precipitation hardening type stainless steel is preferable, and its thermal expansion coefficient is preferably 2 × 10 ⁻⁵ (° C. ⁻¹ ) or less. And what has corrosion resistance substantially equivalent to SUS316 in the forced corrosion test with the electrolyte aqueous solution can be used as the material of the casting die 13 and further immersed in a mixed solution of dichloromethane, methanol and water for 3 months. Even if it has corrosion resistance that does not cause pitting (perforation) at the gas-liquid interface, it is used. Furthermore, it is preferable that the casting die 13 is manufactured by grinding a material that has passed one month or more after casting. This prevents the casting dope from flowing uniformly in the casting die 13 and prevents streaks and the like from occurring in the casting film described later. The finishing accuracy of the wetted surface of the casting die 13 is preferably 1 μm or less in terms of surface roughness, and the straightness is preferably 1 μm / m or less in any direction. The slit clearance of the casting die 13 can be adjusted in the range of 0.5 mm to 3.5 mm by automatic adjustment. About the corner | angular part of the liquid-contact part of the lip | tip end of the casting die 13, that R is 50 micrometers or less over the whole width. Moreover, it is preferable that the shear rate of the casting dope in the casting die 13 is adjusted to be 1 (1 / sec) to 5000 (1 / sec).

  Although the width | variety of the casting die 13 is not specifically limited, It is preferable that it is 1.1 times-2.0 times the width of the film used as a final product. Moreover, it is preferable to attach a temperature controller to the casting die 13 so that the temperature during film formation is maintained at a predetermined temperature. The casting die 13 is preferably a coat hanger type. Furthermore, it is more preferable that thickness adjusting bolts (heat bolts) are provided at predetermined intervals in the width direction of the casting die 13 and the casting die 13 is provided with an automatic thickness adjusting mechanism using a heat bolt. The heat bolt is preferably subjected to film formation by setting a profile according to the amount of pump 32 (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. The thickness difference between any two points in the width direction of the product film, excluding the casting edge portion, is adjusted within 1 μm, and the difference between the minimum value and the maximum value in the width direction thickness is adjusted to 3 μm or less. Preferably, adjusting to 2 μm or less is more preferable. 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 end of the casting die 13. 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 13, and have no adhesion to the dope are preferable. Specifically, tungsten carbide (WC), Al ₂ O ₃ , TiN, Cr ₂ O _{3 and the} like can be mentioned, among which WC is particularly preferable. The WC coating can be performed by a thermal spraying method.

  In order to prevent the casting dope flowing out to the slit end of the casting die 13 from locally drying and solidifying, it is preferable to attach a solvent supply device (not shown) to the slit end. In this case, a solvent for solubilizing the casting dope (for example, a mixed solvent of 86.5 parts by weight of dichloromethane, 13 parts by weight of acetone, and 0.5 parts by weight of n-butanol) is added to both ends of the casting bead and the die. It is preferable to supply near the periphery of the three-phase contact line formed by the slit end and the outside air. It is preferable to supply at 0.1 mL / min to 1.0 mL / min to each one side of the end portion in order to prevent mixing of foreign matters into the cast film. In addition, as a pump which supplies this liquid, it is preferable to use a pump with a pulsation rate of 5% or less.

  A casting band 16 is provided below the casting die 13 so as to span the rotating rollers 14 and 15. The rotating rollers 14 and 15 are rotated by a driving device (not shown), and the casting band 16 travels endlessly with the rotation. It is preferable that the casting band 16 can move at a moving speed, that is, a casting speed of 10 m / min to 200 m / min. In order to set the surface temperature of the casting band 16 to a predetermined value, it is preferable that the heat transfer medium circulation device 60 is attached to the rotary rollers 14 and 15. The casting band 16 is preferably one whose surface temperature can be adjusted to -20 ° C to 40 ° C. A heat transfer medium flow path (not shown) is formed in the rotating rollers 14 and 15 used in this embodiment, and the heat transfer medium maintained at a predetermined temperature passes through the flow path. The temperatures of the rotary rollers 14 and 15 are maintained at a predetermined value.

  The width of the casting band 16 is not particularly limited, but it is preferable to use a casting band having a range of 1.1 to 2.0 times the casting width of the casting dope. Further, it is preferable that the length is 20 m to 200 m, the thickness is 0.5 mm to 2.5 mm, and the surface roughness is polished to be 0.05 μm or less. The casting band 16 is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength. Moreover, it is preferable to use the thickness unevenness of the entire casting band 16 of 0.5% or less.

It is also possible to use the rotating rollers 14 and 15 directly as a support. In this case, it is preferable that the rotation can be performed with high accuracy so that the rotation unevenness is 0.2 mm or less. In this case, it is preferable that the average roughness of the surfaces of the rotary rollers 14 and 15 is 0.01 μm or less. Therefore, the surface of the rotating roller is subjected to chrome plating or the like so as to have sufficient hardness and durability. In addition, it is necessary to suppress the surface defects of the support (the casting band 16 and the rotating rollers 14 and 15) to the minimum. Specifically, there is no pinhole of 30 μm or more, and the number of pinholes of 10 μm or more and less than 30 μm is 1 / m ² or less, and the number of pinholes of less than 10 μm is preferably ² / m ² or less.

  The casting die 13 and the casting band 16 are accommodated in the casting chamber 61. The casting chamber 61 is provided with a temperature control facility (not shown) for keeping the internal temperature at a predetermined value, and a condenser (condenser) 63 for condensing and recovering the volatile organic solvent. Yes. A recovery device 64 for recovering the condensed organic solvent is provided outside the casting chamber 61. Further, it is preferable that a decompression chamber 65 for controlling the pressure of the back surface of the casting bead formed from the casting die 13 to the casting band 16 is disposed, and this is also used in the present embodiment. .

  Blower ports 71, 72, 73 are provided near the peripheral surface of the casting band 16 in order to evaporate the solvent in the casting film 70. Further, a wind shielding plate 74 is provided at the air blowing port 71 in the vicinity of the casting die 13 in order to suppress the surface variation of the casting film 70 due to the blowing air being blown onto the casting film 70 immediately after casting. It is preferable.

  The crossover section 80 is provided with a blower 81, and a crusher 91 for finely cutting the scrap at the side end of the cut film 90 is connected to the ear clip device 20 downstream of the tenter dryer 17. Yes.

  The drying chamber 21 is provided with a number of rollers 100, and an adsorption recovery device 101 for adsorbing and recovering the solvent gas generated by evaporation is attached. In FIG. 1, the cooling chamber 22 is provided downstream of the drying chamber 21, but a humidity control chamber (not shown) may be provided between the drying chamber 21 and the cooling chamber 22. A forced static elimination device (static elimination bar) 102 for adjusting the charged voltage of the film 90 to a predetermined range (for example, −3 kV to +3 kV) is provided downstream of the cooling chamber 22. In FIG. 1, an example in which the forced static elimination device 102 is on the downstream side of the cooling chamber 22 is illustrated, but the configuration is not limited to this installation position. Furthermore, in this embodiment, a knurling roller 103 for applying knurling to both edges of the film 90 by embossing is appropriately provided downstream of the forced static elimination device 102. The winding chamber 23 is provided with a winding roller 110 for winding the film 90 and a press roller 111 for controlling the tension during the winding.

  Next, an example of a method for producing the film 90 using the film production line 10 as described above will be described below. The dope 12 is always made uniform by the rotation of the stirrer 31. The dope 12 may be mixed with an additive such as a plasticizer during the stirring.

  The dope 12 is sent to the filtering device 33 by the pump 32 and filtered there. The matting agent liquid 41 is fed into the pipe 43 by the pump 42. The ultraviolet absorbent solution 46 is fed through a pipe 48 by a pump 47. The matting agent solution 41 in the pipe 43 is mixed in the ultraviolet absorbent solution 46 in the pipe 48. Thereafter, the mixture is stirred and mixed by the static mixer 49 to obtain a uniform additive solution. The additive solution is fed through the pipe 48 and mixed with the dope 12 fed into the pipe 34. Thereafter, the mixture is stirred and mixed by the static mixer 35 to obtain a casting dope having a substantially uniform composition. The mixing ratio of the dope 12, the matting agent solution 41, and the ultraviolet absorber solution 46 is not particularly limited, but is 90% by weight: 5% by weight: 5% by weight to 99% by weight: 0.5% by weight: 0. Preferably it is in the range of 5% by weight.

The casting dope is cast on the casting band 16 from the casting die 13. The driving of the rotating rollers 14 and 15 is preferably adjusted so that the tension generated in the casting band 16 is 10 ⁴ N / m to 10 ⁵ N / m. The relative speed difference between the casting band 16 and the rotating rollers 14 and 15 is adjusted to be 0.01 m / min or less. The speed fluctuation of the casting band 16 is preferably 0.5% or less, and the meandering in the width direction that occurs when the casting band 16 rotates once is preferably 1.5 mm or less. In order to control this meandering, a detector (not shown) that detects the positions of both ends of the casting band 16 is provided, and based on the measured value, feedback control is performed on a position controller (not shown) of the casting band 16; It is more preferable to adjust the position of the casting band 16. Further, it is preferable that the casting band 16 immediately below the casting die 13 is adjusted so that the vertical position variation accompanying the rotation of the rotary roller 14 is 200 μm or less. Moreover, it is preferable that the temperature of the casting chamber 61 shall be -10 degreeC-57 degreeC with temperature control equipment (not shown). The solvent evaporated in the casting chamber 61 is condensed and liquefied by the condenser 63 and then recovered by the recovery device 64, and then regenerated and reused as a dope preparation solvent.

  A casting bead is formed from the casting die 13 to the casting band 16, and a casting film 70 is formed on the casting band 16. The temperature of the casting dope during casting is preferably -10 ° C to 57 ° C. Further, in order to stabilize the casting bead, the back surface of the casting bead is preferably controlled to a desired pressure value by the decompression chamber 65. The back surface of the bead is preferably decompressed in the range of −2000 Pa to −10 Pa than the front surface. Further, it is preferable that a jacket (not shown) is attached to the decompression chamber 65 and the temperature is controlled so that the internal temperature is kept at a predetermined temperature. The temperature of the decompression chamber 65 is not particularly limited, but is preferably set to be equal to or higher than the condensation point of the organic solvent used. In order to keep the shape of the casting bead desired, it is preferable to attach a suction device (not shown) to the edge portion of the casting die 13. The edge suction air volume is preferably in the range of 1 L / min to 100 L / min.

  The casting film 70 moves as the casting band 16 travels. At this time, drying air is applied to the casting film 70 through the air blowing ports 71, 72, 73, and evaporation of the solvent is promoted. The surface of the casting film 70 may change due to the blowing of the dry air, but the wind shielding plate 74 suppresses this change. In addition, it is preferable that the surface temperature of the casting band 16 is -20 degreeC-40 degreeC.

  After the casting film 70 has self-supporting properties, the casting film 70 is peeled off from the casting band 16 while being supported by the peeling roller 121 as the wet film 120. The amount of residual solvent at the time of stripping is preferably 20% by weight to 250% by weight based on the solid content. Thereafter, the transfer section 80 provided with a large number of rollers is conveyed, and the wet film 120 is fed into the tenter dryer 17. In the transition part 80, the drying of the wet film 120 is advanced by sending the drying air of desired temperature from the air blower 81. FIG. At this time, the temperature of the drying air is preferably 20 ° C to 250 ° C. In the transition section 80, it is also possible to apply a draw tension to the wet film 120 by making the rotation speed of the downstream roller faster than the rotation speed of the upstream roller.

  The wet film 120 sent to the tenter dryer 17 is dried while being conveyed while being gripped by clips at both ends. Moreover, it is preferable to divide the inside of the tenter dryer 17 into temperature zones and adjust the drying conditions appropriately for each zone. It is also possible to stretch the wet film 120 in the width direction using the tenter dryer 17. It is preferable to stretch at least one of the longitudinal direction and the width direction of the wet film 120 by 0.5% to 300% in at least one of the transition portion 80 and the tenter dryer 17. The drying of the wet film 120 by the tenter dryer 17 will be described in detail later.

  The wet film 120 is dried to a predetermined residual solvent amount by the tenter dryer 17 and then sent to the downstream side as a film 90. Both ends of the film 90 are cut at both edges by the edge-cutting device 20. The cut side end is sent to the crusher 91 by a cutter blower (not shown). By the crusher 91, the film side end portion is crushed into chips. Since this chip is reused for dope preparation, this method is effective in terms of cost. In addition, although it can also abbreviate | omit about the cutting process of this film both ends, it is preferable to carry out in any one from the said casting process to the process of winding up the said film.

  The film 90 from which both side ends have been removed is sent to the drying chamber 21 and further dried. Although the temperature in the drying chamber 21 is not specifically limited, It is preferable that it is the range of 50 to 160 degreeC. In the drying chamber 21, the film 90 is conveyed while being wound around the roller 100, and the solvent gas generated by evaporation is absorbed and collected by the adsorption and recovery device 101. The air from which the solvent component has been removed is blown again as dry air inside the drying chamber 21. The drying chamber 21 is more preferably divided into a plurality of sections in order to change the drying temperature. In addition, when a preliminary drying chamber (not shown) is provided between the ear opener 20 and the drying chamber 21 and the film 90 is preliminarily dried, the film temperature is prevented from rising sharply in the drying chamber 21. The shape change of the film 90 can be further suppressed.

  The film 90 is cooled to approximately room temperature in the cooling chamber 22. A humidity control chamber (not shown) may be provided between the drying chamber 21 and the cooling chamber 22, and air adjusted to a desired humidity and temperature can be blown onto the film 90 in the humidity control chamber. It is preferable. Thereby, generation | occurrence | production of the curling of the film 90 and the winding defect at the time of winding can be suppressed.

  Moreover, the charged voltage while the film 90 is conveyed is set to a predetermined range (for example, −3 kV to +3 kV) by the forced static eliminating device (static elimination bar) 102. Although the example provided in the downstream of the cooling chamber 22 is shown in FIG. 1, it is not limited to the position. Furthermore, it is preferable to provide a knurling roller 103 and to impart knurling to both edges of the film 90 by embossing. In addition, it is preferable that the unevenness | corrugation of the knurled location is 1 micrometer-200 micrometers.

  Finally, the film 90 is taken up by the take-up roller 110 in the take-up chamber 23. At this time, it is preferable to wind the sheet while applying a desired tension with the press roller 111. More preferably, the tension is gradually changed from the start to the end of winding. The film 90 to be wound is preferably at least 100 m in the longitudinal direction (casting direction). Moreover, it is preferable that the width | variety of the film 90 is 600 mm or more, and it is more preferable that they are 1400 mm or more and 1800 mm or less. The present invention is also effective when it is larger than 1800 mm. The present invention is also applied when manufacturing a thin film having a thickness of 15 μm or more and 100 μm or less.

  The stretching relaxation of the wet film 120 by the tenter dryer 17 in the solution casting method according to the present invention will be described with reference to FIG. The tenter dryer 17 includes an inlet portion 130 that holds both ends of the wet film 120 by holding means, an extending portion 131 that widens the width of the wet film 120, a relaxation portion 132 that reduces the width of the wet film 120, and a wet film. And an outlet 133 for releasing the holding of 120.

  A clip is used as the holding means. A number of clips are connected to the chain, and the chain meshes with the sprocket and travels endlessly guided by the rail. As the chain moves, the wet film 120 is conveyed from the inlet portion 130 to the outlet portion 133 via the extending portion 131 and the relaxing portion 132. The rail includes a shift mechanism and is displaced by the shift mechanism. Since the movement path of the chain changes due to the rail displacement, the trajectory along which the clip moves changes accordingly. By changing the trajectory of the clip, the width of the wet film 120 is changed. Further, the temperature of the inside of the tenter dryer 17 is preferably controlled in the range of 60 ° C. to 180 ° C. in order to dry the wet film 120. More preferably, in order to change the drying conditions over time, it is preferable to divide the interior of the tenter dryer 17 into a plurality of sections in the direction of the conveyance path and perform temperature control for each section. The number of sections is, for example, 2-5.

  Both end portions of the wet film 120 are gripped by clips (not shown) at the inlet 17a of the tenter dryer 17, that is, at the upstream end of the inlet portion 130. In the following description, the width of each film indicated by reference characters L1 to L6 is a dimension between the positions of both ends sandwiched by clips. The width of the wet film 120 when the grip is started by the clip is L1 (mm), the width of the wet film 120 when the width is maximized by being stretched by the stretching portion 131 is L2 (mm), and the exit portion 133 is The width of the film 90 when the grip is released is L3.

  The wet film 120 is conveyed without changing the width at the entrance 130 and is sent to the stretching unit 131. The wet film 120 is stretched in the width direction by the stretching portion 131. Thereafter, the wet film 120 is relaxed in the width direction by the relaxing portion 132. After relaxation, the wet film 120 is sent out as a film 90 from the outlet 17b while maintaining a constant width L3 (mm).

  The width of the wet film 120 when 0.1 minute has passed from the inlet 17a is L4 (mm). In FIG. 2, the position of the wet film 120 when 0.1 minutes have passed from the inlet 17 a, that is, the position of L <b> 4 is in the stretched portion 131, but this position depends on the conveyance speed of the wet film 120. change. Therefore, this position may be within the range of the inlet portion 130. The stretching ratio X from when gripping is started until 0.1 minutes elapses is a value obtained by the equation X (%) = {(L4−L1) / L1} × 100. In the present invention, the stretching ratio X is preferably -10.0% or more and 1.0% or less, more preferably -5.0% or more and 0.5% or less, and most preferably -2.0% or more. 0.5% or less. If the stretch ratio X (%) is less than -10.0%, the wet film 120 may sag, the wet film 120 may come into contact with the tenter dryer 17, and scratches or wrinkles may occur. On the other hand, if it exceeds 1.0%, the wet film 120 is stretched abruptly, so that the polymer molecules may be oriented and the in-plane retardation (Re) may increase. In this case, a bowing phenomenon may occur.

  In addition, in the extending | stretching part 131, it is not necessary to expand a width | variety at a fixed speed | rate, and it is not necessary to expand a width | variety continuously. For example, the enlargement of the width and the holding of the constant width may be performed alternately.

  Relaxation starts from the inlet 132a of the relaxation part 132. FIG. 2 shows a case where two-stage relaxation is performed by the relaxation unit 132, that is, two relaxations with different relaxation rates are performed. Of the two relaxations, the first one is the first section 132b, and the other is the second section 132c. However, relaxation may be performed at a constant relaxation rate without changing the relaxation rate in the relaxation unit 132 without providing the first and second sections 132b and 132c, or three or more relaxations with different relaxation rates. May be implemented.

  FIG. 2 shows a case where the second section 132c is a section having a higher relaxation rate than the first section 132b, but the relaxation speeds of both may be reversed. The wet film 90 having a width L2 at the inlet 132a of the relaxing portion 132 has a width L5 (mm) in the first section 132b and a width L6 (mm) in the second section 132c.

  The relaxation rates in the first and second sections 132b and 132c are [{(L2-L5) / L2} × 100] and [{(L5-L6) / L5} × 100], respectively. It is a value divided by the passing time of 132c. In the present invention, when the relaxation rate is changed in the relaxation unit 132, the largest relaxation rate is Y. Therefore, in this embodiment, Y is the relaxation rate in the second section. Then, when the time passing through the second section is T, Y calculated by the equation Y (% / min) = [{(L5−L6) / L5} × 100] / T is 0.0% / Min or more and 5.0% / min or less is preferable, more preferably 0.0% / min or more and 3.0% / min or less, and most preferably 0.0% / min or more and 1.0% or less. / Min or less. If Y exceeds 10% / min, the wet film 120 may shrink rapidly, resulting in deterioration of the surface state of the film, for example, occurrence of slipping or wrinkling. When the relaxation rate is made constant by the relaxation unit 132, the constant value may be Y.

  In the present invention, X (%) and Y (% / min) satisfy the condition of 5X + Y <10, more preferably satisfy the condition of 5X + Y <6.0, and satisfy the condition of 5X + Y <5.0. It is more preferable that the condition of 5X + Y <1 is satisfied.

  In the solution casting method of the present invention, when casting the dope, two or more kinds of dopes can be 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 the dope is cast from the die slit to the support. Moreover, when performing simultaneous lamination | stacking co-casting, it is preferable that the dope which contact | connects an external field has a larger alcohol composition ratio than an internal dope among the casting beads formed from a die slit to a support body.

  From casting die, decompression 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 Until now, it is described in detail in paragraphs [0617] to [0889] of JP-A-2005-104148. These descriptions are also applicable to the present invention.

[Performance / Measurement method]
The performance of the wound cellulose acylate film and the measuring 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 sort of matting agent 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 detail in paragraphs [0890] to [1087] of JP-A-2005-104148. It also includes the conditions and methods. These are also applicable to the present invention.

(Use)
The cellulose acylate film is particularly useful as a polarizing plate protective film. Usually, two polarizing plates each having a cellulose acylate film bonded to a polarizer are bonded to a liquid crystal layer to produce a liquid crystal display device. However, the arrangement of the liquid crystal layer and the polarizing plate is not limited, and various known arrangements can be employed. Japanese Patent Application Laid-Open No. 2005-104148 describes in detail TN type, STN type, VA type, OCB type, reflective type, and other examples of liquid crystal display devices. This method can also be applied to the present invention. The application 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. Details are described in paragraphs [1088] to [1265] of JP-A-2005-104148.

  Moreover, the cellulose triacetate film (TAC film) excellent in an optical characteristic can be obtained with the manufacturing method of this invention. The TAC film can be used as a polarizing plate protective film or a base film for a photographic photosensitive material. Further, it can be used as an optical compensation film for improving the viewing angle dependency of a liquid crystal display device for television. In particular, it is effective for applications that also serve as a protective film for a polarizing plate. Therefore, it is used not only in the conventional TN mode but also in the IPS 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. Further, the description will be made in detail in Experiment 1, and for Experiments 2 to 6 according to the present invention and Experiments 7 to 9 which are comparative examples, descriptions of the same conditions as in Experiment 1 are omitted. The experimental results are summarized in Table 1 later.

  The formulation for preparing the polymer solution (dope) used for film production is shown below.

[Experiment 1]
[Preparation of dope]
The prescription of the compound used for the preparation of the dope 12 is shown below.
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
92% by weight of solid content (solute) having a composition ratio of dichloromethane
8% by weight of methanol
The dope 12 was prepared by appropriately adding to a mixed solvent consisting of The solid content concentration of the dope 12 was adjusted to 19.3% by weight. The dope 12 was filtered with a filter paper (Toyo Filter Paper Co., Ltd., # 63LB) and further filtered with a sintered metal filter (Nihon Seisen Co., Ltd. 06N, nominal pore size 10 μm), and further filtered with a mesh filter. Placed in tank 11.

[Cellulose triacetate]
The cellulose triacetate used here has a residual acetic acid content of 0.1% by weight 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 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 cotton as a raw material. In the following description, this is called cotton raw material TAC.

[Preparation of matting agent solution]
A matting agent solution 41 was prepared from the following formulation. As the TAC, the same TAC used for the preparation of the dope 12 was used.
Silica (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) 0.67% by weight
Cellulose triacetate 2.93% by weight
Triphenyl phosphate 0.23% by weight
Biphenyl diphenyl phosphate 0.12% by weight
Dichloromethane 88.37 wt%
Methanol 7.68% by weight
A matting agent solution 41 was prepared from the above formulation, dispersed with an attritor so that the volume average particle size was 0.7 μm, and then filtered with an Astropore 10 filter manufactured by Fuji Photo Film Co., Ltd. And it put into the stock tank 40 for mat agent liquids.

[Preparation of UV absorber solution]
An ultraviolet absorber solution 46 was prepared from the following formulation. As the TAC, the same TAC used for the preparation of the dope 12 was used.
2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole 5.83% by weight
2 (2′-hydroxy 3 ′, 5′-di-tert-amylphenyl) benzotriazole 11.66% by weight
Cellulose triacetate 1.48% by weight
Triphenyl phosphate 0.12% by weight
Biphenyl diphenyl phosphate 0.06% by weight
Dichloromethane 74.38 wt%
Methanol 6.47% by weight
An ultraviolet absorbent solution 46 was prepared from the above formulation, filtered through an Astropore 10 filter manufactured by Fuji Photo Film Co., Ltd., and placed in a stock tank 45 for the ultraviolet absorbent solution.

  Moreover, the mixed solvent A of 86.5 weight part of dichloromethane, 13 weight part of acetone, and 0.5 weight part of 1-butanol was produced.

  The matting agent solution 41 was sent into the pipe 43 by the pump 42, and the ultraviolet absorbent solution 46 was sent into the pipe 48 by the pump 47. The matting agent solution 41 was mixed with the ultraviolet absorber solution 46 and then mixed and stirred by a static mixer 49 to obtain an additive solution. The dope 12 was fed into the pipe 34 by the pump 32, passed through the filtration device 33 and filtered, and then the additive solution was mixed. The solution was mixed and stirred with a static mixer 35 to obtain a dope for casting.

  The film 90 was manufactured using the film manufacturing line 10 shown in FIG. The pump 32 has a function of increasing the pressure on the primary side, and liquid was fed by performing feedback control on the upstream side of the pump 32 with an inverter motor so that the pressure on the primary side became 0.8 MPa. The pump 32 used had a volume efficiency of 99.2% and a discharge rate variation rate of 0.5% or less. The discharge pressure was 1.5 MPa.

  The casting die 13 was cast by adjusting the flow rate of the dope for casting at the discharge port of the casting die 13 so that the width of the casting die 13 was 1.8 m and the film thickness of the dried film was 80 μm. . The casting width of the casting dope from the discharge port of the casting die 13 was 1700 mm. The casting speed was 45 m / min to 55 m / min. In order to adjust the temperature of the dope for casting to 36 ° C., a jacket (not shown) was provided on the casting die 13 and the inlet temperature of the heat transfer medium supplied into the jacket was set to 36 ° C.

  The casting die 13 and the piping were all kept at 36 ° C. during film formation. The casting die 13 was a coat hanger type die. The casting die 13 was provided with thickness adjusting bolts at a pitch of 20 mm and equipped with an automatic thickness adjusting mechanism using a heat bolt. This heat bolt can also set a profile according to the amount of liquid delivered by the pump 32 by a preset program, and is fed back by an adjustment program based on the 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.

  Further, a decompression chamber 65 for decompressing this portion was installed on the primary side of the casting die 13. The decompression degree of the decompression chamber 65 is adjusted so that a pressure difference of 1 Pa to 5000 Pa is generated before and after the casting bead, and this adjustment is made according to the casting speed. At that time, the pressure difference on both sides of the casting bead was set so that the length of the casting bead was 20 mm to 50 mm. The decompression chamber 65 is provided with a mechanism that can be set to a temperature higher than the condensation temperature of the gas around the casting portion. Labyrinth packings (not shown) were provided on the front and back surfaces of the beads at the die discharge port. Also, openings were provided at both ends of the die discharge port of the casting die. Further, an edge suction device (not shown) for adjusting the disturbance of both edges of the casting bead was attached to the casting die 13.

As the material of the casting die 13, precipitation hardening type stainless steel having a thermal expansion coefficient of 2 × 10 ⁻⁵ (° C. ⁻¹ ) or less was used. This had a corrosion resistance substantially equal to that of SUS316 in a forced corrosion test with an aqueous electrolyte solution. 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 13 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-contacting part of the lip | tip end of the casting die 13, 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 for casting inside the casting die 13 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 13 by a thermal spraying method to provide a cured film.

  Further, in order to prevent the casting dope flowing out from being locally dried and solidified, a mixed solvent A for solubilizing the casting dope is added to both sides of the casting bead at the discharge port of the casting die 13. Each 0.5 ml / min was supplied to the interface between the end and the discharge port. The pulsation rate of the pump supplying the mixed solvent was 5% or less. Further, the pressure on the back side of the casting bead was lowered by 150 Pa from the front side by the decompression chamber 65. A jacket (not shown) was attached to keep the internal temperature of the decompression chamber 65 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 stainless steel endless band having a width of 1.9 m and a length of 70 m was used as the casting band 16 as a support. The casting band 16 was polished so that the thickness was 1.5 mm and the surface roughness was 0.05 μm or less. The material is made of SUS316 and has sufficient corrosion resistance and strength. The thickness unevenness of the entire casting band 16 was 0.5% or less. The casting band 16 was driven by two rotating rollers 14 and 15. Further, the relative speed difference between the casting band 16 and the rotating rollers 14 and 15 was adjusted to be 0.01 m / min or less. At this time, the speed fluctuation of the casting band 16 was set to 0.5% or less. Further, both end positions of the casting band 16 were detected and controlled so that the meandering in the width direction of one rotation was limited to 1.5 mm or less. The positional fluctuation in the vertical direction between the die lip tip and the casting band 16 immediately below the casting die 13 was set to 200 μm or less. The casting band 16 was installed in a casting chamber 61 having wind pressure fluctuation suppressing means (not shown). A casting dope was cast from the casting die 13 on the casting band 16.

As the rotating rollers 14 and 15, a roller capable of feeding a heat transfer medium therein was used so that the temperature of the casting band 16 could be adjusted. A 5 ° C. heat transfer medium was passed through the rotating roller 14 on the casting die 13 side, and a 40 ° C. heat transfer medium was passed through the other rotating roller 15 for drying. The surface temperature of the center part of the casting band 16 immediately before casting was 15 ° C., and the temperature difference between both side ends was 6 ° C. or less. The casting band 16 preferably has no surface defects, has no pinholes of 30 μm or more, has 1 to 10 μm to 30 μm pinholes / m ² or less, and has 2 pinholes of less than 10 μm / Those with m ² or less were used.

  The casting film 70 formed from the casting dope cast on the casting band 16 was first fed with drying air flowing parallel to the casting film 70 to dry the casting film 70. As for the temperature of the drying air, 140 ° C. drying air was blown from the upstream air blowing port 71 above the casting band 16. Further, 140 ° C. dry air was blown from the air blowing port 72 on the downstream side, and 65 ° C. dry air was blown from the air blowing port 73 below the casting band 16. The oxygen concentration in the dry atmosphere on the casting band 16 was maintained 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 61, a condenser (condenser) 63 was provided, and its outlet temperature was set to -3 ° C.

  Static pressure fluctuations in the vicinity of the casting die 13 were suppressed to ± 1 Pa or less. After the casting film 70 had self-supporting properties, it was peeled off as the wet film 120 while being supported by the peeling roller 121 from the casting band 16. In order to suppress peeling failure, the peeling speed (peeling roller draw) with respect to the speed of the casting band 16 was appropriately adjusted in the range of 100.1% to 110%. The solvent gas generated by drying was condensed and liquefied by a condenser 63 at −3 ° C. and recovered by a recovery device 64. 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 120 was conveyed through the two rollers of the crossing section 80 and sent to the tenter dryer 17. In the crossing section 80, 60 ° C. dry air was blown from the blower 81 to the wet film 120.

  The wet film 120 sent to the tenter dryer 17 was transported through the drying zone of the tenter dryer 17 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. Further, in the tenter dryer 17, hot air at 90 ° C. is adjusted in advance so that the wind speed in the width direction is constant, and the normal direction of the wet film 120 (that is, the vertical direction) From the direction). The gas composition of the drying air was set to a saturated gas concentration at −10 ° C. The amount of residual solvent in the film 90 at the outlet of the tenter dryer 17 was 14% by weight to 17% by weight. The tenter dryer 17 was also stretched in the width direction while being transported. Note that the clip is conveyed so that the final stretch ratio (= (L3-L1) / L1 × 100) obtained from the width of the wet film 120 at the inlet 17a and the outlet 17b of the tenter dryer 17 is 4.5%. Adjusted the road. The stretching ratio (tenter driven draw) from the peeling roller 121 to the entrance of the tenter dryer 17 was 103.0%.

  The solvent evaporated in the tenter dryer 17 was provided with a condenser (condenser) for condensation recovery, condensed at a temperature of −3 ° C., liquefied and recovered. The condensed solvent was reused after adjusting the water content to 0.5 wt% or less. And it sent out from the tenter type dryer 17 as the film 90.

  The stretching ratio X (= {(L4−L1) / L1} × 100) for 0.1 minute (= 6 seconds) after the wet film 120 was conveyed to the stretching portion 131 was set to 0.11%. In addition, the relaxation rate in the relaxation unit 132 is made constant so that Y (= [{(L5−L6) / L5} × 100] / T) in the relaxation unit 132 becomes 0 (% / min). The 5X + Y value in this case was 0.53.

The ear-cutting device 20 cuts off both ends of the film 90 within 30 seconds from the exit of the tenter dryer 17. Ears 50 mm on both sides were cut with an NT-type cutter, and the cut ears were blown to a crusher 91 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 17 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 21 described later, the film 90 was preheated in a predrying chamber (not shown) to which 100 ° C. drying air was supplied.

  The film 90 was dried at high temperature in the drying chamber 21. The drying chamber 21 was divided into four sections, and drying air at 120 ° C., 130 ° C., 130 ° C., and 130 ° C. was supplied from a blower (not shown) from the upstream side. The conveyance tension of the film 90 by the roller 100 was set to 100 N / m, and the film was dried for about 5 minutes until the residual solvent amount finally reached 0.3% by weight. The wrap angle of the roller 100 (film winding center angle) was 80 ° to 190 °. The material of the roller 100 was made of aluminum or carbon steel, and hard chrome plating was applied to the surface. The roller 100 has a flat surface shape and a dimple processed surface shape. All film position fluctuations due to the rotation of the roller 100 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 wind was removed by adsorption using the adsorption / recovery device 101. The adsorbent used here was activated carbon, and desorption was performed using dry nitrogen. The recovered solvent was reused as a dope preparation solvent after adjusting the water content to 0.3 wt% 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 weight%, and most of the remainder was collect | recovered by adsorption collection.

  The dried film 90 was conveyed to the 1st humidity control chamber (not shown). A drying air of 110 ° C. was supplied to the transition portion between the drying chamber 21 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. Furthermore, the film 90 was conveyed to the 2nd humidity control chamber (not shown) which suppresses generation | occurrence | production of the curl of the film 90. In the second humidity control chamber, air of 90 ° C. and humidity of 70% was directly applied to the film 90.

  The film 90 after humidity control was cooled to 30 ° C. or lower in the cooling chamber 22, and then subjected to ear cutting at both ends again with an ear cutting device (not shown). The forced charge removal device (charge removal bar) 102 was installed so that the charged voltage of the film 90 during conveyance was always in the range of −3 kV to +3 kV. Further, knurling was applied to both ends of the film 90 by a knurling roller 103. The knurling is imparted by embossing from one side of the film 90, the width for imparting the knurling is 10 mm, and the knurling is applied by the knurling roller 103 so that the height of the irregularities is 12 μm higher than the average thickness of the film 90. The pressure was set.

  Then, the film 90 was conveyed to the winding chamber 23. The winding chamber 23 was kept at a room temperature of 28 ° C. and a humidity of 70%. Inside the winding chamber 23, an ion wind static elimination device (not shown) was also installed so that the charged voltage of the film 90 was −1.5 kV to +1.5 kV. The product width of the film 90 (thickness 80 μm) thus obtained was 1340 mm.

[Measurement of slow axis deviation]
The axis deviation angle was measured with an automatic birefringence meter (KOBRA-21DH, manufactured by Oji Instruments Co., Ltd.). A sample was accurately sampled at 5 cm × 5 cm using a cutting plotter at a position 15 cm from the end of the obtained film 90 (hereinafter referred to as film end 1) and from the center of the film. The angle formed by the slow axis with respect to the longitudinal direction of the film 90 was measured with an automatic birefringence meter, and the slow axis deviation was evaluated by the magnitude of the difference between the slow axis at the film edge and the film center. This value is hereinafter referred to as an axis deviation value 1. The axial deviation value 1 was 2.2 °. Further, the film edge (hereinafter referred to as film edge 2) at a position 5 cm from the edge of the film 90 was also cut and measured under the same conditions as those for the film edge 1. This value is hereinafter referred to as an axis deviation value 2. The axial deviation value 2 was 8.7 °.

  Axis deviation value 1 and axis deviation value 2 are both very good (◎) when the axis deviation value 2 is less than 10 °, and the axis deviation value 1 is less than 10 °, but the axis deviation value 2 is 10 ° or more and less than 45 °. Good (◯), axis deviation value 1 is less than 10 °, but slightly poor (Δ) when axis deviation value 2 is 45 ° or more, and poor (×) when axis deviation value 1 is 10 ° or more. A four-step evaluation was performed. In Experiment 1, all the axial deviation values were very good, and the evaluation of the film was very good (◎).

[Experiment 2 to Experiment 5]
Experiments 2 to 5 were performed under the same conditions as Experiment 1 except that X and Y were set to the values shown in Table 1. The evaluation of the film obtained in any experiment was extremely good (◎).

[Experiment 6]
Experiment 6 was performed under the same conditions as Experiment 1 except that X and Y were set to the values shown in Table 1. The evaluation of the film obtained in any experiment was good (◯).

[Experiment 7 and Experiment 8]
Experiment 7 and Experiment 8 were performed under the same conditions as Experiment 1 except that X and Y were set to the values shown in Table 1. The evaluation of the film obtained in any experiment was slightly poor (Δ).

[Experiment 9]
Experiment 9 was performed under the same conditions as Experiment 1 except that X and Y were set to the values shown in Table 1. Evaluation of the obtained film was bad (x).

  The dope of Example 1 was replaced with another dope. In the second embodiment, only conditions different from those in the first embodiment will be described, and description of the same conditions as in the first embodiment will be omitted.

[Experiment 1]
The composition of the dope 12 of Example 1 was changed to the following, and the other conditions were the same as those in Experiment 1 of Example 1. Table 2 shows conditions such as values of X and Y, and evaluation results.
[composition]
Cellulose triacetate (TAC) 100 parts by mass (acetyl group substitution degree 2.81 (acetylation degree 60.2%), Mw / Mn = 2.7, viscosity average polymerization degree 305, viscosity of 6% by mass in dichloromethane solution 350 mPa · s)
-Dichloromethane (first solvent) 430 parts by mass-Methanol (second solvent) 48 parts by mass-Plasticizer A 7.6 parts by mass-Plasticizer B 3.8 parts by mass The above-mentioned plasticizer A is triphenyl phosphate ( TPP), plasticizer B is biphenyl diphenyl phosphate (BDP).

  An additive liquid A was prepared with the retardation control agent shown in Chemical Formula 1, a part of the dope 12 and a solvent of dichloromethane: methanol = 9: 1 (mass ratio) and filtered.

  Furthermore, fine particles (trade name: Aerosil R972, Nippon Aerosil Co., Ltd.), a part of the dope 12 and a solvent of dichloromethane: methanol = 9: 1 (mass ratio) were mixed to prepare an additive liquid B. . In the additive liquid B, the following fine particles were dispersed by an attritor so that the volume average particle diameter was 0.7 μm. The additive liquid B after dispersion was filtered.

  The additive liquid B was mixed with the additive liquid A using an in-line mixer, and this mixed liquid was mixed with the dope 12 using an in-line mixer. In this way, a liquid having a matting agent of 1% by mass and a retardation control agent of 6% by mass was obtained for casting when the film 90 was formed. Other conditions are the same as those in the first embodiment.

[Experiment 2 to Experiment 5]
Experiments 2 to 5 were performed under the same conditions as Experiments 1 to 5 except that X and Y were set to the values shown in Table 2. The evaluation of the film obtained in any experiment was extremely good (◎).

[Experiment 6]
Experiment 6 was performed under the same conditions as Experiment 6 of Example 1 except that X and Y were set to the values shown in Table 2. The evaluation of the film obtained in any experiment was good (◯).

[Experiment 7 and Experiment 8]
Experiment 7 and Experiment 8 were performed under the same conditions as Experiments 7 and 8 of Example 1 except that X and Y were set to the values shown in Table 2. The evaluation of the film obtained in any experiment was slightly poor (Δ).

[Experiment 9]
Experiment 9 was performed under the same conditions as Experiment 9 of Example 1 except that X and Y were set to the values shown in Table 2. Evaluation of the obtained film was bad (x).

  As shown in Table 1 and Table 2, the film 90 obtained in Experiment 1 to Experiment 7 in which 5X + Y is less than 6 was preferable because the axial displacement was small over the entire width. In particular, Experiment 1 to Experiment 5 in which the stretch ratio X (%) was less than 0.50% was extremely preferable. From this, it can be seen that the occurrence of bowing can be prevented by suppressing stretching for 0.1 minute after the wet film 120 is held by the tenter clip of the tenter dryer 17, or by not performing stretching.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Film production line 17 Tenta dryer 90 Film 120 Wet film 131 Stretching part 131a Stretching part inlet 131b Stretching start width 132 Relaxing part 132a Relaxing part inlet 132b Maximum relaxation speed section L4 Stretching start width L5 Maximum width relaxation rate width

Claims (4)

A casting film forming step of casting a dope containing cellulose acylate and a solvent on a support to form a cast film; and a peeling step of drying the cast film and stripping the film from the support as a film. In the solution casting method having a gripping drying step of gripping both ends of the film and drying while transporting the film,
The gripping and drying step includes
A first width holding step of starting gripping and holding the width of the film;
Stretching step is performed after the first width holding step, the film is stretched in the width direction to increase the width,
A relaxation step that is performed after the stretching step and reduces the width of the film;
A second width holding step that is performed following the relaxation step and holds the width until the grip is released,
When the width of the film at the start of gripping is La and the width of the film when 0.1 minute has elapsed from the start of gripping is Lb, {(Lb−La) / La} × 100 A solution casting method, wherein a desired stretching ratio X (unit:%) and a relaxation ratio Y (unit:% / min) per unit time in the relaxation step satisfy a condition of 5X + Y <1. In the stripping step, the cast film having a residual solvent amount of 20% by weight to 250% by weight is stripped,
2. The solution casting method according to claim 1, wherein in the gripping and drying step, the film is dried to 14 wt% to 17 wt%.   3. The solution casting method according to claim 1, wherein the stretching ratio X (%) is 1.0% or less. Solution casting how according 3 any one claims 1, characterized in that the relaxation rate Y per unit time 5.0% / min or less.

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