JP2011207050A - Casting device and solution film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To move a support body at further high speed by forming a strip-like casting film on the support body from dope flowing out in a reduced pressure environment, and evaporating a solvent from the casting film until the casting film is brought into a state that the casting film can be stripped off.SOLUTION: In a solution film forming method, a casting chamber 12 is provided with a casting die 21, a casting drum 22, a stripping roller 24 and a pressure reducing device 88. The outlet port of the casting chamber 12 is connected to a sealing device 61. The airtightness of the casting chamber 12 is maintained by the sealing device 61. The pressure reducing device 88 sucks atmosphere air in the casting chamber 12. The casting chamber 12 is brought into a pressure-reduced state by the suction of the pressure reducing device 88. Dope 28 flowing from the casting die 21 serves a the casting film 31 on the casting drum 22. The casting film 31 which can be stripped off is stripped off by a stripping roller 24 to serve as a wet film 35. The wet film 35 is conveyed to the outside of the casting chamber 12.

Description

  The present invention relates to a casting apparatus and a solution casting method.

  BACKGROUND ART A thermoplastic film having light permeability (hereinafter referred to as a film) is lightweight and easy to mold, and thus is widely used as an optical film. Among them, cellulose ester films using cellulose acylate and the like are optical films (for example, retardation film and polarizing plate protection) which are constituent members of liquid crystal display devices whose market has been expanding in recent years, including photographic photosensitive films. Used in film, etc.).

  The film is produced by a solution casting method. The solution casting method uses a casting die to flow a polymer solution containing a polymer and a solvent (hereinafter referred to as a dope), and forms a casting film on a support. Next, after the cast film can be peeled off, it is peeled from the support to form a wet film. Then, the wet film solvent is evaporated to form a film.

  Further, there are a drying method and a cooling gelation method as methods for making the cast film in a state where it can be peeled off. In the drying method, the solvent is evaporated from the cast film on the support until the amount of the residual solvent in the cast film falls within a predetermined range. On the other hand, in the cooling gelation system, the casting film on the support is cooled in order to reduce the fluidity of the solvent contained in the casting film.

  In order to improve the production efficiency of the film, it is necessary to improve the moving speed of the support and shorten the time required from the formation of the casting film to the peeling of the casting film. The cooling gelation method requires less time for the cast film to be peelable than the drying method. For this reason, a cooling gelation system is often adopted as a method for mass-producing films. By adopting this cooling gelation method, it becomes easy to improve the moving speed of the support to “50 m / min to 200 m / min” (for example, Patent Document 1).

  On the other hand, when the moving speed of the support is improved, an accompanying wind that flows along the surface of the moving support is generated. When the accompanying wind strikes a portion (hereinafter referred to as a bead) between the casting die and the support in the dope flowing out from the casting die, the bead vibrates. This vibration of the bead results in uneven thickness of the cast film and eventually uneven thickness of the film.

  Therefore, in order to suppress the harmful effects of the accompanying wind, the gas on the back side of the bead (upstream in the movement direction of the support) is sucked, and the pressure on the back side of the bead is compared with that on the front side (downstream in the movement direction of the support). And a reduced pressure chamber is provided (for example, Patent Documents 2 to 3). According to this decompression chamber, film thickness unevenness can be prevented by increasing the pressure difference between the back side and the front side of the bead as the moving speed of the support increases.

Japanese Patent Laid-Open No. 11-221833 JP 2000-290388 A JP 2005-193691 A

  However, when the speed of movement of the support is further increased (for example, in a range exceeding 100 m / min), the scale of the accompanying wind increases. Therefore, in order to prevent the harmful effects of the accompanying wind, it is necessary to increase the pressure difference between the back side and the front side of the bead according to the scale of the accompanying wind. However, the further increase of the pressure difference using the decompression chamber induces the vibration of the bead as a result of the pressure fluctuation in the periphery of the bead and in the decompression chamber, as pointed out in Patent Documents 2-3. As described above, the inventions described in Patent Documents 2 to 3 exhibit a certain effect as a means for solving the harmful effects of the accompanying wind when the moving speed of the support is low, but when the moving speed of the support is high. Is difficult to use as a means to solve the harmful effects of accompanying winds.

  Furthermore, when further increasing the moving speed of the support, since the casting film is not in a state that can be peeled off at the conventional peeling position, a part of the casting film is peeled off. It is not removed and remains on the support (referred to as a peeling failure), or the wet film does not have a sufficient elastic modulus, making it difficult to transport the wet film (referred to as a transport failure).

  The present invention solves such a problem, and an object of the present invention is to provide a casting apparatus and a solution casting method that realize further speeding up of a support.

  The solution casting method of the present invention is carried out in a casting chamber provided with a casting die for continuously flowing out a dope containing a polymer and a solvent and a moving support, and a belt-like casting from the flowing out dope. A film forming step for forming a film on the support, and a first drying step for evaporating the solvent from the casting film, which is performed in the casting chamber, until the casting film is peelable. And stripping the cast membrane that has undergone the first drying step from the support to make a wet film, and a second drying step to evaporate the solvent from the wet film to make a film. The casting chamber is in a reduced pressure state.

  It is preferable that the moving speed of the support is 100 m / min or more and 300 m / min or less. Further, in the preparatory step performed before the film forming step, a tip forming step for forming the tip of the belt-shaped casting film, a conveying step for carrying out the tip from the outlet of the casting chamber, It is preferable that a sealing step for sealing the outlet of the casting chamber and a decompression step for reducing the pressure in the casting chamber are sequentially performed.

  The casting apparatus of the present invention comprises a casting die for continuously flowing out a dope containing a polymer and a solvent, a support for supporting the dope flowing out from the casting die, and forming a casting film from the dope. A casing that houses the casting die and the support, a drying unit that evaporates the solvent from the casting film, and an outlet of the casing that exposes the casting film peeled off from the support to the outside And a sealing means for maintaining a pressure difference between the inside and the outside of the casing, and the drying means includes a pressure reducing means for reducing the pressure inside the casing.

  According to the present invention, a film forming step of continuously flowing out a dope containing a polymer and a solvent to a moving support, and forming a strip-shaped casting film on the support from the outflowed dope, and the casting Since the first drying step of evaporating the solvent from the cast film is performed in a reduced pressure environment until the film becomes peelable, a film can be produced more efficiently than before.

It is explanatory drawing which shows the outline | summary of a 1st solution casting apparatus. It is sectional drawing which shows the outline | summary of a 1st sealing apparatus. It is an enlarged view which shows the outline | summary of the conveyance path provided in the sealing device. It is sectional drawing which shows the outline | summary of a sealing device when an upper side sealing member exists in a retracted position. It is a side view which shows the outline | summary of a 2nd sealing apparatus. It is explanatory drawing which shows the outline | summary of the 2nd solution casting apparatus. It is explanatory drawing which shows the outline | summary of a front-end | tip part formation process. It is explanatory drawing which shows the outline | summary inside the sealing device after a conveyance process.

(Solution casting method)
As shown in FIG. 1, the solution casting apparatus 10 includes a casting chamber 12, a pin tenter 13, a drying chamber 15, a cooling chamber 16, and a winding chamber 17. In the casting chamber 12, a casting die 21, a casting drum 22, and a peeling roller 24 are provided.

  The casting die 21 flows out a dope 28 containing a polymer and a solvent, and a slit outlet through which the dope 28 flows out is provided at the tip of the casting die 21. The casting drum 22 is positioned below the casting die 21 and is disposed so that the axial direction is horizontal. The casting drum 22 is arranged so that the peripheral surface 22a is close to the slit outlet. Furthermore, the casting drum 22 is rotatable about an axis. When the casting drum 22 is rotated by a driving device (not shown) under the control of a control unit (not shown), the peripheral surface 22a of the casting drum 22 moves at a predetermined speed in the Z1 direction. The dope 28 flowing out from the slit exit of the casting die 21 is extended on the peripheral surface 22a, and as a result, a belt-like casting film 31 is formed. The casting die 21 and the casting drum 22 are preferably made of stainless steel, and more preferably made of SUS316 from the viewpoint of having sufficient corrosion resistance and strength.

  A temperature control device 32 is connected to the casting drum 22. The temperature adjustment device 32 includes a temperature adjustment unit that adjusts the temperature of the heat transfer medium. The temperature control device 32 circulates the heat transfer medium adjusted to a desired temperature between the temperature adjusting unit and the flow path provided in the casting drum 22. By circulating the heat transfer medium, the temperature of the peripheral surface 22a of the casting drum 22 can be maintained at a desired temperature.

  The casting chamber 12 is provided with a drying unit 33 that evaporates the solvent from the casting film 31. The drying unit 33 includes a condensing device 33a that condenses the solvent contained in the atmosphere in the casting chamber 12, and a collecting device 33b that collects the condensed solvent. The drying unit 33 maintains the concentration of the solvent contained in the atmosphere in the casting chamber 12 within a certain range under the control of a control unit (not shown).

  The stripping roller 24 is disposed downstream of the casting die 21 in the Z1 direction. The stripping roller 24 strips the casting film 31 formed on the peripheral surface 22 a and guides it as a wet film 35 to the downstream side of the casting chamber 12.

  A pin tenter 13, a drying chamber 15, a cooling chamber 16, and a winding chamber 17 are sequentially installed downstream of the casting chamber 12.

  The pin tenter 13 is for performing a drying process for evaporating the solvent from the wet film 35, and includes a pin for holding the ear portion of the wet film 35, a moving unit for moving the pin downstream, and a dry air to the wet film. And a drying section. The film 40 is obtained from the wet film 35 by a drying process in the pin tenter 13. The film 40 sent out from the pin tenter 13 passes through the ear-cutting device 41 that cuts off the ear portion where the pin penetration marks remain, and is then sent out to the drying chamber 15.

  A large number of rollers 42 are provided in the drying chamber 15, and the film 40 is wound around and conveyed. The atmospheric pressure in the drying chamber 15 is atmospheric pressure. Further, the temperature and humidity of the atmosphere in the drying chamber 15 are adjusted by an air conditioner (not shown). In the drying chamber 15, the film 40 is dried. An adsorption recovery device 43 is connected to the drying chamber 15. The adsorption recovery device 43 recovers the solvent evaporated from the film 40 by adsorption.

  The cooling chamber 16 cools the film 40 until the temperature of the film 40 reaches substantially room temperature. Between the cooling chamber 16 and the winding chamber 17, a static elimination bar 45, a knurling roller 46, and an edge cutting device 47 are provided in this order from the upstream side. The charge removal bar 45 is discharged from the cooling chamber 16 and performs a charge removal process for removing electricity from the charged film 40. The knurling application roller 46 applies a winding knurling to both ends of the film 40 in the width direction. The edge-cutting device 47 cuts both ends of the film 40 in the width direction so that knurling remains at both ends of the cut film 40 in the width direction.

  In the winding chamber 17, a press roller 51 and a winding machine 53 having a winding core 52 are installed. The film 40 sent to the winding chamber 17 is pressed against the winding core 52 while being pressed by the press roller 51. It is wound up into a roll shape.

  A sealing device 61 is provided at the transition portion 60 between the casting chamber 12 and the pin tenter 13. As shown in FIG. 2, the sealing device 61 has a casing 62. The casing 62 has a transfer area 62r for the wet film 35 that connects the outlet 12o of the casting chamber 12 and the inlet 13i of the pin tenter 13. In the transport area 62r, the first roll 71 and the second roll 72 are alternately arranged at a predetermined pitch from the outlet 12o side to the inlet 13i side. The first roll 71 and the second roll 72 may be driven rolls or drive rolls.

  An upper block 75 is provided above the first roll 71 and the second roll 72, and a lower block 76 is provided below the first roll 71 and the second roll. The upper block 75 and the second roll 72 are connected, and the lower block 76 and the first roll 71 are connected. The distance between the first roll 71 and the upper block 75, the distance between the second roll 72 and the lower block 76, and the distance between the first roll 71 and the second roll 72 are each slightly larger than the thickness of the wet film 35. Any material that can maintain the airtightness of the casting chamber 12 may be used. In this way, a meandering seal path 77 (see FIG. 3) is formed in the transport area 62r by the first roll 71, the second roll 72, the upper block 75, and the lower block 76.

  As shown in FIGS. 2 and 4, the upper seal member 81 including the second roll 72 and the upper block 75 has a seal position where the seal path 77 is formed, and a retreat position where the seal position is retracted above the seal position (FIG. 4). It is possible to move between

  The upper seal member 81 is connected to the moving mechanism 84. The moving mechanism 84 moves the upper seal member 81 between the seal position and the retracted position under the control of a control unit (not shown).

  The temperature control device 32 is attached to the first roll 71 and the second roll 72. Thereby, the temperature of each peripheral surface of the 1st roll 71 and the 2nd roll 72 is adjusted in the predetermined range (for example, -5 degreeC or more and 15 degrees C or less).

  Returning to FIG. 1, a decompression device 88 is connected to the casting chamber 12. The decompression device 88 sucks the gas in the casting chamber 12 until the pressure value read from the pressure sensor becomes a predetermined value while reading a pressure sensor (not shown) provided in the casting chamber 12. Thereby, the decompression device 88 can adjust the atmospheric pressure in the casting chamber 12 within a predetermined range.

  Next, the operation of the present invention will be described. The dope 28 is sent to the casting die 21 by a pump (not shown). The polymer concentration in the dope 28 is preferably 5% by weight or more and 40% by weight or less, and more preferably 15% by weight or more and 25% by weight or less. The temperature of the dope 28 is kept substantially constant in the range of 30 ° C. to 35 ° C., and the temperature of the peripheral surface 22a of the casting drum 22 is kept substantially constant in the range of 0 ° C. to 10 ° C.

(Film formation process)
In the casting chamber 12, the casting die 21 flows out the dope 28 toward the peripheral surface 22a of the casting drum 22 that rotates in the Z1 direction. Although the moving speed of the peripheral surface 22a is not specifically limited, For example, it is preferable that it is 100 m / min or more and 300 m / min or less. A band-shaped cast film 31 made of the dope 28 is formed on the peripheral surface 22a.

(First drying step)
The casting film 31 on the peripheral surface 22a is conveyed in the Z1 direction. The solvent evaporates from the cast film 31 on the peripheral surface 22a by the drying unit 33. In addition, the casting film 31 is cooled by contact with the casting drum 22. By cooling, the dope 28 forming the cast film 31 is gelled. As a result of evaporation of the solvent and cooling, the cast film 31 is in a peelable state.

  Here, the gelation includes a state in which the fluidity of the dope is lost in addition to a state in which the colloidal solution is solidified in a jelly shape. Note that “the fluidity of the dope is lost” means that when the solute is a polymer, the fluidity is lost while the solvent is retained in the molecular chain of the solute, and as a result, the fluidity of the solution is reduced. This includes a lost state and a state in which the fluidity of the solution is lost due to the interaction between the solvent molecules and the solute molecules when the solute is a low molecule.

(Stripping process)
Thereafter, the stripping roller 24 strips the cast film 31 that can be stripped from the casting drum 22 as a strip-shaped wet film 35 and guides it to the pin tenter 13 through the crossover 40.

  The amount of residual solvent in the cast film 31 at the time of peeling is preferably 200% by weight or more and 300% by weight or less. In the present invention, the amount of the solvent remaining in the cast film 31 and each film is shown on the basis of the dry amount as the residual solvent amount. Moreover, the measurement method takes a sample from the target film, and when the weight of this sample is x and the weight after drying the sample is y, it is calculated as {(xy) / y} × 100. .

(Second drying step)
The pin tenter 13 conveys the wet film 35 while holding both ends of the wet film 35. Further, the pin tenter 13 applies dry air to the wet film 35 to evaporate the solvent from the wet film 35. As a result, the film 40 can be obtained from the wet film 35.

  The edge-cutting device 41 cuts both ends of the film 40 sent out from the pin tenter 13. The film 40 with both ends cut off is sent to the drying chamber 15. In the drying chamber 15, a drying process at atmospheric pressure is performed. Thereby, the solvent evaporates from the film 40. Thereafter, the film 40 sequentially passes through the cooling chamber 16 and the like, and is subjected to predetermined processing.

  The film 40 delivered from the cooling chamber 16 is sequentially subjected to charge removal processing by the charge removal bar 45, knurling application processing by the knurling application roller 46, and ear cut processing by the ear cut device 47. The film 40 sent to the winding chamber 17 is wound around the winding core 52 while being pressed by the press roller 51 and becomes a roll.

  As shown in FIG. 4, the upper sealing member 81 of the sealing device 61 is in the sealing position. For this reason, the sealing device 61 is in a state capable of maintaining a pressure difference between the inside and the outside of the casting chamber 12. As shown in FIG. 1, when the decompression device 88 sucks the atmosphere in the casting chamber 12, the pressure inside the casting chamber 12 is maintained at a lower state (depressurized state) than the outside. The reduced pressure state is preferably such that the solvent does not foam. Moreover, it is preferable that the atmospheric | air pressure difference of the inside of the casting chamber 12 and the exterior is 0.1 kPa or more and 10 kPa or less, for example.

  In the reduced pressure state, the solvent tends to evaporate from the casting film 31. For this reason, the time required for the casting film 31 to be in a peelable state can be shortened. In addition, by reducing the pressure in the casting chamber 12, the size of the accompanying air generated in the vicinity of the peripheral surface 22a can be suppressed, so that adverse effects caused by the accompanying air can be suppressed. As described above, according to the present invention, even if the moving speed of the peripheral surface 22a of the casting drum 22 is improved, it is possible to suppress a peeling failure and a conveyance failure as well as a failure due to the vibration of the bead. Therefore, according to the present invention, it is possible to further increase the speed of the solution casting method.

  Moreover, as a result of decompressing the inside of the casting chamber 12, the oxygen concentration contained in the atmosphere in the casting chamber 12 also decreases. Therefore, according to the present invention, the explosion-proof level in the casting chamber 12 can be made lower than that in the prior art.

  In the above embodiment, the film forming process, the first drying process, and the peeling process in the casting chamber 12 are performed in a reduced pressure environment. However, the present invention is not limited to this, and the film forming process, the first drying process, and the peeling process are performed. The taking step may be performed under a reduced pressure environment, and the film forming step, the first drying step, the stripping step, and the second drying step may be performed under a reduced pressure environment. FIG. 5 shows a casting chamber 12 of a solution casting apparatus for performing the former method, and FIG. 6 shows a solution casting apparatus 10 for performing the latter method. In FIG. 6, the pin tenter 13 evaporates the solvent from the wet film 35 under reduced pressure.

(Preparation process)
In addition, it is preferable to perform a preparatory process before a film formation process. In the preparation step, the tip portion forming step, the unloading step, and the seal member moving step are sequentially performed under atmospheric pressure, and then the pressure reducing step is performed.

  In the tip portion forming step, as shown in FIG. 7, the casting die 21 flows the dope 28 on the casting drum 22, and the tip portion 31 a of the casting film 31 is formed on the casting drum 22. In the carry-out process, the tip 31 a of the casting film 31 peeled off from the casting drum 22 is passed through the sealing device 61 and then carried out to the pin tenter 13. In the sealing step, as shown in FIG. 8, the upper seal member 81 in the retracted position is moved to the sealing position (see FIG. 2). Thereafter, in the decompression step, the decompression device 88 sucks the atmosphere of the casting chamber 12. Thereby, the atmospheric pressure in the casting chamber 12 is maintained in a lowered state. It should be noted that the speed-up process for setting the rotation speed of the casting drum 22 to be higher than that in the tip portion forming process and the unloading process is performed between the seal member moving process and the pressure reducing process, in parallel with the pressure reducing process, or It is preferable to carry out after the step.

  In the said embodiment, although the casting drum 22 was used as a support body, this invention is not limited to this, You may use a casting band. The casting band can be moved by passing the casting band around the roller arranged so that the axial direction is horizontal and rotating the roller.

  In the above-described embodiment, the cast film can be peeled off by the cooling gelation method, but the present invention is not limited to this, and the cast film may be peeled off by the drying method.

  The film 40 obtained by the present invention can be used particularly for a retardation film and a polarizing plate protective film.

  The width of the film 40 is preferably 600 mm or more, and more preferably 1400 mm or more and 2500 mm or less. The present invention is also effective when the width of the film 40 is greater than 2500 mm. Moreover, it is preferable that the film thickness of the film 40 is 30 micrometers or more and 120 micrometers or less.

  The in-plane retardation Re of the film 40 is preferably 20 nm or more and 300 nm or less, and the thickness direction retardation Rth of the film 40 is preferably −100 nm or more and 300 nm or less.

The method for measuring the in-plane retardation Re is as follows. In-plane retardation Re is a letter obtained by conditioning a sample film at a temperature of 25 ° C. and a humidity of 60% RH for 2 hours, and measuring it from the vertical direction at 632.8 nm with an automatic birefringence meter (KOBRA21DH Oji Scientific Co., Ltd.). The foundation value was used. Re is expressed by the following equation.
Re = | n1-n2 | × d
n1 is the refractive index of the slow axis, n2 is the refractive index of the fast axis 2, and d is the thickness (film thickness) of the film.

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

(polymer)
The polymer that can be used in the present invention is not particularly limited as long as it is a thermoplastic resin, and examples thereof include cellulose acylate, a lactone ring-containing polymer, a cyclic olefin, and polycarbonate. Of these, cellulose acylate and cyclic olefin are preferred, cellulose acylate containing an acetate group and propionate group, and cyclic olefin obtained by addition polymerization, more preferably cyclic olefin obtained by addition polymerization. It is.

(Cellulose acylate)
As the cellulose acylate, cellulose triacetate (TAC) is particularly preferable. Among the cellulose acylates, the substitution degree of the acyl group to the hydroxyl group of cellulose is represented by the following formulas (I) to (III), and A and B represent the substitution degree of the acyl group with respect to the hydrogen atom in the hydroxyl group of cellulose. , A is the degree of substitution of the acetyl group, and B is the degree of substitution of the acyl group having 3 to 22 carbon atoms. In addition, it is preferable that 90 weight% or more of TAC is a particle | grain of 0.1-4 mm. However, the polymer that can be used in the present invention is not limited to cellulose acylate.
(I) 2.0 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9

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

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

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

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

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

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

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

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

  Recently, a solvent composition not using dichloromethane has been studied for the purpose of minimizing the influence on the environment. In this case, an ether having 4 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and an alcohol having 1 to 12 carbon atoms are preferable. Sometimes used. For example, a mixed solvent of methyl acetate, acetone, ethanol, and n-butanol can be mentioned. These ethers, ketones, esters and alcohols may have a cyclic structure. 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, and these descriptions can also be applied to the present invention. The same applies to additives such as solvents and plasticizers, deterioration inhibitors, UV absorbers (UV agents), optical anisotropy control agents, retardation control agents, dyes, matting agents, release agents and release accelerators. JP-A-2005-104148 describes in detail in paragraphs [0196] to [0516], and these descriptions can also be applied to the present invention.

(Experiment 1)
The film 40 was manufactured using the solution casting apparatus 10 of FIG. Details are as follows. The moving speed VZ1 of the peripheral surface 22a in the preparation step was 100 m / min, the temperature of the peripheral surface 22a of the flow surface drum 22 was approximately 10 ° C., and the atmospheric pressure in the casting chamber 12 was 100 kPa. Under these conditions, the tip portion forming step, the unloading step, and the sealing step were performed. In the decompression step, the pressure in the casting chamber 12 was reduced to the target pressure P. The target atmospheric pressure P was 100 Pa. After the preparation step, the moving speed VZ2 of the peripheral surface 22a was set to 200 m / min. A solution casting method was performed under these conditions to produce a film 40.

(Experiment 2)
A film 40 was manufactured in the same manner as in Experiment 1 except that the target pressure P was set to 1 kPa in the decompression step.

(Experiment 3)
A film 40 was manufactured in the same manner as in Experiment 1 except that the target pressure P was set to 10 kPa in the decompression step.

(Experiment 4)
A film 40 was produced in the same manner as in Experiment 1 except that the decompression step was not performed.

(Evaluation)
The following evaluation was performed about the film 40 obtained in Experiments 1-4.

1. Evaluation of peelability The peelability was evaluated based on the following criteria.
○: The cast film could be peeled off from the support.
X: The cast film was not in a peelable state, and the cast film could not be peeled from the support.

2. Evaluation of thickness unevenness The thickness unevenness was evaluated based on the following criteria. When the maximum film thickness in the longitudinal direction is THmax, the minimum film thickness in the longitudinal direction is THmin, and the average film thickness in the longitudinal direction is THave, the thickness unevenness M is expressed by (THmax−THmin) / THave × 100.
○: M was less than 2%.
X: M was 2% or more.

  Table 1 shows the evaluation results of each evaluation item in the films obtained in Experiment 1 to Experiment 4. In Table 1, the numbers assigned to the evaluation results represent the numbers assigned to the evaluation items.

DESCRIPTION OF SYMBOLS 10 Solution casting equipment 12 Casting chamber 21 Casting die 22 Casting drum 31 Casting film 35 Wet film 40 Film 61 Sealing device 88 Decompression device

Claims (5)

It is performed in a casting chamber provided with a casting die for continuously flowing out a dope containing a polymer and a solvent and a moving support, and a belt-like casting film is formed on the support from the outflowed dope. A film forming step;
A first drying step that is performed in the casting chamber and evaporates the solvent from the casting film until the casting film is in a peelable state;
A stripping step of stripping the cast film that has undergone the first drying step from the support to form a wet film;
A second drying step of evaporating the solvent from the wet film to form a film,
The solution casting method, wherein the casting chamber is in a reduced pressure state.   The solution casting method according to claim 1, wherein the moving speed of the support is 100 m / min or more and 300 m / min or less. In the preparatory process performed before the film forming process,
A tip portion forming step for forming a tip portion of the belt-shaped casting film;
A conveying step of carrying out the tip from the outlet of the casting chamber;
A sealing step for sealing the outlet of the casting chamber;
The solution casting method according to claim 1 or 2, wherein a decompression step of decompressing the casting chamber is sequentially performed. A casting die for continuously discharging a dope containing a polymer and a solvent;
A support that supports the dope flowing out of the casting die and forms a casting film from the dope;
A casing that houses the casting die and the support;
Drying means for evaporating the solvent from the cast film;
A sealing means for connecting the outlet membrane of the casing that takes out the cast film peeled off from the support to the outside, and maintaining a pressure difference between the inside and the outside of the casing;
The said drying means is provided with the pressure reduction means to reduce the atmospheric | air pressure inside the said casing, The casting apparatus characterized by the above-mentioned.   The casting apparatus according to claim 4, wherein the moving speed of the support is 100 m / min or more and 300 m / min or less.

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