JP4515297B2 - Solution casting method - Google Patents

Description

  The present invention relates to a solution casting method, and more particularly to a solution casting method in which solvent gas generated during film deposition is recovered and reused.

  A film formed from cellulose acylate, particularly cellulose triacetate having an average degree of acetylation of 57.5% to 62.5% (hereinafter referred to as TAC film) is photographic sensitive because of its toughness and flame retardancy. It is 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) of a liquid crystal display device whose market is expanding in recent years. .

  The TAC film is usually produced by a solution casting method. The solution casting method can produce a film having excellent physical properties such as optical properties as compared with other production methods such as a melt casting method. In the solution casting method, a polymer solution (hereinafter referred to as a dope) is prepared by dissolving a polymer in a mixed solvent containing dichloromethane or methyl acetate as a main solvent. The dope is cast on a support from a casting die to form a casting film. After the cast film has a self-supporting property on the support, it is peeled off from the support as a film (hereinafter, this film is referred to as a soft film), and equipped with a tenter dryer and a number of rollers. The film is taken up as a film after being dried in a drying chamber (see Non-Patent Document 1).

  In the solution casting method, a large amount of solvent (solvent) is used, but an adsorption recovery facility that does not discharge the solvent out of the system is used for the purpose of suppressing air pollution and reducing the cost by reusing the solvent. . The recovered solvent is stored in a tank (hereinafter referred to as a stock tank). Further, the inside of the tank is pressurized in accordance with the exchange of the solvent between the stock tank and the tank in which the dope is placed (hereinafter referred to as the mixing tank) and the evaporation of the solvent in the stock tank. In addition, the gas containing the evaporated solvent is called solvent gas in the following description.

  In order to prevent the stock tank from bursting, it is necessary to discharge the solvent gas out of the system. As one of the methods, there is a method in which a vent gas pipe is provided from a stock tank to an adsorption recovery facility, and solvent gas is adsorbed and recovered. This may be a dedicated adsorption / recovery facility or an adsorption / recovery facility attached to the drying chamber when the film is produced. In these cases, solvent gas adsorption and recovery equipment is widely used in which water vapor generated in boiler equipment is used as a desorption source. However, the adsorption recovery equipment cannot be operated and the solvent gas cannot be recovered during the period when the boiler equipment for supplying water vapor is stopped during the period of regular repair. Note that since the solvent gas has a high concentration and a small air volume, a method of temporarily adsorbing the adsorbent on the adsorbent and performing a desorption process when resuming film formation can be applied (see, for example, Patent Document 1).

Japan Society for Invention and Innovation Public Technical Bulletin No. 2001-1745 JP 2000-300094 A

  However, in the method described in Patent Document 1, a solvent is retained in the adsorbent for a long time, and there is a risk of heat generation and ignition. In addition, the method using a dedicated adsorption / recovery facility requires the operation of a boiler that generates water vapor, and as a method for adsorbing / recovering a solvent gas having a high concentration and a small air volume, it causes a high cost. Furthermore, it is necessary to stop the generation of water vapor when maintaining and managing the boiler. Meanwhile, in order to perform the solvent gas adsorption recovery process, it is necessary to install a spare boiler, which causes high costs.

  The object of the present invention is to reduce the cost by continuously performing the solvent gas adsorption treatment recovery while suppressing the discharge of the solvent outside the film-forming equipment to prevent environmental pollution and improving the solvent reuse rate. An object of the present invention is to provide a solution casting method that can also be achieved.

  The solution casting method of the present invention is a method in which a dope containing a polymer and a solvent is cast on a support, peeled off as a film, dried in a drying section, and the solvent generated after casting the dope In the solution casting method for recovering the volatile component of the solvent in a container and reusing it as a raw material for the dope, first adsorption recovery means for adsorbing and recovering the solvent volatile component in the air in the drying section with a first adsorbent, and A second adsorbing / recovering means for adsorbing and recovering a solvent volatile component that volatilizes from the solvent in the container with the second adsorbent; and the solvent volatile component adsorbed on the first adsorbent and adsorbed on the second adsorbent. The method for desorbing solvent volatile components is different.

  The method of desorbing the solvent volatile component adsorbed on the first adsorbent is a method of supplying water vapor, and the method of desorbing the solvent volatile component adsorbed on the second adsorbent heats the second adsorbent. A method is preferred. More preferably, the second adsorbent is heated with an electric heater.

  The solvent volatile component adsorbed on the second adsorbent is preferably desorbed by depressurization. While maintaining and managing the first adsorption recovery means, the solvent volatile components generated from the container are adsorbed and recovered by the second adsorption recovery means, desorbed to liquefy the solvent, and reused as the dope raw material It is preferable. While the first adsorption recovery unit is stopped, it is preferable that the volatile solvent component in the atmosphere in the drying unit is adsorbed on the adsorbent of the second adsorption recovery unit.

  In the case of the boiling point of the solvent stored in the vessel or a mixed solvent composed of a plurality of solvents, the boiling point of the vessel is preferably 10 ° C. or more lower than the boiling point of the solvent. It is preferable to adjust the fluctuation range of the temperature of the liquid temperature and the temperature of the container within 10 ° C.

  The polymer is preferably cellulose acylate, more preferably cellulose acetate, and most preferably cellulose triacetate. It is preferable that the solvent is a mixed solvent containing a plurality of solvents, and the main solvent is either dichloromethane or methyl acetate.

  According to the solution casting method of the present invention, a dope containing a polymer and a solvent is cast on a support, peeled off as a film, dried in a drying section, and generated after casting the dope. In a solution casting method in which a volatile component of the solvent is recovered in a container and reused as a raw material for the dope, a first adsorption recovery unit that adsorbs and recovers the solvent volatile component in the air in the drying unit with a first adsorbent; And a second adsorbing and recovering means for adsorbing and recovering a solvent volatile component volatilized from the solvent in the container with the second adsorbent, and the solvent volatile component adsorbed on the first adsorbent and the second adsorbent Since the method for desorbing the adsorbed solvent volatile component is different, the desorption is performed by a method suitable for the amount of the solvent volatile component, so that the cost can be reduced.

  According to the solution casting method of the present invention, a dope containing a polymer and a solvent is cast on a support, peeled off as a film, dried in a drying section, and generated after casting the dope. In a solution casting method in which a volatile component of the solvent is recovered in a container and reused as a raw material for the dope, a first adsorption recovery unit that adsorbs and recovers the solvent volatile component in the air in the drying unit with a first adsorbent; A method of desorbing the solvent volatile components adsorbed on the first adsorbent using the second adsorbent recovery means for adsorbing and recovering the solvent volatile components volatilized from the solvent in the container with the second adsorbent supplies water vapor And the method of desorbing the solvent volatile component adsorbed on the second adsorbent is a method of heating the second adsorbent, and while maintaining the first adsorption recovery means, the container Volatilization of solvents generated from Since the solvent is adsorbed and recovered by the second adsorption recovery means, desorbed to liquefy the solvent, and reused as the dope raw material, the solvent can be recovered at low cost even when the film is not formed. Thus, the release of the solvent into the atmosphere can be prevented.

  According to the solution casting method of the present invention, a dope containing a polymer and a solvent is cast on a support, peeled off as a film, dried in a drying section, and generated after casting the dope. In a solution casting method in which a volatile component of the solvent is recovered in a container and reused as a raw material for the dope, a first adsorption recovery unit that adsorbs and recovers the solvent volatile component in the air in the drying unit with a first adsorbent; A method of desorbing the solvent volatile components adsorbed on the first adsorbent using the second adsorbent recovery means for adsorbing and recovering the solvent volatile components volatilized from the solvent in the container with the second adsorbent supplies water vapor And the method of desorbing the solvent volatile component adsorbed on the second adsorbent is a method of heating the second adsorbent, and the drying unit is stopped while the first adsorption recovery means is stopped. Volatile solvent components in the atmosphere By adsorbing to the adsorbent of the second adsorption / recovery means, it is possible to recover the solvent volatile components in the air in the drying section even when a trouble occurs in the first adsorption / recovery means. Can be prevented.

(material)
As the cellulose acylate, it is preferable to use a cellulose acylate in which the degree of substitution of the hydroxyl group of cellulose satisfies all of the following formulas (I) to (III). Hereinafter, what satisfies the following formula is referred to as TAC.
(I) 2.5 ≦ A + B ≦ 3.0
(II) 0 ≦ A ≦ 3.0
(III) 0 ≦ B ≦ 2.9
In the formula, A and B represent the substitution degree of the acyl group substituted with the hydroxyl group of cellulose, A is the substitution degree of the acetyl group, and B is the substitution degree of the acyl group having 3 to 22 carbon atoms. . In addition, it is preferable to use particles having 90% by mass or more of TAC of 0.1 mm to 4 mm.

  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.).

  A halogenated hydrocarbon having 1 to 7 carbon atoms is 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 of the film, and optical properties of the film, in addition to dichloromethane, 1 to 5 alcohols having 1 to 5 carbon atoms It is preferable to mix several types. 2 mass%-25 mass% are preferable with respect to the whole solvent, and, as for content of alcohol, 5 mass%-20 mass% are more preferable. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like, but methanol, ethanol, n-butanol or a mixture thereof is preferably used.

  Recently, solvent compositions that do not use dichloromethane are also known to minimize environmental impact. For example, ethers having 4 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, and esters having 3 to 12 carbon atoms are preferable, and these are appropriately mixed and used. These ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as a solvent. The solvent may have other functional groups such as alcoholic hydroxyl groups. In the case of a solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

  Details of cellulose acylate are described in paragraphs [0140] to [0195] of Japanese Patent Application No. 2004-264464. These descriptions are also applicable to the present invention. In addition, additives such as a solvent and a plasticizer, an anti-degradation agent, an ultraviolet absorber, an optical anisotropy control agent (retardation control agent), a dye, a matting agent and a release agent are also disclosed in Japanese Patent Application No. 2004-264464. [0196] paragraph [0516] paragraph.

(Preparation of dope)
After the polymer and additive are put in the solvent, the dope is prepared by dissolving by any known dissolution method. This dope generally removes foreign matters by filtration. For filtration, various known filter media such as filter paper, filter cloth, non-woven fabric, metal mesh, sintered metal, and perforated plate can be used. By filtering, foreign matters and the like in the dope can be removed. A film formed using the dope can reduce defects.

  In addition, the dope once dissolved can be heated to further improve the solubility. A method is known for heating while stirring in a stationary tank. Furthermore, there is also a method of heating while transferring the dope using various heat exchangers such as a multi-tube heat exchanger or a jacket pipe with a static mixer. In addition, performing a cooling step after the heating step is also an effective method for improving the solubility. Moreover, it is also possible to heat more than the boiling point of the solvent of dope by pressurizing the inside of a heating apparatus. By performing these heat treatments, the solubility of the solute can be improved, the dope filtration load can be reduced, and foreign matters in the formed film can be reduced.

  Regarding the method of dissolving the raw materials, raw materials and additives, the filtering method of the dope, the defoaming method, and the method of adding the additive when preparing the dope, the paragraphs [0517] to [0616] of Japanese Patent Application No. 2004-264464 are described. Are described in detail. Those descriptions are also applicable to the present invention.

(Solution casting method)
The solution casting method will be described with reference to an example in which TAC is used as a polymer, but the polymer used in the present invention is not limited to TAC. FIG. 1 shows a film production facility 10 used in the solution casting method according to the present invention. An adjusted dope 12 is placed in the mixing tank 11. A stirring blade 13 for stirring the dope 12 is provided in the mixing tank 11. The dope 12 is fed to the casting die 15 by the pump 14. In addition, it is preferable to provide the filtration apparatus 16 in the middle and to perform dope 12 filtration.

  A casting band 22 is provided below the casting die 15 so as to span the rollers 20 and 21. The casting band 22 travels endlessly as the rollers 20 and 21 are rotated by a driving device (not shown). The dope 12 is cast on the casting band 22 from the casting die 15 to form a casting film 23. After the casting film 23 has self-supporting properties on the casting band 22, it is peeled off from the casting band 22 as a soft film 25 while being supported by the peeling roller 24. The flexible film 25 is dried by the tenter dryer 26 while being stretched and relaxed in the casting width direction to form a film 27. It is also possible to provide stretching in the casting direction by providing a number of rollers between the peeling roller 24 and the tenter dryer 26 and adjusting the rotational speed of each roller. The casting die 15, the casting band 22, the tenter dryer 26 and the like are provided in the casting chamber 28. A method for treating the volatile solvent generated from the dope 12 in the casting chamber 28 will be described in detail later.

  The film 27 is conveyed to a drying chamber 31 provided with a number of rollers 30. The film 27 is dried while being conveyed while being wound around a large number of rollers 30. Although the temperature in the drying chamber 31 is not specifically limited, It is preferable that it is the range of 50 to 150 degreeC. The film 27 conveyed from the drying chamber 31 is wound up by a winder 32. In addition, it is preferable to provide a static eliminator and control the charged voltage of the film 27 while being wound from the drying chamber 31 by the winder 32 in order to suppress the adhesion at the time of winding. Further, it is preferable to provide a knurling device and emboss both edges of the film 27 in order to achieve good winding. Furthermore, by providing an ear-cut device and cutting both edges of the film, it is possible to suppress the winding failure and to reduce the commercial value when storing as a film roll. The recovery of the volatile solvent in the drying chamber 31 will be described in detail later.

  The film 27 to be wound is preferably at least 100 m in the longitudinal direction (casting direction). The casting width direction is preferably 600 mm or more, and more preferably 1400 mm or more and 1800 mm or less. Moreover, it is applicable also when it is wider than 1800 mm. The thickness of the film 27 can also be applied when manufacturing a thin film having a thickness of 15 μm to 100 μm.

  The casting method is not limited to single layer casting as shown in FIG. You may perform the method of carrying out simultaneous lamination co-casting or sequential lamination co-casting of 2 or more types of dope. Moreover, you may combine both casting methods. 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. The film composed of multiple layers by co-casting preferably has an air surface side layer thickness and / or a support surface side layer thickness of 0.5% to 30% of the total film thickness. .

  Casting die, structure such as support, casting method (co-casting using single layer, feed block and / or multi-manifold), casting film peeling method, stretching, drying conditions for each process, handling method, curl The winding method, the solvent recovery method, and the film recovery method after flatness correction are described in detail in paragraphs [0617] to [0889] of Japanese Patent Application No. 2004-264464. These descriptions are also applicable to the present invention.

[Performance / Measurement method]
(Curl degree / thickness)
The performance of the wound cellulose acylate film and the measuring method thereof are described in paragraphs [0112] to [0139] of Japanese Patent Application No. 2004-264464. 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.

  A method for applying a surface-treated functional layer for realizing various functions and properties on a cellulose acylate film is described in Japanese Patent Application No. 2004-264464, from [0890] paragraph to [1087] paragraph. It is included. 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 No. 2004-264464 describes in detail TN type, STN type, VA type, OCB type, reflection 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 Japanese Patent Application No. 2004-264464.

  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. Furthermore, it can also be used as an optical compensation film for improving the viewing angle dependency of a liquid crystal display device for television applications. In particular, it is effective for applications that also serve as a protective film for a polarizing plate. Therefore, it is used not only for the conventional TN mode but also for 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.

(Volatile solvent treatment in casting chamber)
The atmosphere in the casting chamber 28 contains a large amount of volatile solvent. That is, since the casting film 23 and the flexible film 25 are in the initial drying stage, they contain a large amount of organic solvent. Therefore, the volatile solvent is removed by the condensation recovery facility 40. The condensation recovery facility 40 includes a blower, a heat exchanger, a condenser, and the like (all not shown). The air in the casting chamber 28 (hereinafter referred to as casting chamber atmosphere) is blown to the heat exchanger by a blower. In the heat exchanger, heat exchange is performed with the low-temperature drying air described later, and the temperature of the casting chamber atmosphere is lowered. The casting chamber atmosphere is blown to a condenser cooled to, for example, −15 ° C. to + 5 ° C., and the volatile solvent condenses and becomes the solvent 41. The solvent 41 is sent to the distillation tower 42 and a subsequent processing step is performed. This processing step will be described later. Further, the casting chamber atmosphere from which the volatile solvent has been removed is blown again into the casting chamber 28 as dry air. At this time, heat is exchanged by the above-described casting chamber atmosphere and heat exchanger to raise the temperature. When the heat exchange does not increase the temperature as dry air, the temperature is adjusted to a desired temperature (for example, 40 ° C. to 180 ° C.) by the heater and then blown into the casting chamber 28 as dry air.

(Volatile solvent treatment in the drying room)
The atmosphere in the drying chamber 31 (hereinafter referred to as drying chamber atmosphere) also contains a volatile solvent. Since the drying of the film 27 in the drying chamber 31 is progressing, an additive such as a plasticizer is contained in a larger amount than the casting chamber atmosphere in addition to the volatile organic. Therefore, volatile components in the drying chamber atmosphere are removed using a recovery facility 50 (hereinafter referred to as main adsorption recovery facility) separate from the casting chamber atmosphere.

  The drying chamber atmosphere is processed by the main adsorption recovery facility 50. The air in the drying chamber 31 is sent out using the blower 51. The heat exchanger 52 exchanges heat with the drying air to lower the temperature of the drying chamber atmosphere. Thereafter, the air in the drying chamber is blown into one of the plurality of adsorption tanks 53 and 54. Volatile components in the drying chamber atmosphere are adsorbed by the adsorbents in the adsorption tanks 53 and 54. The drying chamber atmosphere from which the volatile components have been removed is blown into the drying chamber 31 as drying air. After adjusting the drying chamber atmosphere to a desired temperature with the temperature controller 55, heat exchange with the drying chamber atmosphere is performed with the heat exchanger 52, and the air is blown into the casting chamber 31 as drying air of 50 ° C. to 180 ° C.

  Water vapor 56 generated in a boiler (not shown) is supplied from one downstream side to one of the adsorption tanks 53 and 54 that are not used for adsorption of volatile components. The water vapor containing the volatile component is sent to the condenser 57 to be condensed and liquefied. Thereafter, the liquid is sent to the solvent processing device 58. The solvent 59 and the waste liquid 60 are separated by the solvent processing device 58. The waste liquid 60 is discarded after the waste liquid treatment is performed. Further, the solvent 59 is sent to the distillation tower 42.

  Each of the components of the solvent is fractionated by the distillation tower 42 and sent to the respective stock tanks 70 and 71. The stock tanks 70 and 71 are provided with stirring blades 72 and 73. It is preferable to stir the solvents 74 and 75 so that no gas is contained during storage. It is advantageous from the viewpoint of cost that the solvents 74 and 75 are sent to the mixing tank 11 and reused as the solvent for preparing the dope 12.

(Stock tank volatile solvent treatment)
Some of the solvents 74 and 75 are volatilized while being stored in the stock tanks 70 and 71. The inside of the stock tanks 70 and 71 is pressurized by the volatile solvent. The stock tanks 70 and 71 and the main adsorption / recovery equipment 50 are connected by vent gas pipes 76 and 77. During solution film formation, the volatilized solvent gas is blown to the main adsorption / recovery facility 50, so that the pressure in the stock tanks 70 and 71 is within a certain pressure range (for example, within atmospheric pressure ± 2000 Pa, more preferably within atmospheric pressure ± 300 Pa). ) Can be adjusted. In addition, it is preferable to attach an atmos valve 78 to the vent gas pipes 76 and 77.

  The main adsorption / recovery facility 50 is configured not to release the solvent gas discharged from the drying chamber 31 and the solvent gas accompanying the solvent transfer into the atmosphere. While the film 27 is being formed, the main adsorption / recovery facility 50 is also stopped. At this time, solvent gas generation from the drying chamber 31 and solvent 74 and 75 transfer are eliminated. However, evaporation of the solvent accompanying the change in temperature occurs, and the inside of the stock tanks 70 and 71 is in a pressurized state. Therefore, in order to prevent the stock tanks 70 and 71 from being damaged, it is necessary to discharge the solvent gas to the outside of the system. Usually, the solvent gas is mainly processed by blowing into the adsorption / recovery facility 50 as described above. However, it is disadvantageous in terms of cost to operate the main adsorption / recovery facility 50 only for processing the solvent gas in the stock tanks 70 and 71 when film production is stopped. Further, when performing maintenance and inspection of the main adsorption / recovery facility 50, it becomes impossible to blow the volatilized solvent gas to the main adsorption / recovery facility 50. In this case, the solvent gas is adsorbed and recovered by operating another adsorption facility. However, this method cannot be operated during the regular repair period when the boiler is stopped. Moreover, the main adsorption | suction collection | recovery equipment 50 also needs periodic repair, and the period when the operation must be stopped arises.

  Therefore, the vent gas pipes 76 and 77 are connected to the auxiliary adsorption recovery facility 80. The sub-adsorption / recovery facility 80 performs the adsorption / desorption process using a vacuum pump operated by electricity without using water vapor. When the operation of the main adsorption recovery facility 50 is stopped or the operation of the boiler is stopped, the solvent gas evaporated in the stock tanks 70 and 71 is recovered by the sub adsorption recovery facility 80. In addition, even when the electric power is generated by the boiler equipment and the electricity is supplied to the film manufacturing equipment 10, the electric power supplied from a general electric power company is supplied by the auxiliary adsorption recovery equipment 80 so that the operation can be performed even when the boiler stops. It is preferable to use it.

  A three-way valve 82 is attached to the vent gas pipes 76 and 77. Whether the main adsorption / recovery facility 50 or the sub-adsorption / recovery facility 80 is used is selected as the solvent gas processing facility by selecting the valve of the three-way valve 82. When the secondary adsorption facility 80 is used, the suction pump 81 is operated to suck the solvent gas into the secondary adsorption recovery facility 80 through the three-way valve 82 and the switching device 83. Thereafter, the solvent gas is passed through the condenser 84. The solvent component contained in the solvent gas is liquefied by the condenser 84. The solvent 85 is sent to the distillation tower 42, fractionated into each component, sent to the corresponding stock tanks 70 and 71, and stored. In addition, it is preferable that the outlet temperature of the condenser 84 is in a range of 0 ° C. to 30 ° C. because an adsorption load in an adsorption tank described later can be reduced.

  Components that are not condensed and liquefied by the condenser 84 are blown to one of the adsorption tanks 87 and 88 via the switching device 86. FIG. 1 shows a form in which the adsorption is collected in the adsorption tank 87. The solvent gas having adsorbed components adsorbed in the adsorption tank 87 is blown to the switching unit 83 and then blown to the condenser 84 again. As a result, the solvent gas is not discharged outside the sub-adsorption recovery facility 80, which is preferable from the viewpoint of environmental conservation. Note that activated carbon, silica gel, zeolite, or the like is preferably used as the adsorbent filled in the adsorption tanks 87 and 88.

  The adsorption tank 88 has been subjected to adsorption recovery before the solvent gas is adsorbed and recovered in the adsorption tank 87. The components adsorbed in the adsorption tank 88 are desorbed by being evacuated by the vacuum pump 89 via the switching device 86. By blowing the desorbed gas (hereinafter referred to as desorbed gas) to the condenser 90, the volatile components in the desorbed gas are condensed and liquefied to become the solvent 91. The solvent 91 is sent to the distillation tower 42 and fractionated into components, and then sent to the corresponding stock tanks 70 and 71 for storage. Note that the degree of vacuum is preferably in the range of 1 Pa to 10 Pa with the vacuum pump 89. Further, it is preferable that an open point 92 is attached upstream of the auxiliary adsorption recovery facility 80 so that the inside of the stock tanks 70 and 71 is not directly sucked even if the vacuum pump 89 malfunctions.

  It is preferable to attach heaters 93 and 94 to the adsorption tanks 87 and 88. When the vacuum desorption is performed, the adsorption tanks 87 and 88 are heated by the heaters 93 and 94 to facilitate desorption of the adsorbed components from the adsorbents of the adsorption tanks 87 and 88. An electric heater is preferably used as the heater. The heating temperature by the heaters 93 and 94 is not particularly limited. However, in order to facilitate vacuum desorption by the vacuum pump 89, it is preferable to set the temperature in the range of 100 ° C to 200 ° C. Moreover, when performing vacuum desorption, it is preferable that the other end of the adsorption tank 88 is connected to a part of the sub-adsorption recovery facility 80 (switching machine 83 in FIG. 1). Thereby, inhalation of the atmosphere outside the system is prevented and the adsorption load of the adsorption tank 88 can be reduced.

  From the volume of the stock tanks 70 and 71, the amount of solvent stock, and the temperature change in the stock tanks 70 and 71, the amount of solvent gas generated by evaporation and volume expansion is obtained, and the scale of the sub-adsorption recovery facility 80 is made preferable. A structure in which a heat insulating material is attached to the stock tanks 70 and 71 is preferable. In addition, it is preferable to lower the liquid temperature and temperature in the stock tank by flowing cooling water in the cooling jacket structure or by spraying water from the outside of the stock tank. More preferably, the scale of the sub-adsorption / recovery facility 80 can be reduced by reducing the evaporation amount of the solvent by lowering the boiling point of the solvent stored in the stock tanks 70 and 71 by 10 ° C. or more. There are also methods for lowering the temperature in the tank, such as water spraying from the outside of the tank, and a tank structure with a jacket structure, and water such as well water and cold water is passed through the outer jacket part. become. In particular, when water is sprayed outside the tank, algae, mold, etc. are generated, which may impair the beauty. Therefore, it is preferable to lower the temperature of the stock tanks 70 and 71 using a jacket, a coil cooler, or the like.

  Further, by selecting the valve position of the three-way valve 82, it is possible to perform an adsorption recovery process of the solvent gas in the atmosphere of the drying chamber 31. This is because, for example, when the operation is stopped for periodic inspection of the boiler, the solvent gas in the drying chamber 31 is temporarily adsorbed and recovered by the sub-adsorption recovery equipment 80, thereby changing the piping of the main adsorption equipment, the boiler Can be changed. In this case, the solvent adsorption capacity of the secondary adsorption recovery facility 80 is the same as that of the main adsorption recovery facility 50.

  EXAMPLES Hereinafter, although Example 1 is given and this invention is demonstrated in detail, the aspect of this invention is not limited to these. In Example 1, a PSA type (pressure swing adsorption type) adsorption facility that does not require water vapor was attached to the film production facility 10 as a sub-adsorption recovery facility 80. Two stock tanks 70, 71 were connected by vent gas pipes 76, 77, and were connected to the main adsorption recovery facility 50 and the sub-adsorption recovery facility 80 by a three-way valve 82. A heat insulating material was wound around the stock tank 70 and maintained at 30 ° C. or lower, which was 10 ° C. lower than the boiling point 40 ° C. of dichloromethane which is the main component of the storage solvent.

  The film 27 was formed using a dope 12 having a TAC weight of 19% by weight, a solvent (dichloromethane: methanol: 1-butanol = 320: 83: 3 (weight ratio)), a plasticizer, and the like. Film formation was performed such that the film forming speed was 35 m / min, the casting width was 1800 mm, and the thickness was 80 μm. After the film 27 was manufactured, the operation of the main adsorption recovery facility 50 was stopped, and the operation of the sub adsorption recovery facility 80 was started.

In the summer when the temperature is 25 ° C. at night and 30 ° C. during the day, the total capacity of the stock tank 70 is 100 m ³ and the mixed solvent of dichloromethane and methanol (weight ratio 92: 8) 74 is half 50 m ^{3 of the} tank. Due to evaporation and volume expansion of the solvent (mainly dichloromethane), 19 kg of dichloromethane was discharged from the stock tank 70 during the 12 hours when the temperature rose. This sampled solvent gas and analyzed the density | concentration with the commercially available gas chromatograph. Further, the air velocity at the vent gas opening was measured with a Pitot tube, the air volume was determined, and the amount of dichloromethane discharged was calculated from the concentration × the air volume. The release rate during discharge is 1.6 kg / hr, and at night when the temperature drops, the volume shrinks, so the Atmos valve (the negative pressure side is atmospheric pressure -490 Pa, the pressure side is the pressure side) Was operated at atmospheric pressure +980 Pa).

In order to perform the adsorption treatment, a sub-adsorption recovery facility 80 having a solvent adsorption recovery processing capacity of 2 kg / hr exceeding the discharge amount was used. Silica gel was used as the adsorbent for the adsorption tanks 87 and 88. The desorption method was performed by vacuum desorption (pressure: about 3 Pa) with a vacuum pump 89. By operating during the period when the main adsorption recovery facility 50 is stopped, the amount of the solvent 74 in the stock tank 70 can be maintained at 50 m ³ . The recovered solvent 85 was subjected to distillation treatment in the distillation tower 42 together with the solvent 59 recovered from the main adsorption recovery facility 50 and the solvent 41 recovered from the condensation recovery facility 40, and used as a solvent for preparing the dope 12. When the composition ratio of each solvent component after distillation was measured by gas chromatography, it was 91.8% by weight for dichloromethane and 8.2% by weight for methanol, both of which were of high quality. Later, when a film 27 was formed under the same conditions as the film forming conditions using a solvent containing the recovered solvent as a raw material, the film 27 having excellent retardation and retardation (Re value) of 34 nm was obtained. Obtained.

  The present invention will be described in detail with reference to Example 2, but the embodiment of the present invention is not limited thereto. In addition, the experiment was performed under the same conditions as in Example 1 unless otherwise specified. A TSA type (temperature swing adsorption type) adsorption facility using an electric heater without requiring water vapor was attached to the film production facility 10 as a secondary adsorption recovery facility 80. After the production of the film 27 was stopped, the operation of the main adsorption / recovery facility 50 was stopped and the operation of the sub-adsorption / recovery facility 80 was started.

As the secondary adsorption recovery equipment 80, one having a solvent adsorption recovery processing capacity of 2 kg / hr exceeding the discharge amount was used. In the desorption method, vacuum adsorption and desorption using a vacuum pump 89 (pressure of about 3 Pa) and the electric heaters 93 and 94 were set to 160 ° C. to heat the adsorption tanks 87 and 88. By operating during the period when the main adsorption recovery facility 50 is stopped, the amount of the solvent 74 in the stock tank 70 can be maintained at 50 m ³ . The recovered solvent 85 was subjected to distillation treatment in the distillation tower 42 together with the solvent 59 recovered from the main adsorption recovery facility 50 and the solvent 41 recovered from the condensation recovery facility 40, and used as a solvent for preparing the dope 12. When the composition ratio of each solvent component after distillation was measured by gas chromatography, it was 91.8% by weight for dichloromethane and 8.2% by weight for methanol, both of which were of high quality. Later, when the film 27 was formed under the same conditions as the film forming conditions using a solvent containing the recovered solvent as a raw material, a film 27 having a retardation value (Re value) of 34 nm and excellent optical characteristics was obtained. It was.

  The present invention can be preferably applied when storing a solvent in a stock tank.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Film manufacturing equipment 27 Film 41, 59, 74, 75, 85, 91 Solvent 42 Distillation tower 50 Main adsorption recovery equipment 56 Water vapor 70, 71 Stock tank 80 Sub-adsorption recovery equipment 89 Vacuum pump 93, 94 Heater

Claims (6)

A dope containing a polymer and a solvent is cast on a support, peeled off as a film, dried in a drying section, and the volatile component of the solvent generated after casting the dope is recovered in a container. In the solution casting method to be reused as the raw material of the dope,
A first adsorbing / recovering means for adsorbing and collecting a solvent volatile component in the air in the drying section with a first adsorbing material; Means and
A solution casting method characterized in that a method for desorbing a solvent volatile component adsorbed on the first adsorbent and a solvent volatile component adsorbed on the second adsorbent are different. The method of desorbing the solvent volatile component adsorbed on the first adsorbent is a method of supplying water vapor,
2. The solution casting method according to claim 1, wherein the method of desorbing the solvent volatile component adsorbed on the second adsorbent is a method of heating the second adsorbent.   3. The solution casting method according to claim 2, wherein the second adsorbent is heated with an electric heater.   4. The solution casting method according to claim 1, wherein the solvent volatile component adsorbed on the second adsorbent is depressurized and desorbed.   While maintaining and managing the first adsorption recovery means, the solvent volatile components generated from the container are adsorbed and recovered by the second adsorption recovery means, desorbed to liquefy the solvent, and reused as the dope raw material The solution casting method according to any one of claims 1 to 4, wherein:   The volatile solvent component in the atmosphere in the drying unit is adsorbed on the adsorbent of the second adsorption recovery unit while the first adsorption recovery unit is stopped. The solution casting method described.

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