JP2009066569A - Method and device for recovering filter aid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently recover and dry filter aid after filtration in a filter aid type filtration system. <P>SOLUTION: The filter aid is dispersed in raw material dope and filtered through a first or second filter. The filter aid is accumulated on a filter medium support body in a filter, and the raw material dope is filtered using the filter medium comprising the filter medium support body and an accumulated layer. When the filtering pressure is increased, a plurality of the filters are switched over, and cleaning liquid is run into the used filter for cleaning. Slurry 90 obtained by cleaning is sent to a separator 87 and separated into residue 90a and solution 90b. A bottomed cylindrical wire mesh strainer 95 is disposed in the separator 87. The strainer 95 is composed of a first wire mesh 95a forming a periphery and a second wire mesh 95b forming a bottom. A ratio of the first wire mesh/second wire mesh is set to 1.5-10, with the mesh thereof set to 50-500. The mesh ratio allows roughly even accumulation of the filter aid in the strainer 95, to efficiently dry the filter aid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for recovering a used filter aid in a filter device for filtering a polymer solution with a filter aid.

  Various display devices such as liquid crystal displays use various polymer films including a polarizing plate protective film and a viewing angle widening film. As a method for producing such a polymer film for optical use, there are a melt film forming method and a solution film forming method. In the solution casting method, a polymer solution containing a polymer and a solvent (hereinafter referred to as a dope) is cast on a traveling support to form a cast film, and then the cast film is peeled off from the support. This is a method of drying into a film, and there is no problem of heat damage as in the melt film-forming method. Therefore, it is optimal as a method for producing a polymer film that requires high transparency and optical characteristics.

  By the way, the dope contains foreign substances that are insoluble in the solvent of the dope and originally contained in the dope raw material, and impurities such as dust and dirt mixed in preparing the dope. . However, when a dope containing impurities is used, impurities are deposited on the support as dirt, and it becomes difficult to peel off the casting film from the support, and the finished film causes light scattering at the impurities, etc. Cause problems. For this reason, it is necessary to remove impurities in the dope as much as possible before being subjected to casting.

  Therefore, in the solution casting method, the dope before casting is usually filtered with a porous filter medium for the purpose of removing impurities in the dope. As the filter medium, a filter paper, a metal filter, a filter cloth or the like is used. However, each of the filter media has a problem that the passage hole is blocked as time passes from the start of filtration, and the filtration time is prolonged, or the filtration efficiency increases due to an increase in filtration pressure or a reduction in filtration flow rate. For this reason, when using a metal filter, measures are taken to clean and regenerate the metal filter by supplying a cleaning liquid to the metal filter in the direction opposite to the filtration direction and circulating it. However, even if these measures are taken, they are temporary, and the present situation is that the filtration efficiency has not been fundamentally improved.

Moreover, it is difficult to remove impurities that are hardly soluble in a solvent only by using a filter medium such as a filter paper, a metal filter, or a filter cloth. Thus, for example, Patent Document 1 proposes an auxiliary filtration method that removes hardly soluble impurities by using a filter aid in addition to the filter medium. The filter aid is an inert particle or powder, such as silicon dioxide (SiO ₂ ). This filter aid is used by being randomly deposited on a filter medium support such as a wire mesh filter. When the dope is passed through the filter medium on which such a deposited layer is formed, impurities can be adsorbed and recovered by the filter aid regardless of whether it is poorly soluble or not, and thus a highly clear filtrate can be obtained. It is done. In addition, if a filter aid is used, clogging of the filter medium can be suppressed, so that productivity can be improved.
JP 2004-107629 A

  By the way, in the filtration method using a filter aid, since the deposition layer (also called cake) on the filter medium increases as the filtration proceeds, a step of collecting the cake is required. When the cake is recovered in the solution casting method, since the dope is filtered, the cake contains a solvent. Accordingly, as in the usual general auxiliary filtration method, opening the filter and collecting the cake causes scattering of the solvent, which causes environmental problems as well as solvent loss. In addition, it is conceivable to collect the cake as a slurry together with the cleaning liquid in a closed piping system, but there is also a problem of solvent scattering for the recovered slurry, and the problem that efficient cake recovery is difficult. There is.

  The present invention has been made in view of the above-described problems, and allows the used filter aid to be efficiently recovered without scattering the solvent, and can further shorten the drying time of the filter aid. An object of the present invention is to provide a method and an apparatus for recovering the filter paper aid.

  The present invention relates to a filter aid for recovering the filter aid from the filter after filtering a polymer solution using a filter having a filter medium formed with a precoat having a filter aid deposited on a filter medium support. In the recovery method, a cleaning liquid is supplied to the filter, the filter aid and the cleaning liquid are recovered from the filter as a slurry, and the filter is cleaned in the filter cleaning process. The slurry is circulated through a washing liquid path having a separator and the slurry is separated into the filter aid and the washing liquid by the separator, and the filter aid captured in the separation step is separated from the separator. A filter aid drying step for drying inside the separator, wherein the separator comprises a separator body and a filter medium accommodated in the separator body, and the filter medium has a bottom at one end of the cylinder. Wire mesh A Torena, wherein the second wire mesh of constituting the bottom than the first wire mesh of constituting the cylinder is large.

  The present invention also provides a filtration method for recovering the filter aid from the filter after filtering the polymer solution using a filter having a filter medium formed with a precoat having a filter aid deposited on the filter medium support. In the auxiliary agent recovery device, a cleaning liquid is supplied to the filter, the filter auxiliary and the cleaning liquid are recovered from the filter as a slurry, and the filter is cleaned, and the filter cleaning unit The slurry recovered in step (b) is circulated through a cleaning liquid path having a separator, and the separator separates the slurry into the filter aid and the cleaning liquid by the separator, and the filter aid captured by the separator is the A filter aid drying section for drying in the separator, the separator being housed in the separator body, and a bottomed cylindrical wire mesh strainer having a bottom at one end of the cylinder; Consisting of the above Wherein the second wire mesh of constituting the bottom than the first wire mesh of constituting the cylinder is large.

  In the present invention, the first wire mesh and the second wire mesh are in the range of 50 to 500, and the ratio of the mesh of the second wire mesh and the mesh of the first wire mesh (second wire mesh / first wire mesh). (Mesh) is 1.5 or more and 10 or less. The first wire mesh and the second wire mesh have a tatami-woven structure. The metal strainer is characterized in that an inner diameter of the cylinder is smaller than a height of the cylinder. Further, the viscosity of the slurry is 200 mPas or less, and the concentration is 0.15 to 25% by weight.

The present invention is characterized in that the flow of the slurry in the separator is vertically downward. The final deposition thickness of the filter aid in the separator is 0.5 to 50 cm. The filter aid trapped on the filter medium is dried by a heater provided in the separator body or a dry gas circulation unit that sends a dry gas to the separator body. As the filter aid, SiO ₂ having an average particle diameter of 20 to 50 μm is used, and the polymer is cellulose acylate.

  According to the present invention, the cleaning liquid is supplied to the filter, the filter aid and the cleaning liquid are recovered from the filter as a slurry to wash the filter, and the slurry recovered by this cleaning is supplied to the cleaning liquid path having the separator. The solvent is separated from the filter aid in a closed system by circulating and separating the slurry into the filter aid and the washing liquid by the separator, and drying the filter aid captured by the separation in the separator. can do. Therefore, scattering of the solvent can be eliminated and the filter aid and the solvent can be efficiently recovered.

  Further, the separator is composed of a separator body and a filter medium accommodated in the separator body, and the filter medium is a bottomed cylindrical wire mesh strainer having a bottom at one end of the cylinder, and constitutes the cylinder. By making the mesh of the second wire mesh that constitutes the bottom larger than the mesh of the first wire mesh, the bottom of the passage resistance of the slurry can be made larger than the peripheral surface. Therefore, more slurry can flow through the circumferential surface of the cylinder than slurry flowing through the bottom, and the deposition thickness of the filter aid formed on the bottomed cylindrical strainer can be reduced between the circumferential surface and the bottom surface. It can be made almost uniform. For this reason, when drying the filter aid in the separator, it is possible to proceed with drying almost uniformly, and it is possible to suppress the occurrence of poor drying and an increase in drying time.

  A solution casting apparatus 10 shown in FIG. 1 includes a raw material dope preparation unit 11, a filtration unit 12, and a film forming unit 13.

  The raw material dope preparation unit 11 includes a meter 14, a solvent tank 15, an additive tank 16, a dissolution tank 17, and a storage tank 18. A polymer 20 is placed in the meter 14, and the polymer 20 is weighed and put into the dissolution tank 17. A solvent 21 is stored in the solvent tank 15, and the input amount to the dissolution tank 17 is adjusted by controlling the open / close valve 23. An additive 22 is stored in the additive tank 16, and the input amount to the dissolution tank 17 is adjusted by controlling the open / close valve 24.

  The polymer 20 according to the present invention is not particularly limited as long as it is applicable to the solution casting method. Among these, if cellulose acylate is used, a film having high transparency and excellent optical properties can be obtained, and therefore, it is suitable for optical applications such as a protective film for polarizing plates and an optical compensation film. Among them, when cellulose acetate is used, and particularly cellulose triacetate having an average degree of acetylation of 57.5% to 62.5% is used, a film having excellent optical properties can be obtained. The above-mentioned degree of acetylation means the amount of bound acetic acid per unit weight of cellulose, and can be determined according to the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). In this embodiment, granular cellulose triacetate is used. In addition, when using a granular polymer, it is preferable that 90 weight% or more is a particle size of 0.1-4 mm from a compatible viewpoint with a solvent, More preferably, a particle size is 1-4 mm. It is.

  The solvent 21 is preferably a halogenated hydrocarbon, an ester, a ketone, an ether, an alcohol, or the like, but is not particularly limited, and may be appropriately selected in consideration of solubility with the polymer to be used. The solvent 21 may be one type of compound or a mixed solvent in which a plurality of compounds are mixed. Specifically, halogenated hydrocarbons (eg, dichloromethane, etc.), esters (eg, methyl acetate, methyl formate, ethyl acetate, amyl acetate, butyl acetate, etc.), ketones (eg, acetone, methyl ethyl ketone, cyclohexanone, etc.) ), Ethers (eg, dioxane, dioxolane, tetrahydrofuran, diethyl ether, methyl-t-butyl ether, etc.), alcohols (eg, methanol, ethanol, etc.) and the like.

  The additive 22 may be appropriately selected according to the desired characteristics of the film 19. For example, a plasticizer, an ultraviolet absorber, a peeling accelerator, a fluorine surfactant, and the like can be given. Among these, as the plasticizer, phosphate ester type (for example, triphenyl phosphate (hereinafter referred to as TPP), tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate (hereinafter referred to as BDP). ), Trioctyl phosphate, tributyl phosphate, etc.), phthalate esters (eg, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, etc.), glycolate esters (eg, triacetin, tributyrin, butyl phthalyl butyl glycolate) Ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc.). Among these, TPP is particularly preferable for making cellulose acylate into a film. In addition, a well-known thing can be used for a plasticizer besides the above, and it does not specifically limit. Further, as the ultraviolet absorber, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds are preferable, and among them, benzotriazole compounds and benzophenone compounds are preferable. Compounds are particularly preferred.

  The dissolution tank 17 includes a stirring blade 27 that is rotated by a motor 26. As the stirring blade 27 rotates, the polymer 20, the solvent 21, and the additive 22 in the solvent tank 15 are stirred. By this stirring, a crude solution 30 in which the solute such as the polymer 20 is not completely dissolved in the solvent is obtained.

  The crude solution 30 in the dissolution tank 17 is temporarily stored in the storage tank 18. As a result, the dissolution tank 17 is emptied, and a continuous batch system in which the crude dissolution solution 30 is repeatedly formed becomes possible. The storage tank 18 is also provided with a stirring blade 32 that is rotated by a motor 31. By rotating the stirring blade 32, the crude solution 30 is stirred and made uniform.

  The crude solution 30 in the storage tank 18 is sent to the heater 40 via the pump 35 and the pipe 36. As the heater 40, an in-line mixer such as a multi-tube heat exchanger or a static mixer is used. The crude solution 30 is heated by the heater 40. The heating temperature is preferably 50 to 120 ° C., and the heating time is preferably 5 to 30 minutes. By this heating, the solute such as the polymer 20 necessary for solution film formation is completely dissolved without modification, and the raw material dope 41 is prepared. Thus, the raw material dope 41 prepared is made into 14 to 24 weight% as solid content concentration of a cellulose ester. In addition, you may concentrate the raw material dope 41 by the flash concentration method etc. as needed.

  The raw material dope 41 heated by the heater 40 is sent to the cooler 42. The cooler 42 cools the material dope 41 to the boiling point of the main solvent or less. The cooled raw material dope 41 is sent to the body feed tank 45 of the filtration unit 12 by the pump 43.

  The filtration unit 12 includes a body feed tank 45, a filter aid tank 46, a first filter 47, a second filter 48, a precoat liquid circulation unit 49, a cleaning liquid circulation unit 50, and a casting dope storage tank 51. The raw material dope 41 is filtered using the filter aid 44 to produce a casting dope 52. In addition, valves V1 to V7 are attached to the pipes connecting the tanks 45, 46 and 51 and the filters 47 and 48, and the pipes are switched by opening and closing the valves V1 to V7. Switching of the devices 47 and 48, cleaning processing of the used filters 47 and 48, pre-coating processing, etc. are performed. Thereby, the raw material dope 41 is continuously filtered, and the casting dope 52 is obtained. The valves V1 to V7 installed in the filtration unit 12 are not limited to this embodiment, and may be increased or decreased as necessary. Moreover, the pump which is not illustrated is arrange | positioned suitably at the location as needed.

A filter aid solution 56 is stored in the filter aid tank 46. The filter aid solution 56 is sent to the body feed tank 45 via the pump 57 and the valve 58. The filter aid solution 56 is obtained by dispersing a desired filter aid 44 in a solvent in advance, and is used for the purpose of improving the trapping efficiency of impurities contained in the raw material dope 41. The filter aid 44 is not particularly limited. For example, granular diatomaceous earth (SiO ₂ ) or a derivative derived from a cellulosic compound is preferably used. Moreover, it is preferable that said solvent contains at least 1 or more types of the same solvent as the solvent contained in the raw material dope 41 from a compatible viewpoint with dope. The addition amount of the filter aid 44 to the raw material dope 41 is 0.01 to 10% by weight, preferably 0.05 to 5% by weight, and more preferably 0.1 to 2% by weight. The type, composition, average particle diameter, and bulk density of the filter aid 44 are described in detail in JP-A-2004-107629, and this description can also be applied to the present invention.

  A raw material dope 41 and a filter aid solution 56 are placed in the body feed tank 45. The body feed tank 45 includes a stirring blade 54 that is rotated by a motor 53. By rotating the stirring blade 54, a certain ratio of the filter aid solution 56 can be uniformly dispersed in the raw material dope 41.

  When auxiliary filtration is performed using the first filter 47, the line is switched so that the body feed tank 45 is connected to the first filter 47 by opening and closing the valves V1 to V6. The raw material dope 41 mixed with the filter aid 44 is sent to the first filter 47. In the first filter 47, as shown in FIG. 2, a filter aid 44 is randomly deposited on a filter medium support 60 made of a wire mesh filter to form a deposited layer 62. These filter medium supports 60 and A filter medium 63 is composed of the deposited layer 62.

  In addition, after the cleaning process of the first filter 47, only the filter medium support 60 is present, and in this state, proper auxiliary filtration cannot be performed. Therefore, the deposited layer 62 having a constant thickness is formed on the filter medium support 60. Form. This initial deposited layer 62 is a precoat 62 a, and this precoat 62 a is formed by circulating the precoat liquid 61 (see FIG. 3) through the first filter 47 for a predetermined time by the precoat liquid circulation section 49.

  As shown in FIG. 2, in the first filter 47, only the raw material dope 41 passes through the filter medium 63, and the filter aid 44 is randomly deposited on the filter medium 63 to form a deposited layer 62. When the raw material dope 41 passes through the filter medium 63 composed of the deposited layer 62 and the filter medium support 60, the impurities 64 are adsorbed and collected by the filter aid 44, and also due to the numerous voids formed in the deposited layer 62. A relatively large impurity is captured. Therefore, when the raw material dope 41 passes through the filter medium 63, the impurities 64, undissolved substances, and the like are filtered, and a filtrate with high clarity is obtained. This filtrate is supplied to the film forming unit 13 as a casting dope 52, and a high-quality film 19 free from impurities is manufactured.

  The second filter 48 is configured in the same manner as the first filter 47. Then, the filtration is performed by one filter 47, the washing is performed by the other filter 48, and the pre-coating process is subsequently performed. And continuous filtration is attained by performing washing | cleaning / precoat process and filtration process alternately. Although two filters 47 and 48 are used, the number of filters 47 and 48 is not limited to this, and may be three or more. And it filters with one filter, for example, the 1st filter 47, and when the filtration pressure becomes high, it switches to the other 2nd filter 48, and performs continuous filtration. Then, the first filter 47 that has been switched due to an increase in the filtration pressure is cleaned by removing the filter aid 44 and the filtered material as a slurry (see FIG. 4) by the cleaning liquid circulation unit 50. After the cleaning, the precoat liquid circulating unit 49 circulates the precoat liquid 61 to the first filter 47 to form a precoat 62a as shown in FIG. After the precoat 62a is formed, it enters a standby state for the next switching. In addition to arranging a plurality of filters 47 and 48 in parallel, they may be arranged in series. In this case, the efficiency of collecting impurities by filtration can be increased.

  Next, the precoat process and the cleaning process of the filters 47 and 48 will be described. As shown in FIG. 3, the precoat liquid circulation unit 49 includes a precoat liquid preparation tank 65, a precoat liquid storage tank 66, valves 65a and 67, a pump 68, turbidimeters 69a and 69b, and a controller 72. I have. In addition to a predetermined amount of the raw material dope 41 containing the filter aid 44 being sent from the body feed tank 45 via the pump 45a to the precoat liquid preparation tank 65, a diluting solvent 70 is sent from the solvent tank 71 via the valve 71a. A predetermined amount is sent to form a precoat liquid 61 in which the raw material dope 41 containing the filter aid 44 is diluted to a constant concentration. The precoat liquid 61 is stirred and uniformed by a stirring blade 65c that is rotationally driven by a motor 65b.

The precoat liquid 61 has a solid content concentration of cellulose ester of 0.25 to 7% by weight, and the addition amount of the filter aid 44 to the precoat liquid 61 is 0.01 to 10% by weight. In addition, Preferably the solid content concentration of a cellulose ester is 0.5 to 5 weight%, and the addition amount of the filter aid 44 is 0.25 to 5 weight%. More preferably, the solid content concentration of the cellulose ester is 2 to 4% by weight, and the addition amount of the filter aid 44 is 0.7 to 2% by weight. In addition, when the solid content concentration of the cellulose ester with respect to the precoat liquid 61 is less than 0.25% by weight or when the addition amount of the filter aid 44 is less than 0.01% by weight, the viscosity becomes low, and the filter aid. As a result, the sedimentation property of the precoat is increased and the uniformity of the precoat cannot be ensured. In addition, when the solid content concentration of the cellulose ester exceeds 7% by weight or when the additive of the filter aid exceeds 10% by weight, the viscosity increases, the pressure loss increases, and the flow rate can be increased. Disappear. As the filter aid 44, SiO ₂ having an average particle diameter of 10 to 70 μm is used, and an average particle diameter of 20 to 50 μm is more preferable. The filter medium support is a 350 mesh wire mesh made of SUS.

  As shown in FIG. 3, in the precoating process, first, the precoat liquid 61 is sent from the precoat liquid storage tank 66 to the first filter 47, passes through the filter medium support 60, and then returns to the precoat liquid storage tank 66. Circulated. When passing through the filter medium support 60, as shown in FIG. 2, the filter aid 44 in the precoat liquid 61 gradually deposited on the filter medium support 60, and the deposited layer 62 had a predetermined thickness. In some cases, it is determined that the formation of the precoat 62a is completed, and the precoat process is ended. In FIG. 3, the precoat liquid preparation tank 65 and the precoat liquid storage tank 66 are provided, but the precoat liquid storage tank 66 is omitted, and the precoat liquid preparation tank 65 performs preparation and storage, and the precoat liquid 61 is added. It may be circulated.

The flow rate of the precoat liquid with respect to the filter medium support 60 in the precoat forming step is 3.3 to 80 L / m ² / min, preferably 20 to 60 L / m ² / min. When the flow rate exceeds 80 L / m ² / min, the deposited layer 62 cannot be formed on the filter medium support 60. Further, if the flow rate is less than 3.3 L / m ² / min, the strong precoat 62a cannot be formed.

The terminal sedimentation rate of the filter aid in the precoat forming step is controlled to 10 ^{−4 to 1} cm / sec. This terminal sedimentation rate is preferably 10 ⁻³ to 10 ⁻² cm / sec. In order to obtain a terminal sedimentation velocity within this range, the liquid viscosity and the auxiliary particle size are changed. When the terminal sedimentation rate is less than 10 ⁻⁴ cm / sec, the pressure loss is large and the flow rate cannot flow. When it exceeds 1 cm / sec, a uniform precoat cannot be formed.

  The concentration of the filter aid in the precoat solution is in the range of 0.01 to 10.0% by weight, preferably 0.1 to 2.0% by weight. If the filter aid concentration exceeds 6.0% by weight, interference sedimentation occurs and a uniform precoat cannot be formed. Further, if the filter aid concentration is less than 0.1% by weight, it takes a long time to form the precoat and the efficiency is lowered.

  Opening the filter 47 and checking the formation thickness of the precoat 62a is not preferable because it requires labor, and there is a possibility that the surface of the precoat 62a may be crushed due to contact with air. Therefore, a first turbidity meter 69 a is provided in a connecting pipe 74 between the outlet side of the precoat liquid storage tank 66 and the inlet side of the filter 47, and a second pipe 73 is provided between the precoat liquid storage tank 66 and the filter 47. A turbidimeter 69b is provided, and the controller 72 determines whether or not the formation of the precoat 62a is complete based on the outputs of the turbidimeters 69a and 69b. That is, when the precoat 62a is formed, the filtration performance is stabilized, and most of the filter aid 44 in the precoat liquid is captured by the filter medium 63, so that the filter aid in the precoat liquid 61 from the outlet of the filter 47 is obtained. Agent 44 is drastically reduced. The decrease of the filter aid 44 is monitored by the controller 72 via the turbidimeters 69a and 69b, and when the output of the turbidimeters 69a and 69b is equal to or lower than a predetermined value, it is determined that the formation of the precoat 62a is completed. To do. After determining the completion of the precoat formation, the process proceeds to the next precoat liquid extraction step. Although the first and second turbidimeters 69a and 69b are provided, the completion of the formation of the precoat 62a may be detected only by the first turbidimeter 69a. However, by using the second turbidity meter 69b as well, it is possible to reliably detect the completion of the formation of the precoat 62a based on the turbidity on the inlet side and outlet side of the filtrate of the filter 47.

  The turbidimeters 69a and 69b are only required to be able to detect the amount of the filter aid 44 of the precoat liquid 61, and the detection method is not limited. For example, an absorptiometric method or a laser scattered light method that detects turbidity is used.

  The total amount of filter aid in the precoat solution in the precoat formation step is determined in advance based on the relationship between the precoat and the amount of filter aid in the precoat. That is, the precoat having a certain strength and the amount of the filter aid at that time are obtained by experiments and the like, and when the precoat is formed using a certain amount of the filter aid, a certain strength is obtained. Shall. For the sake of safety, it is preferable that the amount of circulating filter aid is preliminarily determined by experiments or the like, for example, several% to more than 10%. Therefore, when the turbidimeter output becomes a certain value or less and a clarified liquid can be obtained, it is determined that most of the filter aid has been used for precoat formation, and the completion of formation of a precoat having a predetermined strength can be known. it can.

  FIG. 6 is a graph showing the relationship between the total amount of filter aid in the precoat liquid and the thickness and strength of the precoat formed at this time, and the thickness of the precoat increases as the total amount of filter aid increases. A predetermined strength can be obtained.

  After determining the completion of the formation of the precoat 62a, the precoat liquid 61 in the filter 47 is extracted by its own weight. As described above, due to the drainage due to its own weight, it becomes a mild condition in which the drainage rate is lowered as compared with the method of pressurizing and pushing using dry air or dry nitrogen, and a skin layer is formed on the surface of the deposited layer 62. Disappear. Further, at the time of extraction by its own weight, the valve V7 of the communication pipe 75 that communicates the precoat liquid storage tank 66 and the filter 47 is opened and communicated, so that the solvent saturated gas 76 is removed from the precoat liquid at the time of liquid removal by its own weight. The filter 47 can be replenished from the storage tank 66. By substituting the inside of the filter 47 with the solvent saturated gas 76, there is no formation of a burrs of the deposited layer 62 due to solvent drying or a skin layer in which the burrs spread over a wide range, and the next filtration. Processing can be performed stably.

  Next, the cleaning process will be described. When any one of the filters 47 and 48 is used and the deposition layer 62 becomes a certain thickness or more and the filtration pressure increases, the filters 47 and 48 are switched. For example, when the filtration is performed by the first filter 47 and the filtration pressure of the first filter 47 increases and the switching time comes, the valves V1 to V6 are switched and the second filter 47 is switched from the first filter 47 to the second filter. The flow path is switched so that the raw material dope 41 flows to the vessel 48, and continuous filtration is performed. After switching to the second filter 48, the first filter 47 is drained and washed, and then the above-described precoat treatment is performed. Note that this switching is preferably performed by gradually increasing or decreasing the flow rate of each other.

  As shown in FIG. 4, the cleaning liquid circulation unit 50 includes a cleaning liquid tank 80, a cleaning tank 81, a recovery tank 82, a supply pipe 83, a recovery pipe 84, pumps 78 a, 79 a, 85, 92 a, and a heater 86. And a separator 87 and a strainer drying section (drying air circulation section) 88 (see FIG. 5). The supply pipe 83 is connected to the solvent outlet of the cleaning tank 81 and the dope outlet of the first filter 47, and the supply pipe 83 is provided with a pump 85 and a heater 86. The recovery pipe 84 is connected to the solvent inlet of the cleaning tank 81 and the dope inlet of the first filter 47. A cleaning liquid 89 is stored in the cleaning liquid tank 80, and a predetermined amount of the cleaning liquid 89 is sent into the cleaning tank 81 by opening / closing control of the valve 80a. The cleaning liquid 89 is not particularly limited as long as it can clean the filter medium 63 of the filters 47 and 48, but the solvent is at least one of the solvents constituting the dope solvent. The total solvent constituting the dope solvent is more preferable.

  A multi-tube heat exchanger is used as the heater 86, and the cleaning liquid 89 is heated by the heater 86. The heating temperature is set to a temperature equal to or higher than a value 20 ° C. lower than the boiling point of the cleaning liquid 89 at normal pressure under the condition that the cleaning liquid 89 does not boil. By heating the cleaning liquid 89 and supplying it to the filter 47 in this way, the cleaning effect of the filter 47 can be improved.

  The cleaning liquid 89 sent to the filter 47 through the supply pipe 83 passes through the filter medium 63 in the direction opposite to that of the raw material dope 41 during the filtration process, and is returned to the cleaning tank 81 through the recovery pipe 84. As a result, the cleaning liquid 89 is circulated and supplied to the filter 47, and the deposited layer 62 on the filter medium support 60 is peeled off from the filter medium support 60. The deposited layer (cake) 62 after being peeled is dispersed in the cleaning liquid 89 to become a slurry 90, discharged from the filter 47 and returned to the cleaning tank 81. The turbidity of the slurry 90 is measured using a turbidimeter 84a. When the turbidity of the slurry 90 reaches a target value, a part (or all) of the cleaning tank 81 is discharged from the discharge pipe 78 and the pump 78a. To the recovery tank 82. When the discharge of the slurry 90 to the recovery tank 82 is completed, a new cleaning liquid 89 is replenished from the cleaning liquid tank 80 to the cleaning tank 81. Then, when the predetermined cleaning time has been reached and the turbidity of the slurry 90 has become below a certain value, the circulation of the cleaning liquid 89 is stopped. After this stop, the cleaning liquid 89 is extracted from the first filter 47. This extraction is performed reliably and quickly by sending the solvent saturated gas 76, nitrogen gas, or the like of the cleaning liquid into the first filter 47.

  The slurry 90 sent to the recovery tank 82 is sent to a separator 87 via a pipe 91, and is separated into a residue 90a and a solution 90b by the separator 87. A circulation pipe 79 between the recovery tank 82 and the washing tank 81 is provided with a pump 79a and a viscometer 79b.

  The viscometer 79b constantly measures the viscosity of the recovered slurry 90. Then, the cleaning liquid 89 is poured into the cleaning tank 81 so that the viscosity of the slurry 90 is always within a certain range based on the viscosity measured by the viscometer 79b. Thereby, for example, after the viscosity of the slurry 90 is set to 200 mPa · s or less, the slurry 90 can be sent to the separator 87. Here, when the viscosity of the slurry 90 is 200 mPa · s or less, separation and recovery can be performed while securing a flow rate. However, since the slurry 90 having a viscosity exceeding 200 mPa · s has a high viscosity, workability by the separator 87 is deteriorated.

  The separator 87 has a bottomed cylindrical separator body 87a, a lid 87b attached to the separator body 87a via a hinge portion 87c so as to be opened and closed, and an air vent pipe 87d attached to the lid 87b. Further, a strainer storage portion 87e is formed in the separator main body 87a, and a strainer 95 is stored vertically in the strainer storage portion 87e. By placing the strainer 95 vertically, the flow of the slurry 90 in the separator 87 is vertically downward, and an efficient separation operation can be performed. The separator main body 87a is provided with a slurry supply port 87f and a dry air discharge port 87g at the top thereof.

  As shown in FIG. 7, the strainer 95 is made of a cylindrical metal mesh with a bottom, and is attached to one end of the cylindrical first metal mesh 95a and the first metal mesh 95a, and the second disk-shaped second metal constituting the bottom. It is comprised from the metal mesh 95b and the attachment flange 95c attached to the other end of the 1st metal mesh 95a. An inner diameter D of the first wire mesh 95a is smaller than a length L of the first wire mesh 95a. Thus, by making the inner diameter D smaller than the length L, the cake thickness can be reduced, the resistance of the liquid at the time of recovery is small, and the amount of processing liquid can be increased. Moreover, the drying load after the cake recovery can be reduced.

  Further, the mesh of the second wire mesh 95b constituting the bottom is larger than the mesh of the first wire mesh 95a constituting the cylinder. The meshes of the first and second wire meshes 95a and 95b are 50 or more and 500 or less, respectively, and the ratio between the mesh of the second wire mesh 95b and the mesh of the first wire mesh 95a (second wire mesh / first wire mesh). Is 1.5 or more and 10 or less. Preferably, each mesh is 60 or more and 480 or less, and the mesh ratio is 2 or more and 8 or less.

  The first wire mesh 95a and the second wire mesh 95b have a tatami woven structure, and are preferably a flat woven structure or a twill woven structure. Further, it is preferable to reinforce the strainer 95 with punching metal or the like as necessary. In this case, the opening ratio of the reinforcing material such as punching metal is preferably 30% or more.

  In the illustrated example, one strainer 95 is arranged for each separator. However, a plurality of strainers 95 may be arranged for each separator. In this case, a plurality of strainers are arranged. By having it, the amount of the separation liquid can be increased, and it becomes possible to efficiently separate the filter aid and the filtrate.

  Also in this separator 87, the residue 90a acts as a filter aid, and the residue 90a and the solution 90b can be reliably separated. It should be noted that immediately after the separation, there is no precoat formed by the residue 90a, and the separation cannot be performed reliably. For this reason, the slurry 90 is circulated between the separator 87 and the recovery tank 82 using the circulation pipes 92 and 93 at the start of separation so that a precoat having a predetermined thickness is formed. At the start of separation, the air in the separator 87 is extracted from the air vent pipe 87d. By performing this air venting, the slurry 90 is reliably filled in the separator 87, and reliable filtration can be performed.

The flow rate of the slurry 90 to the separator 87 is 50 to 1500 L / min per unit filtration area (1 m ² ). When the flow rate is less than 50 L, the treatment time becomes long, which is not preferable. On the other hand, when the flow rate exceeds 1500 L, the apparatus becomes large and the equipment cost increases, which is not preferable.

  The circulation pipes 92 and 93 have a pump 92a and valves 92b and 93b. When the precoat is formed in the same manner as in FIG. 2 due to the circulation of the slurry 90, the separation effect is obtained. Therefore, the valve 93b is switched to change the circulation treatment to the separation treatment, and the solution 90b after the separation is recovered. Send to tank 94. The recovered solution 90b can be reused for dope preparation and cleaning.

  The separator 87 is provided with a pressure gauge 96 to detect the filtration pressure in the separator 87. When the filtration pressure value reaches a predetermined value, it is determined that the thickness of the separation filter medium has reached the use limit, and the separation process ends. The final deposition thickness of the residue (filter aid) 90a in the separator 87 is preferably 0.5 to 50 cm. If this final deposition thickness is less than 0.5 cm, the filtration area of the separator 87 is required, which disadvantageously increases the size of the apparatus. On the other hand, if the final deposition thickness exceeds 50 cm, the pressure loss for separation increases, and flow restriction and pressure resistance restriction occur, which is not preferable.

  After the separation process, a drying air 97 is sent to the residue 90a in the strainer 95 by the strainer drying unit 88 shown in FIG.

  The strainer drying unit 88 includes a drying air circulation pipe 120, valves 121 and 122, a solvent gas concentration sensor 123, a solvent gas recovery device 124, a drying air circulation device 125, and a drying unit controller 126. During the drying process, the valves 93b, 121, 122 are opened and closed, the slurry circulation pipes 92, 93 are closed, and the drying air circulation pipe 120 is opened. Then, the drying air 97 is sent into the separator 87 by the drying air circulation device 125. By this dry air 97, the solution 90b is volatilized from the residue 90a. In addition to the circulation of the drying air 97, the drying method may be performed by a direct heating method using a burner, a heater, or a jacket method, or may be used in combination. The drying air 97 may use other gas besides air. Further, the residue 90 a may be dried by sending steam to the separator 87 instead of the drying air 97.

  The drying air 97 used for drying is in a state containing a solvent gas. For this reason, the solvent 21 is recovered and removed from the drying air 97 by the solvent gas recovery device 124. Thereafter, the drying air 97 from which the solvent 21 has been removed is heated to a predetermined temperature by the heating unit in the drying air circulation device 125 and then supplied again into the separator 87 as the drying air 97.

  As the drying proceeds, the solvent gas concentration in the drying air circulation pipe 120 decreases. This is detected by the drying unit controller 126 based on the output value of the solvent gas concentration sensor 123, and when the concentration sensor 123 reaches a certain value, it is determined that the drying is finished. If it determines with completion | finish of drying, the drying part controller 126 will lower | hang the drying wind preset temperature of the strainer drying part 88 as needed, and will send this to the separator 87 as cooling air, and the strainer 95 and residue 90a in the separator 87 will be sent. Cool down. After they have cooled to near room temperature, alarm 126a informs the operator that the drying is complete. After the drying is completed, the operator opens the lid 87b (shown by a two-dot chain line in FIG. 5) of the separator 87 and takes out the residue 90a from the strainer 95. The residue 90a is taken out by replacing the strainer 95 with an empty one, and the residue 90a may be directly sucked from the strainer 95 in the separator main body 87a by a vacuum type suction device (not shown).

  In addition to opening the separator 87 and taking out the residue 90a after drying, it may be performed fully automatically. In this case, a suction nozzle that can be raised and lowered is arranged on the lid 87b of the separator main body 87a, and descends after the residue 90a is dried, so that the residue in the strainer 95 is automatically sucked. The residue 90a after drying can be reused as a filter aid. In addition, when reusing, it may be used as it is or may be mixed with a new filter aid 44 at an appropriate ratio.

  The slurry 90 is fed from the recovery tank 82 to the separator 87 by a pump 79a, and a pressure feeding method using a carrier gas such as nitrogen gas by a pressurizing device (not shown) or a method using a dead weight due to a drop is used. May be. In order to ensure a smooth flow of the slurry 90, the concentration of the slurry 90 is preferably 0.15 wt% or more and 25 wt% or less. The concentration of the slurry 90 is the ratio of the residue 90a contained in the slurry 90. In the case of the slurry 90 in which this concentration exceeds 25% by weight, it is difficult to feed the slurry 90, and it is particularly difficult to feed the slurry 90 using its own weight. On the other hand, when the slurry concentration is less than 0.15% by weight, the collection time of the residue 90a becomes long, and the collection efficiency is remarkably lowered.

  As described above, the pre-coat operation is performed on the filter 47 after the cleaning process by the pre-coat liquid circulation unit 49 to form the pre-coat 62a on the filter medium support 60 as shown in FIG. Although the cleaning process and the precoat process have been described only for the first filter 47, the same cleaning process and the precoat process are also performed for the second filter 48.

  The cleaning liquid circulation unit 50 uses the cleaning tank 81, the recovery tank 82, and the separator 87. However, the recovery tank 82 is omitted, and a separator 87 is provided instead of the recovery tank 82. Recovery and separation may be performed.

  As shown in FIG. 8, the film forming unit 13 includes a casting chamber 100, a transfer portion 101, a tenter 102, a drying chamber 103, and a winder 104, and the film 106 is formed using the casting dope 52. Made. In the casting chamber 100, a casting die 107 in which a discharge port for the casting dope 52 is formed, a casting drum 108 acting as a support, and a peeling roller 109 are arranged.

  The casting dope 52 from which impurities have been removed is cast on a casting drum 108 that is rotating endlessly through a casting die 107, whereby a casting film 111 is formed. The surface temperature of the casting drum 108 is preferably substantially constant within a range of −10 ° C. to 10 ° C. If the dope is cast on such a casting drum 108, the dope is quickly cooled, so that a gel-like casting film 111 is formed within a short time. As the casting drum 108 rotates, gelation of the casting film 111 proceeds, and the casting film 111 having self-supporting properties is peeled off from the casting drum 108 as a wet film 113 while being supported by the peeling roller 109.

  In the crossover part 101, the wet film 113 is supported by a large number of rollers, and drying proceeds while being transported. In the tenter 102, both end portions of the wet film 113 are held by holding means such as pins, and then dried while being transported to form a film 106. Thereafter, the film 106 is wound up into a roll shape by the winding roller 105.

  A filter 114 is installed on the upstream side of the casting die 107, and the dope before being used for casting is filtered. This further removes impurities in the casting dope. In this embodiment, an apparatus including a metal filter is used, but the filtration method is not particularly limited, and filter paper is also preferably used. Here, the pores of the filter preferably have an average pore diameter of 100 μm or less in order to remove even fine impurities. If the average pore size is too small, the time required for filtration becomes longer, so the filtration efficiency is lowered. On the other hand, if the average pore diameter is too large, it is difficult to capture fine impurities in the casting dope 52. A filter may be appropriately selected in consideration of productivity and the like.

  From casting die, decompression chamber, support structure, co-casting, peeling method, stretching, drying conditions for each step, handling method, curling, winding method after flatness correction, solvent recovery method, film recovery method Up to this point, the details are described in paragraphs [0617] to [0889] of JP-A-2005-104148, and these descriptions can also be applied to the present invention.

  The film obtained by the present invention has high transparency and retardation value and low humidity dependency. Therefore, although it can use suitably as a retardation film of a polarizing plate especially, it can utilize also as a protective film for protecting the surface of a polarizing plate. Regarding specific uses of the cellulose ester film of the present invention, in Japanese Patent Application Laid-Open No. 2005-104148, for example, from [1088] paragraph to [1265] paragraph, as a liquid crystal display device, TN type, STN type, VA type, The OCB type, the reflection type, and other examples are described in detail, and this description can also be applied to the present invention.

  Examples of the present invention and comparative examples will be shown below to specifically describe the present invention. However, the present invention is not limited to these examples and comparative examples.

  A material dope 41 was prepared by mixing the following various dope materials. In this example, as the solvent 21, a mixed solvent in which dichloromethane, methanol, and 1-butanol were mixed was used.

[Dope raw material]
Cellulose triacetate 100 parts by weight Dichloromethane 320 parts by weight Methanol 83 parts by weight 1-butanol 3 parts by weight Plasticizer A 7.6 parts by weight Plasticizer B 3.8 parts by weight UV agent a 0.7 part by weight UV agent b 0.3 part by weight Part citrate ester mixture 0.006 parts by weight fine particles 0.05 parts by weight

  The cellulose triacetate has a substitution degree of 2.84, a viscosity average polymerization degree of 306, a water content of 0.2% by weight, a viscosity of 6% by weight in a dichloromethane solution of 315 mPa · s, an average particle diameter of 1.5 mm, and a standard Powder with a deviation of 0.5 mm, plasticizer A is triphenyl phosphate, plasticizer B is diphenyl phosphate, UV agent a is 2 (2'-hydroxy-3 ', 5'-di- -Tert-butylphenyl) benzotriazole, UV agent b is 2 (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) -5-chlorobenzotriazole, and the citrate compound is It is a mixture of citric acid, monoethyl ester, diethyl ester and triethyl ester. The fine particles have an average particle diameter of 15 nm and a Mohs hardness of about 7. It is of silicon. Moreover, at the time of preparation of the raw material dope 41, a retardation control agent (N-N-di-m-toluyl-N-P-methoxyphenyl-1,3,5-triazine-2,4,6-triamine) was used as a film. It added so that it might become 4.0 weight% with respect to the total weight at the time.

  Next, in the solution casting apparatus 10 shown in FIG. 1, the raw material dope 41 was filtered using the filter 47 in the filtration unit 12. At this time, diatomaceous earth having an average particle diameter of 35 μm was used as a filter aid, and a precoat formation treatment was performed before the raw material dope 41 was filtered in advance, and after the precoat was formed, the precoat solution was extracted.

In the precoat solution, diatomaceous earth having an average particle size of 35 μm as a filter aid, a dope solution containing 20% by weight of cellulose triacetate, and a solvent for dilution are placed in the precoat solution preparation tank 65, and the precoat solution has a filter aid concentration of the precoat solution. This was prepared so that the cellulose concentration was 3.0 wt% and the cellulose concentration was 3.5 wt%, and stored in the precoat liquid storage tank 66 after the preparation. This precoat liquid was circulated between the filter 47 and the precoat liquid storage tank 66 at a flow rate of 20 L (liter) / min / m ² to form a precoat on the filter medium support in the first filter. As the filter medium support 60, a 350 mesh wire mesh made of SUS was used.

And the filter aid density | concentration was detected from the turbidimeter output using the photoelectric sensor (F71RAN) by Takenaka Electronics Co., Ltd. as the 1st and 2nd turbidimeters 69a and 69b. Since the second turbidity meter 69b is disposed in the outlet side pipe 73 of the filter 47, it became 0% by weight 3 minutes after the start of circulation of the precoat liquid. Further, the first turbidity meter 69a arranged in the inlet side piping 74 of the filter 47 gradually decreases from the initial value of 2.0% by weight when the circulation of the precoat liquid is started, and becomes 0% by weight after 30 minutes. became. At this point, it was determined that precoat formation was complete. The total amount of filter aid in the circulating precoat liquid is determined from the total amount of filter aid when a predetermined strength is obtained. In this embodiment, the amount of filter aid is 0.75 kg / m ² (filtration area 1 m ² Per filter aid). The amount of the filter aid is an amount that forms an average thickness of 3 mm with respect to the total filtration area of the filter medium support.

Moreover, the terminal sedimentation rate of the filter aid at the time of precoat formation was 10 ^<-3 > cm / sec. The final sedimentation velocity of the filter aid was measured by sedimentation distance measurement and calculation using the Stokes equation. The time required for forming the precoat 62a was 1 hour.

After the formation of the precoat 62a is completed, the precoat liquid 61 is extracted from the first filter 47 by its own weight. At this time, the valve V7 of the communication pipe 75 is opened, the precoat liquid storage tank 66 and the first filter 47 are communicated, and the solvent corresponding to the amount of the precoat liquid 61 extracted in conjunction with the extraction of the precoat liquid 61 due to its own weight. A saturated gas 76 is replenished in the first filter 47. Thus, unlike the conventional case where the formed precoat 62a is drained by applying pressure with dry air or dry nitrogen, a skin layer is not formed on the surface of the precoat 62a. Further, by adjusting the opening degree of the valve V7 of the communication pipe 75, the extraction flow rate of the precoat liquid 61 can be set to 1 × 10 ⁻³ m / s or less with respect to the surface of the precoat layer. By setting the extraction speed of the precoat liquid 61 to 1 × 10 ⁻³ m / s or less, a precoat 62a having no collapse was obtained. At this time, when the filter 47 was opened and the inside was confirmed, it was confirmed that a precoat 62a having a uniform predetermined thickness was obtained. When the precoat formation treatment was performed again under the same conditions, the same results were obtained.

  The raw material dope 41 was filtered using the precoat 62a formed as described above, and when the filtration pressure reached a predetermined value, it was determined that filtration was impossible, and the filtration unit was switched. Thereafter, the washing liquid was circulated through a filter having a used filter aid and recovered by a separator 87. The strainer 95 set in the separator 87 is a bottomed cylindrical wire mesh having an inner diameter of 400 mm and a length of 800 mm.

The strainer 95 has a filtration area of 1 m ² , and the first wire net 95a is a 100 mesh flat woven weave. The second wire mesh 95b is a 300-mesh flat woven one. The viscosity of the slurry 90 was 10 mPa · s, and the concentration of the slurry 90 was 3%. The slurry 90 was supplied from the upper part of the strainer 95, the filtrate was taken out from the lower part, and the filter aid was collected in the strainer 95.

  In the initial stage of the recovery operation, the separator 87 was vented using the air vent pipe 87d, and the air vent time was 1.5 minutes. The slurry 90 was pumped to the separator 87 using 0.1 MPa nitrogen gas, and the flow rate of the slurry 90 was 160 L / min. The thickness of the cake residue in the strainer 95 after the recovery was 10 cm at the peripheral surface portion and 11 cm at the bottom surface portion, which was a substantially uniform thickness. In addition, since the residue 90a slightly leaked from the strainer 95 and mixed into the solution 90b at the initial stage of the recovery operation, it was returned to the liquid supply source tank after the initial circulation and the clarification was confirmed.

  After separating the residue 90a and the solution 90b by the separator 87, the solution 90b in the strainer 95 is driven out by air, and 40 ° C. drying air is circulated in the separator 87 by the strainer drying unit 88 as a drying air circulation unit. I let you. 48 hours after circulating and supplying the dry air, the solvent content in the residue 90a was 0.2% or less. In addition, a highly clear solution 90b could be obtained.

[Comparative Example 1]
The conditions were the same as in Example 1 except that the viscosity of the slurry 90 was 210 mPa · s. The flow rate of the slurry 90 was 10 L / min, and the separation treatment time between the residue 90a and the solution 90b became longer.

[Comparative Example 2]
The conditions were the same as in Example 1 except that the concentration of the slurry 90 was 27%. Due to the high slurry concentration, it was not possible to pump the slurry to the separator 87 with nitrogen gas.

[Comparative Example 3]
The conditions were the same as in Example 1 except that the slurry flow to the strainer 95 was directed from the vertically downward direction to the upward direction. The slurry 90 settled during the feeding, and the residue 90a could not be recovered in the strainer 95.

[Comparative Example 4]
The conditions were the same as in Example 1 except that the first wire mesh 95a constituting the strainer 95 was 40 mesh and the second wire mesh 95b was 60 mesh. Leakage of the residue 90a into the filtered solution 90b was so severe that the clarity of the filtered solution 90b could not be ensured.

[Comparative Example 5]
The conditions were the same as in Example 1 except that the first wire mesh 95a constituting the strainer 95 was 500 mesh and the second wire mesh 95b was 700 mesh. Filtration resistance was strong, and the flow rate was 10 L / min, which had practical problems.

[Comparative Example 6]
A strainer 95 (diameter: 1100 mm × length: 200 mm) having a filtration area of 1.6 m ² was used, and pressure feeding was performed with 0.1 MPa of nitrogen gas. The thickness after residue collection was 100 cm. The other conditions were the same as in Example 1. The flow rate was 8 L / min, and there was a problem in practical use.

[Comparative Example 7]
The conditions were the same as in Example 1 except that the slurry 90 was not initially circulated. The residue 90a was mixed with the filtered solution 90b, and further filtration was required for reuse.

[Comparative Example 8]
The conditions were the same as in Example 1 except that air was not removed during the initial circulation of the slurry 90. The slurry 90 was not filled in the upper half of the strainer 95, a liquid interface was formed, and it was fluctuated. Therefore, the residue 90a was constantly mixed with the filtered solution 90b, and the clarity of the filtered solution 90b could not be ensured.

[Comparative Example 9]
The slurry 90 was pumped to the separator 87 using 0.01 MPa of nitrogen gas, and the air venting time was 7 minutes. During the air venting time, the filter aid settles and deposits on the lower part of the strainer 95. The thickness of the residual layer in the lower part becomes as thick as 60cm and the thickness unevenness occurs. It took a week for the time.

[Comparative Example 10]
The conditions were the same as in Example 1 except that the drying air temperature was 4 ° C. It took 1.5 weeks for the drying time.

[Comparative Example 11]
The conditions were the same as in Example 1 except that the drying air temperature was 145 ° C. Although the drying time was 0.5 days, corrosion occurred in the strainer 95.

[Comparative Example 12]
The conditions were the same as in Example 1 except that plain weave was used for the first and second wire meshes. There were many leaks of the residue 90a to the filtration solution 90b, and the clarity of the filtration solution 90b could not be ensured.

[Comparative Example 13]
The conditions were the same as in Example 1 except that a cylindrical strainer with a bottom having an inner diameter of 1200 mm and a length of 800 mm was used and the slurry 90 was pumped to the separator 87 using 0.1 MPa of nitrogen gas. The thickness of the residue 90a after collection was 0.3 cm, and the clarity of the filtered solution 90b could not be ensured.

[Comparative Example 14]
The conditions were the same as in Example 1 except that the first wire mesh 95a constituting the strainer 95 was 100 mesh and the second wire mesh 95b was 130 mesh. The peripheral portion thickness of the residue 90a after recovery was 9.5 cm, and the bottom portion thickness was 15 cm. In the drying process, it took 46 hours for the solvent concentration in the residue 90a to be 0.2 wt% or less.

[Comparative Example 15]
The conditions were the same as in Example 1 except that the first wire mesh 95a constituting the strainer 95 was 100 mesh and the second wire mesh 95b was 1200 mesh. The strength of the second wire mesh 95b was weak and the strainer 95 was damaged, and the clarity of the filtered solution 90b could not be ensured.

[Comparative Example 16]
The conditions were the same as in Example 1 except that the concentration of the slurry 90 was 0.14%. It took 20 times or more time to collect the residue 90a with the strainer 95 as compared with Example 1.

[Example 2]
The conditions were the same as in Example 1 except that liquid was fed from the tank 30 m above to the strainer 95 by its own weight. The flow rate of the filtrate was 50 L / min, and a clear liquid could be secured.

[Example 3]
The conditions were the same as in Example 1 except that the slurry 90 was sent to the strainer 95 by a pump without being pumped by gas. Results almost the same as those of Example 1 were obtained.

[Example 4]
During drying, the same conditions as in Example 1 were used except that the strainer 95 was directly heated with steam. The drying period was 36 hours.

Based on the above results, the strainer 95 has a filtration area of 1 m ² , the first wire mesh 95a is a 100 mesh plain woven, the second wire mesh 95b is a 300 mesh flat woven, and the viscosity of the slurry 90 is 10 mPa · s, the concentration of the slurry 90 is 3%, the slurry 90 is supplied from the upper part of the strainer 95, the filtered solution 90b is taken out from the lower part, and the slurry 90 is circulated between the separator 87 and the recovery tank 82 at the beginning of the recovery operation. In addition, the separator 87 is evacuated, and the slurry liquid is supplied by either pressure feeding with 0.1 MPa nitrogen gas, pressure feeding with a pump, or pressure feeding with its own weight due to a drop of 30 m. It can be recovered efficiently and the clarity of the filtered solution 90b can be ensured. Further, the thickness of the residue 90a in the recovered strainer 95 can be 10 cm at the peripheral surface portion and 11 cm at the bottom surface portion, and the thickness can be made substantially uniform. By performing hot air drying and direct drying on the residue 90a having a substantially uniform thickness, the solvent in the residue 90a can be dried in a drying time of about one day, and the filter aid is efficiently recovered. can do.

It is the schematic which shows an example of the solution casting apparatus which implemented this invention. It is sectional drawing which expands and shows the filter medium and precoat in a filter. It is the schematic which shows a precoat liquid circulation part. It is the schematic which shows a washing | cleaning-liquid circulation part. It is the schematic which shows a strainer drying part. It is a diagram which shows an example of the relationship between the filter aid total amount in the circulating precoat liquid, and the intensity | strength of the precoat at this time. It is a perspective view which shows a strainer. It is the schematic which shows a film forming unit.

Explanation of symbols

41 Raw material dope 44 Filter aid 47 First filter 48 Second filter 49 Precoat liquid circulation part 50 Washing liquid circulation part 60 Filter medium support 61 Precoat liquid 62 Deposited layer 62a Precoat 63 Filter medium 64 Impurity 87 Separator 87e Strainer storage part 88 Strainer drying section 90 Slurry 90a Residue 90b Solution 95 Strainer 95a First wire mesh 95b Second wire mesh 120 Dry air circulation piping

Claims (18)

In a method for recovering a filter aid, the polymer solution is filtered using a filter having a filter medium formed with a precoat on which a filter aid is deposited on a filter medium support, and then the filter aid is recovered from the filter. ,
A filter cleaning step of supplying a cleaning liquid to the filter, recovering the filter aid and the cleaning liquid as a slurry from the filter, and cleaning the filter;
A separation step of circulating the slurry collected in the filter washing step to a washing liquid path having a separator and separating the slurry into the filter aid and the washing liquid by the separator;
A filter aid drying step of drying the filter aid captured in the separation step in the separator;
The separator is composed of a separator body and a filter medium housed in the separator body,
The filter medium is a bottomed cylindrical wire mesh strainer having a bottom at one end of a cylinder, wherein the mesh of the second wire mesh constituting the bottom is larger than the mesh of the first wire mesh constituting the cylinder. To recover the filter aid.   The first wire mesh and the second wire mesh are in the range of 50 to 500, and the ratio of the second wire mesh and the first wire mesh (second wire mesh / first wire mesh) is 1.5. The method for recovering a filter aid according to claim 1, which is 10 or more.   The method of claim 2, wherein the first wire mesh and the second wire mesh have a tatami weave structure.   The method for recovering a filter aid according to any one of claims 1 to 3, wherein the metal strainer has an inner diameter of the cylinder smaller than a height of the cylinder.   The method for recovering a filter aid according to any one of claims 1 to 4, wherein the slurry has a viscosity of 200 mPas or less and a concentration of 0.15 to 25% by weight.   The method of recovering a filter aid according to any one of claims 1 to 5, wherein the slurry flow in the separator is vertically downward.   The method for recovering a filter aid according to any one of claims 1 to 6, wherein a final deposition thickness of the filter aid in the separator is 0.5 to 50 cm.   The method for recovering a filter aid according to any one of claims 1 to 7, wherein the filter aid captured on the filter medium is dried by a heater provided in the separator body.   The method for recovering a filter aid according to any one of claims 1 to 8, wherein the filter aid trapped on the filter medium is dried by a dry gas circulation section that sends a dry gas to the separator main body. . The recovery of the filter aid according to any one of claims 1 to 9, wherein SiO ₂ having an average particle size of 20 to 50 µm is used as the filter aid, and the polymer is cellulose acylate. Method. In a filter aid recovery apparatus for recovering the filter aid from the filter after filtering the polymer solution using a filter having a filter medium formed with a precoat having a filter aid deposited on the filter medium support. ,
Supplying a cleaning liquid to the filter, collecting the filter aid and the cleaning liquid as a slurry from the filter, and a filter cleaning unit for cleaning the filter;
A separator that circulates the slurry collected in the filter cleaning unit to a cleaning liquid path having a separator and separates the slurry into the filter aid and the cleaning liquid by the separator;
A filter aid drying unit for drying the filter aid captured by the separation unit in the separator;
The separator is composed of a separator main body, and a bottomed cylindrical wire mesh strainer housed in the separator main body and having a bottom at one end of the cylinder, and the mesh of the first wire mesh constituting the cylinder. Compared with the filter aid recovery device, the mesh of the second wire mesh constituting the bottom is larger than that of the filter aid.   The first wire mesh and the second wire mesh are in the range of 50 to 500, and the ratio of the second wire mesh and the first wire mesh (second wire mesh / first wire mesh) is 1.5. 12. The filter aid recovery device according to claim 11, wherein the recovery amount is 10 or less.   13. The filter aid recovery apparatus according to claim 12, wherein the first wire mesh and the second wire mesh have a tatami weave structure.   The filter aid recovery device according to any one of claims 11 to 13, wherein the metal strainer has an inner diameter of the cylinder smaller than a height of the cylinder.   15. The filter aid recovery apparatus according to claim 11, wherein the slurry flow in the separator is vertically downward.   16. The filter aid recovery apparatus according to claim 11, wherein a final deposition thickness of the filter aid in the separator is 0.5 to 50 cm.   17. The filter aid recovery apparatus according to claim 11, further comprising a heater provided in the separator main body for drying the filter aid captured on the filter medium.   The filter aid according to any one of claims 11 to 17, further comprising a dry gas circulation unit that sends a dry gas to the separator main body in order to dry the filter aid captured on the filter medium. Recovery equipment.

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