Method for producing solution-processed film and film

Abstract

To provide a method for producing a solution-processed film which has few crater-like quality defects and can provide stable processability when used, for example, as a gas barrier protective film.SOLUTION: A method for producing a solution-processed film by forming a polymer solution into a sheet includes a step of filling a filter, which is filled with a solvent in advance, with the polymer solution from an inlet side of the filter. A viscosity of the polymer solution filled from the inlet side of the filter in the above step is 2000 poise or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a solution-cast film that has few crater-shaped quality defects and can obtain stable processability, for example, when used for a gas barrier protective film.

Background Art

[0002] Dry methods, wet methods, dry-wet methods, etc. are known as solution-casting methods. Generally, in solution casting, a polymer solution is cast onto a support such as a drum, endless belt, or carrier film from a slit die to form a sheet, and a dryer that dries the solvent from the obtained sheet-like film, and a solvent extraction treatment device that immerses the sheet produced by this dryer in a liquid to extract the solvent contained in the sheet, and a transverse stretching machine that expands the sheet from which the solvent has been completely removed or the solvent concentration has been reduced by this solvent extraction treatment device in the width direction, and a winding machine that winds the film obtained by this transverse stretching machine into a roll. A film is produced by a film-forming machine equipped with these components. In such a solution-casting method, if a gas such as air is contained in the polymer solution, immediately after the polymer solution is cast onto the support, the gas expands due to the release of the pressure that has been applied until then, resulting in pinhole defects that penetrate the film and / or crater-shaped defects that do not penetrate the film but look like volcanic craters on the film surface. With the recent demand for stable film supply, the demand for improving pinhole defects and crater defects has become particularly strong, and problems have particularly emerged in the production of solution-cast films in which pinhole defects and crater defects are likely to occur on the film surface. In addition, there is also a problem of a decrease in the yield in the electronic device module mounting process of electronic components using a gas barrier protective film.

[0003] As a technique for reducing bubbles that cause these pinhole or crater defects, Patent Document 1 proposes suppressing pinholes by removing foreign matter of 3 μm or more in the polymer solution with a filter, setting the dustiness of the dry air used in the solution film-forming process to 5,000 or less, and further providing a defoaming step to remove bubbles in the polymer solution.

[0004] Patent Document 2 proposes a method of narrowing the gap between the cast polymer and the support in the step of casting the polymer solution onto the support.

[0005] Patent Document 3 proposes a method of reducing the viscosity of the polymer solution and making it easier to degas bubbles in the polymer solution by stirring the polymer solution while heating it.

[0006] Patent Document 4 proposes a film-forming method in which a polymer solution is filled into a filter previously filled with a solvent from the inlet side of the filter to perform film formation, suppressing expansion due to pressure release of gases such as air dissolved in the polymer solution, and significantly suppressing bubbles in the polymer solution.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] The pinhole defect can be improved by the technology described in the above-mentioned patent document. However, even if the technology described in the above-mentioned patent document is used, it is not possible to sufficiently improve the occurrence of crater defects, in which the gas contained in the polymer solution expands due to heat during the time it takes for the gas to reach the surface of the polymer solution, causing large crater defects on the surface. This problem is particularly noticeable when the film thickness is 10 μm or more. In addition, the gas barrier properties of the film deteriorate in the areas where crater defects occur on the film surface, which is a major problem when the film is used as a gas barrier protective film.

[0009] The present invention aims to provide a film production method that significantly suppresses air bubbles in the polymer solution, which are the cause of crater defects on the surface, which are a problem in solution-cast films. In addition, the present invention aims to provide a film with few quality defects such as crater defects on the film surface and good yield when used as a gas barrier protective film, for example. [Means for solving the problems]

[0010] The present invention comprises the following configurations. (1) A method for producing a solution casting film by forming a polymer solution into a sheet, comprising a step of filling a filter filled with a solvent from an inlet side of the filter with the polymer solution, and the viscosity of the polymer solution filled from the inlet side of the filter in the step is 2000 poise or more. (2) The method for producing a solution casting film according to (1) above, in which the supply rate of the polymer solution filled from the inlet side of the filter in the step is changed within a range of 20 kg / hr to 200 kg / hr. (3) The method for producing a solution casting film according to (2) above, in the above step, the supply rate of the polymer is increased stepwise from 20 kg / hr to 50 kg / hr to 100 kg / hr to 200 kg / hr, and then decreased stepwise again to 20 kg / hr to 50 kg / hr, with this cycle being repeated for at least two cycles. The method for producing a solution-cast film according to any one of (1) to (3), wherein the polymer is an aromatic polyamide. (5) A film solution-cast by the production method according to any one of (1) to (4). (6) The film according to (5), wherein the polymer is an aromatic polyamide. (7) The film according to (5) or (6), wherein the film thickness is 10 μm or more and less than 30 μm. (8) The film according to any one of (5) to (7), wherein the number of crater defects having a minor axis of 0.1 mm or more present on the film surface is 7 or less per 1000 m2. (9) A gas barrier protective film having the film according to any one of (5) to (8). [Advantages of the Invention]

[0011] According to the method for producing a solution-cast film of the present invention, it is possible to significantly suppress bubbles in the polymer solution, which are the cause of crater defects on the surface, which are a problem in solution-cast films. [Brief Description of the Drawings]

[0012]

Figure 1

[0013] The present invention will be described in detail below together with preferred embodiments, but the present invention is not limited thereto.

[0014] The method in the present invention is a method for producing a solution-cast film in which a polymer solution is formed into a sheet shape, and has a step of filling a filter filled with a solvent in advance with the polymer solution from the inlet side of the filter, and the viscosity of the polymer solution filled from the inlet side of the filter in the step is 2000 poise or more.

[0015] The polymers applied in the present invention include aromatic polyamides, aromatic polyimides, polyarylates, polyacrylonitriles, polycarbonates, cellulose polymers such as cellulose diacetate and cellulose triacetate, vinyl acetate, polyvinyl alcohol, and the like. In particular, aromatic polyamides have a high viscosity when in solution, and it is difficult for bubbles generated by the vaporization of dissolved gas to escape, so the effect of the present invention is particularly high. Also, aromatic polyamides have a low gas permeability when made into a film and are suitable for gas barrier protective films.

[0016] The solvent pre-filled in the filter in the present invention preferably contains the same components as the solvent in which the polymer is dissolved and is a liquid that forms a liquid state at normal temperature and normal pressure. Such solvents are not particularly limited as long as they have a low drying load and can dissolve the polymer. For example, methyl acetate, ethyl acetate, amyl acetate, ethyl formate, acetone, cyclohexanone, methyl acetoacetate, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,4-dioxane, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, methylene chloride, dimethyl sulfoxide, dimethylacetamide, sulfuric acid, and the like can be mentioned. Also, the polymer concentration in the polymer solution generally preferably ranges from 2 to 40% by mass, although it depends on the type of polymer. By setting the polymer concentration to 40% by mass or less, it is possible to suppress the decrease in productivity due to the increase in the viscosity of the polymer solution. Also, by setting the polymer concentration to 2% by mass or more, the solvent removal efficiency can be improved, and furthermore, the case where the polymer solution cannot be held on the support due to the decrease in the viscosity of the polymer solution can be suppressed.

[0017] The polymer solution in the present invention is one in which the polymer is dissolved in the solvent, and depending on the purpose, lubricants, conductive particles, plasticizers, antioxidants, and other additives may be contained without any problem.

[0018] The filter in the present invention is installed in a process upstream of the slit die through which the polymer solution is extruded in order to remove foreign substances in the polymer solution that can cause quality defects in the film, and refers to a device that encloses a filter medium.

[0019] The type of the filter medium is not particularly limited as long as it can remove foreign substances in the polymer solution, but from the viewpoints of productivity and quality, a leaf disk type filter having a high filtration area ratio per volume and a high filtration accuracy is preferable. The leaf disk type filter is housed in the filter in a shape in which a plurality of sheets are stacked and assembled on a support column, and then an inner flow path of the filter is secured by an upper lid.

[0020] The filter filled with the solvent in the present invention refers to a filter in a state where the filter is filled with the solvent. Here, the state of being filled with the solvent means a state where the space in the filter excluding the filter medium is filled with the solvent.

[0021] As a method of filling the filter with the solvent, it is preferable to feed the solvent with a pump or the like from a position below the center in the height direction of the filter and extract the gas in the filter from a position above the center in the height direction of the filter. When the solvent is fed from a position above the center in the height direction of the filter, the flow of the fed solvent becomes an obstacle, and the gas in the filter is difficult to be discharged from the filter. More preferably, the solvent is fed with a pump or the like from the lowermost position in the height direction of the filter, and the gas in the filter is extracted from the uppermost part in the height direction of the filter. In addition, it is preferable to perform the above operation at the same atmospheric pressure as the surrounding atmosphere without reducing the pressure inside the filter.

[0022] In the present invention described above, it is preferable that the pressure in the filter filled with the solvent in advance is less than 0.5 MPa until the polymer solution is filled from the inlet side of the filter.

[0023] When the filter filled with the solvent increases the pressure inside the filter, the gas remaining in the filter medium passes through the filter medium and forms a large amount of fine bubbles outside the filter medium. Since the fine bubbles have very small buoyancy and stay outside the filter medium in the filter, this is not preferable. The pressure inside the above-described filter is preferably 0.3 MPa or less.

[0024] Also, when the contact angle between the solvent and the filter medium is 90 degrees or more, when the filter is filled with the solvent, bubbles may be generated on the surface of the filter medium. Therefore, after filling the inside of the filter with the solvent, the solvent is once extracted, and after wetting the inside of the filter and the filter medium with the solvent, it is preferable to fill the inside of the filter with the solvent again.

[0025] In addition, as described above, when the solvent is fed by a pump or the like from a position below the center in the height direction of the filter and the solvent is discharged from a position above the center in the height direction of the filter, by continuing the liquid feeding until no gas is observed in the discharged solvent, it becomes possible to appropriately fill the inside of the filter with the solvent.

[0026] Next, a specific example of a method for filling the filter of the present invention with a solvent will be described with reference to FIG. 1.

[0027] FIG. 1 shows a state in which a liquid feeding device 4 for supplying a solvent, a slit die 5, a liquid feeding device 6 for supplying a polymer solution, a first system external extraction 7, a second system external extraction 8, a filter primary side switching valve 9, a filter secondary side switching valve 10, a solvent filling extraction switching valve 11, a solvent extraction valve 12, and a solvent filling valve 13 are respectively connected by piping around a filter 1. The filter 1 is assembled with a plurality of filter media 2 laminated on a support column 3, and is assembled in a state where an internal flow path of the filter is secured by an upper lid.

[0028] In such a line, an example of the procedure for filling the inside of the filter with the solvent and filling the polymer solution from the inlet side of the filter is as follows. · Switch the filter primary side switching valve 9 so as to go from the filter 1 to the first system external extraction 7. · Switch the filter secondary side switching valve 10 and the solvent filling / discharging switching valve 11 so that the solvent is supplied from the liquid feeding device 4 that supplies the solvent to the filter 1. · Open the solvent discharging valve 12 and the solvent filling valve 13. · Using the liquid feeding device 4 that supplies the solvent, supply the solvent into the filter 1, and discharge the gas and the solvent in the filter 1 from the first system external discharge 7. · Close the solvent filling valve 13.

[0029] In the present invention, it is important that the viscosity of the polymer solution filled from the inlet side of the filter into the filter pre-filled with the solvent is 2000 poise or more. When filling the filter pre-filled with the solvent with the polymer solution, by increasing the viscosity of the polymer solution to the above-mentioned range or higher, it becomes easier to remove the air bubbles in the filter. The viscosity of the polymer solution is preferably 2500 poise or more, and more preferably 3000 poise or more. As the upper limit, from the viewpoint of the pressure resistance performance of the liquid feeding device that supplies the polymer solution and the filter medium, it is preferably 4000 poise or less.

[0030] The means for increasing the viscosity of the polymer solution is not particularly limited, and examples thereof include a method of increasing the polymer concentration of the polymer solution and a method of lowering the temperature of the polymer solution. A preferable means is to lower the temperature of the polymer solution. When the polymer concentration in the polymer solution is increased, it tends to flow out intermittently when discharging the polymer solution from the die, and the surface may be disturbed when made into a sheet.

[0031] In the present invention, it is preferable to vary the supply rate of the polymer solution filled from the inlet side of the filter in the above-described step within a range of 20 kg / hr or more and 200 kg / hr or less. By setting the supply rate of the polymer solution to 20 kg / hr or more, sufficient pressure is generated to extrude the bubbles in the filter accompanying the supply of the polymer solution, and the effect of removing bubbles can be easily obtained. By setting the supply rate of the polymer solution to 200 kg / hr or less, it is possible to suppress the pressure from affecting the filter medium and causing a decrease in the filtration accuracy. Further, by varying the supply rate of the polymer solution within the above-described range, the bubbles in the filter can be changed and easily discharged. Preferably, the supply rate of the polymer solution is varied within a range of 25 kg / hr or more and 150 kg / hr or less. By varying the supply rate of the polymer solution, when the supply rate is increased, the bubbles adhering to the filter medium and the like contract and peel off, and when the supply rate is decreased, the peeled bubbles expand and are easily carried away by the supply rate and discharged.

[0032] Further, in the above-described step, it is preferable to perform the cycle in which the supply rate of the polymer is increased stepwise from a supply rate of the polymer solution of 20 kg / hr or more and 50 kg / hr or less to 100 kg / hr or more and 200 kg / hr or less, and then decreased stepwise again to 20 kg / hr or more and 50 kg / hr or less, two or more cycles. More preferably, it is 3 or more cycles and 10 or less cycles.

[0033] Next, a specific example of the method of filling a polymer solution from the inlet side of a filter filled with a solvent in advance of the present invention will be described with reference to FIG. 1, but the present invention is not construed as being limited to such an example.

[0034] · Switch the primary-side switching valve 9 of the filter filled with the solvent in advance so as to go from the liquid-feeding device 6 that supplies the polymer solution to the filter 1. At this time, control the temperature of the polymer solution so that the viscosity of the polymer solution becomes 2000 poise or more. · Using a liquid feeder 6 that supplies a polymer solution, supply the polymer solution into the filter 1 at 20 kg / hr, and extract the solvent in the filter 1 from the first system external extraction 7 via the solvent extraction valve 12. · Close the solvent extraction valve 12, and switch the solvent filling / extraction switching valve 11 so that it leads from the filter 1 to the second system external extraction 8. · Using a liquid feeder 6 that supplies a polymer solution, supply the polymer solution into the filter 1 again at 20 kg / hr, and sufficiently extract the solvent in the filter 1 from the second system external extraction 8 via the solvent filling / extraction switching valve 11. At this time, control the temperature of the polymer solution so that the viscosity of the polymer solution becomes 2000 poise or more. · As a purge in the filter, using a liquid feeder 6 that supplies a polymer solution, supply the polymer solution into the filter 1, and increase the supply rate of the polymer solution from 20 kg / hr to a maximum of 200 kg / hr in steps via the solvent filling / extraction switching valve 11 from the second system external extraction 8, and then repeat decreasing it to 20 kg / hr in steps. At this time, control the temperature of the polymer solution so that the viscosity of the polymer solution becomes 2000 poise or more. · Switch the filter secondary side switching valve 10 so that it leads from the filter 1 to the slit die 5. · Using a liquid feeder 6 that supplies a polymer solution, supply the polymer solution into the filter 1 again, and feed it to the slit die 5 via the filter secondary side switching valve 10.

[0035] In the present invention, for example, with respect to a filter filled with a solvent as described above, a polymer solution is filled from the inlet of the filter, and a solution casting film is manufactured.

[0036] Note that the inlet of the filter as referred to herein means the inlet on the opposite side of the outlet of the filter that is discharged toward the slit die in the path through which the polymer solution flows. By feeding the polymer solution into the filter in this way, the solvent in the filter is pushed out and the solvent is replaced by the polymer solution. The pushed-out solvent is preferably discharged out of the system from a separate outlet of the filter provided at a position closer to the slit die. If the solvent is pushed out from the outlet of the filter toward the slit die, the polymer concentration in the polymer solution will be less than 2% by mass, the removal efficiency of the solvent will decrease, and furthermore, due to the decrease in the viscosity of the polymer solution, the polymer solution may not be retained on the support.

[0037] When performing film formation, the above method can reduce the bubbles in the polymer solution when the polymer solution flows along the direction of gravity inside the filter (when the filter is arranged in such a way during film formation), and it is particularly effective.

[0038] In this way, when the above-described method is applied, the polymer solution from which foreign matters have been removed by the filter is cast onto a support such as a drum, an endless belt, or a carrier film via the slit die.

[0039] The temperature of the polymer solution during casting is preferably set to a temperature below the boiling point of the solvent used, as this can prevent the generation of bubbles.

[0040] The slit die includes a coat hanger die and a T-die, and any of them can be preferably used. Also, the slit die may be single-layer or multi-layer.

[0041] For adjusting the film thickness, it can be adjusted by the polymer solution concentration, the liquid feeding amount of the pump, the slit gap of the slit die, the liquid feeding pressure to the slit die, and the moving speed of the support so as to obtain the desired thickness.

[0042] Next, when the solvent in the polymer solution cast on the support has evaporated and becomes peelable, it is peeled off. Or, the polymer solution cast on the support is cooled to be gelled and then peeled off.

[0043] To evaporate the solvent, there are methods such as blowing warm air from the side where the polymer solution is cast and the back side of the support, heating with a heating liquid from the back side of the support, heating with radiant heat, and combining these methods.

[0044] The sheet peeled off from the support is then fed to a solvent extraction device for removing the solvent contained in the sheet. This solvent extraction is carried out by immersing the sheet in a liquid for extracting the solvent while being conveyed by a conveying roll. Here, the solvent extraction device refers to the period from when the sheet is first introduced into the above liquid until immediately before the tenter stretching machine for heat treatment described later.

[0045] The sheet from which the solvent has been removed by the solvent extraction device is then conveyed to a tenter stretching machine by a plurality of conveying rolls. If necessary, the sheet is stretched longitudinally using a roll stretching machine or the like and / or stretched or shrunk laterally using a tenter in the tenter stretching machine to obtain a film having desired properties.

[0046] The thickness of the film in the present invention is preferably 10 μm or more and less than 30 μm. When the film thickness is 10 μm or more, it is preferable because sufficient gas barrier properties can be obtained when used as a gas barrier protective film. Since the gas barrier properties of the gas barrier protective film depend on the film thickness, a thicker film is preferable. On the other hand, when forming a film with a film thickness of 30 μm or more, a sufficient heat treatment time is required for the amount of solvent processed by the casting machine, and the size of the casting machine increases. Making the film thickness less than 30 μm is preferable because it improves the gas barrier properties and is excellent in productivity and economy.

[0047] The film in the present invention has 7 crater defects with a minor axis of 0.1 mm or more present on the film surface per 1000 m 2The following are preferred. The crater defect referred to in the present invention means a defect in which a gas such as air contained in the polymer solution expands due to the release of the pressure applied until then immediately after the polymer solution is cast onto the support, and the gas appears like a crater on the film surface. The number of crater defects having a minor axis of 0.1 mm or more is 7 per 1000 m 2 By setting it as follows, it is possible to suppress the local decrease in the gas barrier property of the crater defect portion and the deterioration of the yield when used for a gas barrier protective film used in the electronic device module mounting process of electronic components. Preferably, the number of crater defects having a minor axis of 0.1 mm or more is 5 per 1000 m 2 The following is the case.

[0048] The film thus obtained can be used for a gas barrier protective film used in the electronic device module mounting process of electronic components.

Example

[0049] Hereinafter, examples of the present invention will be shown, but the present invention is not limited to these examples.

[0050] (Film thickness) Using a high-precision digital micrometer MDH-25MB (manufactured by Mitutoyo Corporation), in the direction orthogonal to the film conveyance direction (MD), in a state where 10 sheets are overlapped, the portion excluding the edge portion of 50 mm was measured at 10 mm intervals, and the value divided by the number of overlapped sheets was used as the average value as the film thickness.

[0051] (Filter) As the filter, a 12-inch leaf disk type fiber sintered filter equivalent to 1 μm cut manufactured by Nippon Seisen Co., Ltd. was stacked 80 sheets on a support column, compressed with a weight of 100 kgf, and assembled into a filter housing. The capacity inside the filter is 40 liters.

[0052] (Solvent) N-methyl-2-pyrrolidone (NMP) was used as the solvent.

[0053] (A-layer polymer solution) 20% by mass of colloidal silica with a primary particle size of 45 nm was added to dehydrated NMP and dispersed with an ultrasonic disperser for 10 hours. This particle solution was added to a monomer solution before polymerization in which 2-chlorop-phenylenediamine corresponding to 85 mol% and 4,4'-diaminodiphenyl ether corresponding to 15 mol% were dissolved so that the silica became 2% by mass per polymer. To this solution, 2-chloroterephthalic acid chloride corresponding to 98.5 mol% was further added, and after polymerization by stirring for 2 hours, it was neutralized with lithium carbonate to obtain an aromatic polyamide solution with a polymer concentration of 11% by mass.

[0054] The polymer solution thus obtained was treated by being left standing under pressure with nitrogen at room temperature and 2 kPa for 3 hours to obtain an A-layer polymer solution.

[0055] (B-layer polymer solution) A monomer solution before polymerization in which 2-chlorop-phenylenediamine corresponding to 85 mol% and 4,4'-diaminodiphenyl ether corresponding to 15 mol% were dissolved was added to dehydrated NMP. To this solution, 2-chloroterephthalic acid chloride corresponding to 98.5 mol% was further added, and polymerization was carried out by stirring for 2 hours.

[0056] To this solution, silica particles with an average particle size of 16 nm were added at 15.0% by mass based on the polymer and stirred for 1 hour, and then neutralized with lithium carbonate to obtain an aromatic polyamide solution with a polymer concentration of 10.8% by mass.

[0057] The polymer solution thus obtained was treated by being left standing under pressure with nitrogen at room temperature and 2 kPa for 3 hours to obtain a B-layer polymer solution.

[0058] (Number of times of use after filling the filter) As a rinsing operation inside the filter, a liquid feeding device 6 for supplying a polymer solution supplies the polymer solution at 35 degrees into the filter 1 again. The polymer solution is supplied from the second system external extraction 8 via the solvent filling and extraction switching valve 11. After gradually increasing the supply rate from 25 kg / hr to 140 kg / hr over 6 minutes, it is gradually decreased to 25 kg / hr over 4 minutes, and one cycle is defined as waiting for 10 minutes at a supply rate of 25 kg / hr.

[0059] (Polymer solution viscosity) Using a B-type viscometer type BS manufactured by Tokyo Keiki Co., Ltd., with rotor No. 7, and measuring each polymer solution at a rotor rotation speed of 10 rpm, at temperatures of 30 °C, 40 °C, and 50 °C respectively, the relationship between temperature and the polymer solution was obtained, and the viscosity of the polymer solution at each temperature was calculated.

[0060] (Measurement of crater defects) For the measurement of crater defects on the film, a foreign object inspection machine manufactured by FUTEC Co., Ltd. was used to image the defects, and the number was counted from the captured image. The measurement location was set to be between the film passing through the transverse stretching machine and the winding. Imaging was performed by irradiating from the lower part of the film and using a CCD camera installed on the upper part of the film. From the image captured by the camera, defects that were circular and had a higher brightness at the center compared to the contour were defined as crater defects. The number of crater defects was obtained by converting the number of those with a minor axis size of 0.1 mm or more to the number per 1,000 m 2 of the film.

[0061] (Example 1) The filter was assembled in the line according to FIG. 1, with the filter inlet where the polymer solution is fed upward and the filter outlet where the polymer solution flows out downward, and implemented in the following order. · Switch the primary side switching valve 9 of the filter to lead from the filter 1 to the first system external extraction 7, switch the secondary side switching valve 10 and the solvent filling and extraction switching valve 11 of the filter to lead from the liquid feeding device 4 for supplying the solvent to the filter 1, and open the solvent extraction valve 12 and the solvent filling valve 13. · Next, with the liquid delivery device 4 for supplying the solvent, the solvent was fed into the filter 1 at a supply rate of 40 kg / hr. After confirming that the solvent flowed out from the first system external extraction port 7, the supply was continued for 0.5 hours, and then the solvent filling valve 13 was closed. · Next, the filter primary side switching valve 9 was switched so as to go from the liquid delivery device 6 for supplying the polymer solution to the filter 1. With the liquid delivery device 6 for supplying the polymer solution, the polymer solution was fed into the filter 1, and the supply was continued until the polymer solution in the filter 1 flowed out from the first system external extraction port 7 via the solvent extraction valve 12. · Next, the solvent extraction valve 12 was closed, and the solvent filling extraction switching valve 11 was switched so as to go from the filter 1 to the second system external extraction port 8. · Next, as the purge inside the filter, with the liquid delivery device 6 for supplying the polymer solution, the polymer solution at 35 degrees was fed again into the filter 1. The supply rate of the polymer solution was gradually increased from 25 kg / hr to 140 kg / hr over 6 minutes via the solvent filling extraction switching valve 11 from the second system external extraction port 8, then gradually decreased to 25 kg / hr over 4 minutes, and the supply was waited for 10 minutes at a supply rate of 25 kg / hr. This was repeated 5 times. · Next, the filter secondary side switching valve 10 was switched so as to go from the filter 1 to the slit die 5.

[0062] In this way, a solvent-filled filter was prepared.

[0063] The A-layer polymer solution was degassed by a degassing machine at a supply rate of 80 kg / hr while heating to 65°C, filtered by the solvent-filled filter, and supplied to the slit die.

[0064] At the same time, the B-layer polymer solution was degassed by a degassing machine at a supply rate of 80 kg / hr while heating to 65°C, filtered by the solvent-filled filter, and supplied to the slit die.

[0065] Using the supplied A-layer polymer solution and B-layer polymer solution, a solution-cast film with an A / B two-layer structure was produced in a film-forming chamber with a cleanliness of class 1,000 as follows.

[0066] First, the supplied A-layer polymer solution was laminated on the surface of the endless belt serving as the support that does not come into contact with the B-layer polymer solution on the surface in contact with the endless belt. Then, it was cast onto an endless belt (support) having protrusions with a height and depth of 30 μm or more and no foreign matter via a slit die.

[0067] Next, it was heated with hot air at 180°C for 2 minutes in a dryer to evaporate the solvent, and the self-supporting sheet was continuously peeled off from the endless belt. Then, as a solvent extraction treatment device, the sheet was introduced into a water tank with a concentration gradient of NMP to perform water extraction of the remaining solvent and the inorganic salts generated by neutralization, and it was stretched 1.06 times in the longitudinal direction. Subsequently, as a transverse stretching machine, after drying the moisture with a stenter at 280°C, stretching and heat treatment 1.05 times in the width direction were performed for a total of 1.5 minutes, and it was gradually cooled at a rate of 20°C / second. Finally, the film was wound up with a winder to obtain an aromatic polyamide film having an A / B two-layer structure with a thickness of 12 μm. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

[0068] (Example 2) An aromatic polyamide film was obtained in the same manner as in Example 1, except that the temperature of the polymer solution re-supplied into Filter 1 was set to 40°C as the sieve in the filter. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

[0069] (Example 3) An aromatic polyamide film was obtained in the same manner as in Example 1, except that the temperature of the polymer solution re-supplied into Filter 1 was set to 45°C as the sieve in the filter. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

[0070] (Comparative Example 1) An aromatic polyamide film was obtained in the same manner as in Example 1, except that the temperature of the polymer solution re-supplied into Filter 1 was set to 50°C as the sieve in the filter. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

[0071] (Comparative Example 2) An aromatic polyamide film was obtained in the same manner as in Example 1, except that as the reuse inside the filter, the temperature of the polymer solution re-supplied into Filter 1 was set to 50°C and the number of reuse times was set to 10 times. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

[0072] (Comparative Example 3) An aromatic polyamide film was obtained in the same manner as in Example 1, except that as the reuse inside the filter, the temperature of the polymer solution re-supplied into Filter 1 was set to 50°C, the number of reuse times was set to 10 times, and the resulting film thickness was set to 26 μm. The measured physical property values of the obtained aromatic polyamide film are shown in Table 1.

Explanation of Signs

[0073] 1 Filter 2 Filter medium 3 Support column 4 Liquid feeding device for supplying solvent 5 Slit die 6 Liquid feeding device for supplying polymer solution 7 Extraction 1 outside the system 8 Extraction 2 outside the system 9 Filter primary side switching valve 10 Filter secondary side switching valve 11 Solvent filling extraction switching valve 12 Solvent extraction valve 13 Solvent filling valve

[0074]

Table 1

Claims

1. A method for producing a solution casting film by forming a polymer solution into a sheet, comprising the steps of: The method includes a step of filling a filter, which is filled with a solvent in advance, with a polymer solution from an inlet side of the filter, In the above process, the viscosity of the polymer solution filled from the inlet side of the filter is 2000 poise or more.

2. 2. The method for producing a solution casting film according to claim 1, wherein the supply rate of the polymer solution filled from the inlet side of the filter in said step is changed within a range of 20 kg / hr to 200 kg / hr.

3. 3. The method for producing a solution casting film according to claim 2, wherein the supply rate of the polymer is increased stepwise from 20 kg / hr to 50 kg / hr to 100 kg / hr to 200 kg / hr, and then decreased stepwise to 20 kg / hr to 50 kg / hr, and the cycle is repeated for at least two cycles.

4. 3. The method for producing a solution casting film according to claim 1, wherein the polymer is an aromatic polyamide.

5. A film produced by the method according to claim 1 or 2.

6. The film of claim 5 wherein the polymer is an aromatic polyamide.

7. 6. The film according to claim 5, having a thickness of 10 μm or more and less than 30 μm.

8. The number of crater defects with a minor diameter of 0.1 mm or more on the film surface is 7 per 1000 m ２ 6. The film of claim 5, wherein:

9. A gas barrier protective film comprising the film according to claim 5 .

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