Support film for forming polymer film from solution, laminate thereof, and method of forming polymer film

Abstract

To provide a support film for producing a polymer film that suppresses curling and is free from flaws on the film surface during the polymer film forming process.SOLUTION: Provided is a support film used for forming polymer films from solution, wherein the heat shrinkage of the support film in a direction (hereinafter referred to as the "TD direction") perpendicular to the longitudinal direction (hereinafter referred to as the "MD direction") is 0.4% or more, and the thickness of the support film is 150 μm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a support film for solution casting of a polymer film, a laminate thereof, and a method for casting a polymer film.

Background Art

[0002] As methods for casting polymer films, a solution casting method and a melt casting method are known. As a solution casting method, for example, a method of applying and drying a solution in which a polymer is dissolved in an appropriate solvent to a support film such as a plastic film is known. On the other hand, as a melt casting method, for example, a method of melt-extruding a molten resin from a T-die is generally adopted.

[0003] As a kind of polymer film, for example, a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane used in the field of electrochemistry such as fuel cells and water electrolysis are known. Fluorine-based polymer electrolytes have a relatively low melting point and are suitable for the melt casting method. On the other hand, for casting hydrocarbon-based polymer electrolytes with a relatively high melting point, the solution casting method is preferable.

[0004] Hitherto, as a support film for solution casting suitable for casting a polymer electrolyte membrane, a film having a specified range of thermal shrinkage rate (see, for example, Patent Documents 1 and 2), a film provided with a reinforcing layer having a certain hardness (see, for example, Patent Document 3), etc. have been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the solution casting of polymer films such as polymer electrolyte membranes, in the drying process of evaporating the solvent in the polymer solution coated on the support film, M-shaped (wavy) curls are generated in the direction orthogonal to the longitudinal direction (transport direction: MD direction) of the support film (width direction: TD direction), and the polymer film may come into contact with an air nozzle, a drying furnace outlet shutter, etc., resulting in scratches. When scratches occur, the yield is reduced. In particular, the above problem becomes more prominent as the thickness of the polymer film increases. With respect to such problems, the support film (release film) described in the above patent document could not solve them sufficiently.

[0007] Therefore, an object of the present invention is to provide a support film capable of suppressing the generation of curls and accompanying scratches in the solution casting process of a polymer film in view of the problems of the above prior art.

Means for Solving the Problems

[0008] The present inventors considered that the above problems were caused by an increase in the difference between the drying shrinkage rate of the polymer film and the thermal shrinkage rate of the support film in the film forming process of the polymer film, and thus arrived at the present invention.

[0009] That is, in order to achieve the above object, the present invention adopts the following configuration. [1] A support film used for solution casting of a polymer film, wherein the thermal shrinkage rate in the direction orthogonal to the longitudinal direction (hereinafter referred to as the "MD direction") of the support film (hereinafter referred to as the "TD direction") is 0.4% or more, and the thickness of the support film is 150 μm or more, a support film for solution casting of a polymer film. [2] The support film for solution casting of a polymer film according to [1], wherein the ratio (TD / MD) of the thermal shrinkage rate in the TD direction to the thermal shrinkage rate in the MD direction of the support film is 0.50 to 0.95. [3] The support film for solution casting of a polymer film according to [1] or [2], wherein the support film does not have a release layer. [4] The support film for solution casting of the polymer film according to any one of [1] to [3], wherein the dry thickness of the polymer film is 40 μm or more. [5] The support film for solution casting of the polymer film according to any one of [1] to [4], wherein the tensile elastic modulus of the polymer film is 300 MPa or more. [6] The support film for solution casting of the polymer film according to any one of [1] to [5], wherein the polymer film is a film composed of a polymer having an aromatic ring in the main chain. [7] The support film for solution casting of the polymer film according to any one of [1] to [6], wherein the polymer film is a polymer electrolyte membrane. [8] A laminate of the support film according to any one of [1] to [7] and the polymer film. [9] The laminate according to [8], wherein the thickness of the polymer film is 40 μm or more.

[10] The laminate according to [8] or [9], wherein the tensile elastic modulus of the polymer film is 300 MPa or more.

[11] The laminate according to any one of [8] to

[10] , wherein the polymer film is a film composed of a polymer having an aromatic ring in the main chain.

[12] The laminate according to any one of [8] to

[11] , wherein the polymer film is a polymer electrolyte membrane.

[13] A method for producing a polymer film, comprising a step of applying a polymer solution to the support film according to any one of [1] to [7], and a step of drying the applied polymer solution.

[14] The method for producing a polymer film according to

[13] , wherein the polymer solution is a solution in which a polymer is dissolved in a solvent containing an aprotic polar solvent.

[15] The method for producing a polymer film according to

[13] or

[14] , wherein after carrying out the coating step and the drying step while conveying the support film unwound from a support film supply roll, it is wound up in a roll shape.

[16] The method for producing a polymer film according to any one of

[13] to

[15] , which has an acid treatment step following the drying step.

Advantages of the Invention

[0010] By using the support film of the present invention in the solution casting of a polymer film, the occurrence of curl (hereinafter simply referred to as "curl") in the casting process is suppressed, and as a result, the occurrence of scratches on the polymer film is suppressed.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be variously modified and implemented according to the object and application of the present invention. The support film for solution casting of a polymer film according to an embodiment of the present invention may be simply referred to as a "support film" hereinafter.

[0013] [Support Film] The support film according to an embodiment of the present invention is preferably composed of a synthetic resin. The synthetic resin is not particularly limited, but a thermoplastic resin is preferred. For example, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polycarbonate, polyetherimide, polyphenylene sulfide, polyimide, polystyrene, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, perfluoroalkoxy fluororesin, etc. can be mentioned. Among these, polyester is preferred from the viewpoints of chemical resistance, heat resistance, and price, and polyethylene terephthalate is particularly preferred.

[0014] The support film according to an embodiment of the present invention has a heat shrinkage rate in the direction orthogonal to the longitudinal direction (hereinafter referred to as the "MD direction") (hereinafter referred to as the "TD direction") of 0.4% or more. The heat shrinkage rate in the present invention is the heat shrinkage rate after heating the support film at 150 ° C for 30 minutes, and is measured in accordance with ASTM-D1204 (1984). The heat shrinkage rate of 0.4% or more specified in the present invention is set higher than that of the support films generally known in the past. Thus, by making the heat shrinkage rate in the TD direction of the support film relatively high at 0.4% or more, the difference from the dry shrinkage rate of the polymer film formed by solution casting becomes small, and it is presumed that the generation of curl is suppressed. And, by combining with the thickness of the support film being 150 μm or more, the curl suppressing effect becomes large.

[0015] From the above viewpoints, the heat shrinkage rate in the TD direction of the support film is preferably 0.5% or more, more preferably 0.6% or more, and particularly preferably 0.7% or more. On the other hand, if the heat shrinkage rate in the TD direction of the support film becomes too large, wrinkles may occur in the polymer film, or the thickness accuracy (thickness uniformity) in the TD direction of the polymer film may decrease. Therefore, the heat shrinkage rate is preferably 1.7% or less, more preferably 1.5% or less, and particularly preferably 1.3% or less.

[0016] The heat shrinkage rate in the MD direction of the support film generally tends to be larger than that in the TD direction. However, if the heat shrinkage rate in the MD direction becomes too large compared to that in the TD direction, the curl suppressing effect and the thickness accuracy of the formed polymer film may decrease. From the above viewpoints, the ratio (TD / MD) of the heat shrinkage rate in the TD direction to the heat shrinkage rate in the MD direction is preferably in the range of 0.50 to 0.95, more preferably in the range of 0.60 to 0.92, and particularly preferably in the range of 0.65 to 0.90. Specifically, the heat shrinkage rate in the MD direction is preferably in the range of 0.6 to 1.8%, more preferably in the range of 0.7 to 1.6%, and particularly preferably in the range of 0.8 to 1.4%.

[0017] The support film according to the embodiment of the present invention is made of a plastic resin. Generally, the rigidity of a plastic resin film increases in proportion to the cube of the thickness. For suppressing curl, it is preferable that the support film has higher rigidity. From this viewpoint, the thickness of the support film is preferably 180 μm or more, more preferably 200 μm or more, still more preferably 230 μm or more, and particularly preferably 250 μm or more. On the other hand, if the thickness of the support film becomes too large, the winding roll diameter after film formation becomes large, which causes a decrease in production efficiency and an increase in the cost of materials. From these viewpoints, the thickness of the support film is preferably 500 μm or less, more preferably 450 μm or less, and particularly preferably 400 μm or less.

[0018] The support film according to the embodiment of the present invention may have a release layer. As the release agent, silicone resin or fluororesin is generally used for the release layer. However, from the viewpoint of suppressing the transfer and mixing of the release agent into the polymer film, it is preferable that the support film according to the embodiment of the present invention does not have a release layer.

[0019] [Polymer film] The support film according to an embodiment of the present invention is suitably used for solution casting of a polymer film. The polymer constituting the polymer film is not particularly limited as long as it can be solution cast. Examples of the polymer include polyethylene, polypropylene, polystyrene, polyacrylate, polymethacrylate, polyvinyl chloride, polyvinylidene chloride, polyester, polycarbonate, polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene, polyarylene ketone, polyether ketone, polyether ether ketone, polyether ketone ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, polyimide sulfone, polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, perfluoroalkoxy fluororesin, ethylene-chlorotrifluoroethylene copolymer, and the like. Among these, polymers having a relatively high melting point are suitable for solution casting. Specifically, the melting point of the polymer is preferably 200°C or higher, more preferably 250°C or higher. The upper limit of the melting point of the polymer is not particularly limited, but is preferably 500°C or lower.

[0020] The degree of curl generation in the drying process of the polymer film coated on the support film increases as the drying shrinkage of the polymer film increases. One of the factors contributing to the increase in the drying shrinkage of the polymer film is the high tensile elastic modulus of the polymer film. That is, the higher the tensile elastic modulus of the polymer film, the greater the tendency for curl to increase. Therefore, the support film according to an embodiment of the present invention is more suitably used for solution casting of a polymer film having a relatively high tensile elastic modulus.

[0021] Also, the drying shrinkage of the polymer film tends to be larger in the aromatic polymer film than in the aliphatic polymer film. Therefore, the support film according to the embodiment of the present invention is more preferably used for solution casting of the aromatic polymer film. Here, the aromatic polymer means a polymer having an aromatic ring in the main chain. That is, the support film according to the embodiment of the present invention is more preferably used for solution casting of a polymer film composed of a polymer having an aromatic ring in the main chain. Examples of the aromatic ring include hydrocarbon-based aromatic rings and heterocycles. Among them, hydrocarbon-based aromatic rings are preferred. As the aromatic polymer film, for example, the aromatic hydrocarbon-based polymer electrolyte membrane described later is a preferred example.

[0022] From the above viewpoints, the polymer film in the present invention preferably has a tensile elastic modulus of 300 MPa or more, more preferably 500 MPa or more, and particularly preferably 700 MPa or more. The upper limit of the tensile elastic modulus of the polymer film is not particularly limited, but is preferably 6,000 MPa or less.

[0023] Also, another factor that increases the drying shrinkage of the polymer film is that the thickness of the polymer film is large. Therefore, the support film according to the embodiment of the present invention is suitable for solution casting of a polymer film having a relatively large thickness. From the above viewpoints, the dry thickness of the polymer film in the present invention is preferably 40 μm or more, more preferably 50 μm or more, further preferably 60 μm or more, and particularly preferably 70 μm or more. The upper limit of the dry thickness of the polymer film is not particularly limited, but is preferably 250 μm or less.

[0024] As described above, the support film according to the embodiment of the present invention is particularly preferably used for solution casting of a polymer film having a relatively high tensile elastic modulus and / or a relatively large thickness.

[0025] The support film according to the embodiment of the present invention is particularly preferably used for solution casting of a polymer electrolyte membrane. The polymer electrolyte membrane is used as a proton conductive membrane in electrochemical applications such as fuel cells and water electrolysis devices. The polymer electrolyte membrane contains a polymer having an ionic group as a polymer electrolyte. The ionic group may be an ionic group having either cation exchange ability or anion exchange ability. As such a functional group, a sulfonic acid group, a sulfonimide group, a sulfuric acid group, a phosphonic acid group, a phosphoric acid group, a carboxylic acid group, an ammonium group, a phosphonium group, and an amino group are preferably used. Among these, a sulfonic acid group, a sulfonimide group, and a sulfuric acid group are preferable, and a sulfonic acid group is particularly preferable from the viewpoint of raw material cost.

[0026] The content of the ionic group in the polymer electrolyte can be represented by the ion exchange capacity (IEC). The IEC of the polymer electrolyte is preferably 0.5 meq / g or more, more preferably 1.0 meq / g or more, and particularly preferably 1.5 meq / g or more. Also, the IEC is preferably 5.0 meq / g or less, more preferably 3.5 meq / g or less, and particularly preferably 3.0 meq / g or less.

[0027] Here, IEC is the molar amount of the ionic group introduced per unit dry weight of the polymer electrolyte, and the larger this value, the larger the introduction amount of the ionic group. In the present invention, IEC is defined as the value obtained by the neutralization titration method. The calculation of IEC by neutralization titration can be performed by the method described in the examples.

[0028] As the polymer electrolyte, fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes are generally known. However, as the polymer electrolyte in the present invention, a hydrocarbon-based polymer electrolyte is suitable because of its relatively high melting point (for example, 200°C or higher) and relatively high tensile elastic modulus (300 Mpa or higher). That is, the polymer membrane in the present invention is preferably a polymer electrolyte membrane, more preferably a hydrocarbon-based polymer electrolyte membrane, and particularly preferably an aromatic hydrocarbon-based polymer electrolyte membrane.

[0029] Examples of aromatic hydrocarbon-based polymers include aromatic hydrocarbon-based polymers having an aromatic ring in the main chain. The aromatic ring may include not only a hydrocarbon-based aromatic ring but also a heterocyclic ring. Further, it may include some aliphatic-based units together with the aromatic ring units.

[0030] Specific examples of the aromatic hydrocarbon-based polymer include polymers having a structure selected from polysulfone, polyethersulfone, polyphenylene oxide, polyarylene ether, polyphenylene sulfide, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene-based polymers, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyamide, polyimide, polyetherimide, and polyimide sulfone in the main chain together with the aromatic ring.

[0031] The above polysulfone is a general term for structures having a sulfone bond in the molecular chain, the above polyethersulfone is a general term for structures having an ether bond and a sulfone bond in the molecular chain, and the above polyether ketone is a general term for structures having an ether bond and a ketone bond in the molecular chain. The aromatic hydrocarbon-based polymer may have a plurality of these structures.

[0032] As the aromatic hydrocarbon-based polymer, polyether ketone-based polymers are particularly preferred. Examples of the polyether ketone-based polymer include polyether ketone, polyether ketone ketone, polyether ether ketone, polyether ether ketone ketone, polyether ketone ether ketone ketone, and the like.

[0033] Polyether ketone polymers are crystalline and have the property of being insoluble in common solvents. To dissolve such crystalline polymers in common solvents, it is preferable to introduce hydrolyzable groups into the polymers. For example, polyether ketone polymers are polymers having ether bonds and ketone bonds in the molecular chain, and a method of substituting the ketone sites (ketone groups) in the polymer with hydrolyzable groups such as acetal groups and ketal groups can be mentioned. These hydrolyzable groups are known as protecting groups that can be derived from ketone groups and give ketone groups by hydrolysis. Examples of the hydrolysis treatment include the acid treatment described later.

[0034] The polymer electrolyte membrane is preferably a polymer electrolyte membrane used in a water electrolysis device. In a water electrolysis device, water is electrolyzed to generate oxygen at the anode and hydrogen at the cathode. However, there is a concern about safety due to the hydrogen generated at the cathode moving to the anode and mixing with oxygen. Therefore, the polymer electrolyte membrane disposed between the anode and the cathode preferably has low hydrogen permeability. From this viewpoint, hydrocarbon-based polymer electrolyte membranes are preferable because they have lower hydrogen permeability than fluorine-based polymer electrolyte membranes. Also, since the larger the thickness of the polymer electrolyte membrane, the smaller the hydrogen permeation amount, as described above, the thickness is preferably 40 μm or more, more preferably 50 μm or more, still more preferably 60 μm or more, and particularly preferably 70 μm or more. The upper limit is preferably 250 μm or less.

[0035] Also, the polymer electrolyte membrane preferably has a small dimensional change rate in both the dry state and the wet state. From this viewpoint, a higher tensile elastic modulus is preferable. The tensile elastic modulus of the polymer electrolyte membrane is preferably 300 MPa or more, more preferably 500 MPa or more, and particularly preferably 700 MPa or more. The upper limit is preferably 3,000 MPa or less.

[0036] [Laminated body] A structure in which a polymer film is formed on a support film according to an embodiment of the present invention is referred to as a "laminate". The support film is finally peeled off from the laminate. The formed polymer film is usually subjected to various processes according to the intended use. The support film of the laminate is peeled off from the laminate, for example, before, during, or after the following processing steps. That is, the support film serves to protect the polymer film during storage, distribution until the next processing step, or during the next processing step.

[0037] For example, taking a polymer electrolyte membrane used in electrochemistry such as a fuel cell or water electrolysis as an example, the formed polymer electrolyte membrane may be subjected to an acid treatment for protonation, but this acid treatment is preferably carried out in the state of the laminate from the viewpoint of preventing deformation and damage of the polymer electrolyte membrane. In addition, when the polymer electrolyte membrane is applied to the above-mentioned electrochemical applications, a catalyst layer is laminated on the polymer electrolyte membrane, but for the same reason as above, it is preferably carried out in the state of the laminate.

[0038] In addition, when the purpose is to manufacture the polymer film itself, the support film may be peeled off during the film-forming process of the polymer film.

[0039] The polymer film contained in the laminate is preferably the polymer film described above. For example, the thickness of the polymer film is preferably 40 μm or more, the tensile elastic modulus of the polymer film is preferably 300 MPa or more, and the polymer film is preferably composed of a polymer having an aromatic ring in the main chain.

[0040] When the polymer film contained in the laminate is a polymer electrolyte membrane, the polymer electrolyte membrane is preferably the polymer electrolyte membrane described above. For example, the polymer electrolyte membrane is preferably a hydrocarbon-based polymer electrolyte membrane, and particularly preferably an aromatic hydrocarbon-based polymer electrolyte membrane.

[0041] [Solution Casting Method of Polymer Film] A solution casting method of a polymer film will be specifically described, but the present invention is not limited thereto. The solution casting method of the polymer film according to an embodiment of the present invention includes a step of applying a polymer solution to a support film (hereinafter referred to as an application step) and a step of drying the applied polymer solution (hereinafter referred to as a drying step).

[0042] In the application step, the thickness of the polymer film can be adjusted by controlling the concentration and application amount of the polymer solution. The polymer solution is prepared by dissolving a polymer in a suitable solvent. As the solvent, for example, aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphonamide are preferred. In particular, when the polymer is a hydrocarbon-based polymer electrolyte, it is preferable to use a solvent containing an aprotic polar solvent.

[0043] The solid content concentration of the polymer in the polymer solution is preferably in the range of 1 to 40% by mass, more preferably in the range of 2 to 35% by mass, and particularly preferably in the range of 3 to 30% by mass.

[0044] In the application step, the greater the wet application amount when applying the polymer solution, the greater the tendency for the drying shrinkage of the polymer film. That is, the solution casting method of the polymer film according to an embodiment of the present invention is more suitable when the wet application amount when applying the polymer solution is relatively large. The above wet application amount is preferably 150 g / m 2 or more, preferably 200 g / m 2 or more, and particularly preferably 250 g / m 2 or more. The upper limit is preferably 800 g / m 2 or less.

[0045] The drying process is a process of evaporating the solvent from the polymer solution coated on the support film. As the drying method, a floating dryer, a heating furnace, or a heating roll can be used alone or in combination. Among these, a floating dryer is preferred. The floating dryer is a method of drying while blowing hot air from above and below the support film coated with the polymer solution and conveying it in a floating state.

[0046] The drying temperature is preferably 50 to 200 °C, more preferably 60 to 170 °C, and particularly preferably 70 to 160 °C. Also, the drying temperature can be changed stepwise within the above temperature range. For example, it can be set stepwise so that the temperature is relatively low in the initial stage of drying and relatively high in the later stage of drying. Specifically, the initial stage of drying can be set to 50 to 90 °C, the middle stage of drying to 90 to 120 °C, and the later stage of drying to 120 to 200 °C.

[0047] The above coating process and drying process are preferably carried out in a roll-to-roll manner. The roll-to-roll method is a method of carrying the support film unwound from the support film supply roll, performing the coating process and the drying process, and then winding it up in a roll shape.

[0048] In the solution casting method of the polymer film according to the embodiment of the present invention, after the drying process and before winding up, the support film may be peeled off, or it may be wound up in a laminated state (laminate) without peeling. In the present invention, it is preferable to wind up in a laminated state (laminate) of the support film and the polymer film. The reason is as described above.

[0049] Hereinafter, a film forming apparatus for carrying out the solution casting of the polymer film in a roll-to-roll manner will be described. FIG. 1 is a schematic side view of an example of a film forming apparatus that can be used for the film forming method of the polymer solution according to the embodiment of the present invention.

[0050] The film forming apparatus 1 includes an unwinding device 10, a coating device 20, a drying furnace 30, and a winding device 40. A polymer solution (not shown) is applied by the coating device 20 to the support film 12 unwound from the support film supply roll 11 pivotally supported by the unwinding device 10, and dried in the drying furnace 30, thereby forming a polymer film (not shown) on the support film 12. The laminate 13 with the polymer film formed on the support film 12 is wound into a roll by the winding device 40 to produce a laminate roll 14.

[0051] Examples of the coating device 20 include a slit die coater, a gravure coater, a bar coater, a roll coater, a doctor coater, a knife coater, a direct roll coater, a spray coater, a dip coater, a curtain coater, an extrusion coater, and a spin coater. Among these, a slit die coater is preferred because the coating width can be controlled with relatively high accuracy.

[0052] As the drying furnace 30, a floating dryer, a heating furnace, or a heating roll can be used alone or in combination. In this embodiment, a floating dryer is used. FIG. 2 is a schematic side view of the floating dryer. A plurality of air nozzles 31 are arranged in the upper and lower parts of the floating dryer 30, and hot air is blown from the upper and lower air nozzles 31 toward the support film 12 to dry the support film 12 while transporting it in a floating state. The distance (vertical distance) between the upper and lower air nozzles is usually arranged to be about 30 to 100 mm.

[0053] The floating dryer is configured to suck the solvent gas volatilized inside the dryer with an exhaust fan and send it to the facility that processes the solvent gas so that the solvent gas does not leak outside the apparatus. Therefore, it is necessary to maintain a negative pressure inside the dryer, and shutters 32 and 33 are installed at the inlet and outlet of the dryer, respectively. The shutters 32 and 33 are adjusted so that the support film 12 and the laminate 13 can pass through with a gap that is just enough, for example, 30 to 100 mm.

[0054] As described above, the support film coated with the polymer solution is configured to pass through a narrow gap. When curling occurs during the drying process of the polymer film, it may come into contact with the air nozzle or the shutter, and the polymer film may be scratched. Such problems are solved by using the support film of the present invention.

[0055] When the polymer membrane is a polymer electrolyte membrane, it preferably has an acid treatment step for protonation after film formation. The acid treatment step is preferably carried out in the state of the laminate. The acid treatment step is preferably carried out subsequent to the drying step. More specifically, the acid treatment step can be carried out continuously after the drying step, or can be carried out in a separate step after the laminate is once wound up. The acid treatment step has, for example, a step of immersing in an acidic solution, a water washing step, and a drying step in this order. As the acid treatment apparatus, for example, the apparatuses described in JP-A-2011-194593 and WO 2017 / 141710 can be used.

Examples

[0056] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. The various measurement methods and evaluation methods are as follows.

[0057] (1) Measurement of the molecular weight of the polymer The number average molecular weight and weight average molecular weight of the polymer solution were measured by GPC. HLC-8022GPC manufactured by Tosoh Corporation was used as an integrated device of an ultraviolet detector and a differential refractometer. Also, two TSK gel SuperHM-H (inner diameter 6.0 mm, length 15 cm) manufactured by Tosoh Corporation were used as GPC columns. Measurement was carried out at a flow rate of 0.2 mL / min using an N-methyl-2-pyrrolidone solvent (N-methyl-2-pyrrolidone solvent containing 10 mmol / L of lithium bromide), and the number average molecular weight and weight average molecular weight were determined by conversion to standard polystyrene.

[0058] (2) Measurement of ion exchange capacity (IEC) of the polyelectrolyte Measurement was carried out by the neutralization titration method shown in the following i) to iv). The measurement was carried out 3 times, and the average value was taken. i) After proton-exchanging the polyelectrolyte and wiping off the moisture of the polyelectrolyte sufficiently washed with pure water, it was vacuum dried at 100 °C for 12 hours or more to obtain the dry weight. ii) 50 mL of a 5 wt% aqueous sodium sulfate solution was added to the polyelectrolyte and left standing for 12 hours for ion exchange. iii) The resulting sulfuric acid was titrated using a 0.01 mol / L aqueous sodium hydroxide solution. As an indicator, 0.1 w / v% of a commercially available phenolphthalein solution for titration was added, and the point at which it turned light purplish red was taken as the end point. iv) IEC was determined by the following formula. IEC (meq / g) = [concentration of aqueous sodium hydroxide solution (mmol / ml) × dropwise addition amount (ml)] / dry weight of sample (g).

[0059] (3) Measurement of the thickness of the support film and the polymer film Measurement was carried out using Mitutoyo ID-C112 type set on Mitutoyo granite comparator stand BSG-20. Five points were measured and averaged for each.

[0060] (4) Measurement of the tensile elastic modulus of the polymer film In accordance with JIS K7127 (1999), using a precision universal testing machine Autograph "AG-Xplus" manufactured by Shimadzu Corporation, measurement was carried out 5 times under the following conditions and averaged. <Measurement Conditions> Temperature: 23°C ± 2°C Humidity: 50% ± 5% (RH) Load cell: 5N Distance between chucks: 30mm Sample width: 10mm.

[0061] (5) Measurement of Thermal Shrinkage Rate Measured in accordance with ASTM-D1204 (1984), the support film was cut into rectangles with a length of 250 mm × width of 10 mm in the TD direction and MD direction respectively to obtain samples. Marks were drawn on the samples at intervals of 200 mm, and measurements were taken for each of the 5 samples under the following conditions, and the average value of these was taken as the thermal shrinkage rate. · Heating conditions: Temperature 150°C, treatment time 30 minutes · Load: No load · Thermal shrinkage rate (%) = ((A - B) / A) × 100 (A: Distance between marks before heat treatment, B: Distance between marks after heat treatment).

[0062] (6) Confirmation of the Occurrence Status of Scratches on the Polymer Film Formed The coated width (700 mm) × length 5 m area of the polymer film formed was visually observed, and evaluation was carried out based on the following criteria according to the number of scratches. S: 0 pieces A: 1 - 5 pieces B: 6 - 10 pieces C: 11 - 20 pieces D: 21 - 30 pieces E: 31 pieces or more.

[0063] <Support Film> As the support film, the following polyethylene terephthalate (PET) films were prepared. · Support Film 1: “Lumirror” (registered trademark) #300-X10S (thickness 300 μm) manufactured by Toray Industries, Inc., TD direction thermal shrinkage rate 0.8%, MD direction thermal shrinkage rate 1.1% · Support Film 2: “Lumirror” (registered trademark) #250-X10S (thickness 250 μm) manufactured by Toray Industries, Inc., TD direction thermal shrinkage rate 0.8%, MD direction thermal shrinkage rate 1.2% · Support Film 3: "Lumirror" (registered trademark) #125-X10S (thickness 125 μm) manufactured by Toray Industries, Inc., with a heat shrinkage rate of 1.5% in the TD direction and 2.0% in the MD direction · Support Film 4: "Lumirror" (registered trademark) #350-S10 (thickness 350 μm) manufactured by Toray Industries, Inc., with a heat shrinkage rate of 0.5% in the TD direction and 0.8% in the MD direction · Support Film 5: "Lumirror" (registered trademark) #188-T60 (thickness 188 μm) manufactured by Toray Industries, Inc., with a heat shrinkage rate of 0.2% in the TD direction and 0.9% in the MD direction · Support Film 6: "Lumirror" (registered trademark) #125-T60 (thickness 125 μm) manufactured by Toray Industries, Inc., with a heat shrinkage rate of 0.3% in the TD direction and 1.0% in the MD direction.

[0064] [Synthesis of Hydrocarbon-based Polymer Electrolyte] A hydrocarbon-based polymer electrolyte composed of a polyetherketone (PEK)-based block copolymer was synthesized in the following manner.

[0065] [Synthesis Example 1] (Synthesis of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane (K-DHBP) represented by the following general formula (G1)) 49.5 g of 4,4'-dihydroxybenzophenone, 134 g of ethylene glycol, 96.9 g of trimethyl orthoformate, and 0.50 g of p-toluenesulfonic acid monohydrate were charged and dissolved in a 500 mL flask equipped with a stirrer, a thermometer, and a distillation tube. Then, the mixture was kept warm and stirred at 78 - 82 °C for 2 hours. Further, the internal temperature was gradually raised to 120 °C, and heating was continued until the distillation of methyl formate, methanol, and trimethyl orthoformate completely stopped. After cooling this reaction solution to room temperature, the reaction solution was diluted with ethyl acetate, and the organic layer was washed with 100 mL of a 5% aqueous potassium carbonate solution, separated, and the solvent was distilled off. 80 mL of dichloromethane was added to the residue to precipitate crystals, which were filtered and dried to obtain 52.0 g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane. When this crystal was analyzed by GC, it was found to be 99.8% 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane and 0.2% 4,4'-dihydroxybenzophenone.

[0066] [Chemical formula]

[0067] [Synthesis Example 2] (Synthesis of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following general formula (G2)) 109.1 g of 4,4'-difluorobenzophenone (Aldrich reagent) was reacted in 150 mL of fuming sulfuric acid (50% SO3) (Wako Pure Chemical Industries, Ltd. reagent) at 100 °C for 10 hours. Then, it was gradually added to a large amount of water, neutralized with NaOH, and 200 g of sodium chloride (NaCl) was added to precipitate the compound. The obtained precipitate was filtered off and recrystallized from an ethanol aqueous solution to obtain disodium-3,3'-disulfonate-4,4'-difluorobenzophenone represented by the following chemical formula (G2). The purity was 99.3%.

[0068] [Chemical formula]

[0069] [Synthesis Example 3] (Synthesis of nonionic oligomer a1 represented by the following general formula (G3)) 16.59 g of potassium carbonate (Aldrich reagent, 120 mmol), 25.83 g of K-DHBP obtained in Synthesis Example 1 (100 mmol), and 20.3 g of 4,4'-difluorobenzophenone (Aldrich reagent, 93 mmol) were placed in a 2,000 mL SUS polymerization apparatus equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap. After nitrogen substitution, 300 mL of N-methyl-2-pyrrolidone (NMP) and 100 mL of toluene were added, dehydrated at 160 °C, then the temperature was raised to remove toluene, and polymerization was carried out at 180 °C for 1 hour. Reprecipitation purification was performed with a large amount of methanol to obtain a terminal hydroxy form of nonionic oligomer a1. The number average molecular weight of this terminal hydroxy form of nonionic oligomer a1 was 10,000.

[0070] A 500 mL three-necked flask equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap was charged with 1.1 g (Aldrich reagent, 8 mmol) of potassium carbonate and 20.0 g (2 mmol) of the terminal hydroxy form of the above nonionic oligomer a1. After purging the inside of the apparatus with nitrogen, 100 mL of NMP and 30 mL of cyclohexane were added. After dehydration at 100 °C, the temperature was raised to remove cyclohexane. Further, 4.0 g (Aldrich reagent, 12 mmol) of decafluorobiphenyl was added, and the reaction was carried out at 105 °C for 1 hour. Reprecipitation purification was performed with a large amount of isopropyl alcohol to obtain a nonionic oligomer a1 (terminal: fluoro group) represented by the following general formula (G3). The number average molecular weight was 11,000.

[0071] [Chemical formula]

[0072] [Synthesis Example 4] (Synthesis of an ionic oligomer a2 represented by the following general formula (G4)) A 2,000 mL SUS polymerization apparatus equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap was charged with 27.6 g (Aldrich reagent, 200 mmol) of potassium carbonate, 12.9 g (50 mmol) of K-DHBP obtained in Synthesis Example 1, 9.3 g (Aldrich reagent, 50 mmol) of 4,4'-biphenol, 40.1 g (95 mmol) of disodium-3,3'-disulfonate-4,4'-difluorobenzophenone obtained in Synthesis Example 2, and 17.9 g (Wako Pure Chemical Industries, Ltd., 82 mmol) of 18-crown-6. After purging with nitrogen, 300 mL of NMP and 100 mL of toluene were added. After dehydration at 150 °C, the temperature was raised to remove toluene, and polymerization was carried out at 170 °C for 6 hours. Reprecipitation purification was performed with a large amount of isopropyl alcohol to obtain an ionic oligomer a2 (terminal: OM group) represented by the following general formula (G4). The number average molecular weight was 21,000. In formula (G4), M represents Na or K. Also, n represents a positive integer.

[0073] [Chemical formula]

[0074] [Synthesis Example 5] (Synthesis of PEK-based block copolymer b1) To a 2,000 mL SUS polymerization apparatus equipped with a stirrer, a nitrogen inlet tube, and a Dean-Stark trap, 0.56 g (Aldrich reagent, 4 mmol) of potassium carbonate and 21 g (1 mmol) of ionic oligomer a2 (terminal: OM group) were added, and the system was purged with nitrogen. Then, 100 mL of NMP and 30 mL of cyclohexane were added, and after dehydration at 100 °C, the temperature was raised to remove cyclohexane. Then, 11 g (1 mmol) of nonionic oligomer a1 (terminal: fluoro group) was added, and the reaction was carried out at 105 °C for 24 hours. The PEK-based block copolymer b1 was obtained by reprecipitation purification into a large amount of isopropyl alcohol. The weight-average molecular weight of this PEK-based block copolymer b1 was 350,000, and the ion-exchange capacity (IEC) was 2.1 meq / g.

[0075] [Synthesis Example 6] (Synthesis of polyether ketone-based block copolymer b2) A PEK-based block copolymer b2 was synthesized in the same manner as the PEK-based block copolymer b1, except that the ionic oligomer a2 was 33.6 g (1.6 mmol). The weight-average molecular weight of this PEK-based block copolymer b2 was 390,000, and the ion-exchange capacity (IEC) was 2.7 meq / g.

[0076] [Preparation of Polymer (Hydrocarbon-based Polymer Electrolyte) Solution] <Polymer Solution 1> The PEK-based block copolymer b1 synthesized above was dissolved in N-methyl-2-pyrrolidone (NMP), and further pressure-filtered using a glass fiber filter to prepare a polymer solution. The solid content concentration of this Polymer Solution 1 was 17% by mass.

[0077] <Polymer Solution 2> The PEK-based block copolymer b2 synthesized above was dissolved in N-methyl-2-pyrrolidone (NMP), and further pressure-filtered using a glass fiber filter to prepare a polymer solution. The solid content concentration of this polymer solution 2 was 17% by mass.

[0078] <Polymer solution 3> A polyarylene polymer obtained by sulfonating poly(4-phenoxybenzoyl-1,4-phenylene) with a weight average molecular weight of 95,000 using concentrated sulfuric acid (85 mol% sulfonated with respect to the repeating unit) was dissolved in a mixed solution of 640 parts by mass of N-methyl-2-pyrrolidone (NMP) and 210 parts by mass of methanol to prepare a polymer solution 3 with a solid content concentration of 15% by mass.

[0079] [Example 1] <Film formation of polymer film> Using the film-forming apparatus shown in FIGS. 1 and 2, the polymer solution 1 was applied to the support film 1 so that the dry thickness became 50 μm, dried, and a polymer film was formed on the support film 1, and this laminate was wound up in a roll shape. The drying temperature of the float dryer was set to 80 °C at the initial stage of drying, 110 °C at the middle stage, and 140 °C at the final stage. The vertical distance between the upper and lower air nozzles in the float dryer was 60 mm, and the gap widths of the inlet shutter and the outlet shutter were each set to 60 mm. The length of the support film used in the TD direction was 900 mm, and the coating width of the polymer solution was set to 700 mm. The tensile modulus of the obtained polymer film was measured by the method described in (4) above, and the occurrence of scratches was evaluated by the method described in (6) above.

[0080] [Examples 2 to 9 and Comparative Examples 1 to 9] A polymer film was formed and evaluated in the same manner as in Example 1, except that the type of the support film and the thickness of the polymer film were changed as shown in Table 1.

[0081] [Examples 11 to 13 and Comparative Examples 11 to 13] A polymer film was formed and evaluated in the same manner as in Examples 4 to 6 and Comparative Examples 4 to 6, except that the polymer solution 1 was changed to the polymer solution 2.

[0082] [Examples 21 to 23 and Comparative Examples 21 to 23] A polymer film was formed and evaluated in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3, except that Polymer Solution 1 was changed to Polymer Solution 3.

[0083] [Evaluation] The tensile modulus of the polymer film, the thermal shrinkage rate of the support film, and the occurrence of scratches are shown in Tables 1 and 2.

[0084] [Table 1]

[0085] [Table 2] [Explanation of Reference Signs]

[0086] 1 Film-forming apparatus 10 Unwinding apparatus 11 Support film supply roll 12 Support film 13 Laminate 14 Laminate roll 20 Coating apparatus 30 Drying furnace (floating dryer) 31 Air nozzle 32 Inlet shutter 33 Outlet shutter 40 Winding apparatus

Claims

1. A support film used for solution casting of a polymer film, wherein the thermal shrinkage rate in the direction orthogonal to the longitudinal direction of the support film (hereinafter referred to as the "MD direction") (hereinafter referred to as the "TD direction") is 0.4% or more, and the thickness of the support film is 150 μm or more, a support film for solution casting of a polymer film.

2. The support film for solution casting of a polymer film according to claim 1, wherein the ratio (TD / MD) of the thermal shrinkage rate in the TD direction to the thermal shrinkage rate in the MD direction of the support film is 0.50 to 0.

95.

3. The support film for solution casting of a polymer film according to claim 1, wherein the support film does not have a release layer.

4. The support film for solution casting of a polymer film according to claim 1, wherein the dry thickness of the polymer film is 40 μm or more.

5. The support film for solution casting of a polymer film according to claim 1, wherein the tensile elastic modulus of the polymer film is 300 MPa or more.

6. The support film for solution casting of a polymer film according to claim 1, wherein the polymer film is a film composed of a polymer having an aromatic ring in the main chain.

7. The support film for solution casting of a polymer film according to claim 1, wherein the polymer film is a polymer electrolyte membrane.

8. A laminate of the support film according to any one of claims 1 to 7 and a polymer film.

9. The laminate according to claim 8, wherein the thickness of the polymer film is 40 μm or more.

10. The laminate according to claim 8, wherein the tensile elastic modulus of the polymer film is 300 MPa or more.

11. The laminate according to claim 8, wherein the polymer film is a film composed of a polymer having an aromatic ring in the main chain.

12. The laminate according to claim 8, wherein the polymer film is a polymer electrolyte membrane.

13. A method for producing a polymer film, comprising a step of applying a polymer solution to the support film according to any one of claims 1 to 7, and a step of drying the applied polymer solution.

14. The method for producing a polymer film according to claim 13, wherein the polymer solution is a solution obtained by dissolving a polymer in a solvent containing an aprotic polar solvent.

15. The method for producing a polymer film according to claim 13, wherein the support film unwound from a support film supply roll is conveyed, and after the coating step and the drying step are carried out, it is wound up in a roll shape.

16. The method for forming a polymer film according to claim 13, which has an acid treatment step following the drying step.

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