Release film for manufacturing membrane electrode assembly

Abstract

The release film (2) has a base material layer (4) and a release layer (6) laminated on the base material layer (4). The main material of the release layer (6) is polystyrene resin. Preferably, the polystyrene resin is an alkyl-substituted polystyrene resin. Preferably, the alkyl-substituted polystyrene resin is poly (4-methylstyrene) and poly (4-tert-butylstyrene). The release layer (6) has a surface free energy of 42.0 mJ / m2 or less. An ion exchange resin layer can be formed on the release film (2).

Description

Technical Field

[0001] This specification discloses a release membrane used in the manufacturing process of a membrane electrode assembly (MEA) as a component of a solid polymer fuel cell. This specification further discloses a method for manufacturing this MEA. Background Technology

[0002] Solid polymer fuel cells have a membrane electrode assembly (MEA). The MEA comprises a solid polymer electrolyte membrane and two catalyst layers. Each catalyst layer is bonded to the surface of the electrolyte membrane. Both the electrolyte membrane and the catalyst layers are ion exchange resin layers.

[0003] In the fabrication of the membrane electrode assembly, an electrolyte membrane is formed on a first release membrane, and a catalyst layer is formed on a second release membrane. The catalyst layer abuts against the electrolyte membrane. The catalyst layer is bonded to the electrolyte membrane by heating and pressurizing the electrolyte membrane and the catalyst layer. Then, the first release membrane is peeled off from the electrolyte membrane. The first release membrane requires appropriate adhesion to the electrolyte membrane and appropriate peelability. The second release membrane is then peeled off from the catalyst layer. The second release membrane also requires appropriate adhesion to the catalyst layer and appropriate peelability.

[0004] Japanese Patent Application Publication No. 2014-175116 discloses a release film having a substrate layer and a release layer. The release layer is made of syndiotactic polystyrene. This release film exhibits excellent peelability to the ion exchange resin layer.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-175116 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Conventional release membranes do not provide sufficient peelability for the ion exchange resin layer. In particular, there is a need to improve the peelability of the proton conduction membrane, which serves as the electrolyte membrane.

[0010] The applicant's intention is to provide a release film with excellent peelability to ion exchange resin layers.

[0011] Solution for solving the problem

[0012] The release film disclosed in this specification can be used to manufacture membrane electrode assemblies. The release film has a substrate layer and a release layer laminated on the substrate layer. The main material of the release layer is a polystyrene-based resin. The surface free energy of the release layer is 42.0 mJ / m². 2the following.

[0013] Invention Effects

[0014] This release film exhibits excellent peelability to both the electrolyte membrane and the catalyst layer. It can contribute to the productivity of membrane electrode assemblies. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view showing a portion of a release film according to one embodiment.

[0016] Figure 2 It shows that it was used Figure 1 A flowchart of a method for manufacturing a release membrane electrode assembly. Detailed Implementation

[0017] Hereinafter, preferred embodiments will be described with appropriate reference to the accompanying drawings. The various components and combinations thereof in each embodiment are examples. Without departing from the spirit of this disclosure, changes such as omissions and substitutions of the components in the embodiments are possible, and other components may be added to the embodiments. The scope of this specification is not to be limited by the embodiments. The various solutions disclosed in this specification can also be combined with any other features disclosed in this specification.

[0018] [Release film]

[0019] Figure 1 The image shows a release film 2. The release film 2 has a substrate layer 4 and a release layer 6. The release layer 6 is laminated onto the substrate layer 4. The release film 2 may have other layers located between the substrate layer 4 and the release layer 6. The release film 2 may also have other layers located beneath the substrate layer 4.

[0020] [Substrate layer]

[0021] The substrate layer 4 is typically made of thermoplastic resin. As described later, the release film 2 is used in the manufacturing process of the membrane electrode assembly. In this manufacturing process, the release film 2 is heated. Then, tension is applied to the release film 2 during the manufacturing process. The thermoplastic resin, which is not easily stretched even when tension is applied at high temperatures, forms the substrate layer 4, thus suppressing the elongation of the release film 2. The release film 2, which is not easily stretched, can suppress the accidental peeling of the electrolyte membrane or catalyst layer, described later, during the manufacturing process of the membrane electrode assembly.

[0022] Examples of suitable thermoplastic resins for the substrate layer 4 include: polypropylene, cyclic polyolefins, polyesters, polyamides, polyimides, polycarbonates, polyphenylene ethers, polyphenylene sulfides, and cellulose esters. Polyesters are particularly preferred from the viewpoint of excellent heat resistance and flexibility. Examples of preferred polyesters include poly(C2-4) alkylene arylate resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Two or more resins may be used in combination in the substrate layer 4. The substrate layer 4 can be made of a thermosetting resin. The substrate layer 4 can be a composition containing resin and additives.

[0023] From the viewpoint of suppressing the elongation of the release film 2, the substrate layer 4 is preferably a stretch film. Uniaxial stretch film and biaxial stretch film can be used as the substrate layer 4. From the viewpoint of strength, biaxial stretch film is preferred. The longitudinal stretch ratio and transverse stretch ratio of the biaxial stretch film are preferably 1.5 or more, more preferably 2.5 or more, and particularly preferably 3.0 or more.

[0024] Figure 1 In the diagram, arrow T1 indicates the thickness of the substrate layer 4. The thickness T1 is preferably 1 μm or more and 300 μm or less. A substrate layer 4 with a thickness T1 of 1 μm or more can suppress the elongation of the release film 2 during the manufacturing process of the membrane electrode assembly. From this viewpoint, a thickness T1 is more preferably 10 μm or more, and particularly preferably 20 μm or more. A substrate layer 4 with a thickness T1 of 300 μm or less will not hinder the productivity of the membrane electrode assembly. From this viewpoint, a thickness T1 is more preferably 200 μm or less, and particularly preferably 100 μm or less.

[0025] [Release layer]

[0026] A typical release layer 6 is a resin film. The surface free energy of this release layer 6 is 42.0 mJ / m². 2 As described below, in the manufacturing process of the membrane electrode assembly, an electrolyte membrane is formed on the release membrane 2. The release membrane 2 is peeled off from the electrolyte membrane. The release membrane 2 needs to be peelable from the electrolyte membrane. In the manufacturing process of the membrane electrode assembly, a catalyst layer is also formed on the release membrane 2. The release membrane 2 is peeled off from the catalyst layer. The release membrane 2 needs to be peelable from the catalyst layer. The release layer 6 is in direct contact with the electrolyte membrane or the catalyst layer. The surface free energy is 42.0 mJ / m 2 The release layer 6 below facilitates the peeling of the electrolyte membrane and catalyst layer. From this perspective, the surface free energy is more preferably 41.5 mJ / m². 2 The following is particularly preferred: 41.0 mJ / m 2 The lower limit of achievable surface free energy is 20 mJ / m. 2 .

[0027] The surface free energy γs was calculated using the contact angles of water, diiodomethane, and bromonaphthalene measured by a contact angle meter. The contact angles were measured at 23°C and 60% RH. The measurement was taken 5 seconds after the liquid was added. The surface free energy γs was calculated based on the Kitazaki-Hata theory. The formula used for the calculation is as follows.

[0028] γs=γsd+γsp+γsh

[0029] In this mathematical formula, γsd represents the dispersion component, γsp represents the polar component, and γsh represents the hydrogen bonding component. As a suitable device for measurement, the fully automated contact angle meter "DMs-401 (Kyowa Interface Science Co., Ltd.)" can be cited as an example. Calculations can be performed using the calculation software within the contact angle meter's software (FAMAS).

[0030] As the material for release layer 6, various resins capable of achieving the aforementioned surface free energy can be used. Examples of preferred resins include: polystyrene resin, cyclic polyolefin resin, polypropylene resin, and polymethylpentene resin.

[0031] Polystyrene resin is particularly suitable for release layer 6. Polystyrene resin can be obtained by polymerizing aromatic vinyl monomers. Examples of aromatic vinyl monomers include: styrene; alkyl-substituted styrene; alkoxy-substituted styrene such as methoxystyrene and ethoxystyrene; halogen-substituted styrene such as o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-bromostyrene, and o-fluorostyrene; α-alkyl-substituted styrene; aryl-substituted styrene; and vinylnaphthalene. Polystyrene resin can be obtained from two or more monomers.

[0032] The preferred monomer is alkyl-substituted styrene. In alkyl-substituted styrene, a portion of the hydrogen atoms of the benzene ring are replaced by an alkyl group. Examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl. Examples of alkyl-substituted styrene include o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-ethylstyrene, p-isopropylstyrene, butylstyrene, p-tert-butylstyrene, and 2,4-dimethylstyrene. The polymerization energy of alkyl-substituted styrene yields alkyl-substituted polystyrene resins. These alkyl-substituted polystyrene resins contribute to achieving a polymerization energy of 42.0 mJ / m³. 2 The following surface free energy. This alkyl-substituted polystyrene resin contributes to the peelability of the release layer 6 ion exchange resin layers.

[0033] Polystyrene resins can also be obtained by copolymerizing alkyl-substituted styrene with other monomers. In this case, the ratio of alkyl-substituted styrene to all monomers is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 80 mol% or more. Examples of other monomers include: α-olefin monomers such as ethylene, propylene, butene, hexene, and octene; acrylic monomers such as (meth)acrylic acid, (meth)acrylate, (meth)ethyl acrylate, (meth)cyclohexyl methacrylate, and (meth)phenyl acrylate; cyanide monomers such as (meth)acrylonitrile; unsaturated polycarboxylic acid monomers such as maleic acid and their anhydrides; diene monomers such as butadiene and isoprene; and cyclic diene monomers such as cyclopentadiene and dicyclopentadiene.

[0034] Proton-conducting membranes are known as high-performance electrolyte membranes. These membranes have a high sulfonic acid density. This sulfonic acid hinders the peelability of the release membrane 2 from the proton-conducting membrane. In the manufacture of membrane electrode assemblies where the electrolyte membrane is a proton-conducting membrane, the peelability of the release membrane 2 is crucial. From the viewpoint of peelability of the proton-conducting membrane, polystyrene resins such as poly(4-methylstyrene) and poly(4-tert-butylstyrene) are particularly suitable for the release layer 6.

[0035] Polystyrene resins exist in three types: those with a random stereostructure (atactic polystyrene resin), those with an isotactic structure (isosactic polystyrene resin), and those with a syndiotactic stereostructure (syndiotactic polystyrene resin). From the viewpoint of providing adequate adhesion to the ion exchange resin layer, atactic polystyrene resin is preferred. Atactic polystyrene resin can be obtained by free radical polymerization of aromatic vinyl monomers. Atactic polystyrene resin is amorphous.

[0036] From the viewpoint of the heat resistance of release layer 6, the weight-average molecular weight of the polystyrene resin is preferably 10,000 or more, more preferably 100,000 or more, and particularly preferably 150,000 or more. From the viewpoint of ease of manufacture, the weight-average molecular weight is preferably 1,000,000 or less, more preferably 500,000 or less, and particularly preferably 350,000 or less. The weight-average molecular weight is determined by gel permeation chromatography using polystyrene conversion.

[0037] The material of release layer 6 may be a composition comprising polystyrene-based resin and additives. Alternatively, the material of release layer 6 may be a composition comprising polystyrene-based resin and other resins. Or, the material of release layer 6 may be a composition comprising polystyrene-based resin, other resins, and additives. In any composition, the ratio of polystyrene-based resin to the total amount of resin is 50% by mass or more. In other words, the main material of release layer 6 is polystyrene-based resin. More preferably, the ratio of polystyrene-based resin is 70% by mass or more, and particularly preferably 80% by mass or more. This ratio may be 100% by mass.

[0038] Examples of additives that can be included in the composition of release layer 6 include: fillers; lubricants such as waxes, fatty acid esters, and fatty acid amides; antistatic agents; stabilizers such as antioxidants, heat stabilizers, and light stabilizers; flame retardants; viscosity modifiers, thickeners, and defoamers. The composition may contain organic or inorganic particles.

[0039] Figure 1 In the diagram, arrow T2 indicates the thickness of the release layer 6. The thickness T2 is preferably 0.1 μm or more and 20 μm or less. A release membrane 2 with a release layer thickness T2 of 0.1 μm or more exhibits excellent peelability to the ion exchange resin layer. From this viewpoint, a thickness T2 is more preferably 0.3 μm or more, and particularly preferably 0.5 μm or more. A substrate layer 6 with a thickness T2 of 20 μm or less does not hinder the productivity of the membrane electrode assembly. From this viewpoint, a thickness T2 is more preferably 10 μm or less, and particularly preferably 5 μm or less.

[0040] [Thickness ratio]

[0041] The ratio (T2 / T1) of the thickness T2 of the release layer 6 to the thickness T1 of the substrate layer 4 is preferably 5 / 1 or more and 1 / 10 or less, more preferably 3 / 1 or more and 1 / 5 or less, and particularly preferably 2 / 1 or more and 1 / 3 or less.

[0042] [Manufacturing method of release film]

[0043] Examples of lamination methods for the release layer 6 to the substrate layer 4 include: coating, co-extrusion, extrusion lamination, compression bonding, and adhesive bonding. From the perspective of smoothness of the release layer 6, coating is preferred. In coating, a solution or dispersion containing a polystyrene-based resin is applied to the substrate layer 4. Examples of solvents for the solution and dispersion include: aromatic hydrocarbons such as benzene, toluene, and xylene; alicyclic hydrocarbons such as cyclohexane, cyclohexanone, and cyclohexene; halogenated hydrocarbons such as dichloromethane and dichloroethane; cyclic amides such as N-methyl-2-pyrrolidone; and cyclic ethers such as dioxane. Two or more solvents can be used together.

[0044] Preferred coating methods include, for example, roller coating, air knife coating, doctor blade coating, doctor stick coating, reverse coating, bar coating, comma coating, stencil coating, gravure coating, screen coating, spray coating, and spin coating. From a generality point of view, doctor blade coating and bar coating are preferred.

[0045] A coating film is obtained by coating method. The coating film is dried to obtain release layer 6. Release layer 6 is tightly bonded to substrate layer 4.

[0046] The release layer 6 can also be formed on a surface different from the substrate layer 4 by a coating method or the like. This release layer 6 is laminated onto the substrate layer 4 by means of an adhesive layer. The adhesive layer can be formed by an adhesive or a binder. Examples of adhesives include urethane-based adhesives, acrylic-based adhesives, polyester-based adhesives, and polyamide-based adhesives. Examples of binders include rubber-based binders, acrylic binders, olefin-based binders, and silicone-based binders. The thickness of the adhesive layer is preferably 1 μm or more and 40 μm or less.

[0047] [Method for manufacturing membrane electrode assembly]

[0048] Figure 2 An example of a method for manufacturing a membrane electrode assembly is shown. The method includes forming an electrolyte membrane (step 1), forming a front catalyst layer (step 2), bonding (step 3), peeling (step 4), forming a back catalyst layer (step 5), bonding (step 6), and peeling (step 7).

[0049] In the formation of the electrolyte membrane (step 1), firstly, the resin of the electrolyte membrane is dissolved in a solvent to obtain a first coating solution. Preferred solvents include, for example, water; alcohols such as methanol, ethanol, isopropanol, and 1-butanol; ketones such as acetone and methyl ethyl ketone; ethers such as dioxane and tetrahydrofuran; and sulfoxides such as dimethyl sulfoxide.

[0050] The first coating solution was applied to... Figure 1 The coating is applied to the release layer of the release film 2 (first release film). Preferred coating methods include, for example, roller coating, air knife coating, doctor blade coating, doctor bar coating, reverse coating, bar coating, comma coating, die coating, gravure coating, screen coating, spray coating, and spin coating. A coating film is obtained through coating.

[0051] The coating is heated. The heating temperature is preferably 80°C or higher and 200°C or lower, particularly preferably 100°C or higher and 150°C or lower. The coating is dried by heating to obtain an electrolyte membrane. Drying can be carried out at room temperature. The electrolyte membrane and the first release film form a laminate. In this laminate, the electrolyte membrane and the first release film are tightly bonded. The first release film abuts against the back side of the electrolyte membrane. The front side of the electrolyte membrane is exposed.

[0052] In the formation of the front catalyst layer (step 2), firstly, the resin of the catalyst layer is dissolved in a solvent to obtain a second coating solution. The preferred solvent is the same as the solvent described above for the first coating solution. This second coating solution is coated onto the release layer of the second release film. In this embodiment, the specifications of the second release film are the same as those of the first release film. The preferred coating method is the same as the coating method described above for the first coating solution. A coating film is obtained through coating.

[0053] The coating is heated. The heating temperature is preferably 50°C or higher and 150°C or lower, particularly preferably 60°C or higher and 120°C or lower. The coating is dried by heating to obtain a front catalyst layer. Drying can be carried out at room temperature. This front catalyst layer is bonded to a second release film. The second release film abuts against the front side of the front catalyst layer. The back side of the front catalyst layer is exposed.

[0054] In the bonding step (step 3), the back side of the front catalyst layer is overlapped with the front side of the electrolyte membrane. This yields a laminate comprising a first release membrane, an electrolyte membrane, a front catalyst layer, and a second release membrane. The laminate is then heated and pressurized. The heating temperature is preferably 80°C or higher and 200°C or lower, more preferably 100°C or higher and 180°C or lower, and particularly preferably 110°C or higher and 150°C or lower. The pressurization pressure is preferably 0.1 MPa or higher and 20 MPa or lower, more preferably 0.5 MPa or higher and 15 MPa or lower, and particularly preferably 1 MPa or higher and 10 MPa or lower. Through heating and pressurization, the front catalyst layer and the electrolyte membrane are firmly bonded together. As described above, each release membrane 2 has a soft and non-stretchable substrate layer 4. Furthermore, the release membrane 2 includes a release layer 6 that provides adequate adhesion to the ion exchange resin layer. Therefore, during the heating and pressurization process, accidental peeling of the first release membrane from the electrolyte membrane can be prevented. Furthermore, it can suppress the accidental peeling of the second release film from the front catalyst layer.

[0055] In the peeling process (step 4), the first release membrane is peeled off from the electrolyte membrane. The surface free energy of the first release membrane is 42.0 mJ / m. 2 Therefore, the first release membrane can be easily peeled off from the electrolyte membrane. Even when the electrolyte membrane is a proton-conducting membrane, the first release membrane can be easily peeled off from it. Even for electrolyte membranes with an equivalent mass of sulfonic acid of 800 g / mol (SO3H) or less, the first release membrane can be easily peeled off from it. Through peeling, the back side of the electrolyte membrane is exposed.

[0056] In the formation of the back-side catalyst layer (step 5), firstly, the resin of the catalyst layer is dissolved in a solvent to obtain a third coating solution. The preferred solvent is the same as the solvent described above for the first coating solution. This third coating solution is coated onto the release layer of the third release film. In this embodiment, the specifications of the third release film are the same as those of the first release film. The preferred coating method is the same as the coating method described above for the first coating solution. A coating film is obtained through coating.

[0057] The coating is heated. The preferred heating temperature is the same as the temperature described above for the second coating liquid. The coating is dried by heating to obtain a back-side catalyst layer. Drying can be carried out at room temperature. This back-side catalyst layer is bonded to a third release film. The third release film abuts against the back side of the back-side catalyst layer. The front side of the back-side catalyst layer is exposed.

[0058] In the bonding step (step 6), the front side of the back catalyst layer is laminated with the back side of the electrolyte membrane. This yields a laminate comprising a third release membrane, a back catalyst layer, an electrolyte membrane, a front catalyst layer, and a second release membrane. This laminate is then heated and pressurized. The heating temperature is preferably 80°C or higher and 200°C or lower, more preferably 100°C or higher and 180°C or lower, and particularly preferably 110°C or higher and 150°C or lower. The pressurization pressure is preferably 0.1 MPa or higher and 20 MPa or lower, more preferably 0.5 MPa or higher and 15 MPa or lower, and particularly preferably 1 MPa or higher and 10 MPa or lower. Through heating and pressurization, the back catalyst layer and the electrolyte membrane are firmly bonded together. As described above, each release membrane 2 has a soft and non-stretchable substrate layer 4. Furthermore, the release membrane 2 includes a release layer 6 that provides adequate adhesion to the ion exchange resin layer. Therefore, during the heating and pressurization process, accidental peeling of the second release membrane from the front catalyst layer can be prevented. Furthermore, it can suppress the accidental peeling of the third release membrane from the back catalyst layer.

[0059] In the peeling process (step 7), the second release film is peeled off from the front catalyst layer, and the third release film is peeled off from the back catalyst layer. The surface free energy of each release film 2 is 42.0 mJ / m². 2 Therefore, these membranes can be easily peeled off from the catalyst layer. Through peeling, a stack consisting of a back catalyst layer, an electrolyte membrane, and a front catalyst layer is obtained. A gas supply layer, etc., is further stacked on this stack to obtain a membrane electrode assembly.

[0060] The specifications of the second release film may differ from those of the first release film. The specifications of the third release film may also differ from those of the first release film.

[0061] Example

[0062] The effects of the embodiments are explained below, but the scope of this specification should not be interpreted in a limiting way based on the description of these embodiments.

[0063] [Example 1]

[0064] 10% by weight of poly(4-methylstyrene) (Sigma-Aldrich) was dissolved in 90% by weight of toluene to obtain a coating solution. On the other hand, a polyester film ("Cosmoshine (registered trademark) A4100", Toyobo Co., Ltd.) with an easy-to-adhesive layer was prepared as the substrate layer. The thickness of this polyester film was 50 μm. The coating solution was applied to the surface of the easy-to-adhesive layer of this polyester film using a #5 wire rod to obtain a coating film. This coating film was dried at 100°C for 1 minute to obtain the release film of Example 1.

[0065] [Example 2]

[0066] The coating solution was prepared by dissolving 10% by mass of poly(4-tert-butylstyrene) (Sigma-Aldrich) in 90% by mass of toluene. Otherwise, the same procedure as in Example 1 was followed to obtain the release film of Example 2.

[0067] [Comparative Example 1]

[0068] A coating solution was prepared by dissolving 10% by weight of a cyclic olefin resin (“TOPAS-6015”, Polyplastics) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Comparative Example 1.

[0069] [Comparative Example 2]

[0070] A coating solution was obtained by dissolving 10% by weight of a cyclic olefin resin (“ZEONEX480R”, ZEON Corporation, Japan) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Comparative Example 2.

[0071] [Comparative Example 3]

[0072] A coating solution was prepared by dissolving 10% by weight of polyarylate resin (“UNIFINER M-2040”, UNITIKA) in a mixture of 70% by weight of toluene and 20% by weight of methyl ethyl ketone. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Comparative Example 3.

[0073] [Comparative Example 4]

[0074] A coating solution was obtained by dissolving 10% by weight of polystyrene resin (“G200C”, Toyo Styrene) in 90% by weight of toluene. Otherwise, the same procedure as in Example 1 was followed to obtain the release film of Comparative Example 4.

[0075] [Comparative Example 5]

[0076] As a release film for Comparative Example 5, a commercially available resin film (“HN-200”, Kurabo Corporation) was prepared. The resin film was made of syndiotactic polystyrene. The thickness of the resin film was 35 μm.

[0077] [Comparative Example 6]

[0078] As a release film for Comparative Example 6, a commercially available resin film (“Opulent X-88B”, Mitsui Chemicals Co., Ltd.) was prepared. The resin film was made of polymethylpentene. The thickness of the resin film was 25 μm.

[0079] [Comparative Example 7]

[0080] 18 parts by weight of dry lamination adhesive (“TM-570 V”, Toyo-Morton) and 1 part by weight of curing agent (“CAT-RT37”, Toyo-Morton) were dissolved in an appropriate amount of ethyl acetate to obtain an adhesive with a solid content of 35% by weight. The adhesive was applied to a polyester film (“Cosmoshine A4100” mentioned above) with an easy-to-bond layer using a Mayer rod to obtain a coating film. The coating film was held at 80°C for 30 seconds to obtain an adhesive layer. The density of the adhesive layer was 20 g / m². The thickness of the adhesive layer was 2 μm. On the other hand, a biaxially stretched polypropylene film (“TORAYFAN 2500”, TORAY) was prepared. The thickness of the biaxially stretched polypropylene film was 40 μm. The biaxially stretched polypropylene film was overlapped with the adhesive layer and bonded by dry lamination to obtain the release film of Comparative Example 7.

[0081] [Evaluation of peelability-1]

[0082] An ion exchange resin solution (“Nafion DS2020CS”, DuPont) was prepared as the coating solution. The equivalent mass of this ion exchange resin solution was 1100 ± 20 g / mol (SO3H), and the solid content was 21% ± 1% by mass. The coating solution was applied to the release membrane using a Mayer rod to obtain a coating film. The coating film was dried at 100°C for 3 minutes. The coating film was then heat-treated at 160°C for 30 minutes to obtain an ion exchange layer. The ion exchange layer was peeled off from the release membrane using a universal testing machine (“AGS-X”, Shimadzu Corporation), and the peel force was measured. The conditions are described below.

[0083] Width of the test piece: 25mm.

[0084] Angle: 180°.

[0085] Speed: 600 mm / min.

[0086] The obtained peel strength is graded according to the following criteria.

[0087] A: Peel strength is less than 100mN / 25mm.

[0088] B: Peel strength is above 100mN / 25mm.

[0089] The results are shown in Tables 1 and 2 below.

[0090] [Evaluation of peelability-2]

[0091] Four parts by mass of an ion exchange resin solution (“Aquivion (registered trademark) D72-25 BS”, Sigma-Aldrich) and one part by mass of 2-propanol were mixed to obtain a coating solution. The equivalent mass of the ion exchange resin solution was 720 ± 20 g / mol (SO3H), and the solid content was 25% ± 1% by mass. The coating solution was applied to a release membrane using a Mayer rod to obtain a coating film. The coating film was dried at 100°C for 3 minutes. The coating film was then heat-treated at 160°C for 30 minutes to obtain an ion exchange layer. The ion exchange layer was peeled off from the release membrane using a universal testing machine (“AGS-X”, Shimadzu Corporation), and the peel strength was measured. The conditions are as follows.

[0092] Width of the test piece: 25mm.

[0093] Angle: 180°.

[0094] Speed: 600 mm / min.

[0095] The obtained peel strength is graded according to the following criteria.

[0096] A: Peel strength is less than 100mN / 25mm.

[0097] B: Peel strength is above 100mN / 25mm.

[0098] The results are shown in Tables 1 and 2 below.

[0099] [Curl Height]

[0100] The test piece was cut from the release film. The test piece measured 200mm × 200mm. A flat metal plate was placed inside a dryer at 120°C, and the test piece was placed on the plate. After 5 minutes, the test piece and the metal plate were removed from the dryer and allowed to cool to room temperature. The maximum amount of warping from the metal surface on each of the four edges of the test piece was measured. The obtained values ​​were graded according to the following criteria.

[0101] A: The maximum value is less than 1.0cm.

[0102] B: The maximum value is 1.0cm or more.

[0103] The results are shown in Tables 1 and 2 below.

[0104] [Table 1]

[0105]

[0106] [Table 2]

[0107]

[0108] As shown in Tables 1 and 2, the release films of each embodiment exhibit excellent performance. Based on these evaluation results, the advantages of this release film are evident.

[0109] [Public Projects]

[0110] Preferred implementations of the following projects are disclosed.

[0111] [Project 1]

[0112] A release film for manufacturing a membrane electrode assembly, the release film comprising a substrate layer and a release layer laminated thereon, wherein the main material of the release layer is a polystyrene-based resin, and the surface free energy of the release layer is 42.0 mJ / m 2 the following.

[0113] [Project 2]

[0114] According to the release film described in Project 1, the main material of the release layer is alkyl-substituted polystyrene resin.

[0115] [Project 3]

[0116] According to the release film described in Project 2, the main material of the release layer is 4-alkyl-substituted polystyrene resin.

[0117] [Project 4]

[0118] According to the release film described in Project 3, the main material of the release layer is poly(4-methylstyrene) or poly(4-tert-butylstyrene).

[0119] [Project 5]

[0120] According to any one of items 1 to 4, the release film, wherein the main material of the release layer is random polystyrene.

[0121] [Project 6]

[0122] A method for manufacturing a membrane electrode assembly, the method comprising: (1) a step of forming an electrolyte membrane on the surface of a first release membrane, wherein the first release membrane comprises a substrate layer and a release layer laminated thereon, the main material of the release layer being a polystyrene-based resin, and the surface free energy of the release layer being 42.0 mJ / m 2 The steps are as follows: (2) forming a catalyst layer on the surface of the second release film; (3) bonding the catalyst layer to the electrolyte film; and (4) peeling the first release film from the electrolyte film.

[0123] [Project 7]

[0124] According to the manufacturing method described in Project 6, in the above-mentioned step (1), a proton-conducting membrane as the electrolyte membrane is formed.

[0125] [Project 8]

[0126] A laminate comprising a release film and an electrolyte membrane laminated thereon, wherein the release film has a substrate layer and a release layer laminated thereon, the main material of the release layer being a polystyrene-based resin, and the surface free energy of the release layer being 42.0 mJ / m 2 The sulfonic acid equivalent mass of the above electrolyte membrane is below 800 g / mol (SO3H).

[0127] Industrial availability

[0128] The release film described above is suitable for the manufacture of various molded articles formed from ion exchange resins.

[0129] 2: Release film;

[0130] 4: Substrate layer;

[0131] 6: Release layer.

Claims

1. A release film used in the manufacture of a membrane electrode assembly, The release film has a substrate layer and a release layer laminated on the substrate layer. The main material of the release layer is polystyrene resin. The surface free energy of the release layer is 42.0 mJ / m 2 the following.

2. The release film according to claim 1, wherein, The main material of the release layer is alkyl-substituted polystyrene resin.

3. The release film according to claim 2, wherein, The main material of the release layer is 4-alkyl-substituted polystyrene resin.

4. The release film according to claim 3, wherein, The main material of the release layer is poly(4-methylstyrene) or poly(4-tert-butylstyrene).

5. The release film according to claim 1 or 2, wherein, The main material of the release layer is random polystyrene.

6. A method for manufacturing a membrane electrode assembly, the method comprising: (1) In the step of forming an electrolyte membrane on the surface of a first release film, the first release film has a substrate layer and a release layer laminated on the substrate layer, the main material of the release layer is a polystyrene resin, and the surface free energy of the release layer is 42.0 mJ / m 2 the following; (2) The process of forming a catalyst layer on the surface of the second release film; (3) The process of bonding the catalyst layer to the electrolyte membrane; and (4) The process of peeling the first release film from the electrolyte membrane.

7. The manufacturing method according to claim 6, wherein, In the process (1), a proton-conducting membrane, which serves as the electrolyte membrane, is formed.

8. A laminate comprising a release membrane and an electrolyte membrane laminated thereon, The release film has a substrate layer and a release layer laminated on the substrate layer. The main material of the release layer is polystyrene resin, and the surface free energy of the release layer is 42.0 mJ / m. 2 the following, The sulfonic acid equivalent mass of the electrolyte membrane is below 800 g / mol (SO3H).

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