Release film used for production of membrane electrode assembly

Abstract

A release film 2 comprises a base material layer 4 and a release layer 6 that is laminated on the base material layer 4. The main material of the release layer 6 is a polystyrene-based resin. A preferable polystyrene resin is an alkyl group substituted polystyrene resin. Preferable alkyl group substituted polystyrene resins are poly(4-methylstyrene) and poly(4-tert-butylstyrene). The surface free energy of the release layer 6 is not more than 42.0 mJ / m2. An ion exchange resin layer can be formed on the release film 2.

Description

Release film used in the manufacture of membrane electrode assemblies

[0001] The present specification discloses a release film used in the manufacturing process of a membrane electrode assembly, which is a component of a polymer electrolyte fuel cell. The present specification further discloses a method for manufacturing the membrane electrode assembly.

[0002] A polymer electrolyte fuel cell has a membrane electrode assembly. The membrane electrode assembly includes 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 manufacture of a membrane electrode assembly, an electrolyte membrane is formed on a first release film, and a catalyst layer is formed on a second release film. This catalyst layer is brought into contact with the electrolyte membrane. The electrolyte membrane and catalyst layer are heated and pressurized, thereby bonding the catalyst layer to the electrolyte membrane. The first release film is then peeled off from the electrolyte membrane. The first release film is required to have appropriate adhesion to the electrolyte membrane and appropriate releasability. The second release film is peeled off from the catalyst layer. The second release film is required to have appropriate adhesion to the catalyst layer and appropriate releasability.

[0004] Japanese Patent Application Laid-Open No. 2014-175116 discloses a release film having a base layer and a release layer. The release layer is made of syndiotactic polystyrene. This release film has excellent releasability from an ion-exchange resin layer.

[0005] JP 2014-175116 A

[0006] Conventional release films have insufficient releasability from ion-exchange resin layers, and there is a demand for improvement in releasability, particularly from proton conductive membranes serving as electrolyte membranes.

[0007] The present applicant intends to provide a release film that has excellent releasability from an ion exchange resin layer.

[0008] The release film disclosed herein can be used in the production of a membrane electrode assembly. This release film has a substrate layer and a release layer laminated on the substrate layer. The release layer is mainly made of a polystyrene resin. The surface free energy of this release layer is 42.0 mJ / m ２ The following is the result.

[0009] This release film has excellent releasability from the electrolyte membrane and from the catalyst layer, and can contribute to the productivity of the membrane electrode assembly.

[0010] Fig. 1 is a cross-sectional view showing a part of a release film according to an embodiment, and Fig. 2 is a flowchart showing a method for manufacturing a membrane electrode assembly using the release film of Fig. 1.

[0011] Preferred embodiments will be described below with reference to the drawings as appropriate. Each configuration and combination thereof in each embodiment is an example. Modifications such as omission or substitution of configurations in the embodiments are possible, and other configurations can also be added to the embodiments, without departing from the spirit of the present disclosure. The scope of the disclosure of this specification should not be interpreted as being limited by the embodiments. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification.

[0012] [Release Film] Figure 1 shows a release film 2. This release film 2 has a base layer 4 and a release layer 6. The release layer 6 is laminated on the base layer 4. The release film 2 may have another layer located between the base layer 4 and the release layer 6. The release film 2 may have another layer located below the base layer 4.

[0013] [Substrate Layer] A typical material for the substrate layer 4 is a thermoplastic resin. As described below, the release film 2 is used in the manufacturing process of a membrane electrode assembly. In this manufacturing process, the temperature of the release film 2 rises. Furthermore, tension is applied to this release film 2 in the manufacturing process. The substrate layer 4, which is made of a thermoplastic resin that does not stretch easily even when tension is applied in a high-temperature environment, can suppress the stretching of the release film 2. The release film 2 that does not stretch easily can suppress unintended peeling of the electrolyte membrane or catalyst layer, which will be described later, in the manufacturing process of the membrane electrode assembly.

[0014] Examples of thermoplastic resins suitable for the substrate layer 4 include polypropylene, cyclic polyolefin, polyester, polyamide, polyimide, polycarbonate, polyphenylene ether, polyphenylene sulfide, and cellulose ester. Polyester is 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 material of the substrate layer 4 may be a thermosetting resin. The material of the substrate layer 4 may be a composition containing a resin and an additive.

[0015] A preferred base material layer 4 from the viewpoint of suppressing elongation of the release film 2 is a stretched film. A uniaxially stretched film and a biaxially stretched film can be used as the base material layer 4. From the viewpoint of strength, a biaxially stretched film is preferred. The longitudinal stretching ratio and the transverse stretching ratio of the biaxially stretched film are each preferably 1.5 or more, more preferably 2.5 or more, and particularly preferably 3.0 or more.

[0016] In FIG. 1 , an arrow T1 indicates the thickness of the base material layer 4. The thickness T1 is preferably 1 μm or more and 300 μm or less. A base material layer 4 having a thickness T1 of 1 μm or more can suppress elongation of the release film 2 during the manufacturing process of the membrane electrode assembly. From this viewpoint, the thickness T1 is more preferably 10 μm or more, and particularly preferably 20 μm or more. A base material layer 4 having a thickness T1 of 300 μm or less does not inhibit the productivity of the membrane electrode assembly. From this viewpoint, the thickness T1 is more preferably 200 μm or less, and particularly preferably 100 μm or less.

[0017] [Release Layer] A typical release layer 6 is a resin film. The surface free energy of this release layer 6 is 42.0 mJ / m ２ As will be described later, in the manufacturing process of the membrane electrode assembly, an electrolyte membrane is formed on a release film 2. The release film 2 is peeled off from this electrolyte membrane. The release film 2 must be able to be peeled off from the electrolyte membrane. In the manufacturing process of the membrane electrode assembly, a catalyst layer is also formed on the release film 2. The release film 2 is peeled off from this catalyst layer. The release film 2 must be able to be peeled off 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 having a surface free energy of 41.5 mJ / m or less can contribute to the peelability of the electrolyte membrane and the catalyst layer. ２ More preferably, 41.0 mJ / m or less ２ The following is particularly preferred: The lower limit of the achievable surface free energy is 20 mJ / m ２ is.

[0018] The surface free energy γs is calculated using the contact angles of water, diiodomethane, and bromonaphthalene measured with a contact angle meter. The contact angle is measured in an environment with a temperature of 23°C and a humidity of 60% RH. The contact angle is measured 5 seconds after the liquid is dropped. The surface free energy γs is calculated based on the Kitazaki-Hata theory. The formula for calculation is as follows: γs = γsd + γsp + γsh. In this formula, γsd represents the dispersion component, γsp represents the polar component, and γsh represents the hydrogen bond component. An example of a device suitable for measurement is the fully automatic contact angle meter "DMs-401 (Kyowa Interface Science Co., Ltd.)." Calculations can be performed using the calculation software (FAMAS) included in the contact angle meter.

[0019] Various resins capable of achieving the above-mentioned surface free energy can be used as the material of the release layer 6. Preferred examples of the resin include polystyrene resin, cyclic polyolefin resin, polypropylene resin, and polymethylpentene resin.

[0020] A resin particularly suitable for the release layer 6 is polystyrene resin. Polystyrene resin can be obtained by polymerization of aromatic vinyl monomers. Examples of aromatic vinyl monomers include styrene; alkyl-substituted styrenes; alkoxy-substituted styrenes such as methoxystyrene and ethoxystyrene; halogen-substituted styrenes such as o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-bromostyrene and o-fluorostyrene; α-alkyl-substituted styrenes; aryl-substituted styrenes; and vinylnaphthalene. The polystyrene resin may be obtained from two or more types of monomers.

[0021] A preferred monomer is alkyl-substituted styrene. In alkyl-substituted styrene, some of the hydrogen atoms on the benzene ring are substituted with alkyl groups. Examples of the alkyl group include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. Examples of alkyl-substituted styrene include o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-ethylstyrene, p-isopropylstyrene, butylstyrene, p-t-butylstyrene, and 2,4-dimethylstyrene. Polymerization of alkyl-substituted styrene yields an alkyl-substituted polystyrene resin. This alkyl-substituted polystyrene resin has a specific surface area of ​​42.0 mJ / m ２ This alkyl group-substituted polystyrene resin can contribute to achieving a surface free energy of not more than 1000 kJ / cm 2 .mu.m.sup.2 + ...

[0022] Polystyrene-based 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, methyl (meth)acrylate, ethyl (meth)acrylate, cyclohexyl (meth)acrylate, and phenyl (meth)acrylate; vinyl cyanide monomers such as (meth)acrylonitrile; unsaturated polycarboxylic acid monomers and their acid anhydrides such as maleic acid; diene monomers such as butadiene and isoprene; and cyclic diene monomers such as cyclopentadiene and dicyclopentadiene.

[0023] Proton conductive membranes are known as high-performance electrolyte membranes. These proton conductive membranes have a high sulfonic acid density. This sulfonic acid can inhibit the releasability of the release film 2 from the proton conductive membrane. In the production of a membrane electrode assembly in which the electrolyte membrane is a proton conductive membrane, the releasability of the release film 2 is particularly required. From the viewpoint of releasability from the proton conductive membrane, polystyrene resins particularly suitable for the release layer 6 are poly(4-methylstyrene) and poly(4-tert-butylstyrene).

[0024] Polystyrene resins include those with an atactic structure (atactic polystyrene resin), those with an isotactic structure (isotactic polystyrene resin), and those with a syndiotactic structure (syndiotactic polystyrene resin). From the viewpoint of adequate adhesion to the ion exchange resin layer, atactic polystyrene resin is preferred. Atactic polystyrene resin can be obtained by radical polymerization of aromatic vinyl monomers. Atactic polystyrene resin is amorphous.

[0025] From the viewpoint of heat resistance of the 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 production, 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 measured in terms of polystyrene by gel permeation chromatography.

[0026] The material of the release layer 6 may be a composition containing a polystyrene-based resin and an additive. The material of the release layer 6 may be a composition containing a polystyrene-based resin and another resin. The material of the release layer 6 may be a composition containing a polystyrene-based resin, another resin, and an additive. In either composition, the ratio of the polystyrene-based resin to the total amount of resin is 50% by mass or more. In other words, the main material of the release layer 6 is a polystyrene-based resin. The ratio of the polystyrene-based resin is more preferably 70% by mass or more, and particularly preferably 80% by mass or more. This ratio may be 100% by mass.

[0027] Examples of additives that can be contained in the composition of the 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 antifoaming agents. The composition may also contain organic or inorganic particles.

[0028] In FIG. 1 , 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 film 2 having a release layer 6 with a thickness T2 of 0.1 μm or more has excellent releasability for the ion exchange resin layer. From this viewpoint, the thickness T2 is more preferably 0.3 μm or more, and particularly preferably 0.5 μm or more. A release layer 6 with a thickness T2 of 20 μm or less does not inhibit the productivity of the membrane electrode assembly. From this viewpoint, the thickness T2 is more preferably 10 μm or less, and particularly preferably 5 μm or less.

[0029] [Thickness Ratio] The ratio (T2 / T1) of the thickness T2 of the release layer 6 to the thickness T1 of the base 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.

[0030] [Method of Manufacturing Release Film] Examples of methods for laminating the release layer 6 onto the base layer 4 include a coating method, a coextrusion method, an extrusion lamination method, a pressure bonding method, and an adhesive method. From the viewpoint of smoothness of the release layer 6, a coating method is preferred. In the coating method, a solution or dispersion containing a polystyrene-based resin is coated onto the base 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 may be used in combination.

[0031] Preferred coating methods include a roll coater method, an air knife coater method, a blade coater method, a rod coater method, a reverse coater method, a bar coater method, a comma coater method, a die coater method, a gravure coater method, a screen coater method, a spray method, and a spinner method. From the viewpoint of versatility, the blade coater method and the bar coater method are preferred.

[0032] A coating film is obtained by the coating method. The coating film is dried to obtain the release layer 6. The release layer 6 is in close contact with the substrate layer 4.

[0033] A release layer 6 may be formed on a surface different from that of the base layer 4 by a coating method or the like. This release layer 6 is laminated to the base layer 4 via an adhesive layer. The adhesive layer may be formed from an adhesive or a pressure-sensitive adhesive. Examples of adhesives include urethane-based adhesives, acrylic-based adhesives, polyester-based adhesives, and polyamide-based adhesives. Examples of pressure-sensitive adhesives include rubber-based adhesives, acrylic-based adhesives, olefin-based adhesives, and silicone-based adhesives. The thickness of the adhesive layer is preferably 1 μm or more and 40 μm or less.

[0034] [Method for Manufacturing a Membrane Electrode Assembly] An example of a method for manufacturing a membrane electrode assembly is shown in Figure 2. This manufacturing 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).

[0035] In the formation of the electrolyte membrane (STEP 1), first, the resin of this electrolyte membrane is dissolved in a solvent to obtain a first coating liquid. Preferred examples of the solvent include 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.

[0036] This first coating liquid is coated onto the release layer of release film 2 (first release film) shown in Figure 1. Preferred coating methods include a roll coater method, an air knife coater method, a blade coater method, a rod coater method, a reverse coater method, a bar coater method, a comma coater method, a die coater method, a gravure coater method, a screen coater method, a spray method, and a spinner method. A coating film is obtained by coating.

[0037] This coating film is heated. The heating temperature is preferably 80°C or higher and 200°C or lower, and particularly preferably 100°C or higher and 150°C or lower. The coating film dries by heating, and an electrolyte membrane is obtained. Drying may be performed at room temperature. This electrolyte membrane and the first release film constitute a laminate. In this laminate, the electrolyte membrane is in close contact with the first release film. The back side of the electrolyte membrane abuts against the first release film. The front side of the electrolyte membrane is exposed.

[0038] In forming the front catalyst layer (STEP 2), first, the resin of this catalyst layer is dissolved in a solvent to obtain a second coating liquid. Preferred solvents are the same as those described above for the first coating liquid. This second coating liquid 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. Preferred coating methods are the same as those described above for the first coating liquid. A coating film is obtained by coating.

[0039] This coating film is heated. The heating temperature is preferably 50°C or higher and 150°C or lower, and particularly preferably 60°C or higher and 120°C or lower. The coating film is dried by heating, and a front catalyst layer is obtained. Drying may be performed at room temperature. This front catalyst layer is in close contact with the second release film. The front side of the front catalyst layer is in contact with the second release film. The rear side of the front catalyst layer is exposed.

[0040] In the bonding step (STEP 3), the rear surface of the front catalyst layer is mated with the front surface of the electrolyte membrane. This results in a laminate including a first release film, an electrolyte membrane, a front catalyst layer, and a second release film. This laminate is heated and pressurized. The heating temperature is preferably 80°C to 200°C, more preferably 100°C to 180°C, and particularly preferably 110°C to 150°C. The pressing pressure is preferably 0.1 MPa to 20 MPa, more preferably 0.5 MPa to 15 MPa, and particularly preferably 1 MPa to 10 MPa. Heating and pressing firmly adhere the front catalyst layer to the electrolyte membrane. As described above, each release film 2 has a flexible and non-stretchable substrate layer 4. Furthermore, this release film 2 includes a release layer 6 that has adequate adhesion to the ion-exchange resin layer. Therefore, unintended peeling of the first release film from the electrolyte membrane can be suppressed during the heating and pressing process. Furthermore, unintentional peeling of the second release film from the front catalyst layer can be suppressed.

[0041] In the peeling step (STEP 4), the first release film is peeled off from the electrolyte membrane. The surface free energy of the first release film is 42.0 mJ / m ２ Therefore, the first release film can be easily peeled off from the electrolyte membrane. Even when the electrolyte membrane is a proton conductive membrane, the first release film can be easily peeled off from the proton conductive membrane. ３ Even in the case of an electrolyte membrane having a hardness of 0.1 mm or less, the first release film can be easily peeled off from the electrolyte membrane. The peeling exposes the back surface of the electrolyte membrane.

[0042] In forming the backside catalyst layer (STEP 5), the resin of this catalyst layer is first dissolved in a solvent to obtain a third coating liquid. The preferred solvent is the same as that described above for the first coating liquid. This third coating liquid 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 that described above for the first coating liquid. A coating film is obtained by coating.

[0043] This coating film is heated. The preferred heating temperature is the same as that described above for the second coating liquid. The coating film is dried by heating, resulting in a back-side catalyst layer. Drying may be performed at room temperature. This back-side catalyst layer is in close contact with a third release film. The back side of the back-side catalyst layer is in contact with the third release film. The front side of the back-side catalyst layer is exposed.

[0044] In bonding (STEP 6), the front surface of the backside catalyst layer is mated with the backside surface of the electrolyte membrane. This results in a laminate including a third release film, a backside catalyst layer, an electrolyte membrane, a frontside catalyst layer, and a second release film. This laminate is heated and pressurized. The heating temperature is preferably 80°C to 200°C, more preferably 100°C to 180°C, and particularly preferably 110°C to 150°C. The pressurizing pressure is preferably 0.1 MPa to 20 MPa, more preferably 0.5 MPa to 15 MPa, and particularly preferably 1 MPa to 10 MPa. Heating and pressurization firmly adhere the backside catalyst layer to the electrolyte membrane. As described above, each release film 2 has a flexible and non-stretchable substrate layer 4. Furthermore, this release film 2 includes a release layer 6 that has adequate adhesion to the ion-exchange resin layer. Therefore, in the heating and pressurizing step, unintentional peeling of the second release film from the front catalyst layer can be suppressed, and further, unintentional peeling of the third release film from the back catalyst layer can be suppressed.

[0045] In the peeling step (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 / m ２ Therefore, these films can be easily peeled off from the catalyst layer. By peeling, a laminate consisting of the back-side catalyst layer, the electrolyte membrane, and the front-side catalyst layer is obtained. A gas supply layer and the like are further laminated on this laminate to obtain a membrane electrode assembly.

[0046] The specifications of the second release film may be different from those of the first release film, and the specifications of the third release film may be different from those of the first release film.

[0047] The effects of the examples will be explained below, but the scope of the present disclosure should not be construed as being limited based on the description of these examples.

[0048] Example 1 A coating liquid was obtained by dissolving 10% by mass of poly(4-methylstyrene) (Sigma-Aldrich) in 90% by mass of toluene. On the other hand, a polyester film with an easy-adhesion layer (Cosmoshine (registered trademark) A4100, Toyobo Co., Ltd.) was prepared as a substrate layer. The thickness of this polyester film was 50 μm. The coating liquid was applied to the surface of the easy-adhesion layer of this polyester film using a wire bar #5 to obtain a coating film. This coating film was held at a temperature of 100° C. for 1 minute and dried, obtaining the release film of Example 1.

[0049] Example 2 A release film of Example 2 was obtained in the same manner as in Example 1, except that a coating liquid was obtained by dissolving 10% by mass of poly(4-tert-butylstyrene) (Sigma-Aldrich) in 90% by mass of toluene.

[0050] Comparative Example 1 A release film of Comparative Example 1 was obtained in the same manner as in Example 1, except that 10% by mass of a cyclic olefin resin ("TOPAS-6015", Polyplastics Co., Ltd.) was dissolved in 90% by mass of toluene to obtain a coating liquid.

[0051] Comparative Example 2 A release film of Comparative Example 2 was obtained in the same manner as in Example 1, except that 10% by mass of a cyclic olefin resin ("ZEONEX 480R", Zeon Corporation) was dissolved in 90% by mass of toluene to obtain a coating liquid.

[0052] [Comparative Example 3] A release film of Comparative Example 3 was obtained in the same manner as in Example 1, except that a coating liquid was obtained by dissolving 10% by mass of a polyarylate resin ("UNIFINER M-2040", Unitika Ltd.) in a mixed liquid of 70% by mass of toluene and 20% by mass of methyl ethyl ketone.

[0053] [Comparative Example 4] A release film of Comparative Example 4 was obtained in the same manner as in Example 1, except that 10% by mass of polystyrene resin ("G200C", Toyo Styrene Co., Ltd.) was dissolved in 90% by mass of toluene to obtain a coating liquid.

[0054] [Comparative Example 5] A commercially available resin film ("HN-200", Kurabo Industries, Ltd.) was prepared as a release film for Comparative Example 5. The material of this resin film was syndiotactic polystyrene. The thickness of this resin film was 35 μm.

[0055] [Comparative Example 6] A commercially available resin film ("Opulent X-88B", Mitsui Chemicals, Inc.) was prepared as a release film for Comparative Example 6. The material of this resin film was polymethylpentene. The thickness of this resin film was 25 μm.

[0056] Comparative Example 7 18 parts by mass of a dry laminating adhesive ("TM-570V", Toyo-Morton Co., Ltd.) and 1 part by mass of a curing agent ("CAT-RT37", Toyo-Morton Co., Ltd.) were dissolved in an appropriate amount of ethyl acetate to obtain an adhesive with a solids content of 35% by mass. This adhesive was applied to a polyester film with an easy-adhesion layer (the aforementioned "Cosmoshine (registered trademark) A4100") using a Mayer bar to obtain a coating film. This coating film was held at a temperature of 80°C for 30 seconds to obtain an adhesive layer. The density of this adhesive layer was 20 g / m ２ The thickness of this adhesive layer was 2 μm. On the other hand, a biaxially oriented polypropylene film ("Torayfan (registered trademark) 2500", Toray Industries, Inc.) was prepared. The thickness of this biaxially oriented polypropylene film was 40 μm. This biaxially oriented polypropylene film was overlaid on the adhesive layer and bonded by a dry lamination method to obtain a release film of Comparative Example 7.

[0057] [Evaluation of Peelability - 1] An ion exchange resin solution ("Nafion (registered trademark) DS2020CS", DuPont) was prepared as the coating liquid. The equivalent mass of this ion exchange resin solution was 1100±20 g / mol (SO3H) and the solid content was 21% by mass±1% by mass. The coating liquid was applied onto a release film using a Mayer bar to obtain a coating film. This coating film was held at a temperature of 100°C for 3 minutes and dried. This coating film was further subjected to a heat treatment at a temperature of 160°C for 30 minutes to obtain an ion exchange layer. The ion exchange layer was peeled from the release film using an autograph ("AGS-X", Shimadzu Corporation), and the peel force was measured. The conditions were as follows: width of test piece: 25 mm, angle: 180°, speed: 600 mm / min. The obtained peel strength was rated according to the following criteria. A: Peel strength is less than 100 mN / 25 mm. B: Peel strength is 100 mN / 25 mm or more. The results are shown in Tables 1 and 2 below.

[0058] [Removability Evaluation-2] A coating solution was obtained by mixing 4 parts by mass of an ion exchange resin solution ("Aquivion (registered trademark) D72-25BS", Sigma-Aldrich) and 1 part by mass of 2-propanol. The equivalent mass of this ion exchange resin solution was 720±20 g / mol (SO3H) and the solids content was 25% by mass±1% by mass. The coating solution was applied to a release film using a Mayer bar to obtain a coating film. This coating film was held at a temperature of 100°C for 3 minutes and dried. This coating film was further subjected to a heat treatment by holding it at a temperature of 160°C for 30 minutes to obtain an ion exchange layer. The ion exchange layer was peeled from the release film using an autograph ("AGS-X", Shimadzu Corporation), and the peel force was measured. The conditions were as follows. Width of test piece: 25 mm Angle: 180° Speed: 600 mm / min The obtained peel strength was ranked according to the following criteria: A: Peel strength is less than 100 mN / 25 mm B: Peel strength is 100 mN / 25 mm or more The results are shown in Tables 1 and 2 below.

[0059] [Curl Height] A test specimen was cut out from the release film. The size of this test specimen was 200 mm x 200 mm. A metal plate with a flat surface was placed in a dryer at 120°C, and the test specimen was placed on this metal plate. After 5 minutes, the test specimen together with the metal plate was removed from the dryer and cooled to room temperature. The maximum lift amount of the four sides of the test specimen from the metal surface was measured. The obtained values ​​were ranked according to the following criteria: A: Maximum value is less than 1.0 cm; B: Maximum value is 1.0 cm or more. The results are shown in Tables 1 and 2 below.

[0060]

[0061]

[0062] As is clear from Tables 1 and 2, the release films of the examples are excellent in various performances. The superiority of this release film is clear from these evaluation results.

[0063] Disclosed Items Each of the following items discloses a preferred embodiment.

[0064] [Item 1] A substrate layer and a release layer laminated on the substrate layer, wherein the release layer is mainly made of a polystyrene resin, and the surface free energy of the release layer is 42.0 mJ / m ２ A release film used in the manufacture of a membrane electrode assembly, which is as follows:

[0065] [Item 2] The release film according to Item 1, wherein the main material of the release layer is an alkyl group-substituted polystyrene resin.

[0066] [Item 3] The release film according to Item 2, wherein the main material of the release layer is a 4-alkyl-substituted polystyrene resin.

[0067] [Item 4] The release film according to Item 3, wherein the main material of the release layer is poly(4-methylstyrene) or poly(4-tert-butylstyrene).

[0068] [Item 5] The release film according to any one of Items 1 to 4, wherein the main material of the release layer is atactic polystyrene.

[0069] [Item 6] (1) A substrate layer and a release layer laminated on the substrate layer, the release layer being mainly made of a polystyrene resin, and the surface free energy of the release layer being 42.0 mJ / m ２ (1) forming an electrolyte membrane on a surface of a first release film; (2) forming a catalyst layer on a surface of a second release film; (3) bonding the catalyst layer to the electrolyte membrane; and (4) peeling the first release film from the electrolyte membrane.

[0070] [Item 7] The manufacturing method according to Item 6, wherein a proton conductive membrane is formed as the electrolyte membrane in the step (1).

[0071] [Item 8] A laminate comprising a release film and an electrolyte membrane laminated on the release film, wherein the release film has a base layer and a release layer laminated on the base layer, 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 sulfonic acid equivalent mass of the electrolyte membrane is 800 g / mol (SO ３ H) A laminate comprising:

[0072] The release film described above is suitable for producing various molded articles made of ion exchange resins.

[0073] 2...Release film 4...Base material layer 6...Release layer

Claims

1. A substrate layer and a release layer laminated on the substrate layer, the release layer being mainly made of a polystyrene resin, and the surface free energy of the release layer being 42.0 mJ / m ２ A release film for use in the manufacture of a membrane electrode assembly, comprising:

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

3. The release film according to claim 2, wherein the main material of said release layer is a 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 atactic polystyrene.

6. (1) A substrate layer and a release layer laminated on the substrate layer, the release layer being mainly made of a polystyrene resin and having a surface free energy of 42.0 mJ / m ２ (1) forming an electrolyte membrane on a surface of a first release film; (2) forming a catalyst layer on a surface of a second release film; (3) bonding the catalyst layer to the electrolyte membrane; and (4) peeling off the first release film from the electrolyte membrane.

7. The method according to claim 6, wherein in the step (1), a proton conductive membrane is formed as the electrolyte membrane.

8. A laminate comprising a release film and an electrolyte membrane laminated on the release film, wherein the release film has a base layer and a release layer laminated on the base 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 sulfonic acid equivalent mass of the electrolyte membrane is 800 g / mol (SO ３ H) A laminate,

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