Release film for manufacturing membrane electrode assembly

Abstract

The release film (2) is used for manufacturing a membrane electrode assembly. 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 base material layer (4) is polyester. And the release layer (6) comprises random polystyrene. Preferably, the average roughness (Sa) of the back surface of the base material layer (4) is 20 nm or less. Preferably, the thickness of the release layer (6) is from 0.1 [mu] m to 5 [mu] m (inclusive). Preferably, the surface of the release layer (6) has a water contact angle of 92 DEG or less.

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 peeled off from the catalyst layer. The second release membrane requires appropriate adhesion to the catalyst layer and appropriate peelability.

[0004] Japanese Patent Application Publication No. 2014-154273 discloses a release film having a substrate layer and a release layer. The substrate layer is made of polyethylene terephthalate. The surface of the substrate layer is smooth. Therefore, this release film contributes to the long lifespan of the membrane electrode assembly.

[0005] Japanese Patent Application Publication No. 2014-175116 discloses a release film with a release layer made of syndiotactic polystyrene. This release film exhibits excellent peelability to the ion exchange resin layer.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-154273

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-175116 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The Japanese Patent Application Publication No. 2014-154273 discloses a laminate obtained by bonding the front side of a release film to the back side of an ion exchange resin layer. This laminate is wound onto a spool. During winding, the front side of the ion exchange resin layer contacts the back side of different turns of the release film. The substrate layer is smooth, allowing the front side of the ion exchange resin layer to adhere tightly to the back side of the release film. Due to this tight adhesion, when the laminate is removed from the spool, the ion exchange resin layer is pulled by the different turns of the release film. This results in the unexpected peeling of the back side of the ion exchange resin layer from the front side of the same turns of the release film. This phenomenon is called blocking.

[0012] The release film disclosed in Japanese Patent Application Publication No. 2014-154273 has insufficient wettability on its front side. In particular, when aqueous or water-rich coating solutions are used for the ion exchange resin layer, there is a strong demand for improved wettability.

[0013] The release membrane disclosed in Japanese Patent Application Publication No. 2014-175116 has high solvent resistance because the release layer is made of syndiotactic polystyrene. However, coating the ion exchange resin layer with this release membrane presents difficulties. If the release layer is made of low molecular weight syndiotactic polystyrene, coating is possible. However, the use of this polystyrene leads to defects such as curling and fisheyes in the release membrane.

[0014] The release membrane and ion exchange resin layer disclosed in Japanese Patent Application Publication No. 2014-175116 have insufficient adhesion. Therefore, during the manufacturing process of the membrane electrode assembly, the ion exchange resin layer may accidentally peel off from the release membrane.

[0015] The applicant intends to provide a release membrane that is not prone to accidental peeling of the ion exchange resin layer, has excellent wettability, and thus contributes to the productivity of membrane electrode assembly.

[0016] Solution for solving the problem

[0017] 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 thereon. The substrate layer is primarily made of polyester. The release layer comprises random polystyrene.

[0018] Invention Effects

[0019] This release membrane can prevent accidental peeling of the ion exchange resin layer. The release membrane also exhibits excellent wettability. Furthermore, this release membrane can contribute to the productivity of membrane electrode assemblies. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view showing a portion of a release film according to one embodiment.

[0021] Figure 2 It shows that it was used Figure 1 A flowchart of a method for manufacturing a release membrane electrode assembly.

[0022] Figure 3 It is shown Figure 2 A schematic diagram of an example of the manufacturing process. Detailed Implementation

[0023] 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.

[0024] [Release film]

[0025] 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 on the substrate layer 4. The substrate layer 4 has a back side 8 and a front side 10. The release layer 6 has a back side 12 and a front side 14. The release film 2 may have other layers located between the substrate layer 4 and the release layer 6.

[0026] [Substrate layer]

[0027] The substrate layer 4 is typically made of polyester. 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. Subsequently, tension is applied to the release film 2 during the manufacturing process. The substrate layer 4, formed of polyester, is not easily elongated even when tension is applied at high temperatures. This substrate layer 4 can suppress the elongation of the release film 2 during the manufacturing process of the membrane electrode assembly. The release film 2, which is not easily elongated, can suppress the accidental peeling of the electrolyte membrane or catalyst layer, described later, during the manufacturing process of the membrane electrode assembly.

[0028] Polyester and other resins may also be used in the substrate layer 4. In this case, the ratio of polyester to the total amount of resin is 50% by mass or more. In other words, the main material of the substrate layer 4 is polyester. The ratio of polyester is more preferably 70% by mass or more, and particularly preferably 80% by mass or more. This ratio can be 100% by mass. The material of the substrate layer 4 can be a composition containing resin and additives.

[0029] Preferred polyesters include, for example, polyethylene terephthalate, polyethylene terephthalate, polyethylene butylene terephthalate, polyethylene naphthalate, and polyethylene naphthalate. Polyethylene terephthalate and polyethylene naphthalate are more preferred, with polyethylene terephthalate being particularly preferred.

[0030] 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.

[0031] The average roughness Sa of the substrate layer 4 is preferably 20 nm or less. In other words, the surface smoothness of the substrate layer 4 is excellent. As described later, the release layer 6 is relatively thin. Therefore, the surface state of the release layer 6 reflects the surface state of the substrate layer 4. With a substrate layer 4 having excellent surface smoothness, a release layer 6 with excellent surface smoothness can be achieved. As described later, the release layer 6 contributes to the high lifetime of the membrane electrode assembly. From the viewpoint of high lifetime of the membrane electrode assembly, the average roughness Sa of the substrate layer 4 is more preferably 15 nm or less, and particularly preferably 13 nm or less. The lower limit of the achievable average roughness Sa is 1 nm.

[0032] like Figure 1 As shown, the front side 10 of the substrate layer 4 is covered by the release layer 6. Therefore, the average roughness Sa is measured at the back side 8. A non-contact surface shape measurement system ("VertScan2.0", Ryoka Systems) is suitable for the measurement. The measurement conditions are as follows.

[0033] Mode: WAVE.

[0034] Objective lens magnification: 5x.

[0035] 0.5× Tube lens.

[0036] 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.

[0037] [Release layer]

[0038] Release layer 6 is a resin film. Random polystyrene is a suitable resin for release layer 6. As described later, in the manufacturing process of the membrane electrode assembly, an electrolyte membrane is formed on release membrane 2. Release membrane 2 requires good adhesion to the electrolyte membrane. In the manufacturing process of the membrane electrode assembly, a catalyst layer is also formed on release membrane 2. Release membrane 2 requires good adhesion to the catalyst layer. Release layer 6 is in direct contact with the electrolyte membrane or catalyst layer. Release layer 6, being made of random polystyrene, contributes to the adhesion of the electrolyte membrane and the catalyst layer.

[0039] Random polystyrene is an amorphous substance. Random polystyrene resin can be obtained by free radical polymerization of aromatic vinyl monomers. Examples of aromatic vinyl monomers include: styrene; alkyl-substituted styrene such as o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p-ethylstyrene, p-isopropylstyrene, butylstyrene, p-tert-butylstyrene, and 2,4-dimethylstyrene; 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. Random polystyrene can also be obtained from two or more monomers. Release layer 6 can contain two or more random polystyrene monomers.

[0040] From the viewpoint of the heat resistance of release layer 6, the weight-average molecular weight of random polystyrene 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.

[0041] The material of release layer 6 can be a composition comprising atactic polystyrene resin and additives. Alternatively, the material of release layer 6 can be a composition comprising atactic polystyrene and other resins. Or, the material of release layer 6 can be a composition comprising atactic polystyrene, other resins, and additives. In any composition, the ratio of atactic polystyrene to the total amount of resin is preferably 50% by mass or more. In other words, it is preferable that the main material of release layer 6 is atactic polystyrene. The ratio of atactic polystyrene is more preferably 70% by mass or more, particularly preferably 80% by mass or more. This ratio can be 100% by mass.

[0042] 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.

[0043] The water contact angle of the release layer 6 is preferably 92° or less. A release membrane 2 with a water contact angle of 92° or less exhibits excellent adhesion to the ion exchange resin layer. From this viewpoint, a water contact angle of 90° or less is more preferable, and particularly preferably 89° or less. Figure 1 As shown, the back side 12 of the release layer 6 overlaps with the substrate layer 4. Therefore, the water contact angle is measured at the front side 14. Random polystyrene contributes to a small water contact angle.

[0044] 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 layer 6 with a thickness T2 of 0.1 μm or more can adequately adhere to the substrate layer 4. 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 will 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.

[0045] [Thickness ratio]

[0046] 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.

[0047] [Manufacturing method of release film]

[0048] 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 atactic polystyrene is coated onto 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 may be used together.

[0049] 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.

[0050] 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.

[0051] 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 then laminated onto the substrate layer 4 via an adhesive layer. The adhesive layer can be formed by an adhesive or 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.

[0052] [Method for manufacturing membrane electrode assembly]

[0053] 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).

[0054] 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.

[0055] The first coating solution was applied to... Figure 1 The release layer 6 of the release film 2 (first release film) shown is coated. 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.

[0056] 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... Figure 3 The electrolyte membrane 16 is shown. Drying can also be carried out at room temperature. The electrolyte membrane 16 is in close contact with the first release membrane 2a. The back side 18 of the electrolyte membrane 16 abuts against the first release membrane 2a. The front side 20 of the electrolyte membrane 16 is exposed.

[0057] The first release film 2a and the electrolyte membrane 16 constitute a first laminate 22a. This first laminate 22a is wound onto a spool. By winding, a first roll is formed. This first roll has multiple turns of the first laminate 22a. In this first roll, different turns of the first release film 2a abut against the front side 20 of the electrolyte membrane 16. The first roll is stored for a specified period.

[0058] 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 6 of the second release film 2b (refer to...). Figure 1 In this embodiment, the specifications of the second release film 2b are the same as those of the first release film 2a. The preferred coating method is the same as the coating method described above for the first coating liquid. A coating film is obtained through coating.

[0059] 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... Figure 3 The front catalyst layer 24 is shown. Drying can also be carried out at room temperature. The front catalyst layer 24 is in close contact with the second release film 2b. The front side surface 26 of the front catalyst layer 24 abuts against the second release film 2b. The back side surface 28 of the front catalyst layer 24 is exposed.

[0060] The second release film 2b and the front catalyst layer 24 constitute a second stack 22b. This second stack 22b is wound onto another roll. Through winding, a second roll is formed. This second roll has multiple turns of the second stack 22b. In this second roll, different turns of the second release film 2b abut against the back side 28 of the front catalyst layer 24. The second roll is stored for a specified period.

[0061] In the bonding (step 3), the first stack 22a is fed from the first roll. The first release film 2a has excellent adhesion to the electrolyte membrane 16, so even if the surface of the first release film 2a is smooth, adhesion during feeding can be suppressed. In other words, the electrolyte membrane 16 does not adhere to the first release film 2a on different rolls. In the bonding (step 3), the second stack 22b is further fed from the second roll. The second release film 2b has excellent adhesion to the front catalyst layer 24, so even if the surface of the second release film 2b is smooth, adhesion during feeding can be suppressed. In other words, the front catalyst layer 24 does not adhere to the second release film 2b on different rolls.

[0062] The back side 28 of the front catalyst layer 24 of the second stack 22b is superimposed on the front side 20 of the electrolyte membrane 16 of the first stack 22a. Thus, a stack comprising the first release membrane 2a, the electrolyte membrane 16, the front catalyst layer 24, and the second release membrane 2b is obtained. This stack is also referred to as an intermediate stack.

[0063] The intermediate laminate is 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 24 is firmly bonded to the electrolyte membrane 16. 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 2a from the electrolyte membrane 16 can be suppressed. Furthermore, accidental peeling of the second release membrane 2b from the front catalyst layer 24 can be suppressed.

[0064] In the peeling (step 4), the first release film 2a is peeled off from the electrolyte membrane 16. Through peeling, the back side 18 of the electrolyte membrane 16 is exposed. As described above, the surface of the release layer 6 is smooth. Therefore, a smooth back side 18 can be achieved in the electrolyte membrane 16.

[0065] 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 6 of the third release film 2c (refer to...). Figure 1 In this embodiment, the specifications of the third release film 2c are the same as those of the first release film 2a. The preferred coating method is the same as the coating method described above for the first coating liquid. A coating film is obtained by coating.

[0066] The coating film is heated. The preferred heating temperature is the same as the temperature described above for the second coating liquid. The coating film is dried by heating to obtain… Figure 3 The back catalyst layer 30 is shown. Drying can also be carried out at room temperature. The back catalyst layer 30 is in close contact with the third release membrane 2c. The back side surface 32 of the back catalyst layer 30 abuts against the third release membrane 2c. The front side surface 34 of the back catalyst layer 30 is exposed.

[0067] The third release film 2c and the back catalyst layer 30 constitute a third stack 22c. This third stack 22c is further wound onto other rolls. Through winding, a third roll is formed. This third roll has multiple turns of the third stack 22c. In this third roll, the front side 34 of the back catalyst layer 30 abuts against different turns of the third release film 2c. The third roll is stored for a specified period.

[0068] In the bonding process (step 6), the third stack 22c is fed out from the third roll. The third release film 2c has excellent adhesion to the catalyst layer, so even though the surface of the third release film 2c is smooth, adhesion during feeding is suppressed. In other words, the back catalyst layer 30 does not adhere to the third release film 2c of different rolls.

[0069] The front side 34 of the back catalyst layer 30 of the third laminate 22c is laminated with the back side 18 of the electrolyte membrane 16. Thus, a laminate comprising the third release membrane 2c, the back catalyst layer 30, the electrolyte membrane 16, the front catalyst layer 24, and the second release membrane 2b is obtained. 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 30 and the electrolyte membrane 16 are firmly bonded together. As described above, each release membrane 2 has a flexible 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 pressurizing process, accidental peeling of the second release film 2b from the front catalyst layer 24 can be suppressed. Furthermore, accidental peeling of the third release film 2c from the back catalyst layer 30 can be suppressed.

[0070] In the peeling process (step 7), the second release membrane 2b is peeled from the front catalyst layer 24, and the third release membrane 2c is peeled from the back catalyst layer 30. Through these peels, a stack formed by the back catalyst layer 30, the electrolyte membrane 16, and the front catalyst layer 24 is obtained. A gas supply layer, etc., is further stacked on this stack to obtain a membrane electrode assembly. As described above, the back surface 18 of the electrolyte membrane 16 is smooth. Therefore, the back catalyst layer 30 is firmly bonded to the electrolyte membrane 16. This bonding contributes to a long lifespan of the membrane electrode assembly.

[0071] The specifications of the second release film 2b may differ from those of the first release film 2a. The specifications of the third release film 2c may differ from those of the first release film 2a.

[0072] Example

[0073] 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.

[0074] [Example 1]

[0075] 10% by mass of random polystyrene (“G100C”, TOYO STYRENE) was dissolved in 90% by mass of toluene to obtain a coating solution. On the other hand, a polyester film with an easy-to-adhere layer (“Cosmoshine (registered trademark) A4100”, Toyobo Co., Ltd.) was prepared as the substrate layer. This polyester film had a thickness of 50 μm and a surface roughness Sa of 6 nm. The coating solution was applied to the surface of the easy-to-adhere layer of this polyester film using a wire rod #10 to obtain a coating film. This coating film was dried at 100°C for 1 minute to obtain the release film of Example 1.

[0076] [Example 2]

[0077] As the substrate layer, a polyester film ("Lumirror (registered trademark) T60", TORAY Corporation) was used. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Example 2. The polyester film had a thickness of 75 μm and a surface roughness Sa of 13 nm.

[0078] [Example 3]

[0079] The coating solution was prepared by dissolving 10% by weight of random polystyrene (“G200C”, TOYO STYRENE) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Example 3.

[0080] [Example 4]

[0081] The coating solution was prepared by dissolving 10% by weight of random polystyrene (“G320C”, TOYO STYRENE) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Example 4.

[0082] [Example 5]

[0083] The coating solution was prepared by dissolving 10% by weight of random polystyrene (“H350”, TOYO STYRENE) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Example 5.

[0084] [Example 6]

[0085] The coating solution was prepared by dissolving 10% by weight of random polystyrene (“H485”, TOYO STYRENE) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Example 6.

[0086] [Comparative Example 1]

[0087] 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.

[0088] [Comparative Example 2]

[0089] 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.

[0090] [Comparative Example 3]

[0091] A coating solution was obtained by dissolving 10% by weight of a cyclic olefin resin ("ARTONF3500", JSR Corporation) in 90% by weight of toluene. Otherwise, the procedure was the same as in Example 1 to obtain the release film of Comparative Example 3.

[0092] [Comparative Example 4]

[0093] 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 4.

[0094] [Comparative Example 5]

[0095] As the substrate layer, a polyester film ("Lumirror (registered trademark) T60", TORAY Corporation) was used. Otherwise, the procedure was the same as in Comparative Example 1 to obtain the release film of Comparative Example 5. The polyester film had a thickness of 75 μm and a surface roughness Sa of 12 nm.

[0096] [Comparative Example 6]

[0097] As the substrate layer, a polyester film ("DIAFOIL (registered trademark) T100", Mitsubishi Chemical Co., Ltd.) was used. Otherwise, the procedure was the same as in Comparative Example 1 to obtain the release film of Comparative Example 6. The polyester film had a thickness of 75 μm and a surface roughness Sa of 36 nm.

[0098] [Comparative Example 7]

[0099] As a release film for Comparative Example 7, 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, and the surface roughness Sa was 72 nm.

[0100] [Adhesion]

[0101] An ion exchange resin solution (“Nafion (registered trademark) 20 dispersionSolution DE2020CS type”, DuPont) was prepared as the coating solution. This coating solution was applied to the release layer of the release membrane to obtain a coating film. The coating film was held at 100°C for 3 minutes to obtain a laminate of the release membrane and the ion exchange resin layer. The thickness of the ion exchange resin layer was 10 μm. Two test pieces were cut from this laminate. Each test piece was 10 cm × 15 cm in size. The release membrane of the other test piece was brought into contact with the ion exchange resin layer of the first test piece. A roller with a load of 2 kgf was passed back and forth twice over these test pieces to apply pressure. These test pieces were held at 23°C and 65% RH for 24 hours. From one test piece, the other test piece was peeled off within 0.5 to 1.0 seconds. The condition of one test piece was visually observed and graded based on the following criteria.

[0102] A: The ion exchange resin layer peels off significantly from the release membrane.

[0103] B: The ion exchange resin layer peels slightly off from the release film.

[0104] C: The ion exchange resin layer was not completely peeled off from the release membrane.

[0105] The results are shown in Tables 1 and 2 below.

[0106] [Peeling force]

[0107] An ion exchange resin solution (“Nafion (registered trademark) DS2020CS”, DuPont) was prepared as the coating solution. The solids content of this ion exchange resin solution 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. Subsequently, the coating film was heat-treated at 160°C for 30 minutes to obtain a laminate of the release membrane and the ion exchange resin layer. The thickness of the ion exchange resin layer was 4 μm. A test piece was cut from this laminate. The ion exchange resin layer was peeled from the release membrane onto the test piece, and the peel force was measured. The conditions are as follows.

[0108] Device: Autograph “AGS-X”, Shimadzu Corporation.

[0109] Width of the test piece: 25mm.

[0110] Angle: 180°.

[0111] Speed: 600 mm / min.

[0112] The results are shown in Tables 1 and 2 below. In the release membranes of Comparative Examples 3 and 4, the ion exchange resin layer did not peel off.

[0113] [Operability]

[0114] Prepare the same test piece used in the peel strength test. Perform a heat treatment on the test piece. Visually inspect the surface of the test piece and grade it based on the following criteria.

[0115] A: It produces wrinkles.

[0116] B: Slight wrinkles appear.

[0117] C: No wrinkles were produced.

[0118] The results are shown in Tables 1 and 2 below.

[0119] [Table 1]

[0120]

[0121] [Table 2]

[0122]

[0123] 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.

[0124] [Public Projects]

[0125] Preferred implementations of the following projects are disclosed.

[0126] [Project 1]

[0127] A release film for manufacturing a membrane electrode assembly, the release film having a substrate layer and a release layer laminated thereon, wherein the substrate layer is primarily made of polyester and the release layer comprises random polystyrene.

[0128] [Project 2]

[0129] According to the release film of Project 1, the water contact angle of the surface of the release layer is less than 92°.

[0130] [Project 3]

[0131] According to Project 1 or 2, the release film has a thickness of 0.1 μm or more and 5 μm or less.

[0132] [Project 4]

[0133] According to any one of items 1 to 3, the release film has an average roughness Sa of less than 20 nm on the back side of the substrate layer.

[0134] [Project 5]

[0135] A method for manufacturing a membrane electrode assembly includes: (1) forming an electrolyte membrane on the surface of a first release membrane to obtain a first laminate, the first release membrane having a substrate layer and a release layer laminated on the substrate layer, the main material of the substrate layer being polyester and the release layer comprising random polystyrene; (2) winding the first laminate to obtain a roll; (3) forming a catalyst layer on the surface of a second release membrane to obtain a second laminate; (4) feeding the first laminate from the roll and bonding the catalyst layer to the electrolyte membrane to obtain an intermediate laminate; and (5) heating and pressurizing the intermediate laminate.

[0136] [Project 6]

[0137] According to the manufacturing method described in Project 5, in the above-mentioned step (1), the electrolyte film is formed on the surface of the first release film, which has an average roughness Sa of 20 nm or less on the back side and a release layer thickness of 0.1 μm or more and 5 μm or less.

[0138] [Project 7]

[0139] A laminate comprising: (1) a release film having a substrate layer and a release layer laminated thereon, wherein the substrate layer is primarily made of polyester and the release layer comprises random polystyrene; and (2) an electrolyte membrane laminated thereon.

[0140] Industrial availability

[0141] The release film described above is suitable for the manufacture of various molded articles formed from ion exchange resins.

[0142] 2: Release film;

[0143] 2a: First release film;

[0144] 2b: Second release film;

[0145] 2c: Third release film;

[0146] 4: Substrate layer;

[0147] 6: Release layer;

[0148] 8: Back side of the substrate layer;

[0149] 10: Front side of the substrate layer;

[0150] 12: The back side of the release film;

[0151] 14: The front side of the release film;

[0152] 16: Electrolyte membrane;

[0153] 18: The back side of the electrolyte membrane;

[0154] 20: The front side of the electrolyte membrane;

[0155] 22a: First stacked body;

[0156] 22b: Second stack;

[0157] 22c: Third layer;

[0158] 24: Front catalyst layer;

[0159] 26: The front side surface of the front catalyst layer;

[0160] 28: The back side of the front catalyst layer;

[0161] 30: Backside catalyst layer;

[0162] 32: Back side of the catalyst layer;

[0163] 34: The front side of the back catalyst 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 substrate layer is polyester. The release layer comprises random polystyrene.

2. The release film according to claim 1, wherein, The water contact angle of the release layer surface is below 92°.

3. The release film according to claim 1 or 2, wherein, The thickness of the release layer is greater than 0.1 μm and less than 5 μm.

4. The release film according to claim 1 or 2, wherein, The average roughness Sa of the back side surface of the substrate layer is less than 20 nm.

5. A method for manufacturing a membrane electrode assembly, the method comprising: (1) A process of forming an electrolyte membrane on the surface of a first release film to obtain a first laminate, wherein the first release film has a substrate layer and a release layer laminated on the substrate layer, wherein the main material of the substrate layer is polyester and the release layer contains random polystyrene; (2) The process of winding the first stacked body to obtain a roll; (3) The process of forming a catalyst layer on the surface of the second release film to obtain the second stacked body; (4) The process of feeding the first stacked body out of the roll and bonding the catalyst layer with the electrolyte membrane to obtain an intermediate stacked body; as well as (5) The process of heating and pressurizing the intermediate laminate.

6. The manufacturing method according to claim 5, wherein, In the process (1), the electrolyte membrane is formed on the surface of the first release film, which has an average roughness Sa of less than 20 nm on the back side and a release layer thickness of more than 0.1 μm and less than 5 μm.

7. A laminated body, the laminated body comprising: (1) A release film having a substrate layer and a release layer laminated thereon, the substrate layer being primarily made of polyester and the release layer comprising random polystyrene; and (2) Electrolyte membrane, laminated on the release membrane.

Images