Curing method for UV-curing adhesives

Abstract

This invention provides a method for curing UV-curable adhesives that improves the GDL adhesion rate in the manufacturing process of fuel cell cells. [Solution] Some aspects of the present invention are methods for curing a UV-curable adhesive by UV irradiation in the manufacture of a fuel cell cell, wherein the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.075 volume% to 1.75 volume%, and the integrated UV light irradiated onto the UV-curable adhesive is 1800 mJ / cm². 2 More than 7340mJ / cm 2 The following applies to the method within the scope of the following.

Description

[Technical Field]

[0001] Some aspects of the present invention relate to a method for curing UV-curable adhesives. [Background technology]

[0002] A fuel cell has a stack structure in which a predetermined number of single cells, which generate electromotive force through the reaction of a fuel gas (hydrogen) and an oxidizing gas (oxygen), are stacked. Each single cell has a membrane electrode gas diffusion layer assembly (MEGA) and separators arranged on both sides of the MEGA. The MEGA has a membrane electrode assembly (MEA) with anode and cathode catalyst layers on both sides of the electrolyte membrane and gas diffusion layers arranged on both sides of the membrane electrode assembly.

[0003] In the manufacture of fuel cells, UV-curing adhesives may be used to bond a laminate for membrane electrode assemblies to a support frame for supporting the laminate. Patent Document 1 discloses a UV-curing adhesive curing apparatus for use in the manufacture of fuel cells, which is capable of shortening the curing time of such UV-curing adhesives, and is characterized by comprising: an ultraviolet (UV) light source; a flat plate made of a material that does not obstruct UV light and is placed between the UV light source and the workpiece; a clearance between the flat plate and the workpiece that can be filled with N2 gas; and piping that supplies the N2 gas to the clearance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-101082 [Overview of the project] [Problems that the invention aims to solve]

[0005] In fuel cell cells, a gas diffusion layer (GDL) for supplying gas to the catalyst is provided on the surfaces of the anode catalyst layer and the cathode catalyst layer, forming a MEGA (anode-side GDL - anode catalyst layer - electrolyte membrane - cathode catalyst layer - cathode-side GDL). The GDL is porous to ensure gas permeability. The GDL, for example, the cathode-side GDL, is tacked to the electrolyte membrane and the UV-curable adhesive applied to the cathode catalyst layer to prevent shifting during transport during fuel cell manufacturing. UV-curable adhesives develop tackiness by curing with UV light, but curing inhibition occurs due to oxygen in the atmosphere. When curing inhibition occurs, the uncured components of the UV-curable adhesive present near the porous GDL surface are absorbed into the GDL, and the adhesive-derived tackiness also disappears. Therefore, it was desirable to cure the UV-curable adhesive in a low-oxygen atmosphere.

[0006] However, to prevent curing inhibition of UV-curing adhesives, it was confirmed that curing the UV-curing adhesive in an oxygen-free atmosphere eliminated the tackiness.

[0007] Therefore, some aspects of the present invention aim to provide a method for curing a UV-curable adhesive that improves the GDL adhesion rate in the manufacturing process of fuel cell cells. [Means for solving the problem]

[0008] As a result of various studies to solve the above problems, the present inventors have found that in a UV-curable adhesive curing apparatus used in the manufacture of fuel cell cells, the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is set to a range of 0.075 volume% to 1.75 volume%, and the integrated UV light irradiated onto the UV-curable adhesive is set to 1800 mJ / cm². 2 More than 7340mJ / cm 2 We found that curing within the following range improves the GDL adhesion rate, and thus completed several embodiments of the present invention.

[0009] In other words, the gist of some aspects of the present invention is as follows: (1) A method for curing a UV-curable adhesive by UV irradiation in the manufacture of a fuel cell cell, wherein the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.075% by volume or more and 1.75% by volume or less, and the integrated UV light irradiated onto the UV-curable adhesive is 1800 mJ / cm². 2 More than 7340mJ / cm 2 The following methods are within the scope of: (2) The method according to (1), wherein the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.10% by volume or more and 1.50% by volume or less. (3) The total amount of UV light irradiated onto the UV-curing adhesive is 1800 mJ / cm². 2 More than 5700mJ / cm 2 The method described in (1) or (2), within the following range. (4) The method according to any one of (1) to (3) performed in a UV-curing adhesive curing apparatus. (5) A UV-curing adhesive curing apparatus for curing UV-curing adhesives used in the manufacture of fuel cell cells by UV irradiation, comprising a UV light source, a UV irradiation chamber, and a control unit, wherein the UV irradiation chamber and the control unit adjust the oxygen concentration around the UV-curing adhesive at the start of UV irradiation to a range of 0.075 volume% to 1.75 volume%, and the integrated UV light amount irradiated onto the UV-curing adhesive is 1800 mJ / cm². 2 More than 7340mJ / cm 2 A UV-curing adhesive curing device for adjusting within the following range. [Effects of the Invention]

[0010] According to several aspects of the present invention, a method for curing a UV-curable adhesive that improves the GDL adhesion rate in the manufacturing process of fuel cell cells is provided. [Brief explanation of the drawing]

[0011] [Figure 1] This graph shows the relationship between the oxygen concentration in the experiment in the example and the adhesion rate of the gas diffusion layer to the UV-curable adhesive. [Figure 2] It is a graph showing the relationship between the oxygen concentration and the tack force in the experiment in the embodiment. [Figure 3] It is a diagram schematically showing an example of the structure of a fuel cell in some aspects of the present invention. [Figure 4] It is a diagram schematically showing an example of the manufacturing method of a fuel cell in some aspects of the present invention.

Mode for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of some aspects of the present invention will be described in detail. In this specification, the features of some aspects of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of some aspects of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the curing method of the UV-curable adhesive of some aspects of the present invention is not limited to the following embodiments, and can be implemented in various forms with modifications, improvements, etc. that can be made by those skilled in the art without departing from the gist of some aspects of the present invention.

[0013] <Methods of Some Aspects of the Present Invention> Some aspects of the present invention are a method of curing a UV-curable adhesive by UV irradiation in the manufacture of a fuel cell, wherein the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.075% by volume or more and 1.75% by volume or less, and the integrated UV light amount irradiated on the UV-curable adhesive is 1800 mJ / cm 2 or more and 7340 mJ / cm 2 or less, relating to the method.

[0014] Here, the UV-curing adhesive is not limited as long as it is cured by UV irradiation. Examples of UV-curing adhesives include acrylic UV-curing adhesives containing (meth)acrylate and epoxy UV-curing adhesives containing epoxy compounds. The (meth)acrylate may be polybutadiene-based (meth)acrylate, polyisobutylene-based (meth)acrylate, or low molecular weight (meth)acrylate. When using an acrylic UV-curing adhesive, a photoinitiator may be included. The photoinitiator may be a phosphorus-based photoinitiator such as acylphosphine oxide. Furthermore, the thickness of the UV-curing adhesive is not limited. The thickness of the UV-curing adhesive is usually in the range of 10 μm to 150 μm, and in one embodiment, in the range of 20 μm to 100 μm.

[0015] In some embodiments of the present invention, the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.075% by volume or more and 1.75% by volume or less, in one embodiment it is in the range of 0.10% by volume or more and 1.50% by volume or less, and in another embodiment it is in the range of 0.20% by volume or more and 1.0% by volume or less. The oxygen concentration around the UV-curable adhesive at the start of UV irradiation can be determined by measuring the oxygen concentration directly above the UV-curable adhesive. Hereinafter, the atmosphere in which the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is adjusted to the above range will also be referred to as the oxygen concentration-adjusted atmosphere.

[0016] The method for adjusting the oxygen concentration atmosphere is not limited. The oxygen concentration atmosphere may be adjusted by placing the UV-irradiated object containing the UV-curable adhesive in a sealed space and adjusting the oxygen concentration in the sealed space, for example, by an exhaust mechanism and / or an inert gas, such as nitrogen gas and a noble gas, such as argon gas. Alternatively, the oxygen concentration atmosphere may be adjusted by spraying an inert gas onto the UV-irradiated object containing the UV-curable adhesive.

[0017] Furthermore, if the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is within the aforementioned range, the oxygen concentration during UV irradiation after the start of UV irradiation is not limited. Therefore, in some embodiments of the present invention, the atmosphere may be changed from an oxygen concentration-adjusted atmosphere to an atmospheric atmosphere after the start of UV irradiation. In one embodiment, the oxygen concentration around the UV-curable adhesive may be changed from the oxygen concentration-adjusted atmosphere to the oxygen concentration of the atmospheric atmosphere after 0.5 seconds, after 1 second, after 1.5 seconds, after 2 seconds, after 2.5 seconds, or after 3 seconds from the start of UV irradiation.

[0018] In some embodiments of the present invention, the amount of UV light irradiated onto the UV-curable adhesive is the UV irradiance per unit area of ​​the UV-curable adhesive (mW / cm²). 2 The cumulative value of () × UV irradiation time (seconds) is 1800 mJ / cm². 2 More than 7340mJ / cm 2 The range is as follows, and in one embodiment it is 1800 mJ / cm². 2 More than 5700mJ / cm 2 The range is as follows:

[0019] Furthermore, the total amount of UV light irradiated onto a UV-curing adhesive is independent of the UV irradiation atmosphere. Therefore, when UV light is irradiated onto a UV-curing adhesive in both an oxygen-concentration-controlled atmosphere and an air atmosphere, the total amount of UV light irradiated onto the adhesive is the sum of the UV light irradiated in the oxygen-concentration-controlled atmosphere and the UV light irradiated in the air atmosphere.

[0020] By adjusting the oxygen concentration around the UV-curable adhesive at the start of UV irradiation and the amount of integrated UV light irradiated onto the UV-curable adhesive to within the aforementioned range, the GDL adhesion rate to the UV-curable adhesive can be improved to 30% or more under normal circumstances, 40% or more in one embodiment, and 50% in another embodiment. As a result, the tack force of the UV-curable adhesive after curing can be improved to 0.02 MPa or more under normal circumstances, 0.03 MPa or more in one embodiment, and 0.04 MPa or more in another embodiment. This allows for the production of single fuel cell cells without displacement of the gas diffusion layer due to inertia during transport.

[0021] Some aspects of the present invention may be carried out in a UV-curable adhesive curing apparatus. Here, a "UV-curable adhesive curing apparatus" is an apparatus used in the manufacture of fuel cell cells to cure UV-curable adhesives placed between a support frame and an electrolyte membrane, and between the electrolyte membrane and a cathode catalyst layer, by irradiating them with UV (ultraviolet) light for bonding the support frame and MEGA. The UV-curable adhesive curing apparatus includes a UV light source such as a UV-LED, and a UV irradiation chamber equipped with an exhaust mechanism and / or supply piping for inert gases, such as nitrogen gas and rare gases, such as argon gas, for adjusting the irradiation atmosphere, particularly the oxygen concentration, during UV irradiation, especially at the start of UV irradiation.

[0022] The UV-curing adhesive curing apparatus may include a control unit that manages the interval from the start of supplying inert gas from piping to the UV irradiation chamber until the start of UV irradiation from the UV light source to the object to be irradiated with UV light containing the UV-curing adhesive, and optionally, the UV irradiation interval based on the integrated UV light amount to the UV-curing adhesive. The control unit controls the on / off switching of the inert gas supply and the on / off switching of the UV light source. Physically, the control unit includes, for example, a processing unit such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) that stores control programs and control data processed by the CPU, a storage device such as a RAM (Random Access Memory) used mainly as various work areas for control processing, and an input / output interface.

[0023] <Structure of a fuel cell> In some embodiments of the present invention, the fuel cell may consist of only one single cell or may be a fuel cell stack comprising multiple single cells stacked together. In some embodiments of the present invention, both single cells and fuel cell stacks may be referred to as fuel cells. The number of stacked single cells is not limited and may be, for example, two or more and several hundred or less.

[0024] As described above, a single cell comprises an MEA having at least an anode catalyst layer, an electrolyte membrane, and a cathode catalyst layer in that order, and a MEGA including a cathode-side gas diffusion layer and an anode-side gas diffusion layer sandwiching the MEA. The MEGA has the anode-side gas diffusion layer, anode catalyst layer, electrolyte membrane, cathode catalyst layer, and cathode-side gas diffusion layer in that order. In some embodiments of the present invention, the joint between the MEGA and the support frame is also called a MEGA sheet. Figure 3 schematically shows an example of the structure of a fuel cell in some embodiments of the present invention.

[0025] For example, a MEGA sheet can be manufactured as follows. First, a MEGA is prepared consisting of at least one of the cathode-side gas diffusion layers and the anode-side gas diffusion layer, and a film electrode assembly. A UV-curing adhesive is applied to the outer periphery of one surface of the MEGA or to the support frame. The method of applying the UV-curing adhesive is not limited and includes methods such as screen printing or using a dispenser. Next, the support frame is placed on the MEGA so that the UV-curing adhesive applied between the support frame and the MEGA is positioned. After placement, air present between the laminate and the support frame is removed by applying pressure, usually in the range of 0.1 MPa to 0.5 MPa, to firmly adhere the support frame to the laminate. Subsequently, ultraviolet light is irradiated onto the UV-curing adhesive while adjusting the oxygen concentration by blowing an inert gas around the UV-curing adhesive to cure it. Furthermore, depending on the circumstances, the remaining gas diffusion layer of the cathode-side gas diffusion layer and the anode-side gas diffusion layer is placed on a cured UV-curable adhesive on the catalyst layer on which the MEGA on which the support frame is placed does not have a gas diffusion layer, and the gas diffusion layer is tacked by pressurization, usually in the range of 0.1 MPa to 0.5 MPa. Figure 4 schematically shows an example of a fuel cell manufacturing method in several embodiments of the present invention.

[0026] A known support frame can be used. The support frame includes a resin frame that has electrical insulation and airtightness.

[0027] The resin used to construct the resin frame is not limited. Examples of resin frames include engineering plastics such as polyethylene naphthalate resin (PEN), polyethylene terephthalate resin (PET), polyphenylene sulfide resin (PPS), and syndiotactic polystyrene resin (SPS), general-purpose plastics such as polypropylene resin (PP), and mixtures of one or more of these.

[0028] The cathode (oxidizing electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as the catalyst layer. The catalyst layer may include, for example, a catalytic metal that promotes electrochemical reactions, a proton-conducting electrolyte, and an electron-conducting support. As the catalytic metal, for example, platinum (Pt) and alloys made of Pt and other metals, such as a Pt alloy mixed with cobalt and nickel, can be used. As the electrolyte, a fluororesin may be used. As the fluororesin, for example, a Nafion solution may be used. As the support for supporting the catalytic metal, for example, commercially available carbon materials such as carbon can be used.

[0029] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as the gas diffusion layer. The gas diffusion layer may be a conductive material that has gas permeability. Examples of conductive materials include carbon porous materials such as carbon cloth and carbon paper, and metal porous materials such as metal mesh and foamed metal.

[0030] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as a thin film of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. The electrolyte membrane may also be, for example, a Nafion membrane (manufactured by DuPont).

[0031] A single cell may include two separators that sandwich both sides of the membrane electrode gas diffusion layer assembly, if necessary. One of the two separators is the anode-side separator, and the other is the cathode-side separator. In some aspects of the present invention, the anode-side separator and the cathode-side separator are collectively referred to as the separator. The separator may have holes that constitute a manifold, such as supply holes and discharge holes, for circulating fluids such as reaction gas and cooling medium in the stacking direction of the single cell. As the cooling medium, a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures. Alternatively, cooling air can be used as the cooling medium. Examples of supply holes include fuel supply holes, oxidizer gas supply holes, and cooling medium supply holes. Examples of discharge holes include fuel discharge holes, oxidizer gas discharge holes, and cooling medium discharge holes. The separator may have a reaction gas flow path on the surface in contact with the gas diffusion layer. The separator may also have a cooling medium flow path on the surface opposite to the surface in contact with the gas diffusion layer to maintain a constant temperature of the fuel cell. The separator may be a gas-impermeable conductive material. Examples of conductive materials include dense carbon, which is compressed to be gas-impermeable, and press-formed metal plates (e.g., iron, aluminum, and stainless steel). The separator may also have a current-collecting function.

[0032] In some embodiments of the present invention, the fuel gas and the oxidizer gas are collectively referred to as the reaction gas. The reaction gas supplied to the anode is the fuel gas, and the reaction gas supplied to the cathode is the oxidizer gas. The fuel gas is a gas mainly containing hydrogen, but may also be hydrogen. The oxidizer gas is a gas containing oxygen, but may also be air, etc.

[0033] A fuel cell stack may have manifolds such as an inlet manifold through which each supply port is connected, and an outlet manifold through which each discharge port is connected. Examples of inlet manifolds include a fuel inlet manifold, an oxidizer inlet manifold, and a coolant inlet manifold. Examples of outlet manifolds include a fuel outlet manifold, an oxidizer outlet manifold, and a coolant outlet manifold.

[0034] A fuel cell stack may be constructed by sandwiching both ends with a pair of end plates. For the end plates, metals such as stainless steel can be used. Alternatively, engineering plastics containing thermosetting resins such as phenolic resin, epoxy glass, and polyester glass can be used. [Examples]

[0035] The following describes some embodiments of the present invention, but it is not intended to limit the embodiments of the present invention to those shown in these embodiments.

[0036] A UV-curing adhesive (urethane acrylate type) was applied to a PP film in a 10mm x 10mm area, aiming for a thickness of 40μm. Subsequently, it was cured under a low-oxygen atmosphere (0% to 2% by volume, see Table 1) using UV light (600mW / cm²). 2 , or 1900 mW / cm² 2 The sample was irradiated with UV light for 1 second. Then, under atmospheric conditions, the UV-curable adhesive was cured by irradiating it with UV light at the same intensity for 2 seconds. The oxygen concentration was determined by measuring the concentration directly above the sample.

[0037] Next, a gas diffusion layer (carbon porous material) was pressed onto the cured UV-curing adhesive at 0.2 MPa for 2 seconds to allow it to tack. Subsequently, a tensile test was performed on the tacked gas diffusion layer using a push-pull gauge to confirm the tack force and the proportion of the gas diffusion layer remaining on the UV-curing adhesive. Gas diffusion layer adhesion rate (%) = ((Initial gas diffusion layer - Detached gas diffusion layer) / Initial gas diffusion layer) × 100

[0038] [Table 1]

[0039] Figure 1 shows the relationship between oxygen concentration and the adhesion rate of the gas diffusion layer to the UV-curing adhesive. Figure 2 shows the relationship between oxygen concentration and tack force.

[0040] Table 1 and Figures 1 and 2 show that when the oxygen concentration is 0 vol%, the tack force decreases sharply, and the gas diffusion layer adhesion rate also decreases. Furthermore, it was found that both the tack force and the gas diffusion layer adhesion rate decrease even at high oxygen concentrations. This indicates a correlation between tack force and gas diffusion layer adhesion rate. The gas diffusion layer adheres to the UV-curing adhesive because the gas diffusion layer undergoes cohesive failure during testing. Therefore, it is partly due to the strength of the gas diffusion layer itself. If the gas diffusion layer adhesion rate that satisfies the strength when the UV-curing adhesive and the gas diffusion layer are 30% or more, then the oxygen concentration should be in the range of 0.075 vol% to 1.75 vol%, preferably 0.1 vol% to 1.5 vol%, and the integrated UV light irradiated onto the UV-curing adhesive should be 1800 mJ / cm². 2 More than 7340mJ / cm 2 The following range, preferably 1800 mJ / cm² 2 More than 5700mJ / cm 2 It was found that the requirements could be met by setting the scope as follows.

Claims

1. A method for curing a UV-curing adhesive by UV irradiation in the manufacture of a fuel cell cell, The oxygen concentration around the UV-curing adhesive at the start of UV irradiation is in the range of 0.075% by volume or more and 1.75% by volume or less, and The integrated UV light dose irradiated onto the UV-curing adhesive is 1800 mJ / cm². ２ More than 7340mJ / cm ２ The range is as follows: method.

2. The method according to claim 1, wherein the oxygen concentration around the UV-curable adhesive at the start of UV irradiation is in the range of 0.10% by volume or more and 1.50% by volume or less.

3. The integrated UV light dose irradiated onto the UV-curing adhesive is 1800 mJ / cm². ２ More than 5700mJ / cm ２ The method according to claim 1, wherein the range is as follows:

4. The method according to any one of claims 1 to 3, as performed in a UV-curing adhesive curing apparatus.

5. A UV-curing adhesive curing apparatus for curing UV-curing adhesives used in the manufacture of fuel cell cells by UV irradiation, It comprises a UV light source, a UV irradiation chamber, and a control unit. The UV irradiation chamber and control unit adjust the oxygen concentration around the UV-curable adhesive at the start of UV irradiation to a range of 0.075% by volume or more and 1.75% by volume or less, and the integrated UV light irradiated onto the UV-curable adhesive to 1800 mJ / cm². ２ More than 7340mJ / cm ２ This is for adjusting within the following range: UV-curing adhesive curing device.

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