Manufacturing method of fuel cell separator

Abstract

To provide a manufacturing method of a separator for a fuel cell capable of suppressing generation of separator warpage even when first and second conductive films are deposited on a central part of a separator base material.SOLUTION: A manufacturing method includes: setting a deposition condition so that F(t) and G(T) calculated by the following equations (1) and (2) satisfy the condition F(t)+G(T)≤10; and depositing first and second conductive films 21 and 22 on a separator base material 12A covered with mask jigs 31 and 32 using a physical vapor growth method under the set deposition condition. (1): F(t)=1.06×10-4×t2-1.47×10-2×t+1.04. (2): G(t)=2.68×10-4×T2-1.24×10-1×T+1.36. t is a film thickness difference (nm) between the first and second conductive films 21 and 22 and T is the maximum temperature (°C) reached in an area where the first and second film formation regions 17A and 17B are formed at deposition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a separator for a fuel cell. [Background technology]

[0002] Conventionally, a method for manufacturing a separator for a fuel cell (hereinafter referred to as "separator") involves forming a conductive film made of a conductive material on both sides of a metallic separator substrate by physical vapor deposition (PVD) in order to improve corrosion resistance and conductivity (see Patent Document 1). This conductive film is formed to the same thickness on both sides of the separator substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6512577 Summary of the Invention [Problem to be solved by the invention]

[0004] The portion of the separator through which the gas for power generation flows is more corrosive than the portion on the back side through which the coolant flows. Therefore, we envision making the thickness of the conductive film (first conductive film) in the first film formation region on the surface of the separator substrate, where the gas flow path for power generation is formed, thicker than the thickness of the conductive film (second conductive film) in the second film formation region where the coolant flow path is formed. During film formation, the first and second film formation regions are formed in the central portion of the separator substrate in a plan view, so the portions excluding the first and second film formation regions are covered with a masking jig.

[0005] However, the inventors' experiments, which will be described later, have found that if the first and second conductive films are formed under such conditions, the separator after film formation will be significantly warped.

[0006] The present invention has been made in consideration of such problems, and its purpose is to provide a method for manufacturing a separator for a fuel cell that can suppress the occurrence of warping of the separator even when first and second conductive films are formed in the central portion of the separator substrate. [Means for solving the problem]

[0007] In light of the above-mentioned problems, the inventors conducted extensive research and discovered that separator warpage is caused by the following two factors. The first factor is the difference in film thickness between the first and second conductive films. Specifically, when the first and second conductive films are formed by physical vapor deposition, residual stress is generated in the first and second conductive films. The magnitude of this residual stress depends on the film thickness, and as the difference in film thickness increases, a relatively large residual stress acts on one side of the separator, causing the separator to warp after film formation. The inventors discovered that certain conditions exist for this difference in film thickness and separator warpage.

[0008] The second factor is the maximum temperature reached in the areas where the first and second film formation regions are formed during film formation. When the first and second conductive films are formed by physical vapor deposition, the temperature of the first and second film formation regions rises. If the maximum temperature reached in these areas is high, the first and second film formation regions of the separator substrate are locally overheated, causing a large imbalance in the heat distribution, resulting in warping of the separator after film formation. The inventors have discovered that certain conditions exist for the maximum temperature reached in the areas where the first and second film formation regions are formed and the warping of the separator.

[0009] The present invention was made based on the points discovered by the inventors, and the method for manufacturing a separator for a fuel cell according to the present invention is a method for manufacturing a separator for a fuel cell, in which a separator substrate has a first film formation region in which a gas flow path for power generation is formed, and a second film formation region on the back surface of the first film formation region in which a coolant flow path is formed, and in which first and second conductive films made of a conductive material that is more corrosion-resistant than the metal material of the separator substrate are coated in the first and second film formation regions, respectively.

[0010] The first and second film formation regions of the separator manufactured by this manufacturing method are formed in the central portion of the separator substrate when viewed in a plane, and the thickness of the first conductive film coated on the first film formation region is thicker than the thickness of the second conductive film coated on the second film formation region.

[0011] The manufacturing method includes a setting step of setting film formation conditions so that functions F(t) and G(T) calculated by the following equations (1) and (2) satisfy the condition F(t) + G(T) ≦ 10; a masking step of covering the separator substrate with a mask jig so that the first and second film formation regions are exposed; and a film formation step of forming the first and second conductive films on the separator substrate by physical vapor deposition under the film formation conditions. F(t) = 1.06 × 10 -4 ×t 2 -1.47×10 -2 ×t+1.04…(1) G(T) = 2.68 × 10 -4 ×T 2 -1.24×10 -1 ×T+1.36…(2) Here, t is the difference in film thickness (nm) between the first and second conductive films, and T is the maximum temperature (° C.) reached in the portions where the first and second film formation regions are formed during film formation.

[0012] According to the present invention, F(t), a function of the difference in film thickness t between the first and second conductive films, and G(T), a function of the maximum temperature T achieved in the portions forming the first and second film formation regions during film formation, are both quadratic functions used to calculate the amount of warpage of the separator. Therefore, if the first and second conductive films are formed under film formation conditions that satisfy F(t) + G(T) ≦ 10, the amount of warpage of the separator can be reduced to 10 mm or less. The maximum temperature depends on factors such as the film formation speed of the first and second conductive films, and can be determined by setting film formation conditions such as the power applied to the conductive material target, the conveying speed of the separator substrate, the ambient temperature during film formation, and the bias voltage between the target and the separator substrate. [Effects of the Invention]

[0013] According to the present invention, even if the first and second conductive films are formed in the central portion of the separator substrate, warping of the separator can be suppressed. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a stack of unit cells of a fuel cell including a separator manufactured according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view of the unit cell shown in FIG. [Figure 3] FIG. 2 is a cross-sectional view of the separator shown in FIG. [Figure 4] FIG. 10 is a perspective view for explaining a masking step using a mask jig. [Figure 5A] 5A to 5C are schematic diagrams illustrating an example of a film forming process according to the manufacturing method of the embodiment. [Figure 5B] 5A to 5C are schematic diagrams illustrating an example of a film forming process according to the manufacturing method of the embodiment. [Figure 6] 10 is a graph for calculating the formula for F(t) based on the results of Reference Examples 1-1 to 1-7. [Figure 7] 10 is a graph for calculating the formula for G(T) based on the results of Reference Examples 2-1 to 2-5. DETAILED DESCRIPTION OF THE INVENTION

[0015] A method for manufacturing a separator for a fuel cell according to an embodiment of the present invention will be described below with reference to Figures 1 to 7. First, a separator manufactured in this embodiment and a unit cell for a fuel cell including the separator will be described below.

[0016] 1. Regarding the single cell 10 of the fuel cell 1 Fig. 1 is a cross-sectional view of stacked unit cells of a fuel cell including a separator manufactured according to an embodiment of the present invention. Fig. 2 is an exploded perspective view of the unit cell shown in Fig. 1. Fig. 3 is a cross-sectional view of the separator shown in Fig. 1.

[0017] As shown in FIG. 1, a fuel cell 1 according to this embodiment is made up of a plurality of stacked unit cells 10, which are basic units. The unit cells 10 are solid polymer fuel cells that generate electromotive force through an electrochemical reaction between oxygen gas contained in air and hydrogen gas, which is a fuel gas. The air refers to atmospheric air, and air compressed by a compressor (not shown), for example, is supplied to the fuel cell 1. Hydrogen gas filled in a high-pressure tank (not shown) is also supplied to the fuel cell 1. The oxygen gas and hydrogen gas correspond to gases for power generation.

[0018] 2, a single cell 10 constituting the fuel cell 1 includes a power generation assembly 17 and a pair of separators 12, 12 that sandwich the power generation assembly 17. The power generation assembly 17 includes an electrode-gas diffusion layer assembly (MEGA) 11 and a resin frame 14 that surrounds the outer periphery of the MEGA 11.

[0019] 1, the MEGA 11 has a membrane electrode assembly 11A, which includes a polymer electrolyte membrane 11a, catalyst layers 11b and 11c bonded to both sides of the membrane electrode assembly 11a, and gas diffusion layers 11d and 11d bonded to the catalyst layers 11b and 11c. The portion of the membrane electrode assembly 11A exposed from the resin frame 14 serves as a power generation region. The gas diffusion layers 11d and 11d may be omitted from the MEGA 11.

[0020] The polymer electrolyte membrane 11a is a proton-conductive ion-exchange membrane made of a solid polymer material. The catalyst layers 11b and 11c are made of, for example, a porous carbon material carrying a catalyst such as platinum. The catalyst layer 11b arranged on one side of the polymer electrolyte membrane 11a serves as the anode of the fuel cell 1, and the catalyst layer 11c on the other side serves as the cathode of the fuel cell 1. The gas diffusion layer 11d is made of a gas-permeable conductive material such as a porous carbon material such as carbon paper or carbon cloth, or a porous metal material such as a metal mesh or metal foam.

[0021] 2, separator 12 is formed in the same rectangular shape as MEGA 11 in a plan view. A large number of separator grooves (flow paths) 15a-15c are formed, for example, along the longitudinal direction L in the portion of separator 12 that abuts against MEGA 11, thereby forming flow paths 15a-15c through which fuel gas, air, and coolant flow, as shown in FIG. 1. Separator grooves 15 are formed along the long sides of separator 12.

[0022] Specifically, the flow path defined between the gas diffusion layer 11d on one catalyst layer 11b side and the separator 12 is the gas flow path 15a through which hydrogen gas flows. The flow path defined between the gas diffusion layer 11d on the other catalyst layer 11c side and the separator 12 is the gas flow path 15b through which air flows. The flow path formed between the separators 12 is the coolant flow path 15c through which coolant flows. In this embodiment, when hydrogen gas is supplied to one gas flow path 15a and air is supplied to the other gas flow path 15b, an electrochemical reaction occurs in the unit cell 10, generating an electromotive force.

[0023] Furthermore, six flow ports 14a to 14f are formed on both sides of the separator 12 in the longitudinal direction L for individually supplying hydrogen gas, air, and coolant to MEGA 11 or its vicinity, and for discharging the supplied hydrogen gas, air, and coolant from MEGA 11 or its vicinity.

[0024] These flow ports are formed in positions corresponding to the flow ports 14a to 14f of the resin frame 14 and have the same size as the corresponding flow ports. In Fig. 2, the flow ports 14a to 14f of the separator 12 corresponding to the flow ports 14a to 14f of the resin frame 14 are denoted by the same reference numerals as the flow ports 14a to 14f of the resin frame 14.

[0025] Specifically, hydrogen flow port 14a through which hydrogen gas flows, coolant flow port 14b through which coolant flows, and air flow port 14c through which air flows are formed in this order on one side of separator 12. Furthermore, air flow port 14d through which air flows, coolant flow port 14e through which coolant flows, and hydrogen flow port 14f through which hydrogen gas flows are formed in this order on the other side of separator 12. One of the flow ports through which each fluid flows is a flow port for supplying fluid to MEGA 11 or its vicinity, and the other is a flow port for discharging fluid from MEGA 11 or its vicinity.

[0026] For example, one hydrogen flow port 14a serves as a flow port for supplying hydrogen to MEGA 11, and the other hydrogen flow port 14f serves as a flow port for discharging hydrogen from MEGA 11. Hydrogen flow port 14a and hydrogen flow port 14f are disposed at diagonal corners of separator 12, so that hydrogen gas can flow between diagonal corners of MEGA 11.

[0027] As shown in Fig. 3, the separator 12 includes a metallic separator substrate 12A. The separator substrate 12A has a first film formation region 17A and a second film formation region 17B on both sides thereof. The first film formation region 17A faces the power generation region of the membrane electrode assembly 11A and is a region in which gas flow channels 15a and 15b are formed, through which gas for power generation flows. The second film formation region 17B is a region on the back side of the first film formation region 17A and is a region in which a coolant flow channel 15c, through which a coolant such as cooling water flows, is formed.

[0028] The first film formation region 17A and the second film formation region 17B are formed in the central portion of the separator substrate 12A in a plan view of the separator substrate 12A. That is, the first film formation region 17A and the second film formation region 17B are surrounded by a non-film formation region where no film is formed. In this embodiment, the first film formation region 17A is coated with a first conductive film 21, and the second film formation region 17B is coated with a second conductive film 22.

[0029] When the fuel cell 1 generates electricity, each unit cell 10 is exposed to a corrosive environment (a high-potential, low-pH environment). If the fuel cell 1 continues to operate in such a corrosive environment, iron may leach out of the separator substrate 12A, which is made of, for example, stainless steel. The leached iron may deteriorate the MEGA 11 and ultimately reduce the performance of the fuel cell 1. Therefore, the first conductive film 21 and the second conductive film 22 are made of a conductive material that is more corrosion-resistant than the metal material of the separator substrate 12A. For example, if the separator substrate 12A is made of stainless steel, the conductive material is a titanium material (pure titanium or a titanium alloy) and a carbon material.

[0030] Here, the thickness t1 of the first conductive film 21 is thicker than the thickness t2 of the second conductive film 22. In this embodiment, the first conductive film 21 is composed of a titanium film 21a and a carbon film 21b. The first film formation region 17A is coated with a titanium film 21a made of the above-mentioned titanium material, and the titanium film 21a is coated with a carbon film 21b made of amorphous carbon or the like. Similarly, the second conductive film 22 is composed of a titanium film 22a and a carbon film 22b. The second film formation region 17B is coated with a titanium film 22a, and the titanium film 22a is coated with a carbon film 22b.

[0031] In this embodiment, the thickness of the carbon film 21b of the first conductive film 21 is the same as the thickness of the carbon film 22b of the second conductive film 22. Therefore, the thickness of the titanium film 21a of the first conductive film 21 is greater than the thickness of the titanium film 22a of the second conductive film 22. As a result, although the power generation gas flow paths 15a, 15b are more susceptible to corrosion than the coolant flow path 15c, by making the thickness of the titanium film 21a greater than the thickness of the titanium film 22a, the corrosion resistance of the gas flow paths 15a, 15b can be ensured.

[0032] 2. Manufacturing method of separator 12 A method for manufacturing the separator 12 according to this embodiment will be described below. First, a separator substrate 12A is prepared. Here, the separator substrate 12A is a base member of the separator 12, and is formed by press-molding once or twice or more times from a substrate (thin plate or foil material) of austenitic stainless steel, for example, SUS304 (JIS standard). This press-molding forms gas flow channels 15a (15b) and coolant flow channels 15c, etc., in the separator substrate 12A, and forms flow ports 14a to 14f. The thickness of the separator substrate 12A is 70 μm to 150 μm. m It is preferable that the thickness is in the range of 100 μm or more, provided that the thickness is in this range.

[0033] 2-1. About the setup process In the setting step, the film formation conditions are set so that the values ​​of F(t) and G(T) calculated by the following equations (1) and (2) satisfy the condition F(t)+G(T)≦10. F(t) = 1.06 × 10 -4 ×t 2 -1.47×10 -2 ×t+1.04…(1) G(T) = 2.68 × 10 -4 ×T 2 -1.24×10 -1 ×T+1.36…(2)

[0034] t is the difference in thickness (unit: nm) between the first conductive film 21 and the second conductive film 22. Here, when the carbon films 21b and 22b have the same thickness, t is the difference in thickness between the titanium films 21a and 22a. The thicknesses of the first conductive film 21 and the second conductive film 22 are preferably in the range of 30 to 450 nm, and more preferably in the range of 75 to 450 nm. The difference in thickness between the first conductive film 21 and the second conductive film 22 is preferably in the range of 35 to 350 nm, more preferably in the range of 35 to 285 nm, and even more preferably in the range of 185 to 285 nm. The thicknesses of the carbon films 21b and 22b are preferably in the range of 15 to 25 nm to reduce the contact resistance of the separator 12. From the viewpoint of corrosion resistance, the titanium films 21a and 22a preferably have a thickness in the range of 15 nm to 400 nm, and the thickness of the carbon film 21b (22b):thickness of the titanium film 21a (22a) preferably falls within the range of 1:1 to 1:10.

[0035] T is the maximum temperature (unit: °C) reached in the portion of the separator substrate 12A where the first and second film formation regions 17A and 17B are formed. This means that this portion is the hottest portion of the separator substrate 12A during film formation. The "maximum temperature T" here refers to the maximum temperature reached in this portion during film formation of the first and second conductive films 21 and 22. The maximum temperature T depends on factors such as the film formation speed of the first and second conductive films 21 and 22, and can be determined by setting film formation conditions such as the power applied to the conductive material target, the conveyance speed of the separator substrate 12A, the ambient temperature during film formation, and the bias voltage between the target and the separator substrate 12A. The maximum temperature T is preferably in the range of 250 to 410 °C, and more preferably in the range of 280 to 350 °C.

[0036] Therefore, the film thickness difference t and the maximum temperature T can be determined by setting various film formation conditions. Note that the relationship between these can be determined in advance by conducting experiments in which the film formation conditions are changed. Note that the setting process may be performed before preparing the separator substrate 12A.

[0037] 2-2. Masking process 4 is a perspective view illustrating the masking step using mask jigs 31 and 32. In the masking step, separator substrate 12A is covered with mask jigs 31 and 32 so that first film formation region 17A and second film formation region 17B are exposed.

[0038] Specifically, in the masking process, the separator substrate 12A is placed in a housing portion 33a of a frame-shaped spacer 33, and mask jigs 31 and 32 are sandwiched between the separator substrate 12A and the spacer 33. The mask jigs 31 and 32 have openings 31a and 32a corresponding to the sizes of the first film formation region 17A and the second film formation region 17B, respectively, so that the first film formation region 17A (second film formation region 17B) can be exposed through the opening 31a (32a) of the mask jig 31 (32). In this way, the separator substrate 12A is attached to either of the mask jigs 31 and 32 by sandwiching them between the spacer 33, thereby obtaining an assembly 30 of the separator substrate 12A.

[0039] The mask jigs 31, 32 and the spacer 33 are made of metal such as stainless steel, and the thickness of the spacer 33 is such that the separator substrate 12A does not undergo plastic deformation when the mask jigs 31, 32 are sandwiched between the separator substrate 12A.

[0040] 2-3. Film formation process 5A is a schematic diagram illustrating an example of a film formation process according to the manufacturing method of the embodiment, and FIG. 5B is a schematic diagram illustrating another example of a film formation process according to a manufacturing method of another embodiment. In the film formation process, first conductive film 21 and second conductive film 22 are formed on assembly 30 (separator substrate 12A to which mask jigs 31, 31 are attached) by physical vapor deposition (PVD) under the film formation conditions set in the setting process.

[0041] Here, examples of physical vapor deposition include vacuum deposition, sputtering, ion plating, ion beam mixing, etc. In physical vapor deposition, film-forming particles are generated from a target, and the film-forming particles are caused to adhere to first film-forming region 17A and second film-forming region 17B, thereby forming first conductive film 21 and second conductive film 22.

[0042] 5A is composed of a vacuum section 41, a heating / etching section 42, a titanium film-forming section 43, a carbon film-forming section 44, and an air-opening section 45. The assembly 30 (separator substrate 12A) is transported by a transport device (not shown) in this order (in the direction of the arrows) with the first film-forming region 17A and the second film-forming region 17B exposed, and is continuously processed.

[0043] First, the assembly 30 is transported to a vacuum section 41, where the atmosphere is reduced in pressure. While maintaining this state, the assembly 30 is transported to a heating and etching section 42. Here, the separator substrate 12A is heated by a heater (not shown) to adjust the temperature, and the surfaces of the first film formation region 17A and the second film formation region 17B are etched.

[0044] Next, the assembly 30 is transported to the titanium film forming section 43, where titanium particles 20A are deposited on the first and second film forming regions 17A and 17B by, for example, sputtering, to form titanium films 21a and 22a. Here, the titanium particles 20A are particles generated from a titanium target (not shown).

[0045] In this embodiment, to prevent the temperature of the first and second film formation zones 17A and 17B from rising during film formation, a titanium film is formed in one of the first and second film formation zones 17A and 17B first, and then in the other. The power applied to the titanium target, the bias voltage on the separator substrate 12A side, and the temperature in the titanium film formation unit 43 are adjusted to achieve the film formation conditions set in the setting step, and the titanium films 21a and 22a are sequentially formed. In this embodiment, because the power generation gas passes through the first film formation zone 17A, the titanium films 21a and 22a are sequentially formed so that the thickness of the titanium film 21a formed in this zone is thicker than the thickness of the titanium film 22a formed in the second film formation zone 17B.

[0046] Next, the assembly 30 is transported to a carbon film forming section 44, where carbon particles 20B are attached to the titanium films 21a and 22a by, for example, arc ion plating, to form carbon films 21b and 22b. Here, the carbon particles 20B are particles generated from a carbon target (not shown).

[0047] In this embodiment, to prevent the temperature of the first and second film formation zones 17A and 17B from rising during film formation, the carbon film 21b (22b) is formed in one of the first and second film formation zones 17A and 17B, and then the carbon film 22b (21b) is formed in the other. The current applied to the carbon target, the bias voltage on the separator substrate 12A side, and the temperature within the carbon film formation unit 44 are adjusted to achieve film formation conditions that satisfy F(t) + G(T) ≦ 10, and the carbon films 21b and 22b are sequentially formed. The assembly 30 is then transported to the open-air section 45, and the separator substrate 12A is removed from the assembly 30.

[0048] Alternatively, film formation may be performed using a film formation apparatus 50 shown in Fig. 5B. The film formation apparatus 40 shown in Fig. 5B includes a vacuum chamber 51, which houses a rotating jig 56 for mounting the separator substrate 12A (assembly 30). The rotating jig 56 is a mounting jig that holds the assembly 30 upright so that one of the first and second film formation regions 17A, 17B of the separator substrate 12A faces the inner wall of the vacuum chamber 51. An etching source 52, a heater 53, a carbon evaporation source 54, and a titanium evaporation source 55 are provided on the inner wall of the vacuum chamber 51.

[0049] During film formation, the assembly 30 is attached to the rotating jig 56 in an upright position so that the first film formation region 17A of the separator substrate 12A faces the inner wall of the vacuum chamber 51. Next, the separator substrate 12A is set on the rotating jig 56, and the rotating jig 56 is rotated at a predetermined rotation speed. At this time, the separator substrate 12A is heated by the heater 53, and while maintaining this heated state, the first film formation region 17A of the separator substrate 12A is etched by the etching source 52.

[0050] Next, titanium particles generated from a titanium evaporation source 55 are deposited in the first film formation zone 17A by sputtering, forming a titanium film 21a. Next, carbon particles generated from a carbon evaporation source 54 are deposited on the titanium film 21a by arc ion plating, forming a carbon film 21b. After the first conductive film 21 is deposited in the first film formation zone 17A, the assembly 30 is inverted and reattached to the rotating jig 56, and the second conductive film 22 is deposited in the second film formation zone 17B in the same manner. As described above, the first and second conductive films 21 and 22 are deposited so as to satisfy the film formation condition F(t)+G(T)≦10.

[0051] According to this embodiment, both F(t), a function of the difference t in film thickness between the first and second conductive films 21 and 22, and G(T), a function of the maximum temperature T reached during film formation in the portions where the first and second film formation regions 17A and 17B are formed, are quadratic functions that calculate the amount of warpage of the separator 12. Therefore, if the first and second conductive films 21 and 22 are formed under film formation conditions that satisfy F(t) + G(T) ≦ 10, the amount of warpage of the separator 12 can be reduced to 10 mm or less. If F(t) + G(T) ≦ 7 is satisfied, the amount of warpage of the separator 12 can be reduced to 7 mm or less, so it is more preferable to satisfy this condition.

[0052] 3. Derivation of film formation conditions in the setting process The derivation of the above-mentioned formulas (1) and (2) is shown below. First, a separator substrate 12A was prepared by press-molding a 0.1 mm (100 μm) thick foil made of stainless steel (JIS standard: SUS304). Next, the separator substrate 12A was placed on a surface plate with the first film formation region 17A facing downward, and the maximum height from the surface plate was defined as the amount of warpage A.

[0053] Next, an assembly 30 was prepared in which masking jigs 31 and 32 made of stainless steel (JIS standard: SUS304) were attached so that the first and second film formation regions 17A and 17B of the separator substrate 12A were exposed. The thickness of the spacer 33 was 1 mm, and the thickness of the masking jigs 31 and 32 was 2 mm.

[0054] Mask jigs 31 and 32 were set on separator substrate 12A, and first conductive film 21 and second conductive film 22 were formed on each side by PVD in first film formation region 17A and second film formation region 17B, respectively.

[0055] The film formation conditions here were as follows: after evacuating the vacuum chamber 51, the chamber was heated to 150°C with the heater 53, evacuated, argon gas was introduced, and sputter cleaning was performed on the first film formation region 17A of the separator substrate 12A at a vacuum level of 0.2 Pa. The titanium film 21a was formed by magnetron sputtering, and the carbon film 21b was formed by arc ion plating.

[0056] Here, a thermocouple was attached to the separator substrate 12A to measure the temperature during film formation. The film formation rate during film formation was controlled so that the maximum temperature reached in the portions of the separator substrate 12A where the first and second film formation regions 17A and 17B were formed (film formation region temperature in Table 1) was 280°C, and the first and second conductive films 21 and 22 were formed. In the levels of Reference Examples 1-1 to 1-7 shown in Table 1, the thickness of the titanium film 21a was made thicker than the thickness of the titanium film 22a, and the thicknesses of the carbon films 21b and 22b were made the same. The difference in film thickness between the first conductive film 21 and the second conductive film 22 is shown in Table 1. The Ti column in Table 1 indicates the film thickness of each of the titanium films 21a and 22a, and the C column indicates the film thickness of each of the carbon films 21b and 22b.

[0057] After the first and second conductive films 21, 22 were formed, the warpage B of the separator 12 (separator substrate 12A) manufactured by the method described above was measured. Here, for each of Reference Examples 1-1 to 1-7, "warpage B - warpage A = warpage change" was measured. The results are shown in Table 1. Note that a negative warpage change indicates a smaller warpage, but if the temperature in the film formation area is low, the dimensions can be corrected using a mask jig during film formation, which reduces the warpage.

[0058] Here, Fig. 6 shows the plotted results of the relationship between film thickness difference and warpage change amount for Reference Examples 1-1 to 1-7 shown in Table 1. In Fig. 6, the plotted points are located almost on a quadratic curve, so an approximation formula for the quadratic curve was calculated based on these points. The approximation formula is a formula in which the warpage change amount is a function of film thickness difference t, with F(t), and corresponds to the above-mentioned formula (1).

[0059] [Table 1]

[0060] Next, separators were manufactured using the same film-forming method as in Reference Examples 1-1 to 1-7. In Reference Examples 2-1 to 2-4, the film-forming speed of first and second conductive films 21, 22 was changed by adjusting the power or current applied to the conductive material target, the atmospheric temperature during film formation, the bias voltage between the target and the separator substrate, etc., and the warpage change amount was measured for Reference Examples 2-1 to 2-4 using the same method as described above, in which the maximum temperature reached during film formation in the portions where first film-forming region 17A and second film-forming region 17B were formed (film-forming region temperature in Table 1) was adjusted. The results are shown in Table 2.

[0061] In Reference Examples 2-1 to 2-4, the thickness of each of the titanium film 21a of the first conductive film 21 and the titanium film 22a of the second conductive film 22 is 200 nm, as shown in the Ti column of Table 2. The thickness of each of the carbon film 21b of the first conductive film 21 and the carbon film 22b of the second conductive film 22 is 50 nm, as shown in the C column of Table 3.

[0062] Here, Fig. 7 shows the plot results of the relationship between the maximum temperature achieved and the amount of warpage change for Reference Examples 2-1 to 2-4 shown in Table 2. Since the plotted points in Fig. 7 are located almost on a quadratic curve, an approximation formula for the quadratic curve was calculated based on these points. The approximation formula is a formula in which the amount of warpage change is G(t) as a function of the maximum temperature achieved T, and corresponds to the above-mentioned formula (2).

[0063] [Table 2]

[0064] From the above results, it is believed that the warpage of separator 12 can be reduced to approximately 10 mm or less if the film formation conditions are set so that the values ​​of F(t) and G(T) calculated by the following equations (1) and (2) satisfy the condition F(t) + G(T) ≦ 10. Here, for example, if the film thickness difference t is set to 300 nm, F(t) is 4. In this case, to reduce the warpage to 10 mm or less, the maximum temperature T should not exceed 380°C so that G(T) is 6 or less, as is clear from FIG. 7.

[0065] 4. Results of contact resistance of conductive film In Reference Examples 3-1 to 3-6, the second conductive film 22 was formed only in the second film formation region 17B of the separator substrate 12A using a method similar to that described above. Specifically, the thicknesses of the titanium film 22a and the carbon film 22b of the second conductive film 22 are as shown in the Ti and C columns in Table 3, respectively.

[0066] The contact resistance of the formed second conductive film 22 was measured. The result is shown in Contact Resistance 1 of Table 3. Next, as a durability test, the film was immersed in FCC-20 manufactured by Nippon Chemical Industry Co., Ltd. as a coolant for 200 hours, and then the contact resistance of the second conductive film 22 was measured. The result is shown in Contact Resistance 2 of Table 3.

[0067] [Table 3]

[0068] From the results in Table 1, both the contact resistance 1 after film formation and the contact resistance 2 after the durability test were 1.5 mΩcm 2 The following are Reference Examples 3-3 and 3-4, and from this, it is preferable that the titanium films 21a, 22a formed on the first and second conductive films 21, 22 are at least 10 nm or more, and further, it is preferable that the carbon films 21b, 22b are at least 15 nm or more.

[0069] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0070] 1: fuel cell, 10: single cell, 12A: separator substrate, 12: separator, 15a, 15b: gas flow path, 15c: coolant flow path, 17A: first film formation area, 17B: second film formation area, 21: first conductive film, 22: second conductive film, 31, 32: mask jig

Claims

[Claim 1] A method for manufacturing a separator for a fuel cell, comprising: a separator substrate having a first film formation region in which a gas flow path for power generation is formed; and a second film formation region in which a coolant flow path is formed on a back surface of the first film formation region; and coating the first and second film formation regions with first and second conductive films made of a conductive material having higher corrosion resistance than a metallic material of the separator substrate, the separator substrate is made of austenitic stainless steel, The thickness of the separator substrate is in the range of 70 μm to 150 μm, the first and second film formation regions are formed in a central portion of the separator substrate in a plan view of the separator substrate, a thickness of the first conductive film covering the first film formation region is greater than a thickness of the second conductive film covering the second film formation region; the first and second conductive films are respectively composed of a titanium film formed on the surface of the separator substrate and a carbon film formed on the surface of the titanium film; the thickness of the titanium film is in the range of 15 nm to 400 nm; the thickness of the carbon film is in the range of 15 nm to 50 nm; The manufacturing method includes: a setting step of setting film formation conditions so that functions F(t) and G(T) calculated by the following formulas (1) and (2) satisfy the condition F(t)+G(T)≦10; a masking step of covering the separator substrate with a mask jig so that the first and second film formation regions are exposed; a film-forming step of forming the first and second conductive films on the separator substrate by physical vapor deposition under the film-forming conditions; A method for producing a separator for a fuel cell, comprising: F(t)=1.06×10-4×t ２ -1.47×10 －２ ×t+1.04…(1) G(T)=2.68×10-4×T ２ -1.24×10 －１ ×T+1.36…(2) Here, t is the difference in film thickness (nm) between the first and second conductive films, and T is the maximum temperature (°C) reached in the portions where the first and second film formation regions are formed during film formation.

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