JP2021005531A - Composite material, and separator for fuel battery, cell, and stack using the same - Google Patents

Abstract

To provide a composite material with excellent conductivity and corrosion resistance, especially, excellent adhesion between a base material and a carbon layer.SOLUTION: A composite material comprises a carbon layer having conductivity on at least one surface of a plate-like metal base material. The carbon layer is a composite material that contains a carbonaceous material and a matrix resin made of a thermosetting resin, and satisfies the following (*). (*) When a differential thermal analysis is executed for the carbon layer under nitrogen atmosphere and at a programming rate of 10°C/min, a strength value under a temperature of 200°C in a temperature differential curve (DDTA curve) of the differential thermal analysis (DTA curve) to be obtained is 0.035 μV/°C or less, and the strength value at a temperature of 300°C is 0.050 to 0.080 μV/°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a composite material having a carbon layer containing a matrix resin composed of a carbonaceous material and a thermosetting resin on at least one surface of a plate-shaped metal base material, and particularly, adhesion between the base material and the carbon layer. For example, separators for fuel cells such as solid polymer fuel cells, current collectors for redox flow type secondary batteries, gaskets for petroleum refining, petroleum chemistry, etc. Regarding composite materials that can also be used in packing and the like.

In recent years, polymer electrolyte fuel cells have been attracting attention from the viewpoint of environmental protection. Examples of such a fuel cell and a fuel cell separator are shown in FIGS. 7 and 8 (a) and 8 (b), respectively.
Here, FIG. 7 is an exploded view showing the configuration of the unit cells constituting the fuel cell 17, and FIG. 8 is a diagram showing the configuration of the fuel cell separator 5 shown in FIG. 7. 8 (a) is a plan view, and FIG. 8 (b) is a cross-sectional view taken along the line XY of FIG. 8 (a).

The polymer electrolyte fuel cell 17 uses two MEA (membrane / electrode assembly) fuels, which are composed of a polymer electrolyte membrane 6, an anode (fuel electrode) 7, and a cathode (oxidizer electrode) 8. The configuration 10 sandwiched between the battery separators 5 via the gasket 9 is used as a unit cell, and dozens to hundreds of these are stacked to form a stack, and a fuel gas (hydrogen gas), which is a fluid, is used as a cathode at the anode 7. By supplying the oxidative gas (oxygen gas) which is a fluid to No. 8, the current is taken out from the external circuit. As an example, the fuel cell separator 5 has a plurality of gas supply / discharge grooves 11 and a gas supply on one or both sides of a thin plate-like body, as shown in FIGS. 8A and 8B. The shape has an opening 12 for supplying fuel gas or oxidation gas to the discharge groove 11 and a fixing hole 13 for arranging MEAs side by side so that the fuel gas flowing in the fuel cell and the oxidation gas do not mix. In addition to having the function of separating into, it also plays an important role of transferring the electric energy generated by the MEA to the outside and dissipating the heat generated by the MEA to the outside.

Therefore, the characteristics required for the separator for polymer electrolyte fuel cells include the above-mentioned supply of fuel gas and the like, the function as a flow path for discharging the water generated at the cathode and the gas after the reaction, and the use in the battery. Has long-term durability (corrosion resistance) in the environment (high temperature, corrosiveness, low pH, etc.), and has low electrical resistance and excellent conductivity in order to reduce power generation loss (high conductivity, low contact resistance). In addition to the characteristics such as gas impermeable to completely separate fuel gas and oxidation gas on both sides and supply them to the electrodes, molding processability or bolt tightening and vibration during assembly assuming in-vehicle use It is also required to have strength and flexibility (flexibility) that does not crack.

Conventionally, various studies have been made on the development of such a separator. In particular, since a metal-based material is superior in processability to a carbon-based material, it is possible to reduce the thickness of the separator. There is an advantage that the weight can be reduced. However, separators mainly made of metal-based materials basically have poor corrosion resistance, and in particular, in order to withstand the usage environment of fuel cells, further improvement in corrosion resistance is required. For example, a thermosetting resin is used as a matrix. , A molded product (resin layer) formed by mixing this with a filler such as graphite, and a technique of coating this with a thin metal plate to form a separator have been reported (see Patent Document 1). In the technique described in Patent Document 1, in order to ensure the curing of the resin layer (thermosetting resin), post-cure is performed at a temperature of 130 to 300 ° C. for about 3 to 5 hours.

Further, according to a study by the inventors of the present application, a stainless steel plate carbon composite material in which a carbon layer composed of carbon powder and resin powder is laminated on at least one side of a base material made of metal (for example, stainless steel) is available. It has been confirmed that it is useful for the required performance of corrosion resistance, conductivity and flexibility, rather than the carbon separator and the metal separator which have been studied before (see Patent Documents 2 and 3). .. In these Patent Documents 2 and 3, when a thermosetting resin (phenol resin, epoxy resin) is used as the resin powder, the molding temperature (this press) is 150 ° C.

WO 01/085849 Japanese Unexamined Patent Publication No. 2017-071218 JP-A-2017-071219

By the way, in the field of polymer electrolyte fuel cells and the like, technological development is progressing day by day, and especially in the field of fuel cells for automobiles, further thinning and higher performance of separators are required. Further improvement is required for the performance of each separator.
Here, although the corrosion resistance is particularly improved by the technique of providing the resin layer and the carbon layer as in Patent Documents 1 to 3, according to the further study by the inventors of the present application, the carbon layer is provided. It has been found that it is a difficult technique to form on a metal base material with good adhesion, and in fact, an adhesive layer is provided between the metal base material and the carbon layer to improve the adhesion. However, in some cases, there is a concern that the carbon layer may peel off in a fuel cell environment. For example, with respect to the resin layer described in Patent Document 1, there is a possibility that post-curing for a long time causes deterioration of the resin and causes a decrease in adhesion strength. Although various measures can be considered to eliminate such concerns about adhesion, if the blending ratio of the carbonaceous material and the matrix resin in the carbon layer is changed, characteristics other than adhesion [for example, contact resistance (conductiveness) ) And corrosion resistance] are concerned, and there is a limit to drastic improvement from the improvement of the composition of the carbon layer. Also, on the metal substrate side, improvement of the metal species and composition leads to many trials, and for example, if a separate surface treatment is attempted, the process becomes complicated or other than adhesion. There is concern that it may affect the characteristics [for example, contact resistance (conductivity) and corrosion resistance].

Therefore, the inventors of the present application continued to study factors and measures for further improving the adhesion between the base material and the carbon layer, and surprisingly, molding (hot) when forming the carbon layer. It was confirmed that it was affected by the press) conditions, especially the hot press time. Then, as a result of diligent efforts to find a method for quantitatively evaluating how the decrease in adhesion of the carbon layer due to such hot pressing is caused, the inventors of the present application are as follows. New findings were obtained.

That is, verification was carried out using a thermosetting resin (phenol resin) as the matrix resin of the carbon layer, but when a differential thermal analysis (DTA) was performed on the carbon layer in which the adhesion was deteriorated, the difference obtained was obtained. No particular tendency was observed in the thermal analysis curve (DTA curve), but it is very surprising that in the differential curve (DDTA) obtained by further differentiating this DTA curve with temperature, it is near a specific temperature. It was found that a remarkable peak appeared in. As a result of examining this in more detail, when the hot pressing time for forming the carbon layer is relatively short and the curing is insufficient, the temperature of the DDTA curve is strong at around 200 ° C. It was confirmed that a peak appeared, which was close to the melting point of the thermosetting resin (phenol resin) used, and was presumed to be derived from the uncured resin component. On the other hand, when the curing was carried out by excessively lengthening the time for forming the carbon layer, it was confirmed that a strong peak appeared near the temperature of 300 ° C. on the DDTA curve, which caused the cured resin to become brittle. It was speculated that it was derived from the fact that it was stored.

Then, the inventors of the present application comprehensively examine these findings, and in order to improve the adhesion between the metal base material and the carbon layer as compared with the conventional case, optimize the conditions for thermal curing. In order to support this, it was found that it is necessary to confirm the differential curve (DDTA curve) obtained by further differentiating the DTA curve obtained by differential thermal analysis with temperature as described above. , The present invention has been completed.

The present invention has been invented based on the above findings, and an object of the present invention is, for example, a separator for a fuel cell such as a polymer electrolyte fuel cell, and a redox flow type secondary battery. It is a composite that can be used for current collector plates, gaskets and packings for petroleum refining, petroleum chemistry, etc., and has excellent conductivity and corrosion resistance, and in particular, excellent adhesion between the base material and the carbon layer. It is to provide materials. Another object of the present invention is to provide a separator, cell and stack for a fuel cell using such a composite material. Furthermore, in the process of finding such a composite material, a method for evaluating the degree of hardening / embrittlement of the carbon layer, which leads to a decrease in adhesion, from differential thermal analysis is the first finding in the present invention. It is also an object of the present invention to provide the evaluation method.

That is, the gist of the present invention is as follows.
(1) A composite material having a conductive carbon layer on at least one surface of a plate-shaped metal base material.
The carbon layer is a composite material containing a carbonaceous material and a matrix resin made of a thermosetting resin and satisfying the following (*).
(*) When the differential thermal analysis is performed on the carbon layer under a nitrogen atmosphere at a heating rate of 10 ° C./min, the temperature is 200 ° C. in the temperature differential curve (DDTA curve) of the differential thermal analysis curve (DTA curve) obtained. The intensity value at 300 ° C. is 0.035 μV / ° C or less, and the intensity value at a temperature of 300 ° C. is 0.050 to 0.080 μV / ° C.
(2) The composite material according to (1), wherein the thermosetting resin is a phenol resin.
(3) The composite material according to (1) or (2), wherein the thickness of the carbon layer is 30 μm to 200 μm.
(4) The composite material according to any one of (1) to (3), wherein the metal base material is made of a stainless steel material or a titanium material.
(5) A fuel cell separator provided with the composite material according to any one of (1) to (4) above.
(6) A fuel cell cell provided with the fuel cell separator according to (5) above.
(7) A fuel cell stack including the fuel cell cell according to (6) above.

According to the present invention, it is possible to provide a composite material which is excellent in conductivity and corrosion resistance and which is particularly excellent in adhesion between a base material and a carbon layer, and carbon which affects such adhesion. It is also possible to provide a method for evaluating the degree of hardening / embrittlement of a layer from differential thermal analysis. Since the composite material according to the present invention has such characteristics, it can be suitably used as a separator, a cell and a stack for a polymer electrolyte fuel cell.

FIG. 1 is a graph showing the DTA curve and the DDTA curve of the carbon layer, and shows the result of the carbon layer according to Test Example 1. FIG. 2 is a graph showing the DTA curve and the DDTA curve of the carbon layer, and shows the results of the carbon layer according to Test Example 4 [(i) and (ii) in the figure are 200 ° C., respectively). And how to obtain each strength value at 300 ° C. ]. FIG. 3 is a graph showing the DTA curve and the DDTA curve of the carbon layer, and shows the result of the carbon layer according to Test Example 5. FIG. 4 is a schematic explanatory view of a molding method for producing a carbon layer or a composite material. FIG. 5 is a schematic explanatory view of a method of laminating a slurry portion (carbon material and matrix resin), an adhesive layer, and a base material in the production of the composite material of the present invention. FIG. 6 is a schematic explanatory view of a method for measuring contact resistance. FIG. 7 is an exploded view showing a configuration example of a unit cell constituting the fuel cell. FIG. 8A is a plan view showing an example of a fuel cell separator, and FIG. 8B is a cross-sectional view showing a cross section taken along line XY of FIG. 8A.

Hereinafter, the composite material according to the embodiment of the present invention and the method for producing the same will be described in detail.
The composite material of the present embodiment is provided with a conductive carbon layer on at least one surface of a plate-shaped metal base material, and the carbon layer is composed of a carbonaceous material and a matrix resin composed of a thermosetting resin. Including, and as will be described later, those having a predetermined characteristic in a differential curve (DDTA curve) obtained by differentiating the differential thermal analysis curve (DTA curve) obtained when a differential thermal analysis is performed on a carbon layer with temperature. In particular, it is characterized by adopting such a carbon layer structure.

<Base material>
The base material used in the present embodiment is processed into a plate shape, and is not particularly limited as long as it is made of metal. For example, stainless steel material, titanium material, carbon steel and the like can be mentioned, but titanium material and stainless steel material having relatively good corrosion resistance are preferable. The stainless steel refers to a steel having a chromium (Cr) content of 10.5% by mass or more, and may be, for example, austenitic, martensitic, ferritic or a two-phase system of austenitic and ferritic. Further, the titanium material may be either pure titanium or a titanium alloy.

The size and the like of this plate-shaped metal base material can be appropriately changed and adjusted according to the purpose and use of use. Regarding the thickness of the base material, the preferable lower limit is 0.010 mm, the more preferable lower limit is 0.015 mm, and the further preferable lower limit is 0.020 mm, while the preferable upper limit is 0.20 mm, the more preferable upper limit is 0.18 mm, and the further preferable upper limit is 0.15. mm. If the thickness of the base material is less than the above lower limit, the strength of the material may be insufficient, while if it exceeds the above upper limit, for example, it may be integrated when used as a separator for a fuel cell. May affect. Therefore, the thickness of the base material is preferably in the above range.

The base material may be appropriately surface-treated within the scope of the object of the present invention. For example, an oxide film such as a passivation film may be formed to improve corrosion resistance, etc., and metal plating (for example, electroplating method) or acid cleaning (for example, hydrogen fluoride) may be formed to improve conductivity. The surface treatment may be performed by cleaning, dipping, etc. with an acid, nitric acid, or an acid solution containing a mixed acid thereof).

<Carbon layer>
Next, a conductive carbon layer is formed on at least one side of the base material obtained above. The carbon layer contains a carbonaceous material and a matrix resin made of a thermosetting resin.

The carbonaceous material may be any as long as it has conductivity, and its properties are not limited. As the carbonaceous material, for example, any one or more selected from powders such as natural graphite powder, artificial graphite powder, expanded graphite powder, expanded graphite powder, scaly graphite powder, and spheroidal graphite powder. Can be mentioned as a mixture of. Further, if necessary, carbon powder such as carbon black (for example, acetylene black, Ketjen black, etc.) may be contained.
The particle size of this carbonaceous powder is represented by the value of D ₅₀ (cumulative 50% by volume) calculated by a particle size counter of a laser diffraction type particle size distribution measuring device (for example, "Mastersizer 2000" manufactured by Malvern). The average particle size to be formed is usually 4 μm or more and 150 μm or less, preferably 10 μm or more and 30 μm or less, and if it is smaller than 4 μm, the specific surface area is large, so that the resin is difficult to be used for adhesion between particles or a substrate, and is possible. The flexibility may be inferior, and conversely, if it is larger than 150 μm, it is difficult to obtain a smooth surface when forming the carbon layer, and the defect rate may increase.

The properties of the matrix resin are not limited, but it must have the characteristics of curing and embrittlement by differential thermal analysis, which will be described later. Therefore, a thermosetting resin is used. Examples of the thermosetting resin include phenol resins and / or epoxy resins, but from the viewpoint of dimensional stability, ease of processing, etc., it is preferable to use phenol resins, of which they are liquid at room temperature. It is more preferable to use a resol type phenol resin because it is easy to apply the resin uniformly. As such a resol type phenol resin, for example, AH-1305 manufactured by Lignite Co., Ltd. and MEH-8000H manufactured by Meiwa Kasei Co., Ltd. can be preferably used.

A carbon layer is formed by using such a carbonaceous material and a matrix resin made of a thermosetting resin. The method for forming the carbon layer is not particularly limited. For example, the surface of the base material is filled with a mixture containing a carbonaceous material (carbonaceous powder or the like) and a matrix resin (resin powder or the like) and hot-pressed. Examples thereof include a method in which a slurry in which a resin powder and a carbonaceous powder are dispersed in a solvent is applied to the surface of a base material using a doctor blade or the like, dried, and then hot-pressed. Preferably, a powder mixture containing a carbonaceous powder and a resin powder is warmly compression-molded (hot-pressed) to prepare a sheet-shaped carbon layer in advance, and the obtained carbon layer is hot-pressed again on the surface of the base material. It is better to use the hot press method of laminating. By forming the carbon layer by this hot pressing method and laminating the carbon layer, there is an advantage that the carbon layer can be continuously formed on the surface of the base material.

Then, in the present embodiment, it has been found that the carbon layer has the following characteristics, especially when the differential thermal analysis is performed on the carbon layer. The specific method of differential thermal analysis is as follows.
That is, first, a sample (carbon layer) is placed in a differential thermal analyzer, and a differential thermal analysis (DTA) is performed under a nitrogen atmosphere at a heating rate of 10 ° C./min. The differential thermal analysis curve (DTA curve) obtained by this shows a gradual increase as the temperature rises as shown in FIGS. 1 to 3, and although details cannot be grasped, this is the curing of the resin. Is presumed to indicate that Although no particular feature is captured in this DTA curve, when this DTA curve is differentiated by temperature, a differential curve (DDTA curve) as shown in the same FIGS. 1 to 3 can be obtained.

Then, when the obtained DDTA curve was examined in detail, the following was found.
That is, first, as shown in FIG. 2, it was found that a strong peak was observed at a temperature of around 200 ° C. This is an example in which the hot pressing time at the time of forming the carbon layer is shorter than that of Test Example 1 and the like described later (Test Example 4 described later). The peak that appears near this temperature of about 200 ° C. is close to the melting point of the thermosetting resin (phenol resin) used. Therefore, considering the relationship with the hot press conditions, it is derived from the uncured resin component. It is presumed. On the other hand, as shown in FIG. 3, it was also found that a strong peak was observed at a temperature of around 300 ° C. This is an example in which the hot pressing time at the time of forming the carbon layer is lengthened as compared with Test Example 1 and the like described later (Test Example 5 described later), and is a peak in which the resin is sufficiently cured. From this, it is presumed that the curing of the resin has progressed excessively, taking into consideration the evaluation results described later.

On the other hand, with respect to the carbon layer according to Test Example 1 shown in FIG. 1, when the DDTA curve obtained in the same manner was observed, it was not confirmed as a clear peak even at the above 200 ° C. and 300 ° C. .. That is, considering these facts, the appearance of peaks at 200 ° C. and 300 ° C. on such a DDTA curve and the value at that temperature even if no peak appears [in this embodiment, this value of the DDTA curve is used. For convenience, it is referred to as "intensity value" (μV / ° C.). ], The degree of uncured and over-cured (embrittlement) of the resin in the carbon layer can be confirmed, and based on this, the degree of hardening / embrittlement of the carbon layer is within a certain range. For the first time, it was found that the adhesion between the base material and the carbon layer can be improved by this.

Then, based on the above results, the carbon layer in the composite material of the present embodiment does not have peaks at 200 ° C. and 300 ° C. in the DDTA curve, and the intensity value (μV / temperature) at 200 ° C. is 0. It is preferably .035 or less, and the resin component due to the uncured resin is reduced as much as possible. Regarding the calculation of the intensity value, as shown in FIGS. 1 to 3 (particularly, FIG. 2), the measurement points at the temperatures of 80 ° C. to 130 ° C. on each DDTA curve are linearly approximated by the least squares method, and this is used as the baseline. Then, at a temperature of 200 ° C., the difference (absolute value) between the baseline and the measured value on the DDTA curve was determined, and the same was true for the temperature of 300 ° C. When the strength value at a temperature of 200 ° C. exceeds the above, it is presumed that the degree of curing of the resin in the carbon layer is insufficient, and therefore the adhesion between the base material and the carbon layer in the fuel cell environment is lowered. May not be suppressed. However, since the resin component derived from this uncured may be detected at least about 0.0001 μV / temperature, the strength value at 200 ° C. is usually 0.0001 to 0.035 μV / temperature. It is better to be.

On the other hand, the intensity value (μV / temperature) at 300 ° C. in the DDTA curve is preferably 0.050 to 0.080, preferably 0.055 to 0.075. The strength value is also at least about 0.050 because it is assumed that curing may proceed slightly in a part of the carbon layer due to slight variations in the resin structure (composition) and the degree of hot pressing. On the contrary, if it exceeds 0.080, the resin is obviously excessively cured and embrittlement progresses, and there is a possibility that the decrease in the adhesion between the base material and the carbon layer cannot be sufficiently suppressed in the fuel cell environment. There is.

Here, in order to have the degree of hardening / embrittlement of the carbon layer (thermosetting resin) as described above, the conditions of heat treatment (for example, hot pressing) are optimized. Taking the case where the thermosetting resin is a phenol resin as an example, in the case where the phenol resin is 20 to 30% by mass based on the total of the carbonaceous material and the phenol resin in the carbon layer, the heat treatment temperature is 180 to 200 ° C. It is preferable that the heat treatment time is about 1000 to 3000 seconds. The pressure for hot pressing depends on the degree of molding, but is usually about 10 to 60 MPa. That is, the conditions of the heat treatment (for example, hot pressing) are optimized so as to be within the above-mentioned desired degree of hardening / embrittlement depending on the amount of the thermosetting resin used and the type thereof.

Further, in the present embodiment, the mass ratio of the resin to the total mass of the carbonaceous material (C) in the carbon layer and the matrix resin (R) composed of the thermosetting resin [mass%, R / (C + R) ] Is preferably 10 to 30% by mass, more preferably 15 to 20% by mass. If the proportion of the resin is less than 10% by mass, it may be difficult to form the carbon layer, while if it exceeds 30% by mass, sufficient conductivity may not be obtained. The volume ratio (C / R) of these is preferably 6/4 to 9/1, and more preferably 7/3 to 8/2. If the volume ratio (C / R) is smaller than 6/4, the ratio of carbonaceous material may be low and the conductivity may be affected. On the contrary, if it is larger than 9/1, the ratio of matrix resin is low. May affect flexibility, corrosion resistance and flexibility.

The thickness of the carbon layer is preferably 30 to 200 μm. More preferably, it is 40 to 180 μm. If the thickness of the carbon layer is less than 30 μm, sufficient corrosion resistance may not be obtained. On the other hand, if the thickness exceeds 200 μm, it may be integrated or flexible when used as a separator for a fuel cell, for example. It may affect the sex.

Further, in the present embodiment, an adhesive layer forming step of forming an adhesive layer on the surface of the base material may be carried out prior to the formation of the carbon layer. In that case, the base material and the carbon layer are laminated via the adhesive layer. By providing such an adhesive layer, the adhesion between the base material and the carbon layer is improved, and the surface of the base material is covered with the adhesive layer. Therefore, for example, as a polymer electrolyte fuel cell. When used, it has the advantage of improved durability against corrosive environments. The thickness of such an adhesive layer is preferably 0.1 μm or more and 10 μm or less. If the thickness is less than 0.1 μm, the adhesive strength may decrease, and if it exceeds 10 μm, the conductivity of the produced composite material may be affected.

The adhesive composition for forming such an adhesive layer is not particularly limited, but for example, a 1 wt% -phenol resin adhesive composition (solvent: ethylene glycol monobutyl ether, resole type phenol resin). : Product name AH-1305 manufactured by Rignite Co., Ltd., epoxy resin adhesive composition (trade name: YSLV-80XY manufactured by Nittetsu Chemical & Materials Co., Ltd.) and the like can be used.

In this way, a conductive carbon layer is formed on at least one surface of the plate-shaped metal base material to produce the composite material according to the present embodiment. The composite material obtained by the method of the present embodiment preferably has a contact resistance of 10 mΩ · cm ² or less, more preferably 5 mΩ · cm ² or less, and further preferably 3 mΩ · cm ² or less. Moreover, it is preferable that the contact resistance does not substantially change even in an environment corresponding to the usage environment of the fuel cell.

The composite material of the present embodiment is excellent in both conductivity (low contact resistance) and corrosion resistance, and in particular, is extremely excellent in adhesion between the base material and the carbon layer. For example, a polymer electrolyte fuel cell. It is suitably used in applications such as separators for fuel cells for batteries, current collectors for redox flow type secondary batteries, gaskets and packings for petroleum refining and petroleum chemistry. When used as a separator for a polymer electrolyte fuel cell, for example, as shown in FIG. 7, two MEAs composed of a solid polymer electrolyte membrane 6, an anode (fuel electrode) 7, and a cathode (oxidizing agent electrode) 8 are provided. With the fuel cell separator 5 of the above, the configuration 10 sandwiched between the gaskets 9 can be used as a unit cell, and dozens to hundreds of these can be stacked to form a stack.

Hereinafter, the composite material of the present embodiment, its manufacturing method, and each performance evaluation will be specifically described based on a test example.

1. 1. Preparation of plate-shaped metal base material The following three types of commercially available products are used as the base material, and all of them are surface-treated at a temperature of 80 ° C. for 5 minutes using an acid aqueous solution (4% by mass hydrofluoric acid). Immersion).
(1) Pure titanium material (JIS type 1, thickness 50 μm)
(2) Austenitic stainless steel (SUS316L, thickness 50 μm)
(3) Ferritic stainless steel (SUS444, thickness 50 μm)

2. 2. Formation of carbon layer [Formation of adhesive layer]
An adhesive layer was formed on the surface of the base material after the surface treatment with the above acid aqueous solution to obtain a base material with the adhesive layer. Specifically, using an applicator, the adhesive composition was applied to the surface of the substrate so that the coating thickness was 10 μm, and dried at room temperature for 10 minutes to form an adhesive layer.
As the adhesive composition, a resol-type phenol resin (trade name: AH-1305 manufactured by Lignite Co., Ltd.) dissolved in ethylene glycol monobutyl ether so as to be 1 wt% was used.

[Formation of carbon layer]
As carbonaceous material, 95% by mass spheroidal graphite powder (manufactured by YAS, SG6, average particle size: 6.74 μm) and 5% by mass of acetylene black (manufactured by Denka Co., Ltd., Li-100, average). A mixed material with a particle size of 35 nm) was used, and a resole-type phenol resin (manufactured by Lignite Co., Ltd., AH-1305) was used as the matrix resin. Then, the carbonaceous material and the matrix resin were dissolved in a solvent (ethylene glycol monobutyl ether) having a mass three times that of the matrix resin to prepare a slurry. Three types of slurries were prepared in which the mass of the matrix resin was 14% by mass, 22% by mass, and 45% by mass with respect to the total mass of the carbonaceous material and the matrix resin.
Then, each of these slurries is applied to the adhesive layer forming surface of the base material on which the adhesive layer is formed, heated at 80 ° C. for 5 minutes using a hot plate to dry the solvent, and the slurry on the base material is dried. Each preform body (reference numeral 1') in which the part (reference numeral 3) was pre-cured was used (FIG. 5). Subsequently, each of the preform bodies (reference numeral 1') was hot-pressed using the press device (desktop hot press MP-SCL manufactured by Toyo Seiki Seisakusho Co., Ltd.) shown in FIG. 4, whereby the preform body was finally cured. The resulting carbon layer was obtained as each composite material of the present embodiment. The pressure of the hot press was 20 MPa, and the temperature and time were as shown in Table 1. The thickness of one side of the carbon layer of the obtained composite material is as shown in Table 1. An adhesive layer and a carbon layer were similarly formed on the base material surface on one side.

The evaluation of each composite material obtained above was performed as follows.
[Differential thermal analysis of carbon layer]
About 30 mg of only the carbon layer was scraped from each composite material using tweezers. The scraped sample was enclosed in an aluminum container with a diameter of 4 mm and a height of 2.5 mm. Then, the differential thermal analysis was performed on each sample enclosed in the aluminum container under the following conditions to obtain a differential thermal analysis curve (DTA curve) and further to obtain a temperature differential curve (DDTA curve) of this DTA curve.
・ Measuring device: Hitachi High-Tech Science Corporation differential thermal weight simultaneous measuring device TG / DTA7300
・ Atmospheric gas: Nitrogen ・ Atmospheric gas flow rate: 200mL / min
・ Temperature temperature condition: 10 ℃ / min
・ Achieved temperature: 1000 ℃

Subsequently, in each of the DDTA curves obtained above, as shown in FIGS. 1 to 3, an approximate straight line is obtained from the measurement points at 80 ° C. to 130 ° C. by the least squares method, and this approximate straight line is extended to 300 ° C. or higher. Using the straight line as the baseline, the difference (absolute value) between the value on the DDTA curve at 200 ° C and 300 ° C and the baseline was obtained, and the intensity value (μV / ° C) at a temperature of 200 ° C and the intensity at 300 ° C, respectively. The value (μV / ° C.) [For example, the absolute values of (i) and (ii) shown in FIG. 2 correspond to the respective intensity values at 200 ° C. and 300 ° C., respectively. It is obtained in the same manner in FIGS. 1 and 3. ].
The results are shown in Table 1.

[Measurement of matrix resin content in carbon layer]
The cross section of each test material was observed using SEM (JSM-7800F manufactured by JEOL Ltd.). For the carbon layer, 10 visual fields were randomly measured, and the ratio of the presence of the resin and the ratio of the presence of the carbonaceous material were measured and calculated from the image of the measurement visual field to obtain the average volume content of the resin. Then, the densities of the resin and the carbonaceous material were set to 1.2 g / cm ³ and 0.85 g / cm ³ , respectively, and each was recalculated to mass%.
The results are shown in Table 1.

[Evaluation of corrosion resistance]
The test material was immersed in a fuel cell simulated environment, and the corrosion resistance was evaluated by the presence or absence of a precipitate in the solution. Specifically, by processing each composite material 20 mm × 20 mm, which chloride 300ppm ion (Cl ^-) precipitation of the solution after immersion for 240 hours to contain 80 ° C. in sulfuric acid solution but a (pH 3) The presence or absence of was confirmed and evaluated according to the following criteria.
The results obtained are shown in Table 2 below.
⊚: No precipitate and no discoloration in the solution ○: No precipitate but discoloration in the solution ×: With precipitate

[Evaluation of surface conductivity (contact resistance)]
The contact resistance with carbon paper was measured. FIG. 6 is a diagram showing a configuration of a device for measuring the contact resistance of the test material, and the contact resistance was measured using this device.
First, a test material (reference numeral 14) produced by processing each composite material into a size of 15 mm × 15 mm is used as a pair of carbon paper (reference numeral 15) used as a gas diffusion layer for a fuel cell [TGP manufactured by Toray Industries, Inc. -H-90], which was sandwiched between a pair of gold-plated platinum electrodes (reference numeral 16). The area of each carbon paper 15 was 1 cm ² . Next, a load of 10 kgf / cm ² (9.81 × 10 ⁵ Pa) was applied between the pair of platinum electrodes 16. In FIG. 6, the direction of the load is indicated by a white arrow. In this state, a constant current was passed between the pair of platinum electrodes 16, and the voltage drop between the carbon paper 15 and the test material 14 generated at this time was measured. The resistance value was calculated based on this result. Since the obtained resistance value is the sum of the contact resistances of both sides of the test material 14, this was divided by 2 to obtain the contact resistance value per one side of the test material 14, which was evaluated according to the following criteria.
The results obtained are shown in Table 2 below.
◎: less than ^{5mΩ · cm 2 ○: 5mΩ ·} cm 2 or more, 10mΩ · cm ² less than ×: 10mΩ · cm ² or more

[Evaluation of adhesion between base material and carbon layer (before evaluation of corrosion resistance)]
After preparing each composite material, each was processed into a size of 50 mm × 50 mm within 24 hours to obtain each test piece. The adhesion strength of this test piece was evaluated using the cross-cut method. Using a cutter knife, 11 notches reaching the base material, which is the core material, from the coating surface side of the carbon layer were made in parallel with the test piece at 2 mm intervals. Then, 11 more cuts were made so as to be perpendicular to it, and 100 grids were formed. A tape peeling test was performed on the grid. As the tape, cellophane tape (registered trademark) manufactured by Nichiban Co., Ltd. was used. Adhesion was evaluated based on the degree to which the carbon layer was peeled off when the tape attached to the evaluation surface was peeled off.
The results obtained are shown in Table 2 below.
⊚: No peeling is observed in any of the lattices ○: The carbon layer is peeled at 0 or more and less than 5% ×: The carbon layer is peeled by 5% or more

[Evaluation of adhesion between base material and carbon layer (after evaluation of corrosion resistance)]
Each composite was processed into a 20 mm × 20 mm test piece, which was immersed in a sulfuric acid solution (pH 3) at 80 ° C. containing 300 ppm chloride ion (Cl ⁻ ) for 240 hours. Then, the test piece taken out was evaluated for adhesion by using the same cross-cut method as described above.
The results obtained are shown in Table 2 below.
⊚: No peeling is observed in any of the lattices ○: The carbon layer is peeled at 0 or more and less than 5% ×: The carbon layer is peeled by 5% or more

As can be seen from the results of Tables 1 and 2 above, in Test Examples 1 and 6 to 8 in which the ratio of the resin to the slurry and the conditions of hot pressing were optimized, the strength values of 200 ° C. and 300 ° C. in the carbon layer were predetermined. It was possible to obtain a composite material which was not only excellent in contact resistance and corrosion resistance but also very excellent in adhesion between the base material and the carbon layer.

On the other hand, in the composite material according to Test Example 2 in which the resin ratio is smaller than that in Test Example 1, the strength value at 300 ° C. in the carbon layer becomes large under the same hot press conditions as in Test Example 1, which means that the resin is cured. Is presumed to have progressed excessively and became brittle. As a result, the adhesion after the durability test was particularly inferior.

On the contrary, in the composite material according to Test Example 3 in which the resin ratio was larger than that of Test Example 1, the strength value at 200 ° C. in the carbon layer became large under the same hot press conditions as in Test Example 1. It is presumed that the uncured resin component remains and the resin is not sufficiently cured. In this Test Example 3, since the amount of resin was relatively large, the contact resistance could not be satisfied in the first place. Further, since the resin is not sufficiently cured, the adhesion is particularly poor after the durability test.

Further, even if the resin ratio in the slurry is the same as that of Test Example 1, when the hot pressing time is shortened (Test Example 4) or lengthened (Test Example 5), Test Example 3 or Test Example, respectively. Similar results to 2 are obtained, and in Test Example 4 where the hot press time is short, the strength value at 200 ° C., which is presumed to be derived from the uncured resin, is large, and conversely, in Test Example 5 where the hot press time is long. The strength value at 300 ° C., which is presumed to be derived from excessive curing, increased, and all of them were inferior in adhesion between the base material and the carbon layer.

1'... preform body, 1 ... composite material, 2 ... adhesive layer, 3 (1') ... slurry part, 4 ... base material, 5 ... fuel cell separator, 6 ... solid polymer electrolyte membrane, 7 ... anode (Fuel electrode), 8 ... Cathode (oxidizer electrode), 9 ... Gasket, 10 ... Unit cell, 11 ... Gas supply / discharge groove, 12 ... Opening, 13 ... Fixing hole, 14 ... Test material, 15 ... Carbon paper , 16 ... platinum electrode, 17 ... polymer electrolyte fuel cell, 100 ... press device, 101 ... male type, 102 ... female type, 103 ... mold, 104 ... machine frame, 105 ... hydraulic cylinder.

Claims (7)

A composite material having a conductive carbon layer on at least one side of a plate-shaped metal base material.
The carbon layer is a composite material containing a carbonaceous material and a matrix resin made of a thermosetting resin and satisfying the following (*).
(*) When the differential thermal analysis is performed on the carbon layer under a nitrogen atmosphere at a heating rate of 10 ° C./min, the temperature is 200 ° C. in the temperature differential curve (DDTA curve) of the differential thermal analysis curve (DTA curve) obtained. The intensity value at 300 ° C. is 0.035 μV / ° C or less, and the intensity value at a temperature of 300 ° C. is 0.050 to 0.080 μV / ° C. The composite material according to claim 1, wherein the thermosetting resin is a phenol resin. The composite material according to claim 1 or 2, wherein the thickness of the carbon layer is 30 μm to 200 μm. The composite material according to any one of claims 1 to 3, wherein the metal base material is made of stainless steel or titanium. A fuel cell separator comprising the composite material according to any one of claims 1 to 4. A fuel cell cell provided with the fuel cell separator according to claim 5. A fuel cell stack comprising the fuel cell cell according to claim 6.

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