JP6928448B2 - Method for forming a conductive carbon film, method for manufacturing a conductive carbon film coating member, and method for manufacturing a separator for a fuel cell - Google Patents

Description

The present invention relates to a method for forming a conductive carbon film, a method for manufacturing a conductive carbon film coating member, and a method for manufacturing a separator for a fuel cell.

In recent years, fuel cell vehicles have been attracting increasing attention as one of the next-generation vehicles to replace vehicles equipped with an internal combustion engine. Technology development related to fuel cells has been actively carried out for some time, and various technologies have been developed so as to satisfy the required characteristics. For example, a separator, which is a component of a fuel cell, is required to have conductivity, corrosion resistance, strength, etc. As a technology to meet these required characteristics, a carbon film having conductivity on the surface of a work (base material) (hereinafter, "" It is known to form a conductive carbon film ").

Patent Document 1 discloses a method of adding an element such as boron to a carbon film in order to impart conductivity to the carbon film. Patent Document 2 discloses a method of forming a conductive carbon film by a plasma chemical vapor deposition method using a high-frequency power source (hereinafter, “high-frequency plasma CVD method”). Patent Document 3 describes a plasma chemical vapor deposition method using a DC power source using a carbocyclic compound gas such as benzene, toluene, xylene and naphthalene and a heterocyclic compound gas such as pyridine, pyrazine and pyrrole (hereinafter referred to as , "DC Plasma CVD Method") discloses a method of forming a conductive carbon film.

Japanese Unexamined Patent Publication No. 2012-188688 Japanese Unexamined Patent Publication No. 2012-146616 Japanese Unexamined Patent Publication No. 2008-4540

When a conductive carbon film is formed by using additive elements as in Patent Document 1, a plurality of raw materials and post-treatment are required in the film forming process, which complicates the carbon film manufacturing process. Further, by adding an element to the carbon film, various properties (mainly corrosion resistance) of the carbon film may be changed.

When a high-frequency power source is used for the plasma processing device as in Patent Document 2, the device structure is inevitably complicated, and it becomes difficult to manufacture the device at low cost. Further, the high-frequency plasma CVD method is not suitable for film formation processing of a large number of workpieces, and is not suitable for mass production of conductive carbon film coating members such as fuel cell separators.

On the other hand, if a DC power supply is used for the plasma processing apparatus as in Patent Document 3, the apparatus structure becomes simpler than that of the plasma processing apparatus using the high frequency power supply, and it is possible to perform film formation processing of a large number of workpieces. However, the density of the plasma generated by the DC plasma CVD method is smaller than the density of the plasma generated by the high frequency plasma CVD method. Therefore, Patent Document 3 uses a gas of a carbocyclic compound such as benzene, toluene, xylene and naphthalene, which is easily decomposed when the raw material gas is supplied, and a gas of a heterocyclic compound such as pyridine, pyrazine and pyrrole. ing. Since these cyclic compounds are liquid raw materials, when these cyclic compounds are used as the raw material gas, it is essential to provide a heating mechanism such as a heater in the gas supply line in order to gasify the raw materials. Become. This complicates the structure of the plasma processing apparatus and makes the apparatus expensive.

The present invention has been made in view of the above circumstances, and an object of the present invention is to enable a conductive carbon film having excellent corrosion resistance to be formed even with a plasma processing apparatus having a simple structure.

The present invention for solving the above problems is a method for forming a conductive carbon film on a work by a DC plasma CVD method, wherein acetylene gas and hydrogen gas are formed in the process of forming the conductive carbon film. Is maintained, the flow ratio of the acetylene gas to the hydrogen gas is 1 to 5, and the film formation temperature is set to 520 ° C. or higher and 750 ° C. or lower to turn the acetylene gas into plasma.

The present invention from another viewpoint is a method for manufacturing a conductive carbon film coating member, wherein a conductive carbon film is formed on a work by using the above-mentioned method for forming a conductive carbon film, and the conductive carbon film is coated. It is characterized by manufacturing the members.

The present invention from yet another viewpoint is a method for manufacturing a separator for a fuel cell, characterized in that a conductive carbon film is formed on the surface of a separator member for a fuel cell by using the above-mentioned method for forming a conductive carbon film. It is supposed to be.
From yet another point of view, the present invention is a method for manufacturing a separator for a fuel cell, which has a carbon number as a raw material gas in a step of forming a conductive carbon film on the surface of a separator member for a fuel cell by a DC plasma CVD method. Using only a chain hydrocarbon gas of 4 or less, or a mixed gas composed of the chain hydrocarbon gas and hydrogen gas, the chain hydrocarbon gas is converted into plasma at a film formation temperature of 520 ° C. or higher and 750 ° C. or lower. It is characterized by doing.

According to the present invention, a conductive carbon film having excellent corrosion resistance can be formed even with a plasma processing apparatus having a simple structure.

It is a figure which shows the schematic structure of the plasma processing apparatus which concerns on embodiment of this invention. It is a figure which shows the film formation flow of the conductive carbon film which concerns on embodiment of this invention. It is a figure which shows the schematic structure of the contact resistance measuring apparatus. It is a figure which shows the schematic structure of the corrosion test apparatus.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

In the present embodiment, the plasma processing apparatus 1 as shown in FIG. 1 is used to form a conductive carbon film on the surface of the work W (base material) by the DC plasma CVD method. The plasma processing device 1 includes a chamber 2 in which plasma processing of the housed work W is performed, a table 3 on which the work W is placed, and a DC pulse power supply 4 connected to the table 3. A gas inlet 5 for supplying the raw material gas of the conductive carbon film is provided above the table 3, and the gas inlet 5 is connected to a gas supply source 6 outside the chamber. A gas exhaust pipe 7 for exhausting the atmospheric gas in the chamber is provided on the side wall portion of the chamber 2, and the gas exhaust pipe 7 is connected to the vacuum pump 8. A heater 9 is provided in the chamber so as to cover the periphery of the work W, and the work W is heated by the heater 9. The temperature of the work W is measured from the glass window of the chamber 2 using an infrared radiation thermometer (not shown). The material of the work W is not particularly limited as long as it is a material used for a member (fuel cell separator, etc.) covered with a conductive carbon film, but for example, a metal material such as pure titanium or a titanium alloy may be used. Will be adopted.

The configuration of the plasma processing apparatus 1 is not limited to that described in this embodiment. Other device configurations may be used as long as the device can form a carbon film by the DC plasma CVD method. For example, in the present embodiment, the DC pulse power supply 4 is used as the power supply for plasma generation, but it does not have to be the pulse power supply. However, if plasma is generated by the DC pulse power supply 4, the plasma density is increased, and high-energy ions can be supplied to the work W to densify the film. It is also possible to suppress the occurrence of arcing. Therefore, it is preferable to use the DC pulse power supply 4 as the power supply for plasma generation.

Next, a method for forming the conductive carbon film will be described. In the present embodiment, a conductive carbon film is formed on the work W according to the process shown in FIG. 2, and a member coated with the conductive carbon film is manufactured.

<Work W set, vacuuming>
First, the work W is carried into the chamber 2 and the work W is set at a predetermined position. After that, the pressure in the chamber is evacuated to, for example, 10 Pa or less.

<Heating process>
Next, a small amount of hydrogen gas is supplied into the chamber to operate the heater 9. In this heating step, the temperature of the work W is heated to near the plasma processing temperature of, for example, about 500 ° C. Here, exhaust is performed so that the pressure in the chamber is maintained at, for example, about 200 Pa.

<H ₂ + Ar cleaning process>
Next, the work W is further heated by setting the set temperature of the heater 9 to, for example, 520 ° C. or higher. Further, in addition to hydrogen gas, argon gas is further supplied. Here, exhaust is performed so that the pressure in the chamber is maintained at, for example, about 200 Pa. Then, the DC pulse power supply 4 is operated, and the work surface is cleaned by the _{H 2 + Ar bombard treatment.} The voltage, frequency, duty ratio, etc. of the DC pulse power supply 4 are appropriately set so that the gas supplied into the chamber becomes plasma.

<Film formation process>
Next, the set temperature of the heater 9 is adjusted so that the temperature of the work W is 520 ° C. or higher. In addition, the supply of hydrogen gas and argon gas is stopped, and the supply of chain hydrocarbon gas having 4 or less carbon atoms is started as a raw material gas. In this state, the DC pulse power supply 4 is operated to turn the chain hydrocarbon gas into plasma. As a result, a conductive carbon film is formed on the surface of the work W.

Examples of the chain hydrocarbon gas having 4 or less carbon atoms include methane gas, acetylene gas, propane gas and butane gas, and among these, acetylene gas is preferably used. Acetylene gas is industrially inexpensive and easily available. Further, acetylene gas has a lower plasma discharge voltage than methane gas, propane gas, butane gas, etc., and can suppress power supply costs. Further, if acetylene gas is used, the film formation rate can be increased as compared with methane gas.

In the present embodiment, a single type of chain hydrocarbon gas is supplied when the raw material gas is supplied, but a plurality of types of chain hydrocarbon gas may be mixed and supplied. Further, the hydrogen gas may be supplied together with the chain hydrocarbon gas. When supplying acetylene gas and hydrogen gas in the _{film forming process, acetylene gas and hydrogen gas are gradually changed to a predetermined flow rate from the H 2} + Ar cleaning process to the film forming process, so that arcing is less likely to occur. .. When the flow rate ratio of acetylene gas to hydrogen gas (C ₂ H ₂ / H ₂ ) is 1 to 5, it becomes easy to suppress the occurrence of arcing, and a stable film forming process can be performed. From the viewpoint of performing a more stable film forming process, it is preferable to set _{the flow rate ratio (C 2} H ₂ / H _{2) of acetylene gas to hydrogen gas to 3 to 4.}

The pressure in the chamber in the film forming step (hereinafter, “deposition pressure”) is preferably 20 to 1000 Pa. The film forming pressure is more preferably 150 to 500 Pa.

The temperature of the work W in the film forming step (hereinafter, “deposition temperature”) needs to be 520 ° C. or higher. When the film formation temperature is less than 520 ° C., the amount of hydrogen in the carbon film formed on the work surface increases, and a carbon film having no conductivity is formed. On the other hand, if the film formation temperature exceeds 750 ° C., the corrosion resistance may deteriorate, and it is necessary to further improve the heat insulating property of the chamber 2, and the size of the plasma processing apparatus 1 is increased only for the purpose of ensuring the heat insulating property. Is also a concern. Therefore, the upper limit of the film formation temperature is preferably 750 ° C. A more preferable lower limit of the film formation temperature is 580 ° C. The more preferable upper limit of the film formation temperature is 670 ° C.

<Cooling process>
After forming the conductive carbon film, the heater 9, the supply of the raw material gas, and the DC pulse power supply 4 are stopped to cool the work W. After that, the work W is carried out from the chamber 2.

The conductive carbon film in this embodiment is formed by the above procedure. This conductive carbon film is a film having a low contact resistance value even after a long time has passed since the film was formed. Then, according to the method for forming the conductive carbon film of the present embodiment, since the raw material gas used in the film forming step is a chain hydrocarbon gas having 4 or less carbon atoms, the gas inlet 5 from the gas supply source 6 No heating mechanism is required to vaporize the raw materials in the gas lines up to. That is, according to the method for forming the conductive carbon film of the present embodiment, it is possible to form the conductive carbon film having excellent corrosion resistance with the plasma processing apparatus 1 having a simpler structure.

Further, when a liquid raw material such as benzene or toluene is used, it is assumed that it will be difficult to supply the raw material gas in consideration of the increase in size of the plasma processing apparatus 1, but in the present embodiment, carbon is used as the raw material. Since the chain hydrocarbon gas of several 4 or less is used, the raw material gas can be supplied even if the plasma processing apparatus 1 is enlarged. That is, if the method for forming the conductive carbon film of the present embodiment is used, the size of the plasma processing apparatus 1 can be increased to increase the mass production capacity, so that the production cost can be suppressed.

Although the embodiments of the present invention have been described above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

A carbon film was formed on the surface of the work using the DC plasma CVD method, and the conductivity and corrosion resistance of the carbon film were evaluated.

A plasma processing apparatus having the structure shown in FIG. 1 was used for the carbon film film forming process. A DC pulse power supply was used as the power source for plasma generation, and a titanium plate was used as the work. The formation flow of the carbon film is the same as that described in the above-described embodiment, but in this embodiment, a plurality of types of carbon films are formed by changing the treatment conditions. In the following description of the film formation flow, first, the processing conditions of Example 1 will be described. Table 1 below shows the processing conditions of Example 1. The flow rates of hydrogen gas, argon gas, acetylene gas, and methane gas in the following description are volumetric flow rates at 0 ° C. and 1 atm.

<Workset, evacuation>
After the work is carried into the chamber, the inside of the chamber is evacuated for 30 minutes to reduce the pressure in the chamber to 10 Pa or less. At this time, the heater is not operated.

<Heating process>
Next, 40 ccm (0 ° C., 1 atm) of hydrogen gas is supplied into the chamber, and the displacement is adjusted so that the pressure in the chamber is 220 Pa. Then, the set temperature of the heater is set to 500 ° C., and the work is heated for 60 minutes. This heating step heats the work to 500 ° C., which is close to the plasma processing temperature. The work temperature in the chamber is measured with an infrared radiation thermometer. Before measuring the temperature of the work, the emissivity of the infrared radiation thermometer is corrected. The emissivity is corrected by heating the workpiece in which the thermocouple is embedded under the same conditions as in this heating step, and comparing the temperature measured by the thermocouple with the temperature measured by the infrared radiation thermometer. conduct. In this example, the emissivity was corrected so that the difference between the temperature measurement result by the thermocouple and the temperature measurement result by the infrared radiation thermometer was within ± 5 ° C.

<H ₂ + Ar cleaning process>
Next, the work is heated to 580 ° C. with the set temperature of the heater set to 580 ° C. Further, in addition to hydrogen gas, argon gas is supplied at a flow rate of 40 ccm (0 ° C., 1 atm). At the same time, the displacement is adjusted to maintain the pressure in the chamber at 220 Pa. Further, the voltage of the DC pulse power supply is set to 300 V, the frequency is set to 25 kHz, and the duty ratio is set to 80%. As a result, the H ₂ + Ar bombard treatment is started, and the work surface is cleaned.

<Film formation process>
Next, while maintaining the temperature of the work at 580 ° C., the supply of hydrogen gas and argon gas is stopped, and the acetylene gas is supplied at a flow rate of 250 ccm (0 ° C., 1 atm). By adjusting the displacement, the pressure in the chamber (deposition pressure) is maintained at 220 Pa. Also, the voltage of the DC pulse power supply is raised to 600V. As a result, the acetylene gas is turned into plasma, and carbon is adsorbed on the surface of the work. This state is maintained for 10 minutes, and a carbon film having a predetermined film thickness is formed on the surface of the work.

<Cooling process>
After that, the heater, the supply of acetylene gas, and the DC pulse power supply are stopped to cool the work.

The carbon film of Example 1 is formed under such treatment conditions. The processing conditions for the film formation steps of the other examples and comparative examples are shown in Table 2 below.

When only acetylene gas or only methane gas is supplied as the raw material gas, the treatment conditions up to the film forming step in the other Examples and Comparative Examples other than Example 1 are the same as those in Example 1. On the other hand, in Examples 20 and 21 in which a mixed gas of acetylene gas and hydrogen gas is used as the raw material gas, in addition to the processing conditions of the film forming process, the processing conditions of the heating process and the H ₂ + Ar cleaning process are also the processing conditions of Example 1. Is partially different. Table 3 below shows the processing conditions of Example 20. The treatment conditions of Example 21 differ only in the flow rate of acetylene gas from the treatment conditions of Example 20.

Next, a method for evaluating the conductivity and corrosion resistance of the carbon film formed under the above treatment conditions will be described. The conductivity is evaluated based on the contact resistance measurement test results. In addition, the corrosion resistance is evaluated by measuring the contact resistance value again after the corrosion test and based on the difference in the contact resistance value before and after the corrosion test. The test method for each test is as follows.

(Contact resistance measurement test)
The contact resistance was measured by the measuring device 20 shown in FIG. Specifically, the carbon paper 23 is placed on the carbon film 22 formed on the surface of the titanium plate 21, and the carbon paper 23 is sandwiched between the two metal plates 24. Then, a load of 1.1 MPa is applied to each of the two metal plates 24 by the load cell from the direction perpendicular to the contact surface with the titanium plate 21 or the carbon paper 23. In this state, a DC current of 1 A is passed from the constant current DC power supply 25 between the two metal plates 24. Then, the electric resistance value is calculated by measuring the potential difference between the titanium plate 21 and the carbon paper 23 60 seconds after the start of the load. This value is taken as the contact resistance value of the carbon film 22. In this embodiment, if the contact resistance value measured in this way is 10 mΩ · cm ² or less, it is determined that the carbon film has sufficient conductivity. The area of the contact surface where the carbon film 22 and the carbon paper 23 come into contact is 13 mm × 17 mm.

(Corrosion test)
The corrosion test was carried out by the test apparatus 30 shown in FIG. _{Specifically,} a container 31 containing the H 2 SO ₄ solution, prepared container 32 containing the KCl solution, the counter electrode 33 (Pt) in _H 2 SO ₄ solution in the container 31, KCl container 32 solution The reference electrode 34 (Ag / AgCl) is arranged so as to be immersed therein. Further, as the sample electrode 35, a titanium plate coated with a carbon film is arranged so as to be immersed in _{the H 2} SO _{4 solution of the container 31.} In addition, a Luggin capillary 36 is provided as a salt bridge between the _{H 2} SO _{4 solution and the K Cl solution.} In the test apparatus 30 configured in this way, the set voltage of the potentiostat was set to 0.9 V (SHE: standard hydrogen electrode) and left for 65 hours. The H ₂ SO ₄ solution has an aqueous solution temperature of 80 ° C., a pH of 3, a Cl ^- ion concentration of 100 ppm, and an F ^- ion concentration of 50 ppm.

The contact resistance values before and after the corrosion test are shown in Table 2 above.

In Table 2, the film thickness of the carbon film is also shown. The film thickness of the carbon films of Examples 5, 11 and Comparative Example 2 was measured by performing SEM cross-sectional observation after FIB (focused ion beam) processing. After that, the same sample was subjected to semi-quantitative analysis by EPMA, the ratio of C and Ti (C / Ti) was calculated, and a calibration curve was prepared based on (C / Ti) × film thickness. For other samples, the film thickness was calculated by semi-quantitative analysis of EPMA using this calibration curve.

As shown in Table 2, among the carbon films formed using acetylene gas, the carbon film of Comparative Example 1 has a contact resistance value of more than ^{10 mΩ · cm 2 at the stage before the corrosion test, and has poor conductivity.} It is enough. On the other hand, the carbon films of Examples 1 to 16 and Comparative Example 2 have sufficient conductivity at the stage before the corrosion test. However, the carbon film of Examples 1 to 16 has a contact resistance value ^{of less than 10 mΩ · cm 2} even after the corrosion test and still has sufficient conductivity, but the carbon film of Comparative Example 2 is corroded. The contact resistance value after the test ^{exceeds 10 mΩ · cm 2} , and the conductivity is insufficient. That is, the carbon film of Examples 1 to 16 is a film having excellent corrosion resistance, and the carbon film of Comparative Example 2 is a film having inferior corrosion resistance. In view of the results of Examples 9 and 10 or Examples 11 to 15, it can be seen that the difference in film formation pressure does not affect the conductivity and corrosion resistance of the carbon film. Therefore, the difference in conductivity and corrosion resistance between the carbon film of Example 16 and the carbon film of Comparative Example 1 is due to the film formation temperature, not the film formation pressure. In view of the results of this example, it can be seen that a conductive carbon film having excellent corrosion resistance can be obtained by setting the film formation temperature to 520 ° C. or higher, preferably 530 ° C. or higher.

In Examples 17 to 19, methane gas is used as a raw material gas instead of acetylene gas, but the results of the corrosion test show that a conductive carbon film having excellent corrosion resistance can be obtained. Therefore, even if methane gas other than acetylene gas, propane gas, butane gas, or other chain hydrocarbon gas is used as the raw material gas, a conductive carbon film having excellent corrosion resistance is formed if the film formation temperature is 520 ° C. or higher. can do.

In Examples 20 and 21, a mixed gas of acetylene gas and hydrogen gas is used as the raw material gas in the film forming process, but according to the result of the corrosion test, a conductive carbon film having excellent corrosion resistance can be obtained. You can see that. Further, when the acetylene gas and the hydrogen gas are supplied in the film forming step, the arcing can be made less likely to occur by gradually changing the acetylene gas and the hydrogen gas to a predetermined flow rate. Considering the results of this example, when the acetylene gas and the hydrogen gas are supplied in the film forming process, the flow ratio of the acetylene gas to the hydrogen gas (C ₂ H ₂ / H ₂ ) is maintained at 1 to 5. At the same time, by gradually increasing the flow rate of each gas until the target flow rate of each gas is reached, the conductive carbon film can be formed in a state where the occurrence of arcing is suppressed.

The present invention can be applied to the formation of a conductive carbon film used for a fuel cell separator or the like.

1 Plasma processing device 2 Chambers 3 units 4 DC pulse power supply 5 Gas inlet 6 Gas supply source 7 Gas exhaust pipe 8 Vacuum pump 9 Heater 20 Contact resistance measuring device 21 Titanium plate 22 Carbon film 23 Carbon paper 24 Metal plate 25 Constant current DC power supply 30 Corrosion test equipment 31 Container 32 Container 33 Counter electrode 34 Reference electrode 35 Sample electrode 36 Luggin capillary W work

Claims (6)

A method for forming a conductive carbon film on a work by a DC plasma CVD method.
In the process of forming a conductive carbon film, acetylene gas and hydrogen gas are supplied to provide
Maintaining a state in which the flow rate ratio of the acetylene gas and the hydrogen gas is 1 to 5,
A method for forming a conductive carbon film, in which the acetylene gas is turned into plasma at a film forming temperature of 520 ° C. or higher and 750 ° C. or lower. When supplying the pre Symbol acetylene gas and the hydrogen gas, while maintaining the state in which the flow rate ratio of the hydrogen gas and the acetylene gas is 1 to 5, until the flow rate of each gas reaches the target flow rate, the gas The method for forming a conductive carbon film according to claim 1, wherein the flow rate of the gas is gradually changed. The method for forming a conductive carbon film according to claim 1 or 2 , wherein a DC pulse power source is used as a power source for plasma generation. Conductive carbon for producing a member coated with the conductive carbon film by forming the conductive carbon film on the work by using the method for forming the conductive carbon film according to any one of claims 1 to 3. A method for manufacturing a film coating member. A method for producing a fuel cell separator, wherein the conductive carbon film is formed on the surface of the fuel cell separator member by using the method for forming the conductive carbon film according to any one of claims 1 to 3. It is a method of manufacturing a separator for a fuel cell.
In the step of forming a conductive carbon film on the surface of the separator member for a fuel cell by the DC plasma CVD method, only a chain hydrocarbon gas having 4 or less carbon atoms or the chain hydrocarbon gas and hydrogen gas is used as a raw material gas. Using only a mixed gas consisting of
A method for producing a separator for a fuel cell, in which the chain hydrocarbon gas is turned into plasma at a film formation temperature of 520 ° C. or higher and 750 ° C. or lower.

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