JP2007182357A - Aftertreatment method of carbon material thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aftertreatment method of a carbon material thin film formed by an electrodeposition process using a nonaqueous electrodeposition liquid added with a dispersant, by which the resistance value of the film is lowered, and the obtained film is suitably applied to the surface of substrates such as a separator for a polymer electrolyte fuel cell. <P>SOLUTION: This aftertreatment method comprises heat treating a carbon material thin film formed by an electrodeposition process using a nonaqueous electrodeposition liquid added with a dispersant at 200-500°C under an inert gas atmosphere. As the carbon material thin film formed by the electrodeposition process using the nonaqueous liquid added with the dispersant, one obtained by the following process is suitably used: a carbon material is dispersed in a hydrocarbon-based solvent added with a basic polymer type dispersant, electric voltage is applied in the solvent by making a material to be coated as anode, and forming a carbon material thin film on the surface of the anode material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a post-treatment method for a carbon material thin film. More specifically, the present invention relates to a post-treatment method for a carbon material thin film that lowers the resistance value and is suitably applied to the surface of a substrate such as a separator for a polymer electrolyte fuel cell.

  Carbon materials have excellent performance in many aspects such as electrical conductivity, thermal conductivity, corrosion resistance, heat resistance, black colorability, and chemical stability, so they are used in various applications, especially those that require corrosion resistance. Since it is difficult to use metallic materials for the prevention material, electromagnetic shielding material, fuel cell separators that need to have electrical conductivity and corrosion resistance, or the negative electrode of lithium secondary batteries, graphite, carbon black, carbon fiber, etc. Carbon materials are used.

In these applications, a method of forming by adding a carbon material as a conductive filler to a resin or rubber or the like, a method of adding a resin or rubber or the like as a binder to a carbon material, and the like are generally used. . On the other hand, the method of thinning the carbon material only on the surface of the target object can satisfy both the electrical characteristics and the strength characteristics, and therefore, particularly the fuel cell separator or lithium in which the electrical conductivity and discharge characteristics of the surface are important. Used for the negative electrode of secondary batteries.
JP-A-10-334927

  Examples of methods for thinning a carbon material include vapor deposition, CND, spin coating, spray coating, dip coating, electrostatic coating, and electrodeposition. An electrodeposition method that can form a uniform film thickness is effective. This electrodeposition method is classified into two types, an aqueous electrodeposition liquid and a non-aqueous electrodeposition liquid.

As a water-based electrodeposition method, cationic electrodeposition coating, which is used for undercoating of automobile bodies, is common. This is a method in which an object to be coated is immersed in an electrodeposition coating, an electric current is passed between the object to be coated as a cathode, and a coating film is deposited on the cathode to form a film. When the carbon material is dispersed in the paint, the carbon material moves to the cathode side along with the electrodeposition paint, and is formed into a composite film on the object to be coated. In this method, since the electrodeposition paint also acts as a dispersant, the dispersibility of the carbon material in the electrolytic solution is good, and furthermore, the electrodeposition paint has a large flow rate, so that the amount of electrodeposition is large and a film can be formed in a short time. However, since the surface of the object to be coated is a composite film of an electrodeposition paint and a carbon material, the carbon density of the surface of the object to be coated is low.
Journal of the Adhesion Society of Japan Vol.27, No.9, 401 (1991)

On the other hand, many non-aqueous electrodeposition methods relate to aluminum materials that cannot be electrodeposited in water, but carbon materials are also dispersed in a solvent composed of a basic compound of low molecular weight such as acetonitrile and triethylamine. A method has been proposed in which an object to be coated is immersed in this electrodeposition liquid as an anode, a current is passed between the electrode and a counter electrode, and graphite is deposited on the anode to form a film. However, in this method, since the charged graphite moves and precipitates due to the electric field, there is an advantage that the carbon density on the surface of the object to be coated is increased. On the other hand, the dispersibility of the graphite in the electrodeposition liquid is poor, and Since the migration speed is slow, the amount of electrodeposition is small, and there is a disadvantage that a long time is required for film formation.
Surface Technology Vol. 53, No. 10, p. 685 (2002)

  Carbon nanotubes have excellent electrical and thermal conductivity, and are expected to be used in various applications that take advantage of these properties. However, since carbon nanotubes are usually intertwined, thin film formation Is a material that is very difficult to make into a thin film. On the other hand, since the carbon nanotube is an expensive material, it is currently required to exhibit the effect by using a small amount.

From such a request, as a method of thinning the carbon nanotube, a method of forming a carbon nanotube using an electric field, specifically, by dispersing the carbon nanotube in a dimethylformamide solvent, A method of applying a voltage to the electrode and adsorbing the carbon nanotube on the anode side has been proposed. However, in this method, since the amount of carbon nanotube dispersion is small, there remains a problem to be solved such that the amount of adsorption is small.
JP 2005-235425 A

  In addition, a porous carbon body made of a carbon sheet such as carbon paper, carbon non-woven fabric, or carbon woven fabric is used as a base material for the diffusion layer (GDL) of the fuel cell electrode. The base material is required to have high conductivity and a large specific surface area. In particular, when used as a gas diffuser, it is required that the electricity generated by the electrolyte on one side of the gas diffuser must be passed through the separator on the opposite side, so that it has excellent conductivity. The larger the contact area between the gas diffuser and the separator, the smaller the contact resistance. In the case of a gas diffuser, the surface contact resistance is often more problematic than the internal conductive resistance.

  However, increasing the bulk density of the gas diffuser as a means for increasing the contact area with the separator is not preferable because the gas diffusion resistance increases, so the density of the gas diffuser is decreased and the surface contact area is decreased. As a means to do this, a conductive porous layer is separately provided on the surface of the gas diffuser.

  Since carbon nanotubes have excellent electrical conductivity and a very large specific surface area, they are highly promising as porous carbon body materials having high electrical conductivity and a large specific surface area. However, the carbon nanotubes are in a state where the cohesion is very strong and intricately entangled, and the bulk density is very low, so simply by dispersing this in a solvent and supporting it on the gas diffuser, The homogeneity of the carbon nanotube layer cannot be obtained, and a sufficient resistance reduction effect of the gas diffuser cannot be obtained.

Further, when a conductive filler is added to the resin, if the amount of the conductive filler is increased in order to improve the conductivity, the characteristics as the resin are lost, and the moldability and strength are remarkably lowered. On the other hand, if the amount of the conductive filler is reduced, desired electrical characteristics cannot be obtained. In the case of forming a separator for a fuel cell by adding a conductive filler to the resin, in order to solve such a problem, there is a proposal that the separator has a high electrical resistance layer and the surface has a low electrical resistance layer. It is difficult to control the thickness of the surface layer, and resistance unevenness is likely to occur.
JP 2004-192855 A

  An object of the present invention is a carbon material thin film formed by an electrodeposition method using a non-aqueous electrodeposition liquid to which a dispersant is added, the resistance value of which is reduced, and a separator for a polymer electrolyte fuel cell, etc. Another object of the present invention is to provide a post-treatment method for a carbon material thin film that is suitably applied to the surface of a substrate.

  An object of the present invention is to provide a hydrocarbon thin film obtained by heat-treating a carbon material thin film formed by an electrodeposition method using a non-aqueous electrodeposition liquid to which a dispersant is added at 200 to 500 ° C. in an inert gas atmosphere. Achieved by post-processing.

  As a carbon material thin film formed by an electrodeposition method using a non-aqueous electrodeposition liquid to which a dispersant is added, a carbon material is dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added. A material in which a coating material is used as an anode in a solvent and a carbon material thin film is formed on the surface of the anode material is preferably used.

  The carbon material is dispersed in a carbon material thin film formed by an electrodeposition method using a non-aqueous electrodeposition liquid to which a dispersant is added, preferably a hydrocarbon solvent to which a basic polymer type dispersant is added. Dispersant that remained in the thin film by applying a voltage in the solvent with the material to be coated as an anode and forming a carbon material thin film on the surface of the anode material by heat treatment in an inert gas atmosphere Evaporates, volatilizes or decomposes to increase the concentration of the carbon material, preferably carbon nanotubes, in the thin film, so that the resistance value of the thin film can be effectively reduced.

  In addition, when a carbon nanotube thin film is formed by an electrodeposition method, the amount of carbon nanotube used is small and the thickness of the thin film can be controlled. For example, such a carbon nanotube thin film can be used as a fuel cell separator. In addition to excellent conductivity and low resistance, the thin film is held by the entanglement due to the shape of the carbon nanotubes, so there is flexibility and pressure unevenness occurs when the fuel cell stack is fastened. However, a stable resistance value can be maintained.

The formation of such a carbon nanotube thin film can be applied to all of a carbon separator, a fired carbon separator, a resin / graphite separator, a metal separator, etc., and can be made conductive by masking. It is also possible to form only the necessary rib portion. Furthermore, the method of the present invention can be applied without restriction on the roughness of the separator as shown in the following patent document, and the manufacturing cost of the separator can be reduced regardless of the surface state of the separator.
JP 2004-6432 A

  The carbon material thin film formed by the electrodeposition method using the non-aqueous electrodeposition liquid to which the dispersant is added preferably disperses the carbon material in the hydrocarbon solvent to which the basic polymer type dispersant is added, In this solvent, a coating material is used as an anode, and a voltage is applied to form a carbon material thin film on the surface of the anode material. Therefore, this embodiment will be described.

  Examples of the carbon material include carbon nanotube, carbon black, graphite, carbon fiber, fullerene, and the like. Preferably, from the viewpoint of excellent electrical conductivity and thermal conductivity, the carbon nanotube is from the viewpoint of electrical characteristics and bulk density. Carbon black or graphite is used. These can be used without particular limitation as long as they are dispersed in a solution, such as single-walled carbon nanotubes or multi-walled carbon nanotubes as carbon nanotubes, ketjen black, acetylene black, etc. as carbon black, and graphite. As such, either artificial graphite or natural graphite is used.

  As the basic polymer type dispersant, a molecular weight of several thousand to several tens of thousands can be used without particular limitation as long as it has an ester structure, and a fatty acid ester or the like, preferably a polyester acid amide amine salt is used. Used. In practice, commercially available products such as Enomoto Kasei products Disparon DA-703-50, DA-705, DA-725, DA-234 and the like are used. In addition, the company's product Disparon DA-325, which is an amine salt of polyether phosphate, is also used. These are used by being added to a hydrocarbon solvent in a proportion of 1 to 20% by weight, preferably 3 to 10% by weight. If the use ratio is less than this, the object of the present invention is not achieved. On the other hand, if the use ratio is more than this, a large amount of the basic polymer type dispersant is adhered to the formed thin film, which is not preferable.

  The average particle size of carbon material, preferably carbon nanotubes (50% particle size by wet laser scattering method) dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added is preferably 100 to 1000 nm, preferably The thickness is preferably set to 500 to 800 nm. Such adjustment to the average particle diameter is also performed using a ball mill or the like, but is preferably performed using an ultrasonic homogenizer. If an ultrasonic cleaner is used instead of an ultrasonic homogenizer, the average particle diameter of the carbon nanotube aggregates in the dispersion will be 1000 nm or more, and if a pot-type ball mill is used, the carbon nanotubes may break. is there.

  Examples of the hydrocarbon solvent include aromatic hydrocarbon solvents, and preferably xylene or toluene is used. These hydrocarbon solvents are generally used in an amount of about 100 to 1000 times the carbon material.

  The anode of the coating material is not particularly limited as long as it is conductive, and a non-conductive base material subjected to electroless plating can be used, for example, an electrode for a fuel cell made of resin and graphite Gas diffuser base material or separator base material, antistatic base material, electromagnetic wave shield base material, lithium battery electrode base material, field emission display base material, heat dissipation base material, etc. are used, preferably carbon paper, carbon non-woven fabric, A carbon sheet substrate that is a porous carbon body such as a carbon woven fabric is used.

  The principle of forming the carbon material thin film is as follows, for example, in the case of carbon nanotubes. Carbon nanotubes are refined by heating, acid treatment, etc. to remove the metal catalyst used in production. At this time, defective portions present in the carbon nanotubes are oxidized, and functional groups such as carbonyl groups and hydroxyl groups are generated. Carbon nanotubes are considered to have an anionic charge in water. Therefore, if an electric field is applied to a solution in which carbon nanotubes are dispersed, the carbon nanotubes move to and adhere to (adsorb on) the fuel cell separator substrate that is the anode, and the attached carbon nanotubes are connected due to the ease of aggregation. Will be formed.

  Therefore, the carbon material thin film is formed by adhering (adsorbing) the carbon material on the anode material by applying a voltage to the anode in a hydrocarbon solvent to which a basic polymer type dispersant is added. Is called. Here, the applied voltage is 1 to 1000 V, preferably 5 to 500 V. When the applied voltage is lower than this, the amount of adhesion of the carbon material decreases, whereas when larger than this, The adhesion film of the carbon material is not uniform, and the power efficiency is deteriorated, which is not preferable. The application time varies depending on the amount of film formation required, but it can be applied, for example, for 1 to 3000 seconds, preferably 30 to 1000 seconds, or periodically. At this time, in order to prevent sedimentation of the carbon material, a film is also formed while stirring the dispersion solution. Further, by performing masking at the time of film formation, the carbon material can be attached only to a portion requiring conductivity.

  The carbon material thin film is formed by applying an AC electric field using a device that controls an AC voltage, such as a pulse function generator, in a hydrocarbon solvent to which a basic polymer type dispersant is added. It is also performed by applying a voltage to the anode to adhere (adsorb) the carbon material on the anode material. Here, the applied voltage is about 1 to 100 V, preferably about 3 to 20 V, particularly preferably about 5 V, the frequency is about 0.1 to 1000 Hz, preferably about 1 to 10 Hz, and the application time is required. Depending on the amount of film to be formed and the distance between electrodes (generally set to about 3 to 5 mm), for example, it can be applied for 10 to 1000 minutes, preferably 20 to 200 minutes or periodically.

  The anode material having the carbon material thin film formed on the surface is taken out of the dispersion solution, and then washed and dried so as to remove other than the carbon material formed on the surface.

  By repeating the above steps, the film thickness of the carbon material formed on the anode material surface can be increased. That is, by setting the number of repetitions of the above steps, the film thickness of the carbon material to be formed can be controlled to a desired thickness, for example, about 1 to 50 μm.

  The carbon material thin film thus formed, preferably the carbon nanotube thin film, is heated at about 200 to 500 ° C., preferably about 230 to 350 ° C. in an inert gas atmosphere such as nitrogen gas or argon gas. . This heat treatment evaporates, volatilizes, or decomposes the dispersing agent such as the basic polymer type dispersant remaining in the thin film, thereby increasing the concentration of the carbon material, preferably carbon nanotubes in the thin film. Effectively lowers the value.

  Next, the present invention will be described with reference to examples.

Comparative Example 1
(a) 19% by weight of resol type phenolic resin (Showa polymer product MCS-302), artificial graphite (Japanese graphite product PAG-H100; average particle size 100 μm) 80% by weight and stearic acid (internal mold release agent) 1% by weight Were premixed with a Henschel mixer, the premixed mixture was kneaded at 100 ° C. for 10 minutes using a pressure kneader, cooled and pulverized with a power mill to obtain a molding material. Using this molding material, molding was performed under the conditions of a temperature of 170 ° C. and a pressure of 50 MPa for 5 minutes to obtain a separator material molded product of 100 × 10 × 2.1 mm.
(b) To 90 ml of xylene, 10 ml of polyester acid amide amine salt (Tsubakimoto Kasei product Disparon DA-703-50; 50% xylene solution) is added, and to this solution, vapor grown multi-walled carbon nanotubes (Nikkiso product; fiber diameter 10 ~ 500 mg of 30 nm and an average fiber length of 1 to 100 μm) was added, and irradiation dispersion treatment was performed for 12 hours at an output of 300 W using an ultrasonic homogenizer (BRANSON SONIFIER 450) to obtain a multi-walled carbon nanotube dispersion. The average particle size (50% particle size) by wet laser scattering was 600 nm.
(c) The separator material molded product was used as an electrode, and a PTFE spacer was used so that the distance between the electrodes was 2 cm. A carbon nanotube film was formed on the anode by applying a voltage of 200 V for 15 minutes (film formation area: 10 cm ² , thickness: 2 mm). An SEM photograph of the formed thin film is shown in FIG. When this thin film was observed with a scanning electron microscope, a carbon nanotube adsorption layer having a thickness of about 30 μm was confirmed.
(d) When this carbon nanotube thin film layer was peeled off and analyzed by TGA, the content of carbon nanotubes contained in the thin film was 85% by weight, and the remaining 15% by weight was a dispersant. The formed separator was processed to have a surface area of 1 cm ² , sandwiched between gold-plated electrodes, and measured for a resistance value in the thickness direction with a load of 1 MPa, it was 12.0 mΩ · cm ² . In addition, peeling of a thin film layer is performed by forced means, such as shaving off an interface with a blade or thermal transfer.

Example 1
The film-formed separator obtained in the step (c) of Comparative Example 1 was baked at 250 ° C. for 10 hours in an inert gas (N ₂ gas) atmosphere. In the TGA analysis of the exfoliated carbon nanotube thin film layer in step (d), the content of carbon nanotubes contained in the thin film was 94% by weight, and the remaining 6% by weight was a dispersant. Similarly, when the resistance value in the thickness direction was measured, it was 9.7 mΩ · cm ² .

Example 2
The film-formed separator obtained in the step (c) of Comparative Example 1 was baked at 300 ° C. for 10 hours in an inert gas (N ₂ gas) atmosphere. In the TGA analysis of the exfoliated carbon nanotube thin film layer in step (d), the content of carbon nanotubes contained in the thin film was 96% by weight, and the remaining 4% by weight was a dispersant. Similarly, when the resistance value in the thickness direction was measured, it was 9.2 mΩ · cm ² .

Reference Example The separator material molded product obtained in the step (a) of Comparative Example 1 was sandwiched between gold-plated electrodes, and the resistance value in the thickness direction was measured with a load of 1 MPa, which was 13.7 mΩ · cm ² .

Comparative Example 2
The separator material molded product obtained in step (a) of Comparative Example 1 was immersed in the multi-walled carbon nanotube dispersion obtained in step (b) and then dried at room temperature for 1 hour to form a carbon nanotube thin film. I let you. As in the step (d), when the carbon nanotube thin film was peeled off and TGA analysis was performed, the content of carbon nanotubes contained in the thin film was 25% by weight, and the remaining 75% by weight was a dispersant. Similarly, the resistance value in the thickness direction was measured and found to be 24.0 mΩ · cm ² .

From the above results, the following can be said.
(1) A separator coated with a carbon nanotube thin film by an electrodeposition method has a lower resistance value than a separator that does not compare this (Comparative Example 1-Reference Example 1).
(2) When the carbon nanotube thin film coated on the separator is baked in an inert gas atmosphere, even lower resistance values are obtained (Examples 1 to 2—Comparative Example 1).
(3) The separator coated with the carbon nanotubes by the dipping method has a smaller amount of carbon nanotubes contained in the thin film and exhibits a higher resistance value than the uncoated separator (Reference Example-Comparative Example 2).

  The carbon material thin film obtained by using the post-treatment method of the carbon material thin film according to the method of the present invention includes a fuel cell separator made of resin and graphite, an antistatic material, an electromagnetic shielding material, a lithium battery electrode, a field emission display, and the like. It is used effectively. In addition, since carbon nanotubes are excellent in thermal conductivity, they are also effectively used as heat dissipation materials.

  In particular, a separator base material made of resin and graphite is molded (molded) by adding a resin to a conductive filler, but has a skin layer containing a large amount of resin on the surface side and has conductivity. Since there are only a few spots where graphite appears on the surface, the conductivity required on the surface of the fuel cell separator cannot be obtained sufficiently, and there is a problem that the contact resistance increases. By applying the carbon material thin film obtained by the method of the present invention to the separator surface, a conductive network is formed on the separator surface, the conductivity on the surface can be improved, and the resistance value can be effectively reduced. Can do.

It is a SEM photograph of the carbon nanotube thin film formed on the separator material molding by the electrodeposition method.

Claims (13)

  After the carbon material thin film characterized by heat-treating the carbon material thin film formed by the electrodeposition method using the non-aqueous electrodeposition liquid to which the dispersant is added at 200 to 500 ° C. in an inert gas atmosphere. Processing method.   A carbon material thin film formed by an electrodeposition method using a non-aqueous electrodeposition liquid to which a dispersant is added disperses the carbon material in a hydrocarbon solvent to which a basic polymer type dispersant is added. 2. The post-treatment method for a carbon material thin film according to claim 1, wherein a voltage is applied using the material to be coated as an anode to form a carbon material thin film on the surface of the anode material.   The post-treatment method for a carbon material thin film according to claim 2, wherein the carbon material is carbon nanotube, carbon black, or graphite.   The post-treatment method for a carbon material thin film according to claim 2, wherein the basic polymer type dispersant is a polyester acid amide amine salt.   The post-treatment method for a carbon material thin film according to claim 2, wherein the hydrocarbon solvent is an aromatic hydrocarbon solvent.   The electrode gas diffuser base material or separator base material for a fuel cell, an antistatic base material, an electromagnetic wave shielding base material, a lithium battery electrode base material, a field emission display base material, or a heat dissipation base material is used as a coating material anode. The post-processing method of the carbon material thin film of 2.   The post-treatment method of a carbon material thin film according to claim 2, wherein a carbon sheet substrate is used as an anode to be coated.   The carbon material thin film post-processing method according to claim 7, wherein the carbon sheet is carbon paper, carbon non-woven fabric, or carbon woven fabric.   The carbon according to claim 2, wherein the carbon material dispersed in the hydrocarbon solvent to which the chlorinated polymer type dispersant is added has an average particle size of 100 to 1000 nm (50% particle size by wet laser scattering method). Post-processing method for material thin film.   The carbon material thin film post-treatment method according to claim 9, wherein the carbon material is a carbon nanotube.   The post-treatment method for a carbon material thin film according to claim 9 or 10, wherein the average particle diameter of the carbon material is adjusted to 100 to 1000 nm using an ultrasonic homogenizer.   A carbon material thin film post-treated by the method according to claim 1.   An electrode gas diffuser or separator for a fuel cell having the carbon material thin film according to claim 12 formed on its surface, an antistatic material, an electromagnetic shielding material, a lithium battery electrode, a field emission display, or a heat dissipation material.