JPWO2013146720A1 - Water-based conductive paint - Google Patents

Abstract

A water-based conductive paint used for forming a fuel cell separator, wherein the water-based conductive paint includes a conductive material, a binder, and water, and the conductive material is a carbon-based material, and the conductive material Is contained in the water-based conductive paint in an amount of 50 to 75 wt%, and the binder contains an acrylonitrile-butadiene copolymer having an iodine value of 20 or less.

Description

  The present invention relates to a water-based conductive paint used for forming a fuel cell separator.

The fuel cell is one of energy supply methods that have been studied for the purpose of reducing the environmental load. In particular, the polymer electrolyte fuel cell is expected to be used as a household cogeneration system or an automobile power source because it operates at a relatively low temperature as compared with other fuel cells. A polymer electrolyte fuel cell using hydrogen and oxygen (air) has a structure in which a power generation member composed of a hydrogen electrode, a solid polymer electrolyte membrane, an oxygen (air) electrode, etc. is sandwiched between separators supplying hydrogen and oxygen. ing.
As a separator for a polymer electrolyte fuel cell as described above, a molded product in which a composite material of conductive carbon and a resin such as epoxy is formed into an uneven plate shape, or a press-molded corrosion-resistant metal plate is known. ing. However, the composite material using conductive carbon has a problem that the molding time is long, it cannot be thinned, it is easy to crack, and it is very expensive for practical use. It was. On the other hand, press-molded products of corrosion-resistant metal plates are easier to reduce in thickness than composite materials, and can cope with problems such as cracking and chipping, but when corrosion-resistant metal plates are too thin, they are press-molded. There is a problem that cracks are easily formed in the corners of the unevenness, and that if the thickness is increased in order to prevent the occurrence of cracks, it is heavy.

  Therefore, Patent Document 1 employs a method of forming a conductive coating film in order to give corrosion resistance to the surface of a separator base material made of a metal plate that can be easily processed, and in that case, styrene-butadiene copolymer is used as a binder. It has been proposed to use conductive paints comprising coalesced, acrylic-styrene copolymers or acrylic-silicone copolymers.

International Publication No. 2003/044888

  By the way, when a conductive coating film formed of a conductive coating is formed on the separator substrate surface and used inside the fuel cell, the conductive coating film is required to have heat resistance. The heat resistance of the conductive coating film formed by the paint was not sufficient.

  An object of the present invention is to provide a water-based conductive coating material suitable for forming a fuel cell separator having excellent heat resistance.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor uses a water-based conductive paint containing an acrylonitrile-butadiene copolymer having an iodine value in a specific range as a binder, as a fuel excellent in heat resistance. It has been found that a battery separator is formed.

That is, according to the water-based conductive paint of the present invention,
(1) A water-based conductive paint used for forming a fuel cell separator, wherein the water-based conductive paint includes a conductive material, a binder, and water, and the conductive material is a carbon-based material, Content of conductive material is 50-75 wt% in the water-based conductive paint, and the binder contains an acrylonitrile-butadiene copolymer having an iodine value of 20 or less,
(2) The water-based conductive paint according to (1), wherein the binder has a dispersed particle size of 0.05 μm or more and 0.4 μm or less,
(3) The water-based conductive paint according to (1) or (2), wherein the acrylonitrile-butadiene copolymer is a hydrogenated acrylonitrile-butadiene copolymer hydrogenated by an aqueous layer hydrogenation method. ,
(4) The aqueous conductivity according to any one of (1) to (3), wherein a weight ratio of the binder to the carbonaceous material is 1.5: 100 to 8: 100 as a solid content. paint,
(5) The carbon-based material includes graphite and carbon black, and a weight ratio of the graphite to the carbon black is 90:10 to 60:40. (1) to (4) The water-based conductive paint according to any one of the above items is provided.

  According to the present invention, an aqueous conductive paint suitable for forming a fuel cell separator having excellent heat resistance is provided.

  Hereinafter, the water-based conductive paint of the present invention will be described. The water-based conductive paint of the present invention is a water-based conductive paint used to form a fuel cell separator, and the water-based conductive paint includes a conductive material, a binder, and water, and the conductive material is a carbon-based material. It is a material, Comprising: Content of the said electroconductive material is 50-75 wt% in the said water-system electroconductive coating material, The said binder contains the acrylonitrile butadiene copolymer whose iodine number is 20 or less, It is characterized by the above-mentioned. .

(Conductive material)
In the water-based conductive paint of the present invention, carbon or the like is used as the conductive material. As carbon, graphite, carbon black and the like can be used, and it is preferable to use graphite and carbon black in combination. When graphite and carbon black are used in combination, the weight ratio of graphite / carbon black is preferably 90:10 to 60:40. If the ratio of graphite is too small, the viscosity of the water-based conductive paint obtained is increased and fluidity on the substrate is lost, so that it is not suitable for coating. Moreover, when the ratio of graphite is too large, the smoothness of the coating film to be formed decreases, and as a result, the value of contact resistance increases.

  The amount of carbon in the water-based conductive paint, that is, the solid content concentration of carbon is usually 50 to 75 parts by weight, preferably 53 to 73 parts by weight, more preferably 55 to 70 parts by weight in 100 parts by weight of the water-based conductive paint. Part. If the solid content concentration is lower than this range, the time and energy for drying the water-based conductive coating increases, and the cost for obtaining the conductive coating increases. Furthermore, it becomes difficult to control the thickness of the conductive coating film obtained.

  Further, if the solid content concentration is higher than this range, the viscosity of the water-based conductive paint increases and fluidity is lost, so that it is not suitable for coating. Moreover, even if a conductive coating film is formed in this case, a crack occurs in the conductive coating film.

(binder)
In the water-based conductive coating material of the present invention, the binder comprises acrylonitrile-butadiene copolymer (NBR). The iodine value of NBR is usually 20 or less, preferably 18 or less, more preferably 15 or less. Here, the iodine value is determined according to JIS K6235;

  NBR is a copolymer of acrylonitrile and 1,3-butadiene. The weight ratio of acrylonitrile to 1,3-butadiene used for copolymerization is preferably 5:95 to 30:70. When the ratio of acrylonitrile is too large, cracks occur in the conductive coating film when the conductive coating film is formed. Moreover, when the ratio of acrylonitrile is too small, the peeling strength with the base material of a separator will fall.

  Moreover, the manufacturing method of NBR is not specifically limited, Any methods, such as a solution polymerization method, suspension polymerization method, block polymerization method, and emulsion polymerization method, can be used. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Examples of the polymerization initiator used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

  In the present invention, it is preferable to obtain an acrylonitrile-butadiene copolymer having an iodine value in the above range by a hydrogenation reaction. In the hydrogenation reaction, carbon-carbon derived from polymerized units capable of forming a conjugated diene monomer in the unsaturated polymer (copolymer comprising acrylonitrile and 1,3-butadiene) obtained by the above polymerization method. Only unsaturated bonds are selectively hydrogenated.

  As a selective hydrogenation method for selectively hydrogenating only carbon-carbon unsaturated bonds derived from polymerized units capable of forming a conjugated diene monomer in an unsaturated polymer, a publicly known method may be used. However, since the obtained binder can be made into fine particles, the aqueous layer hydrogenation method is preferable. Among the aqueous layer hydrogenation methods, the NBR polymerization is also performed. More preferred is an aqueous layer direct hydrogenation method in which the aqueous dispersion of NBR obtained is carried out in an aqueous layer by an emulsion polymerization method or the like and hydrogenated in the same aqueous layer.

  When the binder used in the present invention is produced by the oil layer hydrogenation method, the following method is preferred. That is, first, a dispersion of an unsaturated polymer prepared by emulsion polymerization is coagulated by salting out, dissolved in an organic solvent through filtration and drying. Subsequently, the unsaturated polymer dissolved in the organic solvent is subjected to a hydrogenation reaction (oil layer hydrogenation method) to obtain a hydride, and the obtained hydride solution is coagulated, filtered and dried. A binder to be used is obtained.

  When an alkali metal caprate is used as an emulsifier, the caprate in the binder finally obtained in each step of coagulation, filtration and drying by salting out the dispersion of the unsaturated polymer is used. It is preferable to prepare such that the amount is 0.01 to 0.4% by weight. For example, a known coagulant such as magnesium sulfate, sodium chloride, calcium chloride, or aluminum sulfate can be used in coagulation by salting out of the dispersion, but preferably an alkali such as magnesium sulfate, magnesium chloride, or magnesium nitrate. By using an earth metal salt; or a Group 13 metal salt such as aluminum sulfate; the amount of caprate contained in the unsaturated polymer can be reduced. Therefore, it is preferable to use an alkaline earth metal salt or a Group 13 metal salt as the coagulant, more preferably an alkaline earth metal salt, and finally by controlling the amount of use and the solidification temperature, The amount of caprate in the obtained binder can be within the above range. The amount of the coagulant used is preferably 1 to 100 parts by weight, more preferably 5 to 50 parts by weight, particularly preferably 10 to 50 parts by weight, when the amount of unsaturated polymer to be hydrogenated is 100 parts by weight. It is. The coagulation temperature is preferably 10 to 80 ° C.

  The solvent for the oil layer hydrogenation method is not particularly limited as long as it is a liquid organic compound that dissolves the unsaturated polymer, but benzene, toluene, xylene, hexane, cyclohexane, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, cyclohexanone, and acetone are preferable. used.

  As a catalyst for the oil layer hydrogenation method, any known selective hydrogenation catalyst can be used without limitation, and a palladium-based catalyst and a rhodium-based catalyst are preferable, and a palladium-based catalyst (such as palladium acetate, palladium chloride, and palladium hydroxide) is used. More preferred. Two or more of these may be used in combination, but when a rhodium catalyst and a palladium catalyst are used in combination, it is preferable to use a palladium catalyst as the main active ingredient. These catalysts are usually used by being supported on a carrier. Examples of the carrier include silica, silica-alumina, alumina, diatomaceous earth, activated carbon and the like. The amount of the catalyst used is preferably 10 to 5000 ppm, more preferably 100 to 3000 ppm, in terms of the amount of metal of the hydrogenation catalyst, relative to the amount of the unsaturated polymer to be hydrogenated.

  The hydrogenation reaction temperature in the oil layer hydrogenation method is preferably 0 to 200 ° C., more preferably 10 to 100 ° C., and the hydrogen pressure is preferably 0.1 to 30 MPa, more preferably 0.2 to 20 MPa. The reaction time is preferably 1 to 50 hours, more preferably 2 to 25 hours.

  Alternatively, when the binder used in the present invention is produced by the aqueous layer hydrogenation method, the dispersion of the unsaturated polymer prepared by emulsion polymerization is diluted by adding water as necessary to perform a hydrogenation reaction. It is preferable.

  Here, in the aqueous layer hydrogenation method, hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst to hydrogenate (I) an aqueous layer direct hydrogenation method, in the presence of an oxidizing agent, a reducing agent and an activator. There are (II) water layer indirect hydrogenation methods in which hydrogenation is carried out by reduction.

  (I) In the aqueous layer direct hydrogenation method, the concentration of the unsaturated polymer in the aqueous layer (concentration in the dispersion state) is preferably 40% by weight or less in order to prevent aggregation.

  The hydrogenation catalyst used is not particularly limited as long as it is a compound that is difficult to decompose with water. As specific examples of hydrogenation catalysts, palladium catalysts include palladium salts of carboxylic acids such as formic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; palladium chloride, dichloro (cyclooctadiene) palladium, dichloro (norbornadiene) ) Palladium chloride such as palladium and ammonium hexachloropalladium (IV); Iodide such as palladium iodide; Palladium sulfate dihydrate and the like. Of these, palladium salts of carboxylic acids, dichloro (norbornadiene) palladium and ammonium hexachloropalladium (IV) are particularly preferred. The amount of the hydrogenation catalyst used may be determined as appropriate, but is preferably 5 to 6000 ppm, more preferably 10 to 4000 ppm in terms of the amount of metal of the hydrogenation catalyst with respect to the amount of the unsaturated polymer to be hydrogenated. is there.

  The reaction temperature in the aqueous layer direct hydrogenation method is preferably 0 to 300 ° C, more preferably 20 to 150 ° C, and particularly preferably 30 to 100 ° C. If the reaction temperature is too low, the reaction rate may decrease. Conversely, if the reaction temperature is too high, side reactions such as a hydrogenation reaction of a nitrile group may occur. The hydrogen pressure is preferably 0.1 to 30 MPa, more preferably 0.5 to 20 MPa. The reaction time is selected in consideration of the reaction temperature, hydrogen pressure, target hydrogenation rate, and the like.

  On the other hand, in the (II) aqueous layer indirect hydrogenation method, the concentration of the unsaturated polymer in the aqueous layer (concentration in the dispersion state) is preferably 1 to 50% by weight, more preferably 1 to 40% by weight. .

  Examples of the oxidizing agent used in the water layer indirect hydrogenation method include oxygen, air, and hydrogen peroxide. The amount of these oxidizing agents used is a molar ratio to the carbon-carbon double bond (oxidant: carbon-carbon double bond), preferably 0.1: 1 to 100: 1, more preferably 0.8: 1. ~ 5: 1.

  As the reducing agent used in the aqueous layer indirect hydrogenation method, hydrazines such as hydrazine, hydrazine hydrate, hydrazine acetate, hydrazine sulfate, and hydrazine hydrochloride, or compounds that liberate hydrazine are used. The amount of these reducing agents used is a molar ratio to the carbon-carbon double bond (reducing agent: carbon-carbon double bond), preferably 0.1: 1 to 100: 1, more preferably 0.8: 1-5: 1.

  As the activator used in the water layer indirect hydrogenation method, ions of metals such as copper, iron, cobalt, lead, nickel, iron, tin and the like are used. These activators are used in a molar ratio to the carbon-carbon double bond (activator: carbon-carbon double bond), preferably 1: 1000 to 10: 1, more preferably 1:50 to 1: 2.

  The reaction in the aqueous layer indirect hydrogenation method is carried out by heating within the range from 0 ° C. to the reflux temperature, whereby the hydrogenation reaction is carried out. The heating range at this time is preferably 0 to 250 ° C, more preferably 20 to 100 ° C, and particularly preferably 40 to 80 ° C.

  In both the direct hydrogenation method and the indirect hydrogenation method in the aqueous layer, it is preferable to carry out solidification by salting out, filtration and drying after the hydrogenation. The salting out is performed in the same manner as the salting out of the dispersion of the unsaturated polymer in the oil layer hydrogenation method, in order to control the amount of caprate in the binder after the hydrogenation reaction. Alternatively, a Group 13 metal salt is preferably used, and an alkaline earth metal salt is particularly preferably used. Further, the filtration and drying steps subsequent to coagulation can be performed by known methods.

  Moreover, the method for producing the binder used in the present invention is particularly preferably a method in which the hydrogenation reaction is carried out in two or more stages. Even when the same amount of hydrogenation catalyst is used, the hydrogenation reaction efficiency can be increased by carrying out the hydrogenation reaction in two or more stages. That is, when the polymerization unit capable of forming a conjugated diene monomer is converted into a linear alkylene structural unit, the iodine value of the binder can be further reduced.

  In addition, when the hydrogenation reaction is performed in two or more stages, it is preferable to achieve 50% or more hydrogenation at the first stage hydrogenation reaction rate (hydrogenation ratio) (%), and 70% or more. More preferably, the hydrogenation is achieved. That is, when the value obtained by the following formula is the hydrogenation reaction rate (%), this value is preferably 50% or more, and more preferably 70% or more.

Hydrogenation reaction rate (hydrogenation rate) (%)
= 100 × (carbon-carbon double bond amount before hydrogenation reaction−carbon-carbon double bond amount after hydrogenation reaction) / (carbon-carbon double bond amount before hydrogenation reaction)
In addition, the amount of carbon-carbon double bonds can be analyzed using NMR.

  After completion of the hydrogenation reaction, the hydrogenation catalyst in the dispersion is removed. As the method, for example, an adsorbent such as activated carbon or ion exchange resin can be added to adsorb the hydrogenation catalyst with stirring, and then the dispersion can be filtered or centrifuged. It is also possible to leave the hydrogenation catalyst in the dispersion without removing it.

  Moreover, the average particle diameter (dispersion particle diameter) of the binder when the binder used in the present invention is dispersed in the dispersion medium in a particulate form is preferably 0.05 to 0.4 μm, more preferably 0.1 to 0.1 μm. 0.3 μm.

  The binder used in the present invention is used in the state of a dispersion or a solution in which the binder is dispersed in a dispersion medium. As a dispersion medium, it is preferable to use water from the viewpoint of being excellent in environmental viewpoint and having a high drying speed. That is, the binder used in the present invention is preferably prepared and used as an aqueous dispersion in the aqueous conductive paint of the present invention.

  The amount of the binder used in the water-based conductive paint of the present invention is preferably 1.5 to 10 parts by weight, more preferably 1.8 to 8 parts by weight, and still more preferably as a solid content with respect to 100 parts by weight of the conductive material. Is 2 to 6 parts by weight.

The binder used in the present invention may contain a polymer compound such as an acrylate polymer in addition to the NBR. The acrylate polymer has the general formula (1): CH ₂ ═CR ¹ —COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkyl group or a cycloalkyl group. R ² further represents An ether group, a hydroxyl group, a carboxylic acid group, a fluorine group, a phosphoric acid group, an epoxy group, and an amino group.), A polymer containing a monomer unit derived from a compound represented by , A homopolymer of the compound represented by the general formula (1), or a copolymer obtained by polymerizing a monomer mixture containing the compound represented by the general formula (1).

  Specific examples of the compound represented by the general formula (1) include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate. , Alkyl acrylates such as octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl Methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, hep Methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. These (meth) acrylic acid esters can be used alone or in combination of two or more. Of these, 2-ethylhexyl acrylate and n-butyl acrylate are preferably used.

  In the present invention, “(meth) acryl” means “acryl” or “methacryl”.

  The acrylate polymer may be a copolymer of the above-described (meth) acrylic acid ester and a monomer copolymerizable therewith. As such a copolymerizable monomer, Examples thereof include an α, β-unsaturated nitrile compound and a vinyl compound having an acid component.

  Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile and the like. These may be used alone or in combination of two or more.

  Examples of the vinyl compound having an acid component include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid. These may be used alone or in combination of two or more. Among these, it is preferable to use acrylic acid.

(Water-based conductive paint)
The aqueous conductive paint of the present invention can be obtained by mixing the above-described conductive material and binder. The method for mixing the conductive material and the binder is not particularly limited. For example, the conductive material and the binder can be obtained by kneading the binder dispersion and the conductive material in a batch kneader. When mixing, a water-soluble polymer such as sodium polyacrylate, polyvinyl alcohol, polyvinyl pyrrolidone or the like may be added and mixed as a dispersant.

(Additive)
If necessary, an additive may be added to the water-based conductive paint of the present invention. Examples of the additive include silicon-based and fluorine-based antifoaming agents, viscosity modifiers such as polyacrylic acid and polyvinyl alcohol as an additive. Examples of the method for producing the aqueous conductive paste include a method of kneading each material using a kneader such as a disper, roll, Banbury mixer, or extruder. A kneading machine preferably used is a closed kneading machine such as a Banbury mixer.

(Conductive coating)
A conductive coating film can be formed by applying and drying the water-based conductive paint of the present invention on a metal material or a carbon material used as a base material for a fuel cell separator. The resistance value of the conductive coating film is preferably 5 mΩcm or less, and more preferably 4 mΩcm or less. When the resistance value of the conductive coating film is too large, the power generation efficiency decreases when used as a fuel cell separator. Moreover, it is preferable that the rate of change of the resistance value of the conductive coating film after the wet heat treatment at 80 ° C., 80% RH and 1000 hours is 10% or less. If the rate of change of the resistance value of the conductive coating after the heat treatment is too large, the life when used as a separator of a fuel cell is shortened.

  Examples of the coating method include a die coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and brush coating. By forming a conductive coating film on a substrate, it can be used as a separator for a fuel cell, an electromagnetic wave absorber, a conductive circuit, a conductive connector or the like.

  According to the present invention, a conductive paint suitable for forming a fuel cell separator having a conductive coating film excellent in heat resistance can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, it is not limited to these Examples. In the examples and comparative examples, “part” and “%” are based on weight unless otherwise specified. Each characteristic in an Example and a comparative example was measured in accordance with the following method.

(Fluidity: Appearance of sheet dried with water-based conductive paint)
A coating film was formed on a PET film with a doctor blade having a gap of 500 μm using the water-based conductive paint obtained in Examples and Comparative Examples, and dried at 90 ° C. for 1 hour to obtain a conductive paint sheet. The appearance of the surface of the conductive coating sheet was visually observed to determine the presence or absence of cracks and the stability of the coating film thickness. In Table 1, when there was no defect such as a crack, it was indicated as ◯, and when there was a defect such as a crack, it was indicated as x.

(Adhesion)
A coating film was formed on a SUS plate with a doctor blade having a gap of 500 μm using the water-based conductive paint obtained in Examples and Comparative Examples, and dried at 90 ° C. for 1 hour to obtain a conductive paint sheet. This conductive paint sheet was cut into a straight line with a cutter knife, and the presence or absence of carbon falling off from the end face was observed. A case where no dropout occurred was marked as ◯, and a case where partial dropout was observed was marked as ×.

(Resistance value)
A coating film was formed on a PET film with a doctor blade having a gap of 500 μm using the water-based conductive paint obtained in Examples and Comparative Examples, and dried at 90 ° C. for 1 hour to obtain a conductive paint sheet. The conductive paint sheet was cut into a predetermined size, and a metal terminal was brought into contact with the surface to measure the volume resistivity. It shows that the volume resistivity is good when it is 500 mΩcm or less.

(Moisture and heat resistance test)
The test piece for which the resistance value was measured was subjected to a wet heat treatment for 1000 hours using a constant temperature and humidity chamber at 80 ° C. and 80% RH, and then dried at room temperature to measure the resistance value after the wet heat treatment. The rate of change (%) of the resistance value after the wet heat treatment with respect to the resistance value (resistance value before the wet heat treatment) was determined.

(Smoothness: surface roughness)
A coating film was formed on a PET film with a doctor blade having a gap of 500 μm using the water-based conductive paint obtained in Examples and Comparative Examples, and dried at 90 ° C. for 1 hour to obtain a conductive paint sheet. The surface roughness of the conductive paint sheet was measured with a laser depth meter. Ra was determined according to JIS B0633: '01. Ra has shown that it is smooth that it is 20 micrometers or less.

Example 1
(Production of binder polymer A and aqueous binder dispersion A)
In a stainless pressure-resistant reactor equipped with a stirring device, seed latex (latex of polymer particles having a particle diameter of 70 nm obtained by polymerizing 38 parts of styrene, 60 parts of methyl methacrylate, and 2 parts of methacrylic acid) as a solid content 3 parts, 20 parts of acrylonitrile, 80 parts of 1,3-butadiene, 100 parts of ion-exchanged water, and 0.5 part of sodium alkyldiphenyl ether disulfonate were added and stirred. The reactor was warmed to 80 ° C. After adding 10 parts of a 4% aqueous potassium persulfate solution, the previous dispersion was added over 2 hours for polymerization. After completion of the addition, the reaction was continued for 1 hour while maintaining the reaction temperature. The polymerization conversion rate was 97%. The reaction system was cooled to room temperature to stop the polymerization reaction, and the pressure was reduced to remove unreacted monomers. Ion exchange water was added to adjust the solid content concentration to 45% and the pH of the dispersion to 7.5 to obtain a NBR dispersion. The pH of the dispersion was adjusted by adding a 10% aqueous ammonia solution.

Next, a hydrogenation reaction was performed. That is, 400 milliliters (total solids 48 grams) of the polymer obtained with water adjusted to a total solids concentration of 12% by weight was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen was added. After flowing gas for 10 minutes to remove dissolved oxygen in the polymer, 75 mg of palladium acetate was dissolved and added as a hydrogenation catalyst in 180 ml of water added with 4 times moles of nitric acid with respect to Pd. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. )
Next, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate was further dissolved and added as a hydrogenation catalyst in 60 ml of water to which 4 times moles of nitric acid had been added relative to Pd. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid content concentration became 40% to obtain binder A and binder aqueous dispersion A. The iodine value of the obtained binder polymer A was 12. Moreover, the average particle diameter (dispersion particle diameter) of the binder polymer A measured using a particle diameter measuring machine (Coulter LS230: manufactured by Coulter, Inc.) was 130 μm.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion A and carbon were kneaded with a batch kneader for 30 minutes to prepare an aqueous conductive paint. Here, 60 parts of carbon was used with respect to 100 parts of the obtained water-based conductive paint. Further, 5 parts of binder polymer A was used with respect to 100 parts of carbon. Further, as carbon, 30 parts of carbon black was used with respect to 70 parts of graphite.

(Example 2)
(Production of binder polymer B and binder aqueous dispersion B)
Binder polymer B was produced in the same manner as in Example 1 except that the composition of the monomer mixture used for the polymerization was 30 parts of acrylonitrile and 70 parts of 1,3-butadiene, and a binder aqueous dispersion B was obtained. The obtained binder polymer B had an iodine value of 13. Moreover, the average particle diameter (dispersion particle diameter) of the obtained binder polymer B was 150 μm.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion B and carbon were kneaded with a batch kneader for 30 minutes to prepare an aqueous conductive paint. Here, 62 parts of carbon was used with respect to 100 parts of the obtained conductive paint. Further, 5 parts of binder polymer B was used with respect to 100 parts of carbon. As the carbon, 20 parts of carbon black was used with respect to 80 parts of graphite.

(Example 3)
(Production of binder polymer C and binder aqueous dispersion C)
A binder polymer dispersion C was obtained in the same manner as in Example 1 except that the hydrogenation reaction time in the second stage was 12 hours in the hydrogenation reaction. In addition, the iodine value of the obtained binder polymer C was 8. Moreover, the average particle diameter (dispersion particle diameter) of the obtained binder polymer C was 160 μm.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion C and carbon were kneaded with a batch kneader for 30 minutes to prepare an aqueous conductive paint. Here, 58 parts of carbon was used with respect to 100 parts of the water-based conductive paint obtained. Moreover, 6 parts of binder polymer C was used with respect to 100 parts of carbon. Further, as carbon, 30 parts of carbon black was used with respect to 70 parts of graphite.

Example 4
(Production of binder polymer D and binder aqueous dispersion D)
A binder polymer dispersion D was obtained in the same manner as in Example 1 except that the composition of the monomer mixture used for polymerization was 30 parts acrylonitrile and 70 parts 1,3-butadiene. The obtained binder polymer D had an iodine value of 8. Moreover, the average particle diameter (dispersion particle diameter) of the obtained binder polymer D was 150 micrometers.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion D and carbon were kneaded with a batch kneader for 30 minutes to prepare an aqueous conductive paint. Here, 55 parts of carbon was used with respect to 100 parts of the obtained water-based conductive paint. Further, 3 parts of binder polymer D was used with respect to 100 parts of carbon. Further, as carbon, 30 parts of carbon black was used with respect to 70 parts of graphite.

(Example 5)
(Manufacture of binder polymer E and binder aqueous dispersion E)
In a stainless steel reactor equipped with a stirrer, seed latex (polymer particle latex obtained by polymerizing 38 parts of styrene, 60 parts of methyl methacrylate and 2 parts of methacrylic acid) at a solid content 3 parts, 50 parts of butyl acrylate, 40 parts of 2-ethylhexyl acrylate, 10 parts of acrylic acid, 150 parts of ion-exchanged water and 0.5 part of sodium alkyldiphenyl ether disulfonate were added and stirred. The reactor was warmed to 80 ° C. After adding 10 parts of 4% potassium persulfate aqueous solution, the previous dispersion was added over 5 hours to polymerize. After completion of the addition, the reaction was continued for 3 hours while maintaining the reaction temperature. The polymerization conversion rate was 93%. The reaction system was cooled to room temperature to stop the polymerization reaction, and the pressure was reduced to remove unreacted monomers. Ion exchange water was added to adjust the solid content concentration to 45% and the pH of the dispersion to 7.5, thereby obtaining a binder polymer E and a binder aqueous dispersion E. The pH of the dispersion was adjusted by adding a 10% aqueous ammonia solution.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion E, the binder aqueous dispersion A and carbon were kneaded with a batch kneader for 30 minutes to prepare a water-based conductive paint. Here, 55 parts of carbon is used for 100 parts of the obtained water-based conductive paint, and binder water is used so that binder polymer A is 1.5 parts and binder polymer E is 1.5 parts with respect to 100 parts of carbon. A water-based conductive paint was produced in the same manner as in Example 1 except that the dispersions A and E were used.

(Example 6)
(Production of binder polymer F and binder aqueous dispersion F)
In a stainless steel reactor equipped with a stirrer, seed latex (polymer particle latex obtained by polymerizing 38 parts of styrene, 60 parts of methyl methacrylate and 2 parts of methacrylic acid) at a solid content 3 parts, 20 parts of butyl acrylate, 70 parts of 2-ethylhexyl acrylate, 10 parts of acrylic acid, 120 parts of ion-exchanged water and 0.5 part of sodium alkyldiphenyl ether disulfonate were added and stirred. The reactor was warmed to 80 ° C. After adding 10 parts of 4% potassium persulfate aqueous solution, the previous dispersion was added over 5 hours to polymerize. After completion of the addition, the reaction was continued for 3 hours while maintaining the reaction temperature. The polymerization conversion rate was 93%. The reaction system was cooled to room temperature to stop the polymerization reaction, and the pressure was reduced to remove unreacted monomers. Ion exchange water was added to adjust the solid content concentration to 45% and the pH of the dispersion to 7.5 to obtain a binder polymer F and a binder aqueous dispersion F. The pH of the dispersion was adjusted by adding a 10% aqueous ammonia solution.

(Manufacture of water-based conductive paint)
The obtained binder aqueous dispersion F, the binder aqueous dispersion A, and carbon were kneaded with a batch kneader for 30 minutes to prepare a water-based conductive paint. Here, 30 parts of carbon is used with respect to 100 parts of the obtained water-based conductive coating material, binder aqueous dispersion A, 2 parts of binder polymer A and 1 part of binder polymer F with respect to 100 parts of carbon, respectively. A water-based conductive paint was produced in the same manner as in Example 1 except that F was used.

(Comparative Example 1)
(Production of binder polymer G and binder aqueous dispersion G)
A binder polymer was produced in the same manner as in Example 2 except that the reaction time was 15 minutes in the hydrogenation reaction, and a binder polymer G and a binder aqueous dispersion G were obtained. The iodine value of the obtained binder polymer G was 40. Moreover, the average particle diameter (dispersion particle diameter) of the obtained binder polymer G was 130 μm.

(Manufacture of water-based conductive paint)
The obtained binder polymer aqueous dispersion G and carbon were kneaded with a batch kneader for 30 minutes to produce a water-based conductive paint. Here, 55 parts of carbon was used with respect to 100 parts of the obtained water-based conductive paint. Further, 5 parts of binder polymer G was used with respect to 100 parts of carbon. Moreover, as carbon, 70 parts of carbon black was used with respect to 30 parts of graphite.

(Comparative Example 2)
(Production of binder polymer A and aqueous binder dispersion A)
In the same manner as in Example 1, binder polymer A and binder aqueous dispersion A were produced to obtain binder aqueous dispersion A.

(Manufacture of water-based conductive paint)
A water-based conductive paint was produced in the same manner as in Example 1 except that 80 parts of carbon was used with respect to 100 parts of the water-based conductive paint.

(Comparative Example 3)
(Production of binder polymer A and aqueous binder dispersion A)
In the same manner as in Example 1, binder polymer A and binder aqueous dispersion A were produced to obtain binder aqueous dispersion A.

(Manufacture of water-based conductive paint)
A water-based conductive paint was produced in the same manner as in Example 1 except that 30 parts of carbon was used for 100 parts of the water-based conductive paint and 3 parts of binder polymer A was used for 100 parts of carbon.

  Table 1 shows the results of evaluating the flowability, resistance value, resistance value change and smoothness of the water-based conductive paints produced in Examples 1 to 6 and Comparative Examples 1 to 3 by the wet heat resistance test. In Comparative Example 2, the wet heat resistance test and the surface roughness measurement could not be performed.

  As shown in Table 1, when a binder containing an acrylonitrile-butadiene copolymer having a carbon solid content concentration of 50 to 75 parts and an iodine value of 20 or less with respect to 100 parts of the water-based conductive paint is used, Property, resistance value, resistance value change and smoothness by the heat and humidity resistance test are all good.

Claims (5)

A water-based conductive paint used to form a fuel cell separator,
The water-based conductive paint includes a conductive material, a binder and water,
The conductive material is a carbon-based material, and the content of the conductive material is 50 to 75 wt% in the water-based conductive paint,
The water-based conductive paint, wherein the binder contains an acrylonitrile-butadiene copolymer having an iodine value of 20 or less.   The water-based conductive paint according to claim 1, wherein the binder has a dispersed particle size of 0.05 µm or more and 0.4 µm or less.   The water-based conductive paint according to claim 1 or 2, wherein the acrylonitrile-butadiene copolymer is a hydrogenated acrylonitrile-butadiene copolymer hydrogenated by an aqueous layer hydrogenation method.   The weight ratio of the said binder and the said carbonaceous material is 1.5: 100-8: 100 as solid content, The water-system conductive paint as described in any one of Claims 1-3 characterized by the above-mentioned. The carbon-based material includes graphite and carbon black,
5. The water-based conductive paint according to claim 1, wherein a weight ratio of the graphite and the carbon black is 90:10 to 60:40.