Conductive dispersion and conductive film

Abstract

To provide a conductive dispersion having low viscosity and excellent flowability, even if containing an alcohol-based organic solvent or a ketone-based organic solvent in a dispersion medium and containing graphite and carbon black at high concentrations and further to provide a conductive film having good conductivity containing graphite and carbon black.SOLUTION: There is provided a conductive dispersion containing graphite, carbon black, a dispersant (C) and a medium (D), wherein the graphite includes graphite (A) having an average primary particle diameter of 3 to 12 μm, the carbon black includes carbon black (B) having a BET specific surface area of 130 to 1400 m2 / g, the dispersant (C) contains an amphoteric surfactant and / or a polyvinyl acetal and the medium (D) contains an alcohol-based organic solvent or a ketone-based organic solvent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive dispersion and a conductive film.

Background Art

[0002] Conductive materials such as carbon are widely used in paints, coating materials, coating agents, films, sheets, inks, magnet modifying materials, various electronic device members, electrode materials for batteries, and the like. When producing a conductive dispersion containing such a conductive material, in order to improve production process efficiency or conductivity, it is important how to disperse the conductive material in a solvent at a high concentration and uniformly so that it can be easily applied.

[0003] Generally, in a conductive dispersion using a carbon material, as one of the means for improving conductivity, graphite and carbon black are used in combination. Graphite is a particle with an average primary particle size on the micro order, which is composed of layers in which carbon atoms are two-dimensionally bonded, and has very high conductivity as a powder. However, when graphite is dispersed alone and coated to form a conductive film, there is a problem that a conductive path (route) between particles is not well formed, resulting in a conductive film with low conductivity. On the other hand, carbon black is a particle with an average primary particle size on the nano order generated by incomplete combustion of organic substances, and is inferior to graphite in terms of conductivity. On the other hand, since carbon black particles form small aggregates called structures, there are conductive paths regardless of the form, and high conductivity is easily obtained. Therefore, it is considered that by using graphite and carbon black in combination, carbon black plays the role of a conductive path between graphite particles, and a conductive film with high conductivity can be obtained.

[0004] For example, Patent Document 1 discloses a system in which graphite and carbon black are used in combination at a mass ratio of 4:1 to 1:4 in isophorone, diacetone alcohol, and methoxypropoxypropanol. Further, Patent Document 2 discloses a combined system of graphite and carbon black using water as a medium and an epoxy resin as a binder. Furthermore, Patent Document 3 discloses a combined system of graphite and carbon black using (modified) polyvinyl alcohol or an acrylic resin as a dispersant and an amide-based or alcohol-based organic solvent as a medium.

[0005] On the other hand, in a combined system of graphite and carbon black, in order to obtain high conductivity, it is desirable to blend a large amount of carbon black with respect to graphite. However, carbon black generally has poor wettability with respect to alcohol-based organic solvents and ketone-based organic solvents, which are often used in various applications, and in most cases, poor dispersion occurs. Therefore, in most cases, well-known conventional conductive dispersions containing carbon black are limited to media such as water and N-methyl-2-pyrrolidone. When producing a conductive film using a conductive dispersion, it is often necessary to blend a resin to obtain the desired properties. However, when attempting to produce a conductive film using a conductive dispersion using such a limited medium, the types of resins that can be used in combination are greatly restricted, making it difficult to obtain a conductive film having the desired properties. Therefore, there has been a demand for a conductive dispersion containing an alcohol-based organic solvent or a ketone-based organic solvent as a medium that can be applied to various uses.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem to be solved by the present invention is to provide a conductive dispersion having low viscosity and excellent fluidity, which contains an alcoholic organic solvent or a ketonic organic solvent in a dispersion medium and contains graphite and carbon black. Another problem is to provide a conductive film having good conductivity and containing graphite and carbon black.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that, in a combination of graphite having a specific average primary particle diameter and carbon black having a specific BET specific surface area, by using a specific dispersant, even if an alcoholic organic solvent or a ketonic organic solvent is included, a conductive dispersion having low viscosity and excellent fluidity can be obtained, and thus the present invention has been accomplished. That is, the present invention relates to a conductive dispersion containing graphite, carbon black, a dispersant (C) and a medium (D), wherein the graphite contains graphite (A) having an average primary particle diameter of 3 to 12 μm, the carbon black contains carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g, the dispersant (C) contains an amphoteric surfactant and / or polyvinyl acetal, and the medium (D) contains an alcoholic organic solvent or a ketonic organic solvent.

[0009] The present invention also relates to the above conductive dispersion containing 5 to 50 parts by mass of carbon black with respect to 100 parts by mass of graphite.

[0010] The present invention also relates to the above conductive dispersion containing 10 to 50 parts by mass of the dispersant (C) with respect to 100 parts by mass of the total amount of graphite and carbon black.

[0011] The present invention also relates to the above conductive dispersion, wherein the dispersant (C) contains an amphoteric surfactant having an acid value of 5 to 30 mgKOH / g and an amine value of 10 to 50 mgKOH / g.

[0012] Further, the present invention relates to the above conductive dispersion in which the medium (D) contains an alcoholic organic solvent (D1) having a structure represented by the following general formula (1). General formula (1) R 1 R 2 C(OH)CR 3 R 4 (OR 5 ) 〔In general formula (1), R 1 , R 2 , R 3 and R 4 are each independently a hydrogen atom or a monovalent hydrocarbon group, and R 5 is a monovalent hydrocarbon group.〕

[0013] Further, the present invention relates to the above conductive dispersion in which 50% by mass or more of the alcoholic organic solvent (D1) is contained in 100% by mass of the medium (D).

[0014] Further, the present invention relates to the above conductive dispersion further containing an epoxy resin (E).

[0015] Further, the present invention relates to a conductive film containing graphite, carbon black, and a dispersant (C), wherein the graphite contains graphite (A) having an average primary particle diameter of 3 to 12 μm, the carbon black contains carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g, the dispersant (C) contains an amphoteric surfactant or polyvinyl acetal, and the total amount of graphite and carbon black is 50 to 91% by mass.

[0016] Further, the present invention relates to the above conductive film further containing an epoxy resin (E) and containing 25 to 100 parts by mass of the total amount of the dispersant (C) and the epoxy resin (E) with respect to 100 parts by mass of the total amount of graphite and carbon black.

[0017] Furthermore, the present invention relates to the above conductive film containing 10 to 50 parts by mass of a dispersant (C) with respect to a total amount of 100 parts by mass of graphite and carbon black.

[0018] Furthermore, the present invention relates to the above conductive film having a conductivity of 20 S / cm or more.

Effects of the Invention

[0019] According to the present invention, even when an organic solvent containing an alcohol-based organic solvent or a ketone-based organic solvent in a dispersion medium is used, it has become possible to obtain a conductive dispersion having low viscosity and excellent fluidity and containing graphite and carbon black. Further, by using this conductive dispersion, it has become possible to obtain a conductive film having good conductivity and containing graphite and carbon black.

Modes for Carrying Out the Invention

[0020] In this specification, a numerical range specified using "~" shall include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value.

[0021] <Conductive Dispersion> The conductive dispersion of the present invention (hereinafter also referred to as "the present dispersion") is a conductive dispersion containing graphite, carbon black, a dispersant (C), and a medium (D). The graphite contains graphite (A) having an average primary particle diameter of 3 to 12 μm, the carbon black contains carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g, the dispersant (C) contains an amphoteric surfactant and / or polyvinyl acetal, and the medium (D) contains an alcohol-based organic solvent or a ketone-based organic solvent. Further, the present dispersion can also be used by further blending an epoxy resin (E). Hereinafter, each constituent raw material constituting the present dispersion will be described in detail.

[0022] <Graphite (A)> The graphite used in the present invention contains graphite (A). The average primary particle size of graphite (A) is 3 to 12 μm, preferably 5 to 12 μm, and more preferably 10 to 12 μm. By setting the average primary particle size to 3 μm or more, it is possible to obtain good packing properties while reducing the number of contact interfaces between particles, and the conductivity when forming a conductive film becomes good. Further, by setting the average primary particle size to 12 μm or less, a conductive film with a smooth surface can be obtained, and a conductive film with good appearance can be manufactured. Note that the "average primary particle size" in this specification is a value obtained by the following method. That is, using a scanning electron microscope, images are taken at an arbitrary three locations at a magnification of 1000 times. Subsequently, 100 arbitrary particles are selected from each image, and the vertical length at the particle center is measured. The arithmetic mean value of the obtained measurement values is defined as the average primary particle size.

[0023] Examples of graphite (A) include flaked graphite UP-5N (average primary particle size 5 μm) and UP-10N (average primary particle size 10 μm) manufactured by Nippon Graphite Industries, Ltd., scaly graphite MCP-10 (average primary particle size 10 μm), spheroidized graphite CGR-12 (average primary particle size 12 μm), and the like.

[0024] Graphite (A) preferably has a powder resistivity of 1×10 -3 ~3×10 -2 Ω·cm. The powder resistivity of graphite (A) is obtained by measuring the density and volume resistivity of 1 g of graphite (A) using a powder resistor (manufactured by Mitsubishi Chemical Analytech Co., Ltd., MCP-PD51) under measurement pressures of 4 kN, 8 kN, 12 kN, 16 kN, and 20 kN, and approximating the density-volume resistivity plot with an exponential function. It is the value at 1 g / cm 3

[0025] The content rate of graphite (A) contained in all the graphite is preferably 50 mass% or more, more preferably 80 to 100 mass%, and particularly preferably substantially 100 mass%. By using such graphite, the conductive film can obtain particularly good conductivity and appearance.

[0026] ​<Carbon black (B)> The carbon black used in the present invention includes carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g. The BET specific surface area of the carbon black (B) is preferably 300 m 2 / g or more, more preferably 700 m 2 / g or more, and particularly preferably 1000 m 2 / g or more. Also, it is preferably 1300 m 2 / g or less, and more preferably 1270 m 2 / g or less. By setting the BET specific surface area to 130 m 2 / g or more, the number of particles per unit mass becomes sufficiently large, so that the conductivity when forming the conductive film becomes good. Also, by setting the BET specific surface area to 1400 m 2 / g or less, a conductive film with good appearance and sufficient strength can be obtained. In addition, the "BET specific surface area" in this specification is a value calculated by the BET method (Brunauer, Emmett, and Teller method). That is, after pretreating carbon black by heating it to 100 °C or higher under vacuum, the nitrogen adsorption amount when flowing a helium-nitrogen mixed gas (helium: nitrogen = 7:3) under liquid nitrogen temperature (-196 °C) is measured, and it is a value calculated by the multi-point method.

[0027] Preferably, 5 to 50 parts by mass of carbon black is contained with respect to 100 parts by mass of graphite, and more preferably 10 to 20 parts by mass is contained. By containing 5 parts by mass or more of carbon black with respect to 100 parts by mass of graphite, the carbon black effectively fills the voids formed between the graphite particles, and the conductivity when forming the conductive film becomes good. Also, by containing 50 parts by mass or less of carbon black with respect to 100 parts by mass of graphite, the dispersibility of the carbon black becomes good, and both the handleability of the dispersion and the high conductivity of the conductive film can be achieved.

[0028] The average primary particle diameter of carbon black (B) is preferably 20 to 40 nm. By setting it within this range, the number of particles per unit mass becomes sufficiently large, so that the conductivity when forming a conductive film becomes particularly good. Note that the average primary particle diameter of carbon black (B) can be obtained by the same method as that of graphite (A).

[0029] The production method of carbon black (B) is not particularly limited, and examples thereof include the furnace method, the contact method, the thermal method, the acetylene method, and the lamp black method.

[0030] Examples of carbon black (B) include Mitsubishi Carbon Black #3400B (BET specific surface area: 165 m 2 / g) manufactured by Mitsubishi Chemical Corporation, DENKA BLACK Li Li-435 (BET specific surface area: 133 m 2 / g) manufactured by Denka Co., Ltd., Ketjenblack EC-300J (BET specific surface area: 800 m 2 / g) and Ketjenblack EC-600JD (BET specific surface area: 1270 m 2 / g) manufactured by Lion Specialty Chemicals Co., Ltd., and the like.

[0031] The powder resistivity of carbon black (B) is preferably 2×10 -2 ~7×10 -2 Ω·cm. Note that the powder resistivity of carbon black (B) can be obtained by the same method as that of graphite (A).

[0032] The content of carbon black (B) contained in the total carbon black is preferably 50% by mass or more, more preferably 80 to 100% by mass, and particularly preferably substantially 100% by mass. By using such carbon black, a conductive film with good conductivity can be obtained.

[0033] The total content ratio of graphite and carbon black (collectively referred to as "carbon materials" in some cases) contained in the conductive dispersion of the present invention is preferably 20% by mass or more, more preferably 24% by mass or more. When it is 20% by mass or more, the storage stability becomes good. Also, even if the content ratio of the carbon material is high, when it is 35% by mass or less, a dispersion with low viscosity and excellent fluidity is obtained. Further, in the case of a conductive dispersion containing the epoxy resin (E) described later, although the content ratio of the carbon material tends to be relatively lower compared to the case of not containing the epoxy resin (E), for example, it is 20% by mass or more and 24% by mass or less.

[0034] <Dispersant (C)> Next, the dispersant (C) contained in the conductive dispersion of the present invention will be described. The dispersant (C) contains an amphoteric surfactant and / or polyvinyl acetal, and preferably contains an amphoteric surfactant.

[0035] The blending amount of the dispersant (C) with respect to 100 parts by mass of the total amount of graphite and carbon black is preferably 10 to 50 parts by mass, more preferably 10 to 30 parts by mass, and particularly preferably 10 to 20 parts by mass. By setting it in this way, a dispersion with low viscosity, excellent fluidity, and particularly good handleability can be obtained.

[0036] <Amphoteric surfactant> The amphoteric surfactant is a surfactant having an acid value and an amine value, and is a surfactant having an acidic group and a basic group in one molecule.

[0037] The acid value of the amphoteric surfactant is preferably 5 to 30 mgKOH / g. By having an acid value of 5 to 30 mgKOH / g, the dispersibility of the carbon material and the storage stability of the dispersion are improved.

[0038] In addition, the amine value of the amphoteric surfactant is preferably 10 to 50 mgKOH / g, more preferably 20 to 40 mgKOH / g, and even more preferably 20 to 35 mgKOH / g. By having an amine value of 10 to 50 mgKOH / g, the dispersibility of the carbon material and the storage stability of the dispersion are improved.

[0039] The amphoteric surfactant preferably contains a structural unit derived from polyethyleneimine and a structural unit derived from fatty acid in its chemical structure respectively. Thereby, the dispersibility of the carbon material and the storage stability of the dispersion are improved.

[0040] The weight average molecular weight of the amphoteric surfactant is preferably 1000 to 50000, more preferably 1000 to 30000, and particularly preferably 1000 to 20000.

[0041] The ratio of the amphoteric surfactant contained in the dispersant (C) is preferably 50% by mass or more, more preferably 80 to 100% by mass, and particularly preferably substantially 100% by mass. By using such a dispersant (C), a dispersion with low viscosity, excellent fluidity, and particularly good handleability can be obtained.

[0042] <Polyvinyl acetal> The polyvinyl acetal used in the present invention is a polymer containing a vinyl acetal structure represented by the following general formula (2) and a vinyl alcohol structure represented by the formula (3) as partial structures. The polyvinyl acetal may contain a vinyl acetate structure represented by the following formula (4) as a partial structure.

[0043] Formula (2)

Chemical formula

[0044] Formula (3)

Chemical formula

[0045] Formula (4)

Chemical formula

[0046] There are no particular restrictions on the method for producing the polyvinyl acetal used in the present invention, and various polyvinyl acetals synthesized by known methods or various commercially available products can be used. As a typical synthesis method, a polymer obtained by polymerizing a vinyl alcohol precursor such as vinyl acetate is saponified with an alkali, and part or all of it is converted into a vinyl alcohol structure represented by formula (3), and then aldehydes are reacted with it for acetalization. At this time, the type of aldehyde to be reacted can be a single type or a plurality of types.

[0047] The content of the polyvinyl acetal having the structure of the general formula (2) in the polyvinyl acetal is preferably 65 to 83% by mass.

[0048] The content of the polyvinyl acetal having the structure of formula (3) in the polyvinyl acetal is preferably 16 to 26% by mass.

[0049] The content of the polyvinyl acetal having the structure of formula (4) in the polyvinyl acetal is preferably 10% by mass or less, more preferably 5% by mass or less. Also, the lower limit is not particularly limited, but for example, it is 0.1% by mass or more.

[0050] The weight average molecular weight of the polyvinyl acetal is preferably 15,000 to 130,000.

[0051] Examples of polyvinyl acetal include Esrec BL-10 (weight average molecular weight 1.5×10 4 , hydroxyl group mass 19%, acetalization degree mass 78%) and Esrec BH-S (weight average molecular weight 6.6×10 4 , hydroxyl group mass 16%, acetalization degree mass 78%) manufactured by Sekisui Chemical Co., Ltd. etc.

[0052] <Medium (D)> Next, the medium (D) contained in the conductive dispersion of the present invention will be described. The medium (D) is a medium containing an alcohol-based organic solvent or a ketone-based organic solvent, and is preferably a liquid medium under normal pressure at 25°C. The medium (D) preferably contains an alcohol-based organic solvent.

[0053] <Alcohol-based organic solvent> The alcohol-based organic solvent has a chemical structure in which a hydrogen atom of a hydrocarbon is substituted with a hydroxyl group, and is a solvent that is liquid under normal pressure at 25°C.

[0054] The alcohol-based organic solvent is preferably an aliphatic alcohol-based organic solvent, and more preferably contains an alcohol-based organic solvent (D1) having a structure represented by the following general formula (1). General formula (1) R 1 R 2 C(OH)CR 3 R 4 (OR 5 ) 〔In general formula (1), R 1 , R 2 , R 3 and R 4 are each independently a hydrogen atom or a monovalent hydrocarbon group, and R 5 is a monovalent hydrocarbon group.〕

[0055] R 1 , R 2 , R 3 , R 4 and R 5As the monovalent hydrocarbon group in [the compound], a monovalent aliphatic hydrocarbon group is preferred, and an alkyl group is more preferred. Further, as the alkyl group, an alkyl group having 1 to 4 carbon atoms is preferred.

[0056] R 1 、R 2 、R 3 、R 4 Examples of the monovalent hydrocarbon group in R, R, R, R, and R include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and the like.

[0057] Specific examples of the alcohol-based organic solvent (D1) include ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and the like.

[0058] The alcohol-based organic solvent (D1) preferably has a boiling point of 100 to 200 °C under normal pressure (1013 hPa). When the boiling point is 100 °C or higher, rapid drying immediately after coating can be suppressed, so that a conductive film with good appearance can be formed. Further, when the boiling point is 200 °C or lower, a film can be formed at low temperature and in a short time.

[0059] The content ratio of the alcohol-based organic solvent (D1) contained in the medium (D) is preferably 50% by mass or more, more preferably 70 to 100% by mass, and even more preferably 100% by mass. By setting it in this way, the dispersibility of the dispersion, the film-forming property of the conductive film, and the appearance can be highly compatible.

[0060] Examples of alcohol-based organic solvents other than the alcohol-based organic solvent (D1) include ethanol, 1-propanol, 2-propanol, 1-butanol, and the like.

[0061] <Ketone-based organic solvent> The ketone-based organic solvent has a ketone group in its chemical structure and is a solvent that is liquid at 25 °C under normal pressure. The ketone-based organic solvent is preferably an aliphatic ketone-based organic solvent.

[0062] The ketone-based organic solvent is not particularly limited, and examples thereof include methyl ethyl ketone and cyclohexanone.

[0063] <Method for producing a conductive dispersion> The method for producing the conductive dispersion of the present invention is not particularly limited. For example, a dispersant (C) and a medium (D) are mixed to form a uniform solution or dispersion, and then a carbon material is added. After sufficiently stirring and mixing, the dispersion treatment is carried out to produce it. Further, when producing a conductive dispersion containing an epoxy resin (E), after the above dispersion treatment, it is preferable to add the epoxy resin (E) and stir and mix.

[0064] Examples of the apparatus that can be used for stirring and mixing include kneading and mixing apparatuses such as a disper, a planetary mixer, a trimix, a homogenizer mixer, and a kneader, a tumbler mixer, an attritor, and a roll mill. In the stirring and mixing, it is preferable that the mixed liquid be in a homogeneous and fluid state.

[0065] Examples of the disperser used for the dispersion treatment include kneading and mixing apparatuses such as a bead mill, a colloid mill, a planetary mixer, a trimix, a homogenizer mixer, and a kneader, an attritor, a roll mill, and a rotating and revolving mixer. The disperser to be used can be appropriately set according to the handleability of the conductive dispersion and the degree of aggregation of the carbon material.

[0066] The temperature during the dispersion is preferably 10 to 75°C, more preferably 20 to 70°C, and particularly preferably 30 to 70°C in terms of suppressing the dispersibility of the carbon material, the solubility of the dispersant (C), and the wear of the apparatus.

[0067] The dispersion time is appropriately adjusted while checking the particle size of the carbon material. The dispersion time varies depending on the apparatus, but is usually preferably about 6 to 48 hours.

[0068] <Epoxy resin (E)> This dispersion may contain a resin. When it contains a resin, it is preferably further contains an epoxy resin (E). The epoxy resin (E) is a thermosetting resin that can be cured by crosslinking the epoxy groups contained in the polymer. By blending the epoxy resin (E), a conductive film with higher adhesion and strength can be obtained. When containing the epoxy resin (E), it is preferably blended so that the total amount of the dispersant (C) and the epoxy resin (E) is 25 to 100 parts by mass with respect to 100 parts by mass of the total amount of graphite and carbon black.

[0069] The epoxy resin (E) is not particularly limited, and examples thereof include bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, aliphatic type epoxy resin, and glycidylamine type epoxy resin.

[0070] The epoxy resin (E) is cured by adding a curing agent and heating, so that the epoxy groups are ring-opened and the crosslinking reaction proceeds. The blending amount of the curing agent is preferably 1 to 1.2 equivalents with respect to the epoxy equivalent of the epoxy resin (E). By setting within this range, a conductive film with good adhesion and strength can be formed.

[0071] In the market, a one-component type in which the epoxy resin (E) and the curing agent are premixed and a two-component type in which the epoxy resin (E) and the curing agent are separated and mixed before use can be obtained respectively. When using the one-component type, since a curing agent that can react all the epoxy groups is already contained, a cured product (conductive film) can be obtained by heating to the reaction temperature. When using the two-component type, a cured product (conductive film) can be obtained by adding a sufficient amount of the curing agent to the epoxy groups and reacting.

[0072] The curing temperature of the epoxy resin (E) varies depending on the epoxy resin and curing agent used, but is preferably 25°C to 300°C, more preferably 40 to 200°C, and particularly preferably 100 to 170°C.

[0073] Examples of the epoxy resin (E) include RO-8508 (one-component epoxy resin, glass transition temperature of the cured product: 260°C), RO-8512 (one-component epoxy resin, glass transition temperature of the cured product: 350°C), RO-8532 (one-component epoxy resin, glass transition temperature of the cured product: 280°C), etc. manufactured by Sunresin Co., Ltd.

[0074] The curing agent for the epoxy resin (E) is not particularly limited, and examples thereof include acid anhydrides, amines, imidazoles, phenolic resins, polyamide resins, polymercaptans, polysulfide resins, latent curing agents, etc.

[0075] <Other components (F)> The conductive dispersion of the present invention may further contain, if necessary, other components (F) such as leveling agents, defoaming agents, reaction accelerators, rheology modifiers, colorants (excluding graphite and carbon black), stabilizers such as antioxidants, flame retardants, plasticizers, ion scavengers, etc. The other components (F) can be used alone or in combination of two or more.

[0076] <Conductive film and method for producing the same> The conductive film of the present invention can be obtained, for example, by coating the conductive dispersion of the present invention on a substrate.

[0077] The content of the total amount of graphite and carbon black contained in the conductive film is preferably 50 to 91% by mass. When it is 50% by mass or more, high conductivity can be obtained. Also, when it is 91% by mass or less, the appearance of the conductive film is good.

[0078] When the conductive film contains the epoxy resin (E), the content of the total amount of the dispersant (C) and the epoxy resin (E) with respect to 100 parts by mass of the total amount of graphite and carbon black is preferably 25 to 100 parts by mass. In this range, the conductive film can achieve both high conductivity and good appearance.

[0079] In the conductive film, the content of the dispersant (C) with respect to a total amount of 100 parts by mass of graphite and carbon black is preferably 10 to 50 parts by mass, more preferably 10 to 30 parts by mass, and particularly preferably 10 to 20 parts by mass. In this range, the conductive film can achieve both high conductivity and good appearance.

[0080] The method for coating the conductive dispersion on the substrate is not particularly limited, and examples thereof include various known methods such as die coating method, dip coating method, roll coating method, doctor coating method, gravure coating method, screen printing method, etc. The type of the substrate is not particularly limited, and various known substrates such as resin film, resin sheet, metal plate, filling into a mold or a casting mold can be used.

[0081] The drying method of the film coated with the conductive dispersion is not particularly limited, and for example, it can be dried by various known dryers such as a blowing dryer, a warm air dryer, an infrared heater, a far-infrared heater, etc.

[0082] The film coated with the conductive dispersion may be aged. The aging period is, for example, about 1 to 5 days at 40 °C and about 10 hours at 180 °C. Further, if necessary, aging may be performed in a plurality of temperature steps.

[0083] The conductivity of the conductive film is preferably 20 S / cm or more. There is no particular limitation on the upper limit value of the conductivity, but it is generally 60 S / cm or less. When the conductivity of the conductive film is 20 S / cm or more, it becomes easy to use for various members that require high conductivity.

Examples

[0084] Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" in the examples means "parts by mass" and "%" means "% by mass".

[0085] <Graphite> <<Graphite (A)>> · Graphite A-1: Flaked graphite. Average primary particle size: 3 μm. Produced by dry-grinding flaked graphite UP-5N with 200 parts of 1.25 mm Φ zirconia beads as the media. Hereinafter referred to as A-1. · Flaked graphite UP-5N (manufactured by Nippon Graphite Co., Ltd.): Flaked graphite. Average primary particle size: 5 μm. Hereinafter referred to as UP-5N. · Flaked graphite UP-10N (manufactured by Nippon Graphite Co., Ltd.): Flaked graphite. Average primary particle size: 10 μm. Hereinafter referred to as UP-10N. · Spheroidized graphite CGB-12R (manufactured by Nippon Graphite Co., Ltd.): Spheroidized graphite. Average primary particle size: 12 μm. Hereinafter referred to as CGB-12R. <<Graphite that is not Graphite (A)>> · Carbonaceous powder SCL-1 (manufactured by SEC Carbon Co., Ltd.): Carbonaceous material. Average primary particle size: 2 μm. Hereinafter referred to as SCL-1. · Scaly graphite CB-150 (manufactured by Nippon Graphite Co., Ltd.): Scaly graphite. Average primary particle size: 40 μm. Hereinafter referred to as CB-150.

[0086] <Carbon black> <<Carbon black (B)>> · Mitsubishi Carbon Black #3400B (manufactured by Mitsubishi Chemical Corporation): Carbon black. Average primary particle size: 21 nm, BET specific surface area: 165 m 2 / g. Hereinafter referred to as #3400B. · DENKA BLACK Li Li-435 (manufactured by Denka Co., Ltd.): Carbon black. Average primary particle size: 23 nm, BET specific surface area: 133 m 2 / g. Hereinafter referred to as Li-435. · Ketjenblack EC-300J (manufactured by Lion Specialty Chemicals Co., Ltd.): Carbon black. Average primary particle size: 40 nm, BET specific surface area: 800 m 2 / g. Hereinafter referred to as EC-300J. · Ketjenblack EC-600JD (manufactured by Lion Specialty Chemicals Co., Ltd.): Carbon black. Average primary particle size: 34 nm, BET specific surface area: 1270 m 2 / g. Hereinafter referred to as EC-600JD. <<Carbon black that is not Carbon black (B)>> · Tokablack #3845 (manufactured by Tokai Carbon Co., Ltd.): Carbon black. Average primary particle size: 40 nm, BET specific surface area: 57 m 2 / g. Hereinafter, it is referred to as #3845. · DENKA BLACK Li Li-400 (manufactured by Denka Co., Ltd.): Carbon black. Average primary particle size: 48 nm, BET specific surface area: 39 m 2 / g. Hereinafter, it is referred to as Li-400.

[0087] <Dispersant (C)> <<Amphoteric Surfactant>> · Ajisper PB821 (manufactured by Ajinomoto Fine-Techno Co., Inc.): Amphoteric surfactant. A polymer having a basic group and a skeleton derived from lactone. Acid value: 17 mgKOH / g, amine value: 10 mgKOH / g. Hereinafter, it is referred to as PB-821. · Spredox D-441 (manufactured by DOXA Co., Ltd.): Amphoteric surfactant. A polymer having a polyethyleneimine skeleton, a skeleton derived from fatty acid, a polyether skeleton, and a skeleton derived from lactone. Acid value: 17.5 mgKOH / g, amine value: 35 mgKOH / g. Hereinafter, it is referred to as D-441. · SOLSPERSE 28000 (manufactured by Lubrizol Corporation): Amphoteric surfactant. Acid value: 29 mgKOH / g, amine value: 45 mgKOH / g. Hereinafter, it is referred to as SP28000. · SOLSPERSE 38500 (manufactured by Lubrizol Corporation): Amphoteric surfactant. Acid value: 9 mgKOH / g, amine value: 20 mgKOH / g. Non-volatile content: 40% by mass (including methoxypropyl acetate as a solvent). Hereinafter, it is referred to as SP38500. · SOLSPERSE 39000 (manufactured by Lubrizol Corporation): Amphoteric surfactant. A polymer having a polyethyleneimine skeleton, a skeleton derived from fatty acid, and a skeleton derived from lactone. Acid value: 16.5 mgKOH / g, amine value: 30 mgKOH / g. Hereinafter, it is referred to as SP39000. · SOLSPERSE M385 (manufactured by Lubrizol Corporation): Amphoteric surfactant. Acid value: 11.5 mgKOH / g, amine value: 40 mgKOH / g. Non-volatile content: 50% by mass (including methoxypropyl acetate as a solvent). Hereinafter, it is referred to as SPM385. <<Polyvinyl Acetal>> · Esrec BH-6 (manufactured by Sekisui Chemical Co., Ltd.): Polyvinyl acetal. Weight-average molecular weight 9.2×10 4 , hydroxyl group 21% by mass, degree of acetalization 78% by mass. Hereinafter, referred to as BH-6. <<Amphoteric Surfactant and Dispersant Other than Polyvinyl Acetal>> · Efka FA 4620 (manufactured by BASF): Comparative example dispersant. Acidic polyether. Acid value 290 mgKOH / g. · DISPERBYK-109 (manufactured by BYK): Comparative example dispersant. Alkylol amidoamide. Amine value 140 mgKOH / g. Hereinafter, referred to as BYK-109. · DISPERBYK-111 (manufactured by BYK): Comparative example dispersant. Polymer having an acidic group, a polyether skeleton, and a skeleton derived from lactone. Acid value 129 mgKOH / g. Non-volatile content 95% by mass. Hereinafter, referred to as BYK-111. · SOLSPERSE20000 (manufactured by Lubrizol): Comparative example dispersant. Polymer having a basic group and a polyether skeleton. Amine value 32 mgKOH / g. Hereinafter, referred to as SP20000. · Gosnex T-330 (manufactured by Mitsubishi Chemical Corporation): Comparative example dispersant. Modified polyvinyl alcohol. Hereinafter, referred to as T-330. · Polyvinylpyrrolidone K-30 (manufactured by Nippon Shokubai Co., Ltd.): Comparative example dispersant. Polyvinylpyrrolidone. Hereinafter, referred to as K-30.

[0088] <Medium (D)> <<Alcohol-based Organic Solvent>> · Ethylene glycol monobutyl ether. Hereinafter, referred to as butyl cellosolve. · Propylene glycol monomethyl ether. Hereinafter, referred to as PGME. <<Ketone-based Organic Solvent>> · Methyl ethyl ketone. Hereinafter, referred to as MEK. · Cyclohexanone. <<Mixture of Alcohol-based Organic Solvent and Ketone-based Organic Solvent>> · Mixed solvent 1: Mixed solvent composed of 70% by mass of butyl cellosolve and 30% by mass of MEK. <Other solvents> · Distilled water. Hereinafter referred to as water. · Dibutyl ether.

[0089] <Epoxy resin (E)> One-component high heat-resistant epoxy resin RO-8508 (manufactured by Sun Yurec Co., Ltd.): One-component epoxy resin. Glass transition temperature after curing: 260°C. Hereinafter referred to as RO-8508.

[0090] <Evaluation of dispersant>

[0091] [Acid value] The acid value of the dispersant was measured as follows: 80 mL of acetone and 10 mL of water were added to 0.5 - 1 g of a sample solution in which the dispersant was dissolved in acetone, and the mixture was stirred until uniformly dissolved. Using a 0.1 mol / L aqueous KOH solution as the titrant, titration was performed using an automatic titrator ("COM-555" manufactured by Hiranuma Sangyo Co., Ltd.) to measure the acid value (mgKOH / g) of the sample solution. Then, the acid value of the dispersant was calculated from the acid value and non-volatile content concentration of the sample solution. When the dispersant did not dissolve in acetone, butyl cellosolve was used.

[0092] [Amine value] The amine value of the dispersant is the value obtained by converting the measured total amine value (mgKOH / g) to non-volatile content in accordance with the method of ASTM D 2074. When the dispersant did not dissolve in a predetermined solvent (ethanol), butyl cellosolve was used.

[0093] [Weight average molecular weight (Mw)] The weight average molecular weight (Mw) of the dispersant was measured by gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector. Using HLC-8220GPC (manufactured by Tosoh Corporation) as the apparatus, two separation columns were connected in series, and for both packing materials, two "TSK-GEL SUPER HZM-N" were connected in series and used. The oven temperature was 40 °C, tetrahydrofuran (THF) was used as the eluent, and the measurement was carried out at a flow rate of 0.35 mL / min. The dispersant was dissolved in THF so that the concentration became 1 mass%, and 20 μL was injected from the injection port of the apparatus for measurement. The molecular weight is the converted value of standard polystyrene.

[0094] <Manufacture of Conductive Dispersion (1)> [Example 1-1] 64 parts of butyl cellosolve as an alcoholic organic solvent and 6 parts of PB-821 as an amphoteric surfactant were charged into a glass bottle, and they were sufficiently stirred and mixed to dissolve PB-821. Next, 25 parts of UP-5N as graphite (A) and 5 parts of #3400B as carbon black (B) were added, and using 140 parts of 1.25 mmΦ zirconia beads as media, they were dispersed for 1 hour with a Scan dex to obtain a conductive dispersion.

[0095] <Evaluation of Conductive Dispersion and Conductive Film> Regarding the manufactured conductive dispersion, the viscosity (dispersion state) and storage stability were evaluated by the following methods and criteria. Also, regarding the film (conductive film) of the conductive dispersion, the appearance and conductivity were evaluated by the following methods and criteria.

[0096] [Viscosity Evaluation] The conductive dispersion was stirred and mixed at 1600 rpm for 60 seconds using a stirrer (Mazers Star KK-250S, manufactured by Kurabo Industries Ltd.), and immediately after that, the rotational viscometer ViscoQC TMUsing an Anton Paar 100, measurements were taken at a sample temperature of 25°C, a rotor rotation speed of 6 rpm, and a measurement time of 1 minute, and then at a rotor rotation speed of 60 rpm and a measurement time of 1 minute. When the viscosity of the sample measured at a rotation speed of 60 rpm was less than 100 mPa·s, rotor No. 1 was used; when the viscosity was 100 mPa·s or more and less than 500 mPa·s, rotor No. 2 was used; when the viscosity was 500 mPa·s or more and less than 2000 mPa·s, rotor No. 3 was used; and when the viscosity was 2000 mPa·s or more and 10000 mPa·s or less, rotor No. 4 was used. The evaluation criteria were as follows. The following viscosities are those measured at a rotation speed of 60 rpm. 〇: 2000 mPa·s or less (good). △: More than 2000 mPa·s and 4000 mPa·s or less (fair). ×: More than 4000 mPa·s or no fluidity (poor).

[0097] [Storage Stability Test] The conductive dispersion was placed in a vial and allowed to stand at 25°C for 1 week, and then evaluated by checking for the presence or absence of sediment after shaking the vial. If there was sediment, it was further stirred with a spatula and evaluated by checking whether the sediment was redispersed. The evaluation criteria were as follows. ◎: No sediment (particularly good). ○: Slight sediment, but the sediment is easily redispersed by stirring with a spatula for less than 1 minute (good). △: There is sediment, but the sediment is redispersed by stirring with a spatula for 1 minute or more (fair). ×: There is sediment and it is not redispersed by stirring with a spatula. (Poor).

[0098] [Appearance of Conductive Film] The conductive dispersion was stirred and mixed at 1600 rpm for 60 seconds using a stirrer (Mazer Star KK-250S, manufactured by Kurabo Industries Ltd.). Immediately after that, it was dropped onto a polyethylene terephthalate (PET) film in an amount of about 1 to 2 g, and after coating with an applicator so that the film thickness of the conductive film became 8 μm, it was dried in an oven at 150 °C for 1 hour to produce a conductive film. Then, the appearance was evaluated visually and by touch. The evaluation criteria were as follows. ◎: There are no roughness or unevenness, and it is homogeneous and without unevenness (particularly good). ○: It has no roughness or unevenness, but there is very slight unevenness (good). △: There is roughness or unevenness in part of the conductive film (acceptable). ×: There is roughness or unevenness throughout the conductive film (defective).

[0099] [Conductivity] The conductivity was evaluated by the following method using the conductive film produced by evaluating the appearance of the conductive film. Regarding the produced conductive film, the film thickness at three arbitrary points was measured using a length measuring instrument (Digimicro MH-15M, manufactured by Nikon Corporation), and the average value thereof was calculated. Next, the surface resistivity at three arbitrary points was measured using a resistivity meter (Loresta-GX MCP-T700, manufactured by Nitto Seiko Analytic Co., Ltd., four-probe method), and the average value of the surface resistivity was calculated. Then, the conductivity (unit: S / cm) was calculated from the average value of the film thickness and the average value of the surface resistivity according to the following formula (6) to evaluate the conductivity of the conductive dispersion. Formula (6) Conductivity (S / cm) = 1 / (Average value of surface resistivity (Ω / sq) × Average value of film thickness (cm)) The evaluation criteria were as follows. ◎: Conductivity is 30 S / cm or more (particularly good). ○: Conductivity is 20 S / cm or more and less than 30 S / cm (good). △: Conductivity is 10 S / cm or more and less than 20 S / cm (acceptable). ×: Conductivity is less than 10 S / cm (defective).

[0100] [Examples 1-2 to 1-17, Comparative Examples 1-1 to 1-7] Except for changing the materials and amounts used in Example 1-1 as described in Table 1, dispersions of Examples 1-2 to 1-17 and Comparative Examples 1-1 to 1-7 were prepared in the same manner as in Example 1-1.

[0101] All of the conductive dispersions obtained in Examples 1-1 to 1-17 had good viscosity, conductivity, and appearance of the conductive film, and were good dispersions. From Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-2, it was found that when a medium (D) containing an alcohol-based organic solvent or a ketone-based organic solvent was used as the medium, a good conductive dispersion was obtained, and when a medium (D) containing an alcohol-based organic solvent was used, a better conductive dispersion was obtained. Also, from Examples 1-6 to 1-17 and Comparative Examples 1-3 to 1-7, it was found that when a dispersant (C) containing an amphoteric surfactant or polyvinyl acetal was used as the dispersant, a good conductive dispersion was obtained. In particular, from Examples 1-13 to 1-17, it was found that when an amphoteric surfactant was used as the dispersant, a particularly good dispersion was obtained even at a high concentration. The dispersions of Comparative Examples 1-3 to 1-7 had high viscosity or poor fluidity, so the evaluation of storage stability, appearance, and conductivity could not be performed.

[0102]

Table 1

[0103] <Manufacture of Conductive Dispersion (2)> [Example 2-1] 73.6 parts of butyl cellosolve as an alcohol-based organic solvent and 2.4 parts of D-441 as an amphoteric surfactant were charged into a glass bottle, and sufficiently stirred and mixed to dissolve D-441. Then, 20 parts of UP-10N as graphite (A) and 4 parts of #3400B as carbon black (B) were added, and using 140 parts of 1.25 mm Φ zirconia beads as the medium, it was dispersed with a Scan dex for 1 hour to obtain a conductive dispersion.

[0104] [Examples 2-2 to 2-11, Comparative Examples 2-1 to 2-5] Dispersions of Examples 2-2 to 2-11 and Comparative Examples 2-1 to 2-5 were prepared in the same manner as in Example 2-1, except that the materials and amounts used in Example 2-1 were changed as described in Table 2.

[0105] All of the conductive dispersions obtained in Examples 2-1 to 2-11 had good viscosity, conductivity, and appearance of the conductive film, and were good dispersions. From Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-2, it was found that good conductive dispersions can be obtained when using carbon black (B) with a BET specific surface area of 140 to 1400 m 2 / g. Also, from Examples 2-5 to 2-7 and Comparative Examples 2-3 to 2-4, it was found that good conductive dispersions can be obtained when using graphite (A) with an average primary particle diameter of 3 to 12 μm.

[0106] [Table 2]

[0107] [Production of Conductive Dispersion Containing Epoxy Resin (E)] [Example 3-1] 91.24 parts of the conductive dispersion (dispersion 2-1) produced in Example 2-1 was charged into a plastic container, and 8.76 parts of RO-8508 as the epoxy resin (E) was charged. Using a stirrer (Mazers Star KK-250S, manufactured by Kurabo Industries Ltd.), it was stirred and mixed at 1600 rpm for 60 seconds to obtain a conductive dispersion containing the epoxy resin (E). The component ratio in the conductive film prepared from this conductive dispersion containing the epoxy resin (E) is shown in Table 3.

[0108] [Examples 3-2 to 3-15, Comparative Examples 3-1 to 3-5] Dispersions of Examples 3-2 to 3-15 and Comparative Examples 3-1 to 3-5 were obtained in the same manner as in Example 3-1, except that the materials and compounding amounts used in Example 3-1 were changed as described in Table 3.

[0109] [Table 3]

[0110] <Manufacture of Conductive Film> [Example 4-1] The conductive dispersion containing the epoxy resin (E) produced in Example 3-1 was stirred and mixed at 1600 rpm for 60 seconds using a stirrer (Mazers Star KK-250S, manufactured by Kurabo Industries Ltd.). Next, it was immediately dropped onto a PET film at about 1 to 2 g, and after coating with an applicator so that the film thickness of the conductive film became 8 μm, it was heated in an oven at 140 °C for 1 hour to perform drying and curing reactions, thereby obtaining a conductive film.

[0111] <Evaluation of Conductive Film> For the manufactured conductive film, the appearance and conductivity were evaluated according to the following criteria.

[0112] <Appearance> The appearance of the conductive film was evaluated by visually checking and touching. The evaluation criteria were as follows. ◎: No roughness or unevenness, homogeneous and without unevenness (particularly good). ○: Not rough or uneven, but slightly uneven (good). △: There is roughness or unevenness in a part of the conductive film (acceptable). ×: There is roughness or unevenness throughout the conductive film (defective).

[0113] <Conductivity> Except for the evaluation criteria, it was evaluated by the same method as the above conductivity evaluation. The evaluation criteria were as follows. ◎: Conductivity is 35 S / cm or more (particularly good). ○: Conductivity is 30 S / cm or more and less than 35 S / cm (good). △: Conductivity is 20 S / cm or more and less than 30 S / cm (acceptable). ×: Conductivity is less than 20 S / cm (defective).

[0114] [Example 4-2 to 4-15, Comparative Example 4-1 to 4-5] Conductive films of Examples 4-2 to 4-15 and Comparative Examples 4-1 to 4-5 were obtained in the same manner as in Example 4-1, except that the materials and amounts used in Example 4-1 were changed as described in Table 4.

[0115] All of the conductive films obtained in Examples 4-1 to 4-15 had good appearance and conductivity. Further, from these results, it can be seen that good conductive films can be obtained when graphite (A) having an average primary particle diameter of 3 to 12 μm as graphite and carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g as carbon black are used respectively. On the other hand, all of the conductive films obtained in Comparative Examples 4-1 to 4-3 had poor conductivity, and it can be seen that the average primary particle diameter of graphite (A) and the BET specific surface area of carbon black (B) are important. In addition, the conductive films obtained in Comparative Examples 4-4 and 4-5 both had poor appearance and were not suitable for evaluating conductivity. The conductive film obtained in Comparative Example 4-4 is presumed to have poor appearance because the average primary particle diameter of graphite is too large. Also, although a seemingly good dispersion could be prepared in Comparative Example 4-5, it is presumed that the compatibility with the epoxy resin (E) was poor and the appearance became poor.

[0116]

Table 4

Claims

1. A conductive dispersion comprising graphite, carbon black, a dispersant (C) and a medium (D), The graphite contains graphite (A) with an average primary particle diameter of 3 to 12 μm, the carbon black contains carbon black (B) with a BET specific surface area of 130 to 1400 m 2 / g, the dispersant (C) contains an amphoteric surfactant and / or polyvinyl acetal, and the medium (D) contains an alcohol-based organic solvent or a ketone-based organic solvent, a conductive dispersion.

2. The conductive dispersion according to claim 1, comprising 5 to 50 parts by mass of carbon black with respect to 100 parts by mass of graphite.

3. The conductive dispersion according to claim 1, comprising 10 to 50 parts by mass of the dispersant (C) with respect to 100 parts by mass of the total amount of graphite and carbon black.

4. The conductive dispersion according to claim 1, wherein the dispersant (C) contains an amphoteric surfactant having an acid value of 5 to 30 mgKOH / g and an amine value of 10 to 50 mgKOH / g.

5. The conductive dispersion according to claim 1, wherein the medium (D) contains an alcohol-based organic solvent (D1) having a structure represented by the following general formula (1). General formula (1) R 1 R 2 C(OH)CR 3 R 4 (OR 5 ) 〔In general formula (1), R 1 , R 2 , R 3 and R 4 are each independently a hydrogen atom or a monovalent hydrocarbon group, and R 5 is a monovalent hydrocarbon group.〕

6. The conductive dispersion according to claim 5, containing 50% by mass or more of the alcohol-based organic solvent (D1) in 100% by mass of the medium (D).

7. The conductive dispersion according to any one of claims 1 to 6, further comprising an epoxy resin (E).

8. A conductive film containing graphite, carbon black, and a dispersant (C), wherein the graphite contains graphite (A) having an average primary particle diameter of 3 to 12 μm, the carbon black contains carbon black (B) having a BET specific surface area of 130 to 1400 m 2 / g, and the dispersant (C) contains an amphoteric surfactant or polyvinyl acetal, and the total amount of the graphite and the carbon black is 50 to 91% by mass.

9. The conductive film according to claim 8, further comprising an epoxy resin (E) and containing 25 to 100 parts by mass of the total amount of the dispersant (C) and the epoxy resin (E) with respect to 100 parts by mass of the total amount of graphite and carbon black.

10. The conductive film according to claim 8, comprising 10 to 50 parts by mass of the dispersant (C) with respect to 100 parts by mass of the total amount of graphite and carbon black.

11. The conductive film according to claim 8, having a conductivity of 20 S / cm or more.

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