WO2018230508A1

WO2018230508A1 - Electrically conductive foam

Info

Publication number: WO2018230508A1
Application number: PCT/JP2018/022255
Authority: WO
Inventors: 敦紀菊地
Original assignee: 株式会社イノアック技術研究所; 株式会社イノアックコーポレーション
Priority date: 2017-06-13
Filing date: 2018-06-11
Publication date: 2018-12-20
Also published as: JP7239277B2; TW201906928A; CN110730799B; KR102338096B1; JP2019001999A; KR20200016221A; CN110730799A

Abstract

Provided is an electrically conductive foam which has excellent various properties including electrical conductivity under low voltages, highly isotropic electrical conductivity, electrically conductive material-retentive properties, cushioning properties (low hardness) and moldability, and can be used under any environments. An electrically conductive foam produced by foaming an emulsion composition having an electrically conductive material dispersed therein by a mechanical frothing method and then curing the resultant foam, wherein the electrically conductive material contains at least spherical graphite having such a structure that the basal face thereof is folded.

Description

Conductive foam

The present invention relates to a conductive foam.

Existing conductive foams include foams that are made conductive by compounding conductive materials with various materials such as rubber and urethane, and products that are made conductive by processing such as impregnation and surface treatment. For example, Patent Document 1 proposes a conductive foam obtained by foaming a latex composition containing a conductive filler and a rubber latex such as SBR latex, NR latex, and NBR latex. The primary reason why such a foam is required to have conductivity is that it is possible to achieve both conductivity and cushioning properties (low hardness).

Japanese Unexamined Patent Publication No. 2004-202989

However, the rubber foam has high hardness although high conductivity is obtained. In addition, in the production of rubber foam, the environment in which it can be used is limited due to the influence of the additive (sulfur). In addition, although urethane foam can obtain low hardness, it has low electrical conductivity and cannot provide uniform conductivity. Furthermore, the impregnation process can suppress the addition amount of the conductive material in a small amount as compared with the compound product and can obtain high conductivity, but the conductive material is easily dropped, and the usable environment is limited. In the surface treatment, the amount of conductive material added can be minimized as in the impregnation process. However, there is a dropout, and there is no conductivity in the thickness direction, and only the surface resistance and the usage method are limited. From the above, it is a fact that conductive foams are not so often used in the field of electronics, and as a form of conductive foam, a metal plate bent into a U-shape is used. The thing (not shown) which ensured electroconductivity by the method of inserting | pinching a foam between etc. is employ | adopted.

Therefore, the present invention is excellent in various properties such as conductivity under low voltage, highly isotropic conductivity, conductive material retention, cushioning property (low hardness), moldability, etc., regardless of environment. It is an object to provide a conductive foam that can be used.

The present inventors have conducted intensive research and found that the above problems can be solved by forming a foam using an emulsion composition containing a specific conductive material and emulsion, and completed the present invention. That is, the present invention is as follows.

The present invention (1)
A conductive foam obtained by foaming an emulsion composition in which a conductive material is dispersed by a mechanical froth method and then curing, wherein the conductive material has at least a basal surface curved It is a conductive foam characterized in that it contains spherical graphite having
The present invention (2) is the conductive foam according to the invention (1) containing 30% by mass to 50% by mass of the conductive material based on the total mass of the conductive foam.
The present invention (3)
The conductive foam of the invention (1) or (2), further containing a conductive filler different from the spherical graphite as the conductive material.
The present invention (4)
The conductive foam of the invention (3), wherein the conductive material contains the spherical graphite and a conductive filler in a mixing ratio (mass ratio) of 9: 1 to 5: 5.
The present invention (5)
The conductive foam of the invention (3) or (4), wherein the conductive filler is conductive carbon.
The present invention (6)
The conductive foam according to any one of the inventions (1) to (5), wherein the emulsion composition contains at least one resin material of a urethane resin and an acrylic resin.
The present invention (7)
The conductive foam according to any one of the inventions (1) to (6), which is in the form of a sheet.
The present invention (8)
The conductive foam according to any one of the inventions (1) to (7), which is laminated on a substrate.

According to the present invention, it is excellent in various properties such as conductivity under low voltage, highly isotropic conductive performance, conductive material retention, cushioning property (low hardness), moldability, etc., regardless of environment. A usable conductive foam can be provided.

It is a conceptual diagram which shows an example of the electrical conduction mechanism in the conductive foam which concerns on this embodiment containing spherical graphite and a conductive filler.

Hereinafter, the conductive foam of the present invention and the production method thereof will be described in detail according to the following items.
1. Conductive foam 1-1. Raw material 1-1-1. Emulsion composition 1-1-2. Conductive material 1-1-2-1. Spherical graphite 1-1-2-2. Conductive filler 1-1-3. Additive 1-1-3-1. Foaming agent 1-1-3-2. Crosslinking agent 1-1-3-3. Other 1-2. Production method of conductive foam 1-2-1. Each component of the raw material composition 1-2-2. Preparation method of raw material composition 1-2-3. Composition and properties of raw material composition 1-2-4. Foaming step 1-2-5. Curing step 1-2-6. Molding method 1-3. Use of conductive foam

1. Conductive foam In this specification, “conductive” refers to a material having a resistance of, for example, a volume resistance value of 10 ⁸ Ω · cm or less.
The conductive foam according to the present invention is a conductive foam obtained by curing an emulsion composition containing a resin, a conductive material, and a foaming agent after foaming by a mechanical floss method. The shape of the conductive foam is not particularly limited, but is preferably a sheet having a thickness of 0.05 mm to 2.0 mm.

The form of the bubbles in the conductive foam of the present invention is not particularly limited, but is preferably an open cell from the viewpoint of heat dissipation and flexibility. The “open cell” refers to a state in which a resin film that separates adjacent bubbles has a through-hole, and adjacent bubbles communicate with each other in a three-dimensional manner. In addition, the “open cell” structure has the property of allowing outside air to pass into the foam. In the present invention, it is not strictly required that all the holes communicate with each other, and even if a partially closed hole exists inside, if there is a property that the outside air can pass through as a whole, “continuous” Let it be a “bubble” structure. The form of bubbles can be confirmed by observing with an electron microscope.

The apparent density (in accordance with JIS K7222) of the conductive foam according to the present invention is preferably 100 kg / m ³ to 700 kg / m ³ because both the conductivity and flexibility are excellent, and preferably 200 to 600 kg / m. ³ is more preferable. When the apparent density is lower than the above range, the conductivity is lowered. On the other hand, when the apparent density exceeds the above range, the flexibility is lowered and the hardness is increased. As a result, the shape followability to a complicated structure is deteriorated.
Note that when “density” is simply described in the present specification, it means “apparent density”.

The conductive foam is characterized in that the conductive material contains spherical graphite having a structure in which at least the basal surface is curved, and the spherical graphite has extremely low anisotropy in its conductive performance, and is conductive. The conductive property of the foam itself is also characterized by extremely low anisotropy. That is, the conductive foam has a conductive performance that is not related to the conductive direction. In the sheet-shaped conductive foam, the conductivity in the thickness direction (the normal direction of the sheet) is particularly in other directions. It is a conductive foam characterized by little difference from the conductive performance.

The conductive foam according to the present invention may contain 30% by mass to 50% by mass of the conductive material based on the total mass. When the conductive material is smaller than 30% by mass, the conductive performance of the conductive foam may be insufficient. That is, it becomes difficult to develop high conductive performance at a low applied voltage. When the conductive material is larger than 50% by mass, the moldability, flexibility and material strength of the conductive foam may be lowered.

The conductive material contained in the conductive foam according to the present invention can be in a state where the conductive materials are not in contact with each other. Even when the conductive materials are not in contact with each other, conductivity can be imparted by hopping or a Pool-Frenkel effect. The Pool-Frenkel effect affects the distance between conductive materials, and the longer the distance, the longer the distance for flying electrons, so a higher voltage needs to be applied. Therefore, it is necessary to increase the amount of the conductive material in order to develop conductivity under a low voltage. However, as described above, there are problems such as deterioration of moldability, flexibility and material strength of the conductive foam. Will occur.

In the conductive foam according to the present invention, in addition to the spherical graphite having a structure in which the basal surface is bent, a conductive filler can be further added as a conductive material. In such a case, the blending ratio of the spherical graphite and the conductive filler is preferably 9: 1 to 5: 5. When the mixing ratio is in this range, the conductivity is remarkably improved. That is, the volume resistance value decreases. By adding a conductive filler in addition to the spherical graphite, there is a conductive filler in the gap between the spherical graphite, making it easy for electrons to fly from the conductive material to the conductive material. Because. Hereinafter, this point will be described in detail.

As an electric conduction mechanism in the conductive foam of the present invention, hopping type electric conduction in which a plurality of tunneling is repeated in an insulating resin forming a matrix is used. For this purpose, it is necessary to pass a current between the conductive materials, and the distance between the electrodes (between the conductive materials) needs to be extremely narrow at a low voltage. That is, as shown in FIG. 1, with a structure in which nano-sized conductive filler is dispersed with respect to micron-sized spherical graphite, the limit film thickness of the matrix resin and the distance between the conductive materials can be achieved. A region where the conductive materials are not in contact with each other can be a conduction portion. Specifically, when the conductive filler is carbon-based, the specific gravity of the spherical graphite and the conductive filler have substantially the same specific gravity, so the ratio according to the mixing ratio (for example, the ratio of 9: 1 to 5: 5) Therefore, the electric conduction mechanism in the conductive foam of the present invention having better performance can be obtained.

The conductive foam according to the present invention can be laminated on a substrate as a sheet. The material of the base material is not particularly limited as long as it can suppress the seepage of the raw material of the conductive foam.
For example, a resin film such as a PET film, a nonwoven fabric, a woven fabric, paper, an adhesive tape, an airless tape in which an adhesive layer has an uneven shape, and the like can be given.
The thickness of the substrate is not particularly limited, but a thickness of 10 μm to 100 μm is suitable. By laminating with the base material, it becomes possible to protect the conductive foam from damage and to facilitate handling by supporting the base material at the time of use.

Further, the base material may be peeled off depending on the use of the conductive foam, or may be used as it is without being peeled off. When peeling and using, the base material which carried out the mold release process can be used.

Moreover, the said base material can use what has electroconductivity. The conductive substrate is not particularly limited, and examples thereof include a PET film that has been subjected to a release treatment, an aluminum tape, a conductive adhesive tape, and a non-woven fabric or paper that has been subjected to a conductive treatment by a method such as impregnation. By using such a base material, it is possible to use the base material without peeling off the base material for applications in which conductivity in the thickness direction of the conductive foam sheet is required.

1-1. Raw material The conductive foam according to the present invention uses, for example, an emulsion composition, a conductive material, a foaming agent (anionic surfactant) as a raw material, and water, a crosslinking agent and other additives as a dispersion medium. (The foaming gas used in the foaming process is described in the foaming process).

1-1-1. Emulsion composition The emulsion raw material of the emulsion composition used when manufacturing the foam which concerns on this invention is not specifically limited, What is necessary is just an emulsion which can form a foam by a well-known method. Examples include urethane emulsions, acrylic emulsions, styrene emulsions, EVA (ethylene vinyl acetate copolymer) resin emulsions, vinyl chloride emulsions, epoxy emulsions, etc. One or a plurality of emulsions can be used. . In particular, it is preferable to use at least one emulsion among urethane emulsion and acrylic emulsion. Furthermore, it is more preferable to use at least an acrylic emulsion. Moreover, material strength can be further imparted by using a urethane emulsion. Moreover, the urethane resin foam obtained has excellent flexibility and low compressive residual strain.

Hereinafter, (1) urethane emulsion and (2) acrylic emulsion will be described in detail.

(1) Urethane Emulsion The production method of the urethane emulsion (water dispersion of urethane resin) that can be used in the present invention is not particularly limited, but the following methods (I) to (III) can be exemplified.
(I) An active hydrogen-containing compound, a compound having a hydrophilic group, and an organic solvent solution or an organic solvent dispersion of a urethane resin having a hydrophilic group obtained by reacting a polyisocyanate are neutralized as necessary. A method of obtaining a urethane resin emulsion by mixing an aqueous solution containing an agent.
(II) Is an aqueous solution containing a neutralizing agent mixed with an active hydrogen-containing compound, a compound having a hydrophilic group, and a terminal isocyanate group-containing urethane prepolymer having a hydrophilic group obtained by reacting polyisocyanate? Alternatively, a method of obtaining a urethane resin emulsion by adding a neutralizing agent to a prepolymer in advance, mixing water and dispersing in water, and then reacting with polyamine.
(III) An aqueous solution containing a neutralizing agent and a polyamine is mixed with an active hydrogen-containing compound, a compound having a hydrophilic group, and a terminal isocyanate group-containing urethane prepolymer having a hydrophilic group obtained by reacting a polyisocyanate. Or a method in which a neutralizing agent is added to the prepolymer in advance and then an aqueous solution containing polyamine is added and mixed to obtain a urethane resin emulsion.

Polyisocyanates used in the urethane resin method include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4 ′. -Diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4 , 4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate Dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4,4 Examples include '-dicyclohexylmethane diisocyanate and 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate. In addition, trivalent or higher polyisocyanates may be used in combination as long as the effects of the invention are not impaired.

The active hydrogen-containing compound is not particularly limited, and known polyols such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyester amide polyols, polythioether polyols, polybutadiene-based polyolefin polyols, and the like. A polyol can be illustrated. Two or more of these high molecular weight compounds may be used in combination.

Here, the urethane emulsion according to this embodiment is preferably one or more selected from the group consisting of a polyether urethane emulsion, a polyester urethane emulsion, a polyether carbonate urethane emulsion, and a polycarbonate urethane emulsion.

The polyester-based urethane emulsion according to the present embodiment is not limited in any way. For example, in the above production method, a polyester polyol (for example, a polymer obtained by dehydration condensation of a polybasic acid and a polyhydric alcohol, ε-caprolactone, It can be produced by using a polymer obtained by ring-opening polymerization of a lactone such as α-methyl-ε-caprolactone, a reaction product of a hydroxycarboxylic acid and a polyhydric alcohol, or the like.

The polycarbonate-based urethane emulsion according to the present embodiment is not limited at all. For example, in the production method, polycarbonate polyol {for example, diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and the like, and diaryl carbonate (For example, a reaction product with a cyclic carbonate (eg, propylene carbonate), etc.).

The polyether-based urethane emulsion according to the present embodiment is not limited in any way, but can be manufactured, for example, by using a polyether polyol {eg, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, etc.) in the above manufacturing method. It is.

In the polyether carbonate urethane emulsion according to this embodiment, the urethane resin contains both a carbonate group and an ether group (...- O-CO-O- [RO-R ']-O-CO-O- The structure is not limited at all, and can be produced by using a polyether polyol and a polycarbonate polyol in combination in the production method, for example.

In the methods (I) to (III), an emulsifier may be further used as long as the effects of the invention are not impaired. Examples of such emulsifiers include nonionic emulsifiers such as polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene sorbitol tetraoleate; fatty acid salts such as sodium oleate , Anionic emulsifiers such as alkyl sulfate salts, alkylbenzene sulfonates, alkyl sulfosuccinates, naphthalene sulfonates, alkane sulfonate sodium salts, sodium alkyl diphenyl ether sulfonates; polyoxyethylene alkyl sulfates, polyoxyethylene alkylphenyls Nonionic anionic emulsifiers such as sulfates can be exemplified.

The conductive foam of the present invention uses a urethane emulsion as a raw material (the foam contains a urethane resin), so that the conductive foam is obtained by blending a conductive material. It is possible to obtain a foam having various characteristics such as properties, hardness, suppression of dropping of the conductive material, and hydrolysis resistance at a high level.

(2) Acrylic emulsion The production method of the acrylic emulsion (acrylic resin aqueous dispersion) that can be used in the present invention is not particularly limited, but in the presence of a polymerization initiator, if necessary, an emulsifier and a dispersion stabilizer, For example, a (meth) acrylic acid ester monomer is an essential polymerizable monomer component, and if necessary, a mixture of other polymerizable monomers copolymerizable with these monomers is copolymerized. Can be obtained. Two or more acrylic emulsions may be used in combination. The glass transition temperature of the acrylic emulsion is preferably in the range of 0 ° C to 80 ° C.

Examples of the polymerizable monomer that can be used for preparing the acrylic emulsion include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth ) Hexyl acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, octadecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, nonyl (meth) acrylate, ( (Meth) acrylic acid such as dodecyl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate Ester monomers; acrylic acid, methacrylic acid, β-carboxyethyl Unsaturation having carboxyl group such as (meth) acrylate, 2- (meth) acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, maleic acid half ester, maleic anhydride, itaconic anhydride Bond-containing monomers: Glycidyl group-containing polymerizable monomers such as glycidyl (meth) acrylate and allyl glycidyl ether; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) Hydroxyl group-containing polymerizable monomers such as acrylate and glycerol mono (meth) acrylate; ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethyl Examples thereof include roll propane tri (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, diallyl phthalate, divinylbenzene, and allyl (meth) acrylate.

In addition, what is necessary is just to use a well-known emulsifier etc., when using an emulsifier at the time of preparation of acrylic emulsion.

Note that these emulsions may contain a surfactant (emulsifier) for dispersing the resin. The surfactant for resin dispersion is a surfactant for dispersing a water-dispersible resin (unlike an anionic surfactant, it does not have to have an effect as a foaming agent). Such a surfactant may be appropriately selected according to the water-dispersible resin to be selected.

-Dispersion medium In this invention, as a dispersion medium of an emulsion composition, although water is an essential component, the mixture of water and a water-soluble solvent may be sufficient. Examples of the water-soluble solvent include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl cellosolve, polar solvents such as N-methylpyrrolidone, and the like, one or more of these. A mixture of the above may be used.

1-1-2. Conductive Material The conductive material described below may be blended as a powder, but is preferably used as an aqueous dispersion in which the powder is dispersed in water. By using an aqueous dispersion, it is easy to uniformly disperse within the composition when it is added to the emulsion composition.

1-1-2-1. Spherical graphite Spherical graphite has high electrical conductivity and contributes to the development of electrical conductivity of the conductive foam of the present invention. The graphite that can be used in the present invention is spherical. In the present invention, the term “spherical” does not mean only a true spherical shape, but a shape in which the true spherical shape is slightly deformed like a disc shape, the surface is not uniform, and a cabbage-like appearance in which layers are superimposed on the surface In general, the shape includes, for example, a shape that is not grasped as a true spherical shape. However, the crystal form of natural graphite is a hexagonal crystal form. Generally, untreated graphite is scaly and is distinguished from this. That is, the present invention requires the use of graphite that has been subjected to at least spheroidizing treatment. The spheroidization treatment includes a simple treatment method such as pulverization of scale-like natural graphite, but a treatment method in which pressure is isotropically applied to graphite is preferable. The treatment can be performed by a method of isotropically applying pressure to graphite using a pressure medium such as a gas (inert gas such as argon) or a liquid (for example, water). Depending on the presence or absence of heating, a distinction is made between hot isostatic pressing and cold isostatic pressing. Either may be used. By performing this treatment, it is possible to obtain spherical graphite having an isotropic high conductivity whose outer shape is spherical and whose inner empty wall (scale layer) is reduced.

The above spheroidized spherical graphite is specified as spherical graphite having a structure in which the basal surface is bent from the other side. Here, the “basal plane” means a plane orthogonal to the C axis of the graphite crystal (hexagonal system). That is, it is preferable that the spherical graphite of the present invention has a distortion in the crystal system of natural graphite. This distortion can be grasped by measuring the X-ray diffraction pattern and confirming the presence or absence of peak broadening or 2θ value shift as compared with natural graphite. In addition to confirming whether or not the conductive foam contains spherical graphite, it is confirmed by measuring the X-ray diffraction pattern of the raw graphite, and any two or more cross sections of the conductive foam are observed with a microscope. However, it can also be confirmed by checking whether or not the shape of the graphite equivalent portion is circular. Specifically, the surfaces of the conductive foam that are orthogonal to each other are observed with a microscope, and the shape of the graphite-corresponding portion in any image is a circular shape with a minor axis / major axis ratio of less than 1/2. It can be said that the conductive foam contains spherical graphite.

Examples of spherical graphite that can be used in the present invention include those obtained by spheroidizing non-spherical graphite powder such as flake graphite by a high-speed airflow impact method using a hybridization system; and petroleum-based or petroleum-based graphite And the like obtained by curing spherical carbon particles having crystallized pitch and thermosetting resin to obtain a powder, and graphitizing the powder. The former is preferable from the viewpoint of isotropic conductivity.

As the spherical graphite, a commercially available product can be suitably used, and specific examples thereof include spherical graphite manufactured by Nippon Graphite Industries Co., Ltd. The average particle diameter (median diameter) of the spherical graphite used in the present invention is about 1 to 100 μm. The thickness is preferably 5 to 80 μm, more preferably 8 to 80 μm. Ensuring the conductivity of the conductive foam and ensuring its flexibility tends to decrease when one is improved. However, when spherical graphite with a relatively small average particle size is used, both properties are reduced. It is preferable because it can improve the balance. The preferred average particle size range varies depending on the final shape of the conductive foam, but in the sheet-like form having a thickness of about 0.1 to 1.0 mm, it is preferably about 5 to 30 μm, and 10 to 20 μm. More preferably.

1-1-2-2. Conductive filler The conductive filler added to the spherical graphite used in the production of the conductive foam of the present invention (conductive filler other than the spherical graphite having a structure in which the basal surface is curved) is used as the conductive material of the foam. The material is not particularly limited as long as it has the property of improving the properties, and general metal materials, conductive carbon, ion conductive materials, and the like can be exemplified, but conductive carbon is preferable. Examples of the conductive carbon include nano-sized conductive carbon such as carbon nanotube, carbon black (for example, acetylene black), graphene, and the like, graphite, carbon fiber, and graphite (spherical graphite having a structure in which a basal surface is curved) And graphite) and activated carbon. These conductive carbons are effective in that the specific gravity is light compared to a metal filler of the same size, and the weight of the conductive foam is difficult to increase even if the amount added is increased. In addition, the conductive carbon is rich in flexibility, that is, has low elasticity as compared with the metal filler, so that the conductive foam can be made flexible, that is, low in hardness. It is also excellent in that the price is low. These conductive materials can be used alone or in combination of two or more.

The average length of the conductive filler (average diameter in the case of a substantially spherical shape) is preferably 1 nm to 100 nm, and more preferably 5 nm to 50 nm. By using such a conductive filler, it becomes possible to interspersed between the spherical graphite, and the conductivity of the conductive foam is improved.
Furthermore, the conductive filler preferably has an aspect ratio of 5 or less, more preferably 3 or less, and even more preferably 2 or less. When the aspect ratio exceeds 5, anisotropy may appear in the conductive performance of the conductive foam.
Here, the value of “aspect ratio” is a value obtained by dividing the average length of the conductive filler by the average diameter. The “average length” and “average diameter” are values obtained by observing and measuring at least 100 particles of the conductive filler and measuring the average value. More specifically, the “average diameter” is a particle cross-sectional area calculated based on a vertical cross section in the vicinity of the center in the length direction of the particle imaged by SEM observation, and a diameter of a circle having the same area as the cross-sectional area is calculated. It is the average value of the area diameter derived | led by doing. The average diameter and average length are measured averages of 100 particles.

1-1-3. Additive 1-1-3-1. Foaming agent The foaming agent that can be used in the production of the conductive foam of the present invention is a substance capable of stabilizing gas bubbles by mixing gas into the raw material mixture, and anionic foaming agents can be exemplified. .

Specific examples of the anionic surfactant are not particularly limited. Sodium laurate, sodium myristate, sodium stearate, ammonium stearate, sodium oleate, potassium oleate soap, castor oil potassium soap, palm Oil potassium soap, sodium lauroyl sarcosine, sodium myristoyl sarcosine, sodium oleyl sarcosine, sodium cocoyl sarcosine, palm oil alcohol sodium sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium alkylsulfosuccinate, sodium dialkylsulfosuccinate, sodium lauryl sulfoacetate, Examples include sodium alkylbenzene sulfonate and sodium α-olefin sulfonate.

Here, the anionic surfactant used in this embodiment is preferably 10 or more, more preferably 20 or more, in order to facilitate dispersion in the emulsion composition. The above is particularly preferable.

・ HLB
In the present invention, the HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Oda method. The method of obtaining HLB by the Oda method is "Introduction to New Surfactants", pages 195 to 196, published by Sakai Shoten on March 20, 1957, "Synthesis and Applications of Surfactants" 492- It is described on page 502, and can be obtained by HLB = (inorganic numerical value / organic numerical value) × 10. Here, the inorganic and organic numerical values are calculated from the values shown in Tables 3, 3 and 11 of the above “Introduction to New Surfactant”.

Moreover, an amphoteric surfactant may be used as the foaming agent according to the present invention. Especially when an anionic surfactant and an amphoteric surfactant are used in combination, the charge of the hydrophilic group between the molecules of the anionic surfactant is repelled, and the molecules of the anionic surfactant are kept at a certain distance from each other. In addition, since the electrically neutral double-sided surfactant enters between the molecules of the anionic surfactant, the bubbles can be further stabilized and the size of the bubbles can be reduced. For this reason, delamination strength can be improved. Therefore, it is preferable to use an anionic surfactant and an amphoteric surfactant in combination.

The amphoteric surfactant is not particularly limited, and examples include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Betaine type amphoteric surfactants have the above-mentioned effects. Since it is high, it is preferable.

Examples of amino acid-type amphoteric surfactants include N-alkyl or alkenyl amino acids or salts thereof. In the N-alkyl or alkenyl amino acid, an alkyl group or an alkenyl group is bonded to a nitrogen atom, and one or two “—R—COOH” (wherein R represents a divalent hydrocarbon group, preferably An alkylene group, particularly preferably having 1 to 2 carbon atoms.). In a compound in which one “—R—COOH” is bonded, a hydrogen atom is further bonded to the nitrogen atom. One “—R—COOH” is called a mono form, and two are called a di form. As the amphoteric surfactant according to the present invention, any of these mono- and di-forms can be used. In the N-alkyl or alkenyl amino acid, the alkyl group or alkenyl group may be linear or branched. Specifically, examples of the amino acid type amphoteric surfactant include sodium lauryldiaminoethylglycine, sodium trimethylglycine, sodium cocoyl taurine, sodium cocoyl methyl taurine, sodium lauroyl glutamate, potassium lauroyl glutamate, lauroyl methyl-β-alanine and the like. It is done.

Examples of betaine-type amphoteric surfactants include alkyl betaines, imidazolinium betaines, carbobetaines, amide carbobetaines, amide betaines, alkylamide betaines, sulfobetaines, amide sulfobetaines, and phosphobetaines. Specifically, as a betaine type amphoteric surfactant, lauryl betaine, stearyl betaine, lauryl dimethylaminoacetic acid betaine, stearyl dimethylaminoacetic acid betaine, lauric acid amidopropyl dimethylaminoacetic acid betaine, isostearic acid amidoethyl dimethylaminoacetic acid betaine, Isostearic acid amidopropyl dimethylaminoacetic acid betaine, isostearic acid amidoethyl diethylaminoacetic acid betaine, isostearic acid amidopropyl diethylaminoacetic acid betaine, isostearic acid amidoethyl dimethylaminohydroxysulfobetaine, isostearic acid amidopropyl dimethylaminohydroxysulfobetaine, isostearic acid amidoethyl diethylamino Hydroxysulfobetaine, isostearamide Lopyldiethylaminohydroxysulfobetaine, N-lauryl-N, N-dimethylammonium-N-propylsulfobetaine, N-lauryl-N, N-dimethylammonium-N- (2-hydroxypropyl) sulfobetaine, N-lauryl- N, N-dimethyl-N- (2-hydroxy-1-sulfopropyl) ammonium sulfobetaine, lauryl hydroxysulfobetaine, dodecylaminomethyldimethylsulfopropylbetaine, octadecylaminomethyldimethylsulfopropylbetaine, 2-alkyl-N-carboxy Methyl-N-hydroxyethylimidazolinium betaine (2-lauryl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, 2-stearyl-N-carboxymethyl-N-hydro Shi betaine, etc.), coconut oil fatty acid amidopropyl betaine, coconut oil fatty acid amide propyl hydroxy sultaine and the like.

Examples of the amine oxide type amphoteric surfactants include lauryl dimethylamine-N-oxide and oleyldimethylamine-N-oxide.

Among the amphoteric surfactants mentioned above, it is preferable to use a betaine type amphoteric surfactant, and among the betaine types, alkylbetaine, imidazolinium betaine, and carbobetaine are particularly preferable. Examples of alkylbetaines that can be used in the present invention include stearyl betaine and lauryl betaine. Examples of imidazolinium betaines include 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine. .

Furthermore, a nonionic surfactant may be used as the foaming agent according to the present invention. The nonionic surfactant is not particularly limited, and nonionic surfactants such as fatty acid alkaminolamide, ether, ester, and the like can be exemplified.

1-1-3-2. Cross-linking agent The cross-linking agent used in the production of the conductive foam of the present invention is not particularly limited, and a necessary amount may be added depending on the application and the like. It can be selected according to the type. As the crosslinking agent, a known crosslinking agent can be used, and the resin compounding system used includes an epoxy crosslinking agent, a melamine crosslinking agent, an isocyanate crosslinking agent, a carbodiimide crosslinking agent, an oxazoline crosslinking agent, and the like. An appropriate amount can be used according to the kind of the functional group and the amount of the functional group.

1-1-3-3. Others Other known additives such as thickeners, cell nucleating agents, plasticizers, lubricants, colorants, antioxidants, fillers, reinforcing agents, flame retardants, antistatic agents, surface treatment agents, etc. Good.

1-2. Method for Producing Conductive Foam A method for producing a conductive foam of the present invention comprises a foaming step of foaming (mechanical foaming) a raw material composition, which is an emulsion composition in which a conductive material is dispersed, by a mechanical floss method, Curing the foamed raw material composition.
According to this method, the conductive foam of the present invention can be stably produced.

1-2-1. Each component of the raw material composition The raw material composition used in the method for producing a conductive foam according to the present invention includes at least a conductive material containing spherical graphite having a structure with a curved basal surface and the emulsion composition. Further, it may contain a polyfunctional compound that contributes to the curing of the resin component of the emulsion, that is, a crosslinking agent or a foaming agent. Preferred examples of the foaming agent and the crosslinking agent are the same as the preferred examples of the respective components described for the conductive foam.

In order to prepare as a raw material composition, it is preferable to further contain a solvent. Examples of solvents that can be used include water, organic solvents (for example, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl cellosolve, one kind of polar solvent such as N-methylpyrrolidone, or In the present invention, it is preferable to use only water. When an organic solvent is used, the viscosity of the raw material composition is lower than when water is used, and there is a possibility that bubbles are defoamed. Therefore, it is preferable not to include an organic solvent, but it may be included at a ratio that does not affect the bubble formation stability (for example, the viscosity does not decrease to such an extent that the moldability is impaired).

1-2-2. Preparation method of raw material composition The raw material composition is prepared by preparing an aqueous dispersion of the resin, an aqueous dispersion of a conductive material such as the spherical graphite, and mixing them to prepare a conductive material such as the spherical graphite. This is preferable because the raw material composition can be prepared without causing aggregation of the functional material. There are no particular restrictions on the solid content concentration of the resin in the aqueous emulsion of the resin and the solid content concentration of the conductive material in the aqueous dispersion of the conductive material, but generally 50% by mass to 90%. It is about mass%. If a surfactant as a foaming agent is mixed in advance in the aqueous dispersion of the conductive material, the dispersion stability of the conductive material in the resin when mixed with the aqueous emulsion of the resin is further improved. Therefore, it is preferable. In particular, it is preferable to use at least one surfactant having good wettability as the foaming agent because the dispersion stability of the conductive material in the resin is further improved. Among them, it is preferable to use at least one selected from the above-mentioned anionic surfactants having good bubble formation stability and wettability, and to use at least one selected from the above-mentioned nonionic surfactants having good wettability. Is more preferable. For example, the aqueous dispersion of the conductive material can be prepared by mixing the conductive material with an aqueous solution or suspension of a surfactant (foaming agent) having a solid content of about 20 to 60% by mass. In an embodiment using other additives such as a cross-linking agent and other heat conductive materials, other additives are added to the aqueous dispersion of the conductive material and mixed with an aqueous emulsion of the resin. It is preferable to prepare a raw material composition.

1-2-3. Composition and Properties of Raw Material Composition The total solid content concentration of the raw material composition is about 40 to 80% by mass, and preferably 50 to 70% by mass. Generally, in the total solid content of the raw material composition, the total mass of the resin (and optionally added crosslinking agent) and the conductive material is 95% or more, and the foaming agent (specifically, surface active agent) The total mass of other additives such as (agent) is 5% or less. However, the preferred mass ratio of each material in the solid content varies depending on the type of material used. In addition, the viscosity of the raw material composition is suitably about 10,000 to 200,000 mPa · s in order to stably form bubbles in the following foaming step.

1-2-4. Foaming step In the foaming step, mechanical foaming is performed in which the raw material composition is stirred to generate bubbles. The mechanical foaming (mechanical flossing) method is a method in which a raw material composition is stirred with a stirring blade or the like, and a gas such as air in the atmosphere is mixed into the emulsion composition and foamed. As the stirring device, a stirring device generally used in the mechanical foaming method can be used without particular limitation. For example, a homogenizer, a dissolver, a mechanical floss foaming machine, or the like can be used. In the present invention, by performing the foaming process by the mechanical foaming method, the formation of closed cells is suppressed, the formation of open cells is dominant, and the density of the foam after curing is prevented from being increased. A highly porous material is obtained.

The stirring conditions are not particularly limited, but the stirring time is usually 1 to 10 minutes, preferably 2 to 6 minutes. In addition, the stirring speed in the above mixing is preferably 200 rpm or more in order to make bubbles fine (more preferably 500 rpm or more), and preferably 2000 rpm or less (800 rpm or less for smooth discharge of foam from the foaming machine). More preferred). There is no particular limitation on the temperature condition of the foaming process, but it is usually room temperature. When the curing step described later is also performed simultaneously with foaming, heating may be performed to advance the reaction of the functional group.

1-2-5. Curing step In the curing step, the resin component is cured. By this step, the raw material composition becomes a structure as a conductive foam. The curing process is performed after the foaming process. Heating is preferably performed in order to evaporate the solvent (water) in the raw material composition and to advance the crosslinking reaction. The heating temperature and heating time may be any temperature and time at which the raw material can be crosslinked (cured). For example, the heating temperature and heating time may be about 80 to 150 ° C. (especially about 120 ° C. is preferable) for about 1 hour.

Further, the curing step may be performed as one step of a molding process for making the obtained conductive foam into a desired shape. For example, in an embodiment in which a sheet-like conductive foam is produced, the curing step may be performed as one step of the casting method. Specifically, the raw material composition subjected to “(4) foaming step” is cast to a desired thickness on the surface of the base material, and heated to evaporate the solvent (water), while allowing the crosslinking reaction to proceed. It can be cured to produce a sheet on the substrate surface.

1-2-6. Molding Method In order to make the conductive foam of the present invention into a desired shape, it can be molded by various conventionally known methods. An appropriate molding method can be selected according to the desired final shape. When manufacturing a sheet-like conductive foam, a casting method can be used. The bubble introduction process (foaming process) is preferably performed before the molding process. In the embodiment where the emulsion composition has a crosslinked structure, the formation of the crosslinked structure, that is, the progress of the crosslinking reaction may be performed simultaneously with the molding process.

1-3. Use of conductive foam The conductive foam according to the present invention not only has conductivity and conductivity retention (prevention of falling off of conductive material), but also has excellent cushioning properties (flexibility). Therefore, the followability to the mating member is excellent, and the reaction force (restoring force) of the conductive foam itself can be reduced. For this reason, when sandwiched between the members, while securing sufficient conductivity, the mating member (IC chip or substrate wiring, substrate warpage, etc.) is damaged or the wiring is disconnected. Can be used without causing any damage. In particular, in recent years, electronic devices have become thinner, lighter, and smaller, and there is a tendency for the space inside the electronic devices to be reduced, and the internal structure has become complicated, making the cushions thinner and better than ever. There is an increasing demand for conductive foams having properties (flexibility). In addition to being sandwiched between members, it can be used for various purposes regardless of its application method and usage environment (for example, grounding materials, shielding materials, cushioning materials, protective materials, and substrate insertion materials in electronic parts and devices). Etc.). In addition, the conductive foam according to the present invention can be made into a conductive foam having excellent characteristics without containing silicone. If silicone is not contained, silicone for electronic parts and devices can be obtained. It can be used without worrying about contamination.

≪Production example≫
<Raw material>
Acrylic emulsion: Acrylic nitrile-acrylic acid alkyl ester-itaconic acid copolymer (solid content 60% by mass)
-Urethane emulsion: Polyether carbonate urethane emulsion (solid content 60%)
Anionic surfactant 1: ammonium stearate (solid content 30%)
Anionic surfactant 2: sodium alkylsulfosuccinate (solid content 35%)
Amphoteric surfactant 1: lauryldimethylaminoacetic acid betaine (solid content 30%)
-Amphoteric surfactant 2: Lauryl betaine (solid content 36%)
Nonionic surfactant 1: Fatty acid alkanolamide (solid content 50%)
Crosslinking agent 1: Hydrophobic HDI isocyanurate (solid content 100%)
Graphite 1: Spherical graphite having a structure in which the basal surface is bent (average particle size 20 μm)
Graphite 2: Spherical graphite having a structure in which the basal surface is bent (average particle size: 10 μm)
Graphite 3: scale-like graphite (average particle size 20 μm)
Conductive filler 1: conductive carbon (Mitsubishi Chemical Corporation, product number: # 3230B, average particle size 20 nm, pH 6.0)
Conductive filler 2: Conductive carbon (Mitsubishi Chemical Corporation, product number: # 3040B, average particle size 50 nm, pH 6.0)
Substrate 1: PET film that has been subjected to mold release treatment

<Preparation of conductive foam>
(Example 1)
As an emulsion, an acrylic emulsion is used as a main ingredient, and 5 parts by weight of an anionic surfactant 1 or 3 parts by weight of an anionic surfactant based on the total amount of the emulsion (the total amount of solids and non-solids is 100 parts by weight). 2, 2 parts by weight of amphoteric surfactant 1, 1.5 parts by weight of amphoteric surfactant 2, 0.5 parts by weight of nonionic surfactant 1, 23.5 parts by weight of graphite 1, 2.6 The foam raw material was prepared by mixing 1 part by mass of the conductive filler 1 and 3 parts by mass of the crosslinking agent 1. After foaming by adding air to the raw material, the foam according to Example 1 was obtained by heat treatment.

(Examples 2 to 31, Comparative Examples 1 to 10)
In Examples 2 to 22 and Comparative Examples 1 to 10, foams were obtained in the same manner as in Example 1 except that the types and addition amounts of graphite or conductive carbon were changed as shown in Tables 1 to 3 and 5 below. . In Examples 23 and 24, the main agent in Examples 1 and 2 was changed from acrylic emulsion to urethane emulsion. Similarly, in Examples 25 and 26, the main agent in Examples 1 and 2 was acrylic and 50 masses of urethane emulsion. The foam was obtained by changing into parts. Examples 27 to 31 are foams prepared by adjusting the thickness and density of Example 1.
≪Foam evaluation method≫
<Thickness>
The thickness was measured with a thickness gauge.
<Density>
It was measured by calculating the weight per unit volume.
<Appearance>
The state of the cell and the surface of the foam were evaluated visually. “○” when the cell is uniform and the surface is not rough, “△” when the cell is slightly rough, “when the cell is very rough, or the cell is not formed, or the surface state is severe” “×”.

<Conductive performance>
In accordance with JIS K 6911, each foam was punched to Φ100 mm, and the volume resistance value and the surface resistance value were calculated from the current value at an applied voltage of 1 V using a DC voltage / current source (6243) manufactured by ADC Co., Ltd. .
(Volume resistance value)
The case where the volume resistivity is less than 1.0 × 10 ³ Ωcm "○", volume resistivity 1.0 × 10 ³ Ωcm or more, the case of less than 1.0 × 10 ⁵ Ωcm "△", volume resistivity Was evaluated as “×” when 1.0 × 10 ⁵ Ωcm or more.
(Anisotropy evaluation)
The volume resistance value and the surface resistance value were converted into common logarithms, and the anisotropy of the conductive performance was evaluated from the absolute value of the difference obtained by subtracting the volume resistance value from the surface resistance value.
The case where the absolute value of the difference obtained by subtracting the volume resistance value from the surface resistance value is less than 1.5 is “◯”, 1.5 or more, less than 2.00 is “△”, and 2.00 or more is “ × ”. From the results of volume resistance evaluation and anisotropy evaluation, those having no “x” were evaluated as conductive foams having high conductivity / isotropy under low voltage.

<Hardness>
The measurement was performed according to JIS K 6254. Specifically, the magnitude of the repulsive stress was measured when crushing 25% of the thickness of a sample punched out to a diameter of 50φ using an autograph at a speed of 1 mm / min (the sample was entirely covered with a 100φ compression plate). Compress and measure). The case where the 25% CLD hardness was less than 100 kPa was evaluated as “◯”, the case where the 25% CLD hardness was 100 kPa or more and less than 200 kPa was evaluated as “Δ”, and the case where the 25% CLD hardness was 200 kPa or more was evaluated as “x”.

≪Foam evaluation result≫
The evaluation results of the foams according to Examples and Comparative Examples are shown in Tables 1 to 5. From the results, it can be understood that the conductive foam according to the present invention exhibits conductivity (volume resistance value) at an applied voltage as low as 1 V, and that the conductivity anisotropy is low. It can also be understood that the conductivity is remarkably improved in the embodiment in which conductive carbon is further added as the conductive filler.

Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on June 13, 2017 (Japanese Patent Application No. 2017-116157), which is incorporated by reference in its entirety. Also, all references cited herein are incorporated as a whole.

Claims

A conductive foam obtained by foaming an emulsion composition in which a conductive material is dispersed by a mechanical froth method and then curing, wherein the conductive material has at least a basal surface curved A conductive foam comprising spherical graphite having the following.
2. The conductive foam according to claim 1, comprising 30% by mass to 50% by mass of the conductive material based on the total mass of the conductive foam.
The conductive foam according to claim 1 or 2, further comprising a conductive filler different from the spherical graphite as the conductive material.
4. The conductive foam according to claim 3, wherein the conductive material contains the spherical graphite and a conductive filler in a blending ratio (mass ratio) of 9: 1 to 5: 5.
The conductive foam according to claim 3 or 4, wherein the conductive filler is conductive carbon.
The conductive foam according to any one of claims 1 to 5, wherein the emulsion composition contains at least one resin material of urethane resin and acrylic resin.
The conductive foam according to any one of claims 1 to 6, wherein the conductive foam is in a sheet form.
The conductive foam according to any one of claims 1 to 7, wherein the conductive foam is laminated on a substrate.