KR102338096B1 - conductive foam - Google Patents

Abstract

Provided is a conductive foam that is excellent in various properties such as conductivity under low voltage, high isotropic conductivity, conductive material retention, cushioning properties (low hardness), moldability, and the like, and can be used regardless of environment. A conductive foam obtained by curing an emulsion composition in which a conductive material is dispersed is foamed by a mechanical process method, and the conductive material contains at least spherical graphite having a structure in which the base surface is folded.

Description

conductive foam

The present invention relates to a conductive foam.

Conventional conductive foams include foams to which conductivity is imparted by compounding conductive materials with various materials such as rubber and urethane, and products imparted with conductivity by processing such as impregnation or surface treatment. For example, Patent Document 1 discloses a conductive foam material obtained by foaming a conductive filler and a latex composition containing rubber latex such as SBR latex, NR latex, and NBR latex. The major reason why such a foam is required to impart conductivity is that both conductivity and cushioning properties (low hardness) can be achieved.

Patent Document 1: Japanese Patent Laid-Open No. 2004-202989

However, the rubber foam has high hardness, although high conductivity is obtained. In addition to this, the environment in which it can be used is limited under the influence of additives (sulfur) in the production of rubber foams. Moreover, although the urethane foam has low hardness, in addition to having low electroconductivity, uniform electroconductivity is not acquired. In addition, the impregnation process can suppress the addition amount of the conductive material to a small amount compared to the compound product, and high conductivity can be obtained, but the conductive material is easy to drop off, and the environment in which it can be used is limited. In addition, in the surface treatment, the addition amount of the conductive material is suppressed to the necessary minimum as in the impregnation processing, but there is drop-off and there is no conductivity in the thickness direction, so only the surface resistance and the method of use are limited. From the above, it is a fact that a foam having conductivity is not widely employed in the field of electronics, and as an aspect of a foam having conductivity, a method of arranging a foam between metal plates bent in a U-shape, etc. to ensure conductivity ( not shown) is employed.

Accordingly, the present invention is to provide a conductive foam that is excellent in various properties such as conductivity under low voltage, isotropic high conductivity, conductive material retention, cushioning property (low hardness), moldability, etc., and can be used without selecting an environment. do.

MEANS TO SOLVE THE PROBLEM The present inventors made earnest research, and found that the said subject could be solved by setting it as a foam using a specific electroconductive material and the emulsion composition containing an emulsion, and completed this invention. That is, the present invention is as follows.

The present invention (1) is a conductive foam obtained by foaming and curing an emulsion composition in which a conductive material is dispersed by a mechanical froth method, wherein the conductive material is at least spherical graphite having a structure in which the base surface is folded. It is a conductive foam characterized in that it contains.

This invention (2) is the conductive foam of the said invention (1) which contains 30-50 mass % of said conductive materials based on the total mass of the said conductive foam as a reference.

This invention (3) is the electroconductive foam of the said invention (1) or (2) which further contains the electroconductive filler different from the said spheroidal graphite as said electroconductive material.

This invention (4) is the electrically conductive foam of the said invention (3) which contains the said spheroidal graphite and a conductive filler in a mixing ratio (mass ratio) 9:1-5:5 as said conductive material.

The present invention (5) is the conductive foam according to the invention (3) or (4), wherein the conductive filler is conductive carbon.

The present invention (6) is the conductive foam according to any one of the inventions (1) to (5), wherein the emulsion composition includes at least one of a urethane resin and an acrylic resin.

The present invention (7) is the conductive foam according to any one of the above inventions (1) to (6) in the form of a sheet.

The present invention (8) is 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 possible to provide a conductive foam that is excellent in various properties such as conductivity under a low voltage, high isotropy conductive performance, conductive material retention, cushioning property (low hardness), moldability, etc., and can be used without selecting an environment. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a conceptual diagram which shows an example of the electrically conductive mechanism in the electroconductive foam which concerns on this embodiment containing spheroidal graphite and an electroconductive filler.

Hereinafter, the conductive foam of the present invention and its manufacturing method 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. nodular 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. Etc

1-2. Method for producing conductive foam

1-2-1. Each component of the raw material composition

1-2-2. Method for preparing raw material composition

1-2-3. Composition and properties of raw material composition

1-2-4. Foaming process

1-2-5. hardening process

1-2-6. molding method

1-3. Uses of conductive foam

1. Conductive foam

"Electroconductivity" in this specification means that a volume resistance value has resistance of 10 ⁸ ohm*cm or less, for example.

The conductive foam according to the present invention is a conductive foam obtained by foaming an emulsion composition containing a resin, an electrically conductive material and a foaming agent by a mechanical process method, followed by curing. Although the shape of the said electroconductive foam is not specifically limited, Preferably it is a sheet shape with a thickness of 0.05 mm - 2.0 mm.

Although there is no restriction|limiting in particular about the form of the cell|bubble in the electroconductive foam of this invention, From a viewpoint of heat dissipation property and a softness|flexibility, it is preferable that it is an open cell. In addition, the "open bubble" refers to a state in which there is a through hole in the resin film which sandwiches the adjacent bubbles, and the adjacent bubbles are connected three-dimensionally. Moreover, if it is a "open cell" structure, there exists a property that external air can pass to the inside of a foam. In the present invention, strictly speaking, communication between all the pores is not required, and even if some closed holes exist inside, if there is a property that external air can pass as a whole, it is called a "open cell" structure. About the shape of a bubble, it can confirm by observing with an electron microscope.

The apparent density (according to JIS K7222) of the conductive foam according to the present invention is preferably 100 kg/m 3 to 700 kg/m 3 because it is excellent in both conductivity and flexibility, and more preferably 200 to 600 kg/m 3 . When the apparent density is lower than the above range, the conductivity becomes low. In addition, when the apparent density exceeds the above range, the flexibility becomes low and the hardness increases. As a result, the shape followability to a complicated structure deteriorates.

In addition, in this specification, when it describes only as "density", it shall mean "appearance density".

In addition, the conductive foam is characterized in that the conductive material contains spherical graphite having a structure in which at least a basal plane is folded, and the spherical graphite has extremely low anisotropy in its conductive performance, and the conductivity of the conductive foam itself It is characterized in that the anisotropy is extremely low also in terms of performance. That is, in the above-mentioned conductive foam, the conductive foam has conductive performance irrespective of the conductive direction, and in the sheet-shaped conductive foam, in particular, the electrical conductivity in the thickness direction (the normal direction of the sheet) differs from the conductive performance in other directions. It is a conductive foam characterized in that there is little.

The electroconductive foam which concerns on this invention can contain 30 mass % - 50 mass % of the said electroconductive material based on the total mass. When the said electroconductive material is less than 30 mass %, there exists a possibility that the electroconductive performance of an electroconductive foam may become inadequate. That is, it becomes difficult to express high electroconductive performance in a low applied voltage. When the said electroconductive material is larger than 50 mass %, the moldability of an electroconductive foam, softness|flexibility, and material strength may fall.

In addition, the electroconductive material contained in the electroconductive foam which concerns on this invention can be made into the state in which each electroconductive material is not in contact. Even when the conductive materials are not in contact, conductivity can be imparted by hopping or the Poole Frenkel effect. The Poole Frenkel effect affects the distance between conductive materials, and as the distance increases, the distance through which electrons fly increases, so that it is necessary to apply a higher voltage. Accordingly, it is necessary to increase the amount of the conductive material in order to develop conductivity under a low voltage, but as described above, problems such as a decrease in moldability, flexibility, and material strength of the conductive foam occur.

The electroconductive foam which concerns on this invention can add to the spherical graphite which has a structure in which the said base surface was folded as an electroconductive material, and also can add an electroconductive filler. In such a case, the mixing ratio of the spherical graphite and the conductive filler is preferably 9:1 to 5:5. When the said compounding ratio is in this range, electroconductivity improves remarkably. That is, the volume resistance value falls. This is because, by adding a conductive filler in addition to the spherical graphite, the conductive filler exists in the gap between the spherical graphites, and it becomes possible to make it easier for electrons to fly from the conductive material to the conductive material. Hereinafter, this point will be described in detail.

As the electric conduction mechanism in the conductive foam of the present invention, a hopping type electric conduction in which a plurality of tunneling is repeated in the resin of the insulator constituting the matrix is used. For that purpose, it is necessary to flow an electric current between the conductive materials, and it is necessary that the distance between the electrodes (between the conductive materials) is extremely narrow with a low voltage. That is, as shown in Fig. 1, 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 by the structure in which the nano-sized conductive filler is dispersed, and each conductive material is A region that is not in contact with each other can be used as a conductive portion. Specifically, when the conductive filler is carbon-based, the specific gravity of the spherical graphite and the conductive filler are approximately the same. The electric conduction mechanism in the electroconductive foam of this invention which is further excellent in performance is obtained.

The conductive foam according to the present invention can be laminated on a substrate in the form of a sheet. Although the material of a base material is not specifically limited, What is necessary is just to be able to suppress the exudation of the raw material of the said electroconductive foam.

For example, resin films, such as a PET film, a nonwoven fabric, woven fabric, paper, an adhesive tape, the airless tape etc. in which the adhesive layer has an uneven|corrugated shape are mentioned.

Moreover, although the thickness of a base material is not specifically limited, either, The thickness of 10 micrometers - 100 micrometers is preferable. By laminating with a base material, it becomes possible to protect the said electroconductive foam from damage, and to become easy handling by the support by a base material at the time of use, etc. become possible.

Moreover, depending on the use of the said electroconductive foam, a base material may be peeled and used, or may be used as a laminated body without peeling. When peeling and using, the base material which carried out the release process can be used.

Moreover, as the said base material, what has electroconductivity can be used. Although the base material which has the said electroconductivity is not specifically limited, The nonwoven fabric, paper etc. which carried out the electroconductive process by methods, such as PET film, aluminum tape, a conductive adhesive tape, and immersion process which carried out the release process are mentioned. By using such a base material, it becomes possible to use, without peeling a base material, about the use for which the electroconductivity of the thickness direction of an electroconductive foam sheet|seat is calculated|required.

1-1. Raw material

The conductive foam according to the present invention can use, for example, an emulsion composition, a conductive material, a foaming agent (anionic surfactant), water, a crosslinking agent, and other additives as a dispersion medium as a raw material (also used in the foaming process) The gas for foaming will be explained in the foaming step).

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, It may be an emulsion which can form foam by a well-known method. For example, urethane emulsion, acrylic emulsion, styrene emulsion, EVA (ethylene vinyl acetate copolymer) resin emulsion, vinyl chloride emulsion, epoxy emulsion, etc. can be mentioned, and one or a plurality of emulsions can be used. In particular, it is preferable to use at least one of the urethane emulsion and the acrylic emulsion. In addition, it is more preferable to use at least an acrylic emulsion. Moreover, material strength can be provided further by using a urethane emulsion. Moreover, the obtained urethane resin foam is excellent in a softness|flexibility, and compression residual distortion becomes low.

Hereinafter, (1) urethane emulsion and (2) acrylic emulsion are described in detail, respectively.

(1) Urethane emulsion

Although it does not specifically limit as a manufacturing method of the urethane emulsion (water dispersion of a urethane resin) usable in this invention, The following methods (I) - (III) can be illustrated.

(I) an organic solvent solution or organic solvent dispersion liquid of an active hydrogen-containing compound, a compound having a hydrophilic group, and a urethane resin having a hydrophilic group obtained by reacting a polyisocyanate, if necessary, an aqueous solution containing a neutralizing agent is mixed, and the urethane resin emulsion how to get

(II) An aqueous solution containing a neutralizing agent 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 after adding a neutralizing agent to the prepolymer in advance, water A method of obtaining a urethane resin emulsion by mixing and dispersing in water, 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 after adding a neutralizing agent to the prepolymer in advance , a method of adding and mixing an aqueous solution containing a polyamine to obtain a urethane resin emulsion.

Examples of the polyisocyanate used in the method of the urethane resin include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, and 4,4'-diphenyl. Methane diisocyanate, 2, 4'-diphenyl methane diisocyanate, 2, 2'-diphenyl methane diisocyanate, 3, 3'-dimethyl-4, 4'-biphenylene diisocyanate, 3, 3'-dime Toxy-4, 4'-biphenylene diisocyanate, 3, 3'-dichloro-4, 4'-biphenylene diisocyanate, 1, 5-naphthalene diisocyanate, 1, 5-tetrahydro naphthalene diisocyanate, tetra Methylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethyl hexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylene diisocyanate, tetra Methyl xylene diisocyanate, hydrogenated xylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl methane diisocyanate, 3,3'-dimethyl-4, 4'-dicyclohexyl methane diisocyanate etc. can be exemplified. Moreover, in the range which does not impair the effect of invention WHEREIN: You may use together polyisocyanate more than trivalence.

The active hydrogen-containing compound is not particularly limited, and polyolefins such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyester amide polyols, polythioether polyols, and polybutadiene series Well-known polyols, such as a polyol, can be illustrated. These high molecular weight compounds may use 2 or more types together.

Here, the urethane emulsion according to this aspect is preferably at least one selected from the group consisting of a polyether-based urethane emulsion, a polyester-based urethane emulsion, a polyether carbonate-based urethane emulsion, and a polycarbonate-based urethane emulsion.

The polyester-based urethane emulsion according to the present embodiment is not limited at all, but, 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, α It can be produced by using a polymer obtained by ring-opening polymerization of a lactone such as -methyl-ε-caprolactone, a reaction product of hydroxycarboxylic acid and a polyhydric alcohol, etc.).

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

The polyether-based urethane emulsion according to the present embodiment is not limited at all, and for example, in the above production method, polyether polyol (for example, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, etc.) is used. It is possible.

In the polyether carbonate-based urethane emulsion according to this aspect, the urethane resin contains both a carbonate group and an ether group (...-O-CO-O-[RO-R']-O-CO-O-... It is not limited at all, if it contains), For example, in the said manufacturing method, it can manufacture by using a polyether polyol and a polycarbonate polyol together.

In the above methods (I) to (III), an emulsifier may also be used within a range that does not impair the effects of the invention. Examples of such emulsifiers include nonionic emulsifiers such as polyoxyethylene nonyl phenyl ether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenyl ether, and polyoxyethylene sorbitol tetraoleate; anionic emulsifiers such as fatty acid salts such as sodium oleate, alkyl sulfate ester salts, alkyl benzene sulfonates, alkyl sulfosuccinates, naphthalene sulfonates, alkane sulfonate sodium salts, and alkyl diphenyl ether sulfonate sodium salts; Nonionic anionic emulsifiers, such as polyoxyethylene alkyl sulfate and polyoxyethylene alkyl phenyl sulfate, etc. can be illustrated.

The conductive foam of the present invention is a conductive foam obtained by blending a conductive material by using a urethane emulsion as a raw material (the foam contains a urethane resin). It becomes possible to make a foam equipped with various characteristics, such as suppression of drop-off|omission and hydrolysis resistance, at a high level.

(2) Acrylic emulsion

Although it does not specifically limit as a manufacturing method of the acrylic emulsion (water dispersion of acrylic resin) usable in this invention, For example, (meth)acrylic acid ester monomer is essential in the presence of a polymerization initiator, an emulsifier and a dispersion stabilizer as needed. It can be obtained by setting it as the polymerizable monomer component of and by copolymerizing the mixture of these monomers and other polymerizable monomer copolymerizable as needed. Moreover, you may use combining 2 or more types of acrylic emulsion. 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 in the preparation of the acrylic emulsion include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, ( (meth) acrylate octyl, (meth) acrylic acid octadecyl, (meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid cyclohexyl, (meth) acrylic acid nonyl, (meth) acrylic acid dodecyl, (meth) acrylic acid stearyl, (meth) (meth)acrylic acid ester-based monomers such as isobornyl acrylic acid, (meth)acrylic acid dicyclopentanyl, (meth)acrylic acid phenyl, and (meth)acrylic acid benzyl; Acrylic acid, methacrylic acid, β-carboxyethyl (meth)acrylate, 2-(meth)acryloyl propionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, maleic acid half ester, maleic anhydride, unsaturated bond-containing monomers having a carboxyl group, such as itaconic anhydride; glycidyl group-containing polymerizable monomers such as glycidyl (meth)acrylate and aryl glycidyl ether; hydroxyl group-containing polymerizable monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, and glycerol mono(meth)acrylate; Ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylol propane tri(meth)acrylate, polyethylene glycol di(meth)acrylate , polypropylene glycol di(meth)acrylate, diarylphthalate, divinylbenzene, aryl(meth)acrylate, and the like can be exemplified.

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

Moreover, these emulsions may contain surfactant (emulsifier) etc. for resin dispersion. The surfactant for dispersing the resin is a surfactant for dispersing the water-dispersible resin (unlike anionic surfactants, it is not necessary to have an effect as a foaming agent). What is necessary is just to select such a surfactant suitably according to the water-dispersible resin to be selected.

・Dispersion medium

In the present invention, although water is an essential component as the dispersion medium of the emulsion composition, a mixture of water and a water-soluble solvent may be used. The water-soluble solvent is, for example, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve and butyl cellosolve, and a polar solvent such as N-methylpyrrolidone, and one of these or You may use a mixture of 2 or more types, etc.

1-1-2. conductive material

Although the conductive material described below may be blended as a powder, it is preferably used as an aqueous dispersion in which the powder is dispersed in water. By setting it as an aqueous dispersion, when it is added to an emulsion composition, it becomes easy to disperse|distribute it uniformly in a composition.

1-1-2-1. nodular graphite

Spherical graphite has high electroconductivity and contributes to electroconductive expression of the electroconductive foam of this invention. The graphite usable in the present invention is spherical. In the present invention, "spherical" does not mean only a perfect spherical shape, a shape that is slightly deformed from a perfect spherical shape to a disk state, a shape having a non-uniform surface, and a shape having an appearance like a cabbage layered on the surface, etc. is intended to include those that cannot be grasped in a perfect spherical shape. However, the crystal form of natural graphite is hexagonal, and in general, untreated graphite is in the form of scales (scaly shape), so it is distinguished from this. That is, it is required for this invention to use the graphite to which the spheroidizing process was given at least. Although the spheroidizing treatment includes a simple treatment method such as pulverizing natural graphite in the form of scales, it is preferably a treatment method in which pressure is applied isotropically to the graphite. The treatment can be carried out by using a pressurized medium such as a gas (inert gas such as argon) or liquid (eg water) and applying pressure to the graphite isotropically, or the like. Depending on the presence or absence of heating, it is classified as a hot isotropic pressurization process and a cold isotropic pressurization process. You may use any. By carrying out this process, the spherical graphite which has a spherical shape and the hollow wall (between the scale layers) inside was reduced and has isotropic high electroconductivity is obtained.

The spheroidal graphite by which the said spheroidization process was carried out is specified as spheroidal graphite which has the structure which folded the base surface from the other side. Here, the "base plane" refers to the plane orthogonal to the C-axis of the graphite crystal (hexagonal system). That is, as for the spherical graphite of this invention, it is preferable that distortion generate|occur|produces in the crystal system of natural graphite. This distortion can be grasped|ascertained by measuring the X-ray diffraction pattern and confirming the presence or absence of the broadening of a peak or the presence or absence of the shift of the 2θ value compared with natural graphite. In addition to confirming whether or not the conductive foam contains spherical graphite by measuring the X-ray diffraction pattern of the raw graphite, any two or more cross-sections of the conductive foam are observed under a microscope, and the shape of the graphite equivalent portion is circular. It can also be confirmed by whether or not it is the same as Specifically, microscopic observation of the mutually orthogonal surfaces of the conductive foam, and if the shape of the graphite equivalent portion in any image is the same as a circle with the ratio of short diameter to long diameter less than 1/2, the conductive foam contains spherical graphite can be said to be doing

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

As spherical graphite, a commercial item can also be used suitably, As the specific example, the spherical graphite etc. made by the Nippon Graphite Industry Co., Ltd. are mentioned. The average particle diameter (median diameter) of the spherical graphite used for this invention is about 1-100 micrometers. Preferably it is 5-80 micrometers, More preferably, it is 8-80 micrometers. As for securing the conductivity of the conductive foam and ensuring its flexibility, improvement in one tends to decrease the other, but it is preferable to use spherical graphite having a relatively small average particle size, since both properties can be improved in a balanced way. Although the preferable average particle diameter range varies depending on the final shape of the conductive foam, in the sheet-like form having a thickness of about 0.1 to 1.0 mm, it is preferably about 5 to 30 µm, more preferably 10 to 20 µm.

1-1-2-2. conductive filler

The conductive filler (conductive filler other than the spherical graphite having a structure in which the base surface is folded) added to the spherical graphite used when manufacturing the conductive foam of the present invention is not particularly limited as long as it has a property of improving the conductivity of the foam. , Although general metallic materials, conductive carbon, ion conductive materials, etc. can be illustrated, it is preferable that it is conductive carbon. As conductive carbon, for example, carbon nanotube, carbon black (eg, acetylene black, etc.), nano-sized conductive carbon such as graphene, graphite, carbon fiber, graphite (spherical graphite having a structure in which the base surface is folded) other graphite) and activated carbon. Compared with the metal filler of the same size, these conductive carbons are effective in that specific gravity is light and the weight of a conductive foam does not increase easily even if it increases addition amount. Moreover, compared with a metal filler, since the said conductive carbon is rich in flexibility, ie, it is low elasticity, it becomes possible to make a conductive foam flexible, ie, low hardness. Moreover, it is excellent also in the point that a price is cheap. These conductive materials can be used alone or in combination of two or more.

Moreover, 1 nm - 100 nm are preferable and, as for the average length (average diameter in the case of a substantially spherical shape) of the said electroconductive filler, 5 nm - 50 nm are more preferable. By using such an electroconductive filler, it becomes possible to disperse|distribute between the said spherical graphite, and the electroconductivity of an electroconductive foam improves.

In addition, the aspect ratio of the conductive filler is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less. When an aspect-ratio exceeds 5, there exists a possibility that anisotropy may appear in the electroconductive performance of an electroconductive foam.

Here, the value of "aspect ratio" is a value obtained by dividing the average length of the conductive filler by the average diameter. "Average length" and "average diameter" are the values calculated|required from the SEM observation of an electroconductive filler, observation and measurement of at least 100 particle|grains, and the average value. More specifically, the "average diameter" is calculated by calculating the cross-sectional area of the particles based on the vertical cross-section in the vicinity of the longitudinal center of the particles imaged by SEM observation, and calculating the diameter of a circle having the same area as the cross-sectional area. It is the average value of the derived area diameters. The average diameter and average length are the measured averages of 100 particles.

1-1-3. additive

1-1-3-1. foaming agent

The foaming agent that can be used when manufacturing the conductive foam of the present invention is a substance capable of mixing a gas into the raw material mixture and stabilizing the foam, and an anionic foaming agent can be exemplified.

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

Here, in order to make the anionic surfactant used in this aspect easily disperse|distribute to an emulsion composition, it is preferable that it is 10 or more, It is more preferable that it is 20 or more, It is especially preferable that it is 30 or more.

·HLB

In addition, in this invention, an HLB value means a hydrophilicity-hydrophobicity balance (HLB) value, and is calculated|required by the Oda method. The method of obtaining HLB by the Oda method is “Introduction to New Surfactants” on pages 195-196 and March 20, 1957 at Maki Bookstore published by Ryohei Oda et al., “Synthesis of Surfactants and Their Applications” It is described on pages 492 to 502, and it can be obtained by HLB = (number of inorganic properties/number of organic properties) x 10. Here, the numerical values of inorganic properties and organic properties are calculated by the values shown in Tables 3, 3, and 11 of the above "Introduction to New Surfactants".

Moreover, you may use an amphoteric surfactant as a foaming agent which concerns on this invention. In particular, when an anionic surfactant and an amphoteric surfactant are used in combination, the charges of the hydrophilic groups between the molecules of the anionic surfactant repel, and while the molecules of the anionic surfactant maintain a certain distance between them, When a neutral amphoteric active agent enters between molecules of anionic surfactant, a bubble can be further stabilized and the size of a bubble can be made small. For this reason, the delamination strength can be improved. Therefore, it is preferable to use an anionic surfactant and an amphoteric surfactant together.

The amphoteric surfactant is not particularly limited, and examples thereof include an amphoteric surfactant such as an amino acid type, a betaine type, and an amine oxide type, and a betaine type amphoteric surfactant is preferable because the above-described effect is higher.

Examples of the amino acid type amphoteric surfactant include N-alkyl or alkenyl amino acids or salts thereof. N-alkyl or alkenyl amino acids have an alkyl or alkenyl group bonded to a nitrogen atom, and one or two "-R-COOH" (wherein R represents a divalent hydrocarbon group, preferably an alkylene group, It has a structure to which the group represented by C1-C2 is especially preferable.). In a compound in which one "-R-COOH" is bonded, a hydrogen atom is further bonded to the nitrogen atom. A compound having one "-R-COOH" is called a mono-form, and a compound having two "-R-COOH" is called a di-form. As the amphoteric surfactant according to the present invention, both of these mono- and di-forms can be used. In the N-alkyl or alkenyl amino acid, the alkyl group or the alkenyl group may be linear or branched. Specifically, as an amino acid type amphoteric surfactant, lauryl diaminoethyl glycine sodium, trimethyl glycine sodium, cocoyl taurine sodium, cocoyl methyl taurine sodium, lauroyl glutamate sodium, lauroyl glutamate potassium, lauroyl methyl -β-alanine etc. are mentioned.

Examples of the betaine type amphoteric surfactant include alkyl betaine, imidazolium betaine, carbo betaine, amide carbo betaine, amide betaine, alkyl amide betaine, sulfo betaine, and amide. sulfo betaine and phospho betaine. Specifically, as a betaine-type amphoteric surfactant, lauryl betaine, stearyl betaine, lauryl dimethyl amino acetate betaine, stearyl dimethyl amino acetate betaine, lauric acid amide propyl dimethyl amino acetate betaine, isostearic acid Amide ethyl dimethyl amino acetate betaine, isostearic acid amide propyl dimethyl amino acetate betaine, isostearic acid amide ethyl diethyl amino acetate betaine, isostearic acid amide propyl diethyl amino acetate betaine, isostearic acid amide ethyl dimethyl amino hydroxy sulfo betaine Phosphorus, Isostearic Acid Amide Propyl Dimethyl Amino Hydroxy Sulfobetaine, Isostearic Acid Amide Ethyl Diethyl Amino Hydroxy Sulfo Betaine, Isostearic Acid Amide Propyl Diethyl Amino Hydroxy Sulfo Betaine, N-Lauryl-N, N-Dimethyl Ammonium-N-propyl sulfobetaine, N-lauryl-N, N-dimethyl ammonium-N-(2-hydroxy propyl) sulfobetaine, N-lauryl-N, N-dimethyl-N-(2- Hydroxy-1-sulfopropyl) ammonium sulfo betaine, lauryl hydroxy sulfo betaine, dodecyl amino methyl dimethyl sulfo propyl betaine, octadecyl amino methyl dimethyl sulfo propyl betaine, 2-alkyl-N-carboxymethyl- N-Hydroxy ethyl imidazolium betaine (2-lauryl-N-carboxymethyl-N-hydroxy ethyl imidazolium betaine, 2-stearyl-N-carboxymethyl-N-hydroxy ethyl imidazolium betaine, etc.), coconut oil fatty acid amide propyl betaine, and coconut oil fatty acid amide propyl hydroxysulfate.

Examples of the amine oxide-type amphoteric surfactant include lauryl dimethyl amine-N-oxide and oleyl dimethyl amine-N-oxide.

Among the amphoteric surfactants described above, it is preferable to use a betaine type amphoteric surfactant, and among the betaine types, alkyl betaine, imidazolium betaine, and carbo betaine are particularly preferable. Examples of the alkyl betaine usable in the present invention include stearyl betaine and lauryl betaine, and the imidazolium betaine includes 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolium betaine .

Moreover, as a foaming agent which concerns on this invention, you may use a nonionic surfactant. It does not restrict|limit especially as a nonionic surfactant, Nonionic surfactants, such as fatty acid alkanolamide, ether, and an ester type, can be illustrated.

1-1-3-2. crosslinking agent

The crosslinking agent used in manufacturing the conductive foam of the present invention is not particularly limited, and may be added in a necessary amount depending on the use and the like, and a specific crosslinking method may be selected according to the type of the water-dispersible resin. A known crosslinking agent can be used as the crosslinking agent, and the type and functional group of the resin compounding system that uses an epoxy-based crosslinking agent, a melamine-based crosslinking agent, an isocyanate-based crosslinking agent, a carbodiimide-based crosslinking agent, an oxazoline-based crosslinking agent, etc. It can be used in an appropriate amount depending on the skill.

1-1-3-3. Etc

In addition, you may use well-known additive components, such as a thickener, a bubble nucleating agent, a plasticizer, a lubricant, a coloring agent, antioxidant, a filler, a reinforcing agent, a flame retardant, an antistatic agent, and a surface treatment agent.

1-2. Method for producing conductive foam

The method for producing a conductive foam of the present invention includes 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 process method, and a step of curing the foamed raw material composition.

According to this method, the electroconductive foam of this invention can be manufactured stably.

1-2-1. Each component of the raw material composition

The raw material composition used for the manufacturing method of the electroconductive foam of this invention contains at least the electroconductive material containing the spherical graphite which has the structure in which the base surface was folded, and the said emulsion composition. Moreover, the polyfunctional compound which contributes to hardening of the resin component of the said emulsion, ie, a crosslinking agent and a foaming agent, may be included. About each preferable example of a foaming agent and a crosslinking agent, it is the same as the preferable example etc. of each component demonstrated about the said conductive foam.

In order to prepare as a raw material composition, it is preferable to further contain a solvent. Examples of usable solvents include water, organic solvents (eg, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl cellosolve, and polarity such as N-methyl pyrrolidone). 1 type or 2 or more types of solvent), but it is preferable to use only water in this invention. When an organic solvent is used, the viscosity of the raw material composition is lowered compared to the case where water is used, and there is a fear that bubbles may be defoamed. Therefore, although it is preferable not to contain an organic solvent, you may contain it in the ratio of the grade which does not affect bubble formation stability (for example, the grade which does not fall to the extent of impairing moldability).

1-2-2. Method for preparing raw material composition

The raw material composition is prepared by preparing the aqueous emulsion of the resin and the aqueous dispersion of the conductive material such as the spherical graphite, and mixing them to prepare the raw material composition without causing aggregation of the conductive material such as the spherical graphite. It is preferable because it can 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 are not particularly limited, but are generally about 50% by mass to 90% by mass. It is preferable that the surfactant serving as a foaming agent is mixed in advance in the aqueous dispersion of the conductive material, because dispersion stability of the conductive material in the resin when mixed with the aqueous emulsion of the resin is further improved. In particular, use of at least one type of surfactant having good wettability as the foaming agent is preferable because dispersion stability of the conductive material into 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 it is more preferable to use at least one selected from the above-mentioned nonionic surfactants having good wettability. For example, the aqueous dispersion of the conductive material can be prepared by mixing the conductive material with an aqueous solution or water suspension of a surfactant (foaming agent) having a solid content of about 20 to 60 mass%. Further, in an embodiment in which other additives such as a crosslinking agent and other thermally conductive material are used, it is preferable to add another additive to the aqueous dispersion of the conductive material and mix with the aqueous emulsion of the resin to prepare the 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 mass%, preferably 50 to 70 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 total mass of other additives such as a foaming agent (specifically, surfactant) is less than 5%. However, the preferable mass ratio of each material in solid content also fluctuates according to the kind etc. of the material used. Moreover, in order to form a bubble stably in the following foaming process, it is suitable for the viscosity of a raw material composition to be about 10000-20000 mPa*s.

1-2-4. Foaming process

In the foaming step, mechanical foaming is performed by stirring the raw material composition to generate bubbles. The mechanical foaming (mechanical process) 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, and for example, a homogenizer, a dissolver, a mechanical pross foaming machine, and the like can be used. In the present invention, by performing the foaming step by the mechanical foaming method, the formation of closed cells is suppressed, the formation of open cells is dominant, the density of the foam after curing is prevented from increasing, and a porous body with high flexibility is obtained.

Although there is no restriction|limiting in particular about stirring conditions, A stirring time is normally 1-10 minutes, Preferably it is 2-6 minutes. In addition, the stirring speed in the above mixing is preferably 200 rpm or more in order to make bubbles fine (500 rpm or more is more preferable), and 2000 rpm or less in order to smoothly discharge the foamed material from the foaming machine (800 rpm) The following are more preferable). Although there is no restriction|limiting in particular also about the temperature condition of a foaming process, Usually, it is normal temperature. When a curing step described later is also performed simultaneously with the foaming, heating may be performed in order to advance the reaction of the functional group.

1-2-5. hardening process

In the curing step, the resin component is cured. Through this step, the raw material composition becomes a structure as a conductive foam. A hardening process is implemented after a foaming process. It is preferable to heat 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, at 80 to 150°C (especially preferably about 120°C) for about 1 hour.

Moreover, the hardening process may be implemented as one process of the shaping|molding process for making the electroconductive foam obtained into a desired shape. For example, in the aspect of manufacturing a sheet-shaped conductive foam, you may implement a hardening process as one process of a casting method. Specifically, the raw material composition subjected to “(4) foaming step” is cast to a desired thickness on the surface of the substrate, heated to evaporate the solvent (water), the crosslinking reaction proceeds and hardens, and is applied to the surface of the substrate. Sheets can be made.

1-2-6. molding method

In order to make the electroconductive foam of this invention into a desired shape, it can mold-process by conventionally well-known various methods. An appropriate molding processing method can be selected according to the desired final shape. In the case of manufacturing the sheet-shaped conductive foam, a casting method can be used. It is preferable to perform the bubble introduction process (foaming process) before a shaping|molding process. Moreover, in the embodiment in which the emulsion composition has a crosslinked structure, the formation of the crosslinked structure, ie, the progress of the crosslinking reaction, may be performed simultaneously with the molding process.

1-3. Uses of conductive foam

According to the conductive foam according to the present invention, since it not only has conductivity and conductivity retention properties (prevention property of the conductive material from falling off), but also has excellent cushioning properties (flexibility), it is excellent in followability to a partner member, and the reaction force of the conductive foam itself It becomes possible to make the (restorative force) small. For this reason, when arranging and using between members, sufficient electrical conductivity is ensured, and damage such as failure or disconnection of wiring is not given to other members (such as wiring of an IC chip or board, bending of a board). can be used In particular, in recent years, electronic devices have become thinner, lighter, and smaller, and the space inside the electronic devices tends to disappear further, and the internal structure is complicated. The demand to an electroconductive foam is increasing. In addition to arranging between members, it can be used for various purposes (for example, grouting materials in electronic parts and devices, shielding materials, cushioning materials, protective materials, board insertion materials, etc.) regardless of the application method or usage environment. it becomes possible In addition, in the conductive foam according to the present invention, it is possible to obtain a conductive foam having excellent properties even if it does not contain silicone. .

Example

≪Production Example≫

<Raw material>

・Acrylic emulsion: acrylnitrile-acrylic acid alkyl ester-itaconic acid copolymer (solid content: 60% by mass)

Urethane emulsion: Polyether carbonate-based urethane emulsion (60% solids)

·Anionic surfactant 1: Ammonium stearate (solid content 30%)

·Anionic surfactant 2: sodium alkylsulfosuccinate (solid content 35%)

·Amphoteric surfactant 1: lauryl dimethyl amino acetate betaine (solid content 30%)

Amphoteric surfactant 2: lauryl betaine (solids 36%)

・Non-ionic 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 base surface is folded (average particle diameter of 20 µm)

Graphite 2: Spherical graphite having a structure in which the base surface is folded (average particle diameter of 10 µm)

Graphite 3: flaky graphite (average particle size 20㎛)

Conductive filler 1: Conductive carbon (manufactured by Mitsubishi Chemical Corporation, part number: #3230B, average particle size 20 nm, pH 6.0)

Conductive filler 2: conductive carbon (manufactured by Mitsubishi Chemical Corporation, part number: #3040B, average particle size 50 nm, pH 6.0)

Substrate 1: PET film with release treatment

<Preparation of conductive foam>

(Example 1)

Using an acrylic emulsion as the main emulsion, 5 parts by mass of anionic surfactant 1 and 3 parts by mass of anionic surfactant 2 and 2 based on the total amount of the emulsion as a standard (the sum of solid content and non-solid content is 100 parts by mass) Negative amphoteric surfactant 1, 1.5 parts by mass of amphoteric surfactant 2, and 0.5 parts by mass of nonionic surfactant 1 were mixed with 23.5 parts by mass of graphite 1, 2.6 parts by mass of conductive filler 1 and 3 parts by mass of crosslinking agent 1 to prepare a foam raw material. The foam according to Example 1 was obtained by applying air to the raw material to make it foam and then heat-treating it.

(Examples 2-31, Comparative Examples 1-10)

In Examples 2 to 22 and Comparative Examples 1 to 10, a foam was obtained in the same manner as in Example 1 except that the type and amount of graphite or conductive carbon were changed as described in Tables 1 to 3 and 5 below. Examples 23 and 24 change the subject matter of Examples 1 and 2 from an acrylic emulsion to a urethane emulsion. Similarly, Examples 25 and 26 change the subject matter of Examples 1 and 2 to acrylic and 50 parts by mass of a urethane emulsion. was changed to each to obtain a foam. Examples 27 to 31 are foams prepared by adjusting the thickness and density of Example 1.

≪Foam evaluation method≫

<thickness>

The thickness was measured by a thickness gauge.

<Density>

It was measured by calculating the weight per unit volume.

<Appearance>

Visual observation evaluated the condition of the cells and the surface of the foam. “○” indicates that the cells are uniform and the surface is not rough, “Δ” indicates that the cells are slightly rough, and “×” indicates that the cells are very rough or the cells are not formed or the surface condition is severe. ' was evaluated.

<Challenge performance>

In conformity with JIS K 6911, each foam is punched with Φ 100 mm, and the volume resistance value and the surface resistance from the current value at an applied voltage of 1 V using a DC voltage/current source 6243 manufactured by ADC Inc. The value was calculated.

(volume resistance value)

The volume resistance value of 1.0 × 10 ³ in the case of less than Ω㎝ "○", and the volume resistance value of 1.0 × 10 ³ Ω㎝ more than, less than 1.0 × 10 ⁵ Ω㎝ case of "△", and the volume resistance value of 1.0 × A ^{case of 10 5} Ωcm or more was evaluated as “x”.

(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 was less than 1.5 was denoted as "○", the case of 1.5 or more and less than 2.00 was denoted as "Δ", and the case of 2.00 or more was denoted as "x". From the result of volume resistance value evaluation and anisotropy evaluation, the conductive foam which has high electroconductivity and isotropy under a low voltage evaluated that there is no "x" in either.

<Hardness>

It measured based on JISK6254. Specifically, the magnitude of the repulsive stress when a sample punched with a diameter of 50φ was crushed by pressing 25% of the thickness at a speed of 1 mm/min using an autograph was measured (the sample was compressed entirely with a compression plate of 100φ and measurement). 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 “×”.

≪Foam evaluation result≫

The evaluation result of the foam concerning an Example and a comparative example is shown to Tables 1-5. From the results, it can be understood that the conductive foam according to the present invention exhibits conductivity (volume resistance value) with a low applied voltage of 1 V, and that the conductive anisotropy is low. Moreover, in the Example which further added conductive carbon as a conductive filler, it can also be understood that electroconductivity is improving remarkably.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

Although this invention was demonstrated in detail with reference to the specific aspect, it is clear for those skilled in the art that various changes and correction are possible without departing from the mind and range of this invention.

In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2017-116157) for which it applied on June 13, 2017, The whole is used by reference. In addition, all references cited herein are incorporated in their entirety.

Claims (11)

A conductive foam obtained by curing an emulsion composition in which a conductive material is dispersed, after foaming it by a mechanical process method, comprising:
The said electroconductive material contains the spherical graphite which has a structure in which the base surface was folded, and the electroconductive filler different from the said spherical graphite at least, The electroconductive foam characterized by the above-mentioned. The method of claim 1,
Based on the total mass of the said electroconductive foam, 30 mass % - 50 mass % of the said electroconductive materials are contained, The electroconductive foam characterized by the above-mentioned. delete 3. The method according to claim 1 or 2,
As the conductive material, the spheroidal graphite and the conductive filler are contained in a mixing ratio (mass ratio) of 9:1 to 5:5. 3. The method according to claim 1 or 2,
The said conductive filler is conductive carbon, The conductive foam characterized by the above-mentioned. 3. The method according to claim 1 or 2,
The emulsion composition is a conductive foam, characterized in that it comprises a resin material of at least one of a urethane-based resin and an acrylic resin. 3. The method according to claim 1 or 2,
A conductive foam, characterized in that it is in the form of a sheet. 3. The method of claim 1 or 2,
A conductive foam laminated on a substrate. 3. The method according to claim 1 or 2,
Conductive foam, characterized in that it further comprises a crosslinking agent in the emulsion composition. A member made of the conductive foam according to claim 1 or 2, comprising:
The member is a member, characterized in that selected from a grouting material, a shielding material, a cushioning material, a protective material, and an insert material of the substrate. The electronic component provided with the electroconductive foam of Claim 1 or 2.

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