Conductive foam
阅读说明：本技术 导电性发泡体 (Conductive foam ) 是由 菊地敦纪 于 2018-06-11 设计创作，主要内容包括：提供一种导电性发泡体,其低电压下的导电性、各向同性高的导电性、导电性材料保持性、缓冲性(低硬度)、成形性等各种特性优异,能够不受环境限制地使用。所述导电性发泡体是利用机械起泡法使分散有导电性材料的乳液组合物发泡后固化而得到的,所述导电性材料至少含有具有使基面褶曲而得到的结构的球状石墨。(Disclosed is a conductive foam which has excellent properties such as conductivity at low voltage, high isotropy, conductive material retention, cushioning properties (low hardness), and moldability, and which can be used without being limited by the environment. The conductive foam is obtained by foaming and then curing an emulsion composition in which a conductive material is dispersed by a mechanical foaming method, and the conductive material contains at least spherical graphite having a structure in which a base surface is wrinkled.)
1. A conductive foam obtained by foaming and then curing an emulsion composition in which a conductive material is dispersed by a mechanical foaming method, characterized in that,
the conductive material contains at least spherical graphite having a structure obtained by folding a base surface.
2. The conductive foam according to claim 1, wherein,
the conductive material is contained in an amount of 30 to 50 mass% based on the total mass of the conductive foam.
3. The conductive foam according to claim 1 or 2, wherein,
the conductive foam further contains, as the conductive material, a conductive filler different from the spherical graphite.
4. The conductive foam of claim 3, wherein,
the conductive foam is prepared from the following components in a ratio (mass ratio) of 9: 1-5: 5 contains the spherical graphite and a conductive filler as the conductive material.
5. The conductive foam according to claim 3 or 4, wherein,
the conductive filler is conductive carbon.
6. The conductive foam according to any one of claims 1 to 5, wherein,
the emulsion composition includes at least one resin material of a polyurethane-based resin and an acrylic resin.
7. The conductive foam according to any one of claims 1 to 6, wherein,
the conductive foam is in a sheet form.
8. The conductive foam according to any one of claims 1 to 7, wherein,
the conductive foam is a conductive foam laminated on a substrate.
Technical Field
The present invention relates to a conductive foam.
Background
Some conventional conductive foams include foams obtained by compounding various materials such as rubber and polyurethane with a conductive material to impart conductivity, and products obtained by processing such as impregnation or surface treatment to impart conductivity. For example, patent document 1 proposes a conductive foamed material obtained by foaming a latex composition containing a conductive filler and a rubber latex such as SBR latex, NR latex, NBR latex. The primary reason why such a foam is required to be provided with conductivity is that conductivity and cushioning properties (low hardness) can be achieved at the same time.
Disclosure of Invention
Problems to be solved by the invention
However, the rubber foam has high hardness although high conductivity is obtained. Further, in the production of the rubber foam, the environment in which the rubber foam can be used is limited by the influence of the additive (sulfur). In addition, although the polyurethane foam has low hardness, the conductivity is low and uniform conductivity cannot be obtained. In addition, although the impregnation process can obtain high conductivity by limiting the amount of the conductive material to a small amount as compared with the composite product, the conductive material is likely to fall off, and the environment in which the conductive material can be used is limited. In addition, the surface treatment limits the addition amount of the conductive material to the necessary minimum, as in the immersion process, but there is peeling, and there is no conductivity in the thickness direction and only surface resistance, and the method of use is limited. As is apparent from the above, a foam having conductivity is not generally used in the field of the electronic industry, and as a form of the foam having conductivity, a form (not shown) in which conductivity is secured by a method of sandwiching the foam between metal plates bent in a U shape is used.
Accordingly, an object of the present invention is to provide a conductive foam which is excellent in various properties such as conductivity at low voltage, high isotropy, conductive material retention, cushioning properties (low hardness), moldability and the like, and which can be used without being limited by the environment.
Means for solving the problems
The present inventors have conducted intensive studies and found that the above problems can be solved by producing a foam using an emulsion composition containing a specific conductive material and an emulsion, and the present invention has been completed. Namely, the present invention is as follows.
The present invention (1) is a conductive foam,
the conductive material is obtained by foaming an emulsion composition in which a conductive material is dispersed by a mechanical foaming method and then curing the composition, and is characterized in that the conductive material contains at least spherical graphite having a structure obtained by folding a basal plane.
The invention (2) is the (1) of the conductive foam, wherein,
the conductive material is contained in an amount of 30 to 50 mass% based on the total mass of the conductive foam.
The invention (3) is the (1) or (2) of the conductive foam, wherein,
the conductive foam further contains, as the conductive material, a conductive filler different from the spherical graphite.
The invention (4) is the invention (3) of the conductive foam, wherein,
the conductive foam is prepared from the following components in a ratio (mass ratio) of 9: 1-5: 5 contains the spherical graphite and a conductive filler as the conductive material.
The invention (5) is the invention (3) or (4) of the conductive foam, wherein,
the conductive filler is conductive carbon.
The invention (6) is the (1) - (5) any of the conductive foam, wherein,
the emulsion composition includes at least one resin material of a polyurethane-based resin and an acrylic resin.
The invention (7) is the conductive foam according to any one of the inventions (1) to (6), wherein,
the conductive foam is in a sheet form.
The invention (8) is the conductive foam according to any one of the inventions (1) to (7), wherein,
the conductive foam is a conductive foam laminated on a substrate.
Effects of the invention
The present invention can provide a conductive foam which is excellent in various properties such as conductivity at low voltage, high isotropic conductive properties, conductive material retention, cushioning properties (low hardness), and moldability, and which can be used without being limited by the environment.
Drawings
Fig. 1 is a schematic view showing an example of a conductive mechanism in the conductive foam of the present embodiment containing spherical graphite and a conductive filler.
Detailed Description
The following items will explain the conductive foam and the production method thereof of the present invention in detail.
1. Conductive foam
1-1. raw materials
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. additives
1-1-3-1 foaming agent
1-1-3-2. crosslinking agent
1-1-3-3. others
1-2. Process for producing conductive foam
1-2-1. Components of the raw material composition
1-2-2 preparation method of raw material composition
1-2-3. composition and Properties of the raw Material composition
1-2-4. foaming step
1-2-5. curing procedure
1-2-6. forming method
1-3. use of conductive foam
1. Conductive foam
The term "conductivity" as used herein means, for example, a volume resistance value of 108Resistance of not more than Ω · cm.
The conductive foam of the present invention is obtained by foaming and then curing an emulsion composition containing a resin, a conductive material and a foaming agent by a mechanical foaming method. The shape of the conductive foam is not particularly limited, but is preferably a sheet with a thickness of 0.05mm to 2.0 mm.
The form of the cells in the conductive foam of the present invention is not particularly limited, but from the viewpoint of heat dissipation and flexibility, the cells are preferably open cells. The term "interconnected cells" refers to a state in which through-holes are present in the resin film that separates adjacent cells, and the adjacent cells three-dimensionally communicate with each other. In addition, in the case of the "open cell" structure, the foam has a property that external air can be introduced into the foam. In the present invention, it is not strictly necessary that all the pores communicate with each other, and even if a partially closed pore exists inside, the pore has a "bubble-continuous" structure as long as the pore has a property of allowing external gas to pass therethrough as a whole. The form of the bubbles can be confirmed by observation with an electron microscope.
The conductive foam of the present invention has an apparent density (according to JIS K7222) of 100kg/m3～700kg/m3In the case of the above, the conductivity and flexibility are excellent, and therefore, the concentration is preferably 200kg/m3～600kg/m3And, then, more preferably. When the apparent density is lower than the above range, the conductivity becomes low. When the apparent density is more than the above range, the flexibility becomes low and the hardness becomes high, resulting in deterioration of shape-following ability to a complicated structure.
In the present specification, the term "apparent density" refers to only "density".
The conductive foam is characterized in that the conductive material contains at least spherical graphite having a structure obtained by folding a base surface, and the anisotropy of the conductive performance of the spherical graphite is extremely low, and the anisotropy of the conductive performance of the conductive foam itself is also extremely low. That is, the conductive foam is characterized by having a conductive property regardless of the conductive direction in the conductive foam, and in the sheet-like conductive foam, particularly, the difference between the conductive property in the thickness direction (the normal direction of the sheet) and the conductive property in the other direction is small.
The conductive foam of the present invention may contain the conductive material in an amount of 30 to 50 mass% based on the total mass of the foam. When the conductive material is less than 30% by mass, the conductive property of the conductive foam may be insufficient. That is, it is difficult to exhibit high conductivity at a low applied voltage. When the conductive material is more than 50 mass%, the moldability, flexibility, and material strength of the conductive foam may be reduced.
The conductive material contained in the conductive foam of the present invention can be in a state where the conductive materials are not in contact with each other. Even in the case where the conductive materials are not in contact with each other, conductivity can be imparted by a hopping (hopping) or a pul-Frenkel (Pool Frenkel) effect. The pul-frenkel effect affects the distance between the conductive materials, and when the distance becomes longer, the distance at which electrons jump becomes longer, and therefore a higher voltage needs to be applied. Therefore, in order to exhibit conductivity at a low voltage, it is necessary to increase the amount of the conductive material, but as described above, problems occur such as a decrease in moldability, flexibility, material strength, and the like of the conductive foam.
In the conductive foam of the present invention, a conductive filler may be added as a conductive material in addition to the spherical graphite having a structure in which the base surface is wrinkled. In this case, the ratio of the spherical graphite to the conductive filler is preferably 9: 1-5: 5. when the compounding ratio is within this range, the conductivity is remarkably improved. That is, the volume resistance value decreases. This is because, by adding a conductive filler to the spherical graphite, electrons can be easily flown from the conductive material to the conductive material by the presence of the conductive filler in the gaps between the spherical graphite. This point will be described in detail below.
As the conductive means in the conductive foam of the present invention, jump-type conductivity in which a plurality of tunnels are repeated in a resin as an insulator constituting a matrix is used. For this reason, it is necessary to flow a current between the conductive materials, and the distance between the electrodes (between the conductive materials) is extremely narrow at a low voltage. That is, as shown in fig. 1, the structure in which the nano-sized conductive filler is dispersed in the micro-sized spherical graphite can realize the limit film thickness of the matrix resin and the distance between the conductive materials, and the region where the conductive materials do not contact each other can be made to be the conductive portion. Specifically, in the case where the conductive filler is a carbon-based one, the specific gravity of the spherical graphite is substantially the same as that of the conductive filler, and therefore, the spherical graphite is uniformly distributed in the matrix space at a ratio based on the compounding ratio (for example, a ratio of 9: 1 to 5: 5), and the conductive mechanism in the conductive foam of the present invention having more excellent performance is obtained.
The conductive foam of the present invention can be laminated on a substrate in the form of a sheet. The material of the base material is not particularly limited as long as the bleeding of the raw material of the conductive foam can be suppressed.
Examples thereof include resin films such as PET films, nonwoven fabrics, woven fabrics, papers, pressure-sensitive adhesive tapes, and airless tapes (エアレステ - プ) in which the pressure-sensitive adhesive layer has an uneven shape.
The thickness of the base material is also not particularly limited, but is preferably 10 μm to 100 μm. The conductive foam can be protected from damage by being laminated on a base material, and handling can be facilitated by being supported by the base material during use.
The substrate may be used after being peeled off depending on the use of the conductive foam, or the laminate may be used as it is without being peeled off. In the case of use after peeling, a substrate subjected to a release treatment may be used.
In addition, a substrate having conductivity may be used as the substrate. The substrate having conductivity is not particularly limited, and examples thereof include a release-treated PET film, an aluminum tape, a conductive pressure-sensitive adhesive tape, a nonwoven fabric or paper subjected to a conductive treatment by a method such as dipping, and the like. By using such a base material, the conductive foam sheet can be used without peeling the base material for applications requiring conductivity in the thickness direction of the conductive foam sheet.
1-1. raw materials
The conductive foam of the present invention can be produced by using, for example, an emulsion composition, a conductive material, a foaming agent (anionic surfactant), water as a dispersion medium, a crosslinking agent, and other additives as raw materials (the foaming gas used in the foaming step is described in the foaming step).
1-1-1 emulsion composition
The emulsion raw material of the emulsion composition used for producing the foam of the present invention is not particularly limited, and may be an emulsion capable of forming a foam by a known method. Examples thereof include a polyurethane emulsion, an acrylic emulsion, a styrene emulsion, an EVA (ethylene-vinyl acetate copolymer) resin emulsion, a vinyl chloride emulsion, and an epoxy emulsion, and one or more kinds of emulsions can be used. It is particularly preferable to use at least one of a polyurethane emulsion and an acrylic emulsion. Further, it is more preferable to use at least an acrylic emulsion. In addition, by using the polyurethane emulsion, the material strength can be further imparted. The resulting polyurethane resin foam is excellent in flexibility and has a low compressive residual strain.
Hereinafter, (1) the polyurethane emulsion and (2) the acrylic emulsion will be described in detail.
(1) Polyurethane emulsion
The method for producing the polyurethane emulsion (aqueous dispersion of polyurethane resin) that can be used in the present invention is not particularly limited, but the following methods (I) to (III) can be exemplified.
(I) A method in which an aqueous solution containing a neutralizing agent is mixed, if necessary, with an organic solvent solution or an organic solvent dispersion of a polyurethane resin having a hydrophilic group obtained by reacting an active hydrogen-containing compound, a compound having a hydrophilic group, and a polyisocyanate to obtain a polyurethane resin emulsion.
(II) A method in which an aqueous solution containing a neutralizing agent is mixed with a polyurethane prepolymer having a terminal isocyanate group and a hydrophilic group, which is obtained by reacting an active hydrogen-containing compound, a compound having a hydrophilic group and a polyisocyanate, or a method in which a neutralizing agent is added to a prepolymer in advance, and then the prepolymer is mixed with water to be dispersed in water, and then the resulting mixture is reacted with a polyamine to obtain a polyurethane resin emulsion.
(III) a method in which an aqueous solution containing a neutralizing agent and a polyamine is mixed with a polyurethane prepolymer containing a terminal isocyanate group and a hydrophilic group, which is obtained by reacting an active hydrogen-containing compound, a compound having a hydrophilic group, and a polyisocyanate, or a method in which a neutralizing agent is added to a prepolymer in advance, and then an aqueous solution containing a polyamine is added and mixed to obtain a polyurethane resin emulsion.
Examples of the polyisocyanate used in the method of the polyurethane resin include: 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4 '-diphenylmethane diisocyanate, 2' -diphenylmethane diisocyanate, 3 '-dimethyl-4, 4' -biphenyl diisocyanate, 3 '-dimethoxy-4, 4' -biphenyl diisocyanate, 3 '-dichloro-4, 4' -biphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 1, 5-tetrahydronaphthalene diisocyanate, tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimethylhexamethylene diisocyanate, 1, 3-cyclohexylene diisocyanate, 1, 4-cyclohexylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 4 ' -dicyclohexylmethane diisocyanate, 3 ' -dimethyl-4, 4 ' -dicyclohexylmethane diisocyanate, and the like. Further, a ternary or higher polyisocyanate may be used in combination within a range not impairing the effects of the invention.
The active hydrogen-containing compound is not particularly limited, and examples thereof include: known polyols such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols, polyesteramide polyols, polythioether polyols, and polyolefin polyols such as polybutadienes. Two or more of these high molecular weight compounds may be used in combination.
Here, the polyurethane emulsion of the present embodiment is preferably at least one selected from the group consisting of a polyether polyurethane emulsion, a polyester polyurethane emulsion, a polyether carbonate polyurethane emulsion, and a polycarbonate polyurethane emulsion.
The polyester-based polyurethane emulsion of the present embodiment is not particularly limited, and can be produced, for example, by using a polyester polyol (for example, a polymer obtained by dehydrating and condensing a polybasic acid and a polyhydric alcohol, a polymer obtained by ring-opening polymerization of a lactone such as e-caprolactone, α -methyl-e-caprolactone or the like, a reaction product of a hydroxycarboxylic acid and a polyhydric alcohol or the like) in the above production method.
The polycarbonate-based polyurethane emulsion of the present embodiment is not limited at all, and can be produced, for example, by using polycarbonate polyol { for example, a reaction product of a diol such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, or hexylene glycol, and a diaryl carbonate (for example, diphenyl carbonate), a cyclic carbonate (for example, propylene carbonate) } in the above production method.
The polyether urethane emulsion of the present embodiment is not limited at all, and can be produced by using polyether polyol { for example, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, etc. } in the above production method.
The polyether carbonate urethane emulsion of the present embodiment is not limited as long as the urethane resin contains both a carbonate group and an ether group (containing … -O-CO-O- [ R-O-R' ] -O-CO-O- … skeleton), and can be produced, for example, by using a polyether polyol and a polycarbonate polyol in combination in the production method.
In the above methods (I) to (III), an emulsifier may be further used within a range not to impair the effects of the invention. Examples of such emulsifiers include: nonionic emulsifiers such as polyoxyethylene nonylphenyl 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, alkylbenzene sulfonates, alkyl sulfosuccinates, naphthalene sulfonates, sodium alkylsulfonates, and sodium alkyldiphenylether sulfonates; nonionic-anionic emulsifiers such as polyoxyethylene alkyl sulfate and polyoxyethylene alkylphenyl sulfate; and the like.
The conductive foam of the present invention can be produced by using a polyurethane emulsion as a raw material thereof (by including a polyurethane resin in the foam), and thus, the conductive foam formed by blending a conductive material with the polyurethane emulsion can have various properties such as appearance, moldability, conductivity, hardness, suppression of falling-off of the conductive material, and hydrolysis resistance at a high level.
(2) Acrylic emulsion
The method for producing the acrylic emulsion (aqueous dispersion of acrylic resin) that can be used in the present invention is not particularly limited, and can be obtained by copolymerizing a mixture of other polymerizable monomers copolymerizable with (meth) acrylic acid ester monomers, for example, as an essential polymerizable monomer component, and further, as necessary, another polymerizable monomer copolymerizable with these monomers in the presence of a polymerization initiator, an emulsifier as necessary, and a dispersion stabilizer. Two or more types of acrylic emulsions may be used in combination. The glass transition temperature of the acrylic emulsion is preferably in the range of 0 ℃ to 80 ℃.
As polymerizable monomers that can be used in the preparation of the acrylic emulsion, there can be exemplified: (meth) acrylate monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, octadecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, nonyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, tetrahydrodicyclopentadiene (meth) acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate; unsaturated bond-containing monomers having a carboxyl group such as acrylic acid, methacrylic acid, β -carboxyethyl (meth) acrylate, 2- (meth) acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, half ester of itaconic acid, half ester of maleic acid, maleic anhydride, and itaconic anhydride; glycidyl group-containing polymerizable monomers such as glycidyl (meth) acrylate and allyl 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, trimethylolpropane tri (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, diallyl phthalate, divinylbenzene, allyl (meth) acrylate, and the like.
When an emulsifier is used for preparing the acrylic emulsion, a known emulsifier can be used.
These emulsions may contain a surfactant (emulsifier) for resin dispersion, etc. The surfactant for resin dispersion means a surfactant for dispersing a water-dispersible resin (unlike an anionic surfactant, may not have an effect as a foaming agent). Such a surfactant may be appropriately selected depending on the selected water-dispersible resin.
Dispersing media
In the present invention, water is an essential component as a dispersion medium of the emulsion composition, but a mixture of water and a water-soluble solvent may be used. Examples of the water-soluble solvent include alcohols such as methanol, ethanol, isopropanol, ethyl carbitol, ethyl cellosolve, and butyl cellosolve; and polar solvents such as N-methylpyrrolidone, and the like, and one kind or a mixture of two or more kinds thereof may be used.
1-1-2. conductive material
The conductive material described below can be directly blended as a powder, but is preferably used in the form of an aqueous dispersion obtained by dispersing a powder in water. By forming the aqueous dispersion, it is easy to uniformly disperse in the composition when added to the emulsion composition.
1-1-2-1. spherical graphite
The spherical graphite has high conductivity, and contributes to the conductive foam of the present invention. The graphite usable in the present invention is spherical. In the present invention, "spherical" is intended to mean not only a spherical shape but also a shape in which the spherical shape is slightly deformed into a disk shape, a shape in which the surface is not smooth and has an appearance such as a cabbage in which layers are overlapped on the surface, and the like, which are not generally regarded as a spherical shape. However, the crystal form of natural graphite is a hexagonal crystal form, and in general, untreated graphite is different from the hexagonal crystal form because it is scaly. That is, in the present invention, it is necessary to use graphite that has been at least spheroidized. The spheroidizing treatment also includes a simple treatment method such as pulverizing scaly natural graphite, but is preferably a treatment method in which a pressure is applied isotropically to graphite. This treatment can be performed by a method of isotropically applying pressure to graphite using a pressure medium such as a gas (an inert gas such as argon) or a liquid (e.g., water). The hot isotropic pressure treatment and the cold isotropic pressure treatment are classified according to the presence or absence of heating. Any of them may be used. By performing this treatment, spherical graphite having a spherical outer shape and reduced inner hollow walls (gaps between scale layers) and having high isotropy in electrical conductivity is obtained.
The spheroidized spherical graphite is defined as spherical graphite having a structure in which basal planes are folded when viewed from the other side. Here, the "basal plane" refers to a plane orthogonal to the C axis of the graphite crystal (hexagonal system). That is, the spherical graphite of the present invention is preferably spherical graphite in which the crystal system of natural graphite is strained. The strain can be grasped by measuring an X-ray diffraction pattern and confirming whether or not there is an expansion of a peak or a shift in a 2 θ value as compared with natural graphite. In addition, the conductive foam containing spherical graphite confirmation, in addition to through the measurement of the raw material graphite X-ray diffraction pattern to confirm, can also be through the conductive foam arbitrary two or more cross sections were observed under a microscope, the graphite corresponding to the shape of the circular. Specifically, when the surfaces of the conductive foam orthogonal to each other are observed under a microscope and the shape of the graphite-corresponding portion in any image is a circular shape having a ratio of short diameter/long diameter of less than 1/2, the conductive foam can be said to contain spherical graphite.
Examples of the spherical graphite usable in the present invention include: spherical graphite obtained by spheroidizing non-spherical graphite fine powder such as flake graphite by an impact method in high-speed air using a hybrid system; and spherical carbon particles obtained by crystallizing petroleum or petroleum pitch; and powders obtained by curing a thermosetting resin and graphitizing the powder. The former is preferable from the viewpoint of isotropic conductivity.
As the spherical graphite, commercially available products can be suitably used, and specific examples thereof include spherical graphite manufactured by japan black lead industries, ltd. The average particle diameter (median diameter) of the spherical graphite used in the present invention is about 1 μm to about 100. mu.m. Preferably 5 to 80 μm, more preferably 8 to 80 μm. In order to ensure the conductivity and the flexibility of the conductive foam, the other tends to be reduced when one is improved, but when spherical graphite having a small average particle diameter is used, the properties of both can be improved in a well-balanced manner, which is preferable. The preferred average particle size range varies depending on the final shape of the conductive foam, but is preferably from about 5 μm to about 30 μm, more preferably from 10 μm to 20 μm, in the form of a sheet having a thickness of from about 0.1mm to about 1.0 mm.
1-1-2-2. conductive filler
The conductive filler (conductive filler other than spherical graphite having a structure obtained by folding a base surface) to be further added to the spherical graphite used in the production of 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, and a general metal material, conductive carbon, ion conductive material, and the like can be exemplified, but conductive carbon is preferable. Examples of the conductive carbon include nano-sized conductive carbons such as carbon nanotubes, carbon black (e.g., acetylene black), and graphene; carbon, carbon fiber, graphite (graphite other than spherical graphite having a structure obtained by folding a basal plane), activated carbon, and the like. These conductive carbons are effective in that the specific gravity is low and the weight of the conductive foam is not easily increased even if the amount of the conductive carbon added is increased, as compared with the metal filler having the same size. In addition, the conductive carbon is more flexible than the metal filler, i.e., has low elasticity, and therefore the conductive foam can be made flexible, i.e., has low hardness. Further, it is excellent in terms of low cost. These conductive materials may be used alone or in combination of two or more.
The conductive filler preferably has an average length (average diameter in the case of a substantially spherical shape) of 1nm to 100nm, more preferably 5nm to 50 nm. By using such a conductive filler, the filler can be dispersed between the spherical graphite particles, and the conductivity of the conductive foam is improved.
The aspect ratio of the conductive filler is preferably 5 or less, more preferably 3 or less, and still more preferably 2 or less. If the aspect ratio is more than 5, the conductive properties of the conductive foam may exhibit anisotropy.
Here, the value of the "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 the conductive filler with SEM, measuring at least 100 particles by observation, and calculating the average value thereof. More specifically, the "average diameter" is an average value of area diameters derived by calculating a cross-sectional area of a particle based on a vertical cross-section near the center in the longitudinal direction of the particle photographed by SEM observation, and calculating the diameter of a circle having the same area as the cross-sectional area. The average diameter and average length are determined averages of 100 particles.
1-1-3. additives
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 that can mix a gas into a raw material mixture and stabilize bubbles, and an anionic foaming agent can be exemplified.
Specific examples of the anionic surfactant are not particularly limited, and include: sodium laurate, sodium myristate, sodium stearate, ammonium stearate, sodium oleate, potassium oleate soap, potassium castor oil soap, potassium coconut oil soap, sodium lauroyl sarcosinate, sodium myristoyl sarcosinate, sodium oleyl sarcosinate, sodium cocoyl alcohol sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium alkyl sulfosuccinate, sodium dialkyl sulfosuccinate, sodium lauryl sulfoacetate, sodium alkyl benzene sulfonate, sodium alpha-olefin sulfonate, and the like.
Here, the anionic surfactant used in the present embodiment is easily dispersed in the emulsion composition, and therefore HLB is preferably 10 or more, more preferably 20 or more, and particularly preferably 30 or more.
·HLB
In the present invention, the HLB value is a hydrophilic-hydrophobic balance (HLB) value, and is obtained by the mini-field method. The method for obtaining HLB by the microtia method is described in "neosurfactant entry" pages 195 to 196 and 3/20/1957, published by Maki bookstores, and 2 people such as microtia, and "synthesis of surfactant and use thereof" pages 492 to 502, and can be obtained by using HLB ═ 10 (inorganic value/organic value). Here, the values of inorganic and organic properties were calculated from the values shown in the above "New surfactant entry" tables 3,3 and 11.
In addition, as the foaming agent of the present invention, an amphoteric surfactant may be used. In particular, when an anionic surfactant and an amphoteric surfactant are used in combination, the charge of the hydrophilic groups of the molecules of the anionic surfactant is repelled, and the electrically neutral amphoteric surfactant enters between the molecules of the anionic surfactant between a certain distance where the molecules of the anionic surfactant are held, whereby the air bubbles can be stabilized more and the size of the air bubbles can be reduced. Therefore, the interlayer peel 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 amphoteric surfactants such as amino acid type, betaine type, and amine oxide type can be exemplified, and betaine type amphoteric surfactants are preferable because the above effects are more excellent.
Examples of the amino acid type amphoteric surfactant include N-alkyl amino acids, N-alkenyl amino acids, and salts thereof. The N-alkyl amino acid or N-alkenyl amino acid has a structure in which an alkyl group or an alkenyl group is bonded to a nitrogen atom, and one or two groups represented by "-R-COOH" (wherein R represents a divalent hydrocarbon group, preferably an alkylene group, and particularly preferably 1 to 2 carbon atoms) are bonded thereto. In compounds to which an "-R-COOH" is bonded, a hydrogen atom is also bonded to the nitrogen atom. A compound having one "-R-COOH" group is referred to as a monomer, and a compound having two groups is referred to as a dimer. As the amphoteric surfactant of the present invention, both of these monomers and dimers can be used. In the N-alkyl amino acid or N-alkenyl amino acid, the alkyl group or alkenyl group may be a straight chain or a branched chain. Specifically, examples of the amino acid type amphoteric surfactant include: sodium lauryl diamino ethyl glycinate, sodium trimethyl glycinate, sodium cocoyl taurate, sodium cocoyl methyl taurate, sodium lauroyl glutamate, potassium lauroyl glutamate, lauroyl methyl-beta-alanine, etc.
As betaine-type amphoteric surfactantSex agents, present for example: alkyl betaines, imidazolinesBetaines, carbonylbetaines, amidocarbonylbetaines, amidobetaines, alkylamidobetaines, sulfobetaines, amidosulfobetaines, phosphobetaines, and the like. Specifically, examples of the betaine amphoteric surfactant include: 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 dimethylamino hydroxysultaine, isostearic acid amidopropyl dimethylamino hydroxysultaine, isostearic acid amidoethyl diethylaminohydroxysultaine, isostearic acid amidopropyl diethylaminohydroxysultaine, N-lauryl-N, N-dimethylammonium-N-propyl sultaine, N-lauryl-N, N-dimethylammonium-N- (2-hydroxypropyl) sulfobetaine, N-lauryl-N, N-dimethyl-N- (2-hydroxy-1-sulfopropyl) ammonium sulfobetaine, lauryl hydroxysulfobetaine, dodecylaminomethyldimethylsulfopropyl betaine, octadecylaminomethyldimethylsulfopropyl betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolineBetaine (2-lauryl-N-carboxymethyl-N-hydroxyethyl imidazoline)Betaine, 2-stearyl-N-carboxymethyl-N-hydroxyethyl imidazoline
Examples of the amine oxide type amphoteric surfactant include lauryl dimethylamine-N-oxide and oleyl dimethylamine-N-oxide.
Among the above amphoteric surfactants, betaine type amphoteric surfactants are preferably used, and among the betaine types, alkylbetaines and imidazolines are particularly preferable
Further, as the foaming agent of the present invention, a nonionic surfactant can be used. The nonionic surfactant is not particularly limited, and examples thereof include nonionic surfactants such as fatty acid alkanolamides, ethers, and esters.
1-1-3-2. crosslinking agent
The crosslinking agent used in the production of the conductive foam of the present invention is not particularly limited, and may be added in a desired amount according to the use or the like, and the specific crosslinking method may be selected according to the kind of the water-dispersible resin. As the crosslinking agent, a known crosslinking agent can be used, and an epoxy crosslinking agent, a melamine crosslinking agent, an isocyanate crosslinking agent, a carbodiimide crosslinking agent, a melamine crosslinking agent, a carbodiimide crosslinking agent, a silicone crosslinking agent,
1-1-3-3. others
Other additives may be used, and known additives such as thickeners, bubble nucleating agents, plasticizers, lubricants, colorants, antioxidants, fillers, reinforcing agents, flame retardants, antistatic agents, and surface treatment agents may be used.
1-2. Process for producing conductive foam
The method for producing a conductive foam of the present invention comprises: a step of foaming (mechanically foaming) a raw material composition, which is an emulsion composition in which a conductive material is dispersed, by a mechanical foaming method; and a step of curing the foamed raw material composition.
According to this method, the conductive foam of the present invention can be stably produced.
1-2-1. Components of the raw material composition
The raw material composition used in the method for producing a conductive foam of the present invention contains at least a conductive material containing spherical graphite having a structure obtained by folding a base surface, and the emulsion composition. In addition, a polyfunctional compound, i.e., a crosslinking agent or a foaming agent, which contributes to curing of the resin component of the emulsion may be contained. Preferred examples of the foaming agent and the crosslinking agent are the same as the preferred examples of the components described above for the conductive foam.
In order to prepare the raw material composition, it is preferable to further contain a solvent. Examples of the solvent that can be used include water and organic solvents (for example, alcohols such as methanol, ethanol, isopropanol, ethyl carbitol, ethyl cellosolve, and butyl cellosolve; and one or two or more kinds of polar solvents such as N-methylpyrrolidone). When an organic solvent is used, the viscosity of the raw material composition is lower than that in the case of using water, and bubbles may be defoamed. Therefore, although it is preferable not to contain an organic solvent, it may be contained in a proportion to such an extent that the bubble formation stability is not affected (for example, the viscosity is not lowered to such an extent that the moldability is impaired).
1-2-2 preparation method of raw material composition
The raw material composition is preferably prepared by preparing an aqueous emulsion of the resin and an aqueous dispersion of the conductive material such as the spherical graphite separately and mixing them, because the raw material composition can be prepared without causing aggregation or the like of the conductive material such as the spherical graphite. 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 about 90% by mass. When 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 into the resin is further improved when the conductive material is mixed with the aqueous emulsion of the resin, which is preferable. In particular, when at least one of surfactants having good wettability is used as a foaming agent, the dispersion stability of the conductive material in the resin is further improved, which is preferable. Among these, at least one selected from the anionic surfactants having good bubble formation stability and good wettability is preferably used, and at least one selected from the nonionic surfactants having good wettability is more preferably used. For example, the aqueous dispersion of the conductive material may be prepared by mixing the conductive material in an aqueous solution or an aqueous suspension of a surfactant (foaming agent) having a solid content of about 20% by mass to about 60% by mass. In the case of using other additives such as a crosslinking agent and other heat conductive materials, it is preferable to prepare a raw material composition by adding other additives to the aqueous dispersion of the electrically conductive material and mixing the resulting mixture with an aqueous emulsion of a resin.
1-2-3. composition and Properties of the raw Material composition
The total solid content concentration of the raw material composition is about 40 to about 80 mass%, preferably 50 to 70 mass%. In general, the total mass of the resin (and the crosslinking agent added as needed) and the conductive material is 95% or more and the total mass of other additives such as a foaming agent (specifically, a surfactant) is 5% or less of the total solid content of the raw material composition. However, the preferable mass ratio of each material in the solid content also varies depending on the kind of the material used, and the like. Further, in order to stably form bubbles in the following foaming step, the viscosity of the raw material composition is suitably from about 10000 to about 200000mPa · s.
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 foaming) method is a method of foaming an emulsion composition by mixing a gas such as air in the atmosphere into the emulsion composition by stirring the raw material composition with a stirring blade or the like. 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 foaming machine, or the like can be used. In the present invention, the foaming step is performed by a mechanical foaming method, whereby the formation of closed cells is suppressed, the formation of open cells is dominant, the increase in density of the cured foam is prevented, and a porous body having high flexibility is obtained.
The stirring conditions are not particularly limited, and the stirring time is usually 1 minute to 10 minutes, preferably 2 minutes to 6 minutes. The stirring speed during the mixing is preferably 200rpm or more (more preferably 500rpm or more) in order to reduce bubbles, and is preferably 2000rpm or less (more preferably 800rpm or less) in order to smoothly discharge the foamed material from the foaming machine. The temperature condition in the foaming step is not particularly limited, and is usually room temperature. When the curing step described later is performed simultaneously with the foaming, heating may be performed to cause the reaction of the functional group.
1-2-5. curing procedure
In the curing step, the resin component is cured. By this step, the raw material composition becomes a structure in the form of a conductive foam. The curing step is performed after the foaming step. Heating is preferably performed in order to evaporate the solvent (water) in the raw material composition and in order to cause the crosslinking reaction to proceed. The heating temperature and the heating time may be a temperature and a time at which the raw material can be crosslinked (cured), and may be set to, for example, 80 ℃ to 150 ℃ (particularly preferably about 120 ℃) for about 1 hour.
The curing step may be performed as one step of molding for forming the obtained conductive foam into a desired shape. For example, in the production of sheet-like conductive foam, the curing step can be performed as one step of a casting method. Specifically, the raw material composition subjected to the "(4) foaming step" may be cast to a desired thickness on the surface of a substrate, heated to evaporate the solvent (water), and cured by a crosslinking reaction to produce a sheet on the surface of the substrate.
1-2-6. forming method
The conductive foam of the present invention can be molded into a desired shape by various conventionally known methods. The appropriate forming method can be selected according to the desired final shape. In the case of producing a sheet-like conductive foam, a casting method can be used. The treatment of introducing bubbles (foaming treatment) is preferably performed before the molding process. In the embodiment in which 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 of the present invention has not only conductivity and conductivity retention (conductive material falling resistance), but also excellent cushioning properties (flexibility), and therefore has excellent followability to mating members, and can reduce the reaction force (restoring force) of the conductive foam itself. Therefore, when the conductive member is sandwiched between members, the conductive member can be used without causing a failure or damage such as disconnection of a wiring to a mating member (an IC chip, a wiring of a substrate, warpage of a substrate, or the like) while securing sufficient conductivity. In particular, in recent years, electronic devices have become thinner, lighter, and smaller, and the space inside the electronic devices tends to further disappear, and the internal structure has become complicated, and there has been a further increased demand for a conductive foam that is thinner and has excellent cushioning properties (flexibility) as compared with the conventional ones. The present invention is not limited to the application method and the use environment, and may be applied to various uses (for example, electronic components, grounding materials in devices, shielding materials, buffer materials, protective materials, interlayer materials of substrates, and the like) other than the sandwiching of the members. In addition, in the conductive foam of the present invention, it is possible to obtain a conductive foam having excellent characteristics without containing polysiloxane, and in the case of not containing polysiloxane, it is possible to use the conductive foam without fear of contamination of electronic parts, devices and the like with polysiloxane.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：水性聚合物组合物