JP2021183701A - Cell porous body and method for producing the same - Google Patents

Abstract

To provide a new cell porous body available as a heat-dissipation member and a method for producing the same.SOLUTION: There are provided a cell porous body containing a matrix resin and a thermally conductive material dispersed into the matrix resin, and containing at least spheroidal graphite as the thermally conductive material; and a method for producing the cell porous body which includes: a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in its side chain, a foaming agent and spheroidal graphite; and a step of reacting functional groups of the resin and/or reacting the functional group with a functional group of a polyfunctional crosslinking agent to cure the resultant substance, where the method includes performing the foaming step and the curing step at the same time and/or performing the curing step after the foaming step.SELECTED DRAWING: None

Description

INDUSTRIAL APPLICABILITY The present invention is a bubble porous body useful as a heat-dissipating member of electronic / electrical equipment products (electronic products), particularly thin / high-performance smartphones, personal computers, televisions and other electronic / electrical equipment products having a complicated internal structure. , And its manufacturing method.

Electronic and electrical equipment products (electronic products), especially products such as smartphones, personal computers, and televisions, are becoming thinner and more sophisticated year by year. On the other hand, as the data processing speed increases, the amount of heat generated increases and the internal structure is complicated, so that heat tends to be trapped. The generated heat may cause problems such as shortening the life of electronic components, deformation of the housing due to thermal expansion, and low-temperature burns. Therefore, a member containing a heat conductive substance is arranged inside the electronic / electrical equipment product for the purpose of heat dissipation. Previously, a member made of a gel such as silicone or acrylic containing a heat conductive substance was used as the member, but the member made of the gel has high heat conductivity but high hardness, and when compressed. Due to the high stress of the material, it lacks flexibility and it is difficult to place it in an electronic / electrical device having a complicated internal structure in recent years so as to follow the internal structure.

Patent Document 1 discloses an effervescent composition that can be used for manufacturing a heat radiating sheet for electronic devices and the like. However, Patent Document 1 does not describe the problem and its solution from the viewpoint of shape followability, that is, flexibility. Further, since this effervescent composition contains a silicone-based surfactant as an essential component, the low-molecular-weight siloxane component is released and deteriorates when the heat-dissipating sheet produced from the composition is exposed to a high temperature. There is a problem and it lacks heat resistance.

Japanese Unexamined Patent Publication No. 2016-65196

The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel porous bubble body that can be used as a heat radiating member and a method for producing the same.
Another object of the present invention is to provide a bubble porous body having appropriate flexibility and followability to the shape of other members without impairing heat dissipation, and a method for producing the same.

As a result of studies for solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using spheroidal graphite as a heat conductive material, and have completed the present invention. The means for solving the above problems are as follows.
[1] A bubble porous body containing a matrix resin and a heat conductive material dispersed in the matrix resin, wherein the heat conductive material contains at least spheroidal graphite.
[2] The bubble porous body of [1], wherein the spheroidal graphite has a structure in which the basal surface is folded.
[3] The bubble porous body according to [1] or [2], wherein the matrix resin is an acrylic resin.
[4] The bubble porous body according to any one of [1] to [3], wherein the heat conductive material further contains a metal oxide.
[5] The bubble porous body according to any one of [1] to [4], which contains 40 to 60% by mass of the heat conductive material based on the total mass of the bubble porous body.
[6] The bubble porous body according to any one of [1] to [5], wherein the heat conductive material contains a metal oxide and a spheroidal graphite in a blending ratio (mass ratio) of 0: 10 to 5: 5.
[7] The bubble porous body according to any one of [1] to [6], which is a continuous bubble porous body.
[8] The 25% compressive load measured in accordance with JIS K 6254 is 20 kPa or less, and the thermal conductivity measured by the probe method using QTM-500 manufactured by Kyoto Denshi Kogyo Co., Ltd. is 0.3 W / m. -A bubble porous body according to any one of [1] to [7], which is K or more.
[9] The air bubble porous body according to any one of [1] to [8], which is used as a heat radiating material for electronic products.
[10] A foaming step of mechanically foaming a liquid composition containing a resin having a functional group in the side chain, a foaming agent and spheroidal graphite, and reacting the functional groups of the resin with each other and / or having polyfunctionality. Including the step of curing by reacting with the functional group of the cross-linking agent.
A method for producing a foamed porous body, in which a foaming step and a curing step are carried out at the same time, and / or a curing step is carried out after the foaming step.
[11] The method for producing [10], wherein the foaming agent has a pH in the neutral to alkaline range of the liquid composition, and the foaming agent contains at least one anionic surfactant.
[12] The method for producing [10] or [11], wherein the bubble porous body is any of the bubble porous bodies of [1] to [9].

According to the present invention, it is possible to provide a novel air bubble porous body that can be used as a heat radiating member and a method for producing the same.
Further, according to the present invention, it is possible to provide a bubble porous body having appropriate flexibility and followability to the shape of other members without impairing heat dissipation, and a method for producing the same.

Hereinafter, the bubble porous body of the present invention and the method for producing the same will be described in detail. In the present specification, "~" means a range including numerical values before and after it.

[Pous medium of bubbles]
The bubble porous body of the present invention is characterized by containing a matrix resin and a heat conductive material dispersed in the matrix resin, and the heat conductive material contains at least spheroidal graphite.
(1) Spheroidal graphite Spheroidal graphite has high thermal conductivity and contributes to the development and / or improvement of heat dissipation of the bubble porous body of the present invention. The graphite that can be used in the present invention is spherical. In the present invention, "spherical" does not mean only a true sphere, but a shape in which the true sphere is slightly deformed like a disk, a cabbage-like appearance in which the surface is not uniform and layers are layered on the surface. In general, it is intended to include shapes that are not grasped as true spherical shapes, such as shapes having. However, the crystal form of natural graphite is hexagonal, and in general, untreated graphite is scaly, so it is distinguished from this. That is, in the present invention, it is necessary to use at least spheroidized graphite. The spheroidizing treatment includes a simple treatment method such as pulverizing scaly natural graphite, but preferably, a treatment method in which pressure is isotropically applied to the graphite is adopted. The treatment can be carried out by a method of isotropically applying pressure to graphite using a pressurized medium such as a gas (an inert gas such as argon) or a liquid (for example, water). Depending on the presence or absence of heating, it is distinguished as hot isotropic pressurization treatment and cold isotropic pressurization treatment. Either may be used. By performing this treatment, highly thermally conductive spheroidal graphite having a spherical outer shape and reduced internal empty walls (scale layers) can be obtained.

The spheroidized spheroidal graphite is specified from another side surface as spheroidal graphite having a structure in which the basal surface is folded. Here, the "basal plane" means a plane orthogonal to the C axis of the graphite crystal (hexagonal system). That is, the spheroidal graphite of the present invention is preferably one in which the crystal system of natural graphite is distorted. This strain can be grasped by measuring the X-ray diffraction pattern and comparing it with natural graphite to confirm the presence or absence of broadening of the peak or the presence or absence of a shift in the 2θ value. In addition, to confirm whether or not the bubble porous body contains spheroidal graphite, in addition to confirming by measuring the X-ray diffraction pattern of the raw material graphite, any two or more cross sections of the bubble porous body are observed under a microscope. It can also be confirmed by whether or not the shape of the graphite-corresponding part is circular. Specifically, the planes orthogonal to each other of the bubble porous body are observed under a microscope, and if the shape of the graphite-equivalent part in any image is a circular shape with a minor axis / major axis ratio of less than 1/2, It can be said that the bubble porous contains spheroidal graphite.

Examples of spheroidal graphite that can be used in the present invention include spheroidized non-spherical graphite fine particles such as scaly graphite by a high-speed airflow impact method using a hybridization system; and petroleum-based or petroleum-based Examples thereof include spherical carbon particles obtained by crystallizing the pitch and those obtained by curing a thermosetting resin to obtain a powder and graphitizing the powder. The former is preferable from the viewpoint of thermal conductivity.

Commercially available products can also be preferably used as the spheroidal graphite, and specific examples thereof include spheroidized graphite manufactured by Nippon Graphite Industry Co., Ltd. The average particle size (median diameter) of the spheroidal graphite used in the present invention is about 1 to 100 μm. When one is improved, the other tends to decrease in terms of ensuring heat dissipation and ensuring flexibility, but it is preferable to use spheroidal graphite having a relatively small average particle size because both properties can be improved in a well-balanced manner. The preferable average particle size range varies depending on the final shape of the bubble porous body, but in the sheet-like form having a thickness of about 0.1 to 1.0 mm, it is preferably about 5 to 30 μm, preferably 5 μm to 15 μm. Is more preferable.

When graphite having an anisotropic shape (rectangular shape, flake shape) other than the spherical shape is used, the heat dissipation property of the bubble porous body also becomes anisotropic, and the improvement of the heat dissipation property by adding graphite becomes insufficient. However, an embodiment in which graphite having an anisotropic shape as an impurity is unavoidably or arbitrarily contained in a small proportion at least to the extent that the effect of the present invention can be obtained is not excluded from the present invention. The spheroidal graphite is preferably 90% by mass or more, preferably 95% by mass or more, and more preferably 99% by mass or more of the total graphite.

(2) Matrix resin The air bubble porous body of the present invention contains a matrix resin. The matrix resin is the main component of the bubble porous body of the present invention. One aspect of the matrix resin is a resin having a three-dimensional network structure in which a plurality of linear polymer chains are crosslinked by a cross-linking agent or a functional group of the polymer chains themselves.

The type of the matrix resin is not particularly limited, and any resin that can form a porous bubble structure, more specifically, a resin that can form a porous structure by foaming treatment can be used. Examples of resins that can be used include acrylic resins; urethane resins; polyolefin resins such as polyethylene and polypropylene; polyvinyl chloride resins; polystyrene resins; amino resins such as melamine resins and urea resins; phenolic resins; In the above embodiment, the matrix resin has a cross-linked structure formed by a cross-linking agent added separately and / or by a functional group possessed by itself. Acrylic resin and urethane resin are preferable because they can stably form a porous structure and can form a flexible porous body when used in combination with graphite. Further, depending on the application, it may be exposed to a high temperature, so a resin having high heat resistance is preferable, and from that viewpoint, an acrylic resin is preferable. In the aspect where the matrix resin is an acrylic resin, even if it is exposed to a high temperature of 150 ° C., heat dissipation is maintained and there is no remarkable thermal deterioration.

Examples of the polymerizable monomer of the acrylic resin include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Heptyl acrylate, (meth) octyl acrylate, octadecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, nonyl (meth) acrylate, dodecyl (meth) acrylate, (Meta) Acrylate-based monomers such as stearyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate; Acrylic acid, methacrylic acid, β-carboxyethyl (meth) acrylate, 2- (meth) acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, maleic acid half ester, maleic anhydride, Unsaturated bond-containing monomer having a carboxyl group such as itaconic anhydride; glycidyl group-containing polymerizable monomer such as glycidyl (meth) acrylate and allyl glycidyl ether; 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl Hydroxyl-containing polymerizable monomers such as (meth) acrylate, polyethylene glycol mono (meth) acrylate, and glycerol mono (meth) acrylate; ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neo. Includes pentyl glycol di (meth) acrylate, trimethyl propantri (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, diallyl phthalate, divinylbenzene, allyl (meth) acrylate and the like.

The main component of the matrix resin is more preferably an acrylic resin having a crosslinked structure. Examples of acrylic resins having a crosslinked structure include a (meth) acrylic acid ester capable of introducing a functional group into the side chain alone, or one or more other monomers capable of introducing a functional group into the side chain (eg, itacone). Includes an acrylic resin that has been copolymerized with (acid, acrylic nitrile) at the same time or after polymerization to promote a cross-linking reaction to form a cross-linked structure. It is preferable to once obtain an acrylic resin having a functional group in the side chain and then form a crosslinked structure. The crosslinked structure can be formed by a reaction between the functional groups of the side chain portion of the resin and / or by a reaction of the functional group with a separately added crosslinking agent. The acrylic resin preferably has a functional group that contributes to forming a crosslinked structure, and examples thereof include a hydroxyl group, a carboxyl group, a nitrile group, a glycidyl group, a sulfone group and the like.

Further, as the cross-linking agent, a conventionally known cross-linking agent can be used, and an example thereof is a polyfunctional compound having two or more functionalities (in the present invention, the "polyfunctional compound" is two or more functional groups. It means a compound having. The functional groups contained in one molecule may be the same or different.). Specifically, crude hexamethylene diisocyanate (crude HDI) which is an aliphatic isocyanate or hexamethylene diisocyanate (HDI) obtained by purifying the crude HDI and HDI isocyanurate and isophoron diisocyanate (IPDI) which are trimerics of HDI. Isocyanate-based cross-linking agents such as block-type polyisocyanates in which the isocyanate groups of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and toluene diisocyanate (TDI), which are aromatic isocyanates, are modified with a blocking agent, epoxy-based cross-linking agents, and melamine-based cross-linking agents. An appropriate amount of an agent, a carbodiimide-based cross-linking agent, an oxazoline-based cross-linking agent, or the like can be used depending on the type of functional group contained in the resin compounding system to be used and the amount of the functional group. An example of the cross-linked structure is a cross-linked structure formed by the reaction of any one or more of the above functional groups of the acrylic resin in the side chain with the diisocyanate group of the cross-linking agent.

(3) Additives The bubble porous body of the present invention may contain other additives in addition to the above-mentioned matrix resin and spheroidal graphite.
An example of an additive is a thermally conductive material other than graphite. By adding other heat conductive materials together with spheroidal graphite, heat dissipation can be further enhanced. Examples of other thermally conductive materials include metal nitrides such as boron nitride and aluminum nitride; metal oxides such as aluminum oxide and magnesium oxide; clay minerals such as talc. The thermal conductivity of the heat conductive material used in combination is preferably 30 W / m · K or more. Further, among the heat conductive materials, there is a material having a high hardness, and if it is used, the flexibility of the bubble porous body of the present invention may be lost. Therefore, it is preferable to use a heat conductive material having a low hardness. Specifically, it is preferable to use a material having a Mohs hardness of 9 or less, more preferably a Mohs hardness of 6 or less. An example of a preferred embodiment from the viewpoint of heat dissipation and flexibility is an embodiment in which the heat conductive material contains a metal oxide having a Mohs hardness in the above range together with spheroidal graphite.

Other examples of additives include one or more of the surfactants. The surfactant contributes to the stable formation of bubbles in the process of foaming treatment. That is, it functions as a foaming agent. It also contributes to the stable dispersion of spheroidal graphite in the matrix resin. In particular, it is preferable to use a surfactant having excellent wettability with respect to spheroidal graphite because high dispersibility of the spheroidal graphite with respect to the matrix resin can be ensured. One or more selected from conventionally known anionic surfactants, nonionic surfactants, and amphoteric surfactants can be used. Examples of surfactants with excellent bubble formation stability and wettability include hydrophilic sulfonates such as sulfosuccinates (eg, sodium dialkyl sulfosuccinate succinate), alkylbenzene sulfonates, and polyoxyethylene alkyl ether sulfates. Includes anionic surfactants, including. Further, examples of the surfactant having excellent wettability include a nonionic surfactant having a polyoxyalkylene chain such as polyoxyethylene alkyl ether and polyoxyethylene fatty acid ester. In the present invention, one or more of the anionic surfactants having excellent bubble formation stability and wettability are used, or one or more of the anionic surfactants and a nonionic interface having excellent wettability are used. It is preferable to use one or more of the activators. Further, one or more amphoteric tenside agents such as amino acid type, betaine type and amine oxide type may be used.

The present invention is also characterized in that a bubble porous body having high heat dissipation can be obtained without using a silicone-based surfactant as a surfactant. Silicone-based surfactants are excellent in bubble formation stability, but have a problem that low-molecular-weight siloxanes are liberated when exposed to high temperatures. INDUSTRIAL APPLICABILITY The present invention can provide a silicone-free air bubble porous body having excellent heat resistance by not using a silicone-based surfactant as a surfactant.

Others such as thickeners, bubble nucleating agents, plasticizers, lubricants, colorants, antioxidants, fillers, reinforcing agents, flame retardants, antistatic agents, surface treatment agents, etc., as long as the effects of the present invention are not impaired. Known additive components may be used.
As a result, the glass transition temperature (Tg) of the obtained porous cell is preferably −80 to 0 ° C. More preferably, it is −60 to −10 ° C. This glass transition temperature can be used as an index of hardness of the bubble porous body. If the Tg is too lower than -80 ° C, the bubble porous body becomes soft and the sheet or the like loses its elasticity, and if the Tg is higher than 0 ° C., the bubble porous body becomes hard and loses flexibility.

(4) Composition The ratio of the heat conductive material contained in the bubble porous body of the present invention is preferably 30 to 70% by mass, preferably 35 to 65% by mass, based on the total mass of the bubble porous body. Is more preferable, and 40 to 60% by mass is further preferable. In the embodiment containing only spheroidal graphite as the heat conductive material, the ratio of spheroidal graphite is preferably in the above range. Further, as described above, the present invention may contain a material other than spheroidal graphite, for example, a metal oxide as the heat conductive material, but the mass ratio of the metal oxide to the spheroidal graphite is 0:10. It is preferably ~ 2: 3, and more preferably 0: 10-5: 5.

(5) Form / Properties The form of the bubbles in the bubble porous body of the present invention is not particularly limited, but open cells are preferable. From the viewpoint of heat dissipation and flexibility, open cells are preferable. The "open cell" means a state in which the resin film separating the adjacent bubbles has a through hole and the adjacent bubbles are three-dimensionally communicated with each other. In addition, the "open cell" structure has the property of allowing outside air to pass through to the inside of the foam. In the present invention, it is not required that all the holes communicate with each other strictly, and even if a partially closed hole exists inside, if there is a property that the outside air can pass through as a whole, it is "continuous". It is assumed to have a "bubble" structure. The morphology of the bubbles can be confirmed by observing with an electron microscope.

If the density of the foam porous body of the present invention is a 250~600kg / ^{m 3,} preferably it is excellent in both the heat radiation property and flexibility, if it is 300~500kg / ^{m 3,} more preferred. If the density is lower than the above range, the heat dissipation property becomes low, and it becomes unsuitable for some applications (for example, for the application of the heat dissipation sheet arranged inside the precision electronic / electrical equipment product). Further, when the density exceeds the above range, the flexibility becomes low and the hardness becomes high, and as a result, the shape followability to a complicated structure becomes poor, and depending on the application (for example, a heat dissipation sheet arranged inside a precision electronic / electrical equipment product). Not suitable for use).

According to the present invention, it is possible to provide a bubble porous body exhibiting high heat dissipation and high flexibility. Specifically, it is abbreviated as "25% CLD (Compression-Load-Deflection)", which means the pressure required to compress a 25% thickness, which is a 25% compression load measured in accordance with JIS K 6254. However, it is possible to provide a bubble porous body having a thermal conductivity of 20 kPa or less and a thermal conductivity of 0.3 W / m · K or more measured by a probe method using QTM-500 manufactured by Kyoto Denshi Kogyo Co., Ltd. .. From the viewpoint of flexibility, the lower the 25% compressive load is, the more preferable it is, but from the viewpoint of handleability and the like, the lower limit of the 25% compressive load is generally about 3 kPa. From the viewpoint of heat dissipation, the higher the thermal conductivity is, the more preferable it is, but in general, the upper limit is about 0.7 W / m · K.

One embodiment of the bubble porous body of the present invention is a sheet-shaped bubble porous body having a thickness of about 0.1 to 1 mm. The bubble porous body of the present invention exhibits sufficiently high heat dissipation even in the form of a thin sheet, and by being in the form of a sheet, taking advantage of its flexibility, it is a precision electronic / electrical device having a complicated internal structure. It can be easily placed in the product. The embodiment can be used as a heat radiating sheet that removes heat that tends to be trapped inside a precision electronic / electrical equipment product and reduces heat deterioration of the precision electronic / electrical equipment product.

(6) Molding Method In order to form the bubble porous body of the present invention into a desired shape, it can be molded by various conventionally known methods. An appropriate molding method can be selected according to the desired final shape. When producing a sheet-shaped porous bubble body, a casting method can be used. The bubble introduction treatment (foaming treatment) is preferably performed before the molding process. Further, in the embodiment in which the matrix resin has a crosslinked structure, the formation of the crosslinked structure, that is, the progress of the crosslinking reaction may be performed at the same time as the molding process.

(7) Applications The porous cell of the present invention is suitable for use as a heat radiating material for electronic and electrical equipment products. In addition, it is also useful as a packing material. Especially suitable for heat dissipation materials for precision electronic and electrical equipment products with complicated internal structures. Some heat-dissipating members have poor heat resistance and are arranged without contacting electronic parts that serve as a heat source. Since the bubble porous body of the present invention, particularly the embodiment in which the matrix resin is an acrylic resin is also excellent in heat resistance, it can be used as a contact type heat radiating material that can come into contact with an electronic component as a heat source.

[Manufacturing method of bubble porous body]
The present invention comprises a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in a side chain, a foaming agent and spheroidal graphite, and reacting the functional groups of the resin with each other and / or having polyfunctionality. It also relates to a method for producing a bubble porous body, which comprises a step of curing by reacting with a functional group of a cross-linking agent of the above, and simultaneously performing a foaming step and a curing step, and / or performing a curing step after the foaming step. ..
According to this method, the bubble porous body of the present invention can be stably produced.

(1) Each component of the liquid composition The liquid composition used in the production method of the present invention contains at least a resin having a functional group in the side chain, a foaming agent, and spheroidal graphite. Further, it may contain a polyfunctional compound that contributes to the curing of the resin, that is, a cross-linking agent. Preferred examples of each of the resin having a functional group in the side chain, the foaming agent, the spheroidal graphite, and the cross-linking agent are the same as the preferable examples of each component described in the above-mentioned [bubble porous body].

Further, it is preferable to contain a solvent in order to prepare it as a liquid composition. Examples of solvents that can be used include water, organic solvents (eg, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl cellosolve, polar solvents such as N-methylpyrrolidone, or one of them. 2 or more) are included, but in the present invention, it is preferable to use only water. When an organic solvent is used, the viscosity of the liquid composition becomes higher than when water is used, and the bubble formation stability and moldability are deteriorated. It is preferable that it does not contain an organic solvent, but it may be contained in a proportion that does not affect the moldability (for example, the viscosity does not improve to the extent that the moldability is impaired).

(2) Method for preparing a liquid composition When the liquid composition is prepared by preparing an aqueous emulsion of the resin and an aqueous dispersion of spheroidal graphite and mixing them, the liquid composition does not cause aggregation of the spheroidal graphite. It is preferable because a liquid composition can be prepared. The solid content concentration of the resin in the aqueous emulsion of the resin and the solid content concentration of the spheroidal graphite in the aqueous dispersion of the spheroidal graphite are not particularly limited, but are generally about 50% by mass to 90% by mass. Is. It is preferable to mix a surfactant as a foaming agent in the aqueous dispersion of spheroidal graphite in advance because the dispersion stability of the spheroidal graphite in the resin when mixed with the aqueous emulsion of the resin is further improved. In particular, it is preferable to use at least one of the surfactants having good wettability as the foaming agent because the dispersion stability of the spheroidal graphite in the resin is further improved. Among them, it is preferable to use at least one selected from the above-mentioned anionic surfactant having good bubble formation stability and wettability, and at least one selected from the above-mentioned nonionic surfactant having good wettability is used. Is more preferable. For example, an aqueous dispersion of spheroidal graphite can be prepared by mixing spheroidal graphite with an aqueous solution or an aqueous suspension of a surfactant (foaming agent) having a solid content of about 20 to 60% by mass. In the embodiment in which other additives such as a cross-linking agent and other thermally conductive materials are used, the other additives are added to the aqueous dispersion of spheroidal graphite and mixed with the aqueous emulsion of the resin to form a liquid. It is preferable to prepare the composition.

(3) Composition / Properties of Liquid Composition The total solid content concentration of the liquid composition is about 50 to 90% by mass, preferably 65 to 85% by mass. Generally, the total mass of the resin (and optionally added cross-linking agent) and spheroidal graphite (other optionally added thermally conductive material) in the total solid content of the liquid composition is 95% or more. , The total mass of other additives such as foaming agents (specifically, surfactants) is 5% or less. However, the preferable mass ratio of each material in the solid content also varies depending on the type of material used and the like. The pH of the liquid composition is preferably in the neutral to alkaline range in order to stably form bubbles, and specifically, the pH is 7 or more, preferably 7 to 11. .. More preferably, it is 7-9. The pH of the liquid composition can be set in the above-mentioned preferable range by adjusting the type and amount of the foaming agent added. Further, it is appropriate that the viscosity of the liquid composition is about 1000 to 20000 mPa · s in order to stably form bubbles in the following foaming step.

(4) Foaming Step In the foaming step, mechanical foaming is carried out by stirring the liquid composition to generate bubbles. The mechanical foaming method is a method in which a liquid composition is stirred with a stirring blade or the like, and a gas such as air in the atmosphere is mixed with the emulsion composition to foam the emulsion composition. 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 floss foaming machine and the like can be used. In the present invention, by carrying out the foaming step by the mechanical foaming method, the formation of closed cells is suppressed, the formation of open cells is dominated, the density of the porous body after curing is prevented from increasing, and it is flexible. A highly porous body is obtained.

The stirring conditions are not particularly limited, but the stirring time is usually 1 to 10 minutes, preferably 2 to 6 minutes. Further, the stirring speed in the above mixing is preferably 200 rpm or more (more preferably 500 rpm or more) in order to make the bubbles finer, and preferably 2000 rpm or less (800 rpm or less is preferable) in order to smooth the discharge of the foam from the foaming machine. More preferred). The temperature condition of the foaming process is not particularly limited, but is usually normal temperature. When the curing step described later is carried out at the same time as the foaming, heating may be performed to promote the reaction of the functional group.

(5) Curing Step In the curing step, the resin is cured by reacting the functional groups of the resin with each other and / or reacting with the functional groups of the cross-linking agent. By this step, the liquid composition becomes a structure as a bubble porous body. The curing step is preferably carried out after the foaming step. Heating is preferred to evaporate the solvent (water) in the liquid composition and to allow the cross-linking reaction to proceed. The heating temperature and heating time may be any temperature and time as long as the raw material can be crosslinked (cured), and may be, for example, about 1 hour at 80 to 150 ° C. (particularly about 120 ° C.).

Further, the curing step may be carried out as one step of a molding process for forming the obtained porous bubble body into a desired shape. For example, in the embodiment of producing a sheet-shaped porous bubble body, the curing step may be carried out as one step of the casting method. Specifically, the liquid composition subjected to the "(4) foaming step" is poured on the surface of the substrate to a desired thickness and heated to evaporate the solvent (water) while advancing the crosslinking reaction. It can be cured to produce a sheet on the surface of the substrate. The base material on which the liquid composition is cast is not particularly limited, and is a resin base material (thickness 25 to 50 μm PET film, preferably the surface of which has been mold-released), a metal base material having a thickness of 2 μm to 100 μm, or a tape shape. A long metal base material cut into a tape shape, a laminated base material of a PET film having a thickness of 1 μm to 30 μm cut into a tape shape and an adhesive layer having a thickness of 2 μm to 100 μm, and a long length cut into a tape shape. An airless laminated base material made of an adhesive layer having a concave-convex shape in which the depth of the concave portion laminated on the film is 2 μm to 100 μm and the height of the convex portion is 2 μm to 100 μm can be used.

One embodiment of the manufacturing method of the present invention is
A foaming step of mechanically foaming a liquid composition containing a resin having a functional group in the side chain, a foaming agent and spheroidal graphite, and
After the foaming step, a casting step of casting the liquid composition on the surface of the base material in the form of a sheet, and a casting step.
A sheet-like bubble porous body including a curing step of reacting the functional groups of the resin with each other and / or reacting with a functional group of a polyfunctional cross-linking agent to obtain a sheet after the casting step. It is a manufacturing method of.

Hereinafter, the effects of the bubble porous body of the present invention and the method for producing the same will be specifically described with reference to Examples.

(material)
-Matrix resin material As the matrix resin material 1, an emulsion of acrylic resin (Tg-40 ° C, pH 9, solid content concentration 60% by mass, solvent is water), which is an acrylic nitrile-acrylic acid alkyl ester-itaconic acid copolymer, is prepared. bottom.
As the matrix resin material 2, a urethane resin emulsion (pH 8, solid content concentration 60% by mass, solvent was water) was prepared.
-Foaming agent The following surfactants were prepared as foaming agents.
As the anionic surfactant 1, a mixed solution of ammonium stearate and water (pH 11 and solid content 30%) was prepared.
As the anionic surfactant 2, a mixed solution of sodium alkylsulfosuccinate and water (pH 9.3, solid content 35%) was prepared.
As an amphoteric tenside agent 1, a mixed solution of coconut oil fatty acid amide propyl betaine and water (pH 7.5, solid content 30%) was prepared.
As the amphoteric tenside agent 2, a mixed solution of myristyl betaine and water (pH 6.5, solid content 36%) was prepared.
A mixture of polyoxyethylene alkyl ether and water (pH 6.5, solid content 50%) was prepared as the nonionic surfactant 1.

-Crosslinking agent A hydrophobic HDI isocyanurate (number of functional groups 3.5) was prepared as a crosslinking agent.
・ Thermally conductive material (graphite)
As graphite 1, a spheroidal graphite powder (average particle size 20 μm) manufactured by Nippon Graphite Industry Co., Ltd. was prepared. In this spheroidal graphite, the basal surface of the graphite crystal (hexagonal system) is folded by the spheroidizing treatment.
As graphite 2, a spheroidal graphite powder (average particle size 10 μm) manufactured by Nippon Graphite Industry Co., Ltd., which differs only in particle size from graphite 1, was prepared.
As graphite 3, a spheroidal graphite powder (average particle size 20 μm) manufactured by Ito Graphite Industry Co., Ltd. was prepared.
Unlike graphite 1 and graphite 2, this graphite has a basal surface of graphite crystals (hexagonal system) processed into a spherical shape without folds (scaly graphite processed into a spherical shape).
As graphite 4, a graphite powder (average particle size 20 μm) manufactured by Ito Graphite Industry Co., Ltd. was prepared. This graphite has not been spheroidized, and the basal surface of the graphite crystal (hexagonal system) is not folded (scaly graphite).
・ Thermally conductive material (other than graphite)
As the metal oxide 1, an oxide powder (shape: spherical shape, average particle size 10 μm, Mohs hardness 6) composed of aluminum and magnesium was prepared.
As the metal oxide 2, an oxide powder (shape: spherical shape, average particle size 20 μm, Mohs hardness 6) composed of aluminum and magnesium was prepared.
As the metal oxide 3, a powder of aluminum oxide (shape: spherical shape, average particle size 20 μm, Mohs hardness 9) was prepared.

(Examples 1 and 2)
In the ratio shown in the table below, graphite 1, anionic surfactant 1, anionic surfactant 2, amphoteric surfactant 1, amphoteric surfactant 2, and nonionic surfactant 1 are mixed, and a cross-linking agent is added thereto. Then, an aqueous dispersion of graphite 1 was prepared, and this was added and mixed with 100 parts by mass of the matrix resin material 1 to prepare liquid compositions for Examples 1 and 2, respectively.
The total solid content concentration of this liquid composition, the solid content concentration of the heat conductive material, and the like are as shown in the table below. The pH of this liquid composition was 8.4. The viscosity was also within the viscosity range that could be mechanically foamed.

Each liquid composition prepared above was foamed by a mechanical foaming method (stirring 500 rpm, stirring time 3 minutes, temperature 23 ° C.), and then the liquid composition was applied to the surface of the PET film substrate which had been subjected to the mold release treatment. The foam was cast in the form of a sheet and heated to 120 ° C. to evaporate the water, and the cross-linking reaction was allowed to proceed to cure the acrylic resin to prepare a bubble porous sheet. The thickness, appearance, density, thermal conductivity (higher is better for heat dissipation), hardness (lower is better for flexibility), and heat resistance of the obtained perforated bubble sheet were measured by the following methods, and the results were obtained. , Shown in the table below.

(Examples 3 and 4)
In the preparation of the above liquid composition, each liquid composition for Examples 3 and 4 having the compositions shown in the following table was prepared in the same manner except that graphite 2 was used instead of graphite 1. The pH of each liquid composition was 8.4, similar to the liquid composition of Example 1.
The sheet-like bubble porous bodies of Examples 3 and 4, respectively, were produced in the same manner as above except that the liquid compositions of Examples 3 and 4 were used, respectively, and evaluated in the same manner. The results are shown in the table below.

(Examples 5 and 6)
In the preparation of the above liquid composition, the respective liquid compositions for Examples 5 and 6 having the compositions shown in the following table were prepared in the same manner except that graphite 3 was used instead of graphite 1. The pH and viscosity of each liquid composition were not significantly different from those in the above examples, and there was no significant difference in bubble formation by the mechanical floss method.
The sheet-like bubble porous bodies of Examples 5 and 6, respectively, were produced in the same manner as above except that the liquid compositions of Examples 5 and 6 were used, respectively, and evaluated in the same manner. The results are shown in the table below.

(Comparative Examples 1 and 2)
In the preparation of the above liquid composition, each liquid composition for Comparative Examples 1 and 2 having the compositions shown in the following table was prepared in the same manner except that graphite 4 was used instead of graphite 1. The viscosity of each liquid composition was remarkably high as compared with the above-mentioned example, and the bubble formation by the mechanical floss method was inferior.
The sheet-like bubble porous bodies of Comparative Examples 1 and 2 were produced in the same manner as above except that the liquid compositions of Comparative Examples 1 and 2 were used, respectively, and evaluated in the same manner. The results are shown in the table below.

(Thickness)
The thickness of each sheet was measured using a thickness gauge having a contact of Φ50 mm. The measured values are shown in the table below.
(density)
The density of each sheet was measured according to JIS K 6401. The measured values are shown in the table below.
(Appearance evaluation)
The appearance of each sheet surface and bubbles (cells) was visually evaluated. Moreover, it was confirmed by a scanning electron microscope (200 times) that all of the prepared sheets were open cells.
"○" when the cell is uniform and the surface is not rough, "△" when the cell is slightly rough or the surface condition is rough, the cell is very rough, the cell is not formed or the surface condition is remarkable. The case where it was rough was evaluated as "x". The results are shown in the table below.

(Thermal conductivity)
The thermal conductivity of each sheet was measured by the probe method using a rapid thermal conductivity meter (QTM-500) manufactured by Kyoto Denshi Kogyo Co., Ltd. "○" when the thermal conductivity is 0.3 W / m · K or more, "△" when the thermal conductivity is 0.2 W / m · K or more and less than 0.3 W / m · K, thermal conductivity When was less than 0.2 W / m · K, it was evaluated as “x”. The evaluation results are shown in the table below.
(Flexibility)
The hardness of each sheet was measured according to JIS K6254. Specifically, a sample punched to a diameter of 50 mm was measured by using an autograph to measure the magnitude of repulsive stress when 25% of the thickness was crushed at a speed of 1 mm / min. For the measurement, AUTOGRAPH AGS-X manufactured by Shimadzu Corporation was used. The case where the 25% CLD was less than 20 kPa was evaluated as "◯", the case where the 25% CLD was 20 kPa or more and less than 50 kPa was evaluated as "Δ", and the case where the 25% CLD was 50 kPa or more was evaluated as "x". The results are shown in the table below.
(Heat-resistant)
Each sheet was left in a constant temperature bath at a temperature of 150 ° C. for 336 hours, then taken out, left at room temperature and humidity for 24 hours, and then sample pieces were prepared and the tensile strength was measured. The tensile strength was measured according to JIS K6251. For the measurement, AUTOGRAPH AGS-X manufactured by Shimadzu Corporation was used. Separately, the tensile strength was measured in the same manner before the treatment at 150 ° C. × 336 hours, and the values of the tensile strength before and after the treatment were substituted into the following formulas to calculate and evaluate the reduction rate.
Decrease rate = (tensile strength after treatment ÷ tensile strength before treatment) x 100
When the rate of decrease was less than 20%, it was evaluated as "◯", when it was 20% or more and less than 30%, it was evaluated as "Δ", and when it was 30% or more, it was evaluated as "x".

From the results shown in the above table, Examples 1 to 6 containing graphites 1 to 3 as spheroidal graphite are comprehensively evaluated in comparison with Comparative Examples 1 and 2 containing graphite 4 as scaly graphite in the same proportion. It can be understood that it is excellent as. In particular, when basal surface fold spheroidal graphite having a relatively small average particle size (less than 20 μm) is used, both thermal conductivity (heat dissipation) and flexibility can be improved without adversely affecting the appearance. It can be understood that the range of composition is widened.

On the other hand, Comparative Examples 1 and 2 using the scaly graphite 4 have poor thermal conductivity (poor heat dissipation) and inferior appearance as compared with Examples 1 to 6. Understandable. It is considered that this is because the liquid composition used as the raw material of each sheet has a high viscosity and bubbles are not stably formed by the mechanical foaming method. Since the viscosity of the liquid tends to increase as the amount of scaly graphite increases, the thermal conductivity should be improved even if the amount of scaly graphite is further increased in order to improve the heat dissipation of the comparative example. That is, from the above results, it can be said that the high thermal conductivity (heat dissipation) and flexibility obtained when spheroidal graphite is used cannot be realized by using scaly graphite.
Further, as shown in the table below, in the preparation of the composition for Comparative Example 1, an attempt was made to improve the thermal conductivity by using the metal oxide 1 together with the graphite 4, but the effect of improving the thermal conductivity was slightly obtained. However, on the other hand, poor appearance became noticeable. That is, it can be understood that the combined use of scaly graphite and the metal oxide has a limit in the effect of improving the thermal conductivity, and the effect of the embodiment of the present invention using spheroidal graphite cannot be obtained.

(Examples 7 to 12)
Instead of preparing the liquid composition of Example 1 or 2, the concentration of graphite 1 or 2 is changed, a metal oxide (another thermally conductive material) is used together with graphite 1 or 2, and the mixing ratio thereof is changed. As a result, each liquid composition for Examples 7 to 21 having the compositions shown in the table below was prepared. The pH of each liquid composition was about 8.4, similar to the liquid composition of Example 1 or 2.
Sheet-shaped bubble porous bodies of Examples 7 to 21 were produced in the same manner as in Example 1 and the like except that each liquid composition having the composition shown in the table below was used.

Examples 7 to 21 described in the above table are examples in which either spheroidal graphite 1 or 2 and metal oxides 1 to 3 are combined. In each case, the thermal conductivity was higher than that of Comparative Examples 1 and 2 using scaly graphite. Among them, Examples 7-14 and 18-21 in which graphite 1 or 2 (particularly graphite 1) and a metal oxide 1 or 2 having a Mohs hardness of less than 9 are combined are carried out using a metal oxide 3 having a Mohs hardness of 9. Compared with Examples 15 to 17, the effect of improving flexibility was excellent. When a metal oxide having a Mohs hardness of less than 9 is used, a decrease in flexibility due to the influence of the metal oxide can be suppressed, and high thermal conductivity and flexibility can be achieved in a well-balanced manner.
It should be noted that even if the embodiment has slightly inferior heat dissipation, it is useful for applications where the requirement for heat dissipation is not strict (for example, packing material), and even if the embodiment has slightly inferior flexibility, the internal structure Can be used as a heat radiating material for electronic and electrical equipment that is not complicated.

(Examples 22 to 31)
Instead of preparing the liquid composition of Example 1, the type of matrix resin can be changed by changing the concentration of graphite 1, using a metal oxide (another thermally conductive material) together with graphite 1, and changing the mixing ratio thereof. By making changes and the like, each liquid composition for Examples 22 to 31 having the compositions shown in the table below was prepared. The pH of each liquid composition was 8.4, similar to the liquid composition of Example 1, but the pH of the liquid composition for Example 31 was 8.0. In addition, some of the liquid compositions have a higher viscosity than the liquid compositions of Example 1 and the like, and are inferior in bubble formation by the mechanical foaming method.
Sheet-shaped bubble porous bodies of Examples 22 to 31 were produced in the same manner as in Example 1 except that the liquid composition of Example 1 was changed to each liquid composition.

When the above evaluations were performed on each of the obtained sheets in the same manner as in Example 1 and the like, all of them were superior to the comparative examples as a comprehensive evaluation and were at a level that could withstand practical use.
From the evaluation results of the examples shown in Tables 1, 3 and 4, in particular, in the examples containing 40 to 60% by mass of the heat conductive material, the ratio of spheroidal graphite to the total heat conductive material is 50% by mass. From the above, it can be understood that a sheet having a good balance of high heat dissipation and flexibility can be obtained.
Further, it can be understood that when an acrylic resin is used as the matrix resin, a sheet having further excellent heat resistance can be obtained.
In the above examples, in order to clarify the effect obtained by blending the spheroidal graphite, the composition of the surfactant in each example was made the same, but the same effect can be obtained even if the composition is changed. ..

Claims (12)

A bubble porous body containing a matrix resin and a heat conductive material dispersed in the matrix resin, wherein the heat conductive material contains at least spheroidal graphite. The bubble porous body according to claim 1, wherein the spheroidal graphite has a structure in which the basal surface is folded. The bubble porous body according to claim 1 or 2, wherein the matrix resin is an acrylic resin. The bubble porous body according to any one of claims 1 to 3, wherein the heat conductive material further contains a metal oxide. The bubble porous body according to any one of claims 1 to 4, which contains 40 to 60% by mass of the heat conductive material based on the total mass of the bubble porous body. The bubble porous body according to any one of claims 1 to 5, wherein the heat conductive material contains a metal oxide and a spheroidal graphite in a blending ratio (mass ratio) of 0: 10 to 5: 5. The bubble porous body according to any one of claims 1 to 6, which is an open cell porous body. The 25% compressive load measured in accordance with JIS K 6254 is 20 kPa or less, and the thermal conductivity measured by the probe method using QTM-500 manufactured by Kyoto Denshi Kogyo Co., Ltd. is 0.3 W / m · K or more. The bubble porous body according to any one of claims 1 to 7. The bubble porous body according to any one of claims 1 to 8, which is used as a heat radiating material for electronic products. A foaming step of mechanically foaming a liquid composition containing a resin having a functional group in the side chain, a foaming agent and spheroidal graphite, and a cross-linking agent having a functional group reacted with each other and / or a polyfunctional cross-linking agent. Including the step of curing by reacting with a functional group,
A method for producing a foamed porous body, in which a foaming step and a curing step are carried out at the same time, and / or a curing step is carried out after the foaming step. The production method according to claim 10, wherein the foaming agent has a pH in the neutral to alkaline range of the liquid composition, and the foaming agent contains at least one anionic surfactant. The production method according to claim 10 or 11, wherein the bubble porous body is the bubble porous body according to any one of claims 1 to 9.