CN110072926B

CN110072926B - Porous foam and method for producing same

Info

Publication number: CN110072926B
Application number: CN201780075780.8A
Authority: CN
Inventors: 菊地敦纪; 几井隆介
Original assignee: Inoac Corp; Inoac Technical Center Co Ltd
Current assignee: Inoac Corp; Inoac Technical Center Co Ltd
Priority date: 2016-12-07
Filing date: 2017-12-05
Publication date: 2022-07-08
Anticipated expiration: 2037-12-05
Also published as: CN110072926A; JP7210665B2; KR20190089864A; WO2018105578A1; TW201835192A; JP6933458B2; TWI735717B; JP2021183701A; KR102369721B1; JP7469408B2; JP2022164877A; JP2018090745A

Abstract

Provided are a novel porous foam body which can be used as a heat-dissipating member, and a method for producing the same. A porous body with cells, comprising a matrix resin and a heat conductive material dispersed in the matrix resin, wherein the heat conductive material contains at least spherical graphite; and a method for producing a porous foam body, characterized by comprising: a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in a side chain, a foaming agent, and spherical graphite; and a curing step of curing the liquid composition by reacting functional groups of the resins with each other and/or by reacting functional groups of a polyfunctional crosslinking agent with each other and/or by reacting functional groups of the resins with functional groups of the polyfunctional crosslinking agent, wherein the foaming step and the curing step are performed simultaneously and/or the curing step is performed after the foaming step.

Description

Porous foam and method for producing same

Technical Field

The present invention relates to a porous foam body useful as a heat radiating member for electronic and electrical equipment products (electronic products), particularly thin and high-performance electronic and electrical equipment products having a complicated internal structure such as smartphones, personal computers, and televisions, and a method for producing the same.

Background

Electronic and electrical equipment products (electronic products), particularly smart phones, personal computers, televisions, and other products, are becoming thinner and higher in performance every year. On the other hand, the heat generation amount increases due to an increase in the data processing speed or the like, and the internal structure becomes complicated, so that heat is likely to be accumulated. The generated heat may cause problems such as short life of the electronic component, deformation of the case due to thermal expansion, and low-temperature burn. Therefore, a member containing a heat conductive substance is disposed inside the electronic and electrical equipment product for the purpose of heat dissipation. Conventionally, as the member, a member formed of a gel of silicone, acrylic or the like containing a heat conductive substance has been used. However, the member formed of the gel has high thermal conductivity, but has high hardness and high stress during compression, and thus lacks flexibility. Therefore, it is difficult to arrange the gel following the internal structure in recent electronic and electric apparatuses having complicated internal structures.

Patent document 1 discloses a foamable composition that can be used for producing a heat sink for electronic equipment or the like. However, patent document 1 does not describe the problem of the shape following property, i.e., the flexibility, and the solution thereof. Further, since the foamable composition contains a silicone surfactant as an essential component, when the heat sink produced from the composition is exposed to high temperature, the low-molecular siloxane component is released and deteriorated, which is a problem, and the heat resistance is poor.

Documents of the prior art

Patent literature

Patent document 1: japanese patent laid-open publication No. 2016-65196

Disclosure of Invention

Problems to be solved by the invention

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 foam body that can be used as a heat radiation member, and a method for producing the same.

Another object of the present invention is to provide a porous foam body having appropriate flexibility and conformability to the shape of another member without impairing heat dissipation properties, and a method for producing the same.

Means for solving the problems

The present inventors have conducted studies to solve the above problems, and as a result, have found that the above problems can be solved by using spherical graphite as a heat conductive material, and have completed the present invention. Means for solving the above problems are as follows.

[1] A porous foam body comprising a matrix resin and a heat conductive material dispersed in the matrix resin, wherein the heat conductive material contains at least spherical graphite.

[2] The porous foam according to [1], wherein the spherical graphite has a structure in which basal planes are folded.

[3] The porous foam according to [1] or [2], wherein the matrix resin is an acrylic resin.

[4] The porous foam body according to any one of [1] to [3], wherein the heat conductive material further contains a metal oxide.

[5] The porous foam body according to any one of [1] to [4], wherein the heat conductive material is contained in an amount of 40 to 60 mass% based on the total mass of the porous foam body.

[6] The porous foam body according to any one of [1] to [5], wherein the heat conductive material contains a metal oxide and spherical graphite at a mixing ratio (mass ratio) of 0:10 to 5: 5.

[7] The porous foam body according to any one of [1] to [6], which is an open-cell porous body.

[8] The porous foam body according to any one of [1] to [7], wherein the ratio of the porous foam body is determined in accordance with JIS K6254: 2016(ISO 7743: 2011) has a 25% compression load of 20kPa or less, and has a thermal conductivity of 0.3W/(m.K) or more as measured by a probe method using QTM-500 manufactured by Kyoto electronics industries, Ltd.

[9] The porous foam body according to any one of [1] to [8] is used for a heat-dissipating member of an electronic product.

[10] A method of manufacturing a porous body with air bubbles, the method comprising:

a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in a side chain, a foaming agent, and spherical graphite; and

a curing step of curing the liquid composition by reacting functional groups of the resins with each other and/or by reacting functional groups of a polyfunctional crosslinking agent with each other and/or by reacting functional groups of the resins with functional groups of the polyfunctional crosslinking agent,

wherein the foaming step is performed simultaneously with the curing step, and/or the curing step is performed after the foaming step.

[11] The production method according to [10], wherein the pH of the liquid composition is in a neutral to alkaline region, and the liquid composition contains at least 1 anionic surfactant as the foaming agent.

[12] The production method according to [10] or [11], wherein the porous cell body is any one of the porous cell bodies of [1] to [9 ].

Effects of the invention

According to the present invention, a novel porous foam body that can be used as a heat radiation member and a method for producing the same can be provided.

Further, according to the present invention, it is possible to provide a porous cellular body having appropriate flexibility and having a capability of following the shape of another member without impairing heat dissipation properties, and a method for producing the same.

Detailed Description

The following will describe the porous foam body of the present invention and a method for producing the same. In the present specification, "to" means a range including the values before and after the range.

[ porous foam body ]

The porous foam body of the present invention is characterized by comprising a matrix resin and a heat conductive material dispersed in the matrix resin, and the heat conductive material contains at least spherical graphite.

(1) Spherical graphite

The spherical graphite has high thermal conductivity, and contributes to the heat dissipation performance and/or improvement of the porous foam body of the present invention. The graphite usable in the present invention is spherical. In the present invention, the term "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 surfaces are not uniform and the surface has a cabbage-like appearance in which the surfaces are overlapped one on another, and the like. However, natural graphite is different from natural graphite in that its crystal system is hexagonal, and untreated graphite is generally 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 the natural graphite in flake form, and a treatment method of isotropically applying pressure to the graphite is preferably employed. 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 method is divided into hot isostatic pressing and cold isostatic pressing according to the presence or absence of heating. Either may be utilized. By performing this treatment, spherical graphite having a spherical shape and a reduced inner hollow wall (gap between scale layers) is obtained, which has high thermal conductivity.

The spheroidized spherical graphite is defined as spherical graphite having a structure in which a basal plane is folded when viewed from the other side. Here, the "basal plane" refers to a plane orthogonal to the C axis of a graphite crystal (hexagonal system). That is, the spherical graphite of the present invention is preferably graphite in which the crystal system of natural graphite is strained. This strain can be grasped by measuring an X-ray diffraction pattern and confirming the presence or absence of peak broadening or the presence or absence of a shift in 2 θ value as compared with natural graphite. Whether or not the porous cell bodies contain spherical graphite can be confirmed by measuring the X-ray diffraction pattern of the raw material graphite, and in addition, whether or not the shape of the graphite-corresponding portion is circular can be confirmed by observing arbitrary 2 or more cross sections of the porous cell bodies under a microscope. Specifically, when the surfaces of the porous bubble bodies that are 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 1/2 or more, the porous bubble bodies 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 a high-speed air stream using a hybrid system; and spherical graphite obtained by solidifying spherical carbon particles obtained by crystallizing petroleum or petroleum pitch and a thermosetting resin to obtain powder and graphitizing the powder; and so on. The former is preferable from the viewpoint of thermal conductivity.

As the spherical graphite, commercially available products can be suitably used, and specific examples thereof include spheroidized graphite manufactured by japan graphite industries, ltd. The average particle diameter (median diameter) of the spherical graphite used in the present invention is about 1 to 100 μm. While it is likely that one of the graphite particles will be reduced when the other is improved in terms of ensuring heat dissipation and ensuring flexibility, it is preferable to use spherical graphite particles having a small average particle size because the properties of both graphite particles can be improved in a well-balanced manner. The preferable average particle diameter range varies depending on the final shape of the porous foam, and the preferable average particle diameter range is about 5 to 30 μm, and more preferably about 5 to 15 μm for a sheet-like form having a thickness of about 0.1 to 1.0 mm.

When graphite having an anisotropic shape other than a spherical shape (rectangular shape, flake (flake) shape) is used, anisotropy occurs in the heat dissipation property of the porous cell body, and the improvement of the heat dissipation property by the addition of graphite is insufficient. However, the manner in which the anisotropically shaped graphite as an impurity is inevitably or optionally contained at a small proportion at least to the extent that the effects of the present invention can be obtained is not a manner to be excluded from the present invention. The spherical 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 porous foam of the present invention contains a matrix resin. The matrix resin is a main component of the porous cellular material of the present invention. One embodiment of the matrix resin is a resin having a three-dimensional network structure in which a plurality of polymer chains in a linear shape are crosslinked by a crosslinking agent or a functional group of the polymer chain itself.

The type of the matrix resin is not particularly limited, and any resin can be used as long as it can form a cellular porous structure, more specifically, a porous structure by a foaming treatment. Examples of the resin that can be used include acrylic resins; a polyurethane resin; polyolefin resins such as polyethylene and polypropylene; a polyvinyl chloride resin; a polystyrene resin; amino resins such as melamine resin and urea resin; a phenolic resin. In the above embodiment, the matrix resin has a crosslinked structure formed by a crosslinking agent separately added and/or a functional group of the matrix resin itself. Acrylic resins and urethane resins are preferred because they can form a porous structure stably and can form a flexible porous body by using graphite together. Further, since the resin may be exposed to a high temperature depending on the application, a resin having high heat resistance is preferable, and from this viewpoint, an acrylic resin is preferable. In the embodiment in which the matrix resin is an acrylic resin, even when exposed to a high temperature of 150 ℃, heat dissipation is maintained without significant thermal degradation.

Examples of the polymerizable monomer of the acrylic resin include (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, dicyclopentanyl (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, itaconic acid half ester, maleic anhydride, and itaconic anhydride; polymerizable monomers containing a glycidyl group 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.

The main component of the matrix resin is more preferably an acrylic resin having a crosslinked structure. Examples of the acrylic resin having a crosslinked structure include acrylic resins obtained by polymerizing a (meth) acrylate ester having a functional group introduced into a side chain alone, or copolymerizing 1 or more kinds of other monomers (e.g., itaconic acid and acrylonitrile) having a functional group introduced into a side chain together with or after polymerization, and then performing a crosslinking reaction to form a crosslinked structure. Once the acrylic resin having a functional group in a side chain is obtained, a crosslinked structure is preferably formed. The crosslinked structure can be formed by a reaction between functional groups of side chain portions of the resin, and/or by a reaction of the functional groups with a crosslinking agent separately added. The acrylic resin preferably has a functional group which contributes to the formation of a crosslinked structure, and examples thereof include a hydroxyl group, a carboxyl group, a nitrile group, a glycidyl group, a sulfo group and the like.

Further, as the crosslinking agent, a conventionally known crosslinking agent can be used, and examples thereof include a polyfunctional compound having 2 or more functions (in the present invention, "polyfunctional compound" means a compound having 2 or more functional groups, and functional groups contained in one molecule may be the same or different). Specifically, crude 1, 6-hexamethylene diisocyanate (crude HDI) as an aliphatic isocyanate or 1, 6-Hexamethylene Diisocyanate (HDI) obtained by purifying the crude HDI, HDI isocyanurate or isophorone diisocyanate (IPDI) which is a trimer of HDI, diphenylmethane diisocyanate (MDI), Toluene Diisocyanate (TDI) and Toluene Diisocyanate (TDI) which are aromatic isocyanates can be used in an appropriate amount according to the kind and amount of functional groups contained in a resin compounding system to be usedIsocyanate crosslinking agents such as blocked polyisocyanates obtained by modifying the isocyanate group of isocyanate (TDI) with a blocking agent; an epoxy crosslinking agent; a melamine based cross-linking agent; a carbodiimide-based crosslinking agent;

oxazoline crosslinking agents, and the like. An example of the crosslinked structure is a crosslinked structure formed by the reaction of any one or more of the functional groups in the side chain and the diisocyanate group of the crosslinking agent.

(3) Additive agent

The porous foam of the present invention may contain other additives together with the matrix resin and the spherical graphite.

One example of an additive is a thermally conductive material other than graphite. By adding other heat conductive materials together with the spherical graphite, heat dissipation can be further improved. Examples of other thermally conductive materials include metal nitrides such as boron nitride, aluminum nitride, and the like; 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 30W/(mK) or more. In addition, among the heat conductive materials, there are materials having high hardness, and when using them, the bubble porous body of the present invention may lose flexibility, so it is preferable to use a heat conductive material having low hardness. Specifically, a material having a mohs hardness of 9 or less, more preferably 6 or less, is preferably used. An example of a preferable embodiment from the viewpoint of heat dissipation and flexibility is an embodiment in which a metal oxide having a mohs hardness within the above range is contained together with spherical graphite as a heat conductive material.

Other examples of additives include 1 or more than 2 of surfactants. The surfactant helps to stably form bubbles during the foaming process. I.e., functions as a blowing agent. In addition, the matrix resin also contributes to the stable dispersion of the spherical graphite. In particular, the use of a surfactant having excellent wettability with respect to spherical graphite is preferable because high dispersibility of spherical graphite with respect to the matrix resin can be ensured. It is possible to use 1 or 2 or more selected from conventionally known anionic surfactants, nonionic surfactants and amphoteric surfactants. Examples of the surfactant having excellent bubble formation stability and wettability include anionic surfactants having a hydrophilic sulfo group such as sulfosuccinates (e.g., sodium dialkylsulfosuccinate), alkylbenzenesulfonates, and polyoxyethylene alkyl ether sulfate salts. Examples of the surfactant having excellent wettability include nonionic surfactants having a polyoxyalkylene chain such as polyoxyethylene alkyl ethers and polyoxyethylene fatty acid esters. In the present invention, it is preferable to use 1 or more of the above anionic surfactants having both excellent bubble formation stability and excellent wettability, or to use 1 or more of the above nonionic surfactants having excellent wettability together with 1 or more of the above anionic surfactants. In addition, 1 or more kinds of amphoteric surfactants of amino acid type, betaine type, amine oxide type, and the like can be used.

The invention also has the following features: even if a silicone surfactant is not used as a surfactant, a porous foam having high heat dissipation properties can be obtained. The silicone surfactant has excellent bubble formation stability, but has a problem that low-molecular siloxane is released when exposed to high temperature. The present invention can provide a silicone-free porous foam having excellent heat resistance without using a silicone surfactant as a surfactant.

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 as long as the effects of the present invention are not impaired.

As a result, the glass transition temperature (Tg) of the porous foam obtained is preferably-80 to 0 ℃. More preferably-60 to-10 ℃. The glass transition temperature can be used as an index of hardness of the porous cellular material. When the Tg is too low as compared with-80 ℃, the cell porous body becomes soft and the hardness of the sheet or the like is lost, and when the Tg is higher than 0 ℃, the cell porous body becomes hard and the flexibility is lost.

(4) Composition of

The proportion of the heat conductive material contained in the porous foam body of the present invention is preferably 30 to 70 mass%, more preferably 35 to 65 mass%, and still more preferably 40 to 60 mass% based on the total mass of the porous foam body. In the embodiment of containing only spherical graphite as the heat conductive material, the ratio of spherical graphite is preferably in the above range. As described above, in the present invention, the heat conductive material may contain a material other than spherical graphite, for example, a metal oxide, and the mass ratio of the metal oxide to the spherical graphite is preferably 0:10 to 2:3, and more preferably 0:10 to 5: 5.

(5) Form and properties

The form of the cells in the porous cell body of the present invention is not particularly limited, and from the viewpoint of heat dissipation and flexibility, the cells are preferably interconnected. The term "interconnected cells" means a state in which the resin film separating adjacent cells has through holes and the adjacent cells are three-dimensionally connected to each other. In addition, in the case of the "open cell" structure, the foam has a property that external air can pass through to the inside of the foam. In the present invention, it is not strictly necessary that all the pores are in communication with each other, and even if there are pores that are partially closed inside, if the pores have a property that the outside air can pass through as a whole, the structure is regarded as an "open cell". The form of the bubbles can be confirmed by observation with an electron microscope.

The density of the porous foam body of the present invention is 250 to 600kg/m³In the case, both of heat dissipation and flexibility are excellent, and therefore, it is preferable that the amount of the heat dissipation agent is 300 to 500kg/m³And, more preferably, the above-mentioned compound. When the density is lower than the above range, the heat dissipation property is lowered, and may become unsuitable depending on the application (for example, application to a heat sink disposed inside a precision electronic and electrical equipment product). Further, when the density exceeds the above range, the flexibility is lowered and the hardness is increased, and as a result, the shape-following property with respect to a complicated structure is deteriorated, and there is a possibility that the density becomes unsuitable depending on the application (for example, the application of a heat sink disposed inside a precision electronic and electrical equipment product).

According to the present invention, a porous foam body exhibiting high heat dissipation and high flexibility can be provided. Specifically, there can be provided a method based on JIS K6254: a 25% Compression Load (which is a pressure required to compress the thickness by 25%. the 25% Compression Load may be abbreviated as "25% CLD (Compression-Load-Deflection)") of 2016(ISO 7743: 2011) of 20kPa or less, and a thermal conductivity of 0.3W/(m · K) or more by a probe method using QTM-500 manufactured by kyoto electronics industries co. The lower the 25% compression load is, the more preferable from the viewpoint of flexibility, but from the viewpoint of workability and the like, the lower limit of the 25% compression load is generally about 3 kPa. From the viewpoint of heat dissipation, the higher the thermal conductivity, the more preferable the thermal conductivity, and the upper limit value is generally about 0.7W/(m · K).

One embodiment of the porous foam body of the present invention is a sheet-like porous foam body having a thickness of about 0.1 to 1 mm. The porous foam body of the present invention exhibits sufficiently high heat dissipation even in a thin sheet-like shape, and can be easily disposed in a precision electronic and electrical equipment product having a complicated internal structure by effectively utilizing its flexibility by being in a sheet-like shape. The above embodiment can remove heat that tends to accumulate inside a precision electronic and electrical equipment product, and can be applied to a heat sink for reducing deterioration of the precision electronic and electrical equipment product due to heat.

(6) Forming method

The porous cellular material of the present invention can be formed by various conventionally known methods so as to have a desired shape. The appropriate forming method can be selected according to the desired final shape. In the case of producing a sheet-like porous cellular body, 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 matrix resin 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.

(7) Use of

The porous bubble body of the present invention is suitable for use as a heat-dissipating member for electronic and electrical equipment products. And is also useful as a filler. The heat dissipation component is particularly suitable for precise electronic and electrical equipment products with complex internal structures. Among the heat dissipating members, there are also ones that have poor heat resistance and are disposed so as not to contact electronic components or the like that become a heat source. The porous cell body of the present invention, particularly the form in which the matrix resin is an acrylic resin, is also excellent in heat resistance, and therefore can be used for a contact heat-dissipating member that can be brought into contact with an electronic component serving as a heat source.

[ method for producing porous foam ]

The present invention also relates to a method for producing a porous foam body, comprising: a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in a side chain, a foaming agent, and spherical graphite; and a curing step of curing the liquid composition by reacting the functional groups of the resins with each other and/or by reacting the functional groups of the polyfunctional crosslinking agent with each other and/or by reacting the functional groups of the resins with the functional groups of the polyfunctional crosslinking agent,

According to this method, the porous cellular material of the present invention can be stably produced.

(1) Components of liquid composition

The liquid composition used in the production method of the present invention contains at least: a resin having a functional group in a side chain, a foaming agent, and spherical graphite. In addition, a polyfunctional compound, i.e., a crosslinking agent, which contributes to curing of the above-described resin may be contained. Preferred examples of the resin having a functional group in a side chain, the foaming agent, the spherical graphite, and the crosslinking agent are the same as the preferred examples of the components described in the above [ porous cell body ].

In order to be formulated as a liquid 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 1 or 2 or more kinds of polar solvents such as N-methylpyrrolidone). When an organic solvent is used, the viscosity of the liquid composition becomes higher than that in the case of using water, and the bubble formation stability and moldability become poor. The organic solvent is preferably not contained, but may be contained in a proportion to such an extent that the moldability is not affected (for example, such an extent that the viscosity is not increased to such an extent that the moldability is impaired).

(2) Method for preparing liquid composition

The liquid composition is preferably prepared by preparing a water-based emulsion of the resin and a water-based dispersion of spherical graphite separately and mixing them, because the liquid composition can be prepared without causing aggregation of spherical graphite and the like. The solid content concentration of the resin in the aqueous emulsion of the resin and the solid content concentration of the spherical graphite in the aqueous dispersion of the spherical graphite are not particularly limited, but generally about 50 to 90 mass%. When a surfactant as a foaming agent is mixed in advance with the aqueous dispersion of spherical graphite, the dispersion stability of spherical graphite into a resin is further improved when the spherical graphite is mixed with an aqueous emulsion of a resin, which is preferable. In particular, when at least 1 kind of surfactant having good wettability is used as the blowing agent, the dispersion stability of the spherical graphite in the resin is further improved, which is preferable. Among these, at least 1 selected from the above anionic surfactants excellent in bubble formation stability and wettability is preferably used, and at least 1 selected from the above nonionic surfactants excellent in wettability is more preferably used. For example, an aqueous dispersion of spherical graphite can be prepared by mixing spherical graphite in an aqueous solution or an aqueous suspension of a surfactant (foaming agent) having a solid content of about 20 to 60 mass%. In the case of using other additives such as a crosslinking agent and other heat conductive materials, it is preferable to add other additives to the aqueous dispersion of spherical graphite and mix the resulting mixture with an aqueous emulsion of a resin to prepare a liquid composition.

(3) Composition, Properties of liquid compositions

The total solid content concentration of the liquid composition is about 50 to 90 mass%, preferably 65 to 85 mass%. In general, the total mass of the resin (and the crosslinking agent added as needed) and the spherical graphite (and other heat conductive material added as needed) 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 liquid composition. However, the preferred mass ratio of each material in the solid component also varies depending on the kind of the material used, and the like. In addition, in order to stably form bubbles, the pH of the liquid composition is preferably in a neutral to alkaline region, specifically, the pH is 7 or more, preferably 7 to 11. More preferably 7 to 9. The pH of the liquid composition can be adjusted to the above-described preferred range by adjusting the type and amount of the foaming agent. In addition, in order to stably form bubbles in the following foaming step, the viscosity of the liquid composition is preferably about 10000 to 200000 mPas.

(4) Foaming step

In the foaming step, the liquid composition is stirred to perform mechanical foaming for generating bubbles. The mechanical foaming (メカニカルフロス) is a method of foaming a liquid composition by mixing a gas such as air in the atmosphere into an emulsion composition by stirring the 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, and the like can be used. In the present invention, the foaming step is performed by a mechanical foaming method, whereby the formation of independent cells is suppressed, the formation of open cells is dominant, the increase in density of the cured porous body 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 to 10 minutes, preferably 2 to 6 minutes. The stirring speed during the mixing is preferably 200rpm or more (more preferably 500rpm or more) in order to make the bubbles fine, 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 conditions in the foaming step are not particularly limited, and are 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.

(5) Curing step

In the curing step, the liquid composition is cured by reacting the functional groups of the resins with each other, and/or by reacting the functional groups of the polyfunctional crosslinking agent with each other, and/or by reacting the functional groups of the resins with the functional groups of the polyfunctional crosslinking agent. By this step, the liquid composition becomes a structure as a porous body of bubbles. The curing step is preferably performed after the foaming step. Heating is preferably performed in order to evaporate the solvent (water) in the liquid composition and to allow the crosslinking reaction to proceed. The heating temperature and the heating time may be any temperature and time that can crosslink (cure) the raw material, and may be, for example, about 1 hour at 80 to 150 ℃ (particularly, about 120 ℃ is suitable).

The curing step may be performed as one step of forming the obtained porous cellular body into a desired shape. For example, in the case of producing a sheet-like porous cellular material, the curing step may be performed as one step of a casting method. Specifically, the liquid 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 simultaneously subjected to a crosslinking reaction to be cured, thereby producing a sheet on the surface of the substrate. The base material for casting the liquid composition is not particularly limited, and a resin base material (a PET film having a thickness of 25 to 50 μm, whose surface is subjected to a mold release treatment as required) may be used; a metal base material having a thickness of 2 to 100 μm or a long metal base material cut into a strip shape; a laminated base material of a PET film having a thickness of 1 to 30 μm and an adhesive material layer having a thickness of 2 to 100 μm, which are similarly cut into a band shape; and an air-free laminated substrate formed of an adhesive layer having a concave-convex shape, a depth of a concave portion of 2 to 100 [ mu ] m, and a height of a convex portion of 2 to 100 [ mu ] m, laminated on a long film cut into a strip shape.

One embodiment of the production method of the present invention is a method for producing a sheet-like porous cellular body, including:

a foaming step of mechanically foaming a liquid composition containing a resin having a functional group in a side chain, a foaming agent, and spherical graphite;

a casting step of casting the liquid composition into a sheet shape on a surface of the base material after the foaming step;

and a curing step of, after the casting step, reacting the functional groups of the resins with each other and/or reacting the functional groups of the polyfunctional crosslinking agent with each other and/or reacting the functional groups of the resins with the functional groups of the polyfunctional crosslinking agent to cure the liquid composition and obtain a sheet.

Examples

Hereinafter, the effects of the porous foam body and the method for producing the same according to the present invention will be specifically described by examples.

(Material)

Matrix resin Material

As the matrix resin material 1, an emulsion of an acrylic resin (Tg-40 ℃, pH 9, solid content concentration 60 mass%, solvent water) as an acrylonitrile-alkyl acrylate-itaconic acid copolymer was prepared.

As the matrix resin material 2, an emulsion of a polyurethane resin (pH 8, solid content concentration 60 mass%, solvent water) was prepared.

Blowing agents

As the foaming agent, the following surfactants were prepared, respectively.

As the anionic surfactant 1, a mixed solution of ammonium stearate and water (pH 11, 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 amphoteric surfactant 1, a mixed solution (pH 7.5, solid content 30%) of coconut oil fatty acid amide propyl betaine and water was prepared.

As amphoteric surfactant 2, a mixed solution of myristyl betaine and water (ph6.5, solid content 36%) was prepared.

As the nonionic surfactant 1, a mixed solution of a polyoxyethylene alkyl ether and water (pH6.5, solid content 50%) was prepared.

Crosslinking agents

As the crosslinking agent, hydrophobic HDI isocyanurate (functional group number 3.5) was prepared.

Heat conducting material (graphite)

As graphite 1, spherical graphite powder (average particle size: 20 μm) manufactured by Nippon graphite industries was prepared. The spheroidized graphite particles are processed into spherical particles, and the basal planes of the graphite crystals (hexagonal system) are folded.

As the graphite 2, spherical graphite powder (average particle diameter: 10 μm) manufactured by Nippon graphite industries, having only a different average particle diameter from that of the graphite 1, was prepared.

As the graphite 3, spherical graphite powder (average particle size 20 μm) manufactured by Ito graphite industries was prepared. Unlike graphite 1 and graphite 2, this graphite is spherical graphite (spherical flaky graphite) processed so that the basal plane of the graphite crystal (hexagonal system) is not folded.

As the graphite 4, a graphite powder (average particle size: 20 μm) manufactured by Ito graphite industries was prepared. The graphite was not spheroidized, and the basal plane of the graphite crystal (hexagonal system) was not folded (flaky graphite).

Heat-conducting material (other than graphite)

As the metal oxide 1, an oxide powder (shape: spherical, average particle diameter 10 μm, Mohs hardness 6) of aluminum and magnesium was prepared.

As the metal oxide 2, an oxide powder (shape: spherical, average particle diameter 20 μm, Mohs hardness 6) of aluminum and magnesium was prepared.

As the metal oxide 3, alumina powder (spherical shape, average particle diameter 20 μm, Mohs hardness 9) was prepared.

(examples 1 and 2)

Graphite 1, anionic surfactant 2, amphoteric surfactant 1, amphoteric surfactant 2 and nonionic surfactant 1 were mixed at the ratios shown in the following table, a crosslinking agent was added thereto to prepare an aqueous dispersion of graphite 1, and the aqueous dispersion was added to 100 parts by mass of the matrix resin material 1 and mixed to prepare liquid compositions for examples 1 and 2, respectively.

The total solid content concentration of the liquid composition and the solid content concentration of the heat conductive material are as shown in the following table. The pH of the liquid composition was 8.4. The viscosity is also a viscosity range in which mechanical foaming is possible.

After foaming each of the liquid compositions prepared as described above by a mechanical foaming method (stirring at 500 revolutions for 3 minutes at 23 ℃), the liquid compositions were cast into a sheet form on the surface of a PET film substrate subjected to a mold release treatment, and the sheet-form porous cellular material was produced by heating to 120 ℃ to evaporate water and simultaneously carrying out a crosslinking reaction to cure an acrylic resin. The thickness, appearance, density, thermal conductivity (the higher the heat dissipation), hardness (the lower the flexibility), and heat resistance of the obtained sheet-like porous cellular material were measured by the following methods, and the results thereof are shown in the following table.

(examples 3 and 4)

Each of the liquid compositions for examples 3 and 4 having the composition shown in the following table was prepared in the same manner as in the preparation of the liquid composition except that graphite 2 was used instead of graphite 1. The pH of each liquid composition was 8.4 as in the liquid composition of example 1.

The sheet-like porous cellular bodies of examples 3 and 4 were produced in the same manner as described above except that the liquid compositions of examples 3 and 4 were used, respectively, and were evaluated in the same manner. The results are shown in the following table.

(examples 5 and 6)

Each of the liquid compositions for examples 5 and 6 having the composition shown in the following table was prepared in the same manner as in the preparation of the liquid composition except that graphite 3 was used instead of graphite 1. The pH and viscosity of each liquid composition were not significantly different from those of the above examples, nor were there significant differences regarding bubble formation by the mechanical foaming method.

The sheet-like porous cellular bodies of examples 5 and 6 were produced in the same manner as described above except that the liquid compositions of examples 5 and 6 were used, respectively, and the same evaluation was performed. The results are shown in the following table.

Comparative examples 1 and 2

Each of the liquid compositions for comparative examples 1 and 2 having the composition shown in the following table was prepared in the same manner except that graphite 4 was used instead of graphite 1 in the preparation of the liquid composition. The viscosity of each liquid composition was significantly higher than that of the above examples, and bubble formation by the mechanical foaming method was poor.

The sheet-like porous cellular bodies of comparative examples 1 and 2 were produced in the same manner as described 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 following table.

(thickness)

The thickness of each sheet was measured using a thickness gauge with a stylus of phi 50 mm. The measured values are shown in the following table.

(Density)

The density of each sheet was based on JIS K7222: 2005(ISO 845: 1988). The measured values are shown in the following table.

(appearance evaluation)

The surface of each sheet and the appearance of bubbles (cells) were evaluated by visual observation. Furthermore, it was confirmed by a scanning electron microscope (200 times) that all of the produced sheets were air-bubble-free.

The case where the cells were uniform and the surface was not rough was evaluated as "o", the case where several cells were rough and the surface state was rough was evaluated as "Δ", and the case where the cells were very rough, no cells were formed or the surface state was remarkably rough was evaluated as "x". The results are shown in the following table.

(thermal conductivity)

The thermal conductivity of each sheet was measured by a probe method using a rapid thermal conductivity meter (QTM-500) manufactured by Kyoto electronics industries, Ltd. The case where the thermal conductivity was 0.3W/(m.K) or more was evaluated as "O", the case where the thermal conductivity was 0.2W/(m.K) or more and less than 0.3W/(m.K) was evaluated as "Delta", and the case where the thermal conductivity was less than 0.2W/(m.K) was evaluated as "X". The evaluation results are shown in the following table.

(flexibility)

Based on JIS K6254: 2016(ISO 7743: 2011) in order to measure the hardness of the respective sheets. Specifically, samples punched out to have a diameter of 50mm were stacked so that the thickness became 1mm or more, and the magnitude of the spring back stress when 25% of the thickness was compressed at a rate of 1 mm/min was measured using an Autograph. For the measurement, AUTOGRAPH AGS-X manufactured by Shimadzu corporation was used. The case where 25% CLD was less than 20kPa was evaluated as "O", the case where 25% CLD was 20kPa or more and less than 50kPa was evaluated as "Δ", and the case where 25% CLD was 50kPa or more was evaluated as "X". The results are shown in the following table.

(Heat resistance)

Each sheet was left to stand in a thermostatic bath at a temperature of 150 ℃ for 336 hours, taken out, left to stand at normal temperature and humidity for 24 hours, and then a sample sheet was prepared and tensile strength was measured. Based on JIS K6251: 2017(ISO 37: 2011). For the measurement, AUTOGRAPH AGS-X manufactured by Shimadzu corporation was used. The tensile strength was measured in the same manner before the treatment at 150 ℃ for 336 hours, and the reduction rate was calculated by substituting the values of the tensile strength before and after the treatment into the following formula.

The reduction rate is (tensile strength after treatment ÷ tensile strength before treatment) × 100

The case where the reduction rate was less than 20% was evaluated as "o", the case where the reduction rate was 20% or more and less than 30% was evaluated as "Δ", and the case where the reduction rate was 30% or more was evaluated as "x".

[ Table 1]

From the results shown in the above table, it is understood that examples 1 to 6 containing graphite particles 1 to 3 as spherical graphite particles are superior to comparative examples 1 and 2 containing graphite particles 4 as flaky graphite particles at the same ratio in comprehensive evaluation. In particular, it is understood that when the basal plane-pleated spherical graphite having a relatively small average particle diameter (less than 20 μm) is used, the range of the composition in which the effect of improving both the thermal conductivity (heat dissipation property) and the flexibility is obtained is widened without adversely affecting the appearance.

On the other hand, it is understood that comparative examples 1 and 2 using the flake graphite 4 are inferior to examples 1 to 6 in appearance in addition to the poor thermal conductivity (poor heat radiation property). This is considered to be because the liquid composition used as a raw material of each sheet has a high viscosity and does not form bubbles stably by the mechanical foaming method. Since the viscosity of the liquid tends to increase as the amount of the flaky graphite increases, even if the amount of the flaky graphite is further increased in order to improve the heat dissipation property of the comparative example, it can be said from the above results that the improvement of the thermal conductivity cannot be achieved, that is, the high thermal conductivity (heat dissipation property) and flexibility obtained in the case of using the spherical graphite cannot be achieved when the flaky graphite is used.

As shown in the table below, in the preparation of the composition for comparative example 1, the metal oxide 1 was used in combination with the graphite 4, and the improvement of the thermal conductivity was attempted, but the effect of improving the thermal conductivity was slightly obtained, but the appearance defect was remarkable. That is, it is understood that when the flaky graphite is used in combination with the metal oxide, the effect of improving the thermal conductivity is limited, and the effect of the embodiment of the present invention using the spherical graphite cannot be obtained.

[ Table 2]

(examples 7 to 12)

Instead of preparing the liquid compositions of examples 1 and 2, the respective liquid compositions for examples 7 to 21 having the compositions shown in the following table were prepared by changing the concentration of graphite 1 or 2, using a metal oxide (other heat conductive material) together with graphite 1 or 2, and changing the mixing ratio thereof. The pH of each liquid composition was about 8.4 as in the liquid composition of example 1 or 2.

Sheet-like porous foam bodies of examples 7 to 21 were produced in the same manner as in example 1 except that each liquid composition having the composition shown in the following table was used.

[ Table 3]

Examples 7 to 21 described in the above table are examples obtained by combining spherical graphite 1 or 2 with any one of metal oxides 1 to 3. The thermal conductivity was higher than that of comparative examples 1 and 2 in which all of the flaky graphite was used. Among them, examples 7 to 14 and 18 to 21 in which graphite 1 or 2 (particularly graphite 1) and metal oxide 1 or 2 having a mohs hardness of less than 9 were combined were superior in flexibility-improving effect to examples 15 to 17 in which metal oxide 3 having a mohs hardness of 9 was used. When a metal oxide having a mohs hardness of less than 9 is used, the reduction in flexibility due to the influence of the metal oxide can be suppressed, and high thermal conductivity and flexibility can be realized in a well-balanced manner.

Even the embodiment with a slightly poor heat dissipation property is useful for applications (for example, a filler) in which a requirement for heat dissipation property is not strict, and even the embodiment with a slightly poor flexibility can be used as a heat dissipation member in an electronic and electrical device having a less complicated internal structure.

(examples 22 to 31)

Instead of the preparation of the liquid composition of example 1, the respective liquid compositions for examples 22 to 31 having the compositions shown in the following table were prepared by changing the concentration of graphite 1, using a metal oxide (other heat conductive material) together with graphite 1, changing the mixing ratio thereof, changing the kind of the matrix resin, and the like. The pH of each liquid composition was 8.4 in the same manner as in the liquid composition of example 1, but the pH of the liquid composition for example 31 was 8.0. In addition, the liquid composition had a higher viscosity than the liquid composition of example 1 and the like, and the mechanical foaming method was inferior in bubble formation.

The same procedures as in example 1 were carried out except that the liquid composition of example 1 was changed to each liquid composition, thereby producing the sheet-like porous cellular bodies of examples 22 to 31, respectively.

[ Table 4]

The obtained sheets were evaluated in the same manner as in example 1, and all of the results were superior to those of comparative examples in comprehensive evaluation and were at a level that could withstand practical use.

As can be understood from the evaluation results of the examples shown in tables 1, 3 and 4 above, particularly when the heat conductive material is contained in an amount of 40 to 60 mass% and the proportion of spherical graphite in the entire heat conductive material is 50 mass% or more, a sheet having a high heat radiation property and flexibility in a well-balanced manner can be obtained.

Further, it is understood that when an acrylic resin is used as the matrix resin, a sheet having further excellent heat resistance is obtained.

In the above examples, in order to clarify the effects obtained by the incorporation of spherical graphite, the compositions of the surfactants in the respective examples were the same, but even if the compositions were changed, the same effects could be obtained.

The present invention has been described in detail with reference to the specific embodiments, but it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

The present application is based on Japanese patent application No. 2016 (Japanese patent application No. 2016) (237524), filed on 2016 (12/7/2016), the entire contents of which are incorporated herein by reference. Further, all references cited herein are incorporated by reference in their entirety.

Claims

1. A porous foam body comprising a matrix resin and a heat conductive material dispersed in the matrix resin, wherein the heat conductive material comprises at least spherical graphite,

wherein the spherical graphite has a structure in which a basal plane is folded, and

wherein the basal plane is a plane orthogonal to the C-axis of the graphite crystal, and the spherical graphite is graphite in which the crystal system of natural graphite is strained.

2. The porous foam body according to claim 1, wherein the matrix resin is an acrylic resin.

3. The porous body according to claim 1 or 2, further comprising a metal oxide as the heat conductive material.

4. The porous foam body according to claim 1 or 2, wherein the heat conductive material is contained in an amount of 40 to 60 mass% based on the total mass of the porous foam body.

5. The porous air bubble body according to claim 1 or 2, wherein the heat conductive material contains a metal oxide and spherical graphite at a mixing ratio of 0:10 to 5:5 by mass.

6. The porous foam body according to claim 1 or 2, which is an open-cell porous body.

7. The porous foam body according to claim 1 or 2, wherein the ratio of the amount of the surfactant is determined in accordance with JIS K6254: 2016(ISO 7743: 2011) has a 25% compression load of 20kPa or less, and has a thermal conductivity of 0.3W/(m.K) or more as measured by a probe method using QTM-500 manufactured by Kyoto electronics industries, Ltd.

8. The porous body for a bubble according to claim 1 or 2, which is used for a heat-dissipating member of an electronic product.

9. A method of manufacturing a porous body with air bubbles, the method comprising:

a curing step of curing the liquid composition by reacting the functional groups of the resins with each other and/or by reacting the functional groups of the polyfunctional crosslinking agent with each other and/or by reacting the functional groups of the resins with the functional groups of the polyfunctional crosslinking agent,

wherein the foaming step is performed simultaneously with the curing step and/or the curing step is performed after the foaming step,

the porous foam body according to any one of claims 1 to 8.

10. The manufacturing method according to claim 9, wherein the pH of the liquid composition is in a neutral to alkaline region, and the liquid composition contains at least 1 anionic surfactant as the foaming agent.