Polyimide hollow particles and method for producing polyimide hollow particles

Abstract

Provided are polyimide hollow particles having a shell portion and a hollow portion surrounded by the shell portion, the polyimide hollow particles having excellent heat resistance and excellent dielectric properties. Also provided is a method for producing such polyimide hollow particles.　Polyimide hollow particles according to the embodiment of the present invention have a shell portion and a hollow portion surrounded by the shell portion, and have a dielectric loss tangent of less than 0.0070 at a measurement frequency of 10 GHz.

Description

Polyimide hollow particles and method for producing polyimide hollow particles

[0001] The present invention relates to polyimide hollow particles and a method for producing the polyimide hollow particles.

[0002] Polyimides are chemically and mechanically stable materials that have excellent heat resistance, solvent resistance, mechanical properties, electrical insulation, etc. Therefore, polyimides can be used as coating materials for electrical insulating parts, molding fillers, electrical and electronic materials, metal and ceramic substitutes, films, varnishes, adhesives, bulk molding materials, composite materials, etc.

[0003] Polyimide particles obtained by granulating polyimide are endowed with properties attributable to their shape and structure in addition to the properties inherent to the polyimide. Furthermore, hollow particles are known as a means of imparting lightness, heat insulation, and the like to particles. Therefore, if polyimide particles are hollowed out to form polyimide hollow particles, in addition to the properties inherent to the polyimide, properties attributable to the hollow structure are imparted, which is expected to improve performance in conventional applications and lead to new applications.

[0004] Patent Document 1 discloses a method for producing polyimide microparticle aggregates, in which a polyamic acid solution prepared by dissolving polyamic acid in an organic solvent containing at least 50% of an amide-based solvent is injected under specific conditions into a poor solvent containing a polyacrylate-based polymer surfactant to prepare a dispersion of polyamic acid microparticles, a pyridine / acetic anhydride mixed solution is added to the prepared dispersion of polyamic acid microparticles to cause chemical imidization to prepare a polyimide microparticle dispersion, the organic solvent and the poor solvent are phase-separated in the prepared polyimide microparticle dispersion, the polyimide microparticles are aggregated at the liquid-liquid interface to form polyimide microparticle aggregates, and the formed polyimide microparticle aggregates are separated, recovered, and then dried.

[0005] However, the polyimide microparticle aggregates obtained by the manufacturing method described in Patent Document 1 contain a polyacrylate ester-based polymer surfactant, which has low heat resistance and is used as a dispersant, in the microparticle aggregates. In addition, the use of a large amount of this dispersant reduces the heat resistance that the polyimide can inherently exhibit, and also deteriorates its dielectric properties.

[0006] Patent Document 2 discloses a method for producing hollow particles having a volume average particle diameter of 0.1 μm to 1 mm, wherein the shell of the hollow particles is composed of one or more layers, the outermost of which is layer (a1) made of polyimide (a1), the method comprising the following steps 1 to 6: Step 1: producing a polyamic acid solution (S1) comprising polyamic acid and a solvent (s1); Step 2: dispersing fine particles (A1) composed of another material (b) in the polyamic acid solution (S1) to produce a dispersion liquid (D1); Step 3: mixing and stirring the dispersion liquid (D2) obtained by dispersing hydrophobic fine particles (A2) in a solvent (s2) that does not dissolve polyamic acid and is compatible with the solvent (s1) with the dispersion liquid (D1) to produce a dispersion liquid (D3) containing precursor particles (A3) in which polyamic acid is adsorbed on the surfaces of the fine particles (A1). Step 4: A step of separating and extracting precursor particles (A3) from the dispersion (D3). Step 5: A step of dispersing the precursor particles (A3) in a hydrophobic solvent (s3) having an SP value of 7 or less and a boiling point equal to or higher than the boiling points of the solvents (s1) and (s2), and performing an imidization reaction at a temperature equal to or higher than the boiling points of the solvents (s1) and (s2) and equal to or lower than the boiling point of the hydrophobic solvent (s3), thereby obtaining a hydrophobic solvent dispersion (D4) of imidized particles (A4). Sixth step: a step of obtaining imidized particles (A4) by separating the particles from the hydrophobic solvent dispersion (D4), washing and drying the particles, and in the case where the fine particles (A1) made of the other material (b) are hollow fine particles, the obtained imidized particles (A4) are obtained as the desired hollow particles. In the case where the fine particles (A1) are solid fine particles, the obtained imidized particles (A4) are added to an aqueous medium to be dispersed, and further a solubilizer or decomposer for the other material (b) is added to remove the material (b) and wash the particles, thereby obtaining the desired hollow particles.

[0007] However, the manufacturing method described in Patent Document 2 is a so-called template method for manufacturing hollow particles, and the particle size of the resulting particles depends on the particle size of the template particle. Furthermore, the template particle remains in the hollow portion surrounded by the shell, which affects the physical properties of the template particle and causes problems such as a decrease in the heat resistance that the polyimide originally exhibits and a deterioration in the dielectric properties.

[0008] Patent Document 3 discloses a method for synthesizing a polyimide resin powder, in which a solution (a) containing a tetracarboxylic acid component in a solvent containing an alkylene glycol-based solvent and a solution (b) containing a diamine component in a solvent containing an alkylene glycol-based solvent are separately prepared, and then solution (b) is added to solution (a) or solution (a) is added to solution (b) to prepare a solution (c) containing a polyamic acid, and solution (c) is then heated to imidize the polyamic acid and precipitate a polyimide resin powder in solution (c).

[0009] However, the polyimide resin powder obtained by the manufacturing method described in Patent Document 3 has a problem in that its dielectric properties are poor because its structure is solid due to the solvent precipitation method.

[0010] Patent No. 5429922 Patent No. 5133107 Patent No. 7243717

[0011] The present invention has been made to solve the above-mentioned problems of the related art, and its main object is to provide polyimide hollow particles having a shell portion and a hollow portion surrounded by the shell portion, which have excellent heat resistance and excellent dielectric properties, and to provide a method for producing such polyimide hollow particles.

[0012] [1] A polyimide hollow particle according to an embodiment of the present invention has a shell portion and a hollow portion surrounded by the shell portion, and has a dielectric loss tangent of less than 0.0070 at a measurement frequency of 10 GHz. [2] The polyimide hollow particle according to [1] above may have a relative dielectric constant of less than 2.5 at a measurement frequency of 10 GHz. [3] In the polyimide hollow particle according to [1] or [2] above, the shell portion may contain a polyimide (P) containing a structural unit A derived from a tetracarboxylic dianhydride having an ester bond. [4] The polyimide hollow particle according to any one of [1] to [3] above may have a 5% thermal weight loss temperature of 370°C or higher when the polyimide hollow particle is heated at a rate of 10°C / min in an air atmosphere. [5] The polyimide hollow particle according to any one of [1] to [4] above may have a volume average particle diameter of 0.1 μm to 100 μm. [6] In the polyimide hollow particle described in any one of [1] to [5] above, the hollow portion may consist of one hollow region, and the shell portion may have one or more void spaces. [7] In the polyimide hollow particle described in any one of [1] to [6] above, the relative dielectric constant at a measurement frequency of 10 GHz may be less than 2.0. [8] A method for producing polyimide hollow particles according to an embodiment of the present invention includes the steps of: preparing an emulsion from a solution containing a polyamic acid formed from a tetracarboxylic dianhydride having an ester bond and a diamine, and a solvent to which a dispersant has been added; performing a chemical imidization reaction in the emulsion; and performing a thermal imidization reaction. [9] In the method for producing polyimide hollow particles described in [8] above, the solution containing the polyamic acid may contain 0% by weight to 10% by weight of an aliphatic / aromatic hydrocarbon resin.

[0013] According to an embodiment of the present invention, polyimide hollow particles having a shell portion and a hollow portion surrounded by the shell portion, which have excellent heat resistance and excellent dielectric properties, can be provided, and a method for producing such polyimide hollow particles can be provided.

[0014] 1 is a schematic cross-sectional view of a polyimide hollow particle in which the hollow portion consists of one hollow region and the shell portion has one or more void spaces. FIG. 2 is a SEM photograph of a cross section of a particle (1) obtained in Example 1. FIG. 3 is a SEM photograph of a cross section of a particle (2) obtained in Example 2. FIG. 4 is a SEM photograph of a cross section of a particle (3) obtained in Example 3. FIG. 5 is a SEM photograph of a cross section of a particle (4) obtained in Example 4. FIG. 6 is a SEM photograph of a cross section of a particle (5) obtained in Example 5. FIG. 7 is a SEM photograph of a cross section of a particle (6) obtained in Example 6. FIG. 8 is a SEM photograph of a cross section of a particle (7) obtained in Example 7. FIG. 9 is a SEM photograph of a cross section of a particle (8) obtained in Example 8. FIG. 10 is a SEM photograph of a cross section of a particle (9) obtained in Example 9. FIG. 11 is a SEM photograph of a cross section of a particle (C1) obtained in Comparative Example 1.

[0015] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0016] ≪≪1. Polyimide Hollow Particles≫≫ ≪1-1. Structure and Properties of Polyimide Hollow Particles≫ The polyimide hollow particles according to an embodiment of the present invention are polyimide particles having a shell portion and a hollow portion surrounded by the shell portion. The polyimide hollow particles according to an embodiment of the present invention have a dielectric loss tangent of less than 0.0070 at a measurement frequency of 10 GHz.

[0017] Here, "hollow" means that the interior is filled with a substance other than resin, such as a gas or liquid, and preferably means that the interior is filled with gas, as this can better demonstrate the effects of the present invention.

[0018] The hollow portion surrounded by the shell portion may consist of one hollow region, or may consist of multiple hollow regions or a porous structure.

[0019] The hollow portion may consist of one hollow region, and the shell portion may have one or more air spaces. Here, the air space has a structure separate from the hollow portion surrounded by the shell portion. Typically, the hollow portion is the largest void (a portion where no polyimide is present) within the polyimide hollow particle, and the portion of the polyimide hollow particle other than the hollow portion located outside the hollow portion is the shell portion. The air space exists inside the shell portion. The shell portion may have two or more air spaces.

[0020] Fig. 1 is a schematic cross-sectional view of a polyimide hollow particle in which the hollow portion consists of one hollow region and the shell portion has one or more void spaces. The polyimide hollow particle 10 shown in Fig. 1 has a shell portion 1 and a hollow portion 2 surrounded by the shell portion 1. In Fig. 1, the shell portion 1 has multiple void spaces 3. As shown in Fig. 1, the hollow portion 2 is preferably a single independent pore. In some cases, the hollow portion may be a single interconnected pore.

[0021] Polyimide has excellent heat resistance. Therefore, polyimide hollow particles according to an embodiment of the present invention, which have a shell portion and a hollow portion surrounded by the shell portion and have a dielectric loss tangent at a measurement frequency of 10 GHz that falls within a predetermined numerical range, have excellent heat resistance and excellent dielectric properties. As described above, a resin composition using polyimide hollow particles according to an embodiment of the present invention can exhibit excellent dielectric properties. Examples of excellent dielectric properties include a low dielectric constant and a low dielectric loss tangent.

[0022] The polyimide hollow particles according to an embodiment of the present invention preferably have a volume average particle diameter of 0.1 μm to 100 μm, more preferably 0.3 μm to 80 μm, and even more preferably 0.5 μm to 50 μm. When the volume average particle diameter of the polyimide hollow particles according to an embodiment of the present invention is within the above range, the effects of the present invention can be more effectively achieved. If the volume average particle diameter is too small outside the above range, the shell thickness becomes relatively thin, and the polyimide hollow particles may not have sufficient strength. If the volume average particle diameter is too large outside the above range, the imidization reaction may not proceed sufficiently, resulting in reduced heat resistance.

[0023] The polyimide hollow particles according to an embodiment of the present invention preferably have a particle size coefficient of variation (CV value) of 80% or less, more preferably 1% to 80%, even more preferably 2% to 75%, particularly preferably 3% to 70%, and most preferably 5% to 65%. When the particle size coefficient of variation (CV value) of the polyimide hollow particles according to an embodiment of the present invention is within the above-mentioned range, the effects of the present invention can be more effectively achieved. If the particle size coefficient of variation (CV value) of the polyimide hollow particles according to an embodiment of the present invention is too large, the amount of coarse particles increases, which may make it difficult to form a thin film or cause thickness variations, for example, when a resin layer is formed from the resin composition. The smaller the particle size coefficient of variation (CV value) of the polyimide hollow particles according to an embodiment of the present invention, the more uniform the particle size, which is preferable. However, taking into account factors such as practical feasibility, the lower limit may be as described above.

[0024] The polyimide hollow particles according to an embodiment of the present invention preferably have a 5% thermal weight loss temperature of 370°C or higher, more preferably 390°C or higher, even more preferably 400°C or higher, and particularly preferably 425°C or higher, when heated at a rate of 10°C / min in an air atmosphere. The upper limit of the 5% thermal weight loss temperature is preferably 600°C or lower. As long as the 5% thermal weight loss temperature is within the above range, the polyimide hollow particles according to an embodiment of the present invention can exhibit excellent heat resistance. If the 5% thermal weight loss temperature is too low, outside the above range, for example, when the polyimide hollow particles are kneaded with a thermosetting resin, the polyimide hollow particles may deform due to heating for the curing reaction, resulting in the loss of hollow portions. This may result in a decrease in the dielectric properties, such as low dielectric effect and low dielectric loss tangent, that the polyimide hollow particles are intended to exhibit in a resin composition.

[0025] <1-2. Shell Portion> The shell portion contains a polyimide (P). The polyimide (P) is obtained, for example, by the reaction of a tetracarboxylic anhydride (a) with a diamine (b). The reaction is typically a polymerization reaction. That is, the polyimide (P) contains, for example, a structural unit A derived from the tetracarboxylic anhydride (a) and a structural unit B derived from the diamine (b). The polyimide (P) is preferably obtained by the reaction of a tetracarboxylic dianhydride (a1) having an ester bond with a diamine (b), in that the effects of the present invention can be more effectively exhibited. That is, the polyimide (P) preferably contains a structural unit A1 derived from the tetracarboxylic dianhydride (a1) having an ester bond. When the shell portion contains a polyimide (P) having such a structure, the effects of the present invention can be more effectively exhibited.

[0026] The tetracarboxylic dianhydride (a1) having an ester bond may have two or more ester bonds, that is, the structural unit A1 may have two or more ester bonds.

[0027] The tetracarboxylic dianhydride (a1) having an ester bond preferably has an aromatic ring, that is, the polyimide (P) preferably contains a structural unit derived from an aromatic tetracarboxylic dianhydride having an ester bond.

[0028] The tetracarboxylic dianhydride (a1) having an ester bond may be a compound represented by the following formula (1):

[0029] In formula (1), A is an arbitrary organic group. A may have 6 or more carbon atoms and may have an aromatic ring. A may have a benzene ring or a naphthalene ring.

[0030] The tetracarboxylic dianhydride (a1) having an ester bond may be an ester of trimellitic anhydride with benzenediol, naphthalenediol, a bisphenol, or isosorbide. The tetracarboxylic dianhydride (a1) having an ester bond is preferably an ester of trimellitic anhydride with benzenediol, naphthalenediol, or a bisphenol, and more preferably an ester of trimellitic anhydride with benzenediol or naphthalenediol. The trimellitic anhydride may or may not have a substituent. The benzenediol is preferably hydroquinone. The naphthalenediol is preferably 2,6-dihydroxynaphthalene. The bisphenol is, for example, bisphenol A, bisphenol S, or the like.

[0031] The tetracarboxylic dianhydride (a1) having an ester bond may be 5,5'-[p-phenylenebis(oxycarbonyl)]diphthalic anhydride (TAHQ) or naphthalene-2,6-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate). Examples of the tetracarboxylic dianhydride (a1) having an ester bond include trade names such as 26DHN-TME, 27DHN-TME, TMPBP-TME, BP-TME, BPS-TME, and BPZ-TME (all manufactured by Honshu Chemical Industry Co., Ltd.).

[0032] The tetracarboxylic acid dianhydride (a1) having an ester bond may be of only one type, or may be of two or more types. As described above, the tetracarboxylic acid anhydride (a) is preferably the tetracarboxylic acid dianhydride (a1) having an ester bond. In some cases, the tetracarboxylic acid anhydride (a) may contain a tetracarboxylic acid anhydride other than the tetracarboxylic acid dianhydride (a1) having an ester bond. The tetracarboxylic acid anhydride (a) may be of only one type, or may be of two or more types.

[0033] The structural unit A1 in the polyimide (P) may be a structural unit represented by the following formula (A-1). The structural unit A represented by formula (A-1) is derived from the tetracarboxylic dianhydride (a1) represented by the above formula (1). In formula (A-1), the nitrogen atom contained in the imide group is derived from a diamine that has reacted with a tetracarboxylic dianhydride having an ester bond.

[0034] In formula (A-1), A is the same as in formula (1). Specific examples of the structural unit A represented by formula (A-1) include the following formulae (A-2) and (A-3).

[0035] The polyimide (P) has a structural unit B derived from a diamine (b). Any appropriate diamine can be used as the diamine (b) as long as the effects of the present invention are not impaired. The diamine (b) may be one type or two or more types. Examples of the diamine (b) include 4,4'-diaminodiphenylmethane (DDM), 4,4'-diaminodiphenyl ether (DPE), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 1,4'-bis(4-aminophenoxy)benzene (TPE-Q), 1,3'-bis(4-aminophenoxy)benzene (TPE-R), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), and the like. ), 4,4'-diamino-2,2'-dimethylbiphenyl (TBHG), o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-methylene-bis(2-chloroaniline), 3,3'-dimethyl-4,4'-diaminobiphenyl 4,4'-diaminodiphenyl sulfide, 2,6'-diaminotoluene, 2,4-diaminochlorobenzene, 1,2-diaminoanthraquinone, 1,4-diaminoanthraquinone, 3,3'-diaminobenzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminobibenzyl, R(+)-2,2'-diamino-1,1'-binaphthalene, S(+)-2,2'-diamino-1,1 Examples of the diamine include aromatic diamines such as 1,2-diaminomethane, 1,4-diaminobutane, tetramethylenediamine, and 1,10-diaminododecane; aliphatic diamines such as 1,4-diaminocyclohexane, 1,2-diaminocyclohexane, bis(4-aminocyclohexyl)methane, and 4,4'-diaminodicyclohexylmethane; 3,4-diaminopyridine; and 1,4-diamino-2-butanone. Blocked diamines may also be used as the diamine.Of these diamines, 4,4'-diaminodiphenyl ether (DPE), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), and 4,4'-diamino-2,2'-dimethylbiphenyl (TBHG) are preferred from the viewpoint of further exhibiting the effects of the present invention.

[0036] The structural unit B is preferably a structural unit derived from 4,4'-diaminodiphenyl ether (DPE), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), or 4,4'-diamino-2,2'-dimethylbiphenyl (TBHG).

[0037] The polyimide (P) may be of one kind or of two or more kinds.

[0038] The content of polyimide (P) in the shell portion is preferably 60% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, and particularly preferably 90% by weight to 100% by weight, in order to further exhibit the effects of the present invention.

[0039] The shell portion may contain any other appropriate component within the range that does not impair the effects of the present invention.

[0040] As described above, the polyimide (P) can be obtained, for example, by the reaction of a tetracarboxylic anhydride (a) with a diamine (b), preferably by the reaction of a tetracarboxylic dianhydride (a1) having an ester bond with a diamine (b). This allows the polyimide hollow particles to have a low dielectric loss tangent.

[0041] The molar ratio of the tetracarboxylic acid anhydride (a) to the diamine (b) can be any appropriate ratio within a range that does not impair the effects of the present invention. The molar ratio of the tetracarboxylic acid anhydride (a) to the diamine (b) is, for example, 1:0.5 to 1:1.7, preferably 1:0.8 to 1:1.6, more preferably 1:0.9 to 1:1.5, and even more preferably 1:1 to 1:1.3.

[0042] The reaction between the tetracarboxylic anhydride (a) and the diamine (b) can be carried out by any appropriate reaction as long as the effects of the present invention are not impaired. For example, a polyamic acid is first formed from the tetracarboxylic anhydride (a) and the diamine (b), and then the polyimide (P) is obtained by imidization.

[0043] The reaction between tetracarboxylic anhydride (a) and diamine (b) is carried out, for example, by adding tetracarboxylic anhydride (a) to a solution in which diamine (b) is dissolved in a solvent and stirring the mixture. Any appropriate solvent can be used as the solvent for dissolving diamine (b), but a solvent that dissolves the polyamic acid obtained after adding tetracarboxylic anhydride (a) is preferred. This simplifies the production process of polyimide hollow particles and makes them suitable for mass production, for example. Examples of such solvents include amide solvents such as N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), as well as 1,3-dimethyl-2-imidazolidinone (DMI). Only one solvent may be used, or two or more solvents may be used.

[0044] When forming the polyamic acid, any other appropriate component that does not fall under either the tetracarboxylic anhydride (a) or the diamine (b) may be contained within a range that does not impair the effects of the present invention.

[0045] The other component may include at least one non-crosslinked polymer selected from the group consisting of polyolefins, styrene-based polymers, (meth)acrylic polymers, styrene-(meth)acrylic polymers, polycarbonates, and styrene-maleic anhydride copolymers. Such non-crosslinked polymers may be of only one type or of two or more types.

[0046] The non-crosslinkable polymer may contain a hydrocarbon-based resin. Any appropriate compound may be used as the hydrocarbon-based resin as long as it does not impair the effects of the present invention. Examples of hydrocarbon-based resins include aliphatic / aromatic hydrocarbon resins, aromatic hydrocarbon resins, alicyclic hydrocarbon resins, and aliphatic hydrocarbon resins. The hydrocarbon-based resin is preferably at least one selected from the group consisting of aliphatic / aromatic hydrocarbon resins, aromatic hydrocarbon resins, and aliphatic hydrocarbon resins, more preferably at least one selected from the group consisting of aliphatic / aromatic hydrocarbon resins and aromatic hydrocarbon resins, and even more preferably an aliphatic / aromatic hydrocarbon resin. This promotes phase separation of polymerized oil droplets during suspension polymerization, resulting in superior low dielectric properties. These hydrocarbon-based resins may be used alone or in combination of two or more.

[0047] Aliphatic / aromatic hydrocarbon resin refers to a hydrocarbon resin in which an aliphatic hydrocarbon and an aromatic hydrocarbon are copolymerized. The aliphatic hydrocarbon constituting the aliphatic / aromatic hydrocarbon resin is an aliphatic hydrocarbon having a polymerizable unsaturated bond. The aliphatic hydrocarbon is typically a diene, an aliphatic fraction obtained by thermal cracking of naphtha. The aliphatic hydrocarbon has, for example, 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms, and more preferably 5 carbon atoms. Examples of such aliphatic hydrocarbons include linear dienes such as isoprene and piperylene; and cyclic dienes such as cyclopentadiene, methylcyclopentadiene, dicyclopentadiene, methyldicyclopentadiene, and dimethyldicyclopentadiene, with linear dienes being preferred. These aliphatic hydrocarbons may be one type or two or more types. The aromatic hydrocarbon constituting the aliphatic / aromatic hydrocarbon resin is typically an aromatic compound having a linear or cyclic substituent containing a polymerizable unsaturated bond. The aromatic hydrocarbon is typically an aromatic fraction obtained by thermal cracking of naphtha. The aromatic hydrocarbon has, for example, 7 to 11 carbon atoms, preferably 8 to 10 carbon atoms. Examples of such aromatic hydrocarbons include cyclic dienes such as styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, divinylbenzene, indene, and methylindene, with styrene, vinyltoluene, and indene being preferred. These aromatic hydrocarbons may be of one type or of two or more types. Aliphatic / aromatic hydrocarbon resins are resins obtained by polymerizing, for example, styrene, vinyltoluene, indene, isoprene, and piperylene. The ratio of aliphatic hydrocarbon components to aromatic hydrocarbon components in the aliphatic / aromatic hydrocarbon resin (aliphatic hydrocarbons / aromatic hydrocarbons) is preferably greater than 30%, more preferably 40% or more, and even more preferably 45% or more, and preferably 70% or less, more preferably 60% or less, and even more preferably 50% or less. The weight average molecular weight (Mw) of the aliphatic / aromatic hydrocarbon resin is, for example, 500 to 5,000, preferably 1,000 to 4,800, more preferably 2,000 to 4,500, and even more preferably 3,000 to 4,000.

[0048] The aromatic hydrocarbon resin refers to a hydrocarbon resin in which aromatic hydrocarbons are copolymerized. The aromatic hydrocarbon has, for example, 7 to 11 carbon atoms, preferably 8 to 10 carbon atoms, and examples of the aromatic hydrocarbons constituting the aliphatic / aromatic hydrocarbon resin include those mentioned above. Examples of the aromatic hydrocarbon resin include resins obtained by polymerizing styrene, vinyltoluene, and indene.

[0049] The alicyclic hydrocarbon resin is, for example, a resin obtained by hydrogenating an aliphatic / aromatic hydrocarbon resin or an aromatic hydrocarbon resin.

[0050] The aliphatic hydrocarbon resin is a hydrocarbon resin obtained by polymerizing an aliphatic hydrocarbon. The aliphatic hydrocarbon constituting the aliphatic hydrocarbon resin has, for example, 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms, and more preferably 5 carbon atoms. Examples of the aliphatic hydrocarbon constituting the aliphatic / aromatic hydrocarbon resin include those described above.

[0051] The content of the hydrocarbon-based resin relative to the total amount of tetracarboxylic anhydride (a), diamine (b), the solvent, and the non-crosslinkable polymer is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight, and even more preferably 0% by weight to 2% by weight, in order to further demonstrate the effects of the present invention. The content of the hydrocarbon-based resin relative to the total amount of tetracarboxylic anhydride (a), diamine (b), the solvent, and the non-crosslinkable polymer may be greater than 0% by weight, 0.1% by weight or more, or even 0.3% by weight or more. The content of the non-crosslinkable polymer relative to the total amount of tetracarboxylic anhydride (a), diamine (b), the solvent, and the non-crosslinkable polymer is preferably 0% by weight to 20% by weight, more preferably 0% by weight to 10% by weight, even more preferably 0% by weight to 5% by weight, and particularly preferably 0% by weight to 2% by weight, in order to further demonstrate the effects of the present invention.

[0052] The imidization is carried out by, for example, at least one selected from the group consisting of a chemical imidization reaction and a thermal imidization reaction, and is preferably carried out by both a chemical imidization reaction and a thermal imidization reaction.

[0053] <1-3. Dielectric Constant and Dielectric Loss Tangent of Polyimide Hollow Particles> In electronic devices, which are one application of hollow particles, the transmission loss caused by the heat conversion of radio waves transmitted for communication in a dielectric is expressed as the product of the square root of the frequency, the dielectric constant, and the dielectric loss tangent. In other words, since the transmission signal is more likely to be converted into heat in proportion to the frequency, the higher the frequency band, the lower the dielectric properties required for communication component (semiconductor component) materials in order to suppress transmission loss.

[0054] Therefore, the dielectric constant of the polyimide hollow particles according to an embodiment of the present invention, at a measurement frequency of 10 GHz, is preferably less than 2.5, more preferably 1.0 to 2.3, even more preferably 1.0 to 2.2, still more preferably 1.0 to 2.1, particularly preferably 1.0 to 2.0, and most preferably 1.0 to less than 2.0.

[0055] The dielectric loss tangent of the polyimide hollow particles according to an embodiment of the present invention, at a measurement frequency of 10 GHz, is preferably 0 to 0.0060, more preferably 0 to 0.0050, even more preferably 0 to 0.0045, and particularly preferably 0 to 0.0040. When the dielectric constant and dielectric loss tangent of the polyimide hollow particles according to an embodiment of the present invention are within the above ranges, the effects of the present invention can be more effectively exhibited.

[0056] The polyimide hollow particles according to an embodiment of the present invention preferably have a dielectric constant of less than 2.5 and a dielectric dissipation factor of less than 0.0050 at a measurement frequency of 10 GHz, more preferably have a dielectric constant of less than 2.3 and a dielectric dissipation factor of less than 0.0045 at a measurement frequency of 10 GHz, and even more preferably have a dielectric constant of less than 2.0 and a dielectric dissipation factor of less than 0.0045 at a measurement frequency of 10 GHz.

[0057] If the dielectric constant exceeds 2.5, even if the polyimide hollow particles are mixed with, for example, a thermosetting resin, a sufficient effect of lowering the dielectric constant cannot be obtained, and there is a risk that transmission loss will occur and the amount of heat generated by the component will increase when used in a high frequency band.

[0058] The values ​​of the dielectric constant and the dielectric loss tangent of the polyimide hollow particles according to the embodiment of the present invention are not limited to those described above. For example, when the polyimide hollow particles according to the embodiment of the present invention are used for applications other than semiconductor components, the values ​​of the dielectric constant and the dielectric loss tangent are not limited to those described above.

[0059] <1-4. Uses of Polyimide Hollow Particles> The polyimide hollow particles according to an embodiment of the present invention can be employed in various applications. In terms of being able to further utilize the effects of the present invention, the polyimide hollow particles according to an embodiment of the present invention are suitable for applications such as semiconductor members (typically, resin compositions for semiconductor members), paint compositions, cosmetics, paper coating compositions, heat insulating compositions, light diffusing compositions, and light diffusing films, and are particularly suitable for resin compositions for semiconductor members and paint compositions.

[0060] <Resin Composition for Semiconductor Member> The polyimide hollow particles according to an embodiment of the present invention can achieve a low dielectric constant and a low dielectric loss tangent and exhibit excellent heat resistance, and therefore can be suitably used in a resin composition for a semiconductor member.

[0061] The resin composition for a semiconductor member according to an embodiment of the present invention includes the polyimide hollow particles according to an embodiment of the present invention.

[0062] The term "semiconductor member" refers to a member that constitutes a semiconductor, such as a semiconductor package or a semiconductor module. In this specification, the term "resin composition for a semiconductor member" refers to a resin composition used for a semiconductor member.

[0063] A semiconductor package is constructed using an IC chip as an essential component and at least one member selected from a mold resin, an underfill material, a mold underfill material, a die bond material, a prepreg for a semiconductor package substrate, a metal-clad laminate for a semiconductor package substrate, and a build-up material for a printed circuit board for a semiconductor package.

[0064] A semiconductor module is constructed using a semiconductor package as an essential component and at least one member selected from a prepreg for printed circuit boards, a metal-clad laminate for printed circuit boards, a build-up material for printed circuit boards, a solder resist material, a coverlay film, an electromagnetic wave shielding film, and an adhesive sheet for printed circuit boards.

[0065] <Coating Composition> The polyimide hollow particles according to an embodiment of the present invention can impart an excellent appearance to a coating film containing the particles, and therefore can be suitably used in a coating composition.

[0066] The coating composition according to an embodiment of the present invention includes polyimide hollow particles according to an embodiment of the present invention.

[0067] The coating composition according to an embodiment of the present invention preferably contains at least one selected from a binder resin and a UV-curable resin. The binder resin may be of only one type or may contain two or more types. The UV-curable resin may be of only one type or may contain two or more types.

[0068] Any suitable binder resin can be used as long as it does not impair the effects of the present invention. Examples of such binder resins include resins soluble in organic solvents or water, and emulsion-type aqueous resins that can be dispersed in water. Specific examples of binder resins include acrylic resins, alkyd resins, polyester resins, polyurethane resins, chlorinated polyolefin resins, and amorphous polyolefin resins.

[0069] As the UV-curable resin, any appropriate UV-curable resin can be used as long as it does not impair the effects of the present invention. Examples of such UV-curable resins include polyfunctional (meth)acrylate resins and polyfunctional urethane acrylate resins. Polyfunctional (meth)acrylate resins are preferred, and polyfunctional (meth)acrylate resins having three or more (meth)acryloyl groups in one molecule are more preferred. Specific examples of polyfunctional (meth)acrylate resins having three or more (meth)acryloyl groups in one molecule include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, 1,2,4-cyclohexane tetra(meth)acrylate, pentaglycerol triacrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol triacrylate, dipentaerythritol pentaacrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol triacrylate, and tripentaerythritol hexaacrylate.

[0070] When the coating composition according to an embodiment of the present invention contains at least one selected from a binder resin and a UV-curable resin, any appropriate content ratio can be adopted depending on the purpose. Typically, the polyimide hollow particles according to an embodiment of the present invention are preferably contained in an amount of 5 to 50% by weight, more preferably 10 to 50% by weight, and even more preferably 20 to 40% by weight, based on the total amount of the binder resin (in terms of solids content in the case of an emulsion-type aqueous resin), the at least one selected from the UV-curable resin, and the polyimide hollow particles according to an embodiment of the present invention.

[0071] When a UV-curable resin is used, a photopolymerization initiator is preferably used in combination. Any appropriate photopolymerization initiator can be used as long as it does not impair the effects of the present invention. Examples of such photopolymerization initiators include acetophenones, benzoins, benzophenones, phosphine oxides, ketals, α-hydroxyalkylphenones, α-aminoalkylphenones, anthraquinones, thioxanthones, azo compounds, peroxides (described in JP 2001-139663 A, etc.), 2,3-dialkyldione compounds, disulfide compounds, fluoroamine compounds, aromatic sulfonium compounds, onium salts, borate salts, active halogen compounds, and α-acyloxime esters.

[0072] The coating composition according to the embodiment of the present invention may contain a solvent. The solvent may be one kind or two or more kinds. When the coating composition according to the embodiment of the present invention contains a solvent, any appropriate content ratio can be adopted depending on the purpose.

[0073] As the solvent, any appropriate solvent can be used as long as it does not impair the effects of the present invention. Such a solvent is preferably a solvent that can dissolve or disperse a binder resin or a UV-curable resin. Examples of such solvents include, for oil-based paints, hydrocarbon solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; and ether solvents such as dioxane, ethylene glycol diethyl ether, and ethylene glycol monobutyl ether. For water-based paints, examples of such solvents include water and alcohols.

[0074] The coating composition according to the embodiment of the present invention may be diluted to adjust the viscosity as needed. Any appropriate diluent may be used depending on the purpose. Examples of such diluents include the solvents mentioned above. The diluent may be one type or two or more types.

[0075] The coating composition according to an embodiment of the present invention may contain other components, such as a coating surface conditioner, a flowability conditioner, an ultraviolet absorber, a light stabilizer, a curing catalyst, an extender pigment, a color pigment, a metal pigment, a mica powder pigment, or a dye, as needed.

[0076] When forming a coating film using the coating composition according to an embodiment of the present invention, any appropriate coating method can be adopted depending on the purpose, such as spray coating, roll coating, brush coating, coating reverse roll coating, gravure coating, die coating, comma coating, and spray coating.

[0077] When forming a coating film using the coating composition according to an embodiment of the present invention, any suitable method can be adopted depending on the purpose. For example, a coating film can be formed by applying the composition to any surface of a substrate, drying the coating film, and then curing the coating film as needed. Examples of substrates include metal, wood, glass, and plastics (PET (polyethylene terephthalate), PC (polycarbonate), acrylic resin, TAC (triacetyl cellulose), etc.).

[0078] <<2. Method for Producing Polyimide Hollow Particles>> The method for producing polyimide hollow particles of the present invention includes the steps of: preparing an emulsion from a solution containing a polyamic acid formed from a tetracarboxylic dianhydride having an ester bond and a diamine, and a solvent to which a dispersant has been added (hereinafter, this step may be referred to as step I); carrying out a chemical imidization reaction in the emulsion (hereinafter, this step may be referred to as step II); and carrying out a thermal imidization reaction (hereinafter, this step may be referred to as step III).

[0079] According to the manufacturing method of the embodiment of the present invention, polyimide hollow particles having excellent heat resistance and excellent dielectric properties can be manufactured. According to the manufacturing method, for example, the polyimide hollow particles according to the embodiment of the present invention can be manufactured easily.

[0080] The method for producing polyimide hollow particles according to an embodiment of the present invention does not rely on a so-called template method using template particles, and therefore has the advantage that the particle size of the resulting polyimide hollow particles does not depend on the particle size of the template particles.Furthermore, the method for producing polyimide hollow particles according to an embodiment of the present invention does not rely on a so-called template method using template particles, and therefore the template particles do not remain in the hollow portion surrounded by the shell portion, and therefore has the advantage that the physical properties of the template particles do not affect the physical properties of the resulting polyimide hollow particles.In particular, the method has the advantage that the heat resistance that polyimide originally exhibits and the dielectric properties due to the hollow portion structure can be fully exhibited.

[0081] Furthermore, the method for producing polyimide hollow particles according to an embodiment of the present invention does not require high temperature and high pressure conditions, and therefore has the advantage of eliminating the need for special production equipment for reactions at high temperature and high pressure, and reducing factors that reduce production efficiency, such as the time required for heating and cooling.

[0082] The method for producing polyimide hollow particles according to the embodiment of the present invention may include any appropriate step other than Step I, Step II, and Step III, as long as the effect of the present invention is not impaired.

[0083] <2-1. Step I> In step I, an emulsion is prepared from a solution containing a polyamic acid formed from a tetracarboxylic dianhydride having an ester bond and a diamine, and a solvent to which a dispersant has been added. Step I may include step IA of preparing an internal oil phase containing a solution containing a polyamic acid formed from a tetracarboxylic dianhydride having an ester bond and a diamine, step IB of preparing an external oil phase containing a dispersant and a solvent, and step IC of preparing an emulsion from the internal oil phase prepared in step I and the external oil phase prepared in step II.

[0084] In step IA, an internal oil phase containing a solution containing a polyamic acid is prepared. The internal oil phase is preferably a solution containing a polyamic acid itself. The solution containing a polyamic acid contains a solvent and a polyamic acid dissolved in the solvent.

[0085] The solution containing the polyamic acid may be prepared by any suitable method as long as the effects of the present invention are not impaired, such as a method of mixing a tetracarboxylic dianhydride having an ester bond with a diamine solution prepared by dissolving a diamine in a solvent, followed by reaction.

[0086] As for the diamine used in the diamine solution, the description of the diamine (b) in the section <<1-2. Shell Portion>> of <<1. Polyimide Hollow Particles>> can be directly applied.

[0087] Any suitable solvent can be used for the diamine solution as long as it substantially dissolves the diamine and does not impair the effects of the present invention. However, a solvent that substantially dissolves both the diamine and the resulting polyamic acid is preferred. This solvent may be used alone or in combination with two or more solvents. Examples of such solvents include amide solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP), as well as 1,3-dimethyl-2-imidazolidinone (DMI). While the solvent preferably consists solely of the above solvents, in some cases, a poor solvent for the polyamic acid may be mixed in to the extent that the polyamic acid dissolves. Examples of poor solvents include 2-propanone, 3-pentanone, tetrahydropyrene, epichlorohydrin, acetone, methyl ethyl ketone (MEK), tetrahydrofuran (THF), ethyl acetate, acetanilide, methanol, ethanol, isopropanol, toluene, and xylene.

[0088] The concentration of the diamine in the diamine solution may be any appropriate concentration within a range that does not impair the effects of the present invention. From the viewpoint of obtaining a polyamic acid through a good reaction, the concentration is preferably 0.01% by weight to 20% by weight, more preferably 0.1% by weight to 10% by weight, even more preferably 0.3% by weight to 9.0% by weight, and particularly preferably 0.5% by weight to 7.0% by weight.

[0089] For the tetracarboxylic acid dianhydride having an ester bond to be used, the description of the tetracarboxylic acid dianhydride (a1) having an ester bond in the section <<1-2. Shell portion>> of <<1. Polyimide hollow particles>> can be directly cited.

[0090] The molar ratio of the tetracarboxylic acid dianhydride having an ester bond to the diamine may be any appropriate ratio within a range that does not impair the effects of the present invention. The molar ratio of the tetracarboxylic acid dianhydride having an ester bond to the diamine is, for example, 1:0.5 to 1:1.7, preferably 1:0.8 to 1:1.6, more preferably 1:0.9 to 1:1.5, and even more preferably 1:1 to 1:1.3.

[0091] As a method for mixing the tetracarboxylic dianhydride having an ester bond with the diamine solution and causing the reaction, any appropriate method can be adopted as long as the effects of the present invention are not impaired. Examples of the method for mixing the tetracarboxylic dianhydride having an ester bond with the diamine solution and causing the reaction include a method of stirring with a stirring bar or stirring blade, and a method of stirring with ultrasonic waves.

[0092] The temperature at which the diamine solution is mixed with the tetracarboxylic dianhydride having an ester bond and reacted can be any appropriate temperature within a range that does not impair the effects of the present invention, preferably 0°C to 130°C, more preferably 5°C to 80°C, even more preferably 10°C to 50°C, particularly preferably 15°C to 40°C, and most preferably 20°C to 30°C.

[0093] The time for mixing the diamine solution with the tetracarboxylic dianhydride having an ester bond and reacting them can be any appropriate time within the range that does not impair the effects of the present invention. From the viewpoint of preparing a solution in which the polyamic acid is dissolved, the time is preferably 10 seconds to 24 hours, more preferably 60 seconds to 12 hours, even more preferably 5 minutes to 6 hours, and particularly preferably 10 minutes to 5 hours.

[0094] According to the above method, a polyamic acid solution is obtained in which polyamic acid, which is generated by the reaction between diamine and tetracarboxylic dianhydride having an ester bond, is dissolved in the solvent of the diamine solution.

[0095] The method for preparing a solution containing polyamic acid is not limited to the above. For example, a polyamic acid solution may be prepared by obtaining polyamic acid microparticles from a tetracarboxylic dianhydride having an ester bond and a diamine, and then dissolving the polyamic acid microparticles in a solvent. However, a method for directly obtaining a polyamic acid solution by mixing a tetracarboxylic dianhydride having an ester bond with a diamine solution and reacting them is a simpler process and more suitable for mass production.

[0096] The internal oil phase may contain any appropriate other components as long as the polyamic acid solution is contained within a range that does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the content of the polyamic acid solution, i.e., the total content of the polyamic acid and the solvent, in the internal oil phase is preferably 80% by weight to 100% by weight, more preferably 90% by weight to 100% by weight, even more preferably 95% by weight to 100% by weight, and particularly preferably 98% by weight to 100% by weight.

[0097] The internal oil phase may contain, as the other component, at least one non-crosslinked polymer selected from the group consisting of polyolefins, styrene-based polymers, (meth)acrylic polymers, styrene-(meth)acrylic polymers, polycarbonates, and styrene-maleic anhydride copolymers. That is, the polyamic acid-containing solution may contain a non-crosslinked polymer. Such non-crosslinked polymers may be of only one type or of two or more types. The non-crosslinked polymer may contain a hydrocarbon-based resin. The hydrocarbon-based resin used as the non-crosslinked polymer may be the same as described in the section 1-2. Shell Portion of 1. Polyimide Hollow Particles. The hydrocarbon-based resin is preferably an aliphatic / aromatic hydrocarbon resin. The hydrocarbon-based resin may function as an oil droplet stabilizer.

[0098] The content of the hydrocarbon-based resin in the solution containing the polyamic acid (i.e., the internal oil phase) is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight, and even more preferably 0% by weight to 2% by weight, in order to further demonstrate the effects of the present invention. The content of the hydrocarbon-based resin in the internal oil phase may be greater than 0% by weight, 0.1% by weight or more, or even 0.3% by weight or more. The content of the non-crosslinkable polymer in the internal oil phase is preferably 0% by weight to 20% by weight, more preferably 0% by weight to 10% by weight, even more preferably 0% by weight to 5% by weight, and particularly preferably 0% by weight to 2% by weight, in order to further demonstrate the effects of the present invention.

[0099] The concentration of the polyamic acid in the internal oil phase may be any appropriate concentration within a range that does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the concentration is preferably 0.1% by weight to 30% by weight, more preferably 1% by weight to 25% by weight, even more preferably 5% by weight to 20% by weight, and particularly preferably 10% by weight to 15% by weight.

[0100] In Step IB, an external oil phase is prepared that includes a dispersant and a solvent.

[0101] Any appropriate dispersant may be used as the dispersant as long as it does not impair the effects of the present invention. The dispersant is, for example, at least one selected from a compound having a siloxane bond and silicon dioxide. The compound having a siloxane bond may be of only one type, or may be of two or more types. The silicon dioxide may be of only one type, or may be of two or more types. From the viewpoint of obtaining better dielectric properties of the polyimide hollow particles, the dispersant is preferably silicon dioxide.

[0102] By using at least one dispersant selected from the group consisting of compounds having siloxane bonds and silicon dioxide, the dispersant itself has high heat resistance, unlike polyacrylate-based polymer surfactants, which have low heat resistance, and therefore does not reduce the heat resistance that the polyimide in the target polyimide particles can inherently exhibit. Furthermore, by using at least one dispersant selected from the group consisting of compounds having siloxane bonds and silicon dioxide, a good emulsion can be obtained even with a small amount of dispersant used, and the chemical imidization reaction from polyamic acid to polyimide can be carried out in a relatively high concentration system, resulting in excellent production efficiency.

[0103] The compound having a siloxane bond is a compound having an Si—O—Si bond, and preferably a compound having a structure represented by formula (2).

[0104] In formula (2), R 1 , R 2 are the same or different and each represents a hydrogen atom or an alkyl group. From the viewpoint of further exhibiting the effects of the present invention, the number of carbon atoms in this alkyl group is preferably 1 to 10, more preferably 1 to 6, even more preferably 1 to 4, particularly preferably 1 or 2, and most preferably 1. In formula (2), R 1 , R 2 From the viewpoint of further exerting the effects of the present invention, each of the groups is preferably an alkyl group, more preferably a methyl group.

[0105] The compound having a siloxane bond is more preferably a compound having a polysiloxane structure in which the structure represented by formula (2) is a repeating unit, and even more preferably a compound having a structure represented by formula (2) (where R 1 is a methyl group, R 2 is a methyl group) as a repeating unit.

[0106] One embodiment of the compound having a siloxane bond is a polysiloxane. By employing a polysiloxane, the effects of the present invention can be more effectively exhibited. One preferred embodiment of the polysiloxane is a self-emulsified product of a high polymerization degree polysiloxane, and a commercially available product thereof is, for example, "KM-9787" manufactured by Shin-Etsu Chemical Co., Ltd.

[0107] Another embodiment of the compound having a siloxane bond is a compound having a structure represented by formula (2) and an azo group (-N=N-). By employing such a compound, the effects of the present invention can be more effectively exhibited.

[0108] The compound having an azo group has a number average molecular weight Mn of preferably 5,000 to 1,000,000, more preferably 10,000 to 800,000, even more preferably 30,000 to 500,000, particularly preferably 40,000 to 300,000, and most preferably 50,000 to 200,000, from the viewpoint of being able to further exhibit the effects of the present invention.

[0109] The compound having an azo group preferably has an amide bond (—NH—CO—) from the viewpoint of further exhibiting the effects of the present invention. By having an amide bond in addition to an azo group (—N═N—), the effects of the present invention can be further exhibited due to the electronic effects and steric effects derived from the azo group and amide group.

[0110] The compound having an azo group more preferably has a cyano group, from the viewpoint of further exerting the effects of the present invention. By having an amide bond and a cyano group in addition to an azo group (—N═N—), the effects of the present invention can be further exerted due to the electronic effects and steric effects derived from the azo group, amide group, and cyano group.

[0111] The compound having an azo group is a compound having a polydimethylsiloxane structure, an azo group, an amide group, and a cyano group, from the viewpoint of further enhancing the effects of the present invention. Any appropriate compound can be used as such a compound as long as it does not impair the effects of the present invention. Specific examples of such compounds include those available under the trade names "VPS-1001" and "VPS-1001N" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., which are known as polymeric azo polymerization initiators containing polydimethylsiloxane units.

[0112] Another embodiment of the compound having a siloxane bond is a compound having a structure represented by formula (2), which can be used as a silicone surfactant. Examples of silicone surfactants include linear or branched polyoxyalkylene / alkyl-co-modified organopolysiloxanes. Specific examples of such compounds include "KF-6048," a product name manufactured by Shin-Etsu Chemical Co., Ltd., which is known as a polyether-modified silicone surfactant.

[0113] One embodiment of silicon dioxide has a specific surface area of ​​10 m 2 By employing such hydrophobic silica particles, the effects of the present invention can be more effectively exhibited.

[0114] The specific surface area of ​​the hydrophobic silica particles is preferably 10 m from the viewpoint of further exhibiting the effects of the present invention. 2 / g to 1000m 2 / g, more preferably 30m 2 / g~500m 2 / g, and more preferably 50m 2 / g to 300m 2 / g.

[0115] Silicon dioxide has a specific surface area of ​​10 m 2 / g or more hydrophobic silica particles, any suitable compound can be used within the range that does not impair the effects of the present invention.Specific examples of such compounds include those under the trade names "Aerosil R972", "Aerosil R972CF", "Aerosil R972V", "Aerosil R974", "Aerosil R976", "Aerosil R976S", and "Aerosil R9200" manufactured by Nippon Aerosil Co., Ltd.

[0116] As the solvent for the external oil phase, any appropriate solvent can be used as long as it does not impair the effects of the present invention. Such solvents may be used alone or in combination of two or more kinds.

[0117] From the viewpoint of obtaining polyimide hollow particles with superior dielectric properties, the solvent is preferably a hydrocarbon solvent, such as pentane, hexane, cyclohexane, heptane, octane, benzene, toluene, xylene, or ethylbenzene.

[0118] From the viewpoint of obtaining polyimide hollow particles with better dielectric properties, it is preferred that the dispersant in the outer oil phase is silicon dioxide and the solvent is a hydrocarbon solvent.

[0119] In some cases, silicone oil may be used as a solvent for the external oil phase. For example, when a silicone surfactant is used as a dispersant, a silicone oil in which the silicone surfactant is soluble may be used.

[0120] The external oil phase may contain any appropriate other components as long as they do not impair the effects of the present invention, as long as they contain a dispersant and a solvent. From the perspective of further enhancing the effects of the present invention, the total content of the dispersant and the solvent in the external oil phase is preferably 80% to 100% by weight, more preferably 90% to 100% by weight, even more preferably 95% to 100% by weight, particularly preferably 98% to 100% by weight, and most preferably substantially 100% by weight. Note that "substantially 100% by weight" means that there are no intentionally added other components, but it may also include the presence of very small amounts of impurities (e.g., less than 1% by weight) that do not affect the effects of the present invention.

[0121] From the viewpoint of further exerting the effects of the present invention, the external oil phase is preferably prepared by dissolving a dispersant in a solvent, and more preferably prepared by dissolving at least one selected from the group consisting of a compound having a siloxane bond and silicon dioxide in a hydrocarbon solvent.

[0122] The concentration of the dispersant in the external oil phase may be any appropriate concentration as long as it does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the concentration is preferably 0.001% by weight to 10% by weight, more preferably 0.005% by weight to 5.0% by weight, and even more preferably 0.01% by weight to 3.0% by weight.

[0123] In step IC, an emulsion is prepared from the internal oil phase prepared in step I and the external oil phase prepared in step II. The emulsion is typically prepared by mixing the internal oil phase and the external oil phase.

[0124] The internal oil phase and the external oil phase are typically mixed by adding the internal oil phase to the external oil phase.

[0125] From the viewpoint of further exhibiting the effects of the present invention, the mixing ratio of the internal oil phase to the external oil phase is preferably 1:5 to 1:500 by weight, more preferably 1:5 to 1:300, and even more preferably 1:5 to 1:100.

[0126] As a method for preparing an emulsion from an internal oil phase and an external oil phase, any appropriate method can be adopted as long as it does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, a method for preparing an emulsion from an internal oil phase and an external oil phase preferably involves adding the internal oil phase to the external oil phase and emulsifying it using an emulsifier or disperser. Examples of emulsifiers and dispersers include batch-type emulsifiers such as homogenizers (manufactured by IKA, etc.), Polytron homogenizers (manufactured by Central Scientific Trading Co., Ltd. or Kinematica, etc.), and homomixer MARK II (manufactured by Primix); Ebara Milder (manufactured by Arihara Manufacturing Co., Ltd.), Filmix (manufactured by Primix), colloid mills (manufactured by Kobe Steel Pantech Co., Ltd., etc.), slasher (manufactured by Mitsui Miike Chemical Engineering Co., Ltd., etc.), trigonal wet mills (manufactured by Mitsui Miike Chemical Engineering Co., Ltd., etc.), and capillaries. Examples of suitable emulsifiers include continuous emulsifiers such as Tron (manufactured by Eurotech, etc.) and Fine Flow Mill (manufactured by Pacific Machinery Co., Ltd.); high-pressure emulsifiers such as Microfluidizer (manufactured by Powrex Corporation), Nanomizer (manufactured by Nanomizer Co., Ltd.), Nanovaita (manufactured by Yoshida Kikai Kogyo Co., Ltd.), and APV Gaulin (manufactured by Gaulin Co., Ltd.); membrane emulsifiers such as membrane emulsifiers (manufactured by Reika Kogyo, etc.); vibration emulsifiers such as Vibromixer (manufactured by Reika Kogyo, etc.); and ultrasonic emulsifiers such as ultrasonic homogenizers (manufactured by Branson, etc.).

[0127] When preparing an emulsion from the internal oil phase and the external oil phase, any appropriate other component may be added within a range that does not impair the effects of the present invention.

[0128] The concentration of polyamic acid in the emulsion prepared from the internal oil phase and the external oil phase may be any appropriate concentration within a range that does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the concentration of polyamic acid in the emulsion prepared from the internal oil phase and the external oil phase is preferably 0.1 wt % or more, more preferably 0.2 wt % to 20.0 wt %, and even more preferably 0.3 wt % to 10.0 wt %.

[0129] <2-2. Step II> In step II, a chemical imidization reaction is carried out in the emulsion prepared in step I.

[0130] In step II, a chemical imidization reaction is preferably carried out by adding a chemical imidization agent to the emulsion.

[0131] Any appropriate chemical imidizing agent can be used as the chemical imidizing agent as long as it does not impair the effects of the present invention. The chemical imidizing agent may be a single agent or two or more agents. An example of such a chemical imidizing agent is a combination of pyridine and acetic anhydride. From the viewpoint of further exhibiting the effects of the present invention, the weight ratio of pyridine to acetic anhydride when using pyridine and acetic anhydride is preferably 1:0.1 to 1:10, more preferably 1:0.3 to 1:3, even more preferably 1:0.5 to 1:2, and particularly preferably 1:0.8 to 1:1.2.

[0132] The amount of the chemical imidizing agent used may be any appropriate amount as long as the effects of the present invention are not impaired. From the viewpoint of further exhibiting the effects of the present invention, the amount of the chemical imidizing agent used is preferably 40 to 1,200 parts by weight, more preferably 60 to 1,000 parts by weight, and even more preferably 80 to 800 parts by weight, relative to 100 parts by weight of the polyamic acid in the internal oil phase.

[0133] The reaction temperature of the chemical imidization reaction can be set to any appropriate temperature depending on the boiling point of the solvent in the external oil phase, as long as the effects of the present invention are not impaired. From the viewpoint of further exhibiting the effects of the present invention, the reaction temperature of the chemical imidization reaction is preferably 100°C or lower, more preferably 0°C to 90°C, and even more preferably 20°C to 80°C.

[0134] The reaction time for the chemical imidization reaction may be any appropriate time within a range that does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the reaction time for the chemical imidization reaction is preferably 0.1 to 50 hours, and more preferably 1.0 to 24 hours.

[0135] The chemical imidization reaction forms hollow polyimide particles in the reaction solution, which can be isolated by solid-liquid separation using any suitable method, washed as needed, and dried as needed to obtain hollow polyimide particles.

[0136] Any suitable method for solid-liquid separation can be adopted as long as it does not impair the effects of the present invention. Examples of such a method for solid-liquid separation include centrifugation.

[0137] <2-3. Step III> In Step III, a thermal imidization reaction is carried out. After the chemical imidization reaction, a thermal imidization reaction is carried out as Step III. Preferably, the polyimide hollow particles formed in Step II are isolated, washed by any appropriate method as needed, and dried by any appropriate method as needed, before Step III is carried out.

[0138] In step III, a thermal imidization reaction is preferably carried out by heat treatment.

[0139] The method for producing polyimide hollow particles according to an embodiment of the present invention includes step III, which allows for sufficient imidization. Furthermore, the heat treatment for the thermal imidization reaction allows for sufficient removal of the solvent of the polyamic acid solution used in the internal oil phase and the solvent of the external oil phase, resulting in satisfactory formation of hollow portions in the hollow particles. This allows for the production of polyimide hollow particles with excellent heat resistance and excellent dielectric properties.

[0140] The heat treatment temperature for the thermal imidization reaction can be set at any appropriate temperature within a range that does not impair the effects of the present invention. However, a temperature at which imidization proceeds sufficiently and the solvent used in the internal oil phase and the external oil phase can be sufficiently removed is preferred. Such a heat treatment temperature is preferably 100°C or higher, more preferably 150°C to 500°C, and even more preferably 250°C to 400°C. The heat treatment temperature for the thermal imidization reaction may or may not be constant. For example, the heating conditions may be gradually increased from a low temperature. The maximum heat treatment temperature is preferably 200°C to 500°C. Within this temperature range, the thermal imidization reaction proceeds easily, thereby improving the mechanical properties and heat resistance of the polyimide hollow particles. A heat treatment temperature of 500°C or less is preferred because it suppresses thermal degradation of the polyimide and prevents deterioration of its properties.

[0141] The heat treatment time for the thermal imidization reaction may be any appropriate time within a range that does not impair the effects of the present invention. From the viewpoint of further exhibiting the effects of the present invention, the heat treatment time is preferably 0.1 to 50 hours, more preferably 1.0 to 24 hours, and even more preferably 1.0 to 12 hours.

[0142] The heat treatment can be carried out in air, under reduced pressure, or in an inert gas atmosphere such as nitrogen, etc. A known heating device can be used for the heat treatment.

[0143] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0144] <Measurement of Volume Average Particle Diameter> The volume average particle diameter of the particles was measured using a Coulter Multisizer (registered trademark) 4e (a measuring device manufactured by Beckman Coulter, Inc.). The measurement was performed using an aperture calibrated according to the Multisizer 4e user's manual published by Beckman Coulter, Inc. The aperture used for the measurement was appropriately selected depending on the assumed volume average particle diameter of the particles to be measured. For example, when the assumed volume average particle diameter was 0.2 μm to 6 μm, an aperture having a size of 10 μm was selected; when the assumed volume average particle diameter was 1.0 μm to 32 μm, an aperture having a size of 50 μm was selected; and when the assumed volume average particle diameter was 2.0 μm to 60 μm, an aperture having a size of 100 μm was selected. If the volume average particle diameter after measurement differed from the assumed volume average particle diameter, the aperture was changed to one having an appropriate size and the measurement was performed again. The measurement sample was a dispersion prepared by dispersing 0.1 g of particles in 10 ml of a 0.1 wt % aqueous solution of a nonionic surfactant using a touch mixer (manufactured by Yamato Scientific Co., Ltd., "TOUCHMIXER MT-31") and an ultrasonic cleaner (manufactured by Vervoclear, "ULTRASONIC CLEANER VS-150") to prepare a dispersion. During the measurement, the contents of the beaker were gently stirred to prevent air bubbles from being introduced, and the measurement was terminated when 100,000 particles had been measured. The volume-average particle diameter of the particles was taken as the arithmetic mean of the particle size distribution based on the volume of 100,000 particles.

[0145] <Cross-section observation> The dried particles were mixed with a photocurable resin "D-800" (manufactured by JEOL Ltd.) and irradiated with ultraviolet light to obtain a cured product. The cured product was then cut with nippers, and the cross-section was smoothed using a cutter. The sample was coated using a sputtering device, "Auto Fine Coater JFC-1300" manufactured by JEOL Ltd. Next, the cross-section of the sample was photographed using the secondary electron detector of a scanning electron microscope, "SU1510" manufactured by Hitachi High-Technologies Corporation.

[0146] <Measurement of 5% Thermal Weight Loss Temperature when Heating at 10°C / min in an Air Atmosphere> The 5% thermal weight loss temperature was measured using a thermogravimetric differential thermal analyzer ("NEXTA STA200RV" manufactured by Hitachi High-Tech Science Corporation). The sampling method and temperature conditions were as follows. 10.5±0.5 mg of sample was packed tightly into the bottom of a platinum measurement container to prepare a measurement sample. The 5% thermal weight loss temperature was measured using alumina as the reference material under an air or nitrogen gas flow rate of 200 mL / min. The TG / DTA curve was obtained by heating the sample from 30°C to 800°C at a heating rate of 10°C / min. The temperature at which the 5% thermal weight loss occurred was calculated from the obtained curve using the analysis software provided with the instrument, and was taken as the 5% thermal weight loss temperature.

[0147] <Dielectric Properties of Particles> The dielectric properties of the particles were measured using a dielectric constant measuring device (ADMS01Nc series) manufactured by AET Corporation. The measurement was performed at a frequency of 10 GHz under the conditions of 23°C and a relative humidity of 51±1%. Based on perturbation theory using a resonator, the relative dielectric constant of the particles and the dielectric loss tangent before the heating test were calculated.

[0148] [Production Example 1]: Synthesis of Polyamic Acid Solution A 0.481 g of 4,4'-diaminodiphenyl ether (hereinafter referred to as DPE) was dissolved in 10.9 g of N,N-dimethylformamide (hereinafter referred to as DMF) to obtain a diamine solution. 0.733 g of 5,5'-[p-phenylenebis(oxycarbonyl)]diphthalic anhydride (hereinafter referred to as TAHQ) was added to the diamine solution and stirred at 25°C. Immediately after addition, the system was heterogeneous, but with continued stirring, the system gradually dissolved due to the progress of interfacial polycondensation, and complete dissolution was confirmed one hour after the addition of TAHQ. In this manner, polyamic acid solution A with a solids content of 10 wt% was obtained.

[0149] [Production Example 2]: Synthesis of Polyamic Acid Solution B 0.768 g of 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as TFMB) was dissolved in 10.9 g of 1,3-dimethyl-2-imidazolidinone (hereinafter referred to as DMI) to obtain a diamine solution. 0.733 g of TAHQ was added to the diamine solution, and the mixture was stirred at 25°C. Complete dissolution was confirmed 3 hours after the addition of TAHQ. In this manner, polyamic acid solution B with a solids content of 10 wt % was obtained.

[0150] [Production Example 3]: Synthesis of Polyamic Acid Solution C 0.441 g of DPE was dissolved in 12.2 g of DMI to obtain a diamine solution. 0.915 g of naphthalene-2,6-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (hereinafter referred to as 26DHN-TME) was added to the diamine solution, and the mixture was stirred at 25°C. Complete dissolution was confirmed one hour after the addition of 26DHN-TME. In this manner, polyamic acid solution C with a solids content of 10 wt % was obtained.

[0151] [Production Example 4]: Synthesis of Polyamic Acid Solution D 0.481 g of DPE was dissolved in 13.5 g of DMI to obtain a diamine solution. 0.813 g of 26DHN-TME was added to the diamine solution and stirred at 25°C. Complete dissolution was confirmed one hour after the addition of 26DHN-TME. In this manner, polyamic acid solution D with a solids content of 10 wt% was obtained.

[0152] [Production Example 5]: Synthesis of Polyamic Acid Solution E 0.768 g of TFMB was dissolved in 14.2 g of DMI to obtain a diamine solution. 0.813 g of 26DHN-TME was added to the diamine solution and stirred at 25°C. Complete dissolution was confirmed 24 hours after the addition of 26DHN-TME. In this manner, polyamic acid solution E with a solids content of 10 wt% was obtained.

[0153] [Production Example 6]: Synthesis of Polyamic Acid Microparticles X A first solution was prepared by dissolving 0.640 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter referred to as BTDA) in 39.4 g of acetone. A second solution was prepared by dissolving 0.400 g of DPE in 39.4 g of acetone. Next, the first and second solutions were mixed at 25°C and irradiated with an ultrasonic homogenizer for 5 minutes to cause a reaction, thereby precipitating polyamic acid microparticles. Thereafter, the mixture was subjected to solid-liquid separation using a centrifuge, washed several times with acetone, and dried to obtain polyamic acid microparticles X.

[0154] [Production Example 7]: Synthesis of Polyamic Acid Solution F 0.509 g of 4,4'-diamino-2,2'-dimethylbiphenyl (hereinafter referred to as TBHG) was dissolved in 11.9 g of 1,3-dimethyl-2-imidazolidinone (hereinafter referred to as DMI) to obtain a diamine solution. 0.733 g of TAHQ was added to the diamine solution, and the mixture was stirred at 25°C. Complete dissolution was confirmed one hour after the addition of TAHQ. In this manner, polyamic acid solution F with a solids content of 10 wt % was obtained.

[0155] Example 1: 4.0 g of polyamic acid solution A obtained in Production Example 1 was used as the internal oil phase. Furthermore, 0.04 g of silica particles (AEROSIL® R972, manufactured by Nippon Aerosil Co., Ltd.) serving as a dispersant and 66.4 g of cyclohexane serving as a solvent were mixed and dissolved to prepare an external oil phase. The internal oil phase was added to the external oil phase, and emulsified and dispersed for 1 minute at 8,000 rpm using a Polytron Homogenizer PT10-35 (manufactured by Central Scientific Trading Co., Ltd.). 0.4 g of acetic anhydride and 0.4 g of pyridine serving as chemical imidizing agents were added to the resulting emulsion, and the mixture was heated at 60°C for 3 hours with stirring to allow the chemical imidization reaction to proceed. The reaction system was then cooled to room temperature, the particles were allowed to settle by centrifugation, and the supernatant was removed. The mixture was then washed twice with cyclohexane and twice with 2-propanol, and dried at 80°C for 24 hours. Thereafter, the mixture was further heat-treated at 260°C for 3 hours to allow the thermal imidization reaction to proceed. Particles (1) were obtained in this manner. The volume average particle diameter of the obtained particles (1) was 15.7 µm. A cross-sectional photograph of the obtained particles (1) is shown in Figure 2. It was confirmed that the obtained particles (1) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more void spaces inside it. The blending amounts and various measurement results are shown in Table 1.

[0156] Example 2 Particles (2) were obtained in the same manner as in Example 1, except that the internal oil phase was 4.0 g of the polyamic acid solution B obtained in Production Example 2. The volume average particle diameter of the obtained particles (2) was 14.8 μm. A cross-sectional photograph of the obtained particles (2) is shown in FIG. 3. It was confirmed that the obtained particles (2) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0157] Example 3 Particles (3) were obtained in the same manner as in Example 1, except that the internal oil phase was changed to 4.0 g of the polyamic acid solution C obtained in Production Example 3. The volume average particle diameter of the obtained particles (3) was 18.9 μm. A cross-sectional photograph of the obtained particles (3) is shown in FIG. 4. It was confirmed that the obtained particles (2) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0158] Example 4 Particles (4) were obtained in the same manner as in Example 1, except that the internal oil phase was 4.0 g of the polyamic acid solution D obtained in Production Example 4. The volume average particle diameter of the obtained particles (4) was 17.3 μm. A cross-sectional photograph of the obtained particles (4) is shown in FIG. 5. It was confirmed that the obtained particles (4) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0159] Example 5 An external oil phase was prepared by mixing and dissolving 83.4 g of silicone oil (KF-96-50cs, manufactured by Shin-Etsu Chemical Co., Ltd.) as a solvent and 0.28 g of a silicone surfactant (KF-6048, manufactured by Shin-Etsu Chemical Co., Ltd.) as a dispersant. Particles (5) were obtained in the same manner as in Example 3, except that the above external oil phase was used. The volume average particle diameter of the obtained particles (5) was 13.2 μm. A cross-sectional photograph of the obtained particles (5) is shown in FIG. 6. It was confirmed that the obtained particles (5) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0160] Example 6 Particles (6) were obtained in the same manner as in Example 1, except that the internal oil phase was 4.0 g of the polyamic acid solution E obtained in Production Example 5. The volume average particle diameter of the obtained particles (6) was 14.2 μm. A cross-sectional photograph of the obtained particles (6) is shown in FIG. 7. It was confirmed that the obtained particles (6) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0161] Example 7 Particles (7) were obtained in the same manner as in Example 1, except that the internal oil phase was 4.0 g of the polyamic acid solution F obtained in Production Example 7. The volume average particle diameter of the obtained particles (7) was 13.9 μm. A cross-sectional photograph of the obtained particles (7) is shown in FIG. 8. It was confirmed that the obtained particles (7) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0162] Example 8 Particles (8) were obtained in the same manner as in Example 7, except that 0.012 g of Petrotack 100V (aliphatic / aromatic hydrocarbon resin, manufactured by Tosoh Corporation) was added to the internal oil phase. The volume average particle diameter of the obtained particles (8) was 14.9 μm. A cross-sectional photograph of the obtained particles (8) is shown in FIG. 9. It was confirmed that the obtained particles (8) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0163] Example 9 Particles (9) were obtained in the same manner as in Example 7, except that 0.020 g of Petrotack 100V (aliphatic / aromatic hydrocarbon resin, manufactured by Tosoh Corporation) was added to the internal oil phase. The volume average particle diameter of the obtained particles (9) was 15.1 μm. A cross-sectional photograph of the obtained particles (9) is shown in FIG. 10. It was confirmed that the obtained particles (9) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more air spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0164] Comparative Example 1: 0.2 g of the polyamic acid microparticles X obtained in Production Example 6 and 0.8 g of DMF as a solvent were mixed and dissolved to prepare an internal oil phase. Furthermore, 0.04 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL (registered trademark) R972") as a dispersant and 66.4 g of cyclohexane as a solvent were mixed and dissolved to prepare an external oil phase. The internal oil phase was added to the external oil phase, and emulsified and dispersed for 2 minutes at 3000 rpm using a Polytron Homogenizer PT10-35 (manufactured by Central Scientific Trading Co., Ltd.). 0.4 g of acetic anhydride and 0.4 g of pyridine as chemical imidizing agents were added to the resulting emulsion, and the mixture was heated at 60°C for 3 hours with stirring to allow the chemical imidization reaction to proceed. The reaction system was then cooled to room temperature, and the particles were precipitated by centrifugation. The supernatant was then removed, washed with cyclohexane and 2-propanol, and dried to obtain particles (C1). The volume average particle diameter of the obtained particles (C1) was 14.0 μm. A cross-sectional photograph of the obtained particles (C1) is shown in FIG. 11. It was confirmed that the obtained particles (C1) were hollow particles having a hollow portion surrounded by a shell, and that in addition to the hollow portion, the shell had a structure having one or more void spaces therein. The blending amounts and various measurement results are shown in Table 1.

[0165] (Comparative Example 2) Emulsification and dispersion treatment was carried out in the same manner as in Comparative Example 1, except that 0.56 g of acrylic resin (product name "Macromonomer AB-6", manufactured by Toagosei Co., Ltd.) was used instead of 0.04 g of silica particles (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL (registered trademark) R972"). However, the emulsion stability was extremely low, coalescence of oil droplets occurred, and an emulsion could not be obtained.

[0166]

[0167] From the results in Table 1, it can be seen that the particles obtained in Examples 1 to 9 were polyimide hollow particles having excellent dielectric properties.

[0168] The polyimide hollow particles according to the embodiment of the present invention and the polyimide hollow particles obtained by the production method according to the embodiment of the present invention can be used as semiconductor materials, etc.

Claims

1. A polyimide hollow particle having a shell portion and a hollow portion surrounded by the shell portion, wherein the polyimide hollow particle has a dielectric loss tangent of less than 0.0070 at a measurement frequency of 10 GHz.

2. The polyimide hollow particles according to claim 1, which have a relative dielectric constant of less than 2.5 at a measurement frequency of 10 GHz.

3. The polyimide hollow particle according to claim 1, wherein the shell portion comprises a polyimide (P) containing a structural unit A derived from a tetracarboxylic dianhydride having an ester bond.

4. The polyimide hollow particles according to claim 1, wherein the 5% thermal weight loss temperature of the polyimide hollow particles when heated at a rate of 10°C / min in an air atmosphere is 370°C or higher.

5. The polyimide hollow particles according to claim 1, having a volume average particle size of 0.1 μm to 100 μm.

6. The polyimide hollow particle according to claim 1, wherein the hollow portion comprises one hollow region and the shell portion has one or more void spaces.

7. The polyimide hollow particles according to claim 1, which have a relative dielectric constant of less than 2.0 at a measurement frequency of 10 GHz.

8. A method for producing polyimide hollow particles, comprising the steps of: preparing an emulsion from a solution containing a polyamic acid formed from a tetracarboxylic dianhydride having an ester bond and a diamine, and a solvent to which a dispersant has been added; carrying out a chemical imidization reaction in the emulsion; and carrying out a thermal imidization reaction.

9. The method for producing polyimide hollow particles according to claim 8, wherein the solution containing the polyamic acid contains 0 to 10% by weight of an aliphatic / aromatic hydrocarbon resin.

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