Hollow carbon particles, method for producing the same, and composition containing hollow carbon particles

Abstract

To provide hollow carbon particles with excellent fluidity and strength. [Solution] Hollow carbon particles comprising a shell with a carbonization rate of 90% or more and a hollow portion surrounded by the shell, wherein the volume average particle diameter Dv is 3.0 to 25 μm, the average porosity is 50 to 90%, and the proportion of particles having only one hollow portion is 90% or more.

Description

[Technical Field]

[0001] The present invention relates to hollow carbon particles and a method for producing the same. The present invention also relates to a hollow carbon particle-containing composition obtained using hollow carbon particles. [Background technology]

[0002] Carbon particles are used as conductive fillers and conductive auxiliary fillers because they exhibit excellent properties such as conductivity and fluidity. Among these, spherical hollow carbon particles are attracting attention as a material that can produce these excellent effects even in relatively small quantities.

[0003] For example, Patent Document 1 describes a method for producing hollow carbon particles, characterized by coating the surface of resin particles obtained by polymerizing polymerizable vinyl monomers with a polymer derived from nitrogen-containing aromatic compounds, and then firing them in an inert gas atmosphere. However, there is a need for hollow carbon particles that achieve a higher level of both fluidity and strength than those obtained in Patent Document 1. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-214301 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide hollow carbon particles that exhibit excellent fluidity and strength. [Means for solving the problem]

[0006] The inventors of the present invention conducted diligent research to solve the above problems and found that the above problems can be solved by hollow carbon particles in which the carbonization rate, volume average particle diameter Dv, and average porosity are within a specific range, and the proportion of particles having only one hollow part is 90% or more, thus completing the present invention.

[0007] In other words, the following hollow carbon particles are provided according to this disclosure.

[0008] [1] Hollow carbon particles comprising a shell with a carbonization rate of 90% or more and a hollow portion surrounded by the shell, The volume-average particle size Dv is 3.0 to 25 μm. The average porosity is 50-90%. Hollow carbon particles in which the proportion of particles with only one hollow section is 90% or more. [2] Hollow carbon particles as described in [1], wherein the ratio of volume-average particle diameter Dv to number-average particle diameter Dp, Dv / Dp, is 1.02 to 2.0. [3] Hollow carbon particles as described in [1] or [2], wherein the proportion of particles with a circularity of 0.93 or less is 10 percent or less. [4] Hollow carbon particles as described in any of [1] to [3], wherein the surface acid content is 0.001 mol / g or more.

[0009] Furthermore, this disclosure provides the following hollow carbon particle-containing compositions and methods for producing hollow carbon particles. A hollow carbon particle-containing composition containing 70% by mass or more of the hollow carbon particles described in any of [5] [1] to [4]. [6] The hollow carbon particle-containing composition according to [5], comprising at least one carbon powder selected from graphite, acetylene black, Ketjenblack, carbon nanotubes, graphene, and carbon nanofibers. A method for producing hollow carbon particles according to any of [7] [1] to [4], A method for producing hollow carbon particles, comprising a firing step of heating hollow resin particles in an inert gas or under reduced pressure at 240 to 2500°C for 0.5 to 40 hours. [8] The firing process comprises a first step of heating the hollow resin particles in an inert gas or under reduced pressure at 240 to 650°C for 0.5 to 20 hours, A method for producing hollow carbon particles according to [7], comprising a second step of heating in an inert gas or under reduced pressure at 700 to 2500°C for 2 to 20 hours after the first step. [9] A method for producing hollow carbon particles according to [7] or [8], further comprising a surface oxidation step of heating the particles at 200 to 600°C in an air atmosphere after the firing step. [Effects of the Invention]

[0010] According to the present invention, hollow carbon particles with excellent fluidity and strength can be provided. [Modes for carrying out the invention]

[0011] <Hollow carbon particles> The hollow carbon particles of the present invention comprise a shell with a carbonization rate of 90% or more and a hollow portion surrounded by the shell, have a volume-average particle diameter Dv of 3.0 to 25 μm, an average porosity of 50 to 90%, and a prevalence of 90 percent or more of particles having only one hollow portion.

[0012] (Carbonization rate of hollow carbon particles) The hollow carbon particles of the present invention comprise a shell (outer shell) with a carbonization rate of 90% or more, and a hollow portion surrounded by the shell. If the carbonization rate of the shell of the hollow carbon particles of the present invention (hereinafter sometimes referred to as "carbonization rate of hollow carbon particles") is too low, it is not possible to achieve both fluidity and strength, and properties such as conductivity cannot be fully exhibited.

[0013] The carbonization rate of the hollow carbon particles of the present invention is not particularly limited as long as it is 90% or more. From the perspective of better exerting the effects of the present invention, it is preferably 91% to 99.9%, more preferably 92% to 99.8%, still more preferably 93% to 99.6%, particularly preferably 95% to 99.3%, and most preferably 97% to 99%.

[0014] In the present disclosure, the carbonization rate means the weight ratio of the heating residue when the hollow carbon particles are heated to 600 °C using a differential thermal thermogravimetric simultaneous measurement device (TG / DTA). As a specific measurement method for the carbonization rate, the measurement method described in the examples can be adopted. The carbonization rate of the hollow carbon particles of the present invention can be adjusted, for example, by adjusting the heating conditions during the production of the hollow carbon particles and the components constituting the raw material particles.

[0015] (Proportion of particles having only one hollow part) The hollow part of the hollow carbon particles of the present invention is a cavity-like space clearly distinguishable from the shell. The hollow carbon particles of the present invention may have one or two or more hollow parts, but in order to obtain a good balance between porosity and strength, those having only one hollow part are preferred.

[0016] The proportion of particles having only one hollow part in the hollow carbon particles of the present invention is 90% by number or more. In other words, out of 100 unit particles (particles) constituting the hollow carbon particles (particles) of the present invention, particles having only one hollow part are present at a ratio of 90 or more. If the proportion of particles having only one hollow part is too low, it is impossible to achieve both fluidity and strength.

[0017] The proportion of particles having only one hollow part is not particularly limited as long as it is 90% by number or more. From the viewpoint of more favorably exhibiting the effects of the present invention, it is preferably 92% to 100% by number, more preferably 93% to 99.9% by number, still more preferably 94% to 99.5% by number, and particularly preferably 95% to 99% by number. The proportion of particles having only one hollow part can be measured by the method described in the examples.

[0018] The hollow carbon particles of the present invention usually have a shell without through-holes and shell defects, and the hollow part is isolated from the outside of the particle by the shell. On the other hand, in the hollow carbon particles of the present invention, the shell may have one or more through-holes, and the hollow part may communicate with the outside of the particle through the through-holes. Further, the shell of the hollow carbon particles and the partition wall separating adjacent hollow parts when there are two or more hollow parts may be porous. In that case, the hollow part has a size that can be clearly distinguished from a large number of minute spaces uniformly dispersed in the porous structure.

[0019] <00​​​​​​​​​​The ratio Dv / Dp of the volume-average particle diameter Dv to the number-average particle diameter Dp of the hollow carbon particles of the present invention is not particularly limited, but from the viewpoint of exhibiting the effects of the present invention more effectively, it is preferably 1.02 to 2.0, more preferably 1.05 to 1.6, even more preferably 1.1 to 1.4, and particularly preferably 1.15 to 1.4. The volume-average particle diameter Dv, the number-average particle diameter Dp, and their ratio Dv / Dp can be determined by a laser diffraction particle size distribution analyzer.

[0022] (Average porosity of hollow carbon particles) The average porosity of the hollow carbon particles of the present invention is 50 to 90%. If the average porosity is outside this range, it is not possible to achieve both fluidity and strength, and the effects such as weight reduction cannot be fully realized. The average porosity of the hollow carbon particles of the present invention is not particularly limited as long as it is between 50 and 90%, but from the viewpoint of being able to better demonstrate the effects of the hollow carbon particles even when the amount of hollow carbon particles is small, it is preferably 55 to 87%, more preferably 60 to 84%, even more preferably 65 to 82%, and particularly preferably 70 to 80%.

[0023] The average porosity (%) of hollow carbon particles is calculated from the apparent density D1 and true density D0 of the hollow carbon particles using the following formula (III). Average porosity (%) of hollow carbon particles = 100 - [Apparent density D1 of hollow carbon particles] ÷ [True density D0 of hollow carbon particles] × 100 (III)

[0024] Here, apparent density D1 corresponds to the total density of the hollow carbon particles, assuming that the hollow portion is part of the hollow carbon particle. True density of hollow carbon particles refers to the density of only the shell portion of the hollow carbon particle. The apparent density D1 and true density D0 of hollow carbon particles can be measured by the method described in the examples.

[0025] (Shape of hollow carbon particles) The shape of the hollow carbon particles of the present invention is not particularly limited as long as a hollow portion is formed inside. The external shape of the hollow carbon particles is not particularly limited, but a spherical shape is preferred for ease of manufacture.

[0026] The external shape of hollow carbon particles can be confirmed, for example, by observing the particles with a scanning electron microscope (SEM) or a TEM. The internal shape of hollow carbon particles can also be confirmed, for example, by observing a cross-section of the particle with a SEM or by observing the particle with a TEM.

[0027] In the hollow carbon particles of the present invention, from the viewpoint of exhibiting the effects of the present invention more effectively, it is preferable that the proportion of particles with low circularity is low. Specifically, in the hollow carbon particles of the present invention, it is preferable that the proportion of particles with a circularity of 0.93 or less is 10 percent or less. In other words, it is preferable that the number of particles with a circularity of 0.93 or less per 100 unit particles (particles) constituting the hollow carbon particles (particles) of the present invention is 10 or less. Furthermore, from the viewpoint of exhibiting the effects of the present invention more effectively, the proportion of particles with a circularity of 0.93 or less is more preferably 0.1 to 10 percent, even more preferably 0.3 to 9.5 percent, especially preferably 1 to 9 percent, particularly preferably 1.5 to 8.5 percent, and most preferably 2 to 8 percent. In addition, the average circularity of the hollow carbon particles of the present invention is not particularly limited, but is preferably 0.935 to 0.995, and more preferably 0.94 to 0.99.

[0028] In this disclosure, circularity is defined as the value obtained by dividing the diameter of a circle having the same area as the projected image of the particle (equivalent circle area diameter) by the diameter of a circle having the same perimeter as the projected image of the particle (equivalent perimeter circle diameter). When the particle is a perfect sphere, the circularity is 1, and the more complex the surface shape of the particle, the smaller the circularity value. The proportion of particles with a circularity of 0.93 or less and the average circularity can be determined as the average circularity when measuring 1000 particles using a flow-type particle image analyzer, and specifically, it can be measured by the method described in the examples.

[0029] (Surface properties of hollow carbon particles) The hollow carbon particles of the present invention are preferably surface-treated. For example, the hollow carbon particles of the present invention are preferably surface-oxidized. Alternatively, the hollow carbon particles of the present invention may be subjected to known surface treatments such as boron treatment, surface coupling treatment, fluorine coating, or diamond coating.

[0030] For example, the surface acid content of hollow carbon particles can be adjusted by surface oxidation treatment. The surface acid content of the hollow carbon particles of the present invention is not particularly limited, but from the viewpoint of exhibiting the effects of the present invention more effectively, it is preferably 0.001 mmol / g or more, more preferably 0.003 mmol / g or more, even more preferably 0.006 mmol / g or more, particularly preferably 0.009 mmol / g or more, and also preferably 0.2 mmol / g or less, more preferably 0.1 mmol / g or less, even more preferably 0.05 mmol / g or less, particularly preferably 0.02 mmol / g or less. When the surface acid content is above the above lower limit, it is possible to suppress the excess of residual acid components adhering to the surface of the hollow carbon particles. As a result, the effects of the present invention can be exhibited more effectively, and dispersibility can also be improved.

[0031] <Method for producing hollow carbon particles> The hollow carbon particles of the present invention are preferably produced by a manufacturing method that includes a firing step of heating hollow resin particles in an inert gas or under reduced pressure at 240 to 2500°C for 0.5 to 40 hours. The present invention also relates to such a manufacturing method.

[0032] [Hollow resin particles] In the firing step of the manufacturing method of the present invention, hollow resin particles are heated under the above conditions. The hollow resin particles used in the manufacturing method of the present invention comprise a resin-containing shell and a hollow portion surrounded by the shell.

[0033] The shell of hollow resin particles contains a resin made of a shell polymer. The shell polymer is a polymer used to form the shell of hollow resin particles and contains crosslinkable monomer units. The crosslinkable monomer that forms the crosslinkable monomer unit is a monomer that has two or more polymerizable functional groups and forms crosslink bonds in the resin through a polymerization reaction. As crosslinkable monomers, compounds having at least one ethylenically unsaturated bond as a polymerizable functional group are generally used.

[0034] Examples of crosslinkable monomers that form crosslinkable monomer units include crosslinkable hydrocarbon monomers and heteroatom-containing crosslinkable monomers.

[0035] The crosslinkable hydrocarbon monomer is not particularly limited, but examples include divinylbenzene, divinyldiphenyl, and divinylnaphthalene, with divinylbenzene being preferred.

[0036] The heteroatom-containing crosslinkable monomers are not particularly limited, but examples include difunctional heteroatom-containing crosslinkable monomers such as diallyl phthalate, allyl (meth)acrylate (meaning allyl acrylate and / or allyl methacrylate; the same applies hereinafter), ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate; and trifunctional or more heteroatom-containing crosslinkable monomers such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol poly(meth)acrylate. Among these, ethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred, ethylene glycol di(meth)acrylate and pentaerythritol tetra(meth)acrylate are more preferred, and ethylene glycol dimethacrylate and pentaerythritol tetraacrylate are even more preferred.

[0037] Preferred crosslinkable monomers include crosslinkable hydrocarbon monomers, ethylene glycol di(meth)acrylate, and pentaerythritol tetra(meth)acrylate, with divinylbenzene, ethylene glycol dimethacrylate, and pentaerythritol tetraacrylate being more preferred.

[0038] Crosslinkable monomers can be used individually or in combination of two or more types. For example, a crosslinkable hydrocarbon monomer can be used in combination with a heteroatom-containing crosslinkable monomer. Furthermore, two or more heteroatom-containing crosslinkable monomers can be used in combination as the heteroatom-containing crosslinkable monomer; for example, a bifunctional heteroatom-containing crosslinkable monomer can be used in combination with a trifunctional or higher heteroatom-containing crosslinkable monomer.

[0039] Shell polymers may consist substantially of only crosslinkable monomer units, or they may contain monofunctional monomer units in addition to crosslinkable monomer units. Monofunctional monomers that form monofunctional monomer units are monomers having only one polymerizable functional group, and compounds having an ethylenically unsaturated bond as the polymerizable functional group are generally used. Examples of monofunctional monomers that form monofunctional monomer units include monofunctional hydrocarbon monomers and heteroatom-containing monofunctional monomers.

[0040] The monofunctional hydrocarbon monomers are not particularly limited, but examples include aromatic vinyl monomers such as styrene, ethyl vinylbenzene, vinyltoluene, α-methylstyrene, p-methylstyrene, and halogenated styrene; monoolefin monomers such as ethylene, propylene, butylene, and 4-methyl-1-pentene; and diene monomers such as butadiene and isoprene. Among these, styrene and ethyl vinylbenzene are preferred.

[0041] The heteroatom-containing monofunctional monomers are not particularly limited, but examples include hydrophilic monofunctional monomers; acrylic monovinyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; vinyl carboxylate ester monomers such as vinyl acetate; vinyl halide monomers such as vinyl chloride; vinylidene halide monomers such as vinylidene chloride; vinylpyridine monomers; and the like.

[0042] Hydrophilic monofunctional monomers are preferably soluble in water at a concentration of 1% by mass or more. Hydrophilic monofunctional monomers are not particularly limited, but examples include monofunctional monomers containing hydrophilic groups, such as acid group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, and polyoxyethylene group-containing monomers.

[0043] Acid group-containing monomers refer to monomers that contain acid groups. Here, acid groups include both proton-donating groups (Brønsted acid groups) and electron-pair-accepting groups (Lewis acid groups). Acid group-containing monomers are not particularly limited as long as they contain acid groups, but examples include carboxyl group-containing monomers and sulfonic acid group-containing monomers. Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butentricarboxylic acid; monoalkyl esters of unsaturated dicarboxylic acids such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate; etc. Examples of sulfonic acid group-containing monomers include styrene sulfonic acid.

[0044] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0045] Examples of monomers containing an amide group include acrylamide and dimethylacrylamide.

[0046] Examples of polyoxyethylene group-containing monomers include methoxypolyethylene glycol (meth)acrylate.

[0047] Monofunctional monomer units can be used individually or in combination of two or more types.

[0048] The content of crosslinkable monomer units in the shell polymer is not particularly limited, but is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. When the content of crosslinkable monomers is within the above range, a dense covalent network is formed in the shell, and the occurrence of shell pores and shell defects is suppressed, resulting in hollow resin particles with excellent strength, and hollow carbon particles with even greater strength.

[0049] The content of monofunctional monomer units in the shell polymer is not particularly limited, but from the viewpoint of obtaining even better strength, it is preferably 0 to 80% by mass, more preferably 0 to 60% by mass, even more preferably 0 to 40% by mass, and particularly preferably 0 to 30% by mass.

[0050] The shell polymer may contain heteroatom-containing monomer units. Examples of heteroatom-containing monomers that form heteroatom-containing monomer units include the heteroatom-containing crosslinkable monomers and heteroatom-containing monofunctional monomers mentioned above.

[0051] The content of heteroatom-containing monomer units in the shell polymer is not particularly limited, but from the viewpoint of further improving the strength of the hollow carbon particles and improving properties such as conductivity, it is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

[0052] [Method for producing hollow resin particles] The hollow resin particles used in the manufacturing method of the present invention can preferably be produced by a manufacturing method comprising the following steps: (A) a mixture preparation step, (B) a suspension step, (C) a polymerization step, and (D) a solvent removal step. The manufacturing method of the present invention may also include a step of producing hollow resin particles by such a method.

[0053] In other words, the hollow resin particles of the present invention are preferably, (A) A mixture preparation step of preparing a mixture containing a polymerizable monomer including a crosslinkable monomer, a hydrophobic organic solvent, a polymerization initiator, and an aqueous medium. (B) A suspension step in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the mixture obtained in the mixture preparation step. (C) A polymerization step in which the suspension obtained in the suspension step is subjected to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and encapsulating a hydrophobic organic solvent in the hollow portion, and (D) It can be manufactured by a manufacturing method that includes a solvent removal step to remove the hydrophobic organic solvent contained in the precursor particles obtained by the polymerization step.

[0054] The above manufacturing method makes it easy to obtain hollow resin particles with a high proportion of particles having only one hollow section, a low proportion of particles with low circularity, and a high average circularity. Furthermore, by using such hollow resin particles as a raw material, it is easy to obtain hollow carbon particles with a high proportion of particles having only one hollow section, a low proportion of particles with low circularity, and a high average circularity. In addition, by adjusting the various physical properties of the raw material hollow resin particles (volume-average particle diameter Dv, ratio Dv / Dp, average porosity, etc.), the various physical properties of the hollow carbon particles can also be adjusted.

[0055] (A) Mixed liquid preparation process The mixed solution preparation step is a step of preparing a mixed solution containing a polymerizable monomer including a crosslinkable monomer, a hydrophobic organic solvent, a polymerization initiator, and an aqueous medium.

[0056] [polymerizable monomers] As polymerizable monomers, the crosslinkable monomers described above and, if necessary, the monofunctional monomers described above are used. The monomer composition of the polymerizable monomers should be such that the monomer composition of the desired shell polymer is obtained.

[0057] The content of polymerizable monomers (total amount of crosslinkable monomers and monofunctional monomers) in the mixed solution prepared in the mixed solution preparation step is not particularly limited, but from the viewpoint of balancing porosity, particle size and strength, and from the viewpoint of keeping the proportion of particles having only one hollow part within the above-mentioned preferred range, it is preferably 15 to 60% by mass, more preferably 25 to 55% by mass, and even more preferably 35 to 50% by mass, based on 100% by mass of the total mass of the components in the mixed solution excluding the aqueous medium.

[0058] [Hydrophobic organic solvents] As the hydrophobic organic solvent, a non-polymerizable and poorly water-soluble organic solvent is used. The hydrophobic organic solvent acts as a spacer material that forms hollow spaces within the particles.

[0059] While not particularly limited, hydrophobic organic solvents can be suitably used, and specific examples include saturated hydrocarbon solvents such as butane, pentane, n-hexane, cyclohexane, heptane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and relatively volatile solvents such as carbon disulfide and carbon tetrachloride.

[0060] Preferably, the hydrophobic organic solvent is such that the saturated hydrocarbon solvent accounts for 50% or more of the total amount of hydrophobic organic solvent (100% by mass). This ensures sufficient phase separation occurs within the droplets of the polymerizable monomer composition prepared in the suspension step described later, making it easier to obtain hollow resin particles having only one hollow portion and suppressing the formation of porous particles. From the viewpoint of further suppressing the formation of porous particles and ensuring that the hollow portions of each hollow resin particle are more uniform, the proportion of the saturated hydrocarbon solvent is preferably 60% or more, and more preferably 80% or more, of the total amount of hydrophobic organic solvent (100% by mass).

[0061] Furthermore, as the hydrophobic organic solvent, hydrocarbon solvents having 5 to 8 carbon atoms are preferred. Hydrocarbon solvents having 5 to 8 carbon atoms are readily encapsulated in the precursor particles during the polymerization process described later, and can be easily removed from the precursor particles during the solvent removal process described later. Among these, hydrocarbon solvents having 6 to 8 carbon atoms are particularly preferred.

[0062] Furthermore, the hydrophobic organic solvent preferably has a dielectric constant of 3 or less at 20°C. Relative dielectric constant is one indicator of the polarity of a compound. When the dielectric constant of the hydrophobic organic solvent is sufficiently small, such as 3 or less, it is thought that phase separation proceeds rapidly in the droplets of the polymerizable monomer composition prepared in the suspension step described later, and hollow parts are easily formed.

[0063] Examples of hydrophobic organic solvents with a relative permittivity of 3 or less at 20°C include heptane (1.9), cyclohexane (2.0), benzene (2.3), and toluene (2.4) (the values ​​in parentheses are the relative permittivity values). Regarding the relative permittivity at 20°C, one can refer to the values ​​listed in public literature (for example, "Chemical Handbook Basic Edition," edited by the Chemical Society of Japan, 4th revised edition, Maruzen Co., Ltd., published September 30, 1993, pp. II-498 to II-503) and other technical information. As for methods for measuring the relative permittivity at 20°C, for example, a relative permittivity test conducted in accordance with JISC 2101:1999, item 23, with the measurement temperature set at 20°C.

[0064] The content of the hydrophobic organic solvent in the mixture is preferably 50 to 500 parts by mass, more preferably 60 to 350 parts by mass, even more preferably 70 to 200 parts by mass, and particularly preferably 80 to 180 parts by mass, per 100 parts by mass of the total mass of polymerizable monomers, from the viewpoint of balancing porosity, particle size, and strength, and from the viewpoint of keeping the proportion of particles having only one hollow part within the preferred range described above.

[0065] [Polymerization initiator] As the polymerization initiator, it is preferable to use an oil-soluble polymerization initiator. By using an oil-soluble polymerization initiator, the polymerization initiator can be suitably incorporated into the droplets of the polymerizable monomer composition in the suspension obtained in the suspension step described later.

[0066] The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less. Examples of oil-soluble polymerization initiators include benzoyl peroxide, lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, t-butyl peroxydiethyl acetate, t-butyl peroxypivalate, 2,2'-azobis(2,4-dimethylvaleronitrile), and azobisisobutyronitrile.

[0067] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the total mass of polymerizable monomers in the mixture. By setting the content of the polymerization initiator within the above range, the polymerization reaction can proceed sufficiently, and there is little risk of the polymerization initiator remaining after the polymerization reaction is completed, as well as little risk of unexpected side reactions occurring.

[0068] [Aqueous medium] Examples of aqueous media include media selected from the group consisting of water, hydrophilic solvents, and mixtures of water and hydrophilic solvents.

[0069] The hydrophilic solvent is not particularly limited as long as it mixes well with water and does not undergo phase separation. Examples include alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0070] Among aqueous media, water is preferred due to its high polarity. When using a mixture of water and a hydrophilic solvent, it is preferable that the overall polarity of the mixture is not too low, from the viewpoint of appropriately forming droplets of the polymerizable monomer composition containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator. When using a mixture of water and a hydrophilic solvent, it is preferable that the mixing ratio (mass ratio) of water to hydrophilic solvent be water:hydrophilic solvent = 99:1 to 50:50.

[0071] [Dispersion stabilizer] Furthermore, it is preferable to use a dispersion stabilizer in the mixture preparation step. That is, the mixture preparation step is preferably a step of preparing a mixture containing a polymerizable monomer, a hydrophobic organic solvent, a polymerization initiator, an aqueous medium, and a dispersion stabilizer.

[0072] The dispersion stabilizer is a compound used in the suspension step described later to disperse droplets of the polymerizable monomer composition in an aqueous medium, and may be either an inorganic dispersion stabilizer or an organic dispersion stabilizer.

[0073] Examples of inorganic dispersion stabilizers include colloidal silica, magnesium hydroxide, calcium phosphate, calcium carbonate, barium sulfate, calcium oxalate, calcium carbonate, magnesium carbonate, barium carbonate, tricalcium phosphate, aluminum hydroxide, magnesium hydroxide, ferric hydroxide, hydroxyapatite, diatomaceous earth, clay, and bentonite.

[0074] Examples of organic dispersion stabilizers include methylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and starch.

[0075] Among these, inorganic dispersion stabilizers are preferred because they have a high dispersion stabilization effect and allow for easier control of the particle size of droplets in polymerizable monomer compositions containing polymerizable monomers, hydrophobic organic solvents, and polymerization initiators. Among inorganic dispersion stabilizers, metal-containing dispersion stabilizers are preferred, and poorly water-soluble inorganic metal salts are more preferred. As poorly water-soluble inorganic metal salts, inorganic metal salts with a solubility of 0.5 g or less per 100 g of water are preferred, such as magnesium hydroxide, calcium hydroxide, barium hydroxide, and calcium phosphate, with magnesium hydroxide being more preferred among these. Dispersion stabilizers can be used individually or in combination of two or more.

[0076] Furthermore, from the viewpoint of further enhancing the dispersion stabilization effect, it is preferable to use the dispersion stabilizer in the form of a dispersion or solution by dispersing or dissolving it in an aqueous medium. That is, in the mixture preparation step, it is preferable to obtain a mixture by mixing the dispersion stabilizer in the form of a dispersion or solution with a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator. The above-mentioned aqueous medium can be used.

[0077] In a dispersion or solution of a dispersion stabilizer, the mixing ratio of the dispersion stabilizer to the aqueous medium is preferably 0.7:100 to 7:100, more preferably 1.0:100 to 4.0:100, and even more preferably 1.4:100 to 3:100, in terms of the mass ratio of "dispersion stabilizer:aqueous medium". By setting the mixing ratio of the dispersion stabilizer to the aqueous medium within the above range, the dispersion stabilization effect can be more appropriately enhanced.

[0078] As a method for preparing a dispersion or solution of a dispersion stabilizer, one may directly mix the dispersion stabilizer with an aqueous medium. However, a preferred method involves reacting two or more compounds that serve as precursors to the dispersion stabilizer (i.e., two or more precursor compounds) in an aqueous medium to produce the dispersion stabilizer.

[0079] When mixing two or more precursor compounds in an aqueous medium, the precursor compounds used are not particularly limited. For example, when using poorly water-soluble hydroxide salts such as magnesium hydroxide, calcium hydroxide, or barium hydroxide as dispersion stabilizers, the two or more precursor compounds may include a combination of a water-soluble polyvalent metal salt and an alkali metal hydroxide.

[0080] Examples of water-soluble polyvalent metal salts include hydrochlorides, sulfates, nitrates, and acetates of polyvalent metals such as magnesium, calcium, aluminum, iron, copper, manganese, nickel, and tin. Among these, water-soluble salts of magnesium and calcium are preferred. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. For example, when magnesium hydroxide is used as a dispersion stabilizer, a combination of magnesium chloride and sodium hydroxide is preferred as two or more precursor compounds.

[0081] There are no particular limitations on the method for mixing two or more precursor compounds in an aqueous medium, but when a combination of a water-soluble polyvalent metal salt and an alkali metal hydroxide is used, a preferred method is to dropwise add the aqueous solution of the alkali metal hydroxide to the aqueous solution of the water-soluble polyvalent metal salt under stirring.

[0082] The content of the water-soluble polyvalent metal salt in the aqueous medium solution is preferably 2 to 8 parts by weight, more preferably 3 to 6 parts by weight, per 100 parts by weight of the aqueous medium solution. Similarly, the content of the alkali metal hydroxide in the aqueous medium solution is preferably 6 to 20 parts by weight, more preferably 8 to 18 parts by weight, per 100 parts by weight of the aqueous medium solution. The above-mentioned aqueous medium can be used.

[0083] [Polar resin] Furthermore, it is preferable to use a polar resin in the mixture preparation step. Specifically, the mixture preparation step is preferably a step of preparing a mixture containing a polymerizable monomer, a hydrophobic organic solvent, a polymerization initiator, an aqueous medium, a dispersion stabilizer used as needed, and a polar resin. By using a polar resin, the particle size of the monomer composition droplets and the shell thickness of the resulting hollow resin particles can be appropriately adjusted.

[0084] In this disclosure, polar resins refer to polymers containing repeating units that include heteroatoms. Specifically, examples include acrylic resins, polyester resins, and vinyl resins containing heteroatoms.

[0085] The polar resin may be a homopolymer or copolymer of heteroatom-containing monomers, or a copolymer of heteroatom-containing monomers and heteroatom-non-containing monomers. When the polar resin is a copolymer of heteroatom-containing monomers and heteroatom-non-containing monomers, the proportion of heteroatom-containing monomer units in 100% by mass of the total repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, in order to easily control the particle size of the hollow resin particles.

[0086] Examples of heteroatom-containing monomers used in polar resins include the heteroatom-containing crosslinkable monomers and heteroatom-containing monofunctional monomers mentioned above. Examples of heteroatom-free monomers include the crosslinkable hydrocarbon monomer units and monofunctional hydrocarbon monomers mentioned above. These monomers can be used individually or in combination of two or more types.

[0087] Among polar resins, it is preferable that the polar resin is an acrylic resin in which the total mass of (meth)acrylic monovinyl monomer units is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, out of 100% by mass of all repeating units constituting the resin, due to its high compatibility with polymerizable monomers and ease of controlling the particle size of hollow resin particles. In particular, it is preferable that the polar resin is an acrylic resin in which all repeating units constituting the resin consist of (meth)acrylic monovinyl monomer units.

[0088] In particular, polar resins that contain polar group-containing monomer units in which heteroatom-containing monomers include polar groups selected from carboxyl groups, hydroxyl groups, sulfonic acid groups, amino groups, polyoxyethylene groups, and epoxy groups are preferred because they allow for easy control of the particle size of hollow resin particles. Among the polar groups contained in the polar group-containing monomer units of the polar resin, carboxyl groups and hydroxyl groups are preferred because they allow for particle size control with small amounts of additive.

[0089] When a polar resin contains monomer units containing polar groups, it is preferable that the polar groups are located at the ends of the main chain or side chains, or are attached to the main chain or side chains in a pendant-like manner, as this makes it easier for the polar resin to be arranged on the outer surface of hollow resin particles and easier to control the particle size of the hollow resin particles.

[0090] As an acrylic resin used as a polar resin, it is preferable that the polymer or copolymer of a polymerizable monomer for polar resins contains 50.0% by mass or more of methyl methacrylate when the total mass of the polymerizable monomer for polar resins is 100% by mass, due to its high compatibility with polymerizable monomers and ease of controlling the particle size of hollow resin particles. In this disclosure, the polymerizable monomer used in the synthesis of polar resins is referred to as a polymerizable monomer for polar resins.

[0091] As an acrylic resin used as a polar resin, more preferably, from the viewpoint of being able to more easily control the particle size of hollow resin particles, it is a copolymer of polymerizable monomers for polar resins containing 50.0% to 99.9% by mass of methyl methacrylate and 0.1% to 5.0% by mass of polar group-containing monomer, and even more preferably, it is a copolymer of polymerizable monomers for polar resins containing 50.0% to 99.0% by mass of methyl methacrylate and 0.1% to 5.0% by mass of polar group-containing monomer, and even more preferably, it is a copolymer of polymerizable monomers for polar resins containing 50.0% to 98.0% by mass of methyl methacrylate and This copolymer of polymerizable monomers for polar resins contains 1.0% to 5.0% by mass of a (meth)acrylic monovinyl monomer that is different from chilled methacrylate and does not contain polar groups, and 0.1% to 5.0% by mass of a monomer containing polar groups. Particularly preferred is a copolymer of polymerizable monomers for polar resins containing 50.0% to 98.0% by mass of methyl methacrylate, 1.0% to 5.0% by mass of a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain polar groups, and 0.2% to 3.0% by mass of a monomer containing polar groups.

[0092] Unlike methyl methacrylate and free of polar groups, the (meth)acrylic monovinyl monomer is preferably at least one selected from ethyl acrylate and butyl acrylate, with ethyl acrylate being particularly preferred, in order to allow control of the glass transition temperature.

[0093] As for the polar group-containing monomer, a (meth)acrylic monovinyl monomer containing a polar group is preferred from the viewpoint of compatibility with polymerizable monomers in the mixture, and a (meth)acrylic monovinyl monomer containing a carboxyl group or a hydroxyl group is even more preferred because particle size can be controlled with a small amount of additive.

[0094] Polar resins can be obtained, for example, by polymerizing polymerizable monomers for polar resins containing heteroatom-containing monomers using polymerization methods such as solution polymerization or emulsion polymerization. Furthermore, if the polar resin is a copolymer, the copolymer may be a random copolymer, a block copolymer, or a graft copolymer, but a random copolymer is preferred. Furthermore, it is preferable that the polar resin be finely ground, as this improves its solubility.

[0095] The number-average molecular weight (Mn) of the polar resin is not particularly limited, but is preferably in the range of 3,000 to 20,000, more preferably in the range of 4,000 to 17,000, and even more preferably in the range of 6,000 to 15,000, as measured by gel permeation chromatography (GPC) using tetrahydrofuran, in terms of polystyrene equivalent. When the number-average molecular weight (Mn) of the polar resin is above the lower limit, the solubility of the polar resin is improved and the particle size of the hollow resin particles can be easily controlled, and when it is below the upper limit, the decrease in shell strength can be suppressed.

[0096] The content of the polar resin is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.35 parts by mass or more, and particularly preferably 0.4 parts by mass or more, per 100 parts by mass of polymerizable monomer in the mixture, while preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, even more preferably 5.0 parts by mass or less, particularly preferably 2.0 parts by mass or less, and most preferably 1.0 part by mass or less. When the content of the polar resin is above the lower limit, it is easier to control the particle size of the hollow resin particles and the thickness of the shell, and it is easier to keep the proportion of particles having only one hollow part within the above preferred range. On the other hand, when the content of the polar resin is below the upper limit, it is possible to suppress the decrease in the content of polymerizable monomer, and thus suppress the decrease in the strength of the shell.

[0097] In the mixture preparation process, the above-mentioned components can be mixed by stirring or other means to obtain the mixture. In this process, other materials may be added as needed in addition to the above-mentioned components. In the mixture preparation process, a mixture is prepared in which an oil phase containing polymerizable monomers, hydrophobic organic solvents, and lipophilic materials such as polymerization initiators is dispersed in an aqueous medium and an aqueous phase containing a dispersion stabilizer, as needed, with particles of a size of several millimeters. Depending on the type of component, the dispersion state of these components in the mixture can be observed with the naked eye.

[0098] Furthermore, in the mixed liquid preparation process, from the viewpoint of ensuring a uniform composition of the shell portion, it is preferable to prepare an oil phase containing a polymerizable monomer, a hydrophobic organic solvent, a polymerization initiator, and a polar resin used as needed, in advance, and then mix this with an aqueous phase (dispersion or solution) obtained by dispersing or dissolving a dispersion stabilizer in an aqueous medium to prepare the mixed liquid. In this case, the mixing ratio of the oil phase to the aqueous phase is preferably 15:85 to 35:65, more preferably 18:82 to 32:68, and even more preferably 20:80 to 30:70, in terms of the mass ratio of "oil phase:aqueous phase". By setting the mixing ratio of the oil phase to the aqueous phase within the above range, it becomes easier to keep the particle size and porosity of the hollow resin particles within the preferred range described above.

[0099] (B) Suspension process The suspension step is a step in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the mixture obtained in the above-described mixture preparation step.

[0100] The suspension method for forming droplets of the polymerizable monomer composition is not particularly limited, but a method of stirring the mixture obtained in the above-described mixture preparation step using a stirring device capable of strong stirring is preferred. The stirring device used in the suspension step is not particularly limited, but for example, a stirring device comprising a stirrer equipped with a stirring blade or rotor and a supply tank for supplying to the stirrer can be used. Furthermore, the stirrer is not particularly limited as long as it is equipped with a stirring blade or rotor, but from the viewpoint of efficiently forming a suspension, a stirrer having a combination of a rotor and stator which are comb-shaped concentric rings, and which rotates the rotor at high speed to circulate the dispersion from the inside of the rotor to the outside of the stator, stirring the dispersion in the gap between the rotor and the stator is preferred.

[0101] Examples of agitators with such a configuration include in-line emulsifiers and dispersers, such as the "Cavitron" (manufactured by Eurotech), "Milder" (manufactured by Taiheiyo Kiko), "Ebara Milder" (manufactured by Ebara Corporation), "TK Pipeline Homo Mixer" (manufactured by Tokushu Kika Kogyo), "Colloid Mill" (manufactured by Shinko Pantech), "Slasher" (manufactured by Nippon Coke Industries), "Trigonal Wet Fine Grinding Machine" (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), and "Fine Flow Mill" (manufactured by Taiheiyo Kiko).

[0102] In the suspension step, a suspension can be obtained in which droplets of the polymerizable monomer composition containing the above-mentioned lipophilic material are uniformly dispersed in an aqueous medium. Such droplets of polymerizable monomer composition are difficult to observe with the naked eye and can be observed using known observation equipment such as an optical microscope. Furthermore, in the suspension step, phase separation occurs within the droplets of polymerizable monomer composition, causing the less polar hydrophobic organic solvent to accumulate inside the droplets. As a result, the obtained droplets will have the hydrophobic organic solvent distributed inside and the material other than the hydrophobic organic solvent distributed around its periphery.

[0103] (C) Polymerization process The polymerization step is a step in which the suspension prepared in the suspension step described above is subjected to a polymerization reaction to prepare a precursor composition having a hollow portion and containing a hydrophobic organic solvent in the hollow portion.

[0104] In the polymerization process, droplets of the polymerizable monomer composition contain a hydrophobic organic solvent, and the polymerizable monomers within the droplets polymerize, forming precursor particles having a shell containing a resin, which is a polymer of the polymerizable monomer, and a hollow portion filled with a hydrophobic organic solvent.

[0105] In the polymerization process, droplets of the polymerizable monomer composition are subjected to the polymerization reaction while encapsulating a hydrophobic organic solvent. This allows the polymerization reaction to proceed easily while maintaining the shape, and makes it easier to control the size and porosity of the precursor particles. Furthermore, because a combination of polymerizable monomer and hydrophobic organic solvent is used, the hydrophobic organic solvent has low polarity relative to the precursor particle shell, and the hydrophobic organic solvent does not readily accrete with the shell. As a result, sufficient phase separation occurs, and only one hollow portion is easily formed.

[0106] There are no particular limitations on the polymerization method; for example, batch, semi-continuous, or continuous methods can be used. The polymerization temperature is preferably 40 to 90°C, and more preferably 50 to 80°C. The polymerization reaction time is preferably 1 to 48 hours, and more preferably 3 to 24 hours.

[0107] The polymerization process yields a precursor composition in which precursor particles containing a hydrophobic solvent are dispersed in an aqueous phase mainly composed of an aqueous medium.

[0108] (D) Solvent removal process The solvent removal process involves removing hydrophobic organic solvents embedded in the precursor particles obtained by the polymerization process.

[0109] Before performing solvent removal in the solvent removal step, it is preferable to perform solid-liquid separation on the precursor composition obtained in the polymerization step to obtain a solid component containing precursor particles encapsulating a hydrophobic organic solvent. After obtaining the solid component containing precursor particles by solid-liquid separation, the hydrophobic organic solvent encapsulated in the precursor particles is removed in the air, thereby replacing the hydrophobic organic solvent inside the precursor particles with air and obtaining hollow resin particles filled with gas.

[0110] The method for separating the precursor composition into solid and liquid components is not particularly limited, and known methods can be used. Examples of solid-liquid separation methods include centrifugal separation, filtration, and static separation. Among these, centrifugal separation or filtration can be used, and centrifugal separation may be used from the viewpoint of ease of operation. After solid-liquid separation, any additional steps such as a pre-drying step may be taken. An example of a pre-drying step is to pre-dry the solid components obtained after the solid-liquid separation step using a drying device such as a dryer or a drying apparatus such as a hand dryer.

[0111] Furthermore, in the solvent removal process, "in the air" strictly refers to an environment where there is absolutely no liquid outside the precursor particles, or an environment where there is only a very small amount of liquid outside the precursor particles that does not affect the removal of the hydrophobic organic solvent. "In the air" can also be rephrased as a state in which the precursor particles are not in a slurry, or a state in which the precursor particles are in a dry powder. In other words, in the solvent removal process, it is desirable to remove the hydrophobic organic solvent in an environment in which the precursor particles are in direct contact with the external gas.

[0112] The method for removing the hydrophobic organic solvent from the precursor particles in air is not particularly limited, and known methods can be employed, such as vacuum drying, heat drying, and airflow drying, which may be used in combination. In particular, when using heat drying, the heating temperature must be above the boiling point of the hydrophobic organic solvent and below the maximum temperature at which the shell structure of the precursor particles does not collapse. Therefore, depending on the shell composition in the precursor particles and the type of hydrophobic organic solvent, the heating temperature is preferably 50 to 200°C, more preferably 70 to 200°C, and even more preferably 100 to 200°C. As a result of the drying operation in air, the hydrophobic organic solvent inside the precursor particles is replaced by the external gas, and hollow resin particles are obtained in which the hollow part is occupied by gas.

[0113] The drying atmosphere is not particularly limited and can be appropriately selected depending on the application of the hollow resin particles. Examples of suitable drying atmospheres include air, oxygen, nitrogen, and argon. Furthermore, hollow resin particles with a temporarily vacuumed interior can be obtained by first filling the inside of the hollow resin particles with gas and then drying them under reduced pressure.

[0114] Alternatively, instead of separating the slurry-like precursor composition obtained in the polymerization process into solid and liquid components, the hydrophobic organic solvent may be removed by replacing the hydrophobic organic solvent encapsulated in the precursor particles with the aqueous medium of the slurry while the slurry contains the precursor particles and an aqueous medium.

[0115] Comparing a method for obtaining hollow resin particles with their hollow parts filled with gas by separating a slurry-like precursor composition into solid and liquid phases and then removing the hydrophobic organic solvent in the precursor particles in the air, with a method for obtaining hollow resin particles with their hollow parts filled with gas by replacing the hydrophobic organic solvent contained in the precursor particles with the water-based medium of the slurry in a slurry containing precursor particles and an aqueous medium, then separating the solid and liquid phases and removing the aqueous medium in the precursor particles in the air, the former method has the advantage that the hollow resin particles are less likely to be crushed in the step of removing the hydrophobic organic solvent, while the latter method has the advantage that the residue of hydrophobic organic solvent is reduced by performing bubbling with an inert gas.

[0116] In addition, after the polymerization step and before the solid-liquid separation step, a method may be used to remove the hydrophobic organic solvent contained within the precursor particles without performing solid-liquid separation of the slurry-like precursor composition obtained in the polymerization step. For example, this could involve evaporating the hydrophobic organic solvent contained within the precursor particles from the precursor composition under a predetermined pressure (high pressure, atmospheric pressure, or reduced pressure); or introducing an inert gas such as nitrogen, argon, or helium, or water vapor, into the precursor composition under a predetermined pressure (high pressure, atmospheric pressure, or reduced pressure) and then evaporating the solvent.

[0117] (E) Other processes Furthermore, the above manufacturing method may include other steps. Examples of other steps include (E-1) a cleaning step and (E-2) a re-replacement step for the hollow portion.

[0118] (E-1) Washing process The above manufacturing method preferably includes a washing step before or after the recovery step. For example, when a dispersion stabilizer is used, it is preferable to include a washing step before the recovery step in which an acid or alkali is added to wash the hollow resin particle slurry containing hollow resin particles and an aqueous medium in order to remove any remaining dispersion stabilizer. If the dispersion stabilizer used is acid-soluble, it is preferable to add an acid to the precursor composition containing the precursor particles and wash the product. On the other hand, if the dispersion stabilizer used is alkali-soluble, it is preferable to add an alkali to the precursor composition containing the precursor particles and wash the product.

[0119] Furthermore, when an acid-soluble dispersion stabilizer is used as the dispersion stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to adjust the pH to preferably 6.5 or lower, more preferably 6 or lower. As the added acid, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as formic acid and acetic acid can be used, but sulfuric acid is particularly preferred because it has a high efficiency in removing the dispersion stabilizer and places little burden on the manufacturing equipment.

[0120] (E-2) Replacement process for the hollow section The hollow portion re-substitution process is a process of replacing the gas or liquid inside the hollow resin particle with another gas or liquid. Such substitution can change the environment inside the hollow resin particle, selectively confine molecules inside the hollow resin particle, or modify the chemical structure inside the hollow resin particle according to the application.

[0121] [Firing process] In the firing step of the manufacturing method of the present invention, hollow resin particles are heated in an inert gas or under reduced pressure at 240 to 2500°C for 0.5 to 40 hours. The carbonization rate of the above hollow resin particles is usually less than 90%. By heating such hollow resin particles under the above conditions, hollow carbon particles of the present invention with a carbonization rate of 90% or more can be easily obtained.

[0122] Inert gases that can be used in the calcination process include nitrogen, argon, and helium. Furthermore, when the calcination process is carried out under reduced pressure, the reduced pressure is preferably 20 kPa or less, and more preferably 10 kPa or less.

[0123] The heating temperature in the firing process may be 240 to 2500°C, but is preferably 260 to 2000°C, more preferably 280 to 1500°C, and even more preferably 300 to 1200°C. The heating time in the firing process may be 0.5 to 40 hours, but is preferably 3.5 to 25 hours, more preferably 4.2 to 17 hours, and even more preferably 5 to 12 hours. If the firing process includes the first and second processes described later, it is preferable that the total firing time of the first and second processes be within the above range. By setting the heating conditions in the firing process within the above range, it becomes easier to adjust the carbonization rate to the above preferred range while suppressing shell damage and deformation.

[0124] The firing process preferably comprises a first step of heating hollow resin particles in an inert gas or under reduced pressure at 240 to 650°C for 0.5 to 20 hours, and a second step of heating in an inert gas or under reduced pressure at 700 to 2500°C for 2 to 20 hours after the first step. The manufacturing method comprising the first and second steps can further increase the carbonization rate of the hollow carbon particles and promote the graphitization of the shell, making it easier to achieve a carbonization rate of 95% or more for the hollow carbon particles. Furthermore, the manufacturing method comprising the first and second steps can produce hollow carbon particles with superior fluidity and strength, as well as superior conductivity and other properties, with high productivity while suppressing shell breakage and deformation.

[0125] Examples of inert gases that can be used in the first and second steps include those mentioned above. Furthermore, when the first and second steps are carried out under reduced pressure, the reduced pressure is preferably 20 kPa or less, and more preferably 10 kPa or less.

[0126] The heating temperature in the first step may be 240 to 650°C, but is preferably 260 to 600°C, more preferably 280 to 550°C, and even more preferably 300 to 500°C. The heating time in the first step may be 0.5 to 20 hours, but is preferably 1 to 10 hours, more preferably 1.2 to 7 hours, and even more preferably 1.5 to 4 hours. By setting the heating conditions in the first step within the above range, it becomes easy to adjust the carbonization rate to the above preferred range while suppressing shell damage and deformation.

[0127] The heating temperature in the second step may be 700 to 2500°C, but is preferably 750 to 2000°C, more preferably 800 to 1500°C, and even more preferably 850 to 1200°C. The heating time in the second step may be 2 to 20 hours, but is preferably 2.5 to 15 hours, more preferably 3 to 10 hours, and even more preferably 3.5 to 8 hours. By setting the heating conditions in the second step within the above range, the carbonization rate of the hollow carbon particles can be further increased, the graphitization of the shell can be promoted, and hollow carbon particles with high productivity can be produced that are even better in terms of fluidity and strength, and also have excellent properties such as conductivity.

[0128] [Surface oxidation process] It is preferable to further include a surface oxidation step after the above firing step, in which the particles are heated at 200 to 600°C in an air atmosphere to perform surface oxidation. By including a surface oxidation step in addition to the firing step, the surface acid content of the hollow carbon particles can be easily kept within the above-mentioned preferred range.

[0129] Furthermore, when the particles are heated to over 600°C during the firing process, the surface oxidation process is preferably a process in which the particles are cooled to a range of 200 to 600°C in an inert gas or under reduced pressure after the firing process, and then the atmosphere is changed to an air atmosphere to perform surface oxidation of the particles. Alternatively, the surface oxidation process may be a process in which the particles are cooled to a range of 200 to 600°C under an air atmosphere. On the other hand, the surface oxidation process may be a process in which the particles heated in the firing process are cooled to below 200°C in an inert gas or under reduced pressure, and then heated again to 200 to 600°C under an air atmosphere.

[0130] The air atmosphere is preferably an environment with a pressure of 90-110 kPa and an oxygen partial pressure of 19-21.5 kPa. The heating temperature in the surface oxidation process may be 200-600°C, but is preferably 200-500°C, and more preferably 200-400°C. The heating time in the surface oxidation process is preferably 0.05-4 hours, and more preferably 0.1-1 hour. By setting the heating conditions in the surface oxidation process within the above range, the carbonization rate of the hollow carbon particles can be further increased, the graphitization of the shell can be promoted, and hollow carbon particles with high productivity, superior fluidity and strength, and superior properties such as conductivity can be produced.

[0131] [Other processes] The manufacturing method of the present invention may further include a surface treatment step, such as boron treatment, surface coupling treatment, fluorine coating, or diamond coating. These surface treatments are usually performed after the firing step described above. These surface treatment steps may be present in place of the surface oxidation step described above, or they may be present together with the surface oxidation step.

[0132] <Hollow carbon particle-containing composition> The present invention also relates to a hollow carbon particle-containing composition containing the hollow carbon particles of the present invention as described above. The hollow carbon particle-containing composition of the present invention has excellent fluidity and strength because it contains the hollow carbon particles of the present invention.

[0133] In a composition containing hollow carbon particles, the content of hollow carbon particles is preferably 70% by mass or more, more preferably 75 to 99.9% by mass, even more preferably 78 to 99.7% by mass, particularly preferably 80 to 99.5% by mass, and most preferably 82 to 99% by mass. By setting the content of hollow carbon particles within the above range, the effects of the hollow carbon particles can be exhibited more effectively.

[0134] [Carbon powder] The hollow carbon particle-containing composition of the present invention preferably contains carbon powder (excluding the hollow carbon particles of the present invention) in addition to the hollow carbon particles of the present invention. When the hollow carbon particle-containing composition consists of the hollow carbon particles of the present invention and carbon powder, the hollow carbon particle-containing composition can exhibit excellent fluidity and strength, as well as excellent conductivity and other properties.

[0135] As the carbon powder, at least one selected from graphite, acetylene black, Ketjenblack, carbon nanotubes, graphene, and carbon nanofibers is preferred, at least one selected from graphite, acetylene black, and Ketjenblack is more preferred, and acetylene black is even more preferred.

[0136] In the hollow carbon particle-containing composition, the carbon powder content is preferably 30% by mass or less, more preferably 0.1 to 25% by mass, even more preferably 0.3 to 22% by mass, particularly preferably 0.5 to 20% by mass, and most preferably 1 to 18% by mass.

[0137] The hollow carbon particle-containing composition of the present invention may contain other components besides the hollow carbon particles and carbon powder of the present invention. For example, the hollow carbon particle-containing composition of the present invention may contain, as conductive particles, (1) metal particles, (2) aggregated metal particles, (3) molten metal particles, (4) styrene-based, phenol-based, epoxy-based resin particles or composite particles of these resin particles and solder, which have been treated with metal plating such as Ni or Au, (5) composite resin particles formed by dispersing metal particles in a flexible resin such as polyurethane resin, and (6) microencapsulated conductive particles. The content of other components in the hollow carbon particle-containing composition is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0138] The hollow carbon particle-containing composition of the present invention is usually in powder form. The powder resistance of the hollow carbon particle-containing composition of the present invention is not particularly limited, but is preferably 10 Ω·cm or less, more preferably 7.5 Ω·cm or less, even more preferably 5 Ω·cm or less, and particularly preferably 2 Ω·cm or less. The lower limit of the powder resistance of the hollow carbon particle-containing composition of the present invention is not particularly limited, but is usually 0.1 Ω·cm or more. The powder resistance can be measured, for example, by the method described in the examples.

[0139] A hollow carbon particle-containing composition can be obtained, for example, by mixing the hollow carbon particles of the present invention with carbon powder or other components.

[0140] <Application> Applications of the hollow carbon particles and hollow carbon particle-containing compositions of the present invention include battery electrode materials for primary batteries, secondary batteries, and fuel cells; electron emission elements; gas storage devices; gas and liquid purification devices; gas and liquid reforming devices; rubber, resin (plastic), urethane, and elastomer additives; lubricants; abrasives; cutting fluids; light absorbers; pastes; cosmetics; and pharmaceutical capsules.

[0141] The hollow carbon particles of the present invention exhibit excellent fluidity and strength, as well as superior electrical and thermal conductivity. Therefore, they can be suitably used as conductive fillers, thermally conductive fillers, fluidizers, and materials combining these. Furthermore, the hollow carbon particle-containing compositions of the present invention can also be suitably used for similar applications.

[0142] In particular, the hollow carbon particles of the present invention have the characteristic that, while acting as a fluidizer under normal conditions, when very high compressive stress is applied, such as during press molding, the hollow portion collapses and becomes denser, further increasing conductivity and thermal conductivity. Therefore, the hollow carbon particles and hollow carbon particle-containing compositions of the present invention can be very suitably used as a fluidizer and conductive filler for the manufacture of compression molded articles where conductivity is required, and as a fluidizer and thermally conductive filler for the manufacture of compression molded articles where thermal conductivity is required. For example, the hollow carbon particles and hollow carbon particle-containing compositions of the present invention can be very suitably used as a fluidizer and conductive filler for composite particles used to form an electrode mixture layer. [Examples]

[0143] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and percentages in the examples and comparative examples are based on mass. In the examples and comparative examples, various physical properties were evaluated as follows.

[0144] [Particle size] The particle size distribution was measured using a laser diffraction particle size distribution analyzer (SALD-3100; manufactured by Shimadzu Corporation), and the volume-average particle diameter Dv, number-average particle diameter Dp, and their ratio Dv / Dp were determined.

[0145] [Carbonization rate of particles] Using a differential thermogravimetric / thermogravimetric analyzer (TG / DTA), particles were heated under the following conditions, and the weight before heating (A) and the weight of the residue at 600°C (B) were measured. The carbonization rate was then calculated according to the formula: Carbonization rate (%) = B / A × 100. Measuring instrument: Seiko Instruments TG / DTA 6200 Measurement range: RT~600℃ Heating rate: 10°C / min Atmosphere: air

[0146] [Average porosity of particles] (Measurement of apparent density D1) First, a capacity of 100cm 3 Approximately 30 cm in a volumetric flask 3 The volumetric flask was filled with particles, and the mass of the filled particles was accurately weighed. Next, the volumetric flask filled with particles was accurately filled with isopropanol to the mark, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density of the particles D1 (g / cm³) was calculated based on the following formula (I). 3 ) was calculated. Equation (I): Apparent density D1 = [particle mass] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature])

[0147] (Measurement of true density D0) After the particles are crushed beforehand, a capacity of 100 cm³ 3 Approximately 10 g of crushed particles was packed into a volumetric flask, and the mass of the packed crushed particles was accurately weighed. Next, isopropanol was added to the volumetric flask in the same manner as the apparent density measurement described above, and the mass of isopropanol was accurately weighed. Based on the following formula (II), the true density of the particles D0 (g / cm³) was calculated. 3 ) was calculated. Formula (II): True density D0 = [Mass of particle fragments] / (100 - [Mass of isopropanol] ÷ [Specific gravity of isopropanol at measurement temperature])

[0148] (Calculation of average porosity) The average porosity (%) of the particles was calculated from the apparent density D1 and true density D0 based on the following formula (III). Formula (III): Porosity (%) = 100 - (Apparent density D1 / True density D0) × 100

[0149] [Proportion of particles with only one hollow section] Hollow particles were dispersed in epoxy resin, cured, cooled to -80°C, and cut with a microtome to prepare thin sections. The thin sections were observed using a TEM (transmission electron microscope). The concentration of hollow particles was adjusted so that 30 to 50 cross-sections could be observed within a 56 × 70 μm area (magnification 1500 to 4000x). In addition, particle cross-sections in the TEM image where the hollow portion was not visible, and hollow particle cross-sections that deviated from 0.5 to 2 times the volume-average particle size, were excluded from evaluation. In the TEM images within the above-mentioned range, the number of hollow particles and the number of particles with only one hollow portion were measured. Next, the 56 × 70 μm area where 30 to 50 hollow particles could be observed, outside the area observed above, was observed and measured in the same manner. Then, observations and measurements were repeated until the total number of hollow particles reached 100 to 150, and the ratio of the total number of particles with only one hollow section to the total number of hollow particles was determined.

[0150] [Particle circularity] Using a flow-type particle image analyzer, the average circularity of the particles and the proportion of particles with a circularity of 0.93 or less were determined under the following conditions. • Measurement device: Flow-type particle image analyzer "FPIA-3000" (manufactured by Sysmex Corporation) • Preparation of particle dispersion: Deionized water was added to the particles to prepare a particle dispersion with a solid content concentration of 0.001 to 0.05% by mass. • Measurement mode: The average circularity was calculated from 1000 measurements using HPF measurement mode and total count mode.

[0151] [Surface acid content of particles] Weigh approximately 1g of particles accurately, and determine 0.01 mol·dm³ -3 The sample was immersed in 100 ml of tetrabutyl hydride (TBA OH) / 4-methyl-2-pentanone (MIBK) solution and stirred with a stirrer for 1 hour. Then, centrifugation was performed, and the supernatant was filtered. The amount of TBA OH remaining in 50 mL of the resulting filtrate was calculated to be 0.01 mol·dm³. -3The acid content was quantitatively analyzed by non-water coulometric titration with a perchloric acid (HClO4) / MIBK solution. From the obtained values, the surface acid content (mmol / g) per gram of particle was determined. An automated coulometric titrator (Kyoto Electronics Ltd., product name "AT-700") was used for the analysis. The entire procedure was performed at room temperature under an argon stream.

[0152] [Assessment of liquidity (angle of repose)] The angle of repose of hollow carbon particles was measured using a tap denser (product name "KYT-4000", manufactured by Seishin Corporation). Specifically, a 50g sample was dropped free-fall from a dedicated input port at the top of the device and piled up in a triangular pyramidal shape on the attached table. Then, the angle between the table and the rising edge of the triangular pyramid was measured with a protractor to determine the angle of repose. A smaller angle of repose indicates superior fluidity. A: Below 35 degrees B: More than 35 degrees and less than 40 degrees C: More than 40 degrees and less than 45 degrees D: More than 46 degrees

[0153] [Evaluation of strength] The strength of hollow carbon particles was evaluated using a powder tester (manufactured by Hosokawa Micron Corporation) in the following manner. First, a sample with a diameter of 5.03 cm, a height of 5.03 cm, and a volume of 100 cm³ was prepared. 3 3g of the sample and 30mg of zirconia microbeads (product name "TZ-B 30", particle size of 95% or more of the particles is 20-38μm, manufactured by Tosoh Corporation) were added to a cylindrical container, and tapping was performed 300 times at a tap height of 1.8cm. After the tapping test was completed, water was added to separate the sample. Using a scanning electron microscope (SEM) at a magnification of 1500x, 100 hollow resin particles in the sample after the tapping test were observed, and the total number of particles that were completely broken and particles that were partially broken was counted to determine the fracture rate of the hollow resin particles. The strength was then evaluated according to the following criteria. A lower fracture rate indicates superior strength. A: The damage rate was less than 3%. B: The damage rate was between 3% and 6%. C: The damage rate was between 6% and 10%. D: The damage rate was 10% or higher.

[0154] [Evaluation of dispersibility (degree of hydrophobicity)] The degree of hydrophobicity of hollow carbon particles was determined using a powder wettability tester (WET-101P; manufactured by Resca Co., Ltd.) as follows. Under laboratory conditions, a 200 mL tall beaker was placed with a 20 mm long stirrer tip and 60 mL of ion-exchanged water at 25°C, and then set in the powder wettability tester (WET-101P; manufactured by Resca Co., Ltd.). 50 mg of sample particles were floated on top of the ion-exchanged water, and the lid and methanol supply nozzle were immediately attached. Measurement was started simultaneously with the start of stirrer stirring. The methanol (special grade methanol; manufactured by Kanto Chemical Co., Ltd.) supply rate was 2.0 mL / min, and the measurement time was 70 minutes. The stirrer stirring speed was set to 380-420 rpm. Initially, the sample particles floated at the interface of the ion-exchanged water, but as the methanol concentration increased, they gradually became wetted by the mixture of ion-exchanged water and methanol and dispersed in the liquid. As a result, the light transmittance of the liquid gradually decreased. From the obtained data, the methanol concentration (vol%) calculated from the methanol supply amount (mL) was plotted on the x-axis, and the light transmittance (voltage ratio) (%) was plotted on the y-axis. The methanol concentration (vol%) at which the light transmittance was midway between the maximum and minimum values ​​was defined as the "indicator of hydrophobicity." Then, the dispersibility (degree of hydrophobicity) was evaluated from the determined "indicator of hydrophobicity" according to the following criteria. Hollow carbon particles with high hydrophilicity have high cohesiveness and decreased dispersibility. On the other hand, hollow carbon particles with a high degree of hydrophobicity exhibit excellent dispersibility, especially in hydrophobic dispersions. A. The hydrophobicity index was 60 vol% or higher. B. The hydrophobicity index was between 40 vol% and 59 vol%. C. The hydrophobicity index was between 20 vol% and 39 vol%. D. The hydrophobicity index was between 0 vol% and less than 20 vol%.

[0155] [Evaluation of conductivity (powder resistance)] Using a powder resistance measurement system (MCP-PD51 type; manufactured by Dain Instruments Co., Ltd.), the resistance value was measured at room temperature while applying a pressure of 5 MPa continuously to a composition containing about 1 g of hollow carbon particles. From the converged resistance value R (Ω), the area S (cm 2 ) and the thickness d (cm) of the compressed sample layer, the powder resistance ρ (Ω·cm) = R×(S / d) was calculated. At the time when the resistance value converged, at least a part of the hollow carbon particles in the composition containing hollow carbon particles was considered to be crushed. It is considered that the smaller the resistance of the shell itself of the hollow carbon particles and the denser the composition containing hollow carbon particles, the smaller the powder resistance ρ. And the smaller the powder resistance ρ, the more it can be judged that the hollow carbon particles and the composition containing hollow carbon particles can give a molded body with excellent conductivity.

[0156] [Production Example 1: Production of Polar Resin A (MMA / AA / EA Copolymer)] 200 parts of toluene was charged into a reaction vessel. After sufficiently replacing the inside of the reaction vessel with nitrogen while stirring the toluene, the temperature was raised to 90 °C. Then, a mixed solution of 96.2 parts of methyl methacrylate (MMA), 0.3 parts of acrylic acid (AA), 3.5 parts of ethyl acrylate (EA), and 2.8 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was dropped into the reaction vessel over 2 hours. Further, the polymerization was completed by holding for 10 hours under toluene reflux, and then the solvent was distilled off under reduced pressure to obtain polar resin A (MMA / AA / EA copolymer).

[0157] In the total mass of 100% of the repeating units constituting the obtained polar resin A (MMA / AA / EA copolymer), the ratio of the repeating units derived from MMA was 96.2%, the repeating units derived from AA was 0.3%, and the repeating units derived from EA was 3.5%. Also, the obtained polar resin A was insoluble in water, and the number average molecular weight of polar resin A was 10,000.

[0158] The number-average molecular weight was determined as polystyrene-equivalent molecular weight by gel permeation chromatography (GPC) using tetrahydrofuran as a carrier at a flow rate of 0.35 ml / min. The apparatus used was a Tosoh HLC8220, with three Shodex® KF-404HQ columns linked together (column temperature 40°C), and a differential refractometer and ultraviolet detector. Molecular weight calibration was performed at 12 points using standard polystyrene (5 million to 3 million) from Polymer Laboratory.

[0159] [Example 1] (1) Mixed liquid preparation process First, the following mixture was prepared as the oil phase. Ethylene glycol dimethacrylate (EGDMA) 31.9 parts Trimethylolpropane triacrylate (TMPTA) 13.7 parts Polar resin A (MMA / AA / EA copolymer) 0.2 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) 1.04 parts Hydrophobic solvent: Cyclohexane 54.5 parts Meanwhile, in a stirred tank, at room temperature, an aqueous solution prepared by dissolving 7.8 parts of magnesium chloride (water-soluble polyvalent metal salt) in 225 parts of deionized water was gradually added under stirring to an aqueous solution prepared by dissolving 5.5 parts of sodium hydroxide (alkali metal hydroxide) in 55 parts of deionized water to prepare a dispersion of magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) (4.0 parts magnesium hydroxide), which was then used as the aqueous phase. A mixture was prepared by mixing the aqueous phase and the oil phase.

[0160] (2) Suspension process The mixture obtained in the above mixture preparation step was suspended by stirring it for 1 minute at a rotation speed of 4,000 rpm using a disperser (Primix Corporation, product name: Homomixer) to prepare a suspension in which monomer droplets containing a hydrophobic solvent were dispersed in water.

[0161] (3) Polymerization process The suspension obtained in the above suspension step was heated in a nitrogen atmosphere from 40°C to 65°C over 30 minutes (heating rate: 50°C / hour), and stirred for 1 hour and 30 minutes under the temperature of 65°C to carry out the first polymerization reaction. Furthermore, 2.3 parts of methyl acrylate were added to the stirring tank, and a second polymerization reaction was carried out by stirring for 2 hours and 30 minutes under a nitrogen atmosphere and a temperature of 65°C. Through the first and second polymerization reactions, a precursor composition was prepared, which is a slurry liquid in which precursor particles containing a hydrophobic solvent are dispersed in water.

[0162] (4) Washing and solid-liquid separation process The precursor composition obtained in the polymerization process described above was washed with dilute sulfuric acid at 25°C for 10 minutes to reduce the pH to 5.5 or less. Next, after separating the water by filtration, 200 parts of freshly deionized water were added to re-form a slurry, and the water washing treatment (washing, filtration, dewatering) was repeated several times at 25°C, followed by filtration separation to obtain the solid. The obtained solid was dried in a dryer at a temperature of 40°C to obtain precursor particles containing a hydrophobic solvent.

[0163] (5) Solvent removal process The precursor particles obtained in the solid-liquid separation process described above were heat-treated in a vacuum dryer at 200°C for 6 hours, then cooled to room temperature under atmospheric pressure using nitrogen to obtain hollow resin particles. The volume-average particle diameter Dv of the hollow resin particles was measured according to the method described above. The results are shown in Table 1.

[0164] (6) Firing process The hollow resin particles obtained in the solvent removal process described above were heated at 500°C for 10 hours under an N2 airflow (first step). Then, while maintaining an N2 atmosphere in the oven, the particles were cooled to below 200°C to obtain hollow carbon particles. For the obtained hollow carbon particles, the volume-average particle diameter Dv, ratio Dv / Dp, carbonization rate, porosity, proportion of particles with only one hollow portion, proportion of particles with a circularity of 0.93 or less, average circularity, surface acid content, fluidity (angle of repose), strength, and dispersibility (degree of hydrophobicity) were measured according to the method described above. The results are shown in Table 2.

[0165] (7) Production of hollow carbon particle-containing composition A hollow carbon particle-containing composition was obtained by mixing hollow carbon particles and acetylene black (Denka Black powder, manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 0.7 μm) in the ratios shown in Table 1. The conductivity (powder resistance) of the obtained hollow carbon particle-containing composition was evaluated according to the method described above. The results are shown in Table 1.

[0166] [Example 2] Hollow resin particles were obtained in the same manner as in Example 1. The obtained hollow resin particles were heated at 300°C for 2 hours under an N2 airflow (Step 1). Next, the oven was filled with an argon atmosphere and baked at 900°C for 4 hours (Step 2). Then, while maintaining the argon atmosphere in the oven, the particles were cooled to below 200°C to obtain hollow carbon particles. The obtained hollow carbon particles and acetylene black were mixed in the ratios shown in Table 2 to obtain a hollow carbon particle-containing composition. The obtained hollow carbon particles and hollow carbon particle-containing composition were measured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0167] [Example 3] Hollow carbon particles were obtained in the same manner as in Example 1. The obtained hollow resin particles were heated at 300°C for 2 hours under an N2 airflow (Step 1). Next, the oven was filled with an argon atmosphere and baked at 900°C for 4 hours (Step 2). Furthermore, the oven was cooled to 200°C while maintaining the argon atmosphere, and then the oven was filled with an air atmosphere and baked at 200°C for 0.2 hours to obtain hollow carbon particles (Surface oxidation step). The obtained hollow carbon particles and acetylene black were mixed in the ratios shown in Table 2 to obtain a hollow carbon particle-containing composition. The obtained hollow carbon particles and hollow carbon particle-containing composition were measured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0168] [Example 4] Hollow resin particles were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide colloidal dispersion used as the aqueous phase was increased by 1.3 times. Then, hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained hollow resin particles were used, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0169] [Example 5] Hollow resin particles were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide colloidal dispersion used as the aqueous phase was reduced to 0.8 times. Then, hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained hollow resin particles were used, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0170] [Example 6] First, the following mixture was prepared as the oil phase. Ethylene glycol dimethacrylate (EGDMA) 35 parts Trimethylolpropane triacrylate (TMPTA) 13.7 parts Polar resin A (MMA / AA / EA copolymer) 0.2 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) 1.04 parts Hydrophobic solvent: Cyclohexane 50 parts Hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained mixture was used as the oil phase, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0171] [Comparative Example 1] Hollow resin particles were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide colloidal dispersion used as the aqueous phase was doubled. Then, hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained hollow resin particles were used, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0172] [Comparative Example 2] Hollow resin particles were obtained in the same manner as in Example 1, except that the amount of magnesium hydroxide colloidal dispersion used as the aqueous phase was reduced to 0.65 times. Then, hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained hollow resin particles were used, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0173] [Comparative Example 3] Hollow carbon particles were obtained in the same manner as in Example 3, except that the firing time in the second step of the firing process was changed from 4 hours to 2 hours. The obtained hollow carbon particles and acetylene black were mixed in the ratios shown in Table 1 to obtain a hollow carbon particle-containing composition. The obtained hollow carbon particles and hollow carbon particle-containing composition were measured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0174] [Comparative Example 4] First, the following mixture was prepared as the oil phase. Ethylene glycol dimethacrylate (EGDMA) 50.0 parts Trimethylolpropane triacrylate (TMPTA) 13.7 parts Polar resin A (MMA / AA / EA copolymer) 0.2 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) 1.04 parts Hydrophobic solvent: Cyclohexane 35.0 parts A suspension was prepared in the same manner as in Example 1, except that the obtained mixture was used as the oil phase. The obtained suspension was heated in a nitrogen atmosphere from 40°C to 65°C over 10 minutes (heating rate: 150°C / hour), and stirred for 1 hour under the temperature of 65°C to carry out the first polymerization reaction. Furthermore, 1 part of methyl acrylate was added to the stirring tank, and a second polymerization reaction was carried out by stirring for 1 hour and 30 minutes under the nitrogen atmosphere and temperature of 65°C. The first and second polymerization reactions prepared a precursor composition, which is a slurry liquid in which precursor particles containing a hydrophobic solvent are dispersed in water. Then, hollow carbon particles and a hollow carbon particle-containing composition were obtained in the same manner as in Example 3, except that the obtained precursor composition was used, and measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0175] [Comparative Example 5] First, the following mixture was prepared as the oil phase. Ethylene glycol dimethacrylate (EGDMA) 37.0 parts Trimethylolpropane triacrylate (TMPTA) 0 parts Polar resin A (MMA / AA / EA copolymer) 0.2 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) 1.04 parts Hydrophobic solvent: Cyclohexane 75.0 parts Hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained mixture was used as the oil phase, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0176] [Comparative Example 6] First, the following mixture was prepared as the oil phase. Ethylene glycol dimethacrylate (EGDMA) 35 parts Trimethylolpropane triacrylate (TMPTA) 13.7 parts Polar resin A (MMA / AA / EA copolymer) 0.1 part 2,2'-Azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) 1.04 parts Hydrophobic solvent: Cyclohexane 50 parts Hollow carbon particles and a composition containing hollow carbon particles were obtained in the same manner as in Example 3, except that the obtained mixture was used as the oil phase, and measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0177] [Table 1]

[0178] [Table 2]

[0179] As is clear from Table 2, hollow carbon particles in which the carbonization rate, volume-average particle diameter Dv, and average porosity were within a specific range, and the proportion of particles with only one hollow portion was 90% or more, exhibited excellent fluidity and strength (Examples 1-6).

[0180] On the other hand, when the carbonization rate, volume-average particle size Dv, or average porosity were outside a specific range, or when the proportion of particles with only one hollow portion was too small, it was not possible to achieve both fluidity and strength (Comparative Examples 1-6).

Claims

1. A hollow carbon particle comprising a shell with a carbonization rate of 90% or more and a hollow portion surrounded by the shell, The volume-average particle size Dv is 3.0 to 25 μm. The average porosity is 50-90%. Hollow carbon particles in which the proportion of particles with only one hollow section is 90% or more.

2. The hollow carbon particle according to claim 1, wherein the ratio of the volume-average particle diameter Dv to the number-average particle diameter Dp, Dv / Dp, is 1.02 to 2.

0.

3. Hollow carbon particles according to claim 1 or 2, wherein the proportion of particles having a circularity of 0.93 or less is 10 percent or less.

4. Hollow carbon particles according to claim 1 or 2, wherein the surface acid content is 0.001 mol / g or more.

5. A hollow carbon particle-containing composition comprising 70% by mass or more of the hollow carbon particles described in claim 1 or 2.

6. The hollow carbon particle-containing composition according to claim 5, comprising at least one carbon powder selected from graphite, acetylene black, Ketjenblack, carbon nanotubes, graphene, and carbon nanofibers.

7. A method for producing hollow carbon particles according to claim 1 or 2, A method for producing hollow carbon particles, comprising a firing step of heating hollow resin particles in an inert gas or under reduced pressure at 240 to 2500°C for 0.5 to 40 hours.

8. The firing process comprises a first step of heating the hollow resin particles in an inert gas or under reduced pressure at 240 to 650°C for 0.5 to 20 hours, A method for producing hollow carbon particles according to claim 7, further comprising a second step of heating in an inert gas or under reduced pressure at 700 to 2500°C for 2 to 20 hours after the first step.

9. The method for producing hollow carbon particles according to claim 7, further comprising a surface oxidation step of heating the particles at 200 to 600°C in an air atmosphere after the firing step, thereby performing surface oxidation of the particles.

Images