Method for manufacturing hollow particles

Abstract

This invention provides a method for producing hollow particles that can manufacture them with high productivity. [Solution] A method for producing hollow particles having a resin-containing shell and a hollow portion surrounded by the shell, comprising: a mixture preparation step of preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium; a suspension step of preparing a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the mixture; a polymerization step of preparing a precursor composition having a hollow portion surrounded by a resin-containing shell and the hollow portion filled with the hydrophobic solvent by starting to raise the temperature of the suspension under a reduced pressure sealed condition of 90 kPaA or less, and subjecting the suspension to a polymerization reaction; and a solvent removal step of removing the hydrophobic solvent contained within the precursor particles.

Description

[Technical Field]

[0001] This invention relates to a method for producing hollow particles. [Background technology]

[0002] Hollow particles (hollow resin particles) have cavities inside and are used as additives to resins, paints, or various molded products for purposes such as weight reduction, heat insulation, and low dielectric constant. Their applications extend to a wide range of fields, including automobiles, bicycles, aerospace, electrical and electronic equipment, construction, home appliances, containers, stationery, tools, and footwear.

[0003] Hollow particles can be produced by methods such as bulk polymerization, solution polymerization, dispersion polymerization, suspension polymerization, and emulsion polymerization. In suspension polymerization, hollow particles are obtained by dispersing droplets of a monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator in an aqueous medium and carrying out polymerization.

[0004] For example, Patent Document 1 discloses a method for producing hollow particles, comprising: a mixture preparation step of preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; a suspension step of preparing a suspension by suspending the mixture; a polymerization step of preparing a precursor composition by subjecting the suspension to a polymerization reaction; a predetermined solvent removal step; and a washing step. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2024 / 095851 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of this disclosure is to provide a method for manufacturing hollow particles that can produce hollow particles with high productivity. [Means for solving the problem]

[0007] According to the method for producing hollow particles described in Patent Document 1, the precursor composition inevitably contains bubbles generated during the polymerization process. The present inventors conducted studies to achieve the above objective and found that there is room to reduce the amount of bubbles in the precursor composition, and that the productivity of hollow particles can be improved by reducing the amount of bubbles.

[0008] In other words, the present invention provides a method for producing hollow particles as described below (first method of production). [1] A method for producing hollow particles comprising a resin-containing shell and a hollow portion surrounded by the shell, A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by starting to raise the temperature of the suspension under reduced pressure and sealed conditions of 90 kPaA or less, and subjecting the suspension to a polymerization reaction, A solvent removal step to remove the hydrophobic solvent contained within the precursor particles, A method for producing hollow particles having the properties of [2] The method for producing hollow particles according to [1], further comprising a transfer step of transferring the precursor composition using a positive displacement pump. [3] The method for producing hollow particles according to [2], wherein a reciprocating pump is used as the positive displacement pump. [4] A method for producing hollow particles according to any one of [1] to [3], wherein the solvent removal step includes a solid-liquid separation step of obtaining the precursor particles separated from the aqueous medium by solid-liquid separation of the precursor composition, and a drying step of removing the hydrophobic solvent contained in the precursor particles under a reduced pressure environment and an inert gas flow.

[0009] Furthermore, the present invention provides the following method for producing hollow particles (second method of production). [5] A method for producing hollow particles comprising a resin-containing shell and a hollow portion surrounded by the shell, A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by subjecting the suspension to a polymerization reaction. A transfer step of transferring the precursor composition using a transfer means equipped with a mechanism for applying centrifugal force under reduced pressure, A solvent removal step to remove the hydrophobic solvent contained within the precursor particles, A method for producing hollow particles having the properties of [6] The method for producing hollow particles according to [5], wherein the solvent removal step includes a solid-liquid separation step of obtaining the precursor particles separated from the aqueous medium by solid-liquid separation of the precursor composition, and a drying step of removing the hydrophobic solvent contained in the precursor particles under a reduced pressure environment and an inert gas flow. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing hollow particles that can be manufactured with high productivity. [Modes for carrying out the invention]

[0011] In this disclosure, the "~" in a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0012] In the present disclosure, hollow particles whose hollow portions are filled with a hydrophobic solvent are considered as intermediates of hollow particles whose hollow portions are filled with gas, and are referred to as "precursor particles". In the present disclosure, the "precursor composition" means a composition including precursor particles.

[0013] The production method of the present disclosure is a method for producing hollow particles including a shell containing a resin and a hollow portion surrounded by the shell. According to the present disclosure, a first production method and a second production method described later are provided.

[0014] According to the production method described in Patent Document 1, since a large amount of bubbles generated in the polymerization step are contained in the precursor composition, there has been a problem that the apparent volume of the precursor composition obtained in the polymerization step is large, and the treatment efficiency such as transfer of the precursor composition and solvent removal treatment is reduced.

[0015] In contrast, according to the first production method of the present invention, by starting the temperature increase of the suspension and carrying out a polymerization reaction under reduced pressure and sealed conditions at a pressure of 90 kPaA or lower, a precursor composition with a reduced amount of bubbles can be obtained, whereby hollow particles can be produced with high productivity. In particular, according to the first production method of the present invention, even when defoaming treatment of the precursor composition is not performed after the polymerization step, a precursor composition with a reduced amount of bubbles can be obtained, so that post-treatments such as transfer of the precursor composition and solvent removal treatment can be performed with high efficiency.

[0016] Further, according to the second production method of the present invention, by transferring the precursor composition obtained in the polymerization step using a specific transfer means, a precursor composition with a reduced amount of bubbles can be obtained, whereby hollow particles can be produced with high productivity.

[0017] In the first and second manufacturing methods of this disclosure, a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium is suspended to prepare a suspension in which droplets of a monomer composition having a distribution structure in which the polymerizable monomer and the hydrophobic solvent are phase-separated, with the polymerizable monomer unevenly distributed on the surface and the hydrophobic solvent unevenly distributed in the center are dispersed in the aqueous medium. When this suspension is subjected to a polymerization reaction, polymers begin to precipitate on the surface of the monomer composition droplets, and as the polymerization reaction proceeds further, the surface of the droplets hardens and a shell is formed, resulting in hollow particles having a hollow part filled with hydrophobic solvent.

[0018] <First manufacturing method> The first manufacturing method of this disclosure is A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by starting to raise the temperature of the suspension under reduced pressure and sealed conditions of 90 kPaA or less, and subjecting the suspension to a polymerization reaction, The process includes a solvent removal step to remove the hydrophobic solvent contained within the precursor particles.

[0019] The above manufacturing method includes a mixture preparation step, a suspension step, a polymerization step, and a solvent removal step, and may also include other steps. Furthermore, to the extent that it is technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single step, or in a different order. For example, the preparation of the mixture and the suspension may be performed simultaneously in a single step, such as adding the materials to prepare the mixture while simultaneously performing the suspension.

[0020] (1) Mixed liquid preparation process In the first manufacturing method of this disclosure, a mixture preparation step is performed to prepare a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. The mixture may further contain other materials, such as dispersion stabilizers, to the extent that they do not impair the effects of this disclosure.

[0021] (A) Polymerizable monomers In this disclosure, a polymerizable monomer is a compound having a functional group capable of addition polymerization (which may be simply referred to as a polymerizable functional group in this disclosure). In this disclosure, a compound having an ethylenically unsaturated bond as the functional group capable of addition polymerization is generally used as a polymerizable monomer.

[0022] In this disclosure, known polymerizable monomers conventionally used for the production of hollow polymer particles can be used as polymerizable monomers, and are not particularly limited. However, it is preferable that the polymerizable monomer contains at least a crosslinkable monomer, and more preferably a non-crosslinkable monomer, in order to facilitate the formation of hollow portions within the particles. When the polymerizable monomer contains a crosslinkable monomer, when the suspension is subjected to a polymerization reaction, the crosslinking density of the polymer precipitated on the surface of the droplet increases, and the precipitates themselves are also crosslinked, thereby increasing the crosslinking density of the shell. As a result, a shell with excellent strength is easily formed, the hollow particles tend to become spherical, and hollow portions clearly distinguishable from the shell are easily formed within the particles.

[0023] In this disclosure, polymerizable monomers having only one polymerizable functional group are referred to as non-crosslinkable monomers, and polymerizable monomers having two or more polymerizable functional groups are referred to as crosslinkable monomers. Crosslinkable monomers can form crosslinked bonds in the polymer through polymerization reactions. Crosslinkable monomers become crosslinkable monomer units in the shell, and non-crosslinkable monomers become non-crosslinkable monomer units in the shell.

[0024] In this disclosure, polymerizable monomers consisting of carbon and hydrogen are referred to as hydrocarbon monomers, crosslinkable monomers consisting of carbon and hydrogen are referred to as crosslinkable hydrocarbon monomers, and non-crosslinkable monomers consisting of carbon and hydrogen are referred to as non-crosslinkable hydrocarbon monomers. Furthermore, polymerizable monomers having a (meth)acryloyl group as a polymerizable functional group are referred to as acrylic monomers, crosslinkable monomers having a (meth)acryloyl group as a polymerizable functional group are referred to as crosslinkable acrylic monomers, and non-crosslinkable monomers having a (meth)acryloyl group as a polymerizable functional group are referred to as non-crosslinkable acrylic monomers. In the case of crosslinkable acrylic monomers, it is sufficient if at least one polymerizable functional group is a (meth)acryloyl group, but it is preferable that all polymerizable functional groups are (meth)acryloyl groups.

[0025] In this disclosure, (meth)acrylate refers to acrylate and methacrylate, respectively; (meth)acrylic refers to acrylic and methacrylic, respectively; and (meth)acryloyl refers to acryloyl and methacryloyl, respectively.

[0026] Examples of crosslinkable monomers include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; linear or branched diolefins such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, and hexadiene; diene monomers such as alicyclic diolefins such as dicyclopentadiene, cyclopentadiene, and ethylidenetetracyclododecene; crosslinkable hydrocarbon monomers such as polybutadiene, polyisoprene, styrene-butadiene block copolymer (SBS), and styrene-isoprene block copolymer (SIS); allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and 3-(meth)acryloyloxy-2-hydroxypropyl (meth)acrylate. Examples include crosslinkable acrylic monomers such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, bisphenol A di(meth)acrylate, and their ethoxylated derivatives; crosslinkable allyl monomers such as diallyl phthalate; crosslinkable macromers such as polyphenylene ethers with vinyl-modified ends and polyphenylene ethers with methacrylic-modified ends. These crosslinkable monomers can be used individually or in combination of two or more types. Among the crosslinkable monomers, crosslinkable hydrocarbon monomers are preferred, aromatic divinyl monomers are more preferred, and divinylbenzene is particularly preferred, from the viewpoint of further reducing the amount of bubbles in the precursor composition and further increasing the productivity of hollow particles.

[0027] Examples of non-crosslinkable monomers include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethyl vinylbenzene, ethyl vinyl biphenyl, and ethyl vinylnaphthalene; linear or branched monoolefins such as ethylene, propylene, and butylene; and alicyclic monoolefins such as vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methano-1,4,4a,9a-tetrahydrofluorene; methyl (meth)acrylate, ethyl (meth)acrylate. (T)Acrylate, Butyl(meth)acrylate, 2-Ethylhexyl(meth)acrylate, Lauryl(meth)acrylate, t-Butylaminoethyl(meth)acrylate, Glycidyl(meth)acrylate, 2-Hydroxyethyl(meth)acrylate, 2-Aminoethyl(meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-Methylol(meth)acrylamide, N-Butoxymethyl(meth)acrylamide, Methoxypolyethylene glycol(meth)acrylate, Ethoxypolyethylene glycol(meth)acrylate Non-crosslinkable acrylic monomers such as propoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, hexaoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol, polypropylene glycol (meth)acrylate, lauroxypolyethylene glycol (meth)acrylate, stearoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol, polypropylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol, propylene glycol mono(meth)acrylate, polyethylene glycol, tetramethylene glycol (meth)acrylate, propylene glycol, polybutylene glycol mono(meth)acrylate, monoethylene glycol mono(meth)acrylate, monoethylene glycol mono(meth)acrylate, etc.; vinyl carboxylate ester monomers such as vinyl acetate; halogenated aromatic vinyl monomers such as halogenated styrene; halogenated vinyl monomers such as vinyl chloride; vinylidene halogenated monomers such as vinylidene chloride;Examples include vinylpyridine monomers; polystyrene with (meth)acrylic-modified ends; and non-crosslinkable macromers such as polymethyl methacrylate with (meth)acrylic-modified ends. These non-crosslinkable monomers can be used individually or in combination of two or more types. Among the non-crosslinkable monomers, non-crosslinkable hydrocarbon monomers are preferred, aromatic monovinyl monomers are more preferred, and styrene and ethyl vinylbenzene are even more preferred, as they further reduce the amount of bubbles in the precursor composition and further increase the productivity of hollow particles.

[0028] In this disclosure, the content of crosslinkable monomers in 100% by mass of polymerizable monomer is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, from the standpoint of improving the strength of the shell, making it easier for hollow particles to maintain a high porosity, and easily exhibiting effects such as weight reduction, heat insulation, and low dielectric constant. The polymerizable monomer may consist of a crosslinkable monomer, but including a combination of a crosslinkable monomer and a non-crosslinkable monomer as the polymerizable monomer may improve the properties of the hollow particles. The content of the crosslinkable monomer in 100% by mass of polymerizable monomer may be, for example, 98% by mass or less. Furthermore, the content of crosslinkable monomers in 100% by mass of polymerizable monomers corresponds to the content of crosslinkable monomer units in 100% by mass of all monomer units of the polymer contained in the shell. Similarly, the content of each monomer in 100% by mass of polymerizable monomers corresponds to the content of each monomer unit in 100% by mass of all monomer units of the polymer contained in the shell.

[0029] From the viewpoint of further reducing the amount of bubbles in the precursor composition and further increasing the productivity of hollow particles, the content of hydrocarbon monomers in 100% by mass of polymerizable monomer is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The polymerizable monomer may consist of hydrocarbon monomers.

[0030] The content of polymerizable monomers in the mixture is not particularly limited, but from the viewpoint of balancing the porosity, particle size, and mechanical strength of the hollow particles, it is preferably 15 to 50% by mass, more preferably 20 to 40% by mass, based on 100% by mass of the total mass of the components in the mixture excluding the aqueous medium. When the content of polymerizable monomers in the mixture is within the above range, hydrophobic solvents can be efficiently removed in the solvent removal step. Furthermore, in order to suppress a decrease in properties in the resulting hollow particles, the content of polymerizable monomers relative to 100% by mass of the total solid content of the material that becomes the oil phase in the mixed liquid, excluding the hydrophobic solvent, is preferably 96% by mass or more, more preferably 97% by mass or more. In this disclosure, "solids" refers to all components excluding the solvent, and liquid polymerizable monomers, etc., are included in the solids.

[0031] (B) Hydrophobic solvents The hydrophobic solvent used in the manufacturing method of this disclosure is a nonpolymerizable and poorly water-soluble organic solvent. The hydrophobic solvent acts as a spacer material, forming hollow spaces within the particles. In the suspension step described later, a suspension is obtained in which droplets of the monomer composition containing the hydrophobic solvent are dispersed in an aqueous medium. In the suspension step, phase separation occurs within the droplets of the monomer composition, resulting in the less polar hydrophobic solvent tending to accumulate inside the droplets. Ultimately, in the droplets of the monomer composition, the hydrophobic solvent is distributed inside, and other materials other than the hydrophobic solvent are distributed around its periphery according to their respective polarities. Then, in the polymerization process described later, an aqueous dispersion containing precursor particles encapsulating a hydrophobic solvent is obtained. That is, as the hydrophobic solvent accumulates inside the particles, a hollow space filled with the hydrophobic solvent is formed inside the resulting precursor particles.

[0032] The hydrophobic solvent can be appropriately selected from known hydrophobic solvents and is not particularly limited. Examples include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents. Among these, hydrocarbon solvents are preferred, and hydrocarbon solvents having 5 to 8 carbon atoms are more preferred. Examples of hydrocarbon solvents include linear hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane and 2-methylpentane, and paraffinic solvents, as well as aliphatic hydrocarbons including cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane and cycloheptane; and aromatic hydrocarbons such as benzene, toluene, and xylene. These hydrophobic solvents can be used individually or in combination of two or more.

[0033] In the suspension process, phase separation between the polymerizable monomer and the hydrophobic solvent is likely to occur within the droplets of the monomer composition. Therefore, it is preferable to select an organic solvent as the hydrophobic solvent that has lower solubility in water than the crosslinkable monomer contained in the polymerizable monomer. Furthermore, if the polymerizable monomer contains hydrocarbon compounds in a proportion exceeding 50% by mass, the hydrophobic solvent is preferably a hydrocarbon solvent, more preferably a chain-type hydrocarbon solvent, even more preferably a chain-type hydrocarbon solvent having 5 to 8 carbon atoms, and even more preferably at least one selected from the group consisting of pentane, hexane, heptane, and octane.

[0034] Furthermore, although not particularly limited, the boiling point of the hydrophobic solvent is preferably 130°C or lower, more preferably 100°C or lower, since it is easily removed in the solvent removal step described later. On the other hand, since it is easily encapsulated in precursor particles, it is preferably 50°C or higher, more preferably 60°C or higher. Furthermore, if the hydrophobic solvent is a mixed solvent containing multiple types of hydrophobic solvents and has multiple boiling points, it is preferable that the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent is less than or equal to the above upper limit, and it is preferable that the boiling point of the solvent with the lowest boiling point among the solvents contained in the mixed solvent is greater than or equal to the above lower limit.

[0035] Furthermore, the hydrophobic solvent preferably has a dielectric constant of 2.5 or less at 20°C. Relative dielectric constant is one indicator of the polarity of a compound. When the dielectric constant of the hydrophobic solvent is sufficiently small, such as 2.5 or less, it is thought that phase separation proceeds rapidly in the droplets of the monomer composition, and hollow spaces are easily formed. Examples of hydrophobic solvents with a relative permittivity of 2.5 or less at 20°C are as follows. (The value in parentheses is the relative permittivity.) Pentane (1.8), hexane (1.9), heptane (1.9), octane (1.9), cyclohexane (2.0). Regarding the relative permittivity at 20°C, values ​​can be found in publicly available 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), as well as other technical information. Methods for measuring the relative permittivity at 20°C include, for example, relative permittivity tests conducted in accordance with JIS C 2101:1999, item 23, with the measurement temperature set at 20°C.

[0036] The porosity of the hollow particles can be adjusted by changing the amount of hydrophobic solvent in the mixture. In the suspension step described later, the polymerization reaction proceeds with oil droplets containing polymerizable monomers, etc., encapsulating the hydrophobic solvent. Therefore, the higher the hydrophobic solvent content, the higher the porosity of the resulting hollow particles tends to be. In this disclosure, the content of the hydrophobic solvent in the mixture is preferably 100 parts by mass or more and 650 parts by mass or less per 100 parts by mass of polymerizable monomer, as this makes it easier to control the particle size of the hollow particles, easier to increase the porosity while maintaining the strength of the hollow particles, and easier to reduce the amount of residual hydrophobic solvent in the particles. More preferably, the content of the hydrophobic solvent in the mixture is 120 parts by mass or more and 500 parts by mass or less per 100 parts by mass of polymerizable monomer, and even more preferably 140 parts by mass or more and 300 parts by mass or less.

[0037] (C) Polymerization initiator In the manufacturing method of this disclosure, it is preferable that the mixture contains an oil-soluble polymerization initiator as the polymerization initiator. In suspension polymerization using an oil-soluble polymerization initiator, there is no opportunity for the polymerization initiator to come into contact with polymerizable monomers dispersed in the aqueous medium. Therefore, by using an oil-soluble polymerization initiator, it is possible to suppress the generation of extra resin particles, such as relatively small, dense particles, in addition to the target resin particles having hollow portions.

[0038] The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic with a solubility in water of 0.2% by mass or less. Examples include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxydiethyl acetate, and t-butyl peroxypivalate; and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0039] When organic peroxides are used as polymerization initiators, there is the advantage that the amount of bubbles in the precursor composition is further reduced, and the productivity of hollow particles is further increased. On the other hand, when azo compounds are used as polymerization initiators, there is the advantage that hydrocarbon residues derived from the initiator are reduced, impurities contained in the hollow particles can be reduced, and because the 10-hour half-life temperature of azo compounds is low, the reaction temperature can be lowered, the volatilization of the encapsulated solvent can be suppressed, and the porosity of the hollow particles can be easily controlled.

[0040] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of polymerizable monomer in the mixture. If the content of the polymerization initiator is above the lower limit, the polymerization reaction can proceed sufficiently, and if it is below the upper limit, there is little risk of the polymerization initiator remaining after the polymerization reaction is completed, and there is little risk of unexpected side reactions occurring.

[0041] Furthermore, when using an azo compound as a polymerization initiator, from the viewpoint of obtaining hollow particles with excellent solvent resistance, the content of the azo compound is preferably 2.4 to 3.6 parts by mass, and more preferably 2.8 to 3.2 parts by mass, per 100 parts by mass of polymerizable monomer in the mixture.

[0042] (D)Aqueous medium In this disclosure, "aqueous medium" means a medium selected from the group consisting of water, hydrophilic solvents, and mixtures of water and hydrophilic solvents. When using a mixture of water and a hydrophilic solvent, it is important that the overall polarity of the mixture does not become too low, from the viewpoint of forming droplets of the monomer composition. In this case, for example, the mass ratio of water to hydrophilic solvent (water:hydrophilic solvent) may be 99:1 to 50:50. The hydrophilic solvent in this disclosure is not particularly limited as long as it mixes well with water and does not undergo phase separation. Examples of hydrophilic solvents include alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0043] The content of the aqueous medium is not particularly limited, but from the viewpoint of keeping the particle size and porosity of the hollow particles within the preferred range described later, the lower limit is preferably 200 parts by mass or more, more preferably 400 parts by mass or more, and even more preferably 600 parts by mass or more, per 100 parts by mass of polymerizable monomer contained in the mixture, and the upper limit is preferably 1000 parts by mass or less, and more preferably 800 parts by mass or less.

[0044] The mixture may further contain other materials different from those described in (A) to (D) above, as long as it does not impair the effects of the present disclosure. For example, the mixture preferably further contains (E) a dispersion stabilizer.

[0045] (E) Dispersion stabilizer Dispersion stabilizers are agents used in the suspension process to disperse droplets of monomer compositions in an aqueous medium. Examples of dispersion stabilizers include inorganic dispersion stabilizers, organic or inorganic water-soluble polymer stabilizers, and surfactants. In this disclosure, it is preferable to use an inorganic dispersion stabilizer as the dispersion stabilizer because it allows for easy control of the droplet size in the suspension, facilitates removal of the dispersion stabilizer by the washing process, and suppresses a decrease in the strength of the hollow particles by preventing the shell from becoming too thin. Examples of inorganic dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and ferric hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used individually or in combination of two or more. Among inorganic dispersion stabilizers, poorly water-soluble inorganic dispersion stabilizers are preferably used. Here, poor water solubility means that the solubility in water at 25°C is preferably less than 1 g / L. Among poorly water-soluble inorganic dispersion stabilizers, metal hydroxides are preferred, and magnesium hydroxide is more preferred.

[0046] In this disclosure, it is particularly preferable to use a poorly water-soluble inorganic dispersion stabilizer in the form of colloidal particles dispersed in an aqueous medium, that is, in the form of a colloidal dispersion containing colloidal particles of the poorly water-soluble inorganic dispersion stabilizer. This allows the inorganic dispersion stabilizer to be easily removed by the washing process described later. A colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include barium hydroxide and calcium hydroxide. The water-soluble polyvalent metal salt can be any water-soluble polyvalent metal salt other than the alkaline earth metal hydroxide compounds mentioned above. Examples include magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred. The method for reacting at least one selected from the alkali metal hydroxide and alkaline earth metal hydroxide mentioned above with the water-soluble polyvalent metal salt mentioned above in an aqueous medium is not particularly limited, but for example, an aqueous solution of at least one selected from the alkali metal hydroxide and alkaline earth metal hydroxide may be mixed with an aqueous solution of the water-soluble polyvalent metal salt. Furthermore, colloidal silica can be used as a colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloid particles.

[0047] Examples of organic water-soluble polymer stabilizers include polyvinyl alcohol, polycarboxylic acids (such as polyacrylic acid), celluloses (such as hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose), polyvinylpyrrolidone, polyacrylimide, polyethylene oxide, and poly(hydroxystearate-g-methylmethacrylate-co-methacrylic acid) copolymers. Examples of inorganic water-soluble polymer stabilizers include sodium tripolyphosphate. A surfactant is a compound that contains both a hydrophilic group and a hydrophobic group in a single molecule, and examples include ionic surfactants such as known anionic surfactants, cationic surfactants, and amphoteric surfactants, as well as nonionic surfactants. Water-soluble polymer stabilizers and surfactants typically have a solubility of 1 g / L or more in water at 25°C.

[0048] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the total mass of the polymerizable monomer and hydrophobic solvent. By having a dispersion stabilizer content above the lower limit, the monomer composition droplets can be sufficiently dispersed so that they do not coalesce in the suspension. On the other hand, by having a dispersion stabilizer content below the upper limit, it is possible to prevent the viscosity of the suspension from increasing during granulation and to avoid the problem of the suspension clogging the granulator. Furthermore, the content of the dispersion stabilizer is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the aqueous medium.

[0049] In the case of hollow particles, from the viewpoint of suppressing deterioration of performance stability, it is preferable to have as little residual dispersion stabilizer as possible, most preferably without dispersion stabilizer, and especially preferably without organic water-soluble polymer stabilizers, inorganic water-soluble polymer stabilizers, and surfactants. By using only inorganic dispersion stabilizers as the dispersion stabilizer, hollow particles can be obtained in which the levels of organic water-soluble polymer stabilizers, inorganic water-soluble polymer stabilizers, or surfactants are below the detection limit.

[0050] A mixture is obtained by mixing the aforementioned materials and other materials as needed, and stirring as appropriate. In this mixture, the oil phase containing (A) polymerizable monomers, (B) hydrophobic solvents, and (C) lipophilic materials such as polymerization initiators is dispersed in an aqueous phase containing (D) an aqueous medium and (E) a dispersion stabilizer, which is used as needed, with particle sizes of several millimeters. Depending on the type of material, the dispersion state of these materials in the mixture can be observed with the naked eye. In the mixture preparation process, the mixture may be obtained by simply mixing the aforementioned materials and other materials as needed, and stirring as appropriate. However, it is preferable to prepare the oil phase and aqueous phase separately in advance and then mix them together to prepare the mixture, as this makes it easier to achieve a uniform shell. By preparing the oil phase and aqueous phase separately in advance and then mixing them, it is possible to produce hollow particles with a uniform shell composition, and it also becomes easier to control the particle size of the hollow particles.

[0051] (2) Suspension process In the suspension step of the first manufacturing method of this disclosure, the mixture obtained in the mixture preparation step is suspended to prepare a suspension in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator are dispersed in an aqueous medium.

[0052] The suspension method for forming droplets of the monomer composition is not particularly limited, and known suspension methods can be employed. Examples of dispersers used when preparing the suspension include horizontal or vertical inline dispersers such as the Milder manufactured by Taiheiyo Kiko Co., Ltd., the Cavitron manufactured by Eurotech Co., Ltd., and inline dispersers manufactured by IKA (e.g., DISPAX-REACTOR® DRS); and emulsifying dispersers such as the Homomixer MARK II series manufactured by Primix Corporation.

[0053] (3) Polymerization process In the polymerization step of the first manufacturing method of this disclosure, the suspension obtained in the suspension step is subjected to a polymerization reaction. Specifically, the suspension is heated under reduced pressure and sealed conditions of 90 kPaA or less, and the suspension is subjected to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent.

[0054] In the polymerization process, the atmosphere is initially set to a reduced-pressure, sealed atmosphere with a pressure of 90 kPaA or less before starting to heat the suspension. If the pressure at the start of heating is too high, the amount of bubbles in the precursor composition will not be sufficiently reduced, and the productivity of hollow particles will decrease. It is preferable to maintain a sealed state during the polymerization reaction.

[0055] The pressure at the start of heating is not particularly limited as long as it is 90 kPaA or less, but is preferably 70 kPaA or less, and more preferably 50 kPaA or less. When the pressure at the start of heating is within the above range, the amount of bubbles in the precursor composition is further reduced, and the productivity of hollow particles is further increased. The lower limit of the pressure at the start of heating is not particularly limited, but is usually 1 kPaA or more, and is preferably 2 kPaA or more from the viewpoint of easy pressure control. The lower limit of the pressure at the start of heating may be 3 kPaA or more, and may be 5 kPaA or more.

[0056] In the polymerization process, it is preferable to first create an inert gas atmosphere before starting to raise the temperature of the suspension. Nitrogen gas, argon gas, and the like can be used as the inert gas.

[0057] The polymerization method is not particularly limited as long as it can create a reduced-pressure, sealed atmosphere at the start of the heating process, but a batch method is preferred.

[0058] The polymerization temperature is not particularly limited, but is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher, from the viewpoint of allowing the polymerization reaction to proceed sufficiently and reducing the content of unreacted polymerizable monomers, and is preferably 90°C or lower from the viewpoint of suppressing evaporation of the aqueous medium. The polymerization reaction time is not particularly limited, but from the viewpoint of allowing the polymerization reaction to proceed sufficiently and reducing the content of unreacted polymerizable monomers, it is preferably 4 hours or more, more preferably 10 hours or more, and from the viewpoint of production efficiency, it is preferably 60 hours or less, more preferably 40 hours or less, and even more preferably 30 hours or less.

[0059] Furthermore, the suspension during the polymerization reaction is usually stirred. The stirring power is not particularly limited, but from the viewpoint of promoting the polymerization reaction, it is preferably 0.01 kW / m 3 The above is more than 0.02 kW / m 3 More preferably 0.03 kW / m 3 Therefore, in order to reduce the proportion of irregularly shaped particles, a preferred value is 0.20 kW / m 3 More preferably, 0.10 kW / m 3 Further, more preferably 0.05 kW / m 3 The following applies:

[0060] When a dispersion stabilizer is used, it is preferable to dissolve the dispersion stabilizer in the precursor composition in an aqueous medium by adding an acid or alkali to the precursor composition after polymerization. If the dispersion stabilizer used is acid-soluble, it is preferable to add an acid; if the dispersion stabilizer used is alkali-soluble, it is preferable to add an alkali.

[0061] If the dispersion stabilizer used is acid-soluble, add acid to the precursor composition to adjust the pH to preferably 6.5 or lower, more preferably 6 or lower. Inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as formic acid and acetic acid, can be used as the added acid. However, sulfuric acid is particularly preferred due to its high efficiency in removing the dispersion stabilizer in subsequent processes and its low burden on the manufacturing equipment.

[0062] (4) Transfer process The first manufacturing method of this disclosure may further include a transfer step after the polymerization step. The transfer step is a step of transferring the precursor composition obtained in the polymerization step for subsequent steps such as a solvent removal step. For example, if the first manufacturing method of this disclosure includes a solid-liquid separation step described later, the first manufacturing method of this disclosure may include a transfer step of transferring the precursor composition from the polymerization vessel to a solid-liquid separation apparatus.

[0063] In the transfer process, for example, the receiving port of the destination container may be set at a lower position than the discharge port of the source container, and the two may be connected by piping, thereby transferring the precursor composition by gravity. Alternatively, the precursor composition may be transferred using a pump.

[0064] Pumps that can be used in the transfer process include positive displacement pumps and non-positive displacement pumps. Examples of positive displacement pumps include reciprocating pumps such as diaphragm pumps, plunger pumps, piston pumps, and bellows pumps; and rotary pumps such as gear pumps, rotary pumps, and screw pumps. Examples of non-positive displacement pumps include centrifugal pumps, axial flow pumps, and inclined pumps. In addition, as a non-positive displacement pump, a transfer means equipped with a mechanism that applies centrifugal force under a reduced pressure environment, as described later, may be used.

[0065] In particular, when transferring the precursor composition using a positive displacement pump, it is believed that the bubbles in the precursor composition are destroyed by the repeated depressurization and pressurization of the precursor composition within the positive displacement pump. Therefore, using a positive displacement pump further reduces the amount of bubbles in the precursor composition and further increases the productivity of hollow particles. As for positive displacement pumps, reciprocating pumps are preferred, and diaphragm pumps are more preferred, from the viewpoint of further reducing the amount of bubbles in the precursor composition even when the transfer speed is relatively high.

[0066] (5) Solvent removal process In the solvent removal step of the first manufacturing method of this disclosure, the hydrophobic solvent contained within the precursor particles obtained in the polymerization step is removed.

[0067] The method for removing hydrophobic solvents contained within precursor particles is not particularly limited, but it is preferable to use a method that includes a solid-liquid separation step to obtain precursor particles separated from an aqueous medium by solid-liquid separation of the precursor composition, and a drying step to dry the precursor particles separated from the aqueous medium, and more preferably a method that further includes a washing step to wash the precursor particles obtained by the solid-liquid separation step.

[0068] (5-1) Solid-liquid separation process In the solid-liquid separation process, precursor particles are obtained by separating the precursor composition from the aqueous medium through solid-liquid separation. The method for separating precursor particles from an aqueous medium is not particularly limited, but examples include centrifugation, filtration, and static separation. Among these, filtration is preferred because it is easy to operate and has high efficiency in removing dispersion stabilizers, which can be used as needed. As for the filtration method, any method can be used, such as natural filtration (atmospheric pressure filtration), reduced pressure filtration, pressure filtration, and centrifugal filtration, and among these, pressure filtration is preferred because it efficiently removes dispersion stabilizers and unreacted polymerizable monomers, which can be used as needed.

[0069] (5-2) Washing process In the washing process, the precursor particles obtained in the solid-liquid separation process are washed to obtain the washed precursor particles. While there are no particular limitations on the method for washing the precursor particles, a preferred method involves repeatedly performing a series of operations: dispersing the precursor particles separated from the aqueous medium in deionized water to re-slurry them, and then separating and recovering the precursor particles again. While there are no particular limitations on the method for separating and recovering precursor particles in the washing process, filtration is preferred, and pressure filtration is more preferred, from the viewpoint of ease of operation and excellent washing efficiency. Furthermore, the series of operations can be carried out until the electrical conductivity of the aqueous medium (or filtrate, if separation and recovery is performed by filtration) removed during the separation and recovery of precursor particles becomes, for example, 10 μS / cm or less.

[0070] (5-3) Drying process The drying step involves drying the precursor particles obtained by the solid-liquid separation step or the washing step described above to remove the hydrophobic solvent contained within the precursor particles. The drying method is not particularly limited, but examples include vacuum drying, heat drying, and airflow drying, and these may be used in combination. In particular, when using the heat drying method, the temperature must be below the maximum temperature at which the shell structure does not collapse. Therefore, depending on the shell composition, the heating temperature may be 50-200°C, 70-200°C, or 100-200°C. Furthermore, pre-drying may be performed during the drying process. Pre-drying may be carried out, for example, by drying the precursor particles using a drying device such as a dryer or a drying apparatus such as a hand dryer. The drying atmosphere is not particularly limited and can be appropriately selected depending on the application of the hollow particles. Examples of drying atmospheres include air, oxygen, nitrogen, and argon. Furthermore, hollow particles with a temporarily vacuumed interior can be obtained by first filling the inside of the hollow particles with gas and then drying them under reduced pressure.

[0071] As a method that offers excellent drying efficiency for precursor particles, it is preferable to dry them under reduced pressure and an inert gas stream to remove hydrophobic solvents contained within the precursor particles. Here, reduced pressure is preferably 2 kPa to 35 kPa, more preferably 4 kPa to 15 kPa. Examples of inert gases include nitrogen, argon, and helium, and are not particularly limited, but nitrogen is preferably used. The flow rate of the inert gas is not particularly limited, but from the viewpoint of improving drying efficiency, it is preferably 30 L / min or more, more preferably 200 L / min or more, and even more preferably 300 L / min or more. The upper limit of the flow rate of the inert gas is not particularly limited, but from the viewpoint of manufacturing cost, it is preferably 500 L / min or less. Drying under reduced pressure and an inert gas stream offers excellent drying efficiency and can be carried out at relatively low temperatures, for example, at 130°C or below. By drying at such relatively low temperatures, manufacturing costs can be reduced. On the other hand, in order to improve drying efficiency, the drying temperature performed under reduced pressure and inert gas flow is preferably 20°C or higher, more preferably 40°C or higher.

[0072] In the solvent removal step, solvent removal methods other than those including the solid-liquid separation step and drying step described above may be used. For example, a hydrophobic solvent may be removed from the precursor particles by bubbling a gas through the precursor composition to obtain an aqueous dispersion of hollow particles. By such a method, an aqueous dispersion of hollow particles in which the hollow portion is filled with the bubbling gas is obtained. Then, hollow particles may be obtained by removing the aqueous medium from the obtained aqueous dispersion of hollow particles. Specifically, the solvent removal method described in International Publication No. 2024 / 095851 may be used.

[0073] (6) Others In addition to the above steps (1) to (5), a particle internal substitution step may be added. A particle internal substitution step is a step in which the gas or liquid inside the hollow particle is replaced with another gas or liquid. Such substitution can change the environment inside the hollow particle, selectively confine molecules inside the hollow particle, or modify the chemical structure inside the hollow particle according to the application.

[0074] <Second manufacturing method> The second manufacturing method of this disclosure is A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by subjecting the suspension to a polymerization reaction. A transfer step of transferring the precursor composition using a transfer means equipped with a mechanism for applying centrifugal force under reduced pressure, The process includes a solvent removal step to remove the hydrophobic solvent contained within the precursor particles.

[0075] The above manufacturing method includes a mixture preparation step, a suspension step, a polymerization step, a transfer step, and a solvent removal step, and may also include other steps. Furthermore, to the extent that it is technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single step, or in a different order. For example, the preparation of the mixture and the suspension may be performed simultaneously in a single step, such as adding the materials to prepare the mixture while simultaneously performing the suspension.

[0076] (1) Mixture preparation step and (2) Suspension step As the mixed liquid preparation step and suspension step in the second production method of the present disclosure, the same aspects as the mixed liquid preparation step and suspension step in the first production method of the present disclosure can be employed, and the preferred aspects are also the same.

[0077] (3) Polymerization Step In the polymerization step of the second production method of the present disclosure, the suspension obtained in the suspension step is subjected to a polymerization reaction, thereby preparing a precursor composition including precursor particles having a hollow portion surrounded by a resin-containing shell and the hollow portion filled with a hydrophobic solvent.

[0078] In the polymerization step, it is preferable to replace the atmosphere with an inert gas atmosphere in advance before starting to raise the temperature of the suspension. Nitrogen gas, argon gas, or the like can be used as the inert gas.

[0079] The polymerization method is not particularly limited, and known polymerization methods such as, for example, a batch method, a semi-continuous method, and a continuous method can be employed.

[0080] The polymerization temperature is not particularly limited, but from the viewpoint of sufficiently proceeding the polymerization reaction to reduce the content of unreacted polymerizable monomers, it is preferably 30°C or higher, more preferably 40°C or higher, still more preferably 50°C or higher, and from the viewpoint of suppressing evaporation of the aqueous medium, it is preferably 90°C or lower. The polymerization reaction time is not particularly limited, but from the viewpoint of sufficiently proceeding the polymerization reaction to reduce the content of unreacted polymerizable monomers, it is preferably 4 hours or more, more preferably 10 hours or more, and from the viewpoint of production efficiency, it is preferably 60 hours or less, more preferably 40 hours or less, still more preferably 30 hours or less. The polymerization pressure is not particularly limited.

[0081] In addition, the suspension during the polymerization reaction is usually stirred. The stirring power of the stirring is not particularly limited, but from the viewpoint of promoting the polymerization reaction, it is preferably 0.01 kW / m 3 or more, more preferably 0.02 kW / m 3 or more, still more preferably 0.03 kW / m 3Therefore, in order to reduce the proportion of irregularly shaped particles, a preferred value is 0.20 kW / m 3 More preferably, 0.10 kW / m 3 Further, more preferably 0.05 kW / m 3 The following applies:

[0082] When a dispersion stabilizer is used, it is preferable to dissolve the dispersion stabilizer in the precursor composition in an aqueous medium by adding an acid or alkali to the precursor composition after polymerization. The specific manner in which the acid or alkali is added to the precursor composition is the same as that described in the first manufacturing method, and the preferred manner is also the same.

[0083] (4) Transfer process The transfer step in the second manufacturing method of this disclosure is a step of transferring the precursor composition obtained in the polymerization step using a transfer means equipped with a mechanism for applying centrifugal force under a reduced pressure environment.

[0084] A preferred transfer means includes a mechanism for applying centrifugal force under reduced pressure, comprising: a mechanism for drawing in a precursor composition using a pressure difference within a reduced pressure chamber; a mechanism for applying centrifugal force to the drawn precursor composition to thin it; and a mechanism for discharging the thinned precursor composition using centrifugal force. An example of such a transfer means is the Bubble Buster manufactured by Ashizawa Finetech Co., Ltd.

[0085] (5) Solvent removal process The solvent removal step in the second manufacturing method of this disclosure can be the same as the solvent removal step in the first manufacturing method of this disclosure, and the preferred mode is also the same.

[0086] <Hollow particles> The hollow particles obtained by the manufacturing methods (first and second) of this disclosure are particles comprising a resin-containing shell (outer shell) and a hollow portion surrounded by the shell.

[0087] The resin contained in the shell is typically a polymerizable monomer polymer used in the manufacturing method of the present disclosure.

[0088] In the hollow particles obtained by the manufacturing method of this disclosure, the hollow portion is a cavity-like space clearly distinguishable from the shell. The shell of the hollow particle may have a porous structure, in which case the hollow portion is of a size that is clearly distinguishable from a multitude of minute spaces uniformly dispersed within the porous structure. It is preferable that the hollow particles have a dense shell. Furthermore, it is preferable that the hollow portion of the hollow particles is filled with a gas such as air, as this facilitates effects such as weight reduction, heat insulation, and low dielectric constant.

[0089] The hollow particles obtained by the manufacturing method of this disclosure may have one or more hollow portions, but it is preferable that they have only one hollow portion in order to maintain a good balance between high porosity and mechanical strength. In the hollow particles, it is preferable that the number proportion of particles having only one hollow portion be 90% or more, and more preferably 95% or more. Furthermore, the shell of the hollow particle, and the partition wall separating adjacent hollow sections when there are two or more hollow sections, may be porous, but it is preferable that they be dense.

[0090] The shape of the hollow particles obtained by the manufacturing method of this disclosure may be, for example, spherical, ellipsoidal, or irregular, but from the viewpoint of the dispersibility and pressure resistance of the hollow particles, a spherical shape is preferred. The hollow particles may contain small amounts of particles with low circularity due to cracking or deformation as impurities, but the proportion of particles with a circularity of 0.85 or less out of 100% by mass of hollow particles is 10% by mass or less, preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and even more preferably 3% by mass or less. By adjusting the stirring conditions in the suspension step, polymerization step, or solvent removal step described above, the proportion of particles with a circularity of 0.85 or less can be kept below the above upper limit. Circularity is defined as the value obtained by dividing the diameter of a circle with the same area as the projected image of the particle (equivalent circle area diameter) by the diameter of a circle with the same perimeter as the projected image of the particle (equivalent perimeter circle diameter). Circularity is 1 when the particle is a perfect sphere, and decreases as the surface shape of the particle becomes more complex. Circularity is measured using a flow-type particle image analyzer with an image resolution of 0.185 μm / pixel.

[0091] The porosity of the hollow particles obtained by the manufacturing method of this disclosure is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and particularly preferably 60% or more, from the viewpoint of dielectric properties, lightness, and heat insulation. The upper limit of the porosity of the hollow particles is not particularly limited, but from the viewpoint of suppressing a decrease in the strength of the hollow particles and making them less susceptible to crushing, it is preferably 95% or less, more preferably 90% or less, and even more preferably 80% or less. The porosity of a hollow particle is calculated from its apparent density and true density.

[0092] The hollow particles obtained by the manufacturing method of this disclosure have a ratio of D95 to D50 (D95 / D50) of preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and even more preferably less than 2.0, where D50 is the cumulative 50% particle diameter by volume and D95 ​​is the cumulative 95% particle diameter by volume. When the above ratio (D95 / D50) is below the above upper limit, the dielectric properties tend to be excellent. Furthermore, when the above ratio (D95 / D50) is below the above upper limit, particles with little variation in performance between particles can be obtained. Furthermore, when the above ratio (D95 / D50) is below the above upper limit, for example, when manufacturing a sheet-like resin structure to which hollow particles are added, a product with a uniform thickness can be manufactured. The lower limit of the above ratio (D95 / D50) is not particularly limited, but from the viewpoint of ease of manufacture, it may be 1.1 or more. Furthermore, the D50 and D95 ​​values ​​for hollow particles can be determined, for example, by measuring the particle size of the hollow particles using a particle size distribution analyzer based on the Coulter counter method, and then obtaining the particle size distribution based on its volume. The Coulter counter method is a method of measuring particle diameter using an electrical resistance method called the Coulter principle.

[0093] The hollow particles obtained by the manufacturing method of this disclosure have a volume-based cumulative 50% particle diameter (D50) that is preferably 1.0 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more, and preferably 50.0 μm or less, more preferably 30.0 μm or less, even more preferably 15.0 μm or less, and even more preferably 10.0 μm or less. When the D50 of the hollow particles is above the lower limit, the dispersion of the hollow particles improves, a uniform shell is easily formed, and variations in shell thickness are suppressed, which tends to improve the pressure resistance of the hollow particles. On the other hand, when the D50 of the hollow particles is below the upper limit, the particle size is sufficiently small, making it suitable for use as a substrate material for electronic circuit boards and the like, and it can be added to thin, small substrates.

[0094] Applications of the hollow particles obtained by the manufacturing method of this disclosure include, for example, low dielectric materials, heat insulating materials, sound insulating materials, and light reflecting materials used in various fields such as automobiles, electrical and electronic equipment, construction, aerospace, and space, as well as as additives in components such as light diffusing materials such as light diffusing films or light diffusing plates, food containers, footwear such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, tools, 3D printer filaments, and buoyancy materials such as syntactic foam.

[0095] The hollow particles obtained by the manufacturing method of this disclosure are suitably used, for example, as an electronic circuit board material. Specifically, by incorporating the hollow particles into the insulating resin layer of an electronic circuit board, the dielectric loss tangent of the insulating resin layer can be reduced while suppressing defects caused by the hollow particles. Furthermore, the hollow particles are suitably used as additives in semiconductor materials such as interlayer insulating materials, dry film resists, solder resists, bonding wires, magnet wires, semiconductor encapsulants, epoxy encapsulants, mold underfills, underfills, die bond pastes, buffer coat materials, copper-clad laminates, and flexible substrates, or as additives in semiconductor materials used in high-frequency device modules, antenna modules, and automotive radars. Among these, they are particularly suitably used as additives in semiconductor materials such as interlayer insulating materials, solder resists, magnet wires, semiconductor encapsulants, epoxy encapsulants, underfills, buffer coat materials, copper-clad laminates, and flexible substrates, or as additives in semiconductor materials used in high-frequency device modules, antenna modules, and automotive radars.

[0096] The hollow particles obtained by the manufacturing method of this disclosure are also useful as additives to insulating resin sheets used in the manufacture of electronic components such as printed circuit boards. An insulating resin sheet containing hollow particles can be manufactured, for example, by preparing a resin composition by mixing a thermoplastic resin, thermosetting resin, thermoplastic elastomer, or a mixture thereof with the hollow particles, and then forming the resin composition into a sheet by coating and drying it on one or both sides of a sheet-like substrate, extrusion molding, or transfer. If the resin or elastomer contained in the insulating resin sheet has adhesive properties, the insulating resin sheet can be used as an adhesive sheet, specifically, for example, as a bonding sheet. A bonding sheet is an insulating adhesive layer forming material used to join a conductor layer and an organic insulating layer when manufacturing a multilayer printed circuit board. The hollow particles obtained by the manufacturing method disclosed herein have a high porosity, are resistant to crushing, and have excellent heat resistance, thus meeting the thermal insulation and cushioning properties required for undercoat materials, as well as the heat resistance suitable for thermal paper applications. Furthermore, the hollow particles are also useful as plastic pigments with excellent gloss and opacity. The hollow particles obtained by the manufacturing method of this disclosure can be used for various purposes depending on the components contained inside, as useful components such as fragrances, chemicals, pesticides, and ink components can be sealed inside by means of immersion treatment, reduced pressure treatment, or pressurized immersion treatment. The hollow particles obtained by the manufacturing method of this disclosure are also suitably used as rust inhibitors. Since the hollow particles are also useful as additives that reduce electrical conductivity, for example, paints containing hollow particles can be used as rust-preventive paints (paint primers, lubricating paints, etc.) to enhance the corrosion resistance and rust prevention of steel materials. Furthermore, rust-preventive additives can be encapsulated in the hollow particles added to the rust-preventive paint. The hollow particles obtained by the manufacturing method of this disclosure can be used as additives in various batteries such as lithium-ion batteries, all-solid-state batteries, and fuel cells used in various fields such as electric vehicles, power tools, auxiliary power supplies, and wind power generation. More specifically, the hollow particles can be used in conductive pastes, porous separator films, surface protective materials for battery packaging materials and battery casing materials used in lithium-ion batteries, solid electrolyte separators and compositions for forming electric double-layer capacitor electrodes used in all-solid-state batteries, and separators and compositions for forming microbial fuel cell electrodes used in fuel cells. [Examples]

[0097] 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 "%" are based on weight. Various measurements were performed according to the following methods.

[0098] <Level of bubble reduction in precursor composition> Based on the conditions during the transfer process, the level of bubble reduction in the precursor composition was evaluated according to the following criteria. A: The amount of bubbles was reduced to an extremely high degree, and no particles leaked out of the storage tank. B: The amount of bubbles was well reduced, and the amount of particles leaked outside the storage tank was greater than 0% by weight and less than 1% by weight (calculated based on the weight of the resulting hollow particles) relative to the total amount of particles in the precursor composition. C: The amount of bubbles was sufficiently reduced, and the amount of particles leaked outside the storage tank was 1% by weight or more but less than 2% by weight of the total particle amount of the precursor composition (calculated based on the weight of the resulting hollow particles). D: The reduction in the amount of bubbles was insufficient, and the amount of particles that leaked out of the storage tank was between 2% and 10% by weight (calculated based on the weight of the resulting hollow particles) of the total particle amount of the precursor composition. E: The reduction in the amount of bubbles was insufficient, and the amount of particles that leaked out of the storage tank was 10% by weight or more of the total particle amount of the precursor composition (calculated by the weight of the resulting hollow particles).

[0099] Furthermore, the greater the amount of bubbles in the precursor composition, the larger the apparent volume of the precursor composition becomes, and the greater the amount of particles leaking from the storage tank. The higher the level of bubble reduction in the precursor composition, the more particle leakage is suppressed and the higher the particle yield, thus indicating higher productivity. In addition, the higher the level of bubble reduction in the precursor composition, the more the supply amount or supply rate of the precursor composition to post-treatment processes such as filtration can be increased, improving the efficiency of post-treatment, thus indicating higher productivity.

[0100] <Transfer rate of precursor composition> The transfer rate of the precursor composition from the polymerization vessel to the storage tank (inside the filtration device) was evaluated according to the following criteria. A faster transfer rate indicates higher productivity. A: Transfer speed is 5m 3 / hour or more B: Transfer speed is 5m 3 Less than / hours

[0101] [Example 1] (1) Mixed liquid preparation process First, the following materials were mixed to form the oil phase. (In Table 1, the type of oil phase is represented as "A".) Divinylbenzene 37.5 parts Ethyl vinylbenzene 1.6 parts t-Butyl peroxydiethyl acetate (oil-soluble polymerization initiator, manufactured by Nuurion Pharmaceuticals, trade name "Trigonox27") 0.89 parts Hydrophobic solvent: Heptane 60.8 parts

[0102] Next, in a stirring tank, an aqueous solution prepared by dissolving 15.7 parts magnesium chloride (water-soluble polyvalent metal salt) in 225 parts deionized water was gradually added under stirring to an aqueous solution prepared by dissolving 11.0 parts sodium hydroxide (alkali metal hydroxide) in 55 parts deionized water to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (8 parts magnesium hydroxide), which was then used as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed solution.

[0103] (2) Suspension process The mixture obtained in the above mixture preparation step was subjected to a suspension process by stirring it for 1 minute at a rotation speed of 4,000 rpm using an emulsifying disperser (Primix Corporation, product name: Homomixer), thereby preparing a suspension in which droplets of monomer composition containing a hydrophobic solvent were dispersed in water.

[0104] (3) Polymerization process The atmosphere of the suspension obtained in the above suspension step was changed to a nitrogen atmosphere, then the pressure was reduced to approximately 3 kPaA (the lower limit of the pressure gauge), and the container was sealed. Then, while maintaining the sealed state, the temperature was raised to 80°C, and the polymerization reaction was carried out by stirring at 80°C for 24 hours. This polymerization reaction yielded a precursor composition, which was a slurry liquid in which precursor particles containing a hydrophobic solvent were dispersed in water.

[0105] The atmosphere of the precursor composition obtained in the polymerization process described above was opened to the air and cooled to 25°C. Next, dilute sulfuric acid was added to the precursor composition and stirred for 10 minutes to obtain a pH-adjusted precursor composition with a pH of 5.5 or lower.

[0106] (4) Transfer process Next, while maintaining the temperature at 25°C, the entire amount of the pH-adjusted precursor composition was transferred from the polymerization vessel to the storage tank (inside the filtration system) using a diaphragm pump (product name "DEPA-80," manufactured by Takumina Co., Ltd.). Based on the conditions during transfer, the level of bubble reduction and the transfer speed of the precursor composition were evaluated using the method described above. The results are shown in Table 1.

[0107] (5) Solvent removal process (5-1) Solid-liquid separation process, (5-2) Washing process Next, the filtration apparatus was operated to perform pressurized filtration of the precursor composition and remove water to obtain dehydrated precursor particles. 200 parts of freshly deionized water were added to the obtained dehydrated precursor particles to re-slurry them, and filtration and dehydration were performed in the same manner as above. This series of steps of re-slurrying, filtration, and dehydration of the precursor particles was repeated until the electrical conductivity of the filtrate was 10 μS / cm or less to obtain precursor particles.

[0108] (5-3) Drying process The precursor particles obtained in the above washing process were pre-dried in a dryer at a temperature of 40°C. Next, the precursor particles were heat-treated in a vacuum dryer under reduced pressure conditions of 200°C and a nitrogen stream for 12 hours to remove the hydrophobic solvent contained within the particles and obtain hollow particles.

[0109] [Example 2] Hollow particles were produced in the same manner as in Example 1, except that the transfer process was changed as described below.

[0110] (4) Transfer process The entire amount of the pH-adjusted precursor composition was transferred from the piping at the bottom of the polymerization vessel (pipe inner diameter: 205 mm) to a storage tank (inside the filtration device) located below the polymerization vessel. In other words, the pH-adjusted precursor composition fell due to its own weight. Based on the conditions during transfer, it was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0111] [Example 3] Hollow particles were produced in the same manner as in Example 2, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 80 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0112] [Example 4] Hollow particles were produced in the same manner as in Example 1, except that the oil phase prepared in the polymerization step was changed as described below. The particles were evaluated in the same manner as in Example 1 based on their condition during the transfer step. The results are shown in Table 1.

[0113] The following materials were mixed to form the oil phase. (In Table 1, the type of oil phase is indicated as "B".) Ethylene glycol dimethacrylate 12.5 parts Trimethylolpropane trimethacrylate 15 parts Divinylbenzene 13 parts Ethyl vinylbenzene 9.5 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (azo polymerization initiator) 1.5 parts Hydrophobic solvent: Hexane 50 parts

[0114] [Example 5] Hollow particles were produced in the same manner as in Example 4, except that the transfer process was changed to the transfer process of Example 2. The conditions during the transfer process were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0115] [Example 6] Hollow particles were produced in the same manner as in Example 5, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 50 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0116] [Example 7] Hollow particles were produced in the same manner as in Example 5, except that the oil phase prepared in the polymerization process was changed as described below, and the pressure at the start of heating in the polymerization process was changed from approximately 3 kPaA to 80 kPaA. The particles were evaluated in the same manner as in Example 1 based on the conditions during transfer in the transfer process. The results are shown in Table 1.

[0117] The following materials were mixed to form the oil phase. (In Table 1, the type of oil phase is indicated by "C".) Ethylene glycol dimethacrylate 12.5 parts Trimethylolpropane trimethacrylate 15 parts Divinylbenzene 13 parts Ethyl vinylbenzene 9.5 parts 2,2'-Azobis(2,4-dimethylvaleronitrile) (azo polymerization initiator) 1.2 parts Hydrophobic solvent: Hexane 50 parts

[0118] [Example 8] Hollow particles were produced in the same manner as in Example 5, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 80 kPaA. The conditions during the transfer process were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0119] [Table 1]

[0120] [Comparative Example 1] Hollow particles were produced in the same manner as in Example 1, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 101 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0121] [Comparative Example 2] Hollow particles were produced in the same manner as in Example 2, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 101 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0122] [Comparative Example 3] Hollow particles were produced in the same manner as in Example 4, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 101 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0123] [Comparative Example 4] Hollow particles were produced in the same manner as in Example 5, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 101 kPaA. The transfer process was evaluated in the same manner as in Example 1 based on the conditions during transfer. The results are shown in Table 1.

[0124] [Table 2]

[0125] As is clear from Tables 1 and 2, by initiating the heating of the suspension and carrying out the polymerization reaction under reduced pressure and sealed conditions of 90 kPaA or less, the amount of bubbles in the precursor composition was reduced, even when using a transfer means with a high transfer rate, and hollow particles could be produced with high productivity (Examples 1-8).

[0126] On the other hand, when the pressure at the start of heating was 101 kPa, using a transfer means with a high transfer speed made it impossible to sufficiently reduce the amount of bubbles in the precursor composition, and hollow particles could not be produced with high productivity (Comparative Examples 1-4).

[0127] [Example i] (1) Mixed liquid preparation process ~ (3) Polymerization process The pH-adjusted precursor composition was obtained in the same manner as in Example 1, except that the pressure at the start of the heating process in the polymerization step was changed from approximately 3 kPaA to 101 kPaA.

[0128] (4) Transfer process Next, the entire amount of the pH-adjusted precursor composition was transferred from the polymerization vessel to the storage tank (inside the filtration device) using a transfer device (product name "Bubble Buster BB400," manufactured by Ashizawa Finetech Co., Ltd.) equipped with a mechanism that applies centrifugal force under reduced pressure while maintaining the temperature at 25°C. Based on the conditions during transfer, the level of bubble reduction and the transfer speed of the precursor composition were evaluated using the method described above. The results are shown in Table 3.

[0129] (5) Solvent removal process Hollow particles were obtained by the same solvent removal process as in Example 1.

[0130] [Example ii] Hollow particles were produced in the same manner as in Example i, except that the oil phase prepared in the polymerization step was changed to the oil phase of Example 4 (oil phase C). The evaluation was performed in the same manner as in Example 1 based on the conditions during transfer in the transfer step. The results are shown in Table 1.

[0131] [Table 3]

[0132] As is clear from Tables 2 and 3, a manufacturing method having a transfer step in which the precursor composition is transferred using a transfer means equipped with a mechanism for applying centrifugal force under reduced pressure reduces the amount of bubbles in the precursor composition and enables the production of hollow particles with high productivity (Examples i-ii).

[0133] On the other hand, when a transfer means equipped with a mechanism for applying centrifugal force under reduced pressure was not used, the amount of bubbles in the precursor composition could not be sufficiently reduced, and hollow particles could not be produced with high productivity (Comparative Examples 1-4).

Claims

1. A method for producing hollow particles comprising a resin-containing shell and a hollow portion surrounded by the shell, A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by starting to raise the temperature of the suspension under reduced pressure and sealed conditions of 90 kPaA or less, and subjecting the suspension to a polymerization reaction, A solvent removal step to remove the hydrophobic solvent contained within the precursor particles, A method for producing hollow particles having the properties of

2. A method for producing hollow particles according to claim 1, further comprising a transfer step of transferring the precursor composition using a positive displacement pump.

3. The method for producing hollow particles according to claim 2, wherein a reciprocating pump is used as the positive displacement pump.

4. A method for producing hollow particles according to claim 1 or 2, wherein the solvent removal step includes a solid-liquid separation step of obtaining the precursor particles separated from the aqueous medium by solid-liquid separation of the precursor composition, and a drying step of removing the hydrophobic solvent contained in the precursor particles under a reduced pressure environment and an inert gas flow.

5. A method for producing hollow particles comprising a resin-containing shell and a hollow portion surrounded by the shell, A mixture preparation step involves preparing a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, and an aqueous medium. A suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the aforementioned mixture. A polymerization step to prepare a precursor composition comprising precursor particles having a hollow portion surrounded by a resin-containing shell, wherein the hollow portion is filled with the hydrophobic solvent, by subjecting the suspension to a polymerization reaction. A transfer step of transferring the precursor composition using a transfer means equipped with a mechanism for applying centrifugal force under reduced pressure, A solvent removal step to remove the hydrophobic solvent contained within the precursor particles, A method for producing hollow particles having the properties of

6. The method for producing hollow particles according to claim 5, wherein the solvent removal step includes a solid-liquid separation step of obtaining the precursor particles separated from the aqueous medium by solid-liquid separation of the precursor composition, and a drying step of removing the hydrophobic solvent contained in the precursor particles under a reduced pressure environment and an inert gas flow.

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