Hollow particle and polymer composition

Abstract

Provided is a hollow particle having excellent miscibility with a polymer and with which it is possible to provide a polymer composition with improved flame retardancy. The hollow particle comprises a shell containing a resin and a hollow section surrounded by the shell, wherein: the resin comprises a shell polymer containing a phosphorus atom-containing monomer unit; and the amount of immersion heat that the hollow particle generates in octane at 30°C is 1-100 J / g, and the amount of immersion heat that the hollow particle generates in formamide at 30°C is 0.1-100 J / g.

Description

Hollow particles and polymer compositions

[0001] The present invention relates to hollow particles and polymer compositions.

[0002] Hollow particles, such as those produced by polymerizing polymerizable monomers, are particles having a cavity inside them, and are used as additives to be added to molding resins for various purposes such as weight reduction.

[0003] As a technique relating to such hollow particles, for example, Patent Document 1 discloses hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the resin is made of a shell polymer containing a crosslinkable monomer unit, and the true density of the hollow particles is 1.18 g / cm ３ or less, and the value of C calculated from a predetermined formula (1) is 1.16 or less.

[0004] International Publication No. 2023 / 127812

[0005] An object of the present invention is to provide hollow particles that have excellent miscibility with polymers and can provide polymer compositions with improved flame retardancy.

[0006] The present inventors have investigated the use of hollow particles having a resin-containing shell and a hollow portion surrounded by the shell as a flame retardant, and have found that by incorporating a phosphorus atom-containing monomer unit into the shell polymer and by controlling the heat amount of immersion of the hollow particles in octane and formamide within a specific range, the hollow particles have excellent miscibility with polymers, thereby providing a polymer composition with improved flame retardancy, which has led to the completion of the present invention.

[0007] That is, the present invention provides the following hollow particles. [1] Hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the resin is a shell polymer containing a phosphorus atom-containing monomer unit, and the heat of immersion in octane at 30°C is 1 J / g or more and 100 J / g or less, and the heat of immersion in formamide at 30°C is 0.1 J / g or more and 100 J / g or less. [2] Hollow particles according to [1], having a volume-average particle diameter of 0.1 to 50 μm. [3] Hollow particles according to [1] or [2], having an average porosity of 50 to 90%. [4] Hollow particles according to any one of [1] to [3], wherein the proportion of particles having only one hollow portion is 90% or more by number. [5] Hollow particles according to any one of [1] to [4], wherein the shell polymer contains a phosphate ester monomer unit. [6] The hollow particle according to any one of [1] to [5], wherein the shell polymer contains a crosslinkable monomer unit. [7] The hollow particle according to any one of [1] to [6], wherein the shell polymer contains a crosslinkable hydrocarbon monomer unit and / or a heteroatom-containing crosslinkable monomer unit. [8] The hollow particle according to any one of [1] to [7], wherein the shell polymer contains at least one monomer unit selected from the group consisting of a 1,3-butanediol dimethacrylate unit, a glycerol dimethacrylate unit, and a glycerol trimethacrylate unit. [9] The hollow particle according to any one of [1] to [8], wherein the shell polymer contains 0.2 to 60 mass% of the phosphorus atom-containing monomer unit.

[0008] That is, according to the present invention, the following polymer compositions are provided.

[10] A polymer composition containing the hollow particles according to any one of [1] to [8] and a polymer.

[11] The polymer composition according to

[10] , wherein the polymer is at least one rubber selected from the group consisting of silicone rubber and acrylonitrile-butadiene copolymer rubber.

[12] The polymer composition according to

[10] , wherein the polymer is at least one resin selected from the group consisting of urethane elastomers, amide elastomers, and olefin elastomers.

[13] The polymer composition according to any one of

[10] to

[12] , further containing a flame retardant.

[0009] It is possible to provide hollow particles that have excellent miscibility with polymers and can give polymer compositions with improved flame retardancy.

[0010] <Hollow Particles> The hollow particles of the present invention are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the resin is a shell polymer containing a phosphorus atom-containing monomer unit, the heat of immersion in octane at 30°C is 1 J / g or more and 100 J / g or less, and the heat of immersion in formamide at 30°C is 0.1 J / g or more and 100 J / g or less.

[0011] The hollow particles of the present invention have excellent miscibility with polymers. Specifically, because the hollow particles of the present invention have excellent affinity with polymers, polymer compositions with excellent hollow particle dispersibility can be produced with high productivity. Furthermore, the hollow particles of the present invention have excellent flame retardancy, making it possible to provide polymer compositions with improved flame retardancy.

[0012] The shell of the hollow particle of the present invention contains a resin made of a shell polymer containing a phosphorus atom-containing monomer unit. If the shell polymer does not contain a phosphorus atom-containing monomer unit, the effect of improving flame retardancy will be insufficient.

[0013] Examples of the phosphorus atom-containing monomer that forms the phosphorus atom-containing monomer unit include phosphate ester monomers. The phosphate ester monomer is a monomer having a phosphate ester structure and a radical reactive group. The phosphorus atom-containing monomers can be used alone or in combination of two or more.

[0014] The phosphate ester structure may be a phosphate monoester structure, a phosphate diester structure, or a phosphate triester structure. The number of phosphate ester structures in the phosphorus atom-containing monomer is not particularly limited as long as it is one or more, but from the viewpoint of further enhancing the effects of the present invention, it is preferably one or two, and more preferably one.

[0015] The radical reactive group preferably includes a group having a carbon-carbon unsaturated double bond, and specific examples thereof include a vinyl group, an acryl group, a methacryl group, an acrylamide group, and an allyl group.

[0016] The phosphate ester monomer is preferably a compound (1) represented by the following general formula (1).

[0017]

[0018] In general formula (1), R １ represents a methyl group or a hydrogen atom, R ２ represents a phenyl group or a hydrogen atom; L represents a divalent organic group; and n represents an integer of 1 to 3.

[0019] R １ is a methyl group or a hydrogen atom. When n is 2 or 3, multiple R １ may be the same as or different from each other. From the viewpoint of further enhancing the effects of the present invention, R １ is preferably a methyl group.

[0020] R ２ is a phenyl group or a hydrogen atom. When n is 1, multiple R ２ may be the same as or different from each other. When n is 1, R ２is preferably a phenyl group. When n is 2 or 3, R ２ is preferably a hydrogen atom.

[0021] Although n is not particularly limited as long as it is 1 to 3, it is preferably 1 or 2. When n is 1, compound (1) represented by general formula (1) corresponds to a non-crosslinkable monomer, and when n is 2 or 3, compound (1) represented by general formula (1) corresponds to a crosslinkable monomer.

[0022] L is not particularly limited as long as it is a divalent organic group. In general formula (1), the group represented by -LO- is preferably a group represented by the following general formula (2).

[0023]

[0024] In general formula (2), R ３ and R ４ each represents a linear or branched alkylene group having 1 to 30 carbon atoms, a represents 0 or 1, b represents an integer of 0 to 300, c represents 0 or 1, and d represents an integer of 1 to 300. n represents an integer of 1 to 3.

[0025] R ３ and R ４ R each represents a linear alkylene group having 1 to 30 carbon atoms or a branched alkylene group having 1 to 30 carbon atoms. ３ and R ４ From the viewpoint of further enhancing the effects of the present invention, the number of carbon atoms in each of the groups is preferably 1 to 10, more preferably 1 to 8, even more preferably 1 to 6, particularly preferably 1 to 4, particularly preferably 1 to 3, and most preferably 2 (ethylene group).

[0026] Although a is not particularly limited as long as it is 0 or 1, it is preferably 1 from the viewpoint of further enhancing the effects of the present invention.

[0027] From the viewpoint of further enhancing the effects of the present invention, b is preferably 0 to 100, more preferably 0 to 50, even more preferably 0 to 10, particularly preferably 0 to 5, and most preferably 0 or 1.

[0028] Although c is not particularly limited as long as it is 0 or 1, from the viewpoint of further enhancing the effects of the present invention, it is preferably 0. In one embodiment, it is preferable that b and c are 0.

[0029] From the viewpoint of further enhancing the effects of the present invention, d is preferably 1 to 100, more preferably 1 to 50, even more preferably 1 to 10, particularly preferably 1 to 5, and most preferably 1 or 2.

[0030] Other phosphorus atom-containing monomers include tris(vinylphenyl)phosphate compounds such as tris(2-vinylphenyl)phosphate, tris(4-vinylphenyl)phosphate, and tris(2,6-dimethyl-4-vinylphenyl)phosphate; phosphate ester group-containing monomers such as (meth)acryloyloxyalkyl (C2-4) phosphate esters [(meth)acryloyloxyethyl phosphate and (meth)acryloyloxyisopropyl phosphate] and alkenyl phosphate esters [vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, and dodecenyl phosphate]; (meth)acryloyloxyalkyl (C2-4) phosphonic acids [(meth)acryloyloxyethyl phosphonic acid, and the like] and alkenyl (C2-12) phosphonic acids [vinyl phosphonic acid, allyl phosphonic acid, and octenyl phosphonic acid, and the like]. Phosphono group-containing monomers include (methacryloyloxymethyl)diethylphosphonate, (methacryloyloxymethyl)diphenylphosphonate, diethyl-p-vinylbenzylphosphonate, diphenyl-p-vinylbenzylphosphonate, dimethylvinylphosphonate, diethylvinylphosphonate, diphenylvinylphosphonate, diphenylvinylphosphine oxide, 9,10-dihydro-9-oxa-vinyl-10-phosphaphenanthrene-10-oxide, ethoxyphenylvinylphosphonate, (2,5-diallyloxyphenyl)diphenylphosphine oxide, 10-(2,5-dimethacryloyloxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, (2,5-dimethacryloyloxyphenyl)diphenylphosphine oxide, and [2,5-bis(4-ethenylphenylmethoxy)phenyl]diphenylphosphine oxide. The term "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

[0031] Compound (1) may be a commercially available product, such as "KAYAMER PM-21" (manufactured by Nippon Kayaku Co., Ltd.), ADEKA REASOAP PP-70 (manufactured by ADEKA Corporation), or "MR-260" (manufactured by Daihachi Chemical Industry Co., Ltd.).

[0032] The shell polymer preferably contains a crosslinkable monomer unit. The crosslinkable monomer forming the crosslinkable monomer unit is a monomer having two or more polymerizable functional groups and forming a crosslinked bond in the resin by a polymerization reaction. As the crosslinkable monomer, a compound having two or more ethylenically unsaturated bonds as polymerizable functional groups is generally used.

[0033] The crosslinkable monomers that form the crosslinkable monomer units include crosslinkable hydrocarbon monomers and heteroatom-containing crosslinkable monomers.

[0034] The crosslinkable hydrocarbon monomer is not particularly limited, but examples thereof include divinylbenzene, 2-phenyl-1,3-butadiene, divinyldiphenyl, divinylnaphthalene, etc., and among these, divinylbenzene and 2-phenyl-1,3-butadiene are preferred. In one embodiment, it is preferred to use at least 2-phenyl-1,3-butadiene as the crosslinkable hydrocarbon monomer.

[0035] Examples of the heteroatom-containing crosslinkable monomer include phosphorus atom-containing crosslinkable monomers (monomers having two or more polymerizable functional groups among the above-mentioned phosphorus atom-containing monomers, specifically, compounds (1) represented by general formula (1) in which n is 2 or 3), and phosphorus atom-free heteroatom-containing crosslinkable monomers (crosslinkable monomers containing a heteroatom other than a phosphorus atom).

[0036] As the phosphorus atom-containing crosslinkable monomer, a phosphorus atom-containing heteroatom-containing crosslinkable monomer (a crosslinkable monomer containing a phosphorus atom and a heteroatom other than a phosphorus atom) is preferred, and a crosslinkable phosphate ester monomer (a monomer having two or more polymerizable functional groups among the above-mentioned phosphate ester monomers) is more preferred. The phosphorus atom-containing crosslinkable monomer preferably has two polymerizable functional groups. In the present invention, "phosphorus atom-containing heteroatom-containing" means containing both a phosphorus atom and a heteroatom other than a phosphorus atom, and "phosphorus atom-free heteroatom-containing" means containing no phosphorus atom but containing heteroatoms other than a phosphorus atom. On the other hand, when extremely high flame retardancy is required, it is also preferable to use a tris(vinylphenyl)phosphate compound as the phosphorus atom-containing crosslinkable monomer.

[0037] Examples of the phosphorus atom-free heteroatom-containing crosslinkable monomer include diallyl phthalate and allyl (meth)acrylate (meaning allyl acrylate and / or allyl methacrylate; the same applies hereinafter). ], difunctional phosphorus atom-free heteroatom-containing crosslinkable monomers such as 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate; and trifunctional or higher phosphorus atom-free heteroatom-containing crosslinkable monomers such as glycerol tri(meth)acrylate, 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, at least one selected from the group consisting of 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, glycerol tri(meth)acrylate, and trimethylolpropane tri(meth)acrylate is preferred.

[0038] From the viewpoint of further enhancing the effects of the present invention, it is preferable to use, as the phosphorus atom-free heteroatom-containing crosslinkable monomer, at least one selected from the group consisting of 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate, and it is more preferable to use at least one selected from the group consisting of 1,3-butanediol dimethacrylate, glycerol dimethacrylate, and glycerol trimethacrylate.

[0039] The crosslinkable monomers can be used alone or in combination of two or more. For example, a crosslinkable hydrocarbon monomer and a heteroatom-containing crosslinkable monomer can be used in combination. 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 functional heteroatom-containing crosslinkable monomer.

[0040] The shell polymer may consist essentially of crosslinkable monomer units, or may contain non-crosslinkable monomer units in addition to crosslinkable monomer units.

[0041] The non-crosslinkable monomer that forms the non-crosslinkable monomer unit is a monomer having only one polymerizable functional group, and a compound having an ethylenically unsaturated bond as the polymerizable functional group is generally used.

[0042] Examples of the non-crosslinkable monomer that forms the non-crosslinkable monomer unit include a non-crosslinkable hydrocarbon monomer and a heteroatom-containing non-crosslinkable monomer. The non-crosslinkable monomers can be used alone or in combination of two or more.

[0043] The non-crosslinkable hydrocarbon monomer is not particularly limited, but examples thereof include aromatic vinyl monomers such as styrene, ethylvinylbenzene, vinyltoluene, α-methylstyrene, p-methylstyrene, 3,4-dimethoxystyrene, and halogenated styrene; monoolefin monomers such as ethylene, propylene, butylene, and 4-methyl-1-pentene; and diene monomers such as butadiene and isoprene. Of these, styrene and ethylvinylbenzene are preferred.

[0044] Examples of the heteroatom-containing non-crosslinkable monomer include phosphorus atom-containing non-crosslinkable monomers (monomers having only one polymerizable functional group among the above-mentioned phosphorus atom-containing monomers) and phosphorus atom-free heteroatom-containing non-crosslinkable monomers (heteroatom-containing non-crosslinkable monomers other than phosphorus atom-containing non-crosslinkable monomers).

[0045] Examples of the phosphorus atom-containing non-crosslinkable monomer include non-crosslinkable phosphate ester monomers (monomers having only one polymerizable functional group among the above-mentioned phosphate ester monomers). Examples of the phosphorus atom-free heteroatom-containing non-crosslinkable monomer include hydrophilic non-crosslinkable monomers; acrylic monovinyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine monomers; and the like.

[0046] The hydrophilic non-crosslinkable monomer preferably has a solubility in water of 1% by mass or more. The hydrophilic non-crosslinkable monomer is not particularly limited, but examples thereof include non-crosslinkable monomers having a hydrophilic group, such as an acid group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, and a polyoxyethylene group-containing monomer.

[0047] The term "acid group-containing monomer" refers to a monomer containing an acid group. The acid group referred to here includes both a proton-donating group (Brønsted acid group) and an electron pair-accepting group (Lewis acid group). The acid group-containing monomer is not particularly limited as long as it has an acid group, and examples thereof 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 butenetricarboxylic acid; and monoalkyl esters of unsaturated dicarboxylic acids such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate. Examples of sulfonic acid group-containing monomers include styrenesulfonic acid.

[0048] Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0049] Examples of the amide group-containing monomer include acrylamide and dimethylacrylamide.

[0050] Examples of polyoxyethylene group-containing monomers include methoxypolyethylene glycol (meth)acrylate.

[0051] The content of the phosphorus atom-containing monomer unit in the shell polymer is not particularly limited, but is preferably 0.2 to 60% by mass, more preferably 0.5 to 50% by mass, even more preferably 1 to 45% by mass, even more preferably 1.5 to 40% by mass, particularly preferably 3 to 35% by mass, and most preferably 4 to 25% by mass. By setting the content of the phosphorus atom-containing monomer unit within the above range, the flame retardancy of the resulting polymer composition can be further improved while maintaining excellent miscibility with the polymer. On the other hand, when extremely high flame retardancy is required, the content of the phosphorus atom-containing monomer unit in the shell polymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most preferably 28% by mass or more.

[0052] The shell polymer preferably contains, among heteroatom-containing monomer units (heteroatom-containing crosslinkable monomer units or heteroatom-containing non-crosslinkable monomer units), a monomer unit other than a phosphorus-atom-containing monomer unit. The content of the phosphorus-atom-free heteroatom-containing non-crosslinkable monomer (heteroatom-containing monomer unit other than a phosphorus-atom-containing monomer unit) in the shell polymer is not particularly limited, but from the viewpoint of further enhancing the effects of the present invention, it is preferably 10 to 60 mass%, more preferably 15 to 50 mass%, and even more preferably 20 to 40 mass%.

[0053] The shell polymer preferably contains hydrocarbon monomer units (crosslinkable hydrocarbon monomer units or non-crosslinkable hydrocarbon monomer units) in addition to heteroatom-containing monomer units (including phosphorus atom-containing monomer units). The ratio of the hydrocarbon monomer units to the heteroatom-containing monomer units in the shell polymer (hydrocarbon monomer units:heteroatom-containing monomer units) is preferably 10:90 to 95:5, more preferably 25:75 to 90:10, and even more preferably 35:65 to 80:20. By keeping the ratio of the contents within the above ranges, it becomes easy to keep the heat quantity of immersion in octane and formamide within a suitable range, thereby further enhancing the effects of the present invention.

[0054] The content of the crosslinkable monomer unit in the shell polymer is not particularly limited, but is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. The content of the crosslinkable monomer unit in the shell polymer may be substantially 100% by mass. When the content of the crosslinkable monomer is within the above range, a covalent bond network is densely spread throughout the shell, and the occurrence of interconnected pores and shell defects in the shell is suppressed, resulting in hollow particles with excellent mechanical strength.

[0055] The content of the non-crosslinkable monomer unit in the shell polymer is not particularly limited, but is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. The content of the crosslinkable monomer unit in the shell polymer may be substantially 0% by mass.

[0056] The content of the crosslinkable hydrocarbon monomer units in the shell polymer is not particularly limited, but from the viewpoint of further enhancing the effects of the present invention, it is preferably 10 to 95 mass %, more preferably 25 to 90 mass %, and even more preferably 35 to 80 mass %.

[0057] The content of the heteroatom-containing crosslinkable monomer unit in the shell polymer is not particularly limited, but from the viewpoint of further enhancing the effects of the present invention, it is preferably 5 to 90 mass %, more preferably 0 to 80 mass %, even more preferably 15 to 70 mass %, and particularly preferably 20 to 65 mass %.

[0058] From the viewpoint of further enhancing the effects of the present invention, it is preferable to use at least one selected from the group consisting of 1,3-butanediol di(meth)acrylate, glycerol di(meth)acrylate, and glycerol tri(meth)acrylate as the heteroatom-containing crosslinkable monomer other than the phosphorus atom-containing crosslinkable monomer (phosphorus atom-free heteroatom-containing monomer). The total content of 1,3-butanediol di(meth)acrylate units, glycerol di(meth)acrylate units, and glycerol tri(meth)acrylate units in the shell polymer is preferably 3 to 60% by mass, more preferably 5 to 50% by mass, and even more preferably 10 to 40% by mass.

[0059] The hollow particles of the present invention are particles having a shell (outer shell) containing the above-mentioned resin and a hollow portion surrounded by the shell. In the present invention, the hollow portion is a hollow space clearly distinguishable from the shell of the hollow particle formed by the resin. The hollow particles of the present invention may have one or more hollow portions, but preferably have only one hollow portion in order to maintain a good balance between high porosity and mechanical strength. Among the hollow particles of the present invention, the proportion of particles having only one hollow portion is preferably 90% by number or more, more preferably 95% by number or more. The proportion of particles having only one hollow portion is measured by the method described in the Examples.

[0060] The hollow particles of the present invention usually have a shell that is free from interconnected pores and shell defects, and the hollow portion is isolated from the outside of the particle by the shell, but the shell may have one or more interconnected pores, and the hollow portion may communicate with the outside of the particle via the interconnected pores. Furthermore, the shell of the hollow particle, and when the hollow particle has two or more hollow portions, the partition walls separating adjacent hollow portions may be porous, provided that the hollow portions are of a size that can be clearly distinguished from the numerous minute spaces uniformly dispersed within the porous structure.

[0061] The hollow portion of the hollow particle of the present invention may be filled with a gas such as air, or may contain a solvent.

[0062] The shape of the hollow particles of the present invention is not particularly limited as long as a hollow portion is formed inside. The outer shape of the hollow particles is not particularly limited, but a spherical shape is preferred from the viewpoint of ease of production.

[0063] The external shape of the hollow particles can be confirmed, for example, by observing the particles with an SEM or TEM, and the internal shape of the hollow particles can be confirmed, for example, by observing the cross section of the particles with an SEM or by observing the particles with a TEM.

[0064] The calorific value of immersion of the hollow particles of the present invention in octane at 30°C is 1 J / g or more and 100 J / g or less, and the calorific value of immersion in formamide at 30°C is 0.1 J / g or more and 100 J / g or less. If at least one of the calorific values ​​of immersion in octane and formamide is outside the above range, the hollow particles will have poor miscibility with the polymer. Specifically, when attempting to mix the hollow particles with a polymer, the hollow particles are prone to agglomeration, making it difficult to disperse the hollow particles in the polymer.

[0065] The calorific value of immersion of hollow particles in octane and formamide can be adjusted, for example, by adjusting the monomer composition of the shell polymer. Specifically, the calorific value of immersion of hollow particles in octane and formamide is measured by the method described in the Examples.

[0066] The heat of immersion of the hollow particles of the present invention in octane at 30°C is not particularly limited as long as it is 1 J / g or more and 100 J / g or less, but is preferably 1 J / g or more and 75 J / g or less, and more preferably 1 J / g or more and 50 J / g or less. By setting the heat of immersion in octane within the above range, miscibility with polymers can be further improved. The heat of immersion in octane tends to increase as the total proportion of carbon atoms and hydrogen atoms among the elements constituting the shell polymer increases.

[0067] The calorific value of immersion of the hollow particles of the present invention in formamide at 30°C is not particularly limited as long as it is 0.1 J / g or more and 100 J / g or less, but is preferably 1 J / g or more and 100 J / g or less, more preferably 5 J / g or more and 95 J / g or less, and even more preferably 10 J / g or more and 90 J / g or less. By setting the calorific value of immersion in formamide within the above range, miscibility with polymers can be further improved. The calorific value of immersion in formamide tends to increase as the proportion of acrylic groups present in the shell polymer increases.

[0068] The apparent density of the hollow particles is 0.15 to 0.8 g / cm ３ is preferably 0.20 to 0.7 g / cm ３ More preferably, it is 0.25 to 0.6 g / cm ３ In this specification, the apparent density of a hollow particle means the density of the entire hollow particle when the hollow portion is considered to be a part of the hollow particle, and the true density of a hollow particle means the density of only the shell portion of the hollow particle.

[0069] The hollow particles of the present invention preferably have an average porosity of 50 to 90%, more preferably 55 to 85%, even more preferably 60 to 82%, and particularly preferably 65 to 80%. By adjusting the average porosity within the above range, the effects of adding the hollow particles (for example, weight reduction effect) can be enhanced.

[0070] The average porosity (%) of the hollow particles is calculated by the apparent density D １ and true density D ０ The average porosity of hollow particles (%) is calculated from the apparent density D of hollow particles. １ ]÷[True density D of hollow particles ０ ]×100

[0071] The volume average particle size (Dv) of the hollow particles of the present invention is not particularly limited, but is preferably 0.1 to 50 μm, more preferably 0.1 to 40 μm, and even more preferably 0.1 to 30 μm.

[0072] The particle size distribution (Dv / Dn) (volume average particle size (Dv) / number average particle size (Dn)) of the hollow particles of the present invention is not particularly limited, but is preferably 1.02 to 2.00, more preferably 1.04 to 1.60, even more preferably 1.06 to 1.40, and particularly preferably 1.08 to 1.30. By setting the particle size distribution (Dv / Dn) of the hollow particles within the above range, deformation of the hollow particles in the polymer composition can be suppressed, and the effects of adding the hollow particles (for example, flame retardancy and weight reduction) can be further enhanced.

[0073] The volume average particle diameter (Dv) and number average particle diameter (Dn) of the hollow particles can be determined, for example, by a laser diffraction particle size distribution analyzer. The particle diameter distribution (Dv / Dn) is the value obtained by dividing the volume average particle diameter (Dv) by the number average particle diameter (Dn).

[0074] The volume average particle size (Dv) and particle size distribution (Dv / Dn) of the hollow particles can be adjusted, for example, by adjusting the monomer composition of the shell polymer, the type and amount of a dispersion stabilizer used in producing the hollow particles by suspension polymerization, and the suspension conditions.

[0075] <Method for Producing Hollow Particles> The hollow particles of the present invention can be preferably produced by a production method including the following steps: (A) a mixed solution preparation step, (B) a suspension step, (C) a polymerization step, (D) a solvent removal step by an in-liquid solvent removal method, and (E) a recovery step.

[0076] That is, the hollow particles of the present invention can be preferably produced by a production method including: (A) a mixed solution preparation step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic organic solvent, a polymerization initiator, and an aqueous medium; (B) a suspending step of suspending the mixed solution obtained in the mixed solution preparation step to prepare a suspension 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; (C) a polymerization step of subjecting the suspension obtained in the suspending step to a polymerization reaction to prepare a precursor composition containing precursor particles having hollow portions and encapsulating a hydrophobic organic solvent in the hollow portions; (D) a solvent removal step of removing the hydrophobic organic solvent encapsulated in the precursor particles from the precursor composition obtained in the polymerization step by an in-liquid solvent removal method to obtain a hollow particle slurry containing hollow particles and an aqueous medium; and (E) a recovery step of recovering hollow particles from the hollow particle slurry obtained in the solvent removal step.

[0077] (A) Mixed Liquid Preparation Step The mixed liquid preparation step is a step of preparing a mixed liquid containing a polymerizable monomer, a hydrophobic organic solvent, a polymerization initiator, and an aqueous medium. The hollow particles of the present invention are preferably produced by a production method including such a step.

[0078] [Polymerizable Monomer] The polymerizable monomers used are those described above. The composition of the polymerizable monomers may be any composition that allows the monomer composition of the intended shell polymer to be obtained.

[0079] The content of the polymerizable monomer in the mixed liquid prepared in the mixed liquid preparation step is not particularly limited, but from the viewpoint of the balance between particle size and mechanical strength, it is preferably 15 to 55 mass %, and more preferably 25 to 50 mass %, relative to 100 mass % of the total mass of the components in the mixed liquid excluding the aqueous medium.

[0080] [Hydrophobic Organic Solvent] A non-polymerizable, poorly water-soluble organic solvent is used as the hydrophobic organic solvent, which acts as a spacer material that forms hollow spaces inside the particles.

[0081] The hydrophobic organic solvent is not particularly limited, but a hydrocarbon solvent can be suitably used, and specific examples thereof include saturated hydrocarbon solvents such as butane, pentane, normal 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.

[0082] As the hydrophobic organic solvent, the proportion of saturated hydrocarbon solvents in a total amount of 100% by mass of the hydrophobic organic solvents is preferably 50% by mass or more. This allows sufficient phase separation to occur within the droplets of the polymerizable monomer composition prepared in the suspension step described below, making it easier to obtain hollow particles having only one hollow portion and suppressing the generation of porous particles. From the viewpoint of further suppressing the generation of porous particles and from the viewpoint of making the hollow portions of each hollow particle more uniform, the proportion of saturated hydrocarbon solvents in a total amount of 100% by mass of the hydrophobic organic solvents is preferably 60% by mass or more, more preferably 80% by mass or more.

[0083] Furthermore, as the hydrophobic organic solvent, a hydrocarbon solvent having 5 to 8 carbon atoms is preferred. A hydrocarbon solvent having 5 to 8 carbon atoms is easily encapsulated in the precursor particles during the polymerization step described below, and can be easily removed from the precursor particles during the solvent removal step described below. Among these, a hydrocarbon solvent having 6 to 8 carbon atoms is particularly preferred.

[0084] Furthermore, from the viewpoint of ease of removal in the solvent removal step described below, the hydrophobic organic solvent preferably has a boiling point of 130°C or less, more preferably 115°C or less, while from the viewpoint of ease of inclusion in the precursor particles, the hydrophobic organic solvent preferably has a boiling point of 30°C or more, more preferably 50°C or more.

[0085] In the present invention, when the hydrophobic organic solvent is a mixed solvent containing multiple types of hydrophobic organic solvents and has multiple boiling points, the boiling point of the hydrophobic organic solvent is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points.

[0086] Furthermore, the hydrophobic organic solvent preferably has a relative dielectric constant of 3 or less at 20°C. The relative dielectric constant is one of the indicators showing the degree of polarity of a compound. When the relative dielectric constant of the hydrophobic organic solvent is sufficiently small, 3 or less, it is considered that phase separation proceeds quickly in the droplets of the polymerizable monomer composition prepared in the suspension step described below, and hollow portions are likely to be formed.

[0087] Examples of hydrophobic organic solvents having a dielectric constant 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 dielectric constant values). For the dielectric constant at 20°C, values ​​described in known literature (for example, "Chemical Handbook: Basics," edited by the Chemical Society of Japan, Revised 4th Edition, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information can be referenced. Examples of methods for measuring the dielectric constant at 20°C include a dielectric constant test conducted in accordance with JIS C 2101:1999-23 at a measurement temperature of 20°C.

[0088] The porosity of the hollow particles can be adjusted by changing the amount of hydrophobic organic solvent in the mixed solution. In the polymerization step, the polymerization reaction proceeds with the hydrophobic organic solvent encapsulated in the droplets of the polymerizable monomer composition. Therefore, the greater the content of the hydrophobic organic solvent, the higher the porosity of the resulting hollow particles tends to be. The content of the hydrophobic organic solvent in the mixed solution is preferably 50 to 500 parts by mass, more preferably 60 to 400 parts by mass, even more preferably 80 to 350 parts by mass, and particularly preferably 100 to 300 parts by mass, per 100 parts by mass of the total mass of the polymerizable monomers. By setting the content of the hydrophobic organic solvent within the above range, the porosity of the hollow particles can be appropriately increased while maintaining their strength.

[0089] [Polymerization initiator] It is preferable to use an oil-soluble polymerization initiator as the polymerization initiator. By using an oil-soluble polymerization initiator as the polymerization initiator, the polymerization initiator can be suitably incorporated into the interior of droplets of the polymerizable monomer composition in the suspension obtained in the suspension step described below.

[0090] 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, and examples of the oil-soluble polymerization initiator 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.

[0091] The content of the polymerization initiator is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 12 parts by mass, relative to 100 parts by mass of the total mass of the polymerizable monomers in the mixed solution. By setting the content of the polymerization initiator within the above range, the polymerization reaction can be sufficiently progressed, and there is little risk of the polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0092] [Aqueous Medium] The aqueous medium may be a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent.

[0093] The hydrophilic solvent is not particularly limited as long as it is sufficiently miscible with water and does not cause phase separation, and examples thereof include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO); and the like.

[0094] Among aqueous media, water is preferred due to its high polarity. When a mixture of water and a hydrophilic solvent is used, it is preferable that the polarity of the entire mixture is not too low, from the viewpoint of properly forming droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator. When a mixture of water and a hydrophilic solvent is used, it is preferable that the mixing ratio (mass ratio) of water to hydrophilic solvent is 99:1 to 50:50.

[0095] In addition, in the mixed solution preparation step, it is preferable to use a dispersion stabilizer in addition to the polymerizable monomer, the hydrophobic organic solvent, the polymerization initiator, and the aqueous medium. That is, the mixed solution preparation step is preferably a step of preparing a mixed solution containing the polymerizable monomer, the hydrophobic organic solvent, the polymerization initiator, the aqueous medium, and the dispersion stabilizer.

[0096] The dispersion stabilizer is a compound that disperses droplets of the polymerizable monomer composition in an aqueous medium in the suspension step described below, and may be either an inorganic dispersion stabilizer or an organic dispersion stabilizer.

[0097] Examples of inorganic dispersion stabilizers include colloidal silica, magnesium hydroxide, calcium phosphate, magnesium phosphate, calcium carbonate, barium sulfate, calcium oxalate, magnesium carbonate, barium carbonate, tricalcium phosphate, aluminum hydroxide, aluminum phosphate, magnesium hydroxide, ferric hydroxide, hydroxyapatite, calcium pyrophosphate, magnesium pyrophosphate, aluminum pyrophosphate, zinc pyrophosphate, zinc phosphate, calcium sulfate, barium sulfate, diatomaceous earth, clay, and bentonite.

[0098] Examples of organic dispersion stabilizers include methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and starch.

[0099] Among these, inorganic dispersion stabilizers are preferred from the viewpoint of having a high dispersion stabilizing effect and making it easier to control the particle size of droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator. Among inorganic dispersion stabilizers, metal-containing dispersion stabilizers are preferred, and poorly water-soluble inorganic metal salts are more preferred. Furthermore, poorly water-soluble inorganic metal salts are preferred, and inorganic metal salts having a solubility of 0.5 g or less in 100 g of water are preferred, such as magnesium hydroxide, calcium hydroxide, barium hydroxide, calcium phosphate, magnesium pyrophosphate, etc. The dispersion stabilizers can be used alone or in combination of two or more.

[0100] In addition, from the viewpoint of further enhancing the dispersion stabilizing 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 mixed liquid preparation step, it is preferable to obtain the mixed liquid by mixing the dispersion stabilizer in the form of a dispersion or solution with the polymerizable monomer, the hydrophobic organic solvent, and the polymerization initiator. Note that the above-mentioned aqueous medium can be used.

[0101] In the dispersion or solution of the dispersion stabilizer, the mixing ratio of the dispersion stabilizer to the aqueous medium, in terms of the mass ratio of "dispersion stabilizer: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. 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.

[0102] In the mixed solution preparation step, the above-mentioned components are mixed by stirring or the like to obtain a mixed solution. In this case, in addition to the above-mentioned components, other materials may be mixed as needed. In the mixed solution preparation step, a mixed solution is prepared in which an oil phase containing a polymerizable monomer, a hydrophobic organic solvent, and a lipophilic material such as a polymerization initiator is dispersed in an aqueous medium and an aqueous phase containing a dispersion stabilizer used as needed, with particles having a particle size of about several μm. The dispersion state of these components in the mixed solution can be observed with the naked eye, depending on the type of each component.

[0103] In addition, in the mixed solution preparation step, from the viewpoint that the composition of the shell portion is likely to be uniform, it is preferable to prepare the mixed solution in advance by preparing an oil phase containing a polymerizable monomer, a hydrophobic organic solvent, and a polymerization initiator, and mixing this with a dispersion or solution obtained by dispersing or dissolving a dispersion stabilizer in an aqueous medium.

[0104] (B) Suspension Step The suspension step is a step of preparing a suspension 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 mixed liquid obtained in the mixed liquid preparation step described above.

[0105] The suspension method for forming droplets of the polymerizable monomer composition is not particularly limited, but a method in which the mixed solution obtained in the mixed solution preparation step described above is stirred using a stirrer capable of strong stirring is preferred. The stirrer used in the suspension step is not particularly limited, but for example, a stirrer equipped with a stirring blade or a rotor and a supply tank for supplying the mixture to the stirrer can be used. The stirrer is not particularly limited as long as it is equipped with a stirring blade or a rotor. However, from the viewpoint of efficiently forming a suspension, a stirrer having a combination of a rotor and a stator that are comb-tooth concentric rings is preferred, in which the rotor is rotated at high speed to circulate the dispersion from the inside of the rotor to the outside of the stator, and the dispersion is stirred in the gap between the rotor and the stator.

[0106] An example of an agitator having such a configuration is an in-line emulsifying disperser, and examples of the in-line emulsifying disperser include those with the product name "Cavitron" (manufactured by Eurotech), the product name "Milder" (manufactured by Pacific Machinery Works), the product name "Ebara Milder" (manufactured by Ebara Corporation), the product name "TK Pipeline Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), the product name "Colloid Mill" (manufactured by Kobe Steel Pantech Co., Ltd.), the product name "Slasher" (manufactured by Nippon Coke and Engineering Co., Ltd.), the product name "Trigonal Wet Fine Pulverizer" (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and the product name "Fine Flow Mill" (manufactured by Pacific Machinery Works).

[0107] In the suspending step, a suspension can be obtained in which droplets of the polymerizable monomer composition containing the lipophilic material are uniformly dispersed in an aqueous medium. Such droplets of the 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 suspending step, phase separation occurs in the droplets of the polymerizable monomer composition, which makes it easy for the low-polarity hydrophobic organic solvent to collect inside the droplets. As a result, the resulting droplets contain the hydrophobic organic solvent in their interiors and materials other than the hydrophobic organic solvent distributed around their peripheries.

[0108] (C) Polymerization Step The polymerization step is a step of subjecting the suspension prepared in the suspension step described above to a polymerization reaction to prepare a precursor composition containing precursor particles having hollow portions, encapsulating a hydrophobic organic solvent in the hollow portions, and having a true density lower than that of water.

[0109] In the polymerization process, the polymerizable monomer in the droplets of the polymerizable monomer composition is polymerized while the droplets still contain the hydrophobic organic solvent, thereby forming precursor particles having a shell containing a resin, which is a polymer of the polymerizable monomer, and a hollow portion filled with the hydrophobic organic solvent.

[0110] In the polymerization step, droplets of the polymerizable monomer composition are subjected to the polymerization reaction while encapsulating the hydrophobic organic solvent, which facilitates the polymerization reaction while maintaining the shape, and facilitates the adjustment of the size and porosity of the precursor particles. Furthermore, since the polymerizable monomer and the hydrophobic organic solvent are used in combination, the polarity of the hydrophobic organic solvent is low relative to the shell of the precursor particles, and the hydrophobic organic solvent is not easily compatible with the shell, which leads to sufficient phase separation and the formation of only one hollow portion.

[0111] The polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be used. The polymerization temperature is preferably 40 to 90°C, more preferably 50 to 80°C. The polymerization reaction time is preferably 1 to 48 hours, more preferably 3 to 24 hours.

[0112] The polymerization step yields a precursor composition in which precursor particles encapsulating a hydrophobic solvent are dispersed in an aqueous phase mainly composed of an aqueous medium.

[0113] (D) Solvent Removal Step by Submerged Desolvation Method The solvent removal step by submerged desolvation method is a step of removing the hydrophobic organic solvent contained in the precursor particles from the precursor composition obtained in the polymerization step by the submerged desolvation method to obtain a hollow particle slurry containing hollow particles and an aqueous medium.

[0114] In the solvent removal process using the submerged desolvation method, the hydrophobic organic solvent encapsulated in the precursor particles in the precursor composition is removed by bubbling a gas through the precursor composition. According to this method, the hydrophobic organic solvent encapsulated in the precursor particles is replaced with the gas, producing hollow particles encapsulating the gas. As a result, a hollow particle slurry containing hollow particles and an aqueous phase mainly composed of an aqueous medium is obtained.

[0115] In addition to the submerged desolvation method, a method for removing the hydrophobic organic solvent contained in the precursor particles can also be considered, in which a solid component containing the precursor particles is separated and recovered from the precursor composition as needed, and then the precursor particles are heated and dried to remove the hydrophobic organic solvent contained in the precursor particles. On the other hand, when the submerged desolvation method is used to remove the hydrophobic organic solvent contained in the precursor particles, it is necessary to heat and dry the precursor particles at a high temperature, which requires a lot of energy and also requires equipment capable of high-temperature heating, resulting in high drying and equipment costs. In contrast, the submerged desolvation method does not require high-temperature heating and is therefore advantageous in terms of energy and cost.

[0116] The gas used in the submerged desolvation method is not particularly limited, but an inert gas such as nitrogen or argon is preferred.

[0117] The bubbling conditions are not particularly limited and are appropriately adjusted depending on the type and amount of the hydrophobic organic solvent so as to remove the hydrophobic organic solvent contained in the precursor particles. The bubbling time is preferably 1 to 48 hours, more preferably 3 to 24 hours. The amount of gas bubbling per minute is preferably 0.1 to 10 times, and more preferably 0.5 to 2 times, the volume of the precursor composition to be subjected to submerged desolvation.

[0118] The temperature during bubbling is not particularly limited, but is preferably equal to or higher than the polymerization temperature in the polymerization step. The temperature during bubbling may be, for example, 50°C or higher and 100°C or lower, or 80°C or higher and 95°C or lower.

[0119] The temperature during bubbling may be equal to or higher than the boiling point of the hydrophobic organic solvent minus 35°C. Bubbling the gas at such a temperature can reduce the amount of hydrophobic organic solvent remaining in the hollow particles. Here, when the hydrophobic organic solvent is a mixed solvent containing multiple types of hydrophobic organic solvents and has multiple boiling points, the boiling point of the hydrophobic organic solvent in the solvent removal step is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points. In order to reduce the amount of hydrophobic organic solvent remaining in the hollow particles, the temperature during bubbling is more preferably equal to or higher than the boiling point of the hydrophobic organic solvent minus 30°C, and even more preferably equal to or higher than the boiling point of the hydrophobic organic solvent minus 20°C.

[0120] (E) Recovery Step The recovery step is a step of recovering hollow particles from the hollow particle slurry obtained in the solvent removal step.

[0121] The method for recovering hollow particles from the hollow particle slurry is not particularly limited, and any known method can be used. For example, solid-liquid separation methods such as centrifugation, filtration, and static separation, drying methods, and combinations of these can be appropriately used. By using the solid-liquid separation method or drying method, the aqueous medium is removed from the hollow particle slurry, and the hollow particles separated from the aqueous medium can be recovered.

[0122] By the solid-liquid separation method, the aqueous medium is removed from the hollow particle slurry, and a solid content containing hollow particles can be recovered. The solid-liquid separation method is not particularly limited, and any known method can be used. For example, it is preferable to adopt a centrifugation method or a filtration method as the solid-liquid separation method. The solid-liquid separation conditions are not particularly limited as long as they allow the aqueous medium to be removed from the hollow particle slurry. It is also preferable to further remove the aqueous medium from the solid content containing hollow particles obtained by the solid-liquid separation method by a drying method.

[0123] By the drying method, the aqueous medium is removed from the hollow particle slurry or the solid fraction obtained after the solid-liquid separation step, and the solid fraction containing hollow particles can be recovered. The drying method is not particularly limited as long as it can remove the aqueous medium. Examples of the drying method include reduced pressure drying, heat drying, flash drying, and combinations of these.

[0124] The drying conditions when using a heat drying method are not particularly limited as long as they allow removal of the aqueous medium. According to the above-mentioned production method, relatively mild drying conditions can be adopted as the drying conditions when using a drying method in the recovery step. The drying temperature is not particularly limited, but is preferably 20 to 100°C, more preferably 25 to 80°C, and even more preferably 30 to 60°C. The drying time is not particularly limited, but is preferably 1 to 48 hours, more preferably 3 to 24 hours. The drying atmosphere is also 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.

[0125] (F) Other Steps The above manufacturing method may also include other steps, such as (F-1) a cleaning step, (F-2) a hollow portion re-replacement step, and (F-3) a surface treatment step.

[0126] (F-1) Washing Step The above-described production 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 of adding an acid or alkali to wash the hollow particle slurry containing hollow particles and an aqueous medium before the recovery step in order to remove any dispersion stabilizer remaining in the hollow particle slurry. When the dispersion stabilizer used is an acid-soluble dispersion stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to perform washing. On the other hand, when the dispersion stabilizer used is an alkali-soluble dispersion stabilizer, it is preferable to add an alkali to the precursor composition containing the precursor particles to perform washing.

[0127] 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 less, more preferably 6 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid.

[0128] (F-2) Hollow Portion Re-Substitution Process The hollow portion re-substitution process is a process of substituting the gas or liquid inside the hollow particles with another gas or liquid. This substitution can change the environment inside the hollow particles, selectively confine molecules inside the hollow particles, or modify the chemical structure inside the hollow particles to suit the application.

[0129] (F-3) Surface Treatment Step The hollow particles may be subjected to a surface treatment. That is, the hollow particles of the present invention may be surface-treated. Examples of the surface treatment method include surface oxidation treatment, boron treatment, surface coupling treatment, fluorine coating, and diamond coating.

[0130] The method for producing hollow particles of the present invention is not limited to the above-described method. For example, instead of the above-described solvent removal step (D) and recovery step (E), a step of subjecting the precursor composition obtained by the polymerization step to solid-liquid separation to obtain a solid content containing precursor particles, and then removing the hydrophobic organic solvent encapsulated in the precursor particles in air may be employed.

[0131] The method for performing solid-liquid separation of the precursor composition is not particularly limited, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and static separation. Among these, centrifugation or filtration can be used, and centrifugation may be used from the viewpoint of ease of operation. After solid-liquid separation, an optional step such as a pre-drying step may be further employed. Examples of the pre-drying step include a step of pre-drying the solid content obtained after the solid-liquid separation step using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0132] Furthermore, in the solvent removal step, "in the air" strictly refers to an environment in which no liquid is present outside the precursor particles, or an environment in which only a trace amount of liquid is present outside the precursor particles, so as not to affect the removal of the hydrophobic organic solvent. "In the air" can also be referred to as a state in which the precursor particles are not present in a slurry, or a state in which the precursor particles are present in a dry powder. That is, in the solvent removal step, 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.

[0133] The method for removing the hydrophobic organic solvent from the precursor particles in air is not particularly limited, and known methods can be used, such as vacuum drying, heat drying, and flash drying, which may be used in combination. In particular, when heat drying is used, the heating temperature must be equal to or higher than the boiling point of the hydrophobic organic solvent and equal to or lower than the maximum temperature at which the shell structure of the precursor particles does not collapse. Therefore, depending on the shell composition and the type of hydrophobic organic solvent in the precursor particles, the heating temperature is preferably 50 to 200°C, more preferably 70 to 200°C, and even more preferably 100 to 200°C. The drying operation in air replaces the hydrophobic organic solvent inside the precursor particles with the external gas, resulting in hollow particles whose hollow portions are filled with gas.

[0134] The drying atmosphere is not particularly limited and can be appropriately selected depending on the application of the hollow particles. Examples of the drying atmosphere include air, oxygen, nitrogen, argon, etc. Alternatively, hollow particles with a temporary vacuum inside can be obtained by filling the inside of the hollow particles with a gas and then drying under reduced pressure.

[0135] The hollow particles of the present invention can provide a polymer composition having improved flame retardancy and have a hollow portion, and therefore are suitable for use as a flame retardant or a weight-reducing agent to be blended in a polymer composition.

[0136] <Polymer composition> The hollow particles of the present invention have excellent miscibility with polymers and are therefore suitable for use in polymer compositions. The present invention also relates to a polymer composition containing the hollow particles of the present invention and a polymer. The polymer composition of the present invention typically comprises the hollow particles of the present invention dispersed in a matrix polymer.

[0137] Examples of the polymer include rubber, resin, etc. The polymer may be used alone or in combination of two or more kinds.

[0138] Examples of rubber include silicone rubber, acrylonitrile-butadiene copolymer rubber (NBR), natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), ethylene-propylene-diene terpolymer (EPDM), etc. Among these, silicone rubber and acrylonitrile-butadiene copolymer rubber are preferred from the viewpoint of even better miscibility with the hollow particles of the present invention.

[0139] Examples of resins include polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimide, polyamideimide, polyetherimide, polyetherketoneketone, polyvinyl chloride, polystyrene, poly(meth)acrylate, polycarbonate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, and thermoplastic elastomers. Examples of thermoplastic elastomers include urethane-based elastomers (e.g., ether-based polyurethanes, ester-based polyurethanes), styrene-based elastomers, olefin-based elastomers (e.g., α-olefin copolymers), amide-based elastomers (e.g., polyether block amide copolymers), and ester-based elastomers. Thermoplastic elastomers generally exhibit rubber elasticity at room temperature (25°C) and are plasticized and moldable at high temperatures.

[0140] When rubber is used as the polymer, the rubber is preferably a polar rubber, and more preferably at least one selected from the group consisting of silicone rubber and acrylonitrile-butadiene copolymer rubber, from the viewpoint of having better miscibility with the hollow particles of the present invention.

[0141] When a resin is used as the polymer, the resin is preferably at least one selected from the group consisting of urethane elastomers, amide elastomers, and olefin elastomers, from the viewpoint of achieving even better miscibility with the hollow particles of the present invention.

[0142] The polymer composition of the present invention may contain other ingredients in addition to the polymer and hollow particles, as long as the object of the present invention is not impaired.

[0143] Other compounding materials may include fillers including organic fillers and inorganic fillers, colorants including dyes and pigments, antistatic agents, end-capping agents, ultraviolet absorbers, ultraviolet inhibitors, heat stabilizers, light stabilizers, anti-fogging agents, anti-misting agents, plasticizers, flame retardants, color inhibitors, antioxidants, release agents, moisture-proof agents, oxygen barrier agents, crystal nucleating agents, compatibilizers, crosslinking agents, crosslinking aids, etc. The above compounding materials may be used alone or in combination of two or more.

[0144] The polymer composition of the present invention may further contain a flame retardant. Examples of the flame retardant (excluding the hollow particles of the present invention) include halogen-based flame retardants such as brominated bisphenol compounds and chlorinated paraffins, phosphorus-based flame retardants such as phosphite compounds and phosphate esters, nitrogen-based flame retardants, metal hydroxide-based flame retardants such as magnesium hydroxide and aluminum hydroxide, antimony compounds such as antimony trioxide, and hindered phenol-based flame retardants.

[0145] Examples of commercially available flame retardants include CP-2000 (manufactured by ALBEMARLE), EB-70 (manufactured by Manac Corporation), PEP-36 (manufactured by ADEKA CORPORATION), CDP (manufactured by Daihachi Chemical Industry Co., Ltd.), PX200 (manufactured by Daihachi Chemical Industry Co., Ltd.), HCA (manufactured by Sankosha), MC-6000 (manufactured by Nissan Chemical Industries, Ltd.), FR-20 (manufactured by ICL JAPAN), FCP-AT3 (manufactured by Suzuhiro Chemical Industry Co., Ltd.), and AO-20 (manufactured by ADEKA CORPORATION).

[0146] The content of the flame retardant in the polymer composition of the present invention is not particularly limited, but is preferably 0.3 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 2 to 15 parts by mass, relative to 100 parts by mass of the polymer.

[0147] Examples of the antioxidant include phenol-based antioxidants such as hindered phenol-based compounds; phosphorus-based antioxidants such as phosphite-based compounds; and amine-based antioxidants.

[0148] The content of the antioxidant in the polymer composition of the present invention is not particularly limited, but is preferably 0.3 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 2 to 15 parts by mass, relative to 100 parts by mass of the polymer.

[0149] The content of hollow particles in the polymer composition of the present invention is not particularly limited, but is preferably 1 to 50 parts by mass, more preferably 3 to 40 parts by mass, and even more preferably 5 to 35 parts by mass, relative to 100 parts by mass of the polymer. By setting the content of hollow particles within the above ranges, the polymer composition becomes even more excellent in hollow particle dispersibility and flame retardancy.

[0150] The volume fraction of hollow particles in the polymer composition of the present invention is not particularly limited, but is preferably 1% by volume or more, more preferably 3% by volume or more, more preferably 5% by volume or more, even more preferably 10% by volume or more, even more preferably 20% by volume or more, particularly preferably 30% by volume or more, and most preferably 35% by volume or more. The volume fraction of hollow particles is also not particularly limited, but is preferably 70% by volume or less, more preferably 60% by volume or less, and even more preferably 55% by volume or less. The volume fraction of hollow particles may be 50% by volume or less. By setting the volume fraction of hollow particles within the above range, the polymer composition will have even better hollow particle dispersibility and flame retardancy.

[0151] The hollow particles of the present invention have excellent miscibility with polymers, and therefore can be easily mixed with polymers even when a relatively large amount of hollow particles is used (e.g., 8.5 parts by mass or more per 100 parts by mass of polymer; 20% by volume or more). Furthermore, even when a larger amount of hollow particles is used (e.g., 20 parts by mass or more per 100 parts by mass of polymer; 40% by volume or more), the hollow particles can be easily mixed with polymers. By mixing a relatively large amount of hollow particles with a polymer, the effects of adding hollow particles (e.g., flame retardancy and weight reduction) can be more effectively achieved.

[0152] The weight reduction rate of the polymer composition of the present invention based on the density of the matrix polymer is, for example, 1% or more, preferably 5% or more, and more preferably 10% or more. In addition, by blending a relatively large amount of hollow particles with the polymer, it is possible to increase the weight reduction rate to, for example, 20% or more, particularly preferably 25% or more. The weight reduction rate can be calculated by the formula: (ρ ０ -ρ １ ) / ρ ０ ×100 (in the formula, ρ ０ is the density of the matrix polymer, ρ １ is the density of the polymer composition).

[0153] The polymer composition can be obtained, for example, by mixing the hollow particles of the present invention, a polymer, and further additives added as needed. When a thermoplastic resin is used as the polymer, the hollow particles of the present invention and further additives added as needed may be added to a molten thermoplastic resin, and the mixture may be melt-kneaded.

[0154] The polymer composition of the present invention may be molded into a desired shape by a known molding method to form a polymer molded article.

[0155] The polymer composition of the present invention has improved flame retardancy due to the hollow particles of the present invention, and is also endowed with various effects such as weight reduction, low dielectric constant, heat insulation, sound insulation, etc. Therefore, the polymer composition of the present invention is suitably used in various applications where flame retardancy is required and, in some cases, various effects such as weight reduction are also required.

[0156] For example, applications of the polymer composition of the present invention include components such as low dielectric materials, heat insulating materials, sound insulating materials, light diffusing plates, light diffusing films, antiglare films, electromagnetic wave absorbing sheets, vibration isolating rubber, gaskets, O-rings and other sealing materials and light reflecting materials used in various fields such as automobiles, electricity, electronics, architecture, aviation, and space, food containers, footwear such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, tools, etc. Among these, the polymer composition is preferably used as a material for electronic circuit boards, and specifically, as an insulating resin for electronic circuit boards.

[0157] The polymer composition of the present invention is also suitable for use as a semiconductor material for interlayer insulating materials, dry film resists, solder resists, bonding wires, bonding sheets, magnet wires, semiconductor encapsulants, epoxy encapsulants, mold underfills, underfills, die bond pastes, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device modules, antenna modules, automotive radars, etc. Among these, the polymer composition is particularly suitable as a semiconductor material for interlayer insulating materials, solder resists, bonding sheets, magnet wires, epoxy encapsulants, underfills, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device modules, antenna modules, automotive radars, etc. The bonding sheet is an insulating adhesive layer-forming material used to bond a conductor layer and an organic insulating layer when producing a multilayer printed wiring board.

[0158] 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. Parts and percentages are by mass unless otherwise specified. Various measurements were carried out according to the following methods.

[0159] <Apparent density of hollow particles> Volume 100 cm ３ About 30 cm ３ The volumetric flask was filled with hollow particles, and the mass of the filled hollow particles was accurately weighed. Next, the volumetric flask filled with the hollow particles was accurately filled with isopropanol up to the marked line, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D of the hollow particles was calculated based on the following formula (II): １ (g / cm ３ The apparent density of the hollow particles, D １ (g / cm ３ ) = [Mass of hollow particles] ÷ (100 - [Mass of isopropanol] ÷ [Density of isopropanol at measurement temperature]) (II)

[0160] <Average porosity of hollow particles> (Measurement of true density of hollow particles) After crushing the hollow particles in advance, ３ Approximately 10 g of crushed pieces of hollow particles was filled into a measuring flask, and the mass of the crushed pieces was accurately weighed. Next, in the same manner as in the measurement of the apparent density, isopropanol was added to the measuring flask, and the mass of the isopropanol was accurately weighed. The true density D of the hollow particles was calculated based on the following formula (I): ０ (g / cm ３ The true density of the hollow particles, D ０ (g / cm ３ ) = [mass of crushed hollow particle pieces] ÷ (100 - [mass of isopropanol] ÷ [density of isopropanol at measurement temperature]) (I)

[0161] (Calculation of porosity of hollow particles) The porosity (%) of hollow particles is calculated by multiplying the apparent density D １ and true density D ０ The porosity of hollow particles (%) was calculated from the above formula (III): 100-[apparent density D of hollow particles] １ ]÷[True density D of hollow particles ０ ]×100 (III)

[0162] <Volume Average Particle Size (Dv) and Particle Size Distribution (Dv / Dn) of Hollow Particles> The volume average particle size (Dv) and number average particle size (Dn) of hollow particles were measured using a particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: Multisizer 4e), and the particle size distribution (Dv / Dn) was calculated. The measurement conditions were an aperture diameter of 50 μm, a dispersion medium: Isoton II (product name), concentration 10%, and the number of particles measured: 100,000. Specifically, 0.2 g of hollow particles was placed in a beaker, and a surfactant aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) was added as a dispersant. 2 ml of dispersion medium was further added to wet the hollow particles, and then 10 ml of dispersion medium was added. The mixture was dispersed in an ultrasonic disperser for 1 minute, and then measured using the particle size distribution analyzer.

[0163] <Proportion of Particles Having Only One Hollow Portion> Hollow particles were dispersed in an 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 hollow particle concentration was adjusted so that 30 to 50 cross sections could be observed within an area of ​​56 × 70 μm (magnification of 1500 to 4000 times). Furthermore, particle cross sections in which no hollow portion image was captured and hollow particle cross sections outside of 0.5 to 2 times the volume average particle diameter were excluded from the evaluation. Within the TEM image within the above range, the number of hollow particles and the number of particles having only one hollow portion were counted. Next, a 56 × 70 μm area outside the area observed above, where 30 to 50 hollow particles could be observed, was observed and measured in the same manner as above. Then, the observation and measurement were repeated until the total number of hollow particles reached 100 to 150, and the ratio of the total number of particles having only one hollow portion to the total number of hollow particles was calculated.

[0164] <Heat of Immersion in Octane> Under a nitrogen atmosphere, hollow carbon particles were sampled in a 10 ml glass ampoule. While maintaining a vacuum inside the glass ampoule with a vacuum pump, the opening of the glass ampoule was burned off with a burner and sealed. The glass ampoule was immersed in octane (n-octane) in an immersion calorimeter (manufactured by SETARAM, model number: C80). The temperature of the octane was maintained at 30°C (±0.5°C). The glass ampoule in the immersion calorimeter was broken, and the hollow carbon particles were immersed in octane. The heat generated during this process was measured. The period from the beginning to the end of the peak was arbitrarily selected, and time integration was performed to calculate the heat of immersion in octane (J / g).

[0165] <Calorimetric value of immersion in formamide> The calorimetric value of immersion in formamide was determined in the same manner as in the measurement of the calorimetric value of immersion in octane, except that formamide was used instead of octane.

[0166] <Miscibility with Polymer> Hollow particles and polymer (rubber, resin) were kneaded in the same manner as in the Examples and Comparative Examples. If the hollow particles were dispersed in the polymer matrix and a polymer composition was obtained, the result was evaluated as "good" or "fair." The kneading state was visually confirmed, and if it took a short time for the hollow particles to disperse in the polymer matrix, the result was judged as "good." On the other hand, if the hollow particles did not disperse due to poor compatibility between the polymer and the hollow particles and the polymer could not be molded into a sheet, the result was evaluated as "poor."

[0167] <Shore A hardness of molded article> The Shore A hardness of the molded article was determined 15 seconds after the start of the indentation in accordance with JIS K 6253-3: 2012. The lower the Shore A hardness, the more excellent the flexibility of the molded article can be determined.

[0168] <Density and Weight Reduction Rate of Molded Body> A rectangular parallelepiped test piece was cut out from the molded body. The density ρ of the molded body was calculated from the weight and the lengths of the three sides of the test piece. １ The density ρ of the polymer (rubber, resin) used was also calculated. ０ and the density of the compact ρ １ The weight reduction rate was calculated based on the following formula: Weight reduction rate [%] = (ρ ０ -ρ１ ) / ρ ０ ×100

[0169] <Flame retardancy of molded article> Five test pieces measuring 125 mm x 13 mm x 3.1 mm were cut out from the molded article. Using the obtained test pieces, a vertical combustion test was carried out in accordance with the UL94V combustion test standard. Specifically, each test piece was attached vertically to a clamp and exposed to a 20 mm flame for 10 seconds twice, and the test results were judged based on the combustion behavior in accordance with the above test standard. The evaluation criteria are shown in Table 1. An evaluation result of "V-2" indicates excellent flame retardancy, an evaluation result of "V-1" indicates even better flame retardancy, and an evaluation result of "V-0" indicates the most excellent flame retardancy.

[0170]

[0171] Example A (1) Mixture Preparation Step First, the following materials were mixed to prepare an oil phase. Non-phosphorus atom-containing heteroatom-containing crosslinkable monomer: 1,3-butanediol dimethacrylate 10 parts Non-phosphorus atom-containing heteroatom-containing crosslinkable monomer: glycerol dimethacrylate 20 parts Crosslinkable phosphate ester monomer: bismethacrylic acid (phosphinicobisoxybisethylene) (trade name "KAYAMER PM-21", manufactured by Nippon Kayaku Co., Ltd.) 25 parts Crosslinkable hydrocarbon monomer: 2-phenyl-1,3-butadiene 45 parts Oil-soluble polymerization initiator: 2,2'-azobis(2,4-dimethylvaleronitrile) 3 parts Hydrophobic solvent: hexane 160 parts

[0172] A 2% by weight aqueous dispersion of magnesium pyrophosphate was used as a dispersion stabilizer, and this was mixed with the oil phase to prepare a mixed liquid.

[0173] (2) Suspension step Next, the mixed solution obtained in the mixed solution preparation step was subjected to a treatment of suspending the mixed solution using an in-line emulsifying disperser (rotation speed: 4000 rpm) to prepare a suspension in which monomer droplets encapsulating a hydrophobic solvent were dispersed in water.

[0174] (3) Polymerization step: The suspension obtained in the suspension step was heated from 40° C. to 80° C. in a nitrogen atmosphere, and then stirred for 24 hours at a temperature of 80° C. to carry out a polymerization reaction. This polymerization reaction yielded a precursor composition that was a slurry liquid in which precursor particles encapsulating a hydrophobic solvent were dispersed in water.

[0175] (4) Solvent Removal Step The hydrophobic solvent contained in the precursor particles was removed by the submerged solvent removal method to obtain a hollow particle slurry containing hollow particles and water. Specifically, nitrogen gas was bubbled through the precursor composition obtained in the polymerization step from the bottom of the container for 12 hours at a temperature of 90°C, thereby replacing the hydrophobic solvent contained in the precursor particles with nitrogen gas. In this case, the amount of nitrogen gas bubbling per minute was set to the same volume as the volume of the precursor composition obtained in the polymerization step.

[0176] (5) Washing Step and Solid-Liquid Separation Step The hollow particle slurry obtained in the solvent removal step was washed with hydrochloric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less. Next, water was separated by filtration, and 200 parts of ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and a solid content was obtained by filtration.

[0177] (6) Moisture Removal Step The solid fraction obtained in the solid-liquid separation step was heat-treated in a vacuum dryer at 40°C for 12 hours to remove moisture from the surfaces of the hollow particles, thereby obtaining hollow particles (A). The hollow particles were evaluated according to the above method. The results are shown in Table 2.

[0178] The polymerization conversion rate was nearly 100%, and the monomer composition of the shell polymer in the hollow particles (A) was roughly consistent with the composition of the polymerizable monomers used in the polymerization (the same was true in the examples and comparative examples described below).

[0179] [Examples B to D, Comparative Examples E to F, Example G] Hollow particles B to F were obtained in the same manner as in Example A, except that the type and amount of the monomer used in preparing the oil phase and the rotation speed of the in-line emulsifying disperser in the suspension step were changed as shown in Table 2, and evaluations were performed in the same manner as in Example A. The results are shown in Table 2.

[0180] In Examples B and D, a non-crosslinkable phosphate ester monomer represented by the following formula (trade name "MR-260", manufactured by Daihachi Chemical Industry Co., Ltd.) was used.

[0181]

[0182] In Example G, a crosslinkable phosphate ester monomer (trade name "VP-1" (a monomer mixture mainly composed of a tris(vinylphenyl)phosphate compound, manufactured by Shikoku Chemicals Corporation) from which toluene was distilled under reduced pressure) was used.

[0183]

[0184] [Example 1] As a polymer, Millable silicone rubber (trade name "Silplus 50Hs", manufactured by Momentive Corporation, density: 1.13 g / cm ３ , Mooney viscosity ML(4) 25°C / DIN 53523:31ME) was used. 100 parts of the above polymer and 25 parts of the hollow particles A obtained in Example A were fed to a roller at 50°C and kneaded for about 10 minutes, resulting in a polymer composition in which the hollow particles A were dispersed in the millable silicone rubber matrix. The resulting polymer composition was then molded with a roller to obtain a sheet-like molded product. The molded product was evaluated according to the above method. The results are shown in Table 3.

[0185] [Examples 2 to 9, Comparative Example 1] Polymer compositions and molded articles were obtained and evaluated in the same manner as in Example 1, except that the type of polymer used and the type and amount of hollow particles were changed as shown in Table 1. The results are shown in Table 3.

[0186] In Examples 7 and 8, the polymer used was nitrile rubber (trade name "Nipol DN3380", manufactured by Nippon Zeon Co., Ltd., density: 0.96 g / cm ３ , bound acrylonitrile content: 33%, Mooney viscosity ML (1+4, 100°C): 80.0) was used.

[0187] [Comparative Example 2] In place of 25 parts of hollow particles A, 8.5 parts of hollow particles F were used, and the same procedure as in Example 1 was used to attempt to knead millable silicone rubber and hollow particles. However, the aggregates of hollow particles remained on the outside of the millable silicone rubber, and the hollow particles were not dispersed inside the millable silicone rubber, so a polymer composition could not be obtained. As a result, a molded product could not be obtained.

[0188] Reference Example 1 Millable silicone rubber alone was molded in the same manner as in Example 1. The obtained molded article was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0189]

[0190] As is clear from Tables 2 and 3, hollow particles having a shell containing a resin made of a shell polymer containing a phosphorus atom-containing monomer unit and having a heat value of immersion in octane and a heat value of immersion in formamide at 30°C within a specific range were able to give polymer compositions having excellent miscibility with polymers and improved flame retardancy (Examples A to D, G and Examples 1 to 9).

[0191] On the other hand, when the shell polymer of the hollow particles did not contain a phosphorus atom-containing monomer unit, the resulting polymer compositions were inferior in flame retardancy (Comparative Examples E and 1).

[0192] Furthermore, hollow particles for which the heat values ​​of immersion in octane and formamide were not within the specific ranges were poor in miscibility with the polymer (Comparative Examples F and 2).

[0193] [Examples 10 to 22, Comparative Examples 3 and 4] In the following Examples and Comparative Examples, the following polymers (resins) and flame retardants were used: Polyurethane elastomer 1: Miractran P380POTA (ether-based polyurethane, manufactured by Tosoh Corporation, specific gravity: 1.11) Polyurethane elastomer 2: Miractran P22MBRNAT (ester-based polyurethane, manufactured by Tosoh Corporation, density: 1.21 g / cm ３ Amide elastomer: Pebax 5533 (polyether block amide copolymer, manufactured by Arkema, density: 1.01 g / cm ３Olefin elastomer: Toughmer A35BWJ (α-olefin copolymer, manufactured by Mitsui Chemicals, Inc., density: 0.90 g / cm ３ Flame retardant 1: PX200 (aromatic condensed phosphate ester, manufactured by Daihachi Chemical Industry Co., Ltd.) Flame retardant 2: PEP-36 (phosphite-based flame retardant, antioxidant, manufactured by Adeka Corporation) Flame retardant 3: AO-20 (hindered phenol-based flame retardant, antioxidant, manufactured by Adeka Corporation)

[0194] Example 10: 100 parts of polyurethane elastomer 1, 29 parts of hollow particles A, and 6 parts of flame retardant 1 were fed to a roller at 150°C and kneaded for about 10 minutes, resulting in a polymer composition in which hollow particles A were dispersed in polyurethane elastomer 1 as a matrix. The resulting polymer composition was then molded with a roller to obtain a sheet-like molded product. The molded product was evaluated according to the above-mentioned method. The results are shown in Table 4.

[0195] [Examples 11 to 16, Examples 19 to 22, Comparative Examples 3 and 4, Reference Example 2] Polymer compositions and molded articles were obtained in the same manner as in Example 9, except that the type and amount of polymer, the type and amount of hollow particles, and the type and amount of flame retardant used were changed as shown in Table 4, and evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0196] [Example 17] 100 parts of amide elastomer, 31 parts of hollow particles A, and 6 parts of flame retardant 1 were fed to a roller at 210°C and kneaded for about 10 minutes, resulting in a polymer composition in which the hollow particles A were dispersed in the amide elastomer matrix. The resulting polymer composition was then molded with a roller to obtain a sheet-like molded product. The molded product was evaluated according to the above method. The results are shown in Table 4.

[0197] [Example 18] A polymer composition and a molded article were obtained in the same manner as in Example 16, except that the type of hollow particles used was changed as shown in Table 4, and evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0198]

[0199] As is clear from Tables 2 and 4, hollow particles having a shell containing a resin made of a shell polymer containing a phosphorus atom-containing monomer unit and having a heat value of immersion in octane and a heat value of immersion in formamide at 30°C within a specific range were able to give polymer compositions with excellent miscibility with polymers and improved flame retardancy (Examples A, B, G and Examples 10 to 22).

Claims

1. Hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the resin is a shell polymer containing a phosphorus atom-containing monomer unit, and the heat of immersion in octane at 30°C is 1 J / g or more and 100 J / g or less, and the heat of immersion in formamide at 30°C is 0.1 J / g or more and 100 J / g or less.

2. The hollow particles according to claim 1, having a volume average particle size of 0.1 to 50 μm.

3. The hollow particles according to claim 1 or 2, having an average porosity of 50 to 90%.

4. Hollow particles according to any one of claims 1 to 3, wherein the proportion of particles having only one hollow portion is 90% or more by number.

5. The hollow particle according to any one of claims 1 to 4, wherein the shell polymer contains a phosphate ester monomer unit.

6. The hollow particle according to any one of claims 1 to 5, wherein the shell polymer contains a crosslinkable monomer unit.

7. The hollow particle according to any one of claims 1 to 6, wherein the shell polymer comprises crosslinkable hydrocarbon monomer units and / or heteroatom-containing crosslinkable monomer units.

8. The hollow particle according to any one of claims 1 to 7, wherein the shell polymer contains at least one monomer unit selected from the group consisting of 1,3-butanediol dimethacrylate units, glycerol dimethacrylate units, and glycerol trimethacrylate units.

9. The hollow particle according to any one of claims 1 to 8, wherein the shell polymer contains 0.2 to 60% by mass of the phosphorus atom-containing monomer unit.

10. A polymer composition containing the hollow particles according to any one of claims 1 to 9 and a polymer.

11. The polymer composition according to claim 10, wherein said polymer is at least one rubber selected from the group consisting of silicone rubber and acrylonitrile-butadiene copolymer rubber.

12. The polymer composition according to claim 10, wherein the polymer is at least one resin selected from the group consisting of urethane elastomers, amide elastomers, and olefin elastomers.

13. The polymer composition according to any one of claims 10 to 12, further comprising a flame retardant.

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