US-12623198-B2 - Method for producing hollow particles

Abstract

The method produces hollow particles which have a high void ratio, which can reduce the residual amount of a sparingly water-soluble solvent used in the production process, and which are less likely to collapse. The method for producing hollow particles which comprise a shell and a hollow portion and which have a void ratio of 50% or more and 90% or less, wherein a suspension treatment of a mixture liquid containing a polymerizable monomer for shell, a polar resin, a hydrocarbon solvent, a sparingly water-soluble inorganic metal salt as a dispersant, and an aqueous medium is carried out to prepare a suspension in which droplets of a monomer composition containing the polymerizable monomer for shell, the polar resin and the hydrocarbon solvent are dispersed in the aqueous medium; a polymerization reaction of the suspension is carried out; and the hydrocarbon solvent is removed from the obtained hollow particles.

Inventors

• Masashi Watanabe

Assignees

• ZEON CORPORATION

Dates

Publication Date

20260512

Application Date

20201202

Priority Date

20191206

Claims (4)

1. 1 . A method for producing hollow particles which comprise a resin-containing shell and a hollow portion surrounded by the shell and which have a void ratio of 50% or more and 90% or less, the method comprising: a suspension step comprising carrying out a suspension treatment of a mixture liquid containing a polymerizable monomer for shell, a polar resin selected from the group consisting of polymers containing a repeating unit which contains a heteroatom, a hydrocarbon solvent, a dispersant, and an aqueous medium to prepare a suspension in which droplets of a monomer composition containing the polymerizable monomer for shell, the polar resin and the hydrocarbon solvent are dispersed in the aqueous medium, a polymerization step comprising subjecting the suspension to a polymerization reaction, and a hydrocarbon solvent removal step comprising removing the hydrocarbon solvent included in the hollow particles obtained by the polymerization step, wherein the polar resin is an acrylic polymer; the acrylic polymer as the polar resin is a copolymer of polymerizable monomers for polar resin, which include a methyl methacrylate and a polar group-containing (meth)acrylic monovinyl monomer; and with respect to a total mass (100% by mass) of the polymerizable monomers for polar resin, a copolymerization ratio of the methyl methacrylate is 50.0% by mass or more and 99.9% by mass or less, and a copolymerization ratio of the polar group-containing (meth)acrylic monovinyl monomer is 0.1% by mass or more and 5.0% by mass or less, and wherein the dispersant is at least one selected from the group consisting of magnesium hydroxide, calcium hydroxide, barium hydroxide and calcium phosphate.
2. 2 . The method for producing the hollow particles according to claim 1 , wherein the mixture liquid contains the polar resin in an amount of from 0.1 parts by mass to 10 parts by mass, with respect to 100 parts by mass of the polymerizable monomer for shell.
3. 3 . The method for producing the hollow particles according to claim 1 , wherein the dispersant is magnesium hydroxide.
4. 4 . The method for producing the hollow particles according to claim 1 , wherein the polymerizable monomers for shell include, with respect to the total mass (100% by mass) of the polymerizable monomers for shell, a crosslinkable monomer in an amount of 70% by mass or more and 100% by mass or less and a non-crosslinkable monomer in an amount of 0% by mass or more and 30% by mass or less.

Description

TECHNICAL FIELD The present disclosure relates to a method for producing hollow particles. More specifically, the present disclosure relates to a method for producing hollow particles which have a high void ratio, which are less likely to collapse, which can reduce the residual amount of volatile compounds used in a production process, such as a non-reactive hydrocarbon solvent and an unreacted monomer, and especially which are less likely to collapse when mixed with other materials such as a resin. BACKGROUND ART Hollow particles produced by polymerizing a monomer (hollow resin particles) can scatter light well and can reduce light transmissivity as compared to resin particles in which their interiors are practically filled with resin; hence, hollow particles are widely used in the applications of, for example, aqueous coating materials and paper coating compositions, as organic pigments and masking agents excellent in optical properties such as opacity and whiteness. Hollow particles are desired to have a high void ratio in order to improve effects such as weight reduction, acquisition of heat insulation properties, opacification and whitening of aqueous coating materials, paper coating compositions, etc. However, when the void ratio of the hollow particles is increased, there are problems in that the shell thickness of the hollow particles is decreased, and the hollow particles easily collapse. Accordingly, hollow particles which have a high void ratio and which are less likely to collapse, are needed. Patent Literature 1 discloses a method for producing hollow resin particles, which is characterized in that a mixed solution containing a monomer mixture, which contains 20 to 70 parts by weight of a polyfunctional monomer having two or more ethylenically unsaturated groups and 80 to 30 parts by weight of a monofunctional monomer, a non-reactive organic solvent, and a non-crosslinkable polymer having a polystyrene equivalent weight average molecular weight of 10000 to 1000000, is dispersed in an aqueous solution containing a dispersion stabilizer or a surfactant, and then the solution is polymerized. Patent Literature 1 mentions that hollow resin particles which have a small grain size, which have fewer pin holes and which have less collapses, are provided by the production method. Patent Literature 2 discloses hollow resin particles such that the particles have one hollow enclosed by a shell and a thermal decomposition initiation temperature of 350° C. or higher, and the shell has a fine through hole having a diameter in the range of 10 nm to 50 nm and has a thickness of the ratio of 0.03 to 0.25 with respect to the average primary particle diameter of the hollow resin particles. Also, Patent Literature 2 mentions that the hollow resin particles are produced by dispersing a mixed solution containing a polyfunctional monomer and a non-reactive solvent in an aqueous solution, and then polymerizing the polyfunctional monomer; the aqueous solution may contain a dispersion stabilizer or a surfactant; and a water-soluble polymerization initiator is preferably used to form the fine through hole having a diameter of 10 nm to 50 nm. Patent Literature 3 discloses a method for producing hollow polymer fine particles comprising a shell of single layer structure and a hollow portion, in which a mixture of (i) at least one crosslinkable monomer (B) or a mixture of at least one crosslinkable monomer (B) and at least one monofunctional monomer (B′), (ii) an initiator (C) and (iii) a sparingly water-soluble solvent (D) having low compatibility with a polymer or copolymer obtained from the at least one crosslinkable monomer (B) or a copolymer of the at least one crosslinkable monomer (B) and the at least one monofunctional monomer (B′) is dispersed in an aqueous solution of a dispersion stabilizer (A), followed by suspension polymerization. Also, Patent Literature 3 mentions that a polymer dispersion stabilizer such as polyvinyl alcohol or a surfactant such as a nonionic surfactant, an anionic surfactant and an amphoteric surfactant can be used as a dispersion stabilizer (A) and among them, a polymer dispersion stabilizer such as polyvinyl alcohol, is preferred. CITATION LIST Patent Literatures [Patent Literature 1] Japanese Patent Application Laid-Open (JP-A) No. 2016-68037[Patent Literature 2] JP-A No. 2016-190980[Patent Literature 3] JP-A No. 2002-80503 SUMMARY OF INVENTION Technical Problem However, the hollow resin particles obtained by the production method of Patent Literature 1 have the following problem: when a coating material or molding material is produced by mixing the hollow resin particles with a resin, or when a molded body is produced by use of the molding material containing the hollow resin particles, the hollow resin particles cannot sufficiently withstand the shear or pressure of biaxial kneading or injection molding, and they are likely to collapse, accordingly. Like the hollow resin particles of Pate