Method for producing hollow resin particles

Abstract

The present invention provides a method for producing hollow resin particles, characterized by comprising the steps of preparing a mixed liquid, preparing a suspension, preparing a precursor composition containing precursor particles, performing solid-liquid separation to obtain precursor particles, and removing the encapsulated hydrocarbon solvent to obtain hollow resin particles. The method for producing hollow resin particles of the present invention enables the high-productivity production of hollow resin particles having a higher porosity than conventional methods and superior heat resistance.

Description

[0001] This application is a divisional application of the invention patent application with application number 201880050093.5. The application date of the original application is July 31, 2018, and the name of the invention is "Method for manufacturing latex and method for manufacturing hollow resin particles". Technical Field

[0002] The present invention relates to a method for producing hollow resin particles having a higher porosity than that of the prior art. Background Art

[0003] Compared to resin particles with essentially no internal voids, hollow resin particles can scatter light well and reduce light transmittance. Therefore, they can be used as organic pigments and masking agents with excellent optical properties such as opacity and whiteness, and are widely used in applications such as water-based paints and paper coating compositions.

[0004] In applications such as water-based coatings and paper coating compositions, it is desirable to increase the porosity of the hollow resin particles used to produce them in order to enhance their lightweighting, thermal insulation, and opacifying properties. However, conventional production methods have proven difficult to achieve both stable production of hollow resin particles with a high porosity while satisfying the production conditions required to achieve the desired physical properties.

[0005] For example, Patent Document 1 discloses a technique in which an emulsion containing a hydrophilic core polymer, a first shell polymer, and a second shell polymer is polymerized to form multistage polymer particles, and the formed multistage polymer particles are neutralized with a base to swell the hydrophilic core polymer, thereby forming particles having voids.

[0006] Furthermore, Patent Document 2 discloses a technique in which a polymerizable monomer component is dispersed in an aqueous dispersion medium in the presence of different polymer microparticles having a different composition, the different polymer microparticles are allowed to absorb the polymerizable monomer component, and then the polymerizable monomer component is polymerized. The document describes the following: In addition to the polymerizable monomer component, the different polymers are allowed to coexist in the aqueous dispersion medium in the form of microparticles or solutions; during polymerization, phase separation of the different polymers forms nuclei within the dispersed particles. Simultaneously with the formation of these nuclei, one of the polymers undergoes polymerization shrinkage; as a result, pores are formed within the polymer.

[0007] In addition, patent document 3 discloses a method for producing hollow polymer particles, which is characterized in that a base is added to a latex containing polymer particles so that the pH of the latex is 8 or above, and then an acid is added so that the pH of the latex is 7 or below, and the above-mentioned polymer particles have at least a three-layer structure including a center layer polymer, an intermediate layer polymer and a surface layer polymer, the above-mentioned center layer polymer is obtained by copolymerizing a monomer mixture of 20 to 60 mass% of a carboxyl group-containing monomer and 80 to 40 mass% of a monomer capable of copolymerizing therewith, the above-mentioned intermediate layer polymer is obtained by copolymerizing a monomer mixture of 1 to 12 mass% of a carboxyl group-containing monomer and 99 to 88 mass% of a monomer capable of copolymerizing therewith, and the above-mentioned surface layer polymer is obtained by polymerizing a monomer that does not contain a carboxyl group.

[0008] In addition, patent documentation 4 discloses a kind of manufacture method of heat-expandable microsphere, and this heat-expandable microsphere is made of the shell that is formed by thermoplastic resin as essential component and the foaming agent that is coated in the shell as essential component.Have on record in this document, can stably manufacture the heat-expandable microsphere with the mean particle size of regulation with good yield when not making expansion performance variation.

[0009] In addition, Patent Document 5 discloses the following: When manufacturing hollow resin particles, the steps include: (1) preparing a dispersed phase comprising a vinyl monomer having no nitrile group, a phase separation accelerator, a volatile solvent, a polymerization initiator, and a reaction catalyst; (2) preparing a continuous phase comprising a solvent and a surfactant; (3) adding the dispersed phase to the continuous phase and stirring the resulting mixture; (4) subjecting the resulting aqueous dispersion to a polymerization reaction under pressure; (5) decompressing the mixture after the polymerization reaction at a temperature above the boiling point of the volatile solvent to obtain an aqueous dispersion; and (6) filtering the obtained aqueous dispersion and drying it to obtain hollow resin particles. This document states that since the resin constituting the shell of the hollow resin particles is formed from a vinyl monomer having no nitrile group, the nitrile group will not be detached even at high temperatures, and the strength of the shell is not easily reduced.

[0010] Patent Document 6 discloses a method for producing hollow polymer particles by polymerizing a dispersion of a hydrophilic monomer, a crosslinking monomer, and other monomers in the presence of an oily substance, and then removing the oily substance from the particles in a liquid phase or a gas phase.

[0011] Patent Document 7 discloses a method for producing hollow particles in which the organic solvent contained in the fine particles is removed in an aqueous medium to cause hollowing, thereby suppressing collapse.

[0012] Patent Document 8 discloses hollow polymer fine particles containing a high proportion of a cross-linkable monomer.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Application Laid-Open No. 11-349839;

[0016] Patent Document 2: Japanese Patent Application Laid-Open No. 62-127336;

[0017] Patent Document 3: Japanese Patent Application Laid-Open No. 6-248012;

[0018] Patent Document 4: International Publication No. 2017 / 002659;

[0019] Patent Document 5: Japanese Patent Application Laid-Open No. 2008-231241;

[0020] Patent Document 6: Japanese Patent Application Laid-Open No. 61-87734;

[0021] Patent Document 7: Japanese Patent Application Laid-Open No. 2013-221070;

[0022] Patent Document 8: Japanese Patent Application Laid-Open No. 2002-80503.

[0023] Problems to be solved by the invention

[0024] However, Patent Document 1 does not describe the evaluation of the void ratio of multistage polymer particles.

[0025] Patent Document 2 also discloses that polymer particles having internal pores can be easily produced. However, the polymer particles disclosed in Patent Document 2 have a problem of low porosity.

[0026] Patent Document 3 describes the production of hollow polymer particles with a shell thickness of 50 nm or less and a high porosity. However, the actual hollow polymer particles disclosed in the examples of Patent Document 3 still have a porosity of approximately 70%. Furthermore, the method described in Patent Document 3 suffers from poor productivity.

[0027] Patent documentation 4 records that, from the aspect of expansion performance, it is preferred to include a nitrile monomer as an essential component. However, resin particles comprising a nitrile monomer generally have poor heat resistance. In addition, the technology of patent documentation 4 also has the following problems: due to the foaming of the blowing agent and the utilization of thermal expansion reaction to expand the microspheres, it is difficult to accurately control the particle size of the microspheres.

[0028] Patent Document 5 also describes a method of forming hollow resin particles by decompressing the particles at a temperature above the boiling point of the volatile solvent, thereby utilizing the pressure of the enclosed volatile solvent during evaporation to push out the resin. However, since the particles expand during simultaneous heat application and decompression, the resulting hollow resin particles exhibit non-uniform particle size.

[0029] The technology of Patent Document 6 has the following problem: when the amount of oily substance is increased to produce hollow particles with a thin shell thickness, the particles will be damaged when the oily substance is removed due to the low strength of the shell, and particles with a high porosity cannot be obtained.

[0030] The hollow particles produced by the method described in Patent Document 7 contain water, and when used in applications such as heat insulating agents, a step of removing the internal water is required. During this step, there is a problem that the particles collapse and the porosity decreases.

[0031] When the ratio of the crosslinkable monomer is high as in the hollow polymer fine particles described in Patent Document 8, a high-temperature and long-term treatment is required to remove the hydrocarbons inside, resulting in a problem of poor productivity. Summary of the Invention

[0032] An object of the present invention is to provide a method for producing a latex containing hollow resin particles having a higher porosity than that of the prior art, and to provide a method for producing hollow resin particles having a higher porosity than that of the prior art.

[0033] Solutions for solving problems

[0034] The present inventors have focused on the use of an oil-soluble polymerization initiator in a method for obtaining a latex containing hollow latex particles by suspension polymerization. Furthermore, the present inventors have focused on the alkali swelling produced by the reaction of a copolymer containing hydrophilic monomer units with a base. Based on these findings, the present inventors have discovered that by using a dispersion obtained by dispersing a suitable material in an aqueous medium, the porosity of the latex particles in the resulting latex can be controlled to be greater than that of conventional techniques.

[0035] Furthermore, the present inventors have noted that, in the method of obtaining hollow resin particles by suspension polymerization, post-polymerization treatment is particularly important in order to maintain a hollow, spherical shape with a high porosity. Furthermore, the present inventors have investigated the type of polymer that constitutes the hollow resin particles to improve their heat resistance. As a result, the present inventors have discovered that by using specific monomers during polymerization and performing solid-liquid separation after polymerization, hollow resin particles with a higher porosity and superior heat resistance than conventional methods can be obtained.

[0036] That is, the first production method of the present invention is a method for producing latex, characterized in that it is a method for producing latex containing latex particles having a hollow portion, comprising the following steps:

[0037] a step of preparing a mixed solution comprising at least one monomer selected from a monovinyl monomer and a hydrophilic monomer, a crosslinking monomer, an oil-soluble polymerization initiator, a fat, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium;

[0038] a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid;

[0039] a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and enclosing a hydrocarbon solvent;

[0040] a step of adding a base to the precursor composition to adjust the pH of the precursor composition to 6.0 or higher; and

[0041] A step of obtaining a latex containing latex particles having a hollow portion by removing the hydrocarbon solvent contained in the precursor particles in the precursor composition.

[0042] In the first production method of the present invention, one or more of the above-mentioned monovinyl monomers and one or more of the above-mentioned hydrophilic monomers may be used in combination.

[0043] In the first production method of the present invention, when the total mass of the one or more monovinyl monomers and the one or more hydrophilic monomers is taken as 100 mass%, the total mass ratio of the one or more hydrophilic monomers can be 10 to 50 mass%.

[0044] In the first production method of the present invention, the number average particle size of the latex particles contained in the obtained latex may be 0.1 to 10 μm.

[0045] In the first production method of the present invention, the porosity of the latex particles contained in the obtained latex may be 70 to 99%.

[0046] The second production method of the present invention is a method for producing hollow resin particles, characterized by comprising the following steps:

[0047] a step of preparing a mixed solution comprising at least one monomer selected from a monovinyl monomer and a hydrophilic monomer (excluding acrylonitrile and methacrylonitrile), a crosslinking monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium, wherein the content of the crosslinking monomer is 25 to 59 parts by mass based on 100 parts by mass of the total mass of the at least one monomer selected from the monovinyl monomer and the hydrophilic monomer and the crosslinking monomer;

[0048] a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid;

[0049] a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and enclosing a hydrocarbon solvent;

[0050] a step of obtaining the precursor particles by subjecting the precursor composition to solid-liquid separation; and

[0051] A step of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the precursor particles in a gas phase.

[0052] In the second production method of the present invention, the monovinyl monomer may be at least one selected from acrylic acid esters and methacrylic acid esters, and the hydrophilic monomer may be at least one selected from acrylic acid and methacrylic acid.

[0053] In the second production method of the present invention, the method for solid-liquid separation of the precursor composition may be centrifugation or filtration.

[0054] In the second manufacturing method of the present invention, the process of preparing the above-mentioned mixed liquid can be a process of mixing an oil phase and an aqueous phase, the above-mentioned oil phase contains at least one monomer selected from the monovinyl monomer and the hydrophilic monomer, a cross-linking monomer, an oil-soluble polymerization initiator and a hydrocarbon solvent, and when the total mass of the at least one monomer selected from the monovinyl monomer and the hydrophilic monomer and the cross-linking monomer is taken as 100 mass parts, the content of the cross-linking monomer is 25 to 59 mass parts, and the above-mentioned aqueous phase contains the above-mentioned suspension stabilizer and the aqueous medium.

[0055] In the second production method of the present invention, the hydrocarbon solvent may have a relative dielectric constant of 3 or less at 20°C.

[0056] In the second production method of the present invention, the hydrocarbon solvent may be a hydrocarbon compound having 5 to 7 carbon atoms.

[0057] In the second production method of the present invention, the hydrocarbon solvent may be contained in an amount of 200 parts by mass or more based on 100 parts by mass of the total mass of the at least one monomer selected from the monovinyl monomer and the hydrophilic monomer and the crosslinking monomer.

[0058] In the second production method of the present invention, the number average particle size of the obtained hollow resin particles can be 0.1 to 10 μm.

[0059] In the second production method of the present invention, the void ratio of the obtained hollow resin particles can be 70 to 99%.

[0060] Effects of the Invention

[0061] As described above, according to the first production method of the present invention, latex containing latex particles having a higher porosity than conventional methods can be efficiently produced.

[0062] As described above, according to the second manufacturing method of the present invention, a polymer containing monomer units derived from a monovinyl monomer and / or a hydrophilic monomer is polymerized, and the obtained precursor composition is subjected to solid-liquid separation after polymerization, and then the hydrocarbon solvent is removed from the precursor particles. Therefore, hollow resin particles having a higher porosity than the prior art and excellent heat resistance can be manufactured with high productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is a schematic diagram showing an example of the first production method (production method of latex) of the present invention.

[0064] Figure 2 This is a schematic diagram illustrating an example of the second production method (the production method of hollow resin particles) of the present invention.

[0065] Figure 3 Schematic diagram showing one embodiment of a suspension in a suspension preparation process.

[0066] FIG4A is a SEM image of the hollow resin particles of Example II-1.

[0067] FIG4B is a SEM image of a cross section of the hollow resin particles of Example II-1.

[0068] Figure 5 Schematic diagram showing a conventional dispersion liquid for emulsion polymerization.

[0069] FIG. 6A is a schematic diagram of a conventional core resin particle.

[0070] FIG6B is a schematic cross-sectional view of a conventional core-shell resin particle.

[0071] FIG6C is a schematic cross-sectional view of a conventional hollow resin particle. DETAILED DESCRIPTION

[0072] Hereinafter, in the present invention, "hollow" refers to a state in which the presence of at least one selected from a liquid portion, a gas portion, and a mixed portion of liquid and gas can be confirmed within the particle by conventional observation methods. In the present invention, a "liquid portion" refers to a continuous portion filled with liquid. In the present invention, a "gas portion" refers to a continuous portion filled with gas. In the present invention, a "mixed portion of liquid and gas" refers to a continuous portion filled with both liquid and gas.

[0073] In the present invention, "hollow portion" refers to the portion of the particle occupied by the hollow space. Whether a particle has a hollow portion can be confirmed by, for example, observing a cross section of the particle under SEM or directly observing the particle under TEM.

[0074] The shell portion of the resin in the particle may not have continuous pores, and the "hollow portion" in the present invention is isolated from the outside of the particle by the shell portion of the particle.

[0075] The shell portion of the resin in the particle may have one or two or more communicating holes, and the "hollow portion" in the present invention is connected to the outside of the particle via the communicating holes.

[0076] In the present invention, "precursor particles" refer to particles whose hollow space is filled with water or a mixture of water and gas, or an aqueous medium or a mixture of an aqueous medium and gas. In the present invention, "precursor composition" refers to a composition containing precursor particles.

[0077] In the present invention, "latex particles having a hollow portion" refers to particles having a hollow portion among particles contained in latex.

[0078] In the present invention, "hollow resin particles" refer to resin particles whose hollow portions are filled with gas.

[0079] The first production method of the present invention is a method for producing latex, characterized in that it is a method for producing latex containing latex particles having a hollow portion, comprising the following steps:

[0080] a step of preparing a mixed solution comprising at least one monomer selected from a monovinyl monomer and a hydrophilic monomer, a crosslinking monomer, an oil-soluble polymerization initiator, a fat, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium;

[0081] a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid;

[0082] a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and enclosing a hydrocarbon solvent;

[0083] a step of adding a base to the precursor composition to adjust the pH of the precursor composition to 6.0 or higher; and

[0084] A step of obtaining a latex containing latex particles having a hollow portion by removing the hydrocarbon solvent contained in the precursor particles in the precursor composition.

[0085] The second production method of the present invention is a method for producing hollow resin particles, characterized by comprising the following steps:

[0086] a step of preparing a mixed solution comprising at least one monomer selected from a monovinyl monomer and a hydrophilic monomer (excluding acrylonitrile and methacrylonitrile), a crosslinking monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium, wherein the content of the crosslinking monomer is 25 to 59 parts by mass based on 100 parts by mass of the total mass of the at least one monomer selected from the monovinyl monomer and the hydrophilic monomer and the crosslinking monomer;

[0087] a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid;

[0088] a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and enclosing a hydrocarbon solvent;

[0089] a step of obtaining the precursor particles by subjecting the precursor composition to solid-liquid separation; and

[0090] A step of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the precursor particles in a gas phase.

[0091] The first and second production methods of the present invention share the same characteristics of suspending a mixed solution containing common raw materials and subjecting the resulting suspension to a polymerization reaction. The first and second production methods are described below in order. The description of the second production method, unless otherwise specified, focuses solely on the fundamental differences from the first production method.

[0092] 1. First Manufacturing Method

[0093] The first production method of the present invention comprises (1) a mixed solution preparation step, (2) a suspension preparation step, (3) a polymerization step, (4) a base addition step, and (5) a solvent removal step. The production method of the present invention is not limited to these five steps.

[0094] Figure 1 This is a schematic diagram illustrating an example of the first production method of the present invention. Figure 1 (1) to (5) in the figure correspond to the above steps (1) to (5). The white arrows between the figures indicate the order of the steps. Figure 1 and the following Figure 2 These are merely schematic diagrams for explanation, and the manufacturing method of the present invention is not limited to the contents shown in these figures. In addition, the structure, size, and shape of the materials used in each manufacturing method of the present invention are not limited to the structure, size, and shape of the various materials in these figures.

[0095] Figure 1 (1) is a schematic cross-sectional view showing one embodiment of a mixed solution in the mixed solution preparation step. As shown in the figure, the mixed solution includes an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 refers to a material such as a hydrocarbon solvent that has low polarity and is difficult to mix with the aqueous medium 1.

[0096] Figure 1 (2) is a schematic cross-sectional view illustrating one embodiment of a suspension in the suspension preparation step. The suspension comprises an aqueous medium 1 and micelles 10 (monomer droplets) dispersed in the aqueous medium 1. The micelles 10 are composed of a suspension stabilizer 3 (e.g., a surfactant) surrounding an oil-soluble monomer composition 4 (including an oil-soluble polymerization initiator 5, etc.).

[0097] Figure 1 (3) is a schematic cross-sectional view illustrating one embodiment of a precursor composition after the polymerization step. The precursor composition includes an aqueous medium 1 and precursor particles 20 dispersed in the aqueous medium 1. The shell 6 located outside the precursor particles 20 is formed by polymerization of the monomers and the like in the micelles 10. The hollow portion within the shell 6 contains a hydrocarbon solvent 7. The shell 6 contains oil 13.

[0098] Figure 1 (4) is a schematic cross-sectional view of one embodiment of the precursor composition after the alkali addition step. The addition of alkali causes fat to dissolve into the external aqueous medium 1, forming shell defects 14. As a result, the hollow portion of the precursor particle 20 communicates with the exterior of the precursor particle 20 via the shell defects 14. The principle of removing fat from the precursor particle 20 will be described later.

[0099] Figure 1(5) is a schematic cross-sectional view showing one embodiment of the latex after the solvent removal step. (5) This figure shows the state in which the hydrocarbon solvent 7 has been removed from the precursor particles 20 in (4) above. As a result, a latex 100B is obtained, which includes latex particles 100A having a hollow portion 8 inside the shell portion 6. The aqueous medium 1 is removed from the latex 100B, and the hollow portion of the resulting latex particles 100A is replaced with a gas to obtain hollow resin particles.

[0100] Hereinafter, the above five steps and other steps will be described in sequence.

[0101] (1) Mixed liquid preparation process

[0102] This step is a step of preparing a mixed liquid, which contains (A) at least one monomer selected from a monovinyl monomer and a hydrophilic monomer, (B) a crosslinking monomer, (C) an oil-soluble polymerization initiator, (D) oil, (E) a hydrocarbon solvent, (F) a suspension stabilizer, and (G) an aqueous medium.

[0103] (A) at least one monomer selected from monovinyl monomers and hydrophilic monomers

[0104] In the present invention, monomer refers to a compound having one functional group capable of polymerization. As a monomer, only a monovinyl monomer can be used, only a hydrophilic monomer can be used, or a monovinyl monomer and a hydrophilic monomer can be used in combination. By polymerization of monomers, a polymer or oligomer is generated. In addition, in the present invention, unless otherwise specified, "at least one monomer selected from monovinyl monomers and hydrophilic monomers" does not include "crosslinking monomers" described later. In addition, in the present invention, sometimes "at least one monomer selected from monovinyl monomers and hydrophilic monomers" is recorded as "(A) monomer".

[0105] In the present invention, the monovinyl monomer refers to a compound having one polymerizable vinyl functional group, and is a compound excluding the hydrophilic monomer described below.

[0106] In the present invention, examples of the monovinyl monomer include at least one acrylic monovinyl monomer selected from acrylic esters and methacrylic esters; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, and halogenated styrenes; monoolefin monomers such as ethylene, propylene, and butene; (meth)acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide, and their derivatives; diene monomers such as butadiene and isoprene; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinyl monomers such as vinylidene chloride; and vinylpyridine monomers. The monovinyl monomer may be at least one acrylic monovinyl monomer selected from acrylic esters and methacrylic esters.

[0107] Examples of acrylic monovinyl monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. In the present invention, (meth)acrylate refers to acrylate and / or methacrylate.

[0108] Among the acrylic monovinyl monomers, it is preferred to use at least one selected from butyl acrylate and methyl methacrylate.

[0109] These monovinyl monomers can be used alone or in combination of two or more.

[0110] In the present invention, a hydrophilic monomer refers to a compound soluble in water, more specifically a compound having a solubility in water of 1% by mass or more. The addition of a hydrophilic monomer to the polymerization process is particularly preferred because it can minimize the amount of aggregates in the resulting latex.

[0111] In the present invention, examples of the hydrophilic monomer include acid group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, and polyoxyethylene group-containing monomers.

[0112] The acid group-containing monomer in the present invention refers to a monomer containing an acid group. The acid group herein includes any of a proton-donating group (Brönsted acid group) and an electron pair-accepting group (Lewis acid group). When an acid group-containing monomer is used as a hydrophilic monomer, hollow resin particles with high heat resistance can be obtained, which is preferred.

[0113] The acid group-containing monomer is not particularly limited as long as it contains an acid group. Examples thereof include ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenyl tricarboxylic acid; carboxyl group-containing monomers such as monoalkyl esters of unsaturated dicarboxylic acids such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate; and sulfonic acid group-containing monomers such as styrenesulfonic acid. Among the acid group-containing monomers, ethylenically unsaturated carboxylic acid monomers are particularly preferred, with at least one acrylic hydrophilic monomer selected from acrylic acid and methacrylic acid, and a maleic acid monomer being more preferred. Even more preferred is an acrylic hydrophilic monomer. When using an acrylic hydrophilic monomer ((meth)acrylic acid) and the aforementioned acrylic monovinyl monomer ((meth)acrylate), the preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 100:0 to 30:70, and a more preferred mass ratio is (meth)acrylic acid:(meth)acrylate = 95:5 to 35:65. Compared to the case of using monomers having, for example, a nitrile group, the use of relatively high-temperature-resistant monomers such as (meth)acrylic acid and the aforementioned (meth)acrylates in this manner can improve the heat resistance of the resulting hollow resin particles. In the present invention, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0114] When a hydroxyl group-containing monomer is used as the hydrophilic monomer, it is preferred because the amount of coagulation in the resulting latex can be suppressed to a minimum. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate monomer, 2-hydroxyethyl methacrylate monomer, 2-hydroxypropyl acrylate monomer, 2-hydroxypropyl methacrylate monomer, and 4-hydroxybutyl acrylate monomer.

[0115] Examples of the amide group-containing monomer include acrylamide monomers and dimethylacrylamide monomers.

[0116] Examples of the polyoxyethylene group-containing monomer include methoxypolyethylene glycol acrylate monomers and methoxypolyethylene glycol methacrylate monomers.

[0117] These hydrophilic monomers can be used alone or in combination of two or more.

[0118] In the first production method, one or more monovinyl monomers and one or more hydrophilic monomers may be used in combination. The reason is as follows.

[0119] Figures 6A to 6C illustrate various stages of a conventional hollow resin particle manufacturing process. Figure 6A is a schematic diagram of a core resin particle 61. Figure 6B is a schematic cross-sectional view of a core-shell resin particle 200B. Figure 6C is a schematic cross-sectional view of a hollow resin particle 200C.

[0120] In the prior art, a core resin particle 61 ( FIG. 6A ) containing an alkali-swellable substance is formed, and a shell 62 ( FIG. 6B ) is formed outside the core resin particle 61. By utilizing the swelling of the core resin particle 61 caused by the addition of alkali, a three-layer hollow resin particle 200C ( FIG. 6C ) is produced, comprising a hollow portion 64, a hollow core 63, and a shell 62. However, the void fraction of the hollow resin particles produced by this method is low, at 55% or less.

[0121] In a preferred embodiment of the first production method, by using a monovinyl monomer and a hydrophilic monomer in combination, the shell of the hollow resin particles can be swollen in the base addition step described later, making it easier to remove the hydrocarbon solvent, and the porosity of the obtained hollow resin particles can be further increased compared to the conventional art.

[0122] When the total mass of the above-mentioned materials (A) to (F) is taken as 100 mass%, the mass proportion of the (A) monomer is preferably 5 to 50 mass%, and more preferably 10 to 40 mass%. When the mass proportion of the (A) monomer is 5 to 50 mass%, the mechanical properties of the hollow resin particles can be further improved compared to the conventional art while maintaining the hollowness of the hollow resin particles in the obtained latex, and the porosity of the hollow resin particles can be further increased compared to the conventional art.

[0123] When the total mass of the one or more monovinyl monomers and the one or more hydrophilic monomers is taken as 100 mass%, the total mass ratio of the one or more hydrophilic monomers is preferably 10 to 50 mass%, and more preferably 15 to 40 mass%. When the total mass ratio of the one or more hydrophilic monomers is 10 to 50 mass%, the alkali can more easily penetrate into the particles in the alkali addition step described below, and hollow portions in the particles are more readily formed. Furthermore, the copolymerization reaction of the monovinyl monomer and the hydrophilic monomer can more stably proceed.

[0124] (B) Cross-linking monomer

[0125] In the present invention, a crosslinking monomer refers to a compound having two or more polymerizable functional groups. The use of a crosslinking monomer can improve the mechanical properties of the shell of the resulting hollow resin particles. Furthermore, because the monomers (A) described above have multiple polymerizable functional groups, they can be linked together, thereby suppressing the dissolution of hydrophilic monomers (particularly acid group-containing monomers) to the outside of the hollow resin particles and improving the heat resistance of the resulting hollow resin particles.

[0126] As a crosslinking monomer, there is no particular limitation as long as it has two or more polymerizable functional groups. Examples of the crosslinking monomer include divinylbenzene, diallyl phthalate, allyl (meth)acrylate, and ethylene glycol di(meth)acrylate. Among them, divinylbenzene and ethylene glycol di(meth)acrylate are preferred.

[0127] When the total mass of the monomer (A) and the crosslinkable monomer (B) is taken as 100 parts by mass, the content of the crosslinkable monomer (B) is preferably 1 to 59 parts by mass, more preferably 3 to 57 parts by mass, and even more preferably 5 to 55 parts by mass. When the content of the crosslinkable monomer (B) is 1 to 59 parts by mass, the risk of the resulting hollow resin particles being sunken is low, thereby maintaining a high porosity of the hollow resin particles. Furthermore, the risk of a large amount of hydrocarbon solvent remaining in the hollow resin particles is also low.

[0128] Furthermore, the mixed liquid may contain other polymerizable monomers in addition to the (A) monomer and the (B) crosslinkable monomer.

[0129] (C) Oil-soluble polymerization initiator

[0130] In the present invention, the suspension polymerization method using an oil-soluble polymerization initiator is used instead of the emulsion polymerization method using a water-soluble polymerization initiator. The advantages of using the suspension polymerization method will be described in detail in "(2) Suspension Preparation Step".

[0131] The oil-soluble polymerization initiator is not particularly limited as long as it is a lipophilic oil-soluble polymerization initiator having a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, dodecanoyl peroxide, t-butyl 2-ethylperoxyhexanoate, 2,2'-azobis(2,4-dimethylvaleronitrile), and azobisisobutyronitrile.

[0132] The content of the oil-soluble polymerization initiator (C) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the total mass of the monomer (A) and the crosslinkable monomer (B). When the content of the oil-soluble polymerization initiator is 0.1 to 10 parts by mass, the polymerization reaction can proceed sufficiently, and the risk of residual oil-soluble polymerization initiator after completion of the polymerization reaction is minimized, thereby minimizing the risk of unpredictable side reactions.

[0133] (D) Grease

[0134] The fat or oil used in the present invention is not particularly limited as long as it is a lipophilic fat or oil having a solubility in water of 0.2% by mass or less, and any of vegetable oils, animal oils, and synthetic oils can be used.

[0135] like Figure 1 As shown in (3), due to its polarity, the oil 13 is entirely or partially offset in the shell 6. When an alkali is added to the precursor composition containing the precursor particles 20 in this state, the oil 13 is saponified (hydrolyzed). As a result, the fatty acids and glycerol constituting the oil 13 are eluted into the external aqueous medium 1, forming shell defects 14 ( Figure 1 (4)). Thus, the inside and outside of the precursor particle 20 are communicated.

[0136] Furthermore, the volume occupied by the fat 13 decreases due to the saponification (hydrolysis) of the fat 13, and the porosity of the obtained hollow resin particles increases. The porosity of the hollow resin particles can be controlled by adjusting the type and amount of fat added.

[0137] Examples of the fats and oils include linoleic oil, lard, olive oil, coconut oil, castor oil, and cottonseed oil.

[0138] The content of the oil (D) is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 5 to 12 parts by mass, based on 100 parts by mass of the total mass of the monomer (A) and the crosslinkable monomer (B). When the oil content is 1 to 20 parts by mass, an appropriate number of shell defects can be formed in the hollow resin particles in the resulting latex, thereby facilitating the removal of the hydrocarbon solvent from the hollow resin particles and improving the mechanical properties of the hollow resin particles while maintaining their hollowness.

[0139] (E) Hydrocarbon solvent

[0140] The hydrocarbon solvent in the present invention has a function of forming a hollow portion inside the particles.

[0141] In the suspension preparation step described below, a suspension is obtained in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium. During the suspension preparation step, phase separation occurs within the monomer droplets, resulting in the hydrocarbon solvent, which has a low polarity, tending to accumulate within the monomer droplets. Ultimately, within the monomer droplets, the hydrocarbon solvent is distributed within the droplets according to their polarity, while other materials other than the hydrocarbon solvent are distributed around the droplets.

[0142] Then, in the polymerization step described below, a precursor composition comprising precursor particles encapsulating the hydrocarbon solvent can be obtained. That is, the hydrocarbon solvent accumulates inside the particles, forming a hollow portion containing the hydrocarbon solvent inside the obtained precursor particles.

[0143] Furthermore, when a hydrophilic monomer (preferably an acid group-containing monomer) is used, the portion containing the hydrophilic monomer unit (preferably an acid group-containing monomer unit) in the shell portion swells in the base addition step described below, making it easier to remove the hydrocarbon solvent.

[0144] The type of hydrocarbon solvent is not particularly limited. Examples of the hydrocarbon solvent include highly volatile solvents such as benzene, toluene, xylene, butane, pentane, hexane, cyclohexane, carbon disulfide, and carbon tetrachloride.

[0145] The hydrocarbon solvent used in the present invention preferably has a relative dielectric constant of 3 or less at 20°C. The relative dielectric constant is one of the indicators of the polarity of a compound. When the relative dielectric constant of the hydrocarbon solvent is sufficiently low, 3 or less, it is believed that phase separation proceeds rapidly within the monomer droplets, facilitating the formation of hollow spaces.

[0146] Examples of solvents having a relative dielectric constant of 3 or less at 20° C. are as follows. The values ​​in parentheses are relative dielectric constants.

[0147] Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4).

[0148] Regarding the relative dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Basic Handbook of Chemistry" edited by the Chemical Society of Japan, 4th revised edition, Maruzen Co., Ltd., published on September 30, 1993, pages II-498 to II-503), as well as other technical information. Examples of methods for measuring the relative dielectric constant at 20°C include a relative dielectric constant test conducted in accordance with Section 23 of JISC 2101:1999, with the measurement temperature at 20°C.

[0149] The hydrocarbon solvent used in the present invention may be a hydrocarbon compound having 5 to 7 carbon atoms. Hydrocarbon compounds having 5 to 7 carbon atoms are easily encapsulated in the precursor particles during the polymerization step and can be easily removed from the precursor particles during the solvent removal step. Among them, hydrocarbon solvents preferably are hydrocarbon compounds having 6 carbon atoms.

[0150] The content of the hydrocarbon solvent (D) is preferably 100 to 900 parts by mass, more preferably 150 to 700 parts by mass, and even more preferably 200 to 500 parts by mass, based on 100 parts by mass of the total mass of the monomer (A) and the crosslinkable monomer (B). When the content of the hydrocarbon solvent (D) is 100 to 900 parts by mass, the porosity of the hollow resin particles in the resulting latex can be increased compared to conventional methods, and the mechanical properties of the hollow resin particles can be improved while maintaining their hollowness.

[0151] (F) Suspension stabilizer

[0152] The suspension stabilizer is an agent for stabilizing the suspended state in the suspension liquid in the suspension polymerization method described later.

[0153] The suspension stabilizer may contain a surfactant. The surfactant is a material that forms micelles in the suspension polymerization method described below, and the micelles contain at least one monomer selected from monovinyl monomers and hydrophilic monomers, a crosslinking monomer, an oil-soluble polymerization initiator, oils and fats, and a hydrocarbon solvent.

[0154] As the surfactant, cationic surfactants, anionic surfactants, and nonionic surfactants can all be used, and they can also be used in combination. Among them, anionic surfactants and nonionic surfactants are preferred, and anionic surfactants are more preferred.

[0155] Examples of the anionic surfactant include sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dialkylsulfosuccinate, and formaldehyde condensate salts of naphthalenesulfonic acid.

[0156] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters.

[0157] Examples of the cationic surfactant include dodecyldimethylammonium chloride and octadecyltrimethylammonium chloride.

[0158] The suspension stabilizer may contain poorly water-soluble inorganic compounds, water-soluble polymers, and the like.

[0159] The content of the suspension stabilizer (F) is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, and even more preferably 0.3 to 1 part by mass, based on the total mass of the monomer (A), the crosslinkable monomer (B), the oil-soluble polymerization initiator (C), and the hydrocarbon solvent (E) being 100 parts by mass. When the content of the suspension stabilizer (F) is 0.1 parts by mass or greater, micelles are more likely to form in the aqueous medium. On the other hand, when the content of the suspension stabilizer (F) is 3 parts by mass or less, increased foaming and decreased productivity are less likely to occur during the hydrocarbon solvent removal step.

[0160] (G) Water-based media

[0161] In the present invention, the aqueous medium refers to a medium selected from water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent.

[0162] The hydrophilic solvent in the present invention is not particularly limited as long as it is fully miscible with water and does not cause phase separation. Examples of the hydrophilic solvent include alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0163] Among aqueous media, water is particularly preferred due to its high polarity. When using a mixture of water and a hydrophilic solvent, it is crucial that the overall polarity of the mixture is not too low from the perspective of monomer droplet formation. In this case, for example, the mixing ratio (by mass) of water to hydrophilic solvent can be set at 99:1 to 50:50.

[0164] (H) Other

[0165] The mixed solution prepared in this step is a composition obtained by simply mixing the above-mentioned materials (A) to (G) and stirring them appropriately. In this mixed solution, the oil phase containing the above-mentioned materials (A) to (E) is dispersed in the aqueous medium in particles having a diameter of approximately several millimeters. The dispersion of these materials in the mixed solution can be observed visually, depending on the type of materials.

[0166] The mixed liquid preparation step may be a step of mixing an oil phase containing (A) a monomer, (B) a crosslinkable monomer, (C) an oil-soluble polymerization initiator, (D) a fat, and (E) a hydrocarbon solvent with an aqueous phase containing (F) a suspension stabilizer and (G) an aqueous medium. By separately preparing the oil phase and aqueous phase in advance and then mixing them, hollow resin particles having a uniform shell composition can be produced.

[0167] (2) Suspension preparation process

[0168] This step is a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the above-mentioned mixed liquid.

[0169] In the suspension prepared in this step, monomer droplets containing the aforementioned materials (A) to (E) and having a particle size of approximately 0.1 μm to 9.0 μm are uniformly dispersed in the aqueous medium. While these monomer droplets are difficult to observe with the naked eye, they can be observed using a known observation device such as an optical microscope.

[0170] As described above, the present invention employs suspension polymerization instead of emulsion polymerization. Therefore, the advantages of using suspension polymerization and an oil-soluble polymerization initiator will be described below in comparison with emulsion polymerization.

[0171] Figure 5 Schematic diagram showing a dispersion liquid for emulsion polymerization. Figure 5 The micelle 60 in FIG. 1 is schematically shown in cross-section.

[0172] exist Figure 56 shows a micelle 60, a micelle precursor 60a, a monomer 53a dissolved in a solvent, and a water-soluble polymerization initiator 54 dispersed in an aqueous medium 51. The micelle 60 is formed by surrounding an oil-soluble monomer composition 53 with a surfactant 52. The monomer composition 53 contains monomers and the like as raw materials for a polymer, but does not contain a polymerization initiator.

[0173] On the other hand, the micelle precursor 60a is an aggregate of the surfactant 52, but does not contain a sufficient amount of the monomer composition 53. The micelle precursor 60a grows into a micelle 60 by absorbing the monomer 53a dissolved in the solvent or by taking part of the monomer composition 53 from other micelles 60.

[0174] The water-soluble polymerization initiator 54 diffuses in the aqueous medium 51 and penetrates into the interior of the micelles 60 and micelle precursors 60a, promoting the growth of the oil droplets within them. Therefore, in the emulsion polymerization method, it is expected that although each micelle 60 is monodispersed in the aqueous medium 51, the particle size of the micelles 60 will grow to several hundred nanometers.

[0175] Figure 3 This is a schematic diagram showing one embodiment of the suspension in this process. Figure 3 The micelle 10 in FIG. 1 schematically shows its cross section. Figure 3 This is only a schematic diagram, and the suspension of the present invention is not limited to Figure 3 The content shown. Figure 3 A part of the above corresponds to Figure 1 (2).

[0176] exist Figure 3 1 shows a case where micelles 10 and monomers 4a (comprising (A) monomer and (B) crosslinkable monomer) dispersed in an aqueous medium are dispersed in an aqueous medium 1. Micelles 10 are formed by surfactant 3 surrounding an oil-soluble monomer composition 4. Monomer composition 4 contains an oil-soluble polymerization initiator 5, monomers (comprising (A) monomer and (B) crosslinkable monomer), and a hydrocarbon solvent (all not shown).

[0177] like Figure 3 As shown, in this process, micro-oil droplets containing the monomer composition 4 are preliminarily formed within micelles 10. Then, polymerization initiation radicals are generated within the micro-oil droplets by an oil-soluble polymerization initiator 5. Therefore, precursor particles having a target particle size can be produced without excessive growth of the micro-oil droplets.

[0178] In addition, the suspension polymerization ( Figure 3 ) and emulsion polymerization ( Figure 5 ) compared, we can see that in suspension polymerization ( Figure 3), the oil-soluble polymerization initiator 5 has no chance of contacting the monomer 4a dispersed in the aqueous medium 1. Therefore, by using an oil-soluble polymerization initiator, the target latex particles having a hollow portion can be generated, and in addition, the generation of excess polymer particles can be prevented.

[0179] An embodiment of this process is shown below. However, the present invention is not limited to the following embodiment.

[0180] The mixed liquid containing the above-mentioned materials (A) to (G) is suspended to form monomer droplets. The method for forming the monomer droplets is not particularly limited, and can be performed using a device capable of strong stirring, such as an (inline) emulsifier disperser (manufactured by Ohyo Kiko Co., Ltd., trade name: Milder) or a high-speed emulsifier disperser (manufactured by PRIMIX CO., LTD., trade name: TKHOMOMIXER MARK II).

[0181] As described above, in this step, phase separation occurs within the monomer droplets, so the low-polarity hydrocarbon solvent tends to accumulate within the monomer droplets. As a result, the resulting droplets contain the hydrocarbon solvent within them, while materials other than the hydrocarbon solvent are distributed around their periphery.

[0182] (3) Polymerization process

[0183] This step involves subjecting the suspension to a polymerization reaction to prepare a precursor composition comprising precursor particles having a hollow portion enclosing a hydrocarbon solvent. The precursor particles herein are particles primarily formed by copolymerization of the aforementioned monomer (A) and the crosslinkable monomer (B).

[0184] The polymerization method is not particularly limited, and examples thereof include batch, semi-continuous, and continuous methods. The polymerization temperature is preferably 40 to 80° C., more preferably 50 to 70° C. The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours.

[0185] Since monomer droplets containing a hydrocarbon-based solvent are used, a hollow space containing a hydrocarbon-based solvent is formed inside the precursor particles as described above.

[0186] (4) Alkali Addition Process

[0187] This step is performed only in the first manufacturing method.

[0188] This step is a step of adding a base to the precursor composition to adjust the pH of the precursor composition to 6.0 or higher. The addition of the base serves as an opportunity to remove the hydrocarbon solvent occupying the hollow portion of the precursor particles.

[0189] In the first manufacturing method of the present invention, the base performs at least two functions. The first function is to swell the portion of the shell containing hydrophilic monomer units (preferably acid-containing monomer units) by reacting the base with the shell of the precursor particles. The second function is to saponify (hydrolyze) the oil in the shell of the precursor particles by reacting the base with the oil to form shell defects. These functions are all opportunities to remove the hydrocarbon solvent occupying the hollow portion of the precursor particles contained in the precursor composition, promote the formation of the hollow portion inside the precursor, and can expand the hollow portion.

[0190] The base used in this step includes both proton-accepting compounds (Brönsted bases) and electron-pair-donating compounds (Lewis bases).

[0191] The base is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; ammonia; amine compounds such as dimethylamine and diethanolamine; alkali metal carbonates (hydrogen carbonates) such as sodium carbonate and potassium hydrogen carbonate; and ammonium carbonates (hydrogen carbonates) such as ammonium hydrogen carbonate. Among these, alkali metal hydroxides are particularly preferred.

[0192] The pH of the precursor composition after adding the base in this step is usually 6.0 or higher, preferably 6.5 or higher, more preferably 7.0 or higher, further preferably 7.5 or higher, and even more preferably 8.0 or higher.

[0193] When the pH of the precursor composition is 6.0 or higher, the fats and oils in the precursor particles can be sufficiently saponified (hydrolyzed), and alkali swelling can be sufficiently performed.

[0194] The amount of the base added is preferably an amount that neutralizes at least a portion of the acid groups in the shell portion of the precursor particles and thereby makes the pH of the resulting precursor composition 6.0 or higher.

[0195] In order to add an alkali to the precursor composition and swell the portion of the shell of the precursor particles containing hydrophilic monomer units (preferably acidic monomer units), the alkali needs to be fully diffused in the precursor composition. Therefore, it is desirable to stir the mixture thoroughly after adding the alkali. The treatment time after adding the alkali is generally about 15 to 60 minutes. Sometimes, the addition of the alkali may reduce the stability of the precursor composition. To prevent this, an anionic surfactant or a nonionic surfactant may be added to the precursor composition alone or in combination before adding the alkali.

[0196] By performing the subsequent solvent removal step, a latex is obtained. Unless further acid or base is added, the pH of the latex is the same as the pH of the precursor composition in this step. Therefore, the pH of the resulting latex is preferably 6.0 or higher, more preferably 6.5 or higher, even more preferably 7.0 or higher, even more preferably 7.5 or higher, and particularly preferably 8.0 or higher.

[0197] (5) Solvent removal process

[0198] This step is a step of removing the hydrocarbon solvent contained in the precursor particles in the precursor composition. By carrying out this step, a latex containing latex particles having a hollow portion can be obtained.

[0199] When removing the hydrocarbon solvent, the hydrocarbon solvent can be replaced by gas or other liquid (for example, an aqueous medium in which latex particles are suspended). By appropriately selecting the gas or other liquid, the environment inside the obtained latex particles can be changed, or hollow resin particles can be manufactured from the latex particles.

[0200] When the above-mentioned hydrocarbon solvent is used, the obtained precursor composition can be subjected to, for example, a decompression treatment, a distillation treatment, a steam stripping treatment, a gas bubbling treatment, or a combination of two or more of these treatments to easily remove the hydrocarbon solvent from the hollow portion of the precursor particles. Furthermore, the hydrocarbon solvent occupying the hollow portion can be easily replaced with water or an aqueous medium, thereby obtaining a latex containing latex particles in which the hollow portion is occupied by water or an aqueous medium.

[0201] (6) Others

[0202] As a step other than the above-mentioned (1) to (5), for example, a step of appropriately drying a precursor composition or latex, wherein the precursor composition comprises precursor particles containing a hydrocarbon solvent, and the latex comprises latex particles obtained by replacing the hydrocarbon solvent contained in the precursor particles with water or an aqueous medium. This step allows the interior of the precursor particles to be replaced with a gas (e.g., air, an inert gas, etc.), resulting in the production of hollow resin particles. In the drying step, it is preferred to use a precursor composition containing precursor particles or a latex containing latex particles.

[0203] (7) Latex

[0204] The properties of the latex obtained in the above manner are not particularly limited. The latex can be used to form a heat-insulating layer of thermal paper, for example.

[0205] The number average particle size of the latex particles contained in the obtained latex is preferably 0.1 to 10 μm, more preferably 0.5 to 8 μm, even more preferably 1 to 6 μm, even more preferably 1.5 to 5 μm, and particularly preferably 2 to 4 μm. This number average particle size can be determined by measuring the particle sizes of 1,000 to 10,000 latex particles contained in the latex using a flow-type particle image analyzer or the like, and calculating the number average value.

[0206] The porosity of the latex particles contained in the resulting latex is preferably 70% or greater, more preferably 72% or greater, even more preferably 74% or greater, even more preferably 78% or greater, particularly preferably 80% or greater, and even more preferably 82% or greater. To maintain particle strength, the porosity of the latex particles may be 99% or less, or 95% or less. This porosity can be determined by measuring the maximum particle size and the maximum diameter of the voids for 200 latex particles using a transmission electron microscope and simply averaging the porosities obtained from these measurements.

[0207] Hollow resin particles can be obtained by drying the latex.

[0208] (8) Hollow resin particles

[0209] The properties of the hollow resin particles are not particularly limited. Examples of the physical properties of the hollow resin particles include number average particle size, shape, and porosity. Evaluation criteria for the hollow resin particles include the amount of volatile organic compounds contained in the hollow resin particles and the heat resistance of the hollow resin particles.

[0210] a. Number average particle size of hollow resin particles

[0211] The number average particle size of the hollow resin particles is preferably 0.1 to 10 μm, more preferably 0.5 to 8 μm, further preferably 1 to 6 μm, further preferably 1.5 to 5 μm, and particularly preferably 2 to 4 μm.

[0212] The number average particle size of the hollow resin particles can be determined by measuring the particle size distribution using, for example, a laser diffraction particle size distribution measuring apparatus and calculating the number average value.

[0213] The coefficient of variation of the number average particle size of the hollow resin particles can be determined by measuring the number-based particle size distribution using, for example, a laser diffraction particle size distribution measuring apparatus and dividing the standard deviation by the number average particle size.

[0214] In the first production method of the present invention, the hollow portion is formed without expanding the shell portion. Therefore, hollow resin particles having a small coefficient of variation in number average particle size (i.e., hollow resin particles having a narrow particle size distribution) can be obtained. Furthermore, the narrower the particle size distribution of the hollow resin particles, the smoother the coating film containing the hollow resin particles can be formed.

[0215] b. Shape of hollow resin particles

[0216] The shape of the hollow resin particles is not particularly limited as long as a hollow portion is formed inside, and examples thereof include spherical, ellipsoidal, and irregular shapes. Among these, a spherical shape is particularly preferred from the perspective of ease of production.

[0217] The particles may have one or more hollow parts inside, or may be porous. In order to maintain a good balance between the high porosity of the hollow resin particles and the mechanical strength of the hollow resin particles, the particles preferably have only one hollow part inside.

[0218] The average circularity of the hollow resin particles may be 0.950 to 0.995.

[0219] A typical example of the shape of hollow resin particles is a bag formed by a thin membrane and expanded by being filled with gas. Its cross-section is shown below. Figure 2 In this example, a thin film is provided on the outside and the inside is filled with gas.

[0220] The particle shape can be confirmed by, for example, SEM or TEM. Alternatively, the shape of the interior of the particle can be confirmed by SEM or TEM after cross-cutting the particle using a known method.

[0221] c. Porosity of hollow resin particles

[0222] The void ratio of the hollow resin particles is preferably 70% or greater, more preferably 72% or greater, even more preferably 74% or greater, even more preferably 78% or greater, particularly preferably 80% or greater, and even more preferably 82% or greater. To maintain particle strength, the void ratio of the hollow resin particles may be 99% or less, or 95% or less.

[0223] The void ratio (%) of the hollow resin particles can be calculated by the following formula (I) based on the apparent density D1 and true density D0 of the hollow resin particles.

[0224] Formula (I)

[0225] Void ratio (%) = 100 - (apparent density D1 / true density D0) × 100

[0226] The method for measuring the apparent density D1 of the hollow resin particles is as follows. First, 3 Fill the volumetric flask to about 30 cm 3 The mass of the hollow resin particles is accurately weighed. Next, the volumetric flask filled with the hollow resin particles is accurately filled with isopropyl alcohol up to the standard line, taking care not to introduce bubbles. The mass of the isopropyl alcohol added to the volumetric flask is accurately weighed, and the apparent density D1 (g / cm 3 ).

[0227] Formula (II)

[0228] Apparent density D1 = [mass of hollow resin particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0229] The apparent density D1 corresponds to the specific gravity of the entire hollow resin particles when the hollow portion is regarded as a part of the hollow resin particles.

[0230] The method for measuring the true density D0 of the hollow resin particles is as follows. The hollow resin particles are crushed in advance and then 3 A volumetric flask was filled with about 10 g of crushed pieces of hollow resin particles, and the mass of the crushed pieces was accurately weighed. Then, isopropyl alcohol was added to the volumetric flask in the same manner as in the above-mentioned apparent density measurement, and the mass of isopropyl alcohol was accurately weighed. The true density D0 (g / cm2) of the hollow resin particles was calculated based on the following formula (III): 3 ).

[0231] Formula (III)

[0232] True density D0 = [mass of crushed pieces of hollow resin particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0233] The true density D0 corresponds to the specific gravity of only the shell portion of the hollow resin particle. As is clear from the above-described measurement method, when calculating the true density D0, the hollow portion is not considered as part of the hollow resin particle.

[0234] The porosity of the hollow resin particles can also be expressed in another way, that is, the proportion of the hollow part in the specific gravity of the hollow resin particles.

[0235] d. Volatile organic compound content of hollow resin particles

[0236] The hollow resin particles of the present invention generally contain volatile organic compounds in an amount of 5% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, further preferably 2% by mass or less, further preferably 1% by mass or less, and particularly preferably less than 1% by mass.

[0237] In the present invention, "volatile organic compounds contained in the hollow resin particles" refers to organic compounds having a boiling point of 400°C or less among the organic compounds contained in the hollow resin particles. Typical examples of volatile organic compounds include hydrocarbon solvents and unreacted monomers used in the production method described below, but are not limited to these typical examples.

[0238] The method for determining the amount of volatile organic compounds contained in hollow resin particles is as follows. About 100 mg of hollow resin particles are added to a 30 mL screw-capped glass bottle and accurately weighed. Next, about 10 g of tetrahydrofuran (THF) is added and accurately weighed. The mixture in the glass bottle is stirred with a stirrer for 1 hour to extract the volatile organic compounds contained in the hollow resin particles. After stopping the stirring and allowing the resin components of the hollow resin particles that are insoluble in THF to precipitate, a filter (made by Advantech Co., Ltd., trade name: Membrane Filter 25JP020AN) is mounted on a syringe, the precipitate is filtered to obtain a sample solution, and the sample solution is injected into a gas chromatograph (GC) for analysis. The amount of volatile organic compounds per unit mass of the hollow resin particles (mass %) is calculated based on the peak area of ​​GC and a pre-made standard curve. The specific analysis conditions are as follows.

[0239] (Analysis Conditions)

[0240] Apparatus: GC-2010 (manufactured by Shimadzu Corporation)

[0241] Column: DB-5 (manufactured by Agilent Technologies Inc.)

[0242] df=0.25μm 0.25mm ID×30m

[0243] Detector: FID

[0244] Carrier gas: nitrogen (linear velocity: 28.8 cm / s)

[0245] Inlet temperature: 200℃

[0246] Detector temperature: 250°C

[0247] Oven temperature: increase from 40°C to 230°C at a rate of 10°C / min and maintain at 230°C for 2 minutes.

[0248] Sample volume: 2 μL

[0249] e. Heat resistance of hollow resin particles

[0250] The hollow resin particles of the present invention are unlikely to collapse in external and internal shapes even under high temperature conditions, and thus can maintain their hollowness.

[0251] As an indicator of heat resistance, for example, the density change rate d before and after heat treatment of the hollow resin particles can be considered.

[0252] The density change rate d is calculated as follows. First, the hollow resin particles are heat-treated by standing in an electric furnace set at 200°C for 10 minutes. Next, the hollow resin particles are removed from the furnace and their apparent density is measured using the same method as described above for measuring the apparent density D1.

[0253] The apparent density of the hollow resin particles after heat treatment is defined as D a The apparent density of the hollow resin particles before heat treatment is set as D b (=the above-mentioned apparent density D1), the density change rate d (%) was calculated based on the following formula (IV).

[0254] Formula (IV)

[0255] d={|D a -D b | / D b}×100

[0256] The smaller the density change rate d is, the smaller the influence of the heat treatment on the hollow resin particles is, that is, the higher the heat resistance of the hollow resin particles is.

[0257] 6. Application of hollow resin particles

[0258] Hollow resin particles can be used, for example, as undercoating materials for thermal paper. Typically, undercoating materials require thermal insulation and cushioning properties, as well as heat resistance suitable for thermal paper applications. The hollow resin particles of the present invention meet these requirements due to their high porosity, durable hollow shape, small number average particle size, and high heat resistance.

[0259] Hollow resin particles can also be used, for example, as plastic pigments with excellent gloss and hiding power. Furthermore, hollow resin particles can be obtained by encapsulating useful ingredients such as fragrances, pharmaceuticals, pesticides, and ink components within the hollow resin particles through impregnation, reduced pressure impregnation, or pressurized impregnation. These hollow resin particles can be used for a variety of applications depending on the ingredients contained within.

[0260] 2. Second Manufacturing Method

[0261] The production method of the present invention comprises (1) a mixed solution preparation step, (2) a suspension preparation step, (3) a polymerization step, (4) a solid-liquid separation step, and (5) a solvent removal step. The production method of the present invention is not limited to these five steps.

[0262] Figure 2 This is a schematic diagram showing an example of the second production method of the present invention. Figure 2 (1) to (5) in the figure correspond to the above steps (1) to (5). The white arrows between the figures indicate the order of the steps.

[0263] Figure 2 (1) and (2) correspond to Figure 1 (1) or (2). In addition, Figure 2 (3) corresponds to the case 6 except that the case 6 does not contain grease 13. Figure 1 (3).

[0264] Figure 2 (4) is a schematic cross-sectional view showing an embodiment of the precursor particles after the solid-liquid separation step. Figure 2 (4) shows that from the above Figure 2 The state of separating the aqueous medium 1 in the state of (3).

[0265] Figure 2 (5) is a schematic cross-sectional view showing one embodiment of the hollow resin particles after the solvent removal step. Figure 2 (5) shows that from the above Figure 2 The hydrocarbon solvent 7 is removed from the state of (4). As a result, hollow resin particles 100C having a hollow portion 8 inside the shell 6 are obtained.

[0266] Hereinafter, the above-mentioned five steps and other steps will be described in order, focusing on the differences from the first manufacturing method.

[0267] (1) Mixed liquid preparation process

[0268] This step is a step of preparing a mixed solution containing (A) at least one monomer selected from a monovinyl monomer and a hydrophilic monomer (excluding acrylonitrile and methacrylonitrile), (B) a crosslinking monomer, (C) an oil-soluble polymerization initiator, (E) a hydrocarbon solvent, (F) a suspension stabilizer, and (G) an aqueous medium.

[0269] In the second production method, there is no need to use (D) fats and oils as in the first production method. In the second production method, it is preferred that the mixed liquid does not contain fats and oils.

[0270] In the second production method, neither acrylonitrile nor methacrylonitrile is used as a hydrophilic monomer. This is because, as shown in Comparative Example II-5 described below, these monomers containing a heat-sensitive nitrile group have poor heat resistance, resulting in a low porosity in the obtained particles.

[0271] In the mixed liquid used in the second production method, the content of the crosslinking monomer (B) is generally 25 to 59 parts by mass, preferably 28 to 58 parts by mass, more preferably 30 to 57 parts by mass, and even more preferably 35 to 55 parts by mass, based on 100 parts by mass of the total mass of the monomer (A) and the crosslinking monomer (B). When the content of the crosslinking monomer (B) is 25 to 59 parts by mass, the risk of collapse of the resulting hollow resin particles is low, thereby maintaining a high porosity of the hollow resin particles. Furthermore, the risk of a large amount of hydrocarbon solvent remaining in the hollow resin particles is also low.

[0272] Furthermore, the mixed liquid may contain other polymerizable monomers in addition to the (A) monomer and the (B) crosslinkable monomer.

[0273] The mixed liquid preparation step may be a step of mixing an oil phase containing at least one monomer selected from the monovinyl monomer and the hydrophilic monomer, a crosslinking monomer, an oil-soluble polymerization initiator, and a hydrocarbon solvent, wherein the crosslinking monomer content is 25 to 59 parts by mass based on 100 parts by mass of the total mass of the at least one monomer selected from the monovinyl monomer and the hydrophilic monomer and the crosslinking monomer, and an aqueous phase containing the suspension stabilizer and an aqueous medium. By separately preparing the oil phase and aqueous phase in this manner and then mixing them, hollow resin particles having a uniform shell composition can be produced.

[0274] (2) Suspension Preparation Step and (3) Polymerization Step

[0275] These two steps in the second production method are not particularly different from those in the first production method.

[0276] (4) Solid-liquid separation process

[0277] This step is a step of obtaining precursor particles by subjecting the above-mentioned precursor composition to solid-liquid separation.

[0278] As shown in Comparative Example II-3 described later, when the hydrocarbon solvent contained in the precursor particles is removed from a slurry containing an aqueous medium, there is a problem that if water equal in volume to the hydrocarbon solvent removed from the precursor particles does not enter the particles, the resulting hollow resin particles will be damaged.

[0279] One method for preventing this problem is to raise the pH of the slurry constituting the precursor composition to 6.0 or higher, then swell the shells of the precursor particles with an alkali, and then remove the hydrocarbon solvent (see the first production method described above). In this case, the shells of the precursor particles become flexible, allowing the hydrocarbon solvent in the interior of the precursor particles to be rapidly replaced with water, resulting in water-encapsulated precursor particles.

[0280] In contrast, in the second production method, after solid-liquid separation of the slurry after the polymerization step, the resulting solid component is dried in the gas phase. In this case, air equal in volume to the hydrocarbon solvent removed from the interior of the precursor particles readily enters the particles, resulting in hollow resin particles that retain their hollow shape. Furthermore, precursor particles containing the hydrocarbon solvent tend to be less susceptible to damage than precursor particles containing water.

[0281] The reason why precursor particles containing a hydrocarbon solvent are less susceptible to damage than precursor particles containing water is not clear, but the following principle is presumed when the free volume of the polymer constituting the shell is taken into consideration.

[0282] In the model of liquid structure proposed by H. Eyring, liquids are composed of molecules and free volume (i.e., space without molecules). This free volume is formed by a collection of molecular-sized pores in liquids, and at normal temperatures and pressures, free volume accounts for approximately 3% of the liquid. This model is also applicable to solid structures composed of regular molecules, such as polymers.

[0283] In the present invention, the polymer that constitutes the shell of the precursor particles generally has a high polarity. Therefore, it can be considered that water readily binds to the polymer, allowing water molecules to readily penetrate the free volume of the polymer. In other words, the solubility coefficient of water molecules in the polymer is high. On the other hand, hydrocarbon solvents, due to their low polarity, are less likely to bind to the polymer. In other words, the solubility coefficient of hydrocarbon solvent molecules in the polymer is low. As a result, hydrocarbon solvent molecules are less likely to penetrate the free volume of the polymer.

[0284] Therefore, in particles containing water, water molecules penetrate the free volume of the polymer constituting the shell, reducing the space within the shell where no molecules exist. Consequently, the air permeability of the shell decreases, hindering the inflow of air accompanying the evaporation of water during drying, and thus making the particles susceptible to damage. In contrast, in particles containing a hydrocarbon solvent, hydrocarbon solvent molecules are less likely to penetrate the free volume of the polymer, maintaining high air permeability within the shell. Consequently, during the solvent removal process, the exchange of hydrocarbon solvent with air proceeds rapidly, resulting in hollow resin particles with a maintained hollow interior.

[0285] The method for solid-liquid separation of the precursor composition is not particularly limited as long as it is a method for separating the solid component comprising the precursor particles and the liquid component comprising the aqueous medium without removing the hydrocarbon solvent contained in the precursor particles, and a known method can be used. As the method for solid-liquid separation, for example, centrifugation, filtration, static separation, etc. can be enumerated, and in particular, centrifugation or filtration can be used. From the viewpoint of ease of operation, centrifugation can be adopted.

[0286] After the solid-liquid separation step and before the solvent removal step described below, an optional step such as a pre-drying step may be performed. Examples of the pre-drying step include a step of pre-drying the solid component obtained after the solid-liquid separation step using a drying device such as a dryer or a drying apparatus such as a hand dryer.

[0287] (5) Solvent removal process

[0288] This step is a step of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the precursor particles in a gas phase.

[0289] Strictly speaking, "in the gas phase" in this process refers to an environment in which no liquid components are present outside the precursor particles, or an environment in which only a very small amount of liquid components are present outside the precursor particles, which does not affect the removal of the hydrocarbon solvent. "In the gas phase" can also be described as a state in which the precursor particles are not present in the slurry, or a state in which the precursor particles are present in the dry powder. In other words, in this process, it is crucial to remove the hydrocarbon solvent in an environment in which the precursor particles are in direct contact with the external gas.

[0290] As shown in Examples II-1 to II-4 described below, the fact that the hollow resin particles maintain their spherical shape after vacuum drying and restoration to normal pressure in the solvent removal step is considered to be evidence of high air permeability of the shell itself.

[0291] Generally, it is known that nylon, ethylene vinyl alcohol (EVOH), etc. have improved air permeability under high humidity. The reason is understood to be that these polymers are plasticized by water molecules, resulting in a higher mobility of the polymer. However, the hollow resin particles of the present invention, particularly the hollow resin particles obtained by the second manufacturing method, are believed to have a high degree of crosslinking, and it is therefore speculated that the influence of plasticization caused by the action of the aqueous medium is relatively small. Therefore, in the present invention, the air permeability of the shell portion of the hollow resin particles can be considered to be a property inherent to the polymer constituting the shell portion.

[0292] The method for removing the hydrocarbon solvent in the precursor particles in the gas phase is not particularly limited, and a known method can be employed, such as reduced pressure drying, heat drying, airflow drying, or a combination of these methods.

[0293] In particular, when using a heat drying method, the heating temperature must be above the boiling point of the hydrocarbon solvent and below the maximum temperature at which the shell structure of the precursor particles is not damaged. Therefore, the heating temperature is determined based on the composition of the shell of the precursor particles and the type of hydrocarbon solvent. For example, the heating temperature can be 50-200°C, 70-180°C, or even 100-150°C.

[0294] By the drying operation in the gas phase, the hydrocarbon solvent inside the precursor particles is replaced by the external gas, and as a result, hollow resin particles having the hollow portion occupied by the gas can be obtained.

[0295] The drying atmosphere is not particularly limited and can be appropriately selected depending on the intended use of the hollow resin particles. Examples of the drying atmosphere include air, oxygen, nitrogen, and argon. Alternatively, hollow resin particles having a temporarily evacuated interior can be obtained by temporarily filling the interior of the hollow resin particles with a gas and then drying under reduced pressure.

[0296] (6) Others

[0297] In addition to the above steps (1) to (5), there is also the step of replacing the gas inside the hollow resin particles with another gas or liquid. This replacement can change the environment inside the hollow resin particles, selectively enclose molecules inside the hollow resin particles, or modify the chemical structure inside the hollow resin particles according to the intended use.

[0298] The description about the first manufacturing method mentioned above can be applied to the second manufacturing method as long as there are no obstacles. In addition, the description about the second manufacturing method mentioned above can also be applied to the first manufacturing method as long as there are no obstacles.

[0299] Example

[0300] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, parts and % are by mass unless otherwise specified.

[0301] The test methods performed in the present examples and comparative examples are as follows.

[0302] <Example Series I>

[0303] I-1. Production of Latex Containing Hollow Resin Particles

[0304] [Example I-1]

[0305] (1) Mixed liquid preparation process

[0306] The following materials were added to a pressure-resistant container equipped with a stirring device containing 325 parts of ion-exchanged water as an aqueous medium, and the contents of the container were stirred to disperse the following materials in the ion-exchanged water to prepare a mixed solution.

[0307] 0.3 parts of anionic surfactant

[0308] 6 parts of butyl acrylate (BA)

[0309] 15 parts of methyl methacrylate (MMA)

[0310] 9 parts of methacrylic acid (MAA, hydrophilic monomer (acid group-containing monomer))

[0311] 100 parts of cyclohexane

[0312] 3 parts linseed oil

[0313] 2 parts divinylbenzene

[0314] 0.63 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Corporation, trade name: V-65)

[0315] (2) Suspension preparation process

[0316] The mixed liquid was stirred and suspended by an emulsifying disperser to prepare a suspension in which monomer droplets containing cyclohexane were dispersed in water.

[0317] (3) Polymerization process

[0318] The suspension was added to a reaction vessel containing 0.6 parts of anionic surfactant. The temperature was raised to 65°C and maintained at 65°C for 3 hours to allow for a polymerization reaction. This polymerization reaction produced a precursor composition containing precursor particles containing cyclohexane. The reaction vessel was then cooled to room temperature.

[0319] (4) Alkali Addition Process

[0320] A 10% by mass sodium hydroxide aqueous solution was added to the cooled precursor composition in the reaction vessel until the pH of the mixture in the reaction vessel reached 7.0. The sodium hydroxide aqueous solution was added while stirring the precursor composition using the inline emulsifier.

[0321] (5) Solvent removal process

[0322] 0.1 to 0.5 parts by mass of a defoaming agent was further added to 100 parts by mass of the precursor composition that had undergone the above-described alkali addition step, and the mixture was maintained at 70°C for 6 hours while nitrogen was blown in at a flow rate of 6 minutes / liter to remove cyclohexane from the precursor particles, thereby obtaining a latex (Example I-1). Observation under a transmission electron microscope revealed that the latex contained latex particles having a hollow portion (the same applies hereinafter).

[0323] [Example I-2]

[0324] A latex was obtained by the same production method as in Example I-1 except that the pH was changed from 7.0 to 7.5 in the "(4) alkali addition step" of Example I-1 (Example I-2).

[0325] [Example 1-3]

[0326] A latex was obtained by the same production method as in Example I-1 except that the pH was changed from 7.0 to 8.5 in the "(4) alkali addition step" of Example I-1 (Example I-3).

[0327] [Comparative Example I-1]

[0328] A latex (Comparative Example I-1) was obtained by the same production method as in Example I-1 except that the "(4) alkali addition step" of Example I-1 was not performed. The particles contained in this latex were not latex particles having a hollow portion.

[0329] [Comparative Example I-2]

[0330] A latex (Comparative Example I-2) was obtained by the same production method as in Example I-1 except that the pH was changed from 7.0 to 5.0 in the "(4) Alkali Addition Step" of Example I-1. The particles contained in this latex were not hollow latex particles.

[0331] [Comparative Example I-3]

[0332] A latex (Comparative Example I-3) was obtained by the same production method as in Example I-1 except that divinylbenzene was not added in the "(1) Dispersion Preparation Step" of Example I-1. The particles contained in this latex were not hollow particles.

[0333] [Comparative Example I-4]

[0334] A latex (Comparative Example I-4) was obtained by the same production method as in Example I-1, except that acrylic acid (MAA, a hydrophilic monomer (acid group-containing monomer)) was not added in the "(1) Dispersion Preparation Step" of Example I-1. The particles contained in this latex were not hollow latex particles.

[0335] [Comparative Example 1-5]

[0336] A latex (Comparative Example I-5) was obtained by the same production method as in Example I-1 except that linseed oil was not added in the "(1) Dispersion Preparation Step" of Example I-1. The particles contained in this latex were not hollow latex particles.

[0337] I-2. Evaluation of latex

[0338] The porosity and number average particle size of the latex particles contained in each of the latexes of Examples I-1 to I-3 and Comparative Examples I-1 to I-5 were measured. The details are as follows.

[0339] (1) Porosity of Latex Particles with Hollow Parts

[0340] Using a transmission electron microscope (trade name "H-7500", manufactured by Hitachi, Ltd.), the maximum particle size and the maximum diameter of the hollow portion of 200 latex particles containing a hollow portion contained in the latexes of Examples I-1 to I-3 were measured. Using these two measured values, the porosity of each latex particle was calculated according to the following formula (A), and the simple average of these values ​​was used as the porosity of the latex particles.

[0341] Formula (A)

[0342] Void ratio (%) = {(maximum diameter of hollow part) 3 / (maximum particle size) 3}×100

[0343] In addition, since no hollow portion was observed in the latex particles contained in the latexes of Comparative Examples I-1 to I-5, the void ratio was not calculated.

[0344] (2) Number average particle size of latex particles

[0345] During the measurement, the concentration of latex particles in the latex is adjusted to 3000 to 10000 particles / μL, and then the particle size of 1000 to 10000 particles is measured using a flow particle image analyzer (trade name "FPIA-3000", manufactured by Sysmex Corporation), and the number average value is calculated. The obtained value is used as the number average particle size of the latex particles.

[0346] The measurement and evaluation results of each latex of Examples I-1 to I-3 and Comparative Examples I-1 to I-5 are shown in Table 1. As described above, since no hollow portion was observed in the latex particles contained in the latexes of Comparative Examples I-1 to I-5, the porosity of these latex particles is not described in Table 1.

[0347] [Table I-1]

[0348] I-3. Examination Next, with reference to Table I-1, the evaluation results of the latex were examined.

[0349] According to Table I-1, the latex particles contained in the latex of Comparative Example I-1 had a number average particle size of 4.1 μm and had no hollow portion. Therefore, it can be seen that without adding an alkali to the precursor composition, latex particles without a hollow portion were obtained. This is presumably because, without adding an alkali, the portion of the precursor particle shell containing the hydrophilic monomer unit does not swell with alkali and does not allow oil and fat to dissolve.

[0350] According to Table I-1, the latex particles contained in the latex of Comparative Example I-2 had a number average particle size of 4.0 μm and had no hollow portion. Therefore, even if an alkali is added to the precursor composition, latex particles without hollow portions are obtained unless the pH of the precursor composition is 6.0 or higher. This is presumably because, unless the pH of the precursor composition is 6.0 or higher, the portion of the precursor particle shell containing the hydrophilic monomer unit does not swell sufficiently with alkali.

[0351] According to Table I-1, the shells of the latex particles contained in the latex of Comparative Example I-3 dissolved and aggregated, making it impossible to measure the number average particle size, and the latex particles also lacked a hollow portion. Therefore, it can be seen that without the use of a crosslinking monomer, latex particles without a hollow portion were obtained. This is believed to be because, although the addition of an alkali causes the hydrophilic monomer units in the shell of the precursor particles to swell with alkali, the absence of a crosslinking monomer causes this portion to elute into the aqueous medium, resulting in the inability to maintain a hollow portion and causing the precursor particles to be damaged.

[0352] According to Table I-1, the latex particles contained in the latex of Comparative Example I-4 had a number average particle size of 4.4 μm and had no hollow portion. Therefore, it can be seen that without using a hydrophilic monomer, latex particles without a hollow portion were obtained. This is presumably because without using a hydrophilic monomer, the resulting precursor particles did not swell with alkali.

[0353] According to Table I-1, the latex particles contained in the latex of Comparative Example I-5 had a number average particle size of 4.3 μm and no hollow portion. Therefore, it can be seen that when no oil or fat is used, latex particles without hollow portions are obtained. This is presumably because when no oil or fat is used, the shells of the precursor particles do not have defects, and therefore the encapsulated hydrocarbon solvent cannot be removed during the solvent removal step.

[0354] On the other hand, according to Table I-1, the number average particle size of the latex particles contained in the latexes of Examples I-1 to I-3 was 4.3 to 4.4 μm, and the porosity was 80% in each case.

[0355] Therefore, it was demonstrated that by sequentially preparing a mixed liquid, a suspension, and a precursor composition, and then adding an alkali to the resulting precursor composition to remove the hydrocarbon solvent contained in the precursor particles, a latex containing latex particles having a higher porosity than conventional methods can be efficiently produced. Furthermore, hollow resin particles can be obtained by subjecting the latex to a drying step.

[0356] <Example Series II>

[0357] II-1. Production of Hollow Resin Particles

[0358] [Example II-1]

[0359] (1) Mixed liquid preparation process

[0360] First, the following materials (a1) to (d1) are mixed, and the resulting mixture is used as the oil phase.

[0361] (a1) 41 parts of methacrylic acid

[0362] (b) 59 parts of ethylene glycol dimethacrylate

[0363] (c) 3 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Corporation, trade name: V-65)

[0364] (e1) 300 parts of cyclohexane

[0365] Next, 3 parts of (f) surfactant were added to 800 parts of (g) ion-exchanged water, and the resulting mixture was used as the aqueous phase.

[0366] The aqueous phase and the oil phase are mixed to prepare a mixed solution.

[0367] (2) Suspension preparation process

[0368] The mixed liquid was stirred and suspended using an emulsifying disperser to prepare a suspension in which monomer droplets containing cyclohexane were dispersed in water.

[0369] (3) Polymerization process

[0370] The suspension was stirred for 4 hours under a nitrogen atmosphere at 65° C. to perform a polymerization reaction. Through the polymerization reaction, a precursor composition containing precursor particles containing cyclohexane was prepared.

[0371] (4) Solid-liquid separation process

[0372] The resulting precursor composition was centrifuged using a cooling high-speed centrifuge (manufactured by Kokusan, Inc., trade name: H-9R) with rotor MN1, a rotation speed of 3000 rpm, and a centrifugal separation time of 20 minutes to dehydrate the solid component. The dehydrated solid component was then dried in a dryer at 40°C to obtain cyclohexane-encapsulated precursor particles.

[0373] (5) Solvent removal process

[0374] The precursor particles were heated in a vacuum dryer at 150°C for 15 hours to obtain resin particles of Example II-1. Scanning electron microscopic observation and porosity values ​​confirmed that the resin particles were spherical and had only one hollow portion.

[0375] [Example II-2]

[0376] Resin particles of Example II-2 were obtained by the same manufacturing method as in Example II-1, except that the materials and amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1. Scanning electron microscopic observation and porosity values ​​confirmed that the resin particles were spherical and had only one hollow portion.

[0377] [Example II-3]

[0378] Resin particles of Example II-3 were obtained by the same manufacturing method as in Example II-1, except that the materials and addition amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1, and filtration was used in the "(4) Solid-Liquid Separation Step." Scanning electron microscopic observation and porosity values ​​confirmed that the resin particles were spherical and had only one hollow portion.

[0379] The solid-liquid separation step using filtration in Example II-3 is described below. The precursor composition obtained in the polymerization step was dehydrated using a pressure filter (Advantech Toyo Corporation, trade name: KST-90-UH) and qualitative filter paper (Advantech Toyo Corporation, No. 2) at a pressure of 0.29 MPa. The dehydrated solid component was dried in a dryer at 40°C to obtain cyclohexane-encapsulated precursor particles.

[0380] [Example II-4]

[0381] Resin particles of Example II-4 were obtained by the same manufacturing method as in Example II-1, except that the materials and amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1. Scanning electron microscopic observation and porosity values ​​confirmed that the resin particles were spherical and had only one hollow portion.

[0382] [Comparative Example II-1]

[0383] Resin pellets of Comparative Example II-1 were obtained by the same manufacturing method as in Example II-1, except that the materials and addition amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1. The volatile organic compound content in these resin pellets was 30% by mass, confirming that a significant amount of hydrocarbon solvent remained in the resin pellets. Furthermore, the true density of these resin pellets could not be measured. Scanning electron microscopic observation confirmed that these resin pellets were spherical.

[0384] [Comparative Example II-2]

[0385] Resin pellets of Comparative Example II-2 were obtained by the same manufacturing method as in Example II-3, except that the materials and amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-3. Scanning electron microscopic observation revealed that these resin pellets were damaged and had irregular shapes.

[0386] [Comparative Example II-3]

[0387] A precursor composition containing precursor particles containing cyclohexane was prepared by the same "(2) Suspension Preparation Step" and "(3) Polymerization Step" as in Example II-1, except that the materials and amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1. The precursor composition was then subjected to the same "(2) Suspension Preparation Step" and "(3) Polymerization Step" as in Example II-1. The precursor particles then contained cyclohexane. Subsequently, 0.3 parts of a defoaming agent was added to the precursor composition, and nitrogen was blown in at a flow rate of 6 min / L while maintaining the temperature at 90°C for 15 hours to remove the cyclohexane from the precursor particles.

[0388] The obtained precursor particles were heated at 40° C. for 24 hours in an atmospheric pressure dryer to completely remove moisture, thereby obtaining resin particles of Comparative Example II-3. Scanning electron microscopic observation revealed that these resin particles were damaged and irregular in shape.

[0389] [Comparative Example II-4]

[0390] Resin pellets of Comparative Example II-4 were obtained by the same manufacturing method as in Example II-1, except that the materials and addition amounts shown in Table II-1 were used in the "(1) Mixed Liquid Preparation Step" of Example II-1. The volatile organic compound content in these resin pellets was 55% by mass, confirming that a large amount of hydrocarbon solvent remained in the resin pellets. Furthermore, the true density of these resin pellets could not be measured. Scanning electron microscopic observation confirmed that these resin pellets were spherical.

[0391] [Comparative Example II-5]

[0392] First, the following materials (a2), (α1), (α2), (c), and (e2) are mixed, and the resulting mixture is used as an oil phase.

[0393] (a2) 5 parts of methyl methacrylate

[0394] (α1) 60 parts of acrylonitrile

[0395] (α2) 35 parts of methacrylonitrile

[0396] (c) 5 parts of azobisisobutyronitrile

[0397] (e2) 30 parts of isopentane

[0398] Next, 200 parts of (y) colloidal silica dispersion (average particle size 5 nm, colloidal silica effective concentration 20% by mass) were added to 600 parts of (g) ion-exchanged water, and the resulting mixture was used as the aqueous phase.

[0399] The aqueous phase and the oil phase are mixed to prepare a mixed solution.

[0400] The mixed solution was stirred at 4000 rpm for 1 minute using a disperser (manufactured by PRIMIX, trade name: HOMOMIXER) to suspend the mixture, and the obtained suspension was stirred at 60° C. for 10 hours to carry out a polymerization reaction.

[0401] The suspension after the polymerization reaction was filtered, and the obtained solid content was dried in a dryer at 40° C. to obtain thermally expandable microcapsules.

[0402] 100 parts of the obtained heat-expandable microcapsules were heat-treated at 180° C. for 3 minutes in a gas phase using a dryer to obtain resin particles (hollow resin particles) of Comparative Example II-5.

[0403] II-2. Measurement and evaluation of resin particles

[0404] The following measurements and evaluations were performed on each of the resin pellets of Examples II-1 to II-4 and Comparative Examples II-1 to II-5. The details are as follows.

[0405] (1) Determination of the number average particle size of resin particles and calculation of the coefficient of variation

[0406] The particle diameter of each resin particle was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name: SALD-2000), and the number average value thereof was calculated. The obtained value was defined as the number average particle diameter of the resin particles.

[0407] The coefficient of variation is a value obtained by dividing the standard deviation of the number-based particle diameters obtained by the above-mentioned measurement by the number average particle diameter.

[0408] (2) Observation of particle shape

[0409] Fig. 4A is a SEM image of the hollow resin particles of Example II-1. Fig. 4B is a SEM image of a cross section of the hollow resin particles of Example II-1.

[0410] The SEM observation conditions are as follows.

[0411] Scanning electron microscope:

[0412] Made by JEOL, Inc., Model: JSM-7610F (Figure 4A)

[0413] Made by Hitachi, Ltd., Model: S-4700 (Figure 4B)

[0414] Accelerating voltage: 5.0 kV (Figure 4A, Figure 4B)

[0415] Magnification: 3000x (Figure 4A), 2500x (Figure 4B)

[0416] From these figures, it can be confirmed that the particles of Example II-1 are hollow inside and that, despite being hollow inside, they are not damaged and maintain a spherical shape.

[0417] (3) Measurement of the density of resin particles and calculation of the porosity

[0418] a. Determination of apparent density of resin particles

[0419] First, in the capacity of 100cm 3 Fill the volumetric flask to about 30 cm 3 The resin particles are added to the volumetric flask and the mass of the filled resin particles is accurately weighed. Next, the volumetric flask filled with the resin particles is accurately filled with isopropyl alcohol up to the standard line, taking care not to introduce bubbles. The mass of the isopropyl alcohol added to the volumetric flask is accurately weighed and the apparent density D1 (g / cm2) of the resin particles is calculated based on the following formula (II): 3 ).

[0420] Formula (II)

[0421] Apparent density D1 = [mass of resin pellets] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0422] b. Determination of true density of resin particles

[0423] After the resin particles are crushed in advance, the 3 A volumetric flask is filled with about 10 g of crushed resin pellets, and the mass of the crushed pellets is accurately weighed.

[0424] Then, isopropyl alcohol was added to the volumetric flask in the same manner as in the measurement of the apparent density. The mass of the isopropyl alcohol was accurately weighed and the true density D0 (g / cm2) of the resin pellets was calculated based on the following formula (III): 3 ).

[0425] Formula (III)

[0426] True density D0 = [mass of crushed resin pellets] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0427] c. Calculation of void ratio

[0428] The void ratio (%) of the hollow resin particles can be calculated from the apparent density D1 and true density D0 of the hollow resin particles using the following formula (I).

[0429] Formula (I)

[0430] Void ratio (%) = 100 - (apparent density D1 / true density D0) × 100

[0431] (4) Volatile organic compound content in hollow resin particles

[0432] The method for determining the amount of volatile organic compounds contained in hollow resin particles is as follows. About 100 mg of hollow resin particles are added to a 30 mL screw-capped glass bottle and accurately weighed. Next, about 10 g of tetrahydrofuran (THF) is added and accurately weighed. The mixture in the glass bottle is stirred with a stirrer for 1 hour to extract the hydrocarbon solvent remaining inside the particles. After stopping the stirring and allowing the resin components of the hollow resin particles that are insoluble in THF to precipitate, a filter (made by Advantech Co., Ltd., trade name: Membrane Filter 25JP020AN) is mounted on a syringe, the precipitate is filtered to obtain a sample solution, and the sample solution is injected into a gas chromatograph (GC) for analysis. Based on the peak area of ​​GC and a pre-made standard curve, the amount of volatile organic compounds per unit mass of the hollow resin particles (mass %) is calculated. The specific analysis conditions are as follows.

[0433] (Analysis Conditions)

[0434] Apparatus: GC-2010 (manufactured by Shimadzu Corporation)

[0435] Column: DB-5 (manufactured by Agilent Technologies Inc.)

[0436] df=0.25μm 0.25mm ID×30m

[0437] Detector: FID

[0438] Carrier gas: nitrogen (linear velocity: 28.8 cm / s)

[0439] Inlet temperature: 200℃

[0440] Detector temperature: 250°C

[0441] Oven temperature: increase from 40°C to 230°C at a rate of 10°C / min and maintain at 230°C for 2 minutes.

[0442] Injection volume: 2 μL

[0443] (5) Evaluation of heat resistance of resin pellets

[0444] First, the resin pellets were heat-treated by standing for 10 minutes in an electric furnace set at 200°C. Next, the resin pellets were removed from the furnace and their apparent density was measured using the same method as described in "(3) Measurement of Density of Resin Pellets and Calculation of Void Ratio" above.

[0445] The apparent density of the resin particles after heat treatment is defined as D a The apparent density of the resin particles before heat treatment is set as D b , the density change rate d (%) was calculated based on the following formula (IV).

[0446] Formula (IV)

[0447] d={|D a -D b | / D b}×100

[0448] The smaller the density change rate d is, the smaller the influence of the heat treatment on the resin particles is, that is, the higher the heat resistance of the resin particles is.

[0449] The measurement and evaluation results of each resin pellet of Examples II-1 to II-4 and Comparative Examples II-1 to II-5 are shown in Table II-1 below. In Table II-1, "<1" indicates that the amount of volatile organic compounds is less than 1% by mass.

[0450] [Table II-1]

[0451] II-3. Investigation

[0452] Hereinafter, the evaluation results of each resin pellet will be examined with reference to Table II-1.

[0453] Table II-1 shows that the resin particles of Comparative Example II-1 were spherical. However, residual hydrocarbons were as high as 30%, indicating insufficient solvent removal within the particles, and the desired hollow resin particles were not obtained. This is believed to be because the amount of crosslinking monomer added was as high as 65 parts by mass, based on 100 parts by mass of the total mass of at least one monomer selected from the monovinyl monomer and the hydrophilic monomer, and the crosslinking monomer. This resulted in a high degree of crosslinking, making cyclohexane difficult to permeate. The production method of Comparative Example II-1 requires a long time for the solvent removal step, resulting in low productivity.

[0454] According to Table II-1, the resin particles of Comparative Example II-2 were damaged and irregular in shape. This is believed to be because the amount of crosslinking monomer added was as low as 20 parts by mass, based on 100 parts by mass of the total mass of at least one monomer selected from the monovinyl monomer and the hydrophilic monomer, and the crosslinking monomer. This resulted in a low degree of crosslinking, and as a result, the particles lacked the shell strength to withstand the temporary negative pressure applied internally during cyclohexane removal.

[0455] According to Table II-1, the resin particles of Comparative Example II-3 were damaged and irregular in shape. Only resin particles with a porosity as low as 33% were obtained. Therefore, it can be seen that if solid-liquid separation is not performed to remove the cyclohexane contained in the particles in an aqueous medium, the resin particles will be damaged. The reasons for this can be speculated as follows. First, it can be considered that when cyclohexane is to be removed in an aqueous medium, water molecules outside the particles enter the interior of the particles to replace the cyclohexane. In addition, water molecules further fill the free volume of the polymer that constitutes the particle shell. Therefore, it can be considered that the air permeability inside the polymer decreases. As a result, in the subsequent solvent removal step, air equivalent to the amount of water molecules that escaped to the outside of the particles did not enter the interior of the particles. Therefore, the hollow part cannot be maintained and the resin particles are damaged.

[0456] According to Table II-1, the resin particles of Comparative Example II-4 were spherical. However, the amount of volatile organic compounds was as high as 55% by mass, and the solvent removal inside the particles was insufficient, failing to produce the desired hollow resin particles. This is believed to be due to the high degree of crosslinking, which hindered the permeation of cyclohexane, as only crosslinkable monomers were used. The production method of Comparative Example II-4 exhibits low productivity due to the long solvent removal step.

[0457] According to Table II-1, the density change rate d of the resin pellets of Comparative Example II-5 after heat treatment was 87%, the highest among the resin pellets tested in this experiment. This indicates that, even when no crosslinking monomer is used and acrylonitrile and methacrylonitrile, which together account for 95% by mass of the total monomers, heat treatment leads to a sharp decrease in the porosity of the resin pellets. This is presumably due to the lack of a crosslinking monomer that imparts heat resistance to the shell of the resin pellets, and the use of large amounts of heat-sensitive acrylonitrile and methacrylonitrile instead, resulting in poor heat resistance in the resulting resin pellets.

[0458] On the other hand, according to Table II-1, the hollow resin particles of Examples II-1 to II-4 have an amount of volatile organic compounds as low as less than 1% by mass, are spherical, have a porosity as high as 75% or more, and have a density change rate d after heat treatment as low as less than 5%.

[0459] Therefore, it can be proved that by using the above-mentioned materials, preparing a mixed liquid, a suspension, and a precursor composition in sequence, and after solid-liquid separation of the obtained precursor composition, removing the hydrocarbon solvent contained in the precursor particles, hollow resin particles with a higher porosity than the existing technology and excellent heat resistance can be produced with high productivity.

[0460] Description of Reference Numerals

[0461] 1: Water-based medium;

[0462] 2: Low polarity materials;

[0463] 3: Suspension stabilizer;

[0464] 4: Monomer composition;

[0465] 4a: Monomer dispersed in aqueous medium;

[0466] 5: Oil-soluble polymerization initiator;

[0467] 6: Shell;

[0468] 7: hydrocarbon solvents;

[0469] 8: hollow part;

[0470] 10: micelles;

[0471] 13: Grease;

[0472] 14: Shell defect;

[0473] 20: precursor particles;

[0474] 51: Aqueous medium;

[0475] 52: surfactant;

[0476] 53: Monomer composition;

[0477] 53a: monomer dissolved into aqueous medium;

[0478] 54: water-soluble polymerization initiator;

[0479] 60: micelles;

[0480] 60a: micelle precursor;

[0481] 61: core resin particles;

[0482] 62: shell;

[0483] 63: hollow core;

[0484] 64: hollow part;

[0485] 100A: latex particles with a hollow portion;

[0486] 100B: latex;

[0487] 100C: hollow resin particles;

[0488] 200B: core-shell particles;

[0489] 200C: hollow particles.

Claims

1. A method for producing hollow resin particles, characterized in that: The following steps are included: a step of preparing a mixed solution comprising a monovinyl monomer, an acrylic hydrophilic monomer, a crosslinking monomer, an oil-soluble polymerization initiator, a hydrocarbon solvent, a suspension stabilizer, and an aqueous medium, wherein the monovinyl monomer is at least one acrylic monovinyl monomer selected from acrylates and methacrylates, the acrylic hydrophilic monomer is at least one acrylic hydrophilic monomer selected from acrylic acid and methacrylic acid, and the crosslinking monomer is at least one selected from divinylbenzene and ethylene glycol di(meth)acrylate, and wherein the content of the crosslinking monomer is 25 to 59 parts by mass based on 100 parts by mass of the total mass of the monovinyl monomer, the acrylic hydrophilic monomer, and the crosslinking monomer, and the total mass ratio of the acrylic hydrophilic monomer is 15 to 50% by mass based on 100% by mass of the total mass of the monovinyl monomer and the acrylic hydrophilic monomer; a step of preparing a suspension in which monomer droplets containing a hydrocarbon solvent are dispersed in an aqueous medium by suspending the mixed liquid; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion and enclosing a hydrocarbon-based solvent; a step of obtaining the precursor particles by subjecting the precursor composition to solid-liquid separation; as well as A step of obtaining hollow resin particles by removing the hydrocarbon solvent contained in the precursor particles in a gas phase.

2. The manufacturing method according to claim 1 or 2, characterized in that: The method for separating the precursor composition into solid and liquid is centrifugation or filtration.

3. The manufacturing method according to claim 1 or 2, characterized in that The process of preparing the mixed liquid is a process of mixing an oil phase and an aqueous phase. The oil phase comprises the monovinyl monomer, the acrylic hydrophilic monomer, the crosslinking monomer, the oil-soluble polymerization initiator, and the hydrocarbon solvent, wherein the content of the crosslinking monomer is 25 to 59 parts by mass when the total mass of the monovinyl monomer, the acrylic hydrophilic monomer, and the crosslinking monomer is taken as 100 parts by mass, and the total mass ratio of the acrylic hydrophilic monomer is 15 to 50 parts by mass when the total mass of the monovinyl monomer and the acrylic hydrophilic monomer is taken as 100% by mass. The aqueous phase includes the suspension stabilizer and an aqueous medium.

4. The manufacturing method according to claim 1 or 2, characterized in that: At 20° C., the hydrocarbon solvent has a relative dielectric constant of 3 or less.

5. The manufacturing method according to claim 1 or 2, characterized in that: The hydrocarbon solvent is a hydrocarbon compound having 5 to 7 carbon atoms.

6. The manufacturing method according to claim 1 or 2, characterized in that: The hydrocarbon solvent is at least 200 parts by mass based on 100 parts by mass of the total mass of the monovinyl monomer, the acrylic hydrophilic monomer, and the crosslinking monomer.

7. The manufacturing method according to claim 1 or 2, characterized in that: The obtained hollow resin particles have a number average particle size of 0.1 to 10 μm.

8. The manufacturing method according to claim 1 or 2, characterized in that: The obtained hollow resin particles have a porosity of 70 to 99%.

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