Method for producing hollow resin particles

Abstract

Provided is a method for producing hollow resin particles, in which the residual quantity of a hydrocarbon-based solvent temporarily retained inside the particles in a production process is reduced, and damage is suppressed. A method for producing hollow resin particles, characterized in having: a step for preparing a mixture that contains polymerizable monomers, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step for preparing a suspension in which the mixture is suspended; a step for subjecting the suspension to polymerization to prepare a precursor composition that contains precursor particles, which have hollow sections and in which the hydrocarbon-based solvent is included in the hollow sections; and a step for removing the hydrocarbon-based solvent included in the precursor particles, the polymerizable monomers containing crosslinkable monomers in a ratio of 40-100 mass%, and the step for removing the hydrocarbon-based solvent being performed by a specific method.

Description

[Technical field]

[0001] The present disclosure relates to a method for producing hollow resin particles. More specifically, the present disclosure relates to a method for producing hollow resin particles with a reduced amount of residual non-reactive hydrocarbon solvent once retained inside the particles during the production process. [Background technology]

[0002] Hollow resin particles produced by polymerizing a polymerizable monomer are particles with a cavity inside the particle, and can scatter light well and reduce light transmittance compared to solid particles whose insides are substantially filled with resin. Therefore, hollow resin particles are widely used as organic pigments or masking agents with excellent optical properties such as opacity and whiteness in water-based paints, paper coating compositions, etc., and are also used as additives for molded bodies such as light reflectors, heat insulating materials, and sound insulating materials.

[0003] Patent Document 1 discloses a method for producing hollow polymer particles having a single-layer shell and a large porosity in a short process and by a simple method, in which a crosslinkable monomer or a mixture of a crosslinkable monomer and a monofunctional monomer, an initiator, and a poorly water-soluble solvent are dispersed in an aqueous solution of a dispersion stabilizer, and suspension polymerization is performed. Patent Document 1 discloses a method for removing the solvent present in the hollow portion, in which hollow polymer particles in the form of a suspension or powder are dried under conditions of a temperature of 20 to 300°C and a pressure of about 1 to 100,000 Pa, natural evaporation, reduced pressure treatment, etc. In the examples of Patent Document 1, hollow polymer particles are isolated and dried under conditions of a temperature of about 70°C and a pressure of about 100,000 Pa (atmospheric pressure), to evaporate the hexadecane (boiling point 287°C) in the core portion.

[0004] Patent Document 2 discloses a method for producing hollow resin particles having high porosity and sustained release properties due to the pores formed in the shell, in which a mixed solution containing a polyfunctional monomer and a non-reactive solvent is dispersed in an aqueous solution, and then the polyfunctional monomer is polymerized. Patent Document 2 only discloses a method for removing the non-reactive organic solvent in the hollow resin particles, in which the hollow resin particles are heated at the boiling point T of the non-reactive organic solvent ±10°C.

[0005] On the other hand, Patent Document 3 describes a method for producing hollow resin particles by heating and expanding a thermally expandable microcapsule, in which a volatile liquid and / or a sublimable solid is encapsulated as an expansion agent in a polymer shell made of a thermoplastic polymer, and the heat transfer area / effective volume is 10 m. -1 As described above, a method for continuously supplying and discharging to and from an indirect heating type agitation dryer is disclosed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-80503 A [Patent Document 2] JP 2016-190980 A [Patent Document 3] JP 2007-191694 A Summary of the Invention [Problem to be solved by the invention]

[0007] In a production method for obtaining hollow resin particles by polymerizing a polymerizable monomer in an aqueous medium by a suspension polymerization method, a method of drying hollow resin particles at a temperature about the boiling point of the organic solvent or lower has been conventionally adopted as a method for removing the poorly water-soluble organic solvent contained in the hollow resin particles, as disclosed in Patent Documents 1 and 2. However, the present inventors have found that when the proportion of a crosslinkable monomer is increased as a polymerizable monomer forming the shell of the hollow resin particles in order to increase the strength of the shell, a large amount of organic solvent may remain inside the hollow resin particles even if the hollow resin particles are dried by a conventional method.

[0008] The present disclosure has been made in consideration of the above-mentioned situation, and an object of the present disclosure is to provide a method for producing hollow resin particles, which can reduce the amount of residual hydrocarbon-based solvent that is retained inside the particles during the production process and can obtain hollow resin particles that are suppressed from being broken. [Means for solving the problem]

[0009] A first method for producing hollow resin particles according to the present disclosure includes: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; obtaining the precursor particles separated from the aqueous medium by subjecting the precursor composition to solid-liquid separation; and removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles separated from the aqueous medium, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The present invention is characterized in that the heating and drying temperature T0 (°C) in the step of removing the hydrocarbon-based solvent satisfies T1+70≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon-based solvent and T2 (°C) is the thermal decomposition starting temperature of the precursor particles.

[0010] In the production method according to the first aspect of the present disclosure, the boiling point T1 of the hydrocarbon solvent is preferably 70 to 90°C. In the production method according to the first aspect of the present disclosure, the hollow resin particles preferably have a porosity of 50 to 95%. In the production method of the first present disclosure, the pressure during the heat drying in the step of removing the hydrocarbon-based solvent is preferably 0 to 101.3 kPa. In the production method according to the first aspect of the present disclosure, the hydrocarbon solvent is preferably a hydrocarbon solvent having 4 to 7 carbon atoms. In the production method according to the first aspect of the present disclosure, the precursor particles used in the step of removing the hydrocarbon-based solvent preferably have a water content of 50% or less. In the first manufacturing method of the present disclosure, the step of removing the hydrocarbon-based solvent is preferably a step of heating and drying the precursor particles separated from the aqueous medium together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in a stirring vessel while stirring, thereby coating the surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles.

[0011] A second method for producing hollow resin particles according to the present disclosure includes: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The step of removing the hydrocarbon-based solvent is characterized in that the hydrocarbon-based solvent contained in the precursor particles is removed by heating and drying the precursor particles while stirring them in a vertical stirring vessel equipped with a shaft extending in the direction of gravity and a stirring blade.

[0012] In the production method according to the second aspect of the present disclosure, the hollow resin particles preferably have a porosity of 50 to 95%. In the second manufacturing method of the present disclosure, it is preferable that the heating and drying temperature T0 (°C) in the step of removing the hydrocarbon-based solvent satisfies T1≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon-based solvent and T2 (°C) is the thermal decomposition onset temperature of the precursor particles. In the production method according to the second aspect of the present disclosure, the stirring vessel used in the step of removing the hydrocarbon solvent is preferably cylindrical or conical. In the second production method of the present disclosure, it is preferable to further include, after the step of preparing the precursor composition and before the step of removing the hydrocarbon-based solvent, a step of subjecting the precursor composition to solid-liquid separation to obtain the precursor particles separated from the aqueous medium. In the second manufacturing method of the present disclosure, the step of removing the hydrocarbon-based solvent is preferably a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in the stirring vessel while stirring, thereby coating the surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles.

[0013] A third method for producing hollow resin particles according to the present disclosure includes: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The method is characterized in that the step of removing the hydrocarbon-based solvent is a step of removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles while stirring them in a horizontal stirring vessel equipped with a horizontally extending shaft and stirring blades.

[0014] In the production method according to the third aspect of the present disclosure, the hollow resin particles preferably have a porosity of 50 to 95%. In the third manufacturing method of the present disclosure, it is preferable that the heating and drying temperature T0 (°C) in the step of removing the hydrocarbon-based solvent satisfies T1≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon-based solvent and T2 (°C) is the thermal decomposition onset temperature of the precursor particles. In the third manufacturing method of the present disclosure, the step of removing the hydrocarbon solvent is preferably carried out using a continuous dryer equipped with a stirring vessel of a multi-shaft horizontal stirring type having a plurality of shafts extending horizontally and stirring blades. In the third production method of the present disclosure, it is preferable to further include, after the step of preparing the precursor composition and before the step of removing the hydrocarbon-based solvent, a step of subjecting the precursor composition to solid-liquid separation to obtain the precursor particles separated from the aqueous medium. In the third manufacturing method of the present disclosure, the step of removing the hydrocarbon-based solvent is preferably a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in the stirring vessel while stirring, thereby coating the surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles. Effect of the Invention

[0015] According to the manufacturing method of the present disclosure as described above, it is possible to manufacture hollow resin particles in which the amount of residual hydrocarbon solvent once retained inside the particles during the manufacturing process is reduced and breakage is suppressed. [Brief description of the drawings]

[0016] [Figure 1] 1A to 1C are diagrams illustrating an example of a manufacturing method according to the present disclosure. [Diagram 2] FIG. 1 is a schematic diagram showing one embodiment of a suspension used in the manufacturing method of the present disclosure. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing an example of a vertical agitator dryer used in the production method of the second present disclosure. [Figure 4] FIG. 2 is a schematic cross-sectional view showing another example of a vertical agitator dryer used in the production method of the second present disclosure. [Diagram 5] FIG. 11 is a schematic cross-sectional view showing an example of a horizontal agitator dryer used in the production method of the third present disclosure. [Figure 6] 6 is a cross-sectional view of the horizontal agitation dryer shown in FIG. 5 along the line AA. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] In the present disclosure, a particle having a shell and a hollow portion surrounded by the shell and filled with a hydrocarbon solvent is considered to be an intermediate of the hollow resin particle obtained by the manufacturing method of the present disclosure, and is referred to as a precursor particle. In the present disclosure, a composition containing the precursor particle is referred to as a precursor composition. In addition, in the present disclosure, the use of "to" in a numerical range means that the numerical values ​​before and after it each independently represent a lower limit and an upper limit. In the present disclosure, "productivity" refers to the weight (kg) of the obtained hollow resin particles divided by the heat drying time (h) in the solvent removal step, and then the effective volume (m 3 ) divided by (kg / (h m 3 For hollow resin particles in which the amount of residual hydrocarbon solvent has been sufficiently reduced, this value (kg / (h m 3 The larger the ratio, the higher the productivity. In the present disclosure, the vertical stirring method is a stirring method performed by a stirring vessel equipped with a shaft extending in the direction of gravity and a stirring blade, and the horizontal stirring method is a stirring method performed by a stirring vessel equipped with a shaft extending in the horizontal direction and a stirring blade. Here, the shaft extending in the direction of gravity and the shaft extending in the horizontal direction may be slightly inclined, for example, within ±5° with respect to the direction of gravity and the horizontal direction, respectively. In this disclosure, a dryer that performs drying in a stirring vessel with a vertical stirring method may be referred to as a vertical stirring dryer, and a dryer that performs drying in a stirring vessel with a horizontal stirring method may be referred to as a horizontal stirring dryer.

[0018] I-1. First method for producing hollow resin particles according to the present disclosure A method for producing hollow resin particles according to a first aspect of the present disclosure includes the steps of: preparing a mixed solution containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; obtaining the precursor particles separated from the aqueous medium by subjecting the precursor composition to solid-liquid separation; and removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles separated from the aqueous medium, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The present invention is characterized in that the heating and drying temperature T0 (°C) in the step of removing the hydrocarbon-based solvent satisfies T1+70≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon-based solvent and T2 (°C) is the thermal decomposition starting temperature of the precursor particles.

[0019] In the first manufacturing method of the present disclosure, a mixture containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium is suspended, whereby the polymerizable monomer and the hydrocarbon solvent are phase-separated, and a suspension is prepared in which droplets having a distribution structure in which the polymerizable monomer is unevenly distributed on the surface side and the hydrocarbon solvent is unevenly distributed in the center are dispersed in the aqueous medium. The manufacturing method of the first disclosure follows a basic technique of subjecting such a suspension to a polymerization reaction to harden the surfaces of the droplets, thereby forming particles having a shell made of resin and a hollow portion filled with the hydrocarbon solvent. The hollow resin particles obtained by such a basic technique are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell. The hollow portion is a hollow space that is clearly distinguished from the shell formed by the resin material. The shell of the hollow resin particles may have a porous structure, and in that case, the hollow portion has a size that is clearly distinguishable from the numerous minute spaces uniformly dispersed within the porous structure. In the hollow resin particles manufactured according to the basic technology as described above, the hollow portion is once filled with a hydrocarbon-based solvent in the manufacturing process. However, for example, when the hollow resin particles are mixed with other materials such as resin and used, if the hollow resin particles contain a hydrocarbon-based solvent, the hydrocarbon-based solvent in the hollow resin particles may volatilize and cause foaming or fire. In addition, compared with hollow resin particles with a low content of hydrocarbon-based solvent, hollow resin particles with a high content of hydrocarbon-based solvent have a high specific gravity, so there is also a problem that the hollow resin particles are less effective as a lightweight material. Therefore, hollow resin particles from which the hydrocarbon-based solvent has been sufficiently removed are required. On the other hand, hollow resin particles produced by setting the ratio of crosslinkable monomer in polymerizable monomer to 40 to 100% by mass have a dense covalent bond network in the shell, resulting in the formation of a strong shell. In such hollow resin particles, the hydrocarbon solvent present in the hollow portion does not easily permeate the shell, making it difficult to sufficiently remove the hydrocarbon solvent by conventional methods. In contrast, in the first manufacturing method of the present disclosure, the precursor particles containing the hydrocarbon-based solvent are first separated from the aqueous medium, and then heated and dried at a temperature that is equal to or higher than the boiling point T1 (°C) of the hydrocarbon solvent + 70°C and equal to or lower than the thermal decomposition starting temperature T2 - 5°C of the precursor particles, thereby making it possible to sufficiently remove the encapsulated hydrocarbon-based solvent while suppressing damage to the particles.

[0020] The effect of reducing the amount of residual hydrocarbon solvent in the hollow resin particles by the first manufacturing method of the present disclosure is particularly effective when producing hollow resin particles having a shell that has no communicating pores and no shell defects. Generally, hollow resin particles include those in which the shell does not have a through hole connecting the hollow part to the outside space of the particle, and the hollow part is isolated from the outside of the particle by the shell, and those in which the shell has one or more through holes, and the hollow part is connected to the outside of the particle through the through hole. The size of the through hole of the hollow resin particle is appropriately adjusted according to the size of the hollow resin particle, but is usually 10 to 500 nm in diameter. In addition, in the present disclosure, the shell defect of the hollow resin particle means a crack-like defect that is extremely large compared to the size of the particle. Although it depends on the size of the hollow resin particle, a crack having a length of 1 μm or more is generally recognized as a shell defect because it significantly reduces the strength of the hollow resin particle. When the shell of a hollow resin particle has communicating holes or shell defects, there is a problem that the hollow resin particle is easily crushed when kneaded with other materials such as resin, and the other materials are easily allowed to penetrate into the hollow resin particle through the communicating holes or shell defects. Therefore, there is a demand for hollow resin particles having a shell that does not have communicating holes or shell defects. In the present disclosure, the shell being free of interconnecting holes and shell defects means that the shell is substantially free of interconnecting holes and shell defects. When 100 hollow resin particles are observed under SEM, if 5 or fewer hollow resin particles have interconnecting holes or shell defects, the shell is deemed to have no interconnecting holes or shell defects. Hollow resin particles having a shell without interconnecting holes and shell defects can be produced, for example, by using a bifunctional crosslinking monomer as the crosslinking monomer in the polymerizable monomer forming the shell in the first production method of the present disclosure. It is presumed that the bifunctional crosslinking monomer in the polymerizable monomer prevents the polymerization rate of the polymerizable monomer in the polymerization step from becoming too fast, making it difficult for the shell to become distorted, and therefore difficult for interconnecting holes and shell defects to be formed.

[0021] The manufacturing method of the first disclosure includes the following steps (1) to (5), and may further include other steps, but is not limited to these. In addition, in the manufacturing method described in the present disclosure, two or more steps of each step may be performed simultaneously as one step, or the order may be changed, as long as it is technically possible. For example, the preparation of the mixture and the preparation of the suspension may be performed simultaneously in one step, such as suspending while simultaneously adding the materials for preparing the mixture. (1) Mixed liquid preparation process A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium. (2) Suspension process A step of preparing a suspension in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrocarbon solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the mixed liquid. (3) Polymerization process A step of subjecting the suspension to a polymerization reaction to prepare a precursor composition containing precursor particles having hollow portions and containing a hydrocarbon-based solvent in the hollow portions. (4) Solid-liquid separation process A step of subjecting the precursor composition to solid-liquid separation to obtain precursor particles separated from the aqueous medium; and (5) Solvent removal process A step of removing the hydrocarbon solvent contained in the precursor particles by heating and drying the precursor particles separated from the aqueous medium.

[0022] FIG. 1 is a schematic diagram showing an example of the manufacturing method of the first disclosure. In FIG. 1, (1) to (5) correspond to the steps (1) to (5). The white arrows between the drawings indicate the order of the steps. Note that FIG. 1 is merely a schematic diagram for explanation, and the manufacturing method of the first disclosure is not limited to those shown in the drawing. Furthermore, the structure, dimensions, and shape of the materials used in each manufacturing method of the present disclosure are not limited to the structure, dimensions, and shape of the various materials in these drawings. 1(1) is a cross-sectional schematic diagram showing one embodiment of the mixed liquid in the mixed liquid preparation step. As shown in this figure, the mixed liquid contains 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 that has low polarity and is difficult to mix with the aqueous medium 1. In the present disclosure, the low-polarity material 2 contains a polymerizable monomer, a hydrocarbon solvent, and a polymerization initiator. FIG. 1 (2) is a cross-sectional schematic diagram showing one embodiment of a suspension in a suspension preparation step. The suspension includes an aqueous medium 1 and droplets 10 of a polymerizable monomer composition dispersed in the aqueous medium 1. The droplets 10 of the polymerizable monomer composition include a polymerizable monomer, a hydrocarbon-based solvent, and a polymerization initiator, but the distribution of each material in the droplets is not uniform. The droplets 10 of the polymerizable monomer composition have a structure in which the hydrocarbon-based solvent 4a and the material other than the hydrocarbon-based solvent 4b including the polymerizable monomer and the polymerization initiator are phase-separated, the hydrocarbon-based solvent 4a is unevenly distributed in the center, and the material other than the hydrocarbon-based solvent 4b is unevenly distributed on the surface side. 1(3) is a cross-sectional schematic diagram showing one embodiment of the precursor composition after the polymerization step. The precursor composition contains an aqueous medium 1 and precursor particles 20 dispersed in the aqueous medium 1. A shell 6 forming the outer surface of the precursor particle 20 is formed by polymerization of the polymerizable monomer in the droplet 10 of the polymerizable monomer composition. The hollow portion inside the shell 6 is filled with a hydrocarbon solvent 4a. Fig. 1(4) is a schematic cross-sectional view showing one embodiment of the precursor particles after the solid-liquid separation step. The precursor particles after the solid-liquid separation step are precursor particles 20 separated from the aqueous medium 1 in the precursor composition shown in Fig. 1(3). Fig. 1 (5) is a cross-sectional schematic diagram showing one embodiment of hollow resin particles after the solvent removal step. The hollow resin particles 100 after the solvent removal step are particles obtained by removing the hydrocarbon solvent 4a contained in the precursor particles 20 after the solid-liquid separation step shown in Fig. 1 (4), and have a hollow portion 7 inside the shell 6. The steps (1) to (5) included in the production method of the first disclosure, as well as other steps that the production method of the first disclosure may further include, will be described below in order.

[0023] (1) Mixed liquid preparation process This step is a step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium. The mixed liquid may further contain other materials such as a suspension stabilizer.

[0024] [Polymerizable monomer] The polymerizable monomer is a compound having a polymerizable functional group, and a compound having an ethylenically unsaturated bond as the polymerizable functional group is generally used. In the present disclosure, the polymerizable monomer includes at least a crosslinkable monomer, and may further include a non-crosslinkable monomer. Here, the non-crosslinkable monomer is a polymerizable monomer having only one polymerizable functional group, and the crosslinkable monomer is a polymerizable monomer having two or more polymerizable functional groups and forming a crosslinked bond in the resin by a polymerization reaction. Since the crosslinkable monomer has a plurality of polymerizable functional groups, by including a crosslinkable monomer as the polymerizable monomer, the monomers can be linked to each other in the polymerization process, and the crosslink density of the shell can be increased.

[0025] Examples of the crosslinkable monomer include difunctional crosslinkable monomers such as divinylbenzene, divinyldiphenyl, divinylnaphthalene, diallyl phthalate, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate; and trifunctional or higher crosslinkable monomers such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Among these, bifunctional crosslinkable monomers are preferred, and divinylbenzene, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate are more preferred, with ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate being even more preferred, since they are less likely to form communicating holes and shell defects in the shell. These crosslinkable monomers can be used alone or in combination of two or more kinds. In the present disclosure, (meth)acrylate means either acrylate or methacrylate, and (meth)acrylic means either acrylic or methacrylic.

[0026] As the non-crosslinkable monomer, a monovinyl monomer is preferably used. A monovinyl monomer is a compound having one polymerizable vinyl functional group. Examples of the monovinyl monomer include (meth)acrylic monovinyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and (meth)acrylic acid; aromatic vinyl monomers such as styrene, vinyl toluene, α-methylstyrene, p-methylstyrene, and halogenated styrene; monoolefin monomers such as ethylene, propylene, and butylene; (meth)acrylamide monomers and derivatives thereof such as (meth)acrylamide, N-methylol (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; diene monomers such as butadiene and isoprene; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; and vinylpyridine monomers. As the monovinyl monomer, a (meth)acrylic monovinyl monomer is preferable, since the polymerization reaction is likely to be stable and hollow resin particles having high heat resistance can be obtained, and at least one selected from (meth)acrylic acid, butyl acrylate, and methyl methacrylate is more preferable. These non-crosslinkable monomers can be used alone or in combination of two or more kinds.

[0027] The polymerizable monomer used in the present disclosure contains the crosslinkable monomer in a ratio of 40 to 100% by mass relative to 100% by mass of the total amount of the polymerizable monomers, which is the total amount of the crosslinkable monomer and the non-crosslinkable monomer. Since the content ratio of the crosslinkable monomer is equal to or greater than the lower limit, the content ratio of the crosslinkable monomer unit in the shell of the hollow resin particle is sufficiently high, and a covalent bond network is densely spread throughout the shell, so that the obtained hollow resin particle has excellent strength, is difficult to be crushed, and is difficult to be deformed by heat or the like applied from the outside. The content ratio of the crosslinkable monomer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more from the viewpoint of improving the strength of the hollow resin particle, while the content ratio of the crosslinkable monomer is preferably 90% by mass or less, more preferably 80% by mass or less from the viewpoint of suppressing the occurrence of continuous holes and shell defects in the shell.

[0028] The polymerizable monomer used in the present disclosure may contain the non-crosslinkable monomer in a ratio of 60% by mass or less. When the polymerizable monomer contains the non-crosslinkable monomer, the occurrence of interconnected pores and shell defects is easily suppressed. When the polymerizable monomer contains the non-crosslinkable monomer, the non-crosslinkable monomer is preferably contained in a proportion of 10% by mass or more, more preferably 20% by mass or more, relative to 100% by mass of the total amount of the polymerizable monomers, which is the combined amount of the crosslinkable monomer and the non-crosslinkable monomer. When the content ratio of the non-crosslinkable monomer is equal to or more than the lower limit, the occurrence of shell interconnecting holes and shell defects is more easily suppressed. On the other hand, in order to improve the strength and heat resistance of the hollow resin particles by sufficiently containing the crosslinkable monomer, the content ratio of the non-crosslinkable monomer is preferably 50% by mass or less, more preferably 40% by mass or less.

[0029] The content of the polymerizable monomer (total amount of non-crosslinkable monomer and crosslinkable monomer) in the mixed liquid is not particularly limited, but from the viewpoint of the balance between the porosity, particle size, and mechanical strength of the hollow resin particles, and from the viewpoint of reducing the amount of residual hydrocarbon solvent, it is usually 15 to 55 mass%, more preferably 25 to 40 mass%, relative to 100 mass% of the total mass of the components in the mixed liquid excluding the aqueous medium.

[0030] [Hydrocarbon solvents] In the present disclosure, a hydrocarbon-based solvent is used as the non-polymerizable and poorly water-soluble organic solvent, which acts as a spacer material that forms a hollow space inside the particles. The type of the hydrocarbon solvent is not particularly limited. Examples of the hydrocarbon solvent include saturated hydrocarbon solvents such as butane, pentane, normal hexane, cyclohexane, heptane, and octane, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and relatively volatile solvents such as carbon disulfide and carbon tetrachloride.

[0031] The hydrocarbon solvent preferably contains a saturated hydrocarbon solvent in a total amount of 100% by mass. This allows sufficient phase separation to occur in the droplets of the polymerizable monomer composition, making it easy to obtain hollow resin particles having only one hollow portion, and suppresses the generation of porous particles. The ratio of the saturated hydrocarbon solvent is preferably 60% by mass or more, more preferably 80% by mass or more, in order to further suppress the generation of porous particles and to make the hollow portions of each hollow resin particle uniform.

[0032] Moreover, the hydrocarbon solvent is preferably a hydrocarbon solvent having 4 to 7 carbon atoms. A hydrocarbon compound having 4 to 7 carbon atoms is 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, a hydrocarbon solvent having 5 or 6 carbon atoms is particularly preferred.

[0033] In addition, although not particularly limited, the hydrocarbon solvent preferably has a boiling point of 90° C. or less, more preferably 85° C. or less, in that it is easily removed in the solvent removal step described below, while the hydrocarbon solvent preferably has a boiling point of 70° C. or more, more preferably 75° C. or more, in that it is easily encapsulated in the precursor particles. In the present disclosure, when the hydrocarbon-based solvent is a mixed solvent containing multiple types of hydrocarbon-based solvents and has multiple boiling points, the boiling point of the hydrocarbon-based solvent refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points.

[0034] In addition, the hydrocarbon solvent preferably has a relative dielectric constant of 3 or less at 20°C. The relative dielectric constant is one of the indices that indicate the polarity of a compound. When the relative dielectric constant of the hydrocarbon solvent is sufficiently small, 3 or less, it is considered that phase separation proceeds quickly in the droplets of the polymerizable monomer composition, and hollow portions are easily formed. Examples of solvents with a dielectric constant of 3 or less at 20°C are as follows. The value in parentheses is the dielectric constant value. Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4). For the relative dielectric constant at 20°C, values ​​described in known documents (for example, "Chemical Handbook Basic Edition" edited by the Chemical Society of Japan, revised 4th edition, Maruzen Co., Ltd., published on September 30, 1993, pages II-498 to II-503) and other technical information can be referenced. Examples of methods for measuring the relative dielectric constant at 20°C include a relative dielectric constant test performed in accordance with JISC 2101:1999, Section 23, at a measurement temperature of 20°C.

[0035] The porosity of the hollow resin particles can be adjusted by changing the amount of the hydrocarbon solvent in the mixed solution. In the polymerization step described below, the polymerization reaction proceeds in a state in which the droplets of the polymerizable monomer composition contain the hydrocarbon solvent, so that the porosity of the obtained hollow resin particles tends to increase as the content of the hydrocarbon solvent increases. In the present disclosure, the content of the hydrocarbon-based solvent in the mixed solution is preferably 50 to 500 parts by mass relative to 100 parts by mass of the total mass of the polymerizable monomer, since it is easy to control the particle size of the hollow resin particles, it is easy to increase the porosity while maintaining the strength of the hollow resin particles, and it is easy to reduce the amount of residual hydrocarbon-based solvent in the particles. The content of the hydrocarbon-based solvent in the mixed solution is more preferably 60 to 400 parts by mass, even more preferably 70 to 300 parts by mass, and even more preferably 80 to 200 parts by mass relative to 100 parts by mass of the total mass of the polymerizable monomer.

[0036] [Polymerization initiator] In the present disclosure, it is preferable to use an oil-soluble polymerization initiator as the polymerization initiator. By using an oil-soluble polymerization initiator as the polymerization initiator, the polymerization initiator is incorporated into the inside of droplets of the polymerizable monomer composition in the suspension obtained in the suspension step described below. The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylvaleronitrile), and azobisisobutyronitrile.

[0037] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the total mass of the polymerizable monomers in the mixed liquid. By having the content of the polymerization initiator be 0.1 to 10 parts by mass, the polymerization reaction can be sufficiently progressed, and there is little risk of the polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0038] [Polar resin] In the present disclosure, the mixed liquid may further contain a polar resin. In the present disclosure, the polar resin is selected from the group consisting of polymers containing a repeating unit containing a heteroatom. Specific examples of the polar resin include acrylic resins, polyester resins, and vinyl resins containing heteroatoms. The polar resin may be a homopolymer or copolymer of a heteroatom-containing monomer, or a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer. When the polar resin is a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer, the ratio of the heteroatom-containing monomer unit in 100% by mass of all repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of easy control of the particle size and shell thickness of the hollow resin particles.

[0039] Examples of heteroatom-containing monomers used in polar resins include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, acrylic acid, methacrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, Examples of the monomers include (meth)acrylic monovinyl monomers such as 4-hydroxybutyl acrylate glycidyl ether; aromatic vinyl monomers containing heteroatoms such as halogenated styrene and styrene sulfonic acid; vinyl carboxylate ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine monomers; carboxyl group-containing monomers such as ethylenically unsaturated carboxylic acid monomers such as crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; and epoxy group-containing monomers such as allyl glycidyl ether. These heteroatom-containing monomers may be used alone or in combination of two or more. Examples of heteroatom-free monomers used in polar resins include aromatic vinyl monomers not containing heteroatoms, such as styrene, vinyltoluene, α-methylstyrene, and p-methylstyrene; monoolefin monomers, such as ethylene, propylene, and butylene; and diene monomers, such as butadiene and isoprene. These heteroatom-free monomers can be used alone or in combination of two or more.

[0040] Among them, the polar resin is preferably an acrylic resin in which the total mass of (meth)acrylic monovinyl monomer units is preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 90 mass% or more, of all repeating units constituting the resin (100 mass%), from the viewpoints of high compatibility with the polymerizable monomer and ease of control of the particle size and shell thickness of the hollow resin particles. In particular, it is preferable that the acrylic resin is an acrylic resin in which all repeating units constituting the resin are composed of (meth)acrylic monovinyl monomer units.

[0041] In addition, the polar resin preferably contains a polar group-containing monomer unit containing at least one polar group selected from a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group, in order to easily control the particle size and shell thickness of the hollow resin particles. As the polar group, at least one selected from a carboxyl group and a hydroxyl group is preferable in terms of enabling particle size control with a small amount of addition. Examples of polar group-containing monomers include carboxyl group-containing monomers such as ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid; amino group-containing monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; polyoxyethylene group-containing monomers such as methoxypolyethylene glycol (meth)acrylate; and epoxy group-containing monomers such as glycidyl (meth)acrylate, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether. These polar group-containing monomers can be used alone or in combination of two or more. When the polar resin contains a polar group-containing monomer unit, it is preferable that the polar group is located at the end of the main chain or side chain, or is bonded in a pendant manner to the main chain or side chain, since this makes it easier to control the particle size and shell thickness of the hollow resin particles.

[0042] When the polar resin does not contain the polar group-containing monomer unit, the heteroatom-containing monomer unit contained in the polar resin preferably contains a monomer unit derived from an alkyl(meth)acrylate, from the viewpoints of high compatibility with the polymerizable monomer and ease of control of the particle size and shell thickness of the hollow resin particles, and among these, from the viewpoint of high polarity, it is preferable to contain a monomer unit derived from an alkyl(meth)acrylate, preferably having an alkyl group with 3 or less carbon atoms, more preferably an alkyl group or ethyl group, and even more preferably an alkyl group in which the alkyl group is a methyl group.

[0043] The acrylic resin, which is the polar resin, is preferably a polymer or copolymer of a polymerizable monomer for polar resin containing 50.0% by mass or more of methyl methacrylate when the total mass of the polymerizable monomer for polar resin is taken as 100% by mass, because it has high compatibility with the polymerizable monomer and is easy to control the particle size and shell thickness of the hollow resin particles. In this disclosure, the polymerizable monomer used in the synthesis of the polar resin may be referred to as the polymerizable monomer for polar resin. The acrylic resin, which is the polar resin, is more preferably a copolymer of a polymerizable monomer for a polar resin containing 50.0% by mass or more and 99.9% by mass or less of methyl methacrylate and 0.1% by mass or more and 5.0% by mass or less of the polar group-containing monomer, even more preferably a copolymer of a polymerizable monomer for a polar resin containing 50.0% by mass or more and 99.0% by mass or less of methyl methacrylate and 0.1% by mass or more and 5.0% by mass or less of the polar group-containing monomer, and ...8.0% by mass or less of methyl methacrylate and 0.1% by mass or more and 5.0% by mass or less of the polar group-containing monomer. The copolymer is a copolymer of polymerizable monomers for polar resins, which contains 1.0% by mass or more and 5.0% by mass or less of a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain the polar group, and 0.1% by mass or more and 5.0% by mass or less of the polar group-containing monomer, and is particularly preferably a copolymer of polymerizable monomers for polar resins, which contains 50.0% by mass or more and 98.0% by mass or less of methyl methacrylate, 1.0% by mass or more and 5.0% by mass or less of a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain the polar group, and 0.2% by mass or more and 3.0% by mass or less of the polar group-containing monomer. The (meth)acrylic monovinyl monomer which is different from methyl methacrylate and does not contain a polar group is preferably at least one selected from ethyl acrylate and butyl acrylate, and particularly preferably ethyl acrylate, in terms of being able to control the glass transition temperature. As the polar group-containing monomer, from the viewpoint of compatibility with the polymerizable monomer, a (meth)acrylic monovinyl monomer containing a polar group is preferred, and from the viewpoint of enabling particle size control with a smaller addition amount, a (meth)acrylic monovinyl monomer containing a carboxyl group or a hydroxyl group is more preferred, and (meth)acrylic acid is particularly preferred.

[0044] The polar resin can be obtained, for example, by polymerizing a polymerizable monomer for a polar resin, which contains the heteroatom-containing monomer, by a polymerization method such as solution polymerization or emulsion polymerization. Furthermore, when the polar resin is a copolymer, the copolymer may be any of a random copolymer, a block copolymer, or a graft copolymer, but is preferably a random copolymer. In addition, the polar resin is preferably pulverized as finely as possible in order to improve the solubility.

[0045] The number average molecular weight (Mn) of the polar resin is not particularly limited, but is preferably 3000 to 20000, more preferably 4000 to 17000, and even more preferably 6000 to 15000, in terms of polystyrene measured by gel permeation chromatography (GPC) using tetrahydrofuran. When the number average molecular weight (Mn) of the polar resin is equal to or more than the lower limit, the solubility of the polar resin is improved, and the particle size and shell thickness of the hollow resin particles can be easily controlled, and when it is equal to or less than the upper limit, a decrease in shell strength can be suppressed.

[0046] When the mixed solution contains the polar resin, the content of the polar resin is preferably 0.1 to 10.0 parts by mass, more preferably 0.3 to 8.0 parts by mass, and even more preferably 0.5 to 8.0 parts by mass, relative to 100 parts by mass of the polymerizable monomer. When the content of the polar resin is equal to or more than the lower limit, the particle size and shell thickness of the hollow resin particles can be easily controlled, while when the content is equal to or less than the upper limit, a decrease in shell strength can be suppressed.

[0047] [Suspension stabilizer] In the present disclosure, the mixed liquid preferably contains a suspension stabilizer. The suspension stabilizer is not particularly limited as long as it functions to disperse droplets of the polymerizable monomer composition in the aqueous medium in the suspension step described below. Examples of the suspension stabilizer include surfactants. As the surfactant, any of cationic surfactants, anionic surfactants, and nonionic surfactants can be used, and they can also be used in combination. Among these, anionic surfactants and nonionic surfactants are preferred, and anionic surfactants are more preferred. Examples of the anionic surfactant include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dialkylsulfosuccinate, and formalin condensate salts of naphthalenesulfonic acid. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, and polyoxyethylene sorbitan alkyl ester. Examples of the cationic surfactant include didecyldimethylammonium chloride and stearyltrimethylammonium chloride.

[0048] In addition, a poorly water-soluble inorganic compound may be used as the suspension stabilizer. When the mixed liquid contains the polar resin, it is preferable to use a poorly water-soluble inorganic compound as the suspension stabilizer from the viewpoint of easily controlling the particle size of the hollow resin particles. Examples of poorly water-soluble inorganic compounds include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and ferric hydroxide, and the like. Among them, metal hydroxides are preferred, and magnesium hydroxide is particularly preferred. In the present disclosure, the poorly water-soluble inorganic compound is preferably an inorganic compound having a solubility of 0.5 g or less in 100 g of water.

[0049] The content of the suspension stabilizer is preferably 0.1 to 4 parts by mass, more preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the total mass of the polymerizable monomers in the mixed liquid. When the content of the suspension stabilizer is 0.1 parts by mass or more, droplets of the polymerizable monomer composition are easily formed in the aqueous medium. On the other hand, when the content of the suspension stabilizer is 4 parts by mass or less, a decrease in productivity due to foaming is unlikely to occur in the step of removing the hydrocarbon solvent.

[0050] [Aqueous medium] In the present disclosure, an aqueous medium means a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent. The hydrophilic solvent in the present disclosure is not particularly limited as long as it is sufficiently 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). Among aqueous media, water is preferably used due to its high polarity. When using a mixture of water and a hydrophilic solvent, it is important that the polarity of the entire mixture is not too low from the viewpoint of forming droplets of the polymerizable monomer composition. In this case, for example, the mixture ratio (mass ratio) of water to hydrophilic solvent may be water:hydrophilic solvent=99:1 to 50:50, etc.

[0051] The above-mentioned materials and other materials as necessary are mixed and appropriately stirred to obtain a mixed liquid. In the mixed liquid, the oil phase containing the above-mentioned polymerizable monomer, polymerization initiator, and lipophilic materials such as a hydrocarbon solvent is dispersed in an aqueous phase containing a suspension stabilizer and an aqueous medium with a particle size of about several mm. The dispersion state of these materials in the mixed liquid can be observed with the naked eye depending on the type of material. In the mixed solution preparation step, the mixed solution may be obtained by simply mixing the above-mentioned materials and other materials as necessary and appropriately stirring the mixture. However, in order to make the shell composition more uniform, it is preferable to prepare the oil phase and the aqueous phase separately in advance and mix them to prepare the mixed solution.

[0052] (2) Suspension process The suspension process is a process of preparing a suspension in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrocarbon-based solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the above-mentioned mixed liquid. The method of suspending the polymerizable monomer composition to form droplets is not particularly limited, but may be carried out using a device capable of strong stirring, such as an (in-line type) emulsifying disperser (manufactured by Pacific Machinery Works, product name: Milder) or a high-speed emulsifying disperser (manufactured by Primix Corporation, product name: TK Homomixer MARK II type). In the suspension prepared in the suspending step, droplets of the polymerizable monomer composition containing the above-mentioned polymerizable monomer, polymerization initiator, and lipophilic material such as a hydrocarbon solvent and having a particle size of about 1.0 to 100.0 μm are uniformly dispersed in the aqueous medium. Such droplets of the polymerizable monomer composition are difficult to observe with the naked eye, and can be observed with a known observation device such as an optical microscope. In the suspension step, phase separation occurs in the droplets of the polymerizable monomer composition, and the hydrocarbon solvent having low polarity tends to collect inside the droplets. As a result, the resulting droplets have the hydrocarbon solvent distributed inside and materials other than the hydrocarbon solvent distributed around the periphery.

[0053] Fig. 2 is a schematic diagram showing one embodiment of the suspension in the suspension step. A droplet 10 of the polymerizable monomer composition in Fig. 2 is a schematic diagram showing its cross section. Note that Fig. 2 is merely a schematic diagram, and the suspension in the present disclosure is not necessarily limited to that shown in Fig. 2. 2 shows a state in which droplets 10 of a polymerizable monomer composition and a polymerizable monomer 4c are dispersed in an aqueous medium 1. The droplets 10 are formed by surrounding an oil-soluble polymerizable monomer composition 4 with a suspension stabilizer 3. The polymerizable monomer composition 4 contains a polymerization initiator 5, as well as a polymerizable monomer and a hydrocarbon solvent (none of which are shown). The droplets 10 of the polymerizable monomer composition are minute oil droplets containing the polymerizable monomer composition 4, and the polymerization initiator 5 generates polymerization initiation radicals inside the minute oil droplets. Therefore, precursor particles of the desired particle size can be produced without causing the minute oil droplets to grow too much. In the suspension polymerization shown in Fig. 2, the polymerization initiator 5 is incorporated into the droplets 10 of the polymerizable monomer composition, so that the polymerizable monomer 4c dispersed in the aqueous medium 1 has no opportunity to come into contact with the polymerization initiator 5. Therefore, it is possible to suppress the generation of excess polymer particles such as dense solid particles having a relatively small particle size in addition to the desired hollow resin particles. An oil-soluble polymerization initiator is usually used as the polymerization initiator 5 incorporated into the droplets 10 of the polymerizable monomer composition.

[0054] (3) Polymerization process This step is a step of preparing a precursor composition containing precursor particles having hollow portions and encapsulating a hydrocarbon solvent in the hollow portions by subjecting the above-mentioned suspension to a polymerization reaction. In the polymerization process, the polymerizable monomer in the droplets of the polymerizable monomer composition is polymerized while the droplets still contain the hydrocarbon-based solvent, thereby forming precursor particles having a shell containing a resin, which is a polymerized product of the polymerizable monomer, and a hollow portion filled with the hydrocarbon-based solvent. In the first manufacturing method of the present disclosure, droplets of the polymerizable monomer composition are subjected to a polymerization reaction while containing a hydrocarbon-based solvent, so that the polymerization reaction proceeds easily while maintaining the shape, and the size and porosity of the precursor particles are easily adjusted. In addition, since a polymerizable monomer and a hydrocarbon-based solvent are used in combination, the polarity of the hydrocarbon-based solvent is low with respect to the shell of the precursor particles, and the hydrocarbon-based solvent is not easily compatible with the shell, so that phase separation occurs sufficiently and the hollow portion is likely to be only one. In addition, the size and porosity of the precursor particles can be easily adjusted by adjusting the amount of the hydrocarbon-based solvent. The polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be used. The polymerization temperature is preferably 40 to 80° C., more preferably 50 to 70° C. The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours.

[0055] (4) Solid-liquid separation process This step is a step of obtaining precursor particles containing the hydrocarbon solvent and separated from the aqueous medium by subjecting the above-mentioned precursor composition to solid-liquid separation.

[0056] The method for performing solid-liquid separation of the precursor composition is not particularly limited, and a known method can be used. Examples of the solid-liquid separation method include centrifugation, filtration, and static separation, and among these, centrifugation or filtration can be used, and filtration may be used from the viewpoint of ease of operation.

[0057] In this step, after the precursor composition is subjected to solid-liquid separation, the precursor particles may be pre-dried before the solvent removal step described below is performed. Note that the pre-drying is performed to remove the remaining aqueous medium from the solid obtained by the solid-liquid separation of the precursor composition without removing the hydrocarbon solvent contained in the precursor particles. The pre-drying is preferably performed as necessary so that the water content of the precursor particles obtained by this step falls within a preferred range described below. The pre-drying is preferably carried out under a temperature condition of, for example, 100° C. lower than the temperature T0 (° C.) of the heat drying in the solvent removal step described below (T0-100 (° C.)) from the viewpoint of removing the aqueous medium without removing the hydrocarbon solvent. The pre-drying is usually carried out under a temperature condition of 40° C. or higher in order to sufficiently remove the aqueous medium. The pressure when the pre-drying is carried out may be adjusted in a range of 0 to 101.3 kPa according to the temperature of the pre-drying, within a range in which damage to the precursor particles can be suppressed. The preliminary drying can be carried out by a known drying method, for example, a method using a drying device such as a dryer or a drying appliance such as a hand dryer, or the like, or may be carried out by the same method as the solvent removal step described below.

[0058] (5) Solvent removal process This step is a step of removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles separated from the aqueous medium. In this step, the precursor particles obtained by the solid-liquid separation step are heated and dried in air, so that the hydrocarbon solvent inside the precursor particles is replaced with gas, and hollow resin particles filled with gas can be obtained. Here, "in air" strictly speaking means an environment in which no liquid components are present outside the precursor particles, and an environment in which only a very small amount of liquid components that do not affect the removal of the hydrocarbon solvent are present outside the precursor particles. "In air" can also be expressed as a state in which the precursor particles are separated from the slurry, or a state in which the precursor particles are present in a dry powder. That is, in this step, the hydrocarbon solvent is removed in an environment in which the precursor particles are in direct contact with the external gas.

[0059] The precursor particles used in the solvent removal step are not particularly limited, but preferably have a moisture content of 50% or less, more preferably 15 to 45%. This improves the fluidity of the precursor particles when they are stirred and dried, improving the transportability of the precursor particles to a stirring vessel and the drying efficiency, thereby shortening the drying time. In addition, the adhesion of powder to the stirring blades is suppressed, improving the heat transfer efficiency, thereby improving productivity. In the present disclosure, the moisture content can be calculated by the following formula (i). Formula (i) Moisture content (%)={(w1-w2) / w1}×100 In the formula (i), w1 represents the mass of the measurement sample, and w2 represents the mass of the measurement sample after drying at 105°C for 1 hour and then cooling to 25°C.

[0060] In addition, the permeability (%) of the hydrocarbon solvent from the precursor particles is preferably 5% or less, which is calculated as the rate of change between the mass (w3) of precursor particles A obtained by drying the precursor particles used in the solvent removal step at 40° C. for 24 hours and the mass (w4) of precursor particles B obtained by further drying the precursor particles A at 105° C. for 2 hours and then cooling to 25° C. In addition, the permeability of the hydrocarbon solvent is preferably 5% or less from the viewpoint of the strength of the shell, but if it exceeds 3%, it is preferable from the viewpoint of improving productivity. The permeability of the hydrocarbon solvent can be calculated by the following formula (ii). Formula (ii) Hydrocarbon solvent permeability (%) = {(w3-w4) / w3} x 100 (In the formula (ii), w3 and w4 are as defined above.) When the permeability of the hydrocarbon solvent is 5% or less, the precursor particles are estimated to have a shell free of interconnecting pores and shell defects, and to have excellent shell strength. When hollow resin particles having a permeability of the hydrocarbon solvent of 5% or less are produced by a conventional method, a large amount of the hydrocarbon solvent remains in the particles, but by using the first production method of the present disclosure, hollow resin particles having a permeability of the hydrocarbon solvent of 5% or less and a reduced amount of the residual hydrocarbon solvent can be obtained. In each of the production methods disclosed herein, by using a bifunctional crosslinkable monomer as the crosslinkable monomer in the polymerizable monomer, a shell having a permeability to the hydrocarbon solvent of 5% or less can be formed.

[0061] In the solvent removal step, the temperature T0 of the heat drying when removing the hydrocarbon solvent contained in the precursor particles is a drying temperature set according to the drying device used. In the present disclosure, the drying device used for the heat drying performed in the solvent removal step may be a direct heating type that directly heats the particles with hot air or the like, or an indirect heating type that heats the particles by contacting them with a jacket or the like into which a heat medium is injected. The heat drying temperature T0 is basically the temperature inside the drying chamber, but when an indirect heating type drying device is used, the temperature of the heat medium can be regarded as the temperature inside the drying chamber, so the temperature of the heat medium can be the heat drying temperature T0. In the present disclosure, the temperature T0 of the heating and drying in the solvent removal process satisfies T1+70≦T0≦T2-5, and preferably satisfies T1+75≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon solvent contained in the precursor particles and T2 (°C) is the thermal decomposition onset temperature of the precursor particles. In the present disclosure, the thermal decomposition starting temperature T2 (°C) of the precursor particles is measured using analysis software based on the heat loss of the precursor particles measured by TG-DTA (thermogravimetric differential thermal analysis) under an air atmosphere. As the TG-DTA device (thermogravimetric simultaneous differential thermal analysis device), for example, the EXSTAR6000 series manufactured by Seiko Instruments Inc. can be used, and as the analysis software, the analysis software included with the device can be used. Specifically, the TG-DTA curve of the precursor particles is obtained by precisely weighing out about 15 mg of the precursor particles to be used in the solvent removal step, and measuring under the following conditions in an air atmosphere using alumina as a reference material. Air flow rate: 230mL / min Heating rate: 10℃ / min Measurement temperature range: 30℃ to 800℃ From the obtained TG-DTA curve, the thermal decomposition onset temperature of the precursor particles can be obtained using analysis software. In this disclosure, the thermal decomposition onset temperature is obtained in accordance with JIS K7120:1987 "Thermogravimetric measurement method for plastics", and in the case of a single-stage mass reduction, the thermal decomposition onset temperature is the onset temperature of mass reduction, and in the case of a multi-stage mass reduction, the first onset temperature of mass reduction is the thermal decomposition onset temperature.

[0062] The thermal decomposition starting temperature T2 (°C) of the precursor particles used in this step is preferably 150 to 350°C, more preferably 200 to 300°C, since hollow resin particles having excellent heat resistance can be obtained.

[0063] The heat drying time in this step is appropriately set depending on the heat drying method, and is not particularly limited, but is usually 30 minutes to 1500 minutes, and from the viewpoint of productivity, is preferably 800 minutes or less, and more preferably 500 minutes or less.

[0064] The pressure during the heat drying in this step is preferably 0 to 101.3 kPa, more preferably 0 to 71 kPa, and even more preferably 0 to 10 kPa, from the viewpoint of suppressing damage to the hollow resin particles.

[0065] The drying atmosphere in this step for the heat drying is not particularly limited and can be appropriately selected depending on the application of the hollow resin particles. Examples of the drying atmosphere include air, oxygen, nitrogen, argon, etc. From the viewpoint of safety and drying efficiency, it is preferable to use an inert gas atmosphere such as nitrogen and argon, but from the viewpoint of simplicity, an air atmosphere may be used. By the drying operation in air, the hydrocarbon solvent inside the precursor particles is replaced by the external gas, and as a result, hollow resin particles in which the hollow portion is occupied by gas are obtained. When the heat drying is performed under vacuum conditions, hollow resin particles with a vacuum inside are temporarily obtained, and then, by returning to normal pressure, hollow resin particles having a hollow portion filled with gas can be obtained.

[0066] The amount of precursor particles charged during the heat drying in this step is appropriately adjusted depending on the heat drying method, and is not particularly limited, but is usually 0.1 to 100 L, and from the viewpoint of mass production, it is preferably 10 L or more.

[0067] The method of heat drying in this step can be a known method and is not particularly limited. For example, there can be mentioned static drying, in which the precursor particles are dried while being left static, stirring drying, air flow drying, etc., in which the precursor particles are dried while being stirred in air. Among them, stirring drying is preferred because it can remove the hydrocarbon solvent from a large amount of precursor particles in a short time and is excellent in productivity.

[0068] Examples of dryers for static drying include shelf-type vacuum dryers such as a rectangular vacuum dryer (model number: ADP300) manufactured by Yamato Scientific Co., Ltd. When the solvent removal step is carried out by static drying, the cake of precursor particles is usually placed in a dryer and dried. From the viewpoint of removing the hydrocarbon solvent in the precursor particles in a short time, the cake of precursor particles preferably has a thickness of 1 cm or less. The effective volume of the drying chamber of the dryer for static drying is usually 0.0001 to 1 m 3 It is.

[0069] The dryer for performing the stirring and drying is not particularly limited as long as it is equipped with a stirring vessel capable of drying the desired material while stirring it, and for example, a stirring dryer equipped with a stirring vessel capable of adjusting the temperature and internal pressure can be preferably used. By using such a stirring dryer, the precursor particles can be heated and dried while being stirred in the stirring vessel. The stirring dryer usually has a larger effective volume than a dryer that performs static drying. The effective volume of the stirring vessel equipped in the stirring dryer is usually 0.0001 m 3 That's it, and from the perspective of mass production, it's 3m 3 From the viewpoint of productivity, it is usually 20 m 3 Less than or equal to 15m 3 It may be the following.

[0070] Examples of the types of agitation dryers include direct heating types such as fluidized bed dryers, and indirect heating types that are provided with a jacket around the periphery of a stirring vessel through which a heat medium flows. Examples of the agitator dryer include a vertical agitator dryer used in the second production method of the present disclosure described below, and a horizontal agitator dryer used in the third production method of the present disclosure described below. The vertical agitator dryer is preferred because it can improve the yield of hollow resin particles, while the horizontal agitator dryer is preferred because it has excellent heat transfer efficiency, which can shorten the heating and drying time in the solvent removal step, and is therefore excellent in productivity. Furthermore, the horizontal agitator dryer is more likely to have a larger heat transfer area / effective volume ratio than the vertical agitator dryer, which makes it easier to improve drying efficiency and therefore productivity.

[0071] In the stirring and drying method performed in the first manufacturing method of the present disclosure, from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, the stirring blade tip speed calculated by the following formula (iii) is preferably 2.0 m / s or less, more preferably 1.5 m / s or less, even more preferably 0.8 m / s or less, and even more preferably 0.6 m / s or less. From the viewpoint of improving productivity, the stirring blade tip speed is preferably 0.1 m / s or more, more preferably 0.3 m / s or more. Formula (iii) Impeller tip speed (m / s) = Pi x impeller diameter (m) × Rotation speed ( s -1 ) The impeller diameter is defined as twice the maximum linear distance from the central axis of the shaft to the tip of the impeller when observed from the central axis direction of the shaft.

[0072] In the stirring and drying method performed in the first production method of the present disclosure, the rotation speed of the stirring blade is preferably 70 rpm or less, more preferably 40 rpm or less, and even more preferably 30 rpm or less, from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, and is preferably 5 rpm or more, and more preferably 10 rpm or more, from the viewpoint of improving productivity.

[0073] In addition, when the heat drying in this step is performed by stirring drying, this step is preferably a step of heating and drying the precursor particles separated from the aqueous medium together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in a stirring vessel while stirring, thereby coating the surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles. By coating the surfaces of the precursor particles with the fine particles, the fluidity of the precursor particles during stirring is improved, and the drying efficiency by stirring drying is improved, resulting in improved productivity of hollow resin particles. The fine particles that cover the surfaces of the precursor particles are at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles. Examples of materials for the inorganic fine particles include silica, calcium carbonate, alumina, titanium oxide, zinc oxide, tin oxide, calcium phosphate, and cerium oxide, etc. Among these, silica, calcium carbonate, and alumina are preferred as materials for the inorganic fine particles, and silica and calcium carbonate are more preferred. Examples of materials for the organic fine particles include styrene resins, acrylic resins, polyamide resins, styrene acrylic resins, polylactic acid resins, silicone resins, fluorine resins, melamine-formaldehyde condensates, benzoguanamine-formaldehyde condensates, urethane resins, epoxy resins, polyester resins, waxes, etc. These materials may be subjected to crosslinking treatment or surface treatment, etc. In addition, it is preferable that the organic fine particles have a heat resistance temperature equal to or higher than the temperature of the heating and drying in the solvent removal step. These inorganic fine particles and organic fine particles may be used alone or in combination of two or more kinds. As the fine particles that cover the surfaces of the precursor particles, inorganic fine particles are particularly preferred because they are excellent in improving the fluidity of the precursor particles during stirring.

[0074] The average primary particle diameter of the fine particles covering the surface of the precursor particles is usually 10 to 120 nm, preferably 15 to 90 nm, and more preferably 20 to 80 nm. When the average primary particle diameter of the fine particles is equal to or greater than the lower limit, the fine particles are likely to function as spacers that suppress contact between the precursor particles. When the average primary particle diameter is equal to or less than the upper limit, the fine particles are likely to uniformly cover the precursor particles, and therefore the fluidity of the precursor particles can be improved, and drying efficiency can be improved.

[0075] The specific gravity of the fine particles that cover the surfaces of the precursor particles is not particularly limited, but is preferably 1.5 to 4.5, more preferably 1.8 to 3.5, and even more preferably 2.0 to 2.5. When the specific gravity of the fine particles is within the above range, it is possible to achieve both the dispersibility of the precursor particles and the weight reduction of the obtained hollow resin particles. Examples of inorganic fine particle materials with a specific gravity of 2.0 to 2.5 include silica. Examples of inorganic fine particle materials with a specific gravity of more than 2.5 and less than 3.5 include calcium carbonate. Examples of inorganic fine particle materials with a specific gravity of more than 3.5 include titanium oxide and alumina.

[0076] The content of the fine particles covering the surface of the precursor particles is preferably adjusted so that the coverage of the fine particles in the obtained hollow resin particles falls within a preferred range described below, and is not particularly limited, but is usually 0.1 to 180 parts by mass, preferably 1 to 100 parts by mass, and more preferably 2 to 50 parts by mass, relative to 100 parts by mass of the precursor particles used in the solvent removal step. By making the content of the fine particles equal to or more than the lower limit, it is possible to sufficiently improve drying efficiency and productivity, and by making the content equal to or less than the upper limit, it is possible to suppress an increase in the specific gravity of the obtained hollow resin particles.

[0077] (6) Other processes The manufacturing method of the first present disclosure may further include other steps different from the steps (1) to (5) above. Examples of the other steps include a cleaning step and a hollow portion re-replacement step.

[0078] The washing step is a step of removing the water-insoluble inorganic compound from the precursor composition when the water-insoluble inorganic compound is used as the suspension stabilizer, and is usually carried out after the polymerization step and before the solid-liquid separation step. A preferred method for the washing step is, for example, a method in which an acid is added to the precursor composition to adjust the pH to preferably 6.5 or less, more preferably 6 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is particularly preferred because it has a high efficiency in removing poorly water-soluble inorganic compounds and places a small burden on the production equipment.

[0079] The hollow re-substitution process is a process of replacing the gas inside the hollow resin particles with other gases or liquids. Such substitution can change the environment inside the hollow resin particles, selectively confine molecules inside the hollow resin particles, or modify the chemical structure inside the hollow resin particles according to the application. In the first manufacturing method of the present disclosure, the solvent removal process can obtain hollow resin particles whose hollow parts are filled with gas such as air, but a hollow re-substitution process can be carried out thereafter to obtain hollow resin particles whose hollow parts contain a solvent other than the hydrocarbon solvent.

[0080] I-2. Hollow resin particles The shape of the hollow resin particles obtained by the first manufacturing method of the present disclosure is not particularly limited as long as a hollow portion is formed inside. The outer shape of the hollow resin particles is not particularly limited, but a spherical shape is preferable from the viewpoint of ease of manufacturing. The hollow resin particles obtained by the first manufacturing method of the present disclosure may have one or more hollow parts, but preferably have only one hollow part in order to maintain a good balance between high porosity and mechanical strength. The shell of the hollow resin particles and, when the hollow resin particles have two or more hollow parts, the partition walls separating adjacent hollow parts may be porous. The hollow resin particles obtained by the production method according to the first aspect of the present disclosure may have an average circularity of 0.950 to 0.995. An example of the shape of the hollow resin particle obtained by the manufacturing method of the first disclosure is a bag made of a thin film and inflated with gas, and its cross-sectional view is shown in hollow resin particle 100 in (5) of Fig. 1. In this example, a thin film is provided on the outside, and the inside is filled with gas. The external shape of the hollow resin particles can be confirmed, for example, by observing the particles with a SEM or a TEM, and the internal shape of the hollow resin particles can be confirmed, for example, by observing the cross section of the particles with a SEM or by observing the particles with a TEM.

[0081] The volume average particle size of the hollow resin particles obtained by the production method according to the first disclosure of the present invention is not particularly limited, but is preferably 1.0 to 100.0 μm, more preferably 2.0 to 30.0 μm, and even more preferably 3.2 to 9.0 μm. When the volume average particle diameter of the hollow resin particles is equal to or greater than the lower limit, aggregation between the hollow resin particles is suppressed, thereby improving productivity. When the volume average particle diameter is equal to or less than the upper limit, the hollow resin particles are less likely to be crushed, thereby providing high mechanical strength.

[0082] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow resin particles obtained by the production method of the first present disclosure may be, for example, 1.1 to 2.5. When the particle size distribution is equal to or less than the upper limit, particles having less variation in compressive strength properties and heat resistance among particles can be obtained. Furthermore, when the particle size distribution is equal to or less than the upper limit, for example, when a sheet-shaped molded product is produced, a product having a uniform thickness can be produced. The volume average particle diameter (Dv) and number average particle diameter (Dn) of the hollow resin particles can be determined by, for example, measuring the particle diameter of the hollow resin particles using a laser diffraction particle size distribution measuring device, calculating the number average and volume average, and using the obtained values ​​as the number average particle diameter (Dn) and volume average particle diameter (Dv) of the particles. The particle size distribution is determined by dividing the volume average particle diameter by the number average particle diameter.

[0083] The porosity of the hollow resin particles obtained by the first manufacturing method of the present disclosure is preferably 50 to 95%, more preferably 55 to 90%, and even more preferably 60 to 85%. When the porosity is equal to or greater than the lower limit, the hollow resin particles are excellent in lightness, heat resistance, and heat insulation, and the hydrocarbon solvent is less likely to remain inside the particles. When the porosity is equal to or less than the upper limit, the hollow resin particles are less likely to have interconnecting holes and shell defects in the shell, are less likely to be crushed, and have excellent strength.

[0084] The porosity of the hollow resin particles obtained by the first manufacturing method of the present disclosure is calculated from the apparent density D1 and true density D0 of the hollow resin particles. When a hydrocarbon-based solvent remains in the hollow resin particles, the porosity of the hollow resin particles calculated by the following method decreases as the amount of the remaining hydrocarbon-based solvent increases. In contrast, the theoretical porosity described below is the porosity when it is assumed that no hydrocarbon-based solvent remains in the hollow resin particles, and represents the ratio of the hollow portion to the specific gravity of the hollow resin particles. The method for measuring the apparent density D1 of hollow resin particles is as follows. 3 About 30 cm 3The hollow resin particles are filled into the measuring flask, and the mass of the filled hollow resin particles is precisely weighed. Next, the measuring flask filled with the hollow resin particles is precisely filled with isopropanol up to the marked line, while being careful not to introduce air bubbles. The mass of isopropanol added to the measuring flask is precisely weighed, and the apparent density D1 (g / cm) of the hollow resin particles is calculated based on the following formula (I): 3 ) to calculate Formula (I) Apparent density D1 = [mass of hollow resin particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature]) The apparent density D1 corresponds to the specific gravity of the entire hollow resin particle when the hollow portion is considered to be a part of the hollow resin particle.

[0085] The method for measuring the true density D0 of hollow resin particles is as follows. After crushing the hollow resin particles, 3 The measuring flask is filled with about 10 g of crushed pieces of hollow resin particles, and the mass of the crushed pieces is accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol is added to the measuring flask, and the mass of the isopropanol is accurately weighed, and the true density D0 (g / cm) of the hollow resin particles is calculated based on the following formula (II). 3 ) to calculate Formula (II) True density D0 = [mass of crushed pieces of hollow resin particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature]) 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-mentioned measurement method, the hollow portion is not considered to be part of the hollow resin particle when calculating the true density D0.

[0086] The porosity (%) of the hollow resin particle is calculated from the apparent density D1 and the true density D0 of the hollow resin particle by the following formula (III). Formula (III) Porosity (%) = 100 - (apparent density D1 / true density D0) x 100 The porosity of the hollow resin particles thus determined may be referred to as an actually measured porosity, in order to distinguish it from a theoretical porosity, which will be described later.

[0087] The theoretical porosity of the hollow resin particles obtained by the first manufacturing method of the present disclosure can be calculated from the mass Ws of the hydrocarbon solvent charged in the mixed liquid preparation step, the specific gravity Gs of the hydrocarbon solvent, the mass Wr of the solid raw materials constituting the hollow resin particles, and the true density D0 of the hollow resin particles, according to the following formula (IV). Formula (IV) Theoretical porosity (%)=(Ws / Gs)÷{(Ws / Gs)+(Wr / D0)}×100 (In the formula (IV), Ws, Gs, Wr and D0 are as defined above.) Here, the raw material of the solid content constituting the hollow resin particles is the polymerizable monomer, and the polar resin and fine particles added as necessary, and does not include materials that do not form hollow resin particles by decomposition, such as the polymerization initiator, etc. In this disclosure, the solid content refers to everything other than the solvent, and for example, liquid monomers and those dissolved in the solvent are included in the solid content. Moreover, the true density D0 of the hollow resin particle in the above formula (IV) is the true density D0 calculated by the above formula (II).

[0088] The hollow resin particles obtained by the first manufacturing method of the present disclosure have a residual hydrocarbon solvent rate calculated from the theoretical porosity and the actually measured porosity of the hollow resin particles described above according to the following formula (V) of preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.2% or less. Formula (V) Hydrocarbon solvent residual rate (%) = 100 - (actual porosity / theoretical porosity) x 100 By having the residual rate of the hydrocarbon-based solvent be equal to or less than the upper limit, there is no risk of the hydrocarbon-based solvent in the hollow resin particles evaporating and causing foaming or fire when the hollow resin particles are kneaded with other materials, and the specific gravity of the hollow resin particles can be reduced, thereby improving their effectiveness as a lightweight material.

[0089] The hollow resin particles obtained by the manufacturing method according to the first aspect of the present disclosure may have a shell thickness of 0.01 to 5.00 μm, and preferably 0.10 to 1.00 μm, which makes it possible to suppress a decrease in mechanical strength while maintaining the porosity of the hollow resin particles. The shell thickness of the hollow resin particles can be calculated by calculating the inner diameter r of the hollow resin particles according to the following formula (1) using the volume average particle diameter R1 and theoretical porosity of the hollow resin particles, and then calculating the shell thickness of the hollow resin particles according to the following formula (2) using the inner diameter r and the volume average particle diameter R1. 4 / 3π×(R1 / 2) 3 ×Theoretical porosity=4 / 3π×(r / 2) 3 Formula (1) Shell thickness = (R1-r) / 2 Equation (2) The difference between the shell thickness calculated in this manner and the average thickness measured at 20 points on the shell is usually within ±10% of these average values, so the shell thickness calculated as described above can be regarded as the shell thickness of the hollow resin particles. The thickness at each point of the shell of a hollow resin particle used to calculate the average thickness at 20 points on the shell can be measured, for example, by breaking the hollow resin particle and observing pieces of the shell using an SEM.

[0090] Furthermore, according to the first manufacturing method of the present disclosure, the moisture content of the obtained hollow resin particles can be less than 1%. When the moisture content of the hollow resin particles is less than 1%, the hollow resin particles can be made even lighter.

[0091] Furthermore, when the surfaces of the hollow resin particles obtained by the first manufacturing method of the present disclosure are covered with the fine particles, the hollow resin particles may have a coverage rate of the fine particles calculated by the following formula (A) of 60 to 180%, and from the viewpoint of productivity, it is preferably 65% ​​or more, while from the viewpoint of weight reduction, it is preferably 175% or less, more preferably 170% or less, and even more preferably 160% or less. The coverage rate of the hollow resin particles by the fine particles relative to the surface area is calculated by the volume average particle diameter R2 (nm) of the hollow resin particles assuming that they do not contain fine particles, the apparent density S (g / cm) of the hollow resin particles assuming that they do not contain fine particles and hydrocarbon solvents, 3 ), the average primary particle size d (nm), the specific gravity s of the particles, and the amount n (parts by mass) of the particles added is calculated according to the following formula (A). The amount n (parts by mass) of the particles added is the amount of the particles added per 100 parts by mass of hollow resin particles, which is assumed to contain no particles or hydrocarbon solvent. Formula (A) Coverage rate of particles (%) = {3 1 / 2 / 2π}×{(R2×S) / (d×s)}×n (In the formula (A), R2, S, d, s and n are as defined above.) The volume average particle diameter (R2) of the hollow resin particles, which is assumed to contain no fine particles, can be regarded as the same as the volume average particle diameter of the precursor particles. The apparent density (S) of the hollow resin particles, which is assumed to contain no fine particles or hydrocarbon solvent, can be regarded as the same as the apparent density of the particles obtained by drying the precursor particles at 230°C for 24 hours. The apparent density of the particles obtained by drying the precursor particles at 230°C for 24 hours can be measured by the same method as the apparent density D1 of the hollow resin particles.

[0092] According to the first manufacturing method of the present disclosure, the weight (kg) of the obtained hollow resin particles is divided by the heat drying time (h) performed in the solvent removal step, and the effective volume (m 3 ) divided by (kg / (h m 3 )) can be, for example, 0.01 or more, preferably 3 or more, more preferably 30 or more, and even more preferably 100 or more. 3 The larger the ratio of the diameter of the hollow resin particles to the diameter of the hollow resin particles, the more hollow resin particles can be produced in a short period of time, resulting in excellent productivity.

[0093] I-3. Uses of hollow resin particles The hollow resin particles obtained by the manufacturing method according to the first aspect of the present disclosure may be used, for example, as an undercoat material for thermal paper. In general, undercoat materials are required to have heat insulating properties and shock absorbing properties (cushioning properties), and are also required to have heat resistance suitable for thermal paper applications. The hollow resin particles obtained by the manufacturing method according to the first aspect of the present disclosure are also useful, for example, as plastic pigments with excellent gloss and hiding power. In addition, the hollow resin particles obtained by the first manufacturing method of the present disclosure have excellent strength and are therefore not easily crushed when kneaded with other materials such as resins. When added to a molded body, the hollow resin particles have excellent effects as a lightweight material, heat insulating material, soundproofing material, vibration damping material, etc., and are therefore suitable as an additive for molded bodies, and are particularly suitable for use as an additive for resin molded bodies. Moreover, the hollow resin particles obtained by the first manufacturing method of the present disclosure can have useful components such as fragrances, medicines, agricultural chemicals, ink components, etc. encapsulated therein by means of immersion treatment, reduced pressure or pressure immersion treatment, etc. Such hollow resin particles encapsulating useful components can be used for various purposes depending on the components contained therein.

[0094] II-1. Second method for producing hollow resin particles according to the present disclosure In the conventional manufacturing method of obtaining hollow resin particles by polymerizing a polymerizable monomer in an aqueous medium by a suspension polymerization method, as described above, when the ratio of a crosslinkable monomer is increased as the polymerizable monomer forming the shell of the hollow resin particle in order to increase the strength of the shell, there is a problem that a large amount of organic solvent may remain inside the hollow resin particle even after the hollow resin particle is dried. In addition, the conventional manufacturing method has a problem that when the organic solvent remaining inside the particle is dried and removed, it is difficult to dry and remove the organic solvent from a large amount of particles in a short time, making it difficult to improve productivity. A second object of the present disclosure is to provide a method for producing hollow resin particles with excellent productivity, which can reduce the amount of residual hydrocarbon solvent that is retained inside the particles during the production process and can obtain hollow resin particles with reduced breakage.

[0095] A second method for producing hollow resin particles according to the present disclosure includes the steps of: preparing a mixed solution containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The step of removing the hydrocarbon-based solvent is characterized in that the hydrocarbon-based solvent contained in the precursor particles is removed by heating and drying the precursor particles while stirring them in a vertical stirring vessel equipped with a shaft extending in the direction of gravity and a stirring blade.

[0096] According to the second manufacturing method of the present disclosure, the amount of residual hydrocarbon solvent that is retained inside the particles during the manufacturing process is reduced, and hollow resin particles that are inhibited from being broken can be efficiently manufactured.

[0097] The manufacturing method according to the second disclosure follows the same basic technique as the manufacturing method according to the first disclosure described above. In the manufacturing method according to the second disclosure, the precursor particles containing the hydrocarbon-based solvent are heated and dried while being stirred in a vertical stirring vessel, thereby making it possible to sufficiently remove the encapsulated hydrocarbon-based solvent in a short time while suppressing damage to the particles, and thus achieving excellent productivity of hollow resin particles. In addition, in the second production method of the present disclosure, a vertical stirring method is adopted as the stirring method, and thus the yield of hollow resin particles can be increased compared to the case of adopting a horizontal stirring method or the like. The effect of reducing the amount of residual hydrocarbon solvent in the hollow resin particles by the second manufacturing method of the present disclosure is particularly effective when hollow resin particles having a shell without interconnected pores and shell defects are manufactured. The hollow resin particles having a shell without interconnected pores and shell defects can be manufactured, for example, by using a bifunctional crosslinkable monomer as the crosslinkable monomer in the polymerizable monomer that forms the shell, as in the first manufacturing method of the present disclosure.

[0098] An example of the manufacturing method according to the second disclosure includes a method including (1) a mixed liquid preparation step, (2) a suspension step, (3) a polymerization step, (4) a solid-liquid separation step, and (5) a solvent removal step. The production method according to the second disclosure includes at least a mixed solution preparation step, a suspension step, a polymerization step, and a solvent removal step among the steps (1) to (5) above. The production method according to the second disclosure further includes a solid-liquid separation step, which is preferable in that it makes it easy to remove the hydrocarbon solvent in the hollow resin particles and improves productivity. The steps (1) to (4) are the same as the steps (1) to (4) in the production method of the first disclosure. Fig. 1 is also a schematic diagram showing an example of the production method of the second disclosure, and Fig. 2 is also a schematic diagram showing one embodiment of the suspension in the suspension step in the production method of the second disclosure. The solvent removal step in the production method according to the second embodiment of the present disclosure will be described below.

[0099] The solvent removal step in the second production method of the present disclosure is a step of removing the hydrocarbon solvent contained in the precursor particles by heating and drying the precursor particles. This step is preferably carried out after the solid-liquid separation step, and is preferably carried out using the precursor particles separated from the aqueous medium. In this step, the precursor particles are heated and dried in air to replace the hydrocarbon solvent in the precursor particles with gas, thereby obtaining hollow resin particles filled with gas. Here, "in air" is as described in the above-mentioned first production method of the present disclosure. In the production method according to the second embodiment of the present disclosure, the water content and the hydrocarbon solvent permeability of the precursor particles used in the solvent removal step are the same as those in the production method according to the first embodiment of the present disclosure described above.

[0100] In the second manufacturing method of the present disclosure, in the solvent removal step, the precursor particles are heated and dried while being stirred in a vertical stirring vessel equipped with a shaft extending in the direction of gravity and a stirring blade. Examples of the vertical stirring dryer used for such heating and drying include a direct heating type and an indirect heating type, and among them, an indirect heating type vertical stirring dryer is preferred. The stirring blade is preferably fixed to a shaft. Examples of the stirring blade include a spiral ribbon type, a screw type, a paddle type, a full zone type, and the like, but are not particularly limited. The stirring blade and the shaft may be a heat transfer stirring blade and a heat transfer shaft, respectively, through which a heat medium can flow. The shape of the stirring vessel provided in the vertical stirring dryer used in the second manufacturing method of the present disclosure is preferably cylindrical or conical. Note that the conical stirring vessel is usually installed so that the direction from the bottom to the apex of the cone is the direction of gravity. The ratio (b / a) of the maximum distance b in the direction perpendicular to the shaft to the length a of the shaft in the stirring vessel provided in the vertical stirring dryer is usually 0.5 to 2.0. In particular, when the ratio is preferably 0.9 or less, and more preferably 0.8 or less, the heat transfer rate and the stirring efficiency are improved. On the other hand, when the installation space is limited, it is preferable that the ratio (b / a) is 1.0 or more, because the effective volume of the stirring vessel increases and the productivity is improved.

[0101] FIG. 3 is a cross-sectional schematic diagram of an example of a vertical agitation dryer used in the manufacturing method of the second disclosure, and FIG. 4 is a cross-sectional schematic diagram of another example of a vertical agitation dryer used in the manufacturing method of the second disclosure. Each vertical agitation dryer 30A shown in FIG. 3 and FIG. 4 is equipped with a vertical agitation type agitation vessel 33 equipped with a shaft 31 extending in the direction of gravity and an agitation blade 32 fixed to the shaft 31, and the outer periphery of the agitation vessel 33 is covered with a jacket 34 through which a heat medium can flow. In the vertical agitation dryer 30A shown in FIG. 3, the shape of the agitation vessel is conical, and the agitation blade is paddle-type. In the vertical agitation dryer 30A shown in FIG. 4, the shape of the agitation vessel is cylindrical, and the agitation blade is full zone type. In each agitation dryer 30A shown in FIG. 3 and FIG. 4, the precursor particles supplied from the supply port 35 are agitated and dried in the agitation vessel 33, and are discharged from the discharge port 36 as hollow resin particles from which the hydrocarbon-based solvent has been removed.

[0102] The vertical agitator dryer may have a gear box. The installation position of the gear box is not particularly limited as long as the heat resistance temperature of the gear box is equal to or higher than the temperature of the heat medium, but when the heat resistance temperature of the gear box is lower than the temperature of the heat medium, the gear box is preferably installed at a position not exposed to the heat medium, for example, the gear box is preferably installed outside the jacket.

[0103] Examples of commercially available vertical agitation dryers that are preferably used include "Rebocone" manufactured by Okawara Manufacturing Co., Ltd. and "PV Mixer" manufactured by Kobelco Eco-Solutions Co., Ltd. "Rebocone" is a dryer that performs drying in a conical agitation vessel using a vertical agitation method, and is equipped with a spiral ribbon-type agitation blade fixed to the shaft. "PV Mixer" is a dryer that performs drying in a conical agitation vessel using a vertical agitation method, and is equipped with a paddle-type agitation blade fixed to the shaft.

[0104] In the solvent removal step, the temperature T0 of the heat drying when removing the hydrocarbon solvent contained in the precursor particles is a drying temperature set according to the drying device used, and is the same as the above-mentioned manufacturing method of the first disclosure. In the manufacturing method of the second disclosure, the temperature T0 of the heat drying in the solvent removal step preferably satisfies T1≦T0≦T2-5, more preferably satisfies T1+70≦T0≦T2-5, and even more preferably satisfies T1+140≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon solvent contained in the precursor particles and T2 (°C) is the thermal decomposition start temperature of the precursor particles.

[0105] The time for the heat drying in this step is preferably from 80 to 210 minutes, more preferably from 80 to 160 minutes, from the viewpoint of productivity.

[0106] In the manufacturing method of the second disclosure, the thermal decomposition starting temperature T2 (°C) of the precursor particles used in the solvent removal step, the pressure during the heat drying in the solvent removal step, the drying atmosphere in which the heat drying is performed, and the amount of the precursor particles charged during the heat drying are the same as those in the manufacturing method of the first disclosure described above.

[0107] The effective volume of the stirring vessel of the vertical stirring dryer used in the second production method of the present disclosure is usually 0.0001 m 3 From the perspective of mass production, 3 More preferably, the length is 20 m or more. From the viewpoint of productivity, the length is usually 20 m or more. 3 Less than or equal to 15m 3 It may be the following.

[0108] In the stirring and drying method carried out in the second manufacturing method of the present disclosure, from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, the stirring blade tip speed calculated by the formula (iii) explained in the first manufacturing method of the present disclosure is preferably 2.0 m / s or less, more preferably 1.5 m / s or less, even more preferably 0.8 m / s or less, and even more preferably 0.6 m / s or less. From the viewpoint of improving productivity, the stirring blade tip speed is preferably 0.1 m / s or more, more preferably 0.3 m / s or more.

[0109] In the stirring and drying method performed in the second manufacturing method of the present disclosure, the rotation speed of the stirring blade is preferably 70 rpm or less, more preferably 40 rpm or less, and even more preferably 30 rpm or less, from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, and is preferably 5 rpm or more, and more preferably 10 rpm or more, from the viewpoint of improving productivity.

[0110] In addition, in the manufacturing method of the second disclosure, the solvent removal step is preferably a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in a stirring vessel while stirring, in the same manner as in the case of stirring and drying in the manufacturing method of the first disclosure described above, to coat the surfaces of the precursor particles with the fine particles and remove the hydrocarbon solvent contained in the precursor particles. The fine particles that cover the surface of the precursor particles may be the same as those used in the manufacturing method of the first disclosure described above, and the fine particles preferred in the manufacturing method of the first disclosure can also be preferably used in the manufacturing method of the second disclosure. The preferred content of the fine particles is also the same as that in the manufacturing method of the first disclosure.

[0111] The production method of the second disclosure may further include other steps different from the steps (1) to (5) above. Examples of the other steps include steps similar to the other steps that may be included in the production method of the first disclosure described above.

[0112] II-2. Hollow resin particles The hollow resin particles obtained by the second production method of the present disclosure have the same shape, volume average particle size, particle size distribution, porosity, residual rate of hydrocarbon solvent, shell thickness, water content, and fine particle coverage as the hollow resin particles obtained by the above-mentioned first production method of the present disclosure. On the other hand, according to the second manufacturing method of the present disclosure, the weight (kg) of the obtained hollow resin particles is divided by the heat drying time (h) performed in the solvent removal step, and the effective volume (m3 ) divided by (kg / (h m 3 )) can be preferably 15 or more, more preferably 30 or more, and even more preferably 50 or more.

[0113] II-3. Uses of hollow resin particles The hollow resin particles obtained by the manufacturing method according to the second disclosure may have the same applications as those obtained by the manufacturing method according to the first disclosure described above. The applications suitable for the hollow resin particles obtained by the manufacturing method according to the first disclosure are also suitable for the hollow resin particles obtained by the manufacturing method according to the second disclosure.

[0114] III-1. Third method for producing hollow resin particles according to the present disclosure The third object of the present disclosure is similar to the second object of the present disclosure, and is to provide a method for producing hollow resin particles with excellent productivity, which can reduce the amount of residual hydrocarbon solvent that is retained inside the particles during the production process and can obtain hollow resin particles with reduced breakage.

[0115] A third method for producing hollow resin particles according to the present disclosure includes the steps of: preparing a mixed solution containing a polymerizable monomer, a hydrocarbon solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The method is characterized in that the step of removing the hydrocarbon-based solvent is a step of removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles while stirring them in a horizontal stirring vessel equipped with a horizontally extending shaft and stirring blades.

[0116] According to the third manufacturing method of the present disclosure, the amount of residual hydrocarbon solvent that is retained inside the particles during the manufacturing process is reduced, and hollow resin particles that are inhibited from being broken can be efficiently manufactured.

[0117] The manufacturing method of the third disclosure follows the same basic technique as the manufacturing method of the first disclosure described above. In the manufacturing method of the third disclosure, precursor particles containing a hydrocarbon-based solvent are heated and dried while being stirred in a horizontal stirring vessel, thereby making it possible to sufficiently remove the encapsulated hydrocarbon-based solvent in a short time while suppressing damage to the particles, and thus achieving excellent productivity of hollow resin particles. In the horizontal mixing method, the ratio of the heat transfer area to the effective volume of the mixing vessel (heat transfer area / effective volume) is large, resulting in excellent heat transfer efficiency. This results in good efficiency in drying and removing the hydrocarbon solvent, even for precursor particles with a strong shell, and excellent productivity.

[0118] The effect of reducing the amount of residual hydrocarbon solvent in the hollow resin particles by the third manufacturing method of the present disclosure is particularly effective when hollow resin particles having a shell without interconnected pores and shell defects are manufactured. The hollow resin particles having a shell without interconnected pores and shell defects can be manufactured, for example, by using a bifunctional crosslinkable monomer as the crosslinkable monomer in the polymerizable monomer that forms the shell, as in the first manufacturing method of the present disclosure.

[0119] An example of the manufacturing method according to the third disclosure includes a method including (1) a mixed liquid preparation step, (2) a suspension step, (3) a polymerization step, (4) a solid-liquid separation step, and (5) a solvent removal step. The production method of the third disclosure includes at least a mixed solution preparation step, a suspension step, a polymerization step, and a solvent removal step among the steps (1) to (5) above. The production method of the third disclosure further includes a solid-liquid separation step, which is preferable in that it makes it easy to remove the hydrocarbon solvent in the hollow resin particles and improves productivity. The steps (1) to (4) are the same as the steps (1) to (4) in the production method of the first disclosure. Fig. 1 is also a schematic diagram showing an example of the production method of the third disclosure, and Fig. 2 is also a schematic diagram showing one embodiment of the suspension in the suspension step in the production method of the third disclosure. The solvent removal step in the third manufacturing method of the present disclosure will be described below.

[0120] The solvent removal step in the third production method of the present disclosure is a step of heating and drying the precursor particles to remove the hydrocarbon solvent contained in the precursor particles. This step is preferably carried out after the solid-liquid separation step, and is preferably carried out using the precursor particles separated from the aqueous medium. In this step, the precursor particles are heated and dried in air to replace the hydrocarbon solvent in the precursor particles with gas, thereby obtaining hollow resin particles filled with gas. Here, "in air" is as described in the above-mentioned first production method of the present disclosure. In the third production method of the present disclosure, the water content and the hydrocarbon solvent permeability of the precursor particles used in the solvent removal step are the same as those in the above-mentioned first production method of the present disclosure.

[0121] In the third manufacturing method of the present disclosure, in the solvent removal step, the precursor particles are heated and dried while being stirred in a horizontal stirring vessel equipped with a horizontally extending shaft and stirring blades. Examples of the horizontal stirring dryer used for such heating and drying include a direct heating type and an indirect heating type, and among them, an indirect heating type horizontal stirring dryer is preferred. The stirring blade is preferably fixed to the shaft. Examples of the stirring blade include a spiral ribbon type, a screw type, a paddle type, a full zone type, and the like, and are not particularly limited. The stirring blade and the shaft may be a heat transfer stirring blade and a heat transfer shaft, respectively, through which a heat medium can flow. By using at least one of the heat transfer stirring blade and the heat transfer shaft, the heat transfer efficiency is improved, and therefore the efficiency of drying and removing the hydrocarbon solvent is improved, and the productivity of the hollow resin particles can be improved. Examples of the shape of the stirring vessel provided in the horizontal stirring dryer include a cylindrical shape, a conical shape, a spherical shape, and a square prism shape. The ratio (b / a) of the maximum distance b in the direction perpendicular to the shaft to the length a of the shaft in the stirring vessel provided in the horizontal stirring dryer is usually 0.2 to 1.5 inside the vessel. In particular, when the ratio is preferably 0.5 or less, the heat transfer rate and the stirring efficiency are improved. On the other hand, when the installation space is limited, it is preferable that the ratio (b / a) is 0.6 or more, since the effective volume of the stirring vessel increases and the productivity is improved.

[0122] In addition, the horizontal agitation dryer can be easily made into a multi-shaft type having a plurality of shafts, and can be made into a continuous type. From the viewpoint of productivity, in the third manufacturing method of the present disclosure, it is preferable to carry out the solvent removal step using a continuous type dryer equipped with an agitation vessel of a multi-shaft horizontal agitation type having a plurality of shafts extending horizontally and an agitation blade.

[0123] In addition, the horizontal agitator dryer can easily increase the ratio of heat transfer area to effective volume, which makes it easy to improve drying efficiency and thereby productivity. The ratio of heat transfer area to effective volume in the horizontal agitator dryer is preferably 3 to 40, and more preferably 10 to 40. Here, the heat transfer area is the total area of ​​the part where heat can be applied to the particles, that is, the area of ​​the part in the stirring vessel where the particles can come into contact and can be heated by a heat medium. The effective volume is the volume of the area in the stirring vessel where the particles can move, and is calculated by subtracting the volume of the parts in the stirring vessel, such as the stirring blades and shaft, from the total volume inside the stirring vessel.

[0124] FIG. 5 is a schematic cross-sectional view of an example of a horizontal stirring dryer used in the third manufacturing method of the present disclosure, and FIG. 6 is a cross-sectional view of the horizontal stirring dryer shown in FIG. 5. The horizontal stirring dryer 30B shown in FIGS. 5 and 6 includes a horizontal stirring vessel 33 equipped with two shafts 31 extending in the horizontal direction and stirring blades 32 fixed to each shaft 31, and the outer periphery of the stirring vessel 33 is covered with a jacket 34 through which a heat medium can flow. In the horizontal stirring dryer 30B shown in FIGS. 5 and 6, the shape of the stirring vessel is a square column, and the stirring blades are paddle-shaped. In each stirring dryer 30B shown in FIGS. 5 and 6, precursor particles supplied from a supply port 35 are stirred and dried in the stirring vessel 33, and are discharged from a discharge port 36 as hollow resin particles from which the hydrocarbon-based solvent has been removed.

[0125] In the horizontal agitator dryer, the installation position of the gear box is not particularly limited as long as the heat resistance temperature of the gear box is equal to or higher than the temperature of the heat medium. However, if the heat resistance temperature of the gear box is lower than the temperature of the heat medium, it is preferable that the gear box is installed in a position where it is not exposed to the heat medium, for example, it is preferable that the gear box is installed outside the jacket.

[0126] Examples of commercially available horizontal agitator dryers that can be preferably used include the product named "Paddle Dryer" manufactured by Nara Machinery Works, Ltd., the product named "Solid Air (registered trademark) SJ" manufactured by Hosokawa Micron Corporation, and the product named "CD Dryer" manufactured by Kurimoto Iron Works, Ltd.

[0127] In the solvent removal step, the temperature T0 of the heat drying when removing the hydrocarbon solvent contained in the precursor particles is a drying temperature set according to the drying device used, and is the same as the above-mentioned manufacturing method of the first disclosure. In the manufacturing method of the third disclosure, the temperature T0 of the heat drying in the solvent removal step preferably satisfies T1≦T0≦T2-5, more preferably satisfies T1+70≦T0≦T2-5, and even more preferably satisfies T1+140≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon solvent contained in the precursor particles and T2 (°C) is the thermal decomposition start temperature of the precursor particles.

[0128] The time for the heat drying in this step is preferably 30 to 90 minutes, more preferably 30 to 70 minutes, from the viewpoint of productivity.

[0129] In the third manufacturing method of the present disclosure, the thermal decomposition starting temperature T2 (°C) of the precursor particles used in the solvent removal step, the pressure during the heat drying in the solvent removal step, the drying atmosphere in which the heat drying is performed, and the amount of the precursor particles charged during the heat drying are the same as those in the above-mentioned first manufacturing method of the present disclosure.

[0130] The effective volume of the stirring vessel provided in the horizontal stirring dryer used in the third manufacturing method of the present disclosure is 3 m from the viewpoint of mass production. 3 Preferably, it is 5m or more. 3 More preferably, the length is 20 m or more. From the viewpoint of productivity, the length is usually 20 m or more. 3 Less than or equal to 15m 3 It may be the following.

[0131] In the stirring and drying method carried out in the third manufacturing method of the present disclosure, from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, the stirring blade tip speed calculated by the formula (iii) explained in the first manufacturing method of the present disclosure is preferably 2.0 m / s or less, more preferably 1.5 m / s or less, even more preferably 0.8 m / s or less, and even more preferably 0.6 m / s or less. From the viewpoint of improving productivity, the stirring blade tip speed is preferably 0.1 m / s or more, more preferably 0.3 m / s or more.

[0132] In the stirring and drying method performed in the third manufacturing method of the present disclosure, the rotation speed of the stirring blade is preferably 70 rpm or less, more preferably 40 rpm or less, and even more preferably 30 rpm or less from the viewpoint of suppressing damage to the precursor particles or hollow resin particles, and is preferably 5 rpm or more, and more preferably 10 rpm or more from the viewpoint of improving productivity.

[0133] In addition, in the third manufacturing method of the present disclosure, the solvent removal step is preferably a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in a stirring vessel while stirring, in the same manner as in the case of stirring and drying in the above-mentioned first manufacturing method of the present disclosure, to coat the surfaces of the precursor particles with the fine particles and to remove the hydrocarbon solvent contained in the precursor particles. The fine particles that cover the surface of the precursor particles may be the same as those used in the manufacturing method of the first disclosure described above, and the fine particles preferred in the manufacturing method of the first disclosure may also be preferably used in the manufacturing method of the third disclosure. The preferred content of the fine particles is also the same as that in the manufacturing method of the first disclosure.

[0134] The manufacturing method of the third disclosure may further include other steps different from the steps (1) to (5) above. Examples of the other steps include steps similar to the other steps that may be included in the manufacturing method of the first disclosure described above.

[0135] III-2.Hollow resin particles The hollow resin particles obtained by the third production method of the present disclosure have the same shape, volume average particle size, particle size distribution, porosity, residual rate of hydrocarbon solvent, shell thickness, water content, and fine particle coverage as the hollow resin particles obtained by the above-mentioned first production method of the present disclosure. On the other hand, according to the third manufacturing method of the present disclosure, the weight (kg) of the obtained hollow resin particles is divided by the heat drying time (h) performed in the solvent removal step, and the effective volume (m3 ) divided by (kg / (h m 3 )) can be preferably 100 or more, more preferably 150 or more, and even more preferably 300 or more.

[0136] III-3. Uses of hollow resin particles The hollow resin particles obtained by the manufacturing method of the third disclosure may have the same applications as those of the hollow resin particles obtained by the manufacturing method of the first disclosure described above. The applications suitable for the hollow resin particles obtained by the manufacturing method of the first disclosure are also suitable for the hollow resin particles obtained by the manufacturing method of the third disclosure. EXAMPLES

[0137] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that parts and % are by weight unless otherwise specified. Among the Example I series corresponding to the manufacturing method of the first disclosure, Examples I-1 to I-7, I-9, I-12 to I-13, and I-17 to I-18 are reference examples. However, Examples I-7, I-9, I-12, and I-13 are included in the manufacturing method of the second disclosure, and Examples I-17 and I-18 are included in the manufacturing method of the third disclosure.

[0138] <Example I Series> [Production Example 1: Production of Polar Resin A (MMA / AA / EA Copolymer)] 200 parts of toluene were added to the reaction vessel, and the inside of the reaction vessel was thoroughly replaced with nitrogen while stirring the toluene, and then the temperature was raised to 90°C, and then a mixed solution of 96.2 parts of methyl methacrylate (MMA), 0.3 parts of acrylic acid (AA), 3.5 parts of ethyl acrylate (EA), and 2.8 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was dropped into the reaction vessel over 2 hours. The mixture was further kept under toluene reflux for 10 hours to complete polymerization, and then the solvent was distilled off under reduced pressure to obtain polar resin A (MMA / AA / EA copolymer). Of the total mass of repeating units constituting the obtained polar resin A (MMA / AA / EA copolymer), 100%, the proportion of repeating units derived from MMA was 96.2%, the proportion of repeating units derived from AA was 0.3%, and the proportion of repeating units derived from EA was 3.5%. The number average molecular weight of the resulting polar resin A (MMA / AA / EA copolymer) was 10,000.

[0139] [Example I-1] (1) Mixed liquid preparation process The following materials were mixed, and the resulting mixture was used as the oil phase. Methacrylic acid 40 parts Ethylene glycol dimethacrylate 60 parts 2,2'-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) 3 parts Cyclohexane (boiling point 81°C) 187 parts On the other hand, 3.0 parts of a surfactant was added to 650 parts of ion-exchanged water, and the resulting mixture was used as an aqueous phase. A mixture was prepared by mixing the water phase and the oil phase.

[0140] (2) Suspension preparation process The mixture was stirred and suspended in an in-line type emulsifying disperser to prepare a suspension in which droplets of the polymerizable monomer composition encapsulating cyclohexane were dispersed in water.

[0141] (3) Polymerization process The suspension was stirred for 4 hours in a nitrogen atmosphere at a temperature of 65° C. to carry out a polymerization reaction, thereby preparing a precursor composition containing precursor particles encapsulating cyclohexane.

[0142] (4) Solid-liquid separation process The precursor composition was filtered to obtain a cake of precursor particles separated from the water.

[0143] (5) Solvent removal process 0.25 L of the obtained cake of precursor particles was molded into a thickness of 0.1 cm, placed in a tray vacuum dryer, and heated and dried under an air atmosphere under the conditions shown in Table 1 to obtain hollow resin particles of Example I-1.

[0144] [Examples I-2 to I-5, Comparative Examples I-1 to I-2] In Example I-1, the hollow resin particles of Examples I-2 to I-5 and Comparative Examples I-1 to I-2 were produced in the same manner as in Example I-1, except that the conditions of the heat drying performed in the "(5) Solvent Removal Step" were changed as shown in Table 1.

[0145] [Example I-6] The hollow resin particles of Example I-6 were produced in the same manner as in Example I-1, except that in Example I-1, the amount of methacrylic acid added to the oil phase in the "(1) mixed solution preparation step" was changed to 20 parts, the amount of ethylene glycol dimethacrylate was changed to 80 parts, and the conditions for heat drying in the "(5) solvent removal step" were changed as shown in Table 1.

[0146] [Example I-7] Hollow resin particles of Example I-7 were produced in the same manner as in Example I-1, except that the "(5) solvent removal step" in Example I-1 was changed as follows. In the solvent removal process of Example I-7, 0.1 L of the cake of precursor particles (cake thickness: 3 cm) obtained by the solid-liquid separation process was placed in the stirring vessel of a vertical cylindrical stirring dryer and heated and dried under the conditions shown in Table 2. The vertical cylindrical agitation dryer used in Example I-7 was equipped with a cylindrical agitation vessel of a vertical agitation type, and was equipped with a full-zone type agitation blade fixed to a shaft extending in the direction of gravity. In the agitation vessel, the ratio (b / a) of the maximum distance b in the direction perpendicular to the shaft to the length a of the shaft was 1.67, and the effective volume of the agitation vessel was 0.0001 m. 3 It was.

[0147] [Example I-8] In Example I-7, 2.2 parts of calcium carbonate (average primary particle size: 20 nm, specific gravity: 2.71) was added to the stirring vessel of the vertical cylindrical stirring dryer when the cake of precursor particles was added, and the heating and drying time was changed as shown in Table 2. Except for this, the hollow resin particles of Example I-8 were produced in the same manner as in Example I-7.

[0148] [Example I-9] The hollow resin particles of Example I-9 were produced in the same manner as in Example I-7, except that the amount of methacrylic acid added to the oil phase in the "(1) mixed solution preparation step" was changed to 20 parts and the amount of ethylene glycol dimethacrylate was changed to 80 parts.

[0149] [Example I-10] Hollow resin particles of Example I-10 were produced in the same manner as in Example I-1, except that the "(5) solvent removal step" in Example I-1 was changed as follows. In the solvent removal step in Example I-10, 50 L of the cake of precursor particles (cake thickness: 80 cm) obtained by the solid-liquid separation step and 2.6 parts of calcium carbonate (average primary particle size: 20 nm) were placed in the stirring vessel of a vertical conical stirring dryer, and heated and dried under the conditions shown in Table 2 in an air atmosphere to obtain the hollow resin particles of Example I-10. The vertical conical agitation dryer used in Example I-10 was equipped with a vertical agitation type conical agitation vessel and a spiral ribbon type agitation blade fixed to a shaft extending in the direction of gravity. In the agitation vessel, the ratio (b / a) of the maximum distance b in the direction perpendicular to the shaft to the length a of the shaft was 0.74, and the effective volume of the agitation vessel was 0.05 m. 3 It was.

[0150] [Example I-11] In Example I-10, the "(1) mixed liquid preparation step" and the "(4) solid-liquid separation step" were changed as follows, and the conditions for the heat drying performed in the "(5) solvent removal step" were changed as shown in Table 2. Except for this, the hollow resin particles of Example I-11 were produced in the same manner as in Example I-10. In the mixed solution preparation step in Example I-11, the following materials were mixed, and the resulting mixture was used as an oil phase. Ethylene glycol dimethacrylate 100 parts Polar resin A (MMA / AA / EA copolymer) obtained in Production Example 1: 0.5 parts 2,2'-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) 3 parts Cyclohexane 120 parts Meanwhile, in a stirring tank at room temperature (25°C), an aqueous solution of 5.5 parts of sodium hydroxide (alkali metal hydroxide) in 55 parts of ion-exchanged water was gradually added to an aqueous solution of 7.8 parts of magnesium chloride (water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water under stirring to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (4 parts magnesium hydroxide) as the aqueous phase. A mixture was prepared by mixing the water phase and the oil phase. In the solid-liquid separation step in Example I-11, first, the precursor composition obtained by the polymerization step was washed with dilute sulfuric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less, and then the water was separated by filtration. Then, 200 parts of fresh ion-exchanged water was added to reslurry the mixture, and the water was separated by filtration. This water washing treatment was repeated several times at room temperature (25°C) to obtain a cake of precursor particles separated from the water.

[0151] [Example I-12] The hollow resin particles of Example I-12 were produced in the same manner as in Example I-10, except that calcium carbonate was not added to the stirring vessel and the heat drying time was changed to the time shown in Table 2.

[0152] [Example I-13] The hollow resin particles of Example I-13 were produced in the same manner as in Example I-10, except that the amount of methacrylic acid added to the oil phase in the "(1) mixed solution preparation step" was changed to 20 parts, the amount of ethylene glycol dimethacrylate was changed to 80 parts, calcium carbonate was not added to the stirring vessel, and the heat drying time was changed to the time shown in Table 2.

[0153] [Example I-14] In Example I-1, the "(5) Solvent Removal Step" was changed as follows, except that I- In the same manner as in Example I-14, hollow resin particles were produced. In the solvent removal step of Example I-14, 12 L of the cake of precursor particles (cake thickness: 30 cm) obtained by the solid-liquid separation step and 2.6 parts of calcium carbonate (average primary particle size: 20 nm) were placed in a stirring vessel of a two-shaft horizontal continuous stirring dryer, and heated and dried under the conditions shown in Table 2 in an air atmosphere to obtain hollow resin particles of Example I-14. The twin-shaft horizontal continuous agitation dryer used in Example I-14 is equipped with a cylindrical agitation vessel of a horizontal agitation type, two shafts extending in the horizontal direction, and a paddle-type heat transfer agitation blade fixed to the shaft. The ratio (b / a) of the maximum distance b in the direction perpendicular to the shaft to the length a of the shaft is 0.6, and the effective volume of the agitation vessel is 12 m. 3 and the ratio of heat transfer area to effective volume was 25.8.

[0154] [Example I-15] Hollow resin particles of Example I-15 were produced in the same manner as in Example I-14, except that the heat drying conditions in Example I-14 were changed as shown in Table 2.

[0155] [Example I-16] In Example I-14, the "(1) mixed liquid preparation step" and the "(4) solid-liquid separation step" were changed in the same manner as in Example I-11, and the conditions for the heat drying performed in the "(5) solvent removal step" were changed as shown in Table 2. Except for this, the hollow resin particles of Example I-16 were produced in the same manner as in Example I-14.

[0156] [Example I-17] The hollow resin particles of Example I-17 were produced in the same manner as in Example I-14, except that calcium carbonate was not added to the two-shaft horizontal continuous agitator dryer and the heat drying time was changed to the time shown in Table 2.

[0157] [Example I-18] In Example I-14, the amount of methacrylic acid added to the oil phase in the "(1) mixed liquid preparation step" was changed to 20 parts, the amount of ethylene glycol dimethacrylate was changed to 80 parts, calcium carbonate was not added to the two-shaft horizontal continuous stirring dryer, and the heat drying time was changed to the time shown in Table 2. Except for this, the hollow resin particles of Example I-18 were produced in the same manner as in Example I-14.

[0158] <Measurement of precursor particles> In each of the Examples and Comparative Examples, about 4 g of the precursor particles obtained in the solid-liquid separation step was sampled and subjected to the following measurements before the solvent removal step was carried out.

[0159] A. Temperature at which the precursor particles begin to decompose (T2) About 15 mg of the precursor particles obtained in the above "(4) solid-liquid separation step" was precisely weighed out and used as a measurement sample. A TG-DTA device, Model TG / DTA6200 (EXSTAR6000 series) manufactured by Seiko Instruments Inc., was used as the TG-DTA device, and measurements were performed under the following conditions in an air atmosphere to obtain a TG-DTA curve. Air flow rate: 230mL / min Heating rate: 10℃ / min Measurement temperature range: 30℃ to 800℃ From the obtained TG-DTA curve, the thermal decomposition onset temperature was calculated using the analysis software attached to the device.

[0160] B. Moisture content of precursor particles The moisture content was calculated from the mass (w1) of about 0.1 mg of the precursor particles obtained in the above "(4) solid-liquid separation step" and the mass (w2) of the weighed precursor particles after drying at 105° C. for 1 hour, cooling to 25° C., and then weighing again, using the mass (w2) according to the following formula (i). For drying, a dryer with a temperature error of 1° C. or less in the drying chamber was used. Formula (i) Moisture content (%)={(w1-w2) / w1}×100

[0161] C. Permeation of hydrocarbon solvents from precursor particles The precursor particles obtained in the above "(4) solid-liquid separation step" were dried at 40° C. for 24 hours, and about 3 g of the precursor particles A were sampled and further precisely weighed to about 0.1 mg to obtain a mass (w3). The precisely weighed precursor particles A were further dried at 105° C. for 2 hours, and then cooled to 25° C. to obtain a mass (w4) of precursor particles B. From these masses, the permeability of the hydrocarbon solvent from the precursor particles was calculated according to the following formula (ii). For drying, a dryer with a temperature error of 1° C. or less in the drying chamber was used. Formula (ii) Hydrocarbon solvent permeability (%) = {(w3-w4) / w3} x 100

[0162] D. Volume average particle size of precursor particles The particle size of the precursor particles obtained in the above "(4) solid-liquid separation step" was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, product name: SALD-2000), and the volume average was calculated to obtain the volume average particle size of the precursor particles.

[0163] <Measurement and evaluation of hollow resin particles> The hollow resin particles obtained in each of the Examples and Comparative Examples were subjected to the following measurements and evaluations.

[0164] 1. SEM observation of hollow resin particles 100 hollow resin particles obtained in each Example and Comparative Example were observed by SEM to confirm the presence or absence of pores of 100 nm or more on the surface of each particle. When there were less than 5 hollow resin particles with pores of 100 nm or more, the particle damage was evaluated as "absent," and when there were 5 or more hollow resin particles with pores of 100 nm or more, the particle damage was evaluated as "present."

[0165] 2. Volume average particle size of hollow resin particles The particle size of the hollow resin particles was measured using a laser diffraction particle size distribution measuring instrument (manufactured by Shimadzu Corporation, product name: SALD-2000), and the volume average was calculated to obtain the volume average particle size of the hollow resin particles.

[0166] 3. Density and porosity of hollow resin particles 3-1. Measurement of apparent density of hollow resin particles First, 100cm capacity 3 About 30 cm 3 The hollow resin particles were filled with 1000 g of hollow resin particles, and the mass of the filled hollow resin particles was precisely weighed. Next, the measuring flask filled with the hollow resin particles was precisely filled with isopropanol up to the marked line, while being careful not to introduce air bubbles. The mass of isopropanol added to the measuring flask was precisely weighed, and the apparent density D1 (g / cm) of the hollow resin particles was calculated based on the following formula (I). 3 ) was calculated. Formula (I) Apparent density D1 = [mass of hollow resin particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature])

[0167] 3-2. Measurement of true density of hollow resin particles After crushing the hollow resin particles in advance, 3 Approximately 10 g of crushed pieces of hollow resin particles were filled into a measuring flask, and the mass of the packed crushed pieces was accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol is added to the measuring flask, the mass of isopropanol is accurately weighed, and the true density D0 (g / cm) of the hollow resin particles is calculated based on the following formula (II). 3 ) was calculated. Formula (II) True density D0 = [mass of crushed pieces of hollow resin particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature])

[0168] 3-3. Calculation of actual porosity The measured porosity of the hollow resin particle was calculated from the apparent density D1 and true density D0 of the hollow resin particle according to the following formula (III). Formula (III) Measured porosity (%) = 100 - (apparent density D1 / true density D0) x 100

[0169] 3-4. Calculation of theoretical porosity The theoretical porosity of the hollow resin particles was calculated from the mass Ws of the hydrocarbon solvent and the specific gravity Gs of the hydrocarbon solvent in the mixed liquid preparation step, the mass Wr of the solid raw materials constituting the hollow resin particles, and the true density D0 of the hollow resin particles calculated above, according to the following formula (IV). Formula (IV) Theoretical porosity (%)=(Ws / Gs)÷{(Ws / Gs)+(Wr / D0)}×100 The hydrocarbon solvent used in each Example and Comparative Example was cyclohexane, and the specific gravity of cyclohexane was 0.778. The charged mass Wr of the solid raw materials constituting the hollow resin particles was the total charged mass of the polymerizable monomer, the polar resin, and calcium carbonate used as the fine particles.

[0170] 4.Shell thickness of hollow resin particles The inner diameter r of the hollow resin particles was calculated from the volume average particle diameter R1 and theoretical porosity of the hollow resin particles according to the following formula (1), and the shell thickness of the hollow resin particles was calculated from the inner diameter r and the volume average particle diameter R1 according to the following formula (2). 4 / 3π×(R1 / 2) 3 ×Theoretical porosity=4 / 3π×(r / 2) 3 Formula (1) Shell thickness = (R1-r) / 2 Equation (2)

[0171] 5. Residual rate of hydrocarbon solvents in hollow resin particles From the theoretical porosity and the actually measured porosity of the hollow resin particles, the residual rate of the hydrocarbon solvent in the hollow resin particles was calculated according to the following formula (V). Formula (V) Hydrocarbon solvent residual rate (%) = 100 - (actual porosity / theoretical porosity) x 100

[0172] 6. Moisture content of hollow resin particles The moisture content was calculated by the above formula (i) from the mass (w1) of about 0.1 mg of hollow resin particles precisely weighed out and the mass (w2) of the hollow resin particles precisely weighed out after drying at 105° C. for 1 hour and cooling to 25° C. The same dryer as that used to determine the moisture content of the precursor particles was used for drying.

[0173] 7. Coverage of fine particles in hollow resin particles In the examples in which fine particles were added in the solvent removal step, the volume average particle diameter R2 (nm) of the hollow resin particles assumed to contain no fine particles, the apparent density S (g / cm) of the hollow resin particles assumed to contain no fine particles and no hydrocarbon solvent, 3 ), the average primary particle size d (nm) of the microparticles, and the specific gravity s and amount added n (parts by mass) of the microparticles (based on 100 parts by mass of hollow resin particles assumed to contain no microparticles or hydrocarbon solvents) were used to calculate the coverage rate (%) of the microparticles relative to the surface area of ​​the hollow resin particles using the following formula (A). Formula (A) Coverage rate of particles (%) = {3 1 / 2 / 2π}×{(R2×S) / (d×s)}×n As the volume average particle diameter R2 of the hollow resin particles assumed to contain no fine particles, the volume average particle diameter of the precursor particles obtained above was used. The apparent density S of the hollow resin particles, which is assumed to contain no fine particles or hydrocarbon solvents, was determined by measuring the apparent density of the precursor particles, which were the same as those used to produce the hollow resin particles, by leaving them to stand and drying them at 230°C for 24 hours, in the same manner as in "3-1. Measurement of the apparent density of hollow resin particles" above.

[0174] 8. Productivity The weight (kg) of the obtained hollow resin particles was divided by the heat drying time (h) performed in the solvent removal step, and the effective volume (m 3 ) divided by (kg / (h m 3 ) was calculated as an indicator of productivity.

[0175] 9.Powder adhesion to the mixing blades In the examples using an agitator dryer, the agitator blades of the dryer were visually inspected immediately after the hollow resin particles were removed from the dryer to check for the presence or absence of powder adhesion. The drying efficiency is superior when no powder adhesion is present on the agitator blades.

[0176] 10. Crushing strength The crushing strength of the obtained hollow resin particles was measured under the following test conditions using a microparticle crushing strength measuring device NS-A100 (manufactured by Nano Seeds Corporation). (Test conditions) Measurement method: A sample of hollow resin particles was scattered onto a stage by free fall, and the crushing force was measured using a crushing needle. Measurement temperature: room temperature (25℃) Analysis method: A crushing needle was pressed into a hollow resin particle sample at a compression speed of 0.3 μm / s, and a waveform chart of the load F required to crush the hollow resin particle was recorded. The difference between the peak value at the time of crushing and the baseline (when no load is applied) was taken as the crushing force F [N]. The crushing strength S [Pa] was calculated using the following formula (B). Formula (B) S = 2.8F / (π×D 2 ) In the formula (B), F is as described above, and D is the particle diameter [m] of the hollow resin particle. The distance from the tip of the crushing needle (indenter) to the stage (flat surface) when the crushing needle contacted the hollow resin particle was measured from the image during measurement using image analysis software (product name: WinROOF, manufactured by Mitani Shoji Co., Ltd.), and this was taken as the particle diameter D of the hollow resin particle. The higher the crushing strength, the higher the strength of the hollow resin particles.

[0177] [Table 1]

[0178] [Table 2]

[0179] [Consideration] In Comparative Example I-1, the temperature of the heat drying for removing the hydrocarbon solvent was too low, so the obtained hollow resin particles had a large amount of residual hydrocarbon solvent inside. The hollow resin particles obtained in Comparative Example I-1 had a high specific gravity due to the inclusion of the hydrocarbon solvent in the hollow portion, so the above value (kg / (h m 3 ) could not be used as an indicator of productivity, and the crushing strength was not worth measuring. In Comparative Example I-2, the temperature of heat drying to remove the hydrocarbon solvent was too high, and the obtained hollow resin particles were highly damaged, with many pores of 100 nm or more in the shell. Note that the hollow resin particles obtained in Comparative Example I-2 were highly damaged, and therefore the porosity and residual rate of hydrocarbon solvent could not be determined. In addition, in Comparative Example I-2, the hollow resin particles obtained were highly damaged, and the desired hollow resin particles were not obtained, so the above-mentioned value (kg / (h m 3 ) was not calculated, and the crushing strength was not measured.

[0180] In Examples I-1 to I-18, in the production of hollow resin particles by suspension polymerization, the ratio of crosslinkable monomer in the polymerizable monomer was 40 to 100 mass%, and the temperature T0 of the heating and drying to remove the hydrocarbon solvent was set to T1+70≦T0≦T2-5, where T1 (°C) is the boiling point of the hydrocarbon solvent and T2 (°C) is the thermal decomposition starting temperature of the precursor particles. As a result, the obtained hollow resin particles were spherical and undamaged, and the hydrocarbon solvent was sufficiently removed. Among them, in Examples I-7 to I-18, the heat drying for removing the hydrocarbon solvent was performed by stirring and drying, and thus the productivity was excellent. Furthermore, in comparison with Examples I-8, I-10 to I-11, and I-14 to I-16, which used the same stirring device, Examples I-7, I-12, and I-17, respectively, the productivity was improved in Examples I-8, I-10 to I-11, and I-14 to I-16, in which the stirring and drying of the precursor particles was performed together with the fine particles. This is considered to be because the surface of the precursor particles was covered with the fine particles during the stirring and drying, and as a result, the fluidity of the precursor particles was improved, and the drying and removal efficiency of the hydrocarbon solvent was improved, and further, the adhesion of the powder to the stirring blade was suppressed. In addition, when Examples I-11 and I-16 are compared with Examples I-10, I-12 and Examples I-14, I-15, and I-17, which used the same stirring device, the productivity was improved in Examples I-11 and I-16, which had a hydrocarbon solvent permeability of 5%. This is thought to be because in Examples I-11 and I-16, the shell was slightly permeable to the hydrocarbon solvent at 105°C, which improved the efficiency of removing the hydrocarbon solvent from the precursor particles. In addition, in Examples I-6, I-9, I-11, I-13, I-16 and I-18, in which the content of the crosslinkable monomer in the polymerizable monomer used for producing the hollow resin particles was relatively high, the crushing strength of the hollow resin particles was improved. This is believed to be because the content of the crosslinkable monomer unit in the shell of the hollow resin particles was increased, thereby improving the strength of the hollow particles.

[0181] Example II Series [Example II-1] The hollow resin particles of Example II-1 were produced in the same manner as in Example I-10 of the Example I series.

[0182] [Example II-2] The hollow resin particles of Example II-2 were produced in the same manner as in Example I-11 of the Example I series.

[0183] [Example II-3] The hollow resin particles of Example II-3 were produced in the same manner as in Example I-12 of the Example I series.

[0184] [Example II-4] The hollow resin particles of Example II-4 were produced in the same manner as in Example I-7 of the above-mentioned Example I series, except that the heat drying conditions were changed as shown in Table 3.

[0185] [Example II-5] The hollow resin particles of Example II-5 were produced in the same manner as in Example I-8 of the above-mentioned Example I series, except that the heat drying conditions were changed as shown in Table 3.

[0186] [Comparative Examples II-1 to II-5] Hollow resin particles of Comparative Examples II-1 to II-5 were produced in the same manner as in Example II-1, except that the solvent removal step in Example II-1 was changed as follows. In the solvent removal process of Comparative Examples II-1 to II-5, the cake of precursor particles obtained by the solid-liquid separation process was formed into the amount and thickness shown in Table 3, placed in a shelf vacuum dryer, and heated and dried under the conditions shown in Table 3.

[0187] <Measurement of precursor particles> The precursor particles obtained in the solid-liquid separation step of each of the Examples and Comparative Examples were subjected to the same measurements as those in the Example I series.

[0188] <Measurement and evaluation of hollow resin particles> The hollow resin particles obtained in each of the Examples and Comparative Examples were subjected to the same measurements and evaluations as those in the Example I series.

[0189] [Table 3]

[0190] [Consideration] In Comparative Examples II-1 to II-5, the heat drying to remove the hydrocarbon solvent was performed by static drying, and stirring drying using a vertical stirring method was not performed. In Comparative Examples II-1 and II-2, static drying was performed at 180°C, and as a result, a large amount of hydrocarbon solvent remained in the obtained hollow resin particles even though the amount of precursor particles charged was reduced for the same drying time as in Example II-1. The hollow resin particles obtained in Comparative Examples II-1 and II-2 had a large specific gravity due to the inclusion of hydrocarbon solvent in the hollow portion, and therefore the above-mentioned value (kg / (h m 3 ) could not be used as an indicator of productivity, and the crushing strength was not worth measuring. In Comparative Examples II-3 and II-4, static drying at 230° C. enabled the removal of the hydrocarbon solvent from the hollow resin particles, but resulted in poor productivity. In Comparative Example II-5, the hollow resin particles obtained were dried at 280°C and had many pores of 100 nm or more in the shell, which resulted in a lot of breakage. In Comparative Example II-5, the hollow resin particles obtained were often broken and the desired hollow resin particles were not obtained, so the value (kg / (h m) which is an index of productivity was not obtained. 3 ) was not calculated, and the crushing strength was not measured.

[0191] In Examples II-1 to II-5, in the production of hollow resin particles by suspension polymerization, the ratio of crosslinkable monomer in the polymerizable monomer was 40 to 100 mass%, and the heat drying to remove the hydrocarbon-based solvent was performed while stirring the precursor particles in a vertical stirring vessel. As a result, the obtained hollow resin particles were unbroken and spherical, the hydrocarbon-based solvent was sufficiently removed, and further, the productivity was excellent. Among them, in comparison with Examples II-1, II-2 and II-5 and Examples II-3 and II-4, which used the same stirring device, respectively, the productivity was improved in Examples II-1, II-2 and II-5, in which the stirring drying of the precursor particles was performed together with the fine particles. This is considered to be because the surfaces of the precursor particles were covered with the fine particles during the stirring drying, improving the fluidity of the precursor particles, thereby improving the efficiency of drying and removing the hydrocarbon solvent, and further suppressing the adhesion of powder to the stirring blades. In addition, comparing Example II-2 with Examples II-1 and II-3 using the same stirring device, the productivity was improved in Example II-2, in which the permeability of the hydrocarbon solvent was 5%. This is believed to be because in Example II-2, the shell was slightly permeable to the hydrocarbon solvent at 105°C, which improved the efficiency of removing the hydrocarbon solvent from the precursor particles. In addition, in Example II-2, in which the content of the crosslinkable monomer in the polymerizable monomer used for producing the hollow resin particles was relatively high, the crushing strength of the hollow resin particles was improved. This is believed to be because the content of the crosslinkable monomer unit in the shell of the hollow resin particles was increased, thereby improving the strength of the hollow particles.

[0192] <Example III Series> [Example III-1] The hollow resin particles of Example III-1 were produced in the same manner as in Example I-14 of the Example I series.

[0193] [Example III-2] The hollow resin particles of Example III-2 were produced in the same manner as in Example I-15 of the Example I series.

[0194] [Example III-3] The hollow resin particles of Example III-3 were produced in the same manner as in Example I-16 of the Example I series.

[0195] [Example III-4] The hollow resin particles of Example III-4 were produced in the same manner as in Example I-17 of the Example I series.

[0196] [Comparative Examples III-1 to III-5] Hollow resin particles of Comparative Examples III-1 to III-5 were produced in the same manner as in Example III-1, except that the "solvent removal step" in Example III-1 was changed as follows. In the solvent removal process of Comparative Examples III-1 to III-5, the cake of precursor particles obtained by the solid-liquid separation process was formed into the amount and thickness shown in Table 4, placed in a shelf vacuum dryer, and heated and dried under the conditions shown in Table 4.

[0197] <Measurement of precursor particles> The precursor particles obtained in the solid-liquid separation step of each of the Examples and Comparative Examples were subjected to the same measurements as those in the Example I series.

[0198] <Measurement and evaluation of hollow resin particles> The hollow resin particles obtained in each of the Examples and Comparative Examples were subjected to the same measurements and evaluations as those in the Example I series.

[0199] [Table 4]

[0200] [Consideration] In Comparative Examples III-1 to III-5, the heat drying to remove the hydrocarbon solvent was performed by static drying, and stirring drying using a horizontal stirring method was not performed. In Comparative Examples III-1 and III-2, static drying was performed at 180°C, and as a result, a large amount of hydrocarbon solvent remained in the obtained hollow resin particles even if the amount of precursor particles charged was reduced for the same drying time as in Example III-1. In Comparative Examples III-3 and III-4, static drying was performed at 230°C. As a result, in the Comparative Examples where the amount of precursor particles charged was 10 L, III- In Comparative Example III-3, a large amount of hydrocarbon-based solvent remained in the obtained hollow resin particles. In Comparative Example III-4, in which the amount of precursor particles charged was reduced to 0.25 L, the hydrocarbon-based solvent in the hollow resin particles could be removed, but the productivity was poor. The hollow resin particles obtained in Comparative Examples III-1 to III-3 had a high specific gravity due to the inclusion of the hydrocarbon-based solvent in the hollow portion, and therefore the above-mentioned value (kg / (h m 3 ) could not be used as an indicator of productivity, and the crushing strength was not worth measuring. In Comparative Example III-5, the hollow resin particles obtained were dried at 280°C and had many pores of 100 nm or more in the shell, which resulted in a lot of breakage. In Comparative Example III-5, the hollow resin particles obtained were often broken, and the desired hollow resin particles could not be obtained. Therefore, the value (kg / (h m), which is an index of productivity, was not obtained. 3 ) was not calculated, and the crushing strength was not measured.

[0201] In Examples III-1 to III-4, in the production of hollow resin particles by suspension polymerization, the ratio of crosslinkable monomer in the polymerizable monomer was 40 to 100 mass%, and the heat drying to remove the hydrocarbon solvent was performed while stirring the precursor particles in a horizontal stirring vessel. As a result, the obtained hollow resin particles were unbroken and spherical, the hydrocarbon solvent was sufficiently removed, and further, the productivity was excellent. Among them, in comparison between Examples III-1 to III-3 and Example III-4, the productivity was improved in Examples III-1 to III-3 in which the stirring and drying of the precursor particles was carried out together with the fine particles. This is considered to be because the surfaces of the precursor particles were covered with the fine particles during the stirring and drying, which improved the fluidity of the precursor particles, improved the efficiency of drying and removing the hydrocarbon solvent, and further suppressed the adhesion of the powder to the stirring blades. In addition, comparing Example III-3 with Examples III-1, III-2, and III-4, Example III-3, which had a hydrocarbon solvent permeability of 5%, had a higher productivity. This is believed to be because, in Example III-3, the shell was slightly permeable to the hydrocarbon solvent at 105°C, which improved the efficiency of removing the hydrocarbon solvent from the precursor particles. In addition, in Example III-3, in which the content of the crosslinkable monomer in the polymerizable monomer used for producing the hollow resin particles was relatively high, the crushing strength of the hollow resin particles was improved. This is believed to be because the content of the crosslinkable monomer unit in the shell of the hollow resin particles was increased, thereby improving the strength of the hollow particles. [Explanation of symbols]

[0202] 1 Aqueous medium 2 Low polarity material 3. Suspension stabilizers 4. Polymerizable monomer composition 4a Hydrocarbon solvents 4b Materials other than hydrocarbon solvents 4c Polymerizable monomers dissolved in aqueous media 5. Polymerization initiator 6. Shell 7 Hollow part 10 Droplets of polymerizable monomer composition 20 Precursor particles 30A Vertical Agitator Dryer 30B Horizontal agitator dryer 31 Shaft 32 Mixing blade 33 Mixing vessel 34 Jacket 35 Supply port 36 Outlet 100 Hollow resin particles

Claims

1. A method for producing hollow resin particles, comprising the steps of: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; obtaining the precursor particles separated from the aqueous medium by subjecting the precursor composition to solid-liquid separation; and removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles separated from the aqueous medium, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, The boiling point T of the hydrocarbon solvent １ (° C.) and the thermal decomposition starting temperature T ２ (° C.), the heating and drying temperature T ０ (°C) is T １ +70≦T ０ ≦T ２ Meets -5, a step of heating and drying the precursor particles separated from the aqueous medium together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles while stirring in a stirring vessel, thereby coating the surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles, the step of producing hollow resin particles comprising the steps of:

2. The boiling point T of the hydrocarbon solvent １ The method for producing hollow resin particles according to claim 1, wherein the temperature is 70 to 90° C.

3. 3. The method for producing hollow resin particles according to claim 1, wherein the hollow resin particles have a porosity of 50 to 95%.

4. The method for producing hollow resin particles according to any one of claims 1 to 3, wherein the pressure during the heat drying in the step of removing the hydrocarbon solvent is 0 to 101.3 kPa.

5. The method for producing hollow resin particles according to any one of claims 1 to 4, wherein the hydrocarbon solvent is a hydrocarbon solvent having 4 to 7 carbon atoms.

6. 6. The method for producing hollow resin particles according to claim 1, wherein the precursor particles used in the step of removing the hydrocarbon solvent have a water content of 50% or less.

7. A method for producing hollow resin particles, comprising the steps of: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, A method for producing hollow resin particles, characterized in that the step of removing the hydrocarbon-based solvent is a step of removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles while stirring them in a vertical stirring vessel equipped with a shaft extending in the direction of gravity and a stirring blade.

8. The method for producing hollow resin particles according to claim 7, wherein the hollow resin particles have a porosity of 50 to 95%.

9. The boiling point T of the hydrocarbon solvent １ (° C.) and the thermal decomposition starting temperature T ２ (° C.), the heating and drying temperature T ０ (°C) is T １ ≦T ０ ≦T ２ The method for producing hollow resin particles according to claim 7 or 8, wherein the viscosity of the hollow resin particles satisfies -5.

10. The method for producing hollow resin particles according to any one of claims 7 to 9, wherein the stirring vessel used in the step of removing the hydrocarbon solvent is cylindrical or conical.

11. The method for producing hollow resin particles according to any one of claims 7 to 10, further comprising a step of subjecting the precursor composition to solid-liquid separation after the step of preparing the precursor composition and before the step of removing the hydrocarbon-based solvent, thereby obtaining the precursor particles separated from the aqueous medium.

12. The method for producing hollow resin particles according to any one of claims 7 to 11, wherein the step of removing the hydrocarbon-based solvent is a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in the stirring vessel while stirring, thereby coating surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles.

13. A method for producing hollow resin particles, comprising the steps of: A step of preparing a mixed liquid containing a polymerizable monomer, a hydrocarbon-based solvent, a polymerization initiator, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrocarbon-based solvent, and the polymerization initiator are dispersed in the aqueous medium; a step of subjecting the suspension to a polymerization reaction to prepare a precursor composition including precursor particles having hollow portions and containing the hydrocarbon solvent in the hollow portions; and removing the hydrocarbon solvent contained in the precursor particles, The polymerizable monomer contains a crosslinkable monomer in a ratio of 40 to 100% by mass, A method for producing hollow resin particles, characterized in that the step of removing the hydrocarbon-based solvent is a step of removing the hydrocarbon-based solvent contained in the precursor particles by heating and drying the precursor particles while stirring them in a horizontal stirring vessel equipped with a horizontally extending shaft and a stirring blade.

14. The method for producing hollow resin particles according to claim 13, wherein the hollow resin particles have a porosity of 50 to 95%.

15. The boiling point T of the hydrocarbon solvent １ (° C.) and the thermal decomposition starting temperature T ２ (° C.), the heating and drying temperature T ０ (°C) is T １ ≦T ０ ≦T ２ The method for producing hollow resin particles according to claim 13 or 14, wherein the viscosity of the hollow resin particles satisfies -5.

16. The method for producing hollow resin particles according to any one of claims 13 to 15, wherein the step of removing the hydrocarbon solvent is carried out using a continuous dryer equipped with a stirring vessel of a multi-shaft horizontal stirring system equipped with a plurality of shafts extending horizontally and stirring blades.

17. The method for producing hollow resin particles according to any one of claims 13 to 16, further comprising a step of subjecting the precursor composition to solid-liquid separation after the step of preparing the precursor composition and before the step of removing the hydrocarbon-based solvent, thereby obtaining the precursor particles separated from the aqueous medium.

18. The method for producing hollow resin particles according to any one of claims 13 to 17, wherein the step of removing the hydrocarbon-based solvent is a step of heating and drying the precursor particles together with at least one type of fine particles selected from the group consisting of inorganic fine particles and organic fine particles in the stirring vessel while stirring, thereby coating surfaces of the precursor particles with the fine particles and removing the hydrocarbon-based solvent contained in the precursor particles.

Images