Aqueous dispersion, hollow particles, and method for producing aqueous dispersion

Abstract

To provide an aqueous dispersion that contains hollow particles made of acid-modified polyphenylene ether, which are lightweight and less prone to cracking.SOLUTION: An aqueous dispersion contains hollow particles, each composed of an acid-modified polyphenylene ether resin and having a shell part and a hollow part, and a medium. The acid-modified polyphenylene ether resin is a polyphenylene ether resin modified with at least one functional group selected from the group consisting of a sulfo group, a carboxy group, a carboxylic anhydride group, and a phosphoric acid group, and the medium comprises a basic compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aqueous dispersion containing hollow particles, hollow particles, and a method for producing the aqueous dispersion. [Background technology]

[0002] Hollow particles having voids inside the particle have been developed in various types, as they are excellent in low dielectric properties, heat insulating properties, low refractive index, etc. Conventionally, hollow particles made of inorganic materials such as glass and metal oxides have been used, but inorganic materials have a problem in that they are high in density and are unsuitable for applications requiring light weight.

[0003] Against this background, hollow particles made of organic polymers have been studied in recent years. For example, Patent Document 1 discloses hollow particles containing a resin having fluorine atoms. However, fluorine components are toxic to the environment and the human body, and are also inferior in terms of lightness, so hollow particles that do not contain fluorine components have been desired.

[0004] In view of this situation, hollow particles made of a non-fluorine-based resin component have been proposed in Patent Documents 2 and 3. However, the hollow particles described in these documents have the problem that they are poor in flexibility and are brittle and prone to cracking because they are made of a resin component that has been made high in molecular weight by copolymerizing a crosslinkable monomer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-213366 [Patent Document 2] Japanese Patent Publication No. 2023-072023 [Patent Document 3] Japanese Patent Publication No. 2023-021971 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of these problems, an object of the present invention is to provide hollow particles that do not contain fluorine components, are made of a lightweight resin component, and are flexible and not easily broken. [Means for solving the problem]

[0007]

[0009] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have discovered that an aqueous dispersion containing hollow particles that are less likely to break can be obtained by a method that does not rely on copolymerization of a crosslinkable monomer, and have arrived at the present invention.

[0008] (1) An aqueous dispersion containing hollow particles made of an acid-modified polyphenylene ether resin and having a shell portion and a hollow portion, and an aqueous medium, wherein the acid-modified polyphenylene ether resin is a polyphenylene ether resin acid-modified with at least one functional group selected from the group consisting of a sulfo group, a carboxy group, a carboxylic anhydride group, and a phosphate group, and the aqueous medium contains a basic compound. (2) The aqueous dispersion of (1), wherein the acid-modified polyphenylene ether resin has an acid value of 0.5 to 80 mgKOH / g. (3) The aqueous dispersion of (1) or (2), wherein the basic compound is ammonia or an organic amine compound having a boiling point of 250°C or less. (4) The aqueous dispersion of any one of (1) to (3), wherein the hollow particles have a volume average particle size of 10 to 5,000 nm. (5) Hollow particles obtained by removing the aqueous medium from the aqueous dispersion of any one of (1) to (4). (6) A method for producing the aqueous dispersion of any one of (1) to (4), comprising the following steps (I) and (II): (I) A step of mixing an acid-modified polyphenylene ether resin with a basic compound and an aqueous medium, and further stirring the mixture under heating at 70°C or higher to convert the acid-modified polyphenylene ether resin into an aqueous dispersion. (II) A step of adding water at 35°C or less all at once to the aqueous dispersion of acid-modified polyphenylene ether resin obtained in (I) above, wherein the temperature of the aqueous dispersion of acid-modified polyphenylene ether resin before the addition of water is 40°C or higher. [Effects of the Invention]

[0009] According to the present invention, an aqueous dispersion containing lightweight, shatter-resistant hollow particles made of an acid-modified polyphenylene ether resin can be obtained. Furthermore, by removing the medium from the aqueous dispersion of the present invention, it is possible to easily obtain hollow particles made of an acid-modified polyphenylene ether resin that are shatter-resistant and maintain their hollow portions. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram showing the cross-sectional structure of hollow particles contained in the aqueous dispersion obtained in Example 2 of the present invention. [Figure 2] FIG. 2 is a diagram showing the cross-sectional structure of hollow particles contained in the aqueous dispersion obtained in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. The aqueous dispersion of the present invention contains hollow particles and an aqueous medium. The hollow particles are made of an acid-modified polyphenylene ether resin and have a shell portion and a hollow portion. Here, "hollow" means that the interior is filled with a substance other than resin, such as a gas or liquid, and preferably means that the interior is filled with a gas, which can further enhance the effects of the present invention.

[0012] The shell portion and the hollow portion surrounded by the shell portion may consist of one hollow region, or may consist of multiple hollow regions.

[0013] The shell and the hollow portion enclosed by the shell may have a porous structure. When the hollow portion has a porous structure, the hollow portion may consist of one hollow region (continuous pores), multiple hollow regions (closed pores), or a mixture of these.

[0014] <Acid-modified polyphenylene ether resin> The acid-modified polyphenylene ether resin constituting the shell of the hollow particles must be acid-modified with at least one functional group selected from the group consisting of a sulfo group, a carboxy group, a carboxylic anhydride group, and a phosphate group. When the acid-modified polyphenylene ether resin constituting the shell has these functional groups, hollow spaces are more likely to be formed inside the particles in the production of an aqueous dispersion, which will be described later. From the viewpoint of the ease of forming hollow spaces inside the particles, it is preferable that the acid-modified polyphenylene ether resin has at least one functional group selected from the group consisting of a carboxy group and a carboxylic anhydride group.

[0015] The method for producing the acid-modified polyphenylene ether resin used in the present invention is not particularly limited, and examples thereof include a method in which a polyphenylene ether resin and a vinyl compound having the above-mentioned functional group are heated to a temperature equal to or higher than the melting point of the polyphenylene ether resin in the presence of a radical generator to cause a reaction, or a method in which a polyphenylene ether resin and a vinyl compound having the above-mentioned functional group are dissolved in an organic solvent and then heated and stirred in the presence of a radical generator to cause a reaction. By these methods, the vinyl compound having the above-mentioned functional group can be graft-copolymerized onto the polyphenylene ether resin. In addition, in a method for producing a polyphenylene ether resin acid-modified with a sulfo group, a method of treating the polyphenylene ether resin with a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, or chlorosulfonic acid can also be employed.

[0016] Examples of vinyl compounds having a sulfo group that can be used include vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and salts of these compounds.

[0017] Examples of vinyl compounds having a carboxy group that can be used include acrylic acid, methacrylic acid, maleic acid, fumaric acid, oleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, cinnamic acid, maleic acid monoalkyl esters, fumaric acid monoalkyl esters, and salts of these compounds.

[0018] Examples of vinyl compounds having a carboxylic acid anhydride group that can be used include maleic anhydride, itaconic anhydride, aconitic anhydride, acrylic anhydride, and methacrylic anhydride.

[0019] Examples of vinyl compounds having a phosphoric acid group that can be used include vinylphosphonic acid, allylphosphonic acid, 2-hydroxyethyl methacrylic acid phosphate, and salts of these compounds.

[0020] Examples of radical generators include organic peroxides such as di-tert-butyl peroxide, dicumyl peroxide, tert-butyl hydroperoxide, tert-butylcumyl peroxide, benzoyl peroxide, dilauryl peroxide, cumene hydroperoxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, and di-tert-butyl diperphthalate, and azo compounds such as azobisisobutyronitrile. Compounds such as 2,3-dimethyl-2,3-diphenylbutane, 2,3-diethyl-2,3-diphenylbutane, 2,3-diethyl-2,3-diphenylhexane, and 2,3-diethyl-2,3-di(p-methylphenyl)butane can also be used as radical generators. These compounds can be appropriately selected and used depending on the reaction temperature.

[0021] In the present invention, the acid value of the acid-modified polyphenylene ether resin is preferably 0.5 to 80 mgKOH / g, more preferably 1.5 to 50 mgKOH / g, even more preferably 3 to 45 mgKOH / g, and particularly preferably 5 to 25 mgKOH / g. If the acid value of the acid-modified polyphenylene ether resin is less than 0.5 mgKOH / g, it may be difficult to form an aqueous dispersion of the acid-modified polyphenylene ether resin in the method described below. Furthermore, if the acid value of the acid-modified polyphenylene ether resin exceeds 80 mgKOH / g, it may be difficult to form hollow portions inside the particles in the production of the aqueous dispersion described below.

[0022] The number-average molecular weight of the acid-modified polyphenylene ether resin is preferably 2,000 to 100,000, more preferably 5,000 to 90,000, even more preferably 8,000 to 80,000, and particularly preferably 8,000 to 55,000. If the number-average molecular weight of the acid-modified polyphenylene ether resin is less than 2,000, the resulting hollow particles may have poor shell strength. If the number-average molecular weight of the acid-modified polyphenylene ether resin exceeds 100,000, the melt viscosity or solution viscosity increases during acid modification in the above method, which tends to reduce processability.

[0023] The hollow particles contained in the aqueous dispersion of the present invention preferably have a volume average particle diameter of 10 to 5,000 nm, more preferably 10 to 1,000 nm, even more preferably 20 to 600 nm, and particularly preferably 20 to 300 nm. If the volume average particle diameter of the hollow particles contained in the aqueous dispersion is less than 10 nm, the shell thickness tends to be relatively thin, which may reduce the strength of the particles. If the volume average particle diameter of the hollow particles contained in the aqueous dispersion exceeds 5,000 nm, the surface smoothness of the coating film obtained by coating and drying the aqueous dispersion may be impaired.

[0024] The volume average particle size of the hollow particles contained in the aqueous dispersion can be measured, for example, by dynamic light scattering.

[0025] The aqueous dispersion of the present invention must contain a basic compound. This neutralizes at least one functional group selected from the group consisting of sulfo groups, carboxy groups, carboxylic anhydride groups, and phosphate groups introduced into the polyphenylene ether resin, and the electrostatic repulsion between the resulting anions inhibits interparticle aggregation, further improving the stability of the aqueous dispersion. Any basic compound can be used as long as it can neutralize the functional groups. The basic compound added for this purpose is preferably volatile, as it is less likely to remain when hollow particles are obtained by drying the aqueous dispersion.

[0026] The basic compound is preferably, for example, ammonia or an organic amine compound having a boiling point of 250° C. or less. If the boiling point exceeds 250° C., it may be difficult to remove the organic amine compound from the aqueous dispersion by drying.

[0027] Examples of basic compounds that can be contained in the aqueous dispersion of the present invention include ammonia, trimethylamine, triethylamine, isopropylamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, ethylamine, diethylamine, isobutylamine, dipropylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, n-butylamine, 2-methoxyethylamine, 3-methoxypropylamine, 2,2-dimethoxyethylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine, pyrrole, pyridine, lithium hydroxide, potassium hydroxide, sodium hydroxide, etc. Among these, ammonia, triethylamine, and N,N-diethylethanolamine are preferred from the viewpoints of ease of formation of hollow spaces inside the particles and volatility.

[0028] <Method for producing aqueous dispersion> The method for producing the aqueous dispersion of the present invention preferably comprises the following steps (I) and (II). (Step I: Preparation of an aqueous dispersion of acid-modified polyphenylene ether resin) The method for producing the aqueous dispersion of hollow particles of the present invention involves mixing an acid-modified polyphenylene ether resin with a basic compound and an aqueous medium, and then stirring the mixture under heating at 70°C or higher, thereby obtaining a liquid in which fine particles (hollow particles) made of the acid-modified polyphenylene ether resin and having a shell portion and a hollow portion are dispersed in an aqueous medium.

[0029] The aqueous dispersion of the acid-modified polyphenylene ether resin is preferably carried out under a pressurized condition of 0.15 MPa or more. Pressurizing to 0.15 MPa or more promotes the microparticulation of the acid-modified polyphenylene ether resin, i.e., the dispersion in the aqueous medium. The method for pressurizing to 0.15 MPa or more is not particularly limited, but examples thereof include a method of heating in a sealed container.

[0030] The aqueous medium may be a mixture of water and an organic solvent, and the organic solvent content is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less of the aqueous medium. If the organic solvent content exceeds 70% by mass, there is a concern that it may have a negative effect on the human body from the viewpoint of the working environment.

[0031] In order to obtain a good aqueous dispersion, the organic solvent preferably has a solubility in water at 20°C of 10 g / L or more, more preferably 20 g / L or more, and even more preferably 50 g / L or more. The organic solvent also preferably has a boiling point at normal pressure of less than 250°C, more preferably less than 200°C. If the boiling point of the organic solvent exceeds 250°C, it may be difficult to remove the organic solvent in the solvent removal step described below.

[0032] Specific examples of organic solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amyl alcohol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, and cyclohexanol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, and cyclohexanone; ethers such as tetrahydrofuran and dioxane; ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, and 3-methyl acetate. Examples of suitable organic solvents include esters such as butyl ether, methyl propionate, ethyl propionate, diethyl carbonate, and dimethyl carbonate, glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol ethyl ether acetate, as well as 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 3-methoxy-3-methyl-1-butanol, methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate, 1,2-dimethylglycerin, 1,3-dimethylglycerin, and trimethylglycerin. These organic solvents may be used alone or in combination of two or more.

[0033] Among the above organic solvents, ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monomethyl ether are preferred because they are highly effective in microparticulating the acid-modified polyphenylene ether resin, i.e., in dispersing it in an aqueous medium.

[0034] (Step II: Addition of Water) In step II, after the acid-modified polyphenylene ether resin is prepared as an aqueous dispersion in step (I) above, water at 35°C or less is added all at once while the temperature of the aqueous dispersion is 40°C or higher. This fixes the structure of the hollow particles, making it possible to suppress the formation of so-called solid particles that do not have hollow portions. The temperature of the aqueous dispersion before adding water all at once is preferably 40°C or higher and 65°C or lower, more preferably 40°C or higher and 60°C or lower, and even more preferably 41°C or higher and 55°C or lower. If the temperature of the aqueous dispersion before adding water all at once is lower than 40°C, solid particles are more likely to be formed, and if it exceeds 65°C, aggregation is more likely to occur when water is added.

[0035] After the formation of the aqueous dispersion of the acid-modified polyphenylene ether resin is completed, a part or all of the organic solvent contained in the medium may be removed, if necessary, by a desolvation treatment generally called "stripping." The desolvation treatment can be carried out by methods such as heating or reducing pressure. The desolvation treatment may be carried out after either step I or step II, or after both steps I and II.

[0036] By removing the aqueous medium from the aqueous dispersion of the present invention, hollow particles made of an acid-modified polyphenylene ether resin can be obtained. These hollow particles may be in the form of a powder as an aggregate. The method for removing the aqueous medium is not particularly limited, but examples thereof include air drying, heat drying, reduced pressure drying, and freeze drying. Examples of the heat drying method include methods using a circulating air dryer, a spray dryer, a fluidized bed dryer, etc. [Example]

[0037] (1) Number-average molecular weight of acid-modified polyphenylene ether resin The number average molecular weight was measured by gel permeation chromatography (GPC) using a Shodex LF-804 x 2 (Resonac) column, chloroform at 50°C as the eluent, and a refractometer (RI) as the detector. The number average molecular weight was calculated from the relationship between the molecular weight of a standard polystyrene sample measured under the same conditions and the elution time.

[0038] (2) Method for measuring the acid value of acid-modified polyphenylene ether resin 0.15 g of acid-modified polyphenylene ether resin was refluxed in 20 mL of tetrahydrofuran (THF). After confirming that the resin was completely dissolved, the solution was stirred while maintaining the temperature at 60°C. A few drops of cresol red indicator were added to this THF solution of acid-modified polyphenylene ether resin, and the solution was titrated with a 0.1 mol / L solution of potassium hydroxide in methanol. The acid value of the acid-modified polyphenylene ether resin was calculated from the titration amount.

[0039] (3) Volume average particle size of hollow particles made of acid-modified polyphenylene ether resin The volume average particle size was determined using a Microtrac particle size distribution analyzer UPA150 (Model No. 9340) manufactured by Nikkiso Co., Ltd. The refractive index of the resin used to calculate the volume average particle size was set to 1.55.

[0040] Production Example 1: Acid-modified polyphenylene ether resin P-1 56 g of polyphenylene ether resin (number average molecular weight 23,000) was placed in a Labo Plastomill (Labo Plastomill R-60, manufactured by Toyo Seiki Co., Ltd.) and heated to 260°C under a nitrogen atmosphere. Then, 5 g of maleic anhydride and 5.8 g of 1,1,3,3-tetramethylbutyl hydroperoxide were added over 10 minutes while stirring at 80 rpm while maintaining the system temperature at 260°C. The reaction was continued for another 5 minutes. After cooling, the resin was dissolved in 300 g of toluene to prepare a solution. This solution was poured into a large excess of methanol to precipitate the resin. The resin was washed several times with acetone to remove unreacted maleic anhydride and decomposition products of 1,1,3,3-tetramethylbutyl hydroperoxide. It was then dried under reduced pressure in a vacuum dryer to obtain acid-modified polyphenylene ether resin P-1. The resulting acid-modified polyphenylene ether resin had a number average molecular weight of 20,000 and an acid value of 27.6 mgKOH / g.

[0041] Production Example 2: Acid-modified polyphenylene ether resin P-2 Except for using 3.5 g of fumaric acid instead of 5 g of maleic anhydride, an acid-modified polyphenylene ether resin P-2 was obtained in the same manner as in Production Example 1. The number average molecular weight of the obtained acid-modified polyphenylene ether resin was 19,000 and the acid value was 15.8 mgKOH / g.

[0042] Example 1: Aqueous dispersion E-1 containing hollow particles Using a stirrer equipped with a sealable, pressure-resistant 1 L glass container equipped with a heater and a pressure gauge, 300 g of acid-modified polyphenylene ether resin P-1, tetrahydrofuran, triethylamine, and pure water were added to the glass container according to the composition ratio shown in Table 1. The system was sealed, the stirring blade was rotated at 300 rpm, and the heater was turned on to heat the system. After confirming that the temperature inside the system had reached 120°C, the system was stirred for 60 minutes while maintaining the temperature at 120°C. At this time, the pressure gauge indicated 0.41 MPa. After that, while air-cooling the system and stirring at 300 rpm, the temperature of the aqueous dispersion inside the glass container was confirmed to have dropped to 50°C, and 200 g of pure water at 27°C was added. The system was then cooled to 25°C, and the aqueous dispersion inside the glass container was filtered through a stainless steel filter (78 mesh plain weave) to obtain aqueous dispersion "E-1" containing hollow particles composed of acid-modified polyphenylene ether resin P-1. The volume average particle size of the hollow particles in this aqueous dispersion was measured by the method described above and was found to be 0.10 μm.

[0043] [Table 1]

[0044] The aqueous dispersion "E-1" was dried under reduced pressure in a vacuum dryer to obtain a powder consisting of an aggregate of hollow particles. This powder was cut using an ion milling device (Gatan, Ilion model 693) and cross-sections were observed using a field emission scanning electron microscope (Hitachi High-Technologies, SU8020). Hollow particles were confirmed to have a shell portion made of acid-modified polyphenylene ether resin and a hollow portion.

[0045] Example 2: Aqueous dispersion E-2 containing hollow particles An aqueous dispersion "E-2" containing hollow particles made of acid-modified polyphenylene ether resin P-2 was obtained in the same manner as in Example 1, except that P-2 was used instead of acid-modified polyphenylene ether resin P-1. The pressure gauge indicated 0.41 MPa when the temperature in the system was maintained at 120°C. The volume average particle diameter of the hollow particles in this aqueous dispersion was measured using the method described above and found to be 0.15 μm. The aqueous dispersion "E-2" was dried under reduced pressure in a vacuum dryer to obtain a powder consisting of an aggregate of hollow particles. This powder was cut using an ion milling device, and cross-sections were observed using a field emission scanning electron microscope, revealing hollow particles comprising a shell portion made of an acid-modified polyphenylene ether resin and a hollow portion. A photograph of the hollow particles observed using a field emission scanning electron microscope is shown in Figure 1 (Example 2 was observed at a magnification of 30,000 times).

[0046] Example 3: Aqueous dispersion E-3 containing hollow particles An aqueous dispersion "E-3" of hollow particles made of acid-modified polyphenylene ether resin P-2 was obtained in the same manner as in Example 2, except that the composition ratio was changed to that shown in Table 1. The pressure gauge indicated 0.40 MPa when the temperature in the system was maintained at 120°C. The volume average particle diameter of the hollow particles in this aqueous dispersion was measured using the method described above and was found to be 0.23 μm. The aqueous dispersion "E-3" was dried under reduced pressure in a vacuum dryer to obtain a powder consisting of an aggregate of hollow particles. This powder was cut using an ion milling device and the cross section was observed using a field emission scanning electron microscope, revealing hollow particles having a shell portion made of an acid-modified polyphenylene ether resin and a hollow portion. A photograph of the hollow particles observed using a field emission scanning electron microscope is shown in Figure 2 (Example 3 was observed at a magnification of 10,000 times).

[0047] Comparative Example 1: Aqueous Dispersion E-4 Containing Solid Particles In Example 2, after confirming that the temperature of the aqueous dispersion in the glass container had dropped to 27°C, 200 g of pure water at 27°C was added. The system was cooled to 25°C, and the aqueous dispersion in the glass container was filtered through a stainless steel filter (78 mesh plain weave). An aqueous dispersion of fine particles made of acid-modified polyphenylene ether resin P-2, "E-4," was obtained in the same manner as in Example 2. The volume average particle diameter of the fine particles in this aqueous dispersion was measured by the method described above, and was found to be 0.08 μm. Aqueous dispersion "E-4" was dried under reduced pressure in a vacuum dryer to obtain a powder, which is an aggregate of fine particles. This powder was cut using an ion milling device and the cross section was observed using a field emission scanning electron microscope. Only solid particles were observed, and it was found that no hollow particles were formed.

Claims

1. An aqueous dispersion containing hollow particles made of an acid-modified polyphenylene ether resin and having a shell portion and a hollow portion, and an aqueous medium, wherein the acid-modified polyphenylene ether resin is a polyphenylene ether resin acid-modified with at least one functional group selected from the group consisting of a sulfo group, a carboxy group, a carboxylic acid anhydride group, and a phosphate group, and the aqueous medium contains a basic compound.

2. 2. The aqueous dispersion according to claim 1, wherein the acid-modified polyphenylene ether resin has an acid value of 0.5 to 80 mgKOH / g.

3. 3. The aqueous dispersion according to claim 1, wherein the basic compound is ammonia or an organic amine compound having a boiling point of 250°C or less.

4. 3. The aqueous dispersion according to claim 1, wherein the hollow particles have a volume average particle size of 10 to 5,000 nm.

5. Hollow particles obtained by removing the aqueous medium from the aqueous dispersion according to claim 1 or 2.

6. A method for producing the aqueous dispersion according to claim 1 or 2, comprising the following steps (I) and (II): (I) A step of mixing an acid-modified polyphenylene ether resin with a basic compound and an aqueous medium, and further stirring the mixture under heating conditions of 70°C or higher, thereby dispersing the acid-modified polyphenylene ether resin in water. (II) A step of adding water at 35°C or lower all at once to the aqueous dispersion of the acid-modified polyphenylene ether resin obtained in (I) above, wherein the temperature of the aqueous dispersion of the acid-modified polyphenylene ether resin before the addition of water is 40°C or higher.

Images