Method for manufacturing hollow particles

Abstract

The present invention provides a method for producing hollow particles with high porosity and not easy to break. The method for producing hollow particles produces hollow particles having a shell containing a resin and a hollow part surrounded by the shell, and having a porosity of 50% or more. The method for producing hollow particles comprises: a process of preparing a mixed solution containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium; a process of preparing a suspension containing droplets of a monomer composition of the first polymerizable monomer and the hydrocarbon solvent dispersed in an aqueous medium by suspending the mixed solution; a process of supplying the suspension to a polymerization reaction; the content of the crosslinking monomer in 100 parts by mass of the first polymerizable monomer is 75 to 100 parts by mass, and in the process of supplying the suspension to the polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer reaches 93% or more by mass, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20° C. is added, and then supplied to the polymerization reaction.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing hollow particles. Background Art

[0002] Hollow particles (hollow resin particles) are particles having voids inside the particles. Compared with solid particles whose interior is substantially filled with resin, hollow particles can scatter light well and reduce light transmittance. Therefore, as organic pigments and masking agents having excellent optical properties such as opacity and whiteness, they are widely used in applications such as aqueous coatings and paper coating compositions, and are further used as lightweighting agents and heat insulating agents for resins, coatings, etc. used in various fields such as automobiles, electrics, electronics, and construction.

[0003] In order to enhance the lightweighting, heat insulating, opacity, whitening, etc. effects of various compositions and molded articles containing hollow particles, the hollow particles preferably maintain a high porosity during and after kneading with other materials and during molding. However, if the porosity of the hollow particles is increased, the shell thickness of the hollow particles becomes thinner, and thus they become easily broken. Therefore, hollow particles with a high porosity and low breakage tendency are required.

[0004] A method for manufacturing hollow resin particles is disclosed in Patent Document 1. The method is characterized in that a mixed solution containing a monomer mixture composed of 20 to 70 parts by weight of a polyfunctional monomer having two or more ethylenically unsaturated groups and 80 to 30 parts by weight of a monofunctional monomer, a non-reactive organic solvent, and a non-crosslinked polymer having a weight average molecular weight of 10,000 to 1,000,000 in terms of polystyrene is dispersed in an aqueous solution containing a dispersion stabilizer or a surfactant, and then polymerization is carried out. Patent Document 1 describes that small-sized hollow resin particles with few pinholes and few breakages can be provided by this manufacturing method.

[0005] A hollow resin particle is disclosed in Patent Document 2. It is a hollow resin particle having a hollow surrounded by a shell. The hollow resin particle has a thermal decomposition start temperature of 350°C or higher, the shell has fine through-holes with diameters in the range of 10 to 50 nm, and has a thickness ratio of 0.03 to 0.25 with respect to the average primary particle diameter of the hollow resin particle. In addition, Patent Document 2 describes that the hollow resin particle is manufactured by dispersing a mixed solution containing a polyfunctional monomer and a non-reactive solvent in an aqueous solution and then polymerizing the polyfunctional monomer.

[0006] A method for producing hollow polymer particles composed of a single-layer structure shell and a hollow part is disclosed in Patent Document 3. The method is characterized in that in an aqueous solution of a dispersion stabilizer (A), a mixture composed of the following components (i) to (iii) is dispersed and suspension polymerization is carried out. The above components (i) to (iii) are: (i) at least one crosslinkable monomer (B) or a mixture of at least one crosslinkable monomer (B) and at least one monofunctional monomer (B'); (ii) an initiator (C); (iii) a water-insoluble solvent (D) having low compatibility with a polymer or copolymer obtained from at least one crosslinkable monomer (B), or a copolymer of at least one crosslinkable monomer (B) and at least one monofunctional monomer (B').

[0007] Prior art documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-68037;

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-190980;

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2002-80503. Summary of the invention

[0012] Problems to be solved by the invention

[0013] However, regarding the hollow resin particles described in Patent Document 1, when the hollow resin particles are mixed with a resin to prepare a coating or a molding material, and when a molded article is manufactured using the molding material containing the hollow resin particles, since they cannot sufficiently withstand the shear and pressure in biaxial kneading and injection molding, there is a problem that they are easily broken.

[0014] The hollow resin particles described in Patent Document 2 are the same as those in Patent Document 1, and there is a problem that they are easily broken because they cannot sufficiently withstand the shear and pressure in biaxial kneading and injection molding. In addition, since the hollow resin particles described in Patent Document 2 have fine through-holes, there is a problem that resin intrudes into the inside of the particles during the injection molding of the molding resin composition containing the hollow resin particles. The fine through-holes of the hollow resin particles sometimes impart beneficial functions to the hollow resin particles, but on the other hand, since they are the parts where the shell is defective, they also become the cause of reducing the strength of the hollow resin particles and easily causing breakage.

[0015] Although the hollow resin particles described in Patent Document 3 are less likely to break compared to the hollow resin particles described in Patent Documents 1 and 2, there is a problem that they are deformed due to the shear and pressure in biaxial kneading and injection molding, and the porosity is reduced.

[0016] An object of the present invention is to provide a method for manufacturing hollow particles having a high porosity and being difficult to break.

[0017] Solution to the problem

[0018] The present inventors have found that in the method for obtaining hollow particles by suspension polymerization, in order to manufacture hollow particles having a high porosity and being difficult to break, it is particularly effective to add a second polymerizable monomer as a hydrophilic monomer and continue the polymerization reaction when the polymerization conversion rate of the first polymerizable monomer containing a large amount of crosslinkable monomer reaches a specific value or more.

[0019] The present invention provides a method for manufacturing hollow particles, which is a method for manufacturing hollow particles having a shell containing a resin and a hollow portion surrounded by the shell and a porosity of 50% or more. The method for manufacturing the hollow particles includes the following steps:

[0020] A step of preparing a mixed solution containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium;

[0021] A step of preparing a suspension in which droplets of a monomer composition containing the first polymerizable monomer and the hydrocarbon solvent are dispersed in the aqueous medium by suspending the above mixed solution;

[0022] A step of supplying the suspension to a polymerization reaction;

[0023] The above mixed solution contains a crosslinkable monomer as the first polymerizable monomer, and the content of the crosslinkable monomer in 100 parts by mass of the first polymerizable monomer is 75 to 100 parts by mass.

[0024] In the step of supplying the suspension to a polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20 °C is added, and then supplied to the polymerization reaction.

[0025] In the method for manufacturing hollow particles of the present invention, it is preferable that in the step of supplying the suspension to a polymerization reaction, the addition amount of the second polymerizable monomer is 3 to 15 parts by mass with respect to 100 parts by mass of the first polymerizable monomer.

[0026] In the method for manufacturing hollow particles of the present invention, it is preferable that the first polymerizable monomer contains a bifunctional crosslinkable monomer and a crosslinkable monomer having three or more functional groups as the crosslinkable monomer.

[0027] In the method for manufacturing the hollow particles of the present invention, it is preferable that the above-mentioned first polymerizable monomer contains a crosslinkable monomer having three or more polymerizable functional groups, i.e., a trifunctional or higher crosslinkable monomer, as the above-mentioned crosslinkable monomer, and the content of the trifunctional or higher crosslinkable monomer in 100 parts by mass of the above-mentioned first polymerizable monomer is 5 to 50 parts by mass.

[0028] In the method for manufacturing the hollow particles of the present invention, it is preferable that the above-mentioned first polymerizable monomer contains at least one bifunctional crosslinkable monomer selected from divinylbenzene, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate as the above-mentioned crosslinkable monomer.

[0029] In the method for manufacturing the hollow particles of the present invention, it is preferable that the above-mentioned first polymerizable monomer contains at least one trifunctional or higher crosslinkable monomer selected from pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol poly(meth)acrylate as the above-mentioned crosslinkable monomer.

[0030] In the method for manufacturing the hollow particles of the present invention, it is preferable that the above-mentioned mixed solution contains at least one selected from rosin acid, higher fatty acids, and metal salts thereof.

[0031] In the method for manufacturing the hollow particles of the present invention, it is preferable that the above-mentioned dispersion stabilizer is an inorganic dispersion stabilizer, and more preferably, the above-mentioned inorganic dispersion stabilizer is a metal salt that is poorly soluble in water.

[0032] Advantages of the Invention

[0033] As described above, according to the manufacturing method of the present invention, it is possible to manufacture hollow particles with a high porosity and low brittleness, and in particular, it is possible to manufacture hollow particles that are not easily broken when kneaded with other materials such as resins. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a diagram illustrating an example of the manufacturing method of the present invention.

[0035] Figure 2 It is a schematic diagram showing an embodiment of the suspension liquid in the suspension step. DETAILED DESCRIPTION OF THE INVENTION

[0036] In addition, in the present invention, "~" in the numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0037] In addition, in the present invention, (meth)acrylate represents various acrylates and methacrylates, (meth)acrylic acid represents various acrylic acids and methacrylic acids, and (meth)acryloyl represents various acryloyls and methacryloyls.

[0038] In addition, in the present invention, a polymerizable monomer refers to a compound having a functional group capable of addition polymerization (in the present invention, sometimes only referred to as a polymerizable functional group). In the present invention, as the polymerizable monomer, a compound having an ethylenic unsaturated bond as a functional group capable of addition polymerization is usually used.

[0039] As the polymerizable monomer, there are non-crosslinkable monomers and crosslinkable monomers. A non-crosslinkable monomer is a polymerizable monomer having only one polymerizable functional group, and a crosslinkable monomer is a polymerizable monomer having two or more polymerizable functional groups and forming a crosslinked bond in the resin through a polymerization reaction.

[0040] In addition, in the present invention, a polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20 °C is referred to as a hydrophilic monomer, and a polymerizable monomer having a solubility of less than 0.3 g / L in distilled water at 20 °C is referred to as a non-hydrophilic monomer.

[0041] The hollow particles obtained by the production method of the present invention are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell.

[0042] In the present invention, the hollow portion is a hollow space that is clearly distinguishable from the shell of the hollow particles formed of a resin material. The shell of the hollow particles may have a porous structure, and in this case, the hollow portion has a size that can be clearly distinguished from the majority of minute spaces uniformly dispersed within the porous structure.

[0043] The hollow portion of the hollow particles can be confirmed, for example, by SEM observation of the particle cross-section, or by directly observing the particles through TEM.

[0044] In addition, the hollow portion of the hollow particles may be filled with a gas such as air, may be in a vacuum or reduced pressure state, or may contain a solvent.

[0045] Hereinafter, the production method of the hollow particles of the present invention and the hollow particles obtained by the production method of the present invention will be described in detail.

[0046] 1. Production method of hollow particles

[0047] The production method of the hollow particles of the present invention is characterized in that it is a method for producing hollow particles having a shell containing a resin and a hollow portion surrounded by the shell and having a porosity of 50% or more, and includes the following steps:

[0048] A step of preparing a mixed solution containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium;

[0049] A step of preparing a suspension in which droplets of a monomer composition containing the first polymerizable monomer and the hydrocarbon solvent are dispersed in the aqueous medium by suspending the above mixed solution;

[0050] A step of supplying the above suspension to a polymerization reaction;

[0051] The above mixed solution contains a crosslinkable monomer as the first polymerizable monomer, and the content of the crosslinkable monomer in 100 parts by mass of the first polymerizable monomer is 75 to 100 parts by mass.

[0052] In the step of supplying the above suspension to a polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20 °C is added, and then supplied to the polymerization reaction.

[0053] The method for manufacturing hollow particles of the present invention follows the following basic technique: by suspending a mixed solution containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium, a suspension in which droplets having the following distribution structure are dispersed in the aqueous medium is prepared. The above distribution structure is a phase separation of the first polymerizable monomer and the hydrocarbon solvent, and a distribution structure in which the first polymerizable monomer tends to exist on the surface side and the hydrocarbon solvent tends to exist in the central part. By supplying this suspension to a polymerization reaction, the surface of the droplets is solidified to form hollow particles having a hollow part filled with the hydrocarbon solvent.

[0054] In such a basic technique, in the step of supplying the suspension to a polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer containing a specific amount or more of a crosslinkable monomer reaches 93% by mass or more, a second polymerizable monomer as a hydrophilic monomer is added, and then supplied to the polymerization reaction, whereby hollow particles that are not easily broken even with a high porosity can be manufactured.

[0055] As a polymerizable monomer for forming the shell of hollow particles, by using a large amount of a crosslinkable monomer, the content ratio of the crosslinkable monomer units in the shell becomes larger, and the covalent bond network densely spreads in the shell. As a result, a shell having excellent strength, not easily broken, and not easily deformed by heat applied from the outside can be formed. However, when a large amount of a crosslinkable monomer is used, unreacted polymerizable functional groups tend to remain in the shell. Since the more unreacted polymerizable functional groups remain, the rougher the crosslinked structure of the shell becomes, the strength of the shell tends to decrease. Therefore, it is considered that the remaining unreacted polymerizable functional groups in the hollow particles obtained by the conventional manufacturing method are one of the reasons for reducing the strength of the shell.

[0056] In contrast, in the manufacturing method of the present invention, a suspension in which droplets of a monomer composition containing a first polymerizable monomer containing a large amount of crosslinkable monomers are dispersed in an aqueous medium is supplied to a polymerization reaction. After the first polymerization reaction is carried out until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, a second polymerizable monomer as a hydrophilic monomer is added and then the second polymerization reaction is carried out, whereby the reaction rate of the polymerizable monomers as a whole including the first polymerizable monomer and the second polymerizable monomer can be increased.

[0057] In addition, in the present invention, particles having a shell of a polymer containing a first polymerizable monomer and a hollow portion filled with a hydrocarbon-based solvent obtained by the above first polymerization reaction are sometimes referred to as first precursor particles, and a composition containing the first precursor particles is sometimes referred to as a first precursor composition. In addition, considering an intermediate of hollow particles in which the hollow portion is filled with gas, particles having a shell of a polymer containing a first polymerizable monomer and a second polymerizable monomer and a hollow portion filled with a hydrocarbon-based solvent obtained by the above second polymerization reaction are sometimes referred to as second precursor particles, and a composition containing the second precursor particles is sometimes referred to as a second precursor composition.

[0058] In the manufacturing method of the present invention, by making the solubility of the second polymerizable monomer in distilled water at 20 °C be the above specific value or more, when added to the first precursor composition, it is easily introduced into the shell of the first precursor particles. It is considered that the second polymerizable monomer as a hydrophilic monomer has an affinity for both the first polymerizable monomer and the aqueous medium, so when added to the first precursor composition, it is introduced into the shell formed by the first polymerizable monomer, promoting the thermal movement of the shell. It is speculated that in the second polymerization reaction, in a state where the second polymerizable monomer is introduced into the shell formed by the first polymerizable monomer, since the polymerization reaction is carried out while promoting the thermal movement of the shell, the reaction rate is high, and the polymerization reaction of the polymerizable functional groups of the second polymerizable monomer introduced into the shell and the remaining unreacted first polymerizable monomer proceeds sufficiently, and the crosslinked structure becomes dense, so a shell with excellent strength is formed.

[0059] The manufacturing method of the hollow particles of the present invention includes a step of preparing a mixed solution, a step of preparing a suspension, and a step of supplying the suspension to a polymerization reaction, and may further include steps other than these. In addition, as long as it is technically feasible, two or more of the above steps and other additional steps can be carried out simultaneously as one step, or the order can be changed. For example, like suspending while introducing the materials for preparing the mixed solution, the preparation of the mixed solution and the suspension can be carried out simultaneously in one step.

[0060] As a preferred example of the manufacturing method of the hollow particles of the present invention, a manufacturing method including the following steps can be cited.

[0061] (1) Mixed liquid preparation step

[0062] Step of preparing a mixed liquid containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium

[0063] (2) Suspension step

[0064] Step of preparing a suspension in which droplets of a monomer composition containing a first polymerizable monomer and a hydrocarbon solvent are dispersed in an aqueous medium by suspending the above-mentioned mixed liquid

[0065] (3) Polymerization step

[0066] (3-1) First polymerization step

[0067] Step of performing a first polymerization reaction of supplying the above-mentioned suspension to a polymerization reaction until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, thereby preparing a first precursor composition containing first precursor particles, the first precursor particles having a shell of a polymer containing a first polymerizable monomer and a hollow portion filled with a hydrocarbon solvent

[0068] (3-2) Second polymerization step

[0069] Step of performing a second polymerization reaction by adding a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C to the above-mentioned first precursor composition, thereby preparing a second precursor composition containing second precursor particles, the second precursor particles having a shell of a polymer containing a first polymerizable monomer and a second polymerizable monomer and a hollow portion filled with a hydrocarbon solvent

[0070] (4) Solid-liquid separation step

[0071] Step of obtaining second precursor particles having a hydrocarbon solvent encapsulated in the hollow portion by performing solid-liquid separation on the above-mentioned second precursor composition, and

[0072] (5) Solvent removal step

[0073] Step of removing the hydrocarbon solvent encapsulated in the second precursor particles obtained by the above solid-liquid separation step to obtain hollow particles

[0074] Figure 1 is a schematic diagram showing an example of the manufacturing method of the present invention Figure 1 in (1) to (5) corresponds to the above respective steps (1) to (5). The white arrows between the respective figures indicate the order of the respective steps. In addition, Figure 1It is only a schematic diagram for illustration, and the manufacturing method of the present invention is not limited to the manufacturing method shown in the figure. In addition, the structure, size, and shape of the materials used in each manufacturing method of the present invention are not limited to the structure, size, and shape of various materials in these figures.

[0075] Figure 1 (1) is a cross-sectional schematic diagram showing an embodiment of the mixed solution in the mixed solution preparation step. As shown in this figure, the mixed solution 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 with low polarity and is difficult to mix with the aqueous medium 1. In the present invention, the low-polarity material 2 contains a first polymerizable monomer and a hydrocarbon solvent.

[0076] Figure 1 (2) is a cross-sectional schematic diagram showing an embodiment of the suspension in the suspension step. The suspension contains an aqueous medium 1 and droplets 10 of a monomer composition dispersed in the aqueous medium 1. The droplets 10 of the monomer composition contain a first polymerizable monomer and a hydrocarbon solvent, but the distribution within the droplets is not uniform. The droplets 10 of the monomer composition have the following structure: the hydrocarbon solvent 4a undergoes phase separation from the material 4b other than the hydrocarbon solvent containing the first polymerizable monomer, the hydrocarbon solvent 4a tends to exist in the central part, the material 4b other than the hydrocarbon solvent tends to exist on the surface side, and a dispersion stabilizer (not shown) adheres to the surface.

[0077] Figure 1 (3) is a cross-sectional schematic diagram showing an embodiment of a composition (second precursor composition) containing hollow particles (second precursor particles) that enclose a hydrocarbon solvent in the hollow part obtained through the polymerization step. This composition contains an aqueous medium 1 and hollow particles (second precursor particles) 20 that enclose a hydrocarbon solvent 4a in the hollow part and are dispersed in the aqueous medium 1. The shell 6 forming the outer surface of the second precursor particles 20 is a shell formed by the polymerization of the first polymerizable monomer in the droplets 10 of the monomer composition and the polymerization of the subsequently added second polymerizable monomer.

[0078] Figure 1 (4) is a cross-sectional schematic diagram showing an embodiment of hollow particles (second precursor particles) that enclose a hydrocarbon solvent in the hollow part after the solid-liquid separation step. This Figure 1 (4) represents the state of removing the aqueous medium 1 from the state of (3) above. Figure 1 (3).

[0079] Figure 1 (5) is a cross-sectional schematic diagram showing an embodiment of the hollow particles after the solvent removal step. This Figure 1 (5) represents the state of removing the aqueous medium 1 from the state of (3) above. Figure 1The state of (4) excludes the state of the hydrocarbon-based solvent 4a. By removing the hydrocarbon-based solvent from the hollow particles (second precursor particles) in which the hydrocarbon-based solvent is enclosed in the hollow portion, hollow particles 100 having a gas-filled hollow portion 8 inside the shell 6 are obtained.

[0080] Hereinafter, the above five processes and other processes will be described in sequence.

[0081] (1) Mixed solution preparation process

[0082] This process is a process for preparing a mixed solution containing a first polymerizable monomer, a hydrocarbon-based solvent, a dispersion stabilizer, and an aqueous medium.

[0083] The mixed solution preferably further contains a particle size control agent. In addition, the mixed solution preferably contains an oil-soluble polymerization initiator as a polymerization initiator. In addition, within the range not impairing the effects of the present invention, the mixed solution may further contain other materials such as a suspension stabilizer.

[0084] Regarding the materials of the mixed solution, they will be described in the order of (A) first polymerizable monomer, (B) particle size control agent, (C) oil-soluble polymerization initiator, (D) hydrocarbon-based solvent, (E) dispersion stabilizer, and (F) aqueous medium.

[0085] (A) First polymerizable monomer

[0086] The first polymerizable monomer contains at least a crosslinkable monomer, and may further contain a non-crosslinkable monomer within the range not impairing the effects of the present invention.

[0087] As the first polymerizable monomer, from the aspect of being able to obtain hollow particles with a stable polymerization reaction and high heat resistance, (meth)acrylic acid-based polymerizable monomers having (meth)acryloyl as a polymerizable functional group can be preferably used.

[0088] [Crosslinkable monomer]

[0089] Since the crosslinkable monomer has a plurality of polymerizable functional groups, it can connect monomers to each other and can increase the crosslink density of the shell.

[0090] Examples of the crosslinkable monomer include bifunctional crosslinkable monomers having two polymerizable functional groups such as divinylbenzene, divinylbiphenyl, divinylnaphthalene, diallyl phthalate, allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, 2-hydroxy-3-(meth)acryloxypropyl (meth)acrylate; trifunctional or higher crosslinkable monomers having three or more polymerizable functional groups such as trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane) tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and ethoxylates thereof. These crosslinkable monomers can be used alone or in combination of two or more thereof.

[0091] In addition, among these crosslinkable monomers, examples of the hydrophilic crosslinkable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C include ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl methacrylate, vinyl methacrylate, 2-hydroxy-3-methacryloxypropyl acrylate, and the like.

[0092] In addition, the crosslinkable monomer contained as the first polymerizable monomer may be a hydrophilic crosslinkable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C or a non-hydrophilic crosslinkable monomer having a solubility of less than 0.3 g / L in distilled water at 20°C, and there is no particular limitation.

[0093] The first polymerizable monomer preferably contains at least a bifunctional crosslinkable monomer, and more preferably contains a combination of a bifunctional crosslinkable monomer and a trifunctional or higher crosslinkable monomer as the crosslinkable monomer. When the first polymerizable monomer contains a trifunctional or higher crosslinkable monomer, a covalent bond network can be more densely distributed in the shell, which is excellent in this regard. However, there is a tendency that unreacted polymerizable functional groups tend to remain after the first polymerization reaction. In the production method of the present invention, even when the first polymerizable monomer contains a trifunctional or higher crosslinkable monomer, by adding a hydrophilic monomer as the second polymerizable monomer to carry out the second polymerization reaction, the polymerization reaction of the unreacted polymerizable functional groups remaining after the first polymerization reaction is likely to proceed. Therefore, by making the first polymerizable monomer contain a trifunctional or higher crosslinkable monomer, the crosslinked structure of the shell can be made denser, the strength of the hollow particles can be increased, and they are not easily broken.

[0094] From the aspect of easily obtaining hollow particles with stable polymerization reaction, excellent strength and heat resistance, as the bifunctional crosslinkable monomer, divinylbenzene, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate are preferred, and ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate are more preferred.

[0095] From the same viewpoint, as the crosslinkable monomer having three or more functional groups, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol poly(meth)acrylate are preferred, and pentaerythritol tetra(meth)acrylate is more preferred.

[0096] In 100 parts by mass of the first polymerizable monomer, the content of the crosslinkable monomer is 75 to 100 parts by mass. By making the content of the crosslinkable monomer 75 parts by mass or more, since the content ratio of the crosslinkable monomer units in the shell of the hollow particles is sufficiently large, the covalent bond network densely spreads in the shell. As a result, the strength is excellent, it is not easily broken, and it is not easily deformed by heat or the like applied from the outside.

[0097] The content of the crosslinkable monomer in 100 parts by mass of the first polymerizable monomer is preferably 80 to 100 parts by mass, more preferably 85 to 100 parts by mass, and further preferably 90 to 100 parts by mass.

[0098] The content of the bifunctional crosslinkable monomer in 100 parts by mass of the first polymerizable monomer is not particularly limited. As the lower limit, it is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, further preferably 70 parts by mass or more, and still further preferably 75 parts by mass or more. As the upper limit, it is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, further preferably 90 parts by mass or less.

[0099] When the first polymerizable monomer contains a crosslinkable monomer having three or more functional groups as the crosslinkable monomer, the content of the crosslinkable monomer having three or more functional groups in 100 parts by mass of the first polymerizable monomer is not particularly limited. As the lower limit, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further preferably 15 parts by mass or more. As the upper limit, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, further preferably 30 parts by mass or less, and still further preferably 25 parts by mass or less.

[0100] [Non-crosslinkable monomer]

[0101] The first polymerizable monomer may further contain a non-crosslinkable monomer.

[0102] 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 acid 2-ethylhexyl esters, (meth)acrylic acid lauryl esters and other (meth)acrylic acid alkyl esters having an alkyl group with 6 or more carbon atoms; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, and halogenated styrene; monoolefin monomers such as ethylene, propylene, and butene; diene monomers such as butadiene and isoprene; carboxylic acid vinyl esters such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; non-hydrophilic non-crosslinkable monomers such as vinylpyridine monomers, and (meth)acrylic acid alkyl esters having an alkyl group with 1 to 5 carbon atoms such as (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, and (meth)acrylic acid butyl ester; (meth)acrylamides and their derivatives such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; (meth)acrylonitrile; hydrophilic non-crosslinkable monomers such as non-crosslinkable monomers containing polar groups.

[0103] As the non-crosslinkable monomer containing a polar group, non-crosslinkable monomers containing a polar group selected from a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group can be preferably selected. More specifically, examples include: monomers containing a carboxyl group such as ethylenically unsaturated carboxylic acid monomers such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; monomers containing a hydroxyl group such as (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, and (meth)acrylic acid 4-hydroxybutyl ester; monomers containing a sulfonic acid group such as styrene sulfonic acid; monomers containing an amino group such as (meth)acrylic acid dimethylaminoethyl ester and (meth)acrylic acid diethylaminoethyl ester; monomers containing a polyoxyethylene group such as methoxypolyethylene glycol (meth)acrylate; monomers containing an epoxy group such as (meth)acrylic acid glycidyl ester, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether.

[0104] These non-crosslinkable monomers can be used alone or in combination of two or more.

[0105] As the non-crosslinkable monomer used as the first polymerizable monomer, from the aspect of obtaining hollow particles with excellent strength, hydrophilic non-crosslinkable monomers are preferred, (meth)acrylic acid alkyl esters having an alkyl group with 1 to 5 carbon atoms are more preferred, (meth)acrylic acid alkyl esters having an alkyl group with 1 to 4 carbon atoms are further preferred, and (meth)acrylic acid methyl ester is even more preferred.

[0106] In the first polymerizable monomer, the polymerizable monomer other than the crosslinkable monomer is a non-crosslinkable monomer. The content of the non-crosslinkable monomer in the first polymerizable monomer is 0 to 25 parts by mass in 100 parts by mass of the first polymerizable monomer. From the aspect of suppressing the reduction of the reactivity of the first polymerizable monomer and increasing the strength of the hollow particles so that they are not easily broken, the content of the non-crosslinkable monomer in the first polymerizable monomer is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, further preferably 10 parts by mass or less, and particularly preferably the first polymerizable monomer does not contain a non-crosslinkable monomer.

[0107] The content of the first polymerizable monomer in the mixed solution is not particularly limited. From the viewpoint of the balance of the porosity, particle size, and mechanical strength of the hollow particles, it is usually 15 to 55% by mass, more preferably 25 to 40% by mass, based on the total mass of the components in the mixed solution excluding the aqueous medium.

[0108] (B) Particle size controller

[0109] The mixed solution preferably further contains a particle size controller. By including a particle size controller in the mixed solution, the particle size of the droplets of the monomer composition and the thickness of the shell of the obtained hollow particles can be appropriately adjusted. Therefore, hollow particles that are not easily broken even with a high porosity can be obtained.

[0110] As the particle size controller, for example, at least one selected from rosin acid, higher fatty acids, and their metal salts or the polar resin described below can be used. These particle size controllers can appropriately adjust the particle size of the droplets of the monomer composition containing the first polymerizable monomer and the hydrocarbon solvent in the subsequent suspension process. In the suspension process, droplets of the monomer composition are formed in the aqueous medium by the action of the dispersion stabilizer. In the droplets of the monomer composition, the material other than the hydrocarbon solvent containing the first polymerizable monomer undergoes phase separation from the hydrocarbon solvent, and the hydrocarbon solvent tends to exist in the central part, while the material other than the hydrocarbon solvent tends to exist on the surface side. It is speculated that when the mixed solution contains a particle size controller, there is a structure in which the particle size controller tends to exist near the surface of the droplets of the monomer composition and the dispersion stabilizer adheres to the surface of the droplets. Such a material distribution structure is formed based on the different affinities of each material for the aqueous medium. It is considered that by including a particle size controller in the mixed solution, the droplets of the monomer composition in the suspension have the above-described material distribution structure, and due to the interaction between the dispersion stabilizer and the particle size controller on the droplet surface, the dispersibility of the droplets caused by the dispersion stabilizer changes, and the particle size of the droplets of the monomer composition can be appropriately adjusted.

[0111] As a particle size control agent, since the particle size of droplets can be appropriately adjusted with a small content, at least one selected from rosin acid, higher fatty acids, and metal salts thereof is preferred, and at least one selected from rosin acid and its alkali metal salts is more preferred.

[0112] The rosin acid preferably used as a particle size control agent can be obtained from rosins such as gum rosin, tall oil rosin, and wood rosin.

[0113] Examples of the components contained in the rosin acid obtained from these rosins include rosin acid, dehydroabietic acid, palustric acid, isopimaric acid, pimaric acid, etc. The component ratio of rosin acid is not constant and varies depending on the type of rosin, the pine species of the raw material, the place of origin, etc.

[0114] As the rosin acid and its metal salts used in the present invention, rosin acid and its alkali metal salts containing 50% by mass or more of rosin acid, dehydroabietic acid, palustric acid, and their hydrides, etc., are preferred.

[0115] As the higher fatty acid used as a particle size control agent, higher fatty acids having 10 to 25 carbon atoms not including the carbon atom in the carboxyl group are preferred. Examples of the preferred higher fatty acids include lauric acid (CH3(CH2) 10 COOH), tridecanoic acid (CH3(CH2) 11 COOH), myristic acid (CH3(CH2) 12 COOH), pentadecanoic acid (CH3(CH2) 13 COOH), palmitic acid (CH3(CH2) 14 COOH), heptadecanoic acid (CH3(CH2) 15 COOH), stearic acid (CH3(CH2) 16 COOH), arachidic acid (CH3(CH2) 18 COOH), behenic acid (CH3(CH2) 20 COOH), and lignoceric acid (CH3(CH2) 22 COOH), etc.

[0116] Examples of the metal for the metal salt of rosin acid or higher fatty acid include alkali metals such as Li, Na, K, and alkaline earth metals such as Mg, Ca, etc. Among them, alkali metals are preferred, and at least one selected from Li, Na, and K is more preferred.

[0117] As a particle size control agent, when at least one selected from rosin acid, higher fatty acids, and metal salts thereof is used, the total content of rosin acid, higher fatty acids, and metal salts thereof is preferably 0.0001 part by mass or more and 0.1 part by mass or less, more preferably 0.001 part by mass or more and 0.01 part by mass or less, and still more preferably 0.0015 part by mass or more and 0.006 part by mass or less, relative to the total of 100 parts by mass of the first polymerizable monomer and the hydrocarbon solvent. By making the above content not less than the above lower limit value, it is possible to easily control the particle size and the shell thickness of the hollow particles and improve the strength of the hollow particles. On the other hand, by making the above content not more than the above upper limit value, it is possible to suppress a decrease in the content ratio of the polymerizable monomer, and thus it is possible to suppress a decrease in the strength of the shell and further suppress breakage of the hollow particles.

[0118] The polar resin preferably used as the particle size control agent is a polymer containing a repeating unit containing a heteroatom. Specifically, acrylic resins, polyester resins, vinyl resins containing heteroatoms, etc. can be cited.

[0119] The above polar resin may be a homopolymer or copolymer of a heteroatom-containing monomer, or a copolymer of a heteroatom-containing monomer and a heteroatom-free monomer. When the above polar resin is a copolymer of a heteroatom-containing monomer and a heteroatom-free monomer, from the viewpoint of easily controlling the particle size of the hollow particles, in all the repeating units constituting the copolymer in 100% by mass, the proportion of the heteroatom-containing monomer units is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more.

[0120] As the heteroatom-containing monomers for polar resins, for example, (meth)acrylic acid monomers having (meth)acryloyl groups such as 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, glycidyl ether of 4-hydroxybutyl (meth)acrylate; heteroatom-containing aromatic vinyl monomers such as halogenated styrene, styrenesulfonic acid; carboxylic acid vinyl 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 olefinically unsaturated carboxylic acid monomers like crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, tricarballylic acid; epoxy group-containing monomers such as allyl glycidyl ether, etc. These heteroatom-containing monomers can be used alone or in combination of two or more.

[0121] As the heteroatom-free monomers for polar resins, for example, heteroatom-free aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene; monoolefin monomers such as ethylene, propylene, butene; diene monomers such as butadiene, isoprene. These heteroatom-free monomers can be used alone or in combination of two or more.

[0122] Particularly from the aspect of high compatibility with the above-mentioned first polymerizable monomer and easy control of the particle size of hollow particles, the above polar resin is preferably an acrylic resin in which, in all the repeating units constituting 100% by mass of the resin, the total mass of (meth)acrylic acid-based mono-vinyl monomer units is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably an acrylic resin in which all the repeating units constituting the resin are composed of (meth)acrylic acid-based mono-vinyl monomer units.

[0123] From the aspect of easily controlling the particle size of the hollow particles, the above-mentioned polar resin particularly preferably contains a monomer unit of a polar group-containing monomer containing a polar group selected from a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group among the above-mentioned heteroatom-containing monomers. As the polar group-containing monomer for the polar resin, monomers similar to the non-crosslinkable monomers containing polar groups that the above-mentioned first polymerizable monomer may contain can be cited, for example. The polar group-containing monomers can be used individually or in combination of two or more. As the polar group contained in the monomer unit of the polar group-containing monomer contained in the polar resin, from the aspect of being able to control the particle size with a small addition amount, a carboxyl group and a hydroxyl group are preferred.

[0124] When the above-mentioned polar resin contains a monomer unit of a polar group-containing monomer, from the aspect that the polar resin is easily disposed on the outer surface of the hollow particles and the particle size of the hollow particles is easily controlled, it is preferred that the above-mentioned polar group is located at the end of the main chain or side chain, or is bonded to the main chain or side chain in a pendant form.

[0125] When the polar resin does not contain the monomer unit of the polar group-containing monomer, as the monomer unit of the heteroatom-containing monomer contained in the polar resin, from the aspect of high compatibility with the above-mentioned first polymerizable monomer and easy control of the particle size of the hollow particles, it is preferred to contain a monomer unit derived from an (alkyl) acrylate, and particularly from the aspect of high polarity, it is preferred to contain a monomer unit derived from an (alkyl) acrylate as described below, and the (alkyl) acrylate preferably has 3 or less carbon atoms in the alkyl group, more preferably the alkyl group is methyl or ethyl, and further preferably the alkyl group is methyl.

[0126] For the above-mentioned acrylic resin as the polar resin, particularly from the aspect of high compatibility with the above-mentioned first polymerizable monomer and easy control of the particle size of the hollow particles, when the total mass of the polymerizable monomers for the polar resin is 100% by mass, it is preferably a polymer or copolymer of a polymerizable monomer for the polar resin containing 50% by mass or more of methyl methacrylate. In addition, in the present invention, the polymerizable monomers used for synthesizing the polar resin are referred to as polymerizable monomers for the polar resin.

[0127] The above-mentioned polar resin can be obtained, for example, by polymerizing a polymerizable monomer for the polar resin containing the above-mentioned heteroatom-containing monomer using a polymerization method such as solution polymerization or emulsion polymerization.

[0128] In addition, when the above-mentioned polar resin is a copolymer, the copolymer can be any one of a random copolymer, a block copolymer, or a graft copolymer, and a random copolymer is preferred.

[0129] In addition, from the aspect of improving solubility, it is preferred to pulverize the above-mentioned polar resin more finely.

[0130] The number average molecular weight (Mn) of the above-mentioned polar resin is not particularly limited, and in terms of the polystyrene conversion value measured by gel permeation chromatography (GPC) using tetrahydrofuran, it is preferably in the range of 3,000 or more and 20,000 or less, more preferably in the range of 4,000 or more and 17,000 or less, and still more preferably in the range of 6,000 or more and 15,000 or less. By making the number average molecular weight (Mn) of the above-mentioned polar resin be above the above lower limit value, the solubility of the polar resin can be improved, and the particle size of the hollow particles can be easily controlled. By making it be below the above upper limit value, a decrease in the strength of the shell can be suppressed.

[0131] When using a polar resin as a particle size control agent, the content of the polar resin is preferably 0.1 part by mass or more and 10.0 parts by mass or less, more preferably 0.3 part by mass or more and 8.0 parts by mass or less, and still more preferably 0.5 part by mass or more and 8.0 parts by mass or less, relative to 100 parts by mass of the first polymerizable monomer. By making the above content be above the above lower limit value, the particle size and shell thickness of the hollow particles can be easily controlled, and the strength of the hollow particles can be improved. On the other hand, by making the above content be below the above upper limit value, a decrease in the content ratio of the polymerizable monomer can be suppressed, so a decrease in the strength of the shell can be suppressed, and further crushing of the hollow particles can be suppressed.

[0132] (C) Oil-soluble polymerization initiator

[0133] In the present invention, the mixed liquid preferably contains an oil-soluble polymerization initiator as the polymerization initiator. As a method of polymerizing the droplets of the monomer composition after suspending the mixed liquid, there are an emulsion polymerization method using a water-soluble polymerization initiator and a suspension polymerization method using an oil-soluble polymerization initiator, and suspension polymerization can be carried out by using an oil-soluble polymerization initiator.

[0134] The oil-soluble polymerization initiator is not particularly limited as long as it is a lipophilic initiator having a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, tert-butyl peroxy-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and the like.

[0135] When the total mass of the first polymerizable monomer in the mixed liquid is set to 100 parts by mass, the content of the oil-soluble polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and still more preferably 1 to 5 parts by mass. By making the content of the oil-soluble polymerization initiator be 0.1 to 10 parts by mass, the polymerization reaction proceeds sufficiently, and the possibility of the oil-soluble polymerization initiator remaining after the polymerization reaction is small, and the possibility of an unexpected side reaction is small.

[0136] (D) Hydrocarbon solvent

[0137] In the present invention, a hydrocarbon solvent is used as a non-polymerizable and water-insoluble organic solvent. The hydrocarbon solvent functions as a spacer for forming a hollow portion inside the particles. In the suspension process described later, a suspension is obtained in which droplets of a monomer composition containing the hydrocarbon solvent are dispersed in an aqueous medium. In the suspension process, phase separation occurs within the droplets of the monomer composition, and as a result, the hydrocarbon solvent with low polarity tends to aggregate inside the polymerizable monomer droplets. Eventually, in the droplets of the monomer composition, according to their respective polarities, the hydrocarbon solvent is distributed inside, and other materials except the hydrocarbon solvent are distributed at the edges.

[0138] Then, in the polymerization process described later, an aqueous dispersion containing hollow particles encapsulating the hydrocarbon solvent is obtained. That is, by aggregating the hydrocarbon solvent inside the particles, a hollow portion filled with the hydrocarbon solvent is formed inside the obtained precursor particles.

[0139] The type of the hydrocarbon solvent is not particularly limited. Examples of the hydrocarbon solvent include saturated hydrocarbon solvents such as butane, pentane, n-hexane, cyclohexane, heptane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and solvents with relatively high volatility such as carbon disulfide and carbon tetrachloride.

[0140] The porosity of the hollow particles can be adjusted by changing the amount of the hydrocarbon solvent in the mixture. In the suspension process described later, since the polymerization reaction is carried out in a state where the hydrocarbon solvent is encapsulated in oil droplets containing a crosslinkable monomer and the like, there is a tendency that the higher the content of the hydrocarbon solvent, the higher the porosity of the obtained hollow particles.

[0141] In the hydrocarbon solvent with a total amount of 100% by mass, the proportion of the saturated hydrocarbon solvent in the hydrocarbon solvent is preferably 50% by mass or more. Thereby, by sufficiently causing phase separation within the droplets of the monomer composition, it is easy to obtain hollow particles having only one hollow portion, and the generation of porous particles can be suppressed. From the aspect of further suppressing the generation of porous particles and the aspect that the hollow portions of each hollow particle are likely to become uniform, the proportion of the saturated hydrocarbon solvent is preferably 60% by mass or more, and more preferably 80% by mass or more.

[0142] In addition, as the hydrocarbon solvent, a hydrocarbon solvent having 4 to 7 carbon atoms is preferred. A hydrocarbon compound having 4 to 7 carbon atoms can be easily encapsulated in the first precursor particles during the polymerization process and can be easily removed from the second precursor particles during the solvent removal process. Particularly preferably, a hydrocarbon solvent having 5 or 6 carbon atoms.

[0143] In addition, the hydrocarbon-based solvent is not particularly limited. From the aspect of being easily removed in the subsequent solvent removal step, a solvent having a boiling point of 130 °C or lower is preferred, and a solvent having a boiling point of 100 °C or lower is more preferred. In addition, from the aspect of being easily encapsulated in the first precursor particles, as the hydrocarbon-based solvent, a solvent having a boiling point of 50 °C or higher is preferred, and a solvent having a boiling point of 60 °C or higher is more preferred.

[0144] In addition, the hydrocarbon-based solvent preferably has a relative dielectric constant of 3 or less at 20 °C. The relative dielectric constant is one of the indexes indicating the polarity of a compound. It can be considered that when the relative dielectric constant of the hydrocarbon-based solvent is 3 or less and sufficiently small, phase separation proceeds rapidly in the droplets of the monomer composition, and it is easy to form a hollow.

[0145] Examples of the solvent having a relative dielectric constant of 3 or less at 20 °C are as follows. The value in parentheses is the relative dielectric constant value.

[0146] Heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4).

[0147] Regarding the relative dielectric constant at 20 °C, the values described in publicly 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, Heisei 5, pages II-498 to II-503) and other technical information can be referred to. As a method for measuring the relative dielectric constant at 20 °C, for example, a relative dielectric constant test conducted in accordance with 23 of JISC2101:1999 at a measurement temperature of 20 °C can be cited.

[0148] In the present invention, from the aspects of easily controlling the particle diameter of the hollow particles, easily increasing the porosity while maintaining the strength of the hollow particles, and easily reducing the amount of residual hydrocarbon-based solvent in the particles, the content of the hydrocarbon-based solvent in the mixed liquid is preferably 50 parts by mass or more and 500 parts by mass or less with respect to the total mass of 100 parts by mass of the first polymerizable monomer. The content of the hydrocarbon-based solvent in the mixed liquid is preferably 60 parts by mass or more and 400 parts by mass or less, more preferably 70 parts by mass or more and 300 parts by mass or less, and further preferably 80 parts by mass or more and 200 parts by mass or less with respect to the total mass of 100 parts by mass of the first polymerizable monomer.

[0149] (E) Dispersion stabilizer

[0150] The dispersion stabilizer is an agent that disperses droplets of the monomer composition in an aqueous medium during the suspension process. In the present invention, from the aspects of easily controlling the particle size of the droplets in the suspension, being able to narrow the particle size distribution of the obtained hollow particles, and suppressing the shell from becoming too thin and suppressing the reduction in the strength of the hollow particles, it is preferable to use an inorganic dispersion stabilizer as the dispersion stabilizer. This effect caused by the inorganic dispersion stabilizer is particularly easily exerted when the inorganic dispersion stabilizer is used in combination with the above-mentioned particle size control agent.

[0151] Examples of the inorganic dispersion stabilizer 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 alumina and titanium oxide; and inorganic compounds such as metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and iron hydroxide. These inorganic dispersion stabilizers can be used singly or in combination of two or more.

[0152] Among the above-mentioned inorganic dispersion stabilizers, inorganic metal salts that are hardly soluble in water such as the above-mentioned sulfates, carbonates, phosphates, and metal hydroxides are preferred, metal hydroxides are more preferred, and magnesium hydroxide is particularly preferred.

[0153] In addition, in the present invention, the inorganic metal salt that is hardly soluble in water is preferably an inorganic metal salt having a solubility of 0.5 g or less in 100 g of water.

[0154] The content of the dispersion stabilizer is not particularly limited. Relative to the total mass of 100 parts by mass of the first polymerizable monomer and the hydrocarbon solvent, it is preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8.0 parts by mass. By making the content of the dispersion stabilizer above the above lower limit value, the droplets of the monomer composition can be sufficiently dispersed in the suspension and do not aggregate into one body. On the other hand, by making the content of the dispersion stabilizer below the above upper limit value, it is possible to prevent the viscosity of the suspension from rising during granulation and avoid the problem that the suspension cannot pass through the granulator.

[0155] In addition, the content of the dispersion stabilizer is usually 2 parts by mass or more and 15 parts by mass or less, preferably 3 parts by mass or more and 8 parts by mass or less relative to 100 parts by mass of the aqueous medium.

[0156] (F) Aqueous medium

[0157] In the present invention, the aqueous medium refers to a medium selected from water, hydrophilic solvents, and mixtures of water and hydrophilic solvents.

[0158] The hydrophilic solvent in the present invention is not particularly limited as long as it is a solvent that is sufficiently mixed with water and does not undergo phase separation. Examples of the hydrophilic solvent include: alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO), etc.

[0159] In an aqueous medium, water is preferably used because of its high polarity. In the case of using a mixture of water and a hydrophilic solvent, from the viewpoint of forming droplets of the monomer composition, it is important that the polarity of the whole mixture does not become too low. In this case, for example, the mixing ratio (mass ratio) of water to the hydrophilic solvent can be water∶hydrophilic solvent = 99∶1 to 50∶50, etc.

[0160] A mixed solution is obtained by mixing the above-mentioned respective materials and other materials as required and appropriately stirring them, etc. In this mixed solution, an oil phase containing the above-mentioned (A) first polymerizable monomer, (B) particle size controller, (C) oil-soluble polymerization initiator, and (D) hydrocarbon solvent and other lipophilic materials is dispersed in an aqueous phase containing (E) dispersion stabilizer and (F) aqueous medium, etc., in a size of about several millimeters in particle diameter. The dispersion state of these materials in the mixed solution can be observed with the naked eye according to the type of material.

[0161] In the mixed solution preparation step, the above-mentioned respective materials and other materials as required can be obtained as a mixed solution only by mixing and appropriately stirring them, etc., but from the aspect that the shell is likely to become uniform, it is preferable to separately prepare in advance an oil phase containing the first polymerizable monomer, particle size controller, and hydrocarbon solvent and an aqueous phase containing the dispersion stabilizer and aqueous medium, and mix them to prepare the mixed solution.

[0162] In this way, on the basis of separately preparing the oil phase and the aqueous phase in advance and mixing them, hollow particles with a uniform composition of the shell part can be manufactured.

[0163] (2) Suspension step

[0164] The suspension step is a step of preparing a suspension in which droplets of the monomer composition containing the hydrocarbon solvent are dispersed in the aqueous medium by suspending the above-mentioned mixed solution.

[0165] The suspension method for forming droplets of the monomer composition is not particularly limited. For example, it is carried out using a device capable of strong stirring such as an (in-line type) emulsifying disperser (manufactured by Pacific Machine Works Co., Ltd., trade name: Milder), a high-speed emulsifying disperser (manufactured by PRIMIX Corporation, trade name: T.K.HOMOMIXER MARK II type), etc.

[0166] In the suspension prepared in the suspension step, droplets of the monomer composition containing the above-mentioned lipophilic materials and having a particle diameter of about 4 to 60 μm are uniformly dispersed in the aqueous medium. Such droplets of the monomer composition are difficult to observe with the naked eye and can be observed, for example, by a known observation device such as an optical microscope.

[0167] In the suspension step, since phase separation occurs in the droplets of the monomer composition, the hydrocarbon-based solvent with low polarity tends to aggregate inside the droplets. As a result, in the obtained droplets, the hydrocarbon-based solvent is distributed inside, and the materials other than the hydrocarbon solvent are distributed at the edges.

[0168] Figure 2 It is a schematic diagram showing an embodiment of the suspension in the suspension step. Figure 2 The droplets 10 of the monomer composition in [the figure] schematically show its cross-section. In addition, Figure 2 It is only a schematic diagram, and the suspension in the present invention is not necessarily limited to Figure 2 the suspension shown. Figure 2 A part of [the figure] corresponds to the above Figure 1 (2).

[0169] Figure 2 In [the figure], the droplets 10 of the monomer composition and the first polymerizable monomer 4c dispersed in the aqueous medium 1 are shown dispersed in the aqueous medium 1. The droplet 10 is formed by surrounding the oil-soluble monomer composition 4 with the dispersion stabilizer 3.

[0170] The monomer composition contains an oil-soluble polymerization initiator 5, and a first polymerizable monomer and a hydrocarbon-based solvent (both not shown).

[0171] The droplet 10 is a minute oil droplet containing the monomer composition 4, and the oil-soluble polymerization initiator 5 generates polymerization initiation radicals inside the minute oil droplet. Therefore, the minute oil droplet will not grow excessively, and precursor particles with the target particle size can be manufactured.

[0172] In the suspension polymerization method using such an oil-soluble polymerization initiator, there is no chance for the polymerization initiator to contact the polymerizable monomer 4c dispersed in the aqueous medium 1. Therefore, by using the oil-soluble polymerization initiator, in addition to the resin particles having the target hollow part, the generation of unnecessary polymer particles such as dense particles with relatively small particle sizes can be suppressed.

[0173] (3) Polymerization step

[0174] (3-1) First polymerization step

[0175] In the manufacturing method of the present invention, the polymerization step is carried out in two stages.

[0176] In the first polymerization step, the above suspension is supplied to the first polymerization reaction of the polymerization reaction until the polymerization conversion rate of the above first polymerizable monomer reaches 93% by mass or more, thereby preparing a first precursor composition containing first precursor particles, and the first precursor particles have a shell of a polymer containing the first polymerizable monomer and a hollow part filled with a hydrocarbon-based solvent.

[0177] In the first polymerization reaction, by supplying droplets of the monomer composition in a state of being encapsulated in a hydrocarbon-based solvent to the polymerization reaction, the polymerization reaction easily proceeds while maintaining the shape. Therefore, in the first polymerization reaction, by adjusting the amount of the hydrocarbon-based solvent, the amount of the particle size control agent, the type of the dispersion stabilizer, etc., the size and porosity of the obtained hollow particles can be easily adjusted. In addition, since the above-described first polymerizable monomer and the hydrocarbon-based solvent are used in combination, the hydrocarbon-based solvent has a low polarity with respect to the shell of the first precursor particles, and since the hydrocarbon-based solvent is difficult to conform to the shell, phase separation sufficiently occurs, and it is easy to form only one hollow portion.

[0178] In the first polymerization reaction, there is no particular limitation on the polymerization method, and for example, a batch (intermittent) method, a semi-continuous method, a continuous method, etc. can be adopted.

[0179] In the first polymerization reaction, the polymerization temperature is preferably 40 to 80°C, more preferably 50 to 70°C.

[0180] In addition, in the first polymerization reaction, the rate of temperature increase when raising the temperature to the polymerization temperature is preferably 10°C / h to 60°C / h, more preferably 15°C / h to 55°C / h.

[0181] In addition, the reaction time of the first polymerization reaction is preferably 0.5 to 5 hours, more preferably 1 to 3 hours.

[0182] In the production method of the present invention, the first polymerization reaction proceeds until the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, and further preferably 99% by mass or more.

[0183] In addition, in the present invention, the polymerization conversion rate is obtained by the following formula (A) based on the mass of the solid component of the first precursor particles obtained by the first polymerization reaction and the mass of the unreacted first polymerizable monomer remaining after the first polymerization reaction. In addition, in the present invention, the solid component is all components other than the solvent, and liquid polymerizable monomers, etc. are included in the solid component. In addition, the mass of the unreacted first polymerizable monomer can be measured using gas chromatography (GC).

[0184] Polymerization conversion rate (% by mass) = 100 - (mass of unreacted first polymerizable monomer / mass of solid component of first precursor particles) × 100 Formula (A)

[0185] (3-2) Second polymerization step

[0186] In the second polymerization step, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C is added to the first precursor composition obtained in the first polymerization step described above to conduct a second polymerization reaction, thereby preparing a second precursor composition containing second precursor particles, the second precursor particles having a shell of a polymer containing a first polymerizable monomer and a second polymerizable monomer and a hollow portion filled with a hydrocarbon-based solvent.

[0187] In the second polymerization reaction, the polymerization reaction is carried out in a state where the second polymerizable monomer is incorporated into the shell of the first precursor particles. It is presumed that the thermal motion of the shell of the first precursor particles is promoted by incorporating the second polymerizable monomer. Therefore, in the second polymerization reaction, the polymerizable functional groups of the first polymerizable monomer remaining unreacted in the shell and the second polymerizable monomer undergo a polymerization reaction to form a dense crosslinked structure.

[0188] The second polymerizable monomer is not particularly limited as long as it is a polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C. In particular, from the aspect of improving the strength of the hollow particles, a non-crosslinkable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C, that is, a hydrophilic non-crosslinkable monomer, is preferred. Examples of the hydrophilic non-crosslinkable monomer used as the second polymerizable monomer include the same monomers as those used as the first polymerizable monomer. Examples include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 5 carbon atoms, (meth)acrylamides and their derivatives, (meth)acrylonitrile, and non-crosslinkable monomers containing polar groups.

[0189] In addition, from the aspect that the second polymerizable monomer is incorporated into the shell of the first precursor particles and easily promotes thermal motion and improves the strength of the hollow particles, the solubility of the second polymerizable monomer in distilled water at 20°C is preferably 2 g / L or more, more preferably 10 g / L or more, further preferably 15 g / L or more, still further preferably 20 g / L or more, and particularly preferably 50 g / L or more. In addition, the upper limit of the solubility of the second polymerizable monomer in distilled water at 20°C is not particularly limited and is usually 80 g / L or less.

[0190] In addition, from the aspect that the second polymerizable monomer is incorporated into the shell of the first precursor particles and easily promotes thermal motion and improves the strength of the hollow particles, the molecular weight of the second polymerizable monomer is preferably 200 or less, more preferably 100 or less. The lower limit of the molecular weight of the second polymerizable monomer is not particularly limited and is usually 50 or more.

[0191] From the aspect of improving the strength of the hollow particles, as the second polymerizable monomer, it is preferably at least one selected from (meth)acrylic acid alkyl esters having an alkyl group with 1 to 5 carbon atoms and (meth)acrylonitrile, and more preferably at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and acrylonitrile.

[0192] Relative to 100 parts by mass of the first polymerizable monomer, the addition amount of the second polymerizable monomer is preferably 3 to 15 parts by mass, and more preferably 4 to 10 parts by mass. When the addition amount of the second polymerizable monomer is above the above lower limit value, the effect of promoting the polymerization reaction is improved by adding the second polymerizable monomer, and the crosslinked structure of the shell of the hollow particles becomes denser, whereby the strength of the hollow particles is increased and they are less likely to break. On the other hand, when the addition amount of the second polymerizable monomer is below the above upper limit value, a decrease in the content ratio of the first polymerizable monomer relative to the total polymerizable monomers used for forming the shell can be suppressed. Since the first polymerizable monomer contains a large amount of crosslinkable monomers, by suppressing the decrease in the content ratio of the first polymerizable monomer, hollow particles having excellent strength and containing a large amount of crosslinked structures formed by crosslinkable monomers can be obtained.

[0193] In the second polymerization reaction carried out after adding the second polymerizable monomer, there is no particular limitation on the polymerization method. For example, the same polymerization method as used in the first polymerization reaction can be employed.

[0194] In the second polymerization reaction, the polymerization temperature is preferably 40 to 80 °C, and more preferably 50 to 70 °C.

[0195] The reaction time of the second polymerization reaction is preferably 1 to 6 hours, and more preferably 2 to 4 hours.

[0196] According to the production method of the present invention, the residual amount of the unreacted polymerizable monomer after the second polymerization reaction is preferably 750 ppm or less, more preferably 500 ppm or less, and further preferably 300 ppm or less.

[0197] In addition, in the present invention, the residual amount of the unreacted polymerizable monomer after the second polymerization reaction refers to the ratio of the mass of the unreacted polymerizable monomer directly remaining to the mass of the solid component of the hollow particles obtained by the second polymerization reaction. In addition, the mass of the unreacted polymerizable monomer can be measured using gas chromatography (GC).

[0198] (4) Solid-liquid separation step

[0199] This step is to perform solid-liquid separation on the second precursor composition containing hollow particles (second precursor particles) encapsulating a hydrocarbon-based solvent obtained by the above polymerization step, thereby obtaining a solid component containing the second precursor particles.

[0200] The method for solid-liquid separation of the second precursor composition is not particularly limited, and known methods can be used. Examples of the solid-liquid separation method include, for example, centrifugation, filtration, static separation, etc. Among these, centrifugation or filtration can be employed, and from the viewpoint of operational simplicity, centrifugation can be adopted.

[0201] After the solid-liquid separation step and before the subsequent solvent removal step, any step such as a pre-drying step can be carried out. Examples of the pre-drying step include, for example, a step of pre-drying the solid component obtained after the solid-liquid separation step using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0202] (5) Solvent removal step

[0203] This step is a step of removing the hydrocarbon-based solvent encapsulated in the hollow particles (second precursor particles) obtained through the above solid-liquid separation step.

[0204] By removing the hydrocarbon-based solvent encapsulated in the second precursor particles in a gas, the hydrocarbon-based solvent inside the second precursor particles is exchanged with air, and hollow particles filled with gas are obtained.

[0205] Strictly speaking, "in a gas" in this step means an environment where there is no liquid component at all outside the second precursor particles, and an environment where there is only an extremely small amount of liquid component outside the second precursor particles that does not affect the removal of the hydrocarbon-based solvent. The so-called "in a gas" can also be expressed as a state where the second precursor particles do not exist in a slurry, or can also be expressed as a state where the second precursor particles exist in dry powder. That is, in this step, it is important to remove the hydrocarbon-based solvent in an environment where the second precursor particles are in direct contact with the external gas.

[0206] The method for removing the hydrocarbon-based solvent in the second precursor particles in a gas is not particularly limited, and known methods can be adopted. Examples of such methods include, for example, vacuum drying, heat drying, fluidized bed drying, or a combination of these methods.

[0207] In particular, in the case of using the heat drying method, the heating temperature needs to be above the boiling point of the hydrocarbon-based solvent and below the highest temperature at which the shell structure of the second precursor particles does not collapse. Therefore, depending on the composition of the shell in the second precursor particles and the type of the hydrocarbon-based solvent, for example, the heating temperature can be 50 - 200 °C, or can be 70 - 200 °C, or can also be 100 - 200 °C.

[0208] Through the drying operation in a gas, the hydrocarbon-based solvent inside the second precursor particles is replaced by the external gas, and as a result, hollow particles with gas occupying the hollow part are obtained.

[0209] Drying environment is not particularly limited and can be appropriately selected according to the purpose of the hollow particle. As drying environment, for example, air, oxygen, nitrogen, argon, etc. can be considered. In addition, once the hollow particle is filled with gas, by reduced pressure drying, a hollow particle temporarily in vacuum can be obtained.

[0210] As another method, instead of subjecting the slurry-like second precursor composition obtained in the polymerization step to solid-liquid separation, the hydrocarbon solvent may be removed from the slurry containing the second precursor particles and the aqueous medium by replacing the hydrocarbon solvent contained in the second precursor particles with the aqueous medium of the slurry.

[0211] In this method, the hydrocarbon solvent included in the second precursor particles can be removed by bubbling an inert gas into the second precursor composition at a temperature equal to or higher than the boiling point of the hydrocarbon solvent minus 35° C.

[0212] Here, when the above-mentioned hydrocarbon solvent is a mixed solvent containing multiple hydrocarbon solvents and has multiple boiling points, the boiling point of the hydrocarbon solvent in the solvent removal process refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, that is, the highest boiling point among the multiple boiling points.

[0213] From the perspective of reducing the residual amount of the hydrocarbon solvent in the hollow particles, the temperature when the inert gas is bubbled into the second precursor composition is preferably a temperature equal to or higher than the temperature minus 30°C from the boiling point of the hydrocarbon solvent, and more preferably a temperature equal to or higher than the temperature minus 20°C. In addition, the temperature during bubbling is usually a temperature equal to or higher than the polymerization temperature in the above-mentioned polymerization step. There is no particular limitation, and the temperature during bubbling can be 50°C or higher and 100°C or lower.

[0214] The inert gas for bubbling is not particularly limited, and examples thereof include nitrogen gas, argon gas, and the like.

[0215] The bubbling conditions can be appropriately adjusted according to the type and amount of the hydrocarbon solvent so as to remove the hydrocarbon solvent contained in the second precursor particles. There are no particular limitations. For example, the inert gas may be bubbled at 1 to 3 L / min for 1 to 10 hours.

[0216] In this method, an aqueous slurry containing an aqueous medium in the second precursor particles can be obtained. The slurry is solid-liquid separated to obtain hollow particles, which are then dried to remove the aqueous medium in the hollow particles, thereby obtaining hollow particles in which the hollow part is occupied by gas.

[0217] A method of subjecting a slurry-like second precursor composition to solid-liquid separation, removing a hydrocarbon-based solvent from the second precursor particles in a gas, and thereby obtaining hollow particles with a gas-filled hollow part has the advantage that the hollow particles are less likely to break in the process of removing the hydrocarbon-based solvent compared to a method of subjecting a slurry containing second precursor particles and an aqueous medium to solid-liquid separation after replacing the hydrocarbon-based solvent encapsulated in the second precursor particles with the aqueous medium of the slurry, removing the aqueous medium from the second precursor particles in a gas, and thereby obtaining hollow particles with a gas-filled hollow part. The latter method has the advantage that the residual amount of the hydrocarbon-based solvent is reduced by bubbling with an inert gas.

[0218] In addition, when replacing the hydrocarbon-based solvent encapsulated in the second precursor particles with water, if water in the same volume as the hydrocarbon-based solvent detached from the particles does not enter the particles, there is a problem that the obtained hollow resin particles will break. As a method to prevent this from occurring, for example, it can be considered to make the pH of the slurry 7 or more and then swell the shell of the particles by alkali dissolution and remove the hydrocarbon-based solvent. At this time, since the shell of the particles obtains flexibility, the replacement of the hydrocarbon-based solvent inside the particles with water proceeds rapidly.

[0219] (6) Others

[0220] As processes other than the above (1) to (5), for example, the following (6-a) cleaning process and the following (6-b) re-replacement process of the hollow part can be added.

[0221] (6-a) Cleaning process

[0222] The cleaning process is a process of adding an acid or a base for cleaning in order to remove a dispersion stabilizer remaining in the second precursor composition containing the second precursor particles before the above solvent removal process. When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in an acid, it is preferable to add an acid to the second precursor composition containing the second precursor particles for cleaning. On the other hand, when the dispersion stabilizer used is an inorganic compound soluble in a base, it is preferable to add a base to the second precursor composition containing the second precursor particles for cleaning.

[0223] In addition, as the dispersion stabilizer, when using an inorganic dispersion stabilizer soluble in an acid, it is preferable to add an acid to the second precursor composition containing the second precursor particles and adjust the pH to preferably 6.5 or less, more preferably 6 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as formic acid and acetic acid can be used. From the viewpoint of high removal efficiency of the dispersion stabilizer and small burden on manufacturing equipment, sulfuric acid is particularly preferred.

[0224] (6-b) Re-replacement process of the hollow part

[0225] The re-replacement process of the hollow part is a process of replacing the gas and liquid inside the hollow particles with other gases and liquids. Through such replacement, the environment inside the hollow particles can be changed, molecules can be selectively enclosed inside the hollow particles, and the chemical structure inside the hollow particles can be modified according to the use.

[0226] 2. Hollow particles

[0227] It can be speculated that the hollow particles obtained by the manufacturing method of the present invention are not easily broken even with a high porosity because of the dense cross-linked structure of the shell. As an index of the dense cross-linked structure of the shell, in the impregnation test of the hollow particles where 0.1 mg of hollow particles are added to 4 mL of acetone at 25 °C, shaken at an oscillation speed of 100 rpm for 10 minutes, and then allowed to stand for 48 hours, the hollow particles obtained by the manufacturing method of the present invention preferably have less than 5% by mass of the hollow particles precipitated in acetone. In the above impregnation test, it can be considered that the fewer the hollow particles precipitated in acetone, the denser the structure of the shell that is difficult for acetone to penetrate.

[0228] In addition, in the hollow particles obtained by the manufacturing method of the present invention, the connected pores and shell defects of the shell are extremely few. In SEM observation, the number of hollow particles having connected pores or shell defects among 100 hollow particles can be 5 or less.

[0229] Generally, in hollow particles, there are: hollow particles in which the shell does not have a connected pore connecting the hollow part and the external space of the particle; hollow particles in which the shell has one or more connected pores and the hollow part communicates with the outside of the particle through the connected pores. Although it also depends on the size of the hollow particles, the diameter of the connected pores is usually about 10 to 500 nm. The connected pores sometimes impart beneficial functions to the hollow particles, but on the other hand, since they are the parts where the shell is defective, they also become the cause of reducing the strength of the hollow particles and being prone to breakage.

[0230] In addition, the hollow particles sometimes have extremely large crack-like shell defects compared to the size of the particles. Although it also depends on the size of the hollow particles, since cracks with a length of 1 μm or more usually significantly deteriorate the strength of the hollow particles, they are considered shell defects.

[0231] In addition, in the above impregnation test of the hollow particles, when the hollow particles precipitated in acetone are less than 5% by mass, it can be regarded that among 100 such hollow particles, the number of hollow particles having connected pores or shell defects is 5 or less. In addition, even when the shell does not have connected pores and shell defects, there are cases where the precipitated hollow particles are 5% by mass or more in the above impregnation test of the hollow particles. Therefore, in the above impregnation test of the hollow particles, when the precipitated hollow particles are less than 5% by mass, it is considered that the connected pores and shell defects of the shell are extremely few and the shell has a dense cross-linked structure.

[0232] The shape of the hollow particles obtained by the production method of the present invention is not particularly limited as long as a hollow portion is formed inside, and examples thereof include spherical, ellipsoidal, and amorphous shapes. Among these, a spherical shape is preferred from the viewpoint of ease of production.

[0233] The hollow particles may have one or two or more hollow portions. In addition, when the hollow particles have two or more shells and hollow portions, the partition wall surface separating adjacent hollow portions may also be porous. In order to maintain a good balance between the high porosity of the hollow particles and the mechanical strength of the hollow particles, it is preferred that only one hollow portion is present inside the particles.

[0234] The average roundness of the hollow particles may be from 0.950 to 0.995.

[0235] An example of an image of the shape of the hollow particles is a bag made of a thin film and inflated with gas, and its cross-sectional view is as shown by the hollow particle 100 in (5) of Figure 1 In this example, one thin film is provided on the outside, and the inside thereof is filled with gas.

[0236] The particle shape can be confirmed by, for example, SEM and TEM. In addition, the shape inside the particles can be confirmed by observing with SEM and TEM after cutting the particles into wafers by a known method.

[0237] The lower limit of the volume average particle diameter of the hollow particles is preferably 4.0 μm or more, more preferably 4.5 μm or more, and further preferably 5.0 μm or more. On the other hand, the upper limit of the volume average particle diameter of the hollow particles is preferably 60.0 μm or less, more preferably 55.0 μm or less, and further preferably 50.0 μm or less.

[0238] When the volume average particle diameter of the hollow particles is equal to or greater than the above lower limit value, the cohesiveness between the hollow particles becomes smaller, and thus excellent dispersibility can be exhibited. In addition, when the volume average particle diameter of the hollow particles is equal to or less than the above upper limit value, the hollow particles are not easily broken, and thus have high mechanical strength.

[0239] The particle size distribution (volume average particle diameter (Dv) / number average particle diameter (Dn)) of the hollow particles can be, for example, 1.1 or more and 2.5 or less. By making the particle size distribution 2.5 or less, particles with small deviation in compressive strength characteristics and heat resistance between particles can be obtained. In addition, by making the particle size distribution 2.5 or less, for example, when manufacturing a sheet-shaped molded body, a product with uniform thickness can be manufactured.

[0240] Regarding the volume average particle diameter (Dv) and number average particle diameter (Dn) of the hollow particles, for example, the particle diameter of the hollow particles can be measured by a laser diffraction particle size distribution measuring device, and the number average and volume average values can be calculated respectively. The obtained values are used as the number average particle diameter (Dn) and volume average particle diameter (Dv) of the particles. The particle size distribution is the value obtained by dividing the volume average particle diameter by the number average particle diameter.

[0241] The porosity of the hollow particles obtained by the production method of the present invention is 50% or more, preferably 60% or more. By making the porosity the above lower limit value or more, the lightness, heat resistance, and heat insulation of the hollow particles are excellent. The upper limit of the porosity of the hollow particles of the present invention is not particularly limited, but from the aspect of suppressing the reduction of the strength of the hollow particles and making them not easily broken, it is preferably 90% or less, more preferably 85% or less, and further preferably 80% or less.

[0242] The porosity of the hollow particles obtained by the production method of the present invention is calculated from the apparent density D1 and true density D0 of the hollow particles.

[0243] The method for measuring the apparent density D1 of the hollow particles is as follows. First, fill about 30 cm 3 of hollow particles into a volumetric flask with a capacity of 100 cm 3 , and accurately weigh the mass of the filled hollow particles. Then, in the volumetric flask filled with hollow particles, carefully fill isopropyl alcohol up to the calibration line while preventing air bubbles from entering. Accurately weigh the mass of the isopropyl alcohol added to the volumetric flask, and calculate the apparent density D1 (g / cm 3 ) of the hollow particles based on the following formula (Ⅰ).

[0244] Formula (I)

[0245] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0246] The apparent density D1 corresponds to the specific gravity of the entire hollow particle when the hollow part is regarded as a part of the hollow particle.

[0247] The method for measuring the true density D0 of the hollow particles is as follows. After previously crushing the hollow particles, fill about 10 g of the fragments of the hollow particles into a volumetric flask with a capacity of 100 cm 3 , and accurately weigh the mass of the filled fragments. Then, add isopropyl alcohol to the volumetric flask in the same manner as the measurement of the apparent density, accurately weigh the mass of the isopropyl alcohol, and calculate the true density D0 (g / cm 3 ) of the hollow particles based on the following formula (II).

[0248] Formula (II)

[0249] True density D0 = [mass of fragments of hollow particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0250] The true density D0 corresponds to the specific gravity of only the shell part in the hollow particles. As is clear from the above measurement method, the hollow part is not regarded as a part of the hollow particles when calculating the true density D0.

[0251] The porosity (%) of the hollow particles is calculated by the following formula (III) from the apparent density D1 and the true density D0 of the hollow particles.

[0252] Formula (III)

[0253] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0254] The porosity of the hollow particles can be expressed as the proportion of the hollow part in the specific gravity of the hollow particles.

[0255] The thickness of the shell of the hollow particles obtained by the production method of the present invention is preferably 0.1 μm or more, more preferably 0.2 μm or more, and further preferably 0.3 μm or more as the lower limit, and preferably 6 μm or less, more preferably 5 μm or less, and further preferably 4 μm or less as the upper limit. Since the thickness of the shell of the hollow particles is the above lower limit value or more, the strength of the shell is improved. On the other hand, since the shell of the hollow particles obtained by the production method of the present invention has a dense structure, even if the thickness of the shell is thinner than the above lower limit value, the strength of the obtained hollow particles is excellent and they are not easily broken.

[0256] In addition, the thickness of the shell of the hollow particles can be calculated as follows: The inner diameter r of the hollow particles is calculated by the following formula (1) using the volume average particle diameter R and the porosity of the hollow particles, and the shell thickness is calculated by the following formula (2) using the inner diameter r and the volume average particle diameter R. In addition, the porosity in the following formula (1) is a value expressed as a ratio.

[0257] 4 / 3π×(R / 2) 3 ×porosity = 4 / 3π×(r / 2) 3 Formula (1)

[0258] Shell thickness = (R - r) / 2 Formula (2)

[0259] Since the difference between the thickness of the shell calculated in this way and the average value of the thicknesses at 20 places of the actually measured shell is usually within ±10% of these average values, the thickness of the shell calculated as above can be regarded as the thickness of the shell of the hollow particles.

[0260] When determining the average thickness at 20 of the shell of the hollow particles, the thickness at each part of the shell of the hollow particles can be measured, for example, by observing the fragments of the shell obtained by crushing the hollow particles with SEM.

[0261] The hollow particles obtained by the production method of the present invention are not easily broken during kneading with other materials and during molding after kneading. When added to a molded body, they are excellent as lightweight materials, heat insulating materials, sound insulating materials, damping materials, etc., and are therefore particularly preferably used as additives for molded bodies. The hollow particles of the present invention are also not easily broken during kneading with resins and during molding after kneading, and are therefore particularly preferably used as additives for resin molded bodies.

[0262] The molded body containing the hollow particles of the present invention, as the resin, may contain, for example, thermoplastic resins or thermosetting resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, epoxy resin, acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-styrene (AS) resin, poly(meth)acrylate, polycarbonate, polyamide, polyimide, polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene. In addition, the molded body containing the hollow particles of the present invention may also contain organic or inorganic fibers such as carbon fiber, glass fiber, aromatic polyamide fiber, and polyethylene fiber. In a molded body formed using a thermoplastic or thermosetting resin, and in a molded body formed using a thermoplastic or thermosetting resin and a material further containing fibers, the hollow particles obtained by the production method of the present invention can also be contained as a filler.

[0263] As uses of the resin molded body containing the hollow particles of the present invention, for example, it can be used for components such as light reflection materials, heat insulating materials, sound insulating materials, and low dielectrics in various fields such as automobiles, electrics, electronics, construction, aviation, and space, food containers, shoes such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, tools, etc.

[0264] In addition, since the hollow particles of the present invention have a high porosity, are not easily broken, and have excellent heat resistance, they satisfy the heat insulation and cushioning properties required for the bottom coating material, and also satisfy the heat resistance suitable for the use of thermal paper. In addition, the hollow particles of the present invention are also useful as plastic pigments with excellent gloss, hiding power, etc.

[0265] Furthermore, since the hollow particles of the present invention can enclose useful components such as fragrances, drugs, pesticides, and ink components inside by means of impregnation treatment, reduced pressure or pressure impregnation treatment, etc., they can be used in various applications according to the components contained inside.

[0266] Examples

[0267] Hereinafter, examples and comparative examples are given to illustrate the present invention more specifically, but the present invention is not limited to these examples. In addition, parts and % are based on mass unless otherwise specified.

[0268] [Example 1]

[0269] (1) Mixed solution preparation step

[0270] First, the following materials are mixed as the oil phase.

[0271] First polymerizable monomer: 80 parts of ethylene glycol dimethacrylate and 20 parts of pentaerythritol tetraacrylate

[0272] 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator, manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65)

[0273] 0.007 parts of rosin acid (manufactured by Arakawa Chemical Industries, Ltd., trade name: disproportionated rosin RONDIS R-CH, softening point 150°C or higher, acid value: 150 - 160 mgKOH / g)

[0274] 187 parts of cyclohexane

[0275] Next, in a stirring tank, at room temperature, an aqueous solution prepared by dissolving 17.1 parts of magnesium chloride (water-soluble polyvalent metal salt) in 494 parts of ion-exchanged water is slowly added dropwise, with stirring, to an aqueous solution prepared by dissolving 12.1 parts of sodium hydroxide (alkali metal hydroxide) in 121 parts of ion-exchanged water to prepare a dispersion of magnesium hydroxide colloid (metal hydroxide colloid insoluble in water) (4 parts of magnesium hydroxide), as the water phase.

[0276] The obtained water phase and oil phase are mixed to prepare a mixed solution.

[0277] (2) Suspension step

[0278] The mixed solution obtained in the above mixed solution preparation step is stirred for 1 minute at a rotation speed of 4000 rpm by a disperser (manufactured by PRIMIX Corporation, trade name: homogenizer (HOMOMIXER)) to make it suspended, and a suspension in which droplets of the monomer composition containing cyclohexane are dispersed in water is prepared.

[0279] (3) Polymerization step

[0280] The suspension obtained in the above suspension process is heated from 40 °C to 65 °C over 30 minutes in a nitrogen atmosphere (heating rate: 50 °C / hour), and stirred at 65 °C for 1 hour and 30 minutes to carry out the first polymerization reaction, obtaining a first precursor composition containing first precursor particles. The polymerization conversion rate at the end of the first polymerization reaction is 99.2% by mass. Then, 5 parts of methyl acrylate is added as a second polymerizable monomer to the stirring tank, and stirred at 65 °C for 2 hours and 30 minutes in a nitrogen atmosphere, thereby carrying out the second polymerization reaction. Through this second polymerization reaction, a second precursor composition containing second precursor particles encapsulating cyclohexane is obtained.

[0281] (4) Cleaning process and solid-liquid separation process

[0282] The above second precursor composition is washed with dilute sulfuric acid (25 °C, 10 minutes) to make the pH 5.5 or less. Then, after separating water by filtration, 200 parts of fresh ion-exchanged water is added for re-slurrying, and water washing treatment (washing, filtration, dehydration) is repeatedly carried out several times at room temperature (25 °C), and the solid component is obtained by filtration separation. The obtained solid component is dried at 40 °C with a dryer to obtain second precursor particles encapsulating cyclohexane.

[0283] (5) Solvent removal process

[0284] The second precursor particles obtained in the above solid-liquid separation process are heat-treated in a vacuum dryer at 200 °C under vacuum conditions for 6 hours, thereby removing the hydrocarbon-based solvent encapsulated in the particles, obtaining the hollow particles of Example 1. From the observation results of a scanning electron microscope and the porosity value of the obtained hollow particles, it was confirmed that these particles are spherical and have a hollow part.

[0285] [Examples 2 - 5]

[0286] In Example 1, the material of the second polymerizable monomer added in the above “(3) Polymerization process” was changed as shown in Table 1, and except for this, the hollow particles of Examples 2 - 5 were manufactured by the same steps as in Example 1.

[0287] [Example 6]

[0288] In Example 1, in the above “(1) Mixed solution preparation process”, the material and amount of the first polymerizable monomer were changed as shown in Table 1, and except for this, the hollow particles of Example 6 were manufactured by the same steps as in Example 1.

[0289] [Examples 7 - 8, 10]

[0290] In Example 1, in the above-mentioned “(3) Polymerization step”, the addition amount of methyl acrylate added as the second polymerizable monomer was changed as shown in Table 1. Except for this, hollow particles of Examples 7 to 8 and 10 were produced by the same steps as in Example 1.

[0291] [Example 9]

[0292] In Example 1, in the above-mentioned “(1) Mixed solution preparation step”, abietic acid used as a particle size control agent was not added. Except for this, hollow particles of Example 9 were produced by the same steps as in Example 1.

[0293] [Comparative Example 1]

[0294] In Example 1, in the above-mentioned “(3) Polymerization step”, the second polymerizable monomer was not added and the second polymerization reaction was not carried out. Except for this, hollow particles of Comparative Example 1 were produced by the same steps as in Example 1.

[0295] [Comparative Example 2]

[0296] In Example 1, in the above-mentioned “(3) Polymerization step”, 5 parts of styrene (solubility in distilled water at 20 °C is 0.2 g / L) was added as the second polymerizable monomer instead of 5 parts of methyl acrylate. Except for this, hollow particles of Comparative Example 2 were produced by the same steps as in Example 1.

[0297] [Comparative Example 3]

[0298] In Example 1, in the above-mentioned “(3) Polymerization step”, the reaction time of the first polymerization reaction was changed from 1 hour and 30 minutes to 30 minutes. When the total polymerization conversion rate of ethylene glycol dimethacrylate and pentaerythritol tetraacrylate as the first polymerizable monomers reached 91.0% by mass, the second polymerizable monomer was added to carry out the second polymerization reaction. Except for this, hollow particles of Comparative Example 3 were produced by the same steps as in Example 1.

[0299] [Comparative Example 4]

[0300] In Example 1, in the above-mentioned “(1) Mixed solution preparation step”, the materials and amounts of the first polymerizable monomers were changed as shown in Table 1. Except for this, hollow particles of Comparative Example 4 were produced by the same steps as in Example 1.

[0301] [Comparative Example 5]

[0302] In Example 1, in the above-mentioned “(1) Mixed solution preparation step”, the materials and amounts of the first polymerizable monomer were changed as shown in Table 1. In the above-mentioned “(3) Polymerization step”, the second polymerizable monomer was not added and the second polymerization reaction was not carried out. Except for this, hollow particles of Comparative Example 5 were manufactured by the same steps as in Example 1.

[0303] [Table 1]

[0304]

[0305] [Evaluation]

[0306] 1. Polymerization conversion rate

[0307] In the polymerization step of each example and each comparative example, 50 g of the first precursor composition generated in the first polymerization reaction was collected and subjected to pressure filtration to obtain the first precursor particles (including moisture and hydrocarbon solvent) contained in the first precursor composition, and it was accurately weighed to the unit of 1 mg. 27 g of ethyl acetate was added to about 3 g of the accurately weighed first precursor particles, and after stirring for 15 minutes, 13 g of methanol was added, and then stirred for 10 minutes. The obtained solution was allowed to stand to precipitate the insoluble components, and the supernatant of the solution was collected as a measurement sample. 2 μL of the measurement sample was injected into a gas chromatograph, and the amount of polymerizable monomer in the sample was quantitatively determined by gas chromatography (GC) under the following conditions, and it was used as the mass of the unreacted first polymerizable monomer. In addition, the first precursor particles obtained by pressure filtration were dried at 200 °C for 2 hours to remove moisture and hydrocarbon solvent, and the mass of the solid component of the first precursor particles was determined. Then, the polymerization conversion rate was calculated by the following formula (A).

[0308] Polymerization conversion rate (mass %) = 100 - (mass of unreacted first polymerizable monomer / mass of solid component of first precursor particles) × 100 Formula (A)

[0309] <GC conditions>

[0310] Chromatographic column: TC-WAX (0.25 mm × 30 m)

[0311] Chromatographic column temperature: 80 °C

[0312] Injection temperature: 200 °C

[0313] FID detection side temperature: 200 °C

[0314] For the hollow particles obtained in each example and each comparative example, the content ratio (mass %) of each monomer unit in the polymer contained in the shell is shown in Table 2.

[0315] In addition, the following measurements and evaluations were performed on the hollow particles obtained in each example and each comparative example. The results are shown in Table 2.

[0316] 2. Volume-average particle size of hollow particles

[0317] The particle size of the hollow particles was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, trade name: SALD-2000), and the volume average was calculated as the volume-average particle size.

[0318] 3. Density and porosity of hollow particles

[0319] 3-1. Measurement of apparent density of hollow particles

[0320] First, approximately 30 cm 3 of hollow particles were filled in a volumetric flask with a capacity of 100 cm 3 , and the mass of the filled hollow particles was accurately weighed. Next, while taking care not to let air bubbles enter, isopropyl alcohol was accurately filled up to the calibration mark in the volumetric flask filled with hollow particles. The mass of the isopropyl alcohol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm 3 ) of the hollow particles was calculated based on the following formula (I).

[0321] Formula (I)

[0322] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0323] 3-2. Measurement of true density of hollow particles

[0324] After pre-crushing the hollow particles, approximately 10 g of fragments of the hollow particles were filled in a volumetric flask with a capacity of 100 cm 3 , and the mass of the filled fragments was accurately weighed.

[0325] Then, isopropyl alcohol was added to the volumetric flask in the same manner as in the measurement of the apparent density, the mass of the isopropyl alcohol was accurately weighed, and the true density D0 (g / cm 3 ) of the hollow particles was calculated based on the following formula (II).

[0326] Formula (II)

[0327] True density D0 = [mass of fragments of hollow particles] / (100 - [mass of isopropyl alcohol] ÷ [specific gravity of isopropyl alcohol at the measurement temperature])

[0328] 3-3. Calculation of porosity

[0329] The porosity of the hollow particles is calculated based on the apparent density D1 and the true density D0 of the hollow particles according to the following formula (III).

[0330] Formula (III)

[0331] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0332] 4. Thickness of the shell of the hollow particles

[0333] The inner diameter r of the hollow particles is calculated using the volume average particle diameter R and the porosity of the hollow particles according to the following formula (1), and the thickness of the shell of the hollow particles is calculated using the inner diameter r and the volume average particle diameter R according to the following formula (2).

[0334] 4 / 3π × (R / 2) 3 × porosity = 4 / 3π × (r / 2) 3 Formula (1)

[0335] Shell thickness = (R - r) / 2 Formula (2)

[0336] 5. Immersion test

[0337] In an environment at 25°C, 0.1 mg of hollow particles are added to 4 mL of acetone, and after shaking for 10 minutes under the condition of a shaking speed of 100 rpm using a shaker, it is left standing for 48 hours, and the proportion of the precipitated hollow particles is determined and evaluated according to the following evaluation criteria. In addition, the hollow particles precipitated in acetone are separated by a centrifuge and dried, and the mass of the hollow particles precipitated in acetone is measured. By calculating the proportion of the mass of the hollow particles precipitated in acetone relative to the total mass of the hollow particles immersed in acetone, the proportion of the precipitated hollow particles is obtained.

[0338] (Evaluation criteria for the immersion test)

[0339] 〇: The precipitated hollow particles are less than 5% by mass

[0340] ×: The precipitated hollow particles are 5% by mass or more

[0341] 6. Residual monomer content

[0342] 3 g of the hollow particles are accurately weighed to the nearest 1 mg, 27 g of ethyl acetate is added and stirred for 15 minutes, then 13 g of methanol is added and stirred for another 10 minutes. The resulting solution is left standing to precipitate the insoluble components, and the supernatant of this solution is collected as the test sample for measurement. 2 μL of the test sample for measurement is injected into a gas chromatograph, and the amount of unreacted polymerizable monomer in the sample is quantitatively determined by gas chromatography (GC) under the following conditions. The content ratio of the unreacted polymerizable monomer contained in the hollow particles is calculated as the residual monomer content.

[0343] <Conditions of GC>

[0344] Chromatographic column: TC-WAX (0.25 mm × 30 m)

[0345] Column temperature: 80 °C

[0346] Injection temperature: 200 °C

[0347] FID detection side temperature: 200 °C

[0348] 7. Residual porosity rate in the molded body

[0349] Mix 90 parts of polypropylene as a thermoplastic resin (manufactured by Mitsubishi Chemical, product name: MA1B, specific gravity 0.90 g / cm 3 ) and 10 parts of the hollow particles obtained in each example or each comparative example using a blender. Then, using a twin-screw kneader (manufactured by Toshiba Machine Co., Ltd., product name: TEM-35B), knead, extrude, and pelletize under the following kneading conditions to obtain pellets of the resin composition.

[0350] <Kneading conditions>

[0351] Screw diameter 37 mm, L / D = 32

[0352] Screw rotation speed 250 rpm

[0353] Resin temperature 190 °C

[0354] Feeding rate 20 kg / hour

[0355] Heat the obtained pellets of the resin composition at 80 °C for 6 hours and dry them. Then, use an injection molding device to perform molding under the following molding conditions to obtain a molded body with dimensions of 80 mm × 10 mm × thickness 4 mm.

[0356] <Molding conditions>

[0357] Barrel temperature: 230 °C

[0358] Mold temperature: 40 °C

[0359] Injection pressure: 70 MPa

[0360] Use a: specific gravity of the molded body after injection molding, b: specific gravity of the molded body assuming the pores are maintained (calculated value), and c: specific gravity of the molded body assuming all hollow particles are broken (calculated value) to calculate the residual porosity rate through the following formula (B).

[0361] Residual porosity rate (%) = [1 - {(c - a) / (c - b)}] × 100 Formula (B)

[0362] In addition, the specific gravity of the molded article after injection molding was measured by the water displacement method in accordance with JIS K 7112.

[0363] Assume that the specific gravity b of the molded article maintaining the pores is calculated by the following formula (C).

[0364] b = 1 / { (P A / P G ) + (R A / R G )} Formula (C)

[0365] In the calculation formula for obtaining the above b, P A represents the addition amount of hollow particles, P G represents the specific gravity of hollow particles, R A represents the addition amount of thermoplastic resin, and R G represents the specific gravity of thermoplastic resin.

[0366] Assume that the specific gravity c of the molded article in which all hollow particles are broken is calculated by the following formula (D).

[0367] c = [ R G × R A + { D0 × P A × (1 - P V / 100)} ] / { R A + P A × (1 - P V / 100) ) Formula (D)

[0368] In the calculation formula for obtaining the above c, R A represents the addition amount of thermoplastic resin, R G represents the specific gravity of thermoplastic resin, D0 represents the true density of hollow particles, P A represents the addition amount of hollow particles, and P V represents the porosity (%) of hollow particles.

[0369] [Table 2]

[0370]

[0371] In addition, in Table 1 and Table 2, the meanings of the abbreviations are as follows.

[0372] MMA: Methyl methacrylate

[0373] MA: Methyl acrylate

[0374] EA: Ethyl acrylate

[0375] BA: Butyl acrylate

[0376] AN: Acrylonitrile

[0377] ST: Styrene

[0378] [Investigation]

[0379] As shown in Table 2 above, it is clear that the porosity of the hollow particles obtained in each comparative example is as high as 65%, but the residual porosity of the molded body of the resin composition containing the hollow particles is low, and the hollow particles are easily broken.

[0380] In Comparative Example 1, since the addition of the second polymerizable monomer was not carried out, the amount of residual monomers contained in the obtained hollow particles was large. In the impregnation test, the hollow particles precipitated in acetone were 5% by mass or more. In Comparative Example 1, it is presumed that since the polymerization reaction was carried out in one step, unreacted polymerizable functional groups remained in the shell, and the crosslinked structure of the shell was rough. Therefore, the obtained hollow particles easily permeated acetone and were easily broken.

[0381] In Comparative Example 2, since styrene having a solubility of 0.2 g / L in distilled water at 20°C was used instead of a hydrophilic monomer having a solubility of 0.3 g / L or more in distilled water at 20°C as the second polymerizable monomer, the amount of residual monomers contained in the obtained hollow particles was large. In the impregnation test, the hollow particles precipitated in acetone were 5% by mass or more. In Comparative Example 2, it is presumed that since the second polymerizable monomer was difficult to incorporate into the shell, unreacted polymerizable functional groups remained in the shell, and the crosslinked structure of the shell was rough. Therefore, the obtained hollow particles easily permeated acetone and were easily broken.

[0382] In Comparative Example 3, the timing of adding the second polymerizable monomer was before the polymerization conversion rate of the first polymerizable monomer reached 93% by mass. Therefore, the amount of residual monomers contained in the obtained hollow particles was large. In the impregnation test, the hollow particles precipitated in acetone were 5% by mass or more. In Comparative Example 3, it is presumed that since the timing of adding the second polymerizable monomer was too early, unreacted polymerizable functional groups remained in the shell, and the crosslinked structure of the shell was rough. Therefore, the obtained hollow particles easily permeated acetone and were easily broken.

[0383] In Comparative Example 4, since the content of the crosslinkable monomer in 100 parts by mass of the first polymerizable monomer was less than 75 parts by mass, the amount of residual monomers contained in the obtained hollow particles was large. In the impregnation test, the hollow particles precipitated in acetone were 5% by mass or more. In Comparative Example 4, it is presumed that since the content of the crosslinkable monomer in the first polymerizable monomer was small and there were many remaining unreacted non-crosslinkable monomers, the crosslinked structure of the shell was rough. Therefore, the obtained hollow particles easily permeated acetone and were easily broken.

[0384] In Comparative Example 5, since methyl methacrylate was not used as the second polymerizable monomer but was added to the mixed solution in one step together with the first polymerizable monomer, the amount of residual monomers contained in the obtained hollow particles was large. In the impregnation test, the hollow particles precipitated in acetone were 5% by mass or more. In Comparative Example 5, it is presumed that since the polymerization reaction was carried out in one step, unreacted polymerizable functional groups remained in the shell, and the crosslinked structure of the shell was rough. Therefore, the obtained hollow particles were easily permeated by acetone and easily broken.

[0385] In contrast, it was clarified that the porosity of the hollow particles obtained in each Example was as high as 65%, the porosity retention rate of the molded body of the resin composition containing the hollow particles was high, and the molded body had a high void ratio and was not easily broken.

[0386] In Examples 1 to 10, since the first polymerizable monomer contained in the mixed solution included 75 to 100 parts by mass of a crosslinkable monomer in 100 parts by mass of the first polymerizable monomer, when the polymerization conversion rate of the first polymerizable monomer reached 93% by mass or more in the polymerization step, a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C was added and then supplied to the polymerization reaction. Therefore, almost no unreacted polymerizable monomers remained in the obtained hollow particles. In the impregnation test, the hollow particles precipitated in acetone were less than 5% by mass. In Examples 1 to 10, it is presumed that although a large amount of crosslinkable monomer was used, since almost no unreacted polymerizable functional groups remained in the shell, the crosslinked structure of the shell became dense. Therefore, hollow particles that were not easily permeated by acetone and not easily broken even with a high porosity were obtained.

[0387] Explanation of reference numerals

[0388] 1 Aqueous medium

[0389] 2 Low-polarity material

[0390] 3 Dispersion stabilizer

[0391] 4 Monomer composition

[0392] 4a Hydrocarbon solvent

[0393] 4b Materials other than hydrocarbon solvents

[0394] 4c Polymerizable monomer dispersed in the aqueous medium

[0395] 5 Oil-soluble polymerization initiator

[0396] 6 Shell

[0397] 8 Hollow part

[0398] 10 Droplet

[0399] Hollow particles (second precursor particles) containing a hydrocarbon-based solvent in the hollow portion

[0400] 100 Hollow particles with the hollow portion filled with gas

Claims

1. A method for manufacturing hollow particles, which is a method for manufacturing hollow particles having a shell containing a resin and a hollow portion surrounded by the shell and a porosity of 50% or more. The method for manufacturing the hollow particles includes the following steps: A step of preparing a mixed solution containing a first polymerizable monomer, a hydrocarbon solvent, a dispersion stabilizer, and an aqueous medium; A step of preparing a suspension in which droplets of a monomer composition containing the first polymerizable monomer and the hydrocarbon solvent are dispersed in the aqueous medium by suspending the mixed solution; A step of supplying the suspension to a polymerization reaction; The mixed solution contains a crosslinkable monomer as the first polymerizable monomer, and the content of the crosslinkable monomer in 100 parts by mass of the first polymerizable monomer is 75 to 100 parts by mass, and the crosslinkable monomer contains at least a bifunctional crosslinkable monomer. In the step of supplying the suspension to the polymerization reaction, when the polymerization conversion rate of the first polymerizable monomer reaches 93% by mass or more, 3 to 15 parts by mass of a second polymerizable monomer is added relative to 100 parts by mass of the first polymerizable monomer, and then supplied to the polymerization reaction. The second polymerizable monomer is selected from (meth)acrylic acid alkyl esters having an alkyl group with 1 to 5 carbon atoms; (meth)acrylamides and their derivatives; (meth)acrylonitrile, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, glycidyl (meth)acrylate, and glycidyl ether of 4-hydroxybutyl acrylate, and at least one of them has a solubility of 0.3 g / L or more in distilled water at 20°C.

2. The method for manufacturing hollow particles according to claim 1, wherein, The first polymerizable monomer further contains a crosslinkable monomer having three or more functional groups as the crosslinkable monomer.

3. The method for manufacturing hollow particles according to claim 2, wherein, The content of the crosslinkable monomer having three or more functional groups in 100 parts by mass of the first polymerizable monomer is 5 to 50 parts by mass.

4. The method for manufacturing the hollow particles according to claim 1 or 2, wherein, The first polymerizable monomer contains at least one selected from divinylbenzene, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate as the bifunctional crosslinkable monomer.

5. The method for manufacturing hollow particles according to claim 2 or 3, wherein, The first polymerizable monomer contains at least one selected from pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol poly(meth)acrylate as the crosslinkable monomer having three or more functional groups.

6. The method for manufacturing hollow particles according to claim 1 or 2, wherein, The mixed solution contains at least one selected from rosin acid, higher fatty acids, and their metal salts.

7. The method for manufacturing hollow particles according to claim 1 or 2, wherein, The dispersion stabilizer is an inorganic dispersion stabilizer.

8. The method for manufacturing the hollow particles according to claim 7, wherein, The inorganic dispersion stabilizer is a metal salt hardly soluble in water.

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