JP6122698B2 - Method for producing fine particles - Google Patents

Description

  The present invention relates to a method for producing fine particles, and more particularly to a method capable of easily producing fine particles having a uniform particle diameter.

  Resin fine particles are used in industrial fields such as inkjet, color filters, electronic paper, and copying machines. It is desired that the resin fine particles have a small average particle size and a small particle size distribution.

  As a method for producing resin fine particles, various polymerization methods such as emulsion polymerization and suspension polymerization are known. In recent years, since a reaction can be carried out efficiently in a narrow space, the use of a microreactor has been studied as a method for producing resin fine particles. Since Patent Document 1 is a highly monodisperse with a narrow particle size distribution and has a target particle size in the nano order, a dispersed phase composed of a polymerizable monomer from an opening connected to a continuous phase flowing through a microreactor. In a production method for producing monodispersed fine particles by producing droplets that are dispersed in a continuous phase composed of a dispersed phase and polymerizing them, a monodispersed microscopical force is applied to the droplets by applying a uniform shearing force from the outside. A method for producing highly monodispersed fine particles that obtain monodispersed fine particles having an average particle diameter of 50 nm to 500 nm by forming droplets will be described.

JP 2008-031419 A

  However, in the method of Patent Document 1, the polymerizable monomer in the dispersed phase may flow out to the continuous phase, and the solid content concentration in the droplets varies from droplet to droplet. This state resulted in undesirable emulsification, and as a result, it was difficult to make the particle size distribution uniform.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method for producing fine particles that can easily produce fine particles having a uniform particle diameter.

  In one aspect of the present invention, a method for producing fine particles includes a step of preparing an organic phase containing a monomer constituting the fine particles, a polymerization initiator, and a coloring component, and an aqueous phase containing water, magnesium chloride, and a dispersant. A mixing step of mixing the organic phase and the aqueous phase, and an emulsification step of circulating the mixture of the organic phase and the aqueous phase formed in the mixing step through a static mixer to obtain an oil-in-water emulsion. And a polymerization step of polymerizing the monomer by heating the emulsion under a nitrogen atmosphere.

  Preferably, the static mixer includes a plurality of supply channels, a merge portion to which the plurality of supply channels are connected, and a discharge channel connected to the merge portion. A part or all of these are composed of channels having an equivalent diameter of 1 μm to 2 mm.

  Preferably, the dispersant has a vinyl group in its molecular structure.

  Preferably, the dispersant is polyvinyl pyrrolidone.

  Preferably, the organic phase monomer comprises methyl methacrylate.

  Preferably, the organic phase comprises an additional monomer, the additional monomer being composed of any of N, N-diethylaminoethyl methacrylate, ethylene glycol dimethacrylate, and mixtures thereof.

  Preferably, the coloring component is a pigment.

  Preferably, the polymerization initiator is a radical polymerization initiator that generates radicals by light or heat.

  Preferably, the polymerization initiator is an azo compound.

  Preferably, in the emulsification step, the pressure when the mixture is circulated through the static mixer is in the range of 10 kPa to 1000 kPa.

  Preferably, in the emulsification step, the circulation time for circulating the mixture in the static mixer is 5 minutes or more.

  Preferably, the weight ratio (organic phase / aqueous phase) of the aqueous phase and the organic phase of the mixture is 1/10 to 1/2.

  Preferably, the method further includes a step of mixing an emulsion and an aqueous solution containing water, magnesium chloride and a dispersant after the emulsification step and before the polymerization step, wherein the concentration of magnesium chloride in the aqueous solution is magnesium chloride in the aqueous phase. Lower than the concentration of.

  Preferably, the aqueous phase dispersant and the aqueous solution dispersant have different molecular weights.

  According to the present invention, fine particles having a uniform particle diameter can be easily produced.

Schematic which shows an example of the manufacture flow of microparticles | fine-particles. Schematic which shows the structure of a microdevice. 2 is an SEM image of the fine particles obtained in Example 1. 3 is an SEM image of fine particles obtained in Comparative Example 1. 4 is an SEM image of fine particles obtained in Comparative Example 2.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention will be described by the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment are utilized. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims.

  Here, in the drawing, portions indicated by the same symbols are similar elements having similar functions. In addition, in the present specification, when a numerical range is expressed using “˜”, upper and lower numerical values indicated by “˜” are also included in the numerical range.

  The method for producing fine particles of the present embodiment includes a step of preparing an organic phase containing a monomer constituting the fine particles, a polymerization initiator and a coloring component, and an aqueous phase containing water, magnesium chloride and a dispersing agent, A mixing step of mixing an aqueous phase, an emulsification step of obtaining an oil-in-water emulsion by circulating a mixture of an organic phase and an aqueous phase formed in the mixing step through a static mixer, and an emulsion And a polymerization step of polymerizing the monomer by heating in a nitrogen atmosphere.

  The inventor diligently studied a method for producing fine particles that can be used to easily produce fine particles having a uniform particle size. As a result, in a method for producing fine particles comprising a mixing step of an organic phase and an aqueous phase, an emulsification step of producing an oil-in-water emulsion, and a polymerization step of polymerizing the monomer component of the emulsion, It has been found that by adding magnesium chloride to the phase, fine particles having a uniform particle diameter can be easily produced, and the present invention has been completed.

  Hereinafter, the method for producing fine particles of the present embodiment will be described with reference to the production flow of fine particles in FIG.

  The organic phase includes a monomer constituting the fine particles, a polymerization initiator, and a coloring component. Regarding the preparation of the organic phase, a monomer component that is a monomer constituting the fine particles and a pigment that is a coloring component are dispersed and mixed in advance, and the polymerization initiator is dissolved in the dispersion and mixed solution to thereby dissolve the organic phase. Is prepared. As for the dissolution of the polymerization initiator, the polymerization initiator alone may be added to the dispersion / mixture. Alternatively, a part of the monomer component constituting the dispersion / mixture may be dissolved in advance and then added.

  Suitable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, and lauryl (meth) acrylate. , (Meth) acrylic acid ester having 1 to 20 carbon atoms, such as stearyl (meth) acrylate, isostearyl (meth) acrylate, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene , Styrene monomers such as α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, vinyl chloride, vinyl acetate Etc. In particular, methyl methacrylate is preferable from the viewpoint of polymerizability.

  Additional monomers may be included in the organic phase. Suitable additional monomers include N-methylaminoethyl (meth) acrylate, N-ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N N, N-dibutylaminoethyl acrylate, N, N-di-tert-butylaminoethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate, 2-N-piperidylethyl (meth) acrylate, etc. (Meth) acrylic acid aminoalkyl esters, aminostyrene, dimethylaminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylaminoethylstyrene, etc. Amino alkyl derivatives of styrene, 2-vinylpyridine, 4-vinylpyridine, can be used from the viewpoint of the polymerizable monomers and the like is a charge control agent having a pyridyl group such as 2-vinyl-6-methylpyridine. Furthermore, an electron donating compound such as a quaternary ammonium salt can also be used. In particular, since N, N-diethylaminoethyl methacrylate has a tertiary amine, it can be suitably used from the viewpoint of charge control. Aromatic divinyl compounds such as diethylene glycol dimethacrylate, divinylbenzene, divinylnaphthalene, and derivatives thereof, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, t-butylamino Diethylenically unsaturated carboxylic acid esters such as ethyl methacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, N, N-divinylaniline, divinyl ether, divinyl sulfide, all divinyl compounds of divinyl sulfonic acid and 3 A compound having one or more vinyl groups can be used from the viewpoint of promoting crosslinking. In particular, ethylene glycol dimethacrylate can be suitably used from the viewpoint of stabilizing the cross-linked structure, whereby the fine particle structure is strengthened.

  Further, as suitable coloring components, pigments, C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 108, 109, 110, 117, 120, 138, 153, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48: 2, 48: 2, 48: 3, 48: 4, 49: 1, 52: 2, 53: 1, 57: 1, 60: 1, 63: 1, 63: 2, 64: 1, 81, 83, 88, 101 (Bengara), 104, 105, 106, 108, 112, 114, 122 (Quinacridone magenta), 123, 146 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17: 1, 56, 60, 63, C.I. I. Pigment green 1, 4, 7, 8, 10, 17, 18, 36, and the like. Here, as a suitable pigment, pigment yellow 128, pigment red 254, pigment blue 15: 3, etc. are mentioned from a viewpoint of hue and weather resistance.

  Suitable polymerization initiators include radical polymerization initiators that generate radicals by light or heat. Suitable radical polymerization initiators include oil-soluble azo compounds (for example, V-601, azo initiators, manufactured by Wako Pure Chemical Industries, Ltd.) from the viewpoints of versatility, ease of polymerization, and safety.

  The aqueous phase contains water, magnesium chloride and a dispersant. Regarding the preparation of the aqueous phase, the aqueous phase is prepared by mixing and dissolving water, a dispersant and magnesium chloride in a certain ratio.

  Suitable dispersants include polymer dispersants having a vinyl group in the molecular structure from the viewpoints of stability of particles in the emulsification step and polymerization step and improvement in particle size distribution. Suitable polymer dispersants having a vinyl group include polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), and the like. When using a polymer dispersant, the required stability differs between the emulsification step and the polymerization step. Therefore, for example, in the case of PVP, it is more preferable to use a combination of different molecular weights such as K30 and K90 (manufactured by Wako Pure Chemical Industries, Ltd.) as the polymer dispersant.

  Next, the mixing process will be described. The organic phase and the aqueous phase are supplied to the circulation tank 10 and stirred by the stirrer 12 having a stirring blade. The organic phase and the aqueous phase are mixed in the circulation tank 10 to obtain a mixture of the organic phase and the aqueous phase. In order to obtain an oil-in-water emulsion, the mixing ratio (weight ratio) between the aqueous phase and the organic phase is adjusted so that the aqueous phase becomes a continuous phase and the organic phase becomes a dispersed phase. The weight ratio (organic phase / aqueous phase) between the aqueous phase and the organic phase of the mixture is less than 1. The lower the weight ratio, the more stable the emulsion can be formed. Therefore, the weight ratio is preferably 1/2 or less, more preferably 1/9 or less. Preferably, it is 1/10 or more.

  The apparatus used for stirring is not particularly limited, and commercially available products are preferably used. Specifically, a combination of a beaker and a magnetic stirrer, or a combination of a tank and a stirring blade is preferably used.

  An emulsification process for producing an oil-in-water emulsion will be described. The emulsification step is achieved by passing the mixture of the organic phase and the aqueous phase through a static mixer 16 such as an in-line mixer via the pump 14. Here, about the static mixer 16, commercial items, such as Star Lam Mixer made from IMM, can be used, for example. In the emulsification step, for example, a micro device described in Japanese Patent No. 4339163 can be used as the static mixer 16. By using such a micro device, it becomes easier to achieve monodispersion of fine particles. FIG. 2 is a schematic view showing the structure of the microdevice 30, and the equivalent diameter of a part or all of the flow paths is 1 μm to 2 mm. Here, the equivalent diameter of the flow path is a diameter De of a circular tube that can be regarded as equivalent from the viewpoint of flow with the flow path, where S is the cross-sectional area of the flow path and L is the peripheral length of the cross-section of the flow path. = 4S / L. The microdevice 30 is connected to the plurality of supply channels 32 (32a, 32b, 32c, 32d, 32e, 32f, 32g, 32h) and the plurality of supply channels 32, and the mixture from the plurality of supply channels 32 is removed. A merging portion 34 for mixing and a discharge passage 36 connected to the merging portion 34 and for discharging the mixed fluid to the outside of the merging portion 34 are provided.

  As shown in FIG. 1, from the viewpoint of homogenizing the degree of dispersion of the emulsion, the mixture is circulated between the circulation tank 10 and the static mixer 16, so that a plurality of the mixtures are supplied to the static mixer 16. It is preferable to pass through. In particular, by constructing a circulation path having the static mixer 16, the number of times the mixture passes through the static mixer 16 can be efficiently increased.

  It is necessary to carry out the circulation time in the case of circulation more than the time when the dispersion state of the emulsion becomes stable. Specifically, it is preferably 5 minutes or longer, more preferably 30 minutes or longer, and most preferably 50 minutes or longer. The circulation time means the time from the start of pumping to the static mixer 16 from the tank to the end of pumping. Assuming that one circulation time is 1 minute, when the circulation time is 5 minutes, the mixture passes through the static mixer 16 five times.

  Regarding the construction of the circulation path, a pump 14 for pumping the mixture to the static mixer 16 and a circulation tank 10 for receiving the circulated mixture may be provided. Furthermore, various sensors (pressure gauge, flow meter), various valves (pressure adjustment valve, extraction valve), etc. may be provided in the circulation path as necessary.

  Here, in the present embodiment, the pressure during emulsification is important. The pressure during pumping is preferably in the range of 10 kPa to 1000 kPa, more preferably in the range of 20 kPa to 1000 kPa. By setting the pressure within the above range, it is possible to prevent the emulsion from becoming coarse or the emulsion from becoming unnecessarily fine. As long as the performance of the pump 14 for pumping satisfies the above pressure range, a commercially available pump can be used regardless of its structure.

  The oil-in-water emulsion produced through a predetermined circulation time in the emulsification process is transferred to the polymerization process. As shown in FIG. 1, the emulsion is supplied from the circulation tank 10 to the jacketed polymerization tank 20 by switching the valve 18. The jacketed polymerization tank 20 includes a tank 20a and a tank jacket 20b surrounding the tank 20a. The temperature of the tank 20a is controlled by the tank jacket 20b. A stirrer 22 is provided in the tank 20a. Nitrogen is supplied to the tank 20a. By heating the emulsion for a certain period of time in a nitrogen atmosphere, the monomer component (monomer) in the organic phase is polymerized in the tank 20a to produce fine particles. When using an oil-soluble azo initiator V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, it is preferable to heat at 60 ° C. for 3 hours or more, and to heat at 65 ° C. for 3 hours or more. More preferred.

  In the tank 20a, it is preferable to mix an emulsion containing water, magnesium chloride, and a dispersant, and the concentration of magnesium chloride in the aqueous solution is particularly lower than the concentration of magnesium chloride in the aqueous phase. preferable. By mixing the low-concentration magnesium chloride and the emulsion, the concentration of magnesium chloride in the emulsion can be lowered. Thereby, stable polymerization can be realized. Moreover, it is preferable that the aqueous phase dispersant and the aqueous solution dispersant have different molecular weights. As described above, the required stability differs between the emulsification step and the polymerization step. Therefore, a dispersant having a molecular weight different from the molecular weight of the dispersant contained in the aqueous phase is included in the aqueous solution. By mixing this aqueous solution with the emulsion, a dispersant suitable for polymerization can be supplied to the emulsion. In the polymerization step, it is preferable to use a dispersant having a higher molecular weight than the emulsification step. The reason is that a dispersant having a high molecular weight has higher heat stability and can be expected to prevent coalescence of the emulsion during polymerization.

  According to the present embodiment, fine particles having a particle diameter of 100 to 10000 nm and monodispersed (CV value 20 to 30%) can be easily produced. The particle size is obtained by processing the reflection electron microscope (SEM) image with general image processing software (in this application, using ImageJver 1.46) to calculate the diameter of individual particles, and taking the number average of all particle diameters. Can be measured. Further, the CV value can be obtained by CV = σ / Mn × 100 from the average particle diameter Mn and the standard deviation σ obtained above.

  Hereinafter, the present invention will be described in more detail with reference to examples of the present invention. However, the present invention is not limited to these examples.

Example 1
The organic phase component and the aqueous phase component were adjusted as shown below. For the organic phase component, 36.5 parts by weight of methyl methacrylate (monomer), 4.6 parts by weight of diethylaminoethyl methacrylate (additional monomer), 4.05 parts by weight of Pigment Red 254 (pigment) were weighed, and the diameter was 1 mm. 120 parts by weight of zirconia beads were further added. These were dispersed with a rocking mill (RM-10, manufactured by Seiwa Giken Co., Ltd.) for 1 hour to obtain a colored monomer dispersion A. Further, 0.9 part by weight of ethylene glycol dimethacrylate (additional monomer) and 0.45 part by weight of an oil-soluble azo initiator V-601 (polymerization initiator) are mixed and dissolved to give 30 parts by weight of a colored monomer. By adding to dispersion A, polymerizable colored monomer dispersion B was obtained.

For the aqueous phase component, 1.6 parts by weight of PVP (K-30, dispersant) is mixed and dissolved in 200 parts by weight of water, and 85 parts by weight of magnesium chloride hexahydrate is further dissolved. Obtained. The polymerizable coloring monomer dispersion B and the aqueous solution C obtained above were mixed in a circulation tank with stirring at 250 rpm. Subsequently, it was circulated for 50 minutes under the conditions of the external temperature of the circulation tank of 50 ° C. and the circulation pressure of 21 kPa through the microdevice of FIG. Here, an aqueous solution E in which 0.8 parts by weight of PVP (K-90, dispersant) and 22 parts by weight of magnesium chloride are mixed and dissolved in 150 parts by weight of water is prepared, and the obtained emulsion D and aqueous solution E are prepared. The mixture was mixed in a glass jacketed polymerization tank. Thereafter, the tank was purged with nitrogen at 300 cm ³ / min for 30 minutes. A water dispersion F containing fine particles of the pigment / polymer composite was obtained by heating at a tank jacket temperature of 70 ° C. for 3 hours. The aqueous dispersion F was purified by centrifugal separation and subjected to SEM measurement. As a result, the average particle size was 10.7 μm and the CV value was 22%. FIG. 3 is an SEM image of the fine particles obtained in Example 1.

(Comparative Example 1)
The organic phase component and the aqueous phase component were adjusted as shown below. For the organic phase component, a polymerizable colored monomer dispersion B was prepared in the same manner as in Example 1. As for the aqueous phase component, 1.6 parts by weight of PVP (K-30, dispersant) was mixed and dissolved in 200 parts by weight of water, and 50 parts by weight of sodium chloride was dissolved to obtain an aqueous solution G. The polymerizable coloring monomer dispersion B and the aqueous solution G obtained above were mixed in a circulation tank with stirring at 250 rpm. Next, it was circulated for 50 minutes under the conditions of an external temperature of the circulation tank of 50 ° C. and a circulation pressure of 21 kPa through the microdevice of FIG. Here, an aqueous solution I in which 0.8 parts by weight of PVP (K-90, dispersant) and 50 parts by weight of sodium chloride were mixed and dissolved in 200 parts by weight of water, and the obtained emulsion H and aqueous solution I were prepared. The mixture was mixed in a glass jacketed polymerization tank. Thereafter, the tank was purged with nitrogen at 300 cm ³ / min for 30 minutes. By heating at a tank jacket temperature of 70 ° C. for 3 hours, the monomer component in the organic phase was polymerized to obtain an aqueous dispersion J containing pigment / polymer composite fine particles. The aqueous dispersion J was purified by a centrifugal separation method and subjected to SEM observation. As a result, the average particle size was 10.9 μm and the CV value was 38%. FIG. 4 is an SEM image of the fine particles obtained in Comparative Example 1.

(Comparative Example 2)
The organic phase component and the aqueous phase component were adjusted as shown below. For the organic phase component, a polymerizable colored monomer dispersion B was prepared in the same manner as in Example 1. As for the aqueous phase component, 1.6 parts by weight of PVP (K-30, dispersant) was mixed and dissolved in 200 parts by weight of water, and 50 parts by weight of calcium chloride was further dissolved to obtain an aqueous solution K. The polymerizable colored monomer dispersion B obtained above and the aqueous solution K were mixed in a circulation tank with stirring at 250 rpm. Subsequently, it was circulated for 50 minutes under the conditions of the external temperature of the circulation tank of 50 ° C. and the circulation pressure of 21 kPa through the microdevice of FIG. Here, an aqueous solution M in which 0.8 parts by weight of PVP (K-90, dispersant) and 50 parts by weight of calcium chloride are mixed and dissolved in 200 parts by weight of water is prepared, and the obtained emulsion L and aqueous solution M are prepared. The mixture was mixed in a glass jacketed polymerization tank. Thereafter, the tank was purged with nitrogen at 300 cm ³ / min for 30 minutes. By heating at a tank jacket temperature of 70 ° C. for 3 hours, the monomer component in the organic phase was polymerized to obtain an aqueous dispersion N containing pigment / polymer composite fine particles. As a result of purifying the aqueous dispersion N by centrifugation and carrying out SEM observation, the average particle size was 10.4 μm and the CV value was 31%.

(Evaluation)
In Example 1, fine particles having a uniform particle size were obtained as shown in FIG. On the other hand, in Comparative Examples 1 and 2, as shown in FIGS. 4 and 5, fine particles having variations in particle diameter were obtained. In the present embodiment, it was possible to easily produce fine particles having a uniform particle diameter.

  DESCRIPTION OF SYMBOLS 10 ... Circulation tank, 12 ... Stirrer, 14 ... Pump, 16 ... Static mixer, 18 ... Valve, 20 ... Polymerization tank with jacket, 20a ... Tank, 20b ... Tank jacket, 30 ... Micro device, 32 ... Supply flow path, 34 ... confluence, 36 ... discharge flow path

Claims (13)

A step of preparing an organic phase containing a monomer, a polymerization initiator, and a coloring component constituting the fine particles, and an aqueous phase containing water, magnesium chloride, and a dispersing agent;
A mixing step of mixing the organic phase and the aqueous phase;
An emulsification step of obtaining an oil-in-water emulsion by circulating a mixture of the organic phase and the aqueous phase formed in the mixing step via a static mixer;
A polymerization step of polymerizing the monomer by heating the emulsion under a nitrogen atmosphere;
A method for producing fine particles having
The static mixer includes a plurality of supply channels, a merging portion to which the plurality of supply channels are connected, and a discharge channel connected to the merging portion, the plurality of supply channels and the A method for producing fine particles, wherein a part or all of the discharge flow path is composed of flow paths having an equivalent diameter of 1 μm to 2 mm. The method for producing fine particles according to claim 1 , wherein the dispersant has a vinyl group in its molecular structure. The method for producing fine particles according to claim 2, wherein the dispersant is polyvinylpyrrolidone. Method for producing fine particles according to any one of the 3 composed claim 1 wherein the monomer of the organic phase is methyl methacrylate. The method for producing fine particles according to claim 4, wherein the organic phase contains an additional monomer, and the additional monomer is composed of any of N, N-diethylaminoethyl methacrylate, ethylene glycol dimethacrylate, and a mixture thereof. Method for producing fine particles according to any one of claims 1-5 wherein the coloring component is a pigment. Method for producing fine particles according to any one of the polymerization initiator is from claim 1 is a radical polymerization initiator that generates radicals by light or heat 6. The method for producing fine particles according to any one of claims 1 to 7 , wherein the polymerization initiator is an azo compound. In the said emulsification process, the pressure at the time of circulating the said mixture to the said static mixer is the range of 10 kPa-1000 kPa, The manufacturing method of the microparticles | fine-particles of any one of Claim 1 to 8 . The method for producing fine particles according to any one of claims 1 to 9 , wherein in the emulsification step, a circulation time for circulating the mixture in the static mixer is 5 minutes or more. The method for producing fine particles according to any one of claims 1 to 10 , wherein a weight ratio (organic phase / aqueous phase) of the aqueous phase and the organic phase of the mixture is 1/10 to 1/2. A step of preparing an organic phase containing a monomer, a polymerization initiator, and a coloring component constituting the fine particles, and an aqueous phase containing water, magnesium chloride, and a dispersing agent;
A mixing step of mixing the organic phase and the aqueous phase;
An emulsification step of obtaining an oil-in-water emulsion by circulating a mixture of the organic phase and the aqueous phase formed in the mixing step via a static mixer;
A polymerization step of polymerizing the monomer by heating the emulsion under a nitrogen atmosphere;
A method for producing fine particles having
After the emulsification step and before the polymerization step, the method further includes a step of mixing an aqueous solution containing water, magnesium chloride and a dispersant and the emulsion, and the concentration of magnesium chloride in the aqueous solution method for producing fine particles have lower than the concentration of magnesium chloride. The method for producing fine particles according to claim 12 , wherein the dispersant in the aqueous phase and the dispersant in the aqueous solution have different molecular weights.