JP5731261B2 - Method for producing fine particles - Google Patents

Description

  The present invention relates to a method for producing fine particles, and particularly to a technique for efficiently collecting fine particles polymerized in a solvent.

  Emulsion polymerization, suspension polymerization, and seed polymerization are known as methods for synthesizing polymer particles in an aqueous solvent. Which method is used for polymerization varies depending on the type of monomer used, the desired particle size of the product, and the mode of use (whether it is used as a polymerization solution or solid-liquid separation). .

  Suspension polymerization is carried out in an aqueous solvent, so that the heat of polymerization can be easily removed, and the produced fine particles can be removed by filtration, centrifugation, etc., and the desired particle size can be adjusted by the suspension preparation method. Since it is easy to obtain, it has been adopted as an industrial production method for polymer particles (for example, Patent Document 1).

  Further, as a method for separating and recovering the polymerization-generated fine particles from the solvent, various separation methods such as separation by natural sedimentation or centrifugal sedimentation and decantation, separation by filtration, and the like are known (for example, Patent Document 2). (See paragraph [0060]), Patent Document 3 (paragraph [0071])). Furthermore, it is known that separation can be promoted by adding a flocculant such as aluminum sulfate prior to separation (see, for example, Patent Document 4 (paragraph [0035])).

JP 2011-16904 A JP-A-6-73106 JP-A-8-183807 JP 2003-82191 A

  In recent years, there is a demand for fine particles having a volume average particle diameter of about 1 μm, mainly for optical applications. Such fine particles having a small volume average particle size have a problem that even if the fine particles are aggregated using an aggregating agent and then centrifuged at a high centrifugal force, they cannot be sufficiently separated. In particular, a large amount of fine particles having a particle diameter of less than 1 μm remain in the solvent. In addition, when a large amount of surfactant is used in the polymerization in order to stabilize the inside of the polymerization system, it becomes more difficult to separate the fine particles. Therefore, there is a problem that the yield after solid-liquid separation is poor and productivity is poor.

However, when the addition amount of the flocculant is increased in order to increase the separation efficiency of the fine particles, the separability is improved, but the fine particles are firmly bound to each other when the cake after separation is dried. It was difficult to break up.
The present invention has been made in view of the above circumstances, and provides a method for producing fine particles that can efficiently separate and recover fine particles synthesized in an aqueous solvent without increasing the amount of aggregating agent used, and has high productivity. The purpose is to do.

  The method for producing fine particles of the present invention that has solved the above problems is a polymerization step in which a monomer is polymerized in an aqueous solvent to prepare a fine particle-containing liquid, and the pH of the fine particle-containing liquid is adjusted to 11 or more. Then, it is characterized by including a flocculation step of adding a flocculant, a solid-liquid separation step of precipitating the agglomerated fine particles to obtain a cake, and a drying step of drying the obtained cake. The flocculant is preferably an inorganic flocculant, more preferably an aluminum salt, still more preferably aluminum sulfate and / or polyaluminum chloride. The volume average particle diameter of the fine particles in the fine particle-containing liquid is preferably 3 μm or less. The fine particle-containing liquid preferably contains a surfactant.

  In the present invention, the cohesiveness of the fine particles is improved by adjusting the pH of the fine particle-containing liquid when adding the flocculant to 11 or more. For this reason, the aggregated fine particles have improved solid-liquid separation properties and productivity.

  The fine particles of the present invention are produced through a fine particle polymerization step; a fine particle aggregation step; a solid-liquid separation step, and a drying step. Hereinafter, the present invention will be described in detail while following each step. In this specification, “(meth) acryloxy group”, “(meth) acrylate” and “(meth) acryl” are “acryloxy group and / or methacryloxy group”, “acrylate and / or methacrylate” and “acryl and / Or methacryl ".

1. Polymerization Step The fine particle polymerization step is a step of preparing a fine particle-containing liquid by polymerization, and this fine particle-containing liquid is usually prepared by polymerizing a monomer in an aqueous solvent. The fine particle-containing liquid refers to a polymerization reaction liquid after the fine particles are synthesized or a liquid obtained by appropriately adjusting the amount of the aqueous solvent in the polymerization reaction liquid.

  The monomer is not particularly limited, and may be appropriately selected according to the desired physical properties of the fine particles. As the monomer, a vinyl group-containing monomer capable of radical polymerization is preferable. The “vinyl group” includes not only a carbon-carbon double bond but also a polymerizable carbon-carbon double bond such as a (meth) acryloxy group, an allyl group, an isopropenyl group, a vinylphenyl group, and an isopropenylphenyl group. A substituent having a bond is also included.

  The vinyl group-containing monomer includes a monomer (1) having one vinyl group in the molecule, one vinyl group in the molecule and a functional group other than the vinyl group (a protic hydrogen such as a carboxyl group or a hydroxyl group). Monomer having a terminal group such as a containing group and an alkoxy group) (2) a crosslinkable vinyl group-containing monomer having three or more vinyl groups in one molecule (hereinafter referred to as “crosslinkable vinyl”). Sometimes referred to as a “group-containing monomer”). These monomers (1) to (3) may be used alone or in combination of two or more.

  Examples of the monomer (1) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, Alkyl (meth) acrylates such as hexyl (meth) acrylate; Cycloalkyl (meth) acrylates such as cyclopropyl (meth) acrylate and cyclopentyl (meth) acrylate; Fragrances such as phenyl (meth) acrylate and benzyl (meth) acrylate Ring-containing (meth) acrylates; alkylstyrenes such as styrene, methylstyrene, and butylstyrene; styrene monofunctional monomers such as halogen-containing styrenes such as chlorostyrene; and the like.

  Examples of the monomer (2) include monomers having a carboxyl group such as (meth) acrylic acid; hydroxy group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, p- Monomers having hydroxy groups such as hydroxy group-containing styrenes such as hydroxystyrene; alkoxy groups-containing (meth) acrylates such as 2-methoxyethyl (meth) acrylate, alkoxy such as alkoxystyrenes such as p-methoxystyrene Monomer having a group; and the like.

  Examples of the monomer (3) (crosslinkable vinyl group-containing monomer) include allyl (meth) acrylates such as allyl (meth) acrylate; ethylene glycol di (meth) acrylate and 1,4-butanediol. Alkanediol di (meth) acrylates such as di (meth) acrylate and 1,6-hexanediol di (meth) acrylate; diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate , Di (meth) acrylates such as polyalkylene glycol di (meth) acrylate such as polypropylene glycol di (meth) acrylate and polytetramethylene glycol di (meth) acrylate; and trimethylolpropane tri (meth) acrylate (Meth) acrylates; tetra (meth) acrylates such as pentaerythritol tetra (meth) acrylate; hexa (meth) acrylates such as dipentaerythritol hexa (meth) acrylate; divinylbenzene, divinylnaphthalene, and derivatives thereof Aromatic hydrocarbon-based crosslinking agents (preferably styrenic polyfunctional monomers such as divinylbenzene); heteroatom-containing crosslinking agents such as N, N-divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfonic acid; .

  At the time of polymerization, in addition to the above-described monomers, at a suitable stage, for example, pigments, plasticizers, polymerization stabilizers, fluorescent brighteners, magnetic powders, ultraviolet absorbers, antistatic agents, flame retardants, etc. A monomer component may be added. In addition, these non-monomer components may be mixed with the monomer in advance to give a monomer composition, which may be added to an aqueous solvent, or the monomer and each non-monomer component May be charged separately in a solvent and mixed in a solvent.

In the fine particle polymerization step, fine particles (organic polymer particles) are obtained by polymerizing the monomer alone or with a non-monomer component in an aqueous solvent.
The aqueous solvent preferably contains 50% by mass or more of water, more preferably 80% by mass or more, and still more preferably 90% by mass or more. The aqueous solvent may include a water-soluble organic solvent. In particular, when producing fine particles having a particle diameter of 3 μm or less, it is preferable to include a water-soluble organic solvent. In this case, the content of the water-soluble organic solvent is 1% by mass or more, more preferably 2% by mass or more, and preferably 5% by mass or less, more preferably 4% by mass or less, in 100% by mass of the aqueous solvent. The water-soluble organic solvent is dissolved in 1 part by mass or more in 100 parts by mass of water at 25 ° C. Examples of the water-soluble organic solvent include lower alcohols; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; ethers such as dioxane and diethyl ether. These may be used alone or in combination of two or more. Among these, alcohols having 4 or less carbon atoms are preferable from the viewpoints that they have a low boiling point, are easily volatilized, and hardly remain in particles after drying, and are easy to handle. Examples of the lower alcohol having 4 or less carbon atoms include methyl alcohol, ethyl alcohol, isopropyl alcohol (IPA), n-propyl alcohol, n-butyl alcohol, isobutyl alcohol, s-butyl alcohol, and t-butyl alcohol. In particular, IPA having 3 carbon atoms and n-propyl alcohol are preferable. Among them, IPA having a lower boiling point is most preferable because it easily volatilizes when polymer fine particles are dried.

  As a method for polymerizing the monomer, a known polymerization method such as suspension polymerization, seed polymerization or emulsion polymerization can be employed. Among these, suspension polymerization and emulsion polymerization are preferable because fine particles having a small particle diameter can be efficiently produced.

Hereinafter, suspension polymerization will be described as an example of the polymerization method.
In general, suspension polymerization is a liquid obtained by dispersing and suspending a monomer component or a monomer composition containing a monomer component and a non-monomer component in an aqueous solvent. This is a method of obtaining a dispersion liquid (fine particle-containing liquid) in which polymer particles are dispersed and contained in water by polymerizing a droplet suspension composition. When preparing the droplet suspension composition, conventionally known dispersion, suspension methods, and apparatuses can be employed as means for suspending the monomer composition in water. For example, T.W. K. A high-speed stirrer such as a homomixer or a line mixer (eg, Ebara Milder (registered trademark)) can be used. Here, in order to control and stabilize the particle diameter of the droplets of the monomer composition, it is preferable that a dispersion stabilizer coexists during the preparation of the droplet suspension composition.

  Examples of the dispersion stabilizer include water-soluble polymers such as polyvinyl alcohol, gelatin, sodium polyacrylate, polysodium methacrylate; sodium lauryl sulfate, polyoxyethylene alkylphenyl ether sulfate (for example, polyoxyethylene distyrylphenyl) Anionic surfactants such as ether sulfate ammonium); cationic surfactants such as alkylamine salts and quaternary ammonium salts; zwitterionic surfactants such as lauryl dimethylamine oxide; polyoxyethylene alkyl ethers and the like Nonionic surfactants; protein dispersants such as zein and casein; inorganic dispersants such as silica particles, talc, clay, diatomaceous earth, bentonite; and other alginates are used. Among these, nonionic surfactants and anionic surfactants are preferable, and anionic surfactants are more preferable.

  What is necessary is just to adjust the usage-amount of the said dispersion stabilizer suitably according to the size of the polymer particle desired. For example, when it is desired to obtain polymer particles having a particle diameter of 3 μm or less, 0.01 parts by mass to 10 parts by mass is preferable with respect to 100 parts by mass of the monomer component, and more preferably 0.05 parts by mass to 5 parts by mass. Part by mass, more preferably 1 part by mass to 2 parts by mass.

  A polymerization initiator is used for the polymerization of the monomer component. Here, the polymerization initiator may be present in the suspension composition at the time of the polymerization reaction, but at the time of preparing the droplet suspension composition, the monomer (monomer composition) phase or the aqueous phase. It is preferable to disperse and dissolve in a monomer, and it is more preferable to dissolve in a monomer (monomer composition) phase. The polymerization reaction is preferably performed with stirring. For the stirring, stirring using a conventionally known stirring blade such as a paddle blade, a turbine blade, a blue margin blade, or a propeller blade may be employed.

  As the polymerization initiator, any of those usually used for radical polymerization can be used. For example, a peroxide initiator, an azo initiator, or the like can be used. Examples of the peroxide initiator include benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochlorobenzoyl peroxide, and orthomethoxybenzoyl peroxide. Examples of the azo initiator include dimethyl-2,2′-azobisisobutyrate, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2, And 2'-azobis (2,3-dimethylbutyronitrile). These polymerization initiators are preferably used in an amount of 0.01 to 20 parts by mass (more preferably 0.1 to 10 parts by mass) with respect to 100 parts by mass of the monomer component. For the polymerization reaction, a method of initiating polymerization by irradiation of radiation or applying heat can be adopted, but a method of initiating polymerization by heating is simple.

  The polymerization temperature is preferably 55 ° C to 100 ° C (more preferably 60 ° C to 95 ° C), and the polymerization reaction is 2 hours to 7 hours (more preferably 2.5 hours to 5 hours, further preferably 3 hours to 4.5 hours) is preferred. The polymerization reaction is preferably performed in the range of pH 4 to pH 10 (more preferably pH 5 to pH 9).

  In suspension polymerization, a known additional means may be added. For example, fine particles obtained by suspension polymerization can be used as a core for obtaining core-shell particles. The core-shell particle is obtained by coating the core particle with a shell having a property different from that of the core particle, thereby imparting the shell property to the core. The core-shell particles are prepared by adding a shell monomer component having a composition different from the monomer composition of the core particles to an aqueous solvent containing the core particles, and dispersing and suspending the shell monomer component. It is obtained by preparing a suspension for shell, polymerizing monomer components and coating the core particles with the polymer (shell). As the monomer component for shell, any of the monomers exemplified as monomers that can be used for the core can be used. The preferred ranges of the polymerization temperature and polymerization time for polymerizing the shell are the same as the polymerization conditions for the core particles.

  The volume average particle diameter of the fine particles in the fine particle-containing liquid is preferably 3 μm or less, more preferably 2.5 μm or less, still more preferably 2.0 μm or less, and particularly preferably 1.7 μm or less. For particles with a small volume average particle size, it is common to use a large amount of surfactant during polymerization, and as a result, they are dispersed and stable in the liquid. Is difficult to separate and collect. However, in the present invention, even such fine particles can be efficiently separated and recovered. In addition, although the minimum of the volume average particle diameter of microparticles | fine-particles is not specifically limited, Usually, it is about 0.5 micrometer, and is about 10 nm in the case of emulsion polymerization.

The true density of the fine particles in the fine particle-containing liquid is preferably 1.5 g / cm ³ or less, more preferably 1.3 g / cm ³ or less. Particles with a low true density have a small difference in specific gravity with an aqueous solvent and are generally difficult to separate and collect by centrifugation. However, in the present invention, even such low-density fine particles can be separated and recovered efficiently. . The lower limit of the true density of the fine particles is not particularly limited, but is usually about 0.9 g / cm ³ . Examples of such fine particles having true density include vinyl polymer fine particles obtained by polymerizing a vinyl group-containing monomer.

2. Aggregation step In the aggregation step, an aggregating agent is added to the fine particle-containing liquid. The fine particle-containing liquid may be either a polymerization reaction liquid or a liquid obtained by appropriately adjusting the amount of the aqueous solvent in the polymerization reaction liquid, but the polymerization reaction liquid is preferably used as it is. Further, as a method for adjusting the amount of the aqueous solvent in the polymerization reaction solution, for example, an aqueous solvent is further added to the polymerization reaction solution, or the polymerization reaction solution is heated and decompressed to remove a part of the aqueous solvent. Good.

  In the present invention, the pH of the fine particle-containing liquid is set to 11 or more and the flocculant is added. By setting the pH of the fine particle-containing liquid at the time of addition of the flocculant to 11 or more, the cohesiveness of the fine particles is improved and the aggregates are easily settled. Therefore, the fine particles and the aqueous solvent can be efficiently separated, and the productivity of the fine particles is improved.

The reason why the cohesiveness is improved by setting the pH to 11 or more is not necessarily clear, but is considered as follows. When the fine particles in the fine particle-containing liquid repel each other due to the electric double layer formed on the surface of each fine particle, the addition of an ionic substance flocculant such as a metal salt or ammonium salt can charge the particle surface. The amount decreases, and the van der Waals force (intermolecular attractive force) acts to aggregate the fine particles. At this time, if the pH of the fine particle-containing liquid is 11 or more, the ion concentration in the fine particle-containing liquid increases due to the ionic species derived from the agent (for example, sodium hydroxide) added to adjust the pH to 11 or higher. Therefore, the charge amount on the particle surface is further reduced, and the cohesiveness is improved.
In addition, aluminum sulfate, polyaluminum chloride and the like consume alkali components in the system and hydrolyze to produce aluminum hydroxide, which causes aggregation of fine particles. For this reason, it is considered that by adding the aqueous solvent after adjusting the pH to 11 or more, hydrolysis of aluminum sulfate or the like is promoted and the aggregation effect is further enhanced.

  The pH of the fine particle-containing liquid when adding the flocculant is preferably 11.2 or more, more preferably 11.4 or more. The upper limit of the pH is not particularly limited, but is usually about 12. Although the method of adjusting pH is not specifically limited, The method of adding an alkali metal compound is mentioned. Examples of the alkali metal compound include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; tetraalkylammonium hydroxides and the like.

  The temperature of the fine particle-containing liquid when adding the flocculant is preferably 5 ° C or higher, more preferably 10 ° C or higher, further preferably 12 ° C or higher, preferably 100 ° C or lower, more preferably 90 ° C or lower, Preferably it is 85 degrees C or less.

  In the aggregating step, after adding the aggregating agent, the fine particles are aggregated by stirring. The stirring time may be adjusted as appropriate, but is preferably 10 minutes or more, more preferably 20 minutes or more, still more preferably 30 minutes or more, preferably 120 minutes or less, more preferably 60 minutes or less, still more preferably 40 Is less than a minute. Further, the pH of the fine particle-containing liquid after stirring is preferably 7.5 or more, more preferably 8.0 or more, still more preferably 8.2 or more, preferably 11 or less, more preferably 10 or less, still more preferably. Is 9 or less.

  The fine particle concentration in the fine particle-containing liquid when adding the flocculant is preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably 50%. It is at most 40% by mass, more preferably at most 40% by mass. When the concentration of fine particles is within the above range, the cohesiveness of the fine particles is improved, and separation and recovery are easier.

  As the flocculant, both inorganic flocculants and organic flocculants (polymer flocculants) can be used. Examples of inorganic flocculants include aluminum salts such as aluminum chloride, aluminum sulfate, polyaluminum chloride, and polyaluminum hydroxide; iron salts such as ferric chloride and polyferric sulfate; ammonium sulfate, ammonium chloride, ammonium nitrate, and the like. Inorganic ammonium salts, quaternary ammonium salts, bivalent or higher metal complexes, and the like. Examples of the polymer flocculant include polyacrylamide. Among these, inorganic flocculants are preferable from the viewpoint that the fine particles are not colored and the effects of the present invention are remarkable, more preferably aluminum salts, and still more preferably aluminum sulfate and / or polyaluminum chloride.

  The amount of the flocculant used is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and preferably 1 part by mass or less, more preferably 0.5 parts by mass with respect to 100 parts by mass of the fine particles. Hereinafter, it is more preferably 0.1 parts by mass or less. If the amount of the aggregating agent is within the above range, the agglomeration property of the fine particles can be improved and the fine particles after drying can be easily crushed.

3. Solid-liquid separation step In the solid-liquid separation step, fine particles are allowed to settle, and the supernatant liquid is removed to obtain a fine particle cake. As described above, in the present invention, since the pH at the time of adding the flocculant is adjusted, the sedimentation property of the fine particles is increased, and solid-liquid separation can be performed efficiently.
Examples of the method for precipitating fine particles include a natural sedimentation method and a centrifugal sedimentation method. Among these, the centrifugal sedimentation method is preferable because fine particles can be sedimented more efficiently.
In the case of employing centrifugal sedimentation, the applied centrifugal force (gravity acceleration) is preferably 1000 G or more, more preferably 1500 G or more, and further preferably 1800 G or more. The greater the applied centrifugal force, the better the separation and the more efficient collection of finer particles. The upper limit of the centrifugal force is not particularly limited, but for example, the smaller the centrifugal force such as 4000 G (preferably 3000 G, more preferably 2500 G), the lower the energy cost such as electric power, and the effect of the present invention becomes remarkable. In addition, when employ | adopting centrifugal sedimentation, although the time which applies a centrifugal force should just be adjusted suitably, it is normally 1 minute-30 minutes.

  The method for removing the supernatant liquid from which the fine particles are precipitated is not particularly limited, and can be removed by, for example, decantation. In addition, when the centrifugal sedimentation method is employed, a cyclone type centrifugal separator, a separation plate centrifugal separator, a cylindrical centrifugal separator, a decanter centrifugal separator, or the like can be used. Moreover, you may use the centrifuge which can perform sedimentation of microparticles | fine-particles and removal of a supernatant liquid simultaneously. In this way, a fine cake is obtained by removing the supernatant.

  The solid content in the cake obtained by solid-liquid separation is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 55% by mass or more. The upper limit of the solid content in the cake is not particularly limited, but is about 60% by mass. The solid content in the supernatant after solid-liquid separation is preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less. It is.

4). Drying step In the drying step, the obtained cake is dried. The drying method is not particularly limited, and examples include natural drying, hot air drying, and reduced pressure drying. The fine particles after drying may be crushed as necessary.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention. In the following, “part” means “part by mass” and “%” means “% by mass” unless otherwise specified.

Volume average particle size Particle size distribution measuring device (polymerization reaction solution was diluted with a 1% aqueous solution of a surfactant (Daiichi Kogyo Seiyaku Co., Ltd., “Hytenol (registered trademark) N-08”)) as a measurement sample. The particle diameter of 30000 particles was measured using “Coulter Multisizer III type” manufactured by Beckman Coulter, Inc., and the volume-based average particle diameter was determined.

True Density For the fine particles obtained in the production example, the true density was measured using an Ultra Pycnometer 1000 (manufactured by Yuasa Ionics).

Solid content A sample (cake or supernatant) was placed in an aluminum cup of known mass, and the sample mass was measured with a precision balance. The aluminum cup was heated on a hot plate heated to 130 ° C. for 1 hour. After heating, the mass of the dried residue in the aluminum cup was weighed with a precision balance. The amount of solid content in the sample was determined by the following formula.
Solid content (%) = 100 × dry residue mass after heating / sample mass before heating

Production Example 1 Synthesis of Suspension of Fine Particles Having Core-Shell Structure Preparation of Shell Suspension Polyoxyethylene distyrylphenyl ether sulfate ammonium salt (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., “Hitenol (registered trademark) NF) -08 ") 181 parts of deionized aqueous solution in which 0.35 parts were dissolved, 34 parts of styrene (St), and DVB-570 (divinylbenzene purity 57%, manufactured by Nippon Steel Chemical Co., Ltd.) A mixture with 5 parts was added. T.A. K. Using a homomixer (suspension type; manufactured by Primix), the mixed solution in the flask was stirred at 4500 rpm for 2 minutes to prepare a suspension for shell.

Polymerization of the core A separate flask was charged with 331 parts of a deionized aqueous solution in which 2.4 parts of the polyoxyethylene distyrylphenyl ether sulfate ammonium salt had been dissolved.
216 parts of methyl methacrylate (MMA), 24 parts of ethylene glycol dimethacrylate (EGDMA), 12 parts of isopropyl alcohol, and 4.8 parts of lauryl peroxide were mixed well to prepare a core mixture, which was added to the flask. T.A. K. The mixture was stirred at 7000 rpm for 20 minutes using a homomixer to make the mixed solution in the flask a uniform suspension. This suspension was transferred to a flask equipped with a stirrer, an inert gas introduction tube, a reflux condenser, a thermometer, and a dropping funnel, and 600 parts of deionized water was further added. While blowing nitrogen gas, the flask was immersed in an oil bath set at a temperature of 65 ° C., the temperature inside the flask was raised, and polymerization of the core was started.

Shell polymerization After starting the core polymerization, immediately after the flask internal temperature exceeded the oil bath temperature (65 ° C.) and reached the peak temperature and showed a maximum value, the suspension for shell was prepared using a dropping funnel. It was dripped. After completion of dropping, the oil bath temperature was set to 75 ° C., the temperature inside the flask was raised to 75 ° C., and the reaction was carried out for 1 hour. Thereafter, the oil bath temperature was further set to 85 ° C., the flask internal temperature was raised to 85 ° C., and stirring was continued at this temperature for 3 hours, followed by cooling. The fine particle suspension (polymerization reaction liquid) after completion of the reaction was measured with a Coulter Multisizer. The volume average particle diameter of the produced fine particles was 1.2 μm. The fine particle concentration in the polymerization reaction solution was 17.5% by mass.

Particle Aggregation Operation The fine particle suspension (pH 4.2) after completion of the reaction was cooled to 15 ° C. 11.9 parts of 5% by weight NaOH was added to the cooled fine particle suspension and stirred for 30 seconds. Immediately thereafter, 46 parts of 0.3% aluminum sulfate aqueous solution (sulfuric acid band) was used as a flocculant (based on 100 parts by weight of fine particles). Then, 0.05 part by mass of aluminum sulfate) was added and the mixture was further stirred for 30 minutes to aggregate the fine particles. The fine particle suspension had a pH of 11.5 when the flocculant was charged, and the pH of the liquid after stirring for 30 minutes after the flocculant was charged was 8.5. The liquid in which the fine particles were aggregated was centrifuged into a cake and a supernatant using a desktop small centrifuge (“NT-4”, manufactured by Matsumoto Seisakusho). Centrifugation was performed at 2000 G for 5 minutes. The solid contents of the cake and the supernatant liquid were 45% by mass and 0.5% by mass, respectively. The cake was dried for 8 hours using a hot air drier set at a drying temperature of 80 ° C. to obtain fine particles. The true density of the obtained fine particles was 1.2 g / cm ³ .

Production Example 2
In the agglomeration operation of the particles of Production Example 1, 11.9 parts of 5 mass% NaOH was added to the fine particle suspension cooled to 15 ° C., stirred for 30 seconds, and then immediately using 0.3% aluminum sulfate aqueous solution as a flocculant. 46 parts (0.05 parts by mass of aluminum sulfate with respect to 100 parts by mass of fine particles) was added, and the mixture was further stirred for 30 minutes to aggregate the fine particles. The fine particle suspension had a pH of 11.5 when the flocculant was charged, and the pH of the liquid after stirring for 30 minutes after the flocculant was charged was 8.5. After the temperature of the liquid in which the fine particles were aggregated was raised to 30 ° C. while stirring (at this time, the pH of the liquid was 7.9), a desktop small centrifuge (“NT-4”, manufactured by Matsumoto Seisakusho) ) And centrifuged into cake and supernatant. Centrifugation was performed at 2000 G for 5 minutes. The solid contents of the cake and the supernatant liquid were 55% by mass and 0.1% by mass, respectively. The cake was dried for 8 hours using a hot air drier set at a drying temperature of 80 ° C. to obtain fine particles. The true density of the obtained fine particles was 1.2 g / cm ³ .

Production Example 3
In the agglomeration operation of particles in Production Example 1, 46 parts of a 0.3% aluminum sulfate aqueous solution as an aggregating agent in a fine particle suspension cooled to 15 ° C. (0.05 parts by mass of aluminum sulfate with respect to 100 parts by mass of fine particles) The mixture was stirred and stirred for 30 minutes to aggregate the fine particles. The pH of the fine particle suspension at the time of adding the flocculant was 4.2, and the pH of the liquid after stirring for 30 minutes after adding the flocculant was 3.8. The liquid in which the fine particles were aggregated was centrifuged into a cake and a supernatant in the same manner as in Production Example 1. The solid contents of the cake and the supernatant liquid were 36% by mass and 5% by mass, respectively.

Production Example 4
In the agglomeration operation of the particles of Production Example 1, 46 parts (for 100 parts by mass of fine particles, 11.9 parts of 5% by weight NaOH and 0.3% aluminum sulfate aqueous solution as a flocculant were added to the fine particle suspension cooled to 15 ° C. A mixed solution with 0.05 part by mass of aluminum sulfate was added and stirred for 30 minutes to aggregate the fine particles. Note that the pH of the fine particle suspension at the time of charging the mixed solution was 4.2, the pH of the fine particle suspension immediately after adding the mixed solution was 9.2, and the liquid after stirring for 30 minutes after adding the flocculant. The pH of was 8.0. The liquid in which the fine particles were aggregated was centrifuged into a cake and a supernatant in the same manner as in Production Example 1. The solid contents of the cake and the supernatant liquid were 45% by mass and 4.6% by mass, respectively.

Production Example 5
In the agglomeration operation of the particles of Production Example 1, 11.9 parts of 5% by mass ammonia water was added to the fine particle suspension cooled to 15 ° C., stirred for 30 seconds, and immediately added with a 0.3% aluminum sulfate aqueous solution as a flocculant. As 46 parts (0.05 parts by mass of aluminum sulfate with respect to 100 parts by mass of the fine particles) and stirred for 30 minutes to aggregate the fine particles. The pH of the fine particle suspension at the time of adding the flocculant was 10.2, and the pH of the liquid after stirring for 30 minutes after adding the flocculant was 8.8. The liquid in which the fine particles were aggregated was centrifuged into a cake and a supernatant in the same manner as in Production Example 1. The solid contents of the cake and the supernatant liquid were 46% by mass and 3.2% by mass, respectively.

  As shown in Table 1, in Production Examples 1 and 2 in which the flocculant was added after adjusting the pH of the fine particle-containing liquid to 11 or more, compared to Production Example 3 in which the pH at the time of adding the flocculant was not adjusted The amount of solid content in the cake is increased, and the amount of solid content remaining in the supernatant is reduced. Further, comparing these production examples 1 and 2, the production example 2 in which the liquid temperature when the fine particles are precipitated is increased to 30 ° C. is more efficient than the production example 1 having a liquid temperature of 15 ° C. It can be seen that they are separated.

  Production Example 4 is a case where NaOH for adjusting the pH is added to the fine particle-containing liquid in a state of being mixed with the flocculant. Compared with Production Example 3, the amount of solids in the cake increased, but the supernatant The effect of reducing the amount of solid content remaining in the liquid was small. Production Example 5 is a case where the flocculant was added after adjusting the pH of the fine particle-containing liquid to 10.2. Since the pH was low, the solid content in the cake increased, but remained in the supernatant liquid. The effect of reducing the solid content was small.

  The method for producing fine particles of the present invention can efficiently separate and collect fine particles in an aqueous solvent. Therefore, it is particularly suitable for producing fine particles having a volume average particle size of 3 μm or less.

Claims (5)

A polymerization step in which a monomer is polymerized in an aqueous solvent to prepare a fine particle-containing liquid;
An aggregating step of adding an aggregating agent after adjusting the pH of the fine particle-containing liquid to 11 or more;
A solid-liquid separation step in which the agglomerated fine particles are settled to obtain a cake; and
A drying step of drying the resulting cake seen including,
The method for producing fine particles , wherein the flocculant is an aluminum salt, and the amount of the flocculant used is 1 part by mass or less with respect to 100 parts by mass of the fine particles. The method for producing fine particles according to claim 1, wherein the flocculant is aluminum sulfate and / or polyaluminum chloride. The method for producing fine particles according to claim 1 or 2 , wherein the volume average particle size of the fine particles in the fine particle-containing liquid is 3 µm or less. The particulate-containing liquid, method for producing fine particles according to any one of claims 1 to 3 containing a surfactant. The said solid-liquid separation process is a manufacturing method of the microparticles | fine-particles of any one of Claims 1-4 performed by the centrifugal sedimentation method of the centrifugal force 4000G or less.