Fine resin particles and method for producing the same

Abstract

To provide a method for producing fine resin particles that have solvent resistance sufficient to withstand a heating step after dispersion in a solvent and that generate few bubbles during dispersion and have excellent dispersibility in the solvent.SOLUTION: A method for producing resin fine particles includes: a first polymerization step of obtaining seed particles by polymerizing a monomer emulsion comprising a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in a molecule by means of a water-soluble polymerization initiator; and a second polymerization step of polymerizing a monomer emulsion comprising a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in a molecule after allowing the monomer emulsion to be absorbed into the seed particles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to resin fine particles and a method for producing the same.

Background Art

[0002] As methods for producing resin fine particles, there are methods such as suspension polymerization, seed polymerization, emulsion polymerization, soap-free polymerization, and dispersion polymerization. In particular, emulsion polymerization is suitable for creating resin fine particles with a small particle diameter such as submicrons. The obtained fine particles are used in a wide variety of applications, such as light diffusing plates, anti-blocking agents for various film membranes, various film modifiers, spacers between minute parts of various electronic devices, pore formers for various battery members, and core particles of conductive fine particles responsible for electrical connection. Especially when used in the optical field, since it is necessary to consider the influence on optical properties such as haze and light transmittance, resin fine particles obtained by polymerizing (meth)acrylic monomers, styrene monomers, etc. as the particle composition have been preferably used. At that time, there are methods such as dispersing the particles in a solvent and using them, and methods such as kneading directly with the resin raw material. Generally, crosslinked fine particles have high resistance to solvents, heat, etc. and are preferably used. As an example of creating crosslinked fine particles, Patent Document 1 etc. can be mentioned.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, among the crosslinked fine particles, depending on the degree of crosslinking, the solvent resistance is low. When a heating process or the like is added after solvent dispersion, the particles swell, and as a result, there are problems such as not obtaining the target particle diameter during use. Further, in Patent Document 2, although there is a description of particles obtained by a production method that maintains solvent resistance and has good productivity, in all cases, a non-reactive surfactant is used during emulsion polymerization. If the particles obtained by the method described in Patent Document 2 are dried and used as they are, free residual surfactants will be present in the solvent or resin, causing foaming during dispersion, which will lead to factors such as particle aggregation, sedimentation, and particle detachment from the substrate. Also, although it is possible to remove them by washing or the like, this leads to an increase in the number of steps, which is not preferable in terms of production. The present invention has been made in view of the above-described problems, and an object thereof is to provide resin fine particles having solvent resistance that can withstand a heating process after solvent dispersion, generating few bubbles during dispersion, and having excellent dispersibility in a solvent, as well as a method for producing the same.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have found that the above problems can be solved by using specific resin fine particles. The present invention has the following aspects. [1] Resin fine particles obtained by polymerizing a vinyl monomer, characterized in that the gel fraction is 93% or more and the solvent resistance index is 50 or less. [2] Resin fine particles obtained by polymerizing a vinyl monomer, characterized in that the vinyl monomer contains a reactive surfactant having a polyoxyalkylene chain in the molecule, and the terminal of the vinyl polymerization chain of the resin fine particles contains a hydroxyl group derived from a polymerization initiator. [3] The resin fine particles of [2], characterized in that the gel fraction is 93% or more and the solvent resistance index is 50 or less. [4] The resin fine particles according to any one of [1] to [3], characterized in that the volume average particle diameter is 10 to 1000 nm. [5] The resin fine particles according to any one of [1] to [4], characterized in that the coefficient of variation of the volume average particle diameter is 25% or less. [6] The resin fine particles according to any one of [1] to [5], wherein the amount of the residual surfactant is 0.01 to 1 part by mass with respect to 100 parts by mass of the resin fine particles. [7] The resin fine particles according to any one of [1] to [6], wherein the vinyl monomer contains a monofunctional (meth)acrylic monomer and / or a monofunctional aromatic vinyl monomer. [8] The resin fine particles according to any one of [1] to [7], wherein the vinyl monomer contains a polyfunctional (meth)acrylic monomer and / or a polyfunctional aromatic vinyl monomer. [9] A method for producing resin fine particles, comprising: a first polymerization step of polymerizing a monomer emulsion containing a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in the molecule with a water-soluble polymerization initiator to obtain seed particles; and a second polymerization step of polymerizing the monomer emulsion containing a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in the molecule after absorbing the monomer emulsion into the seed particles.

[10] The method for producing resin fine particles according to [9], wherein the vinyl monomer contains at least one selected from a monofunctional (meth)acrylic monomer, a monofunctional aromatic vinyl monomer, a polyfunctional (meth)acrylic monomer, and a polyfunctional aromatic vinyl monomer.

[11] The method for producing resin fine particles according to [9] or

[10] , further comprising a spray drying step of spray drying the resin fine particles obtained in the second polymerization step under conditions of an inlet temperature of 80 to 220°C and an outlet temperature of 50 to 100°C to obtain an aggregate.

[12] The method for producing resin fine particles according to

[11] , further comprising a crushing step of crushing the aggregate to disperse the resin fine particles.

[13] The method for producing resin fine particles according to any one of [9] to

[12] , further comprising a classification step of classifying the resin fine particles.

[14] The resin fine particles according to any one of [1] to [8], which are used as an antiblocking agent for a resin film.

[15] The resin fine particles according to any one of [1] to [8], which are used as an additive for a light diffusing plate. The resin fine particles according to any one of [1] to [8], characterized by being used as a spacer for an electronic device.

Advantages of the Invention

[0006] The present invention provides resin fine particles having solvent resistance capable of withstanding a heating step after solvent dispersion, generating few bubbles during dispersion, and having excellent dispersibility in a solvent, and a method for producing the same. The resin fine particles of the present invention are particles that are not easily swollen even when heated in a state of being dispersed in a solvent, and have a small variation in particle diameter. In addition, since the amount of free surfactant is small, a washing step is not required, and productivity is excellent.

Embodiments for Carrying Out the Invention

[0007] Hereinafter, the present invention will be described in detail. [Resin Fine Particles] The resin fine particles of the present invention are resin fine particles obtained by polymerizing a vinyl monomer, and are resin fine particles characterized in that the gel fraction is 93% or more and the solvent resistance index is 50 or less. Further, they are resin fine particles obtained by polymerizing a vinyl monomer, wherein the vinyl monomer contains a monofunctional vinyl monomer, a polyfunctional vinyl monomer, and a reactive surfactant having a polyoxyalkylene chain in the molecule, and the terminal of the vinyl polymerization chain of the resin fine particles contains a hydroxyl group.

[0008] <Vinyl Monomer> The resin fine particles of the present invention are obtained by polymerizing a vinyl monomer. The vinyl monomer in the present invention is one or more selected from a monofunctional vinyl monomer having one vinyl group in one molecule and a polyfunctional vinyl monomer having two or more vinyl groups in one molecule. Examples of the monofunctional vinyl monomer include monofunctional (meth)acrylic monomers and monofunctional aromatic vinyl monomers. Examples of the polyfunctional vinyl monomer include polyfunctional (meth)acrylic monomers and polyfunctional aromatic vinyl monomers. In this specification, "(meth)acryl" refers to acrylic or methacrylic, and "(meth)acrylate" refers to acrylate or methacrylate.

[0009] Examples of monofunctional (meth)acrylic monomers include (meth)acrylic acid alkyl esters in which the alkyl group bonded to the ester has 1 to 20 carbon atoms, such as methyl (meth)acrylate (methyl methacrylate, methyl acrylate), ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and (meth)acrylic acid cyclohexyl, (meth)acrylic acid isobornyl, (meth)acrylic acid dicyclopentanyl and other (meth)acrylic acid esters having an alicyclic structure in the ester moiety. Among these, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and decyl (meth)acrylate, in which the alkyl group bonded to the ester has 1 to 10 carbon atoms, are general-purpose and preferred. Particularly in applications where heat resistance is required, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate are preferred. These alkyl (meth)acrylates may be used alone or in combination of two or more.

[0010] Examples of monofunctional aromatic vinyl monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, t-butylstyrene, vinylnaphthalene, styrenesulfonic acid, styrenesulfonates (such as sodium styrenesulfonate and ammonium styrenesulfonate), vinylbenzoic acid, hydroxystyrene, and the like. Among these, styrene, α-methylstyrene, and sodium styrenesulfonate are preferred. These monofunctional aromatic vinyl monomers may be used alone or in combination of two or more.

[0011] Examples of the polyfunctional (meth)acrylic monomer include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, decaethylene glycol di(meth)acrylate, pentadecaethylene glycol di(meth)acrylate, pentacontahectaethylene glycol di(meth)acrylate, 1,3-butylene di(meth)acrylate, allyl (meth)acrylate (allyl methacrylate, allyl acrylate), trimethylolpropane tri(meth)acrylate, pentaerythritol tetraacrylate, and the like. Among these, ethylene glycol di(meth)acrylate (ethylene glycol dimethacrylate) and allyl (meth)acrylate (allyl methacrylate) are preferred. These polyfunctional (meth)acrylic monomers may be used alone or in combination of two or more.

[0012] Examples of the polyfunctional aromatic vinyl monomer include divinylbenzene, divinylnaphthalene, and the like. These polyfunctional aromatic vinyl monomers may be used alone or in combination of two or more.

[0013] The mass ratio of the monofunctional vinyl monomer to the polyfunctional vinyl monomer in the vinyl monomer, i.e., monofunctional vinyl monomer / polyfunctional vinyl monomer, can preferably be 1 / 30 to 30 / 1, more preferably 1 / 20 to 20 / 1, and even more preferably 1 / 10 to 10 / 1. The content of the monofunctional (meth)acrylic monomer in the vinyl monomer can preferably be 2 to 95% by mass, more preferably 5 to 90% by mass, and even more preferably 10 to 85% by mass. The content of the monofunctional aromatic vinyl monomer in the vinyl monomer can preferably be 0 to 25% by mass, more preferably 0 to 20% by mass, and even more preferably 0 to 18% by mass. The mass ratio of the monofunctional aromatic vinyl monomer to the monofunctional (meth)acrylic monomer in the monofunctional vinyl monomer can be preferably 0 to 1, more preferably 0 to 0.5, and even more preferably 0 to 0.25, expressed as monofunctional aromatic vinyl monomer / monofunctional (meth)acrylic monomer. The content of the polyfunctional (meth)acrylic monomer in the vinyl monomer can be preferably 0.4 to 98% by mass, more preferably 0.5 to 95% by mass, and even more preferably 0.5 to 91% by mass. The content of the polyfunctional aromatic vinyl monomer in the vinyl monomer can be preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and even more preferably 0 to 15% by mass. The mass ratio of the polyfunctional aromatic vinyl monomer to the polyfunctional (meth)acrylic monomer in the polyfunctional vinyl monomer can be preferably 0 to 33, more preferably 0 to 30, and even more preferably 0 to 28, expressed as polyfunctional aromatic vinyl monomer / polyfunctional (meth)acrylic monomer. For example, the monofunctional vinyl monomer / polyfunctional vinyl monomer can be 2 / 1 to 8 / 1, the content of the monofunctional (meth)acrylic monomer in the vinyl monomer can be 60 to 85% by mass, the content of the monofunctional aromatic vinyl monomer in the vinyl monomer can be 1 to 18% by mass, the monofunctional aromatic vinyl monomer / monofunctional (meth)acrylic monomer can be 0.005 to 0.25, the content of the polyfunctional (meth)acrylic monomer in the vinyl monomer can be 0.3 to 30% by mass, the content of the polyfunctional aromatic vinyl monomer in the vinyl monomer can be 0 to 8% by mass, and the polyfunctional aromatic vinyl monomer / polyfunctional (meth)acrylic monomer can be 0 to 30. Further, for example, the monofunctional vinyl monomer / polyfunctional vinyl monomer can be 1 / 20 to 4 / 1, the content of the monofunctional (meth)acrylic monomer in the vinyl monomer can be 5 to 15% by mass, the content of the monofunctional aromatic vinyl monomer in the vinyl monomer can be 0 to 5% by mass, the monofunctional aromatic vinyl monomer / monofunctional (meth)acrylic monomer can be 0 to 0.05, the content of the polyfunctional (meth)acrylic monomer in the vinyl monomer can be 85 to 98% by mass, the content of the polyfunctional aromatic vinyl monomer in the vinyl monomer can be 0 to 5% by mass, and the polyfunctional aromatic vinyl monomer / polyfunctional (meth)acrylic monomer can be 0 to 5.

[0014] In addition to the above monomers, unsaturated carboxylic acid monomers such as (meth)acrylic acid, hydroxyalkyl (meth)acrylate monomers such as hydroxyethyl (meth)acrylate, (meth)acrylamide monomers, (meth)acrylonitrile monomers, vinyl halide monomers such as vinyl chloride, vinyl carboxylate monomers such as vinyl acetate, olefin monomers such as ethylene, unsaturated imide monomers, vinyl alcohol, etc. can also be used as the vinyl monomer.

[0015] <Gel fraction> The resin fine particles of the present invention may have a gel fraction of 93% or more, preferably 95% or more, more preferably 96% or more. The gel fraction of the resin fine particles of the present invention means the proportion of the cross-linked portion that exhibits solvent insolubility present in the resin fine particles. When the gel fraction is 93% or more, the resin fine particles can be stably dispersed in an organic solvent such as toluene. Further, even when heated thereafter, the resin fine particles do not dissolve.

[0016] <Solvent resistance index> The resin fine particles of the present invention may have a solvent resistance index of 50 or less, preferably 25 or less, more preferably 10 or less. The lower limit value of the solvent resistance index is not particularly limited. The solvent resistance index of the resin fine particles in the present invention is obtained by the following measurement method. -Measurement method of solvent resistance index- Put 1 part by mass of resin fine particles and 50 parts by mass of toluene into a 100 mL plastic container with a lid, stir for 3 minutes using a defoaming stirrer (manufactured by Shin-Kee Co., Ltd., a rotation and revolution mixer (atmospheric pressure type) AR-100 (product name: Awatoriren Taro AR-100 (THINKYMIXER (Non Vacuum) AR-100))), and measure the "volume average particle diameter of resin fine particles" using a dynamic light scattering method thick system nanoparticle size distribution measuring device (manufactured by CORDOUAN Co., Ltd., "VASCO"). Subsequently, put the obtained resin fine particle toluene dispersion into a glass flask with a reflux tube, perform reflux at 130 °C for 24 hours, and then cool. Regarding the obtained resin fine particle toluene dispersion after heating, measure the "volume average particle diameter of resin fine particles after heating" using the above particle size distribution measuring device, and obtain the solvent resistance index according to the following formula. Solvent resistance index (%) = 100×(volume average particle diameter of resin fine particles after heating (nm) - volume average particle diameter of resin fine particles (nm)) / volume average particle diameter of resin fine particles (nm)

[0017] <Reactive surfactant> The resin fine particles of the present invention may be obtained by polymerizing a vinyl monomer containing a reactive surfactant having a polyoxyalkylene chain in the molecule.

[0018] A reactive surfactant having a polyoxyalkylene chain in the molecule is a surfactant having a double bond copolymerizable with a monomer in a polymerization system and a polyoxyalkylene chain which is a polymer of oxyalkylene in the molecule. By using such a reactive surfactant, the mechanical stability of the resin fine particles can be enhanced without the surfactant detaching from the surface of the resin fine particles. Also, even if the usage amount thereof is reduced, polymerization can be carried out without impairing the polymerization stability. Examples of the monomer constituting the polyoxyalkylene chain include oxyalkylene such as ethylene oxide, propylene oxide, and butylene oxide. Also, the reactive surfactant having a polyoxyalkylene chain may be used alone or in combination of two or more.

[0019] Examples of the reactive surfactant include ammonium polyoxyethylene-1-(allyloxymethyl)alkyl ether sulfate (e.g., "Aquaron KH1025" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), polyoxyethylene nonylpropenyl ether sulfate (e.g., "Aquaron HS1025", "Aquaron BC-10" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), polyoxyethylene allyl glycidyl nonylphenyl ether sulfate (e.g., "Adekaria Soap SE" manufactured by ADEKA Corporation), sodium alkyl allyl sulfosuccinate (e.g., "Ereminol JS-2" manufactured by Sanyo Chemical Industries, Ltd.), polyoxyalkylene methacrylate sulfate (e.g., "Ereminol RS-30" manufactured by Sanyo Chemical Industries, Ltd.), bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfate (e.g., "Antox MS-60" manufactured by Nippon Emulsifier Co., Ltd.), ethylene glycol methacrylate sulfate (e.g., "Antox MS-2N", "Antox MS-NH4" manufactured by Nippon Emulsifier Co., Ltd.), and those having other structures (e.g., "Latemul" manufactured by Kao Corporation, "New Frontier" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., "RA-1823", "RA-2320" manufactured by Nippon Emulsifier Co., Ltd., etc.). These are anionic reactive emulsifiers having reactive groups such as propenyl group, allyl group, isopropenyl group, acrylate group, and methacrylate group;

[0020] Polyoxyethylene nonyl propenyl ether (such as "Aquaron RN" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyethylene allyl glycidyl nonyl phenyl ether (such as "Adekaria Soap NE" manufactured by ADEKA Corporation), polyoxyalkylene glycol monoacrylate (such as "Blemmer AET", "Blemmer APT" manufactured by NOF Corporation), lauroxy polyethylene glycol monoacrylate (such as "Blemmer ALE" manufactured by NOF Corporation), lauroxy polyethylene glycol monomethacrylate (such as "Blemmer PLE" manufactured by NOF Corporation), stearoxy polyethylene glycol monomethacrylate (such as "Blemmer PSE" manufactured by NOF Corporation), stearoxy polyethylene glycol - polypropylene glycol monoacrylate (such as "Blemmer ASEP" manufactured by NOF Corporation), allyloxy polyalkylene glycol monomethacrylate (such as "Blemmer PNEP", "Blemmer PNPE" manufactured by NOF Corporation), nonylphenoxy polyoxyalkylene glycol monoacrylate (such as "Blemmer 43ANEP - 500", "Blemmer 70ANEP - 550" manufactured by NOF Corporation), polyethylene glycol - polypropylene glycol polyethylene glycol dimethacrylate (such as "Blemmer 80PDC" manufactured by NOF Corporation), polyethylene glycol polypropylene glycol - polyethylene glycol diacrylate (such as "Blemmer 30ADC" manufactured by NOF Corporation), etc., and nonionic reactive emulsifiers having reactive groups such as propenyl group, allyl group, isopropenyl group, acrylate group, methacrylate group, etc. can be mentioned. The amount of the reactive surfactant used is preferably in the range of 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and still more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the vinyl monomer.

[0021] <Hydroxyl group at the end of the vinyl polymer chain> The resin fine particles of the present invention may contain a hydroxyl group derived from a polymerization initiator at the end of the vinyl polymer chain. Such resin fine particles can be obtained by using a polymerization initiator containing a hydroxyl group during the polymerization of the vinyl monomer. As the polymerization initiator containing a hydroxyl group, for example, an azo - type polymerization initiator containing a hydroxyl group can be mentioned as a preferable one. Examples of the azo polymerization initiator containing a hydroxyl group include 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (trade name "VA-086"), 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} (trade name "VA-080"), 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide} (trade name "VA-082"), 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide} (trade name "VA-085") (all manufactured by Fujifilm Wako Pure Chemical Corporation), and the like. These azo polymerization initiators containing a hydroxyl group may be used alone or in combination of two or more. The amount of the polymerization initiator used is preferably in the range of 0.1 to 2 parts by mass, more preferably 0.2 to 1 part by mass, and still more preferably 0.3 to 0.8 part by mass with respect to 100 parts by mass of the vinyl monomer.

[0022] <Physical properties of resin fine particles, etc.> (Volume average particle diameter and its coefficient of variation) The volume average particle diameter of the resin fine particles of the present invention is not particularly limited and is appropriately set according to the purpose and application. Preferably, it is in the range of 10 to 1000 nm, more preferably 30 to 750 nm, and still more preferably 50 to 500 nm. The coefficient of variation of the volume average particle diameter of the resin fine particles of the present invention is not particularly limited. Preferably, it is in the range of 25% or less, more preferably 23% or less, and still more preferably 21% or less. The coefficient of variation (CV value) of the volume average particle diameter of the resin fine particles is calculated from the following formula. Coefficient of variation of volume average particle diameter of resin fine particles = [(standard deviation of particle size distribution based on volume of resin fine particles) / (volume average particle diameter of resin fine particles)] × 100

[0023] (Amount of residual surfactant) The amount of residual surfactant relative to 100 parts by mass of the resin microparticles of the present invention is not particularly limited and is appropriately set according to the purpose and application. Preferably, it is in the range of 0.01 to 1 part by mass, more preferably 0.03 to 0.7 part by mass, and still more preferably 0.05 to 0.5 part by mass. When a surfactant is used during polymerization, setting the amount of residual surfactant to less than 0.01 part by mass may complicate the process and be disadvantageous in terms of cost and the like. If the amount of residual surfactant is 1 part by mass or more, foaming may occur when the resin microparticles are dispersed in a medium. The amount of residual surfactant of the present invention can be determined, for example, as follows. The resin microparticles were extracted with a solvent and measured using a liquid chromatograph linear ion trap type mass spectrometer (LC / MS / MS apparatus). As the LC / MS / MS apparatus, "UHPLC ACCELA" manufactured by Thermo Fisher Scientific and "Linear Ion Trap LC / MSn LXQ" manufactured by Thermo Fisher Scientific can be used. The content of the surfactant is measured by the method shown below. Approximately 0.01 g of the resin microparticles was precisely weighed into a centrifuge tube, the extract was added, the resin microparticles and the extract were mixed well, ultrasonic extraction was performed, then mixed again, centrifuged, and the obtained supernatant was filtered to obtain a test solution. The concentration of the surfactant in this test solution was measured using an LC / MS / MS apparatus, and the content was calculated from a calibration curve prepared in advance from the peak area value on the obtained chromatogram. Then, from the measured surfactant concentration in the test solution, the weight of the resin microparticles used as the sample (sample weight), and the amount of the extract, the content of the surfactant in the resin microparticles was determined by the following calculation formula. Content of surfactant = Concentration of surfactant in test solution × Amount of extract ÷ Sample weight Note that the calibration curve preparation method is as follows. After preparing an intermediate standard solution of about 1000 ppm of surfactant (methanol solution), it is further diluted stepwise with methanol to prepare standard solutions for calibration curve of 20 ppm, 10 ppm, 5 ppm, and 2.5 ppm. The standard solutions for calibration curve of each concentration are measured under the following conditions, and the peak area values on the chromatogram of monitor ion m / z = 730 - 830 are obtained. The concentrations and area values are plotted, and an approximate curve (quadratic curve) is obtained by the least squares method, which is used as the calibration curve for quantification.

[0024] (Solvent dispersibility) The solvent dispersibility of the resin fine particles of the present invention is evaluated based on the criterion that it is good when the solvent resistance index described above is 50 or less. The fact that the solvent resistance index is 50 or less means that the change in the volume average particle diameter of the resin fine particles after heating is small, which means that the resin fine particles are not swollen and are dispersed without aggregating in the solvent. (Number average particle diameter) The number average particle diameter of the resin fine particles of the present invention is not particularly limited and is appropriately set according to the purpose and application. Preferably, it is in the range of 10 - 1000 nm, more preferably 30 - 750 nm, and even more preferably 50 - 350 nm.

[0025] (Monodispersity) The monodispersity of the resin fine particles of the present invention is not particularly limited and is appropriately set according to the purpose and application. Preferably, it is in the range of 1.2 or less, more preferably 1.15 or less, and even more preferably 1.12 or less. The monodispersity is calculated from the following formula. Monodispersity = (Volume average particle diameter of resin fine particles) / (Number average particle diameter of resin fine particles)

[0026] <Other components> The resin fine particles of the present invention may contain additives such as plasticizers, anti-blocking agents, bubble regulators, cross-linking agents, fillers, lubricants, colorants, fusion promoters, spreading agents, antioxidants, flame retardants, and flame retardant aids within the range that does not impair the effects of the present invention.

[0027] [Manufacturing method of resin fine particles] The resin fine particles can be produced by polymerizing a vinyl monomer in the presence of a polymerization initiator and a surfactant (emulsifier) as necessary.

[0028] <Polymerization initiator> The polymerization initiator used in the polymerization of the resin fine particles of the present invention is not particularly limited, but it is preferable to use a thermally decomposable water-soluble polymerization initiator. Examples of the thermally decomposable water-soluble polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (trade name "VA-086"); 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (trade name "VA-061"); 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (trade name "VA-044"); 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate (trade name "VA-046B"); 2,2'-azobis(2-methylpropionamidine) dihydrochloride (trade name "V-50"); 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate (trade name "VA-057"); 4,4'-azobis(4-cyanovaleric acid) (trade name "V-501"); 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} (trade name "VA-080"); 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide} (trade name "VA-082"); 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide} (trade name "VA-085"); azo compounds such as 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis(1-imino-1-pyrrolidino-2-ethylpropane) dihydrochloride, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, and 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}. Particularly, since it has little influence on the pH of the slurry after polymerization, it is preferably a water-soluble azo-based polymerization initiator. Further, from the viewpoint of improving the dispersibility of the resin fine particles, those having a hydroxyl group in the molecule and capable of introducing a hydroxyl group derived from the polymerization initiator to the terminal of the vinyl polymerization chain of the resin fine particles are preferable.

[0029] In the present invention, a polymerization initiator other than a water-soluble polymerization initiator can also be used. Examples of such polymerization initiators include organic peroxides such as cumene hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, dimethyl bis(tert-butylperoxy)hexane, dimethyl bis(tert-butylperoxy)hexyne-3, bis(tert-butylperoxyisopropyl)benzene, bis(tert-butylperoxy)trimethylcyclohexane, butyl-bis(tert-butylperoxy)valerate, tert-butyl 2-ethylhexaneperoxyacid, dibenzoyl peroxide, paramethane hydroperoxide, and tert-butyl peroxybenzoate; azo compounds such as 2,2'-azobisisobutyronitrile (2,2'-azobis(2-methyl-butyronitrile)), 2,2'-azobis(2-isopropylbutyronitrile), 2,2'-azobis(2,3-dimethylbutyronitrile), 2,2'-azobis(2,4-dimethylbutyronitrile), 2,2'-azobis(2-methylcapronitrile), 2,2'-azobis(2,3,3-trimethylbutyronitrile), 2,2'-azobis(2,4,4-trimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-ethoxyvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-n-butoxyvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 1,1'-azobis(1-acetoxy-1-phenylethane), 1,1'-azobis(cyclohexane-1-carbonitrile), dimethyl-2,2'-azobis(2-methylpropionate), dimethyl-2,2'-azobisisobutyrate, dimethyl-2,2'-azobis(2-methylpropionate), and 2-(carbamoylazo)isobutyronitrile.

[0030] Further, a redox initiator obtained by combining the above-mentioned persulfates and organic peroxide polymerization initiators with reducing agents such as sodium sulfoxylate formaldehyde, sodium bisulfite, ammonium bisulfite, sodium thiosulfate, ammonium thiosulfate, hydrogen peroxide, sodium hydroxymethanesulfinate, L-ascorbic acid and its salts, cuprous salts, and ferrous salts may be used as the polymerization initiator. These polymerization initiators may be used alone or in combination of two or more. Further, these polymerization initiators are preferably used in the range of 0.1 to 2 parts by mass, more preferably 0.2 to 1 part by mass, and still more preferably 0.3 to 0.8 part by mass with respect to 100 parts by mass of the vinyl monomer.

[0031] <Surfactant> The surfactant for producing the resin fine particles of the present invention is not particularly limited, but it is preferable to use a reactive surfactant. Examples of the anionic reactive surfactant include JS-20 and RS-3000 of Eleminol (registered trademark) manufactured by Sanyo Chemical Industries, Ltd., KH-10, KH-1025, KH-05, HS-10, HS-1025, BC-0515, BC-10, BC-1025, BC-20, BC-2020, AR-1025, AR-2025 of Aqualon (registered trademark) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., S-120, S-180A, S-180, PD-104 of Latemul (registered trademark) manufactured by Kao Corporation, SR-1025, SE-10N of Adeka Soap (registered trademark) manufactured by ADEKA Corporation, and the like. Examples of nonionic reactive surfactants include alkyl ether type (commercially available products such as ADEKA Liasol ER-10, ER-20, ER-30, ER-40, Kao Latemul PD-420, PD-430, PD-450, etc.); alkyl phenyl ether type or alkyl phenyl ester type (commercially available products such as Daiichi Kogyo Seiyaku Aqualon RN-10, RN-20, RN-30, RN-50, AN-10, AN-20, AN-30, AN-5065, ADEKA Liasol NE-10, NE-20, NE-30, NE-40, etc.); (meth)acrylate sulfate type (commercially available products such as Nippon Emulsifier RMA-564, RMA-568, RMA-1114, etc.). Among these reactive surfactants, those having a polyoxyalkylene chain in the molecule are preferable from the viewpoints of particle dispersibility, dispersion stability, etc.

[0032] In the present invention, surfactants other than the reactive surfactant can also be used. Such surfactants can be any of anionic surfactants, cationic surfactants, zwitterionic surfactants, and nonionic surfactants.

[0033] Examples of anionic surfactants include sodium oleate; fatty acid soaps such as castor oil potassium soap; alkyl sulfate ester salts such as sodium lauryl sulfate and ammonium lauryl sulfate; alkyl benzene sulfonate salts such as sodium dodecyl benzene sulfonate; alkyl naphthalene sulfonate salts; alkane sulfonate salts; dialkyl sulfosuccinate salts; alkyl phosphate ester salts; naphthalene sulfonic acid formalin condensates; polyoxyethylene alkyl phenyl ether sulfate ester salts; polyoxyethylene alkyl sulfate ester salts, etc.

[0034] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxysorbitan fatty acid esters, polyoxyethylene alkyl amines, glycerin fatty acid esters, oxyethylene-oxypropylene block polymers, and the like.

[0035] Examples of cationic surfactants include alkylamine salts such as laurylamine acetate and stearylamine acetate; quaternary ammonium salts such as lauryltrimethylammonium chloride. Examples of zwitterionic surfactants include lauryldimethylamine oxide, phosphate ester-based surfactants, phosphite ester-based surfactants, and the like.

[0036] These surfactants may be used alone or in combination of two or more. The type of surfactant is appropriately selected and the amount used is appropriately adjusted in consideration of the particle diameter of the resulting resin fine particles, the dispersion stability of the polymerizable monomer during polymerization, and the like.

[0037] The amount of the surfactant used is preferably in the range of 0.3 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, and still more preferably 0.7 to 10 parts by mass with respect to 100 parts by mass of the vinyl-based monomer.

[0038] <Medium> As the medium used during polymerization, either an aqueous medium or a non-aqueous medium can be used. In the present invention, it is preferable to use an aqueous medium. Examples of the aqueous medium include water (such as ion-exchanged water) and a mixed solvent of water and a water-soluble solvent (such as a lower alcohol like ethanol).

[0039] <Dispersant> When an aqueous medium is used during coincidence, a dispersant may be used to stabilize the dispersibility of the droplets of the vinyl monomer and the seed particles. Examples of such dispersants include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose; and inorganic dispersants such as magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium phosphate, magnesium carbonate, and magnesium oxide. When an inorganic dispersant is used, it is preferable to use a surfactant in combination.

[0040] <Polymerization method> In the production of resin fine particles, the polymerization method of the vinyl monomer is not particularly limited as long as it is a known polymerization method. A polymerization initiator and a surfactant (emulsifier) are used as necessary. For example, methods such as seed polymerization, emulsion polymerization, and suspension polymerization can be mentioned.

[0041] Seed polymerization is a method in which resin fine particles composed of a polymer of a vinyl monomer are used as seed particles, the vinyl monomer is absorbed by the seed particles in an aqueous medium, and the vinyl monomer is polymerized inside the seed particles. In this method, by growing the seed particles, resin fine particles with a larger particle diameter than the original seed particles can be obtained. Emulsion polymerization is a polymerization method in which an aqueous medium, a vinyl monomer that is hardly soluble in this medium, and a surfactant (emulsifier) are mixed, and a polymerization initiator that is soluble in the aqueous medium is added thereto to carry out polymerization. Emulsion polymerization is characterized by having little variation in the particle diameter of the obtained resin fine particles. Suspension polymerization is a polymerization method in which a vinyl monomer and an aqueous medium are mechanically stirred to suspend the vinyl monomer in the aqueous medium and polymerize it. Suspension polymerization is characterized by being able to obtain resin fine particles with a small particle diameter and a relatively uniform particle diameter. In the present invention, seed polymerization is most preferable.

[0042] (Seed polymerization) The polymerization method of vinyl monomers for obtaining seed particles used in seed polymerization is not particularly limited, and dispersion polymerization, emulsion polymerization, soap-free emulsion polymerization (emulsion polymerization without using a surfactant as an emulsifier), seed polymerization, suspension polymerization, etc. can be used. In order to obtain resin fine particles with a substantially uniform particle diameter by seed polymerization, it is necessary to first use seed particles with a substantially uniform particle diameter and grow these seed particles substantially uniformly. The seed particles with a substantially uniform particle diameter as a raw material can be produced by polymerizing by polymerization methods such as soap-free emulsion polymerization (emulsion polymerization without using a surfactant), polymerization using a reactive surfactant, and dispersion polymerization of vinyl monomers. The reactive surfactant is not particularly limited, but it is preferable to use a reactive surfactant having a polyoxyalkylene chain in the molecule. Therefore, as the polymerization method for polymerizing vinyl monomers to obtain seed particles, emulsion polymerization, soap-free emulsion polymerization, seed polymerization, and dispersion polymerization are preferable.

[0043] Also in the polymerization for obtaining seed particles, a polymerization initiator may be used as necessary. As the polymerization initiator, the above-mentioned polymerization initiator can be used. The amount of the polymerization initiator used is preferably in the range of 0.1 to 2 parts by mass with respect to 100 parts by mass of the vinyl monomer used for obtaining seed particles. The weight average molecular weight of the obtained seed particles can be adjusted by the amount of the polymerization initiator used.

[0044] In the polymerization for obtaining seed particles, a molecular weight regulator may be used to adjust the weight average molecular weight of the obtained seed particles. As the molecular weight regulator, for example, mercaptans such as n-octyl mercaptan and tert-dodecyl mercaptan; α-methylstyrene dimer; terpenes such as γ-terpinene and dipentene; halogenated hydrocarbons such as chloroform and carbon tetrachloride can be used. The weight average molecular weight of the obtained seed particles can be adjusted by increasing or decreasing the amount of the above-mentioned molecular weight regulator used. The volume average particle diameter of the seed particles can be appropriately adjusted according to the average particle diameter of the resin fine particles. Preferably, it is in the range of 1 to 300 nm, and its average mass is 1 to 100 mg / 100 particles. Further, examples of its shape include a true spherical shape and an elliptical spherical shape (oval shape).

[0045] In the seed polymerization, first, seed particles are added to an emulsion containing a vinyl monomer and an aqueous medium. The above emulsion can be prepared by a known method. For example, a vinyl monomer is added to an aqueous medium and dispersed by a fine emulsifier such as a homogenizer, an ultrasonic processor, or a nanomizer (registered trademark) to obtain an emulsion.

[0046] In the seed polymerization, it is preferable to use 0.3 to 15 parts by mass of a surfactant with respect to 100 parts by mass of the vinyl monomer. As the surfactant, the above-mentioned surfactant can be used. When the amount of the surfactant used is less than the above range, the polymerization stability may be lowered. Further, when the amount of the surfactant used is more than the above range, it is uneconomical in terms of cost.

[0047] The seed particles may be added to the emulsion as they are, or may be added to the emulsion in a form dispersed in an aqueous medium. After the seed particles are added to the emulsion, the vinyl monomer is absorbed by the seed particles. This absorption can usually be carried out by stirring the emulsion at room temperature (about 25°C) for 1 to 12 hours. Further, in order to promote the absorption of the vinyl monomer by the seed particles, the emulsion may be heated to about 30 to 50°C.

[0048] The seed particles swell by absorbing vinyl monomers. The mixing ratio of the vinyl monomer and the seed particles is preferably in the range of 1 to 100 parts by mass, more preferably in the range of 5 to 50 parts by mass of the vinyl monomer with respect to 1 part by mass of the seed particles. When the mixing ratio of the vinyl monomer is less than the above range, the increase in particle diameter due to polymerization becomes small, so the production efficiency decreases. On the other hand, when the mixing ratio of the vinyl monomer is greater than the above range, the vinyl monomer may not be completely absorbed by the seed particles and may undergo emulsion polymerization independently in the aqueous medium, generating resin fine particles with an abnormal particle diameter that is not desired. The end of the absorption of the vinyl monomer by the seed particles can be determined by confirming the expansion of the particle diameter through observation with an optical microscope.

[0049] Next, a resin fine particle dispersion is obtained by polymerizing the vinyl monomer absorbed by the seed particles. Note that a resin fine particle dispersion may also be obtained by repeating the step of absorbing and polymerizing the vinyl monomer in the seed particles a plurality of times.

[0050] When polymerizing the vinyl monomer absorbed by the seed particles, a polymerization initiator may be added as necessary. After mixing the polymerization initiator with the vinyl monomer, the resulting mixture may be dispersed in an aqueous medium, or a mixture of the polymerization initiator and the vinyl monomer separately dispersed in the aqueous medium may be mixed. It is preferable that the particle diameter of the droplets of the vinyl monomer present in the obtained emulsion is smaller than the particle diameter of the seed particles because the vinyl monomer is efficiently absorbed by the seed particles.

[0051] As the above polymerization initiator, the above polymerization initiator can be used. The polymerization initiator is preferably used in the range of 0 to 3 parts by mass with respect to 100 parts by mass of the vinyl monomer.

[0052] The polymerization temperature of the seed polymerization can be appropriately selected according to the type of the vinyl monomer and the type of the polymerization initiator used as necessary. For example, it is 25 to 110 ° C, preferably 50 to 100 ° C. The polymerization time of the seed polymerization can be appropriately selected according to the type of vinyl monomer and the type of polymerization initiator used as required. For example, it is 1 to 12 hours. The seed polymerization may be carried out in an atmosphere of a gas (such as nitrogen) that is inert to the polymerization. In the seed polymerization, it is preferable to raise the temperature after the vinyl monomer and the polymerization initiator used as required are completely absorbed by the seed particles.

[0053] In the seed polymerization, in order to improve the dispersion stability of the resin fine particles, the above-mentioned dispersant may be added to the polymerization reaction system as a dispersion stabilizer. Among these dispersion stabilizers, polyvinyl alcohol and polyvinylpyrrolidone are preferable. The addition amount of the dispersion stabilizer is preferably in the range of 1 to 10 parts by mass with respect to 100 parts by mass of the vinyl monomer.

[0054] In order to suppress the generation of an emulsion polymerization product (resin fine particles with too small a particle size) in the aqueous medium in the polymerization reaction, water-soluble polymerization inhibitors such as nitrites such as sodium nitrite, sulfites, hydroquinones, ascorbic acids, water-soluble vitamin Bs, citric acid, and polyphenols may be added to the aqueous medium. The addition amount of the polymerization inhibitor is, for example, in the range of 0.002 to 0.2 parts by mass with respect to 100 parts by mass of the vinyl monomer.

[0055] As a preferred embodiment of the method for producing the resin fine particles of the present invention, there is a method for producing resin fine particles having a first polymerization step of polymerizing a monomer emulsion containing a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in the molecule with a water-soluble polymerization initiator to obtain seed particles, and a second polymerization step of polymerizing a monomer emulsion containing a vinyl monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in the molecule after absorbing the monomer emulsion into the seed particles. Another preferred embodiment of the method for producing resin fine particles of the present invention is as follows: In the same polymerization vessel purged with nitrogen, a monomer emulsion composed of a vinyl monomer, ion-exchanged water, a surfactant such as a reactive surfactant having a polyoxyalkylene chain in the molecule, etc. is polymerized with a water-soluble polymerization initiator in a first seed particle polymerization step, and a monomer emulsion composed of a vinyl monomer, ion-exchanged water, a surfactant such as a reactive surfactant having a polyoxyalkylene chain in the molecule, etc. is divided or dropped and absorbed by the seed particles and polymerized in a second polymerization step. There is a method for producing resin fine particles through such steps.

[0056] <Drying, Crushing, and Classifying of Resin Fine Particles> After completion of polymerization, the resin fine particles are made into a cake (hydrous cake) containing an aqueous medium by methods such as suction filtration, centrifugal separation, and pressure separation. After passing through a washing step with water and / or a solvent if necessary, they are dried and, if necessary, isolated as a dry powder through crushing and classifying steps. The drying method is not particularly limited, and methods such as spray drying using a spray dryer, freeze drying, and drying by attaching to a heated rotating drum such as a drum dryer can be used. In the present invention, it is preferable to use a spray drying step in which the resin fine particles obtained in the second polymerization step are spray dried under the conditions of an inlet temperature of 80 to 220 °C and an outlet temperature of 50 to 100 °C to obtain an aggregate. The obtained aggregate has good handleability during handling. In the present invention, it is preferable to include a crushing step of crushing the obtained aggregate to disperse the resin fine particles. The crushed and dispersed resin fine particles have good dispersibility in a solvent. Also, in the present invention, it is preferable to include a classifying step of classifying the resin fine particles. For example, it is preferable to include at least one of a classifying step of classifying the resin fine particles obtained in the second polymerization step and a classifying step of classifying the resin fine particles obtained in the crushing step. Classification can be performed by known means.

[0057] [Uses of Resin Fine Particles] The resin fine particles of the present invention can be used for various applications. For example, additives for light diffusing plates, anti-blocking agents for various film membranes, various film modifiers, spacer applications between minute parts of various electronic devices, pore formers for various battery members, core particles of conductive fine particles responsible for electrical connection, and the like can be mentioned. Even when a heating step is added after the resin fine particles of the present invention are dispersed in a solvent during use, the resin fine particles can maintain the target particle diameter without swelling.

Examples

[0058] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the following Examples are merely illustrative of the present invention, and the present invention is not limited only to the following Examples. In the Examples and Comparative Examples, the obtained resin fine particles were evaluated as follows.

[0059] <Gel fraction> After collecting the resin fine particles and precisely weighing them to measure the weight (W1 g), they are immersed in 100 parts by mass of toluene, stirred under reflux at 130°C for 24 hours, and then cooled. The obtained resin fine particle dispersion is centrifuged at 18,000 rpm for 30 minutes using a centrifuge, the supernatant is removed, and it is dried in a vacuum dryer at 60°C for 12 hours to measure the weight (W2 g) of the insoluble matter. Further, the gel fraction of the resin fine particles is determined by the formula of W2 / W1×100.

[0060] <Solvent resistance index> Put 1 part by mass of resin microparticles and 50 parts by mass of toluene into a 100 mL plastic container with a lid, stir for 3 minutes using a defoaming stirrer (manufactured by Shinki Co., Ltd., a rotating and revolving mixer (atmospheric pressure type) AR-100 (product name: Awatori Rentaro AR-100) (THINKYMIXER (Non Vacuum) AR-100)), and measure the "volume average particle diameter of the resin microparticle toluene dispersion" using a dynamic light scattering method thick system nanoparticle size distribution measuring device (manufactured by CORDOUAN Co., Ltd., "VASCO"). Subsequently, put the obtained resin microparticle toluene dispersion into a glass flask with a reflux tube, perform reflux at 130 °C for 24 hours, and then cool. For the obtained resin microparticle toluene dispersion after heating, measure the "volume average particle diameter of the resin microparticle toluene dispersion after heating" using the above particle size distribution measuring device, and obtain the solvent resistance index according to the following formula. Solvent resistance index (%) = 100×(volume average particle diameter of resin microparticles after heating (nm) - volume average particle diameter of resin microparticles (nm)) / volume average particle diameter of resin microparticles (nm)

[0061] <Solvent resistance> Based on the gel fraction and the solvent resistance index, the solvent resistance was evaluated according to the following criteria. ◎: Gel fraction is 93% or more, and solvent resistance index is 10 or less 〇: Gel fraction is 93% or more, and solvent resistance index exceeds 10 and is 25 or less △: Gel fraction is 93% or more, and solvent resistance index exceeds 25 and is 50 or less ×: Gel fraction is less than 93%, and solvent resistance index exceeds 50

[0062] <Solvent dispersibility> Based on the results of the above-mentioned solvent resistance index, the dispersibility in the solvent was evaluated according to the following criteria. ○: Solvent resistance index is 50 or less ×: Solvent resistance index exceeds 50

[0063] <Volume average particle diameter, number average particle diameter> The volume-average particle diameter and number-average particle diameter of the resin fine particles were measured using a laser diffraction / scattering particle size distribution analyzer (model number "LS230", manufactured by Beckman Coulter, Inc.). Specifically, 0.1 g of an aqueous dispersion of resin fine particles (solid content: 20%) and 20 ml of a 2 mass% anionic surfactant solution were placed in a test tube. Subsequently, a test tube mixer (manufactured by AS ONE Corporation, "Test Tube Mixer TRIO HM-1N") and an ultrasonic cleaner (manufactured by AS ONE Corporation, "ULTRASONIC CLEANER VS-150") were used to disperse the mixture for 5 minutes to obtain a dispersion. The volume-average particle diameter and number-average particle diameter of the resin fine particles in the dispersion were measured using a laser diffraction / scattering particle size distribution analyzer while irradiating the dispersion with ultrasonic waves. The measurement conditions of the laser diffraction / scattering particle size distribution analyzer are as follows. Medium = water Refractive index of the medium = 1.333 Refractive index of the solid = refractive index of the resin fine particles PIDS relative concentration: 40 - 55% The optical model during measurement was adjusted according to the refractive index of the manufactured resin fine particles. When one type of monomer was used in the production of the resin fine particles, the refractive index of the homopolymer of that monomer was used as the refractive index of the resin fine particles. When multiple types of monomers were used in the production of the resin fine particles, the refractive index of the resin fine particles was the weighted average value obtained by weighting the refractive indices of the homopolymers of the respective monomers by the usage amounts of the respective monomers. From the measurement results, a particle size distribution based on volume of the resin fine particles was obtained. The arithmetic mean of the particle size distribution based on volume was defined as the volume-average particle diameter of the resin fine particles.

[0064] <Residual surfactant amount> The content of the surfactant in the resin fine particles was measured by extracting the resin fine particles with a solvent and using a liquid chromatography linear ion trap type mass spectrometer (LC / MS / MS apparatus). For the measurement of the surfactant content in the resin microparticles of the examples and comparative examples described below, the "UHPLC ACCELA" manufactured by Thermo Fisher Scientific and the "Linear Ion Trap LC / MSn LXQ" manufactured by Thermo Fisher Scientific were used as the LC / MS / MS devices. In addition, the resin microparticles in the examples and comparative examples described below used Aqualon AR-1025 (purity 25%, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and AN-5065 (purity 65%, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as surfactants. The surfactant content in the resin microparticles of the examples and comparative examples was measured by the method shown below. Approximately 0.01 g of resin microparticles as a sample was precisely weighed into a centrifuge tube, 5 mL of methanol as an extract was added with a whole pipette, and the resin microparticles and the extract were thoroughly mixed. After performing ultrasonic extraction for 15 minutes, it was mixed well again, centrifuged at 3,500 rpm for 60 minutes, and the supernatant obtained thereby was filtered through a GL chromatodisk non-aqueous system 0.20 μm manufactured by GL Sciences Inc. to obtain a test solution.

[0065] The concentrations of surfactants AR-1025 and AN-5065 in this test solution were measured using an LC / MS / MS device. Then, from the surfactant concentration (μg / mL) in the measured test solution, the weight of the resin microparticles used as the sample (sample weight (g)), and the amount of the extract (extract amount (mL)), the content (μg / g) of the surfactant in the resin microparticles was determined by the following calculation formula. The extract amount was 5 mL. Surfactant content (μg / g) = Surfactant concentration in the test solution (μg / mL) × Extract amount (mL) ÷ Sample weight (g) Note that the surfactant concentration was calculated from the calibration curve prepared in advance from the peak area value on the obtained chromatogram using an LC / MS / MS device. The calibration curve preparation method is as follows. After preparing an intermediate standard solution of about 1000 ppm of surfactant (methanol solution), it was further diluted stepwise with methanol to prepare standard solutions for calibration curve at 20 ppm, 10 ppm, 5 ppm, and 2.5 ppm. The standard solutions for calibration curve at each concentration were measured under the following conditions, and the peak area values on the chromatogram of monitor ion m / z = 730 - 830 were obtained. The concentrations and area values were plotted, and an approximate curve (quadratic curve) was obtained by the least squares method, which was used as the calibration curve for quantification. The LC measurement conditions are as follows. Measuring device: UHPLC ACCELA (manufactured by Thermo Fisher Scientific) Column: Hypersil GOLD C18 1.9μm (inner diameter 2.1 mm, length 100 mm) (manufactured by Thermo Fisher Scientific) Column temperature: 40 °C Mobile phase: (A: 10 mM ammonium acetate / B: acetonitrile) Mobile phase conditions: 0 min = 70% B concentration 0 → 0.5 min = 70% → 80% B concentration 0.5 → 1.5 min = 80% B concentration 1.5 → 1.6 min = 80% → 70% B concentration 1.6 → 4 min = 70% B concentration Flow rate: 0.3 mL / min Pump temperature: room temperature (25 °C) Injection volume: 2 μL Measurement time: 4 min The MS measurement conditions are as follows. Measuring device: Linear Ion Trap LC / MSn LXQ (manufactured by Thermo Fisher Scientific Co., Ltd.) Ionization method (Ionization): (ESI / positive) Sheath Gas: 45 arb Auxiliary Gas (AUX Gas): 0 arb Sweep Gas: 0 arb Spray Voltage (I Spray Voltage): 4.0 kV Capillary Temp: 350 °C Capillary voltage: 25 V Tube lens Voltage: 100 V Monitoring Mass (m / z): AR-1025 (SIM = 730~830), AN-5065 (SIM = 730~830)

[0066] <Monodispersity> The monodispersity of the resin fine particles was calculated by the following formula. Monodispersity = (Volume average particle diameter of resin fine particles) / (Number average particle diameter of resin fine particles)

[0067] <Foaming test> 80 ml of ion-exchanged water was poured into a 200 ml beaker with a stir bar at the bottom. 0.8 g of the resin fine particles of each example and comparative example was floated on the water surface, and after stirring at 300 rpm for 30 minutes, the foaming property in the ion-exchanged water was evaluated according to the following criteria. No foaming: No foaming was confirmed on the liquid surface after the foaming test. Foaming occurred: Foaming was confirmed on the liquid surface after the foaming test.

[0068] [Example 1] In a polymerization vessel equipped with a stirring device, a thermometer, and a cooling mechanism, 320 parts by mass of ion-exchanged water and 0.08 part by mass of the reactive surfactant Aqualon AR-1025 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were mixed. 3.8 parts by mass of methyl methacrylate and 0.2 part by mass of ethylene glycol dimethacrylate were thoroughly mixed in another container and added to the polymerization vessel, and the monomer mixture was obtained by stirring at 8000 rpm for 10 minutes using a TK homomixer (manufactured by Primix Corporation). After purging the polymerization vessel with nitrogen for 5 minutes, the temperature was raised to 75 °C, and when 75 °C was reached, a water-soluble polymerization initiator VA-086 (manufactured by Fujifilm Wako Pure Chemical Corporation) dissolved in 10 parts by mass of ion-exchanged water was added and reacted for 1 hour to obtain a slurry (1). Next, 36 parts by mass of ion-exchanged water, 0.3 parts by mass of Aqualon AR-1025 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 0.03 parts by mass of reactive surfactant Aqualon AN-5065 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were mixed in a container different from the one used previously to obtain a surfactant solution. Further, 22 parts by mass of methyl methacrylate, 6 parts by mass of styrene, and 8 parts by mass of ethylene glycol dimethacrylate were well mixed in another container, put into the surfactant solution, and stirred at 8000 rpm for 10 minutes using a TK homomixer (manufactured by Primix Corporation) to obtain a monomer mixture (2). The monomer mixture (2) was charged into the slurry (1) maintained at 75°C in the polymerization vessel in 8 portions over 2 hours. Then, after a 1-hour aging process, the temperature was raised to 100°C and held for 3 hours, followed by cooling to create a slurry containing resin fine particles. The slurry containing resin fine particles was passed through a 400 Mesh nylon screen to classify the resin fine particles, thereby obtaining a classified slurry of resin fine particles. The classified slurry of resin fine particles was spray-dried under the following equipment conditions using a spray dryer (manufactured by Sakamoto Kikai Kenkyusho Co., Ltd., machine name: Spray Dryer, type: Atomizer Take-up System, model number: TRS-3WK) to obtain an aggregate of resin fine particles.

[0069] <Equipment Conditions of Spray Dryer> Slurry supply rate containing resin fine particles: 25 mL / min Atomizer rotation speed: 12000 rpm Air volume: 2 m 3 / min Inlet temperature (temperature of the slurry inlet for introducing the slurry containing resin fine particles, which is provided in the spray dryer and where the slurry containing resin fine particles is sprayed): 150°C Outlet temperature (powder outlet temperature where the aggregate of vinyl-based resin fine particles is discharged, which is provided in the spray dryer): 70°C

[0070] The obtained aggregate of resin fine particles was subjected to a disintegration treatment using a current jet mill (manufactured by Nisshin Engineering Co., Ltd., product name: CJ-10, pulverizing air pressure: 0.5 MPa), and as a result, the target resin fine particles were obtained. The volume-average particle diameter of the obtained resin fine particles was 212 nm, and the coefficient of variation was 19.3%. Further, when evaluation was carried out according to the measurement method of the solvent resistance index, the volume-average particle diameter of the toluene dispersion was 215 nm, the volume-average particle diameter of the toluene dispersion after heating was 228 nm, and the solvent resistance index was 6. When the amount of the residual surfactant in the obtained resin fine particles was measured, it was 0.1 mass%. When the gel fraction of the obtained resin fine particles was measured, it was 96%, and it was confirmed that they had solvent resistance. Further, when a foaming property test was carried out with the obtained resin fine particles, no foaming was observed.

[0071] [Examples 2 to 6, Comparative Examples 1 and 2] Resin fine particles were obtained in the same procedure as in Example 1, except that the production conditions of the resin fine particles were as shown in Table 1. Various physical properties of the obtained resin fine particles are also shown in Table 1.

[0072]

Table 1

[0073] The compound names, etc. and their abbreviations used in the examples and comparative examples are as follows. AR-1025: Anionic reactive surfactant having a polyoxyalkylene chain in the molecule MMA: Methyl methacrylate EGDMA: Ethylene glycol dimethacrylate VA-086: Water-soluble azo polymerization initiator (2,2’-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]) AN-5065: Nonionic reactive surfactant having a polyoxyalkylene chain in the molecule St: Styrene DVB: Divinylbenzene

Claims

1. A method for producing resin microparticles, comprising: a first polymerization step in which a monomer emulsion containing a vinyl-based monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in its molecule is polymerized using a water-soluble polymerization initiator to obtain seed particles; and a second polymerization step in which the monomer emulsion containing a vinyl-based monomer, an aqueous medium, and a reactive surfactant having a polyoxyalkylene chain in its molecule is absorbed into the seed particles and then polymerized.

2. The method for producing resin microparticles according to claim 1, characterized in that the vinyl monomer comprises at least one selected from the group consisting of monofunctional (meth)acrylic monomers, monofunctional aromatic vinyl monomers, polyfunctional (meth)acrylic monomers and polyfunctional aromatic vinyl monomers.

3. 3. The method for producing resin microparticles according to claim 1, further comprising a spray drying step of spray drying the resin microparticles obtained in the second polymerization step under conditions of an inlet temperature of 80 to 220°C and an outlet temperature of 50 to 100°C to obtain aggregates.

4. 4. The method for producing resin fine particles according to claim 3, further comprising a crushing step of crushing the aggregates to disperse the resin fine particles.

5. 5. The method for producing resin fine particles according to claim 1, further comprising a step of classifying the resin fine particles.

6. The method for producing resin fine particles according to any one of claims 1 to 5, which is a method for producing resin fine particles used as an antiblocking agent for a resin film.

7. The method for producing resin fine particles according to any one of claims 1 to 5, which is a method for producing resin fine particles used as an additive for a light diffusion plate.

8. The method for producing resin fine particles according to any one of claims 1 to 5, which is a method for producing resin fine particles used as spacers in electronic devices.

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