JP2020084117A - Composite particles, aqueous coating composition and method for producing the same and coating film - Google Patents

Abstract

To provide functional composite particles which have high productivity and a uniform particle size and have high emulsion stability in an aqueous emulsion.SOLUTION: There are prepared composite particles having a core-shell structure by coating a core part formed of nanoparticles with a shell part containing a vinyl polymer and a nonionic surfactant. The vinyl polymer is connected to the core part via the nonionic surfactant and the ratio of the vinyl polymer is 30 pts.mass or less based on 100 pts.mass of the nanoparticles. The nanoparticles may be colloidal silica. The core part may be colloidal silica. There may be prepared an aqueous coating composition by combination of the composite particles and vinyl polymer particles. A coating film is formed by this composition and the plurality of composite particles may be adhered to the surface of the vinyl polymer particles.SELECTED DRAWING: None

Description

The present invention relates to composite particles that can be used as a functional film-forming component (film-forming component) of an aqueous coating composition such as a paint for indoors, outer walls or roofs, an aqueous coating composition containing the particles, a method for producing the same, and a film.

It has been proposed to combine colloidal silica and an organic polymer to improve the properties of the coating. For example, Japanese Patent No. 3806417 (Patent Document 1) discloses an aqueous coating composition containing dispersed particles as an aqueous coating composition capable of improving the solvent resistance or gel fraction of a coating film, wherein the dispersed particles are: Directly or through a nonionic surfactant, a particle in which a nano-sized particle and a vinyl polymer are bonded, a monomer having a functional group selected from an epoxy group, a hydroxyl group and a hydrolyzable silyl group, and (Meth)acrylic-type monomer, aromatic vinyl-type monomer, vinyl ester-type monomer, a polymer with at least one monomer selected, and the ratio of the monomer having the functional group Is 0.01 to 10 parts by weight with respect to 100 parts by weight of the nano-sized particles, and the dispersed particles have the nonionic surfactant and the nano-sized particles in water at a temperature lower than the cloud point of the nonionic surfactant. In the following, there is disclosed a composition which is particles obtained by mixing a negatively charged nano-sized particle dispersion liquid in (1) and then heating to a temperature not lower than the cloud point to polymerize a vinyl monomer.

However, the dispersed particles contained in this aqueous coating composition are complicated to prepare, have low productivity, and are difficult to control the particle size.

Japanese Patent No. 3806417 (Claim 1)

Therefore, an object of the present invention is to provide a functional composite particle having high productivity, a uniform particle size, and high dispersion stability in an aqueous emulsion, an aqueous coating composition containing the particle, a method for producing the same, and a coating film. To provide.

Another object of the present invention is an aqueous coating composition which is a one-component aqueous composition, has high dispersion stability, and can form a film having high hardness without using a curing agent or a cross-linking agent, and a method for producing the same. And to provide a coating.

Still another object of the present invention is to provide an aqueous coating composition having functionality such as stain resistance, solvent resistance, and heat resistance, and capable of forming a transparent coating, a method for producing the same, and a coating. ..

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, a core portion formed of nanoparticles was found to have a specific ratio of a vinyl polymer and a nonionic interface which is a linking agent between the vinyl polymer and the nanoparticles. It was found that by coating with a shell portion containing an activator, functional composite particles having a uniform particle size and high dispersion stability in an aqueous emulsion and having a core-shell structure can be easily produced, and the present invention has been completed. did.

That is, the composite particle of the present invention has a core-shell structure formed by a core part formed of nanoparticles and a shell part covering the core part and containing a vinyl polymer and a nonionic surfactant. In the composite particle, the vinyl polymer is bonded to the core portion via the nonionic surfactant, and the proportion of the vinyl polymer is 30 parts by mass or less based on 100 parts by mass of the nanoparticles. .. The nanoparticles may be colloidal silica. The average particle size of the composite particles may be 5 to 100 nm, and the polydispersity may be 0.2 or less. The average thickness of the shell portion may be 15 nm or less. The nonionic surfactant may have an ethylenically unsaturated bond and a cloud point of 0 to 80°C. The vinyl polymer may be a copolymer of a C _1-3 alkyl methacrylate and/or aromatic vinyl monomer, a C _1-12 alkyl acrylate, and a carboxyl group-containing vinyl monomer. ..

The present invention includes an aqueous coating composition containing the composite particles and vinyl polymer particles. The ratio of the nanoparticles may be 10 to 1000 parts by mass based on 100 parts by mass of the vinyl polymer in the shell part and the vinyl polymer particles in total. The average particle size of the vinyl polymer particles may be 30 to 500 nm.

The present invention also includes a coating film formed of the above aqueous coating composition, in which a plurality of composite particles are attached to the surface of vinyl polymer particles.

INDUSTRIAL APPLICABILITY In the present invention, a polymerization step of polymerizing a vinyl monomer in the presence of nanoparticles and a nonionic surfactant to prepare composite particles, the obtained composite particles (or a dispersion thereof) and vinyl polymer particles (or And a dispersion step of mixing the dispersion) to prepare an aqueous coating composition.

In the present invention, the core portion formed of nanoparticles is coated with a shell portion containing a nonionic surfactant that is a linking agent between the vinyl polymer and the nanoparticles of a specific ratio of vinyl polymer, A functional composite particle having a core-shell structure having a uniform particle size and high dispersion stability in an aqueous emulsion can be easily produced. Further, when the composite particles and the vinyl polymer particles are combined, the interaction between the composite particles and the vinyl polymer particles is not so strong, so that aggregation can be suppressed, dispersion stability is high, and handleability is excellent. In addition, it is possible to form a coating having high hardness without using a curing agent or a crosslinking agent in spite of being a one-component aqueous composition. Furthermore, since a coating having functionality such as stain resistance, solvent resistance, and heat resistance can be formed, and the obtained coating is also excellent in transparency, the range of applicable applications is wide.

FIG. 1 is a graph showing the particle size distribution of the thin soft acrylic-coated silica nanoparticles and colloidal silica obtained in Example 1 by dynamic light scattering (DLS) analysis. FIG. 2 is an atomic force microscope (AFM) photograph of the thin soft acrylic-coated silica nanoparticles obtained in Example 1. FIG. 3 is an electron micrograph comparing the thin soft acrylic-coated silica nanoparticles obtained in Example 1 with colloidal silica to which only a nonionic surfactant is attached. FIG. 4 is an IR spectrum comparing the thin-walled soft acrylic-coated silica nanoparticles obtained in Example 1 with other colloidal silica. FIG. 5 is a graph showing the particle size distribution of the particles contained in the mixed emulsion obtained in Example 2 and other particles by DLS analysis. FIG. 6 is a photograph for evaluating the transparency of the coating films of the emulsions obtained in Examples 1-2, Comparative Examples 1-2 and Reference Examples 4-5. FIG. 7 is a scanning electron microscope (SEM) photograph of the coating film surfaces of the emulsions obtained in Example 2, Comparative Example 2 and Reference Example 5. FIG. 8 is an AFM photograph of cast films of the emulsions obtained in Example 2, Comparative Example 2 and Reference Examples 3 and 5. FIG. 9 is an AFM photograph of the phase mode of the coating films of the emulsions obtained in Example 2, Comparative Example 2 and Reference Example 5. FIG. 10 is a photograph for evaluating the transparency of the coating films of the emulsions obtained in Example 5, Comparative Example 5 and Reference Example 9.

[Composite particles]
The composite particle of the present invention has a core-shell structure composed of a core part formed of nanoparticles and a shell part containing a vinyl polymer and a nonionic surfactant. This composite particle has a narrow particle size distribution because the surface of nanoparticles having functionality (functionality that improves hardness, stain resistance, solvent resistance, heat resistance, etc.) is covered with a thin shell. It is useful as a functional film-forming component of an aqueous coating composition.

(Nano particles)
The nanoparticles forming the core may be any functional particles for imparting functionality to the coating film formed of the aqueous coating composition, and may be either inorganic particles or organic particles.

As the inorganic particles, silica (colloidal silica, mesoporous silica, etc.); metal oxide (for example, alumina, titanium oxide (rutile type, anatase type, etc.), zinc oxide, zirconium oxide, copper oxide, iron oxide, cobalt oxide, etc. ); Metal (for example, gold, silver, copper, palladium, platinum, nickel, cobalt, aluminum or alloys thereof); Magnetic substance (for example, ferrite such as Fe ₃ O ₄ ); Zeolite; Hydroxyapatite; Carbon material (For example, fullerene, carbon nanotube, graphene (single-layer graphene, multilayer graphene, graphene oxide, etc.), diamond (nanodiamond, etc.), activated carbon (granular activated carbon, powdered activated carbon, etc.), carbon black, etc.; Inorganic pigment (for example, White pigments such as lithopone; Red pigments such as cerium sulfide; Orange pigments such as molybdate orange; Yellow pigments such as complex oxide yellow; Green pigments such as complex oxide green; Blue pigments such as navy blue; Purple such as manganese violet Pigments; black pigments such as complex oxide black; extender pigments such as calcium carbonate). These inorganic particles can be used alone or in combination of two or more kinds.

As the organic particles, polymer particles (for example, silicone resin, crosslinked polyolefin resin, crosslinked polymethylmethacrylate resin, melamine resin, crosslinked polystyrene resin, etc.), organic pigment [for example, azo pigment (for example, permanent red) Red pigments such as brilliant carmine; Orange pigments such as benzidine orange; Yellow pigments such as Hansa yellow and Benzidine yellow); Phthalocyanine pigments (for example, blue pigments such as phthalocyanine blue; green pigments such as phthalocyanine green); Lake pigments ( For example, red pigments such as rhodamine lake; blue pigments such as methyl violet lake; green pigments such as final yellow green); isoindolinone/isoindoline pigments; quinacridone pigments; dioxazine pigments; diketopyrrolopyrrole pigments; quinophthalone pigments; Vat dye-based pigments (for example, perylene/perinone-based, thioindigo-based, anthraquinone-based, etc.)] and the like. These organic particles can be used alone or in combination of two or more.

Among these, inorganic particles such as silica are preferable, and colloidal silica (colloidal silica) is particularly preferable.

Colloidal silica can also be prepared and used by a sol-gel method, and commercially available products (for example, "Adelite AT-40" and "Adelite AT-50" manufactured by ADEKA Corporation, "Snowtex" manufactured by Nissan Kagaku Co., Ltd.). 40", "Snowtex 50", etc.) can also be used. The main component of colloidal silica is silicon dioxide, and alumina, sodium aluminate or the like may be contained as a minor component. The colloidal silica may contain an inorganic base (sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, etc.) or an organic base (amines such as trimethylamine, triethylamine, etc.) as a stabilizer. Colloidal silica is usually negatively charged in water.

The shape of the nanoparticles is not particularly limited, and may be spherical, elliptic spherical, polyhedral [eg, cubic, rectangular parallelepiped, tetrahedral (pyramid), etc.], flat (plate-shaped, scale-like or flaky), It may be layered, rod-shaped or needle-shaped. The particles may also have a porous shape. Of these, spherical is preferred.

The average particle size of nanoparticles (particularly colloidal silica) (hydrodynamic diameter determined by cumulant method by dynamic light scattering: unit is nm) is, for example, 3 to 120 nm, preferably 10 to 100 nm, more preferably 20. ˜70 nm, most preferably about 30 to 50 nm. If the particle size of the nanoparticles is too small, the functionality due to the nanoparticles may not be expressed, or it may be difficult to coat with the vinyl polymer. On the contrary, if it is too large, the dispersion stability after coating decreases. There is a risk.

In the present specification and claims, the average particle size of nanoparticles can be measured based on the cumulant method using a dynamic light scattering photometer, and in detail, by the method described in Examples described later. Can be measured.

In addition, these nanoparticles may be subjected to surface treatment (for example, physical treatment such as plasma treatment, chemical treatment with a treatment agent such as a silane coupling agent).

(Nonionic surfactant)
The nonionic surfactant is contained in the shell part, but is present at the interface with the core part as a linking group between the nanoparticles forming the core part and the vinyl polymer. Nanoparticles such as colloidal silica are usually negatively charged in aqueous media. Therefore, after mixing the nonionic surfactant and the nano-sized particle dispersion liquid at a temperature below the cloud point, the nonionic surfactant is adsorbed and deposited on the surface of the nanoparticles by bringing the temperature to the cloud point or higher, so that the vinyl monomer It provides a place for the polymerization of the monomers. The surface of the nanoparticles can be made hydrophobic by the adsorption of the nonionic surfactant.

The cloud point of the nonionic surfactant means a temperature at which the dispersion system becomes cloudy during the temperature rising process in a system in which nanoparticles are dispersed in an aqueous medium in the presence of the nonionic surfactant. The cloud point can be measured under each reaction condition because it is affected by the concentration of the nonionic surfactant and the electrolyte. The cloud point of the nonionic surfactant is, for example, 0 to 80°C, preferably 10 to 70°C, more preferably about 20 to 60°C.

Nonionic surfactants (dispersants or dispersion stabilizers) include proteins (gelatin, lecithin, etc.), sugar derivatives (agar, starch derivatives, etc.), cellulose derivatives (hydroxyethyl cellulose, etc.), fatty acid esters of polyhydric alcohols [ethylene Glycol monofatty acid ester (eg, oleic acid monoester, stearic acid monoester, etc.), polyethylene glycol monofatty acid ester, propylene glycol monofatty acid ester, glycerin monofatty acid ester (stearic acid monoglyceride, etc.), glycerin difatty acid ester, sucrose fatty acid Ester, sorbitan fatty acid ester (trade name: Span), etc.], vinyl alcohol polymer (polyvinyl alcohol, polyvinyl alcohol modified with a long-chain alkyl group at the end, etc.), polyoxyalkylene (polyoxyethylene, polyoxypropylene) or its derivative [poly Oxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, alkylene oxide adduct of the above fatty acid ester (for example, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sucrose fatty acid ester, polyoxyethylene sorbitan aliphatic ester (trade name Tween) , Polyoxyethylene alkylphenyl ether, etc.)] and the like. As the dispersant, a graft polymer, a block polymer (polyoxyethylene-polyoxypropylene block copolymer, etc.) or a macromer may be used. These nonionic surfactants are capable of polymerizing a vinyl-based monomer for forming a vinyl polymer, and thus have an ethylenic unsaturated bond (such as vinyl group, allyl group, isopropenyl group, (meth)acryloyl group) ( It may be a compound having at least one polymerizable unsaturated bond) introduced therein. These nonionic surfactants can be used alone or in combination of two or more.

Preferred nonionic surfactants include polyoxyethylene alkyl ethers [eg, polyoxyethylene lauryl ether (“Emulgen 108 (cloud point 40° C.)” manufactured by Kao Corporation)), polyoxyethylene stearyl ether (manufactured by Kao Corporation). “Emulgen 409P (cloud point 55° C.)”, etc., polyoxyethylene C _6-20 alkyl ether], polyoxyethylene alkylphenyl ether [eg, polyoxyethylene octyl phenyl ether, polyoxyethylene lauryl phenyl ether, polyoxyethylene] Polyoxyethylene C _6-20 alkyl phenyl ether such as nonyl phenyl ether (“Emulgen 909 (cloud point 40° C.)” manufactured by Kao Corporation)], polyoxyethylene sucrose C _12-20 fatty acid ester, polyoxyethylene Sorbitan C _12-20 fatty acid ester, polyoxyalkylene block copolymer [for example, polyoxyethylene-polyoxypropylene block copolymer ("Pluronic L61 (cloud point 24°C)" manufactured by ADEKA, "Pluronic L-64" (Cloud point 58° C.)”), etc.], polyoxyethylene C _6-20 alkylphenyl ether having at least one ethylenically unsaturated group such as an allyl group [eg, 1-allyloxymethyl-2-nonylphenyloxyethanol] Ethylene oxide adduct (“ADEKA REASOAP (registered trademark) NE-10 (clouding point 40° C.)” manufactured by ADEKA Co., Ltd.) and the like] and the like.

The hydrophilic-lipophilic balance (HLB) of the nonionic surfactant can be selected in a wide range and is, for example, 1 to 30, preferably 3 to 25, more preferably 5 to 20, most preferably 7 to 16.

The proportion of the nonionic surfactant can be selected from the range of about 0.01 to 20 parts by mass with respect to 100 parts by mass of the nanoparticles, and for example, 0.1 to 15 parts by mass, preferably 0.5 to 10 parts by mass, and further It is preferably 1 to 5 parts by mass, and most preferably 2 to 4 parts by mass. When the nanoparticles are colloidal silica, the proportion of the nonionic surfactant is, for example, 0.05 to 15 parts by mass, preferably 0.2 to 10 parts by mass, relative to 100 parts by mass of the silica component (SiO ₂ alone). , More preferably 0.5 to 7 parts by mass, most preferably 1 to 5 parts by mass. If the proportion of the nonionic surfactant is too low, the shell portion may not be sufficiently formed, and if it is too high, the productivity of the composite particles may be reduced.

(Vinyl polymer)
The vinyl polymer forms a shell portion that covers the core portion via the nonionic surfactant, and in the present invention, since the ratio of the vinyl polymer to the nanoparticles is small, the shell portion is the surface of the core portion. Can be formed as a thin film.

The vinyl polymer is a homopolymer or copolymer of a vinyl monomer having an ethylenically unsaturated bond (vinyl monomer).

The vinyl monomer only needs to contain at least one ethylenically unsaturated bond in the molecule, and a vinyl monomer having one ethylenically unsaturated bond in the molecule (sometimes referred to as a monofunctional vinyl monomer. Yes) and vinyl monomers having two or more ethylenically unsaturated bonds in the molecule (sometimes referred to as polyfunctional vinyl monomers).

Typical monofunctional vinyl monomers are (meth)acrylic monomers; aromatic vinyl monomers; carboxyl group-containing vinyl monomers; vinyl ester monomers such as vinyl acetate; vinyl. Sulfonic acid group-containing vinyl monomers such as sulfonic acid; unsaturated polycarboxylic acid derivative monomers such as dimethyl maleate and N-phenylmaleimide; N-vinyl polycarboxylic acid imides such as N-vinylsuccinimide Heterocyclic vinyl monomers such as N-vinylpyrrolidone; N-vinylamide monomers such as N-vinylformamide; halogen-containing vinyl monomers such as vinyl chloride; methyl vinyl ether and the like Vinyl alkyl ether type monomers; olefin type monomers such as ethylene.

Among these monofunctional vinyl monomers, it is preferable to include a (meth)acrylic monomer, an aromatic vinyl monomer, and a carboxyl group-containing vinyl monomer.

Examples of the (meth)acrylic monomer include alkyl(meth)acrylates [eg, methyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, t-butyl(meth)acrylate, n-hexyl. (Meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cetyl (meth)acrylate, n-octadecyl (meth)acrylate and the like linear or branched C _1-20 alkyl (meth ) Acrylate, etc.]; Cycloalkyl(meth)acrylate [eg, C _5-10 cycloalkyl(meth)acrylate, such as cyclohexyl(meth)acrylate, cyclopentyl(meth)acrylate]; Aryl(meth)acrylate [eg, phenyl( _C6-14 aryl (meth)acrylates such as (meth)acrylates and naphthyl (meth)acrylates; aralkyl (meth)acrylates [for example, _C6-14 aryl- such as benzyl (meth)acrylate, phenethyl (meth)acrylates) C _1-6 alkyl (meth)acrylate and the like]; polycyclic (meth)acrylate [for example, C _7-15 such as 2-isobornyl (meth)acrylate and 2-norbornylmethyl (meth)acrylate (2 to 3 ) Cyclic (meth) acrylate etc.]; Hydroxyl group-containing (meth) acrylate [eg hydroxy C _1-4 alkyl (meth) acrylate such as hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate]; Alkoxy group- or phenoxy group-containing (meth)acrylate [for example, (poly)C _1-6 alkoxy C _2-6 alkyl(meth)acrylate such as 2-methoxyethyl (meth)acrylate, ethylcarbitol (meth)acrylate, phenoxy) Phenoxy C _2-6 alkyl (meth)acrylate such as ethyl (meth)acrylate; epoxy group-containing (meth)acrylate [eg, glycidyl (meth)acrylate]; halogen-containing (meth)acrylate [eg, 2,2 , 2-trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate and other haloalkyl C _1-12 (meth)acrylates and the like]; (meth)acrylamides [eg, ( (Meth)acrylamide ; N- methyl (meth) acrylamide, N-t-butyl (meth) _{N-C 1-4} alkyl (meth) acrylamides such as acrylamide; N, N- dimethyl (meth) N, such as acrylamide, N- di _{C 1 -4} alkyl (meth)acrylamide; N-substituted (meth)acrylamide such as 2-(meth)acrylamide-2-methylpropanesulfonic acid, diacetone (meth)acrylamide, (meth)acryloylmorpholine, N-methylol (meth)acrylamide, etc. ]; alkylaminoalkyl(meth)acrylate [eg (mono or di)C _1-4 alkylamino C _1-4 alkyl(meth)acrylate such as dimethylaminoethyl(meth)acrylate]; vinyl cyanide (eg , (Meth)acrylonitrile, etc.) and the like.

Examples of the aromatic vinyl-based monomer include styrene, p-chlorostyrene, t-butylstyrene, α-methylstyrene, vinyltoluene and the like.

Examples of the carboxyl group-containing vinyl monomer include (meth)acrylic acid, itaconic acid, maleic acid and fumaric acid.

The vinyl monomer having two or more ethylenic unsaturated bonds in the molecule (polyfunctional vinyl monomer) includes a polyfunctional (meth)acrylic monomer; a polyfunctional aromatic vinyl monomer. And the like; diene-based monomers such as butadiene; polyfunctional vinyl ester-based monomers; polyfunctional vinyl ether-based monomers and the like.

Among these polyfunctional vinyl monomers, polyfunctional (meth)acrylic monomers and polyfunctional aromatic vinyl monomers are preferable.

Examples of the polyfunctional (meth)acrylic monomer include (poly)alkylene glycol di(meth)acrylate [eg, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth ) Acrylate, (poly) _C2-6 alkylene glycol di(meth)acrylate such as 1,4-butanediol di(meth)acrylate, etc.]; Di(meth)acrylate of alicyclic diol [eg, 1,4- Di(meth)acrylate of cyclohesane dimethanol (or its (poly)C _2-4 alkylene oxide adduct); di(meth)acrylate of aromatic diol (for example, bisphenol A (or its (poly)C ₂ ). _-4 alkylene oxide adduct) di(meth)acrylate, etc.); polyfunctional (meth)acrylamides [eg, N,N′-hexamethylenebis(meth)acrylamide, N,N′-methylenebis(meth)acrylamide, etc. N,N′-(mono to hexa)methylenebis(meth)acrylamide, etc.]; (Meth)acrylate having an ethylenically unsaturated bond-containing group [eg, allyl (meth)acrylate, 5-norbornen-2-yl-methyl (Meth)acrylate, etc.; di(meth)acrylate of polyol [eg, glycerin di(meth)acrylate, etc.]; polyfunctional monomer having three or more (meth)acryloyl groups [eg, glycerin tri(meth)acrylate] Acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, 1,3,5-tri(meth)acryloylhexahydro-s-triazine, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta( (Meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc.] and the like.

Examples of the polyfunctional aromatic vinyl-based monomer include divinylbenzene and the like.

These polyfunctional vinyl monomers may be used to crosslink vinyl polymers. Not only the ethylenically unsaturated bond of the polyfunctional vinyl monomer, but also the vinyl monomer having a reactive functional group such as an epoxy group or a carboxyl group is used, vinyl is used by these functional groups. The polymer may be crosslinked.

These monofunctional and polyfunctional vinyl monomers can be used alone or in combination of two or more. Examples of preferable monofunctional vinyl monomers include (meth)acrylic monomers, aromatic vinyl monomers, vinyl ester monomers, and carboxyl group-containing vinyl monomers. It is preferable to contain a (meth)acrylic monomer. Further, preferred polyfunctional vinyl monomers include polyfunctional (meth)acrylic monomers such as ethylene glycol di(meth)acrylate and polyfunctional aromatic vinyl monomers such as divinylbenzene.

Further, the vinyl polymer may be a homopolymer or a copolymer, and when it is a copolymer, it may be a random copolymer, a block copolymer, an alternating copolymer or a graft copolymer. Good. Further, the shell may include two or more different homo- or copolymers.

The combination (composition) of vinyl monomers in the copolymer can be selected according to the application and is not particularly limited, but typically (a) C _1-3 alkyl methacrylate and/or aromatic vinyl-based monomer In many cases, the polymer, (b) C _1-12 alkyl acrylate, and (c) carboxyl group-containing vinyl monomer.

(A) C _1-3 alkyl methacrylate and/or aromatic vinyl-based monomer (may be referred to as hard component (a)) is a relatively hard component, and affects hardness and heat resistance of the composite particles. give. The glass transition temperature (Tg) of the vinyl monomer homopolymer of the hard component (a) is, for example, 50° C. or higher (eg 50 to 150° C.), preferably 70° C. or higher (eg 70 to 130° C.), and more preferably It may be about 90°C or higher (for example, 90 to 110°C). The glass transition temperature can be measured with a differential scanning calorimeter (DSC) or the like. Typical hard components (a) include methyl methacrylate, ethyl methacrylate, i-propyl methacrylate, styrene, vinyltoluene and the like. These hard components (a) may be used alone or in combination of two or more. Of these hard components (a), methyl methacrylate and styrene are preferable, and methyl methacrylate is particularly preferable.

(B) C _1-12 alkyl acrylate (sometimes referred to as the soft component (b)) is a relatively soft component, and in the composite particles, it exhibits adhesiveness to an adherend, low temperature resistance and the like. The glass transition temperature (Tg) of the vinyl monomer homopolymer of the soft component (b) is, for example, 50° C. or lower (eg, −100 to 50° C.), preferably 30° C. or lower (eg, −70 to 30° C.), and further preferably May be about 0° C. or lower (for example, −55 to 0° C.). Typical soft components (b) include ethyl acrylate, butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate and the like. These soft components (b) can be used alone or in combination of two or more. Among these soft components (b), C _2-10 alkyl acrylates such as butyl acrylate, n-octyl acrylate and 2-ethylhexyl acrylate are preferable, and C _4-8 alkyl acrylates such as butyl acrylate are particularly preferable.

The proportion of the soft component (b) can be selected from the range of about 30 to 300 parts by mass relative to 100 parts by mass of the hard component (a), and is, for example, 50 to 250 parts by mass, preferably 60 to 200 parts by mass, and more preferably 70 to 150 parts by mass, most preferably 80 to 100 parts by mass. When the amount of the soft component (b) is too large, the hardness and heat resistance of the composite particles are likely to decrease, and when it is too small, the adhesiveness of the shell portion may be decreased.

The (c) carboxyl group-containing vinyl monomer (sometimes referred to as a carboxyl group-containing component (c)) improves the dispersibility of the composite particles and exhibits adhesiveness with the adherend in the shell portion. Typical examples of the carboxyl group-containing component (c) include (meth)acrylic acid, itaconic acid, maleic acid and the like. These carboxyl group-containing components (c) can be used alone or in combination of two or more. Among these carboxyl group-containing components (c), for example, (meth)acrylic acid is preferable, and methacrylic acid is particularly preferable.

The proportion of the carboxyl group-containing component (c) is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass, based on 100 parts by mass of the total of the hard component (a) and the soft component (b). It is more preferably 0.1 to 2 parts by mass, and most preferably about 0.3 to 1 part by mass. If the amount of the carboxyl group-containing component (c) is too large, the dispersibility or water resistance (moisture resistance) of the composite particles tends to decrease, while if it is too small, the adhesion of the composite particles may decrease.

The glass transition temperature (Tg) of the vinyl polymer can be selected from the range of about -50°C to 100°C, for example, -30°C to 50°C, preferably -20°C to 30°C, more preferably -10°C to 25°C. , And most preferably about 0 to 15°C. If the glass transition temperature is too low, the mechanical properties may deteriorate, and if it is too high, the adhesiveness may decrease.

The ratio of the vinyl polymer may be 30 parts by mass or less (for example, 0.1 to 30 parts by mass), for example, 0.5 to 20 parts by mass, and preferably 1 to 15 parts by mass with respect to 100 parts by mass of the nanoparticles. Parts by mass, more preferably 1.5 to 10 parts by mass, most preferably about 2 to 7 parts by mass. When the nanoparticles are colloidal silica, the proportion of the vinyl polymer may be, for example, 50 parts by mass or less (for example, 0.3 to 50 parts by mass) with respect to 100 parts by mass of the silica component (SiO ₂ alone). Well, for example, 1 to 30 parts by mass, preferably 2 to 20 parts by mass, more preferably 3 to 10 parts by mass, and most preferably about 4 to 8 parts by mass. If the proportion of the vinyl polymer is too low, the composite particles tend to aggregate in the aqueous coating composition, while if it is too high, it becomes difficult to make the particle diameter of the composite particles uniform, and the functionality of the nanoparticles is improved. It may also be difficult to express.

In the present specification and claims, the ratio of the vinyl polymer to the nanoparticles and the silica component can be calculated based on the total amount of the vinyl monomer used as the raw material.

The total proportion of the vinyl polymer and nonion in the shell part may be 50% by mass or more, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and most preferably 100% by mass. Mass% (only vinyl polymer and nonionic surfactant).

(Characteristics of composite particles)
Since the composite particles have a thin shell portion, the particle size is highly uniform, and the functionality of the nanoparticles is easily exhibited. The average thickness of the shell portion may be 15 nm or less (for example, 1 to 15 nm), for example, 2 to 12 nm, preferably 3 to 10 nm, more preferably 4 to 8 nm, and most preferably 5 to 7 nm.

In the present specification and claims, the average thickness of the shell portion may be measured by observation with a transmission electron microscope (TEM), and the average particle diameter of the composite particles may be changed to the average particle diameter of the nanoparticles. It can also be obtained by reducing.

The average particle size (volume average primary particle size) of the composite particles is, for example, 5 to 100 nm, preferably 10 to 80 nm, more preferably 30 to 70 nm, and most preferably about 50 to 60 nm. If the average particle size of the composite particles is too small, the composite particles tend to aggregate in the aqueous coating composition, and if too large, the mechanical properties of the coating film may deteriorate.

The composite particles of the present invention have high uniformity in particle size, and the polydispersity of the composite particles (the polydispersity of the hydrodynamic diameter evaluated by the polydispersity index obtained by the cumulant method by dynamic light scattering) is 0. 0.2 or less (particularly 0.14 or less), for example 0.01 to 0.15, preferably 0.02 to 0.14, more preferably 0.03 to 0.13, and most preferably 0. .05 to 0.125.

In the present specification and claims, the average particle size and polydispersity (particle size distribution) of the composite particles can be measured based on the cumulant method using a dynamic light scattering photometer, and in detail, It can be measured by the method described in Examples below.

The shape of the composite particles is the same as the shape of the nanoparticles, and is preferably spherical.

[Aqueous coating composition]
The aqueous coating composition of the present invention contains the composite particles and vinyl polymer particles. As the vinyl polymer (second vinyl polymer) constituting the vinyl polymer particles, the vinyl polymer (first vinyl polymer) exemplified as the vinyl polymer constituting the shell part of the composite particles is used. it can. The second vinyl polymer can be selected from the vinyl polymers exemplified as the first vinyl polymer according to the intended coating properties, and like the first vinyl polymer, the second vinyl polymer can be used as the hard component (a). The proportion of the soft component (b) and the carboxyl group-containing component (c) may be adjusted to control the dispersibility in the aqueous coating composition and the mechanical properties of the coating.

The glass transition temperature (Tg) of the vinyl polymer constituting the vinyl polymer particles can be selected from the range of about -50°C to 100°C, and the vinyl constituting the shell portion of the composite particles can be selected from the viewpoint of adhesiveness with the composite particles. The temperature may be the same as that of the polymer, or may be higher than that of the vinyl polymer forming the shell portion of the composite particles (for example, 20 to 100°C, particularly 30 to 80°C).

The vinyl polymer particles may have an average particle size (hydrodynamic diameter determined by cumulant method by dynamic light scattering: unit is nm) of 30 nm or more, for example, 30 to 500 nm, preferably 50 to 300 nm, and further preferably Is 80 to 200 nm, most preferably 100 to 150 nm. If the particle size of the vinyl polymer particles is too small, the coating becomes opaque due to the aggregation of nanoparticles, and precipitation easily occurs.

In the present specification and claims, the average particle size of the vinyl polymer particles can be measured based on the cumulant method using a dynamic light scattering photometer, and in detail, described in Examples described later. It can be measured by the method.

The ratio of the vinyl polymer particles is such that the total amount of the vinyl polymer particles and the first vinyl polymer of the composite particles with respect to the nanoparticles (particularly, the silica component when the nanoparticles are colloidal silica) as the core portion (first The total amount of the vinyl polymer and the second vinyl polymer may be controlled from the viewpoint of adjusting the ratio. That is, in the entire aqueous coating composition, the proportion of nanoparticles is, for example, 10 to 1000 parts by mass, preferably 100 parts by mass with respect to 100 parts by mass of the vinyl polymer (the total of the first vinyl polymer and the second vinyl polymer). Is 20 to 750 parts by mass, more preferably 30 to 500 parts by mass, and most preferably 50 to 350 parts by mass. When the nanoparticles are colloidal silica, the ratio of the silica component (SiO ₂ alone) in the entire aqueous coating composition is 100% vinyl polymer (total of the first vinyl polymer and the second vinyl polymer). The amount is, for example, 5 to 500 parts by mass, preferably 10 to 400 parts by mass, more preferably 30 to 300 parts by mass, more preferably 50 to 250 parts by mass, and most preferably 100 to 180 parts by mass. If the proportion of the vinyl polymer is too low, the mechanical properties such as transparency and flexibility of the coating may be deteriorated. On the contrary, if the proportion is too high, the functionality of nanoparticles such as hardness of the coating may not be expressed. is there.

The aqueous coating composition of the present invention may contain an aqueous solvent in addition to the composite particles and the vinyl polymer particles. Examples of the aqueous solvent include water; lower alcohols such as methanol, ethanol, propanol, and isopropanol; ketones such as acetone. These aqueous solvents can be used alone or in combination of two or more. Of these, water is commonly used.

The solid content concentration of the aqueous coating composition can be selected according to the application etc., and is, for example, 10 to 70% by mass, preferably 30 to 60% by mass, more preferably 35 to 55% by mass, and most preferably 40 to 50% by mass. Is. The solid content concentration may be the concentration of the total amount of the composite fine particles and the vinyl polymer particles.

The aqueous coating composition of the present invention is a conventional additive commonly used in aqueous coating agents, for example, a dispersant, a wetting agent, a thickener, a plasticizer, a surface modifier, an antifoaming agent, a viscosity modifier, a difficult additive. A flame retardant, an antistatic agent, a water-soluble organic solvent, etc. can be used. Further, the aqueous coating composition may optionally contain a pigment, a water-soluble or water-dispersible binder resin, a crosslinking agent, a curing agent, a crosslinking or curing auxiliary agent, and the like.

As the pigment, pigments exemplified as the nanoparticles (for example, coloring pigments such as titanium dioxide and phthalocyanine blue, extender pigments such as calcium carbonate and barium sulfate) may be used, and aluminum powder, mica flakes and the like may be used. A glittering agent or the like may be used. The weight concentration (PWC) of the pigment in the coating composition is usually 1 to 70% by mass, preferably 10 to 65% by mass, and more preferably about 20 to 60% by mass in terms of solid content. If the solid content concentration is too low, the hiding property may be lowered, and if it is too high, the gloss of the coating film may be lowered, or water resistance and mechanical strength may be lowered as the viscosity increases.

The aqueous coating composition of the present invention is usually in the form of an emulsion. In the emulsion, the interaction between the composite particles and the vinyl polymer particles is not so strong even when the first vinyl polymer of the composite particles and the second vinyl polymer of the vinyl polymer particles are the same. Therefore, the aqueous coating composition of the present invention has excellent emulsion stability.

Although the aqueous coating composition of the present invention is a one-component aqueous composition, it can form a film having excellent mechanical properties simply by drying without using a curing agent or a crosslinking agent. As described above, in the emulsion, the composite particles and the vinyl polymer particles are stably dispersed without agglomerating, but when the aqueous solvent is gradually volatilized by drying, the composite particles have a larger particle size. Gradually gather around the vinyl polymer particles and form a composite by the interaction between the composite particles and the vinyl polymer particles. In the coating film, a composite in which a plurality of composite particles are adhered to the surface of the vinyl polymer particles is thus formed by drying, so that the mechanical properties of the coating film are maintained even if the particles contain functional particles. At the same time, the mechanical properties of the coating can be improved.

[Method for producing aqueous coating composition]
The aqueous coating composition of the present invention comprises a polymerization step of preparing a composite particle by polymerizing a vinyl monomer in the presence of nanoparticles and a nonionic surfactant, the resulting composite particle (or a dispersion thereof, particularly an emulsion). And vinyl polymer particles (or a dispersion thereof, especially an emulsion) may be mixed to prepare an aqueous coating composition.

In the polymerization step, the polymerization method is not particularly limited as long as it can form a thin shell portion, but from the viewpoint of efficiently forming a core-shell structure, it is preferable to carry out by emulsion polymerization, in the presence of a nonionic surfactant, nano It is particularly preferable that the particles are obtained by polymerizing a vinyl monomer at a temperature equal to or higher than the cloud point of the nonionic surfactant in a system in which particles are dispersed in an aqueous solvent. In particular, after mixing the nonionic surfactant and the nanoparticle dispersion liquid at a temperature below the cloud point, the temperature is raised to a temperature above the cloud point to deposit the nonionic surfactant on the surface of the nanoparticles and to remove the vinyl monomer. By polymerizing, composite particles in which nanoparticles and a vinyl polymer are effectively bound can be obtained.

As the nonionic surfactant, a plurality of types of nonionic surfactants may be used in combination, but it is preferable to use a single nonionic surfactant from the viewpoint of simplicity and the like. Further, in the present invention, the nonionic surfactant may be present before the initiation of the polymerization of the vinyl polymer to be deposited (bonded) on the surface of the nanoparticles as the core portion, and may be added after the initiation. From the viewpoint of simplicity, it is preferable not to add the nonionic surfactant after the initiation of the polymerization. Also, from the viewpoint of forming a thin shell portion, it is preferable to add the nonionic surfactant in the above-mentioned ratio to the nanoparticles and the vinyl polymer before the polymerization of the vinyl polymer.

The polymerization temperature may be, for example, 20 to 110°C, preferably 30 to 100°C, more preferably 60 to 100°C, and especially about 70 to 90°C.

In the emulsion polymerization, the vinyl monomer may be added all at once to the reaction system (aqueous dispersion of the core portion to which the nonionic surfactant is attached), or may be added stepwise or continuously.

Further, the anionic surfactant may be added after the vinyl monomer is polymerized to form the stabilized seed-like composite particles after the nonionic surfactant is uniformly attached or deposited on the nanoparticles.

In the production method of the present invention, from the viewpoint of efficiently forming the core-shell structure, the concentration of the nonionic surfactant is equal to or higher than the critical micelle concentration (CMC), and the deposition or adhesion of the nonionic surfactant on the nanoparticles. However, it is preferable that the amount is equal to or more than the saturated adsorption amount.

In the present specification, the critical micelle concentration (CMC) means the minimum concentration of micelles produced in the aqueous phase when a surfactant is added in the presence of inorganic or organic particles. This critical micelle concentration changes depending on the content of nanoparticles and the electrolyte concentration, but from the relationship between the surfactant concentration and the surface tension, the concentration at which the surface tension becomes a minimum value is used as an index of the apparent critical micelle concentration. be able to. For example, the presence of these components increases the critical micelle concentration of the nonionic surfactant as compared to the absence of nanoparticles or electrolytes. The saturated adsorption amount can be measured in advance by a conventional method. In the case of nanoparticles having an average particle diameter of 50 nm or less, it is often about 0.5 to 5 parts by mass (for example, 1 to 2 parts by mass) with respect to 100 parts by mass of the nanoparticles.

As the polymerization initiator, for example, peroxides (eg hydrogen peroxide), persulfates (eg potassium persulfate, ammonium persulfate), aqueous azo compounds and redox polymerization initiators can be used. The amount of the polymerization initiator used is, for example, 0.01 to 10 parts by mass, preferably 0.1 to 8 parts by mass, and more preferably 1 to 7 parts by mass with respect to 100 parts by mass of the vinyl monomer. Good.

Chain transfer agents for adjusting the molecular weight of vinyl polymers, such as organic peroxides soluble in vinyl monomers, organic azo compounds, halogenated hydrocarbons (carbon tetrachloride, etc.), mercaptans, thiols, etc. May be used. The amount of the chain transfer agent used may be, for example, 5% by mass or less based on the vinyl monomer.

If necessary, in order to enhance the dispersion stability of the nanoparticles, a pH adjuster [eg, acid (sulfuric acid, hydrochloric acid, etc.), ammonia, amine, etc.] may be added to the emulsion after the polymerization process or reaction. Good. The pH of the reaction system or emulsion may be adjusted to about pH 7 to 9 (for example, pH 7.5 to 8.5).

In the mixing step, the emulsion containing the obtained composite particles and the emulsion containing the vinyl polymer particles prepared by a conventional method are mixed by a conventional method to obtain an aqueous coating composition.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The raw materials used and the evaluation method are as follows.

[Raw materials used]
Colloidal silica (CS-50): "ADEDELITE (registered trademark) AT-50" manufactured by ADEKA Corporation, silica content 50 mass%
Nonionic surfactant (NIS): "ADEKA REASOAP (registered trademark) NE-10" manufactured by ADEKA Corporation, poly(ethylene glycol) mono-[1-(allyloxy)-3-(4-nonylphenoxy)-2- Propyl] ether, ethylene oxide addition mole number 10, cloud point 40°C, HLB 15.3
Non-reactive anionic surfactant: "Perex (registered trademark) SS-H" manufactured by Kao Corporation
Reactive anionic surfactant: "Hitenol (registered trademark) KH-10" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.
Potassium persulfate (KPS): potassium peroxodisulfate, industrial n-butyl acrylate (n-BA): industrial methyl methacrylate (MMA): industrial methacrylic acid (MAA): industrial.

[Scanning electron microscope (SEM) observation]
Samples were gold coated on an aluminum pedestal prior to observation. The coated sample was observed by operating SEM (“VE-7800” manufactured by Keyence Corporation) at an acceleration voltage of 10 kV.

[Scanning transmission electron microscope (STEM) observation]
A diluted sample of the emulsion, which is a sample, was poured into a Cu mesh (Oken Shoji Co., Ltd.) having a grid pitch of 150 μm, dried and evacuated. The obtained sample was observed by operating STEM (“HD-2700” manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 200 kV.

[Dynamic Light Scattering (DLS) Analysis]
The scattering angle was fixed at 90° using a dynamic light scattering photometer ("Photol (registered trademark) ELS-8000" manufactured by Otsuka Electronics Co., Ltd.), and a He/Ne laser (632.8 nm) was applied to the sample at 25°C. ) Was irradiated and the light scattering intensity was measured. The data was analyzed by the cumulant method, and the particle size and polydispersity based on the average value of 3 or more times (the polydispersity of the hydrodynamic diameter evaluated by the polydispersity index obtained by the cumulant method by dynamic light scattering) I asked.

[Fourier transform infrared spectrophotometer (FT-IR) analysis]
Samples, using FT-IR (Perkin Elmer Co., Ltd., "Spectrum (TM) GX Spectrophotometer"), by potassium bromide tablet method and analyzed in a range of 4000～450Cm ^-1 at a resolution ^{4 cm -1.}

[Atomic force microscope (AFM) observation]
The sample was observed in a dynamic force mode (tapping mode) using an atomic force microscope AFM (“SPM-9700” manufactured by Shimadzu Corporation). A commercial silicon chip with a spring constant of 25-35 N/m and a single beam cantilever 125 μm long was used at a resonance frequency of 260-410 kHz.

[Pencil scratch hardness]
The obtained coating film was subjected to a hardness test according to JIS K5600-5-4 based on a usual pencil method to measure the pencil scratch hardness.

Example 1
[Preparation of thin soft acrylic-coated silica nanoparticles (PreEm-1)]
50 mL of an aqueous solution containing 10 g of a nonionic surfactant was dissolved in 400 g of colloidal silica at 40° C., the temperature was raised to 70° C. with stirring, and the mixture was continuously stirred for 1 hour under a nitrogen stream. To the resulting mixture was added 10 g of a monomer mixture of MMA, n-BA and MAA (MMA/n-BA/MAA=34.5/65/0.5 in mass ratio: soft composition), and then persulfate was added. 20 mL of an aqueous solution containing 0.55 g of potassium was further added to initiate polymerization. A sample of thin soft acrylic-coated silica nanoparticles (PreEm-1) consisting of colloidal silica particles coated with a soft acrylic polymer after cooling the entire mixture to 70°C for 2 hours to complete the polymerization and then cooling to room temperature. Got The glass transition temperature (Tg) of the acrylic polymer was -16°C. The solid content of PreEm-1 was 44.5 mass %, and the mass ratio of silica and acrylic polymer in the solid content was silica/acrylic polymer (SiO ₂ /Ac)=100/5. ..

A part of the obtained PreEm-1 was a regenerated cellulose membrane (Spectrum (registered trademark)/Por6, manufactured by Spectrum Laboratories, Inc.) having a cutoff molecular weight of 50 kDa or more (average pore diameter: 6 to 7 nm) for STEM analysis. It was dialyzed against deionized water using Ieda Trading Co., Ltd.). Dialysis was performed for one week with external deionized water replaced every half day. Then, a small amount of the dialyzed sample was filtered through a STEM micron grid Cu mesh (Oken Shoji Co., Ltd.) having a grid pitch of 150 μm and subjected to STEM observation. A portion of the dialyzed sample was dried in air (30° C.) and completely dried in vacuum at room temperature for 1 day. The rest was subjected to FT-IR analysis.

[Evaluation of PreEm-1]
The particle size distribution of the obtained PreEm-1 by DLS analysis is shown in FIG. 1 together with the particle size distribution of colloidal silica by DLS analysis. As is clear from FIG. 1, from the particle size distribution (a) of colloidal silica shown by the solid line, the average particle size of colloidal silica is 46.3 nm, while the particle size of PreEm-1 shown by the broken line. From the distribution (b), the average particle size of PreEm-1 was 57.9 nm, which was slightly larger than that of colloidal silica.

An AFM photograph of the obtained PreEm-1 is shown in FIG. As is clear from FIG. 2, PreEm-1 is a nanometer-sized particle, and although the shell structure of the acrylic polymer cannot be confirmed, the presence of particles having a particle size of about 30 to 70 nm can be confirmed. It was in agreement with the result of DLS analysis.

Next, the result of comparing the obtained PreEm-1 with colloidal silica (CS-50/NIS) to which only the nonionic surfactant is attached is shown in FIG.

In FIG. 3, photograph (a) is a SEM photograph of NIS/CS-50, and photograph (b) is a TEM photograph of NIS/CS-50. On the other hand, the photograph (c) is a SEM photograph of PreEm-1, and the photograph (d) is a TEM photograph of PreEm-1.

When the photographs (a) and (c) are compared, as is apparent from the enlarged portion of each photograph, in the photograph (a), the surface shows a dot-like matrix due to the deposition of NIS. In the photograph (c), it can be confirmed that the surface is denser and smoother than the surface in the photograph (a).

Further, when comparing the photographs (b) and (d), as is clear from the non-enlarged portion of each photograph, in the photograph (b), an interfacial space can be observed between the particles as indicated by the arrow, It shows the presence of NIS deposits on the surface of the silica particles. Also, in the photograph (d), the same interface space can be observed as indicated by the arrow, showing that the coat layer of the acrylic polymer is present on the surface of the silica particles. Further, comparing enlarged portions of the respective photographs, in the photograph (d), the surface of the dark contrast particles is covered with the light contrast coat layer as compared with the photograph (b) in which the dark contrast is shown as a whole. PreEm-1 indicates that the dark-contrast silica particles are covered with the light-contrast polymer layer. Further, the thickness of the coat layer having this bright contrast was about 1 to 3 m, which was in agreement with the results of the DLS analysis and AFM photograph.

From these results, it was proved that PreEm-1 formed a polymer layer by polymerizing acrylic monomers around NIS deposited on the surface of each colloidal silica. This thin polymer layer functions as a blocker for preventing aggregation of particles, and also functions as a polymerization site when forming a nano silica composite (NCE) described later.

Finally, an IR spectrum comparing PreEm-1 with other colloidal silica is shown in FIG. In the chart of FIG. 4, chart (a) is an IR spectrum of CS-50 and chart (b) is an IR spectrum of CS-50/NIS. Further, chart (c) is an IR spectrum of colloidal silica obtained by polymerizing an acrylic monomer in the absence of NIS [Pre(-)], and chart (d) is in the presence of NIS [Pre(+)]. ] It is IR spectrum of the colloidal silica which polymerized the acrylic-type monomer in above, ie, PreEm-1. The charts (a) and (b) have similar spectra, and it is speculated that this is because NIS does not have absorption in the measurement wavelength range. On the other hand, the chart (d) of PreEm-1 showed a weak absorption peak due to carbonyl stretching vibration of the acrylic polymer at a wave number of 1736 cm ^-1 . On the other hand, chart (c) of colloidal silica obtained by polymerizing an acrylic monomer in the absence of NIS did not show such an absorption peak. This result indicates that the polymerization proceeds on the colloidal silica surface only when NIS is present and adheres to the colloidal silica surface.

[Preparation of acrylic particles (AcEm-1)]
By a conventional emulsion polymerization method, 446 g of a monomer mixture of MMA, n-BA and MAA (MMA/n-BA/MAA=34.5/65/0.5 in a mass ratio: soft composition) was reacted as anionic anionic surfactant. Emulsion polymerization was performed in a 2.5 mass% aqueous solution of the agent to obtain a sample of acrylic particles (AcEm-1). The glass transition temperature (Tg) of the acrylic polymer was -16°C. The solid content of AcEm-1 was 47.3 mass %.

[Preparation of mixed emulsion]
Give the Preem-1 and ACEM-1, after _{the SiO} 2 / Ac ratio is mixed so that _{SiO 2 / Ac = 100/100} ( mass ratio) to adjust the solid content to 45 wt%, the emulsion mixture It was

Example 2
In the preparation of the mixed emulsion, PreEm-1 and AcEm-1 were mixed in the same manner as in Example 1 except that the SiO ₂ /Ac ratio was SiO ₂ /Ac=150/100 (mass ratio). An emulsion was obtained.

Example 3
In the preparation of the emulsion mixture, Preem-1 and ACEM-1 and, _SiO 2 / Ac ratio Si / Ac = 200/100 (mass ratio) and a way except that the mixing Example 1 the emulsion mixture in the same manner as Got

Comparative Example 1
[Preparation of Nano Silica Composite-1 (NCE-1)]
To 400 g of colloidal silica at 40° C., 145.55 g of an aqueous solution containing 0.55 g of potassium persulfate was added dropwise under vigorous stirring under a nitrogen stream, the temperature was raised to 70° C., and then MMA, n-BA and MAA were used. 10 g of the monomer mixture (MMA/n-BA/MAA=34.5/65/0.5 by mass ratio: soft composition) was added. The monomer mixture was polymerized by stirring at 70° C. for 1 hour to complete the first stage polymerization. As a second stage polymerization, after adding an aqueous mixture consisting of 0.65 g of potassium persulfate, 14 g of non-reactive anionic surfactant and 56 g of water, 190 g of MMA, n-BA and MAA monomer mixture (mass ratio MMA/ (n-BA/MAA=34.5/65/0.5: soft composition) was continuously added dropwise over 3 hours. The temperature was kept at 70° C., and after the dropping was completed, the temperature was further kept at 70° C. for 1 hour with stirring to complete the second-stage polymerization. The obtained mixture was cooled to room temperature and adjusted to pH 9 to 10 with 25% by mass aqueous ammonia containing 3.6 g of ammonia to obtain a sample of nano silica composite-1 (NCE-1). The Tg of the acrylic polymer was -16°C. The solid content of NCE-1 was about 50 mass %, and the mass ratio of silica to the acrylic polymer in the solid content was silica/acrylic polymer (SiO ₂ /Ac)=100/100.

Comparative example 2
NCE-1 was obtained in the same manner as Comparative Example 1 except that the compounding ratio of the monomer mixture was changed so that the SiO ₂ /Ac ratio became SiO ₂ /Ac=150/100 (mass ratio).

Comparative Example 3
NCE-1 was obtained in the same manner as Comparative Example 1 except that the compounding ratio of the monomer mixture was changed so that the SiO ₂ /Ac ratio was SiO ₂ /Ac=200/100 (mass ratio).

[Particle size distribution of mixed emulsion]
In order to compare the particles contained in the mixed emulsion (PreEm-1/AcEm-1) obtained in Example 2 with the particles contained in NCE-1 obtained in Comparative Example 2, DLS of these particles was compared. The particle size distribution by analysis is shown in FIG. 5 together with the particle size distribution by DLS analysis of AcEm-1, a mixed emulsion of AcEm-1 and colloidal silica (CS-50/AcEm-1). As is clear from FIG. 5, the particle size distribution (b) of CS-50/AcEm-1 which is a mixed emulsion and the particle size distribution (c) of PreEm-1/AcEm-1 are emulsions of acrylic particles alone. In contrast to a certain AcEm-1(a), which has a sharp distribution, the NCE-1 has a particle size distribution (d) which is a gradual distribution over a wide range of 20 to 400 nm and is greatly different. .. Therefore, the particles of Example 2 have a narrower particle size distribution than the particles of Comparative Example 2 and are uniform, so that the function of the particles as a coating composition is easily exhibited.

Since the average particle size of AcEm-1 (110 nm diameter) is larger than CS-50 (46 nm) or PreEm-1 (58 nm), light scattering from smaller particles is weaker than light scattering from larger particles. , Less likely to appear as scattering. However, it was confirmed that when the amounts of CS-50 and PreEm-1 added to AcEm-1 were tripled, shoulders were generated in the small diameter region of the particle size distribution curve. This result indicates that in the emulsion, both CS-50 and PreEm-1 colloidal particles were dispersed independently of AcEm-1 colloidal particles, and the AcEm-1 colloidal particles and PreEm-1 colloidal particles were dispersed. The interaction is shown to be as weak as the interaction between CS-50 colloidal particles and AcEm-1 colloidal particles. Also, if the interaction is strong, the average particle size should be large and not show a single peak. Since the surfaces of these particles are negatively charged, it can be presumed that these particles are repulsive.

[Average Particle Size and Polydispersity of Particles Obtained in Examples 1 to 3 and Comparative Examples 1 to 3]
DLS analysis of the average particle size and polydispersity of the particles in the mixed emulsions (PreEm-1/AcEm-1) obtained in Examples 1 to 3 and the emulsions (NCE-1) obtained in Comparative Examples 1 to 3 Table 1 shows the results obtained in. Furthermore, the measurement results of CS-50, PreEm-1, AcEm-1, CS-50 and AcEm-1 and a mixed emulsion (CS-50/AcEm-1) are also shown in Table 1 as reference examples. Regarding CS-50/AcEm-1, three types of Si/Ac ratios of Si/Ac=100/100, 150/100, 200/100 (mass ratio) were measured.

As is clear from the results in Table 1, the dispersity of the example is smaller than that of the comparative example and the uniformity of the particle size is high. In addition, it can be estimated that the dispersity of Examples 1 to 3 is larger than that of Reference Examples 4 to 6, and the interaction between particles is larger in Reference Example.

[Transparency of coating film]
Using an applicator, each emulsion of CS-50/AcEm-1 (Reference Examples 4 to 5), PreEm-1/AcEm-1 (Examples 1 to 2) and NCE-1 (Comparative Examples 1 to 2) [respectively] Two types having Si/Ac ratios of Si/Ac=100/100 and 150/100 (mass ratio)] were cast on a glass plate to form a liquid coating film having a thickness of 150 μm. This coating film was dried in air overnight to obtain a coating film. A photograph of the obtained coating film is shown in FIG. As is clear from the results of FIG. 6, the emulsions of Examples have better transparency than the emulsions of Reference Examples, and it is recognized that the coating layer of the acrylic polymer suppresses the aggregation of colloidal particles.

[SEM observation of coating film surface]
FIG. 7 shows a SEM photograph of the surface of a coating film (Reference Example 5, Example 2, Comparative Example 2) having a Si/Ac ratio of Si/Ac=150/100 among the coating films. Photograph (a) is a surface photograph of Reference Example 5, photograph (b) is a surface photograph of Example 2, and photograph (c) is a surface photograph of Comparative Example 2. In both cases, aggregation of particles on the surface is observed. Although the state was observed, the dents and grooves formed on the surface were small in the order of Reference Example 5, Example 2, and Comparative Example 2, and Reference Example 5 was the largest (see the arrow and the like). In each case, since a soft acrylic polymer having a Tg of 16° C. is used, the soft (rubbery) polymer layer tends to move from the top to the bottom of the silica particles, and the silica particles aggregated during drying. To form a small bump-shaped surface. Such a tendency was also observed in Comparative Example 2 having a thick coat layer and in which the aggregation of particles was relatively uniform.

[AFM observation of coating film]
Each emulsion of AcEm-1 (Reference Example 3), CS-50/AcEm-1 (Reference Example 5), PreEm-1/AcEm-1 (Example 2) and NCE-1 (Comparative Example 2) was placed on a silicon wafer. After casting, the coating film was obtained by drying under environmental conditions. A photograph of the obtained coating film is shown in FIG. The photograph (a) is the AFM photograph of the reference example 3, the photograph (b) is the AFM photograph of the reference example 5, the photograph (c) is the AFM photograph of the example 2, and the photograph (d) is the comparative example 2. It is an AFM photograph.

As is clear from the photograph (a), a smooth surface having a small number of shallow depressions (depth 4.07 nm) was formed in AcEm-1, which is an emulsion of acrylic particles alone. On the other hand, as is clear from the photographs (b) to (d), in Reference Example 5 and Example 2, which are mixed emulsions, and Comparative Example 2 of NCE-1, a granular morphology accompanied by waviness (height of 130 to 240 nm) was observed. Many depressions, shown and shown in dark color, were formed.

In particular, as is clear from the photograph (b), in Reference Example 5, the matrix polymer probably moved to the lower side of the particles, so that the surface was covered with the agglomerated particles. In fact, FIG. 9 is an AFM photograph of the phase mode of the coating films of the emulsions obtained in Example 2, Comparative Example 2 and Reference Example 5. The photograph (a) of Reference Example 5 is a photograph of Example 2. As compared with (b) and the photograph (c) of Comparative Example 2, it can be confirmed that the polymer layer is sinking below the particles.

Further, as is apparent from the enlarged portion of the photograph (b) of FIG. 8 relating to Reference Example 5, the morphology in which many particles surround the depressions shown in dark color can be observed. The photograph (d) of FIG. 8 for Comparative Example 2 also showed the same granular morphology, but was more homogeneous than in Reference Example 5. In the enlarged portion of the photograph (d), the morphology of particles aggregated around the depression was observed. In Reference Example 5, each particle shows a distorted shape, but it can be presumed that the particles moved to the lower part of the silica particles because the thickness of the acrylic polymer coat layer was large.

Unlike these emulsions, as is clear from the photograph (c) in FIG. 8, the emulsion of Example 2 had the largest undulation (undulation), but a sufficiently dispersed particle morphology was observed. As is clear from the enlarged portion of the photograph (c), it was confirmed that many particles were floating in the AcEm-1 matrix without aggregating. It can be presumed that the deep groove in the photograph (c) is formed by the movement of the soft matrix having few particles inside. It is rational to think that such an interesting morphology causes a strong surface interaction between the particles contained in PreEm-1 and the particles contained in AcEm-1. A careful observation of the non-enlarged portion of the photograph (c) shows that the particles contained in PreEm-1 are partially deposited in the shape of a ball. In the case of the present invention, although there is a difference that it is induced in the drying step of the emulsion film, the phenomenon that particles contained in PreEm-1 are deposited around the particles contained in AcEm-1 is caused by the phenomenon of Pickering emulsion. It can be assumed that it is similar to the formation process. As described above, it was observed that the particle size did not change between the emulsion of the acrylic polymer particles alone and the mixed emulsion, and therefore, in the emulsion state, the particles contained in AcEm-1 and the particles contained in PreEm-1 were included. The interaction with the particles was not strong. On the other hand, it can be inferred that the action induced in the drying step promotes the disappearance of the aqueous medium and the aggregation of the particles contained in PreEm around the particles contained in AcEm.

In contrast, in Reference Example 5 of CS-50/AcEm-1, such surface interaction did not occur even during the drying step, and the silica particles separated from the polymer matrix and aggregated at macro size. , Transparency decreased. Further, in NCE-1 Comparative Example 2, particle aggregation was also induced, but homogeneity was ensured and macro-sized aggregation did not occur.

Example 4
[Preparation of Thin Hard Acrylic Coated Silica Nanoparticles (PreEm-2)]
Colloidal silica coated with a hard acrylic polymer in the same manner as in Example 1 except that the mass ratio of the monomer mixture was changed to MMA/n-BA/MAA=53.3/46.3/0.4. A sample of thin-walled hard acrylic coated silica nanoparticles (PreEm-2) consisting of particles was obtained. The Tg of the acrylic polymer was 10°C. The solid content of PreEm-2 was 44.5% by mass, and the mass ratio of silica and acrylic polymer in the solid content was silica/acrylic polymer (Si/Ac)=100/5.

[Preparation of acrylic particles (AcEm-2)]
10 g of a monomer mixture of MMA, n-BA and MAA (mass ratio of MMA/n-BA/MAA=53.3/46.3/0.4: hard composition) was reacted with a reactive anion by a conventional emulsion polymerization method. Emulsion polymerization was performed in a 1.26% by mass aqueous solution of a surfactant to obtain a sample of acrylic particles (AcEm-2). The glass transition temperature (Tg) of the acrylic polymer was 10°C. The solid content of AcEm-2 was 47.3 mass %.

[Preparation of mixed emulsion]
PreEm-2 and AcEm-2 were mixed so that the Si/Ac ratio was Si/Ac=100/100 (mass ratio), and then the solid content was adjusted to 45% by mass to obtain a mixed emulsion.

Example 5
In the preparation of the mixed emulsion, the mixed emulsion was prepared in the same manner as in Example 4 except that PreEm-2 and AcEm-2 were mixed so that the Si/Ac ratio became Si/Ac=150/100 (mass ratio). Obtained.

Example 6
In the preparation of the mixed emulsion, the mixed emulsion was prepared in the same manner as in Example 4 except that PreEm-2 and AcEm-2 were mixed so that the Si/Ac ratio was Si/Ac=200/100 (mass ratio). Obtained.

Comparative Example 4
[Preparation of Nano Silica Composite-2 (NCE-2)]
Nanosilica composite-2 (NCE-2) sample in the same manner as in Comparative Example 1 except that the mass ratio of the monomer mixture was changed to MMA/n-BA/MAA=53.3/46.3/0.4. Got The Tg of the acrylic polymer was 10°C. The solid content of NCE-2 was about 50 mass %, and the mass ratio of silica to acrylic polymer in the solid content was silica/acrylic polymer (Si/Ac)=100/100.

Comparative Example 5
NCE-2 was obtained in the same manner as in Comparative Example 1 except that the compounding ratio of the monomer mixture was changed so that the Si/Ac ratio was Si/Ac=150/100 (mass ratio).

Comparative Example 6
NCE-2 was obtained in the same manner as in Comparative Example 1 except that the compounding ratio of the monomer mixture was changed so that the Si/Ac ratio was Si/Ac=200/100 (mass ratio).

[Pencil scratch hardness of coating film]
Using an applicator, AcEm-2 (Reference Example 7) and CS-50/AcEm-2 (Reference Examples 8 to 10), PreEm-2/AcEm-2 (Examples 4 to 6) and NCE-2 (comparative). Each emulsion of Examples 4 to 6 [three kinds of Si/Ac ratio of Si/Ac=100/100, 150/100, 200/100 (mass ratio)] was cast on a glass plate to form a liquid having a thickness of 150 μm. A coating film was formed. The coating film was dried overnight in air and then dried at 100° C. for 1 hour using a hot air dryer to obtain a coating film. The results of measuring the pencil scratch hardness of the obtained coating film are shown in Table 2.

As is clear from the results in Table 2, the coating film of Reference Example 7 had a hardness of 2B and was soft. By introducing colloidal silica, the hardness was improved to H in Reference Example 9, but in Reference Example 10 in which the amount of colloidal silica was further increased, the hardness decreased due to the aggregation of silica particles.

On the other hand, in Examples 4 and 5, the hardness was HB and 2H, and in Example 6 having a high silicon content, the hardness was reduced to HB due to the aggregation of the particles contained in PreEm-2. In Comparative Examples 4 to 6, since the surface of the silica particles was covered with the thick polymer layer, the hardness was not improved by the increase of the colloidal silica. From these results, it is possible to adjust the hardness of the coating films of Examples 4 to 6 because the coating films of Examples 4 to 6 have higher hardness than the coating films of Comparative Examples and the silica particles are coated with the acrylic polymer with an appropriate thickness. Therefore, it is possible to adjust the desired mechanical properties.

[Transparency of coating film]
The photographs of the coating films of Reference Example 9, Example 5 and Comparative Example 5 are shown in FIG. Photo (a) is a photo of the coating film of Reference Example 9, photo (b) is a photo of the coating film obtained in Example 5, and photo (c) is a photo of the coating film of Comparative Example 5. .. As is clear from the results of FIG. 10, the coating films of Example 5 and Comparative Example 5 maintained a substantially transparent state, whereas the coating film of Reference Example 9 was semitransparent. This relationship is similar to that of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Examples 4 to 6. From these results, even when different types of acrylic polymers are used, the silica particles coated with a thin acrylic polymer as in the example are effective as an inorganic modifier for acrylic emulsions and other matrix polymers. Available for

[Independence of coating film]
Since the coating film produced on the glass plate is difficult to peel off from the substrate and it is difficult to produce a self-supporting polymer film, the polymer film was produced on a polyethylene plate, and the self-supporting property was evaluated according to the following criteria. ..

◯: A self-supporting film was obtained Δ: A brittle self-supporting film was obtained ×: A self-supporting film was not obtained.

Table 3 shows the evaluation results of the emulsions obtained in Reference Examples 4 to 6 and 8 to 10, Examples 1 to 6 and Comparative Examples 1 to 6.

As is clear from the results in Table 3, in Examples, a self-supporting film was obtained in the range where the silicon content was low, and in Example 6, in the range where the silicon content was high, a self-supporting film was obtained although it was brittle. From these results, it is shown that the emulsions of Examples are easier to control the film strength and are superior in handleability than the Comparative Examples.

The aqueous coating composition containing the composite particles of the present invention is useful as a coating composition, particularly as an indoor (floor material), outer wall or roof coating material, for example, a porous material (concrete panel, cement board, gypsum boat). , Wood, etc.), metal (metal plate such as stainless steel plate, metal mesh etc.), ceramics (porous glass, tile etc.), plastic [polyester, polyamide, polystyrene, polyolefin (polyethylene etc.), engineering plastic etc. It can be used as a paint for forming a film on a substrate such as a molded article (film or plate such as a polyethylene plate, etc.).

Claims (10)

A composite particle having a core-shell structure comprising a core part formed of nanoparticles and a shell part covering the core part and containing a vinyl polymer and a nonionic surfactant, wherein Composite particles in which the coalescence is bonded to the core portion via the nonionic surfactant, and the proportion of the vinyl polymer is 30 parts by mass or less based on 100 parts by mass of the nanoparticles. The composite particles according to claim 1, wherein the nanoparticles are colloidal silica. The composite particle according to claim 1 or 2, which has an average particle size of 5 to 100 nm and a polydispersity of 0.2 or less. The composite particle according to claim 1, wherein the shell part has an average thickness of 15 nm or less. The nonionic surfactant has an ethylenically unsaturated bond and a cloud point of 0 to 80° C., and the vinyl polymer is a C _1-3 alkyl methacrylate and/or an aromatic vinyl-based monomer, and a C _1-. The composite particle according to any one of claims 1 to 4, which is a copolymer of ₁₂ alkyl acrylate and a vinyl monomer containing a carboxyl group. An aqueous coating composition comprising the composite particles according to any one of claims 1 to 5 and vinyl polymer particles. The aqueous coating composition according to claim 6, wherein the proportion of the nanoparticles is 10 to 1000 parts by mass based on 100 parts by mass of the vinyl polymer in the shell part and the vinyl polymer particles in total. The aqueous coating composition according to claim 6 or 7, wherein the vinyl polymer particles have an average particle diameter of 30 to 500 nm. A coating film formed from the aqueous coating composition according to any one of claims 6 to 8, wherein a plurality of composite particles are attached to the surface of vinyl polymer particles. Polymerization step of polymerizing vinyl monomers to prepare composite particles in the presence of nanoparticles and nonionic surfactant, and mixing the resulting composite particles and vinyl polymer particles to prepare an aqueous coating composition The manufacturing method of the aqueous coating composition in any one of Claims 6-8 including a process.