JP2012051771A - Method for producing porous hollow silica particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous hollow silica particle capable of efficiently obtaining a porous hollow silica particle having a particle diameter of a nano size, a hollow inner part, and a through hole having a sufficient size in a shell composed of a silica layer.SOLUTION: The method for producing a porous hollow silica particle includes the steps of: producing a resin particle having a reducing functional group on a surface thereof; fixing a metal particulate to the surface of the resin particle; covering the surface of the resin particle having the metal particulate with a silica layer to produce a core-shell particle; heating the core-shell particle to decompose and remove the resin particle to produce a hollow particle; and irradiating the hollow particle with a laser beam to remove the metal particulate and form a through hole in the shell of the hollow particle.

Description

  The present invention relates to a method for producing perforated hollow silica particles.

  In recent years, attention has been focused on hollow particles having cavities formed inside the shell. Since hollow particles exist, the hollow particles exhibit physical properties different from those of the material constituting the shell. For example, when air is present in the cavity of a hollow particle, the refractive index, dielectric constant and density of the air are small, so the apparent refractive index, dielectric constant and density of the hollow particle as a whole constitute the shell, respectively. It becomes smaller than the refractive index, dielectric constant and density of the material. Utilizing this, hollow silica particles whose shell is made of silica have been put into practical use as a low refractive index material, and for example, are used as a low refractive index material constituting an antireflection film of an image display device or the like. Further, the hollow silica particles can be used as a low dielectric constant material or a low density filler.

  Moreover, various functions can be given by putting another material in the cavity. In this case, the hollow particles function like a very small container. For example, in the field of pharmaceuticals and cosmetics, development of sustained-release pharmaceuticals and sustained-release cosmetics in which active ingredients are encapsulated inside hollow particles has been underway. In addition, the hollow particles can be used as a protective material that isolates substances that deteriorate and deteriorate when they come into contact with external substances from the outside, and as a carrier (drug delivery system carrier) for delivering pharmaceuticals to the site of action in the body. Research is also underway. In the papermaking field, microcapsules enclosing dyes and inks are used as color developing members for pressure sensitive paper.

Hollow particles are expected to be applied to various applications other than the above, but in applications where optical transparency is required, the particle size of the hollow particles is sufficiently small compared to the wavelength of visible light. It is required to be nano-sized. In addition, with the development of science and technology for extremely small materials, represented by nanoscience and nanotechnology, nano-sized hollow particles are also required. In this case, in order to more effectively express the characteristics of being nanoparticles, it is important that the nanoparticles do not aggregate with each other, and each one is present alone and has good dispersibility. is there.
Furthermore, in consideration of putting another material into the cavity, it is necessary to develop hollow particles having nano-sized holes in the shell of the nano-sized hollow particles.

Examples of the method for producing the hollow silica particles include a method of producing basic particles by an aerosol method, heating and drying, a method of spraying, drying and firing a metal compound aqueous sol, a w / o type or an o / w / o type emulsion. A method for preparing water and heating to remove water and oil has been proposed. However, all the hollow particles obtained by these production methods tend to have a large particle diameter and a large thickness of the outer shell (shell) (see, for example, Patent Document 1).
In addition, spherical polymer particles of a styrene polymer or a styrene / divinylbenzene copolymer are uniformly dispersed in an alcohol solution of titanium alkoxide and / or silicon alkoxide or in an alcohol / water mixed solution, and the spherical particles are obtained by hydrolysis reaction. There is disclosed a method for producing core / shell particles in which a uniform titanium compound or silicon compound coating layer is provided on the surface of polymer particles, and further heat-treated as necessary (see, for example, Patent Document 2).

On the other hand, as the particles having pores in the particles, for example, alcohol having a boiling point of 120 ° C. or higher is bonded to silanol groups in spherical silica hydrate fine particles obtained by hydrolyzing and condensing a silane compound in an organic solution. Porous spherical silica particles having a pore diameter of 50 mm or less obtained by firing are disclosed (for example, see Patent Document 3).
In addition, core particles having a short axis and a long axis and having a rotational symmetry with the long axis as the rotation axis are made of strontium carbonate, and this surface is coated with a silica layer, and then strontium carbonate nuclei in dilute hydrochloric acid. A hollow silica particle is disclosed in which a cavity having a shape substantially similar to the outer shape is formed inside the outer shell by dissolving and removing the particle (see, for example, Patent Document 4).

JP-A-4-210228 Japanese Patent Laid-Open No. 4-302592 JP-A-1-230421 JP 2010-37137 A

However, according to each of the above methods, hollow silica particles having a small particle diameter can be obtained, but pores and cavities are formed inside the particles, and a sufficiently large hole cannot be formed in the outer shell. It was. In addition, the holes formed in the outer shell of the hollow silica particles obtained by the conventional method are formed by the core component flowing out in the form of gas from the inside during the particle production process. The material does not have a shape and size sufficient to introduce the material.
The present invention has been made in view of the above situation, and it is efficient to use hollow silica particles having a nano-size particle diameter and hollow inside, and having a sufficiently large through-hole in the outer shell made of a silica layer. It is an object of the present invention to provide a method for producing perforated hollow silica particles that can be obtained in a specific manner.

  As a result of intensive studies to achieve the above object, the present inventors have utilized the effect that the silica layer in the vicinity of the metal fine particles can be selectively etched by plasmon excitation of the metal fine particles by laser light irradiation. Thus, it has been found that perforated hollow silica particles having through holes in the outer shell can be efficiently produced.

That is, the present invention
(1) a step of producing resin particles having a reducing functional group on the surface;
Fixing metal fine particles on the resin particle surface;
Coating the surface of the resin particles having the metal fine particles with a silica layer to produce core / shell particles;
Decomposing and removing the resin particles by heating the core-shell particles to produce hollow particles;
A method for producing perforated hollow silica particles having a step of removing the metal fine particles by irradiating a laser beam and forming a through hole in a shell of the hollow particles;
(2) The step of fixing the metal fine particles on the surface of the resin particles is a step of adsorbing and growing gold reduced from tetrachloroauric acid (HAuCl ₄ ) on the surface of the resin particles dispersed in water, The method for producing perforated hollow silica particles according to (1), wherein the concentration of tetrachloroauric acid is 1.0 × 10 ⁻⁷ mol / dm ³ or more and 1.0 × 10 ⁻³ mol / dm ³ or less,
(3) The method for producing perforated hollow silica particles according to (2), wherein the dispersion in which the resin particles are dispersed in water contains polyvinylpyrrolidone, and the weight average molecular weight of the polyvinylpyrrolidone is 5000 or more and 400000 or less, And (4) In the step of producing the core / shell particles, the porous silica with a hole according to any one of (1) to (3), wherein an average thickness of the silica layer covering the surface of the resin particles is 2 nm to 100 nm. Particle manufacturing method,
Is to provide.

According to the invention of the above (1) of the present invention, the hollow silica particles with perforated hollow silica particles having a particle size of nano-size and hollow inside and having a sufficiently large through-hole in the outer shell made of the silica layer. Can be obtained efficiently.
According to the invention of (2), it is possible to efficiently obtain perforated hollow silica particles having a sufficiently large through hole in the outer shell while further controlling the size of the through hole.
According to the invention of (3), it is possible to efficiently obtain perforated hollow silica particles having a sufficiently large through hole in the outer shell while further controlling the size of the through hole.
According to the invention of (4) above, it is possible to reliably form a hole penetrating the shell while maintaining the hollow particle shape, and to provide a hollow silica particle with a hole having a sufficiently large through hole in the outer shell. Can be obtained efficiently.

It is a transmission electron microscope (TEM) photograph of the resin particle which carry | supported the gold fine particle obtained in Example 1 of this invention. It is a TEM photograph of the core-shell particles coated with the silica layer obtained in Example 1 of the present invention. It is a TEM photograph of the hollow particle after baking obtained in Example 1 of this invention. (A) is a TEM photograph of the hollow particles after laser light irradiation obtained in Example 1 of the present invention, and (B) is an enlarged photograph thereof. It is an ultraviolet-visible absorption spectrum of the hollow particle before and behind laser beam irradiation. It is the TEM photograph after laser beam irradiation of the hollow particle which does not carry | support gold fine particles.

Hereinafter, the present invention will be described with reference to embodiments.
The method for producing perforated hollow silica particles of the present embodiment includes a step of producing resin particles having a reducing functional group on the surface, a step of fixing metal fine particles on the surface of the resin particles, and a resin having the metal fine particles. A step of coating the particle surface with a silica layer to produce core / shell particles, a step of decomposing and removing the resin particles by heating the core / shell particles to produce hollow particles, and a laser beam irradiation And a step of removing the metal fine particles and forming a through hole in the shell of the hollow particles.

Hereinafter, each process of the manufacturing method of the perforated hollow silica particle of this embodiment is demonstrated.
<Process for producing resin particles having a reducing functional group on the surface>
The resin particles in the present embodiment are core particles of core / shell particles described later. The resin particle is a step of growing metal fine particles on the surface of the resin particle, which will be described later, from the viewpoint of efficiently reducing the metal from the metal compound in an aqueous solution. It is necessary to have a functional group that reduces the compound. Examples of the functional group include an amino group, an ammonium group, a hydroxyl group, an aldehyde group, a glycidyl group, and a thiol group. Among these, an amino group is particularly preferably used, and the amino group is more preferably a primary amino group.

  The polymer material used for the resin particles is not particularly limited, but a normal polymer material that is not soluble in water-soluble or water-soluble solvents is preferable. Specifically, vinyl polymers such as polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polystyrene (PS); polyoxymethylene (POM), etc. Polyether; Polyester such as polylactone and polyethylene terephthalate (PET); Polycarbonate (PC); Polyamide such as nylon 6 and nylon 66; Polyurethane; Diene polymer such as polybutadiene (PBd) and polyisoprene (PIP); Melamine / benzoguanamine Polymer; Aromatic polymer; Polyimide; Polycarbonate; Polyurethane; Polysilane; Polysiloxane; Polycaprolactone; Sulfur polymer such as Polycyclic thioether; Cellulose, Protein, D Natural polymers, etc., such as A, and the like. Among these, polyvinyl chloride, polymethyl methacrylate, polystyrene, sulfur-based polymer, and the like are used as suitable materials.

Various means are adopted as means for introducing a reducing functional group into the resin particles. For example, when polymerizing resin particles, polymerization may be performed using a monomer that originally has a reducing functional group in a side chain or the like, or a reducing functional group is introduced into the surface of the obtained resin particle by post-treatment. May be.
When an amino group is introduced as a functional group by polymerization of the specific monomer, the monomers preferably used include aminoalkyl group-containing (meth) acrylic acid esters, aminoalkoxyalkyl group-containing (meth) acrylic acid esters , N-aminoalkyl group-containing (meth) acrylamides and the like. In addition, examples of the monomer suitably used for introducing an ammonium group include quaternary salts of the above monomers with methylene chloride, dimethyl sulfate, diethyl sulfate and the like.

  In addition, as a method for introducing a reducing functional group into the surface of the obtained resin particle by post-treatment, for example, after preparing the resin particle, a desired functional group is introduced from the polymerization start point generated on the particle surface. And a method of graft polymerization of the monomer having on the particle surface. The polymerization starting point can be generated by irradiating γ rays or the like in the presence of fine particles and a monomer. Alternatively, the polymerization initiation point may be generated in advance on the surface of the fine particles by electron beam irradiation or the like and then contacted with the monomer to grow the graft chain.

Some of the resin particles having the reducing functional group may be so-called anion exchange resins. An anion exchange resin has a large number of functional groups on the surface, and has a large number of micropores and is porous, so it has a large specific surface area and can disperse and fix noble metal nanoparticles with a smaller particle size on the surface. This is preferable because it is possible.
The ion exchange resin is generally produced as follows. That is, styrene and divinylbenzene are mixed, a polymerization initiator is added, radical polymerization is performed by a suspension polymerization method to obtain a three-dimensionally crosslinked copolymer, and a functional group is added to the copolymer. It is formed by introducing. When an anion exchange resin is used, a method in which haloalkylation is carried out in the presence of a Lewis acid to introduce a haloalkyl group and then amination is employed. Therefore, when an ion exchange resin is used, the amino group and quaternary amino group are usually linked to the base polymer via an alkylene group such as a methylene group or an ethylene group. Ion exchange resins are roughly classified into a gel type and a porous type (porous type), and the gel type has micropores generated by swelling in water, and ions move in the pores. The size of this pore is determined by the degree of crosslinking of divinylbenzene, and the more divinylbenzene, the smaller the micropore. On the other hand, the porous type has macropores in addition to micropores, and has a structure in which large molecular weight molecules can diffuse into the grains.

In the resin particles having a reducing functional group on the surface used in the present embodiment, the functional group concentration is preferably in the range of 1.0 × 10 ⁻² meq / g to 1.0 meq / g, More preferably, it is the range of 0.5 * 10 ^<-2 > meq / g-0.5 meq / g, More preferably, it is about 0.125 meq / g.

The shape of the resin particles serving as the carrier for the metal fine particles in the present embodiment is not particularly limited, but is preferably a substantially spherical resin particle. Here, “substantially spherical” means that 95% or more of those having a shape factor defined by the ratio of the longest diameter to the shortest diameter of the projected sectional shape of the resin particles is 0.8 or more.
Further, the size is not particularly limited, and the average particle diameter may be appropriately set according to the use of the resin particles supporting the metal fine particles, but is preferably 10 nm or more and 1000 nm or less, more preferably 50 nm or more and 1000 nm or less, and still more preferably. Is 250 nm or more and 1000 nm or less. The average particle diameter is a diameter in the case of a spherical particle, and a long diameter in the case of an elliptical particle. From an observation with a transmission electron microscope (TEM), a particle diameter distribution of about 100 particles was created, and an average value was obtained. Is.

<Step of fixing metal fine particles on resin particle surface>
This step is a step of fixing metal fine particles on the surface of the resin particles having a reducing functional group on the surface obtained by the above step. In this step, for example, a metal compound is added to an aqueous solution in which a resin particle having a reducing functional group is dispersed, and the aqueous solution is stirred at room temperature, whereby the metal ions are reduced to metal atoms. Aggregation occurs, and metal fine particles are adsorbed, grown and fixed on the surface of the resin particles.

  In the present embodiment, preferable examples of the metal constituting the metal fine particles include platinum group elements such as gold, silver, platinum, ruthenium, rhodium, palladium, osmium, and iridium. In the present embodiment, the metal compound that is a metal precursor used for forming the metal fine particles is used as an aqueous solution, so that it is water-soluble and is not particularly limited.

For example, examples of water-soluble metal compounds include metal hydroxides, chlorides, carboxylates and nitrates, metal chlorides and salts thereof, and metal complex compounds. The water-soluble metal compound will be specifically described. Preferred examples of the water-soluble gold compound include tetrachloroauric acid (HAuCl ₄ ), alkali metal tetrachloroauric acid, and gold trichloride (AuCl ₃ ). Gold cyanide (AuCN), potassium gold cyanide {K [Au (CN) ₂ ]}, diethylamineauric acid trichloride [(C ₂ H ₅ ) ₂ NH · AuCl ₃ ], ethylenediamine gold complex (for example, chloride) Complex (Au [C ₂ H ₄ (NH ₂ ) ₂ ] Cl ₃ )), dimethylgold β-diketone derivative gold complex (for example, dimethylgold acetylacetonate ((CH ₃ ) ₂ Au [CH ₃ COCHCOCH ₃ ]), _{(CH 3) 2 Au (CF} 3 COCHCOCH 3), (CH 3) 2 Au (CF 3 COCHCOCF 3), (C 2 H 5) 2 Au (CH 3 COCHCOCH 3), (CH 3) 2 A _{(C 6 H 5 OOCHCOCF 3)} ) and the like.

Examples of platinum group elements include ruthenium, rhodium, palladium, osmium, iridium, and platinum. Among these, examples of the water-soluble platinum compound include platinum hydroxide, chloride, carboxylate and nitrate, chloroplatinic acid and its salt, platinum complex compound and the like. Specific examples of water-soluble platinum compounds include, for example, platinum chloride, chloroplatinic acid, potassium chloroplatinate, bis (ethylene platinum) chloride, cis-dichlorodiamine platinum (II), cis-dichloro-bis-triphenyl. Sulphine platinum (II), platinum (II) acetylacetonate, etc. are mentioned, and other platinum groups such as ruthenium, rhodium, palladium, osmium, iridium and silver are water-soluble compounds similar to gold or platinum. It is done.
These metal compounds may be used alone or in combination of two or more if necessary. The aqueous solution of the metal compound is one in which the metal compound is dissolved in water, but if necessary, a water-soluble organic solvent may be contained as a solvent in addition to water.

In this embodiment, the concentration of the metal compound in the aqueous solution to be reduced varies depending on various conditions such as the type of compound used and the amount of noble metal dispersed and fixed in the solid polymer material, but is not particularly limited. It is preferably used at a concentration of 10 ⁻⁷ mmol / dm ³ or more and 1.0 × 10 ⁻³ mmol / dm ³ or less, more preferably 1.0 × 10 ⁻⁶ mmol / dm ³ or more and 1.0 × 10 ^−4. It is less than mmol / dm ³ .
In particular, when the metal compound used is tetrachloroauric acid (HAuCl ₄ ), the concentration of tetrachloroauric acid is 1.0 × 10 ⁻⁷ mmol / dm ³ or more and 1.0 × 10 ⁻³ mmol / dm ³ or less. It is preferably 1.0 × 10 ⁻⁶ mmol / dm ³ or more and 5.0 × 10 ⁻⁵ mmol / dm ³ or less. If the concentration is too dilute than 1.0 × 10 ⁻⁷ mmol / dm ³ , gold may not be able to be reduced and deposited on the resin particles. If the concentration is too thick than 1.0 × 10 ⁻³ mmol / dm ³ , In addition to this, there is a case where the reduction and precipitation of gold occurs in the solution. Further, by adjusting the concentration of tetrachloroauric acid within the above range, the particle diameter of the immobilized gold fine particles can be controlled.

  The amount of the metal compound with respect to the resin particles varies depending on the size of the dispersed and fixed metal fine particles and how much metal is dispersed and fixed on the surface of the resin particles. The amount of the metal supported on the resin particles can be adjusted, for example, in the range of 0.40% by mass to 35% by mass depending on the concentration and amount of the aqueous solution. Therefore, the concentration of the aqueous solution and the amount of the solution used may be determined according to the amount of metal supported.

  When gold fine particles are formed on the surface of the resin particles, first, the resin particles are dispersed in water, and the gold compound is added to the resin particle dispersion. The gold compound may be added directly to water which is a reaction solution, but it is preferably added to water constituting the reaction solution after being made into an aqueous solution in advance. At this time, the gold compound may be added at once, or may be added in a plurality of times. The reaction solution is preferably stirred slowly. Moreover, it is preferable to add the gold compound after dispersing the resin particles, but after dissolving the gold compound in water, the carrier material may be dispersed therein.

Since the resin particles are usually hydrophobic, they do not wet well with water, but can be dispersed in water by applying ultrasonic waves. At this time, if necessary, a method such as adding a water-soluble organic solvent such as methanol may be employed, or a water-soluble polymer such as polyvinylpyrrolidone (PVP) may be added to the solution.
The water used as the reaction solution for immobilizing the gold fine particles is not particularly limited as long as it is water, but it means to prevent contamination and adhesion of impurities to the formed gold fine particles. Also preferred are those from which organic impurities and metal ions have been removed by distillation, ion exchange treatment, filter treatment, various adsorption treatments and the like. The temperature is not particularly limited as long as it does not cause softening of the resin particles used and is not higher than the boiling point of the solvent, for example, when water is used as the reaction solution, it may be lower than the boiling point of water (100 ° C.). The range is from 0 ° C to 90 ° C.

In addition to the resin particles and the gold compound, it is preferable that a water-soluble polymer such as polyvinyl pyrrolidone, polyvinyl alcohol, or polyacrylamide is added to the aqueous reaction solution as necessary, as described above. These are added as a dispersing agent for resin particles or a protective agent for fine gold particles. In this case, the concentration thereof is 1.0 × 10 ⁻⁶ mol / dm ³ or more and 1.0 × 10 ⁻³ mol / dm ^3. is preferably not more than, and more preferably to 2.0 × 10 ^-5 mol / dm ³ or more 7.0 × 10 ^-4 mol / dm ³ or less.

When the reaction aqueous solution contains a water-soluble polymer, the particle size of the metal fine particles fixed to the resin particle surface can be controlled by the molecular weight of the water-soluble polymer. For example, when the polyvinyl pyrrolidone is used as the water-soluble polymer, it is preferable to use a polymer having a weight average molecular weight of 5,000 to 400,000, preferably 40,000 to 360,000, from the viewpoint of controlling the particle size. More preferred.
The number average molecular weight was measured using gel permeation chromatography (GPC). GPC was measured using an IR detector using HLC-8120GPC, SC-8020 (manufactured by Tosoh Corporation) and THF (tetrahydrofuran) as an eluent. From the results, the number average molecular weight was determined from a calibration curve using a polystyrene standard sample.

Moreover, in this embodiment, you may add a reducing agent to the aqueous solution which reduces a metal as needed. As the reducing agent, a metal ion reducing agent used in gravimetric analysis can be used. Such a reducing agent may be inorganic or organic. Examples of the inorganic reducing agent include sodium borohydride (NaBH ₄ ), sulfur dioxide (SO ₂ ), and sodium nitrite (NaNO). ₂ ) and the like, and examples of the organic reducing agent include hydrazine, formaldehyde, methanol, citric acid and its salt, oxalic acid and its salt, glucose and ethylene glycol. Furthermore, formaldehyde (HCHO), citric acid and its salts (such as sodium citrate salt and magnesium citrate salt), glucose, ethylene glycol and the like can also be used.

In the present embodiment, the average particle size of the metal fine particles supported on the surface of the resin particles is preferably 2 nm or more and 100 nm or less, and preferably 14 nm or more and 32 nm, in relation to the diameter of a through hole formed in the hollow shell particle described later. More preferably, it is as follows.
In addition, the average particle diameter of the metal fine particles was also determined by making a particle size distribution of about 100 metal fine particles from observation with a transmission electron microscope (TEM), as described above.

<Process for producing core / shell particles>
In this step, the surface of the resin particles (hereinafter sometimes referred to simply as “core resin particles”) in which metal fine particles are formed on the surface obtained by the above step is covered with a silica layer to form a core / shell. Make particles. In addition, the silica in this embodiment means the silicon oxide containing an anhydride and a hydrate.
Specifically, the core / shell particles are formed by, for example, adding the silicon alkoxide and a basic catalyst to a dispersion in which the core resin particles are dispersed, and the core resin by a silica layer generated by a hydrolysis reaction of the silicon alkoxide. It is formed by coating the surface of the particles.

As the silicon alkoxide, it is preferable to use at least one compound represented by the following general formula (I).
R ¹ _d Si (OR ² ) _4-d (I)
(In the formula, R ¹ and R ² independently represent a monovalent organic group, and d represents an integer of 0 to ^3. )
In the general formula (I), examples of the monovalent organic group represented by R ¹ and R ² include an alkyl group, an alkenyl group, an aryl group, an allyl group, and a glycidyl group. Especially, it is preferable that the monovalent organic group represented by R < ¹ >, R < ² > is an alkyl group or a phenyl group.

Here, examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and the like. Preferably, the alkyl group has 1 to 5 carbon atoms, and these alkyl groups may be linear or branched. Further, a hydrogen atom may be substituted with a fluorine atom or the like. Examples of the aryl group include a phenyl group, a naphthyl group, a methylphenyl group, an ethylphenyl group, a chlorophenyl group, a bromophenyl group, and a fluorophenyl group. Examples of the alkenyl group include a vinyl group, a propenyl group, a 3-butenyl group, a 3-pentenyl group, and a 3-hexenyl group.
Further, d is preferably 0 or 1, and particularly preferably 0.

  Specific examples of the compound represented by the general formula (I) include, for example, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-iso-propoxysilane, tetra-n-butoxysilane, tetra-sec- Examples include butoxysilane, tetra-tert-butoxysilane, tetraphenoxysilane, and the like, and particularly preferable compounds include tetramethoxysilane and tetraethoxysilane. These may be used alone or in combination of two or more.

The dispersion medium in the dispersion is preferably an alcohol solvent mainly composed of alcohols. Since the solvent used in this step is preferably a solvent that can dissolve water together with the silicon alkoxide, it must be a highly polar organic solvent, for example, a solvent mainly composed of alcohols or ketones. It is. Alcohols have a lower vapor pressure than ketones of the same molecular weight and are therefore preferred over ketones for safety.
As the alcohol, 2-propanol, ethanol, methanol or the like is preferably used.

In this step, it is preferable to add water to the alcohol solvent as necessary. As described above, the silicon alkoxide requires four times the amount of water for complete hydrolysis. On the other hand, since the core resin particles are usually prepared in an aqueous solution, some water is brought into the alcohol solvent together with the core resin particles. In addition, when ammonia is used as the basic catalyst, water contained in the ammonia water is also carried into the alcohol solvent. When water necessary for the hydrolysis reaction is secured by the water brought in in this way, it is not necessary to add water. If these waters are insufficient, it is preferable to add water to the alcohol solvent as necessary.
In the present embodiment, it is preferable that the dispersion medium contains about 25% by mass of water.

When hydrolyzing and condensing the silicon alkoxide, it is preferable to use a basic compound for promoting the hydrolytic condensation as a catalyst.
Examples of basic compounds that can be used as the catalyst include methanolamine, ethanolamine, propanolamine, butanolamine, N-methylmethanolamine, N-ethylmethanolamine, N-propylmethanolamine, N-butylmethanolamine, Amines such as N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-butylethanolamine, N-methylpropanolamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropyl Ammonium hydroxides such as ammonium hydroxide and tetrabutylammonium hydroxide, as well as pyridine, pyrrole, piperazine, pyrrolidine, piperidine, picoline Examples include morpholine, methylmorpholine, diazabicycloocrane, diazabicyclononane, diazabicycloundecene, ammonia, sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide. Then, it is more preferable to use ammonia.
The usage-amount of the said basic compound is the range of 0.00001-20 mol normally with respect to 1 mol of total amounts of the hydrolysable group in silicon alkoxide, Preferably it is the range of 0.00005-10 mol.

  The concentration of the core resin particles in the dispersion medium such as the alcohol solvent is preferably 5.0% by mass or less, and more preferably 0.12% by mass or less. In this way, when the silica layer is formed, the particles are prevented from aggregating and adhering to each other, and thus the core / shell particles having good dispersibility can be obtained. As a result, the dispersibility is good. The hollow silica particles (hollow particles) are obtained.

  Moreover, it is preferable to add an aggregation inhibitor when the core resin particles are dispersed in the dispersion medium. Then, the hydrolysis reaction of the silicon alkoxide is caused in the presence of the aggregation inhibitor, and the surface of the core resin particles is preferably covered with a silica layer. In this way, when the silica layer is formed, the particles are prevented from aggregating and adhering to each other, and thus the core / shell particles having good dispersibility can be obtained. As a result, the dispersibility is good. The hollow silica particles are obtained. Further, it is not necessary to produce hollow silica particles at a low particle concentration in order to prevent adhesion between particles, and the particle concentration can be set high, so that productivity is increased.

As the anti-aggregation agent, it is preferable to use at least one selected from the group consisting of nonionic surfactants such as polyvinyl pyrrolidone, methyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol.
As described above, for example, polyvinyl pyrrolidone may be used in the step of growing metal fine particles, and polyvinyl pyrrolidone may be brought into this step as it is.

The reaction temperature in the hydrolysis condensation is preferably in the range of 0 to 100 ° C, more preferably in the range of 20 to 80 ° C. The reaction time is about 30 to 1500 minutes.
The average thickness of the silica layer (outer shell, shell) in the core / shell particles formed by this step is preferably as thin as possible so that the final perforated hollow silica particles can maintain the strength as a carrier. A larger average diameter (average volume) is preferable, for example, from the viewpoint of holding a large amount of inclusions. Further, in the step of forming a through hole in the shell described later, the thickness of the silica layer is preferably within a specific range in order to reliably form a hole that penetrates the shell while maintaining the hollow particle shape. From these viewpoints, the average thickness of the silica layer is preferably 2 nm to 100 nm, and more preferably 14 nm to 32 nm.
The average thickness of the silica layer (shell) is determined by observing core / shell particles covered with the silica layer by TEM and averaging the thicknesses measured for about 100 particles.

<Process for producing hollow particles>
This step is a step of producing silica-based hollow particles having pores inside by decomposing the resin particles by heating the core / shell particles obtained in the above step.
The hollow particles are produced by heating the core / shell particles obtained above according to the type of core polymer, preferably 100 ° C or higher, more preferably 200 ° C or higher, more preferably 450 ° C or higher. The resin particles constituting the core are decomposed and gasified to be scattered from the inside of the core / shell particles to form pores inside the particles. The atmosphere for heating is not particularly limited, and can be performed in vacuum or in an inert gas atmosphere in addition to the presence of air and oxygen.

In the production of the hollow particles, the core resin particles are not particularly limited, but are preferably not crosslinked in order to completely decompose and facilitate gasification. Thereby, a void | hole can be formed in low temperature for a short time. For example, when the core resin particles are crosslinked, it is necessary to heat at 800 ° C. or higher, more preferably 1100 ° C. or higher. Accordingly, the monomer component of the core polymer is preferably a monomer component mainly composed of a monomer such as styrene, acrylonitrile, vinyl acetate, etc., which is not crosslinked in that it is decomposed by heating.
By passing through this step, the core (resin particles) in the core / shell particles disappear, and hollow particles in which metal fine particles remain on the inner surface of the silica layer (shell) can be obtained.

<Process for forming through holes in shell of hollow particles>
In this step, the hollow particles produced in the above step are irradiated with laser light to cause plasmon excitation of the metal fine particles fixed on the inner surface of the silica layer (shell), and the metal fine particles are destroyed and In this step, the silica layer is also destroyed to form a through hole in the shell of the hollow particles.

The laser used in this step irradiates the hollow particles having the metal fine particles on the inner surface with light to excite the metal fine particles. The wavelength of the laser beam has the visible ultraviolet absorption wavelength of the metal fine particles. The wavelength of the laser beam can be appropriately set depending on the type of the metal fine particles, and may be a fundamental wavelength of an element that oscillates the laser beam, or may be a harmonic converted by a nonlinear optical element, for example. As the wavelength of the laser beam, for example, when the metal fine particles are gold, the visible ultraviolet absorption wavelength of gold is 530 nm. Therefore, as the laser, for example, the second harmonic (532 nm) of an Nd ³⁺ : YAG laser Can be mentioned.

The laser beam is preferably pulsed light, and the pulse width is, for example, in the range of 1 to 10 ns. The irradiation intensity of the laser beam is not particularly limited and can be appropriately adjusted depending on the type of the metal fine particles and the pulse width. However, when gold having a particle size of 30 nm is made of metal fine particles and the pulse width is 5 ns, , Preferably in the range of 100 to 230 mJ / cm ² .

  Since the through-hole obtained in this step is formed by breaking the silica layer as the outer shell with the destruction of the metal fine particles as described above, the diameter of the normal hole is slightly larger than the particle diameter of the metal fine particles. The shape of the opening of the hole is large and at least one of a circular shape, an elliptical shape and a polygonal shape accompanying the destruction of the metal fine particles. That is, the shape of the opening of the through hole in the present embodiment is not a long and narrow shape such as a crack or a split, but a shape having a sufficient width in both the vertical and horizontal directions.

The average diameter of the formed through holes is preferably 5 nm or more and 100 nm or less, and more preferably 17 nm or more and 56 nm or less.
In addition, the average diameter of the said through-hole was set as the average diameter by observing the hollow particle after this process by TEM, measuring the maximum width of all the through-holes which exist in about 100 particle | grains, and averaging these. .

  By the method for producing perforated hollow silica particles of the present embodiment having the steps described above, hollow silica particles having a through hole of a desired size in the outer shell can be efficiently produced. Moreover, the shell layer is relatively uniform, and the hole diameter can be freely controlled.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Various characteristics such as the average particle diameter of the resin particles, metal fine particles and core / shell particles obtained in each step, the silica layer thickness of the hollow particles, and the average diameter of the through holes were measured according to the following methods.

  Particles were observed at an acceleration voltage of 100 kV using a transmission electron microscope (TEM) (manufactured by Hitachi High-Technologies Corporation, trade name: Hitachi Electron Microscope H-7600). The diameter and outer shell thickness of all particles (approximately 100 particles) in the bright field were measured on a photograph, and the average particle diameter and average outer shell thickness were determined. Moreover, the maximum width was measured about all the through-holes of about 100 particles, and the average of them was taken as the average diameter. In addition, the said observation was performed using what disperse | distributed each particle | grains to methanol, was dripped on the TEM grid, and was dried.

<Example 1>
(Fixing of gold fine particles to the resin particle surface)
As the resin particles, amino group-containing polystyrene (PS) particles were used.
First, 0.144 g of polyvinyl pyrrolidone (PVP, manufactured by Kishida Chemical Co., Ltd., trade name: polyvinyl pyrrolidone K-30, weight average molecular weight Mw: 40000) is diluted to 20 cm ³ of ultrapure water in a sample bottle, and ultrasonicated for 10 minutes. A PVP dispersion liquid that was completely dispersed by processing was prepared.
On the other hand, the amino group-containing polystyrene particle dispersion (manufactured by Funakoshi Co., Ltd., Polybead Amino Microspheres, amino group content: 0.125 meq / g, solid content: 2.5 mass%, average particle size: 1.0 μm) 0 .1 g was diluted to 1 cm ³ of ultrapure water in a microtube, centrifuged at 15000 rpm for 5 minutes, and then the supernatant was removed.

The amino group-modified polystyrene particles washed in this way were added to the PVP dispersion, and the cap was capped and stirred with a hot stirrer at 30 ° C. for 30 minutes. Next, 1.05 mm ^{3 of} an HAuCl ₄ aqueous solution having a concentration of 97 mmol / dm ³ was added while vigorously stirring the solution at about 1000 rpm (the HAuCl ₄ concentration in the reaction solution at this time was 1.0 × 10 ⁻⁵ mol / dm ³ ). Thereafter, the lid was put on and stirring was continued slowly for 17 hours. During stirring, the upper part of the hot stirrer was covered with aluminum foil for light shielding. After completion of the reaction, centrifugation was performed at 4000 rpm for 15 minutes to separate the particles, and the supernatant was removed to recover polystyrene particles carrying gold fine particles.

FIG. 1 shows an electron microscope (TEM) photograph of polystyrene particles carrying the obtained gold fine particles.
As shown in the figure, it can be seen that the gold fine particles are supported almost uniformly on the surface of the polystyrene particles. From this observation, the average particle size of the gold fine particles was 12 nm. Moreover, since the particles existed stably without agglomeration, the entire polystyrene particles carrying the gold fine particles are considered to be modified by PVP. Note that the gold fine particles were strongly bonded without being separated from the particle surface even when the ultrasonic treatment was performed.

(Production of core / shell particles)
The polystyrene particles carrying the gold fine particles produced in the above step were diluted into a mixed solution of 20 cm ³ of 2-propanol and 5 cm ³ of ultrapure water in a sample bottle. While this solution was vigorously stirred at about 1000 rpm, 0.8 cm ³ of an aqueous ammonia solution having a concentration of 25% by mass was added, and 30 mm ^{3 of} tetraethoxysilane (TEOS) was immediately added thereto while stirring as it was. Then, it was covered and stirred slowly for 24 hours. During stirring, the upper part of the hot stirrer was covered with aluminum foil for light shielding. After completion of the reaction, the particles are separated by centrifuging at 4000 rpm for 15 minutes, the supernatant is removed, and then washed three times with ethanol, whereby the polystyrene particles supporting the gold fine particles are coated with a silica layer. Shell particles were collected.

FIG. 2 shows an electron microscope (TEM) photograph of the obtained core / shell particles.
As shown in the figure, it can be seen that the silica layer is formed with a uniform film thickness on the surface of the polystyrene particles carrying the gold fine particles, thereby forming an outer shell (shell). Moreover, the shell surface which consists of a silica layer was smooth, and the layer thickness was 32.0 nm.

(Decomposition and removal of resin particles)
The core-shell particles obtained in the above step (polystyrene particles carrying gold fine particles coated with a silica layer, 25 mg in terms of polystyrene) were dispersed in about 0.5 cm ³ of ethanol and dried under reduced pressure in a sample bottle. The dried particles were then baked together with the sample bottle at 450 ° C. for 2 hours. Ethanol 0.5 cm ³ was added to the sample bottle to which the particles after baking adhered, and was dispersed by ultrasonic treatment for several seconds.

FIG. 3 shows an electron microscope (TEM) photograph of the obtained hollow particles after firing.
As shown in the figure, it can be seen from the contrast of the TEM photograph that the polystyrene particles, which are the cores in the core / shell particles, could be removed by baking at 450 ° C. Moreover, it can be confirmed as a black spot in the photograph that the gold fine particles remain inside the hollow particles.

(Forming through holes in hollow particles)
The hollow particles obtained in the above step were diluted with ethanol in a quartz cell with one side of the opening of 1 cm, and the concentration was adjusted so that the absorbance at a wavelength of 532 nm was 0.15. Next, the quartz cell was covered with parafilm, and laser light (wavelength: 532 nm, intensity: 200 mJ / pulse, frequency: 10 Hz) was irradiated for 3 minutes with a YAG laser while gently bubbling the solution with nitrogen gas.

FIG. 4 shows an electron microscope (TEM) photograph of the obtained hollow particles after laser light irradiation.
As shown in FIG. 4A, it can be seen that the portions corresponding to the gold fine particles of the hollow particles in FIG. Further, FIG. 4B shows an enlarged white portion, which is clearly a circular hole, and this hole penetrates the silica layer (shell) in the hollow particle. I understand. Further, FIG. 5 shows ultraviolet / visible absorption spectra of the hollow shell particles before and after laser light irradiation, and the plasmon-derived peak (520 nm) of gold fine particles is larger after irradiation (3 min) than before irradiation (0 min). It turns out that it is decreasing. This result shows that the gold fine particles disappear or become small in the hollow particles.
From the above results, the through hole formed in the shell of the hollow particle is derived from the gold fine particle, and the gold fine particle is plasmon-excited by laser light irradiation, and is destroyed and disappeared, and is formed by destroying the silica layer in the part. It was confirmed that

  Further, the average diameter of the through holes obtained from the TEM photograph is 22 nm, and the average diameter of the through holes is larger than the average particle diameter of the gold fine particles when the gold fine particles and the through hole diameter are compared. ing. The reason for this is that if the silica layer around the gold microparticles is etched (broken) with the laser light irradiation, the average diameter of the holes may be slightly larger. It is conceivable that the holes are connected by the above, and that the silica layer around the holes is damaged by the impact.

<Examples 2 to 4>
In the step of fixing the gold fine particles of Example 1 on the surface of the resin particles, the core / shell particles and hollow particles were formed in the same manner as in Example 1 except that the HAuCl ₄ concentration in the reaction solution was changed as shown in Table 1. Particles and perforated hollow silica particles were prepared.
The gold particle diameter, shell thickness, and through-hole diameter in each are collectively shown in Table 1.

<Examples 5-9>
In the process of producing the core-shell particles of Example 1, the type and amount of the silane coupling agent (tetraethoxysilane (TEOS) / tetramethoxysilane (TMOS)) were changed as shown in Table 1. Except for the above, core-shell particles, hollow particles, and perforated hollow silica particles were produced in the same manner as in Example 1.
The gold particle diameter, shell thickness, and through-hole diameter in each are collectively shown in Table 1.

As shown in Table 1, by changing the HAuCl ₄ concentration in the same reaction system, the average particle diameter of the gold fine particles can be changed, and the average diameter of the through holes in the hollow particles is also changed accordingly. It can be seen that it is possible to Moreover, it turns out that the thickness of a shell layer can be changed by changing the kind and addition amount of a silane coupling agent by the same reaction system.

<Examples 10 to 15>
In the step of fixing the gold fine particles of Example 1 on the surface of the resin particles, the same procedure as in Example 1 was conducted except that the HAuCl ₄ concentration, the weight average molecular weight Mw of PVP and the addition amount were changed as shown in Table 1. Core / shell particles, hollow particles, and hollow silica particles with holes were prepared.
The gold particle diameter, shell thickness, and through-hole diameter in each are collectively shown in Table 1.

Comparing Examples 11 to 13, by changing the molecular weight of PVP in the same reaction system, the average particle diameter of the gold fine particles can be changed, and correspondingly, the average diameter of the through holes in the hollow particles It can also be seen that it can be changed. Further, when Examples 13 to 15 are compared, the average particle diameter of the gold fine particles can be changed also by changing the HAuCl ₄ concentration in the same reaction system. It can be seen that the average diameter can also be changed.

<Comparative Example 1>
Fixation of gold fine particles to the resin particle surface by the same treatment as in Example 1 using general-purpose polystyrene particles (Polysciences, Inc., polystyrene microspheres, average particle size: 500 nm) not subjected to special surface treatment. As a result, high dispersion of gold fine particles on the polystyrene surface did not occur. This indicates that metal fine particles can be supported on the polystyrene surface by reducing and precipitating metal ions starting from a reducing functional group present on the surface in the above examples.

<Comparative example 2>
In Example 1, core / shell particles and hollow particles were produced in the same manner as in Example 1 except that the step of fixing the gold fine particles to the resin particle surface was not performed. FIG. 6 shows a TEM photograph of the sample irradiated with laser light. It can be seen that there is no change in the shape and shape of the hollow particles before laser irradiation, and the destruction of the silica layer occurs by irradiating laser light after supporting gold.

  The method for producing perforated hollow silica particles of the present invention is capable of efficiently producing perforated hollow silica particles that can enclose air and various compounds and materials therein while having a nano-sized particle size. Using the perforated hollow silica particles, the present invention can widely contribute to the automobile industry, general machinery industry, electrical / electronic industry, medical industry and the like.

Claims (4)

Producing resin particles having a reducing functional group on the surface;
Fixing metal fine particles on the resin particle surface;
Coating the surface of the resin particles having the metal fine particles with a silica layer to produce core / shell particles;
Decomposing and removing the resin particles by heating the core-shell particles to produce hollow particles;
A method for producing perforated hollow silica particles, comprising: removing the metal fine particles by irradiating a laser beam; and forming a through hole in a shell of the hollow particles. The step of fixing the metal fine particles on the surface of the resin particles is a step of adsorbing and growing gold reduced from tetrachloroauric acid (HAuCl ₄ ) on the surface of the resin particles dispersed in water, and the gold tetrachloride in the water 2. The method for producing perforated hollow silica particles according to claim 1, wherein the acid concentration is 1.0 × 10 ⁻⁷ mol / dm ³ or more and 1.0 × 10 ⁻³ mol / dm ³ or less.   The method for producing perforated hollow silica particles according to claim 2, wherein the dispersion liquid in which the resin particles are dispersed in water contains polyvinyl pyrrolidone, and the polyvinyl pyrrolidone has a weight average molecular weight of 5,000 to 400,000.   The method for producing perforated hollow silica particles according to any one of claims 1 to 3, wherein in the step of producing the core / shell particles, the average thickness of the silica layer covering the surface of the resin particles is 2 nm or more and 100 nm or less.